Texas Parasol Plans...

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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