Sunday, August 10, 2008

Chugger's Spar


Chugger's spars are built-up C-sections. The shear web is 1/8” aviation grade birch plywood with the face-grain oriented vertically. The par caps or booms are made of hemlock or Douglas Fir. The drawing shows the profile of the spars. Please note that the 144” dimension shown in the drawing is not correct. I know some of you have been following Chugger's progress and that my recent medical problems have left you in the lurch. This posting should provide enough information for you to fabricate your shear webs and spar caps, which must be scarfed.


Scarfing is a standard woodworking procedure used in all wooden aircraft. Solid members, such as the spar caps are scarfed at about 15:1 whereas plywood uses 12:1. You'll note that this is a much flatter angle than is used by boat builders. Mark Langford's web site offers what has to be the best explanation of scarfing you'll find on the internet. Please go there... http://home.hiwaay.net/~langford/kspars.html and see what he has to say before continuing here.

It will take two 48" x 48" sheets of plywood to provide the material needed for the two front and two rear spars. We must also provide for aileron spars, gussets and various doublers, meaning we'll be using a lot more 1/8" plywood. But these two sheets are all we'll need for the spars.

The drawing of the spar (below) is not complete. I've posted it to give you some idea of our goal. I am still working on the best method of transferring the load into the lift-strut and wing root fittings. I would like to use the bay adjacent to the wing root for the fuel tank but this too is still under development.

Your basic guide to aviation woodworking is AC-43.13, the manual showing acceptable methods for the repair of aircraft structures. You can buy a printed copy or download the manual from the FAA's library (see

http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgAdvisoryCircular.nsf/0/99C827DB9BAAC81B86256B4500596C4E?OpenDocument

Wood and fabric is covered by the first three chapters.


The Department of Agriculture, which 'owns' the U.S.Forest Service, got out of the aviation wood inspection business in the 1950's when someone noticed that, since airplanes were now built of metal rather than wood, at our present rate of usage the government had about a three hundred year supply of aviation-certified wood on hand, stacked in warehouses all over the country.

Nowadays, if you buy 'aviation-certified' wood, what you're getting is a promise from the seller that the wood appears to meet those government specs from days of yore. (And when it doesn't? Well... tough darts, Charlie. Maybe they replace it. Or maybe not.)

Another interesting slice of reality for the newbies is to read AC-43.13 (or any of several other references) and see that Sitka Spruce has no magical aeronautical properties. Indeed, there are several commonly available woods that are superior. The reason for the Spruce Myth is buried within the historical context of aviation... and of sailing ships. At the turn of the century and for forty years thereafter, masts, booms and spars were a common item at any lumberyard, not only near sea ports but at any city having water-borne transportation. When those pioneers of aviation needed wood they simply visited the nearest lumber yard. If it didn't happen to have something suitable in stock it was never more than a few days away, thanks to Railway Express.

You can find all of the wood you need to build an airplane inside the wood at your nearest lumber yard or box store. To get at it you will have to re-saw the wood that is there but this isn't as great a disadvantage as it might appear. Using Chugger as an example, the most critically needed pieces are the four main spar caps, about fourteen feet long, three-quarters of an inch thick by an inch and an eighth in height. While the three-quarter inch dimension remains fixed, all other pieces used in the airplane are shorter or shallower than the spar caps. If our Donor Timber was a two by ten joist, for example, ripping it into 3/4 x 1-1/2 laths gives us ten chances to find the perfect stick. And if we don't find it, we can cut out any imperfection and splice around it.


Saturday, August 9, 2008

Giving Credit Where Due

It doth often trouble me to Think
That in this Business we are all to Learne
and none to Teach...
-Robert Cushman, 1619

The Chugger Project is an on-going series of experiments using
inexpensive, commonly available materials to build a simple
single-place airplane. As the work progresses, drawings and photos
are placed in the Files archive of the 'chuggers' Group on Yahoo.
Text and periodic progress reports are posted to my blog.

It's important to note that the primary purpose of these experiments
has to do with materials and methods. For the structure I've simply
scaled up (or down) from proven designs. In doing so, I've tried to
give credit where due, although that isn't as easy as you might think.
Bernard Pietenpol used parallel wing struts on his Aircamper ...but
so did Claude Ryan on the NYP. The scaling is necessary because the
inexpensive, commonly available materials I'm using do not enjoy the
same ratio of strength-to-weight as for aviation-grade materials.

Pete Bowers' Fly Baby has a beautiful empennage. By adapting Pete's
empennage for the 'chugger' project, I'm paying homage to a past
master but in doing so I'm taking advantage of an invaluable
training-aid. Pete's tail-feathers incorporate no less than nine
built-up spars of box- and C-section designs, as well as curved
laminations. For the novice builder, the empennage is their Trade
School. Fabricating the tail-feathers provides a No-Fault opportunity
to acquire the skills they will need to build the wings and fuselage.

Clearly, the Fly Baby's empennage is more complex than the relatively
simple structures found on a Volksplane or Jo-Del but when scaled for
the Chugger , none of the components are especially large, reducing
these training materials to table-top dimensions. If fabricated from
locally available materials such as door skins and Box Store lumber,
the cost of this training exercise is only a few dollars. In fact, if
the goal of the novice is merely to learn how to build a wooden
airplane, there is no reason to build the entire tail, making the cost
even less.

While the parts-count of the Fly Baby tail makes the structure fairly
complex the required skill-level is delightfully low. Most of the
parts are duplicates, allowing you to take advantage of stack-sawing.
For example, the six shear-webs needed to produce the spars for the
elevators and horizontal stabilizer may be cut-out at one go. The
same holds true with the four shear-webs needed to produce the
stern-post and rudder spar. The diagonals in the horizontal
stabilizer are identical, left to right, so they too may be cut-out as
a stack. The only singleton is the shear-web for the diagonal brace
in the vertical stabilizer. That means all thirteen shear-webs can be
produced from only four patterns.

Once the shear-webs have been stack-sawn, Pete recommended attaching
the spar-caps and filler-blocks to them. In effect, the shear-webs
become your patterns. Since you're dealing with straight edges here
you need only apply a bit of glue (to both surfaces, please), tack a
piece of scrap to your bench-top to act as a back-stop, press the
pieces firmly against the bench (don't forget the waxed paper) and
tack them together with a pneumatic pin-nailer. Thanks to the use of
the pin-nailer the work took only a couple of hours Then comes
fitting the filler blocks, which takes longer – a couple of months
longer in my case, thanks to some health problems that had me lolling
around various doctor's offices instead of working in the shop.

In October 2007 I received a comment from Mr. Corrie Bergeron who is
building a Fly Baby. Corrie pointed out that there were other,
equally accurate methods of fabricating the empennage spars and
diagonals than the one advocated by Mr. Bowers. Rather than make the
shear-webs first – and use them as patterns – Corrie fabricated the
guts of the spars first – and used the guts as the pattern for the
shear-webs. Since I'd already tackled the project using Pete's method
I attached Corrie's comments to the appropriate article in my blog
/2007/09/av-chuggers-tail.html

Once back on my feet I was anxious to finish the tail surfaces, hoping
to carry the job right through to covering. But before doing so I
recalled the words of Robert Cushman and thought it only fair to give
Corrie's method a try, allowing readers of the blog to draw their own
conclusions. Accordingly, I made up a simple jig for the spars of the
elevators and horizontal stabilizer.

This may verge on heresy but I found Corrie's method offers several
advantages for a novice builder – or for any builder without a shop
full of tools. Pete's method of stack-sawing is dead-simple and
superbly accurate... if you happen to have a band-saw and a big belt
sander. But for the boxed spars, after attaching the spar-caps and
filler blocks in the recommended manner you're faced with the chore of
figuring out where not to varnish on the other shear-web. Corrie's
method offers greater latitude for the novice builder.

I've not posted any photos of the two methods as yet; I'm trying to
learn how to embed video in the blog. When I do, it may appear that
I'm changing horses in mid-stream when in fact I'm merely showing that
even an old dog is capable of learning a new trick – and of giving
credit where due.

-R.S.Hoover

PS – Robert Cushman was one of the Pilgrims

NOTE: This article was originally uploaded to the Fly Baby Group about two weeks before I was diagnosed with cancer.

Thursday, August 7, 2008

How ya' doing?

How ya' doing?” tumbles out of my in-box a dozen times a day. Surprisingly, most of the queries are from people I've never met. When they provide a valid e-mail address I tell them I'm doing fine and thank them for asking but most aren't meant to be a medical report; most are a simple show of solidarity from one airman to another. And as I've said to them, it is warmly appreciated.

As for the purely medical aspects of 'How ya' doing?' I've completed the radiation therapy phase and have started on chemotherapy. The pain is pretty much under control, my weight-loss appears to be flattening out and I'm getting more sleep. Overall, I think you can say I'm one lucky fellow.

Some say we make our own luck. I've got good evidence that much of it is a shared commodity, transferred from one individual to another by something as simple as asking: 'How ya' doing?'


Just fine, thanks. But a lot of that is because of you.


-R.S.Hoover

Wednesday, August 6, 2008

Cancer Report 01

You keep filling my in-box asking how I'm doing. Your interest is warmly appreciated but I'm afraid my answers -- doing fine, thanks. Doing okay... leave a lot to be desired. So let me use this Report to try and answer the essence of your question.

On Tuesday, the 5th of August 2008, I completed the radiation therapy. The x-rays have supposedly chopped up the tumor, killing most of it. In doing so, the PAIN has been reduced to a magnitude that is relatively easy to manage. And it's really all about controlling the pain.

After being destroyed by the x-rays the tumor doesn't just vanish. Apparently it is blasted into a soupy residue that your body must now eliminate. I'm told this will take about four weeks and will be the most debilitating phase of my treatment, in that I will be extremely weak. There is already some evidence of this. Even with two canes to ensure my stability, walking about forty feet left me too exhausted to return until I'd taken a rest break.

To facilitate the removal of the tumor residue I must force myself to drink about twice the normal amount of fluids. Doing so also serves to dilute any pain-killers you may have taken so that you are forced to keep track of what you've taken and when. Failure to do so gives the pain an opportunity to sneak up on you. If it gets you at the wrong time, you may find yourself immobilized, separated from your pills.

Chemotherapy is the hand-maiden of radiation therapy. Where the x-rays attacked the tumor in a macro fashion, chemotherapy goes after the cancerous cells in a micro-manner, seeking out each individual cell, which it either destroys of prevents from binding to a healthy cell and reproducing. The chemicals used to attack the tumor are toxic and there are a number of side-effects, such as nausea, hair loss and so forth. The chemotherapy began about two weeks ago and will continue for several months at a minimum.

Multiple myeloma destroys bone. Once destroyed, it can not be replaced except through surgery, which is successful in only a few particular cases. The damaged bone is quite fragile. There is the possibility that performing some accustomed chore such as dressing or bathing can over-stress the weakened bone causing it to fracture. There are chemicals that can bind to the damaged bone and provide some re-enforcement and I will begin taking those chemicals as soon as blood tests say the bone is ready to accept them.

So the messages ask: "How are you doing?" And I respond: "Fine; thanks for asking." But as you can see, there's a bit more to it than that. Such as the rash, a nasty side-effect of the chemo. Or the edema in my lower legs, an artifact of the tumor residues. And a dozen other little things that taken on the whole make it impossible to offer a comprehensive answer as to my condition.

Which is why I'd rather look at it from a slightly different perspective.

I'm a pretty lucky guy. I came within an ace of dying from an unsuspected tumor, recognized -- and properly treated by a superbly skilled physician who just happened to be in the ER when I was brought in. I'm doubly lucky in finding myself surrounded by people -- many whom I've never met -- who have provided support and encouragement that has served to level the often difficult path I have been forced to follow.

-R.S.Hoover
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