Alright. I need the help of a mathematician or somebody with a background in aeronautical engineering to check over my work please. I am working on an prop jet design that I plan on busting 200MPH. I want to test the wing design's structural integrity on the ground before I fly it because a wing failure at 200+ could be devastatingly dangerous to spectators. I want the wing to be able to hold up to a 180 degree turn in one second at 250 MPH. I have converted MPH into meters per second and got 111.76 m/s. I divided it by 9.8 to get 11.4 (how many times the force of gravity to be exerted on the wing in a 180 degree turn in one second.) See any problems? Thanks, and happy landings.
-Steve

If you need someone to do the math and calculate the vector forces for you, maybe you should tackle a less-involved project. Also, ANY new plane should NOT be flown with spectators present the first time.

Dr.1

Since you plan to physically test an existing structure, I guess there is no need to worry about the engineering involved in designing a structure to withstand those forces.

180 deg in one second is 30 rpm.

30 rpm is 1800 revolutions per hour.

1800 revolutions in one hour = 250 miles.

1800 * 2 * pi * r = 250 mi.

solving for r,

r(adius) = 116.71 ft (35.57 m).

a = v^2 / r

where a = acceleration, v = velocity and r = radius

250 mph = 111.76 m/s

a = ((111.76 m/s)^2)/(35.57 m) = 351.15 m/s^2

1 g = 9.81 m/s^2

351.15/9.81 = 35.8 g

That's a lot of g's, but not unreasonable, if one has ever watched a formula 1 model airplane race.

Remember, there is at least a 50% safety factor built in to small full-scale aircraft. So the structure must not fail up to at least 54 g if you follow that practice. With a model and no telemetry, I would feel better with a 100% safety factor, or 72 g!. Don't forget to consider the loads on the stab/elevator, and the fuselage and engine mount.

DISCLAIMER: I am not an engineer, and I'm not liable if your plane breaks anything, or hurts anybody. These calculations and $3.50 will get you a cup of coffee at Starbucks!


Good luck, and be careful!


P. S. Dick, are you reading this? A few minutes work on a scratch pad can provide data for ground testing that might prevent an in-flight structural failure. I'd sure rather have it fail on the ground during a test than in the air!

I'm aeronautical engineer... perhaps I can help in detail with your problem. Seems that you're worried about the structural inegrity of your wing on this turn; Am I rigth?
If you send me more info about the design, I'm willing to make a Finite Element Analysis on the most compromissed parts...
See' ya!!!
Guille

Not being technical about it. It is not possible to make a turn that fast or to pull 35 "G". The Formula 1 cars, by the way, pull less than 4 "G". Just thinking out loud: 35 G X weight of the model ( 30# ) = 1050 lbs. So just put a 1050# of weight on the center section with support only at the wingtips and see what happens.

It is very possible. I was talking about Formula 1 model airplanes, not cars which "pull" mostly lateral g's. The numbers given are not unreasonable for Q-500 or especially Form1. I have watched many Form1 races (positively scary!) and just eyeballing the turn radius and rate during a race makes these numbers easy to believe. I have raced Q-500.

Also, the weight needs to be distributed along the span in a way that simulates air loading. Testing is not done with all the weight concentrated at the fuselage. That would be silly.

Sorry, HalH...
Those "g's" are possible. Look at a Formula 1 AIRPLANE race... or F3D... or F5D... or F5B... and the g-loads often exceed 40.

Why did you assume his model would weigh 30 pounds? Is that the way you build model racers? No, I don't think so.

And supporting the wing at the tips while applying the full load to the center section is not a fair ultimate load test.

-David

Safety is my main concern. I know a little bit about design and aerodynamics and am almost positive I will have very little problems making this a safe and pleasing aircraft to fly. I agree that spectators should not be present at the initial test flight, but just because a plane makes it through the first several flights does not mean it will hold up through the next 30. I would hate to endanger anyone and that is why I am going to subject the wing to such a harsh test on the groung before I ever put it on the plane. I know exactly where the forces go on the wing, and where it will be most likely to fail. I have never been good at math, and just needed somebody to check over my work incase I did something wrong. Turns out I did. I appreciate mesae's aid.

I am planning on this model to come in about 5-6 lbs FYI. It's not going to be a racer, just a fun sport plane; something like a Magnum, but faster. I do not plan on it being able to take a pylon at 250, but I wanted to test it to standards higher than it would ever see in flight. I have not started construction yet, but I am planning a swept blue foam wing with carbon fibre spars, balsa LE,TE, and tips, ply center rib, sheeted with 1/16" balsa. I will glass the center section, and if I do not get the rtesults I want in my initial tests with this design, I will reinforce the weaker areas with carbon fibre matte, and glass the whole wing. If that doesn't do it, I will either redesign the wing entirely, or scrap the project. As stated earlier, I want a fun plane, but safety is my first priority.

Thanks all for the help, and I'll let wou know how it goes.
-Steve

How would you test it?

Glad I could help.

Were any ducks harmed in the making of your avatar?

Here is an interesting article about static load testing the Fairchild XNQ-1: http://www.aeromuseum.org/Articles/F...gthTesting.htm

Here is another page with lots of pictures of the more recent static load test for the Xenos 2000 Motor Glider: http://www.sonex-ltd.com/xenos_0301.html
The wing is cantilever supported at the root. The forklift is there to provide support while loading, then lowered to allow the wing to flex as it takes the load.

They may give you some insight on how best to set up your test.

BTW, I applaud your thoughtfulness on this project.

Ha ha! no duck harmed. I was bored as a plank one day last year in music appreciation class and got to doodling.
Thanks again for your help.

I almost forgot something important. It's not quite as bad as you think. You need to subtract the weight of the lifting portions of the wings themselves, including servos and wiring, etc., before multiplying the remaining weight by your test g loading to determine the total sandbag weight. The weight of the wings is sort-of a freebie, since it works to un-deflect the wing while lifting. That's partly why so many full-scale airplanes have fuel in the wings. The wings can be built lighter since they don't have to support as much bending force.

With two identical airplanes that have the same weight:

Worst case is weightless wings with all the weight at the center/fuselage --- maximum bending force on wings.

Best case is all the weight in the positive lifting surfaces, proportional to the amount of lift generated at a given station --- no lateral bending force, but there will still be torsional forces.

i.e. the more of the stuff you were going to carry anyway that you put in the wings, the less bending force the wings will have to support.

Then you might want to to include a small factor to account for tail-down-force (not large, especially if the CG is close to the neutral point, probably less than 5%, increasing as the plane becomes more nose-heavy).

You might also want to add a little for gust forces.

payload in wings is good from a structural point of view, but not so good for handling. Roll inertia increases with heavy wings.

Dynamic soaring gliders are exceeding 300 mph in a continuous loop.
These planes hold together, most of the time.
They're very purpose built, with foam cores and CF and glass skins.
There's a few videos available where the plane's passes are more easily observed by the noise it makes than by actually seeing it!

I'm not familiar with these. Any pics?

Nevermind, I have seen them, I just didn't know what they are called.

Thanks mesae. I am planning on multipying the weight of the fuse (wet) by 50G. I am designing a tappering swept wing (think GP patriot profile) with a simple balsa and ply fuse similar to that of a Q500, with a V tail. no landing gear, hand launch and land in the grass. I know a round fuse would be much more aerodynamic, I have thought about doing one out of fiberglass, but I also want to make this easy and cheap to build.