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  #21  
Old 06-25-2019, 10:37 AM
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vlittle vlittle is offline
 
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Quote:
Originally Posted by crabandy View Post
I decided on the 100MM stroke, 64:1 gear ratio P16-S linear actuator from Actuonix. The P series actuators are more robust than the L series, I would like 125mm stroke but 100 should work.

https://www.actuonix.com/P16-S-Linea...or-p/p16-s.htm

I roughly calculated 31 sq in of oil door area, I currently have 1-2 inches of H2O of lower cowling pressure for most flight speeds. Calculating for 3 inches of H2O (.11psi) is 3.41 lbs of force holding the oil door closed.

I chose the 64:1 gearing not for the 90N (20ish lbs) lifting but the speed is slower, Iím also going to be operating it at an angle (still unknown) that will require more force. Iím hoping for the advertised longer life especially operating in 170-200+ *F. Most every micro servo I looked at was rated at 5 lbs and 50*C (122*F), the P series is still only rated for 50*C.
I have toured the factory and asked the question. At higher temperatures, the internal glue that holds these actuator assemblies together will soften. Forewarned is forearmed.

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  #22  
Old 06-25-2019, 10:40 PM
crabandy crabandy is offline
 
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Thanks for the reply Vern, I do appreciate it.

I spoke to an associate who seemed quite knowledgeable, he stated the plastic on the internals of the motor will get soft and begin to melt around 65-70 *C (149-158F) and at some point shoutout. They experimented with higher temp rated motors but their lifespan was 25% of the lower temp rated motors and have not produced a higher temp version. I havenít found any micro servos rated for hotter.

I may very well be throwing away my time and money just to replace the servo with a push/pull cable. But there seems to be some success out there with the 50*C rated servos out there. Just guessing the antisplat cowl flap servo is rated at 50*C, I wonder what the servo lifespan is on the current fleet? Pretty sure the lower exit where most are mounted are bathed in hotter air than the top of the cowl by the oil door.
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  #23  
Old 06-26-2019, 07:39 AM
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Quote:
Originally Posted by crabandy View Post
Pretty sure the lower exit where most are mounted are bathed in hotter air than the top of the cowl by the oil door.
Easily as hot after shutdown. I have an air temp probe up near the oil filter right now.

If the goal is more mass flow at approach speed and slower, and given the new door closes from the inside, can you actuate pneumatically? A spring holds it open, and increased dynamic pressure closes it?

Spitballing outside the box, how about pneumatically using manifold pressure? A spring holds the door shut. Low MP pulls it open.
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  #24  
Old 06-26-2019, 08:29 AM
crabandy crabandy is offline
 
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Easily as hot after shutdown. I have an air temp probe up near the oil filter right now.

If the goal is more mass flow at approach speed and slower, and given the new door closes from the inside, can you actuate pneumatically? A spring holds it open, and increased dynamic pressure closes it?

Spitballing outside the box, how about pneumatically using manifold pressure? A spring holds the door shut. Low MP pulls it open.
Hmmm, I mostly dismissed the spring hold open and pressure closing idea because:
-about .5Ē H2O difference for opening and closing based on speed/cowling pressures, with the 31 sq inch door about .6 lb so may be doable
-I donít have any higher altitude (13,000-19,000) cowling pressure data, thinking the lower cowling pressure would drop enough to open the door in cruise?

I would also like the door open on initial climb out from hot quick turns, so open with high manifold pressure too.

And Thanks for the spitballing Dan!
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  #25  
Old 06-26-2019, 08:32 AM
crabandy crabandy is offline
 
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Thermostatic Spring............close below 180 and open above 180?
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  #26  
Old 06-26-2019, 09:39 AM
crabandy crabandy is offline
 
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Air pressure, spring and micro electro magnet maybe.
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  #27  
Old 06-26-2019, 10:34 AM
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Originally Posted by crabandy View Post
I don’t have any higher altitude (13,000-19,000) cowling pressure data, thinking the lower cowling pressure would drop enough to open the door in cruise?
For 20K, q = 0.00339 x .5328 x KTAS^2

The second term, density ratio, is higher as altitude is decreased. Your cowl should be good for q*0.75 as an upper plenum pressure.

Quote:
I would also like the door open on initial climb out from hot quick turns, so open with high manifold pressure too.
Doing so would only require a control valve. Close valve before takeoff for an open door at high MP. The MP tap would have a restrictor for safety, just like your MP sensor line, with the valve as a backup. The advantage to such a system is the large available force; typical MP acting on a small pneumatic actuator is much higher than available dynamic pressure.

Just more spit

EDIT...ignore the 75% dnamic pressure. Lower cowl pressure is what we're dealing with here
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Last edited by DanH : 06-26-2019 at 01:20 PM.
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  #28  
Old 06-26-2019, 12:26 PM
Waiex-guy Waiex-guy is offline
 
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Default Behind the firewall?

Can your actuator mount behind the firewall with a short simple actuator arm?
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  #29  
Old 07-18-2019, 11:43 PM
crabandy crabandy is offline
 
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I finally got back after it today, I had a smidge bit of time since I can't do KOSH this year. Bent some .063 for the attach brackets. I had already ordered the servo before the other ideas started stirring, we'll see how long it lasts.



I spent most of my time visualizing different ways to connect both ends, this is what I ended up with. I used nutplates to attatch the servo bracket to the oil door so I can remove the screws and open the oil door if the servo fails. I glued/sanded a chunk of foam on the cowl to match the angle of the rear attach bracket of the servo then glassed over it. I then melted the foam with acetone, roughed up the surface and drilled a hole for a 3/16th bolt. I waxed the bolt and used a metal locknut on the inside of the fiberglass then filled the cavity with a liquidy epoxy flox mixture. I also used epoxy/flox/filler to build up the rear edge of the oil door to fit the hinge. I used tape covered Popsicle sticks as temporary dams.



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Last edited by crabandy : 07-18-2019 at 11:46 PM.
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  #30  
Old 07-24-2019, 12:04 AM
crabandy crabandy is offline
 
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Everything is installed and wrapped the servo with Fiberfrax and foil tape. Thankful I ran a couple extra twisted pairs of 22 awg through the firewall, it made wiring it up a breeze.



Closed and opened.





I had previously installed the cowl flap switch (Ray Allen RS-2) to cover up a poorly placed toggle switch for the auto pilot servos.



Attempting a video of it in action, Should have some flight test numbers tomorrow.

https://andycrabtree.smugmug.com/Oil...ap/i-JbZSPhb/A
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Last edited by crabandy : 07-24-2019 at 12:08 AM.
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