Cowl flaps : Landings and go-arounds

[AJ88V]

1970 C models were built with fixed cowl flaps, but I added them as a mod maybe 15 years ago.

Before taking to the air again after a very long hiatus from flying, I've been developing checklists from scratch as a learning exercise.  One area I'm fuzzy on is operating the cowl flaps.

Reading other folks checklists and a 1966 M20E model Operating Manual, it looks like

• Startup, Taxi, Runup, Takeoff, Climbout OPEN
• Cruise CLOSED (or as needed)
• Landing CLOSED
• Post Landing OPEN

My recollection is that I was leaving cowl flaps closed through touchdown and only opening as part of my after landing checklist before taxi.

But maybe it makes more sense to open cowl flaps on Downwind (or Base or Final)? 

1. In event of Go-Around, the cowl flaps are already open, so no need to worry about that at a high workload moment.
2. The engine should be well out of risk for shock cooling by the time you've descended and entered the pattern.  Power has been low for awhile and you're already slowed down.
3. Opening cowl flaps on downwind leaves one less thing to do when maneuvering on base or entering final, or distracting from landing the plane on final.

Your thoughts? [over]

Edited August 24 by AJ88V

[Ron McBride]

On my F cowl flaps would depend on outside temp.  If it was cold I could take off with them closed and keep the cylinders below 360.   I always landed with them closed.  You need to have an engine monitor to be able to access accurate temps.  

[Coachella Bravo]

I flew a 68' C for about 15 years and 1500 hrs.  IMHO I would leave cowl flaps closed on descent through final to my exit from the runway. Then open for taxi parking /cool down. (This would avoid any over cooling on descent)

 

[Fritz1]

I open cowl flaps after exiting runway, yes, one more check list item after go around, positive rate, gear up cowl flaps open

[Shadrach]

I touch them twice during every flight. Right before I level in cruise and right before I drop the gear.  One less thing to worry about after landing or in the event of a go-around.

[BlueSky247]

Do the cowl flaps make a significant difference in drag?

[EricJ]

20 minutes ago, BlueSky247 said:

Do the cowl flaps make a significant difference in drag?

On my J model if they're fully open they take about 4 knots off my cruise speed.   At slower speeds it probably won't make as much difference.   On other models they aren't as large and don't open as far, so it'll be different for different models.

[Marc_B]

26 minutes ago, BlueSky247 said:

Do the cowl flaps make a significant difference in drag

My POH comments cowl flaps open -4kts, half flaps -2kts. 

[BlueSky247]

Thanks! I was wondering if they could help make up for not having speed brakes, but obviously you wouldn’t want to shock cool the engine. 

[Shadrach]

8 hours ago, BlueSky247 said:

Thanks! I was wondering if they could help make up for not having speed brakes, but obviously you wouldn’t want to shock cool the engine. 

https://www.avweb.com/ownership/shock-cooling-time-to-kill-the-myth/

[Ibra]

11 hours ago, BlueSky247 said:

Do the cowl flaps make a significant difference in drag?

At takeoff and landing speeds, nothing. At cruise speeds, I think about 3kts - 4kts on J 

I leave them open all the time except in cruise or when warming the engine on ground

Edited August 25 by Ibra

[midlifeflyer]

21 hours ago, AJ88V said:

but maybe it makes more sense to open cowl flaps on Downwind (or Base or Final)? 

That's my technique in most airplanes with cowl flaps. Generally on final. My theory is simple (an perhaps wrong). The reason we close them is to reduce the effects of too-rapid cooling. By the time we are on final, we have had a number of power reductions. To the extent rapid cooling is an issue at all, it's over. Just as over as opening them 30 seconds after landing.  The only remaining issue is to have cowl flaps open for the go-around.  People have enough issues with go-arounds; why not remove part of the workload?

[201er]

I don’t see a need in opening the cowl flaps on downwind just in case of a go-around. It’s not an instantaneous demand like mixture or boost pump. Cowl flaps can be extended after the gear and flaps have been retracted. It takes some time for heat to build up.

And if you have an engine monitor and forget to open them, as a backup you can have an alarm remind you before temps get too hot. 

[midlifeflyer]

11 hours ago, BlueSky247 said:

Thanks! I was wondering if they could help make up for not having speed brakes, but obviously you wouldn’t want to shock cool the engine. 

Good engine and speed management technique make up for not having speed brakes.  And the few knots difference with cowl flaps open isn't going  to help in those situations in which you needed speed brakes.

[Shadrach]

Pilots will needlessly complicate even the simplest of devices with overthought procedures.

[jetdriven]

I used to fly with a guy that would do that…. He would put the gear down at the outer marker, and then he would add half flaps, and then full flaps while going  down the glideslope, and then he would open the cowl flaps and mess with the prop and the mixture and everything.   I mean, he made it work out OK but there were a lot of distractions inside the marker where it really all you wanna do is keep the needles centered  and the airspeed where you want it. 
but one thing I did notice was that the CHT’s would crash. Can’t be good for it.  The sole purpose of the cowl flaps is to manage engine temperature, so open at high power and low speed, and closed for the opposite. 

[A64Pilot]

I open mine when I drop the gear, I’ve found the additional cooling I get doing so really makes restarts easier, (as a high time turbine pilot I just can’t bring myself to call them Hot Starts), more than once I’ve had to add power and level out with flaps and gear down because some Student in front of me decides to fly a bomber pattern and if they aren’t open the engine gets warmer than I like and I was forgetting to.

But I think this should be tempered with the fact that I don’t fly in cold Wx, I assume in Feb in upper Wisconsin I’d likely do differently than I do in Fl.

[Marc_B]

On 8/25/2024 at 7:39 AM, midlifeflyer said:

And the few knots difference with cowl flaps open isn't going  to help in those situations in which you needed speed brakes.

I’ve found that both gear and speed brakes both slow down by about 20-25 kts each. Cowl flaps slow by about 4-5kts.