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Tunnel Cooling Flap - electric

KeithB

Well Known Member
In another thread on EXP-119 equipped 14s, a question was asked about converting the Tunnel Cooling Flap to electric operation. I mentioned in another thread that I had done this and got multiple PMs inquiring, so I am posting for the general audience.

My engine is an IO-390 (Thunderbolt build) - not an EXP 119. However, my engine is equipped with a Vetterman 2 x 2-in-1 trombone exhaust that does not use the tunnel. This picture shows the exhaust before installation of the Tunnel Cooling Flap.
IMG_1840.jpg

This results in even more excess cooling capacity than a standard build and enables installation of the Tunnel Cooling Flap designed for the EXP-119. (The Tunnel Cooling Flap goes by several names, even within Van's instructions - "Exit Door", Tunnel Cowl Flap, Tunnel Cooling Flap).

My original motivation was the quest for speed or efficiency, but I actually needed the increased engine temperatures to deal with a sticking exhaust valve (discussed in another thread). Ultimately, I believe I gained 2 or 3 knots in mid altitude cruise (9-10k). My CHTs are about 30 deg F higher and oil temps about 10 degrees higher in cruise with the flap closed. These results are consistent with what some others have also reported.

Most of the installation was straightforward, but adding the push-pull activation cable was going to require a new firewall penetration. This prompted me to look into electric operation. I selected an actuator made by Progressive Automations - their model PA-07. I wanted the entire cover, flap and mechanism to be a single unit with only electrical connections to the plane to facilitate removal, so I redesigned the activation to the aft end of the flap using a geometry similar to that used by AntiSplat's cowl flaps. It took some planning with cutouts, and a little bit of iteration to get the desired range of movement. I have a momentary 2-way rocker switch in the cockpit (similar to one used by many for electric trim). I opted not to have an indicator - up to down or reverse takes about 4 seconds and the actuator auto-stops at the limits.

Here are shots of the mechanism on the bench:
IMG_8762.jpg
IMG_8763.jpg

Builders planning on the EXP-119 engine might consider this modification.
 
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