Contest Idea for PAMPA

I had an idea for a contest.

There is a lot of speculation and opinions bantered about in PAMPA and on this forum as to construction methods. It is often argued that method #A or method #B is "stronger" or "lighter". This is also the same of finishing methods.

What I think I might propose is a contest to measure a lot of these different building methods.

We could propose a standard to build. Say a 12" X 3" X .5" "stab" if you will. You build the stab to the above proportions and submit the sample to a nuetral party for load test. We could do a bending and tourque test for example, similar to a flex board for golf shafts. Weights are placed on one end and the deflection measured.

This would determine a flex. Less flex, higher score.

Then the part would be weighed. The flex score would be divided by the weight in grams, let's say.

There you have your score. Highest strength to weight ratio wins.

I would propose a "wood only" class, a "combo" class, and an "unlimited class. The winner would have to submit a recipe along with the sample.

Once this is completed, I bet most everyone would be surprised as the winner.

If you want to really make it interesting, require a finish that would be "judged" and multiply the final score by the appearance score.

Godzilla,

How dare you propose an easily conducted, quantifiable test of our structures? Why, my man, don't you realize the basic reason a lot of us (all of us?) fly CL Stunt is the event is subjective, not objective?

Besides, from what I read Sparky would just blow us all into the water. Hmmm, wonder why he hasn't responded yet? Just kidding! We know why.

I am interested, but only if you conduct destructive testing...

LAST EDITED ON Aug-09-04 AT 04:57 PM (CDT)
 
>Godzilla,
>
>How dare you propose an easily conducted, quantifiable test
>of our structures? Why, my man, don't you realize the basic
>reason a lot of us (all of us?) fly CL Stunt is the event is
>subjective, not objective?
>
>Besides, from what I read Sparky would just blow us all into
>the water. Hmmm, wonder why he hasn't responded yet? Just
>kidding! We know why.

You do HMMM? No you don't.

>
>I am interested, but only if you conduct destructive
>testing...
>
>Dan

Engineering classes already do such a thing with bridge's and I have participated in these (very tough).

Suggest weighing PRIOR to flexure testing.

Incorporate a standard "mounting" interface.

I will volunteer the use of a light force, computerized tensile tester that would be perfect.

It will even do "x" number of flex cycles to a fixed deflection OR a fixed load.

Does anyone remember the James Stewart movie "No Highway in the Sky"?

FWIW

>Suggest weighing PRIOR to flexure testing.

Sure.

>Incorporate a standard "mounting" interface.

Thought of that. Of course, the flex tester could use a standard "buck" also.

>I will volunteer the use of a light force, computerized
>tensile tester that would be perfect.
>
>It will even do "x" number of flex cycles to a fixed
>deflection OR a fixed load.

You got the idea. I think it would be very enlightening. Sure would put to rest some of the construction "suposition" (Al Rabe word).

Most of all the engineering done in CLPA is someone saying something to the effect of "well, I ran such and such an engine for so many flights and nothing broke" or "that plane was built super light and it flew for so many flights and it never broke". In other words, purely subjective criteria which has no real basis in a true engineering sense.

I know that I let my mouth overload my preverbial butt when speaking to real wizz engineers like Howard, Paul, and Brett. Not because I am stupid, but maybe not as informed.

I know there have been several posts showing construction techniques that are very suspect in my personal view. Of course, construction only need to be as strong as it needs to be. Anything else is "overbuilt".

>Does anyone remember the James Stewart movie "No Highway in
>the Sky"?

No.

I mentioned the standard interface because when trying to clamp-up somethine like a stab, any crushing can lead to failure. If the standard munting block was already a part of the UUT then it can include fillets and bonding just like it was mounted in a fuse.

Also, one only need build half a stab I would think.

Have you come up with a specification document for the samples yet?

I think this could be fun AND educational. We could video tape the testing.

>>Does anyone remember the James Stewart movie "No Highway in
>>the Sky"?
>
>No.

Ah, for a mechanical engineer this should be required viewing;-)

Besides, Jimmy Stewart always had good movies.

You could always follow the serious movie with Airplane or something, just to keep it in perspective.....

Hi Curt Yep, I remember the movie. I don't remember the bi-plane tail, but I do remember the fuselege angled upward at the back and I believe it was a turboprop aircraft. The stewardess,(no flight attendants in those days) was played by a young and pretty Glynis Johns. Ah, so much for trivia!!! Cheers

>Does anyone remember the James Stewart movie "No Highway in
>the Sky"?

If that's the one with the super-zoomie (for early 1950's) swept wing jetliner with a biplane tail, yep.

Point was establishment resistance to aeroelasticity testing (at certain conditions the tail(s) danced off the edge of the structural cliff.)

...may have been inspired by the early DeH Comet jetliner crashes -- different cause there. The DeH Comet passenger windows were too square shaped -- bad structural shape for the pressure changes ground to cruise altitude, and possibly to different vibration freqs from the engines buried in the wing roots.

So, what do I win? <g>

Method "B"... All the way!

[photo not recovered: 3e69bb3870f12ad5.jpg]

"It rubs the lotion on its skin,
it does this whenever it's told..
It rubs the lotion on its skin,
or else it gets the hose again.."

Now, it places the lotion in the basket.
It places the lotion in the basket.
Put the ^%#! lotion in the basket!
Ahhhh!
Aaahhhhh Aaaahhh!"
-Buffalo Bill, from Silence of the Lambs

Now add to that a contest of flying ability, and you've got an event called Precision Aerobatics!

Since there will be wood, combo and unlimited or what ever classes. will there also be Beginner, Intermediate, Advanced and Ex-spurt?

Yes.... but the most meaningful question is ..... will there be a BOS rule?

This is a cool idea and could be really enlightening.

I think you would want to build the satbs full size. Where balsa wood is concerned everyone knows the smaller the stab the more rigid and resistant to torsion it is. Since we are only talking 29" or so I thin kthe full size would be the way to go.

I have a stab I have been working on and I am ready to submitt it. It just doesnt have any mounting. It is just the stab sitting there.

Who is going to figure this idea of Brad's out and setup the rigging? Then we will know how to build it to go into the test rig.

You are right you cant clamp and hang weights. It will snap at the clamp point. maybe it would need to be suspended between to ends and the weighted in the middle.

Then lightly clamped on either end and twisted somehow and the amount of force needed would be calculated.

I have no idea how to bring this to pass.

Well...I was thinking that you would need to define the external dimension "box" so all the test moments can be duplicated easily.

The clamping interface should be a rigid material, readily available, like maybe some type of plywood rectangular box with the stab cutout similar to how a stab might be mounted into a box fuse.

The builder can mount the stab into the "standard" box anyway he disires including some maximum dimension fillet.

For testing, the center box is clamped to the test fixture and deflections and torsional numbers are taken.

Perhaps the mounting box can be provided so known weights are retained on just the structure under test.

There are some real issues with this type testing however. I'm sure Howard or Paul could offer a lengthy dissertation here.

For example, if you want to measure the spanwise deflection by loading a tip, the result will be different is you constrain the structure from twisting or allow it to freely equalize. It can be fixtured either way but the result may favor one form of construction over another. (ie do you apply load at the point of center of area, load at the spar, or in the center of the tip. Each will deflect differently)

If we knew someone that could laser cut plywood box parts, the interface "Kit" could be provided at minimum cost to the participants...hey wait a minute I think we know someone!

Just some thoughts

At first, I was giggling about this idea, but now I think it is a very good one!

Only one thing - I'd like to see a proper article about it for Stunt News (or some other).

Also, I think Doug's suggestion of full length would allow you to get a little better torsion strength data than a shorter piece.

[photo not recovered: 3e69bb3870f12ad5.jpg]

"The question of whether a computer can think is no more nteresting than the question of whether a submarine can swim." -E. W. Dijkstra

>We could do a bending and tourque test for
>example, similar to a flex board for golf shafts. Weights
>are placed on one end and the deflection measured.
>
>This would determine a flex. Less flex, higher score.

Need to be a bit more specific here.
Do you want to minimize how much it flexes under a certain
amount of torque? Or maximize the weight it can support
without failing catastrophically?

I was afraid you might have seen this.

you mean you build a plane just the way the plans show? Unless it's something plain jane like a typical built up stunt stab or a combat stabilator I always build and test at least one prototype. That doesn't mean you can't build it into a plane and fly it, but you gotta at least weigh the sucker.

Boring.

I say build wings and strap them on a non-descript fuselage with a set engine size and 1 minutes worth of fuel. Apply load and see how much it can left without breaking, or without lifting. Oh, I know they do this RC, but we could do itCL as well. Leadout standoffs attached to the fuselage to ensure level flight.

Fly over dirt if possible. Otherwise your just doing the bridge test with a different bridge.