GA Turboprop

[kjensen]

Hi all

I'm doing some research on turboprop engines for general aviation, and I wonder what people here see as the advantages and disadvantages of a turboprop engine? Or just opinions in general..

Advantages:

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Disadvantages:

..
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I will really appreciate your input!

Thank you,
Kristoffer Jensen

[Bill Greenwood]

It sounds bad and smells worse, and it costs a lot more than a piston engine, and may need to fly high always requiring an IFR flight plan in order to get good fuel economy.

[kjensen]

It sounds bad and smells worse, and it costs a lot more than a piston engine, and may need to fly high always requiring an IFR flight plan in order to get good fuel economy.

Do you know how much higher fuel consumption a turboprop have compared to a piston engine?

[martymayes]

Do you know how much higher fuel consumption a turboprop have compared to a piston engine?

It's not enough difference to get excited about. Of course a turboprop has numerous advantages, fewer moving parts, more efficient propeller dia/speed, ability to use a wide range of fuels, reliability. The big disadvantage is cost. With current technology, GA is not quite ready to accept the additional expense.

[uavmx]

I'm shocked in this day and age we don't have a nice IO550 alternative turboprop. Something in the 300-400HP rating that get's comparable fuel burn (probably higher). I think it would be a great seller, but as stated, cost is the big thing. But think about how much you save in MX, reliability, not replacing cylinders all the time, just overall hassle. The TBO on a turboprop could be much higher too. Just do a 2k hr hot section inspection, then fly it to 4k hours easy.

There's got to be enough smart people that can get together and build something that fits those parameters.

[kjensen]

[QUOTE=uavmx;14355]I'm shocked in this day and age we don't have a nice IO550 alternative turboprop. Something in the 300-400HP rating that get's comparable fuel burn (probably higher). I think it would be a great seller, but as stated, cost is the big thing. But think about how much you save in MX, reliability, not replacing cylinders all the time, just overall hassle. The TBO on a turboprop could be much higher too. Just do a 2k hr hot section inspection, then fly it to 4k hours easy.

So in terms of technology, is a turboprop considered better than a piston engine? Who makes the turboprops available today in the 300-400hp range?

[steveinindy]

Do you know how much higher fuel consumption a turboprop have compared to a piston engine?

The difference between the fuel consumption of a high-end reciprocating engine and a turboprop aren't that different if you look at them on a pounds of fuel per horsepower per hour ratio. Of course, when you have an engine that produces 800-1000+ horsepower, it's going to consume more fuel than a 150-200 hp engine. The actual fuel consumption is going to vary based on the engine (for example, the Honeywell/Garrett TPE variants tend to get better economy than a PT-6) and the altitude you're flying at.

Keep in mind that this forum has a distinct lean towards the "low and slow" side of aviation so you're going to get comments like Bill's. A more inclusive forum like http://www.homebuiltairplanes.com/forums might be a better place to ask that. That's normally where I go when I have technical questions about things like turboprops (which is what is the powerplant for my design BTW).



may need to fly high always requiring an IFR flight

Which isn't a bad thing in the mind of those of us who are looking for point A to point B travel. One of the major drawbacks to this forum is the general disdain towards talking to ATC so people tend to look at you like you have two heads or make comments like "You know if you want to go above FL180 you have to talk to ATC all the time right?" when you mention things like turboprops or other high altitude cruise.



I'm shocked in this day and age we don't have a nice IO550 alternative turboprop. Something in the 300-400HP rating that get's comparable fuel burn (probably higher).

Why do you think people switch out the IO-550 and other similar engines for a more powerful turboprop. The benefits of a turboprop become less clear when you're going slower which is what a 300-400 hp range would entail.

[steveinindy]

Who makes the turboprops available today in the 300-400hp range?

Rolls-Royce has one but honestly it's not really worth it.


So in terms of technology, is a turboprop considered better than a piston engine?

It depends on what you're looking to do and who you ask.

[tdm]

Brayton cycle turbines have very high power-to-weight ratios, but suffer from poor thermal efficiency, which is the main reason why many land-based gas turbine plants are going cogeneration or adding a rankine bottoming cycle. (There is even development on magnetohydrodynamic generator bottoming cycles.. although normally MHD is used as a top cycle, with a rankine bottom)

[Kyle Boatright]

There are three primary advantages of turboprops. First, they are more reliable than piston engines. Second, they are smaller and lighter than piston engines. Third, they can run on a number of more common fuels, including diesel and (for some engines) gasoline.

Their disadvantages are that they are expensive to purchase, feed (they *typically* use 50% more fuel per hp delivered than a reciprocating engine), and maintain, relative to piston engines. Also, they are loud and their exhaust smells like a BBQ grill gone wrong.

[steveinindy]

feed (they *typically* use 50% more fuel per hp delivered than a reciprocating engine)

Once again, it depends on what engines you're comparing. A PT-6A which is what a lot of GA pilots think of when you say "turboprop" is a pretty inefficient engine. The difference is probably closer to 15-30% more instead of 50% unless you're going for the difference between a very low end recip and a poor quality turboprop. I based this guess off of the Honeywell/Garrett TPE-331-10AV that I am planning on using for my aircraft is rated at sea level at 0.53 lbs/hp/hr (for 940 shaft hp) as opposed to the various reciprocating engines I could have fallen back upon.

Then again, the fuel consumption kind of balances out once you factor in that you're generally going considerably faster which means you spend less time burning fuel than you would in recip powered aircraft.

The other two benefits of turboprops is that you don't get exposed to lead and there's a reduced risk of fire associated with either fueling or being in a crash involving an aircraft using Jet-A than with a similar aircraft utilizing 100LL or mogas. There's a reason why the Navy uses kerosene based fuels on its aircraft carriers.

[kjensen]

There are three primary advantages of turboprops. First, they are more reliable than piston engines. Second, they are smaller and lighter than piston engines. Third, they can run on a number of more common fuels, including diesel and (for some engines) gasoline.

Their disadvantages are that they are expensive to purchase, feed (they *typically* use 50% more fuel per hp delivered than a reciprocating engine), and maintain, relative to piston engines. Also, they are loud and their exhaust smells like a BBQ grill gone wrong.

OK, I see. Are they considered more reliable than piston engines? And if so does that translate to a safer airplane using a turboprop instead of a piston?

[Bill Greenwood]

Kyle, if your bar b que grill smells like a diesel, then you must be grilling something bad or the neighbors cat got caught in there. Switch out that possum meat for some real brisket.

I think a turbo smells like a diesel garbage truck, and some of them at idle sound like an engine running without oil in the bearings. There was an OV-1, ( Ithink) that parked right behind me at EAA. People would hold their ears or leave the area when it started up. It doesn't seem to effect the people inside the plane, but sure makes it unpleasant for anyone else outside on the airport, and makes hanging around the airport not the relaxing experience it is as some small airfields. I think it is not only the volume of the noise, but the high pitch. Not like hearing Bethoven at a full volume.

And as for as not wanting to have to talk to ATC for all of every flight, darn right. Now sometimes the weather is IMC, and part of getting through it is to talk to ATC. But on a nice CAVU day, particularly if flying in less crowded airspace, I certainly don't want to spend several hours of a flight listening to ATC yammer. It would be like if you went for a walk in the woods or a pleasure drive in the country or a bike ride and you were required to listen and talk to a local cop channel or talk show radio.

[steveinindy]

Are they considered more reliable than piston engines

Yes. That's what he said.


And if so does that translate to a safer airplane using a turboprop instead of a piston?

At least from a mechanical standpoint, yes. The problem is that turboprops are high-performance aircraft and you run into human factors issues....

[kjensen]

Yes. That's what he said.

I see I was a little too quick with my response :) but thanks anyway.

Next question: Are there any new turboprops for less that $75k out there, or is that just wishful thinking?

[steveinindy]

I see I was a little too quick with my response :) but thanks anyway.

Next question: Are there any new turboprops for less that $75k out there, or is that just wishful thinking?

Yeah, very much wishful thinking.

[martymayes]

There's got to be enough smart people that can get together and build something that fits those parameters.

Well, Detroit has played with gas turbine engines in cars for a long time and they have yet to hit on the right combination of practical and affordable. The stumbling block seems to be finding a recipe for mass-producing the internals. Lot of engineering talent and $$$ has been expended looking for solutions.

[martymayes]

Are there any new turboprops for less that $75k out there?

Only if you find a 75% off sale to go with it.

[kjensen]

Yeah, very much wishful thinking.

That's too bad. At what price do you think a turboprop would be interesting for the majority of general aviation?

[Frank Giger]

Steve has hit on the real pro's and con's of engine selection - mission of the aircraft.

If I wanted a true "cross the country" cross country aircraft it would look pretty good as an option. Maybe not so much for taking a friend up for an hour of sight seeing or for some touch and go practice.

Plus we have to avoid the infamous apples-to-oranges on fuel burn. Putting a turboprop engine against a O-200 isn't fair for comparing fuel consumption - one has to go to like horsepower types, where I think it might not be too different.

Not to say that I'd want to pay the bill just to do the runup on a turboprop, mind you...or want to tolerate the hugs and kisses from the maintenance guys when I showed up with one.

[Flyfalcons]

That's too bad. At what price do you think a turboprop would be interesting for the majority of general aviation?

Since the majority of general aviation is flying 200hp or less two to four seaters on short to medium distance flights, it's going to have to be pretty low.

[martymayes]

If technology advances to the point where a turbine engine can be had for a ~50% premium over a comparable piston engine, you'll have the majority of the GA fleet on turbine power in 20 yrs. or less. Obviously, a lesser cost would accelerate the conversion.

A 100 eshp turbine powered LSA would actually be a joy to fly on a local sight seeing mission or hr of touch-and-go training. Pilots would adapt quickly. Flying a piston engine airplane would become more of a curiosity than a necessity...kinda like flying a biplane today.

[Mike Switzer]

Supposedly Allison is still working on a small turbine. I have thought about trying to convert one of CAT's Solar turbines for aircraft use, but the models available in the HP range we are looking at are generally designed for generator use running at a set RPM.

[rwanttaja]

Well, Detroit has played with gas turbine engines in cars for a long time and they have yet to hit on the right combination of practical and affordable. The stumbling block seems to be finding a recipe for mass-producing the internals. Lot of engineering talent and $$$ has been expended looking for solutions.
That's basically the problem. You can build a pretty decent reciprocating engine with some steel and a good machine tool, but turbines are high-precision equipment. They often run hot and need exotic materials. Companies can and have cranked out new aviation recips using CAD-CAM resources (The Rotec and the Sadler radials come to mind) but AFAIK no one has done anything similar with a turbine.

Coupled with their higher fuel consumption and the fact that they're more efficient up high, it's hard to come up with a design that'll be suitable for the run-of-the-mill GA airplane.

Guy came to our EAA meeting once with a Solar T62 APU conversion. Pretty neat package, and I had fantasies about putting one in my Fly Baby. The ONLY thing that made them anything near economically feasible was the availability of used T62s on the surplus market.

Ron Wanttaja

[steveinindy]

And as for as not wanting to have to talk to ATC for all of every flight, darn right. Now sometimes the weather is IMC, and part of getting through it is to talk to ATC. But on a nice CAVU day, particularly if flying in less crowded airspace, I certainly don't want to spend several hours of a flight listening to ATC yammer. It would be like if you went for a walk in the woods or a pleasure drive in the country or a bike ride and you were required to listen and talk to a local cop channel or talk show radio.I guess the fact that I don't view flying as relaxing, especially at low altitude on severe clear days when there is more traffic around, probably has a lot to do with why I like having ATC tuned in. Not to mention that if I will be airborne for several hours it helps to break the monotony.

[kjensen]

What are you guys' opinion on the new Diesels that are out now? Is that something I should consider instead? They seem expensive (compared to gasoline pistons), and I'm not sure if the fuel savings will ever make up for that price difference if I only fly around ~100hr/year. So if the fuel savings won't be the reasons to go for a diesel, are there other advantages other than that? The only other thing I can come up with is the use of diesel/jet-a instead of 100LL. Any other reasons?

[Thomas Stute]

There is another alternative to reciprocating piston engines other than turboprops, the modern rotary engine as developed by the swiss company Mistral Engines http://www.mistral-engines.com/ (http://www.mistral-engines.com). They are perfectly suited for GA with 200 hp to 360 hp. The mistral engines burn leaded/unleaded fuel, avgas, mogas, even ethanol containing fuel. It has already flown in a Maule and in a Piper Arrow. Mistral will be exhibiting their engines on the AERO these days at Friedrichshafen and I'm going to visit them at their booth. I will be posting more when I've got more recent info on their status.

[Mike Switzer]

What are you guys' opinion on the new Diesels that are out now?

Still too heavy for the power they produce, but some of the European automakers are coming up with some promising lighter weight designs. Unfortunately, they are all computer controlled, and I have some reservations about having a single ECU that may fail while over hostile terrain.

[steveinindy]

Unfortunately, they are all computer controlled, and I have some reservations about having a single ECU that may fail while over hostile terrain.

As opposed to the FADECs that are common in turbine engines? I would rather have a ECU than a carburetor.



What are you guys' opinion on the new Diesels that are out now?

Still too heavy for the power they produce

I'm with Mike on this one.


Is that something I should consider instead?

From the sounds of it, you have very little reason to go with something other than a turbocharged reciprocating engine. Unless you're looking at flying really high (as in the flight levels where pressurization is a must), have a NEED to go very fast (such as wanting long range (>1500-2000 miles) while keeping flight times to a minimum) or are going towards the heavier end of the GA spectrum (>5,000 lbs) then you have very few reasons to really be looking at anything other than a good ol' fashioned reciprocating engine.


The only other thing I can come up with is the use of diesel/jet-a instead of 100LL. Any other reasons?

The biggest benefit is that if you want to fly outside of the US, you're best off having something that runs off of Jet-A or a similar kerosene fuel. Also, it removes any need for a possible switch of engines in the event that an unleaded aviation fuel isn't available in all areas when 100LL goes away.

[uavmx]

Rolls Royce seems to be making something that is similar or at least the closest thing to what we are talking about

http://www.rolls-royce.com/civil/products/smallaircraft/model_250/


anybody know what these puppies cost new???

[kjensen]

Also, it removes any need for a possible switch of engines in the event that an unleaded aviation fuel isn't available in all areas when 100LL goes away.

Will 100LL go away as long as there are no direct substitutes? That would mean hundreds of thousands of airplanes won't be able to fly. Even though EPA are trying to scare the aviation community, do you think it ever will happen unless there is a backwards compatible substitute?

[uavmx]

There is another alternative to reciprocating piston engines other than turboprops, the modern rotary engine as developed by the swiss company Mistral Engines http://www.mistral-engines.com/ (http://www.mistral-engines.com). They are perfectly suited for GA with 200 hp to 360 hp. The mistral engines burn leaded/unleaded fuel, avgas, mogas, even ethanol containing fuel. It has already flown in a Maule and in a Piper Arrow. Mistral will be exhibiting their engines on the AERO these days at Friedrichshafen and I'm going to visit them at their booth. I will be posting more when I've got more recent info on their status.

Wow, those look pretty nice, same idea as turbine in terms of less moving parts/reliability (although it's still dependent on ignition system)

Any idea what the different models of theirs costs?

[steveinindy]

Will 100LL go away as long as there are no direct substitutes?

Are you willing to bet a lot of your own money that it won't?


That would mean hundreds of thousands of airplanes won't be able to fly.

Do you really think they give a shit about small aircraft? Just because it's a concern to us, doesn't mean that it even factors into their thinking.


Even though EPA are trying to scare the aviation community, do you think it ever will happen unless there is a backwards compatible substitute?

There's already a solution for the aircraft that anyone in Washington (who isn't a private pilot themselves) cares about. It's called Jet-A.

That said, there's likely to be a replacement either in the form of Swift Fuel or something similar. However, if you want to go to anywhere outside of the US, it's probably best to not rely on something that runs off of a gasoline variant.

[steveinindy]

anybody know what these puppies cost new???

More than what most experimental aircraft cost including the engine. If I had to ball park it, I'd say probably the $150K-250K range.

That said, you could probably get one of the military surplus variants (the T-63) for much less.

[kjensen]

Are you willing to bet a lot of your own money that it won't?

Nope


Do you really think they give a shit about small aircraft? Just because it's a concern to us, doesn't mean that it even factors into their thinking.

Probably not, but if there are 200,000+ people that voice their opinion I would think it could make an impact...


That said, there's likely to be a replacement either in the form of Swift Fuel or something similar. However, if you want to go to anywhere outside of the US, it's probably best to not rely on something that runs off of a gasoline variant.

What about regular auto gasoline? Can't lycoming and continental modify their engines to work on that?

[steveinindy]

Probably not, but if there are 200,000+ people that voice their opinion I would think it could make an impact...

You're assuming that all pilots give a shit and are willing to speak up. A lot of us honestly don't care. I for one will be glad to see the day when leaded gasoline is done away with. I just hope the infrastructure for a replacement is in place prior to it happening.


Can't lycoming and continental modify their engines to work on that?

Theoretically yes, but there are a number of reasons why it's not as easy as it sounds.

Do you mind if I ask your background (age/education/training level)? You ask a lot of questions that make you sound like you're a student pilot and it would be helpful in explaining stuff if I knew where you stand in terms of basic knowledge.


What about regular auto gasoline?

Congratulations by the way, you probably just triggered this thread being turned into another "No ethanol in my gasoline!" debate.

[kjensen]

Do you mind if I ask your background (age/education/training level)? You ask a lot of questions that make you sound like you're a student pilot and it would be helpful in explaining stuff if I knew where you stand in terms of basic knowledge.

I'm a student, university level, and a student-pilot. I'm writing an assignment on disruptive technology for one of our classes. I chose to writing about turbine engines, and while I was writing I just realized that turbine engines have been disruptive in every part of aviation except most of general aviation, which is why I went here to maybe get an answer why that is the case.

[steveinindy]

while I was writing I just realized that turbine engines have been disruptive in every part of aviation except most of general aviation, which is why I went here to maybe get an answer why that is the case.

Ah. Like with most things, it boils down to cost and the existence of technology much more suited to the nature of the "average" pilot's flying. There's also this huge lingering (often just below the surface) disdain for the "kerosene club", as demonstrated by some of the comments here. A lot of it also comes out as by switching to non-reciprocating engines, that is somehow tantamount to an abandonment of what aviation is "supposed to be all about" especially when it comes to the EAA side of things.

[kjensen]

There's also this huge lingering (often just below the surface) disdain for the "kerosene club", as demonstrated by some of the comments here. A lot of it also comes out as by switching to non-reciprocating engines, that is somehow tantamount to an abandonment of what aviation is "supposed to be all about" especially when it comes to the EAA side of things.

So a lot of the pilots won't change because piston engines is sort of an identity to general aviation? Do you think that can change?

[Kyle Boatright]

Will 100LL go away as long as there are no direct substitutes? That would mean hundreds of thousands of airplanes won't be able to fly. Even though EPA are trying to scare the aviation community, do you think it ever will happen unless there is a backwards compatible substitute?

I certainly hope the answer to your question is "No". However, the vast majority of the Cessnas, Pipers, etc. at your local airport can run on 91 octane fuel, which is easy enough to achieve without lead content. Those aircraft wouldn't be grounded if lead was removed from Avgas. The problem is that the expensive aircraft with the most powerful engines in the piston fleet (most anything that is turbocharged or has higher than 8.5:1 compression) need more than 91 octane. Those are the aircraft which work for a living and burn a substantial amount of the Avgas that is consumed.

So the elimination of 100 octane fuel would ground much of the "working" GA fleet, which would have a very negative impact on the rest of the piston fleet, simply because it would cause an even further decline in Avgas sales. That would tip another domino in the decline of piston GA.

[steveinindy]

So a lot of the pilots won't change because piston engines is sort of an identity to general aviation?

The "older" crowd tends to have a very strong allegiance to what they trained with. It's much the same as how someone who was in the military prior to the introduction of the M-16 tends to have a less rosy assessment of it than someone who has known nothing else. However, economics is the bigger issue. Since most of us pay out of our own pockets to fly, you're going to have to show a major benefit in terms of:
-Fuel economy
-Cost of maintenance
-Frequency of maintenance (what's called "time between overhaul")
-Cost of acquisition
...for most pilots to consider switching to a similar

Also, the need to get a supplemental type certificate (STC) for commercially built aircraft to switch out the engine is a big issue for those flying Cessnas, Pipers, Beechcrafts, Cirri, etc. Establishing an STC is not cheap so.....


Do you think that can change
If someone were to meet all or even most of the above criteria, conceivably yes, especially among those of us who are more attracted towards the "business" end of flying than those of us who just like to smash bugs and bore holes in the sky on the weekends. However, do I think it is likely to happen? No, not really. There will always be those who are the reciprocating engine crowd and then there will be those of us who are the "kerosene club". I happen to fall into the latter since the design I am working on currently will have a turboprop engine.

[S3flyer]

Potential lower cost, lower HP turbine announced at SNF: http://www.avweb.com/news/snf/SunNFun2012_Light_Weight_Turbine_206386-1.html

[steveinindy]

Potential lower cost, lower HP turbine announced at SNF: http://www.avweb.com/news/snf/SunNFun2012_Light_Weight_Turbine_206386-1.html

Interesting....I have my reservations about whether it will lead to actual production but wish them the best. That said, a turbine in the hands of a low hour/low frequency pilot could be a risk proposition.....

[kjensen]

Potential lower cost, lower HP turbine announced at SNF: http://www.avweb.com/news/snf/SunNFun2012_Light_Weight_Turbine_206386-1.html

That is an interesting engine. Will this be THE engine that make everyone change to turboprop? If not, why?

[steveinindy]

Will this be THE engine that make everyone change to turboprop? If not, why?
Cost and all the reasons mentioned before. The fact that not everyone wants a turboprop is going to be the biggest one besides cost.

Any other questions? You seem to be repeating the same ones over and over.

[uavmx]

Interesting.... That said, a turbine in the hands of a low hour/low frequency pilot could be a risk proposition.....

Please justify/elaborate on that statement

I would argue the opposite. You think controlling a Throttle, Mixture and Prop has less risk then a single stick operation (okay, there might be a hi/low speed lever depending on turbine design) in terms of pilot proficiency???

[martymayes]

Rolls Royce seems to be making something that is similar or at least the closest thing to what we are talking about

http://www.rolls-royce.com/civil/products/smallaircraft/model_250/


anybody know what these puppies cost new???

That is the same turboshaft engine Allison has been building for 50+ yrs with a propeller gearbox attached. They are pretty neat as the basic engine can be carried in a backpack. However, they are also very complex and expensive. You're talking ~$1000/hp.

[martymayes]

That said, a turbine in the hands of a low hour/low frequency pilot could be a risk proposition.....



Please justify/elaborate on that statement

I would argue the opposite. You think controlling a Throttle, Mixture and Prop has less risk then a single stick operation (okay, there might be a hi/low speed lever depending on turbine design) in terms of pilot proficiency???


I'd like to hear the explanation as well. Selling pilots on turbine power would be easy, training them to fly a turbine would be even easier.

[steveinindy]

I would argue the opposite. You think controlling a Throttle, Mixture and Prop has less risk then a single stick operation (okay, there might be a hi/low speed lever depending on turbine design) in terms of pilot proficiency???

Here's the kicker. It seems that very few pilots get themselves into serious trouble because of those additional levers. Saying that those additional levers are a problem is pretty sketchy. I'd argue that the fuel tank selector knob causes far more problems.

Note: I say "seems" because we don't have good evidence to say conclusively one way or the other because of the lack of FDRs in GA aircraft.


Also, every turboprop I have ever flown in (TBM 850 and numerous twins) have had three (or more) levers (condition, fuel and throttle) just like a recip. Most of them also have their flap control there....



Selling pilots on turbine power would be easy, training them to fly a turbine would be even easier.

The issue I was getting at with a turbine is the lack of "instant" response like you get with a recip. You have to wait a couple to a few seconds to "spool" it up (at least in the larger engines from what I have been told; I'm not a turbine pilot yet myself so I am just repeating what I was told) before you get the full response. Given how many of us manage to get ourselves into the side of the power curve where we really shouldn't be, it would seem that adding something into the mix that makes recovering from that even less likely (because of the slight delay) isn't necessarily a good thing. However, I think it's a minimal risk and inattentive pilots will be inattentive regardless of what they are flying.

[kjensen]

Cost and all the reasons mentioned before. The fact that not everyone wants a turboprop is going to be the biggest one besides cost.

Any other questions? You seem to be repeating the same ones over and over.

What is the cost of that engine? I assumed that it will be lower cost than what's out there. If that is not the case, then just disregard the question.

[steveinindy]

What is the cost of that engine? I assumed that it will be lower cost than what's out there. If that is not the case, then just disregard the question.

We don't know they cost yet since they haven't started selling them yet and are most likely several years from doing so, if they get that far. However, we're not going to see a turbine that can compete cost wise with a reciprocating engine in that particular class because of the nature of turbine manufacturing and the costs of maintenance.

[kjensen]

We don't know they cost yet since they haven't started selling them yet and are most likely several years from doing so, if they get that far. However, we're not going to see a turbine that can compete cost wise with a reciprocating engine in that particular class because of the nature of turbine manufacturing and the costs of maintenance.

Oh ok, I see. Thanks.

[nrpetersen]

No body has pointed out the really fundamental difference between turbine and piston applications - and that is turbines don't scale down in size very easily and do not have anywhere near the operational flexibility and fuel specific consumption of piston engines. Our aircraft max out in the range of 300 hp and turbines have to operate at very high rpm and fuel consumptions to get to this small corner of their operating area.

On the other hand, turbines scale up very easily. Compare the complexity of say a turbine powered 747 vs the same thing powered with multiple piston engines. It would obviously be hopeless to do this and piston engines topped out with the complexity of the P-W 4360 28 cyl engine. Spark ignition piston engines have to limit the combustion chamber size to control detonation and that makes the maximum bore about 6 inches. Only diesels can extend the bore way beyond that which they do by controlling the combustion burn rate with the entrance of fuel.

Turbines do have the distinct advantage of high altitude ops at nearly max power where the drag of a large aircraft can be considerably reduced.

If the turbine engine had been invented first, the piston engine would have been considered a remarkable advance considering turbine material and flexibility problems.

And rotary engines suffer from efficiency problems too - even their seal problems could be licked. The combustion chamber dimensions have to be carefuoly controlled and will always cause a much greater heat loss when compared to the small combusion chamber of a round piston.

[Bob Dingley]

Advantages: Light wt, simplicity, dependability. ( I once flew 45 minutes with 2 NVA bullets in the compressor section. No sweat.)

Disadvantages: $$$, high fuel flow and no forgiveness for unfiltered fuel, defered maintenance and clumsy oafs do burn them up on starting.

The common engines run north of $million. GE, Turbomecca and some PT-6s. The Allison/RR can sometime be found for $100K with dubious pedigree.

Fuel flow on PT-6 runs about 350lbs/hr. Allison/RR 250-C20 (Bell 206) burn 28 gal/hr at 500 ft and 25 gal/hr at 7000.

The best deal for OBAM is the T-62. Used as an APU in large helicopters and M-1 tanks. Seems like they were not designed to be O/H. They were and are sold as surplus. Simple and easy for a good machinist to replace seals and bearings and you get 100 to 150 hp that you can tote under your arm. Plan on 15 gal/hr. Check out the clipped wing Luscombe Speedbird:http://ronkilber.tripod.com/luscombe/luscombe.htm

There is a guy that posted YouTube vids of his Turbine Zenith 701 here in this forum.

A friend of mine had a shop and O/H ed about 18 or 20 of these. He sold one to another pal who was planning to put it in his BD-5. The machinist friend put one in a KR-2. I checked it out in his shop. Excellent work and it followed the turboprop convention for engine control. See the Speedbird link for details.

I moved the throttle control and the input was made to the cutest little fuel control that I've ever seen. When I moved the prop control, a Teleflex cable made a direct mechanical pitch change on the prop. It performed well on ground tests.

Sad to say, Joe, a low time PPL ignored advice to not fly it and resulted in a fatal accident. The power/wt ratio was a factor IMHO. One that I talked to described him going vertical off the runway. Search NTSB for KR-2, May 2005, Galliano, LA.

These turbines were going out the door O/H for less than a VW.

Bob

[martymayes]

What is the cost of that engine? I assumed that it will be lower cost than what's out there. Well, if you define lower cost in small percentages, it may fit the bill. An engine that cost 10% less than it's $300k competitor doesn't seem to register in my checkbook as costing less cause it's still unaffordable.

The problem is current technology is not going to allow a "low cost" gas turbine engine. On the positive, every dozen yrs or so there is renewed interest with ceramics in gas turbine engine development. So there are possibilities. It's just a matter of time.

[steveinindy]

Spark ignition piston engines have to limit the combustion chamber size to control detonation and that makes the maximum bore about 6 inches.

Really? I learned something new. I always wondered how big you could make the cylinder.


On the positive, every dozen yrs or so there is renewed interest with ceramics in gas turbine engine development. So there are possibilities. It's just a matter of time.

There was a really interesting presentation I attended a couple of years back that featured a couple of engineers from one of the research labs over in France that were discussing a new ceramic/metallic hybrid (the description of the material was high-end engineering talk that I didn't fully grasp) that apparently has a "vastly reduced" (their words) rate of manufacturing defects as compared with previous versions and a potentially reduced cost. If it pans out, it might be the thing that finally helps reduce the costs of turbines.

If you're interested Marty, I'll dig through my file cabinets and see if I still have the handouts from that conference.

[Bob Dingley]

Steve, You may have been told about the Turbomecca Arriel 2S2. It has a "single crystal" turbine wheel and the 30 second temp limit is over 1,000 C. I don't know much about metalurgy. The instructors at Flight Safety couldn't explain it either.

Bob

[steveinindy]

That might have been it. It had some almost obscenely high tolerance limits. I'll dig around and see if I have the handouts.

[uavmx]

Here's the kicker. It seems that very few pilots get themselves into serious trouble because of those additional levers. Saying that those additional levers are a problem is pretty sketchy. I'd argue that the fuel tank selector knob causes far more problems.


The issue I was getting at with a turbine is the lack of "instant" response like you get with a recip. You have to wait a couple to a few seconds to "spool" it up (at least in the larger engines from what I have been told; I'm not a turbine pilot yet myself so I am just repeating what I was told) before you get the full response. Given how many of us manage to get ourselves into the side of the power curve where we really shouldn't be, it would seem that adding something into the mix that makes recovering from that even less likely (because of the slight delay) isn't necessarily a good thing. However, I think it's a minimal risk and inattentive pilots will be inattentive regardless of what they are flying.

Yeah, fuel tank selection is a good killer....the other levers you mention with turboprops are the speed lever and the condition lever (fuel cutoff/feather). Those two handles are only messed with on the ground, or if you have to kill an engine. So I would say for the large majority of the time with turboprops, in flight, it's a single lever deal.

The turbine lag you talk about is true, especially with turbines and PT-6 style (the technology would be free power turbine) does have lag. The Honeywell TPE style is that of a direct drive essentially does not. It seems like the majority of these smaller turbines or anything that we are talking about in terms of size would be of the direct drive style, thus eliminating those issues.

And yeah, there is potential to blow up turbines. Hot or hang starting...but hey, it's your money and if you want to blow up your engine, go ahead :rollseyes:

fact is there are PLENTY of ways to die in an airplane.....i don't think the masses flying turboprops would make it any worse.

[martymayes]

Electronic engine controls and single power control lever are real technologies, which go a long way toward idiot proofing engine operation. It's just a matter of pilot/operator culture catching up with technology. Have to put the OWT's to bed cause in the end, there is less risk when flying with turbine power. That was proven a long time ago.

[kscessnadriver]

The turbine lag you talk about is true, especially with turbines and PT-6 style (the technology would be free power turbine) does have lag. The Honeywell TPE style is that of a direct drive essentially does not. It seems like the majority of these smaller turbines or anything that we are talking about in terms of size would be of the direct drive style, thus eliminating those issues.

I'd trade the lag of a PT-6 to not have the TPE that lets everyone within a 1 mile radius know there is an airplane running.

[uavmx]

I'd trade the lag of a PT-6 to not have the TPE that lets everyone within a 1 mile radius know there is an airplane running.

That's because pilots are too lazy to go to low speed. When they are running at 65%, it's not that bad. Bunch of pansies around here!! I love the smell and sound of turbine engines at 0600 :-)

[Bob Dingley]

I'm don't agree that free power turbines such as Lycs, RR, PW, Arriels and GE accelerate slower than single shaft turbines like the TPE (at one time; Garrets). Free power turbines were created instead to overcome lag. I would rate the response on par with some radials that I have flown. R-985, R-1300,R-1340. In all cases, smooth control means good airmanship no matter what you're flying. We do not operate our engines like a red neck in a pick up truck stomping the gas. Free power turbines spool up fast.
Bob

[steveinindy]

I'd trade the lag of a PT-6 to not have the TPE that lets everyone within a 1 mile radius know there is an airplane running.

Eh....we have the same problem with any engine in the hands of someone who doesn't know how to set it properly. We have plenty of PT-6 powered traffic here and even when they are on approach for 23L at KIND (roughly a mile away), you can still hear them if the pilot can't get it through his head how to configure it properly.

*perks up an ear* Speaking of that....


That's because pilots are too lazy to go to low speed.

What UAV said.


love the smell and sound of turbine engines at 0600 :-)

I don't like the smell of any engine but for some reason the smell of diesel is less offensive and vaguely comforting. I like to blame it on all that time I spent volunteering and working on and around diesel powered fire apparatus and ambulances.


would rate the response on par with some radials that I have flown. R-985, R-1300,R-1340.

Interesting. I've never flown anything with a radial so I can't make a comparison in that regard.


In all cases, smooth control means good airmanship no matter what you're flying.

Well said. However, I'm reminded of what my medical director as an EMS provider used to say about developing protocols, procedures and regulations: you keep in mind the guy you barely trust and wouldn't let have your life in his hands. In other words, you always design or write with the lowest common denominator in mind that way there's a sufficient margin of safety for those folks and an even broader one for the guy who is skilled at flying.


We do not operate our engines like a red neck in a pick up truck stomping the gas.

Those of us who know what they are doing. There are plenty of folks who do exactly that and it's one reason why engine shops stay so busy.

[Bob Dingley]

Free power turbines have little lag. Single shaft turbines do. I know for a fact that a PW or RR will spool up faster than my old fuel injected Beech. On the other side of the coin, I can chop power abruptly on a PW or RR with no problem. Try it in a Beech 50 with the old GSO-480s and you may see dimples appear in the cowls from the counterweights.
Bob

[Flyfalcons]

They didn't come up with the term "commander salute" (practiced regularly where I work) because some pilots are lazy.

[kscessnadriver]

Eh....we have the same problem with any engine in the hands of someone who doesn't know how to set it properly. We have plenty of PT-6 powered traffic here and even when they are on approach for 23L at KIND (roughly a mile away), you can still hear them if the pilot can't get it through his head how to configure it properly.

My comment was more about when they are on the ground. Work the ramp sometime. The difference between a C-90 and a MU-2 is amazing.

[steveinindy]

My comment was more about when they are on the ground. Work the ramp sometime. The difference between a C-90 and a MU-2 is amazing.

I fly on a MU-2B (with -10s) for one of my jobs. Both of them are pretty noisy. Honestly, once you get above a certain threshold, the actual noise level is pretty much moot at least in my book. Nearly every twin turboprop is really noisy in my book. I'm not saying there's an actual difference but it seems like once you get above 90 decibels it's a bit like arguing over the various shades of white paint.

Then again, I don't find the noise level from most aircraft all that pleasant which is a major reason why sound reduction is such a focus in my design.

[PF Flyer]

I will put in my 2 cents. No one mentioned Walter 601D turboprops. They are relatively inexpensive, simple, 750hp, and reliable. The fuel burn (from research, not ownership) is approximately 35% higher than a high performance piston. They can be found easily and TBO'd in Florida. There are no mid life hot inspections and IRAN is being increased to 2000 hrs. The calendar IRAN was murky to me. It is either 7 years or as needed for experimental aircraft. Look on Controller or Trade a Plane. You will see several installed....

[steveinindy]

I will put in my 2 cents. No one mentioned Walter 601D turboprops. They are relatively inexpensive, simple, 750hp, and reliable. The fuel burn (from research, not ownership) is approximately 35% higher than a high performance piston. They can be found easily and TBO'd in Florida. There are no mid life hot inspections and IRAN is being increased to 2000 hrs. The calendar IRAN was murky to me. It is either 7 years or as needed for experimental aircraft. Look on Controller or Trade a Plane. You will see several installed....

The only real "problem" with the Walter turboprops (now also available new as the GE H80) is that the "inexpensive" ones have to be viewed with a certain degree of caution and one must- as with any aircraft component- be sure to do their homework to make sure the engine is what you're expecting and to make sure the paperwork is in order so far as inspections, maintenance, etc. To be honest, I wouldn't accept an Soviet era engine without having it independently vetted by an A&P that I know and trust. Then again, that's the approach I take with anything I buy used from someone I don't know.

That said, the 601 series isn't really amenable to what the OP was talking about: a "replacement" for the average GA engine. The only thing disruptive about turbine technology tends to be noise and the bills for maintenance.

[kjensen]

I looked up a little on this Czech engine, TP-100, that Diemech Turbine Solutions will offer. It will be about $100k.. or probably a little more, like $125k. Does this price make this engine attractive as a piston substitute, or is it still too expensive?

[Auburntsts]

I looked up a little on this Czech engine, TP-100, that Diemech Turbine Solutions will offer. It will be about $100k.. or probably a little more, like $125k. Does this price make this engine attractive as a piston substitute, or is it still too expensive?Not in my book -- still costs too much. That engine costs twice as much as a brand new Lycoming IO-540 (fuel injected, 260-300HP, 6 cyl) and 3 times the cost of a good mid-time one.

[steveinindy]

Nope. Not in my book. Until it gets to be equal to or less than the cost of the piston alternative, it's not economically justifiable to replace a piston engine with a turbine engine that is of equal power.

BTW, how's your paper coming along?

[martymayes]

I looked up a little on this Czech engine, TP-100, that Diemech Turbine Solutions will offer. It will be about $100k.. or probably a little more, like $125k. Does this price make this engine attractive as a piston substitute, or is it still too expensive?

Since it can only be installed in homebuilts, it won't get past the curiosity stage. I have doubts the engine can be certificated without doubling the current advertised price.

[Bill]

I looked up a little on this Czech engine, TP-100, that Diemech Turbine Solutions will offer. It will be about $100k.. or probably a little more, like $125k. Does this price make this engine attractive as a piston substitute, or is it still too expensive?

Your "a little more" delta of $125k minus $100k = $25k is what a lot of us want to pay no more than for an engine, period. If you believe $25k is just "a little more," then you're living on a different plane of existence than most of us and this is the wrong place to look for favorable opinions.

[Mike Switzer]

While things may change by the time I get my plane ready for an engine, the engine I currently plan to use will cost between $10,000 - $15,000 max (supercharged aluminum small block Ford with all the options)

All the bells & whistles, any US (normally aspirated) aluminum small block V8 will cost less than $10,000, a big block might hit $15,000 (these are numbers for aluminum blocks & heads, if you don't care about weight it will be cheaper)

If you want to spend more money use a "real" aircraft engine, any turbine or diesel will cost more than that

[steveinindy]

Your "a little more" delta of $125k minus $100k = $25k is what a lot of us want to pay no more than for an engine, period. If you believe $25k is just "a little more," then you're living on a different plane of existence than most of us and this is the wrong place to look for favorable opinions.

That was my thought too. If I'm shelling out $125K for an engine, that's not what I'm going for.


All the bells & whistles, any US (normally aspirated) aluminum small block V8 will cost less than $10,000, a big block might hit $15,000 (these are numbers for aluminum blocks & heads, if you don't care about weight it will be cheaper)

Just out of curiosity what does one of the big blocks weigh? What's the difference in weight between the aluminum blocks and heads vs the other option (I'm assuming some form of steel)?

[Mike Switzer]

Just out of curiosity what does one of the big blocks weigh? What's the difference in weight between the aluminum blocks and heads vs the other option (I'm assuming some form of steel)?

I don't remember for a big block off the top of my head, I will try to look it up later when I have time - but for a Ford 302 the bare aluminum block is 90 - 110 lb depending on which one you buy, the cast iron block is around 200lb. Going of memory here, but I believe a 289 / 302 with aluminum block & heads comes in around 400lb - I am using 500lb for my preliminary W&B calculations to account for accessories, prop, etc.

I know some of the cast iron big block engines came in around 700lb, aluminum block & heads would make them quite a bit lighter.

Another thing to consider if you are looking at an auto engine, (I don't want to use a big block for both weight & space considerations) but as far as I have been able to find out the Chrysler Hemi (the original big block, not the new one) is the only engine that anyone is still making aluminum aftermarket dual plug heads for, which would allow a redundant ignition setup.

[steveinindy]

Going of memory here, but I believe a 289 / 302 with aluminum block & heads comes in around 400lb - I am using 500lb for my preliminary W&B calculations to account for accessories, prop, etc.

Interesting. I would have thought it was a lot more than that but then again my only experience with one has been looking at it when it was in the front end of a vehicle.. Then again, I'm kind of weird in that I don't even change the oil in our car and have little interest in automotive mechanics, but I have a great desire to build an airplane. Go figure.....

[kjensen]

Your "a little more" delta of $125k minus $100k = $25k is what a lot of us want to pay no more than for an engine, period. If you believe $25k is just "a little more," then you're living on a different plane of existence than most of us and this is the wrong place to look for favorable opinions.

I agree with that, should have used different wording. I guess I said "a little" because that delta ($25k) is small compared to the delta between $100k and the price for a new P&W, GE, or RR engine.

[kjensen]

That was my thought too. If I'm shelling out $125K for an engine, that's not what I'm going for.

Do you mean that you would go for another turboprop engine or do you mean you would spend your money on a completely different non-turbine engine?

[kjensen]

Ok this will be my last question:

Hypothetically if that TP-100 had lower fuel burn than a piston, let's say close to what a diesel engine burns (I know that it's not possible, but let's just assume that it was), and it was FAA certified. Would you still stick to the piston even if the price premium was "only" 25-50% over the piston??

Assume even that after 4000 hrs of use the total cost of the engine will be lower than for the piston (assuming lower operating (fuel+maintenance) cost). I know that 4000hrs is almost a lifetime for a GA private pilot.

[steveinindy]

Do you mean that you would go for another turboprop engine or do you mean you would spend your money on a completely different non-turbine engine?

Seeing as there's no good turbine engine for that price and the fact that the low to middle end of GA (which is what we're discussing here) is well served by much easier/cheaper to maintain piston engines....

If I were looking to get a turbine (which I am for the larger design I am working on), the engine is going to run me for at a minimum for $150,000 to $160,000. That's for a 940 hp (at sea level) TPE-331-10 that's used and about half way through it's TBO cycle. New, it's closer to $400,000.

By comparison, a high end turbocharged piston engine for the top end of what most people consider GA (TIO-540-AE2A) will run you about $150,000 new or about $120,000 for a factory rebuild. Unless you have to go freakishly fast (>275-300 knots) or really high (>FL280) to accomplish your "mission", there's no reason to pay more for an engine that is used and sucks more fuel under most circumstances (until you get up into the really high flight levels (>FL350)). It just doesn't make sense.

The only reason I am going for a turbine is because of my desire to go very long distances (think Indianapolis to the northeastern islands in the Caribbean or Boston to LA without refueling ) and the most efficient way to do that is at high altitude and high speed. That more or less requires a turbine powerplant. Most people aren't looking for that sort of thing.

So, if I were your "average" GA pilot and not my own heady blend of slightly crazy, for $125K I'm getting a new top of the line Lycoming and enjoying still being able to pass >80% of the planes at the local airport.

[steveinindy]

let's say close to what a diesel engine burns

So like 3 gph less than a similar piston engine?


Hypothetically if that TP-100 had lower fuel burn than a piston, let's say close to what a diesel engine burns (I know that it's not possible, but let's just assume that it was),

The thing is that it is possible. The issue is that most GA pilots don't do the sort of flying that is suited to turbine engines to have that kind of efficiency. The average cross country flight for a GA pilot is somewhere between 100 and 200 miles. There's literally no benefit to it because even a ten or twenty knot difference in cruising speed over that short of a distance isn't going to make that much of a difference in time. Also take into account that to get to the "sweet spot" altitude for nearly any turbine is going to take you 30-50+ miles. For shorter flights, you'd literally go almost from cruise power to flight idle for the descent because top of climb and top of descent are going to be more or less the same point.


Would you still stick to the piston even if the price premium was "only" 25-50% over the piston??

For low altitude "standard GA" flying? Yes. A turbine is simply a round peg trying to be crammed into the smaller square hole of GA in the majority of flights. I hate to say it (since I'm one of the "fans" of turbines on this forum) but you seemed to have picked an argument for your paper that's more or less defensible and anyone who knows much about flight operations or aircraft engines would be able to rip it apart.


assuming lower operating (fuel+maintenance) cost

Here's the problem: neither of those are cheaper. I'm actually looking at doing the training to become an A&P just so I can maintain my own engine because of the costs associated with turbine maintenance. In most places (unless you're operating at a field that has a LOT of commercial traffic and very little GA....think Honolulu), you're going to pay considerably more for Jet-A than 100LL.


I know that 4000hrs is almost a lifetime for a GA private pilot.

Google "cycle maintenance" or "calendar maintenance". If you have a low use rate, you still have to have it overhauled every few years (5 or 10 depending on the model) because one of the worst things you can do to engines is let them sit. It's asking for corrosion to not at least have it looked at.

[Flyfalcons]

Ok this will be my last question:

Hypothetically if that TP-100 had lower fuel burn than a piston, let's say close to what a diesel engine burns (I know that it's not possible, but let's just assume that it was), and it was FAA certified. Would you still stick to the piston even if the price premium was "only" 25-50% over the piston??

Assume even that after 4000 hrs of use the total cost of the engine will be lower than for the piston (assuming lower operating (fuel+maintenance) cost). I know that 4000hrs is almost a lifetime for a GA private pilot.

You've asked for honest opinions and you've gotten them. Trying to reword the question to fit your desired result isn't exactly real research.

[kjensen]

So like 3 gph less than a similar piston engine?

Yes, something like that. They say that diesel is about 20-30% less than gasoline, so let's assume that this hypothetical turbine engine burns 10-20% less than a gasoline piston, even at low altitude.


For low altitude "standard GA" flying? Yes. A turbine is simply a round peg trying to be crammed into the smaller square hole of GA in the majority of flights.

If you assume that a turbine burns less than a piston even at low altitude, would that change your opinion?

I appreciate your information on this!

[steveinindy]

They say that diesel is about 20-30% less than gasoline, so let's assume that this hypothetical turbine engine burns 10-20% less than a gasoline piston, even at low altitude.

LOL Eh....depends on where you're at. Around here, the difference is $0.17 a gallon at the airport we use ($5.90 vs $5.73).


You've asked for honest opinions and you've gotten them. Trying to reword the question to fit your desired result isn't exactly real research.
What he said.


If you assume that a turbine burns less than a piston even at low altitude, would that change your opinion?


I strongly suggest you take some classes on statistics or how to formulate research questions because positing all these wild hypotheticals that are never going to happen just to suit your desire to prove that a turbine engine can be a "disruptive technology" for general aviation. I can argue that we might be able to lift 747 loads with a weed whacker engine but I'd have to frame it like "Would you think it was viable if gravity were suddenly reduced by 99.999999999999%?". Either way, any rational person who is well versed in the subject (or goes back and checks your citations) is going to leave you doing the academic equivalent of bleeding from your rectum with that sort of theorizing.

Go to your professor and admit you picked a non-viable choice. It's a better choice than trying to BS an argument that- unless your professor drools uncontrollably or smokes joints the size of tampons prior to grading papers- will result in you failing the class. Most professors will support you coming to them and realizing that you've done enough research to know that what you thought initially doesn't pan out.

[Thomas Stute]

I talked to the Mistral people today at the AERO. The status is that the engines have successfully been flown, but the company is too short of money to certify them. They have changed their marketing concept and are now aiming at the homebuilt and experimental market. They claim that there are already some flying in the US. The price for the 200 HP engine is 45000 EURO and the 300 HP costs about 54000 EURO. I think we have to wait until Mistral finds a strong investor for seeing their engines certified.

[kjensen]

You've asked for honest opinions and you've gotten them. Trying to reword the question to fit your desired result isn't exactly real research.

I'm only trying to find where the threshold is, I don't have any favorite here. I will not ask anything anymore, my intention was not to create irritation.

[kjensen]

Point taken. I will not post any more questions. Thanks all for the feedback, I really appreciate it.

[martymayes]

Ok this will be my last question:

Hypothetically if that TP-100 had lower fuel burn than a piston, let's say close to what a diesel engine burns (I know that it's not possible, but let's just assume that it was), and it was FAA certified. Would you still stick to the piston even if the price premium was "only" 25-50% over the piston??


For sure, 25-50% premium for turbine power would change the landscape. Not overnight, but it would eventually push piston engine dominance aside in light planes. None of this is going to happen without a technology breakthrough, cause regardless of the name on the dataplate, can't manufacture a turbine engine at a price that will be competitive with current piston engines.

[martymayes]

The thing is that it is possible. The issue is that most GA pilots don't do the sort of flying that is suited to turbine engines to have that kind of efficiency. The average cross country flight for a GA pilot is somewhere between 100 and 200 miles. There's literally no benefit to it because even a ten or twenty knot difference in cruising speed over that short of a distance isn't going to make that much of a difference in time. Also take into account that to get to the "sweet spot" altitude for nearly any turbine is going to take you 30-50+ miles. For shorter flights, you'd literally go almost from cruise power to flight idle for the descent because top of climb and top of descent are going to be more or less the same point.


Most GA flying does not make efficient use of piston engines. The average GA mission isn't about flying from point A to B on the most efficient climb/cruise/descent profile. Many times point B isn't even involved, flying is from point A to A. Sometimes people fly just to have fun with no concerns about efficiency, you know, see something on the ground so you circle around to have another look. Powering GA with turbine engines would be the greatest thing since the Wright Flyer. Unfortunately, it's not happening with current technology.

I think you're going to be sorely disappointed flying a turbine engine airplane. Fantasy land is going to meet reality head on and they are not going to be anywhere near matching up.

[martymayes]

I think we have to wait until Mistral finds a strong investor for seeing their engines certified.That would be the elusive billionaire that wants to make a small fortune in aviation......

[steveinindy]

I think you're going to be sorely disappointed flying a turbine engine airplane. Fantasy land is going to meet reality head on and they are not going to be anywhere near matching up.How so? It's going to be expensive, kind of boring but it is a means to get from point a to point b. But then again I feel much the same about all flying: it's stretches of boredom punctuated by a couple of minutes of challenges. Maybe it would be different if I were into aerobatics or something. There's no magic or romance or any of the other emotions a lot of people feel towards aviation. It is a scientific and engineering challenge that allows me to learn and challenge myself. A fringe benefit is that I wind up with an interesting and somewhat useful aircraft. If I do it right, this will be rather dull flying in the minds of a lot EAAers. Routine and kind of dull in aviation is a good thing in most cases. I don't have an particular illusions about it. Care to elaborateas to what you mean?

[kjensen]

For sure, 25-50% premium for turbine power would change the landscape. Not overnight, but it would eventually push piston engine dominance aside in light planes. None of this is going to happen without a technology breakthrough, cause regardless of the name on the dataplate, can't manufacture a turbine engine at a price that will be competitive with current piston engines.

Thanks a lot for you input!

[flyvulcan]

Have you seen this (http://www.youtube.com/watch?v=XnSleKc4--U&feature=related) development? It has gone quiet for a couple of years but it is not dead. This model is "only" around 100hp but an "affordable" upscale version is not outside the realms of possibility.

What do people feel would be a price for a 150-180hp turboprop engine that would attract buyers? A new 180hp IO360 is around $32000, what do you think people would pay for a 180hp turboprop to use instead of the IO360 (up to 25% more as previously alluded to or the same price as the equivalent piston)? I'm curious what the general opinion is. The turbine would probably be 30% less efficient, but it could be a sub-120 lbs installation versus 280 lbs for the IO360. 160 lbs is a lot of weight to save on a sub-1000 lbs empty weight aircraft and would have to count for something. Sure, range is compromised due to the higher SFC of the turbine but how much would this come into consideration for someone considering such an engine?

If a turbine cost the same as the equivalent piston, I would put such an engine in my project in a flash as fuel burn doesn't really worry me. The weight saving would count for a lot for me, but what do others think?

[martymayes]

This model is "only" around 100hp but an "affordable" upscale version is not outside the realms of possibility.I agree, it would be short-sighted for someone not to develop a potential family of engines from a single design. 100-400 hp and most of the GA fleet is covered. For 180 hp, 50% over 32k is $48k. All manufacturers would rush to get a turbine 4 place on the market and salivating buyers would line up to buy them.

[uavmx]

Have you seen this (http://www.youtube.com/watch?v=XnSleKc4--U&feature=related) development? It has gone quiet for a couple of years but it is not dead. This model is "only" around 100hp but an "affordable" upscale version is not outside the realms of possibility.



do you have any more info on that?? There's no details in the youtube video, very interesting looking design though!

[flyvulcan]

The turboprop in the video was by N2 Turbines. I had a link to their website and was going to post it but but I just visited the page, only to find that the site lapsed on 04/04/12 so is no longer available. You can find a little information about them on the web, including a second video of their engine. I can recall that either Sport Aviation or Kitplanes magazines ran an article on them a few years back.

[Adrian Bewley]

In the 1990's United Airlines was taking deliveries of B-757 's and I had a Pratt & Whitney tech rep riding jumpseat with us on a trip. UAVMX, when he finished taking engine parameter readings I asked him the EXACT question you have raised about a 300-400 hp turbo prop we could afford in GA. His answer was as long as we machine the blades we cannot get the cost down. I asked about making ceramic blades and he said they were working on that, but I have not heard anything about it since then. Adrian Bewley
I'm shocked in this day and age we don't have a nice IO550 alternative turboprop. Something in the 300-400HP rating that get's comparable fuel burn (probably higher). I think it would be a great seller, but as stated, cost is the big thing. But think about how much you save in MX, reliability, not replacing cylinders all the time, just overall hassle. The TBO on a turboprop could be much higher too. Just do a 2k hr hot section inspection, then fly it to 4k hours easy.

There's got to be enough smart people that can get together and build something that fits those parameters.

[uavmx]

In the 1990's United Airlines was taking deliveries of B-757 's and I had a Pratt & Whitney tech rep riding jumpseat with us on a trip. UAVMX, when he finished taking engine parameter readings I asked him the EXACT question you have raised about a 300-400 hp turbo prop we could afford in GA. His answer was as long as we machine the blades we cannot get the cost down. I asked about making ceramic blades and he said they were working on that, but I have not heard anything about it since then. Adrian Bewley

Yeah, that's obviously where the cost is tied up....not in the technology. Axial flow blades don't seem like that are all that complex to machine.....where as a blisk, or centrifugal compressor seems like it would be very difficult. But again, with all the automation today, all these CNC machines, etc, you'd think that the cost would have come down.

The outer housings are pretty basic, pressed/welded tubes essentially. I think the shafts would be expensive because of the trueness required and often times you have shafts running inside another.

I know another VERY expensive aspect to the manufacturing cost are fuel nozzles. The amount of misting/atomization required, dual flow, conical spray patterns these suckers is complex and on a TPE run around $6k A PEICE!!! (and there's 8 of them....)


There's got to be a way to attack these issues with a group of smart guys and over come these limitations.

[martymayes]

Yeah, that's obviously where the cost is tied up....not in the technology. Axial flow blades don't seem like that are all that complex to machine.....There's got to be a way to attack these issues with a group of smart guys and over come these limitations.

A large chunk of cost is that you can't build turbine engine parts out of plain 'ol steel. Some high temp alloys in raw bar stock form is >$1000 per linear inch. The benefit of ceramic is that it would be cheap if they could find a way to make it work.