RAC Servo Question

[whee]

whee , did you go ahead with electric actuated cowl flaps ?

I did and they work great. My cowl flaps are located on the lower cowl cheeks, I used the servos I mentioned above and have been very happy.

[Nev]

What did you use to actuate the servos from the cockpit ? A switch or rotary potentiometer? Or did you find a way to automate them using the cowl temp ?

[whee]

What did you use to actuate the servos from the cockpit ? A switch or rotary potentiometer? Or did you find a way to automate them using the cowl temp ?

I used a momentary on-off-on toggle switch. It takes about 10 seconds to travel from full closed to full open. The servo has stop switches at each end of throw. I don’t need to know exactly where the flaps are, I just monitor the CHTs and adjust the flaps according.

[rodsmith]

I used a momentary on-off-on toggle switch. It takes about 10 seconds to travel from full closed to full open. The servo has stop switches at each end of throw. I don’t need to know exactly where the flaps are, I just monitor the CHTs and adjust the flaps according.

I haven't installed my actuators yet, but also bought a ray allen position sensor that will provide the cowl flap position indication on the EFIS. Seeing your post, I am sure it is overkill.

[Nev]

Thanks for the feedback guys.

I’m wondering if this can be automated. The fail mode should be fairly low risk because we can alter the CHT’s with mixture, speed, rate of climb etc as backup.

Anyone know if the actuators can be connected via Dynon (which has a CHT feed) to automatically open and close the cowl flaps ? Or via a standalone module ?

[Nev]

I’ve just written to Dynon. I’m wondering if it’s possible to use a trim output from the Dynon to automate the cowl flaps, and configure it along the lines of :

If CHT >400f then trim = full left (open)
If CHT <350f then trim = full right (closed)

Perhaps even the flaps output could be used, they use airspeed inputs to prevent flap overspeeds, so I wonder if it can use CHT input. Most modern RC controllers for model aircraft can do it - if you can think of it, then you can program it.

Something like that. Any input is greatly appreciated. If it can be automated without too much hassle then I’ll do it.

[Battson]

In case it helps, I found cowl flaps to be a binary thing - either you are running too hot, or you aren't.
So operationally, either the flaps are open, or they are closed.
High summer - open at all times. All other seasons - as required, normally closed in cruise and open for climb and landing.

I would not want to fly around opening and closing the flaps partially, to tune the CHTs to the nearest couple of degrees.

I would not want to automate it either. You know you are preparing to takeoff. You know you are going to be landing in 5 minutes. The computer is not going to know that, automation would not help most of the time. It's better to manage ahead of the curve, rather than responding once the problem has already manifested.

[JimParker256]

Yup - keep is simple and light. Whee's simple on/off switch, wiring, and small actuators are both light and simple, but a cable might be about the same weight, so that's a wash to me - personal preference might sway you one way or the other.

Like Batson, I found that in my turbo-normalized Commander 114, I either needed the cowl flaps wide open, or they weren't needed at all. (And that was a non-intercooled turbo-normalizer, so a LOT more heat being managed.)

But that's the great thing about "Experimental"... Some people just like to tinker with things like temp-sensing cowl flap controllers. Others don't. As the builder, YOU get to decide how to build YOUR airplane.

[rodsmith]

My initial intent was manual actuation of the cowl flaps, even bought the cable. Then realized there was no way to make it work due to other equipment on the firewall.

[Bcone1381]

I'm curious how far your CHT's move with Cowl Flap movement from Open to closed, and if you see any change in airspeed.

[JimParker256]

Can't speak to the Bearhawk with cowl flaps, but the Commander 114 lost a full 10 knots in cruise flight if the cowl flaps were left open. It also affects fuel consumption... LOL

And, on a totally unrelated topic - remember that checklists are your friends, and conversation with your co-pilot during level-off checks are NOT a good ideal...

[Battson]

About 15 degrees Celsius, 27 Fahrenheit. No measurable speed loss whatsoever.. I was told that in a Cessna 172 retract, cowl flaps are good for about 7 knots. That's probably a horsepower and airframe + cooling drag consideration

[whee]

I basically have the same opinion as Battson though I do have my flaps partially open on occasion. My cowl exit in the tunnel area is tight and has a muffler talking up about half of it. I planned it this way since I fly frequently in the winter and wanted to be sure I could get my engine temps up. In the heat of summer I have to leave the flaps partially open unless I’m cruising has higher altitudes. I don’t constantly adjust my cow flaps to achieve a certain CHT, they are mostly a set and forget item when in cruise. Manual control allows me to proactively managed my ego every temps rather than reactively. For example, I close my flaps when I start a decent to land. This helps the CHTs cool slower.

I haven’t been able to note a speed loss when my cowl flaps are open. Going from full closed to full open cools my CHTs by about 20F.