M20J Cowl Flaps - Horrific cowl vibration when open

[SuperDaggi]

Been struggling with an issue with my cowl flaps and the situation just worsened… No idea where to even look for the root cause.

If I open my cowl flaps (can only fully open or fully close), I get huge vibrations to the point that I see my entire cowl move from within the cockpit. Also sounds terrible, well beyond the usual loudness of open cowl flaps...

If I close them, then it all stops and goes to normal. No more vibrations, no more cowl movement.

This happened after we replaced the hinges for the cowl flaps, so I guess we found out why the previous ones were worn out... I guess their wear somewhat prevented the vibrations from getting the best of the lower cowl.

Now, I'm wondering what may be causing these vibrations? The hinges are solid, the cowl flaps don't move around much if I try and wiggle them when they're open. Cowl flaps closed, all good, no vibrations or any weird sounds.

Been also having issues with oil temp that I could keep under control opening the cowl flaps until I reach ambient temperatures that do the trick. Now, it doesn't seem like much of an option to keep them open that long. Looking at another M20J, I noticed the left cowl flap looks different from mine (mine is flat, this one looks pretty much like the right one being bent around the exhaust). Wondering if that may help with oil temps?

[EricJ]

Mine did that, but only at fairly high speeds, e.g., 160+kts or so.   If I slowed down it quit.   

We did some repairs and reinforcements and I'm not sure it does it any more.   Make sure that the stiffeners in the cowl that go around the cowl flaps are stiff all the way around.   Somebody (at an MSC) cut one of mine in half to do a repair and didn't double it, and the floppiness may have contributed to the problem.   We've since put a doubler on and I don't recall seeing it happen since.

Edited September 8, 2018 by EricJ

[SuperDaggi]

Thank you! Some good tips, will check on these items.

Temp issues are somewhat weird and depending on who you ask, it's a non-issue. Factory oil temp is always in the green, EDM shows temps in the area of 210+F and will sometimes even rise beyond 220F. As I approach 220F, I can see the oil pressure declining and it'll be in the lower 60s on the EDM, touching the yellow on the factory gauge.

Oil is 15W-50.

Factory oil temp still shows me in the green though and I've seen Youtube videos of people flying M20J, where their oil temp gauge is actually showing a higher temp than mine, even with low power in approach.

What is noticeable is that the oil temp on a cold engine warms up very quickly. Typically by the time I reach the runway, oil temp is sufficient for departure.

Recently changed from ROP to LOP and have been able to keep the oil temp below 210F doing that, depending on OAT even as low as higher 190s.

While we did a big investigation into this, even replacing the oil cooler and vernatherm, I am starting to question if I really have an issue or if I just need to manage oil temp properly using cowl flaps, LOP and power settings.

[takair]

What speeds are you seeing the vibration?  All speeds?  Have you checked that the basic baffle integrity is good?

[LANCECASPER]

7 hours ago, SuperDaggi said:

Been struggling with an issue with my cowl flaps and the situation just worsened… No idea where to even look for the root cause.

If I open my cowl flaps (can only fully open or fully close), I get huge vibrations to the point that I see my entire cowl move from within the cockpit. Also sounds terrible, well beyond the usual loudness of open cowl flaps...

If I close them, then it all stops and goes to normal. No more vibrations, no more cowl movement.

This happened after we replaced the hinges for the cowl flaps, so I guess we found out why the previous ones were worn out... I guess their wear somewhat prevented the vibrations from getting the best of the lower cowl.

Now, I'm wondering what may be causing these vibrations? The hinges are solid, the cowl flaps don't move around much if I try and wiggle them when they're open. Cowl flaps closed, all good, no vibrations or any weird sounds.

Been also having issues with oil temp that I could keep under control opening the cowl flaps until I reach ambient temperatures that do the trick. Now, it doesn't seem like much of an option to keep them open that long. Looking at another M20J, I noticed the left cowl flap looks different from mine (mine is flat, this one looks pretty much like the right one being bent around the exhaust). Wondering if that may help with oil temps?

Who changed the hinges out?

[SuperDaggi]

22 hours ago, takair said:

What speeds are you seeing the vibration?  All speeds?  Have you checked that the basic baffle integrity is good?

Starts pretty much immediately after I apply full throttle for take-off. Didn't notice much of a speed-related difference. Feels like lowering RPM helps a little but it never goes away until I close the cowl flaps. I close them, it's all gone and back to normal. Baffle integrity should be fine but probably worth another close look.

Edited September 9, 2018 by SuperDaggi
Forgot something

[SuperDaggi]

20 hours ago, LANCECASPER said:

Who changed the hinges out?

Done by my local shop who have a lot of Mooney business, so I'm certain they know what they're doing.

[carusoam]

SD,

sounds like you have some loose stuff going on with the cowl flaps...

grab them with your fingers (again) and wiggle them. They shouldn’t move...

Flap controls under normal operations are infinitely adjustable... too ‘lubricated’ they will try to close themselves by the force of the passing wind...

The PIC is supposed to be in control of the flaps, not the pasing wind...  

there are a couple of points/places to keep this from happening...

• hinges wear and can be replaced...
• flap controls have some wear points associated with them... all replacement items.

Vibrations like this aren’t normal.  They will cause things to wear at an accelerating pace if ignored...

 

Got one of those GoPro cameras?  This could make identifying the challenge pretty quick.

 

got any other Mooneys at your field? Ask their owner if you can examine their cowl flaps...

 

Sorry for recapping about three things you did already... but one of them must be fixable...?

Thanks to Jim/BlueSky, for pulling out the doubler details!

 

PP thoughts only, not a mechanic...

Best regards,

-a-

[LANCECASPER]

6 hours ago, SuperDaggi said:

Done by my local shop who have a lot of Mooney business, so I'm certain they know what they're doing.

The fact that it first happened after maintenance/repair is the biggest clue.

I live within a half hour of the Mooney factory and have the former director of maintenance come to my hangar to do owner assist annuals every year. When you hear stories of the mistakes made that people who build these airplanes every day have made over the years, a shop who gets a lot of Mooney business certainly isn't infallible. I would start looking there, but it's your airplane.

[Guest]

Something is causing your cowl flap sides to contact your exhaust system when you close the cowl flaps.  The vibration is is the engine vibration transmitted through the exhaust .

Just a guess of course.

Clarence

[carusoam]

Daggi,

Got any pics?

M20Doc has shared a very interesting idea!

You are saying...

• vibration happens when flaps are full open...
• cowl moves with vibration...
• flaps seem to be well maintained, no loose hinge or controls...
• may not be an aerodynamic vibration...
• Could be something making contact with vibrating engine/exhaust parts...

does the vibration suddenly stop as close the flaps, in the same place, then start again when you open them, in the same place?

You may need to keep your hand on the control, for yours...

Interesting...

PP trying to help out... not a mechanic.

Best regards,

-a-

[Oldguy]

23 hours ago, SuperDaggi said:

Starts pretty much immediately after I apply full throttle for take-off. Didn't notice much of a speed-related difference. Feels like lowering RPM helps a little but it never goes away until I close the cowl flaps. I close them, it's all gone and back to normal. Baffle integrity should be fine but probably worth another close look.

Doesn't sound speed related from your comment above - sounds RPM related. If so, you might be able to go out, run it up and have someone off to the side (WAY off to the side) watch the cowl flaps to see what they appear to be doing. Might even be possible to video it so you can see what is happening sitting down with your mechanic.

[SuperDaggi]

Ok, we spent the best part of yesterday morning trying to figure this out.

Wiggled the cowl flaps and the left one moved a little more than the right one - but there was no significant difference when compared to another M20J we had there. Actually, the cowl flaps on the other one had more wiggle room.

Then, took the mechanism apart (at least the lower part) and looked if there was something that was worn. There was a little wear but nothing significant enough to explain the problem.

Then, by coincidence noticed that the exhaust mount attaching the exhaust to the frame outside of the cowl flap was missing a nut…! Was behind the exhaust pipe, so only visible when lying under the plane.

Attached a nut, rigged the cowl flaps to make sure they're in line with the service manual and went for a test flight. Problem gone! Looks like opening the cowl flaps released the exhaust pipe and the horrific noises were caused by the screw moving within the mount.

Thanks for all the great tips and the help!!!

[Hank]

Gotta love the simple fixes! They're just not always easy to see . . . .

[carusoam]

Great Pirep SuperDaggi!

Thanks to the DOC for pointing out the right thing to look for... engine vibration vs. aerodynamic vibration.

Go MS!

We all become more M20 knowledgeable... one post at a time.  

Best regards,

-a-

[m100psi]

I know this is an old thread, but I'm having exactly the same problem with my M20J.  With cowl flaps open, a little after takeoff I get serious vibration in the cowling.  Closing the cowl flaps almost (but not quite) eliminates the vibration, and it gets a worse again at descent airspeeds even with cowl flaps closed.

Was the missing nut in your case part of the exhaust ring bracket or something else?  This bracket was broken on mine, but it's fixed now and fixing the bracket didn't resolve the vibration.

Thanks,
Matt

[carusoam]

Matt,

Who are you asking the question to?

@SuperDaggi hasn’t been around since July...

But, I sent him a light if he logs in...

Best regards,

-a-

[jetdriven]

If you push the Cowl flaps to trail just before you give it power for takeoff, it is a lot easier on the hinges and the cowling itself.

Our cowl was  in horrible shape. The frames were shot they had screws going through the holes where they used to be rivets, and the whole thing was just a mess. So we replaced all the fiberglass, the cowl flap frames, the hinges, and even the cowl flaps. It’s been like five years now, still looks new

[aaronk25]

Ya I had the vibration go on the J, abs turned out willmar said it was a fowl not fitting correctly. They did some adjustments and grinding and got it all fitting snug. No more vibration!

I believe it was Eric at willmar who did the work.


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[m100psi]

I was asking SuperDaggi assuming he'd get an e-mail for new replies here, but appreciate feedback from everyone.

I haven't tried partial cowl flaps yet...I'll try it next I'm up.

Thanks,
Matt

[Ragsf15e]

Well, since we reopened this cowl flap thread, ill ask... today I noticed my left cowl flap is pretty loose on the front “hinge” part.  Although it looks to just be pinned to the cowling on the front left and right with a rivet or bolt - not a full hinge.  The actuator rod on the back has a little play but the inboard front “pin” has a lot of forward/aft play.  It looks like it’s a blind rivet?

Thoughts on fixing this?  I think this is step one of identifying a weird vibration I’m noticing at level off from climb.  Can’t tell yet if it’s related to speed, elevator play or maybe cowl flaps, but the left cowl Flap clearly needs fixed either way.

thanks!

’68 F

[jetdriven]

On 9/9/2018 at 12:38 PM, SuperDaggi said:

Starts pretty much immediately after I apply full throttle for take-off. Didn't notice much of a speed-related difference. Feels like lowering RPM helps a little but it never goes away until I close the cowl flaps. I close them, it's all gone and back to normal. Baffle integrity should be fine but probably worth another close look.

If you put the cowl flaps in trail just before applying takeoff power, no overheating, no buffeting , nothing...it’s almost like it’s made for that

[m100psi]

This thread is even older now, but just to follow up on my issue, the cowling vibration and cowl flap play ended up being due to a worn upper cowl flap rod end.  The hole around the bushing had expanded.  Repaired and there's no longer any vibration during either climb with cowl flaps open/trailed, or high-speed descent with cowl flaps closed.

[carusoam]

Excellent follow-up Matt!

Since this thread there may have been one or two cowling related vibration issues...

One turned out to be foam insulation missing from gear doors for an Acclaim...

The other one just got underway at problem solving...

Small things seem to make it possible to allow a vibration...  wear, enlarged holes, missing foam...

Best regards,

-a-