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.


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