Linear actuators in engine compartment

[Nev]

I'm getting ready to install cowl flaps on the side of my engine cowlings to enable a tighter temperature control band of CHT. They're driven by 12v linear actuators. The wiring and plugs on them are fairly small, and I'm wondering how it'll hold up to the heat and vibration, obviously not wanting to introduce a weak point. The failure mode is fairly benign - it's very close to how I operate already. The plan is to eventually add a linear actuator to the oil cooler butterfly valve and have them all under one control if feasible.

Has anyone else used linear actuators in the engine compartment that can give me feedback on their experience ?

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[dramsey]

Nev, I helped a neighbor on an RV-10 project and he has an almost identical setup. Here are the ones he used. https://antisplataero.com/products/ez-cool-cowl-flap. They have successfully been used on a bunch of RV’s. My neighbor has only flown off his 40 hrs and is in paint now, but he had no issues with his linear actuators.

[Nev]

Thanks Dennis !

[TrueAirSpeed]

Nev, I have the Anti-Splat cowl flaps on my four place Bearhawk and had your same concerns about the wiring and tiny connectors being damaged by heat and exposure in the engine compartment. To prevent the connectors from coming “unplugged “ after connecting the two ends, I cinched them together with small zip ties. For wire protection I covered them with tubing and secure them to a nearby screw with an Adel Clamp. After 120 hours they seem safe and are functioning as advertised.

Terry

[Nev]

Awesome, thanks Terry.

[svyolo]

I would just want the connectors easy to get to for cowl removal.

[Nev]

I would just want the connectors easy to get to for cowl removal.

Exactly what I'm thinking too. They'll probably live just under the cowl doors on the firewall,

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[gregc]

Why not just chop those crappy connectors off (and as much of the low quality wire as possible) and splice on decent wire and a good grade connector? Yes, the splice will be a weak point but likely better overall than the stock setup.

[kestrel]

That was my first thought when I saw the picture of the connector.

[AKKen07]

Can you elaborate on the better connectors etc? I’m curious what you’d use. Thanks! I have the anti solar ones but haven’t installed yet.

[David Swartzendruber]

If I was changing the connector, my choice would likely be either a Deutsch DTM or Weatherpack.

[rodsmith]

My cowl flap setup is very similar. I set mine up so that I disconnect the actuator at the cowl flap end to remove the cowling, that way the wiring doesn't need to be removed. I cut the connector and most of the wire off. My favorite splice method is to crimp on DSUB pins and sockets and cover with heat shrink.

[gregc]

Assuming the existing wire is at least 22AWG, I would attach a 2 pin Deutsch DTM connector to the existing wire. They make a clip for the connector that could be held by one of the cowl flap mechanism screws. This would allow for removal just by unplugging it.

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[Nev]

They look the biz !

[Nev]

I've ordered the Deutsch crimping tool, pins and plugs. Thanks for the suggestion.

[Battson]

For your consideration, I would suggest applying a generous amount of anti-chafe tape to the metal-to-metal parts in contact (overlapping) around the edge of the cowl flap. Based on what happened with our cowl flaps, I guess things will end up loosening fairly quickly and moving around / vibrating about 1/8". The hinges don't stay tight for long, and this gets worse as they get older. Although it is possible the more robust actuator mechanisim will dampen out that vibration / chafing.

I had a close look at many cowl flaps before re-building mine (version 2). Looking at Cessna aircraft, their cowl flaps all wobble around a bit (172, 182, 185, 206). But most are actuated with a single pushrod, rather than a double-arm + actuator. They are also much more heavily built. I also noticed that many certified designs have the flaps totally free floating with generous clearances around the flaps i.e. no way to make contact with other cowl parts, except the hinge and actuator.

My first set of cowl flaps had tight clearances, and constantly bled "black smoke" (Aluminium oxide) down the cowl exterior. It took me a while to realise that I didn't need tight-fitting cowl flaps. After all, there is a huge hole at the cowl exit right by the flaps, so there's really no need for tight clearances. Air is meant to escape. I considerably increased the clearances on my 'version 2' cowl flaps, along with making them much larger. The increased clearances reduced the amount of chafing and black smoke quite a lot, until the hinges started to wear out. The hinges liberate a lot of black smoke now they have run around 600 flight hours, and have worn out considerably over time. The cowl flap hinges will probably need to be changed before they've run 1,000 hours in service.

[Nev]

Thanks Jon, good to know. I'll get the anti-chafe tape onto the job.

[Daniel]

Great tips! I will keep this in mind as I build my version 1.

[whee]

My actuators have been fine. I try to remember to open them before shutting down in attempt to reduce the chance of them getting heat damaged but I pretty regularly forget to.

Nev, You’re really going to like the cowl flaps!

[Nev]

My actuators have been fine. I try to remember to open them before shutting down in attempt to reduce the chance of them getting heat damaged but I pretty regularly forget to.

Nev, You’re really going to like the cowl flaps!

Hey Whee, how/where did you install yours? Mine are in and running. Mechanically they're fine, but unfortunately I'm seeing very little effect on the CHT's. They do have a small effect on the oil temperature due to their location on the cowl cheeks ! I did a couple of flights with the manometer to double check, and at best there might be a 0.5" change in pressure differential, but only if I really try hard to see it. I'm wondering if it's due to the position of them interfering with the airflow through the lower outlet.

I'm getting a first class lesson the laws of unintended consequences, due to trying fix problems that don't exist

[kestrel]

I've played a bit with exit lips and winterization plates to effect cooling. None of it had much effect. I then did some pressure measurements. If my measurements are correct, by far the greatest drop in pressure in my aircraft is the air getting through the front cooling inlets to the upper high pressure side of the engine. Since I haven't done anything to effect that "choke point", I didn't cause much effect on cooling.

[kestrel]

Nev, I have the Anti-Splat cowl flaps on my four place Bearhawk and had your same concerns about the wiring and tiny connectors being damaged by heat and exposure in the engine compartment. To prevent the connectors from coming “unplugged “ after connecting the two ends, I cinched them together with small zip ties. For wire protection I covered them with tubing and secure them to a nearby screw with an Adel Clamp. After 120 hours they seem safe and are functioning as advertised.

Terry

Terry, can you comment on how effect the Anti-Splat cowl flaps are? Based on comments from Battson and Nev, I wonder if the Anti-Splat ones are large enough? ...or perhaps based on my data, the front needs to be opened up a bit before they are effective?

[TrueAirSpeed]

I have never experienced more than a 5 degree cooling difference with the Anti-splat cowl flaps. And haven't "broken the code" on CHT cooling either. Number 1, 3 and 4 run the coolest. Number 1 sometimes runs 100 degrees cooler than number 2 (that's a puzzle). With numbers 2, 5 and 6 being the warmest.

[Battson]

My #1 and #2 CHT spread is about 100*F too.

[Nev]

Bobby Stokes did some excellent cooling system testing and posted his results HERE. He tested louvres on the side of the cowls, large exit cooling lips, cowl flaps etc. I also did my own testing with a manometer a year ago, and most results were similar to Bobby's, with some small variations. Whereas Bobby found that his side cowl louvres were slightly detrimental to cowl pressure differential, I found a small increase with the louvre design I was using. I also settled on a fairly large exit air cooling lip underneath, and have now flown two summers with it. Changing from my original small exit cooling lip to the large one made a measurable improvement to CHT's throughout.

I had also tested a fixed open cowl flap on one side cowl and got good results with that. Unfortunately I'm not seeing the same numbers with the electric cowl flap in the same place. Possible variations are that although the fixed flap was smaller, it was rigid and set at a fairly steep angle. It also had no obstructions to airflow, whereas the electric cowl flap has he mechanism sitting in the airflow. I'm also thinking that it requires quite a change in air direction to exit the side louvres and may actually be introducing turbulence into the cowling at that point.

The photos below show the original smaller Orange fixed cowl flap, and the larger black cowl flap that I settled on during testing. They take one minute to change over and I originally planned to change them between summer and winter, but ended up leaving the larger one on year-round with good results.

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[Richard E]

Nev,
We went through the same investigations on ZK-RJE. Eventually we decided to benefit from all the research that went into the Cessna 206 and fitted louvres in the same locations as them. No problems since. The cowl flaps underneath don't seem to make much of a difference.
Regarding cooling the engine after use, I think that the most effective way is to pop the oil dip stick cover as in the pic.20230423_171337.jpg

[Nev]

Thanks for the feedback Richard !