What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

VANS FPS intermittent problem

MrNomad

Well Known Member
I've enjoyed the Vans FPS flap positioning system on my 9A for 13 years and it worked fine until this past week. During my December conditional inspection, the system went up and down properly, however, flying back from CGZ the other day, when I requested 10 degrees, it barely moved. A few more attempts (toggle down) and I was able to get 10, then 20 and so on.

Once on the ground, they retracted properly. When I inspected it today, on the ground, covers off, it worked properly up and down. I tested it 10 times and it never failed.

Is it possible that the system needs to be completely disassembled, remove old lube, add new lube, and reassembled? Did I experience wind resistance added to internal friction which prevented the flaps from operating in the air? I am certain my airspeed was < 10 degree flap limit.

Comments welcome. Suggested lube type welcome too.
 
Flap Motor

Van's Flap Motor is known to have grease contamination issues. Please search forums. I installed an alternate flap system from PH Aviation during my new build.
 
I've enjoyed the Vans FPS flap positioning system on my 9A for 13 years and it worked fine until this past week. During my December conditional inspection, the system went up and down properly, however, flying back from CGZ the other day, when I requested 10 degrees, it barely moved. A few more attempts (toggle down) and I was able to get 10, then 20 and so on.

Once on the ground, they retracted properly. When I inspected it today, on the ground, covers off, it worked properly up and down. I tested it 10 times and it never failed.

Is it possible that the system needs to be completely disassembled, remove old lube, add new lube, and reassembled? Did I experience wind resistance added to internal friction which prevented the flaps from operating in the air? I am certain my airspeed was < 10 degree flap limit.

Comments welcome. Suggested lube type welcome too.

Did the motor try to spin when you moved the flap or the motor controller didn't move at all. On the ground if you put some weight on the flap to simulate the air load, do you see the same behavior as in flight?
 
Determine if this is a flap motor issue, or a FPS issue.

The FPS can get “twisted” just enough so the micro switches to not activate on the notched rod. If this happens, first verify you have the FPS properly aligned and the clamp tight on the flap motor tube. This should fix most issue. If the problem is still there the fix is to add a washer on the flap rod journal bearing (as in the bolt that connects the journal bearing to the flap bracket). You will use a bigger washer than the bolt (the washer goes a little over the ball joint) so that you limit how much the journal bearing can rotate in the bracket.

Carl
 
Motor did not move

Did the motor try to spin when you moved the flap or the motor controller didn't move at all. On the ground if you put some weight on the flap to simulate the air load, do you see the same behavior as in flight?

I believe the motor moved very little during the flight which suggests the brushes may be worn or contaminated. During today's ground inspection, I did NOT simulate a load (I should have). Given that I have almost 900 hours on the airframe, I think tomorrow's project is to disconnect the flaps & check for free movement, disconnect the motor and free the assembly so I can inspect everything (including the bearing blocks) for free movement. I recall disassembling a 68 Corvette rear axle to find the lubricant had hardened and looked like candle wax. The bearings were still good and lasted many more years after the wax was removed and bearing grease installed.

Everything in the flap assembly was secure and aligned properly. On the ground, it worked perfectly and sounded OK.

In the Vans article entitled FLAKY FLAP MOTORS, they detail the procedure to disassemble but don't specify the type of grease to be used on the gears.

Grease suggestions welcome and thx for the replies.
 
Last edited:
Results!

After careful disassembly of the flap motor according to Van's procedure, I found a considerable amount of grease on the armature, brushes and commutator. The brushes were in good condition and I so I did not replace them. Instead of using wire to hold the brushes in place for reassembly, I held them in place with an ice pick and my wife tied sewing thread around them & the horseshoe. Once the horseshoe was inserted, I cut the thread with a sharp razor releasing the spring tension. In a subsequent test flight, they worked great so once again I would like to thank everyone for their posts and personally thank Doug for keeping this website alive.

I wish everyone could collaborate like this community.
 
Back
Top