Turbocharged planes - discuss...

M

meritflyer

Well-Known Member
I've been doing some looking around at different aircraft, namely turbocharged. I often hear that turbocharged airplanes are much more likely to encounter excessive wear on the cylinder and it's associated components and in turn, hampers the engine's ability to be reliable and make TBO.

I'll take the Mooney Acclaim for example. The aircraft has a pretty impressive performance sheet - speeds in excess of 240 TAS partly thanks to a TCM TSI0-550-G-turbo-supercharged twin turbo with dual intercoolers. It always seems like engines of this nature as in the original engines found in the Beech Duke and Beech B36TC were subject to a very poor hour life and never quite made it to TBO.

I may be answering my own question so maybe some engine experts can tell me otherwise but can you super/turbocharged these engines, pull maximum performance out of them and still expect them to make TBO and be reliable? It gets very tedious and old to step climb the older turbocharged airplanes. My experience has been different with the newer aircraft which brings me to my next point..


I owned a turbocharged aircraft and it was HOT! Always ran upwards around 400F which ultimately required me to stage cool the engine. This was in a 1979 PA-28-201T. On the flip side, I am flying a Cessna 182T now that seems to have absolutely no issues whatsoever.

Some people say watch the EGT, some say watch the CHT, some say watch both. Maybe some folks on here with some mechanical and/or operational experience can shed some light on the subject.

Are these engines being squeezed for every last drop of performance?
 
"can you super/turbocharged these engines, pull maximum performance out of them and still expect them to make TBO and be reliable?"

Generally speaking and in one word, no.

If you plan on often flying high (flight levels) and running at max crusie power it is highly unlikely if not downright impossible that you will make TBO, and will probably need to "top" the engine well before then. Looking at ads for turbocharged aircraft that are for sale is often evidence of this. Example: "1100 SMOH, 300 STOH"

Indeed, some turbo systems are better than others, and even the older systems in planes like the Piper Arrow can be upgraded with intercoolers and or/ automatic wastegates that will improve upon turbo operation and engine cooling. I have a friend who has both on his turbo Arrow IV, and is quite pleased with the operation.

In the Cessna 210 turbo I now fly, we keep things "moderate", and that means running at no more than 70% power, and when O2 is available, no higher than in the mid teens. We do the same with a Cessna 421 that I also fly. We make TBO with the 421's engines because we do not push them, and are satisfied with 190 kts instead of 220 kts. With the 210, we are happy with 165-175 kts instead of 190-195 kts.

We watch the CHT, and since our engine is intercooled and we don't push things, our biggest concern is shock cooling during descents. Thus, we plan our descents further out and keep the power up to keep the temps from dropping too quickly. Yes, the CHTs will drop, and there is nothing wrong with that as long as the drop is slooooow.

After landing we wait at least 5 minutes with the engine at idle (this can include taxi time). This allows for the turbo to spool down while still receiving and adequate supply of oil from the running engine. When taxi times are short it can be interesting to watch a line man staring at us while we sit there with the engine running for 3 or 4 minutes, as he wonders what the heck we are doing!

Indeed, those are impressive performance figures for planes like the Acclaim, but when you read them you are listening to the marketing department, as you usually need to get up to FL250 and something over 80% power to achieve such performance. That's not practical or wise when it comes to engine health.

Sure, maybe every "blue moon" you might want to do it if you see you will have a 60 kt tail wind up there, but do it all the time and it will become very costly very qucikly.
 
loubetti said:
Sure, maybe every "blue moon" you might want to do it if you see you will have a 60 kt tail wind up there, but do it all the time and it will become very costly very qucikly.
Click to expand...

Did someone say Blue Moon? God I love Blue Moon with a slice of orange..On tap of course.

With regards to your question...I haven't a clue.
 
In my experiance, the biggest single factor leading to engine longevity is how often the airplane is flown. Everything else that we pilots love to debate about falls a distant second.

An airplane that sits around, only flying 50 hours per year has no hope of making TBO, no matter what type and or how it is operated.

OTOH, flight school airplanes a misused and abused, yet they regularly fly well past TBO.

In short, if you want to get maximum life out of your engine, go fly it 1 hour at least once per week. If you do nothing else, this simple act will drasticly increase the life expetancy of your engine.


Back to the OPs question, turbocharging (either normalized or boosted) inherently raises engine temps and therfore reduces the life expectancy of the engine. You will find that almost every turbocharged engine has a lower TBO than it's normally aspirated kin.

You simply must be more "engine concious" when flying a turbo than you can be in a skyhawk. Smooth power changes must be the norm, when you are spooling up a turbine to 50,000 RPM.

The turbo arrow was one of the worst engine instlations (the Duke being the all time dog). With the higher temps, yet no cowl flap to help controll that heat, reliablity seriously dropped.



I personally belive that "shock cooling" has morphed from a freak event useually brought on by gross abuse, into a bogeyman that will cause engines to shatter like glass. The draconian measures to prevent "overcooling" have gone way overboard. Make a modest power reduction that gives you a 500 FPM constant airspeed descent, and you'll be fine.

I flew skydivers in a 182 where we would climb untill the CHT redlined, gave it a mear 2 minutes to cool, then Vne descent. That engine went well past TBO.
 
USMCmech said:
In my experiance, the biggest single factor leading to engine longevity is how often the airplane is flown. Everything else that we pilots love to debate about falls a distant second.

An airplane that sits around, only flying 50 hours per year has no hope of making TBO, no matter what type and or how it is operated.

OTOH, flight school airplanes a misused and abused, yet they regularly fly well past TBO.

In short, if you want to get maximum life out of your engine, go fly it 1 hour at least once per week. If you do nothing else, this simple act will drasticly increase the life expetancy of your engine.


Back to the OPs question, turbocharging (either normalized or boosted) inherently raises engine temps and therfore reduces the life expectancy of the engine. You will find that almost every turbocharged engine has a lower TBO than it's normally aspirated kin.

You simply must be more "engine concious" when flying a turbo than you can be in a skyhawk. Smooth power changes must be the norm, when you are spooling up a turbine to 50,000 RPM.

The turbo arrow was one of the worst engine instlations (the Duke being the all time dog). With the higher temps, yet no cowl flap to help controll that heat, reliablity seriously dropped.



I personally belive that "shock cooling" has morphed from a freak event useually brought on by gross abuse, into a bogeyman that will cause engines to shatter like glass. The draconian measures to prevent "overcooling" have gone way overboard. Make a modest power reduction that gives you a 500 FPM constant airspeed descent, and you'll be fine.

I flew skydivers in a 182 where we would climb untill the CHT redlined, gave it a mear 2 minutes to cool, then Vne descent. That engine went well past TBO.
Click to expand...

First thing, I absolutely agree with the above, its well written.

Second, 240 TAS on the mooney is up somewhere in excess of 23,000 ft. Unless you are going on at least a 500 nm trip in the flight levels its a mute point. You still have to climb up that high, with any sort of passengers and enough gas and oxygen, its going to take a while to get there and at a reduced groundspeed.... probably shouldnt be taking passengers up that high unpressurized, and I will tell you its alot of stress on the body. Plus your only going to be doing it one way to catch a tailwind, not the other way to catch a headwind.

Third, everyone exagerates thier TAS, you cant beat physics. The top single engine pistons are all about the same speed. Sure manufacturers will do every slightest possible thing to get their airplane to go faster, but its not practical. Make the wing smaller and its going to be harder to land....ect ect

Fouth, temp = wear. Run hotter temperatures, get more wear. Run cooler temps, less wear. Do you want to run the engine at a lower temp rich, or at a hotter temp lean? Its a trade off. With the price of gas going up it might be more economical to run lean with hotter temps.

Fifth, dual turbos. Im going to make a compaison between two SE piston aircraft I have operational experience with. A 1978 T210, and 2006 Columbia 400, same horsepower. No cowl flaps for climb on the columbia, cowl flaps are on the 210. Almost the same temps climbing, columbia is a little cooler, but how? Well the fuel rate on the 210 is about 25 gal/ hour in climb and 38 gal/hour climb on the columbia. Two turbo chargers and a engineered high fuel flow on the columbia to keep the temps down are the reasons.

Sixth, dual turbo vs single turbo. Why do these guys put dual turbos on these things? so they can run them lean of peak cruise power which equates to arguably less fuel burn at cruise, lower temps at a given power setting 70%, and claimed reduced engine wear. The dual turbo guys can get more power from their engine at altitude. Hence, they can claim the "fastest piston" at a sacrifice to increased climb fuel burn, cramped areodynamic cabin, poor low airspeed handling, increased maintenance and purchase of two turbos... ect ect

Seventh, shock cooling is a major myth. Take a look at the temp rate change in an engine that is just starting, and just taking off. You will find the rate at which the metals WARMUP are a heck of alot greater than when you are reducing power. Furthermore if you ever start up an engine cold, I say 30F or below, you are doing a hell of alot of damage to the cylenders than any sort of shock cooling. Next time you crank up watch your CHT go from OAT to 150F, almost instantaneously. Same goes for EGT's.

this is a good read - you may have to click the title to get the full article.

my advice, cant beat a 182t

lemmie know what you guys think!
 
300 knot over the ground.. That's amazing. Sounds like Mooney did a great job on this airplane. I was surprised to hear the CHT's at FL250 were sitting mid-300's.

Sounds like a greatly engineered, solid airplane.
 
Indeed, if you want to discuss the detriments of turbocharging airplanes, the Acclaim's TSIO-550 is a poor example. The turbo normalizing system in the Acclaim is one of the most brilliant designs out there. It's not ground boosted, so the max MP is only 33.5". It has twin intercoolers to help cooling. The air inlets are massive. I normally fly it to altitude at 100% power and see oil temp 180-190 in the climb. The oil temp might climb to 200 climbing in the flight levels. Cruise oil temps usually are in the 185-190 range. Cruise CHTs are 350-360 rich of peak and as low as the 290s lean of peak (usually 310-320). These numbers are all at 75% power, which is basically the only way I cruise the airplane.

I have to agree with USMCmech - the most important thing you can do to increase your engine's lifespan is to fly it a lot. TCM even recommends that the big 6 cylinders like the 550 fly one hour per week. A lot of owners do not fly very often, and, as such, abuse their engines. My company buys and sells a lot of airplanes with IO-550s and it's not uncommon for a jug or two to need overhaul on an engine 8 years old but with only 400 hours on it. Conversely, the airplane 10 years old with 1500 hours on it has good compressions on all cylinders. I see no reason that the TSIO-550 in the Acclaim will not follow the same pattern.

Also, I can assure you that the Acclaim does the speeds it's advertised to do. I believe the Columbia 400 does as well, but I have never flown one. One interesting point of mention is that the Columbia 400 is limited to 65% lean of peak at FL250 for cooling reasons. The same engine in the Acclaim is not limited at all. The Acclaim "regular" is good for 237ktas at FL250 - we had one of these that went 237ktas at FL250. I have flown the prototype Type S, which is good for 242ktas - it goes 242ktas. To me, the more impressive speeds on the Acclaim are at more realistic altitudes, 12,000 feet or so. The straight Acclaim is good for about 204 at 12k, whereas the Type S is good for about 215. The airframe mods they did on the airplane work very well.

Other airplanes with other turbocharger installations suffer from numerous ailments. Real old airplanes with manual wastegates and altitude/temp-restricted power settings are at the highest risk of mismanagement simply because of pilot ignorance. One of the nice things about flying a newer airplane is that a lot of these old-fashioned problems are gone. I have flown newer models of Saratoga TC, Mooney Bravo, and 182T and found them all fairly easy to manage. The Cirrus turbo, Bonanza turbo-normalized, and Columbia 400 are all supposedly as easy to manage as the Acclaim, which is actually easier to fly than a normally-aspirated airplane. In the Acclaim, if you want to go fast, you can keep the throttle and mixture all the way forward. In the Ovation (normally-aspirated), you have to lean in the climb and then lean for altitude once you get there.
 
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