Texas Parasol Plans...

Clare,

You seem to be pretty well connected up there.
And you concerns are (believe it or not) well taken.

May I ask if it might be possible to collect whatever information
IS available from that test? Initial assumptions, load distribution,
deflections noted (preferably at any given load, if possible), etc.

Last night there was a message on the Texas Parasol list that indicated
that the spar tube in question had actually kinked.

The only thing I'd heard before is that the rig was in danger of
imminent collapse - but no details as to what was meant by that.


I've never been offered even a scrap of this kind of information - only
the final conclusion. And that rather loudly...

If you really believe there is an issue here, what would it hurt?


Thanks,

Richard

All right, back to the beheadings!


Four days, and not a mumblin' word.
Makes a body wonder, don't it?

Seriously, if the intent is to protect the innocent and unwary, why NOT
respond (and show your work?).

Or? Have I misinterpreted obviously altruistic motives?
(huh!)


I've been trying to raise the RAA web site for several days to see if they
post their articles on the web. But it seems to be snowed under and won't be
back up until the spring thaw.

Fortunately (or otherwise, depending on your point of view?), I just happen
to HAVE a copy of the magazine. It was sent to me by a Canadian fellow (who
I'll not name to avoid allegations of international espionage).

But here it is, and we'll let the reader decide for him/her/it self...

http://www.home.earthlink.net/~tp-1/
page-1.jpg to page-6.jpg

I particularly like the ripe irony of the last paragraph of the article.



There are also a few of the stress analysis reports in pdf format.

ul-spar.pdf The original preliminary report (corrected! The original
original showed an 8 G limit(!), but it was a simple error)

ul-redo.pdf Suggested upgrade to 4.4 Gs at 650 lbs

fastner.pdf rivets, bolts, etc

For what it's worth, none of these are my own works.
They were posted to the Fly5k list by the author and are presented here
for enlightenment and entertainment of (any?) interested readers...

Richard

Richard Lamb wrote:
I've been trying to raise the RAA web site for several days to see if they
post their articles on the web. But it seems to be snowed under and
won't be
back up until the spring thaw.

It works for me .....

And they don't post their articles.

Rob

On Sat, 25 Feb 2006 13:32:14 GMT, Richard Lamb
wrote:


All right, back to the beheadings!


Four days, and not a mumblin' word.
Makes a body wonder, don't it?

Seriously, if the intent is to protect the innocent and unwary, why NOT
respond (and show your work?).

I'm not involved, so I have no work to show.
As for the "Canadian project" - it is basically DEAD.

Or? Have I misinterpreted obviously altruistic motives?
(huh!)


I've been trying to raise the RAA web site for several days to see if they
post their articles on the web. But it seems to be snowed under and won't be
back up until the spring thaw.


Fortunately (or otherwise, depending on your point of view?), I just happen
to HAVE a copy of the magazine. It was sent to me by a Canadian fellow (who
I'll not name to avoid allegations of international espionage).

But here it is, and we'll let the reader decide for him/her/it self...

http://www.home.earthlink.net/~tp-1/
page-1.jpg to page-6.jpg

I particularly like the ripe irony of the last paragraph of the article.

The artical was written by a Canadian who was looking for a good,
cheap, safe way to get into the air. He was reporting on the early
stages of the "Canadian project" and none of the problems with the
wings had been uncovered yet, or at least the testing had not yet been
done. There is also no indication that they were building a heavier
version than yours, other than the mention of designing an all
aluminum wing.

The artical was written more about the Canadian ultralight regs than
about the Parasol.

As for the other attatchments, I'm not an engineer, so I can't speak
for their accuracy - but at least it looks like whoever wrote them did
have a very good understanding of the engineering involved. Myself ? -
it was over my head. I have no idea who wrote them, or what his
qualifications are. Neither do I particularly care.

It's YOUR design. It's up to YOU to either make it safe, and provide
accurate information, or to do one of two things:

Remove the plans from circulation, or mark them clearly as being
"proof of concept" plans requiring some extra engineering - and NOT
FOR FIRST TIME BUILDERS.

OK - 'Nuff said - I'm out here.
I've let everyone on this list know the concerns that were raised, and
the status of the plans. That's all I intended.



There are also a few of the stress analysis reports in pdf format.

ul-spar.pdf The original preliminary report (corrected! The original
original showed an 8 G limit(!), but it was a simple error)

ul-redo.pdf Suggested upgrade to 4.4 Gs at 650 lbs

fastner.pdf rivets, bolts, etc

For what it's worth, none of these are my own works.
They were posted to the Fly5k list by the author and are presented here
for enlightenment and entertainment of (any?) interested readers...

Richard

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Such a shame, Clare, because the 4.4G upgrade is
exactly what you've been asking for?

Richard

On Sun, 26 Feb 2006 00:14:19 GMT, Richard Lamb
wrote:


Such a shame, Clare, because the 4.4G upgrade is
exactly what you've been asking for?

Richard


I've forwarded the references to Gary, see if he says the issue is
adequately addressed. If it is, I'll pass it on back to the group.
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On Sun, 26 Feb 2006 00:14:19 GMT, Richard Lamb
wrote:


Such a shame, Clare, because the 4.4G upgrade is
exactly what you've been asking for?

Richard

You want more input - you got it.

OK, we are NOT engineers, but looking at this with a few more
knowledgeable guys than myself the following observations and
recommendations age just the beginning.

The last PDF with the spar calculations is a problem. On the first
page there is a basic math mistake. We did not go into the
calculations to see if the rest was correct or not. 144 pounds per
wing is 288 pounds total, not 244. The author then assumes that the
lift distribution is equal down the length of the wing, and it is
admitted that this assumption was made to simplify the math.
Unfortunately this removes some of the lift load from the inner spar
and makes the calculated G's quite optimistic. In real life the lift
is usually assumed to center about 44% out from the root. A proper
load test will have an elliptical distribution of sandbags for this
very reason. The equal distribution assumption transfers a lot of sand
out beyond the lift strut attach. This has two effects that give
optimistic conclusions. There is less sand (lift force) at the weak
point 40" out from the root. Also the equal distribution tends to
straighten the inner section of spar, like a teeter totter, so that it
would take more weight to get the spar to buckle between the root and
the lift strut attach. The conclusion is therefore optimistic. Also it
is premature to state from this spar analysis that the wing is OK. The
calculation, even if correctly done, address only the strength of the
front spar.


The testing of the wing performed at Gary's hangar addressed this
non-linear loading.

Just a little more input from another more knowledgeable than
myself. The material that the plans and the airplane use is 6061t6
correct? The calculations show the material or the identifier as being
6061. The problem in the shown calcs is that the numbers he is using
at 68000psi tensile is higher than the ultimate strength of 2024-t4
which is given at 64000. 6061t6 is only 45,000psi ultimate and 39,900
yield.

It's no wonder the wing was failing at 2g.

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Hi Group:

Cla

Looking at the calculations for the spar, spar.pdf I do not see your
interpretation. The 67000 psi value is Bearing Ultimate, not tensile.

A MATWEB lookup is in order:

6061-T6

Tensile ultimate: 45000
Tensile yield : 39000

Bearing ultimate: 88000
Bearing Yield : 56000

The values presented in the spar calculation are correct, and the
bearing ultimate of 67000 is below spec.

So where is the spar calc using bad values except, as you say, in the
initial assumptions of 244 pounds versus 288?

Curtis Scholl


Just a little more input from another more knowledgeable than
myself. The material that the plans and the airplane use is 6061t6
correct? The calculations show the material or the identifier as being
6061. The problem in the shown calcs is that the numbers he is using
at 68000psi tensile is higher than the ultimate strength of 2024-t4
which is given at 64000. 6061t6 is only 45,000psi ultimate and 39,900
yield.

It's no wonder the wing was failing at 2g.

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On Mon, 27 Feb 2006 15:14:24 -0500, Curtis Scholl
wrote:

Cla

Looking at the calculations for the spar, spar.pdf I do not see your
interpretation. The 67000 psi value is Bearing Ultimate, not tensile.

A MATWEB lookup is in order:

6061-T6

Tensile ultimate: 45000
Tensile yield : 39000

Bearing ultimate: 88000
Bearing Yield : 56000

The values presented in the spar calculation are correct, and the
bearing ultimate of 67000 is below spec.


Thjat may well be true, but is "bearing strength" the proper
charachteristic of the material to be used in this calculation?

As I said - not an engineer - just asking.
Please explain for the rest of us how the bearing ultimate and / or
yeild values impact the calculation, vs tensile.
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I've never liked powered ultralights that use the US part 103 definition of
ultralight. The FAA limited the empty weight to far too light a weight.
They could have added a hundred pounds to the empty weight and kept the
other limitations as they are. This would have produced a real viable
airplane class. As it is, the structures are designed without a lot of
redundancy. In the airplane in question here, the design is fine when it's
new but if there's much hangar rash on the leading edge of the wing the load
that the wing can take is greatly reduced.

I read all of the screaming and shouting about this plane's wing and I
finally decided to take a quick and dirty look at the stresses on the front
spar. I choose the front spar arguing that it's going to take most of the
loads anyway. Using a single spar unravels a knotty little problem of
resolving the reactions from the fore and aft lift struts and the two flying
wires. This was only a quick look after all. I just wanted to see if the
wing was in the ball park. Please understand that the real airplane needs
both the fore and aft spars and the fore and aft lift struts in order to
react to the wings chordwise torsion. For convenience, I used a level
spanwise wing loading. This is a conservative approach. We speak of
conservative and non-conservative. A conservative error is one which leads
to an over designed structure. A non-conservative error is one which leads
to an inadequate structure.

I used the drawings that are available on the web. They include the spar
inserts. I have a slight problem with these inserts. Since they aren't a
tight fit, its possible for the edge of the insert to cause a stress riser
on the inside of the spar tube. It's something to keep an eye on.

With my quick and dirty assumptions, I found that the spar would yield at
4.4 g's at 600 pounds gross weight. That is looking at bend moment stresses
only. A betters analysis would raise that number. This includes the
inserts. Without the inserts the spar yield at 2.3 g's at 600 pounds and
2.8 g's at 500 pounds.

Per MIL-HDBK-5 the tensile yield strength 6061-T6 tubing is 35K PSI

Rich