A Shy Person asked:
>Got a question on windshields. Mine is in pretty good shape as far as nicks, chips, smokey corners go, but it does have a lot of fine swirl type scratches in it. Maybe from being washed so many times? Anyways, is there a way to refininsh the surface?
--------------------------------------------------
Dear Shy Person (and the Newsgroup),
No problem. Get yourself some cerium oxide and a felt polishing hob. Make a mixture of cerium oxide & water having the consistency of light cream. Paint it onto a small area of the glass and buff with the felt hob mounted in a low-speed drill motor. Keep the stuff damp -- spritz on more water and add more polishing compound as needed. Dry and buff with a soft cloth, inspect the surface with a loupe of at least 5x (look for tiny 'rainbows' -- refraction from microscopic pits & scratches... if you do a good job, you won't see any). Takes about 20 minutes to polish an area the size of your palm. But worth the effort.
You can get a 'kit' of cerium oxide & polishing hobs from J.C.Whitney. Cheap.
Stantium oxide cuts slower than cerium oxide, gives a finer finish. Ferrous oxide, the red stuff -- and often called 'rouge' for that reasons -- cuts slowest of all, gives the finest finish. But rouge is messy as hell and ferrous oxide can react with rubber & trim.
Polishing the windscreen is a standard procedure for vehicles that accumulate a lot of mileage -- buses, trucks and the like. But if the scoring isn't too bad you may not need to polish -- you can get rid of the refraction problems by filling minor scratches with black wax then buffing the glass smooth. This only works if the scratches aren't too deep.
Rain-X also reduces the effect of light-scatter caused by scratches but a layer of Rain-X can prevent the polish from working so try that last.
-Bob Hoover
Sunday, December 10, 2006
Easy Pickin's
Dan Rose opined:
>Historically, robbing someone meant having your hands cut off. Today, in some states you can be killed for commiting certain crimes. None of these punishments deters would-be criminals.
Whoa, there cowboy. How did 'would-be' criminals get into this conversation? The methods above are designed to deal with known criminals... and they are very effective. (Kinda hard to pick a pocket without any hands :-)
> We have to look at what factors promote crime.
We? If you want to get into the philosophical aspects of the problem you'd better begin by defining government, get the mouse out of your pocket or stop using the Royal 'we.'
People create governments to accomplish collectively what cannot be achieved individually. But our government has already told us -- through case law and other means -- that our personal security and safety is an individual responsibility. Collectively, the cops will try to help... if they can... but we can lodge no complaint when they can't. Ditto for the fire department and so on. Public Safety agencies primarily function after the fact for the simple reason that it's impossible for them to prevent you as an individual from sitting your ass on fire. Or sticking a gun in someone's face. Pass all the laws you want, the root problem is that there is no effective means of ensuring they will be obeyed.
Which brings us back to individual responsibility, Good Citizenship and why I wear a gun.
Individually, the best we can do to prevent crime is to raise our kids right and not offer ourselves up as easy targets. But you don't have to be a legal scholar to see that the courts have told us that good citizenship in today's Amerika ultimately requires us to blow away any asshole who tries to do us harm.
The reason for this unpleasant but necessary duty is pretty simple. When a gun is in your face it's obvious you're dealing with a criminal and that whatever deterrents are in place have not worked. When that happens the best the police can offer is a free ride to the morgue. For one of you. Clearly, it is your duty to ensure the other guy goes into the body-bag. Not only does it guarantee they won't do it again, it saves our society an incredible amount of money.
So wear a weapon, hone your skills and be prepared to use them. Because the best possible crime-deterrent is to stop walking around with Easy Pickin's tattooed on your forehead.
-Bob Hoover
PS -- This will come as a Big Surprise to all the bleeding hearts but ninety-nine times out of a hundred you don't even have to pull the trigger. Once they know you are armed and willing to take a hit, they're gone.
>Historically, robbing someone meant having your hands cut off. Today, in some states you can be killed for commiting certain crimes. None of these punishments deters would-be criminals.
Whoa, there cowboy. How did 'would-be' criminals get into this conversation? The methods above are designed to deal with known criminals... and they are very effective. (Kinda hard to pick a pocket without any hands :-)
> We have to look at what factors promote crime.
We? If you want to get into the philosophical aspects of the problem you'd better begin by defining government, get the mouse out of your pocket or stop using the Royal 'we.'
People create governments to accomplish collectively what cannot be achieved individually. But our government has already told us -- through case law and other means -- that our personal security and safety is an individual responsibility. Collectively, the cops will try to help... if they can... but we can lodge no complaint when they can't. Ditto for the fire department and so on. Public Safety agencies primarily function after the fact for the simple reason that it's impossible for them to prevent you as an individual from sitting your ass on fire. Or sticking a gun in someone's face. Pass all the laws you want, the root problem is that there is no effective means of ensuring they will be obeyed.
Which brings us back to individual responsibility, Good Citizenship and why I wear a gun.
Individually, the best we can do to prevent crime is to raise our kids right and not offer ourselves up as easy targets. But you don't have to be a legal scholar to see that the courts have told us that good citizenship in today's Amerika ultimately requires us to blow away any asshole who tries to do us harm.
The reason for this unpleasant but necessary duty is pretty simple. When a gun is in your face it's obvious you're dealing with a criminal and that whatever deterrents are in place have not worked. When that happens the best the police can offer is a free ride to the morgue. For one of you. Clearly, it is your duty to ensure the other guy goes into the body-bag. Not only does it guarantee they won't do it again, it saves our society an incredible amount of money.
So wear a weapon, hone your skills and be prepared to use them. Because the best possible crime-deterrent is to stop walking around with Easy Pickin's tattooed on your forehead.
-Bob Hoover
PS -- This will come as a Big Surprise to all the bleeding hearts but ninety-nine times out of a hundred you don't even have to pull the trigger. Once they know you are armed and willing to take a hit, they're gone.
Thursday, December 7, 2006
AV - Primary Gliders to the Rescue
I'm guilty of trying to get more people into the air, ideally in airplanes they've built themselves. But it's a tough row to hoe when the person is not a pilot. Toward that end I recently posted a message to the Fly5k mailing list about using a primary glider as part of basic pilot training.
In the message I said you'd have to work pretty hard to spend more than $300 building a primary glider. That generated a bit of mail :-)
Some folks didn't know what I meant when I said ‘primary glider' and a majority of those who did doubted one could be built for that amount. Telling them I was referring to the DFS's SG-38 or one of its variants, and sure they could, didn't help. In fact, each time I tried to clear up some point, such as why the type of wood you use isn't important, it seemed to made matters worse. It took a while for me to realize I was trying to explain the joy of old, comfortable shoes to folks who'd gone bare-foot all their lives :-)
OLD SHOES
Primary Gliders pre-date powered flight. Built with locally available materials, their only aviation-certified component was a healthy dose of common sense. Those early machines came in a variety of shapes, sizes and control schemes. The record shows some had the Right Stuff but most did not. After the Bicycle Brothers showed us How to Do It the variations in primary glider design became fewer. By 1914 the stick and rudder control system had become a de facto standard. World War One proved the practicality of that system over other methods and de facto became de juri. Weight-shifting, shoulder yokes and wing-warping were swept into the dust bin of history, to be re-invented with the advent of the hang-glider.
The present-day form of the Primary Glider originated in Germany during the 1920's and was introduced to the world through an article in the June, 1929 issue of National Geographic Magazine (*). The design continued to evolve (and still does) but was pretty much frozen by 1933 when the DFS published plans for the Model 38 ‘school glider.' ( DFS stands for Deutsche Forschungsanstalt fur Segelflug, the German Research Institute for Soaring Flight.)
Primary gliders proved so effective for imparting basic piloting skills that virtually every airmen of that era began their pilot training in an SG-38 or one of its variants. (‘School Glider' is ‘Shulgleiter' and is normally abbreviated ‘SG.') When you see SG.38 in a an old log book you'll know it means a primary glider, so don't be surprised if it shows three hundred landings but only five hours of flight. (To understand why, see: http://www.youtube.com/watch?v=O2e7tXROSnA )
Plans for the SG-38 were made available to all and examples were built in nearly every country of the world. Many of these departed from the plans in one way or another, reflecting local flying conditions or the availability of materials. Among the many variants were struts instead of wire bracing, a wheel instead of a skid, fairings of various types (nacelles to some), steel-tube fuselage instead of wood - even a steel tube fuselage having a triangular cross-section (which is the type I prefer to build). Some variations even changed the primary's status from glider to powered flight by hanging a motor on the nose. (Anyone who has ever flown a primary gets a big grin on their face the first time they see an Aeronca C2. It's lineage is unmistakable.)
Unaware of the origin of the design or to distinguish a particular variation, Primary Gliders in different countries were often named after the first local builder or the first person to import a completed machine. The Kawasaki Model 24, for example, has struts and a nicely faired pod around the pilot but is otherwise virtually identical to the basic SG-38. Here in the States a primary is often called a ‘Northrup,' honoring the fellow who first imported one from Germany in the early 1920's. (I've not been able to identify him further, other than he was a scion of the Northrup seed company dynasty.) And while we may call it a ‘Northrup' even the most cursory inspection shows it to be the metric-dimensioned SG-38 cloned in inches and feet. (If you'd like to build one you will find plans and building instructions in the old Flying & Glider manuals, reprints of which are available from the EAA(**) for about ten dollars. Later issues of the Flying and Glider Manual depict some of the variants.)
(Note: Not to be confused with John K. Northrop, the brilliant aeronautical engineer whose broad spectrum of engineering innovations contributed significantly to Lockheed, Boeing, Douglas, North American and of course Northrop Aviation's incomparable flying wings.)
While details of their structure might change, the function of all primary gliders remains the same, which is to roar silently down their eight-to-one glide slope at a breathtaking thirty miles an hour. The pilot's task is to keep the wings level and to land straight ahead. Once the basics are mastered life becomes more interesting :-) (Riding the ‘hang' or slope-wind, you may stay aloft for hours, if you wish.)
SUCCESS OR FAILURE?
Some people felt I'd overstated the case regarding the need for pilot training, that everything was just swell within the General Aviation community. As proof, they usually cited air-show revenues or attendance statistics to show there's no cause for alarm; surely no need to advocate anything as arcane as primary gliders.
Pilots and FBO's know otherwise. The reality of General Aviation is spiraling costs, X's on the ground, weeds springing up in front of hangar doors and a steadily growing number of empty seats at EAA meetings. But if you want statistics, I'll give you some.
According to statistics compiled by GAMA (***) the number of student pilots is well below the figure needed to replace our losses and has been for more than twenty years. The best proof of that is the fact the number of American pilots has shrunk by nearly twenty percent over the same period and the downward trend is not only continuing but accelerating. For more than twenty years we've seen the leaders of the aviation community try to turn things around with one ineffectual program after another yet our numbers continue to decline.
We need more pilots rather than more programs. I suggest it's time for each of us to roll up our sleeves and start training our own replacements. Primary gliders happen to be an inexpensive yet immanently practical means of doing exactly that.
A primary glider's role in life is to safely carry a nervous, over-controlling student to a rather bad landing after a flight rarely more than a minute in length. And to do that over and over and over again through the course of a long, sun-burned day until it is too dark to see and you are left alone to hump a sixteen foot wing into a fifteen foot trailer while a squadron of yahoos, surely the worst crop of pilots to ever come out of Mrs. Edward's fourth-grade class, dances around you slightly insane with the thrill of having actually flown. Not as a lectured-to passenger in a 182 smelling of the last fledgling's vomit but as Pilot in Command on a never to be forgotten solo flight through the eery isolation of the air, and well above the land.
Primary gliders are inexpensive and easy to build. And for a good reason. A well maintained primary glider can withstand thousands of student landings but over time it becomes a collection of patches and repairs and accumulated wear until you bite the bullet, condemn the thing to the wood stove and build another. But rarely alone. By seasoning a barrel of patience with a pinch of wit you'll be surprised at the number of kids more than willing to abandon the tube for the shop. Once built, their labor earns them Head of the Line privileges in its use.
A PRACTICAL, INEXPENSIVE OPTION
Primary gliders alone are not the answer. But they have the potential to be a big part of it. Students with primary glider experience are safe to solo a powered trainer in a fraction of the time needed by students with no glider training.
In modern-day America the majority of people who would like to become pilots can not afford to do so. Indeed, the high price of a private pilot's license virtually guarantees the demise of General Aviation as we know it. Primary Gliders are one means of skewing the odds in our favor. They can put more pilots into the air at less cost than existing methods of pilot training. The proof of that is an historical fact and as such, is worthy of thoughtful consideration.
-R.S.Hoover
(*) ‘On The Wings of the Wind,' Seipen, Howard A., National Geographic Magazine, June 1929, pgs 751 - 780
(**) ‘Building Instructions and Plans for the Northrop Glider,' Weston Farmer, 1930 Flying and Glider Manual, pg 53
Reprints of the 1930 Flying and Glider manual are available from the EAA. Ask for Item Number F14168. Price is $6.95 plus shipping & handling. EAA Mail Orders PO Box 3086 Oshkosh, WI 54903-3086 or call: 1-800-843-3612
(***) General Aviation Manufacturers Association 1400 K Street, NW Washington, DC 20005 http://www.generalaviation.org/pages/statistics.shtml
The opening image is of a primary glider over Box Hill, NSW, Australia, circa 1940.
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Wednesday, December 6, 2006
Flashman Returns!
Psst! Hey, kid. You wanna cheap flasher?
L.E.D Flasher Kit, Catalog # LEDKIT $1.75 per kit
12VDC DPDT DIP RELAY, Catalog # RLY-420 $1.50 each.
SPDT 40 AMP RELAY, Catalog # RLY-415 $1.00 each
PN2222A NPN Transistor 5/$0.80
Couple of 1/4 Watt resisters, mebbe a nickel each.
The stuff above is available from All Electronics Corp., www.allelectronics.com
- - - - - - - - -
I came across the LED flasher kit some years ago at a swap-meet, priced at less than the cost of the components. Being a cheapskate (and a ham radio operator) I bought a bunch.
The LED flasher kit consists of a postage-stamp-sized circuit board designed to accept a 555 IC plus a couple of discrete components. The circuit is wired as a basic timer. The discrete components - a couple of resisters and a capacitor - determine the on-off frequency and ratio of the timer's output. I used the kits to teach Cub Scouts and the like how to solder. (Put it together correctly, it'll wink at you :-)
The timer not only makes a good LED flasher, by changing the circuit just a tad it makes a nice oscillator for teaching Morse code. Or, you can fiddle with the circuit a bit more, replace the output LED with a transistor and toggle a DIP-size relay wired dead-bug to the other side of the circuit board. And while the pilot relay may be tiny, it can handle about two amps. That's enough to pick a BIG relay. Or half a dozen 30A relays. Or whatever. The 555 is an extremely versatile chip, its uses limited only by your imagination.
Why bother making up a flasher when you can buy one? I've been using ultra-bright LED's for running lights and the regular flasher wouldn't work with them because they draw so little current. (That's the running lights on a car, of course.) There are flashers that will work with low resistance circuits but they cost more than the home-brewed variety, usually flash at the wrong frequency and, in my experience, are less reliable.
-R.S.Hoover
VW - The Flying Pig
There's a gal on the Vintage VW list who calls her bug 'Boris.' I mentioned Boris at dinner one night then had to explain, or try to explain, that a lot of Volkswagen owners give their bugs and buses names.
My wife gave me one of those looks, asked what I called my bus. Blank. To me, it's just the Green Bus. Before, there was a Brown Bus, before that a Red & White bus.
I said I didn't give names to things. "But you called your airplane 'The Spirit of Vista'," she pointed out. But never flew it to Paris. "If I ever put wings on the bus," I told her, "I'll give it a name." And muttered something about doing it just as soon as pigs could fly. That cracked her up. It also named the bus. "The Flying Pig?" she laughed.
"I couldn't do that," I muttered. I used to have a buddy who was a cop, spent umpteen years building a helicopter. Called it The Flying Pig. Flipped it during a test flight and burned to death. I wouldn't want to steal his thunder. But maybe El Puerco Volador? Is that right? I'm always getting my Spanish mixed up.
A ham radio buddy came over after supper. He's got some strange plumbing problems. Only way to fix it is to use an adaptor that will allow old thin-wall ABS pipe to mate with new schedule 40 PVC pipe, but now that the box stores have driven all the real hardware stores out of business no one carries the adaptors
So we made some.
Turned them up on the lathe. Took only a few minutes. Lathes are handy things and mine's fully automatic. Just grab the knobs and think about something else while the parts sort of make themselves. I was thinking about Flying Pigs.
While I'm working, my buddy is looking around the shop. There's an airplane engine under a bench, two fully dressed Volkswagen engines on scooters, a Datsun engine sulking over in the corner beside an orphaned 2-cylinder air-cooled Diesel engine that might one day power something strange and noisy. Above the diesel hangs a row of heater boxes.
My buddy looks at the five Volkswagen heat exchangers hanging in a row. Five. An engine needs two, a lefty and a righty. So how the hell did I manage to end up with five heat exchangers? I never noticed that before. All new, too.
Six blower housings. Three dog-house, three flat-backs. One of the dog-house housings is an after-market 36-hp style that proved it couldn't flow as much air as stock, ended up not being used. I've no idea how the others came to be in the shop. You leave the door open, stuff wanders in. My hands make another adaptor and my buddy hunkers down, peering under a bench.
Three 12v alternators, two Motorolas, one Bosch. Two 12v generators. A whole scad of 6v generators. Why do I keep that crap? Blowers. I had a nifty idea for using old blowers to make... I'll think of it in a minute.
A whole bunch of intake manifolds. Oops! Make that a bunch and a half; couple more of them hanging over there. Dual-ports and single ports, several of each. DP Kadron bases. SP Kadron bases. That makes... at least two bunches. And carbs. Lotsa carbs. Box of Kadron carbs. Box of Solex carbs. Whole big drawerful of other carbs including a lonely Bug Spray. Future projects, waiting for... the future, I guess.
Mufflers. Yea gawds have I got mufflers! Four stock bug mufflers, at least that many extractors. It's hard to tell with extractors. You toss them in a pile, they start squirming around, get all tangled together, you gotta spray them with a hose, beat them apart with a stick.
Black, greasy thing under a bench. My buddy gives me a look, brows raised. "Tranny," I tell him. Two more, back in there some place, along with a pile of axles. One of the trannys is a rebuilt, ready to run. I've been planning to install it in the '67. I better make a note to myself to get to it Real Soon Now.
Cylinder heads. Pile of them here, row of them there, two on that bench, pile over beside the grinder, couple over by the welding rig. The bench where I do head work has got this big box of valves, another box of fuel pumps, some old, some new. Shelves hold rebuild kits for carbs and pumps and generator brushes and wheel cylinders and a whole slather of reloading equipment for half a dozen different calibers. The reloading stuff should be over on another bench but that one's being used to test a six inch mirror for a reflecting telescope.
Stack of flywheels over by the milling machine, right beside a stack of stock, original, real VW-type Volkswagen hub caps for an early bus. Should be four. I count them twice. There are four. I feel relieved, give those five heat exchangers a glance. Still five of them.
Bus steering gear and steering wheel shaft leaning up in the corner behind the welding machine, like its waiting for a ride, which I suppose in a way it is.
Overhead, running pretty much the full width of the twenty-two foot wide shop is a pair of airplane wings. Volkswagen engine tin-ware is poked up on top of the wings, the smaller pieces hanging down on hooked hunks of welding rod, handy to get at. A stack of sump plates like little Frisbees. Funny gaskets. Sez 'GMC manifold.' There's an old Jimmy down in the grove. My hands finish another coupler as my buddy gazes at stuff hanging on a wire.
"VW air-vanes," I tell him. "Goes inside those things overt here," I nod toward the blower housings. Two sets of air vanes, one reconditioned, painted with gray epoxy primer, others looking like something out of the La Brea Tar Pits, which tells me they came out of an all-original 1967, never-been-touched engine I recently overhauled. The thing blew an oil cooler seal, pumped oil all over for about six months before the guy sold it to a kid. They were both happy as clams, each sure they'd gotten the best of the deal.
I finished making the adaptors for my friend, chatted a while. "You've got a lot of stuff," he said as I saw him on his way. Strong note of admiration, tinged with something else. Relief? Envy? Is it every man's dream to have lots of stuff?
I came back to the shop to wipe down the lathe, cover it, sweep down. Seeing the shop through my buddy's eyes was a strange experience, like when he stood reading the note on the chalkboard over where the phone used to be: "Pullen - Concrete", a reminder about helping Clint Pullen do a little sidewalk out behind his house so his wife's wheelchair wouldn't get caught on the stones. Clint's been dead at least five years. After I moved the phone, I never used the chalkboard again. We did the sidewalk for Alice back in 1977.
I sat looking at the incredible collection of stuff that has crept up on me over the years, looking at it with mixed emotions. Too much stuff is bad for you, nails you down. But my formative years were during World War II, when everything was rationed, you even had to stand in line to buy food. That's when I was taught that throwing away Good Stuff was a sin. We needed all that Stuff to Remember Pearl Harbor, so we could Slap the Jap and Heel the Hun. They made us chant slogans like that in school, then sent us out to scour the neighborhood for scrap metal, knocking on doors, brow-beat old ladies into giving up their aluminum pans.
And they were right.
Have you ever tried to make steel? It's not easy. Better to keep some on hand in case you need it, like that pile of tubing, or those old door panels. You never know when you're liable to need a door panel for a... whatever the hell it came off of. And an old veedub axel makes a fine gun barrel. Remember Pearl Harbor. And Ruby Ridge.
I sat thinking a little too long, started going a little crazy. Bus right outside, pair of airplane wings strapped up across the ceiling of the shop. Five heat exchangers hanging in a row.
El Puerco Volador. Maybe I could use one of them door panels for the rudder.
Copyright © 1995 Robert S. Hoover
My wife gave me one of those looks, asked what I called my bus. Blank. To me, it's just the Green Bus. Before, there was a Brown Bus, before that a Red & White bus.
I said I didn't give names to things. "But you called your airplane 'The Spirit of Vista'," she pointed out. But never flew it to Paris. "If I ever put wings on the bus," I told her, "I'll give it a name." And muttered something about doing it just as soon as pigs could fly. That cracked her up. It also named the bus. "The Flying Pig?" she laughed.
"I couldn't do that," I muttered. I used to have a buddy who was a cop, spent umpteen years building a helicopter. Called it The Flying Pig. Flipped it during a test flight and burned to death. I wouldn't want to steal his thunder. But maybe El Puerco Volador? Is that right? I'm always getting my Spanish mixed up.
A ham radio buddy came over after supper. He's got some strange plumbing problems. Only way to fix it is to use an adaptor that will allow old thin-wall ABS pipe to mate with new schedule 40 PVC pipe, but now that the box stores have driven all the real hardware stores out of business no one carries the adaptors
So we made some.
Turned them up on the lathe. Took only a few minutes. Lathes are handy things and mine's fully automatic. Just grab the knobs and think about something else while the parts sort of make themselves. I was thinking about Flying Pigs.
While I'm working, my buddy is looking around the shop. There's an airplane engine under a bench, two fully dressed Volkswagen engines on scooters, a Datsun engine sulking over in the corner beside an orphaned 2-cylinder air-cooled Diesel engine that might one day power something strange and noisy. Above the diesel hangs a row of heater boxes.
My buddy looks at the five Volkswagen heat exchangers hanging in a row. Five. An engine needs two, a lefty and a righty. So how the hell did I manage to end up with five heat exchangers? I never noticed that before. All new, too.
Six blower housings. Three dog-house, three flat-backs. One of the dog-house housings is an after-market 36-hp style that proved it couldn't flow as much air as stock, ended up not being used. I've no idea how the others came to be in the shop. You leave the door open, stuff wanders in. My hands make another adaptor and my buddy hunkers down, peering under a bench.
Three 12v alternators, two Motorolas, one Bosch. Two 12v generators. A whole scad of 6v generators. Why do I keep that crap? Blowers. I had a nifty idea for using old blowers to make... I'll think of it in a minute.
A whole bunch of intake manifolds. Oops! Make that a bunch and a half; couple more of them hanging over there. Dual-ports and single ports, several of each. DP Kadron bases. SP Kadron bases. That makes... at least two bunches. And carbs. Lotsa carbs. Box of Kadron carbs. Box of Solex carbs. Whole big drawerful of other carbs including a lonely Bug Spray. Future projects, waiting for... the future, I guess.
Mufflers. Yea gawds have I got mufflers! Four stock bug mufflers, at least that many extractors. It's hard to tell with extractors. You toss them in a pile, they start squirming around, get all tangled together, you gotta spray them with a hose, beat them apart with a stick.
Black, greasy thing under a bench. My buddy gives me a look, brows raised. "Tranny," I tell him. Two more, back in there some place, along with a pile of axles. One of the trannys is a rebuilt, ready to run. I've been planning to install it in the '67. I better make a note to myself to get to it Real Soon Now.
Cylinder heads. Pile of them here, row of them there, two on that bench, pile over beside the grinder, couple over by the welding rig. The bench where I do head work has got this big box of valves, another box of fuel pumps, some old, some new. Shelves hold rebuild kits for carbs and pumps and generator brushes and wheel cylinders and a whole slather of reloading equipment for half a dozen different calibers. The reloading stuff should be over on another bench but that one's being used to test a six inch mirror for a reflecting telescope.
Stack of flywheels over by the milling machine, right beside a stack of stock, original, real VW-type Volkswagen hub caps for an early bus. Should be four. I count them twice. There are four. I feel relieved, give those five heat exchangers a glance. Still five of them.
Bus steering gear and steering wheel shaft leaning up in the corner behind the welding machine, like its waiting for a ride, which I suppose in a way it is.
Overhead, running pretty much the full width of the twenty-two foot wide shop is a pair of airplane wings. Volkswagen engine tin-ware is poked up on top of the wings, the smaller pieces hanging down on hooked hunks of welding rod, handy to get at. A stack of sump plates like little Frisbees. Funny gaskets. Sez 'GMC manifold.' There's an old Jimmy down in the grove. My hands finish another coupler as my buddy gazes at stuff hanging on a wire.
"VW air-vanes," I tell him. "Goes inside those things overt here," I nod toward the blower housings. Two sets of air vanes, one reconditioned, painted with gray epoxy primer, others looking like something out of the La Brea Tar Pits, which tells me they came out of an all-original 1967, never-been-touched engine I recently overhauled. The thing blew an oil cooler seal, pumped oil all over for about six months before the guy sold it to a kid. They were both happy as clams, each sure they'd gotten the best of the deal.
I finished making the adaptors for my friend, chatted a while. "You've got a lot of stuff," he said as I saw him on his way. Strong note of admiration, tinged with something else. Relief? Envy? Is it every man's dream to have lots of stuff?
I came back to the shop to wipe down the lathe, cover it, sweep down. Seeing the shop through my buddy's eyes was a strange experience, like when he stood reading the note on the chalkboard over where the phone used to be: "Pullen - Concrete", a reminder about helping Clint Pullen do a little sidewalk out behind his house so his wife's wheelchair wouldn't get caught on the stones. Clint's been dead at least five years. After I moved the phone, I never used the chalkboard again. We did the sidewalk for Alice back in 1977.
I sat looking at the incredible collection of stuff that has crept up on me over the years, looking at it with mixed emotions. Too much stuff is bad for you, nails you down. But my formative years were during World War II, when everything was rationed, you even had to stand in line to buy food. That's when I was taught that throwing away Good Stuff was a sin. We needed all that Stuff to Remember Pearl Harbor, so we could Slap the Jap and Heel the Hun. They made us chant slogans like that in school, then sent us out to scour the neighborhood for scrap metal, knocking on doors, brow-beat old ladies into giving up their aluminum pans.
And they were right.
Have you ever tried to make steel? It's not easy. Better to keep some on hand in case you need it, like that pile of tubing, or those old door panels. You never know when you're liable to need a door panel for a... whatever the hell it came off of. And an old veedub axel makes a fine gun barrel. Remember Pearl Harbor. And Ruby Ridge.
I sat thinking a little too long, started going a little crazy. Bus right outside, pair of airplane wings strapped up across the ceiling of the shop. Five heat exchangers hanging in a row.
El Puerco Volador. Maybe I could use one of them door panels for the rudder.
Copyright © 1995 Robert S. Hoover
VW - Fuel Tank, Rust and Filters
One bit of bad advice you'll frequently hear is to install a fuel filter in your fuel line between the fuel pump and the carb.
Don't do it.
The added mass of the filter combined with the vibration of the engine and road serves to wiggle the brass ferules out of the carb and fuel pump. When that happens if you happen to have some marshmallows with you, fine, otherwise there's little you can do but stand by and watch it burn.
Volkswagen used untreated mild steel for their fuel tanks. Because of the age of the typical Volkswagen, the fuel tank and fuel lines are generally quite rusty; that is the source of the residue you find in the carb bowl. Adding another filter (you already have two) deals only with the symptom, the real solution is to tackle the rust itself.
The factory service manual addresses fuel tank refurbishing in considerable detail but the real secret to success is what you do after you get rid of the rust, which is to use a chemical sealant commonly called 'sloshing compound.' You pour it in and slosh it around, then allow to dry. Be sure to remove the strainer first. This is some very tough stuff, used in metal fuel tanks on aircraft. It is available from J. C. Whitney.
A rusty fuel pipe is a more serious sort of problem since the location of the pipe within the central hump makes replacement difficult, best done when the body is removed from the chassis. I've mentioned another fix, the use of an externally routed replacement fuel line, in one of my earlier articles ('The Stainless Steel Craftsman').
Cleaning your existing filters and even adding another can buy you a little time but please do not install it within the engine compartment. Under the fuel tank is the safest place, followed by under the rear seat deck (ie, near the nose of the transmission). Veedubs love to burn; they're very good at it.
Your fuel system already has two strainers installed, one in the fuel tank, the other in the fuel pump. The latter is often overlooked as a maintenance item. On the late model pumps it is under the top cone, in early pumps it's behind the big brass nut. When you have a rusty fuel system you should clean the fuel pump strainer when you do your oil change. (But be careful, remember the fuel will flow by gravity once the system is opened.)
Rust forms in the fuel system due to an accumulation of water vapor from the atmosphere. When it condenses it collects in the lower-most stampings of the fuel tank, a depression around the fuel outlet fitting, where it produces pin-hole leaks. VW fuel tanks are not made of terne-plate (lead-coated steel normally used for tankage by American auto manufacturers) but are common mild steel sheet. Once liquid water is present in the fuel system it's difficult to remove without draining the tank through the filler neck (ie, up-ending the thing). As a general maintenance item the usual method is to add a 'dryer' to your fuel, as frequently as dictated by your local climate. Gas 'dryer' is nothing more than wood alcohol (methyl methanol?) and is available at any auto parts store. Being hygroscopic, the alcohol mixes with the water and, if there isn't too much water, will be burned as fuel.
The water/rust problem is less frequently seen on veedubs fitted with the full array of pollution control devices, since the fuel tank is not vented directly to the atmosphere.
If your fuel tank is seriously rusted, the wiser course is to replace it rather than repair it. (I'll pause here and wait a minute until all the weldors stop rolling on the floor with laughter.) Replacement fuel tanks are available although the workmanship is rather shoddy; they often arrive already rusty. If you buy one it's a good idea to treat it as if you'd made it yourself, removing the existing paint, smoothing up the welds (bloody dangerous!) and repainting it with a high quality epoxy. The interior should be sloshed as a matter of course. Serious rebuilders have their new or repaired fuel tank powder-coated, which bakes the enamel to both the interior and exterior surfaces. The super-serious (and wealthy) have a new tank fabricated from stainless steel or aluminum.
Working on the fuel tank is one of the easier tasks of VW maintenance (at least, on a bug :-) since it is so accessible, held down with just four clips&bolts, and at waist level. (This isn't true for '68 and later models; the filler neck is especially difficult to re-seal.) Be sure it's empty before working on it -- six pounds per gallon can make a heavy load -- and that you have new fuel line on-hand. The existing fuel line under the tank will probably break like a stick when you try to disconnect it. (Lift one side of the tank, peek under, reach down and wiggle it loose.)
Pulling the fuel tank also gives you an opportunity to remove the fifty pounds of sand & gravel that accumulates on the 'smuggler shelves' behind the wheels when you take the short cut between San Ignacio and La Parisma.
Copyright © 1995 Robert S. Hoover
Don't do it.
The added mass of the filter combined with the vibration of the engine and road serves to wiggle the brass ferules out of the carb and fuel pump. When that happens if you happen to have some marshmallows with you, fine, otherwise there's little you can do but stand by and watch it burn.
Volkswagen used untreated mild steel for their fuel tanks. Because of the age of the typical Volkswagen, the fuel tank and fuel lines are generally quite rusty; that is the source of the residue you find in the carb bowl. Adding another filter (you already have two) deals only with the symptom, the real solution is to tackle the rust itself.
The factory service manual addresses fuel tank refurbishing in considerable detail but the real secret to success is what you do after you get rid of the rust, which is to use a chemical sealant commonly called 'sloshing compound.' You pour it in and slosh it around, then allow to dry. Be sure to remove the strainer first. This is some very tough stuff, used in metal fuel tanks on aircraft. It is available from J. C. Whitney.
A rusty fuel pipe is a more serious sort of problem since the location of the pipe within the central hump makes replacement difficult, best done when the body is removed from the chassis. I've mentioned another fix, the use of an externally routed replacement fuel line, in one of my earlier articles ('The Stainless Steel Craftsman').
Cleaning your existing filters and even adding another can buy you a little time but please do not install it within the engine compartment. Under the fuel tank is the safest place, followed by under the rear seat deck (ie, near the nose of the transmission). Veedubs love to burn; they're very good at it.
Your fuel system already has two strainers installed, one in the fuel tank, the other in the fuel pump. The latter is often overlooked as a maintenance item. On the late model pumps it is under the top cone, in early pumps it's behind the big brass nut. When you have a rusty fuel system you should clean the fuel pump strainer when you do your oil change. (But be careful, remember the fuel will flow by gravity once the system is opened.)
Rust forms in the fuel system due to an accumulation of water vapor from the atmosphere. When it condenses it collects in the lower-most stampings of the fuel tank, a depression around the fuel outlet fitting, where it produces pin-hole leaks. VW fuel tanks are not made of terne-plate (lead-coated steel normally used for tankage by American auto manufacturers) but are common mild steel sheet. Once liquid water is present in the fuel system it's difficult to remove without draining the tank through the filler neck (ie, up-ending the thing). As a general maintenance item the usual method is to add a 'dryer' to your fuel, as frequently as dictated by your local climate. Gas 'dryer' is nothing more than wood alcohol (methyl methanol?) and is available at any auto parts store. Being hygroscopic, the alcohol mixes with the water and, if there isn't too much water, will be burned as fuel.
The water/rust problem is less frequently seen on veedubs fitted with the full array of pollution control devices, since the fuel tank is not vented directly to the atmosphere.
If your fuel tank is seriously rusted, the wiser course is to replace it rather than repair it. (I'll pause here and wait a minute until all the weldors stop rolling on the floor with laughter.) Replacement fuel tanks are available although the workmanship is rather shoddy; they often arrive already rusty. If you buy one it's a good idea to treat it as if you'd made it yourself, removing the existing paint, smoothing up the welds (bloody dangerous!) and repainting it with a high quality epoxy. The interior should be sloshed as a matter of course. Serious rebuilders have their new or repaired fuel tank powder-coated, which bakes the enamel to both the interior and exterior surfaces. The super-serious (and wealthy) have a new tank fabricated from stainless steel or aluminum.
Working on the fuel tank is one of the easier tasks of VW maintenance (at least, on a bug :-) since it is so accessible, held down with just four clips&bolts, and at waist level. (This isn't true for '68 and later models; the filler neck is especially difficult to re-seal.) Be sure it's empty before working on it -- six pounds per gallon can make a heavy load -- and that you have new fuel line on-hand. The existing fuel line under the tank will probably break like a stick when you try to disconnect it. (Lift one side of the tank, peek under, reach down and wiggle it loose.)
Pulling the fuel tank also gives you an opportunity to remove the fifty pounds of sand & gravel that accumulates on the 'smuggler shelves' behind the wheels when you take the short cut between San Ignacio and La Parisma.
Copyright © 1995 Robert S. Hoover
AV - Yo! Fuel Tank!
Riveted aluminum fuel tanks are smart. They're easy to build and superbly practical for the homebuilder since she can make them in whatever shape she needs.
Most folks shy away from this fabrication technique due to the high cost of Pro-Seal, still listed at more than $8/oz in the Aircraft Spruce catalog (P/N 09-38500 "2oz sealant" $17.85). But now that Thiokol's patents on polysulfide sealants have expired seam-sealers that do equally well are available for pennies per pound instead of dollars per ounce. Life Industries is one such source. They make a line of polysulfide sealants for marine applications, including a two-part fuel-proof formulation used to calk fuel tanks & bilges.
With aluminum, the sealant-bonding question - getting the stuff to stick - is a no-brainer. Go to your local Home Depot and buy a quart of JASCO ‘Prep & Primer.' Or buy a quart of ‘AlumaPrep' from Aircraft Spruce. Same stuff, chemically speaking. Of course, the aviation-grade' alumaprep is dramatically more expensive.
Degrease then etch the panels you want the sealant to adhere to for thirty minutes in a solution of ‘Prep & Primer.' (The strength of the solution isn't critical. Anything from 1:1 to 3:1 works fine on clean aluminum. If using Alumaprep, follow their dilution instructions.) ‘Prep & Primer' is a phosphoric acid etchant made specifically for galvanized and aluminum surfaces. Scrub the etched surface with a Scotch-brite pad and neutralize with boiling water. The result will be a matte white finish.
To insure greater integrity of your rivet line, you may wish to use countersunk rivets. The dimple adds depth to the rivet line, making it stiffer without increasing its weight. The 120 degree dies you need for poppers are available from Airparts in Kansas City (www.airpartsinc.com) for about six dollars. And from other folks, too. The dies are used with your regular pop-rivet gun. Of course, if you have a lathe it takes only a few minutes to make such a set of dies and even un-hardened they'll last for several plane's-worth of dimples.
If you've never used flush-head poppers, run a few rows of sets before tackling the tank. The dimpling process enlarges the hole. The geometry here is subtle so be cool, work at the pilot-hole level, opening up the hole to rivet-size after you've dimpled & fitted the row. If you don't, the rivet will be too loose to pop; it'll just pull out. Be very careful when deburring as you'll be working on a corner instead of a flat. A file may be a better choice than a regular deburring tool. (These factors have probably contributed to the Conventional Wisdom that sez flush-head poppers don't work very well. They work just fine, but only when they fit the hole.)
With a pitch of about an inch aluminum poppers provide more than adequate strength for this application. Indeed, the stiffness of steel flush-head poppers dictates a minimum metal-depth of about forty thou. Anything thinner and you're liable to pull the popper through the hole before it can form a large enough shop-head to snap the mandrel.
You can buy flush-head aluminum poppers from J.C.Whitney in boxes of 500 for about $12. (JCW item# 14xx4090A, box of 500, $12.19) The short ones do fine for this type of job.
As with all poppers, be sure to wash them good in MEK prior to use. The manufacture of pop rivets always leaves some amount of lubricant on the finished product. That tiny trace of oil will interfere with the adhesion of the sealant (and of your zinc chromate, when using steel poppers on your other panels).
Steel poppers may be a wiser choice for attaching the flanged aluminum fitting for the tank's outlet. You may of course use steel button-head poppers for the entire tank if you wish. I like the flush-head aluminum jobbies for the seam-lines because they give me a stiffer joint at less weight.
If you prefer to use solid rivets you'll need to provide access for bucking the things. Wag Aero still sells sealed blind-nuts for a reasonable price (Cat# L-676-000 Pkg of 50 for $10.95) Sealed blind nuts are standard for fuel tanks. The threads of the screw are sealed away from the contents of the tank inside a little dome. Slosh the tank, you can still remove the access panel.
Tanks tend to violate the rule for panel size vs edge support so you'll probably want to pound an ‘X' bead into the four sides and the bottom. If the top of the tank is curved it will already be stiff enough but the sides & bottom will tend to be pretty wimpy, especially if you're using soft aluminum. (Almost anything will do for making a tank. Don't tell anyone but I've made tanks out of siding aluminum. )
If you don't understand what I'm talking about here, take a look at a steel Jerry can. Some guys like to roll such flutes into the panel but you can do perfectly well by making up a suitable groove or gap in a board, laying the panel across it and making several light passes along the groove with your rubber mallet.
Fuel tank is usually an irregular box. Occasionally an irregular cylinder. Cylinders support themselves but boxes don't. If the thing has corners, plan on adding a couple of baffles, not only to control the slosh but to stiffen the structure.
Rivet-on flanges for the filler and outlet are available from aircraft suppliers but since they are simple turnings they are easy enough to make if you have a lathe. And even if you don't. There are thousands of hobby-machinists on the Internet, their weapon of choice a little 7x10 lathe that's plenty big enough to whip out a set of fuel tank fittings. To track down such folks just go to the appropriate Newsgroup – rec.crafts.metalworking is but one of dozens of such groups – post a message having ‘Help!' as the subject line, describe the job and tell them where you're located. The squeaking wheel gets the grease - keep shouting until you connect with someone in your area. Like all machinists - which is what these folks are... the size of the machine has nothing to do with it - he'll need an accurately dimensioned drawing to work from and you'll probably need to provide him with the stock. Applying sealants is messy as hell, especially Pro-Seal and the other polysulfides. Masking off the area to be sealed/riveted will help and you might want to consider PK's instead of clecos. Polysulfide sealant is close to the perfect adhesive, it'll stick to anything... and doesn't like to come off. (For dimpled holes you'll need the longer (ie, 3/8") PK's.) Grubby-up a PK, throw it away. You're out maybe two cents.
Give the surface to be sealed a final wipe-down with MEK (or whatever solvent is recommended for you sealant). Allow it to evaporate. Apply the sealant according to the instructions. Most call for a smooth, uniform coating on both surfaces. Not too thick, a few thousandths is all you'll need if your rivet-line is a good fit. And not too wide, about three-quarter of an inch, max. Most of this stuff cures by reaction with water vapor in the air, something present everywhere on our particular planet. Cure time is a function of the width of the sealant-line and the humidity in the air. (That's why the stuff is so popular with boaters – it cures underwater faster than out of it.) The two-part formulation cures faster than the no-mix stuff.
You only need about three ounces of sealant for a ten gallon tank, most of which will go on the flanges, your tools and your clothes. (If you've never used Pro-Seal before, buy a pint :-)
If you use the 2oz kits, the little tubes can be hard to handle without the matching gun, a $75 item. (Aircraft certified, right? :-) A dime's worth of Bondo will allow you to modify a regular calking gun to accept the 2oz aircraft-certified cartridges. If you want to go that route, I'll tell you how to make an adapter.
Aircraft Spruce also lists the stuff in pints [$37] and quarts [$74] but the secret to using bulk-packaged sealants is how to mix & apply the stuff without gluing yourself to the wall. The usual mix ratio is 10:1 and is fairly critical. The use of a ratio'd balance beam, baggies for one component and a Teflon cup for the other is a fairly common procedure. Once you've balanced the beam, pour the One-stuff from the Teflon cup into the Ten-stuff in the plastic baggie then seal up the baggie and mix the stuff by squishing the baggie, like colorizing oleomargarine in days of yore. (That's my yore, not your yore.) Once the color is uniform, snip a corner of the baggie and squeeze the stuff out like decorating a cake, using a scrap of metal as a palette knife to smooth the bead to a uniform thickness across the bond line.
Standard practice when using poppers with a sealed structure is to dip the degreased popper in the sealant just before you stick it in the hole and give it a little twist. Don't get too far ahead with the sticking & twisting before coming back and doing the popping. The structure should be perfectly secured with a PK in about every fourth hole giving you three poppers in a row. When you pop, always do the middle one first. Once it's popped some guys butter a smear of sealant into the mandrel hole but it's not necessary if you're going to slosh the tank.
After your tank is fabricated leave it alone for about three days, until the sealant is cured. After it has cured you can provide yourself with virtual 100% leak-free assurance by sloshing the tank with a PVA fuel tank sealant. J. C. Whitney will sell you a quart of the stuff for about thirty bucks. You need less than a pint but I haven't found anyone who'll sell me that small a quantity. As with the polysulfides, there are only a few companies that make fuel tank sealants and most use functionally identical formulations. The thirty dollar stuff from J.C.Whitney appears to be the same as the hundred dollar stuff with ‘aircraft-certified' on the label. Maybe it's not but it works the same.
Since your tank was already etched, the sloshing sealant is going to form a perfect bond. Plug the outlet, pour in the sloshing sealant (it's a creamy white stuff; the vehicle is MEK) seal up the inlet (I use a hose clamp and piece of inner tube) then commence rolling the tank over and around and up and down... but in a logical fashion. What you want to do is to flow the sloshing sealer over every part of the interior surface.
After sloshing the tank, drain the sealant back into its can and seal it up good. Remove whatever is plugging the drain so air can circulate through the tank, prop it so it can drip out then leave the thing to cure.
Takes about 24 hours.
When it's cured, get your light wand and your bore scope and whatever else you need and inspect the interior surface. It should have a uniform white coating.
The sealant is a form of PVA – polyvinylalcohol. Once cured, it is impervious to virtually all solvents, including gasoline, alcohol and water. I've used the J.C.Whitney stuff on steel, aluminum and fiberglas with excellent results (JCW "Alcohol resistant Gas Tank Sealer" item# 12xx8316Y each $28.99). How well it works depends largely on how well you've prepped the surface. Basic rule is to have it perfectly free of grease, including fingerprints. For aluminum, you need to provide some ‘tooth' to the surface, which is accomplished by the etchant (ie, the Prep & Primer stuff).
Lots of ‘expert' homebuilders damn such tanks with faint praise. Sure it works... but real fuel tanks are always welded, yadayadayada... Sure they are, Mr. Expert. (I invite those experts to join me at FlaBob as we refurbish a P-51... and its riveted, sealed and sloshed fuel tanks.)
Your fuel system should have a strainer in the tank. Smartest one you can get is to MAKE YOUR OWN using a short length of 3003 aluminum tubing, slit about every quarter inch with a hobby saw. The typical hobby saw leaves a kerf about .028" wide, much smaller than the mesh of a cheap finger strainer. Cut enough slots to insure the thing will flow enough fuel.
The tank should be equipped with a shut-off valve. See the Northern Hydraulics catalog. Go to the same source for your gascolator. It ain't aviation-certified but it works and doesn't cost the earth.
Basic fuel tank plumbing is to keep a constant down-ward flow of fairly large diameter tubing from the tank to the gascolator. The idea here is that anything large enough to get through the strainer in the tank will not block the fuel line but will simply end up in the gascolator.
If you're flying a VW, a primer makes for easier starting. Since you hand-prop real engines, put the primer near the gascolator; no need to put any more fuel in the fuselage than absolutely necessary. Great Plains sells a good primer at a fair price.
For lo-buck builders, riveted, sealed and sloshed fuel tanks are a practical alternative to other methods of fabrication, their use so common we tend to forget others may not have heard of them.
-R.S.Hoover
PS - The ‘xx' in the JCW item numbers is different for each catalog but the basic number stays the same.
(Ed.Note: Originally posted to the internet in Oct. 2003)
Most folks shy away from this fabrication technique due to the high cost of Pro-Seal, still listed at more than $8/oz in the Aircraft Spruce catalog (P/N 09-38500 "2oz sealant" $17.85). But now that Thiokol's patents on polysulfide sealants have expired seam-sealers that do equally well are available for pennies per pound instead of dollars per ounce. Life Industries is one such source. They make a line of polysulfide sealants for marine applications, including a two-part fuel-proof formulation used to calk fuel tanks & bilges.
With aluminum, the sealant-bonding question - getting the stuff to stick - is a no-brainer. Go to your local Home Depot and buy a quart of JASCO ‘Prep & Primer.' Or buy a quart of ‘AlumaPrep' from Aircraft Spruce. Same stuff, chemically speaking. Of course, the aviation-grade' alumaprep is dramatically more expensive.
Degrease then etch the panels you want the sealant to adhere to for thirty minutes in a solution of ‘Prep & Primer.' (The strength of the solution isn't critical. Anything from 1:1 to 3:1 works fine on clean aluminum. If using Alumaprep, follow their dilution instructions.) ‘Prep & Primer' is a phosphoric acid etchant made specifically for galvanized and aluminum surfaces. Scrub the etched surface with a Scotch-brite pad and neutralize with boiling water. The result will be a matte white finish.
To insure greater integrity of your rivet line, you may wish to use countersunk rivets. The dimple adds depth to the rivet line, making it stiffer without increasing its weight. The 120 degree dies you need for poppers are available from Airparts in Kansas City (www.airpartsinc.com) for about six dollars. And from other folks, too. The dies are used with your regular pop-rivet gun. Of course, if you have a lathe it takes only a few minutes to make such a set of dies and even un-hardened they'll last for several plane's-worth of dimples.
If you've never used flush-head poppers, run a few rows of sets before tackling the tank. The dimpling process enlarges the hole. The geometry here is subtle so be cool, work at the pilot-hole level, opening up the hole to rivet-size after you've dimpled & fitted the row. If you don't, the rivet will be too loose to pop; it'll just pull out. Be very careful when deburring as you'll be working on a corner instead of a flat. A file may be a better choice than a regular deburring tool. (These factors have probably contributed to the Conventional Wisdom that sez flush-head poppers don't work very well. They work just fine, but only when they fit the hole.)
With a pitch of about an inch aluminum poppers provide more than adequate strength for this application. Indeed, the stiffness of steel flush-head poppers dictates a minimum metal-depth of about forty thou. Anything thinner and you're liable to pull the popper through the hole before it can form a large enough shop-head to snap the mandrel.
You can buy flush-head aluminum poppers from J.C.Whitney in boxes of 500 for about $12. (JCW item# 14xx4090A, box of 500, $12.19) The short ones do fine for this type of job.
As with all poppers, be sure to wash them good in MEK prior to use. The manufacture of pop rivets always leaves some amount of lubricant on the finished product. That tiny trace of oil will interfere with the adhesion of the sealant (and of your zinc chromate, when using steel poppers on your other panels).
Steel poppers may be a wiser choice for attaching the flanged aluminum fitting for the tank's outlet. You may of course use steel button-head poppers for the entire tank if you wish. I like the flush-head aluminum jobbies for the seam-lines because they give me a stiffer joint at less weight.
If you prefer to use solid rivets you'll need to provide access for bucking the things. Wag Aero still sells sealed blind-nuts for a reasonable price (Cat# L-676-000 Pkg of 50 for $10.95) Sealed blind nuts are standard for fuel tanks. The threads of the screw are sealed away from the contents of the tank inside a little dome. Slosh the tank, you can still remove the access panel.
Tanks tend to violate the rule for panel size vs edge support so you'll probably want to pound an ‘X' bead into the four sides and the bottom. If the top of the tank is curved it will already be stiff enough but the sides & bottom will tend to be pretty wimpy, especially if you're using soft aluminum. (Almost anything will do for making a tank. Don't tell anyone but I've made tanks out of siding aluminum. )
If you don't understand what I'm talking about here, take a look at a steel Jerry can. Some guys like to roll such flutes into the panel but you can do perfectly well by making up a suitable groove or gap in a board, laying the panel across it and making several light passes along the groove with your rubber mallet.
Fuel tank is usually an irregular box. Occasionally an irregular cylinder. Cylinders support themselves but boxes don't. If the thing has corners, plan on adding a couple of baffles, not only to control the slosh but to stiffen the structure.
Rivet-on flanges for the filler and outlet are available from aircraft suppliers but since they are simple turnings they are easy enough to make if you have a lathe. And even if you don't. There are thousands of hobby-machinists on the Internet, their weapon of choice a little 7x10 lathe that's plenty big enough to whip out a set of fuel tank fittings. To track down such folks just go to the appropriate Newsgroup – rec.crafts.metalworking is but one of dozens of such groups – post a message having ‘Help!' as the subject line, describe the job and tell them where you're located. The squeaking wheel gets the grease - keep shouting until you connect with someone in your area. Like all machinists - which is what these folks are... the size of the machine has nothing to do with it - he'll need an accurately dimensioned drawing to work from and you'll probably need to provide him with the stock. Applying sealants is messy as hell, especially Pro-Seal and the other polysulfides. Masking off the area to be sealed/riveted will help and you might want to consider PK's instead of clecos. Polysulfide sealant is close to the perfect adhesive, it'll stick to anything... and doesn't like to come off. (For dimpled holes you'll need the longer (ie, 3/8") PK's.) Grubby-up a PK, throw it away. You're out maybe two cents.
Give the surface to be sealed a final wipe-down with MEK (or whatever solvent is recommended for you sealant). Allow it to evaporate. Apply the sealant according to the instructions. Most call for a smooth, uniform coating on both surfaces. Not too thick, a few thousandths is all you'll need if your rivet-line is a good fit. And not too wide, about three-quarter of an inch, max. Most of this stuff cures by reaction with water vapor in the air, something present everywhere on our particular planet. Cure time is a function of the width of the sealant-line and the humidity in the air. (That's why the stuff is so popular with boaters – it cures underwater faster than out of it.) The two-part formulation cures faster than the no-mix stuff.
You only need about three ounces of sealant for a ten gallon tank, most of which will go on the flanges, your tools and your clothes. (If you've never used Pro-Seal before, buy a pint :-)
If you use the 2oz kits, the little tubes can be hard to handle without the matching gun, a $75 item. (Aircraft certified, right? :-) A dime's worth of Bondo will allow you to modify a regular calking gun to accept the 2oz aircraft-certified cartridges. If you want to go that route, I'll tell you how to make an adapter.
Aircraft Spruce also lists the stuff in pints [$37] and quarts [$74] but the secret to using bulk-packaged sealants is how to mix & apply the stuff without gluing yourself to the wall. The usual mix ratio is 10:1 and is fairly critical. The use of a ratio'd balance beam, baggies for one component and a Teflon cup for the other is a fairly common procedure. Once you've balanced the beam, pour the One-stuff from the Teflon cup into the Ten-stuff in the plastic baggie then seal up the baggie and mix the stuff by squishing the baggie, like colorizing oleomargarine in days of yore. (That's my yore, not your yore.) Once the color is uniform, snip a corner of the baggie and squeeze the stuff out like decorating a cake, using a scrap of metal as a palette knife to smooth the bead to a uniform thickness across the bond line.
Standard practice when using poppers with a sealed structure is to dip the degreased popper in the sealant just before you stick it in the hole and give it a little twist. Don't get too far ahead with the sticking & twisting before coming back and doing the popping. The structure should be perfectly secured with a PK in about every fourth hole giving you three poppers in a row. When you pop, always do the middle one first. Once it's popped some guys butter a smear of sealant into the mandrel hole but it's not necessary if you're going to slosh the tank.
After your tank is fabricated leave it alone for about three days, until the sealant is cured. After it has cured you can provide yourself with virtual 100% leak-free assurance by sloshing the tank with a PVA fuel tank sealant. J. C. Whitney will sell you a quart of the stuff for about thirty bucks. You need less than a pint but I haven't found anyone who'll sell me that small a quantity. As with the polysulfides, there are only a few companies that make fuel tank sealants and most use functionally identical formulations. The thirty dollar stuff from J.C.Whitney appears to be the same as the hundred dollar stuff with ‘aircraft-certified' on the label. Maybe it's not but it works the same.
Since your tank was already etched, the sloshing sealant is going to form a perfect bond. Plug the outlet, pour in the sloshing sealant (it's a creamy white stuff; the vehicle is MEK) seal up the inlet (I use a hose clamp and piece of inner tube) then commence rolling the tank over and around and up and down... but in a logical fashion. What you want to do is to flow the sloshing sealer over every part of the interior surface.
After sloshing the tank, drain the sealant back into its can and seal it up good. Remove whatever is plugging the drain so air can circulate through the tank, prop it so it can drip out then leave the thing to cure.
Takes about 24 hours.
When it's cured, get your light wand and your bore scope and whatever else you need and inspect the interior surface. It should have a uniform white coating.
The sealant is a form of PVA – polyvinylalcohol. Once cured, it is impervious to virtually all solvents, including gasoline, alcohol and water. I've used the J.C.Whitney stuff on steel, aluminum and fiberglas with excellent results (JCW "Alcohol resistant Gas Tank Sealer" item# 12xx8316Y each $28.99). How well it works depends largely on how well you've prepped the surface. Basic rule is to have it perfectly free of grease, including fingerprints. For aluminum, you need to provide some ‘tooth' to the surface, which is accomplished by the etchant (ie, the Prep & Primer stuff).
Lots of ‘expert' homebuilders damn such tanks with faint praise. Sure it works... but real fuel tanks are always welded, yadayadayada... Sure they are, Mr. Expert. (I invite those experts to join me at FlaBob as we refurbish a P-51... and its riveted, sealed and sloshed fuel tanks.)
Your fuel system should have a strainer in the tank. Smartest one you can get is to MAKE YOUR OWN using a short length of 3003 aluminum tubing, slit about every quarter inch with a hobby saw. The typical hobby saw leaves a kerf about .028" wide, much smaller than the mesh of a cheap finger strainer. Cut enough slots to insure the thing will flow enough fuel.
The tank should be equipped with a shut-off valve. See the Northern Hydraulics catalog. Go to the same source for your gascolator. It ain't aviation-certified but it works and doesn't cost the earth.
Basic fuel tank plumbing is to keep a constant down-ward flow of fairly large diameter tubing from the tank to the gascolator. The idea here is that anything large enough to get through the strainer in the tank will not block the fuel line but will simply end up in the gascolator.
If you're flying a VW, a primer makes for easier starting. Since you hand-prop real engines, put the primer near the gascolator; no need to put any more fuel in the fuselage than absolutely necessary. Great Plains sells a good primer at a fair price.
For lo-buck builders, riveted, sealed and sloshed fuel tanks are a practical alternative to other methods of fabrication, their use so common we tend to forget others may not have heard of them.
-R.S.Hoover
PS - The ‘xx' in the JCW item numbers is different for each catalog but the basic number stays the same.
(Ed.Note: Originally posted to the internet in Oct. 2003)
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