Wednesday, April 29, 2009

BOB HOOVER... LIVE!

To All:

That's meant to be a kind of joke, see... because I have cancer I'm never too sure I'll wake up in the morning so I thought labeling a post as 'Live' would be something of a play on words.

But the title also emphasizes an on-going problem I'm having with Google and my memory, in that I often forget my User Name and Password, making it impossible for me to either SEND or RECEIVE messages. This morning for example, Google says my current User Names and Passwords will no longer be valid; that I will have to jump through various Google-hoops to make things right. But when you try to do that you get an ERROR MESSAGE saying to try again in a few minutes. The Mystery Time is not defined. Five minutes? No, that's not enough. Ten minutes? Ditto. Indeed, it appears that Google's error-handling procedure may well have an error of its own, in that, while it SAYS to do this and go there, it doesn't actually work. If the problem persists you're told to contact yet another address. Which of course does not work either.

But I am still alive! Honest! And people still send me email asking questions about their VW engines, converted for flight or otherwise. And I keep trying to respond because I assume you would like to receive an answer. But given the amount of errors, trying to stay in touch becomes horribly frustrating.

-R.S.Hoover

Sunday, April 26, 2009

The Chugger

The above is a sketch of 'Chugger,' a minimum cost design meant to be fabricated using wood from the typical lumber yard. The engine is a Volkswagen, converted to put the propeller on the flywheel end of the crankshaft, where it will be immediately adjacent to the thrust bearing.

In American slang a 'chugger' is a person or machine that isn't very sophisticated yet manages to get the job done.

The minimum cost aspect of the design is achieved by using lumber that is locally available. This point keeps popping up, despite the fact the Government has not been in the business of grading wood since the 1950's. What you get when you buy 'aviation-grade' lumber is a piece of wood that has been graded by someone at the saw-mill. Or at the retailers. It will be nice, clear lumber, graded according to those standards of long ago but you won't find a government stamp on it. Most of it will be Sitka Spruce unless you have asked for something different, such as Douglas Fir or perhaps Northern White Pine. (The government inspection criteria covered more than two-dozen species of softwoods commonly used in the structure of lightplanes.)

I continue to receive more messages on this aspect of Chugger's construction than all others combined. I've nothing against the use of certified materials. For example, I still want you to use aviation-grade plywood, although not very much of it.

In recent weeks several prospective builders have swished past the earlier version of the drawings, some are even willing to fly it to the various fly-ins... if I'll give them a flyable copy of Chugger to keep as their own. I take that to mean they've found nothing fatally flawed in the design.

Except for the use of Blog Store lumber.

I think everyone is wrong in that regard and I believe I can prove it.

If you will click on the opening drawing it will expand to fill your screen. The firewall is 24" in height which should allow you to get a rough estimation of the length of the remaining sticks(*).

I will agree that it is difficult to find aviation-grade lumber long enough for spar caps or longerons but the drawing makes it clear that most of the required pieces are quite short. You will have no trouble finding sticks of that size by simply ripping a 2x4 or even a furring strip. Indeed, here in Southern California the decline of our economy has left the lumber department of most blog stores as empty as the Kalahari.. This aspect of wood-quality is equally true for the wing. The point here is that aviation-quality wood is available from local lumber yards. The only tricky part is that you must spend some time grading it.

The common myth that wooden airplanes are made entirely of wood is simply not true. Indeed, many potential builders prefer aluminum or rag & tube because such airframes require fewer tools and far fewer skills.

The second drawing, which should be wandering about near this paragraph is meant to serve two purposes, the first of which is to give the reader some idea as to the number and location of the metal fittings. The idea here is build this much of the fuselage as mock-up for the fitting & welding of the metal fixtures for such things as the landing gear, the wing-strut attach points, and the cabanes. Not shown are the Cub-type landing gear Vee, the control stick and the rudder pedals. These were not shown partly because I forgot to put them in but also because they are so simple they are easy to forget.


As the Chugger's drawngs are developed they are being posted in the Chuggers-alt Group. But nothing is in its final form. As I've said in the Introduction, the Files represent a series of experiments, conducted for the purpose of proving or disproving the practicality of building an airplane that draws most of its materials from local sources.

If you find the Chugger of interest please have the courtesy to read the Introduction.

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

(*) The lumber carried by the Box Stores usually has too many knots to pass the old government standards in lengths of twelve feet or more. But it's not uncommon to find a knotty 2x6 that passes -- or even surpasses -- the old certification specs. Unfortunaely, the longest peice without a knot is only six feet or so.

If you find a stick like that, grab it! After you have re-sawn the stick into 3/4" by 1" sticks, even though it is liable to break at the knot you are still left with two perfectly good pieces! Indeed, if you'll examine the top drawing you will see that the longerons are quite short. While it may be necessary to scarf some pieces together to obtain the needed length, by building the splice right in to the design I should be able to find pieces of the required length without having to re-saw very many pieces.

-R.S.Hoover

Tuesday, April 21, 2009

Harvesting Data

Most guys call it blueprinting. You measure the part then check the measurement against the 'blueprint.' Which hasn't been a real blueprint since the 1930's. Nowadays it's just a file of dimensions and tolerances provided by the manufacturer, usually in their Factory Service Manual. Alas, the task isn't as simple as it seems. In many cases the factory manual cites only metric dimensions, leaving the conversion up to you. In other cases they cite both Metric and English units of measurement... and sometimes gets them wrong, requiring you to keep on your toes when they say one millimeter equals 0.3937" ...when they should have said 0.03937".

An even trickier bit is what happens when you depart from those stock dimensions. When you build a big-bore stroker you are literally designing a new engine. Cutting the heads to accept larger jugs requires you to measure the diameter of your new jugs and then add the anticipated thermal expansion to that dimension, and finally to add some small amount for your tooling wear.

This sort of thing -- the designing of a new engine -- is largely a desk job. No greasy fingernails. And yes, your computer comes in very handy. Not so much for the computation of things but simply for storing them, ideally with drawings.

So where do you come up with those figures that are not listed? Standard engineering manuals, such as Machinery's Handbook will give you the accepted standards for the thermal expansion of your parts but the particular alloy plays a role I'll mention in a moment.

Thermal expansion takes place in all three dimensions. The engineering manuals say that the intra-molecular space will INCREASE as the temperature of the part increases. Some call these dimensions -- the ones not listed for our particular engine -- the experience factor when in fact we've simply memorized the values of interest from tables found in various manuals. Pratt-Whitney and Machinery's Handbook sez 0.003" per inch for cast iron and .007" for cast aluminum... which works well enough for the alloys used by VW in their heads and barrels.

But if you don't know what alloy is being used, you'll be safer if you put the part(s) in an oven and raise them to their anticipated normal temperature. And learn to measure them quick like a bunny, before they can cool off and before they can heat-up your micrometer. That's enough to give you some idea of the problem, which is the fact your heads and barrels will expand at different rates.

Not everyone does it that way. In fact, a lot of 'experts' don't blueprint anything. Their engines usually end up in dune buggies but there's a few who build engines for airplanes. In doing so they follow the same procedures -- and use the same tolerances -- they have used for dune buggies. This entails considerable risk because there are significant differences between the VW engine in a vehicle and one that has been converted for flight. The most evident of these differences is the higher temperatures experienced in engines converted for flight. This higher temperature reflects the fact that a flying Volkswagen is operating at a continuous level of output at least fifty percent greater than that found in any vehicular engine.

The builders of dune insist there is no difference between their engines and those used for flight and that is substantially correct. But there is a profound difference in how the engine is USED and that is easily illustrated by the fact an airplane must sustain itself in the air. To do so demands a higher level of output on a continuous basis.

-R.S.Hoover

Monday, April 20, 2009

The Follower Phenom

Uh-oh. What's this?

In the military one of the targets used on the pistol range was a silhouette of the upper torso. To maintain our proficiency with handguns we would periodically go down to the Pistol Range and shoot holes in those Silhouette Targets. Now Google is putting silhouette targets on one of the pages supporting my Blog. Pistol target with 'Followers' underneath.

Little green Silhouette Targets on the Dashboard page, which I've not visited since... whatever. I dig around here & there... I haven't had much luck as a blogger. For example, I didn't know they paid you for blogging! I'm still not too clear on how it works. Sometimes Google sends me money. And sometimes they don't. After a while they apologize for not sending anything, promise to do better. And don't.

Then there are the things they simply whip outta thin air, full-grown, which they apparently expect me to be fully aware of, when in fact I'm barely aware of them, let alone the weird stuff they are continually creating, apparently having mistaken activity for progress. Like this 'Follower' business. I dig around trying to find out what this latest phenom entails but come up dry.

Surely 'Follower' doesn't actually mean Follower! Because if it did, it would mean I have been promoted to Fearless Leader... like that guy in N. Korea with the bad comb-over. Is that how people see me? As a Nutsy Cookoo? Trouble is, the Korean Cookoo is desperately eager to be a Fearless Leader and I am not. So which is it?

Click the icon and sure enough, a page pops up with a list of people. I recognize a couple of the names but others are complete strangers. Which worries me even more. I'm happy to meet these people; happy they've found something useful in the material I've posted. But to me follower implies leader and that's the part that worries me. Is there something I should be doing to fulfill my new role?

I've tried to find more information about Followers but the only meaningful thing I've heard is that it's people who want to maintain closer ties to me. If that's the case, my email address is veeduber@chuggers.net.

However, if the 'closer ties' means telephone numbers and that sort of thing, when someone calls I generally can't get to the telephone before the ringer times out and the pre-recorded voice tells them to leave a message. I've got a cell phone but I don't know my number. The cell phone was a gift from my wife when I became ill. But I don't use it very often.

When my sister was ill I was expecting her to return my call. When the phone rang I tried running, hoping to catch it before it timed out. Bad idea. I managed to trip myself up and took a bit of a fall. Scared the hell out of my wife and made me feel like an idiot.

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

So... welcome, all you Followers. As your Leader I'm not too sure what my duties are but I'll try to do my best.

Right now I've been studying the strength of various woods, trying to come up with a simple procedure. Turns out, it's not as simple as I thought. I began with the procedures described by the Forest Products Laboratory but if you use their sample sizes you will need some rather large weights, so that by the time I was able to make my samples fail, the patio looked like an annex of the FPL. Which caused me to try using smaller samples, such as 1 square inch rather than four. And most recently, 1/4 of a square inch.

Samples using a quarter of a square inch reduce the test to table-top dimensions but the tests also produce a lot of 'scatter' in their results. Which lead to my trying to use samples that were the actual size of the wood being used. That turned out to be a pretty good idea because in every test I've done, the part was STRONGER than it needed to be.

I've designed the 'Chugger' to have a maximum gross weight of 850 pounds (1870kg) and to withstand four g's. That is, the wing, tail, and engine mount are supposed to survive a momentary overload of 7580Kg or 3400 pounds. So far I've been able to verify this for everything except the landing gear, which I'm still working on.

-R.S.Hoover

On the Wearing Out of Things


.
Strop my old cut-throat razor as good as I can, that ten-cent throw-away it's laying on will give me a better shave. Oh, maybe not for the first stroke or two. Well-steamed whiskers under a layer of hot lather, there's a velvet touch to that first stroke of the blade. But after that the edge on the throw-away will pull steadily ahead until you feel slightly foolish, bobbing and weaving against your image in the outside mirror while the other campers try not to stare.

Little boy whispers too loudly to his dad: "What's that old man doing?" It's called shaving, son. Yes, even with a beard you need to touch-up the trim-work now & then. So rarely that an old fashioned razor makes good sense. That is, I used to think it did. But since I started adding to the planet's land-fill I'm forced to admit that a throw-away gives me a better shave.

The reason why that is true has a lot in common with why a lot of home-builders are throwing away as much as twenty-five percent of their engine's power. 25%

Impossible! (I heard someone say. Probably the grandson of the fellow who said nothing would ever beat his cut-throat razor.) The reason it is possible is because the fellow has never flown -- nor driven -- a professionally-built engine. And before you start telling me that I have to be wrong I'd like you to take another look at that old straight-razor of mine. Sharpen it to perfection and within half a stroke you can feel it starting to drag. That's all it takes to turn the edge. You can restore it by a few judicious strokes on your finest strop but you will have to repeat the process, half a stroke then strop... half a stroke then strop... as your shave progresses. By comparison the machine-sharpened blade in that inexpensive throw-away is good for about one and a half shaves before it even begins to dull.

There's really nothing new in all that. Cutting tools dull in use, especially so when cutting metal. For example, when cutting the bores for the crankshaft and camshaft, they will start with multi-point cutting bar that creates a hole on the high side of the allowed tolerance. After cutting a certain number of crankcases they will gauge the bores, then cut a few more, gauge it again and keep repeating the process of cutting and gauging until the inspector tells the machinist it's time to replace his cutting tools.

In other words, there isn't a single perfect size but a range of sizes that grow steadily smaller as the machinist produces crankcases. This difference in size represents the tolerance for that particular machining operation. (You will find all of the tolerances listed in the factory workshop manual.)

Machining the bores for the two shafts generates a third dimension and its related tolerance. That's the distance between the center-line of the bores. Since the two shafts are coupled together by a pair of gears you will also find a range of acceptable gear sizes, each having its own tolerance.

Volkswagen used nine different sizes of gears. To properly assemble a VW engine your first step is to determine the fit of the valve gear. Which begs the question: What size valve gear does your engine use?

When you assemble an engine using the wrong size of valve gear two things are immediately evident. One is that the steel cam driver gear will commence to chew up the aluminum driven gear, generating lots of swarf to block your filter and contaminate your bearings. The other thing is that the engine will not produce as much power as if would if fitted with the proper gearing. But worst of all is the culmination of those two errors. Not only is the bad to begin with, it will become steadily worse in use.

Engines are incapable of healing themselves. Start with a bad lower end and things can only get worse. But engines are capable of humor. Ask someone what size cam gear their engine uses and the odds are they won't be able to tell you, even though they have just spent half an hour expounding upon their experience as a builder of VW engines. And while they can't tell you what size gear they used -- many will even argue that only one size is available -- they are equally sure that, whatever size was needed is exactly the size they've used :-)

The reason I've mentioned all this has to do with the following scenario: Someone has just spent a sinful amount of money to assemble a 2180cc VW engine. But having done so, when pitted against a supposedly identical airframe and power-plant they have discovered their engine is not quite as powerful as they expected. Indeed, a few have had the unfortunate experience of having a similar airplane fitted with a smaller engine out-climb them. And go faster. And burn less fuel.

Obviously, something is seriously wrong. He's paid all that lovely money and done everything the various experts have told him to do but he's in much the same situation as the fellow with an old straight-razor who discovers he can get a better shave from an imported throw-away that costs only a dime.

Another aspect of this scenario is purely personal and may be an error on my part. As best I can recall, I used to be asked what's wrong with my engine three or four times a year. But since being diagnosed with cancer (June, 2008) it seems that question is popping up more frequently than before. (I can imagine what you're thinking. Believe me, pard, I've been thinking the same thing :-) But win, lose or draw, I think all we can do is play the cards we're dealt. So, whether the question has been coming up more frequently... or even if I'm just thinking it has, it seems worth addressing, which is the purpose of this article.

So how do you help someone diagnose an engine problem via email? It's a bit harder than it may appear because while you must address the engine as a system -- as something that must work together as an harmonious whole -- when the components are produced by a chaotic collection of manufacturers, you must begin at the component level and work your way up. Each component is blueprinted, then components are assembled into sub-assemblies and -- finally -- you can assemble the sub-assemblies into that harmonious whole.

The reason this difficult is not the blueprinting nor the assembling into sub-assemblies. Those tasks, while time consuming, are quite straight-forward. The difficulty arises from what you must do when a part or sub-assembly FAILS to meet its required specifications.

In a factory, any part or sub-assembly that fails to meet spec is simply laid aside to be re-worked, substituting parts until you achieve the desired goal. But the homebuilder is usually working with only ONE ENGINE'S-WORTH OF PARTS. If they are an experienced automotive machinist they may elect to re-manufacture the supposedly 'new' part. Or they can try to get the supply to ship them a replacement. Or whatever. The truth is, the MOST DIFFICULT part of assembling an engine today is simply finding one engine's-worth of parts.

Many of the fellows needing help have removed and dismantled their engine, looking for the Smoking Gun that is preventing them from flying as fast or climbing as quickly as those Other Guys.

But when the engine is still on the airplane, and has flown enough hours to establish a history -- say, a hundred hours or so -- you can leave it alone and assume it has been properly assembled. And yes, it is a risky assumption; a double-edged blade that can cut you both ways. Such as the fellow who casually asks: "You keep mentioning Compression Ratio... What is that, exactly?" Or the fellow who thinks a 300 fpm Rate of Climb is okay... in an airplane that normally climbs at about a thousand feet per minute.

What you're running into here is the fact that in many cases the person seeking advice is unable to evaluate good performance from bad performance because they have only one airplane's-worth of experience. Or the fellow who's engine has more than an eighth of an inch of end-play. But it starts at the first flip of the prop and never gives any problems... So why should he change things?

(Yeah, I'm smiling too. But I'm also serious. I get a lot of questions you really would not believe.)

So the root of the Decision Tree is bifurcated into Component Level Questions and Hundred Hour Questions. For the purpose of this article I'm going to start with the Hundred Hour Questions and do so by starting with the Lower End -- crankshaft, camshaft, con-rods, pistons & jugs, cam gearing, valve timing and so forth: the foundation of the engine.

Ninty-nine times out of a hundred the search ends at the cam gear. There is simply no reason to continue when we lack the basis for setting the valve-train geometry. And when you can't set your valve train geometry the probability of giving away as much as 25% of your power is very real indeed. As is the likelihood that you would not be aware of it. In fact, there is no accepted standard of success when it comes to the conversion of Volkswagen engine for flight. The fellow has assembled an engine and the thing actually ran! Even more amazing, it produced enough power to fly the plane! Clearly, we are dealing with the epitome of success. To have someone come along and imply that things could be even better...

The only down-side to the supposition that any engine which runs and produces enough power to fly the plane is a success is the specter of catastrophic failure. One of the most compelling reasons for the use of an Otto Cycle engine is that it provides a number of easily recognized precursors well in advance of any mechanical failure. But that is only valid when the engine was properly assembled to begin with.

-R.S.Hoover

Sunday, April 19, 2009

Cure!

Gotcha!

Well... sorta gotcha. It's actually 'cure'. Lower case and quotes... because it is a magazine.

Yup, they seem to have one for everything nowadays. It's a quarterly and as you may have guessed, it's a freebie... if you've got the Big C... or have had the Big C... or know someone who has. Or had. Or whatever. If for some incredible reason you don't qualify for a free subscription -- such as living on the planet Logoff -- then it's twenty bucks a year. So... on the up-side it's another source of information for me to add to an already mind-boggling work-load but the down-side is that it appears to be just another outlet for pharmaceutical PR. Still, I have got to read it.

Some of you won't understand the absolute imperative there so lemme run it by you.

Mention car, firearm, airplane or half a dozen other things and all you'll get out of me is a nod; yep; got all that; let's move on. In those areas I am adept. Not a tinkerer nor a casual user but someone who can build you a car. Or an airplane. Or a mechanical clock that keeps reasonably good time. No sense in our discussing those things nor in my reading about them because the odds of encountering something truly new is vanishingly small. Skim it to the point of identifying a linkage to my existing knowledge in that particular field and if you listen very hard you'll hear the gates of my biological copy of Babbage's falling into place. Next topic please. This ability is probably a sex-linked trait as I've only met a handful of women who have it. Oddly enough, while a lot of men -- probably a majority -- have it to some degree, most are not aware of it. Acquisition of this uniquelly male trait has been through peer-group osmosis rather than a conscious effort. Then too, you would probably have to interrogate them rather closely to have them regurgitate the specifics for making steel. But it's all there, mixed up with the inherent male inability to remember dates deemed important to the feminine mind, or to admit to being lost when we haven't got a clue, and the inability not only to lie gracefully but even wanting the native wit to understand the absolute necessity of lying when harmonious interpersonal relationships with opposite sex is the goal. (What does the color of furniture have to do with anything?)

But when it comes to me and cancer, I'm not even up to novice-grade in the knowledge department. Which means if it has ANYTHING to do with cancer, I HAVE to read it. I've no choice in the matter. I was diagnosed with multiple myeloma in June of 2008. At a guess I've probably acquired less than 1% of the available information and even that has to be qualified as meaning information in digital form.

It doesn't matter that the new magazine is a gimme, it's value somewhere between a bathroom wall and a bumper sticker, it is a source of information about cancer so I must at least scan it. But even that takes time.

Maybe I'll send them an article about... some damn thing.

-Bob Hoover

Saturday, April 18, 2009

The Need to Bleed

Every Tuesday or Wednesday my wife drives me to a blood-lab over behind Tri-City Hospital where one of several phlebotomists accepts my donation, usually about two ounces but periodically the amount will be twice as much. Sometimes it is significantly more.

One of the drugs I'm taking reduces the blood's clotting time, a precaution against the formation of blood clots. Unfortunately, the drug also prevents the needle's tiny puncture wound from healing as quickly as it should, so that some blood escapes through the hole into the space between the vein and my skin.

The size of the needle determines how quickly the sample can be taken. Most of the time they use a tiny needle, something so small you can barely feel it. But a tiny needle means a tiny amount of flow and when several samples are needed they generally use a larger needle.

It's all relative, of course. All of the needles are tiny. Indeed, it is remarkable that they are hollow. Or that blood, that thick, dark juice, flows through them at all. But sometimes the hole does not close itself up and blood seeps out of the vein into the space under my skin, leaving a purple rose that may persist for as long as two weeks.

After each blood test the lab sends me a copy of the results which I enter into a suit of software obtained from the International Multiple Myeloma Foundation. The physician requesting the test also receives a copy but in a different format. The software I'm using gives me a series of charts that makes any change graphically evident. The nurses and nurse-practitioners also have access to the results. They are common topics of conversation.

I'm presently taking fifteen drugs or mediations. Some inter-act with one-another and those interactions upset the 'scores' from the blood tests. A common chore is to try and achieve a chemically perfect 'score' without causing any harmful side-effects. When that happens it is considered Good News and the phones start to ring, as thy did this past Friday.

This particular 'score' has been difficult to nail down. Each time we got close it triggered an undesireable interaction. When that happened we would have to go back to the drugs; to tinker with their frequency and amount, then work our way back to a mix of drugs that gave stable results. The results from last week's blood test were 'clean' -- the desired score was achieved without any undesireable interaction.

Next week we'll go for the 'big' test, looking for the unwanted interactions among factors we've already nailed-down; among factors we test only once a month rather than once a week. In the meantime we won't talk about it. It has taken ten months to reach this point. Patience is part of our medicine, along with the drugs and the x-rays, MRI scans and all the rest. Patience... and not getting our hopes up.

-R.S.Hoover

Tuesday, April 7, 2009

Getting Started


.
"Okay," the newbie sez in his message. "What do I have to do to get started? I've got almost a hundred dollars saved up, two junked VW engines I'm taking apart, and I've got access to about a half-car garage."

He goes on to explain that the "half-car garage" is just that. It started out as a two-car garage but one bay was devoted to storage, which took up about half of the space. He's allowed to use the remaining space which -- wonder of wonders! -- contains a Craftsman 10" table saw, a floor-model drill press and a small work bench. There's even a vintage home-made air compressor abandoned by some past tenant -- probably because the thing isn't working.

The air compressor becomes the focus of our messages, which wastes a lot of time and space until he gloms onto an older digital camera declared surplus by a family member who has up-graded to more pixels. With a picture of the recalcitrant compressor the problem is quickly tracked down to the pressure-regulated switch. I had been telling him to look for a black or gray metal box. And there is such a thing... but it is nothing more than an on-off switch. The pressure-regulator switch had lost its box years before probably during an attempt to repair it. All that was left was a leaking diaphragm and a set of adjustable points but not wired.

This wasn't something in need of repair. What it needed was replacement.

"I can't believe it actually works!" he says a few posts-- and about $30 later -- after replacing the regulator switch. Looking back, it was probably a very worth-while bit of work since I was able to refer back to it whenever his confidence needed a boost, which it did in returning the table saw to service.

The saw was rusty, of course. Not the flakey, pitted rust we see here so near the ocean, but the softer, powdery rust that comes from sitting un-used through a decade of mid-western winters.
He didn't quite believe me when I said the cast-iron table of the saw had to come down to a bright finish but after working on a small section he admitted it might be possible, although I'd be long gone before it ever happened. But he kept plugging away, not only on the table saw but on the drill press, restoring them to rather elegantly with the idea of selling. Along he way acquired a zero-clearance shoe for the saw and a vise for the drill press table, for he had come to see the need for such things when building from wood.

The air-compressor acquired a pneumatic brad-driver which, when paired with a jug of foamy glue, allowed him to build things in minutes that would normally take hours. I saw evidence that the half-car shop was becoming more of a home.

An important part of Getting Started was to select a design. Initially he was hot for the VP because he understood it could be built very cheaply. As we spent more time together, electronically speaking, he began exploring other designs and comparing their different methods of fabrication, the need for a zero-clearance shoe to prevent the saw's blade from binding when cutting 1/8" and 1/4" stock, and the need have some organized storage for such stock, since it's small size often leads to problems.

He starts collecting wood and I end up sending him pictures of what's acceptable and what's not. He finally decides to jump in; to build a dummy fuselage based on the FRED but with a number of differences.

There are several First Steps since many of these tasks must be started in parallel with each other, a fact having to do with setting up the saw, then storing what comes out of it.

Table/Building Frame is a major step. It is five selected 2x4's and four selected pieces of 1x12 shelving, eight feet in length, plus half a dozen 1x4's. By 'selected' I mean each piece has been examined for straightness, grain-per-inch, grain run-out and a basic 'feel' for moisture content.

To make the Table/Frame two of the 2x4's get chopped at five feet and butt-spliced to 8' 2x4's, giving a length of 13'. The butt-splice is aligned with 1x4 scab-plates about two feet long, assembled with foamy glue & 6d nails. The basic alignment tool is the floor, which is now carpeted with cardboard. An old comforter becomes the top half of an 'oven with a small light bulb for heat. This produces a pair of 2x4's 13' in length. The remnants of the cut 2x4's are cut to 22" lengths. This is among the hardest of the jobs because the wood is sawn by hand.

The 22" pieces are the ends of what is to be the building frame. One face of the frame is declared to be UP, the other is DOWN. The down face gets a pair of carefully fitted 1x4 diagonals, inlet into the 2x4's with saw & chisel, assembled with 6d's and foamy glue.

The Table/Frame is put aside to cure and the saw is set-up for slicing the shelving into square strips, 5/8" on a side -- the thickness of the shelving. Some of the sticks break across a knot when cut but nothing is thrown away.

The longest sticks are selected for the straightest grain and fewest knots. From the sixty 8' sticks there are several with only one knot and some of those have the knot near one end. These are laid aside for scarfing.

The scarfs are cuts made at an angle of 1 in 15 using a jig built for that purpose. The resulting cut is about ten inches in length. The sticks are marked so their grain is properly oriented when cut, since an up cut must match with a down cut. The goal is to get four longerons at least fourteen feet in length and having just one scarf joint. Despite having 60 pieces to chose from, this happens only once. In all other cases it takes two or more scarfs to make up the required length.

Actually, the fuselage needs only two of these near-perfect longerons: the ones that go on the bottom. The top longeron can have half a dozen or more scarfs since it always lays level. But the lower longeron must be bent and since a scarf joint tends to stiffen the piece, the two sides will have different curves if one is significantly stiffer than the other.

The scarf joints are fabricated with epoxy and great care is taken to ensure the joints are precisely aligned. The pneumatic brad-driver, waxed paper and some scrap wood ensures the sticks are aligned.

USING THE PNEUMATIC BRAD-DRIVER

A major problem with nailing is that the part(s) must have adequate back-up, otherwise much of the energy of the hammer's blow causes the parts being nailed to bounce out of alignment. With the pneumatic brad-driver the brad is driven so quickly that the inertial mass of the parts is usually sufficient to keep them in alignment. The first-time plane-builder must learn all of these things or their labor will be wasted. Indeed, there are so many ways to do things that that it is impossible to simply tell the newbie 'Do it like this...' because his situation may not match that of the person giving the advice.

Once the advantages of using the brad-driver are understood the work begins to go faster.

This is also true with regard to adhesives -- to the glues we are using.

Epoxy is used to splice the longerons because it needs only the pressure of alignment to achieve a good joint, whereas Plastic Resin, Tite-bond III and the urethane glues needs a significant amount of pressure to ensure the adhesive will flow into the capillary structure of the wood. Without adequate pressure to hold the pieces together, the glue will simply force them apart as it cures. When the area of the contacting surfaces is small, you may get sufficient pressure by simply fastening the parts together using brads or pins, but in most cases you will need a couple of brads to keep the parts in alignment plus addition pressure, as provided by a clamp or wedge.

This gluing pressure turns out to be another of the many things the newbie must learn because what appears to be an obvious solution, such as using C-clamps, turns out to be horribly wrong for certain types of glue.

Glues that contain water, such as Weldwood's Plastic Resin or Tite-bond III, cause the wood to swell. This swelling will force the glue-line apart unless there is sufficient pressure to prevent it from doing so. That pressure appears to be about 70 psi. In a similar vein, glues which expand as they cure need a similar amount of pressue although for a different reason. Epoxies do not cause the wood to swell nor does the epoxy expand as it cures. This makes it a near-perfect adhesive, offset by it's lack of convenience (ie, the need to mix components) and its high cost.

Epoxies appear to go through phase of greatly reduced viscosity shortly before hardening. During this hyper-viscosity phase the adhesive appears to be drawn into the micro-structure of the wood by capillary action. While brads or pins are needed to ensure alignment, there is no need for clamping pressure.

In using epoxies without clamps we are taking advantage of the characteristics of that particular adhesive. In later stages we will do the same with the urethane adhesives, hollding small bamboo struts in position with clothes-pins. The adhesive will then expand to completely surround the fixed ends of such struts, forming its own fillets.

In carrying out these exercises our goal is not to build a fuselage, although the finished product will be more than safe enough for that role. Instead, our role is to learn how to build a fuselage using tools, methods and procedures that are unique to our particular situation.

The simple truth is that one set of rules or methods can not be applied to all situations.

BENDING THE LOWER LONGERON TO A 'NATURAL' CURVE

The upper longeron forms our longitudinal reference line. When we start out, it is perfectly horizontal. (And we hope to keep it that way.) But the lower longeron prescribes a graceful curve from the bottom of the firewall, to the bottom of Frame D, and to the bottom of the stern-post. (It really isn't a stern post but we'll call it that to keep from getting it confused with anything else.)

The firewall is twenty-two inches deep, including the thickness of the lower longeron. Using a framing square or other suitable tool, lay-out the centerline of Frame D at 40-1/2" aft of the firewall. It is twenty-four inches deep, including the thickness of the lower longeron. The aft face of the stern-post is 152-3/4" aft of the forward face of the firewall and the stern post is one foot deep, including the thickness of the lower longeron.

There are eleven vertical or diagonal members connecting the upper longeron to the lower. These members are connected to the longerons using a comination of gussets and corner blocking. Using a tape measure and square, we want to transfer the information from the drawing onto the Table/Frame. We want to do this as accurately as possible so that the two side-frames will be as close to identical as possible. Once the fabrication is complete, the Table/Frame deserves a coat of thinned varnish. An area of WHITE paint goes onto varnish at some point. Once the white patch is cured we use an ink marking pen to identify the purpose of the fixture, when it was assemled and by whom. This information patch is usually given a full-coat of varnish.

With rungs on one side and a pair of diagonal braces on the other, the Table/Frame will be quite sturdy. But with a depth of only 3-1/2" it is subject to twisting due to changes in the local temperature & humidity. To straighten it out simply clamp it to your saw-horses.

LIFE WITHOUT SAW-HORSES

Life without saw-horses is a hard life. You must learn to make saw-horses from whatever is available. Such tasks are tests, constantly placed upon you. You must welcome them and offer proof of your worth by solving such problems quickly.

For those of you fortunate enough to find your local Box Store carries a good selection of cedar, suitable not only for the Table/Frame but for the means of supporting it, you will find a Table/Frame made of cedar to be light in weight and easily stored by hanging it on a wall or under the eaves of a building.

To erect the Table/Frame lift one end an fasten two legs to the corners. The keep the legs aligned tack redwood plaster lath between them from head to tail. The result is the Trinity and will not fail. Then go to the other end, raise it up and do the same. Now add additional lath from the rails to the legs so that the Table/Frame is supported to & fro.

Using a heavy mallet or hammer, drive each leg into the ground. Between the ends divide the length by two and put down a leg on the front beam and a leg on the rear beam. Use your brad-driver and plaster-lath to triangulate each of the new legs, first from the front, then from the back. When those triangles have been created, divide the rail on either side of the middle legs in to two and put down another pair of legs.

When you are done the Table/Frame stands on ten legs.

The forward part of the fueselage side will be plated with plywood. The fuselage-side shown at the opening of this article is for the FRED and is plated with 3/32" plywood. But you could use the fuselage for a different airplane and use a different plywood schedule... or none at all.

Notice that the straight top longeron aligns with one edge of the Table/Frame. This alignment is facilitated by adding blocking strips -- short pieces of 1x2 for example -- at a few places between those areas where the struts join the Table/Frame.

Notice that this particular fuselage side-frame uses a Warren Truss. Others may call for a Pratt Truss, a Howe or any of a dozen others.

While the side-rail may seem a bit casual the only practical test is: Does it work? This Table/Frame passes such a test with flying colors.

Once we have assembled a fuselage side we simply make the other side to match. One of the frame becomes the Lefty, the other becomes the Righty and we move on to the next step, which is to join the two side-frames together starting with the cockpit. Once the cockpit area is joined we focus on the nose, then the tail, at which point the fuselage is turned over and the cross-members that constitute the top of the fuselage are installed.

At some point prior to completon of the fuselage we will have fabricated either a wheeled cradle a set of false landing gear so as to make the fuselage mobile. Or, since some of you are simply building the fuselage for the experience, once you have extracted all the data, the fuselage may be stood on its nose in some out of the way corner of the shop.

One very nice advantage of the Table/Frame is that, having produced a fuselage we simply clear away the cross-members that were specific to the fuselage, we can begin fabrication of the spars.


(To Be Continued)

Friday, April 3, 2009

F.R.E.D. the Airplane


.
F.R.E.D. is an airplane designed and built by Mr. Eric Clutton, who will sell you a set of plans, allowing you to build a copy for yourself. F.R.E.D. has a web site but I don't know its address. However, if you type 'F.R.E.D. the airplane' into your browser it should discover FRED's home and point you toward it.

I hold a set of plans for F.R.E.D. because F.R.E.D. uses a Volkswagen engine. Some of the people building F.R.E.D. want to use an engine having the propeller mounted on the clutch-end of the crankshaft. Eric chose to put the prop on the pulley hub and if you want to change things around you try and find someone who already has so you won't have to re-invent the wheel.

When you decide to build an airplane the normal path is often cluttered with the residue of those who have tried and failed. Mr. Clutton has not only tried and succeeded but the people who have purchased his plans have a surprising rate of completion. That isn't to say there aren't a few travails along the way but that is mostly because Mr. Clutton has chosen a path less traveled.

As a family of birds, airplanes have certain shared characteristics. The bird that most closely matches the F.R.E.D. is one having wide wings that are fairly short. In airplane lingo we would say that F.R.E.D. has a low aspect ratio. Aspect Ratio is nothing more than the span of a wing divided by its width. With F.R.E.D. we have a span of twenty-two and a half feet whilst it's chord is only fifty-eight inches, giving us an aspect ratio or AR of about 4.8:1 For comparison, most light-planes have aspect ratios of six or seven. Aspect Ratio can be important because it reflects how much Drag is generated by the wing to produce lift. A high asprect ratio means your design is rather smooth in aerodynamic terms, whereas a low AR says your wing generates a lot of drag. But I should also point out that all such things are relative. A low aspect ratio was one of the trade-offs Mr. Clutton chose to make, in order to come up with a design that suited his particular set of requirements, such as the ability to easily fold the wings, mount a tow bar, hitch F.R.E.D. to his car and tow him home, where his narrow width allowed him to be parked in a garden shed or a single-car garage.

The days when a city was proud of its airport have faded away. American pilots are forced to drive longer distances to even find an airport. And when they do, the cost of renting a hangar or even space on the ramp, is often several hundred dollars per month. Add to that the premium charged for fuel and we find that a large number of pilots can simply no longer afford to fly. F.R.E.D. changes all that. F.R.E.D.'s wings are easily folded by one person. The horizontal stabilizer is removed and a trailer-hitch replaces the tail-wheel. The owner-pilot need only drop the trailer hitch onto the ball and he's outta there. On his way to the airport, the owner of F.R.E.D. may decide to stop by the gas station, where F.R.E.D.'s ten gallon tank may need topping up. Ten gallons of gas will give him at least two hours of flying with a safe reserve and the emphasis here should be on the flying, because the more you do, the better you are.

With just one seat F.R.E.D. isn't for everybody. Indeed, it is just for you. Take F.R.E.D. out a couple of times a month and you'll be a better pilot for it.
久久这里只精品国产99re66