cowl flaps wont close in flight - 1979 M20J

[tbrickey]

I recently purchased a 1979 M20J that is in excellent condition.  I would like to post a few questions on some behaviors I was not expecting.  My expectations are based on prior M20C experience.  First the cowl flaps work fine on the ground.  They fully open and fully close.  However, in flight, I am only able to half close them.  Is this normal?  Second, as I climb to 10,000 feet, the manifold pressure is still showing 29 -30 inches.  I see expected values when the engine is not running and when the engine is at idle.  I have a new powerflow exhaust but don't think that is making the difference.

[danb35]

I expect you have a leak in the case of your MP gauge, which would cause it to read high as ambient pressure decreases.  I can't speak to your question about the cowl flaps, though.

[MooneyMitch]

With regards to the MP reading, I concur that you have a leak.  In my case it was the aluminum line into cylinder head.  Just remove the cowling for access and take a look for anything broken, cracked or loose along the line route.  Hope that helps you. 

[GeorgePerry]

The picture shows the tubing that goes into the #1 Cylinder.  The tubing takes MP from the #1 cylinder and displays in the cockpit. 

[tbrickey]

the egt for cylinders 1 & 3 is also dead so this sounds like a good place to start looking. 

[carusoam]

On the M20C - The gauge is a mechanical vacuum system.  I suppose the J is not much different.

[1] 30" at 10,000 ft?  full open throttle should barely be above 20".  There is not that much atmoshperic pressure available.

[2] There is some magic involved in the aluminum tube used to determine MP.  Be sure the proper bleed hole (calibrated leak) is present.

- If the tube is broken/open, It will show atmospheric pressure.  At 10,000 feet it should be significantly less than 29 or 30"

- If the tube has been replaced, and the proper bleed hole is not present, your MP will be much lower than expected.

- If the bleed hole is too large, your MP will be much higher than expected.

I learned this when the bleed hole in my M20C MP gauge initiated a crack that broke the tube open.  The bleed hole is located right at the back of the MP gauge 1 or 2" up stream, usually pointed downwards. 

The purpose of the bleed hole is to keep the junk that collects in the intake manifold from entering your MP gauge at the time of engine shutdown.  This is a really smart idea.  If you have ever looked up inside the intake tubes and around the intake valves you probably have cleaned a lot of blue (100ll identifying) goo.

If this is any part of your solution, the next question you will be asking is... what is the diameter of that hole?  I was unable to purchase the part from Mooney at the time.  Somebody (Bill Wheat?) was kind enough to go through Microfiche for me.  There is a note on the drawing indicating the diameter.  Of course this was M20C experience, the M20 J may be different.

Also, I did not find the note on the M20C drawing either, it was found on one of the other bio-similars  (d,e,f or g).

Hope this helps move the ball along,

- Anthony -

[DaV8or]

On your cowl flap issue, I would check the play in the hinges and the edges of the flaps for rough spots, burrs, bolts or rivets sticking out. What sounds like is happening is, when you are in flight, the wind is pushing one of both flaps to the side and the edge of the flap is binding on the opening. This would explain why it works perfectly on the ground but only go half way in flight. Perhaps also your exhaust stack could be loose and shifting enough to block the flap from coming up. It's just speculation on my part, but I really believe the the wind is shifting thigs around and causing the problem.

[FlyFstr]

DaV8or makes a good point withthe wind playing a role.

I had an airplane with a trim issue (it felt stuck) that only manifested itself while in flight. On the ground with no wind, it was no problem.

My A&P/IA figured it out quickly. In my case it turned out to be a simple lubrication fix on the linkage (but it was a Beechcraft, not Mooney). 

Please let us know how this issue was resolved. 

[Piloto]

I think you have a defective MP gauge. What does it reads with the engine in idle.  Disconnect the MP line that goes to the engine and by mouth suction it. The gauge should read lower (around 20"). On the cowl flaps verify that there is a spring on the right side of the cowl flap actuating shaft. If the spring is missing the flaps will not lock in flight.

José

[peter]

On the cowl flap - does it not close; or, does it pop open to the trail position when you try to close it?

If the latter, we had the same issue in our 231, resolved by a new spring and an adjustment of the linkage.

[Alan Fox]

On my B I replaced the cowl flap cable with a push button type locking cable , the wind was opening up the flaps at speed and the 50 year old cable did not have enough resistance to keep them closed..  Also , there is not 30 inches of pressure at 10 K feet ,,, You have a bad manifold pressure guage (or a turbo) ...

[M016576]

Quote: tbrickey

I recently purchased a 1979 M20J that is in excellent condition.  I would like to post a few questions on some behaviors I was not expecting.  My expectations are based on prior M20C experience.  First the cowl flaps work fine on the ground.  They fully open and fully close.  However, in flight, I am only able to half close them.  Is this normal?  Second, as I climb to 10,000 feet, the manifold pressure is still showing 29 -30 inches.  I see expected values when the engine is not running and when the engine is at idle.  I have a new powerflow exhaust but don't think that is making the difference.

[mikefox]

Your cowl flap problem is likely the incorrect cable installed.  I have seen exactly that problem before.  Take it to a knowledgeable Mooney mechanic to be certain.

[tbrickey]

With the cowl flaps, I take-off with the flaps open.  When I try to cose them in flight I can only push them half closed.  On the ground after shutting down, I can easily close them fully.  I haven't tried closing them while running on the ground.  That would be a good thing to test.  I will check this tonight.

[wrench]

Is the spring installed or broken on the cowl flap actuator lever (co Pilot side). Note the picture on my J during my first annual, it worked correctly! It was left disconnected on the most recent annual and I had the similar issue.

Bill

[bradp]

Rip van zombie thread :-)

[Joe Larussa]

I had the same problem with the cowl flaps on my 77J. Two things to check. The over center adjustment and anything interfering with the flap. Pilot side has the breather tubes as well as an oil air separator hose if you have one. Took me forever to figure it out because it would close just fine on the ground but not in flight.

[Randy_B]

8 hours ago, Joe Larussa said:

I had the same problem with the cowl flaps on my 77J. Two things to check. The over center adjustment and anything interfering with the flap. Pilot side has the breather tubes as well as an oil air separator hose if you have one. Took me forever to figure it out because it would close just fine on the ground but not in flight.

+1 What Joe said.  The tube and hoses caused the same issue following my annual a few years back. Interfered with the over-center and push pull rods on the pilot side of the firewall.

Edited May 16, 2016 by Randy_B

[Joe Larussa]

In my case it wasn't the flap that was hitting anything but the rod that connects to the flap.