Diesel motors for planes?

[wickedsprint]

Why not put all this work into a small and reliable turboshaft? Like an Allison 250 setup for an airplane.

Lightweight, simple and powerful.

 

[Ted]

Why not put all this work into a small and reliable turboshaft? Like an Allison 250 setup for an airplane.

Lightweight, simple and powerful.

Also expensive and has higher fuel burn than current piston engines, not lower.

 

[wickedsprint]

Also expensive and has higher fuel burn than current piston engines, not lower.

Of course..but the cost of that nice diesel will likely eat up a good chunk if not all of the efficiency savings over a proven lycoming.

 

[Ted]

Of course..but the cost of that nice diesel will likely eat up a good chunk if not all of the efficiency savings over a proven lycoming.

Not necessarily. Early ones will cost more, but expect pricing to go down. I think on a new vs new basis, probably not too far off on pricing.

The hard part for STCs is accepting the existing engines as cores. Continental or Lycoming could do this for a diesel they created. It would be harder for a newcomer to do it.

 

[wickedsprint]

Not necessarily. Early ones will cost more, but expect pricing to go down. I think on a new vs new basis, probably not too far off on pricing.

The hard part for STCs is accepting the existing engines as cores. Continental or Lycoming could do this for a diesel they created. It would be harder for a newcomer to do it.

I agree, I think they would need to be introduced by a proven company and eventually have a narrow enough cost split that efficiency or some other tangible benefit could make up for.

Longer TBO..lower fuel burn etc.

 

[Capt. Geoffrey Thorpe]

Longer TBO..QUOTE]

I wouldn't assume that.

Commercial Diesels last a long time because they are built to last a long time. Just like industrial gasoline motors. But they weigh like they were built to last a long time.

There is nothing inherent in using compression ignition that makes an engine last longer. Remember the GM Diesels from the late 70's?

 

[Ted]

I agree, I think they would need to be introduced by a proven company and eventually have a narrow enough cost split that efficiency or some other tangible benefit could make up for.

Longer TBO..lower fuel burn etc.

Initial TBO will be lower almost certainly. It might eventually get up, but there will be a lot of factors and that isn't guaranteed. Weight will be higher. Fuel burn will be lower. Service ceiling will vary depending on configuration, but to get any reasonable power in the FL250 range expect sequential twin turbos, adding further to weight and complexity.

I still think diesels make sense for GA, but it isn't an easy slam dunk or we'd already be there.

 

[N801BH]

Longer TBO..QUOTE]

........ Remember the GM Diesels from the late 70's?

The 5.7

 

[Ted]

I'd like to throw a Duramax in a plane just for fun. But I'd basically need to design the plane from scratch to make it work.

 

[Henning]

Why not put all this work into a small and reliable turboshaft? Like an Allison 250 setup for an airplane.

Lightweight, simple and powerful.

Huge fuel burn issue, poor performance at low altitude, high cost.

 

[Henning]

Longer TBO..QUOTE]

I wouldn't assume that.

Commercial Diesels last a long time because they are built to last a long time. Just like industrial gasoline motors. But they weigh like they were built to last a long time.

There is nothing inherent in using compression ignition that makes an engine last longer. Remember the GM Diesels from the late 70's?

Well, the 5.7 was an Oldsmobile 350 that they replaced the distributor and plugs with a pump and injectors. Had they used a Chevy 4 bolt main block and forged cranks they probably could have got away with it, as it was the webbing in the mains was too weak. The 6.5 wasn't bad once it was turboed, and the 6.2 is what powers all the Humvees IIRC, these were both mods of the Olds engine.

 

[wickedsprint]

poor performance at low altitude

Compared to what?

 

[Ted]

Well, the 5.7 was an Oldsmobile 350 that they replaced the distributor and plugs with a pump and injectors. Had they used a Chevy 4 bolt main block and forged cranks they probably could have got away with it, as it was the webbing in the mains was too weak. The 6.5 wasn't bad once it was turboed, and the 6.2 is what powers all the Humvees IIRC, these were both mods of the Olds engine.

Right, but the point is that the 5.7 diesel wasn't reliable, even though it was a diesel.

High TBO and diesel don't necessarily go together.

 

[wickedsprint]

Longer TBO..QUOTE]

I wouldn't assume that.

Commercial Diesels last a long time because they are built to last a long time. Just like industrial gasoline motors. But they weigh like they were built to last a long time.

There is nothing inherent in using compression ignition that makes an engine last longer. Remember the GM Diesels from the late 70's?

I wasn't assuming anything. I was giving examples of tangible benefits that might be required to offset the cost split.

 

[Henning]

Compared to what?

Anything else... Just look at the fuel specifics at low altitude for 400hp out of that Allison 250 vs oven an IO-720.

 

[wickedsprint]

I'd like to throw a Duramax in a plane just for fun. But I'd basically need to design the plane from scratch to make it work.

Great engine, loved my 03.

 

[wickedsprint]

Anything else... Just look at the fuel specifics at low altitude.

You said low performance, not fuel specifics.

 

[wickedsprint]

Anything else... Just look at the fuel specifics at low altitude for 400hp out of that Allison 250 vs oven an IO-720.

How much does does an IO-720 weigh?

600lbs vs 200lbs for the Allison

 

[Henning]

You said low performance, not fuel specifics.

That's a measure of performance, output per BTU input.

 

[Ted]

Great engine, loved my 03.

Yeah, and its weight I think is at a point that could be competitive with a turbo piston in the 300-350 HP range.

 

[wickedsprint]

That's a measure of performance, output per BTU input.

In regards to performance, most people I know discuss things like top speed, climb rate and power to weight ratio...all of which will be better with the higher performing lightweight turbine.

That same Allison can be uprated to what...800hp...at 1/3 the weight of that heavy Lycoming.

 

[Henning]

How much does does an IO-720 weigh?

600lbs vs 200lbs for the Allison

We must have different opinions on what defines performance.

How much does that matter when I have to carry 400lbs more fuel to go the same distance? I want to load the same 130 gallons and increase my range 30%+, that's why I want Diesels. If I put on turbines and load the 130 gallons of fuel, I will lose 30% range. I fly solo or single pax in a twin, I usually have 750lbs useful load to spare.

 

[guardrail]

Yeah, and its weight I think is at a point that could be competitive with a turbo piston in the 300-350 HP range.

I think it would be pretty cool, but you do need to factor in the liquid cooling, etc as additional weight. Though the torque would be off the chart, run a seriously steep prop?

 

[Alexb2000]

I'd like to throw a Duramax in a plane just for fun. But I'd basically need to design the plane from scratch to make it work.

Just for conversation: My LLY weights about 900lb. Removing the accessories would help, but you would have the weight of the reduction drive to add also.

The other issue that is challenging even in truck applications is cooling. Of all the challenges, this would be a tough one. Even in my CJ Jeep, when I swapped in a TPI 350 I had to have Ron Davis build a custom radiator to keep it cool. The heat load of a Duramax has to be huge.

 

[Ted]

I think it would be pretty cool, but you do need to factor in the liquid cooling, etc as additional weight. Though the torque would be off the chart, run a seriously steep prop?

The torque wouldn't be off the chart at all. Look at a 350 HP engine at 2575 RPM. That's 713 lb-ft of torque from 6 cylinders. Now the diesel will probably have higher peak pressures because of the nature of diesel ICPs, but nothing a composite prop couldn't handle, and likely conventional. When you factor in the higher RPM and 8 cylinders it might balance out. Belt drive would help dampen out the pulses as one option. I think the Duramax makes its peak power around 3000-4000?

 

[Ted]

Just for conversation: My LLY weights about 900lb. Removing the accessories would help, but you would have the weight of the reduction drive to add also.

The other issue that is challenging even in truck applications is cooling. Of all the challenges, this would be a tough one. Even in my CJ Jeep, when I swapped in a TPI 350 I had to have Ron Davis build a custom radiator to keep it cool. The heat load of a Duramax has to be huge.

I forget the different Duramax designations, so I forget where the LLY falls in the category. My recollection is that the earliest ones weighed the least. Not surprisingly, they were the least reliable (again, my recollection, and I'm not a Duramax guru). You're correct on the weight challenges, but a TIO-540-J2BD weighs in around 650 lbs. Not light. It could be tackled, understanding sacrifices would exist.

I think the cooling could be dealt with fairly easily. Having 200 MPH speed vs. 70 definitely helps on available airflow. Radiators are sized for their particular operation. The trick would be sufficient airflow and surface area with a minimal coolant capacity to minimize weight.

 

[Henning]

Plenty of water cooled 1200-2000+HP engines flying during WWII, they even figured out how to get thrust from the heat. You think that can't be done now? Diesels were flying across the Atlantic before WWII....

 

[Alexb2000]

I forget the different Duramax designations, so I forget where the LLY falls in the category. My recollection is that the earliest ones weighed the least. Not surprisingly, they were the least reliable (again, my recollection, and I'm not a Duramax guru). You're correct on the weight challenges, but a TIO-540-J2BD weighs in around 650 lbs. Not light. It could be tackled, understanding sacrifices would exist.

I think the cooling could be dealt with fairly easily. Having 200 MPH speed vs. 70 definitely helps on available airflow. Radiators are sized for their particular operation. The trick would be sufficient airflow and surface area with a minimal coolant capacity to minimize weight.

LLY is the 04.5-05 version, first one was the LB7 01-04.5 (injector issues), last was the LBZ 06-07.5 (best of the early motors).

What about ground cooling?

The question I have isn't so much about HP, but could it be proped to utilize the awesome torque (600 ft. Lbs.)?

 

[wickedsprint]

How much does that matter when I have to carry 400lbs more fuel to go the same distance? I want to load the same 130 gallons and increase my range 30%+, that's why I want Diesels. If I put on turbines and load the 130 gallons of fuel, I will lose 30% range. I fly solo or single pax in a twin, I usually have 750lbs useful load to spare.

Valid, but your points don't apply to everyone.

Stuff that IO-720 into an MD500 or Bell Jet Ranger and try to convince them it's a higher performance alternative to their Allison/Rolls 250.

 

[Ted]

LLY is the 04.5-05 version, first one was the LB7 01-04.5 (injector issues), last was the LBZ 06-07.5 (best of the early motors).

What about ground cooling?

The question I have isn't so much about HP, but could it be proped to utilize the awesome torque (600 ft. Lbs.)?

Thanks for the clarification. I remembered hearing the LB7 injector issues. But I also seem to recall some of that was due to low power use, at least my 04.5 Cummins had those issues if you didn't drive it hard. Wouldn't be a problem on a plane.

I wouldn't worry about ground cooling. You're at very low power for a limited period of time. Set the cooling up to take advantage of the prop blast. A fan could be added if necessary, but I doubt if it would be. Figure similar to aircraft today.

The 600 ft-lbs of torque is nothing not seen today. As stated above, a J2BD makes over 700 ft-lbs. Your AJ1A makes around 650. Now with a gear reduction you'd have higher torque on the prop than at the crank, but that would just bring it up to the levels of current piston engines. Easy to manage.

What's the max power RPM on your LLY?

 

[guardrail]

The torque wouldn't be off the chart at all. Look at a 350 HP engine at 2575 RPM. That's 713 lb-ft of torque from 6 cylinders. Now the diesel will probably have higher peak pressures because of the nature of diesel ICPs, but nothing a composite prop couldn't handle, and likely conventional. When you factor in the higher RPM and 8 cylinders it might balance out. Belt drive would help dampen out the pulses as one option. I think the Duramax makes its peak power around 3000-4000?

Are you speaking of a specific 350HP 6cyl engine? I don't understand where you got the 713 lb-ft number?- EDIT - I see the answer above, thanks. Didn't realize the torque was that high on the 6cyl's. I guess that's multiplied through gear reduction?

From Wikipedia (LBZ):
Power / Torque: 360 bhp (270 kW) @3000 rpm / 650 lb·ft (881 N·m) @1600 rpm

Double edit, remember the factory HP/TQ settings are also limited due to emissions, etc. Plenty of folks are seeing much higher real world numbers, I suspect in a plane the engine could be dialed up quite a bit.

 

[Ted]

Are you speaking of a specific 350HP 6cyl engine? I don't understand where you got the 713 lb-ft number?- EDIT - I see the answer above, thanks. Didn't realize the torque was that high on the 6cyl's. I guess that's multiplied through gear reduction?

Thaton a direct drive engine. Torque is multiplied through gear reduction, however, so a 421 will be transferring even more torque to its props, on the order of 900 ft-lbs.

From Wikipedia (LBZ):
Power / Torque: 360 bhp (270 kW) @3000 rpm / 650 lb·ft (881 N·m) @1600 rpm

Double edit, remember the factory HP/TQ settings are also limited due to emissions, etc. Plenty of folks are seeing much higher real world numbers, I suspect in a plane the engine could be dialed up quite a bit.

So you could go about this one of two ways. Either dial the RPM back a hair and do it like a Duke - 2900 RPM direct drive. Or even 2700 I bet would be workable to get the desired power. Or keep the 3,000 RPM rated power rating and do a gear reduction - figure 1.5:1 and add 421 props. The former would be lighter weight. The latter would be quieter. You'd probably need an electric prop with the former. I think my preference would be option 1 for weight considerations with an already heavy setup, and just keep a high manifold pressure with a bit less RPM (read: quieter) for cruise.

One other consideration would be engine/cowl size vs prop size. If too much of the prop is covered by the cowl, you might want a gear reduction to support a larger prop.

 

[Skylane81E]

Valid, but your points don't apply to everyone.

Stuff that IO-720 into an MD500 or Bell Jet Ranger and try to convince them it's a higher performance alternative to their Allison/Rolls 250.

Rotary wing aircraft have much different power plant needs than fixed wing. Operators also are more tolerant of very limited range. Look at what turbine engines replaced, the big radials engines in planes going fast and high, not the smaller ones.

 

[Alexb2000]

The 600 ft-lbs of torque is nothing not seen today. As stated above, a J2BD makes over 700 ft-lbs. Your AJ1A makes around 650. Now with a gear reduction you'd have higher torque on the prop than at the crank, but that would just bring it up to the levels of current piston engines. Easy to manage.

What's the max power RPM on your LLY?

The LB7 injector issues were bad, that's why GM warrantied them 200,000 miles. All of the LLY and newer ones use a different head and injector configuration, much better.

I had no idea about aircraft engine torque, thanks, learned something.

LLY: 310 HP at 3,000 RPM, 605 ft. Lb. at 1600 RPM. Duramax's are limited to 3250 RPM, the newer ones (LBZ) max power is 360 HP at 3200 RPM 650 ft. Lb. at 1600 RPM.

Sounds close to an aircraft engine.

 

[Dan Thomas]

600lbs vs 200lbs for the Allison

Plus the weight of a PSRU and its cooling system, which would add 100 pounds anyway, I'd think, to reduce 60,000 RPM to 2500 or so and handle 400 hp doing it.

Soloy did it for the Cessna 206. They're using that same Allison C250, which is now made by Rolls Royce. The airplane's nose isn't that much longer than with the IO-520, telling me that the engine's total weight probably isn't all that much less. Unless they have those huge NiCad batteries up front on the firewall, maybe, for starting it.

http://www.soloy.com/Products/Fixed+Wing+Aircraft/Turbine+Cessna+206+Mark+1/default.aspx

The basic conversion kit is $590,000.

And that, of course, is why you don't see many of them.

Dan

 

[Ted]

The LB7 injector issues were bad, that's why GM warrantied them 200,000 miles. All of the LLY and newer ones use a different head and injector configuration, much better.

I had no idea about aircraft engine torque, thanks, learned something.

LLY: 310 HP at 3,000 RPM, 605 ft. Lb. at 1600 RPM. Duramax's are limited to 3250 RPM, the newer ones (LBZ) max power is 360 HP at 3200 RPM 650 ft. Lb. at 1600 RPM.

Sounds close to an aircraft engine.

Yeah, that sounds like with a bit of boost tweaking it would be fine direct drive. The thing to keep in mind is that diesels these days run massive boost levels, and the turbo won't be able to maintain those to the flight levels like your engine can. So a sequential turbo setup will be needed if that's important, especially for pressurization.

 

[RotorAndWing]

Valid, but your points don't apply to everyone.

Stuff that IO-720 into an MD500 or Bell Jet Ranger and try to convince them it's a higher performance alternative to their Allison/Rolls 250.

 

[wickedsprint]

Rotary wing aircraft have much different power plant needs than fixed wing. Operators also are more tolerant of very limited range. Look at what turbine engines replaced, the big radials engines in planes going fast and high, not the smaller ones.

I disagree, there are plenty of low and slow turbine operators using King Airs,and other regional types.

 

[wickedsprint]

Plus the weight of a PSRU and its cooling system, which would add 100 pounds anyway, I'd think, to reduce 60,000 RPM to 2500 or so and handle 400 hp doing it.

Soloy did it for the Cessna 206. They're using that same Allison C250, which is now made by Rolls Royce. The airplane's nose isn't that much longer than with the IO-520, telling me that the engine's total weight probably isn't all that much less. Unless they have those huge NiCad batteries up front on the firewall, maybe, for starting it.

http://www.soloy.com/Products/Fixed+Wing+Aircraft/Turbine+Cessna+206+Mark+1/default.aspx

The basic conversion kit is $590,000.

And that, of course, is why you don't see many of them.

Dan

I forgot that it would need a PSRU, good point.

 

[kyleb]

King Air?

The smallest engine I'm aware of in a King Air is 550 hp. Not exactly a small engine, and not transferrable to the vast majority of the GA fleet.