On Sun, 19 Feb 2006 00:25:35 GMT, Richard Lamb
wrote:

clare at snyder.on.ca wrote:

Clare, thanks for taking a reasonable position and tone.
Muchly appreciated.
I'll reply as best I can, ok?

Richerd,
You are getting ahead of yourself.
Forget the pictures you saw in the Rec Av magazine. Those were
projects some guys built. They were NOT the tests done by Gary. Gary
did the tests on a wing BUILT ACCORDING TO PLANS, and IT FAILED THE
TEST.

That was not my take from the article, but if I'm wrong on that point,
I'll offer an apology.

The Test:

I've never been offered any description of the set up - only the conclusions.

The wing was supported as it would be on the plane, but inverted. It
was then loaded with sandbags to iminent failure, with the load
properly distributed. It was tested both with and without the jury
strut. The jury strut is VERY CRITICAL (and it's attatchment according
to the plans was not sufficient) and even with the jury strut upgraded
the wing did not meet the specified G rating for the design specified
gross weight. IIRC it is a 500 lb wing, not a 600 - but my memory of
that detail may be fuzzy. What I DO know, is it did NOT meet the
published spec, or the required G load for the published maximum gross
weight.

As I understand it, it was assumed that the front spar would take 100% of the
load. That is, of course, true IF the spar is located at the center of
pressure - as a normal wing is arranged.

There were mo assumptions made. The wing was properly supported and
loaded.

But the wing in question is obviously NOT arranged that way.
The spars are at the leading and trailing edges while the center of pressure
remains back around 30% to 40% of the chord.

The airfoil used is a Clark-Y. There is a minor deviation at the leading edge
due to the 2" diameter of the leading edge being a bit larger than the radius
shown in the tables.

Which also causes aproblem when a larger spar diameter is used. IIRC
it makes the stall more abrupt -which you do NOT want.

At zero degrees AoA the CP is at 40%.
At 12 degrees AoA it has moved forward to 30%

In my work, I've ASSUMED that the front spar would only receive 70% of the
total load. That makes a tremendous difference in the amount of deflection
of the spar, and, seems to be much closer to what we observe in the actual
structure in flight.

I think this also explains why Beeson could build a wing using .035 wall spars
tubes. My crude work on those indicates they wouldn't survive 2 G's at 100%
load. But they do - although with noticeable deflection under load in flight.

And Chuck BUILT the .035 wing, but did not fly it, from what I
understand, as the wing was too flimsy even for HIS level of comfort.

Just to be through, the wing structure should also be mounted at, in this
case, 12 degrees nose down (it's inverted, remember) to account for the
angle of attack at the test load. This will have the effect of pulling the
load vector forward some, but the magnitude is tiny compared to a 30% offset.


The other improvements I noted should/could be made HAVE NEVER BEEN
IMPLEMENTED to the best of my knowledge.

Hey, I'm not saying it's a bad idea.
Like you pointed out there are some real benefits to it.

Rivet heads under the fabric are a pain to work around.
On my first parasol (PBJ) I use a thin piece of wood molding on the
outboard side of the top longeron to avoid that.

On the second one I just used flush rivet - and avoided the problem
without adding the extra weight.


As for the extruded aluminum truss construction, using the sizes
listed in the plans, and the rivets specified, it is difficult, if not
impossible, to achieve proper hole edge clearances in MANY locations.
I know, for an ultralight there are no inspections, so you can get
away with it - but you are NOT building to acceptable aircraft
standards if proper edge clearances can not be maintained.


The edge margins for thin sheet are well known and easily found.
I'm not having much luck locating the tables for Lugs on short notice.

The difference, as I recall, is the relative thickness of the metal being
bolted or riveted. Those extrusions are five times thicker that .025 sheet
metal.

But I'm still looking for it and will post it here when I find it.

1.5 times the hole diameter rings a bell.


Examining the results of some of the accidents, even the one straight in
on the nose fatality, you do not find broken rivets. The angles bent, but
seldom even break. In the bad one, the first bay of the fuselage truss was
crumpled up like an accordion.


The Texas Parasol is just an angle aluminum Baby Ace in concept -
shortened and with bigger tailfeathers to compensate.

It's a Texas airplane, guys. Texans just GOTTA have a lot of tail!

Apparently you built yours one station longer, making it the same
dimensions as the Ace. The wings are the same dimensions and planform
as well, from what I understand. So the CONCEPT is a good one.
The plane CAN be built as a safe, economical, fun-to-fly plane - but
NOT as per plans.

It's still quite a bit smaller than a Baby Ace.

The added 15 inches was for weight and balance purposed only.
A full dressed 2180 VW can weigh well over 200 pounds.
Compared to a light weight 2 stroke, that can create a - situation!

It was nearly TOO much extra tail arm as it was tough getting the CG
far enough _forward_ to stay in an acceptable range. I think we've
got it worked out though. Just had to come up with a lighter tail wheel
and leg.

But tell everyone how you built yours. It was not strictly to plans.
What about the leave in the spar??

I don't know where that rumor came from.
The wing on the new plane was built mainly according to the plans,
with the exception of boxing in the compression struts at the strut
attach bay. My reason for that was that the struts on this plane angle
in a bit at the fuselage end, creating a small compression load at the spar
ends. Probably not really necessary, but it made me feel better.

The internal sleeves are as per plans.

I also added a short .017 sheet metal cover over the leading edge.
I'd not think that's a structural thing - purely cosmetic.

A FULL truce is as close as the corrections to the plans. Just because
nobody's killed themselves YET does not mean the plans, as they exist
today, are safe. By your admission, many builders ARE making changes.

Well, I think that was more of an accusation than an admission, Clare.

I have had one friend who was killed in his.
It was a hard loss to deal with.
And it gave me pause to seriously reconsider.

Please believe me folks, if we had ANY experience that indicated there were
real structural problems with the thing, I'd be the first one to address them.

But the physical evidence simply does not support that claim.

At least - as shown in the plans - and not "improved" to be faster, heavier, etc.


Mission Requirements:

It is intended to be a very inexpensive, very light (ALmost UL), very slow,
SINGLE seat baby buggy.

Hand tools only - with very little welding (the main gear axle clusters) and
little if any machine work needed.

Relatively tolerant of "workmanship" issues.

Protection for the pilot in the advent of an accident. (be real, folks!)

Good flying qualities, and fun to fly.


If that's not what you want, this is not the airplane to build.

And I'd appreciate it if people would NOT try to make it into something it was
never intended to be.
There in lies the real danger.


Richard

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