Tcraft938 Posted November 2, 2020 Report Posted November 2, 2020 I've seen a lot of write-ups on rigging the system, but I have a different twist. I noticed in flight my cowl flap doors open cruise and they open quite a bit. As a result CHTs are in the 270 range. We have insured they are rigged properly by the Service Manual and posts here. On the ground they open the prescribed mount and shut with a little snap. The handle/cable in the cockpit is not changing, so their opening up or not shutting is not changing that. However, I am question one or both of two items on the plane. First, the cowl flap push pull knob in the plane is not like what I see in pictures (silver knob with push button in the middle). What I have looks to me like someone put in a C-150 mixture pull knob/cable. So I'm wondering if as inside the cowl builds pressure that thin wire can't hold the actuating arm it connects to down and it just bends allowing everything to go to the open position. The other consideration is there is a long thin spring that runs from the right seat footwell to the pivot arm that connects to the cowl flap push rod. It appears the spring is there to provide tension to the arm to hold it in the flap closed position. Perhaps that spring over 57 years has become weak and not the tension it was designed to give? If you have time, what are your thoughts on my thinking, and any suggestions on a proper cowl flap pull cable? I'm not demanding the exact one that would have come with the plane, but even a correct size/strength replacement. Thank you Quote
M20F Posted November 2, 2020 Report Posted November 2, 2020 How are you determining they open by X” in air versus Y” on the ground? Quote
Prior owner Posted November 2, 2020 Report Posted November 2, 2020 The clamps on the engine mount that hold the cowl flap shaft can slide up and down if they are not secure. This could cause the cowl flaps to not operate properly. Check 1 Quote
Tcraft938 Posted November 2, 2020 Author Report Posted November 2, 2020 3 hours ago, M20F said: How are you determining they open by X” in air versus Y” on the ground? Plane is a little slower than this time last year and CHT's are running about 30-30 degrees lower. Used a friends GoPro Cam on the wing and saw that if I close them at top of climb, slow airspeed they close slightly but when get near cruise speed they open up the same or wider than when I put them in open position. It must be incredible pressure that builds in there because on the ground I would need to REALLY pull on the cowl flap to force them open when in close position. Quote
Tcraft938 Posted November 2, 2020 Author Report Posted November 2, 2020 2 hours ago, PilotCoyote said: The clamps on the engine mount that hold the cowl flap shaft can slide up and down if they are not secure. This could cause the cowl flaps to not operate properly. Check Thanks, but I checked that. I can move the plane a bit and they don't budge. Also the entire motor mount was blasted primed and painted last year for engine install and there is no signs of the cowl flap mechanism moving. I read on another thread that they all open in flight a little. But it's only going to get colder here in Western NY, and on a 48 degree day cruising with CHTs in the 260-275 range seems crazy low. Quote
Prior owner Posted November 3, 2020 Report Posted November 3, 2020 Just to clarify- you have a knob other than the Mooney knob with the locking button in the center. I’m not familiar with the C150 mixture knob- does it have a locking feature? If so, it may not be up to the task of holding that cowl flap cable.... a typical non-vernier mixture control would require hardly any friction when locked in order to to do the job it was intended for. Is your cowl flap knob pushing out in flight? Also, when they are set up correctly, the cowl flaps don’t require that much force to open or close on the ground. Is the linkage to each cowl flap in the correct hole on the actuating arm? I have seen come that have more than one hole. Quote
Tcraft938 Posted November 3, 2020 Author Report Posted November 3, 2020 1 hour ago, PilotCoyote said: Just to clarify- you have a knob other than the Mooney knob with the locking button in the center. I’m not familiar with the C150 mixture knob- does it have a locking feature? If so, it may not be up to the task of holding that cowl flap cable.... a typical non-vernier mixture control would require hardly any friction when locked in order to to do the job it was intended for. Is your cowl flap knob pushing out in flight? Also, when they are set up correctly, the cowl flaps don’t require that much force to open or close on the ground. Is the linkage to each cowl flap in the correct hole on the actuating arm? I have seen come that have more than one hole. It's a real old style cessna type cable/knob with no lock to it. However the cable/knob do not move from where I have it set in flight. In other words, the cowl flap is not pushing the knob out when it opens. I am able to push the knob in in flight pretty easily but the flaps are not moving while in flight. So I think the cable just bends or kinks. On the ground it does not take much force of the knob at all to smoothly move the flaps open/close. It's just that in the air, what I do with the knob/cable has no affect on the flaps, the stay open. The parts catalog does not show mutliple holes in the arm, just that the flap rods go at the very end, which is where mine are. The catalog does not show the spring I have either. The spring seems to hold tension in the up/flap closed position. Not the greatest pic, but if you look at bottom panel left and below throttle can see a little of the red knob that looks like a late 60's cessna 150 mixture. You don't twist it, nor does it have a lock button. When I get to the hangar I can try to take better pics of it and inside the engine compartment. Thanks for looking at it and comments 1 Quote
carusoam Posted November 3, 2020 Report Posted November 3, 2020 Can you share the video? That would be interesting... My C’s cowl flaps were uncontrollable... They eventually got pinned in one location... as the later Cs got... This was pre-MS times or they probably would have gotten pinned to an exact location... Best regards, -a- Quote
Tcraft938 Posted November 3, 2020 Author Report Posted November 3, 2020 7 hours ago, carusoam said: Can you share the video? That would be interesting... My C’s cowl flaps were uncontrollable... They eventually got pinned in one location... as the later Cs got... This was pre-MS times or they probably would have gotten pinned to an exact location... Best regards, -a- That's exactly what my AP/IA was saying and seriously contemplated doing. However, he wanted the adjustability so I could put them in a few positions and see what works best before pinning. "Before you spend $500 on a used cable that will likely break soon, lets see if having the thing really does much benefit, it must be Mooney found it didn't, or they made other changes to the cowl and/or doghouse to improve air flow". He feels the front cowl enclosure is probably better benefit for the $500. The other confusion I/we have is my Mooney is technically a D but was converted to retractable gear, it's basically a C. The manual says on the D to adjust the cowl flap opening almost 2x wider than on a C. When we had everything apart for the engine install, he put it to the D specification because that is what the plane is and paperwork does not say to change. Plus he was thinking new engine, hot cylinders, summer, climb, open more gives more cooling if needed. However the difference between the two settings is maybe 5 degrees if that. Where they REALLY help more is on the ground/taxi if ATC does not get you out right away. Fortunately most of the controllers at KROC are pretty good about it. Have two that on first flight with new engine, I asked ground to let me know when they thought I could taxi straight to runway and go, I would then start up. Those two controllers to this day remember that and usually try to not have me wait for anything and ask, "how's that new engine doing"? Of course reduced traffic of COVID helps. 1 Quote
Prior owner Posted November 3, 2020 Report Posted November 3, 2020 (edited) The only other things that I can think of- Perhaps Your suspicion that the spring isn’t the correct spring (too soft) is correct, coupled with the end of the cable housing might be sliding back and forth in its firewall clamp under cowl flap pressure in flight, or is it possible that the inner wire is moving inside the knob assembly (where it is crimped/swaged)? It sounds like your AP/IA is doing a pretty good job investigating this problem, and has probably already ruled these out though... My aircraft is also a converted D model, but the arms on my idler arm assembly have two holes (although I don’t know whether the rod assemblies could be adjusted to fit on the other holes or whether it would even operate that way). My assembly is also adjusted according to the model C specs (smaller cowl opening measurement). Ultimately, the cable needs to be disconnected from the idler arm assembly, and the cable operation and the cowl flap assembly need to be checked independent of one another for smooth, positive action. I’d also grab the end of the inner wire with smooth jaw pliers and push/pull against someone in the cockpit to see if the inner wire is secure at the knob end. Good luck with this one...whatever it is, it’s got to be something simple. (Devious, but simple) Edited November 4, 2020 by PilotCoyote Quote
carusoam Posted November 4, 2020 Report Posted November 4, 2020 The aerodynamics inside the doghouse are just mediocre... (being nice) Keeping the cylinders cooled is always a challenge... Have a look at cowling mods that have been done... Everything from closing down the guppy mouth, to changing out the cowl for something newer... Check and make sure the dog house is working as designed... lots of cracked sheet metal, and extra holes can get in the way... There are many seal updates using silicone instead of felt... Air leaks past the starter and alternator have shown up from time to time... PP thoughts only, not a mechanic... Best regards, -a- Quote
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