max turbo temps

[flyersfan31]

So, say your turbocharger redline is 1750. Let's further postulate that peak TIT usually comes around 1700-1710, which is where your mfr suggests you run for max economy. It certainly is economic, reducing fuel flows by about 3.5gph vs 100ROPTIT. Would you feel comfortable flying at those temps?

 

[N801BH]

The exhaust turbine blades on the turbo are pretty darn tough and can stand that heat range for extended durations. The real limiting factor is the oil that circulates through the turbo bearing housing to lubricate and cool it... On the race engines I built we had the luxury of incorporating a water cooled bearing housing and that set the TIT temps somewhat higher since the oil did not get "cooked off' with the high temps.. On planes you do not have the option as 'most' are air cooled and coolant jacket water is not available. IMHO.

Ben
www.haaspower.com

 

[bbchien]

Only if you want to replace your turbo twice in the life of the engine. You'll coke the bearings, and fry the tops.

1750 would be a marketing department limit, therefore. Ever heard of the statement, "If you want to go that fast, buy a faster airplane and run it more slowly". The is from whence the saying came.

 

[flyersfan31]

Only if you want to replace your turbo twice in the life of the engine. You'll coke the bearings, and fry the tops.

1750 would be a marketing department limit, therefore. Ever heard of the statement, "If you want to go that fast, buy a faster airplane and run it more slowly". The is from whence the saying came.

Yeah, that's my thinking, too.

Kinda irresponsible, don't you think. "Here, run at these temps. Trust us...."

 

[Ted]

Limits are not goals.

 

[sba55]

Yeah, that's my thinking, too.

Kinda irresponsible, don't you think. "Here, run at these temps. Trust us...."

It is. And that's how mfr recommendations for almost all engines are written. Which is why a mfr recombination regarding engine management is almost always guaranteed to be bad for you, both from a monetary and a reliability point of view.

Run at 50 dfROP, running LOP is dangerous, etc. Definitely a pattern in aviation, sadly, because unlike for cars, mfr often don't have to pay you if your engine fails....

I wish aviation piston engines could be more like turbine engines in this aspect.

 

[Ken Ibold]

Yeah, that's my thinking, too.

Kinda irresponsible, don't you think. "Here, run at these temps. Trust us...."

A Piper sales guy RECOMMENDED I fly a Matrix at a CHT of 525. It got decent climb at that, but there is a significant difference between selling an airplane and owning an airplane.

 

[Ted]

A Piper sales guy RECOMMENDED I fly a Matrix at a CHT of 525. It got decent climb at that, but there is a significant difference between selling an airplane and owning an airplane.

525F is above the CHT limit on that engine, so even if you did think that limits were goals...

The POH on my Aztec says it will do 200 mph. Yeah, it'll do it... running 25"/2500 RPM and with CHTs of somewhere north of 500. My 180 mph power setting burns about 2/3 the fuel and CHTs are happy. Much better.

 

[skidoo]

Seems like most here do not advocate running at this peak. So, taking the OP limits, what would be better: Running 100 ROP, or cutting back the MP/rpm so that the peak occurs at say 1550 and then running it at that peak for best economy, or would it be better to cut back to that peak temp, and still operate at 50 to 100 ROP?

 

[flyersfan31]

A Piper sales guy RECOMMENDED I fly a Matrix at a CHT of 525. It got decent climb at that, but there is a significant difference between selling an airplane and owning an airplane.

WHAAAAT??????!!!!!!!! That is absolutely nuts!

(One reason not to buy a demo!)

 

[gismo]

Seems like most here do not advocate running at this peak. So, taking the OP limits, what would be better: Running 100 ROP, or cutting back the MP/rpm so that the peak occurs at say 1550 and then running it at that peak for best economy, or would it be better to cut back to that peak temp, and still operate at 50 to 100 ROP?

First of all, the acceptable range of mixtures varies with the HP being delivered. If you're running 60% max rated power or less you can run with whatever mixture keeps CHTs under control (<=380F) and results in a TIT that's certainly below redline and preferably something like 50F below that redline temp (redline TIT is not normally an issue below 60-65%). Above that power you want to stay further and further from the worst case mixture which is around 25F rich of peak EGT/TIT. At 75% power you should either be at least 100 F ROP or 80 F LOP (IIRC) assuming the TIT is also reasonably lower than redline and CHTs remain at or below 380F.

There are three goals with mixture management.

One is to prevent detonation and/or pre-ignition and excessive peak cylinder pressures. This is the primary reason for avoiding high power coupled with mixtures that put the EGT too close to 25 ROP where the pressure is highest and the detonation margins are slimmest.

Another is to keep the CHT well below 400 F where the casting starts to lose strength significantly and problems with valve cooling begin. Lower CHTs also help prevent detonation and pre-ignition.

The third one (on a turbocharged engine) is to prevent premature wear of the turbocharger itself. This is the basis of the TIT redline and depending on the installation, turbo life is enhanced by keeping TIT 10-50F under the published limit.

 

[Ted]

Got a few days behind, and wanted to respond to this.

Lance has a good synopsis. A few things I'd add is the specific power settings that you need to be careful in do depend on the specific engine. Turbocharged engines and higher power engines require more care, whereas lower power engines are more forgiving.

CHT, TIT, and IAT are the biggest things to be concerned about. Detonation will typically manifest itself with CHTs rising, and frequently you'll watch them take off if it gets bad. I am to keep CHTs at or below 380.

I would also generally try to stay a bit further away from TIT limits than 10-50 degrees. Limits are not recommended operating numbers. 1600 or cooler is generally a good number on the ones I run. I have talked to a lot of Navajo operators who have gotten excellent reliability using a TIT of 1450F. There's probably something to that.

 

[flyersfan31]

I feel better now. My SOP is NEVER allow CHT above 380, lean to 1600 or so TIT. I don't climb at 42"/2500 either, except the first 1500ft or to get out of icing. I go to cruise climb 35"/2500/32gph after initial climb-out, observing my 380d CHT limits.

 

[N801BH]

I feel better now. My SOP is NEVER allow CHT above 380, lean to 1600 or so TIT. I don't climb at 42"/2500 either, except the first 1500ft or to get out of icing. I go to cruise climb 35"/2500/32gph after initial climb-out, observing my 380d CHT limits.

32 GPH ? That's quite the thirsty bird.....

 

[flyersfan31]

32 GPH ? That's quite the thirsty bird.....

Just in climb to keep those 350horses cool and humming. Thirsty in level flight too, 20.5gph, but 175TAS is a fun speed; 190 up high. I could do better LOP, but am unwilling to experiment while in warranty. Lycoming is pretty anti-LOP. Like, very.

 

[Ted]

Price of power - 350 hp is going to take a lot of fuel to feed.

Basically, the fuel burns on the Matrix/Malibu are fairly similar to my Aztec how I run it, but I don't have turbos and my engines aren't high powered. I also go slower. When you get to over 300 hp and turbocharged on these engines, well... that's going to cost some fuel, even if your SFCs are the same.

Andrew: Your SOP sounds like what I'd do with your plane.