Using cowl flaps

[Simicro]

Hi,

I must confess that a couple of years ago, it happened to me to do some fancy flying. For example I did not care about cowl flaps.
Today I care. The Bonanza deserves it. So I made various readings on the web and abstracted this:

What
Cowl flaps are small doors located in the bottom of the engine cowling that allow for greater cylinder cooling during takeoff and climb.

Where
Cowl flaps are found on high-performance aircrafts where larger engines with more horsepower generate lots of heat.

When
Cowl flaps are used during the take off and climb phases. Their use comes at the cost of increasing drag. Cowl flaps should be closed during cruise, descent, and landing.

How
The pilot operates the cow flaps via a control within the cockpit.

Now my question
Ok the 2D panel ("post-it") checklist "says": 1) Open cowl flaps after engine start. 2) Check cowl flaps are open before take off. 3) Cruise: cowl flaps closed. 4) Approach-Landing: cowl flaps closed.
I can see that the cowl flaps control is a lever going from 0% to 100%. For take off and climb, how much (%) do I have to open the cowl flaps?

[Oracle427]

Open them all the way for takeoff and climb, you want that heat out of there and CHTs below 400.

Close them up in cruise as required to keep CHTs below 400. It can take some time for CHTs to stabilize, so always include those engine instruments in your instrument scan. A good scan is good practice as you'll catch faults early.

[Orlaam]

I close them in cool/cold weather during warm up on the ground. Is that normal or effective?

[Simicro]

Open them all the way for takeoff and climb, you want that heat out of there and CHTs below 400.

Close them up in cruise as required to keep CHTs below 400. It can take some time for CHTs to stabilize, so always include those engine instruments in your instrument scan. A good scan is good practice as you'll catch faults early.

Roger that Chief Master Sergeant!

Accurate and crystal clear.

Many thanks Oracle427.

[Jarek]

I close them in cool/cold weather during warm up on the ground. Is that normal or effective?

Hi, this is not recommended by engine manufacturer or POH. Perhaps it may lead to unequal heating of upper and lower cylinder/head parts.

[Orlaam]

I close them in cool/cold weather during warm up on the ground. Is that normal or effective?

Hi, this is not recommended by engine manufacturer or POH. Perhaps it may lead to unequal heating of upper and lower cylinder/head parts.

Ok okay. Was thinking it would speed up warm up.

[DHenriques_]

I close them in cool/cold weather during warm up on the ground. Is that normal or effective?

I usually opened cowls post roll out on landings and kept them open for all ground operation especially run-ups.
I'd open them for starts and keep them open during taxi but watching the CHT in the process.
Dudley Henriques

[AKar]

I close them in cool/cold weather during warm up on the ground. Is that normal or effective?

Hi, this is not recommended by engine manufacturer or POH. Perhaps it may lead to unequal heating of upper and lower cylinder/head parts.

Ok okay. Was thinking it would speed up warm up.

Yes it is not generally recommended because of uneven heating and hot spots getting too hot quickly without cooling airflow. In cold conditions, I understand some folks start the engines with cowl flaps closed but open them as soon as the engine idles on its own. I don't comment, because I don't know, about how easy it would be to forget them closed.

-Esa