Turbo for flatlanders

[Clark1961]

The principles behind this vary with the type of engine (including the type of turboprop; the operation of a garret/honeywell vs. a Pratt, for example, is different), but the principle remains the same.

Would someone translate this into English for those of us not attuned to Master Bader's expertise?

 

[wabower]

It's the fundamentals of internal combustion combined with some smoke and mirrors and a little dodge and weave for good measure.

Bottom line is that he trapped himself into an somewhat untenable position and was trying to obfuscate his way out of it.

Would someone translate this into English for those of us not attuned to Master Bader's expertise?

 

[Morne]

So can I drag this conversation back from turboprops for a moment?

It seems like with turbo a critical piece of equipment would be some sort of graphic engine monitor, right?

Also, the benefits are most likely to be seen if you have longer legs like an hour plus, right? No sense climbing high enough for the turbo to help short of that?

 

[Alexb2000]

So can I drag this conversation back from turboprops for a moment?

It seems like with turbo a critical piece of equipment would be some sort of graphic engine monitor, right?

Also, the benefits are most likely to be seen if you have longer legs like an hour plus, right? No sense climbing high enough for the turbo to help short of that?

The thing about a piston turbo is you can fly high or not depending on conditions and the fuel penalty isn't the same as a TP. If you had really strong winds just stay low when into them and high to take advantage coming the other direction. Using XM winds aloft can help you decide where to get the most advantage. On really short trips I don't climb unless weather, turbulence, etc. makes it miserable lower. I've found with passengers, that taking a little longer to climb and descend is OK if the ride is good. The turbo is about adding choices and flexibility IMO.

I am a believer in an engine monitor turbo or NA. Just a great piece of technology either way in any HP bird.

 

[weilke]

The thing about a piston turbo is you can fly high or not depending on conditions and the fuel penalty isn't the same as a TP.d

Yes and no. Mot turbocharged engines have a lower compression than their NA counterparts. As a result, your BSFC is a couple of percent lower. Unless you gain that loss back by the magic of TAS gain, you are going to burn a couple percent more fuel down low for the same speed. This does not apply to the same extent to intercooled turbonormalizer designs.

Yet to meet someone unhappy about his TC plane, some piper and mooney products excluded (where going tubo means a change from a 4cyl Lycoming to a 6-cyl Conti).

 

[jnmeade]

Well, I'll be wrong before I start. I had a T210M in flat country and enjoyed it. Typical trip was Iowa - Texas, 5 hours non-stop at 10-12k. I ran 33" MP and 2250 RPM LOP and burned about 12.6 gph at 150 - 155 KTAS.
I don't have a dog in this fight, just saying what I had and liked.

 

[Everskyward]

It seems like with turbo a critical piece of equipment would be some sort of graphic engine monitor, right?

Now that they are readily available I would say yes, however you aren't going to trash the engine without one. I flew turbocharged airplanes for many years with only a simple EGT.

 

[wabower]

So can I drag this conversation back from turboprops for a moment?

Sure.

It seems like with turbo a critical piece of equipment would be some sort of graphic engine monitor, right?

Highly desirable but not universally installed.

Also, the benefits are most likely to be seen if you have longer legs like an hour plus, right?

In most cases, absent a hard object (like Wheeler Peak) or WX.

No sense climbing high enough for the turbo to help short of that?

See prior.

 

[Skylane81E]

Yes and no. Mot turbocharged engines have a lower compression than their NA counterparts. As a result, your BSFC is a couple of percent lower. Unless you gain that loss back by the magic of TAS gain, you are going to burn a couple percent more fuel down low for the same speed. This does not apply to the same extent to intercooled turbonormalizer designs.

Yet to meet someone unhappy about his TC plane, some piper and mooney products excluded (where going tubo means a change from a 4cyl Lycoming to a 6-cyl Conti).

Airframe matters too, do you have a plane with range and speed to make flying that high worth it?

There is a reason Cessna didn't make T172, and it seems to me that turbos are more previlent on 210s than 182s

 

[wabower]

I liked mine too, bought new and owned it for 19 years.

Well, I'll be wrong before I start. I had a T210M in flat country and enjoyed it. Typical trip was Iowa - Texas, 5 hours non-stop at 10-12k. I ran 33" MP and 2250 RPM LOP and burned about 12.6 gph at 150 - 155 KTAS.
I don't have a dog in this fight, just saying what I had and liked.

 

[DouglasBader]

Would someone translate this into English for those of us not attuned to Master Bader's expertise?

Turboprop engines, like turbojet engines, are designed for efficiency in a particular operating range,which is near the rated operating speed for the engine. You may think of operations at lower speeds as operating in too low a gear in a bicycle or car; one is "lugging it." Operating too fast is working too hard; usually on takeoff.

There is an altitude range, and one particular altitude, at which the flight may be operated under a given set of conditions (aircraft weight, outside air temperature) most efficiently. This is the best specific fuel consumption. If one operates higher than that altitude at that weight and temperature, one is not efficient; speed suffers, and fuel consumption is at a higher rate. The aircraft must fly at a higher angle of attack, drag increases, more power is required to do the same job.

At lower altitudes than optimum for a given weight/temperature, one is not operating efficiently enough. Operating the engine at a lesser power setting means operating at slower, less efficient engine speeds, and specific fuel consumption increases. The purpose of flying high is to reach a point where the engine is able to be operated within it's most efficient range, and this concept is applicable to turboprops, turbojets, and turbofans.

Turboprops can be operated quite efficiently, especially at high altitudes, if the airframe will get there, but the limiting factor is the airframe. This is why the Piaggio does wonderfully at FL410 while the King Air limits out at 270, and struggles much above the low 20's.

Turbocharged piston airplanes don't experience these constraints or benefits; the primary issue with the turbocharger is the ability to restore manifold pressure (or increase it). Turbopropeller engines also experience limiting cross-over effects as they climb, where the engine may be torque-limiting at lower altitudes, it becomes temperature-limiting at higher altitudes: it "torques-out" down low, but "temps-out" up high. Many turboprop engines are this way. The engine will reach torque limits at low altitudes, and temperature limits at high altitudes. Turbine engines differ in one critical aspect from pistons, however, in that adding fuel to a turbine engine keeps increasing speed and temperature, while the same isn't true in a piston engine.

Turbopropeller engines are also their own form of turbocharger; that's the purpose of the compressor and diffuser: increase airflow and pressure, and the engine does this quite well all the way well up into the flight levels. The problem is the wing; it's efficient within a narrow angle of attack range in cruise.

The King Air has a great wing for low altitude operations. It's not a great high altitude wing. The same can be said of most other turboprops, most of which are scarcely efficient, high performers or speed-demons. Turboprops are relatively economical, and they're versatile. They tend to takeoff and land fairl short, fly at reasonably high altitudes, have a modest fuel burn, and they don't break the bank. They're far more reliable than piston airplanes, and they move the operation to a slightly higher state of affairs than a piston airplane. One could say that turboprops are a jack of all trades, but master of none.

It seems like with turbo a critical piece of equipment would be some sort of graphic engine monitor, right?

Critical, no. Very useful, yes.

Multi-point monitoring where one can track and trend individual cylinders is more useful for continued observation of operational engine health. It allows one to spot trouble and account for it early, as well as address individual cylinder inefficiency, injector blockage, etc.

 

[MitchB]

That's not the only difference. Fuel burn decreases, but the airplane doesn't fly nearly as well at higher altitudes. Above about FL240, the airplane is a real dog, and flies with a steep enough angle of attack that in my opinion, it's not much good. The wing really struggles at altitude.

Most light turboprops are in their element in the teens to at best very low 20's. Above that, they're not much good.

Just because you can get there and stay there doesn't say much. It's a dog at altitude; they mostly all are.

I have to jump in here - apologies. This is just bad information. Doug, I think someone has led you astray.

What is your definition of "flys like a dog"?
My experience is in both C-130s and Beech 200 King Airs. I flew both - as a line pilot and Instructor / Check Airman with over 1000 hours in each - in the Navy.
Aerodynamics will tell you the flying characteristics in the flight levels is exactly as it is at 5000 feet at the same indicated airspeed. That is - if your IAS at FL250 is say, 145 kts then the airflow over the wings is the same as 145 IAS at 5000 ft, and the handling is identical. I thought the B200 flew just fine at those airspeeds - even on one engine.

TurboProps fly at a higher TAS and burn less fuel the higher you go. All turbines do. More at less cost. That is the definition of efficiency.
Ultimately, the truth is in the charts.
If an additional 3-4 deg of nose-up attitude in the Flight Levels makes you uncomfortable, perhaps a review of aerodynamics and angle-of-attack could help.

If the owners of the A/C you fly / customers you serve are happy to have slower airplanes that burn more gas, then I guess it's a little easier to convince yourself.

But please - don't preach it as Gospel here.

 

[Ted]

Poor maintenance doesn't make turbos glow. Temperatures do, and the P Navajo's turbos glow at night. One doesn't usually see them in the daytime.

Correct. At night we see our Navajo exhausts glow at our 1450 TIT.

Performance engineers. Aircraft manufacturers. Aeronautical engineers.

Well, I designed the aircraft engines for 5 years. Does that count?

So can I drag this conversation back from turboprops for a moment?

It seems like with turbo a critical piece of equipment would be some sort of graphic engine monitor, right?

Also, the benefits are most likely to be seen if you have longer legs like an hour plus, right? No sense climbing high enough for the turbo to help short of that?

Engine monitors are nice to have on all aircraft, and doubly nice to have on higher performance aircraft with turbochargers.

Turbos will typically only benefit you on really long legs, as Wayne has alluded to. Not just 1+ hour, more like 3+ hour. On my Houston -> Maine trips in the 310, it would save 60-90 minutes out of a typically 9 hour day on the Hobbs. In that case, the savings is huge. In the case of the 5 minutes that it would save me on an hour trip, probably not.

 

[wabower]

DouglasBader

Turboprops can be operated quite efficiently, especially at high altitudes, if the airframe will get there, but the limiting factor is the airframe. This is why the Piaggio does wonderfully at FL410 while the King Air limits out at 270, and struggles much above the low 20's.

YGBSM.

At FL180, ISA, B-200 cruise is 286 KIAS, FF# is 746. SFC is .38.
At FL350, ISA, B-200 cruise is 267 KIAS, FF# is 402. SFC is .67.

Stated differently, the increase in altitude reduces cruise speed by 6% but reduces fuel flow by 46%.

The King Air has a great wing for low altitude operations. It's not a great high altitude wing.

It's obviously good enough to maintain 94% of cruise speed at FL350.

Maybe if the wing was better Beech would have been the turboprop market leader for the past 40+ years rather than . . . oh, never mind, I forgot. They were--and are.

 

[MitchB]

Ted -

Speaking to the 310 specifically, but should apply to more airplanes (differences between turbo / turbo normalizing not withstanding) - Does flying a Turbo 310 at (for example) 160 kts at 8000 ft burn more fuel than a NA 310 at the same speed / alt?

My gut says the energy required is identical, ergo the fuel burn should be the same.
Does it happen in real life?

Ultimately what I guess I'm asking is: I know that the benefits of having a Turbo aren't realized w/o flying higher and or longer - but is there a penalty when you don't - other than increased component inspection / maint costs?

 

[wabower]

Nope, TAS drops between 18 and 35 as indicated in my summary. All Kingairs are fastest at low altitudes, but impractical to operate due to fuel burn. The 90's peak out at ~12,000'.

Please note that it is INDICATED speed that is reduced. TRUE airspeed goes up - significantly - and ultimately Ground speed. And THAT is what we care about, right?

Faster speed over the earth and reduced cost. That's the aviation equivalent of the Super Model who can cook and clean, right?

 

[Ted]

Ted -

Speaking to the 310 specifically, but should apply to more airplanes (differences between turbo / turbo normalizing not withstanding) - Does flying a Turbo 310 at (for example) 160 kts at 8000 ft burn more fuel than a NA 310 at the same speed / alt?

Yes, but not necessarily by much.

My gut says the energy required is identical, ergo the fuel burn should be the same.
Does it happen in real life?

Your theory is good on the surface. The difference is that the presence of the turbo adds restriction on the engine, which reduces available power to the propeller.

The turbo requires energy to spin it, which is extracted from the exhaust. Some of this energy is regained by the fact that the turbo now tries to force more air into the engine, but not all of it. If we did regain all of the energy put into the turbo, then this would violate the laws of thermodynamics.

Because of this, your 22"/2300 RPM combination (approximate) that you're going to get at 8000 ft with the naturally aspirated engine is actually going to produce more power than your 22"/2300 RPM combination with a turbocharged engine. You will also lose some energy because the air going into the engine will be less dense due to heating from the turbocharger, and therefore you have fewer air molecules.

Your losses increase if you have a lower compression engine (which many turbocharged engines do), because higher compression ratios allow more energy to be extracted from the fuel. I believe in the case of the T310 vs. straight 310 you see compression ratio drop from 8.5 to 7.3, so you have an extra loss there.

However, if I were flying at 8,000 ft, I would probably be operating at 24-30" (depending on the engine), and therefore putting more air into the engine to make up for this, and I would be going faster. 6,000 ft would be roughly the tradeoff altitude. Of course, now my fuel burn would increase as a result.

Edit: The above explains why you are making less power at the same power setting, which would result in going slower while burning more fuel (although not very much) at the same power setting. Therefore to go the same speed, you must increased your manifold pressure, increase the work the turbo must do (and therefore the power it takes), and burn more fuel to make the additional power to go the same speed.

Ultimately what I guess I'm asking is: I know that the benefits of having a Turbo aren't realized w/o flying higher and or longer - but is there a penalty when you don't - other than increased component inspection / maint costs?

There is a slight penalty, as explained above.

The execution is also a big question. If you simply bolt turbos onto an otherwise naturally aspirated engine, then the above will be true.

If, however, the turbos allow you to produce extra power in cruise vs. what you were able to produce before (and do so reliably - operating at 100% power all the time is not going to yield reliability), now you have more power and thus can go faster, for a fuel burn sacrifice.

This is why I say that I think the T210, and many of the turbocharged aircraft out there with naturally aspirated equivalents, had poor execution that I would have done differently.

 

[DouglasBader]

Well, I designed the aircraft engines for 5 years. Does that count?

It counts for a lot, but is only part of the equation, as you should know.

Performance is far more than engine design or operation.

At FL180, ISA, B-200 cruise is 286 KIAS, FF# is 746. SFC is .38.
At FL350, ISA, B-200 cruise is 267 KIAS, FF# is 402. SFC is .67.

Stated differently, the increase in altitude reduces cruise speed by 6% but reduces fuel flow by 46%.

KIAS is not the same as KTAS. While indicated airspeed drops, TAS increases, given a uniform temperature lapse.

 

[RotorAndWing]

While indicated airspeed drops, TAS increases, given a uniform temperature lapse.

That's not linear, as you should know.

 

[wabower]

Well, I'm sitting here looking at Beech's B-200 POH, Normal Cruise Power @ ISA chart on page 5-73. It says you are dead wrong. Which answer should I give on the oral, yours or theirs?

It counts for a lot, but is only part of the equation, as you should know.

Performance is far more than engine design or operation.



KIAS is not the same as KTAS. While indicated airspeed drops, TAS increases, given a uniform temperature lapse.

 

[Red Air Rambo]

Turbo's give you options when dealing with weather and winds that you don't have with normally aspirated engines. If there is no advantage to go up high I don't, but it sure is nice to catch a 70 knot tailwind from time to time.

 

[wabower]

Yeahbut it gets a little goofy up there, so some reasonable limit must be imposed for both. At 15,000' with 70 on the tail, groundspeed for a T-210 will be 236, a N/A 210 with the same fuel and cabin load will be 221.

Considering the amount of time that will be spent in those conditions, and the fact that both planes must fight the wind on the return trip, is a turbo worthwhile?

Turbo's give you options when dealing with weather and winds that you don't have with normally aspirated engines. If there is no advantage to go up high I don't, but it sure is nice to catch a 70 knot tailwind from time to time.

 

[weilke]

Airframe matters too, do you have a plane with range and speed to make flying that high worth it?

Sure, only makes sense for an aircraft used for travel.

There is a reason Cessna didn't make T172, and it seems to me that turbos are more previlent on 210s than 182s

If you look at the post-restart strut-wing cessnas, there are probably as many T182Ts as there are 182Ts and in the 206 the turbo outsells the 'plain' one 4:1. In both cases, the airframe remains pretty much the same (except for the oxygen system) and the difference is mostly in the engine.

 

[dell30rb]

Yeahbut it gets a little goofy up there, so some reasonable limit must be imposed for both. At 15,000' with 70 on the tail, groundspeed for a T-210 will be 236, a N/A 210 with the same fuel and cabin load will be 221.

Considering the amount of time that will be spent in those conditions, and the fact that both planes must fight the wind on the return trip, is a turbo worthwhile?

Yeah but how long is it going to take you to climb to 15,000 in a loaded up normally aspirated 210? The turbo will happily climb on up there.. the N/A airplane - not so much.

 

[wabower]

Yeah but how long is it going to take you to climb to 15,000 in a loaded up normally aspirated 210? The turbo will happily climb on up there.. the N/A airplane - not so much.

~Six minutes longer at max climb, a little longer at cruise climb. If you're in a big-honking hurry, just show up a few minutes earlier.

 

[Skylane81E]

~Six minutes longer at max climb, a little longer at cruise climb. If you're in a big-honking hurry, just show up a few minutes earlier.

Zactly. My mid weight 182 was still ~200fpm at a 20,000+ft DA (DA from 430's E6B function at 17,000 MSL in Aug)

 

[Alexb2000]

So those posting that feel so conclusively that a piston turbo isn't worth it in any flight profile, then why do you suppose they are selling so well?

Cirrus SR22T, SR22TN
Beech G36 (announced a factory turbo version) TAT conversion is very popular
Beech G58 (announced a factory turbo version)
Cessna 400, T182T, T206H
Etc.

Any answer works for me except the world is full of stupid people with $500K-2M to spend on a piston aircraft.

 

[denverpilot]

~Six minutes longer at max climb, a little longer at cruise climb. If you're in a big-honking hurry, just show up a few minutes earlier.

But at what groundspeed?

Block to block, the turbo will beat the NA by a non-insignificant margin if the mission for both is regularly above 10,000 MSL. It won't be huge, but it's there.

Everyone only compares cruise numbers and leaves out time-to-climb and the associated effect on groundspeed in most quick comparisons.

 

[wabower]

Max climb speed for both airplanes (on which climb rates are published) is ~identical. The biggest factor in time will be the spread between cruise speed and climb speed for the extra few minutes of climb. While in climb and cruise, however, the T version will burn ~20% more fuel than the N/A.

But at what groundspeed?

Block to block, the turbo will beat the NA by a non-insignificant margin if the mission for both is regularly above 10,000 MSL. It won't be huge, but it's there.

Everyone only compares cruise numbers and leaves out time-to-climb and the associated effect on groundspeed in most quick comparisons.

 

[Skylane81E]

So those posting that feel so conclusively that a piston turbo isn't worth it in any flight profile,

1) they have higher MAX airspeeds, all many people care about
2) there are several missions/locals that very greatly benifit from turbocharging

I met and talked to wone T182 owner who I know only looked at the max TAS number for his decision. Even seemed to think the aerodynamics were different. "My Turbo 182 cant fly that slow with out flaps" (90kts)

 

[wabower]

That wasn't the question. Instead, it was whether signficant tangible gains inure to turbo owners east of the Rockies. The answer is no. As evidenced by the lack of knowledge displayed on this thread, how many buyers do you think really understand the performance differences between the two breeds?

I happen to like the T versions a lot, and will never object if somebody chooses one over the N/A. OTOH, I'm sitting here with roughly 20 years of turbo'd ownership and 20 years of N/A ownership and more than 10,000 hours spread over both versions. I can't remember a single trip that couldn't have been flown in either plane, assuming both versions had ice protection.

So those posting that feel so conclusively that a piston turbo isn't worth it in any flight profile, then why do you suppose they are selling so well?

Cirrus SR22T, SR22TN
Beech G36 (announced a factory turbo version) TAT conversion is very popular
Beech G58 (announced a factory turbo version)
Cessna 400, T182T, T206H
Etc.

Any answer works for me except the world is full of stupid people with $500K-2M to spend on a piston aircraft.

 

[weilke]

Any answer works for me except the world is full of stupid people with $500K-2M to spend on a piston aircraft.

How about: Most new aircraft buyers live in the rocky mountains !

(Cessna stopped making the Corvallis 350 maybe 2 years ago, nobody bought them. Then again, they only sold one (1) 400 last year so that one doesn't seem to be much of a winner either).

 

[Alexb2000]

Just for conversation I have a picture of a 2008 G36TN at 17.5K doing 195KTAS. I would like to post it, but I keep getting some account quota error that I have no idea how to fix???

Anyway-

I have flown a regular 2009 G36 and I didn't see much over 160 at any altitude. Even if you flogged the dog out of it, the turbo is at least 25-30 faster. Same airframe, prop, etc. Who wouldn't trade that for 50-60 lbs. of useful, flat lands or not? BTW the TN STC actually increases gross weight, but that's a little sketchy IMO.

 

[wabower]

You could start with everybody who has flown all over the US for a long time and has been to 17.5 exactly twice and doesn't plan to do so again. Those who understand the scant tangible gains for their trips to Tyler, Tulsa, and many other destinations would be even harder to trap.

Even if you flogged the dog out of it, the turbo is at least 25-30 faster. Same airframe, prop, etc. Who wouldn't trade that for 50-60 lbs. of useful, flat lands or not? BTW the TN STC actually increases gross weight, but that's a little sketchy IMO.

 

[weilke]

BTW the TN STC actually increases gross weight, but that's a little sketchy IMO.

One of the numbers that goes into certified MTOW is the ability to do a go-around with 3.3 percent climb gradient with landing flaps and gear extended. To make it more exciting, that has to be demonstrated at 30C above ISA. If that climb gradient was the limiting factor for mtow, maximizing the power available for that maneuver at above standard temp can give you an increase in mtow.

(if your mtow is limited by the ability of the BRS to suspend the aircraft or if the landing gear mechanism is the limit you dont get a bump)

 

[weilke]

Just for conversation I have a picture of a 2008 G36TN at 17.5K doing 195KTAS. I would like to post it, but I keep getting some account quota error that I have no idea how to fix???

Do you have many of those linked picture attachements in your posts, the kind where you upload it onto the site rather than hotlinking it from a different site like flickr ?

 

[Alexb2000]

Do you have many of those linked picture attachements in your posts, the kind where you upload it onto the site rather than hotlinking it from a different site like flickr ?

I have uploaded pictures, no linking though. I didn't know that there was a quota. Advice to fix it?

 

[andybean]

I have flown a NA Arrow(not the 180 arrow). I have owned 2 Turbo Arrows.
There is no comparison in climb out and or air speed. There may be a larger desparity between the NA Arrow and the Turbo Arrow then compared to the 182 or 210 vs the T182 or T210. Personally its worth the freight for me to have the turbo. The added maintence shortened TBO are all the price you pay to go fast, and go high. The Turbo Arrow engine is a horrible maintenance hog. Even at that, there is nothing like pushing the throttle forward on the roll and feel that turbo kick in. Literally throws you back the seat.

 

[weilke]

I have uploaded pictures, no linking though. I didn't know that there was a quota. Advice to fix it?

Unless the mods have a different way of doing it, I would probably use the search function to look for your old posts that have the 'attachment' logo. Then go in there and delete some old stuff that nobody really cares about.

 

[Morne]

Personally its worth the freight for me to have the turbo. The added maintence shortened TBO are all the price you pay to go fast, and go high. The Turbo Arrow engine is a horrible maintenance hog. Even at that, there is nothing like pushing the throttle forward on the roll and feel that turbo kick in. Literally throws you back the seat.

This is the sort of input I wanted, though I notice from your location that you are NOT a flatlander.

Regardless, can you ballpark quantify the added maintenance/shortened TBO?