EZ-Akro?

[Shin Gou]

Hi,

I have no aeronautical engineering knowledge, maybe that's why I am so
stupid to ask this question. The other day when I read some Long-EZ
tech info and checked out a local EZ project, I know EZ's wing can
easily sustain over 6G loading or much more though no formal stress
test was done, and the whole wing, particularly the spar construction,
is really designed for homebuilders, I mean, no special tools and
skills are required.

So here's my question: Since the EZ's wing construction is so strong,
and easy and cheap to build, why not adapt the wing construction
technique to an acrobatic monoplane design so we can have a low-cost
and high performance plan-built acro plane? I know there must be lots
of engineering study to be done if the EZ wing construction is to be
transplanted to a conventional airplane, but is this idea possible?
Shin Gou

[Bob K.]

Earlier, Shin Gou wrote:

> ...The other day when I read some Long-EZ
> tech info and checked out a local EZ project,
> I know EZ's wing can easily sustain over
> 6G loading or much more though no formal
> stress test was done...

That might be true for a properly built example that has been
maintained well and properly cared for. However, the following article
suggests that the EZ's mix of fiberglass structure and aluminum
attachment fittings might more prone to corrosion than originally
anticipated:

http://www.rutanaircraft.com/htmlpages/canard.html

The article also describes a compression failure of an upper spar cap
made of unidirectional laminate. The failure described sounds like it
was probably caused by poor construction, which isn't necessarily any
fault of the design or designer. However, it suggests that the EZ wing
construction might not be as tolerant as you might like of builder
error.

The article tells EZ operators to placard their aircraft with a maximum
load factor of 2.5g; that wouldn't make for a very effective aerobatic
aircraft. Of course, there might be some later resolution that I
haven't found that repeals the 2.5g limit; if anybody knows of such a
thing I'd appreciate it if you'd describe it in a reply to this post.

Jim Marske often describes his coupon tests of wet-laid unidirectional
carbon and (I think) fiberglass wing spar caps. His tests showed that
it is very difficult to get the kind of materials properties that some
composite designs are predicated on. That's why he and I both like the
Graphlite carbon rods and ribbons so much. They have great materials
properties and achieve them reliably and consistently. The Marske Web
site suggests several schemes for applying the Graphlite materials to
aircraft wing spars:

http://www.continuo.com/marske/carbon/carbon.htm

I would think that one good approach to a small aerobatic aircraft
might be a mix of a Marske-style Graphlite-based wing spar and
Rutan-style moldless foam core for the rest of the wing. Personally, I
dislike moldless foam core construction, and I only use it to make
plugs for molds. However, I understand that there are many folks who
like it, so such a design might find some general acceptance.
Thanks, and best regards to all

Bob K.
http://www.hpaircraft.com

[Marc J. Zeitlin]

Bob K. write:

> The article tells EZ operators to placard their aircraft with a
maximum
> load factor of 2.5g; that wouldn't make for a very effective aerobatic
> aircraft. Of course, there might be some later resolution that I
> haven't found that repeals the 2.5g limit; if anybody knows of such a
> thing I'd appreciate it if you'd describe it in a reply to this post.

I don't believe that there's been any further resolution, but realize
that this restriction ONLY applied to the Vari-EZ aircraft, not the
Long-EZE, COZY III, COZY MKIV, E-Racer, etc. aircraft that use a
completely different wing/spar mounting scheme. On those aircraft,
there is no G-limit restriction other than that of the Utility category
(to which they were designed as a minimum, if not certificated).

--
Marc J. Zeitlin
http://marc.zeitlin.home.comcast.net/
http://www.cozybuilders.org/
Copyright (c) 2004