Aileron pivot tubes?

[EDMO 1078]

I bought 3/4 inch .035 wall 4130 tubing for my aileron pivot tubes - Now, I am beginning to question the wisdom of using steel tubing instead of thicker wall aluminum tubing.  More concerned with the flexing than weight -

This is the same tube that spans the full length of your flaperons.

Anyone have some engineering type thoughts on that?

EDMO

Edited 14 Apr 2014 by Ed In Missouri

[wypaul 448]

I am no engineer ED but my  other plane (Q2) uses aluminum for both the elevator and the ailerons.  Have you made provisions for a mid-span support or will they only be supported at the ends only? I wonder what Just does with theirs or Rans on the S6 or S7.  I have to admit aircraft design is over my head.

[EDMO 1078]

Paul,

    It is probably over my head too - just trying to tread water - reading a lot of engineering and design stuff, but it don't cover everything.   These are the pivot tubes - not push/pull - There are 5? support hinges total on flaps and ailerons - just like the flaperon hinges - the aileron tube runs thru bushings inside the flap tube.   Guessing there is a lot of wing deflection in these birds, so aluminum may be more flexible and forgiving?

Thanks,

EDMO

Edited 15 Apr 2014 by Ed In Missouri

[Luked 71]

Hi Ed,

 

Since no engineers have answered, I'll add my 2 cents.

 

Disclaimer: I'm not an engineer. I did take 2 years of engineering classes when I was younger, so I picked up some basic concepts, but it was almost 20 years ago. I also think engineering is very interesting. Hopefully a qualified engineer will chime in though.

 

Anyway, I found this link using google:

 

http://www.engineeringtoolbox.com/torsion-shafts-d_947.html

 

If you scroll down to "Example - Shear Stress and Angular Deflection in a Hollow Cylinder", you can see how to calculate the maximum stress, and angular deflection for a hollow shaft. There is also a link on that page to shear modulas numbers for various materials. You can use google to find more.

 

I also found an online calculator that does the math for you:

 

http://www.amesweb.info/Torsion/TorsionalStressCalculator.aspx

 

You'll need to know the Ultimate Shear Stress (USS) for the material you are using. For steels, I think it's 60% of Ultimate Tensile Strength (UTS). You want to make sure that the calculations above don't put more stress on the part then the material used can handle. You'll also want to use some factor of safety.

 

You mentioned flexing, so I assume you mean angular deflection. Long shafts can flex out of alignment, but that's more difficult to model, and if your torque tube is supported at multiple points it probably won't be an issue. Anyway, the example in the link above covers angular deflection.

 

To me, the most difficult part of these kinds of problems is not determining if a part is strong enough to withstand a particular load, but determining what types of loads the part will experience, and how severe. I guess that's kind of the art of engineering. How strong should a bicycle frame be? How high of a jump will a kid take it off of?

 

The load on your torque tube could be a fair amount different than the load on a stock flaperon. If it is connected to the aileron by a pushrod, the length of the arm on the torque tube and the length of the control horn will affect the torque in the tube. If your tube is directly driving the aileron (like a flaperon), it could still be different from the stock flaperon because the flaperon might be getting some aerodynamic balancing that the aileron is not. Also, differences in chord length would cause different loads.

 

Basically, figuring out the loads is the hard part to me, calculating the stresses and deflections is easier. That's probably enough rambling. Hopefully that's at least a little helpful. Like Paul said, I'm not an aircraft designer. My brother happens to be a civil engineer, so at least on structural problems, I can have him double check stuff I do, and he can tell me if I'm on the right track or not.

 

Luke D.

 

Edit: I see you are running the aileron torque tube through the flap torque tube. Sounds like a Tailwind. Maybe you should see if you can have a look at a set of Tailwind plans. I think you can still buy them too.

Edited 15 Apr 2014 by Luked

[EDMO 1078]

Luke,

Thanks for the Post -  I have been thru the modules of elasticity bit so many times it hurts.

I got my ideas from the old WW2 German planes, which had flaperons and split ailerons/flaps, which Steve Wittman also copied with the tailwind controls.

My worries about flexing were not concerned about loads, but about stiffness of the steel being more than the aluminum, and this part has to flex with the wing, as the flaperons do.

Almost positive that I will go with the aluminum tube with a heavier wall.

For torque, the shortness of the ailerons, being out of the prop blast, will probably not be as much, and certainly not  more than the full-length flaperons, since about all they have to do is control the roll of the plane.

The most torque pressure will be on the flap portions, and that will be a 1 1/2 inch aluminum tube - lots stronger than the flaperon tubes.

Every time I get worried about design and building, I go to the big-screen TV and put the tape in about the early flying machines and the crazy things that they tried to fly with, and convince myself that I am maybe not that stupid! 

EDMO

Edited 15 Apr 2014 by Ed In Missouri

[Luked 71]

Sorry Ed, I missed that. Binding would be a big concern with that setup. Maybe some type of test jig to test for binding in different load conditions could be helpful.

[EDMO 1078]

Like having one guy push up and pull down on wing while the other works the controls?  I don't have a wind tunnel!

EDMO

[Luked 71]

Like having one guy push up and pull down on wing while the other works the controls?  I don't have a wind tunnel!

EDMO

 

What, no wind tunnel??

 

I was just thinking of something simple to attach the torque tube to that could simulate a flexing wing.

[EDMO 1078]

Nothing simpler than a guy on each wing tip pushing up to lift the plane - Nothing better than two gals in bikinis doing push-up, pull-down exercises on each wing, while I hang on to the big stick!

EDMO

Yes, I wish I could see what tubes the Tailwind uses!

Edited 15 Apr 2014 by Ed In Missouri