Balancing Power and CHTs in Hot Conditions

[Jeff_S]

Hey all,

Flying my Mooney through my first blistering hot summer with it, and have some questions about how people maintain the best balance between power and CHT/EGTs.  Since I got the plane in January, I've been flying it 2500 RPM and LOP at the GAMI-recommended levels based on altitude (generally 20-50 LOP or thereabouts). However, with the hot temps even at altitude lately, I've noticed it hard to keep CHTs below 380° without really giving up a lot of power and speed...down to about 145 KTAS at respectable temps.

And yesterday in Jerry Manthey's Maintenance Class, he came down firmly on the ROP side of the camp so I started playing around with that. Seems like I can run at 100 ROP and get about 157 KTAS but the temps go up pretty quickly, unless I put the cowl flaps in trail and that keeps the temps down about 380 and speed at 154 or so. But that was at about 12 GPH.

So for those folks who routinely operate a J or other normally-aspirated airplane in very high heat, I'd like to know what your secrets are for balancing power with heat mitigation. I'm sure there's no one right answer and every plane is probably a little different but this will help me experiment. Thanks.

[Ned Gravel]

Jeff:

I fly an E model with the doghouse so this may not apply to you, but I think it may anyway.  Before my overhaul last year, I was getting 380 plus on number 4, the furthest away from the nose.  After the overhaul, my MSE re-created baffling to replace the cracked and busted up stuff I had before. 

Now I typically have between 300 and 350 on the hottest days.

The condition and repair of the baffling has a major influence on your CHTs.

IMO.

[KSMooniac]

I agree about checking the baffling, but my experiences are pretty close to yours.  I fly higher in the summer to get to cooler/smoother air, and lean further LOP to keep below 380 dF.  There just isn't much else you can do besides cowl flaps, but that will slow you down further than going more LOP.

Jerry is way behind the times regarding LOP benefits.  From his writings, it is my guesstimate that he just parrots the Lycoming or POH guidance with no further thought.  I'm sure the rest of his Mooney knowledge is quite extensive and valuable (I'm planning to take his last clinic in Wichita) but he just does not fully understand the intricacies of engine management with all that has been re-discovered and taught over the last 10 years.

[Piloto]

I had exactly the same experience as Jim and Scott with my M20J. I found that you do not need to go over 10deg LOP to lower the CHT and not loose more than 5 kts with cowl flaps closed. The lower fuel flow justifies the lower speed if you are not in  a hurry. At 10,000 I can get 150kts at 8gph or less maintining a CHT of 360F.

José

[Jeff_S]

Thanks all. Very helpful, and nice to know my findings are similar to others. I think the best solution is to just fly as high as possible for cooler air, but on a 90 mile flight it doesn't make much sense to go too high.

Jerry's class was very good, although as I feared it was very mechanically oriented so much of what he said just went right over my head. But the best parts came when he just started relating his personal experiences flying Mooneys and I did get some practical advice for generally watching out for my investment. It was definitely worth the time and money to attend.

I will add that Jerry's opinion on ROP vs LOP was not related to a belief (or lack thereof) in the science itself.  He was just questioning the logic of flying slowly in a fast airplane. He said "you bought a Mooney to fly fast! If you want to fly slow, buy a Piper."  Of course he was joking a bit, but just making a point that he could keep his CHTs where he wanted them and get maximum speed and utility out of the Mooney by flying ROP. It seems more a matter of personal preference than any kind of preaching on "the best" way to fly.

[KSMooniac]

ROP vs. LOP is certainly personal preference, but I still maintain that Jerry is speaking from a position of ignorance on the topic.  Flying LOP is undeniably more efficient, cooler, and easier on the engine than flying ROP.  That is not just because us non-turbo guys have to sacrifice a little bit of power and speed to go LOP...I would fly 85% power all day long LOP if I could, and long for a turbo-normalizer so I could do so.  That power setting is much better on the engine than 75% at 50 ROP, too.

[fantom]

LOP vs ROP arguments, for some reason, seem many times directly proportional the AGE OF the person arguing.

Like Jerry, however, I sure hate to give up that 5-7 knots when LOP.

Aso, having my cowl flaps in trail (15 degrees) doesn't impact my airspeed at all.

[RJBrown]

As I fly my MSE 50 knots slower than my Rocket I feel like I am standing still. I already have given up too much speed. Speed is why we fly isn't it? As I crawl along at 150kts saving gas like crazy I miss 20GPH and 200+.

[FlyingAggie]

Is you problem with CHT only during cruise?  Do you have any problems during t/o and climb?  Good baffling will provide lower CHT for both cases and LOP seems to offer options at cruise, but what can you do to lower CHT during t/o and climb?

I have only owned my plane since March and had no problem in the cool to mild temps this spring, but when I returned after an extended trip OCONUS, summer had arrived and suddenly,  I really have to watch my #2 CHT during climbs.  

This article by Mike Busch (http://www.avweb.com/news/savvyaviator/SavvyAviator_65_WhatsYourFuelFlowAtTakeoff_199805-1.html)  has me thinking I need to have my plane checked after having the fuel pump replaced shortly after purchase.  At full power, i.e. 36" MP and 2700 RPM, the fuel flow is 21.3 GPH, which is within the limits, but not at the high end TCM recommends.

I want to know if any other 231/252 owners have had their fuel flows adjusted as described in the Busch article and did it reduce your CHT during t/o and climb?

[Ned Gravel]

Quote: JimR

...... I now climb at 120 mph IAS ROP at WOT in my 201 using the APS Target EGT method ........

Jim 

[Ned Gravel]

Jim:

Thanks.  I had seen this one (as well as the others on the APS site).  I guess I was really looking for the number itself. 

In conversation with my MSC in Waterloo, Ontario and a bunch of other local Mooney drivers, I had sort of settled on 1360-1380 degF as my own Target EGT.  I use the approach described in the APS for 98% of any flight, except for past the first of the three GUMPS checks I do once the J-bar is vertical, when that sort of control is secondary to landing the aircraft.

Any further thoughts I might be able to use?

[danb35]

I use 1250 deg. F as my target EGT, but absolute values vary so widely that it's hard to advise accurately.

[KSMooniac]

I too use 1250-1300 dF for my target on my #1 cylinder.  To establish your target, simply note the EGT for a full-rich T/O at sea level, or as reasonably close as you can get.  1360 sounds too high to me...if you have fuel flow installed you can cross-check and should be right around 18 GPH at takeoff with everything forward on a standard, sea-level day.  It will be a little bit less at higher elevations and/or warmer temps.  If your fuel flow is significantly less than that, then you have another issue that could explain the higher EGTs.

EDIT:  18 GPH for the 200 HP Mooneys.

[Ned Gravel]

Folks:

That is the sort data I was looking for.  Thank you.