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
http://bobhooversblog.blogspot.com/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.

1 comment:

corrie said...

Thanks Bob. I'm honored.