Flap Overspeed Question

Unfortunately yesterday while descending into my home field I discovered my flaps had been inadvertently extended 10 degrees at some point in flight. Whether it was done by my passenger (wife) or myself when we encountered some light to moderate turbulence over southern Kansas it doesn't matter, but the fact is they had been extended 10 degrees for a while and our speeds were up as high as 175 knots in the decent.

As soon as I noticed the problem I retracted the flaps and only extended them again in the pattern for landing. I did not feel or observe anything abnormal about the pattern or landing. Upon visual inspection after the flight I could not see any obvious damage. Does anyone have any recommendations what I should checkout prior to my next flight?

Lesson learned: when encountering significant chop pay close attention to where your hands land when changing radio frequencies or making other aircraft adjustments. Bouncing around is not only uncomfortable but also potentially harmful to good airmanship. Any yes, these RV's are well built sturdy airplanes!

You've got a new Max Flap Extension speed for your landing checklist now

I addded a "Flap Permissive" switch on the panel for this exact scenario. The setup always allows power to the flap motor to retract the flaps. The switch must be in the permissive postion to lower flaps.

Take off checklist is:
- Extend flaps as desired
- Then place the switch in the non-permissive position

Landing checklist
- Place the switch in the permissive postion

All of my planes have the flap switch on the stick. Depending on how you did this it can be easy for a knee board or such to bump the flap switch.

Carl

I seriously doubt any damage was done. A call to engineering at Vans could offer more relief. Of course, everyone is going to recommend an inspection by qualified inspector familiar with make and model.
A good inspection by yourself checking for alignment issues will be telling.
Anything bent will stay bent.
All the best.

Aluminum or steel pushrods?

Aluminum or steel pushrods?

If you have the stock aluminum tubular pushrods, then I would replace them now. If you have the hex cross section aluminum pushrods, I would replace them at next condition inspection.

I calculated once the speed at which the aluminum pushrod tube would buckle and/or the female threads would strip. Both were within the flight envelop for 20 degree flap deflection.
There is a fair chance that you have done some yielding deformation to the female threads cut into the ID of the aluminum tubing. The ID is bigger than the proper tap size for that thread, so it is already a compromised thread to begin with.

You were only at 10 degrees so probably OK, but perhaps the threads are partially yielded - it would be very difficult to tell.

I, and I think many others, have substituted 4130 steel tubes for the flap pushrods. It is a miniscule weight addition, and it raises all the failure modes for the flap actuation system above V_ne.

Its so easy and cheap to do, just replicate the pushrods you have in steel.

Not to hijack the thread but - what is the reason for the low flap speed on the RV's and in particular the 9? Is it the rods that connect the flaps to the actuator? Is it the flaps themselves or is it the flap motor and screw mechanism? Anybody have an answer here?

scsmith said:

...

I calculated once the speed at which the aluminum pushrod tube would buckle and/or the female threads would strip.

<SNIP>

You were only at 10 degrees so probably OK, but perhaps the threads are partially yielded - it would be very difficult to tell.

Click to expand...

So if the rod ends are properly installed with jam nuts, I would expect that the compression loads applied to the assembly would be transmitted from the bearings to the tube via the jam nut bearing surfaces, and not through the female threads of the tube itself. I definitely would not expect to see yielding of the female threads unless the jam nuts were left off or loose.

Skylor

I added a "Flaps Down" EICAS message after doing something similar, no damage to the flaps but I was nowhere near the speed you were.
I agree with the above posters, do a good inspection and if you have the stock alum pushrod now is a good to upgrade.

Jrskygod said:

Not to hijack the thread but - what is the reason for the low flap speed on the RV's and in particular the 9? Is it the rods that connect the flaps to the actuator? Is it the flaps themselves or is it the flap motor and screw mechanism? Anybody have an answer here?

Click to expand...

Good question. It's an issue that I've really had to pay attention to when transitioning from a Cherokee to the -9A. It was hard to overspeed the Cherokee flaps (it was hard to overspeed the Cherokee period), and if you tried, the flap handle was noticeably hard to lift. So I'm told.

skylor said:

So if the rod ends are properly installed with jam nuts, I would expect that the compression loads applied to the assembly would be transmitted from the bearings to the tube via the jam nut bearing surfaces, and not through the female threads of the tube itself. I definitely would not expect to see yielding of the female threads unless the jam nuts were left off or loose.

Skylor

Click to expand...

Well, thats a good point, the large loads are compressive, and the jam-nut contact does short-circuit the threads. That probably expains why the aluminum ones have had acceptable service in the field.

Another item to watch for, is that Vans supplies a rod-end with an integral stud for the attachment to the flap. I found that I had to shim the length of the stud a fair bit to get the bearing positioned correctly, and became concerned about its bending strength. It is necked down to allow a lot of angular deflection of the bearing, so it is smaller diameter than the thread diameter of the stud. Add to that the fact that the integral-stud bearings do not have a positive capture feature that is standard practice for rod ends. So I used a standard rod end with a AN bolt through it (I forget now if it was a 3 or a 4, it is the same thread size as the supplied stud). I used a short section of tubing as a spacer sleever, with washers at both ends, and of course the large AN970 washer to provide the captive feature. Its funny, because when the DAR came to inspect my airplane, he was half-way through his sentence saying that the flap attachment was unacceptable as he climbed under to look, and then stopped, and said, "I'll be damned - you have the first RV I've seen where the flap pushrod bearing is correct." I earned some respect that day

I'm not sure this is applicable to Van's stable of aircraft, but in other high performance aircraft, it is not advisable to retract the flaps upon discovering that said flaps have been in an overspeed condition. Possibility of jamming/deforming/damaging something during the retraction...

John

If the vans airplanes are designed to part 23 or similar standards then the limit load would probably be a 2g turn at Vfe. So there very well might be some margin there in terms of the static load if you were not doing any hard maneuvering. Also you were only at 10 deg, which is also good news. There are a bunch of other load cases, like gust loads, flutter etc and I don't know about those.

I would take the rods off and inspect the for signs of bending and damaged threads. I wouldcheck the structurewhere they attach. They may well be just fine. It would not hurt to inspect the piano hinge and the adjacent skin. Typically the limit load is a conservative combination of a speed and a maneuver, or a gust, then the ultimate load is 50% higher. Don't take this as an encouragement to go out and dive to 200 mph with your flaps down!!! the speed exists for a reason and it should not be exceeded, but exceeding it in level flight by a few mph might not damage anything.

Is there enough aileron available on final to counter a flap that has failed on one side?

I, and I think a few others on the forum, "tested" our flaps similarly at some point When I inquired one of the responses was that when, not if, it happens the recommendation was to slow to flap extension speed before retracting the flaps. I belive the concern was flap repositioning while above flap speeds was more likely to damage things. That said, I didn't replace anything and things appear fine, but I didn't "test" them quite as thoroughly as you

Steel Rods

Where do you purchase the steel replacement rods?

Tankerpilot75 said:

Unfortunately yesterday while descending into my home field I discovered my flaps had been inadvertently extended 10 degrees at some point in flight. Whether it was done by my passenger (wife) or myself when we encountered some light to moderate turbulence over southern Kansas it doesn't matter, but the fact is they had been extended 10 degrees for a while and our speeds were up as high as 175 knots in the decent.

As soon as I noticed the problem I retracted the flaps and only extended them again in the pattern for landing. I did not feel or observe anything abnormal about the pattern or landing. Upon visual inspection after the flight I could not see any obvious damage. Does anyone have any recommendations what I should checkout prior to my next flight?

Lesson learned: when encountering significant chop pay close attention to where your hands land when changing radio frequencies or making other aircraft adjustments. Bouncing around is not only uncomfortable but also potentially harmful to good airmanship. Any yes, these RV's are well built sturdy airplanes!

Click to expand...

I would think you would have noticed a pitch trim change when the flaps were accidentally extended. Although 10 degrees is not a lot of extra lift/drag at pattern speeds, at cruise speeds it may need noticeable trim input.

Bayou Bert said:

Where do you purchase the steel replacement rods?

Click to expand...

Just buy a short length of 4130 steel tubing from Aircraft Spruce. Cut it to length, thread the ends, just as you would the aluminum tubes. Use the same diameter tube, and the same thread size. Its shown on the plans. Sorry I don't recall the actual dimensions.

plehrke said:

I would think you would have noticed a pitch trim change when the flaps were accidentally extended. Although 10 degrees is not a lot of extra lift/drag at pattern speeds, at cruise speeds it may need noticeable trim input.

Click to expand...

You would think that at the very least there would have been a pitch/trim difference but honestly at the time I think it happened (inadvertent flap extension) we were encountering some pretty strong turbulence and my hands were having a little difficulty trying to change radio frequencies. Things were bouncing pretty good and I was changing trim to keep up with airspeed changes for the autopilot.

Ten degree flaps are not a significant source of drag and in fact are really not that noticeable unless your looking for it. And of course, in cruise flight it's not something I expected to see. Only in the decent did I notice my Ray Allen indicator showing that my flaps were partially extended.

On my panel I have three Ray Allen indicators: flaps, aileron trim and elevator trim. In cruise flight I normally look at aileron and elevator trim indicators to help visualize what forces are impacting the aircraft. Sun glare often washes out the flap position indicator. Other than bouncing around, things seemed pretty normal.

I really appreciate everyone's comments and will check the flap rods and nuts for damage and/or malformation. When I bought the plane from the original builder I discovered he had not drilled the elevator tabs correctly and there was a "significant roll rate" at higher cruise air speeds. To compensate for this he had mis-rigged the aircraft so everything was incorrectly aligned (flaps and ailerons) so at pattern airspeed it flew somewhat normally. Identifying and fixing this was not inexpensive! However the aircraft now flies straight and true so I'm pretty sensitive to "aircraft feel."