Flap actuator assembly - RV-7A

Ray Williams · #1 03-20-2011, 05:05 AM

Hi all: I've been working on Dwg 33 Electric Flap Installation for some time. Everything is prepared so today I did a complete test installation to check all is ok. Looking good!

I haven't yet attached the drive motor to a 12v source. However, before I connected the actuator it was clear that the weldment requires much more manual effort to move up and down than I would have expected. Obviously there is substantial friction coming from the flap bearing blocks. Is this normal? Maybe I should have buffed the outboard ends and F-680 centre of the weldment?

Any thoughts will be appreciated.

Best wishes

Walt · #2 03-20-2011, 07:41 AM

I opened up my blocks using a sanding drum until the mechanism moved with a "reasonable" amount of force (slight drag). Having excess friction in the mechanism will just make the motor work harder which translates to shorter motor life.

RV7ator · #3 03-20-2011, 09:21 AM

The holes are line-to-line tight, leaving no tolerance for misalignment. With everything straight, five or so pounds of force at the actuating end should cause movement. Check for:

Drilled holes in mounting blocks not normal to the surface.

Weld fillet rubbing on the edge of the holes (I chamfer the opening slightly).

Too tight clamping of the center block.

Center block tipped

Paint on any of the bearing surfaces.

John Siebold

bruceh · #4 03-20-2011, 11:00 AM

The middle block, which is split, should have a thin washer put between the top and bottom pieces when they are bolted down to relieve some of the clamping pressure. The plastic holes on the end blocks will loosen up over time. I used one of those small rectangular 9V batteries to move my motor up and down. It goes slow, but has plenty of energy to drive the motor.

macrafic · #5 03-20-2011, 11:17 AM

Quote:

Originally Posted by VETE76

I would call vans! there might be a reason for the tight fit, maybe looseness leads to flutter? that motor is strong. the pressure from 100mph+ when you extend them for landing has got to be much greater that the plastic bearings put on them.I would think the looser they are the more unwanted movement is generated in the bearing area, probably not good over time. before i would sand it I would call vans. fwiw

I did communicate with Van's about this. They essentially said that they get a lot of calls about this and, to net it out, the flap motor will not even notice the drag. Build on. I just did this myself and the motor does NOT seem to notice.

So, I'm building on. I'm actually more concerned about the ongoing maintenance that seems to be necessary on the flap motor (cleaning the brushes). Besides the traffic on the forum about this, I talked to a friend yesterday who just completed 50 hours in his plane, and has had to clean the brushes twice. There is a current of belief that the unit is over-lubricated and, after a couple of cleanings, no more grease finds its way to the brushes. It will be a while before I can test this theory.

Walt · #6 03-20-2011, 11:42 AM

Just as a point of reference, maybe I'm just lucky but I've never had any problem with the flap motor in 6 years and almost 1200 hrs of service in one of the hottest climates in the country.

My thoughts are if the motor must work harder to overcome mechanism friction it will get hotter causing the grease to thin out which will then migrate past the seals and onto the armature resulting in "motor failure".

The Blocks are basically inexpensive "bearings", I've never seen flight controls that required excessive friction in the bearings to prevent surface movement or flutter in flight. The flight contol mechanisms/linkages/actuators should not allow flight controls to have any free play in them.

Just my 2c for whatever that's worth