Flap up limit stop switch
 

I recently bought one of the Infinity stick grips for my RV-8. It has an ON/OFF/(ON) switch for the flaps. The up position raises the flaps and stays on until you flip it to the center position.

I am concerned about accidentally hitting it and running the flap motor in the up direction for an extended length of time. The motor won't drive the flaps beyond the full up position (obviously) because the worm gear is designed to stop driving the flaps when they reach the full up position. But the motor would continue to run.

As probably everyone knows, the flap motors are a bit flaky (and expensive). I would like to have a flap up limit switch to cut power to the motor when the flaps are fully up. Can someone suggest a part number and a vendor for this type of part?

thanks,

bruce
N297NW

Hi Bruce

If you search for "microswitch" you will get a gazillion hits like this one, most of which will do what you want. You probably want a "NC" (normally closed) switch that opens as some part of the flap mechanism touches the little lever.

I've wondered if this isn't a good place for one of the little PTC current limiting devices. They are used AFAIK in automotive power windows to prevent the motors from pushing against an obstruction. Properly sized fuses will do this to, but this is an application prone to nuisance trips.

James Freeman

Flap switch
 

If you are *really* worried about it, you can spring for the $225 "FPS" flap positioning system, which will stop the motor when the flaps go up, and provide two stops going down before full flaps. You can get it at Van's.

I've got it, but probably would not install it a second time, after sitting in the airplane, and seeing how easy it is to just look out the window to see the flap position.

http://www.vansaircraft.com/cgi-bin/...me&product=fps

I'm not sure this applies to all models of flap motor, but on mine, when the motor is fully retracted (flaps up), it spins freely with almost no load. Not to say it still won't overheat...

I have the same set up you describe. I went to the local electronics shop and purchased two switches with activation arms about two inches long for about $7 each. They have three fast attach lugs for common, N/O and N/C.
I used one switch to shut off the flap motor at the fully retracted position and one to control the trim speed control. At the flap retract position the trim is slowed, but as soon as you bump the flaps down a tad the trim speeds up.
I can provide a picture or two and even some wiring diagrams if you are so inclined.
I copied this setup from a local RV guy (444TX) and it really works great!
Another setup, with the switches actually mounted to the flap motor shaft with adel clamps, switches as the switch arms contact the under side of the arm rest, looks promising. (Idea by Squaz)
Fell free to email me or respond here if you are interested.

This setup has served me well so far:

http://blog.bowenaero.com/?p=42

I'm at work right now and can't post my pictures, but if you send me an email direct I can email you my setup. The advantage of my setup is low parts count and cost, two and < $5 respectively. Go to your local electronics store or brouse Mouser's online catalog and ask for microswitches. There will be plenty of choices differing mosty in the lever configuration, straight, bent, short, long, with roller and without. Most are dual throw with a Normally Open and a Normally Closed position. My set up is similar to Larry Bowen's except my switches are mounted on the shaft and the lever's make contact with the underside of the armrest

Jerry
AKA Squaz

Here's an update on flap limit switches. After grinding the gears out of my flap motor assembly, I have installed a flap limit switch (similar to Larry's). It's a 15A Microswitch from DigiKey. It's pretty skookum... about 4 inches long with the lever.

Only one 18 AWG wire is required to run back to the main flap positioning switch at the panel, assuming you use the fuselage as a ground point for the Microswitch. See the wiring diagram below.

I chose to do it this way because I have another use for the switched signal (Vfe alarm when flaps extended). If you want to localize wiring to the flap housing, there is another way to do this with a switch and a power diode. If anyone's interested I can post.

Vern Little, 9A

Flap motor indicator light
 

An alternative is to wire an indicator light to your up drive power wire. I'm wiring an amber indicator (dimmable and testable) to mine. It will be at the top of my panel so I should see it quickly. This is much simpler than building a micro switch circuit. Downside is that I must still react whereas the micro switch will do the work for you.

Jekyll

I totally agree... I have one. Unfortunately, even with the lamp at the top of the panel, it's easy to miss. After grinding the gears on a $280 flap motor assembly, I'm not taking any more chances!

Vern

I've updated the previous drawing to add a switch part number. I've had a number of questions related to this, and the purpose of the zener diodes.

The diodes are there to protect the switches from inductive spikes caused by turning the flap motor off. I'm not totally certain that the motor is a bad offender, but they can't hurt.

If I were to do it again, I'd use a bidirectional Transzorb (18 or 20 volt).

Vern Little