Cowl Flaps really work

[dwilson]

My RV10 is a wonderful airplane, but I have always had to moderate my climb in order to keep the CHT's below 400 deg. (My personal goal, not the Lycoming recommendations.)

No longer is this a problem thanks to Allan Nemo's EZ Cool Cowl Flap system! Now I can climb with a full load from sea level to 5000 ft at 1000 ft./min. on a 98 deg. day and the CHTs never break 380 deg.

Here is a short synopsis of the instillation:

1) Positioning and making the hole in the cowl


I decided to put the flap on the side of the cowl as opposed to the bottom so as to avoid interference with the exhaust stack etc...

The hole was cut with a vibrating "cast saw" tool that could be precisely positioned and controlled. The hole was cut a little small and then enlarged with a file/rasp to the perfect size.


(More to come later)

[Kyle Boatright]

Duane,

Did you have louvers installed prior to the cowl flap, or were you <only> using the stock air exit?

[dwilson]

My RV10 cowl is stock with louvers and a standard sized exit.

[dwilson]

When the cowl flap assembly was inserted into the opening the flap stuck out into the breeze a little bit, so a shim of 0.040 aluminum was fashioned to place between the flap frame and the inner wall of the cowl.

You can see the trial pieces that I used in this picture. They are the blue plastic covered bits.

[dwilson]

The cowl wall is a honeycomb composite and a little weak, in my opinion, to support the screw heads that I used to hold the flap assembly in place.

So I took a flat bladed screw driver and cleaned out the honey comb material between the thin inner and outer walls around the mounting hole and around the edge of the opening.
I put tape around the opening both inside and out, mixed up some West Marine resin with flox and cab-o-sil put it in a syringe and injected into the space between the inner and outer walls. I worked it in with popsicle sticks, taped the cowl flap assembly and inserted it into the opening. Then I put the screws gently in place and let it begin to cure.
After an hour or so I backed the screws out a little bit so that they would not be bonded in place.

(Sorry, forgot to take a picture of this step)

[dwilson]

#6 Nut plates were then installed in the cowl flap frame. The nut plates captured the 0.040 shims that had been created.

The opening was sanded to smooth out the injected fiberglass, and the flap was mounted with #6 counter sunk screws.



Forgive the poor picture, but you can see the nut plate here.

[dwilson]

It is important to follow the wiring diagram that Allan provides in the kit. I did not pay close attention at first and the flap did not work properly.

Here is a picture of the switch wired.


And here is a picture of the switch and it's indicator light installed in the panel. (Ignore the "Trim" label above the light, it belongs to the switch above.)

[dwilson]

What a joy it is to be able to take off on a hot day with a full load and quickly climb up to cool altitudes without cooking the cylinder heads!!!

The kit is well made and simple and the instructions are adequate.

I would recommend this modification to anyone who has any issue with cylinder head temps.

[airguy]

It is definitely a valuable add-on for some aircraft, it made a huge difference for my 9A for a max-performance long climb in west Texas summer temps.

[rightrudder]

That is a slick upgrade...thanks for posting the how-to and pics. My CHTs are a little hotter than I'd like on climb-out when ambient temp is 100 F or above. Maybe Santa will bring me one for Christmas, and I can install it during the annual.