Vans RV-4 flap operating arm

Alan George · Post by **Alan George** » Mon Jun 13, 2011 11:20 pm

Our group Vans RV-4 has electric flaps but the left hand flap operating arm is twisting so that all the movement in the rose joint is used up getting the push rod a vertical drop down to the flap. It seems that the circumferential weld has introduced stresses into the left hand flap operating arm and these are gradually coming out and twisting it.

Has anybody had a similar problem? We are thinking of buying a whole new flap operating arm but will we have the same problem in a few years time? Would it be better to straighten the existing left hand flap operating arm?

Thanks for your advice, Alan.

barryc · Post by **barryc** » Tue Jun 14, 2011 9:10 am

Dear Alan
This sounds like a significant structural defect, and as such you will need to enlist the services of your inspector. Have you spoken to Francis yet, if not I strongly suggest that you do before embarking on any course of action.

Kindest

Barry

Alan George · Post by **Alan George** » Wed Jun 15, 2011 10:10 pm

Hi Barry,

I do not believe it is a structural defect but it would be very hard to get a perfect alignment between operating arm and flap so the rose joint takes up some misalignment. It does require careful use of washers to give the push rod a vertical drop down to the flap and I do not believe it should be so critical.

It is on the advice of our inspector, and the second one that did a duplicate inspection as it is a flight control, that we are looking to fix this problem. We intend to swap in a standard flap operating arm on a like for like basis but I was asking for advice if anyone had encountered a similar problem before we do that.

Regards, Alan.

G.Dawes · Post by **G.Dawes** » Thu Jun 16, 2011 8:43 pm

sounds more likely that the rose joints lock nut were not tight . Try loosening realigning and then tightening again. very unlikely that weld stress come out like that.

Mark A · Post by **Mark A** » Sat Jun 18, 2011 6:59 am

I would doubt that any twisting was gradual. If the flap horn has twisted, it must have exceeded its yield stress at some point. The rod reacts the whole aerodynamic moment of the flap about its hinge, so an excedance of flap limiting speed may have overloaded it (easily done in an RV-4).

Have you asked all the group members if they may have exceeded the flap speed? They may have thought that they got away with it without damage and not reported it.

Replacing the twisted horn sounds like a good idea.

mikehallam · Post by **mikehallam** » Sat Jun 18, 2011 9:02 am

Low wing a/c - flap to land - possibly full flap, and struck something like a thick tuft of grass somewhere without obvious skin damage ??

mike hallam