Simple Flap control (only) NEEDED
The fancy flap control systems are great, expensive but great. They add complexity, weight and cost. I don't think they are necessary. True the flap motor will run if you have power to it, even at full up or down. If you have a locking toggle switch for flap control you will have to manually select ?off? or the motor will continue to run. There is a simple solution.
Precision Flap control-It's like measuring with a micrometer and cutting with an Ax
The RV's have simple hinged flaps that add little lift. The real use is for drag in the full down position. The change in stall speed is about 2mph between flap-up and down. To make it complicated with multi flap position control is over-kill. You need 3 positions, UP, 1/2 and DOWN. Intermediate positions during retraction is not needed, because you always can (should) retract the flaps in one motion.**
Simple set up - Worked for me
There is a way to make a simple system that will prevent the flap motor running after reaching full up or down without pilot action and still have simple trouble-free operations. As far as flap indicators, you can look out the window and see the flap position. A flap motor "running" LED would be an OK addition but not necessary. If the flaps are moving the motor is turning.
You only need one intermediate position, about ? travel. The exact ? flap angle is not critical. I used one panel mounted DPDT switch, on-off-(on), where the normal center position is off, UP locks in the on position and DOWN is a momentary position, that returns to center-off when released. You also need one DPST micro switch for a UP limit switch.
This is how it works. The UP position on the flap selector stays locked and DOWN is a momentary contact, which requires you to hold it to operate the motor. When extending the flaps, release the switch and the flap motor stops. Since the UP position locks on, the motor would run until the pilot centers the switch to the off position. However that is where the limit switch comes in. With the flap switched locked to UP, the flap motor runs until the UP limit switch is reached and shuts the motor off. This works very well because this is the way you really operate the flaps.
How DO you really use the Flaps in a RV?
In pattern/ down-wind: Slow to 100mph or less
Abeam: approx ? flap
Base/Final: flaps full down
Land: retract flaps
Go around: Add power, pitch for climb and retract flaps (all at once)**
**After landing you bring the flaps full up. Using the "lock" UP position, the flaps retract without the need to hold the switch. When the flap hits the UP limit switch, the flap motor stops running. Having to hold the switch would be a pain after landing, since you have one hand holding the stick back and the other switching to ground or leaning the engine on roll out and taxi. As for GO AROUNDS, you can retract the flaps all at once. The flap motor is slow anyway. I know, your flight instructor told you not to retract the flaps all at once. There is a big difference in a 150-180 HP RV with simple hinged flaps and a Cessna 150 with Barn Door flaps and 90HP. RV's have excess power and flaps only change the stall speed 2mph. At full power and full flaps a RV will climb very well. Retracting the flaps in one motion will not cause a problem. The fact is a C-150 and it?s 40 degree slotted flaps do make a big difference in lift, so bringing them up too fast can cause sink.
In the RV you add go around power and bring the flaps up all at once and climb with no problem. As a mater of fact, you better bring them up fast as you can exceed the 100mph flap limit quickly with high power. Intermediate stops on retraction is not needed.
Extending the flaps only requires a simple push of the flap switch and hold for a slow count of 3-4. Let the switch go and the switch returns to the off position, motor stops. This is not a big burden to the pilot. Once you use it, you don't think about it. You can "feel" the flaps are in the correct 1/2 or full down position. Remember about ? is good enough, 15-25 degree.
Precision control of the ? flap position is not needed, but once you get good at holding the switch for set time you will bee very close. The only place you need exact position is @ full-up or down, which is set by the installation. When you are ready for full flaps you push and hold the switch for another slow count.
The Micro Switch
The UP micro limit switch is a simple switch with a threaded plunger or a way to make travel adjustments. Heavy duty micro switches have a seperate metal bracket/frame and use a seperate spring loaded plunger to activate the micro switch itself. This protects the switch itself and provides better control and adjustment. The switch is wired in line with the positive circuit for flaps UP. The motor of course works with two wires; switching polarity causes the motor to run in forward or reverse. When the flaps hit the UP position, the micro switch opens the circuit to the positive current and grounds the motor?s "up wire."
Auto systems:
http://www.vansaircraft.com/cgi-bin...12815336-336-39&browse=electrical&product=fps
http://www.aircraftextras.com/FPS-Plus.htm
Ted French (home grown):
http://www3.telus.net/elfrench/rv6 no4.html
The auto flap position systems are very nice. You can even make your own. Ted French has a design on his web site. It uses micro switches, relays and diodes in a clever circuit to achieve single throw multi position flap control.
Some of these systems have provisions to automatically adjust trim to account for flaps or change the rate the trim motor travels for different aircraft speeds. I never found trim to be an issue in my opinion. RV flaps don't produce the pitching moments you get from a high wing Cessna.
Another option you can add is changing the rate the trim motor operates at for approach and cruise. Again, it is not necessary in my opinion. Nice to have but I never found it to be a problem. Since my old RV-4 required full up trim on approach and landing when solo, I would slow down and configure, hold the up trim until the full up trim LED came on. 1 or 2 trim changes in the pattern is not a burden. I did not find trim too slow or fast. Pitch control pressures (which are light) are never an issue. For high speed trim adjustments, I found a short jab at the trim switch would get it dialed in just fine and not too sensitive, so trim motor speed was never an issue either.
Bottom line, more "systems?, wires, connection, interconnections and electronics will increase the chance of it not working someday. Also trouble shooting the wiring or switches can be a pain. My flap control was very reliable, simple and had no problems in 6 years. More connections produce more possible problems.
Cheers George
