Flap motor circuit breaker "pops" intermittently

[cleve_thompson]

I have a RV9A with approximately 175 hours on the air frame and I have found on a few occasions lately that the 5 amp circuit breaker has opened after the flaps a fully lowered down into full flaps positioned. The flaps will go up when the breaker is reset.
I have a "flap positioning switch" as ordered from Van's. The breaker has never popped when lowering to 10 degrees or 20 degrees nor on raising the flaps up.
The flaps work fine on the ground with the flaps positions being raised or lowered as expected. The clutch also works when the switch is held down. Any ideas?
Cleve

[shuttle]

I've read that others have upped the CB/fuse rating to 7.5 Amps. That's what I intend using.

When airborne and dropping the flaps, the motor has to counter the airflow drag on the flaps.
As the flap angle increases the drag increases so the motor has to work increasingly harder, pulling more current. Drag will vary with airspeed so motor workload/current will also vary with airspeed. The higher your airspeed the higher the likelyhood of the 5 Amp CB popping.

When raising the flaps the drag is assisting the motor so less electrical energy needed and thus no CB pop.

[gmpaul]

I have the same problem with popping fuses, so I started using 7.5 amps. This did help but not enough. Mine seems to pop around 80 kts. Do you think that some motors are jest weaker than others and with the 9 large flaps pushes them over the line?

G.P.
RV-9

[shuttle]

I don't know about 'weaker' motors. I'm sure the manufacturer's QA process means they're all pretty much the same when new. But flap motor performance will no doubt slowly deteriorate with age, storage environment, use and maintenance/service regime.

Not that familiar with the -9 wing/flaps but if the flap bottom surface area presented to the airflow is bigger than the -6, -7, -8 then, at the same airspeed, air density and flap angle of incidence then the drag will be greater and hence the strain on the flap motor when driving the flaps down will also be greater.

[N941WR]

Funny but for some reason I used 18 AWG wire and a 10 amp breaker and haven't had a single problem.

In checking the sample in the front of my builder's manual, they used 18 AWG wire and a 10 amp breaker.

[MCA]

Our testing shows that on a -7, the flap motor draws just under an amp on the ground, but almost 5 amps in the air when extending under load.

On my first flight, the 5A flap breaker popped but has not done so since (or with the VP system).

[N941WR]

Originally Posted by MCA

Our testing shows that on a -7, the flap motor draws just under an amp on the ground, but almost 5 amps in the air when extending under load.

On my first flight, the 5A flap breaker popped but has not done so since (or with the VP system).

And I suspect that with the longer flaps on the -9, it draws even more power.

[flickroll]

I control my flaps with a TCW Technologies Intelligent Flap Controller. It and the flap motor are protected by a 3 amp breaker. I have never had the circuit breaker pop, and I routinely dump half flaps or full flaps at the top of the white arc, and will put in 10 degrees when operating below Va. Based on a lot of reading on flap motor circuits prior to this installation I was worried the 3 amp breaker might be too small, but Bob Newman at TCW Tech assured me it would be fine. After 50 hours of trouble free flying I'd say he was right!

[cleve_thompson]

I appreciate the very informative information! I have ordered a 7.5 amp circuit breaker from Spruce and will change it out for the 5 amp one. I think that I already have 18 gauge wiring. I hope this will alleviate the problem!
I do think that the size of the flaps on the 9 make a difference in the strain on the motor.
Joe Blank at Van's said that I should also check the resistance on the circuit to r/o bad connectors etc.
I hope that I will not burn out the motor; although I seem to remember that the breaker only protects the wiring not the motor.

[647jc]

I control my flaps with a TCW Technologies Intelligent Flap Controller. It and the flap motor are protected by a 3 amp breaker.

Jim,

I visited the TCW Web site regarding their Flap Controller and there appears to be an ambiguity between their product description wiring diagram and their installation wiring diagram. The description diagram shows a 3 amp fuse or CB but their installation diagram and document clearly shows a 5 amp fuse or CB. I would really be surprised if a 3 amp fuse or CB would handle the current draw of MOST RV installations, especially an RV9 with the very large flaps.