Thursday, November 30, 2006

AV - Vernon Payne


.
Most of you have never heard of Vernon Payne. He’s best known as the designer of a spiffy little biplane called the Knight Twister. Rag & tube fuselage, solid spruce spars, plywood skins on cantilevered wings. Slicker than snot on a door knob. First flew about 1929 and continues doing so today and very well, too. Ask him nice, Vern would build you a set of wings. Fuselage, too.

For a short while when he was moving out of his place north of Escondido I worked for Vernon. Not what you’d call a real job even though the sweat was real enough. Mostly helping him prepare for the move, which involved finishing a set a wings he was working on, prepping a fuselage and other minor chores.

Skinning the leading edge, Vern soaked each piece of plywood, fitted it to the wing and let it dry in place. The old barn we worked in was good for that sort of thing, hot and dry and no distractions other than Taddy, the shop cat who liked to watch.

After the ply had dried to the required shape Vern would check the fit with a bit of chalk, make any adjustments. The fitted panels of the beautiful double-tapered wings were glued all at once using Weldwood ‘Plastic Resin’ and nailing strips. Lots of nailing strips, most of which were also pre-molded to match their particular rib, both of us working away with our tiny tack hammers, taking our time but not wasting any, doing it right so we wouldn’t have to do it over.

And we’d talk. Vern had boots that was older than me but I wasn’t no kid; I knew who Gilmore was and the joke about aviation-grade horsemeat, which meant Vern could talk without having to explain every other word. I suspect he needed the companionship as much as the help, working all alone out there in that old barn north of Escondido, having to finish those wings and move a life-time of stuff because the Yuppies were kicking him out.

I usually have a sketch book with me, a life-long habit. Vern didn’t like it when he saw me sketching the engine arrangement of his latest project, a two-place VW powered thing he called the Dolphin. I gave him the book, told him to tear out anything he didn’t want me to have. He flipped through it and saw Taddy curled up atop the blueprint cabinet and a chiaroscuro study created by a slice of sunlight falling across a steel tube fuselage. And of Vern too, bent over the wing, pensive look on his face as he examines a tip rib smaller than a pocket ruler. He gave me back the sketch book, didn’t tear anything out.

We got to talking about landing gear, which kind was best; that sort of thing. It was an interesting subject to me because I’d just made a composite gear leg out of wood, fiberglas and good intentions that busted all to hell when I did a drop-test. Vernon told me how the CAA used to have a standard formula for acceptable landing gear strength and a drop-test calculation based on the gross weight, a Jesus factor and the stalling speed of that particular aircraft. Then he said, ‘I just used the worse-case, which was fifty inches.’ Later, I made a note of that on the corner of a sketch of a landing gear. - - Worse case = 50" - - I don’t know exactly when that was. Back in the eighties.

About three years ago I wanted to compare the performance of different types of landing gear for a particular design and made up a drop-tester that allowed precise control of the height and the angle at which the wheel contacted the ground. The gear leg bolted to a plate on the end of a long arm that was raised by a little derrick using a screw-thread winch off a boat trailer. I used a glider hook as the release mechanism and welded a tray to the top of the arm so I could stack on plates of lead and scrap iron for the weight. It’s quite an affair. Really shook the ground when it hit. And busted everything I tried. (Some of you may have seen pictures of the knee-action gear leg I posted over on the Fly5k mailing list. There were a number of others. All initially failed the drop-test.)

I soon became quite the expert at drop-testing. As I gained experience I began to understand how the load gets distributed through the structure and saw ways to make the gear legs stronger without adding too much weight. But always some. It was pretty obvious that most landing gear used on modern airplanes couldn’t even come close to that ancient CAA requirement. By the time I got something that was strong enough to withstand the worse-case fifty-inch drop, it was huge. And heavy. More suitable for the NYP with a full load of fuel than a single-place do-it-yourself puddle jumper with a converted VW on the nose. Fiberglas offered some advantages, as did oleo-pneumatic systems but their cost and complexity put them beyond the means of a first-time builder on a tight budget. It was all rather discouraging.

A couple of days ago I was digging through a file looking for... I can’t remember what... when I came across a blurry copy of a 1930's article by Raoul J. Hoffmann, the aeronautical engineer who crunched the numbers for Matty Laird. Hoffman was one of my dad’s heros and it was a good choice. The article was titled ‘Landing Gear Shock Stresses’ and included the usual boilerplate formulae, a couple of graphs and a few column-inches of text. I’d seen it before, hadn’t looked at it too closely since I’d already decided to emulate Vernon Payne’s method of using the worse-case drop height. But as I scanned the article something jumped out at me.

“...drop from a height in inches equal to .38 times the calculated stalling speed in miles per hour... (but) ...not over 15 inches for conventional airplanes.”

FIFTEEN inches. Not fifty.

I sat down and ran the numbers for my puddle-jumper. Maximum applied load not to exceed 5.5 times the gross weight (I’ve been using 6.0). But the drop test need not exceed fifteen inches. And I'd been using fifty! No wonder my gear legs came out like something off the Dreadnaught.

- - - - - - - - - - - - - - - -

Taddy came to live with us after Vern and his wife moved into a place that didn’t allow pets. They would drop by now and then to say hello, more to Taddy than us but they were nice visits. Vern passed away a few years ago but will never be forgotten. His little bipe is a rare combination of art and science, as was Vernon Payne himself.

Ignorance is mankind's normal state, alleviated by information and experience. Much of that experience is negative; we learn to do things right by doing it wrong. If fate gives us another shot at it, we do it differently the next time around. Once we learn to do things right we become the local expert, the fellow who can show you how to kill a grizzly with a spear or attach a propellor to a pulley hub. But as Smokey Yunick once said, “Most experts aren’t.” And I’d just proved him right because nothing leads us astray faster than the things we think we know. Vern was a pro; he obviously said ‘fifteen’ and I heard it as fifty.

-R.S.Hoover

Photo of the Knight Twister courtesy of Steen Aero http://www.steenaero.com

AV - Ignition Timing

With regard to ignition...

Got a match? Gopher, kitchen, safety... any match will do. You’ll need a few of them for what follows.

Strike a match and measure how long it takes for the chemicals to burn off. Just hold it vertically and count-down starting from the pop of ignition until all of the chemicals are gone. You may chant ‘one-potato, two-potato...’ if you wish :-)

Do that several times and you will see that for same amount of chemical, it takes the same amount of time.

Now try to make it burn faster. Or slower. Blowing (gently) on the flame should give it more oxygen whilst holding it in the steam from a kettle should give it less but the odds are neither will effect the burn-time because the chemicals are a balanced mixture of fuel and oxidizer. That’s what’s referred to as a ‘stoichiometric’ mixture.

As with the match, the fuel-air mixture in a gasoline-fueled internal combustion engine does not explode, it merely burns. Or should :-) If it does explode (ie, detonatation) you’ve got a serious problem on your hands.

Although the match experiment isn’t very precise it offers a hint that combustion of a given quantity of mixture not only takes a certain amount of time, that amount of time is virtually fixed for a given quantity of material. If we set aside the temperature of combustion, which I am doing deliberately for the purpose of this explanation, the only way to alter the amount of time it takes to burn a given quantity of fuel is to alter the composition of the mixture. The key point here is that for a given engine and within the parameters already mentioned (ie, temperature and mixture ratio) combustion takes approximately the same amount of time regardless of engine rpm.

Now consider a spark-ignited Otto-cycle engine.

Even with a cylinder of large displacement, when the fuel-air mixture is compressed, combustion takes only a few thousandths of a second - - a brief flash is all you’ll see through the quartz head of a Test Engine. What happens during that brief flash is the heart & soul of understanding internal combustion engines..

During that brief flash all of the fuel combined with all of the oxygen to produce a given quanta of heat, raising the temperature of the residual gases in the combustion chamber, most of which are nitrogen, to several thousand degrees, at least momentarily and nearest the core. But that brief flash of heat also serves to raise the pressure inside the combustion chamber. Which is good. But only if the pressure rises in an orderly fashion - - and only if the peak pressure occurs after the piston has reached the Top Dead Center point of its up & down movement. If peak pressure occurs too early we might as well go home.

A little bit early isn’t too bad. It wastes power but the engine will still run. Here’s why: Each cylinder of an Otto-cycle engine has only one power pulse for every two revolutions of the crankshaft and that pulse lasts for less than ninety degrees of rotation. The energy needed to rotate the engine through the other 630 degrees has to come from other cylinders or some storage mechanism, such as a flywheel. Whatever method is used, it is sized for the slowest speed at which you want the engine to run, meaning there will always be some amount of excess energy at any higher speed. When peak pressure occurs a little bit early some of that stored energy will be used to get the piston past TDC. Under those conditions the engine’s efficiency is low and fuel consumption is high but the thing will still run.

But if the pressure peak occurs too early, there won’t be enough energy in the system to overcome the timing error and the thing will fail to run, often signaling it’s disgust with a back-fire.

By the same token, we don’t want the pressure peak to occur too late. If the pressure does not peak until the piston is already descending - - which it will do even without a power pulse, thanks to the momentum inherent in the Otto-cycle design - - much of the pressure we’ve worked so hard to produce will be dissipated without doing any useful work; the amount of torque available at the output will fall. When peak pressure occurs too late, the engine will still run but not very efficiently in the thermal sense, and its top speed will be limited, since any increase comes at the a further reduction in torque.

Notice here the distinction between initiation of ignition - - when the spark occurs - - and the moment of peak pressure. Although sequentially related these are two separate events, the interval between them determined by a number of factors such as the shape of the combustion chamber, the octane rating of the fuel, the point of ignition and so on. Most confusion associated with engine tuning stems from addressing only ignition timing and ignoring the timing of the resultant pressure curves.

It should be obvious that an efficient engine is more desirable than an inefficient engine. An efficient engine burns less fuel to produce the same power as an inefficient engine. Efficient engines also tend to last longer. What isn’t so obvious, especially with an antique design such as the air cooled Volkswagen, is that a remarkable improvement in thermal efficiency may be achieved by focusing the keenest attention to the myriad details which contribute to its inefficiency, such as the timing of the cam, valves and ignition, proper waste-heat management and so forth.

At the very least this message should have made two things immediately apparent: Ignition must occur at some time prior to the need for peak pressure, and the precise moment of ignition must vary according to the rpm of the engine.

Which is why I don’t use magnetos. Or any other ignition system having a fixed firing point.

Yeah, I know - - it flys jus’ fine. The question you gotta ask yourself is, how much better could it fly - - and how much fuel are you pissing away.

-R.S.Hoover

Wednesday, November 29, 2006

VW - Deep Sump

Is it a good idea to put one of those larger oil-sump deals on your bus? It sounds like a really good idea, but is there some technical reasons that it would be harmful?

I've never seen a deep sump that didn't leak, apparently because the sump-plate studs -- even when replaced with longer units -- were never meant to carry such a load.

Reduced ground clearance, while never a problem on the drag strip, can cost you an engine in daily driving. I've seen several crankcases with chunks knocked out of them as a result of hitting something with the attached (and quickly detached) deep sump. I've also seen a couple of engines lost when the oil pick-up extension came adrift, started sucking air.

With a filled deep-sump, the oil takes forever to warm-up. And of course you have to keep the thing filled if you want your dip-stick to work :-) Drag-racing, we ran the engine with the minimum of oil, pouring in fresh for each run. It never showed up on the dip-stick because the dip-stick does not extend into the deep sump.

We used to call these things the 'Poor Man's Dry Sump'. Getting the liquid oil out of the crankcase gave us extra rpm, always important when you're trying to catch a clock. For roundy-round, rallys and road courses, we had a better results -- and less expense -- using a windage tray and fabricating extenders for the push-rod tubes. Running at speed, we thought the deeper sump would keep the oil from pooling-up out in the head... and maybe it did, for a few seconds. Fact is, running at speed the extra capacity of the deep sump doesn't mean squat -- we just ended up with an extra quart of oil in the outside head. Live and learn :-)

I thought the added surface area of the deeply finned (and properly fabricated sumps, such as the one Gene Berg made) would result in cooler oil temps. It didn't. The oil took longer to come up to normal operating temperature but once there, it was about as hot as before. Apparently the oil cooler is about twenty times as effective at cooling the oil as any form of sump --- you'd need about five times the surface area of the typical deep-sump before you saw an appreciable drop in your engine's oil temp. There's bound to be some variation here. I'm talking about using a deep-sump in California. Veedubers in Finland probably swear by the things :-)

All of the guys who claimed miraculously low oil temps after bolting on a deep-sump usually had chromed valve covers, chromed push-rod tubes, no thermostat and so on -- they were already running near the red-line before they bolted the thing on -- and most of their claims were based on only a few minutes of run-time -- the extra oil hadn't even warmed up yet.

Deep sumps are suicide off-pavement... or on-pavement for that matter, if you have to negotiate the occasional rough alley or railroad track.

Deep sumps tend to get in the way when you need to drop your engine, forcing you to raise the vehicle higher (bugs) to clear the rear apron and to use a different scooter (buses).

Finally, most of the deep sumps I've seen were very poorly made, the exception being the ones Gene Berg used to sell (I've not seen his most recent offering but I understand it's aluminum. It used to be magnesium and beautifully made, too.) The deep sumps sold locally are bubble-packed crap, cast in Taiwan and have casting inclusions and lots of CASTING SAND RESIDUE. (Someone on the Type2 List... [Thom?] ran into this problem.) It would be suicide to bolt such a thing on an engine.

The bottom line? Deep sumps first appeared on the drag strip. Kiddies bolt them on because they can and because they look kewl and because all the tits & ass VW magazines say it's the thing to do. I ran them on the strip but found them impractical on the road, sought other -- more effective -- solutions.

Your engine, your decision.

-------------------------------

Want to increase your oil capacity? Add a full-flow oil filtration system. The big FRAM PH-8A canister holds nearly a quart of oil, the hoses about half a pint.

-Bob Hoover
-1995

VW - Oil Contaminantss

.
All engines provide some form of crankcase ventilation, normally drawing air in through a filter and exhausting it by means of a road draft tube or engine vacuum. On older American cars the inlet filter was in the oil filler cap and periodically replacing the cap -- and the filter it contained -- was a normal maintenance item. In the Volkswagen, air is drawn in around the fan pulley, exhausted to the air breather. There is no filter.

When building a Volkswagen engine, to insure dependable operation under all conditions the nose of the engine is machined to accept a shaft seal that fits around the hub of the fan pulley, the hub being modified to provide a smooth sealing surface. A filtered air inlet is provided elsewhere on the engine, typically on one of the valve covers. The filter is located on the firewall, plumbed to the engine with hose. The better breather filters provide for moisture trapping. The normal outlet is unchanged. The seal is commonly called a sand seal since it is a virtual necessity when running off pavement.

Without such a seal, whatever is in the air will be drawn into your engine. Even when running a full flow oil filter, it's wise to replace your oil periodically to get rid of chemical contaminants picked up from the air being drawn through the crankcase.

-Bob Hoover
-1995

VW - The By-Pass Solenoid Trick

St. Muir and the By-Pass Solenoid, or "Soul y noid? We don' need no stee-king solenoid!"


This one really gets me hot under the collar, first because it ain't a by-pass-anything, and second because the usual method, using an old Ford starter solenoid a la St. Muir is dumber than hell, partly because it ain't a solenoid at all but a contactor, and finally because you just don't need a starter contactor for this particular job.

The problem is that Volkswagen feeds their starter solenoid 12vdc by way of China. They run the juice all the way up to the front of the vehicle, through the starter switch which isn't all that reliable to begin with, then all the way back to the solenoid -- which is where the juice started its journey to begin with.

By the time those 12 volts have marched up front, squeezed through the switch terminals and hiked all the way back to the solenoid about of half of them are dead and the others have blisters. They jump inside the solenoid, put their electronic shoulders to the wheel but find they're played out by the trip. If the solenoid moves at all it does so sluggishly, often not strongly enough to close the contactor terminals that provide juice to the starter motor.

The fix is to keep those 12 volts from wasting their time and energy on that useless hike by putting in a relay. That's what that Ford contactor is pretending to be. The joke is, the contactor uses almost as much juice as the VW solenoid! A wiser choice is a headlight or horn relay. Cheap, easy to find and easy to mount. Screw it to the fender well inside the engine compartment to help keep the terminals clean.

What the relay does is tell those 12 volts when to go to work on the solenoid. You wire your relay with the same wire originally used for the VW starter solenoid but you install new, heavier wires -- with a shorter run to the battery and solenoid -- from your relay. Since a headlight relay only needs an itty-bitty amount of power to pick or transfer, the original wiring provides more than enough energy despite its long run. And since your new, heavier wiring provides a shorter, neater, cleaner, prettier, healthier and politically more correct run between the battery and the VW starter solenoid, it fires right up every time.

This isn't a new problem. In fact, Volkswagen came out with a fix for it years ago. Their solution? A simply relay packaged as a completely wired kit, including instructions. The part number was something like VK-1 and you could buy it from any dealer for about two bucks.

I understand Gene Berg started selling Ford contactors because he got tired of trying to explain to St. Muir deciples that St. John didn't know very much about elektrissity. I know a whole bunch about elektrissity and I'm still alive, even though I use a headlight relay to pick my solenoid and a horn relay to turn on my back-up light and an itty-bitty microampere relay out of a short-wave radio to tell my external cooling fan when to turn on, although a Ford contactor would have done the job -- sorta -- in each and every case and would have, if St. Muir had thought of back-up lights and cooling fans. ("Back-up lights! We don' need no steeeking back-up lights!")

Sermonette

Cold weather brings home the problem of the voltage drop in the long wiring runs common to a Volkswagen bus. If you want reliable starts and brighter headlights you need to know more about heavier gauge main buss wiring and the use of relays. You are the mechanic-in-charge of your vehicle. Sometimes that calls for you to be an electrician as well.

-Bob
-1996

Ed. Note: I've heard Gene Berg Ent. now offers the original VW relay instead of a Ford contactor. Check their catalog.

VW - Volkswagen Ignition System




Early VW's used an ignition system based on the Kettering patents from the 1920's, in which the battery voltage was stepped up to several thousand volts through the use of a transformer, the thing we call the coil. But transformers only work when the voltage is changing. (Alternating current 'changes' 120 times a second (ie, 60 cycles) so transformers work just fine.) To use a step-up transformer in a car you'll need something to cause the voltage to change. Just turning it on and off will work. Henry Ford used a magnetic-reed oscillator, a kind of vibrating switch. Boss Kettering (he ended up running General Motors) had the genius to connect the ignition transformer through a mechanical switch driven by the engine. Opening and closing the switch provided the changing voltage needed to make the transformer work. The switch of course is the ignition points.

How the Coil Works

The reason a transformer works lies in the physical properties of electrical current. When a current flows through a conductor it generates a magnetic field around the conductor. Conversely, when a conductor is moved through a magnetic field, a voltage will be induced in the conductor. A transformer takes advantage of those principles of inductance by winding one coil over the top of another. At low frequencies you can focus or concentrate the magnetic field by winding the coils around an iron core. And since you can't move the coils relative to one another, the changing voltage in the primary winding serves as the 'movement' needed to induce a voltage in the secondary winding. And as you've probably guessed, the voltage in either winding is proportional to the number of coils in the inductor; if there are more turns in the secondary, its induced voltage will be higher than the voltage in the primary. But there's no such thing as a free lunch, the total amount of energy remains the same. If you pump in 120 watts (that is, ten amps at twelve volts) to develop, say, 30,000 volts in the secondary (about what you need to jump the gap of a spark plug under worst-case conditions) the amperage can't be more than about three-thousandths of an amp (.003). Actually, things never work out that neatly in reality because there are losses in the coil's iron core, etc.

Why The Capacitor is Needed

Those same principles of inductance create a kind of paradox, because when you stop feeding juice to the coil, that is, when the points open and the magnetic field collapses, inducing the 30,000 volt current in the secondary, it also induces a current in the primary as well! It's not very much because there are only a few windings in the primary, but it's enough to jump a small air-gap, such as the one between the just-opening points in the distributor. That tiny spark is enough to erode metal away from the points and if there is any oily vapor inside the distributor, any oil on the points will become carburized; you'll 'burn' the points.

To keep your points from burning as they open and close, you'll need to provide something to absorb that spike of counter-current, something more attractive, electrically speaking, than the air-gap between the points. That's a job for a capacitor. To the counter-current, the capacitor looks like a black hole, an attractive one. The spike of current dives right in. And the points don't burn.

The points have a tough job, switching up to eight amps of current many times per second at highway speed. Indeed, as engine speed increases the efficiency of your ignition system decreases, thanks to heating problems and fundamental electrical laws. This declining efficiency has a serious effect on your spark voltage and results in poor high-speed performance, incomplete combustion and a host of other ills.

But us humans are tricky rascals. To see how tricky, read the articles covering electronic ignition systems.

-Bob Hoover
-1995

(Ed. Note: This article deliberately ignores more sophisticated resonant frequency explanations of the coil-condenser relationship as being unnecessary with regard to vehicle maintenance.)

VW - Let There Be Light!

.
So there you are, purring across the desert in the cool of the night and there's a funny sound from the engine room and the purr gets a little quieter and that damned red light comes on. You just lost the fan belt.

No big deal; you've got a spare. And the lug wrench is the same size as the fan pulley nut and you've even got a screwdriver to keep the pulley from turning while you take off the nut. But the flashlight has those Civil War surplus batteries and gives you one last good-bye glow like a tiny red worm and dies. You're fresh outta light.

Doing it in the Dark

If you got a bug, changing your fan belt in the dark isn't too bad. You've got your flashers going of course, and they throw a little light into the engine room. But let's hope you don't drop anything, you'll be pushing your bug back and forth, playing patty-cake with the ground hoping all those stories you've heard about night-time desert creepy-crawlies aren't true. (They are.)

But you have a neat little trouble light in your kit. It's your static timing light. Connect it up, change the fan belt and you're on your way.

Sure is nice to have the right tools when you need them, eh? What? You say it's back at the house? I don't think that's a very good idea, do you? Why don't you keep it in the door pocket with your fuses.

Whatdaya mean, 'What fusess?'

Reality Check

Most good cars provide a light under the hood, another in the trunk, one in the glove box, a couple under the dash, one by the ash tray... Good cars provide good lighting; they assume you'll drive at night now and then. Cheap cars don't do that, assuming you'll stay home glued to the tube when the sun goes down. The Volkswagen is a cheap car (or usta be!). The only lights you get are the ones required by law.

My 1973 Datsun pickup has a little light under the hood, positioned so you can check the oil. It's a very smart kind of light. (Only after praising the Datsun people for their thoughtfulness did I learn that such a light was a legal requirement in some countries where 1973 Datsuns were sold.)

Letting in the Light

I've got four lights in the engine compartment of my 1965 bus, two in the engine compartments of the Ghia and sedan, two on the baja.

On the Ghia and bugs I put one of the lights on a bracket pop-riveted to the blower housing, positioned so as to illuminate the distributor and that side of the carb. The other light is mounted on the base of the generator tower so I can see the dip stick and the timing marks on the pulley.

The light fixtures I used are high quality new-surplus items manufactured by Grimes, the aviation people. They are solid nickel-plated brass jobbies that cost a couple of bucks each. Pretty small; Grimes calls them 'panel lights'. They use the commonly available #1816 12vdc lamp. (That's the GE number; it cross-references to others that will fit.) The lamp is small, about like a flashlight bulb. If you want more light than it provides there is a halogen replacement.

I got the light fixtures from American Science & Surplus (3605 Howard St., Skokie, IL 60076. (708) 982-0870 ) The part number for the lights is #10572. Cost was about two bucks.

(Ed. Note: About two weeks after I posted this in 1995 people reported the fixture I used was no longer available. Which doesn't change the purpose nor value of this message: You need light in order to do useful work, and other fixtures are available. Nowadays [2006] I'd recommend using LED's rather than incandescent lamps.)


Screwing Them On (or up, your choice)

When mounting the lights on the engines I made up brackets from sheet steel or aluminum. On the bus, I used aluminum angle stock and mounted the lights on the overhead of the engine compartment. In all cases I gave the lights their own fused circuit, installing the fuse and the light switch on a small panel tucked up out of the way. The panel is aluminum, shaped to fit, installed with either screws or pop-rivets.

Since I was running an auxiliary circuit I figured I might as well run a good one, going directly to the battery with a 10 gauge wire. This is easily done in the bus and Ghia, where the battery is in the engine compartment. On the '68 sedan I snuck the wire under the body, fastening it securely at several points and protected inside of black polyethylene tubing, the stuff they use for drip irrigation systems. On the '67 baja I pulled the wire through the body channel with the other wiring.

Why such a big wire? For the cigarette lighter. Or rather, for the cigarette lighter socket. (I smoke a pipe; kinda hard to get going with a cigarette lighter.) The socket is fused with a 25 amp circuit breaker. I use it to power a 12vdc air compressor or a trouble light or a camping lantern or a ham radio or... or whatever you might want to plug into a cigarette lighter socket. I guess the thing would even work as a cigarette lighter, although mine comes with a big red plastic plug to keep out the dirt. (Baja-dust is special stuff, capable of penetrating six inches of steel plate.)

(Ed. Note: The cigarette lighter socket proved its worth on the run to Inuvik when it was used to power my 12v soldering iron with which I repaired a cracked plastic recovery tank on a water-cooled Vanagon.)

No one ever notices the auxiliary lights, unless they see them on at night. The lamps are hooded; the light shines where you're looking, not in your eyes, and on the bus each of the four fixtures is behind a rib or strut. The wiring is wrapped in looms and the looms secured with aircraft-type wiring clamps, secured to the chassis with stainless steel sheet metal screws. The switches and panels are out of the way; you have to look for them to see them. No chrome, no colorful curly wires; everything is built for the long haul and so far, has worked exactly as intended.

Sermonette

I plan to keep my Volkswagens until I fall apart. Until that happens I'm going to keep doing what I like to do, which is to head for places well off the beaten track. The lights and the auxiliary power outlet make things safer and more convenient, and enhance the usefulness of my vehicles. Installing them took a bit of work but if properly done it's a one-time thing, good for the life of the vehicle. Such things are worthy improvements for early Volkswagens.

-Bob Hoover
-1995

AV - Flow-Bench vs Reality

--- In AirVW@yahoogroups.com, CaptonZap asked:

> Have you ever heard of a flow bench that pulses? -----------------------------------------------------

Some fluidics applications -- gates and the like -- are tested using a flow-bench that emulates real-life situations. But I've never heard of such being applied to an automotive flow-bench.

---------------------------------------------------

>I don't know if the difference in > flow would warrant the trouble to make a pulser for the bench. Any thoughts?

--------------------------------------------------

The original purpose of the flow bench for head work was to provide a measure of merit rather than quantified data. But it wasn't long before we saw flow-bench figures converted into purely notional units of cubic feet per minute (what you actually measure is the pressure differential) and used to sell junk to the Kiddie Trade. The same sort of 'bigger is better' hype is used to sell cams, valves, cranks, jugs and so-forth.

After my second tour in Vietnam I built a rather elaborate flow-bench. Over a period of about seven years the most valuable thing it taught me was how little I knew. And I'm not just talking fluid dyamics :-)

As you've already guessed, measuring the flow of air can only provide a measure of merit -- this head flows more (or less) than that head. But fuel-air does not behave the same as air alone. Smoke or other benign suspended colloid, in the proper ratio with air, provides a more realistic test -- and often produces results significantly different than when using air alone.

The idea that a simple measure of merit is good enough for selecting the 'best' heads is only valid for dragsters, where fame & fortune is based on a run-time of six to ten seconds. As soon as you add durability to the equation -- and measure it in hundreds of hours rather than tens of seconds -- you may as well throw away that huge pile of heads you've been working with and start all over. If you do that, don't be surprised if your best efforts looks remarkably similar to the heads off existing aircraft engines :-)

An even tougher test is to discover that after a thousand hours of work you've managed to confirm what Sir Harry Ricardo defined in his book... in 1920.

---------------------------------------

Lemme give you an example of why the flow-rate thing is mostly hype. Let's use a 2180cc engine having a volumetric efficiency of 100% (yeah, I know -- impossible -- but work with me here). 2180cc times 0.06102 equals 133.0236 cubic inches. But were talking a four-cylinder Otto cycle engine so the actual displacement per revolution is just half that or about 66.5 cubic inches per rotation of the crankshaft.

Now pick an rpm, something seriously silly for an airplane, such as 3200... because you want to make the prop horribly inefficient and wear out the engine quick like a bunny. Or whatever :-)

66.5 cubic inches times 3200 rpm is 212,800 cubic inches. Divide that by 1728 and you've got 123 cubic feet per minute.

That's a totally fallacious figure because at that rpm your VE won't be anywhere near 100% but lets use it as a bench mark... or even round it up to 125 cfm just to make the figuring a tad easier.

Keep in mind, that's the also flow through the carb for the entire engine -- all four jugs.

Now take a look at all those trick heads they sell to the kiddies. Huge valves... which run hot and seal worse than smaller valves... but a nice match for the huge ports and cut-away valve guide boss... that gives you flow rates per cylinder as high as 350 cfm. Wow! Gotta be good, eh?

If one jug can flow 350cfm, with four-cylinder Otto cycle engine that means it has the potential to pump 700 cubic feet of air per minute! Gosh! Is that great, or what?

Did anyone notice that the maximum amount of air the engine can use is only 125 cfm? Apparently not, because hi-flow heads sell like hot-cakes :-)

Wanna build an engine for a replicar like the Beck 550 Spyder? Then you want something that can spin seven grand and hit one-forty on the straight-aways. That's when you go for hi-flow heads, six pound flywheel, titanium valves and four 40mm Dellortos.

But not to sling a prop.

The airframe dictates the prop and the prop dictates the engine. That's when you discover that the actual flow-rate of your engine is something less than 90cfm and that even Single-Port heads can give you that. Of course, you put your stock SP heads on the flow-bench and clean up the ports and swirl-polish the valves and attend to a host of other minor chores and come up with a marked improvement in your volumetric efficiency for nothin more than a bit of labor.

Why the interest in volumetric efficiency? Because in a normally aspirated engine peak VE tends to coencide with peak torque. And despite what the hucksters keep yelling, with a fixed-pitched prop mounted directly to the crankshaft the key factor in producing thrust is how much torque you have available at that particular rpm.

-----------------------------------

Which prolly isn't the answer you expected, although you did ask for 'any thoughts' :-)

-R.S.Hoover

Tuesday, November 28, 2006

AV -- The Valve Cover IQ Test

.
Back in the Good Ol' Days, whenever that wuz, one of the most common of the lo-buck tricks me and the other fools applied to Volkswagens was to install a set of rocker arms that had a ratio higher than the stock one-to-one. That should give you the clue that I'm talking the 1950's here. (The rockers on later engines were one-point-one to one and the VW industrial engine that ran on alcohol was one and a quarter to one... but I'll get around to that in another message).

There were lots of tricks in making up a set of 'ratio'd' rockers. You'd usually have to bush the bore, since the VW uses a rocker shaft having a rather small diameter. Once you'd bushed your donor rockers you'd hone them to match the VW shaft. Or not bush them and make a new shaft and modify the heads to accept it. Lotsa ways to skin that particular cat.

American custom is to put the adjusting screw on the push-rod side of the rocker-arm. (Stock VW rockers have the adjuster on valve-side.) Unfortunately, the adjuster would often hit the valve cover, which could be kinda interesting if you hadn't figured that out ahead of time. If you had, you'd heat up the valve cover in the area where the rocker was making contact and forge a little blister to make room for the adjusting screw. Which worked fine, so long as you stuck with the stock cam, which like most chuggers doesn't have a lot of lift.

In the early 1960's following the introduction of the 1300cc engine things got a lot more interesting, with folks offering high lift cams and higher ratio'd rockers specifically for the VW. Now the rockers weren't just hitting the valve cover, they were knocking the thing clean off the engine.

What was needed was a deeper valve cover. And as you've probably guessed, they soon appeared on the scene. Cast aluminum. Leaked like a bitch.

Turns out, those pretty cast aluminum valve covers not only leaked, they ran hotter than the steel covers. That's because folks liked to polish them up, get them shiny as a silver tea pot. And that shiny surface did exactly what all shiny surfaces do and reflected the heat of the oil back into the valve gallery. And of course, they leaked like a bitch.

The leaking is an artifact of the casting, which is just a thin shell. A thin cast shell. Not real strong. Clamp or bolt the thing to the head of a Volkswagen engine, as soon as it heated up it would distort and as soon as it distorted, it would leak.

The solution to the leaking problem was two-fold. First, you had to cast some ribs inside the valve cover; you had to make it stronger. The ribs stiffened it up so that it didn't distort so badly once it heated up. You also had to make the casting thicker. It weighed more of course but nobody cared about that. Second, you had to abandon the stock valve cover gasket and go to a specially molded O-ring type jobbie that socketed to the sealing surface of the cast cover. Expensive as hell but if you wanted to run ratio rockers and wanted to keep enough oil in the engine to finish the course, you didn't have much choice.

They still ran hotter than the steel covers but the cure for that was pretty simple. You blasted those mothers to within an inch of their lives then had them anodized black. The blasting gave them an `infinite' surface and the black dye improved the thermal transfer properties of the anodized layer.

Of course, they ended up costing one hell of a lot more than the stock valve covers and weighed nearly twice as much but that's what was on the engines crossing the finish line first so naturally all the kiddies had to have them. Until they saw what they cost. So the after-market retailers whipped up these cheapie cast covers and sold millions of the things to naive youngsters.

And naive airplane builders, too :-)

Seeing cast aluminum valve covers on a flying Volkswagen is one of those reverse IQ tests that tells you quite a bit about the fellow who built the engine.

Don't take my word for any of this. Go weigh the things. You are the Mechanic-in-Charge of your flying Volkswagen, even if someone else did the work.

Be sure to include the bails with the steel covers. And the studs, barrels, O-rings and what-not with the aluminum covers. Their thermal emissivity is equally easy to check, especially if you have one of those IR thermometers. Most impressive of all is an IR photo. Just put an aluminum cover on one head and a steel cover on the other. Saves you a thousand words.

No one believes it of course. Conventional Wisdom sez cast aluminum covers are a necessity for any flying Volkswagen. Indeed, almost everybody uses them, especially those folks trying to sell you dune buggy engines with a fan on the nose :-)

- - - - - - - - - - - -

So what about the real engine builders running high-ratio rockers with blueprinted valve train geometry that requires a deeper valve cover? You section the original steel covers and make up new bails. Not nearly as pretty but if you're more interested in the steak than the sizzle, sectioned valve covers were the way to go.

Herez how:

Have you got a stock valve cover handy? Weigh it. 345 grams, right? About three-quarters of a pound. That's a VW valve cover. [Look for the VW logo just to the right of the center rib.] There are some after-market covers made from thinner gauge metal that weigh as little as 250 grams [just over half a pound]. Okay, now look at the area of the valve cover just above the flange for the sealing gasket. Notice that the side wall of the valve cover has only a slight amount of draft; it's almost perpendicular to the flange of the sealing rail. (You know it can't be perfectly perpendicular because it's a one-shot stamping; all such stampings require some amount of draft.)

You can section a VW valve cover by nearly an inch, although that would be unusual. The typical high-lift rocker needs less than half an inch of additional clearance. Most guys section the cover at about three-quarter inch above the gasket rail then allow the donor valve cover to overlap. Do a few tack welds to keep things lined up then dress the edge for a gap-free fit. TIG is best here; the valve cover holds the gas and you can really roar along. But gas or even MIG works too. I've heard of them being brazed but I've never seen one done that way.

After it's welded you can clean things up with the grinder. Some guys leave the donor gasket rail hanging right there. They say it stiffens the thing up. When using a stock valve cover for the base I've never found any need for additional stiffness and usually cut away the donor's gasket flange before doing any welding. If you use a stock valve cover as the base and a lighter, after-market cover as the top, it should end up weighing about the same as a stock cover yet it will be about five-eighths deeper.

To section the bails, cut them on the side. Don't cut them to length, allow them to overlap at least 1". Set up a head and a sectioned valve cover as a welding jig but do not install a gasket. Position the parts of the bail so that they overlap uniformly on both sides (I put one wire down below the other, relative to the engine running position). You want the bail tight to the valve cover, and you want a heat-sink on the little end, where it hooks into the head. Do a couple of tack-welds with MIG or TIG then do the finish weld on the bench. I generally use MIG because it's faster; way back when, I used gas. Be sure to keep the heat away from the little end; the bail is music wire - - high carbon steel - - you don't want it to lose its temper. Clean and paint the bail. Use an enamel if you got it and give it a good heat cure. Add the weld to your pre-flight inspection (just look for any cracks in the paint).

Keep in mind, the only reason to section a valve cover is when you need additional clearance. Most engines do perfectly well with stock covers and bails.

- - - - - - - - - - - -

"Ha!" the prize-winning VW-flying fat man barked. "Shows how much you know. You gotta use bolt-on aluminum valve covers because that bail thing will break on you. An' besides, there's no way to safety that bail."

In more than fifty years of almost-daily hands-on VW experience I have never seen a broken valve cover bail that wasn't due to a collision. Nor have I ever even heard of one breaking, except from the fat man in the funny jump suit at the Ramona fly-in twenty years ago.

As for securing the bail, you safety-wire it. Just like we've always done. Go dig up a picture of those little Jodel's from the 1950's, lookit the way the safety wire runs down from the top of the head, around the bail, and is secured to the bottom of the head.

Cast aluminum valve covers are standard equipment for the Dune Buggy set although they are rarely seen at the finish line of off-road events. That's because the stock valve covers cost less, cool better, weigh less and seal better than the typical after-market cast aluminum valve covers. Plus, they tell you a lot about the guy who built the engine :-)

-R.S.Hoover

AV - Honest Engines

.
2180cc equals the total swept volume, or about 133 cubic inches. (Conversion factor: .06102 x cc = cu. inches)

133cid represents all four cylinders. Since this is an Otto Cycle engine and there are only four cylinders, there are only two intake cycles per revolution so we're really only interested in half the swept volume or 66.5 cu. inches.

Airflow is normally measured in cubic feet. There are 1728 cubic inches in a cubic foot and since one revolution pumps 66.5 cubic inches of air that's equal to .03849 cu. feet.

Optimum prop speed is across an rpm range from about 2250 to 2850.

2250 x .03849 = 86.5 cu. feet 2850 x .03849 = 109.7

That's for 100% volumetric efficiency, of course. And that can't happen unless the engine is supercharged. But at those speeds, with the valve train properly set up, a VE of 80% is possible if we can keep the temperatures down. That would give us a flow-rate of about 87 cubic feet per minute.

Air weighs approximately 0.08071 pounds per cubic foot so every minute we are pumping 7.081 pounds of air. (Keep in mind, this is for AIR, not OXYGEN)

The stoichiometric ratio for gasoline and air is 14.7:1 so every minute I'm burning about .481 pounds of gasoline, which means I will burn about 28.9 pounds of gasoline per hour at a throttle setting that produces 2850 rpm at a manifold pressure of about 3" of mercury. Since gasoline weighs about 6 pounds per gallon I will be burning about 4.8 gallons per hour. (Hint: Stoke is based on the mass of the fuel & oxidizer rather than its volume.)

Based on accepted standards for Specific Fuel Consumption (i.e., .5 lbs per horsepower-hour for a well designed air cooled engine) my 2180cc engine should be producing about 57.8 hp. And it probably will. But only during take off. That's because VW has not increased the size of the fins on its cylinder heads since it introduced the heads we all now use. Originally, the heads were designed for the 40 horsepower 1300cc engine. VW eventually bored the engine out to `1600' (actual swept volume 1584cc) but kept the same heads. The fin-area of the heads puts a thermal limitation on the output of any VW engine NO MATTER THE SIZE. The thermal limit is determined by the cylinder head temperatures, which should be kept at or below 325F. if you want the valves to last.

- - - - - - - - - - - - - - - - - - - - - - -

There are lots of variables in any on-paper exercise of this sort but even when everything is selected for the optimum output the difference is barely 10%. In reality, the nominal output of an on- paper engine is usually quite a bit better than anything you'll get from the real thing. Paper engines are goals to shoot for. So you do the best you can, isolating one factor at a time, making modifications to improve that single factor and running another series of tests. It teaches you a lot about engines. And about yourself.

On a broader scale, one of the most interesting aspects of the figures above is that they are in general agreement with figures produced by actual torque measurements on the Whatley test stand recently (Fall, 2003) discussed on various flying Volkswagen groups.

- - - - - - - - - - - - - - - - - - - - - - - - -

The numbers are interesting but the engines themselves are more so. And more fun. I've spelled out the figures I used so you plug in your own numbers for displacement and rpm, which I think you'll find to be the most significant factors. But there's a good chance you'll be mislead and the reason deserves mention.

As you increase the rpm the on-paper horsepower will rise dramatically. All else being equal (it's not, but bear with me here), you'll tend to fix your prop-speed at something more than 2850 rpm. But actual tests with real engines and real propellers shows that the efficiency of your prop falls at a faster rate than can be offset by any increase in horsepower. This is definitely one of the tricky bits because you end up with a `strong 70hp' engine that is producing barely 35hp-worth of thrust. I believe you will find that you can fly farther, faster, by using the longest prop your engine can swing.

Rather than give you a Break Mean Effective Pressure I used a nominal manifold pressure that is conservative compared to real aircraft engines. I used a conservative figure because I'd like to save you the trouble of blowing up an engine :-) Manifold pressure is also easy to measure whereas BMEP is not.

Increasing your compression ratio will improve your BMEP and thus the output of the engine but on the VW, as the output increases the heating effects become critical and announce themselves by a catastrophic drop in your volumetric efficiency... just before you eat it. That's because the incoming fuel-air charge absorbs a lot of that heat, which gives you a very lean burn. At high compression ratios a lean mix leads to detonation, quick like a bunny, and there you are surrounded by white smoke with a blown engine hanging off the test stand.

Which is better than having it happen when you're half way to Catalina. So be cool.

-R.S.Hoover

AV - Dynamo, Again

.
Electricity is produced when you pass a coil of wire through a magnetic field... or pass the magnetic field through the coil of wire.

If you wish to convert mechanical energy into electrical energy, if the input is rotary motion the output will be a sine wave -- alternating current.

The generic term for such devices is 'dynamo.'

The terms 'alternator' and 'generator' are used as a handy means of defining which type of dynamo is being used. In the generator the magnetic field is fixed and the coil(s) rotates through it. The output is an alternating current that is converted to pulsating direct current through the use of a mechanical switching system mounted on the shaft supporting the coil (ie, carbon brushes and a segmented commutator). In an alternator the magnetic field rotates while the coil(s) remains fixed. The alternating current that appears in the coil(s) is converted to direct current by a rectifier.

The output of any dynamo is a function of its rpm, the number of pick- up coils and the intensity of the magnetic field.

The most common means of controlling the output of your dynamo is to control the intensity of the magnetic field by regulating the amount of current that flows through the magnetic field winding.

If a variable output is not required you may replace the magnetic field winding with permanent magnets.

----------------------------

The key points here are that 'alternators' and 'generators' are both dynamos. Each uses brushes. Each has a magnetic field and regulates its output by controlling that field. Since the advent of solid- state rectifiers, alternators have come into general use because they are less expensive to manufacture but they aren't really new. The Leese-Nevil alternator using copper oxide rectifiers has been available since 1921. Nor are permanent magnet dynamos 'new' in that they've been around in the form of magnetos since the 1890's. The reason we're seeing more of them nowadays is a reflection of economies of scale in the production of rare-earth magnets.

-R.S.Hoover

VW - Stainless Steel Craftsman

.
Today I witnessed one of the most astounding feats of craftsmanship I've every seen. Roland Wilhelmy, owner of a '56 VW Sedan that is undergoing a hands-on body-off restoration, replaced the bug's original steel fuel pipe with one of stainless steel. The astounding part is that he didn't take the easy way out and run the new pipe along-side the tunnel, Roland installed the new pipe in the tunnel, and in the original brackets, to boot! And all without cutting or welding on the tunnel.

The early Volkswagen shop manual describes how to do this (Step 1. Remove the body...) but I have never heard of it being done. The labor and shop-space requirements are so high that everyone I know used the Alternative Procedure, running the new fuel pipe through the passenger compartment.

"I didn't like that idea," Roland said quietly.

So how did he do it? I'm not too sure; the shop manual sez you need a helper to guide the thing; Roland did it all by himself. (But I did notice a Pentacle on the floor of his shop :-)

My contribution to the job was to provide him with a piece of solid steel guy-wire exactly .156" in diameter. Working alone, he had already installed the new tubing almost the entire length of the tunnel, managing to thread it through the four intervening support brackets. He slid the heavy wire into the tranny horn where the original fuel pipe exited and somehow managed to insert it into the stainless steel tubing, out of sight inside the tunnel. Returning to the front of the vehicle, he commenced tapping on the end of the new tubing, projecting about four feet beyond the front axel. The stainless steel tubing inched its way around the bend where the tranny horns mate with the tunnel, following the line of the heavy wire, which now acted as a guide. In a few minutes the tip of the new tubing emerged from the tranny horn neat as can be.

Making the terminal bends in the new tubing and coaxing them into their respective positions took a bit more slight-of-hand but the job was finished in less than an hour.

I thought it was about the neatest thing since electric lights but Roland shrugged it off as no big deal. Perhaps not, considering what has gone before. He's already replaced all of the brake lines, done an IRS conversion to the rear suspension and there is a pair of disk brakes lurking up front, along with a steering damper, an important handling improvement lacking in early bugs. And the four-joint TransForm transmission has their special tag showing non-stock gear ratios. Roland is building a Porsche-eater, disguised as a Volkswagen. Yet the original 36hp engine and stock 1965 running gear was neatly stored on welded racks, preserving the option of returning the vehicle to all- original condition. Roland also drives a suspiciously quiet bus that has a few more carbs than most other '65 models.

As I was leaving, I noticed the body of the bug lurking back in a corner of shop, remarkably smooth under about a zillion coats of hand-sanded primer. Strictly stock. Perfectly straight. He's replaced a couple of body panels, including the forward engine compartment curtain, fitting one from a late model chassis, allowing him to use the larger engine's tin without modification. This is the kind of subtle attention to detail that you only see on race-winning road cars. The work was so neatly done I wanted to rub it against my belly. Asked how it was going, he gave another shrug. "Coming along." And grinned. That grin is going to make a lot of Porsche owners trade up to a Yugo.

-Bob Hoover
-Aug 1995

VW - Getting It Home

.

There are a couple of tricks that can get you home, or at least off the freeway should your cable break.

If you advance the idle adjustment screw to about 1,500 rpm you can make about 30 mph. You gotta eat a little clutch to do it, but it will get you off the freeway.

Bailing wire or stainless steel safety wire can be used as a wildly dangerous substitute for an accelerator cable (BT,DT). The problem is, you can't get the stuff straight enough; all those lazy bends bind in the tube going through the tunnel. Push your foot down, engine roars. Lift your foot (as when bearing down on three Mexican women who decided to cross the highway at that particular instant) AND NOTHING HAPPENS! The throttle stays open, you keep doing 90mph, and the women keep sauntering along. (Hello sagebrush, goodbye road.)

The trick? A bungee cord. And grease. Two wraps around the fuel pump then wire the bungee cord to the throttle arm. Grease the dickens outa that sucker before you push it into the tunnel.

The problem? Your foot's going to get awfully tired fighting that bungee cord. And it ain't doing the carb much good, either.

Here's the drill: Fan belt, clutch cable, throttle wire, six feet of rubber fuel line, all in one package. Inside the package is an adjustable wrench big enough to handle the generator nut, a pair of vise grips, two screwdrivers (big & little). The 'package' is a piece of sailcloth about one yard wide by two yards long. Tie it up with about ten feet of light line. Tie it up tight; makes a bundle about as large as a big thermos. Lash it to the roll cage with bungee cords.

I've seen some rigs, the guys don't even carry a regular tool kit. They've got their tools distributed all over the rig, tools and spare parts taped, lashed or wired right beside where they'll be needed. Doesn't make much sense in a daily driver but comes in at the genius level when seconds count. (I remember one guy who appeared to be wearing his tool kit. DNF'd)

-Bob Hoover
-Aug 1995

VW - Keeping Clean

Keeping Clean

>-Bob, >I love the idea of taking charge of my life and not being cheated >by dishonest mechanics, but my first (and last!) attempt to do my >own tune-up left my hands in such a state I'm terrified of >trying it again. I know you'll think it silly, but the appearance >of my hands is very important in my work. >-AnyMouse

----------------------------------------------------------------

Dear AnyMouse,

I don't think it's silly at all; the appearance of my hands is very important in my work as well. For example, if they are dripping blood and missing a finger or two, I tend to get real upset :-)

But in all seriousness you have a valid point. Cars are dirty and that dirt gets onto your hands. And when a good, black greasy goo gets ground into the dead skin around your fingernails and on your knuckles, about the only thing that gets it off is pumice -- you got to grind of the skin to get out the dirt. But when you do that, the result is sore, red hands that aren't much good for a couple of days, even to a hairy-chested mechanical type.

The trick to keeping your hands clean is to not let them get too dirty in the first place; you have to seal up your hands before you get them dirty using stuff like hair gel as a sealant. One brand is called 'Invisible Gloves' and forms a barrier strong enough to protect you from mild chemical burns; people allergic to epoxy resin and the like use it to keep from getting a rash. Just rub the stuff in like hand cream and let it dry. Soap and hot water takes it off.

My grandfather was a Mason, very involved with their affairs. He did all sorts of blacksmithing and machinist work yet had 'gentleman's hands' (my grandmother's choice of words). He used the hair-gel trick. He also scratched a little Ivory soap under his fingernails when he had an especially messy job.

There's a stuff called 'Machinist's Soap' that contains a chemical that will keep your hands from sweating. Politicians probably use more of it than machinists but you get the idea. If you can keep your hands from sweating you can wear surgeon's rubber gloves, or even those cheap throw-away plastic gloves, and still do some useful work.

You can buy both Invisible Gloves and machinist's soap from machinist supply houses (check your Yellow Pages) or outfits like Aircraft Spruce & Specialty Co., of Fullerton, California. They sell a lot of epoxy and the like. They're kind of expensive but you get what you pay for. Call them at (714) 870-7551. But if you check around, chances are you can get hand-stuff locally. (Everyone's got hands.) And after you're all cleaned up, go in and do the dishes! Washing dishes (or just soaking your hands in hot, soapy water) is one trick every mechanic uses to keep his hands presentable. (But most don't have the courage to admit it :-)

The down-side of scrubbing your hands with pumice and the like is that you'll literally wear out your skin. So you use an emollient. Since the days of the Romans common aloe has been used by mechanics, armorers and the like. Just break off a spear of the stuff, crush it in your hands, smear the green goo all over your hands and let it dry. It not only forms a protective barrier, the goo contains an anti-bacterial agent that will keep your hands from getting sore.

The other side of the Getting Dirty coin is keeping your engine clean. It's no different than anything else; if it's dirty, wash it. Auto-parts places carry special stuff for scrubbing engines but your veedub engine is mostly painted metal; treat it like you would your refrigerator or stove. So long as you don't go at it with a fire hose, a little water won't hurt nothing. You don't want to get water in the alternator, or down the carb, and covering the distributor with a plastic bag makes good sense, but aside from that, just jump in there and give that puppy a bath.

If your engine is dirty you're bound to get dirty working on it. So clean it up. No oven cleaner or scouring powder, soap & water will do just fine. I use dishwashing soap, the cheap green stuff, and a stiff paint brush (cutting the bristles shorter makes them stiffer). A toothbrush is just about the handiest thing ever invented when it comes to keeping your engine clean; worry about the nooks & crannies and the open areas will sort of take care of themselves. Once you've gotten the engine clean, spend a little time keeping it that way. It will do both you and the car a lot of good; it's one of the ways you take charge of your life.

Another factor in keeping clean is Dressing For the Occasion. That means long-sleeved shirts buttoned at cuff and collar, long trousers, and shoes that cover your ankle. Working on a car is a job, not an adventure; dress like you're going to do some work. Then let the clothes get dirty instead of you. As to style, I can't say I ever thought about it. Good mechanics tend to be neat by nature; they'd starve to death otherwise. I wear levis or khaki trousers, khaki or denium shirts, good serviceable American-made stuff. You can wash them every day and they'll still last for years. Avoid synthetics and blends; plain cotton is the stuff you want.

There's no mystery to getting grease out of cotton fabric. Use something like trisodiumphospate (try dishwasher soap) or Washing Soda and let the things soak. You're playing chemist here. You've got to give the chemicals a chance to work.

If you own a washing machine, figure out how to make the thing run two or more cycles. On ours, I just leave up the lid. It won't spin with the lid open. Next time I happen by, I reset it to start sloshing again. Do that a couple of time and even the greasiest levis come clean. Sorta faded, but clean. Same thing applies to getting the soap out of your clothes. After you get them clean, run them through another wash cycle with no soap; really rinse them puppies.

If you don't own a washing machine, get a 5-gallon plastic pail and start your own Grungy Laundry. Use a toilet plunger to slosh the clothes; you don't want to get that TSP on your hands.

The other thing you mentioned, the strength factor, is related to your remark about cutting your hand when the wrench slipped, but let me give you a little background on the problem. If you look at a new spark plug you'll see it comes with a washer, that circular metal thing just above the threads. Your spark plug is properly installed when it's tightened enough to compress that washer. There's a torque spec for spark plugs, and as you become more adept as a mechanic you should always torque your plugs to spec, but for now just get them tight enough to compress the washer and they'll work fine.

The compressed washer is why they were so hard to loosen. As you mentioned, once you got the wrench to turn, the plugs unscrewed easily so lets focus on loosening them. The secret here is to use a bit more leverage; a longer wrench. No, you don't have to go out and buy a special wrench, what you want to find is a piece of pipe or tubing that will fit over the wrench you already have. And yes, Craftsman tools are good ones. But Sears probably can't sell you a 'cheater,' which is what you call a piece of pipe when you use it to gain leverage.

What you want is a piece of electrical conduit about a foot long. Or even a piece of plastic water pipe. The diameter is determined by your tool.

When you've got the socket on the spark plug, position the wrench so you can slide the cheater over it and still have room for a short pull. Support the wrench -- you never want to get too rough with spark plugs or you'll break the ceramic insulator -- and take a strain on the cheater. Never jerk on the thing; you've got more than enough strength to loosen the plug if the lever is long enough. The plug will come loose with surprising ease, so don't pull too hard or your hand will come flying off and you'll bark another knuckle.

It didn't come loose? Lengthen the cheater a little and try again. And make sure you're turning the plug in the right direction. On your Ghia the plugs on the passenger side will unscrew when you PULL on the cheater, assuming it is pointing UP. On the driver's side you'll have to PUSH on the cheater. (The manuals will say "Loosen in an anti-clockwise direction," or something equally unclear.)

And of course, you do the same thing when you put in the new plugs. Use your cheater to tighten them. Just be careful not to overdo it; with the right lever you'll have more working muscle than Hulk Hogan.

The principle of lengthening the lever-arm of a tool may also be applied to the generator pulley nut and those 'impossible' lug bolts you mentioned. Fact is, the lug bolts on your wheels should never be run up tight with an air-wrench or you won't be able to change the tire without help. Use a nice l-o-n-g cheater to loosen them, then re-tighten them, snug as you can. You don't have to take them out, just loosen then re-tighten them to your specification. The stock Volkswagen lug wrench was designed to be used with a cheater. Get one made out of pipe, not plastic, and carry it in the boot. That way you'll know you can always change your own tire.

Along with the cheater you may want to carry some of those disposable plastic gloves; tires are dirty too. I've never used the 'paper' coveralls you mentioned but if the 'paper' is Tyvex, I know what you mean and I think it's a wizard idea; there's no reason to get filthy just from changing a tire.

I'm sincerely sorry you hurt yourself working on your car. It wasn't the cars fault, nor yours. The blame has to fall on a society that simply doesn't care all that much for the details of life. I hope this note will provide the encouragement you need to give the mechanical arts another try.

-Bob Hoover
-1995

VW - Custom Hat

He kept looking at my head. Every time I reached for a tool, the guy was alooking at me. I finally eased the creeper all the way under his bus and out the other side, got up and took a peek in the passenger-side mirror to see what was hanging out of my nose. Nothing. And no funny smears of grease. Beard wasn't on fire. Teeth hadn't fallen out. But he kept looking at my head!

Finished up, told him he could rebuild the starter if he wanted to but I didn't know any source of new solenoids and that was the real problem. He didn't care; as a mechanic he probably made a fine programmer. Paid me; told me I could keep the old starter if I wanted it. I didn't, which kinda surprised him (I got enough junk to worry about). Then he sez: "I don't suppose you'd consider selling your hat?" My hat?

Took it off to see the gold coins I'd missed. Nada. Old, faded olive-drab looking thingee, kinda greasy around the bill. Got a little VW bus embroidered on one side; you gotta look for it. Over on the other side it sez 'VANS'.

"Where'dya get it?" He's all puppy-eager. Clean hands. '73 Westy, all polished up and neat.

I couldn't recall. "Some race... " SNORE? Some guy was handing them out to the pit crews.

"Would you take ten dollars for it?"

That caught me. It was a second before I started to laugh.

"Twenty?"

Hell, the damn fool was serious! I handed him the hat; he handed me a twenty. He put on the hat, one size fits all. Drove off happy as a clam.

Couple days later I was over by the airport, stopped in at the VANS sneaker factory, picked me up a new hat. $4.95.

"You wouldn't believe what happened to my old hat," I told the kid. But he didn't want to hear unless it involved ten foot waves. Took my money, gave me the hat.

Veedubers is some strange folk.

-Bob Hoover
-July 1995

VW - Camping, Tents, Baja and Buses

.
I don't use a tent when I knock around down in Baja, not that it doesn't get cold and sometimes, rarely, there are reports of rain. (I've seen rain in Baja, but only from a distance.)

Standard Baja camping equipment is two tarps and four metal poles; metal, because if you use wooden ones some damn fool will put them in the fire. Lotsa rope; rope is very handy stuff in Baja.

You use one tarp as a shade. The only tree in Baja is in front of the mission at San Ignacio and they don't like you to camp there. So you tie one side of the tarp to the roof rack and prop up the other side with your metal poles, lash everything down with rope. Use bridge spikes as stakes to secure the rope. Bridge spikes are those humongous nails you've seen at Home Depot (and wondered what they were for). Now you know. Bridge spikes are Baja tent pegs. (Because you can't drive a wooden tent peg into the ground anywhere south of Maneadero. And some damn fool will put them in the fire.)

You use the other tarp as a ground cloth. That's where you sleep, on the ground cloth. Under the shade. (Down in Baja it's even sunny at night.) You set-up your table on the ground cloth, and your cot, and your Coleman stove. Leave the porta-potti in the bus, along with the icebox. And the magazines. Put the shotgun near the Coleman stove, down by the propane bottle.

In Baja you fish; that's why it's there. You don't shoot; guns are illegal everywhere in Baja except in Tijuana and then only at night in the downtown section. Everywhere else you gotta use a machete. But a machete or even a pistol is no good against flies, least ways not against Baja flies. Oh, I used to use a pistol on them; most guys start out with a pistol. But if you don't hit them suckers square you won't kill them. And a wounded fly will get madder than hell. So use a shotgun. I know; it's not a sure-thing either, but it will knock them down, give you a chance to go after it with your machete. Once you got the wings off them suckers you can get in close, finish them off with your pistol.

It takes about thirty minutes to set up camp in Baja, unless you've got women along. It takes longer with women along; give yourself lots of time. Set up camp, take a stand, knock down the Boss Fly to let the others know you mean business, then go fishing.

Women always want you to bring a tent along. And extra clothes; stuff like that. Truth is, you don't need that much in Baja; the fish don't give a damn what you got on. But woman are handy things to have around, especially in Baja, what with all that gutting and cooking to do. So mebbe you'd better plan on a tent. And wearing clothes.

If you've got a VW bus you can get one of those nifty little tents that hooks on to the spray rails, sets up quick as bunny, lets you get the boat in the water that much sooner. But they're hard to find; you might have to make one.

Here in southern California they've got these fabric supermarkets, big as a football field; sells nothing but fabric. Sailcloth. Upholstery stuff. Foam. Dacron for airplane wings; every sort of fabric you can think of and all the gee-gaws to go with it. Go down there and get you a buncha' tent-fabric, take it to an upholstery shop. Or a sail loft. Hell, mebbe they even got tent shops; check the yellow pages. The fabric will cost more than the sewing and he'll need a pattern. I'll leave the pattern up to you; mebbe you could ask a woman, they mess with patterns. If your wife is handy that way, mebbe you could just take the tent fabric along the next time you go to Baja; give her something to do while you're out fishing; let her run up her own tent.

-Bob

AV - The Wandering Prick Mark




The typical aviation apprentice, military or civilian, is a teenager fresh from high school. Homebuilders are rarely that young but unless their background has been in aviation, they too are an apprentice of sorts, at least with having to undergo the same Rites of Passage of an apprentice aviation machinist or metal smith. One of those Rites is layout work, long the bane of every aviation apprentice. Mature in years, albeit not in aviation, this particular Rite can prove especially trying for the homebuilder because any emphasis put upon layout work often appears to be a waste of time. Every adult is familiar with rulers and pencils; with the measuring and marking of things. Why should doing so for airplanes be any different?

In a purely engineering sense, airplanes are not different from other automotive machines whose design is optimized to yield the highest strength for the least weight, even though that achievement has spawned a body of procedures, techniques and specifications unique to aviation. I’ll address a couple of those aviation-unique things in a moment but in a philosophical sense airplanes will always be different because man can not fly. If a boat or car should fail us, we can swim or walk. But airplanes embody a form of implied trust not found in any other auto motive device, in that the mere use of the thing, properly and correctly, will not kill us.

Each new physician is required to swear that at the very least, he will do no greater harm. There is no Hippocratic Oath for aviation but if there were it would probably be: Let’s try not to kill anybody today. And that’s why airplanes are different.

- - - - - - - - - -

Note: Automotive means a machine capable of moving under its own power. The Society of Automotive Engineers encompasses everything from paddle-wheel steamers to the Lunar Lander.

- - - - - - - - - - -

I hope this doesn’t come as a surprise but when using a machinist’s combination square, steel ruler, tape measure and so forth, your best efforts at laying-out will always be off, plus or minus, by some amount. This is normal. The error reflects the precision of your tools and your experience using them. For example, the width of the markings on your tools introduces some degree of imprecision, as does the way you look at the markings, as well as the manner in which you make marks upon the workpiece. So long as work must be laid out by hand there will always be some degree of error. For the sake of safety, that error is always taken into account in the design of airplanes and the layout of their parts.

(Personal Note: Always buy the best tools you can afford. A quality tool will last your lifetime. Or more. I’m in my sixties. Some of my tools belonged to my grandfather, others to my dad. A quality tool is a practical legacy and daily memorial.)

One of the realities of aviation is that airplanes are still built by people rather than robots and human abilities as tool users varies from one individual to the next. Much of the basic training for aviation sheet metal workers and machinists is devoted to teaching standardized methods that reduce human error to an acceptable norm. Scribing a line or pricking an intersection offers a good example of the subtle differences in our ability to use common tools. In a class of about twenty-five, when using a combination square, pre-set to a given dimension by the instructor (but each student using their own scriber), it is rare for any two lines scribed by the students to fall upon the same point.

A similar variation is seen in the student’s efforts to place a prick mark at the intersection of two lines. Magnified and displayed on a video screen, the crater of the prick mark will be canted to the left or right, depending on the handedness of the student, and however canted, seldom falls exactly upon the intersection. This is not a graded exercise but a demonstration, without which the tasks to follow might seem a waste of time. Everyone knows how to scribe a line and use a prick punch. Or think they do. The demonstration makes it painfully clear that all lines are not created equal :-)

As with any of the manual arts, practice makes master of the man. An experienced machinist, working with his own tools, will usually have a scribing error between one and three thou. For a student, the error is typically between eight and fifteen thou. Learning how to hold and use the tools will reduce the error. A useful exercise is to lay out a grid upon a coupon of aluminum or steel and to prick punch the intersections, an obvious waste of their time... without the prior demonstration.

Keeping a blade or straight-edge flat to the work while holding the scriber at the proper angle does not come naturally to all. Yet these seemingly insignificant details have a profound effect on the magnitude of your scribing error, as does the sharpness of the scriber’s tip and its shape. All scribers have a slightly different shape to their tip. Viewed with 3x glass, most define a ogee curve (ie, ogive, etc., similar to the nose of a Spitzer type bullet). That means the tip of the scriber will always fall some distance away from the blade against which it is pressed. That distance will vary according to the thickness of the blade the angle at which the scriber is held. Learning to polish a symmetrical needle point onto their scriber results in an immediate narrowing of their scribing error. (Some machinists stone a small flat on the side of the scriber’s tip, allowing the tip to fall closer to the blade.)

The fact scribing errors exist isn’t the object of the exercise - the errors are painfully evident when the workpiece is projected on the screen (or when viewed using a low power binocular microscope). The object of the lesson is for each person to understanding the factors that cause such errors. Once the problem is understood, we can move on to weightier subjects, leaving the student to reduce their particular error to an acceptable level through practice and self discipline.

Some error will always remain and while a small error is generally considered better than a large one, the real goal is consistency. Once their error becomes consistent we simply calibrate the student :-)

This calibration is nothing more than teaching the student to recognize their normal working tolerance - how large their particular scribing error happens to be. Once the error factor is known it can be dealt with by adding or subtracting that amount to your tool's settings when laying out a line. One way of doing this is through the use of shims, selected to match your rate of error. I'll have more to say about this in a minute. Right now, I want to address the Wandering Prick Mark.

Visual acuity in humans varies over a wide range and declines with age. Some can see divisions as fine as one hundred twenty eight to the inch at arms length with perfect clarity while others have trouble with sixty-fourths held close up. Even when a fine line is visible, variations in hand-eye coordination result in errors when transferring that line to the workpiece, pricking an intersection or setting a tool. When asked to set the blade of their combination square for a projection of one inch, it's rare for even one of the class to hit it dead on. (And if she does, you simply reset her square and ask her to do it again.) An experienced machinist can usually come within plus or minus 0.003" of a mark with a reasonable rate of repeatability but it's a more difficult thing to do than most realize.

So don't do it. Not with your naked eye. Unless you're an experienced machinist.

At the very least, a magnifying glass should be used when picking up your points. There are inexpensive optical devices that allow you to prick the intersection of two lines with repeatable accuracy of about +/- 0.003", which is very good for even an experienced machinist. (Look under Optical Center Punch in the catalog of your favorite supplier [ie, Travers, MSC, Enco, etc.] You'll also find plans for do-it-yourself versions on machining-related newsgroups.)

In a similar vein, you would not use the naked eye to set the extension of the blade of a combination square unless the allowed tolerance was on the order +/- 0.015" (ie, about a sixty-fourth). Instead, you would use a known standard, such as a stack of Jo blocks on a surface plate and set the blade according to that. The resulting setting will usually be within a couple of thou (usually + zero, minus something). Which should be more than enough. If greater precision is required, you wouldn’t be using a combination square. (What would you use? A template or drill jig, created using something other than hand tools.)

But the odds are you won't have a surface plate or set of Jo blocks in your kit. If you're the typical homebuilder, what you'll have is a collection of tool bits of various sizes, measured and marked so their dimensions are known. And your scribing shim is liable to be a piece of cigaret paper (!).

A cigaret paper is about one thousandth of an inch in thickness - thinner than a human hair. The thickness varies from batch to batch and brand to brand. (Buy yourself a packet of Zig-Zag or Bugler and measure them. You'll see a similar packet in the tool box of most machinists.) Dry paper doesn’t make a very good shim. (Paper tends to compress.) But when paper is treated or filled it serves quite well, as shown by its use for gaskets. On the job, the handiest filler is to simply soak the stuff with kerosene or light machine oil. The dimension of oiled paper is more than stable enough to be used as a shim for casual layout work, setting the height of a sharpened tool bit and so forth. (Indeed, paper shims were the standard method of adjusting cutter depth in rifling machines for more than a hundred years.)

To subtract your scribing error to the setting of the blade, put the shim under the blade of the square where it contacts whatever you’re using for a surface plate. To add your scribing error to the measurement, as when scribing off the frame of the square, simply add the shim to the stack.

In addition to tool bits, which usually range between plus zero and minus two or three and vary for each face (ie, they aren't especially precise), another handy source of inexpensive gauge blocks is precision ground tool steel or tooling plate, which is often within .0005" across one dimension (ie, either thickness or width - more precise than you’ll need to build an airplane).

Unless you’re using real Jo blocks on a certified surface plate, the accuracy of your stack-up gauge will wander around a bit. Its saving grace is that it?s quick to set up, inexpensive, highly portable and more accurate than your eye. If greater accuracy is needed you may set the blade using a beam-type caliper or depth mike but for this type of layout, that degree of precision is rarely needed.

Which begs the question: How good is good enough?

All dimensions have a tolerance related to them. This is an inescapable reality of machine work. (Or life itself, when you think about it. Nothing is perfect.) A dimension and its tolerance is inherently linked; you can’t have one without the other; they are a paired set. And since the two can not exist apart, when tolerance is not stated, it is implied.

Until the creation of the International Organization for Standardization (ISO) in the late 1940's, the minimum accepted tolerances for working layouts for airplanes (as opposed to patterns, fixtures or jigs) were plus or minus 1/64th for fractional dimensions, +/- 0.015" for decimal dimensions and plus or minus one-half of one degree for angles. Manufacturers often had their own minimums but trade schools generally used the tolerances above, as you’ll see by examining any of the manuals from that era.

ISO changed all that. When the United States went metric in the mid-1970's we did away fractional dimensions, which today are rarer than fur on a turtle except in the homebuilt community, reflecting the tools and non-aviation background of the typical homebuilder. You run into fractional dimensions occasionally when doing repair work on pre-ISO airframes but most American aircraft manufacturers had already gone to decimal dimensions by the time ISO arrived.

Today’s homebuilders manage to escape most lay-out chores, thanks to simple CAD programs such as DeltaCAD, a simple 2D replacement for the traditional T-square, triangle and engineer’s scaled ruler. Now we need only print the lay-out full-scale, glue it to the part with a spritz of spray glue and use an optical center-punch to pick up our intersections with an accuracy equal to that of a skilled tool & die maker.

-R.S.Hoover

AV - Douglas Fir Isn't


.

A fir, that is.

Doesn't really matter of course. Unless you're into botany.

But it's not hemlock, either. Although that's what it most closely resembles. Which is why its Latin name means 'False Hemlock.' (Pseudotsugo... pseudo = false, tsugo = hemlock). The complete name is Pseudotsugo menzieii and gives you a hint there's more than one variety of 'Douglas Fir'. In fact, there's about half a dozen 'pseudotsugos' including coastal, mountain, Mexican, Manchurian and a couple others.

Don't worry about it. Go to a lumber yard, ask for Doug Fir, you'll probably get the pacific coastal variety. Other than being a bit brash, Douglas Fir, also known as 'Oregon Pine,' is fine for all aspects of airplane construction, assuming you can afford the weight.

But don't mention airplanes. Tell them you're looking for sucker rods or stair treads or ladder rails. (A sucker rod is that thing going up & down on a windmill. Up to 28 feet long, perfectly clear- grained Doug Fir, up to 4x4 in the middle, thinned down to 2x2 on the ends.) Stair tread stock tends to be heavy, with ring-counts of 16 and up. Ladder rails were long the standard for airplane spars, in both spruce & fir.

Lumber yards that cater to this particular trade usually buy clear-grained balks of Doug Fir in 4x6 or 4x10 rough cuts, up to 32' long. They'll slice off what you need and finish it, too... if they've got the tools. Real lumberyard can start with a tree, give you rungs for a chair.

Here in Sandy Eggo county I think we've got three real lumber yards left. One caters to boaters, one to farmers, the third to yuppies. It's a sixty mile drive to the farmer place but always worth the trip. Little place. Been there forever. They buy about two truck- loads of Select Grade-A DF a year from a little lumber mill in British Columbia, turn it into sucker rods, wagon tongues, ladder rails, pruning poles and the like.

Sitka Spruce is lovely stuff to work with but there are more than a dozen alternatives listed in AC43-13. Lotsa Piper Cubs flew on spars of 'Oregon Pine' and the first Pietenpol used edge-glued Hemlock for spars (according to Mr. Pietenpol).

-R.S.Hoover
PS - Some Douglas Firs are bigger than others :-)