Texas Parasol Plans...

Earlier, Richard Isakson wrote:

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.

Interesting. When I run the moment of inertia for 2" tubing of .058"
wall, I get 0.1667 in^4. Using that number and a yield strength of 35
ksi I get a yield moment of 5833 in/lbs. Do those numbers agree with
yours? Of course, those figures disregard cripling or buckling, which
I've not seen mentioned in this thread.

I suspect that this whole thing will come down to a somewhat subjective
matter of distributions and deflections. The distribution of loads
between the forward and aft spars will make a big difference, and I
think that the wing deflection will start to look scary before the spar
tubes reach yield. But those are just more non-engineer's guesses, and
there's been plenty too much of those already.

Taking this out on a tangent, one thing about little airplanes like
this that I don't understand is why so many of them use tubular spars.
It seems to me that you can get so much better strength/weight and
stiffness/weight using a built-up I-beam or C-section spar. Yeah, it's
a bit more trouble. But the result is either better strength and
stiffness for the same weight, or the same strength for less weight.
But again, that's just my non-engineer wing developer perspective.

Thanks, and best regards to all

Bob K.
http://www.hpaircraft.com/hp-24

("Richard Isakson" wrote)
[snip]
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.


Agreed, almost.

350 lbs would have been great (without floats).

Low stall number is fine, but let's remove the speed limit on the upper end.
If it weighs X and stalls at Y, carries one person and (8g) gallons of
fuel ...who cares about its top-end speed!


Montblack
Hell ...I'M not 103 legal !!! :-)