Balancing Control Surfaces
 

Can anybody out there advise on how control surfaces should be balanced after repainting?

1 get a stick 2 feet long
2 Bang a nail one foot from the end of the stick
3 tie a piece of string to each end of the stick.
4 Tie an aileron onto each piece of string.
5 if the stick is high at one end, add wieghts to that end.

There, balanced ailerons

Har har har. I know the Cub is as low tech as they come but there must be better ways of doing it. Maybe I'll just hold an aileron in each hand, I pretty well balanced, I've got a chip on both shoulders!

The balancing of a control surface is to do with ensuring the surface's CofG is correctly positioned with respect to its hinge line.

An incorrectly balanced surface can develop flutter & rip off the airframe. I recall reading somewhere or other that the flutter it causes can be severe enough to cause catastrophic airframe failure.

[This message has been edited by Tinstaafl (edited 19 September 2000).]

Wow - there's encouragement for you....! Tinstaafl - I'm afraid you're in the realms of airframe design here. Poor old lowNslow has already had Mr Piper design his ailerons, he just needs a steer on the trimming!

lowNslow, if its any help, I can bring many years of trimming out R/C model aircraft for you.

First, with the ailerons off the wing, weigh each one and try to get them as close as poss. Second, weigh the ends to check that they're both similar.

Next, put them back on the aircraft and, (having checked for warps of course) clip them parallel to the TE and re-set the control runs to match. There should be something in your manual about whether they are set level, or with wash-in or wash-out pre-set. Washout is safest if there's any doubt, but 'drooping ailerons' were a feature of many very early designs; airflow picked them up once under way. (My AA-5 for example, has the flaps pre-set with a 3 degree droop which is picked up by the air flow in flight to give them zero degrees under load.)

Everything else should have been designed in for you including mass-balance (best anti-flutter device). Taking any slop out of the control runs is also good practice, but again your rigging instructions should specify that because it can be quite critical.

Here endeth the lesson.... http://www.pprune.org/ubb/NonCGI/cool.gif

BTW, when are we going to see this magnificent silver bird in flight ....?

[This message has been edited by rightstuffer (edited 20 September 2000).]

rightstuffer, the people who did the Cub, didn't wash let alone understand wash-in or wash-out. You had my attention until you mentioned TE. What's that? Given the course of the advice, I would assume that it means "follows the curve of the upper surface and lower surface.


Regarding the drooping ailerons and flaps, was it Maule or Mooney who found that setting the flaps to a few degrees negative deflection decreased the drag of the wing and gave a few extra knots?

When you see the Cub, it will still be "dead fly on windscreen" yellow. I am going to have to tiptoe around disturbing expensive to repaint colours. I'm building up to doing the fabric on the undercarriage (what a wonderfully quaint term that is "how's your undercariage my dear?). So far I've managed to screw up revarnishing my prop, lots of runs, re-sanding, oh b*gger, the varnish still isn't dry!!!!!!!!! Let's do it again then shall we.......... Rats and double rats. Now the house stinks of varnish and the carpet is covered in this white dust. I've been fighting Columbians off for the last 2 days!

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The 16 men of Tain are unsung heroes. CubTrek. To slowly go.....

Chris Lodge - propeller man of note, somewhere near Chelmesford, reconditioned (varnish and chip repair)my old prop for £40.

No Columbians, no glue sniffers, just LSD (low stress days) had it back in less than a week.

sNr

LowNSlow,Disregard earlier post (if you've read it)
If your Cub is on a permit,and your doing an annual and you have removed control surfaces then I presume that you have a PFA inspector involved, ask Him/Her what's required. And yes It's an aerodynamic/vibrational thing not weight. Any structure with an air flow over it becomes prone to resonance, you must have seen the footage of "Galloping gertie" aka the Tacoma narrows bridge. Control surfaces are susceptable to these effects, which is why Mass balance weight is added to move their natural resonance frequency to a range outside of any vibrations caused by airflow in normal flight
Best of luck with the rebuild.


[This message has been edited by Windy Militant (edited 21 September 2000).]

TE = Trailing Edge. I'll pass on anything else I can think of at the flyin.

Trailing edge! Should have worked that one out.

As I have discovered that the sanding part is easy but the varnishing part is a complete and utter pain in the bum, I think I will be giving Mr. Lodge a ring. Thanks stiknruda.

Windy Militant, I thought it was more than weight. I haven't actually removed the offending items yet, just storing up knowledge for when I get the courage to take a paint brush to them.

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The 16 men of Tain are unsung heroes. CubTrek. To slowly go.....