What are cowl flaps?

  • What are cowl flaps? flyingfisch

    What are cowl flaps and what are they used for? It seems I have only heard of them in connection with old planes, are they peculiar to radial engines?

  • They are flaps or doors on the engine cowling that open up in order to provide increased cooling airflow for the engine. They look like this when open. They are generally controlled by a handle in the cockpit (some aircraft have electric cowl flaps with an open/close switch).

    open cowl flaps

    The disadvantage is that the open flaps also increase drag. So on airplanes equipped with cowl flaps, they are generally opened for low-speed, high-power situations such as takeoff. This is the harshest operational regime for the engine since it is at its highest power and relatively low cooling airflow due to low airspeed. They are then closed either reaching cruise or reaching a point where the airplane can transition to a lower-power, higher-speed climb profile.

    They're not specific to radial engines, but do tend to be more common in older aircraft (there are exceptions though). Newer airplane and engine designs are more likely to have sufficient inherent cooling airflow to not require cowl flaps.

    The photo above comes from AVweb, which also has a nice article explaining more about the function and usage of cowl flaps.

  • Cowl flaps are used for engine cooling and you'll find them on many high performance piston aircraft. They are particularly useful during climbout when you are at a high power setting and slow(ish) airspeed. Opening the cowl flaps allows more airflow across the engine but produces some drag. They are typically mounted on the bottom of the engine cowling.

Related questions and answers
  • I recently read about flap load relief systems in some aircraft that attempt to prevent flap overspeeds by automatically retracting flaps under certain conditions. Are these systems common on all large aircraft or are they specific to just a few? How do they work (i.e. under what conditions will they retract flaps)? Do they prevent the possibility of overspeeding flaps altogether, or do they just make it less likely to happen?

  • What are cowl flaps? flyingfisch

    What are cowl flaps and what are they used for? It seems I have only heard of them in connection with old planes, are they peculiar to radial engines?

  • The early Boeing 737 models had wings with triple-slotted flaps that appeared to be derived from the 727. When the 737 was redesigned as the Next Generation series (dash 600 through 900), these flaps were dropped in favor of a double-slotted design. Why did Boeing choose to make this change, and what were the trade offs? Did it impact performance? I had always been under the impression that early 737s were reasonably capable on shorter and rougher runways.

  • When I extend my flaps to 10 degrees, what exactly is the 10 degrees measuring? Is this referring to the angle of the flap blades themselves, the new angle of the wing chord, the change in the new critical angle of attack or something else?

  • I know aircraft commonly have rotary actuators to extend and retract the flaps. I am not sure how many but I think I read two per flap on a 747. My question is what is the result if one actuator fails? I don't know if more then one needs to fail in order for a flap not to extend or retract. I am mostly wondering if could cause an aircraft turn-back because somebody told me it could. However that does not seem right to me. I thought the flaps are extended before take-off so that worst case scenario prior to flight is a minor flight delay to replace it. I suppose if it failed just prior

  • I know on the 737, the leading edge slats deploy at the first flap setting, and the trailing edge flaps deploy after that at higher flaps settings. Why do the slats deploy before the trailing edge flaps?

  • on a C182 that I wanted to rent in Florida and when I raised the flaps right after touchdown the instructor shouted "what the < beep > are you doing? You should never raise the flaps until you've...This question is about light, tricycle, single engine aircraft. I have made it a habit to raise the flaps right after touchdown (when the nosewheel is on the ground). My instructor used to do... of fiddling with the flaps lever (which is a something I don't even have to think about) My question is: Is it really a bad idea to raise the flaps that soon after landing? Or is it actually a good habit? (I

  • I'm just curious as to what the noises are that you can hear as a passenger in the cabin of an airliner? For example (ignore the crew talking), the noise at 7:09 - 7:30 on this video; is that the flaps? What other sounds might a passenger be able to spot?

  • At the club I fly at, there is an older Cessna 172 that has a manual "Johnson Bar" that is used to put the flaps down. In the newer 152, and I believe the rest of the planes (I have yet to fly them), the flaps are controlled via a electronic (or hydraulic?) lever. It appears to me that the manual flaps are more reliable, more maintainable, and a hell of a lot more fun in my opinion. Additionally, the manually flaps don't require a lot of strength to operate IMO. Does anyone know why the automatic design is favored over the manual counterpart? Same question applies to car transmissions...

  • , probably the first of the day. Having done walk-arounds for a Cherokee, I would like to think that I wouldn't allow such an event to happen on a small plane. On the other hand, I realize that it would be impossible to do a thorough inspection on, say, an Airbus A380. What is a typical preflight inspection checklist for a Dash 8 or similar plane? Would it have included, for example, a visual inspection of the flaps that would have allowed the snake to have been spotted?

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