Information Overload

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That's not a joke. Nor a line from a poorly written television show. It's the real thing. And the effect it has on me is rather interesting. You might might find it interesting too, which is why I'm writing this.

I'll assume you know about the cancer and, if not that it's mere mention will be enough for you to track these entries back and come up to speed. Or perhaps not. In either case the cancer is the baseline. The projects -- do-it-yourself airplanes and the engines to power them -- were here first, beating out the cancer by more than a decade. Other projects too, ones not suitable for chatting about over what is basically a party-line telephone. Did you ever have one of those?

Back in the Good Ol' Days, whenever that was, the phone company decided who got telephones and who did not. If you lived on the fringe you might get Party Line Service, which meant you shared your telephone with a number of other people. The way it worked was that you were given a coded ring. Two longs might be the Mason family who lived about a mile farther out of town. In theory, with a two-element code -- a long ring and a short ring -- and a maximum of say four elements you could end up with a lot of 'telephone neighbors' but in practice it didn't work out that well and most Party Lines had only a few subscribers. One reason it didn't work very well was because everyone listened in. The more people to pick up the receiver, the lower the signal strength until it reached the point where you couldn't hear anything.

It took some seriously deep thinking to come up with the Party Line system. And to make it work. A basic tenet of making it work was that the Telephone Company was Always Right. And if you didn't agree, they would simply disconnect your telephone.

When you are the only game in town you'd be surprised how many people found themself agreeing with the Phone Company and overlooking the fact that a whiff of competition would probably have turned things around a lot quicker than any system based on Ma Bell's superiority. In fact, you'd probably have a system pretty much like what we have today, with a cell phone in every pocket.

In a sense, my projects are something like the Party Line in that everyone can listen in. I'll leave you to figure out the other ways my projects are similar to a party line. And the ways it is dissimilar.

Right now the Cancer Project is taking up a steadily increasing share of my time. I'm a bit old to be sending myself back to medical school but when you see the stuff I've been researching and the truly enormous amounts of stuff I've been reading, it would be hard to say I am not a student of medicine. That doesn't mean I'm a good one -- my interest is too narrow -- but my interest should give you some idea of my dedication, as well as my ability to ask the right questions as I come up to speed on the subject. :-)

I'd better put in a smiley there. Because anyone with a lick of sense knows that a few months of reading does not a doctor make. But it can make a patient who is liable to scare the pants of a few physicians.

The point of all this is that medically, I'm coming up on a fairly critical time, one that will impact the amount of time I will have to keep playing with my projects. Wrong decision and it's time to pack my sea-bag.

Making decisions -- good ones -- takes quite a bit of time. I'll leave you to work out how that is impacting the projects that don't have to deal with cancer.

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Up-side stuff: I weighed about 230 pounds when I was diagnosed. (Yeah, I was pretty fat, most of it gained over the last ten years or so.)

Within a matter of weeks I was down to 200, still slowly drifting south. About a month ago -- nine months after I was diagnosed -- my weight was at 164. Which isn't all that bad because it had been at that level for a couple of weeks. Then it started coming back up. I'm now about 175 and the trend looks pretty good. Plus, there's a couple other Gross Indicators that are looking better than they did. You can't say I was on the mend -- there's no cure for multiple myeloma -- but there were signs I was holding my own, all thanks to my wife (seriously) and the team of physicians Dr. Alberto Bessudo had gotten to be part of my Cancer Team.

Down-side stuff: Working undetected, possibly for years, the tumor had honey-combed a couple of the vertebrae in my spine. It had done such a good job of it that one of my vertebrae was a mere shell with so little structural strength that something I did -- some entirely innocent behavior, probably something I've been doing all my life -- caused the muscles to literally crush the vertebrae. It's called a compression fracture and it isn't unusual with multiple myeloma but in my case it is. Because whatever it was I had done (probably picking up an engine) not only crushed the vertebrae, but crushed it so badly that the normal fix simply would not work -- there wasn't enough healthy bone remaining. ( On the MRI scan you can see the remnants of the vertebrae, a sharp-edged scickle of bone. )

I'm still mobile but.. you know that pain thingy I've mentioned a time or two? Well, crush a vertebrae and Pain pretty much takes over. But even that's not going to last much long if I don't get this thing fixed, and the fix is akin to jacking up the boat and putting a new hull under it... if you're familiar with ol' fashioned Navy-type humor. They need to virtually replace the vertebrae with prostetic made of titanium or perhaps carbon fiver. Then they need to plate it with something my body will accept as bone -- and grow to it, creating an inflexible -- but pain free -- Super Vertebrae.

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Care for some applesauce? No, you go right ahead; I've got tons of the stuff. Eating some now as a matter of fact, even though it's a quarter to midnight Getting the munchies is something the doctors take as a Good Sign. (Which should tell you that doctors haven't eaten a lot of applesauce :-)

The Chugger has had me trying to figure out a practical way to make a near-perfect leading edge out of fiberglas, three or four feet at a time using vacuum bagging. Which I can't say I've ever done to any extent but which I think I can figure out.

Basically, you start with a perfect mold of a leading edge. Not just good but perfect. Then you drape it with fiberglas, cover that with a sheet of plastic, suck out some of the air and let it cure. Perfect leading edge skin, easy as that. ( And I'm sure you can see the Great Big Smiley that goes with it. )

Now those of you who have done a bit of plastic-bagging are rolling around on the floor, pointing at the computer screen, laughing so hard it's coming out snort snort snort while your family is wedged in the doorway trying to figure out: a - What happened to the old man? b - Should we dial 911? and c - If I help him up, will he let me use the car?

Well, I did make a pretty good mold. You see, the mold has to be strong. Chord of the nose-skin is twenty-one inches, span is 48. That's over a thousand square inches. And I ain't no dummy... made it nice & strong... better than six layers of fiberglas on top of foam. Beautiful finish with provision for over-lapping ends, channels for peeler strips... all that neat stuff.

Turned on the vacuum pump and in the time between turn it on and looking back at the mold it had folded itself up like a fiberglas taco. (No, not a regular taco... they're way the hell & gone too crunchy.. one of them fish tacos, like Pilar sells down in Todo Santos. Or did, back when you could drive to Todo Santos.) And of course, you've used a resin that will set-up nice & quick (see how smart I am?)

That was a few years ago but I didn't give up. Made the next plug outta Portland Cement. (Don't laugh! Inexpensive and can take an impression accurate to thousandths of an inch. Howard Huges used tons of the stuff making the molds for the 'Spruce Goose.') Skreeded nice & neat (See? A regular genius) Made the finish-coat nice & thick. Slow-setting (Little house for it and all so's I could keep the plaster-coat moist. Lotta thinking went into that puppy.)

Weight? Oh, I donno... couple hunnert pounds I guess. ( Now you can see where the bad back comes from :-)

Okay, so I've managed to outwit myself a few times. Chalk them up as Learning Experiences. And then hide them suckers to keep your friends from laughing themselves silly.

But I haven't given up. Until I caught this cancer thingy.

I'm about down to the Sanding stage on Mold #3. No thinking required, so mebbe I can keep working on it now & then. Along with that propeller. And those two engines over there. (Usta be five.)

Progress. It's our most unexpected product.

-R.S.Hoover

TABLE SAW, Part 1

About two years ago I was coming home from an errand in town and because of traffic, I took a different route. It climbed out of the part of town drained by one creek, up and over a ridge then down into another narrow little valley whose once chuckling creek now flowed out of sight in a concrete tunnel. It's a very pretty little valley, no more than a mile in length, but quiet and cold in the winter, the temperature often dropping below freezing, covering everything with frost.

The seldom traveled road is bordered with hedges which conceal some of the most expensive homes in Vista. Beyond the hedges are paddocks and groves, often several acres in extent. Their smudge pots once made a significant contribution to Vista's rural atmosphere until they were nudged aside by lavishly large homes, horses and people to ride them.

Incredibly, someone was having a garage sale. Portable tables and racks of clothing were arrayed facing the road; a road on which through-traffic was rare and when it did come, was liable to be a local resident like myself, driving an old VW bus. Or an expensive SUV.

I like to stop at garage sales, hoping to find books or tools. I parked and started browsing. A tall, thin woman, perhaps forty years old, left two other women and came tripping over the lawn to ask, "Can I help you find anything?"

She had been looking at the old bus and its equally decrepit driver, but discretely, her head slightly down. Her neck and jaw-line was straight off a bust of Nefertiti. She re-positioned a stack of china teacups and saucers. It looked like Norataki. The stuff was made up in stacks of four, tied with a thin ribbon of pale blue. There was a little white price-tag affixed to the ribbon: $100. There were four stacks, each of four cups and saucers. "It's a shame having to break them up," I said. She gave me a startled look as if surprised I could speak. Or perhaps she misinterpreted my meaning. She waved a hand down the table at other pieces of china.

"I think these were spares," she said in the voice of Paula Prentice. "They were always getting chipped... " She sounded uncertain, turned and walked away, leaving me unattended before a table bearing teacups and silver spoons, one of which was probably in her mouth when she was born.

She came back, now walking with her head up, an easy, graceful walk. Rather than simply raising her voice she'd walked over to the other women, posed the question, came striding back. "No, that's all gone," she said, like the rings from the fingers of her clasped hands. I took that to mean China and if these were the spares... I imagined tables groaning with expensive porcelain, cut crystal and a spare kitchen maid or two.

"Have you any books? Or tools?"

"Books..." I'd stumped her with the sudden leap from China to literature. But she was learning to Cope; a girl grown old in a character straight out of the pages of Fitzgerald. She gave me a wide smile, made another hike. And another return. "There may be something in the boxes..."

The hesitant boxes were under the tables, filled mostly with bound issues of Associations; of Legal this and Corporate that. And cookbooks? But in French.

Alone, under a table all its own, was the Saw amidst a litter of tools remarkable only for their shoddy quality. Some sort of 'Home Owners Kit' from a cut-rate drug store, worth at least $1.98 when new, now marked an improbable $5.00. And the saw. The incongruity of finding a Skil saw; an honest piece of goods, sitting atop a box of trash intrigued me. If there were other boxes snapped up by earlier buyers, how could they have overlooked the Skil saw. I pulled the box toward me but there was no price-tag although there was a swatch of masking tape in a conspicuous position on the handle, probably put there for the missing price.

"What'll you take for the saw?" I swung it up, into her view, threateningly near a pagoda of Norataki, showing her the piece of blank masking tape.

When I swung the saw into view, dangerously near the fragile China she started to extend her hand, an instinctive move to protect the China. Or perhaps the saw. But this had taken place before the cancer, back when I could pick up a ten-pound saw as easily as a piece of cake. Or perhaps she sensed my raw, masculine power... Whatever the cause her protective hand fllew out then withdrew, the movement serving to bring her knuckle to her chin where she tapped it in a speculative manner, sneaking a peek toward the two women, still involved in a negotiation of more importance than than a dirty saw. But this was a woman learning how to cope with such things, probably with some help from a Sunset magazine suppliment telling its Yuppie subscribers how to conduct such affairs, perhaps even a guide on Basic Dickering.

She said, "Make me an offer."

It was said with a bold confidence so unlike her demeanor just a moment before that I gave her a speculative stare that lasted a moment too long. She blushed and I felt ashamed for scaring the girl.

"How does ten dollars sound?" Alright, I'm a rat. The saw was worth at least twice that.

She was flustered now, started to speak, hesitated then admitted: "I'll have to ask," with an exasperated sigh and off she goes across the grass, a long, thin woman, square shoulders and that lovely stalk of a neck, leaving me to wonder. Death? Divorce? A Russian secret agent no longer receiving her stipend from Moscow? A yard sale in that neighborhood was liable to be covered by the Society reporters for the local papers.

A Decision had been reached. Money change hands. Hangers were removed, clothing folded, stuffed into a paper bag. I couldn't remember the last time I'd seen a paper bag. Then the two women came toward me.

The second woman was Mutt to Fitzgerald's Jeff, legs pumping industriously to remain abreast of her taller companion. There was also a sense of diffidence, the shorter, younger woman whose hands were marked by years of work was clearly In Charge, a preppy from Smith walking an Afgan from Harvard Law.

"...the pockets. Because once it's gone, it's gone."

I agreed with a hearty nod as the saw was inspected, first casually then with obvious suspicion. "Wasn't there a tag?" the little woman asked.

"Just the tape," I smiled, peeling it off. Oops!

Concealed by the tape was a sticker saying the saw had been re-worked. Probably a warranty item. In fact, the plastic handle had been branded RECON.

The tall skinny lady didn't understand that the short woman, who was probably teaching her how to run a garage sale, had tried to conceal the fact the saw was reconditioned. I started to put the saw back into the box of junk but the skinny lady asked, "What's wrong?" I put the saw on the table, well away from the China, with the sticker and the branding facing the woman and explained the meaning of the sticker. The short woman interrupted me to tell the other she was going to the house. We watched her walk away.

"Does that mean you don''t want it?" the woman asked and for reasons I can't explain, I dug out my wallet and offered her a ten dollar bill. The woman looked toward the house then at the bill. It fluttered in the cooler air starting to flow down the road. She looked back at me and said, "You can have it, if you want it."

"That wouldn't be fair..." then I realized that it would, since the short woman would probably receive a percentage. A cash payment, neither taxed nor recorded. The woman was hugging herself. She didn't want the money. I thanked her, putting the money in my pocket. She smiled, blinking rapidly. I turned away rather than see her cry.

I used the saw to make a scarfing jig for plywood. It has worked flawlessly. Now I'm using it to make a table saw. I'll post the drawings and photos on the Chuggers_alt Group.

-R.S.Hoover

Ode to my Belly Band

It clasps me. Not too tightly
In a grip of Velcro and lace. Politely
It provides a Nylon squeeze between my shoulders and my knees.
My once bowed back is now Marine Corps straight.

Morphine, my new-found friend, remains in my pocket much longer than before.
But it's there when needed, when strain is exceeded,
On that shelf just there by the door.


Months ago -- that now seem like years -- I thought a brace... some added support... might keep the pain at bay. Not a cure, you understand, but a crutch. Something to help me stay up-right long enough to do some minor chore at sink or stove since it was understood that anything more useful -- the scrubbing of a floor or simply carrying packages in from the car -- was something I could no longer do; something not to ask of me when I was too ashamed to ask for myself... and too damned scared to simply wade in, grab as many bags as I could hold... and sink into a whining, agonized heap so wracked with pain I soon became too terrified to even try. A demon now lived in my guts and would reside there until I die. My friend Morphine, a cheerful if somewhat drowsy fellow happened along, candy for the demon now eagerly fed.

But it nagged at me; the thought there may be some middle-ground as yet unexplored, a side-canyon of canvas, leather and skillful hands that might allow me to slip past the demon's cave without awaken him, if only for those face-saving minutes when the Terror of the South China Sea could flash a salty grin and shoulder my pitiful share of the familial load.

The one from Harbor Freight was made for a fatter American than me. The other they offered was too small. Instead of Kid Shelleen I was given a character from Dick Francis.

The doctors were polite at best, their expressions making you check the soles of your shoes. Clearly, back supports were right up there with apricot pits and movie stars, damned with praise so faint it was blown away on a whiff of resignation. Asking a physician about back supports was on par with asking to clean the windshield of their Porsche at some busy intersection of life.

On the other hand there are tasks for which a belly band is a requirement. Not as a cure for cancer of course but as a statutory requirement meant to stave off injuries rather than cure them. And the people selling such things take their role seriously enough to support web sites and offices. Just as the military surgeon is no longer required to shave the colonel, the belly band man has come of age.

It costs a ton, compared to the stuff from Harbor Freight. But fair is fair; I am the colonel and the belly band man still smells more of Bay Rum than isopropyl alcohol. He speaks knowledgeably Gold Bond versus Mennen and corn starch versus talc.

The first efforts were hilariously wrong; my pride was trying to do the belly band's chore and I was tiring even more quickly because of it. But there was a moment, just before Kid Shelleen surrenders and the Demon emerges from its cage... just for a moment there, when my own muscles, flayed with radiation and depleted with drugs gave up the struggle and let the belly band do its job, when I enjoyed peace of a kind. I still hurt. When the Demon decides it will live in your spinal column there's really nothing you can do. Pain-wise it's like the joke about nine-hundred pound gorillas deciding where to sleep. If you've got Multiple Myeloma, and if it involves your spine, then pain has become your life-long companion. And yes, that's a play on words.

Fortunately, the belly-band man knows those things, whereas if the physican does, he treats it as something of lesser importance. One of the best examples of this is the way the two manage your time. Sure, it's their time too, but when the physican makes you wait an extra hour for a harried seven minutes of discovering he's got the wrong chart and that treatment of my vagina will probably prove unsuccessful, he puts no importance on the matter. After all, he is a Physician, whereas you are... just a patient.

The belly-band man, equally harried, took a time-out to apologize; to ask if we'd like to re-schedule; the person he was with now had some serious issues and it was going to take more time to sort things out. We chose to wait

Mis-handled appointments lead to time compression. The only fair thing to do is to skip ahead and re-schedule, which we could hear the girl doing, trotting back and forth, calling other belly-band fixer-uppers until the brush fire was contained and the cause of all the trouble is finally escorted out the door walking with a gingerly gait I'd learned to recognize. But walking. And by sitting there we saw that missed appointments were the exception rather than the rule.

My belly band isn't quite right even now. But it's moving in that direction. If this were Hollywood we would probably see Kid Shelleen smiling happily, with forty acres and a mule.

-R.S.Hoover

Cutting Aluminum

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Aluminum is marvelous stuff for building airplanes. It is as strong as mild steel -- and even stronger in some cases == yet weighs barely a third as much. The advantage of aluminum over other materials is best illustrated by a design such as the Teenie Two, which has an empty weight just over three hundred pounds. What's remarkable is that when you subtract the weight of the converted VW engine and the landing gear, you're left with barely a hundred pounds.

That hundred pounds represents the aluminum used to fabricate the airframe. And while that sum includes some extrusions, most of the hundred pounds is made up of sheet aluminum.... and of just two thicknesses, .020" and .040", making the Teenie Two one of the most practical and least expensive of any homebuillt. (So why isn't the sky filled with Teenie Two's? Because the plans... all seven pages of them... are as screwed up as Hogan's goat.) Great little airplane; horrible set of plans.

When you set out to make an aluminum airplane one of your first chores is to cut the aluminum. This holds true for every metal airplane. Indeed, a large percentage of the time needed to make such an airplane is taken up by cutting the aluminum.

There are lots of ways of cutting aluminum and as a novice tin-bender we're expected to know quite a few of them, from using a large pair of tin-snips to milling out stacks of ten ribs at a time using nothing more sophisticated than a router.

Oddly enough, one of the most common methods of cutting aluminim -- and a method used virtually every day by everyone from school kids to housewives -- is not to cut the aluminum but to fracture it.

Think I'm kidding? Pick up a cool one and pop the top. You've just cut the aluminum top of the can by fracturing it!

Working with sheet metal we often are tasked with making a cut that is perfectly straight, or at least within the spec allowed by most homebuilts (which happens to be one-eighth of an inch in thirty-two feet... or a sixteenth over sixteen feet.) Which is pretty damn straight. To achieve that degree of precision we simply clamp a straight-edge to the metal to be cut and transfer the 'truth' of the straight-edge to the work-piece by scoring the work-piece with a suitable scriber.

The most commonly used scriber is just that -- a machinist's scriber (think of a dart without vanes). That works fine for small jobs, such as scribing the air-foil of a propeller, but as the thickness of the material increases, we are forced to score (or scribe) the material more deeply. This causes us to reach for scoring tools designed specifically for that task. A nice example of this is the bottom tool in the upper photo. The tool has a silicon carbide cutting edge and is perfectly flat on the left-hand face. This makes the tool suitable for scoring metal up to .032".

The box-cutter (ie, the yellow tool) is probably the tool most commonly used for scoring aluminum sheet. Unfortunately, the blade is not flat-sided; you must learn to hold it at the correct angle. An X-acto Knife or #11 surgeon's scalpel is a better choice when scoring beer-can stock for templates and the like.

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About here someone usually sez: "I don't get it." I've been talking about scoring and scribing and telling you which tool is best for this & that... but I haven't mentioned how the metal is actually cut. Because it's not, of course. Cut, that is. Once the metal is scored we simply flex it back & forth. Not very much... not enough to bend anything. But to just flex the metal. That's all it takes for the metal to fatique... and then to fracture, right along the score-mark.

Long piece of floppy metal? Then clamp a stiffener to it; a piece of wood will do. In fact, flexing even a small piece of metal is sometimes easier if you clamp a piece of wood to it, to act something like a handle as you flex it up & down.

Brothers All

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It's not just pills and radiation that cures cancer. A big part of it, perhaps even more important than xrays and medication, is the people in your corner.

-Bob Hoover

PS - That's Ben on the left, Micheal on the right. I'm the good-looking one in the middle.

How to Carve a Propeller -- Part 1

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A search of the internet will turn up half a dozen How-To articles for making a propeller. What follows is a series of articles explaining how I make my props. My method isn't any better or worse than most of the others; you'll end up with about the same propeller. I'm offering my method because I've found it works a bit better when it comes to teaching folks how to build a prop. I'm not sure why that is so. Perhaps it gives you more confidence or something. In either case, take advantage of those other How-To articles; read them carefully. But keep your money in your jeans until you've given my method a fair trial.

This propeller is for the Chugger's engine. Chugger is a draggy, single-place, all-wood, strut-braced parasol. Chugger's engine is a big-bore stroker based on after-market VW components. The crankshaft is a Chinese import having a stroke of 84mm (stock is 69mm), fitted with 94mm pistons. The stock camshaft is retained but is retarded between -4 and -7 degrees, moving the engine's torque curve to a point well below 3000 rpm. (The stock VW engine had to be able to get a vehicle weighing more than 3,000 lbs under-way from a dead stop. Even with a box of gears that takes a fair amount of torque.)

A high-torque, low-rpm engine requires a prop with a lot of blade area and a diameter of up to 68". This particular propeller has a diameter of 62" with an aerodynamic pitch of 34". One blade of this prop is shown in the illustration above. (Double-click for a larger image.) The illustration is also in the File archive of the Chuggers-Alt Group where it is in DeltaCAD's native formate. If you have DeltaCAD -- they offer a 30-day trial copy for free -- you will be able to print-out the pattern shown above then glue it to a piece of plywood or poster-board.

In the illustration (above) you can see that the propeller blade has been divided into ten segments or Stations, each 3.1" wide. The propeller will use a Clark-Y airfoil, which happens to be flat on the bottom. After laying-out your glued-up blank, the first step in making the prop is to carve that lower surface. Protractors for each Station have been provided in the Files Archive. These are used to verify that the bottom surface of the prop has the proper angle.


In the lower part of the illustration to the RIGHT the WIDTH of the propeller at each Station has been measured. In the upper part of the illustration the geometric pitch for each station has been laid out by dividing the Aerodynamic Pitch in inches (ie, 34) by 6.28 (ie two pi ).

If you haven't obtained a copy of DeltaCAD, which would allow you to use the templates in the Files Archive, by using the dimensions from the two illustration you have enough information to manually lay-out & draw the blade pattern onto 1/4" ply or similar. Take your time finishing the pattern since it will be reproduced in the blades of the propeller. When you are satisfied with your workmanship, mark it in the hub area: 62x34 and give it a coat of varnish.

The horizontal lines in the upper part of the illustration represent the laminations (ie, 3/4"). For this first prop I want you to use full-length laminations. That is, four pieces of 1x6 birch, which is available from most Home Depot stores. (But if this is your first-ever attempt to carve a prop, use 1x6 pine shelving instead of hardwood. Don't worry; it won't go to waste.) In later props you will see that the upper-most three laminations do not need to be run full-length. By using shorter pieces for the upper-most three laminations you can reduce the cost of the wood by almost half. However, when you have a blank that uses partial-length laminations it can be very difficult to carve the lower surface. Here's why:

The lower surface is flat but twisted. You can see that from the different angle at each Station. Normally, we carve the lower surface by using a back-saw to make a reference cut at each Station. The reference cut starts out even with the trailing edge but comes out on the leading edge at some point above the trailing edge. That means the cut is at an angle to the horizontal. If you'll look at the upper part of the illustration above you will see a dotted red line that represents where the lower surface comes out on the upper surface edge of the prop blank. Study that for a minute and you will see that in full-span blank -- one in which all four of the laminations are a full 62" in length, to carve the lower surface we must remove about half of the wood in the prop-blank.

Removing wood isn't difficult; we cut down into the prop-blank with our back-saw not just at every station, but about every inch (!). Then we chunk it out with a mallet and chisel. When compared to a prop-blank that uses laminations of different lengths, this method adds to the work -- although that isn't much of a consideration since we aren't punching a clock... but it also adds to the cost, which can be a major consideration for the lo-buck builder. That's why I'll be showing you how to make-up a blank in which only one lamination is full-length. The other three laminations are only partial-length. I think this is worth mentioning now because a prop-blank that uses full-length laminations is so easy to work with that it may give you the wrong idea about making props. When using a prop-blank made up of partial-length laminations you're going to find that just holding the thing down can be a major problem.

Among the patterns and templates in the Propeller File in the archives of the Chuggers-Alt Group, I have included Airfoil Patterns, Lower Surface Protractors, and 'Chunking' Templates. By applying the templates to your prop-blank, most of the work will be taken care of when you chunk-out the blank.

Remember now, I'm uploading all this stuff to the Files Archive of the Chuggers_Alt Group. DeltaCAD will print them out full-scale. You then cut them out and spray-glue them to a suitable substrait. For the protractors you want something fairly substantial, like 3/4" stock. For the airfoil patterns you want something thin but rigid. Back in the Day we used shim brass, typically between .006" and .010" but nowadays beer-can stock is generally used.

The third illustration in the group above shows the lines needed to chunk-out the upper surface of the propeller blade. As with the lower surface, the upper camber is twisted. You want to keep that in mind as you do your chunking.

When you get done with chunking out the upper surface you'll be left with a lot of corners. That's when you reach for your block plane, draw-knife or an angle-head grinder an angle-head grinder fitted with an #80 grit sanding disk.

The tricky bit here is that any of the above tools leaves a stripe. That is, a flat spot. The more you work at it, the more stripes you'll have and the skinnier they'll be. Rub a piece of chalk on the cambered surface of your gauge, fit it to the matching Station an the chalk should transfer to the 'corners' of the strips. What you want to do is get your stripes down to a width of about 1/8". When you do that, trial-testing with the template leaves a kind of dotted line that makes it easy to see where some strips are a bit too wide, meaning they need a bit more work.

The final finishing involves little more than working your way down through three progressively finer grits of sandpaper, using an orbital-type block sander. For the leading edge, you want a perfectly faired surface. I've found the handiest way to get it is to simply fold some #120 paper in the palm of my hand and work it down until my eye tells me to stop.

The Stations nearest the hub DO NOT follow the rules which apply to the Stations from #3 through #10. These inner-most Stations do not contribute thrust nor cooling, since they are obscured by the spinner. In fact, about 50% of your thrust is produced by the blade of the prop beyond about Station 6. But the inner-most Stations are vital with regard to the structural strength of your prop.

Stations 1 and 2 are simply nice, fat streamlines, with as much camber on the lower surface as on the top. We can do a bit of chunking here but it's mostly an eye-ball job.

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3 March 2009

I haven't uploaded any of these drawings to the Chuggers_Alt Group. The truth is, I've still got about two dozen drawings to do and the airfoils are especially pesky. I also want to include some photos but I've got a pretty full plate. I'm going to go ahead and post this to my Blog but keep in mind that it isn't complete as yet.

-Bob Hoover