cowl flap extension in summer time

[mooney2201]

Does anybody know the proper trailing opening for cowl flaps,on a 1978 m20j. IN THE SUMMERTIME,FOR BETTER OIL TEMP,IN CRUSE..... 

[DonMuncy]

I think it depends on a lot of factors. Outside temps, baffle quality, power settings, etc. But on my plane (231) before a relatively recent overhaul, about 3/4 inch at the back of the cowl flap, seemed to be about right. Try that, fly it some and adjust as necessary.

[Bob_Belville]

1 hour ago, mooney2201 said:

Does anybody know the proper trailing opening for cowl flaps,on a 1978 m20j. IN THE SUMMERTIME,FOR BETTER OIL TEMP,IN CRUSE..... 

If you have a digital Oil Temp and CHT gauges I would and do adjust the cowl flaps based upon those temps. Take note of IAS, you might well find that partially open CFs may lower temps a few degrees and not cost you any speed. Bob Kromer says their careful measurements indicated CF in trail was a good thing.  

[MB65E]

I know there are some Moonies with barn door cowl flaps, but on my E I have not seen any speed delta. Even at 160kts. 

I'll go play with it I guess. Mine are usually closed or slightly trailed. 

-Matt

[ArtVandelay]

Does anybody know the proper trailing opening for cowl flaps,on a 1978 m20j. IN THE SUMMERTIME,FOR BETTER OIL TEMP,IN CRUSE..... 

I close mine, after engine is properly leaned.

[Bob_Belville]

1 hour ago, MB65E said:

I know there are some Moonies with barn door cowl flaps, but on my E I have not seen any speed delta. Even at 160kts. 

I'll go play with it I guess. Mine are usually closed or slightly trailed. 

-Matt

Full open costs me at least 2-3 kts. (I don't see 160 ktas very often - here's one from our return from KGGG.)

[jetdriven]

The J cowl flaps cost 3 knots when trailed in cruise.  You shouldn't be having oil temp problems unless the baffles are old or the center rear baffle sal flops  backward.  Flying with them locked full open tears the hinges out of the fiberglass cowl.  

[Oldguy]

At the Mooney Summit last year, Bob Kromer had a presentation and one item of note for me was the configuration of cowl flaps on a J. They found during flight tests the most effective/efficient aerodynamics and cooling occurred when the cowl flaps had a 3/4" to 1" gap at the rear when fully closed. No gap at the back actually caused air to blow the "tufts" they had attached to the cowl forward during tests. I had my mechanic set them as Bob suggested at annual and have noticed a little better oil temperature as we have warmed up this spring. YMMV.

[MB65E]

Nice to know they were aware of the trail position. I've found you can "feel" where they want to be with the manual cowl flaps during cruise. To close them all there is resistance pushing in. Then if you pull them open you can feel the resistance build again. There is a happy spot where they can ride in the slip stream trailing.  On the Bravo they really disturbe the air when they are fully open. Makes some strange noises.

-Matt

[Bennett]

The LoPresi cowl for J's have side "gills" in addition to variable cowl flaps. Virtually never have to open the cowl flaps even a bit in level flight. I am still breaking in new cylinders (top overhaul at LASAR) and on a really hot day, I open the cowl flaps a bit to reduce temps. Never had to do this before the top overhaul, but each hour of the break-in process brings down the temps. I think all will be normal in another 5-10 hours.

>

[bradp]

On June 6, 2016 at 0:58 PM, Oldguy said:

At the Mooney Summit last year, Bob Kromer had a presentation and one item of note for me was the configuration of cowl flaps on a J. They found during flight tests the most effective/efficient aerodynamics and cooling occurred when the cowl flaps had a 3/4" to 1" gap at the rear when fully closed. No gap at the back actually caused air to blow the "tufts" they had attached to the cowl forward during tests. I had my mechanic set them as Bob suggested at annual and have noticed a little better oil temperature as we have warmed up this spring. YMMV.

Open 3/4-1" when in the trail position or in the closed position?  I've never been able to measure my trail position properly - seems like the mechanism needs back pressure from air flow to open into the trail position.  On the ground I get closed or open.  In the air I get closed, trail, and open.  

[jetdriven]

The SMM only gives you 1/4" 

[Oldguy]

13 hours ago, bradp said:

Open 3/4-1" when in the trail position or in the closed position?  I've never been able to measure my trail position properly - seems like the mechanism needs back pressure from air flow to open into the trail position.  On the ground I get closed or open.  In the air I get closed, trail, and open.  

Brad,

In the fully closed position they are about 3/4" open. Don't use trail on mine.

[Bennett]

On 6 June 2016 at 6:37 PM, Bennett said:  

 

 

 

 

The LoPresi cowl for J's have side "gills" in addition to variable cowl flaps. Virtually never have to open the cowl flaps even a bit in level flight. I am still breaking in new cylinders (top overhaul at LASAR) and on a really hot day, I open the cowl flaps a bit to reduce temps. Never had to do this before the top overhaul, but each hour of the break-in process brings down the temps. I think all will be normal in another 5-10 hours.

 

 

 

 

 

 

 

 

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Awesome.  Just out of interest what was the speed increase post cowl installation?  And the amu s to purchase and install if immay be so bold as to ask. 

The quick and dirty answer is "Too much". Fortunately for me the airplane was equipped that way when I bought her. Actually, I understand that there are more than a few J's with the LoPresti cowl. It is a very fine piece of engineering, beautifully built of carbon fiber and other exotic materials, but I understand that it costs $17,000 or so (including the HID Boom Light). I don't know the install costs. The cowl kit includes new front wheel doors, a fairing behind the doors, and a transition fairing between the top of the cowl and the windshield. LoPresti claims a 7 MPH increase In speed (not specified by altitude, or with or without use of their Ram Air setup- much better than stock).