Painting control surfaces, and balancing?

As a subject for discussion this one is about as complicated as it gets, the short answer is that control balance is critical however the reason may not be a simple balance but also be involved with the stiffness of the airframe structure as a whole.

I once was flying a DR400 that at cruise speed developed an uncontrollable aileron flutter that could only be stopped by slowing the aircraft to a speed below Vs. This problem was solved by adjustment ( increase ) of cable tension.the question being why did the flutter stop ? Was it aileron system rigidity? Increased Control circuit friction ? Wing structure stiffness as the result of increased cable tension ? I simply don’t know, but the flutter never re-appeared as long as the cable tension was correctly adjusted.

Some glider flying controls are very critical and almost impossible to repair due to weight added and the paint can tip the balance ( so to speak ) when checking the balance after the work has been done.

Without detailed knowlage about the TB20 requirements as to balance and total control weight it is not posable to comment on the 2-Pack paint issue excepting to ask of far too much paint was applied in the first place ?

If it is anything like car painting then aftermarket spraying will be a lot thicker than the original factory finish. I still have a paint thickness detector given to me by a friend who had a lifetime in the car biz. It consists of a magnetic pen containing a needle that wont stick if the paint thickness exceeds a given quite small number of thou. Not much good on aluminium I’m afraid!

In hindsight it would have been useful to check weight and the balance before painting as it may not have been correct to start with.

Peter wrote:

I have just read a story about this, where a maint shop just could not get them balanced as per the MM (TB20 I think).

If it is far out of tolerance, some manufacturers don’t seem to balance their own products initially, or due the use of a non aviation paintshop.

Common issues on non aviation painters is:

• Used a lot of filler, to get a nice surface. This adds a lot of weight, far more than paint.
• Excessive paint, I have seen multiple aircraft where, in absence of a dedicated aircraft painter, a good car painters painted an aircraft, resulting in a poor results and runners at every rivet.
• Reducing wheight by sanding of rivets. This can cause seriouse jobs.

Painting an aircraft is a real job, and requires a skilled worker. These will also strip the old paint, instead of sanding and respraying. Stripping paint is also unusual for non aviation painters.