J Model mechanical cowl flaps

[A64Pilot]

When I bought my Mooney it’s cowl flaps when closed were open about an inch, when flown at normal power settings and ROP, which is how it had been operated, the Cyl head temps were fine, just over 50% of the green band, But when flown at altitude and lower power and LOP, cyl head temp was lower than I liked to see.

‘I guess I should have stated that the baffling is in perfect shape with new well sealing silicone seals, 200 hour Gann “performance” engine.

Anyway so I looked up in the MM and it states that they should be adjusted so that they are fully closed but your allowed up to 1/4 inch open in hot wx when fully closed. I adjusted them for fully closed
So today I headed out to Breakfast and was at 2,000 ft, 22 squared and 8GPH, pretty close to peak I think and Cyl head temp was in the green, but higher than I like, so I pulled them to where the over center mechanism was just unlocked which opens them I’d guess a 1/2 inch and temps dropped to the middle of the green.

Is this average for a J model? I don’t as of yet have an analyzer, will have to wait awhile until funds allow it so I’m basing temps off old stock instrumentation.

In the descent on the way back with power back to about 12” with the flaps closed it maintained middle of the green, so I think I’ll keep them where they are, just wondered if anyone else cracks them open for cruise, when in Fl weather down low, OAT was 28C Descent from 3500

‘I used to in the 210 as well. we would open them slightly to what we called trailing meaning if you unlocked them, the position they took themselves, it took pressure to open or close them, I think it was about an inch open.

Edited May 2, 2021 by A64Pilot

[ArtVandelay]

The green arc is 300°-475°F. I would not want to be above the middle of the arc and would not worry about it if a little below.

I always run LOP and so always close the cowl flaps, my temps run 330-360°.

[A64Pilot]

I guess I wasn’t clear in what I was asking.

‘Do most or many cruise with the flaps cracked open in warm/ hot wx, or does everyone cruise with them fully closed and temp in the middle of the green?

If everyone flies around in warm weather with flaps fully closed, then I have a issue I need to chase

[dzeleski]

I couldnt tell you if its normal but my 77 J is setup with about a 1/2 gap when closed. I have never cruised with them anything but closed. In the winter ill even take off with them totally closed. Summer time I keep them open for take off, and then around 5k ill put them to half, once I level off ill fully close.

[PT20J]

There are a couple of different setups on Js. The early ones had a flat cowl flap on the left side and are often rigged with a slight gap. The later ones had a curve to match the right cowl flap and are usually rigged flat.

Skip

[A64Pilot]

Mine is an 81, so I’d assume a flat left. Book says 1/4” max opening for hot weather. I’ll probably rig for that if nothing else to prevent chaffing, but I did like being able to keep cyl head temps in the green on a low power let down by closing them.

[ArtVandelay]

Mine is an 81, so I’d assume a flat left.

Mine is a 78, it has the curve version, the draining hoses are rigged on the left side.

[Hank]

I could swear that Bob Kromer addressed this at one of the last two Mooney Summits, but since the cowl flaps on my C are fixed I don't recall the details. Being open around an inch in the "Closed" sounds right, although a full inch may be a bit too much.

[PT20J]

50 minutes ago, ArtVandelay said:

Mine is a 78, it has the curve version, the draining hoses are rigged on the left side.

Betcha someone switched the left one. The IPC shows the change at S/N 24-1616. My 1978 had the flat one.

16 minutes ago, Hank said:

I could swear that Bob Kromer addressed this at one of the last two Mooney Summits, but since the cowl flaps on my C are fixed I don't recall the details. Being open around an inch in the "Closed" sounds right, although a full inch may be a bit too much.

At MooneyMax a couple of years ago, Bob suggested opening them 1/2 inch and said that this actually increased true airspeed. My current 1994 as electric cowl flaps and I tried cracking them open on the way back home and didn't notice any speed difference and only a few degrees difference in CHTs.

Skip

[jaylw314]

That's interesting, I always thought the J's that didn't have a flat left cowl flap simply had it replaced with a right one!

I fly during the summers down the west coast, so in the 90's on the ground is common.  I remember once needing to cruise with them cracked halfway, but that was before I had some baffle TLC done.  Otherwise, I've always had them closed during cruise.

They seem to be open about a 1/4" when fully closed.

I struggle to keep the CHT's higher than 320F in cold weather during cruise, and I'll routinely take off with cowl flaps half-open when the OAT is 60 or less.

 

[A64Pilot]

I adjusted them to be open 1/4 inch or so when fully closed, max what the book says, but haven’t flown yet, that will be this weekend. I think that will be fine, I’m not adverse to leaving them partially open for cruise

‘If your having trouble getting the cyl head temp warm enough, adjust them so they are fully closed, you can always crack them open a bit if needed. 

‘Down South I always taxi and run up and climb with them fully open, closed is for cruise, on the C-210 I flew normal cruise had them cracked open a bit and only closed them for the descent and landing.

‘Once landed I open the cowl flaps when I retract the wing flaps.

[Mooney in Oz]

On 5/4/2021 at 10:57 AM, A64Pilot said:

I adjusted them to be open 1/4 inch or so when fully closed, max what the book says, but haven’t flown yet, that will be this weekend. I think that will be fine, I’m not adverse to leaving them partially open for cruise

If you want more flexibility with cowl flap control, consider changing the position handle to a vernier type.  Just like the electric control, except it’s mechanical and you can have them open at whatever position you desire.

One of the better mods I’ve had done.

[A64Pilot]

That’s a interesting thought, the C-210 was mechanical but had stops so you knew where they were in intermediate steps.

‘The Mooney’s flaps due to the over center mechanism aren’t linear, meaning the first half of the knob travel opens the flaps only slightly, but they do seem to hold where you leave them. I think that’s going to work out for cruise, I’ll see.

[0TreeLemur]

On 5/5/2021 at 6:59 AM, A64Pilot said:

That’s a interesting thought, the C-210 was mechanical but had stops so you knew where they were in intermediate steps.

‘The Mooney’s flaps due to the over center mechanism aren’t linear, meaning the first half of the knob travel opens the flaps only slightly, but they do seem to hold where you leave them. I think that’s going to work out for cruise, I’ll see.

Last week after leveling out and leaning at 11,500' with OAT 10C (way warmer than standard), I noticed the cyl 3 & 4 CHT's were in the 380's.  Being used to seeing them in the 360's in cruise, and realizing the warm OAT, I opened the cowl flaps in our '83J to the first detent.  Brought CHT's down to 330-340F with no discernible effect on IAS or GS.  Makes a huge difference on CHT's with very little penalty on AS, if any.

[A64Pilot]

Two years later I now usually cruise down low, temps are sometimes like today at 35C at 1,000 ft, that’s 95F and it took the flaps just over centered to keep temps in the middle of green, but I’m now flying 23 squared and 8GPH which using 15 HP per Gl LOP formula gives me 120 HP, 60% power.

I climb full rich full open cowl flaps at 130 kts indicated, 500 FPM and that keeps temps right in the middle of the green, same as cruise, any slower and temps go up.

I’ve noticed no speed difference with cowl flaps just over centered or fully closed, but I’m cruising at 60% power so I wouldn’t expect to.

In Winter I close up the cowl flaps to keep temps up and Summer open them a little, speaking about full closed position.