K MODEL does anyone understand how the "trailing" works for cowl flaps

[willerjim273]

Hello all, 

 

I have read everything I can on the Mooney 231K  Model cow flaps in this forum. A lot of you have said that after you get your airplane back from a maintenance event and  the cowl flaps don't work right. I am in the same boat.

 

 My question is does anybody understand them?  Just received my aircraft back from some routine maintenance and they're completely different. Normally I push the cowl flaps in to close them, in flight,  and I get an intermediate or what you may call “trail” position.  I cannot push them any further. I push some more and they don't seem to want to close. But  after some jockeying they close real nice. The “jockeying" is pulling the toward “open” position, then one big push to achieve “closed”.  I am happy with that. 

 

Now after the maintenance event they seem to be quite a bit different. They are either all the way open or all the way closed, So my question is:  what is the trailing position and how is it attained?  I Cannot seem to understand mechanically why they would go to a trail position?  After a few hours of monkeying around with the cowl off and the mechanism in my face, I don't see how they have any motivation to stop in the middle. I have to  conclude that the only reason they trail is because they are affected by, and are held there by the slip stream in flight. I can send videos. Is it just the aerodynamic forces that allow them to stay in trail?  Thanks!!!

[Slick Nick]

Manual cowl flaps? My MSE (J) has manual cowl flaps, there is an intermediate “trail” position about halfway. The flap mechanism sort of cams over in the closed position to suck them up against the fuselage. There is lots of adjustment to be had, perhaps they are just out of rig after your maintenance? 

[Z W]

I've never worked on a set of manual cowl flaps, but have found that my electric ones benefit from regular lubrication with some tri-flow.

I have also learned that there is a surprisingly large amount of force in flight holding them in the open position. They sometimes do not want to close at higher indicated airspeeds. The force is enough to hold against the motor for a period of time. This is the opposite of what I would have expected, with the slipstream working to put force to close the flap itself. Apparently the cooling air going through the engine compartment is stronger. I now close them just before leveling off for cruise, and at the lower indicated airspeed, I don't see the delay in closing.

I say all that just to say, you might see if some of the differences you're observing could be the result of the indicated airspeed you're flying at the time you attempt to move them.

[PT20J]

My M20K (with manual cowl flaps) POH does not mention a trail position. It states under engine cooling in section 7 that you can partially open them by pulling the control back one to two inches if necessary to maintain satisfactory CHT and oil temperatures. A true trail position would require the cowl flaps to float free of the actuating mechanism with their position being dictated solely by differential air pressure.

From your description, it sounds like they were improperly rigged and were corrected during the recent maintenance.

[willerjim273]

 

Hello all,

Thanks for the replies. 

Yes. I Should have  mentioned they are mechanical, not electric. . The do lock over center and lock in the full open position.

PT quoted the manual:  "you can partially open them by pulling the control back one to two inches if necessary to maintain satisfactory CHT and oil temperatures. A true trail position would require the cowl flaps to float free of the actuating mechanism with their position being dictated solely by differential air pressure."

https://photos.app.goo.gl/kuUC2kidHgE6aViW7 (I assume the link will get through)

From the videos, there is no partially open position. Does anyone have a mechanically trailing position on the ground. Trying to rule that out? On the ground, as the videos show, I have to conclude that unless someone does have a set up that puts them in a "halfway" position  -different from the videos, -  they have to be held "trailing" somehow by the aerodynamic forces. 

Thanks

 

 

MOONEY COWL FLAPS.zip

[PT20J]

@kortopates will likely know. 

[gabez]

what do you mean how they work? there are 3 settings. Open, Closed and trail mode. the latter leaves the cowl flaps slightly open. 
between trail and closed I lose (or gain depending which director) about 3-4 knots so you are trading speed for engine temperature 

 

[Bolter]

18 hours ago, willerjim273 said:

 My question is does anybody understand them?  Just received my aircraft back from some routine maintenance and they're completely different. Normally I push the cowl flaps in to close them, in flight,  and I get an intermediate or what you may call “trail” position.  I cannot push them any further. I push some more and they don't seem to want to close. But  after some jockeying they close real nice. The “jockeying" is pulling the toward “open” position, then one big push to achieve “closed”.  I am happy with that. 

Now after the maintenance event they seem to be quite a bit different. They are either all the way open or all the way closed, So my question is:  what is the trailing position and how is it attained?  I Cannot seem to understand mechanically why they would go to a trail position?  After a few hours of monkeying around with the cowl off and the mechanism in my face, I don't see how they have any motivation to stop in the middle. I have to  conclude that the only reason they trail is because they are affected by, and are held there by the slip stream in flight. I can send videos. Is it just the aerodynamic forces that allow them to stay in trail?  Thanks!!!

I believe the manual cowl flaps from the J are the same (looks similar in the video), but for clarity, my experience is a J not a K.  

Your description of how things used to be does not sound good.  While there is some friction, pulling and pushing may take some strength to get "over-center" it should notrequire jockeying around.  There 2 distinct positions, wide open and fully closed.  The "trailing" position is a bit vague and is just putting the linkage over center from wide open and letting aero forces push the mechanism into some half-open condition.  

There is an adjustment (very important one, in my opinion) to set how open the flaps are when the mechanism is in the closed position.  Closed does not have to be truly closed.  It is the threads and locknuts on the joint in your hand in the video.  Some people adjust it seasonally, I just left it the same all the time.  When "closed" on the panel control knob, the flaps were NOT flush, but half-inch or so, open.  This helps cooling, especially in warmer weather, and gives you a very low drag setting and you do not risk overheating if you forget to open the flaps.  I found this was great in cruise. 

I was usually wide open on taxi and takeoff and "trail" as the control in a half-way position for climb.  In some cases trail was required in cruise, such as very hot days.  

If you were having trouble closing, and the flaps were set to be flush, you could also have been fighting the contact forces and deflecting the flap against the cowling.  

[LANCECASPER]

1 hour ago, gabez said:

what do you mean how they work? there are 3 settings. Open, Closed and trail mode. the latter leaves the cowl flaps slightly open. 
between trail and closed I lose (or gain depending which director) about 3-4 knots so you are trading speed for engine temperature 

 

On the "closed" mode on the 231 from the factory they were supposed to be slightly open, less than an inch for cooling, also better speed. In flight testing Mooney found that completely closed  yielded a lower top speed than slightly open, since it was more efficient to have some air moving through.

[PT20J]

As is frequently the case, the answer can be found in the SMM: