cowl flaps won't stay closed in flight

[DCarlton]

Any idea how much cowl flaps should move full travel when viewed from the outside?    

[Ragsf15e]

14 hours ago, DCarlton said:

Any idea how much cowl flaps should move full travel when viewed from the outside?    

There is a measurement in the maintenance manual.  Maybe for a newer year than yours?

[47U]

15 hours ago, DCarlton said:

Any idea how much cowl flaps should move full travel when viewed from the outside?

From the ‘67 F model mx manual… 1.65” when fully extended, measured at the trailing edge.

Dimension increased slightly for ‘68, but not sure why.  Different linkage design perhaps, but I didn’t review the IPB to see if the parts between ‘67 and ‘68 model years are the same.  

[DCarlton]

1 hour ago, 47U said:

From the ‘67 F model mx manual… 1.65” when fully extended, measured at the trailing edge.

Dimension increased slightly for ‘68, but not sure why.  Different linkage design perhaps, but I didn’t review the IPB to see if the parts between ‘67 and ‘68 model years are the same.  

Thanks for the trouble.  I've gotta get a copy of the maintenance manual printed for reference.  I have the parts manual. 

[M Terry]

Finally got it working. A friend who is a machinists made a replacement for the worn out pin/lever. Our A&P approved the part and the re installation. After fooling around with the rigging it over centers in the closed position and stays closed in cruise flight. I think it gets us about 2 knots in level flight

 

[LANCECASPER]

On 2/15/2023 at 3:22 PM, M Terry said:

Finally got it working. A friend who is a machinists made a replacement for the worn out pin/lever. Our A&P approved the part and the re installation. After fooling around with the rigging it over centers in the closed position and stays closed in cruise flight. I think it gets us about 2 knots in level flight

 

If the cowl flaps are closed flush in cruise flight it's been proven that you will lose a few knots not gain a few knots. You can ask Bob Kromer about that. He helped develop the Mooney 252 and was the test pilot. They got the best speeds with the cowl flaps rigged open a little.

[M Terry]

Yes. The "closed " position has a 1/4 inch gap between the fuselage an the trailing  edge of the cowl flap 

 

 

[Igor_U]

On 2/17/2023 at 2:21 PM, LANCECASPER said:

If the cowl flaps are closed flush in cruise flight it's been proven that you will lose a few knots not gain a few knots. You can ask Bob Kromer about that. He helped develop the Mooney 252 and was the test pilot. They got the best speeds with the cowl flaps rigged open a little.

Lance, this might be true for 252 but is it for M20F?  I don't think that's the case for my plane but then there's always a gap even cowl flaps are closed.

[Fly Boomer]

On 2/17/2023 at 4:21 PM, LANCECASPER said:

If the cowl flaps are closed flush in cruise flight it's been proven that you will lose a few knots not gain a few knots. You can ask Bob Kromer about that. He helped develop the Mooney 252 and was the test pilot. They got the best speeds with the cowl flaps rigged open a little.

Anybody know why "more drag" results in "more speed"?

[PeteMc]

1 hour ago, Fly Boomer said:

Anybody know why "more drag" results in "more speed"?

Wonder if (and not an aerodynamics expert by any means) it has anything to do with more air going through the engine compartment and less back pressure drag?  The slight opening in the cowl flaps might still be out of the airstream and not really add much parasite drag.  And it will allow slightly more air flow or pass-thru and less pressure drag.  (I think I have the correct term and "pressure drag" is term for the wall of air the plane is pushing trough.) 

[Fly Boomer]

4 minutes ago, PeteMc said:

Wonder if (and not an aerodynamics expert by any means) it has anything to do with more air going through the engine compartment and less back pressure drag?  The slight opening in the cowl flaps might still be out of the airstream and not really add much parasite drag.  And it will allow slightly more air flow or pass-thru and less pressure drag.  (I think I have the correct term and "pressure drag" is term for the wall of air the plane is pushing trough.) 

That makes sense.  I was thinking only of the drag of the cowl flap, but a slight opening might reduce the overall drag.  Thanks!

[Ragsf15e]

1 hour ago, Fly Boomer said:

That makes sense.  I was thinking only of the drag of the cowl flap, but a slight opening might reduce the overall drag.  Thanks!

Cooling drag is a big deal for sure.  On the older models, the big guppy mouth lets in too much air and can’t efficiently flow it all down through the cylinder fins.  Evidently, Some of it even comes back out the front!  I don’t remember the reference for that, but we’ve got it around here somewhere.  The slight cowl flap opening minimizes this apparently by helping pull the air through, but better cowl design on later models probably helped a lot more.

[Fly Boomer]

10 hours ago, Ragsf15e said:

Evidently, Some of it even comes back out the front!

At an APS seminar, the GAMI Guys said they tufted the engine in a Bonanza, and put a camera in there.  Just as you say, the airflow was not at all what was expected, and in some cases, flow was reversed.

[Kelpro999]

How about the theory of more warm air under the fuselage reducing surface friction and parasitic drag on antennas and the like…. I have to stop over thinking things.