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

"Bob Kuykendall" wrote ...

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.

For the spar alone those numbers are right and result in the poor spar
performance without the inserts. The maximum bending moment happens at the
strut attach point. This is where the insert sits and that increases the
moment of inertia to 0.3155. This results in the improved load handling
ability.

In the interest of laziness, I didn't look at spar buckling nor did I look
at negative loading. There is a potential for column buckling of the spar
between the root and the strut attach point. As the wing is lifted, the
strut is placed in tension. This places the inboard portion of the spar in
compression. The combination of the compression load and the lift load
could potenially cause buckling. Maybe I'll look at that sometime.

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.

Reading what little has been said about the load testing, I suspect there's
a problem in the way the wing was held. It almost sounds like they didn't
have the rear lift strut attached

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.

I think it's to keep the labor costs down. You might ask Chuck.

Rich

On Tue, 28 Feb 2006 19:31:30 -0800, "Richard Isakson"
wrote:

"Bob Kuykendall" wrote ...

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.

For the spar alone those numbers are right and result in the poor spar
performance without the inserts. The maximum bending moment happens at the
strut attach point. This is where the insert sits and that increases the
moment of inertia to 0.3155. This results in the improved load handling
ability.

In the interest of laziness, I didn't look at spar buckling nor did I look
at negative loading. There is a potential for column buckling of the spar
between the root and the strut attach point. As the wing is lifted, the
strut is placed in tension. This places the inboard portion of the spar in
compression. The combination of the compression load and the lift load
could potenially cause buckling. Maybe I'll look at that sometime.

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.

Reading what little has been said about the load testing, I suspect there's
a problem in the way the wing was held. It almost sounds like they didn't
have the rear lift strut attached


It WAS attatched. It was attatched as if it was on the plane but
upside down.

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.

I think it's to keep the labor costs down. You might ask Chuck.

Rich


*** Free account sponsored by SecureIX.com ***
*** Encrypt your Internet usage with a free VPN account from http://www.SecureIX.com ***

Richard Isakson wrote:

In the interest of laziness, I didn't look at spar buckling

Without the jury struts, IIRC, it cripples long before anything else fails.

Deflection at the jury strut attach point to the strut , during the load
test was, 2 or 2.5 inches when really loaded down.

hth

Rob

("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 !!! :-)

"Montblack" wrote in message
...
("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 !!! :-)

I'm not sure that the subject is worth discussing further at this late date.
But, since we are--the stall speed number is definitely *not* fine!

The problem with the unreasonably low stall speed is that very modest
surface gusts can easily upset an ultralight while taxiing; or worse yet,
while taking off or landing.

350 lbs, one seat, and the speeds now authorized for LSA would have
*dramatically* improved safety with only very modest training--although any
maximum speed of at least 80 Kts would have worked.

Peter

Flagellation of a deceased equine is unsatisfying!