[DanH]

I want to install a servo or linear actuator inside the engine cowling, thus temperature rating becomes important. In-cowl air temperatures can reach 230F. Average temperatures (if such a thing can be said to exist) are 180-200F.

The familiar Ray Allen actuators have a "sorta" temperature rating....the FAQ page suggests 180F as a max. The limiting factor appears to be the nylon gears. They are not cheap, but at $279 you have a complete system with position indication.

There are RC servos with enough torque to do the job, and Eric at Perihelion sells a nice little rotary position controller for them:

http://www.periheliondesign.com/moreproductsfiles/ServoController.pdf

Using that controller you don't really need a position indicator, as knob position tells you servo position. However, the datasheets for standard RC servos seem to suggest 140F (60C) as a max. That rating seems to apply to the metal gear choices too, so I assume internal electronics dictate the limit. I know very little detail about RC servos. Any thoughts?

There are nice linear actuators which can be controlled with the same Perihelion controller (or any other pulse-width controller). Here's an example, but again the temperature rating looks a little weak for the task:

http://www.firgelli.com/pdf/L12_datasheet.pdf

Can anyone suggest a small servo or actuator which might be suited for the engine compartment? Need an inch or less of travel at about 10 lbs max.

 

[rocketbob]

Why not use the ray allen servo but place it somewhere cool and use a simple push/pull cable to it. I have about 50 feet of teflon-lined cable, same stuff spruce uses to make throttle controls with. Let me know if you want a piece and I'll send it to you.

 

[868RM]

servo

Dan, I am using a firgelli to operate the oil cooler shutter . Fastened just above the plenum connected directly to the arm of the shutter. Only 30 hrs. but flew in some 95 degree oat and some high break in temps. It worked fine this morning @ 37 degrees. Ron

 

[DanH]

Why not use the ray allen servo but place it somewhere cool and use a simple push/pull cable to it.

Thanks Bob. May come to that, but the design is a variable cowl exit constructed as a unit....door and actuator on a single cowl belly panel. The beauty of an actuator is simply unplugging an electrical connector to drop the lower cowl.

Dan, I am using a firgelli to operate the oil cooler shutter .

Upper cowl, certainly a warm spot. Which model are you using Ron, the little L12? What are you using for a control?

 

[WingsOnWheels]

The L12 or new L6 actuators seem to be the best bet. If you want variable control you could go the servo route or use their indicator with a momentary toggle. If you are just diong open/close then the limit-switch version with a open/close toggle would be very easy.

 

[868RM]

firgelli

Dan, PQ12 controled with self centering toggle switch.100:1 ratio with potentiometer to send position to garmin G3 but have not wired position wires yet. Winter project. Ron

 

[DanH]

Dan, PQ12 controled with self centering toggle switch.100:1 ratio with potentiometer to send position to garmin G3 but have not wired position wires yet. Winter project. Ron

Appreciate the feedback Ron.

Need short travel and high force for this cowl door, so I'm going to try an L12-S 10mm 210:1.

Traded a note with Firgelli asking about the low max temperature rating. The response indicated it was based on concern for plastic motor parts and the PCB, if present. Thus the choice of an "S" (limit switch) model....don't think it has a PCB. I find it hard to imagine a problem with motor plastics....we'll see.

With no servo PCB, control is just a simple DPDT (like a flap switch), no position indicator.

FWIW, there does not appear be be any readily available actuator rated for 200F and more.

 

[Lars]

This is sort of off the wall, but given the relatively low force and travel requirement, why not cable actuation?

 

[RV7Guy]

Question

Dan, PQ12 controled with self centering toggle switch.100:1 ratio with potentiometer to send position to garmin G3 but have not wired position wires yet. Winter project. Ron

Hey Ron,

I was looking at the Firgelli for the same purpose. What are you using to lock the oil door in position.

I have an idea in mind and was wondering what you might be doing.

Thanks,

 

[868RM]

door

Darwin, I am using the "shutter " type mounted between baffle and oil cooler.It can be tweaked a bit to hold in any position (slight drag). I thought about a hinged door on back side with a scissor type linkage that went over center at full open but that only offered full open and closed or almost closed with good rigidity. I put a stop on the shutters so they are about 20% open in closed position. Seems to be working good so far. The ribbon wire needs to be supported very well. I tried to use one of these servos on my cabin ht. control but broke the ribbon wire even wrapped in shrink tube ( on engine side ).Went to a cable on cabin side until I get support sorted out.If you email me I will send you some pics. Thanks Ron

 

[Sparky]

...FWIW, there does not appear be be any readily available actuator rated for 200F and more.

Airliners use them in several applications. They're readily available if you've got $10,000

 

[DanH]

What are you using to lock the oil door in position.

Remember, a linear actuator has a backdrive force rating proportional to its gear ratio. They can be considered self-locking if you judge the static load correctly. The principle is demonstrated by the large linear actuator used in our flap systems. The flaps remain extended with no applied power because the air load is not high enough to backdrive the actuator.

The little Firgelli L12 will hold 43N, power off, when geared 50:1 for a fast stroke speed. A slow 210:1 gearing will hold 150N (33.75 lbs).

The ribbon wire needs to be supported very well.

Thanks, I was curious about that. The L12 seems to have 28AWG lead wires rather than the PQ12's ribbon.

.....given the relatively low force and travel requirement, why not cable actuation?

Well, the short L12 actuator only weighs 1oz.

It allows a modular approach with everything on the cowl exit panel.

It connects/disconnects to R&R the cowl by pulling a two prong plug.

No new holes in the firewall.

Only a single switch to add in the cockpit.

Wires are much easier to route than cables.

.....but the honest answer is it looks like a fun experiment

 

[RV8R999]

This is sort of off the wall, but given the relatively low force and travel requirement, why not cable actuation?

My first attempt at this project did in fact utilize cable actuation using the vans standard carb heat cable. Too much airload caused the cable to bend with the flap open. A larger diameter cable would work but as Dan mentions, wires are easier than cables and it was cool (no pun intended) to wire the actuator to the stick.

I've tried PWM servos in other projects but found the PWM controllers were susceptible to EMI from avionics causing jittery servo operation. This was 10 plus years ago so maybe better controllers are available.

 

[Lars]

(snipped)

.....but the honest answer is it looks like a fun experiment

So I surmised

I've spec'd lots of linear actuators for various industrial projects over the years. I searched through all the catalogs and sources I could find in a hurry here in my office, but I couldn't find anything better than the Firgelli product line. Temp ratings, when they are listed, are typically below 200? F for the ones I found. Likely because of the plastics, and possibly because of the grease. In any case I'd never heard of Firgelli before. Site bookmarked, those look very handy.

 

[rbibb]

I like the idea of mounting the actuator in whatever form behind the firewall and actuating the flap via cable like the trim cables used on our airplanes.

As for cowl removal - check out cowl flaps on a Mooney. Quick release fittings on actuator arms make fast work. Environmentals under the hood make an electrical actuator designed to work thereunder likely to cost much more than I perceive you have budgeted for the effort.

Richard Bibb

 

[RV8R999]

ray allen servo

Dan, as you know I have been using a standard RA servo for this application for over ~70 flight hours without problem.

THe servo is located 3" above the heat muff of the 4-1 exhaust (same system you are using). I wrapped the servo in reflective alum tape as a precaution.

I was also concerned about the spec temps being very close to what we measured in our cooling experiment but gave it a try anyway.

If the spec is nylon gear limited I suspect the servo would have failed by now. Although I'll admit I am not familiar with how the properties of nylon change due heat cycles near a limit?? Doesn't answer this question but learned more about nylon than I thought I ever would:
http://www.wellmaner.com/assets/files/design-guide.pdf
didn't realize nylons coefficient of linear thermal expansion is 3.75 times that of aluminum...who would of thunk it!

The only health check I could come up with was to measure time to reach full throw and to listen closely during operation (on the ground of course) for signs of binding or wear. So far the servo behaves as if it were new.

70 hours is certainly very low so the jury is still out.

 

[DanH]

Tiny little thing!

Firgelli L12, 10mm travel version, retracted:

 

[DanH]

Follow up.

Looks like I'm going to abandon the little Firgelli L12 for my cowl air exit door application. After 10~15 hours it has developed some freeplay (about 0.020") and I'm thinking it may be an indication of failure in the near future.

Please note my in-cowl temperatures run a bit higher than average. I've gone to great lengths to improve heat transfer and seal the cowl, all in the name of cooling drag reduction. This actuator has been operating between 160F and 200F, well above its spec sheet values. Can't blame the hardware.

 

[RVG8tor]

TCW Technologies

I saw this at Sun N Fun two years ago, I thought it would be handy if I ever add some sort of shutter to the oil cooler. They also make the Safety Trim System.

http://www.tcwtech.com/control_valve_servo_kit.htm

I don't know the specifications on Temp but they advertize use on Oil Cooler Shutters.

Cheers

 

[David Paule]

Funny - in the photo on the site's page, the actuator looks exactly like the Firgelli L12 that DanH is removing.

Dave

 

[David Paule]

....Looks like I'm going to abandon the little Firgelli L12 for my cowl air exit door application. After 10~15 hours it has developed some freeplay (about 0.020") and I'm thinking it may be an indication of failure in the near future.

Please note my in-cowl temperatures run a bit higher than average.....This actuator has been operating between 160F and 200F, well above its spec sheet values. Can't blame the hardware.

Dan, would a blast tube on the actuator fix the situation without significantly adversely affecting your results?

Dave

 

[DanH]

Dan, would a blast tube on the actuator fix the situation without significantly adversely affecting your results?

A blast tube does nothing after shutdown when under-cowl temperatures tend to be highest.

 

[Norman CYYJ]

There is no electronics in actual unit and I doubt that the heat would both the gears or motor or the linear pot.
I think you should get ahold of Tom Martin he did some experimenting with a cowl door.
Have fun.

 

[CharlieWaffles]

Dan, it's on the lower end of the temp range, but its the same servo you mentioned but includes a position sensitive position controller (http://tcwtech.com/control_valve_servo_kit.htm). You could easily adapt to your exit door.

 

[DanH]

The actuator offered by TCW is also a Firgelli L12. It may do fine in that application. Operating a duct butterfly or heater box flap would offer little stress.