How Much Load for a Load Test?

Morgans wrote:

1320 -200 =1120 x 4 = 4480 -200 = 4280

AC weight - wing weight cause wing is supported by the air in real
flying so G's will not load the spar, then multiply by G's _then_;
subtract the weight of the wing, since gravity is pulling on the wing in
the load test, so you can take that many bags bags off.
(since gravity is doing 200 pounds of the work for you)

One fact that should be mentioned is the location of the bags. They
should be placed outwards along the wing in the approximate distribution
of lift. Also, place them centered front to back along the ribs to
represent the center of lift for your airfoil at about an angle of
attack that would be necessary to pull that many G's. When in doubt,
rearward would the way to go. My reason for wanting to do this is to
see if the wing takes on extra twist trailing edge which could lead to a
very nasty early tip stall.

Now, how about the fact that conventional airplanes have a tail that is
pushing down to achieve stable flight. That "weight" has to be "lifted"
by something, and that would have to be the wing. Better get some more
bags. How many? Up close to 10% ? That is only a guess; anyone know?
So 10% of 4480 is 480 more bags, right?

That puts our wing load test up to 4760.

Wait !!! Did you take into account that the fuselage contributes a
substantial percentage of lift depending on the design? If you knew how
much, you could subtract that calculated factor from the weight you are
going to have to put on the wing for the test.

There are other factors you should think about, such as extra loads
placed on the rear spar due to aerodynamic forces created by the flaps
and ailerons. Somewhere about now my head starts to hurt, so I add bit
more for the wife and kids and let it go at that

Whew! There ARE reasons why people go to school to get Aerodynamic
Engineering degrees.

More food for thought?


Good one, Jim.

Brian W

Bob wrote:
On Jul 3, 1:54 pm, Brian Whatcott wrote:
.
Hands up, all who said 3000 lb.
Correct!
The airframe is already
supporting its own (1g) weight. :-)
--------------------------------------------------------------------------------------------------

Shush!

Including the First-Interval in the testing will only lead to bails of
mails about Wright vs Wong.

But if you really wanna hear some screams, mention Valve Jobs. (In
fact, I think I will,,, )

-R.S.Hoover

Electron tubes have been replaced by solid state. I don't think
there are too many valve jobs left.

Dan, U.S. Air Force, retired

On Jul 4, 3:27*pm, Brian Whatcott wrote:
wrote:

...





Glad someone raised this topic. *Too lazy to do it myself. * Assuming
a LSA gross wt. aircraft (1320 lbs.) with a wing that weighs 200 lbs.
and you want to test the wing for 4 g's. * 4 possible
scenarios.....The first three I have seen in "reputable"
publications...you know...the ones you have to PAY for. * The 4th one
is the only other one I could think of. * I think we've decided #1 is
wrong. * Turning the plane upside down and supporting the frame on the
fuselage. * How many bags of manure do you pile on the wing to test.
Assumptions: * each bag of manure weighs 1 lb.

Scenario #1 * * * 1320 x 4 *( 5280 *)
Scenario #2 * * * *1320 - 200 x 4 *( 4480 )
Scenario #3 * * * *1320 - 200 x 4 + 200 *( 4680 *)
Scenario #4 * * * *1320 x 4 - 200 *( 5080 )

Neal F.

What a well-phrased question! * :-)

It would be most reassuring, if one used the heaviest load, no doubt.
But you have specified a test only of the wing.
This wing must carry not only its own weight multiplied by the test
acceleration, but that of the rest of the airplane's gross weight
multiplied by the test factor.
As mounted in the test rig, it is already loaded with one wing weight,
so we should add another 3 wing weights and four weights representing
the aircraft gross less wing weight. What does that come out to, I wonder?

The load mentioned above represents
3 X 200 +
4 X (1320 - 200) =
5080 lbs.
As you can see, this is just another way of expressing your Scenario #4
This is not quite the heaviest option.....

But wait: that 3 times wing weight does not have to be reacted through
the wing attach at all.
That's one reason why fuel tanks in wings are favored - the wing lift
can react the fuel load locally, and that's a less stressful job than
holding the tank up on the end of a (more or less) long lever arm.
So we COULD allow ourselves the benefit of discounting the accelerated
load due to the wing itself, though the wing could still collapse say by
crushing or buckling, lets allow a 50% reduction.
Than we would load the wing with
3 X 200 X 50% +
4 X ( 1320 - 200 - (200 X 50%)) =
* * *(thats an allowance for the self-support of the OTHER wing too)
* total * 300 + 4080 = 4380 lbs
Well, would you look at that: the smallest load of all! *:-)

And that's when we start considering the merits of Barnaby Wainfan's
flying wing, made with flat panels, to boot. The WHOLE weight is locally
reacted by the wing.
How strong is THAT!

After considering the merits, you are going with the biggest number -
it's your life, after all.

Brian W- Hide quoted text -

- Show quoted text -

Check out this website for Irv Culver's design notes for his Windrose
sailplane. Looks like he's using Scenario #2. Laws of physics being
what they are...there's only one correct answer ( Scenario ) Trick is
finding which one is right.

www.continuo.com/windrose/culver.htm

Neal F

Neal Fulco wrote:
On Jul 4, 3:27 pm, Brian Whatcott wrote:
wrote:

...





Glad someone raised this topic. Too lazy to do it myself. Assuming
a LSA gross wt. aircraft (1320 lbs.) with a wing that weighs 200 lbs.
and you want to test the wing for 4 g's. 4 possible
scenarios.....The first three I have seen in "reputable"
publications...you know...the ones you have to PAY for. The 4th one
is the only other one I could think of. I think we've decided #1 is
wrong. Turning the plane upside down and supporting the frame on the
fuselage. How many bags of manure do you pile on the wing to test.
Assumptions: each bag of manure weighs 1 lb.
Scenario #1 1320 x 4 ( 5280 )
Scenario #2 1320 - 200 x 4 ( 4480 )
Scenario #3 1320 - 200 x 4 + 200 ( 4680 )
Scenario #4 1320 x 4 - 200 ( 5080 )
Neal F.
What a well-phrased question! :-)

It would be most reassuring, if one used the heaviest load, no doubt.
But you have specified a test only of the wing.
This wing must carry not only its own weight multiplied by the test
acceleration, but that of the rest of the airplane's gross weight
multiplied by the test factor.
As mounted in the test rig, it is already loaded with one wing weight,
so we should add another 3 wing weights and four weights representing
the aircraft gross less wing weight. What does that come out to, I wonder?

The load mentioned above represents
3 X 200 +
4 X (1320 - 200) =
5080 lbs.
As you can see, this is just another way of expressing your Scenario #4
This is not quite the heaviest option.....

But wait: that 3 times wing weight does not have to be reacted through
the wing attach at all.
That's one reason why fuel tanks in wings are favored - the wing lift
can react the fuel load locally, and that's a less stressful job than
holding the tank up on the end of a (more or less) long lever arm.
So we COULD allow ourselves the benefit of discounting the accelerated
load due to the wing itself, though the wing could still collapse say by
crushing or buckling, lets allow a 50% reduction.
Than we would load the wing with
3 X 200 X 50% +
4 X ( 1320 - 200 - (200 X 50%)) =
(thats an allowance for the self-support of the OTHER wing too)
total 300 + 4080 = 4380 lbs
Well, would you look at that: the smallest load of all! :-)

And that's when we start considering the merits of Barnaby Wainfan's
flying wing, made with flat panels, to boot. The WHOLE weight is locally
reacted by the wing.
How strong is THAT!

After considering the merits, you are going with the biggest number -
it's your life, after all.

Brian W- Hide quoted text -

- Show quoted text -

Check out this website for Irv Culver's design notes for his Windrose
sailplane. Looks like he's using Scenario #2. Laws of physics being
what they are...there's only one correct answer ( Scenario ) Trick is
finding which one is right.

www.continuo.com/windrose/culver.htm

Neal F

Hmmm....I can only offer the trite old aphorism:
Circumstances alter cases."


Best

Brian W