It’s hot and CHTs are a problem! Solution??

[exM20K]

I have never observed more than a few degrees drop in CHT when flying in the rain.

-dan

[GeeBee]

This reiterates what I said but I need to point out your airplane was certified to climb to its service ceiling at Vy without overheating. That means, if you can't do it, it is likely you need to return the engine compartment to its like new status. 

 

https://www.eaa.org/eaa/aircraft-building/builderresources/while-youre-building/building-articles/engines-and-firewalls/engine-cooling-tips

[DXB]

47 minutes ago, GeeBee said:

This reiterates what I said but I need to point out your airplane was certified to climb to its service ceiling at Vy without overheating. That means, if you can't do it, it is likely you need to return the engine compartment to its like new status. 

 

https://www.eaa.org/eaa/aircraft-building/builderresources/while-youre-building/building-articles/engines-and-firewalls/engine-cooling-tips

You are correct of course, but I suspect that overheat standard used was redline at 500F in the 1950s. Accepting CHTs in the mid-high 400s will trash your cylinders within a couple hundred hours. Unfortunately the O-360 Mooneys with the doghouse cool poorly under best conditions (optimal carb fuel flow, perfectly sealed doghouse (which is quite rare), gaping open cowl flaps, correct mag timing, no induction leaks). Add legal STC power mods like Powerflow exhaust and timing advance on the Surefly and things only get worse (ask me how I know).  Unless there's obstacles close in, climbing at 120mph, well above Vy, is the way to go in these particular Mooneys.  I tolerate 430F on 2&4 in climb, and also 410 in cruise if I want to go fast.

[Utah20Gflyer]

1 hour ago, GeeBee said:

This reiterates what I said but I need to point out your airplane was certified to climb to its service ceiling at Vy without overheating. That means, if you can't do it, it is likely you need to return the engine compartment to its like new status. 

 

https://www.eaa.org/eaa/aircraft-building/builderresources/while-youre-building/building-articles/engines-and-firewalls/engine-cooling-tips

Seems like a reasonable position to take.  One would expect a manufacturer to hold to this sort of standard.   But my question would be at what temperature would this test be conducted?   Wouldn’t the cooling potential of 7500 ft DA air be different at 95 degrees versus 0 degrees?  
 

The article had some good information in it. thanks

 

 

 

[GeeBee]

Kerrville is not Anchorage.

[Hank]

12 hours ago, Utah20Gflyer said:

Thank you, this is helpful.  
 

According to google a gallon of gasoline produces 120,000 BTUs.  My plane burns about 16 gallons per hour at full throttle prop at 2700 rpm.   That’s 1,920,000 btus per hour or 32,000 btus per minute.   If you applied one quart of water per minute that would provide 2000 btus of cooling.  That is a 6.25 percent reduction.  
 

A 6.25 percent reduction of a 420 degree CHT is 26.25. I know napkin math isn’t going to be accurate but theoretically that might reduce a 420 degree CHT to 393.75 degrees.  Maybe?

No, it doesn't work that way. A reduction of energy input by 6% will not lower the temperature by 6%, and if it did, it won't be 6% of the reading in °F or °C.

Drop back to the combustion equation, find the energy released; then run the cooling calculations and add the extra cooling from the water. THAT will give you the temperature reduction. 

This can be eyeballed by a short flight through some rain, which will ingest much more than a quart a minute, often cooler than ambient candles watching the CHT.

[PT20J]

CAR 3 cooling requirements:

§ 3.586 Cooling test procedure for singleengine airplanes.  This test shall be conducted by stabilizing engine temperatures in flight and then starting at the lowest practicable altitude and climbing for 1 minute at take-off power.  At the end of 1 minute, the climb shall be continued at maximum continuous power until at least 5 minutes after the occurrence of the highest temperature recorded.  The climb shall not be conducted at a speed greater than the best rateof-climb speed with maximum continuous power unless: (a) The slope of the flight path at the speed chosen for the cooling test is equal to or greater than the minimum required angle of climb (see § 3.85 (a)), and (b) A cylinder head temperature indicator is provided as specified in § 3.675.

§ 3.675 Cylinder head temperature indicating system for air-cooled engines.  A cylinder head temperature indicator shall be provided for each engine on airplanes equipped with cowl flaps.  In the case of airplanes which do not have cowl flaps, an indicator shall be provided if compliance with the provisions of § 3.581 is demonstrated at a speed in excess of the speed of best rate of climb.

 

 

[Fritz1]

yes to all, keep baffles tight, put nose down, run make sure you are getting full rich mixture, Reno racers typically are experimentals, to my best understanding they use as much ADI fluid and spray bar fluid as they use fuel for their run which is typically less than 10 min, think there was a STC'd ADI kit for the 350hp TIO541 used in the Piper Navajo, but this is turbo charged, so tweaking the baffles on a n/a engine to perfection is the path of least resistance and should solve the problem

[A64Pilot]

I have only done cooling climbs on turbines and there are many places where temps are taken, additionally there is extended taxiing, plus extended idling with different positioning of the wind etc., it’s a pretty comprehensive test, oh and on a turbine anyway I had to load the electrical system to max too, which is more difficult than you might suppose, after all the climb tests, you land and go through a comprehensive set of ground tests.

Oh and there is a cal factor that takes into account for cooler days, it’s very conservative so it behooves you test on the hottest day you can if you think passing the test will be difficult.

In our Mooney’s as has been been discussed a climb at 495F is acceptable, but most of us have come to the belief that always keeping temps to 400 or less extends the cylinders life significantly, so it’s not that it won’t pass, it’s that it gets hotter than we like.

I have found in my J even on a hot day that if I climb at the highest airspeed that gives me a 500 FPM climb that my cyl head temps stay right at the F mark on the stock gauge, which is the place it cruises at when LOP. Now I believe a J has better cooling than the older fleet, but I believe that if you accept a slower climb for a higher airspeed tgat it will keep your temps cooler, yes that may mean another lap in holding until your high enough to comfortably cross a ridge line, but it’s either that or cook you heads.

‘Note there is of course some altitude where 500 FPM may be too slow and even some altitude where 500 FPM isn’t possible at any airspeed, but those are higher than I normally fly.

Everything assumes of course that your baffling is in near perfect condition, being new doesn’t mean that, sometimes for example I’ve seen baffling bent the wrong way, baffles should be bent towards the airflow so that air pressure blows it sealed, but sometimes it’s not.

Edited July 12, 2023 by A64Pilot

[A64Pilot]

Would someone who has an analyzer mind telling me the temp on cyl 3 that is the F mark on the stock instrumentation? Take someone who’s analyzer isn’t primary

I’d like to know what temp it is that I’m trying to maintain.

[A64Pilot]

19 minutes ago, Fritz1 said:

yes to all, keep baffles tight, put nose down, run make sure you are getting full rich mixture, Reno racers typically are experimentals, to my best understanding they use as much ADI fluid and spray bar fluid as they use fuel for their run which is typically less than 10 min, think there was a STC'd ADI kit for the 350hp TIO541 used in the Piper Navajo, but this is turbo charged, so tweaking the baffles on a n/a engine to perfection is the path of least resistance and should solve the problem

ADI isn’t meant to keep head temps down, it’s meant to discourage detonation. In fact ADI probably increases head temp as it allows higher power and power means heat.

There has been an ADI STC for bigger Cessna singles to burn Mogas for decades. It works. I think it’s biggest target was for bush planes where Avgas is very difficult / expensive to get, but Mogas is plentiful.

I hope when lead is made illegal that it will be made available for us, but think as long as LL is available not many would buy it, I wouldn’t.

[jlunseth]

On 7/10/2023 at 8:56 PM, Utah20Gflyer said:

I have fixed cowl flaps unfortunately.  Adjustment looks somewhat labor intensive.  From what I remember there is a single hole in the flap and cowl that a bolt goes through to hold it in position.   So a new position would require drilling new holes.  Not a huge deal but would require the attention of my mechanic to supervise the process.   Once new positions were created I could adjust unsupervised. 
 

If you also have fixed flaps how do yours adjust?  
 

Has anyone every done a cabin adjustable cowl flap retrofit?   If so how much is involved?

 

Thanks! 

I live in MN. Going in to the winter I typically have the cowl flaps adjusted so they will fully close, in order to retain heat in the engine compartment. Going in to the summer I have them adjusted to "in trail," which is slightly open. Allowing just a little air to dump out of the bottom makes a big difference in summer heat. I agree with the guys suggesting you increase your speed and decrease the climb rate. I climb at 500 fpm, especially in the summer. Gives me a TAS of about 120 and helps the engine quite a bit compared to even 700 fpm. Check your baffling. Mine is currently being replaced, the old baffling had small folds in the port side which caused the last cylinder on that side to run quite a bit hotter than the others, especially in climb. I have a 231 (turbo charged piston with mechanically adjustable cowl flaps).