C models with fixed cowl flaps

[DXB]

Slow day in the vintage Mooney world so here's another esoteric topic - moving cowl flaps - specifically they disappeared one plane before mine -SN  680002 - rolled off the line.  I don't know if they ever came back on the C or if any other planes lack them. Can anyone enlighten us?  Also, has anyone ever made their fixed cowl flaps movable? Was  it worthwhile from a CHT perspective?  If so I imagine it's a cheaper project than the top overhaul it might prevent.

[Mooneymite]

My 74 C has fixed cowl flaps.  I assumed that fixed cowl flaps happened when Mooney went to the "doghouse",  but perhaps that is not the case.  I fly in the "Hotlanta" environment and have never had my CHT's, or oil temp run higher than the edge of the green even on really hot days.  While fixed cowl flaps may cost some drag at cruise (?) since they can't  be closed, the ease of operation and lack of maintenance required seems like a good trade off, though keeping the doghouse integrity does require some attention.

YMMV

[carusoam]

My 65C went from moveable to fixed... On it's own...

It's mechanism had worn out.  Newer Cs had fixed cowl flaps.  The CB solution followed the newer models.

If I had a JPI and a GPS I could have proved the effects of this simple CB solution.

The single CHT sensor didn't notice a difference with the flaps open some vs open a lot... I don't recall having too cold CHTs.  Too cold EGT was a problem for winter flying at 11,500', not enough cabin heat!

Looking forwards, closing the guppy cowl and having working cowl flaps would be an easy engineering study/data collection exercise.

Expect to collect JPI data over a range of flights and segments.  Take-off and climb on hot days would be of interest.  Effects on cruise speed would be the other point of interest.

Take a look at the O's cowl for pseudo modern ideas... No cowl flaps, good CHTs, very aerodynamic. 

Best regards,

-a-

[macosxuser]

Not specific to the C, but I've found my E gets the flaps closed early in flight, and keeps them closed throughout. CHT's stay below 380 in climb even on 90°F+ days with them closed and leaning normally. I see them as a hassle more than anything else. I'd imagine with the more tightly cowled J's, they became useful again.

[DXB]

Long frustrated by CHTs in climb on my C, I was planning to start a thread asking: "Has anyone converted fixed position cowl flaps on their '68 or later C model to the movable kind? If so, was it a big job? Did it help CHTs in climb much?"  Before posting, I thought I'd best search if there were already any threads on this topic.  Turns out I'd started essentially the same thread in 2016 .  So, anyone?

[Mooneymite]

19 minutes ago, DXB said:

Long frustrated by CHTs in climb on my C, I was planning to start a thread asking: "Has anyone converted fixed position cowl flaps on their '68 or later C model to the movable kind? If so, was it a big job? Did it help CHTs in climb much?"  Before posting, I thought I'd best search if there were already any threads on this topic.  Turns out I'd started essentially the same thread in 2016 .  So, anyone?

Does your C have the doghouse?  If so, I'd start by looking for cooling leaks in the doghouse and adjusting the baffling before I'd take on the complexity of moveable cowl flaps.  I'm not sure where to start on converting the cowl flaps.

[Ragsf15e]

I’d have someone with a C and moveable cowl flaps try a climb with them open and then a similar climb (same leaning, same speed, oat, rpm etc) and see if it makes any difference in CHT.  I have moveable flaps on my F and I move them out of habit and because the checklist says to, but I don’t get the impression they do much for temps.  However I haven’t tested it very well.

[0TreeLemur]

 

2 hours ago, Ragsf15e said:

I’d have someone with a C and moveable cowl flaps try a climb with them open and then a similar climb (same leaning, same speed, oat, rpm etc) and see if it makes any difference in CHT.  I have moveable flaps on my F and I move them out of habit and because the checklist says to, but I don’t get the impression they do much for temps.  However I haven’t tested it very well.

I forgot to open the cowl flaps on our C one day, on t/o with a warm engine, and boy it caused the EDM900 to scream.   EGT color bars went into the yellow fast- like right after wheels up.   Three seconds of WTF???, a check of full rich mixture, and I noticed closed cowl flaps.   Opened them and lowered the nose to 120 kias and things cooled off pretty fast.  They make a large difference.

On t/o with a warm engine, I often must keep speed on climb out to about 110-120 to keep CHT 4 below 410F, with cowl flaps full open.   Haven't tested with partially open cowl flaps.

[Ragsf15e]

14 minutes ago, 0TreeLemur said:

 

I forgot to open the cowl flaps on our C one day, on t/o with a warm engine, and boy it caused the EDM900 to scream.   EGT color bars went into the yellow fast- like right after wheels up.   Three seconds of WTF???, a check of full rich mixture, and I noticed closed cowl flaps.   Opened them and lowered the nose to 120 kias and things cooled off pretty fast.  They make a large difference.

On t/o with a warm engine, I often must keep speed on climb out to about 110-120 to keep CHT 4 below 410F, with cowl flaps full open.   Haven't tested with partially open cowl flaps.

I’d be interested in knowing if they make a difference with your speed holding 120mph.  Mine is an F, so a bit different, and no doghouse, but she’s very sensitive to climb speed and not very much to cowl flap position.  100 mph yields hot chts, 120mph is cool no matter what.  I also lean to target egt on the way up, so it’s not super rich.

[Hank]

34 minutes ago, 0TreeLemur said:

 

I forgot to open the cowl flaps on our C one day, on t/o with a warm engine, and boy it caused the EDM900 to scream.   EGT color bars went into the yellow fast- like right after wheels up.   Three seconds of WTF???, a check of full rich mixture, and I noticed closed cowl flaps.   Opened them and lowered the nose to 120 kias and things cooled off pretty fast.  They make a large difference.

On t/o with a warm engine, I often must keep speed on climb out to about 110-120 to keep CHT 4 below 410F, with cowl flaps full open.   Haven't tested with partially open cowl flaps.

Play with it in your hangar, see where to set it so they're open 1". That's where mine are fixed; there's a thread here somewhere that several of us put pictures in one year or another. My oicture had a tape measure against the cowl flap.

[carusoam]

Flaps way open may help some...

The inherent air flow control of the dog house is the crummy part...

Send another update request to David, regarding his cowl update...

PP thoughts only, not an air flow scientist...

Best regards,

-a-

[David Lloyd]

I think all C models had the doghouse.  Mine is a mid year, 1975 with the doghouse.  I think the F models went to open baffles in 1967.  Maybe the E models too, but not the Cs.  My airplane had cowl flaps maybe from a K were added to my airplane by Mod Works.  Don't remember if that was an STC or 337 without looking it up.  It was just adding salvaged Mooney parts.  The flaps open much more than the older C cowl flaps, about 3" at the rear edge.  They are either open or closed, no in-between.  Cylinder temps always are fairly cool, oil temps always over 200 in climb on a warm day.

[Raptor05121]

I have moveable flaps and with my venerable 60s single-CHT gauge, anything less than open brings my CHTs up. I've never needed to touch my cowl flap control. I'd sooner make it fixed so its one less thing to disconnect when I have to remove the lower cowling.

[Niko182]

5 hours ago, 0TreeLemur said:

I forgot to open the cowl flaps on our C one day, on t/o with a warm engine, and boy it caused the EDM900 to scream.   EGT color bars went into the yellow fast- like right after wheels up. 

Why would the cowl flaps have an effect on EGT's if you don't mind me asking?

[0TreeLemur]

27 minutes ago, Niko182 said:

Why would the cowl flaps have an effect on EGT's if you don't mind me asking?

That is a great question, and I can't exactly answer it, but it happened.   Four yellow EGT bars about the time I lifted off the ground.  Very unusual. 

WAG- Maybe with full power, at low speed, and cowl flaps closed it got an extra 200F hotter below the engine, which added to the temperature read by the EGT probes?

As I wrote, the engine was warm.  I had landed, filled up with fuel and taken off again when this happened.

[DXB]

18 hours ago, Mooneymite said:

Does your C have the doghouse?  If so, I'd start by looking for cooling leaks in the doghouse and adjusting the baffling before I'd take on the complexity of moveable cowl flaps.  I'm not sure where to start on converting the cowl flaps.

I've spent last 7 years of ownership fussing over every little defect in doghouse and as well as all other possible causes of suboptimal cooling, including flying technique. I'm convinced that a terrible combination of poor cowl/baffle design on the C model and very uneven mixture distribution on the carb'd O-360-A1D is a major problem even with all other possible issues addressed. 

That said, I'm not sure the fixed cowl flaps made things much worse on the C. I suspect Mooney tried to fix them at a slightly open position that actually reduces drag by limiting air flow reversal at the front cowl opening and also provides comparable cooling to fully open for my particular engine with the doghouse.  But maybe not - it's easy for folks with movable flaps to model the speed and cooling effects of fixed cowl flap position, so I bet someone here knows the real answer.

Edited March 7, 2021 by DXB

[1967 427]

14 hours ago, 0TreeLemur said:

 

I forgot to open the cowl flaps on our C one day, on t/o with a warm engine, and boy it caused the EDM900 to scream.   EGT color bars went into the yellow fast- like right after wheels up.   Three seconds of WTF???, a check of full rich mixture, and I noticed closed cowl flaps.   Opened them and lowered the nose to 120 kias and things cooled off pretty fast.  They make a large difference.

On t/o with a warm engine, I often must keep speed on climb out to about 110-120 to keep CHT 4 below 410F, with cowl flaps full open.   Haven't tested with partially open cowl flaps.

After reading about may others that don’t seem to have to pay attention to their CHT’s, I thought I was the one that would run into the low 400s if I wasn’t paying attention to what I was doing.  Your money ask exactly the same as mine.  My solution is similar to yours the only difference is, after lowering the nose I will typically pull the power back from 100%.  Obviously this is only on takeoff, in all other situation my cylinder heads typically run between 340 to 370.  Like you said to summit up, “they make a difference”.