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 Post subject: Re: Low cost turbine....
PostPosted: 02 Feb 2021, 12:22 
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I agree that economics plays a big part.

If I can overhaul my existing Cherokee engine and get 2,000 hours out of it at a cost of $15k-20k or so, what is the cost point for comparison?

New engine saves 50% on fuel costs (half due to lower fuel burn, half due to less costly Jet A or even Diesel locally). 10 GPH * $5 a gallon is $50 an hour * 2,000 hours is $100,000. 7 GPH at $3.50 is $25 (rounded) * 2,000 hours = $50,000.

Arguably I'm likely not to fly 2,000 hours off my Cherokee in my lifetime of ownership - most people don't but we can use it for a comparison.

So if a new engine can be brought to market for less than that $75k or so, then you have an argument both in resale and break-even cost savings, plus resale value, but on the converse side you're betting on a new technology that may develop issues, plus the costs of FAA certification (which I'm not even certain they will pursue, courting the LSA and Experimental group).

As for the last part, most of us don't run at 20% of output. The nice thing about a turbine is I can run it 80% at cruise at higher altitude all day long (King Air, MU-2, etc) and get max speed out of the plane. What it does at 20% isn't really in my thought process - that's pretty much ground idle...

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 Post subject: Re: Low cost turbine....
PostPosted: 02 Feb 2021, 12:58 
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Would be cool to have this 122hp version in a Zenith or a Rans. Then again, it's probably going to be a whole lot more expensive than a ULPower or Rotax motor which only burns 4-5gph and will run on mogas.

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 Post subject: Re: Low cost turbine....
PostPosted: 02 Feb 2021, 13:26 
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Username Protected wrote:
Would be cool to have this 122hp version in a Zenith or a Rans. Then again, it's probably going to be a whole lot more expensive than a ULPower or Rotax motor which only burns 4-5gph and will run on mogas.


The guys at TurboTech believe they can be price competitive with the Rotax 912/914 family with cheaper and flexible fuel and lower overall weight.

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 Post subject: Re: Low cost turbine....
PostPosted: 05 Feb 2021, 15:03 
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Username Protected wrote:
Would be cool to have this 122hp version in a Zenith or a Rans. Then again, it's probably going to be a whole lot more expensive than a ULPower or Rotax motor which only burns 4-5gph and will run on mogas.


The guys at TurboTech believe they can be price competitive with the Rotax 912/914 family with cheaper and flexible fuel and lower overall weight.


If I was an investor I would have take their existing design with all the parts and go out and get quotes for all the parts at different volumes. that will tell them at what volume their engine might make money. If it is now running for extended periods of time they know the design well enough to do this.

My gut feel is that they will need to build at least 100,000 a year to hit a cost to make money at $50,000 each. the rule of thumb is to make money in a business building complex systems like a jet engine or automobile etc, at a specific price, you need to build it complete, ready to ship for 25% of the selling price. and in system with this complexity, requiring high quality, certified components, my experience tells me that will be at the 100,000 per year level.

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 Post subject: Re: Low cost turbine....
PostPosted: 06 Feb 2021, 05:06 
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Username Protected wrote:
My gut feel is that they will need to build at least 100,000 a year to hit a cost to make money at $50,000 each. the rule of thumb is to make money in a business building complex systems like a jet engine or automobile etc, at a specific price, you need to build it complete, ready to ship for 25% of the selling price. and in system with this complexity, requiring high quality, certified components, my experience tells me that will be at the 100,000 per year level.


I don't know of ANY product in GA that comes anywhere near that kind of volume !

I guess that might explain why virtually nobody invests in GA ?

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 Post subject: Re: Low cost turbine....
PostPosted: 08 Feb 2021, 12:08 
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Username Protected wrote:
My gut feel is that they will need to build at least 100,000 a year to hit a cost to make money at $50,000 each. the rule of thumb is to make money in a business building complex systems like a jet engine or automobile etc, at a specific price, you need to build it complete, ready to ship for 25% of the selling price. and in system with this complexity, requiring high quality, certified components, my experience tells me that will be at the 100,000 per year level.


I don't know of ANY product in GA that comes anywhere near that kind of volume !

I guess that might explain why virtually nobody invests in GA ?


that is why if it was my co. I would ignore the aviation market in general and look at markets like emergency power generation or hybrid vehicles. there are a few niches in aviation like lightweight generators for hybrid VTOL where weight is worth a lot of money where it would justify a much more expensive engine.

there are niches where light, efficient, small, run on an available fuel lie Jet A, are worth a lot of $

but the real question is what is their true cost to manufacture it at various volumes and then they can look for markets where their technology makes economic sense.

our existing piston power for aircraft structure is hard to beat as long as there is a fuel as all of the development costs are already paid and a good infrastructure exist to maintain.

a good example to think about is what do the new light sport aircraft cost and what is their capability compared to a good used 172 or 182. If you have a pilot's license a 172 is far cheaper to purchase and own compared to one of the new light sport aircraft.

many of us that can afford to own and operate a 172 or 182 or a bonanza cannot afford a new aircraft with the same performance.

I think the real competitor in aviation for this engine are the diesels so I would look at Thielert, Astro, Continental diesels and see where it could fit in. if they can get it to 200 hp I think there is a good market for it. as 150 to preferably 200 hp seems to be the sweet spot for Hp required for a small 4 place aircraft.

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 Post subject: Re: Low cost turbine....
PostPosted: 08 Feb 2021, 12:22 
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it is a fun thought experiment to think how could I use this gas turbine in aviation if I had a 200 hp one?

the first is the 172/ Cherokee class of aircraft. even there its lower efficiency at low powers would be a problem.

perhaps you might use it on a 4 place Bonanza class aircraft in a hybrid mode where about 200 hp is the power required for cruise with enough batteries to supply say 15 minutes or 30 minutes of power for take off and climb and as an emergency back up. The turbine could run at full power all the time where it is most efficient and use it efficiency for cruise.

It is very interesting to look at the total economics etc of a technology to work to find the niches where you have a viable business. ie where it make economic sense or there is some other important reason to spend the extra to use it. (an example is the parachute in the cirrus) Basically, get around behind the customer and look through his eyes to see why he would spend the money.


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 Post subject: Re: Low cost turbine....
PostPosted: 09 Feb 2021, 10:31 
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It is producing 97 HP at 8.4 GPH. This may be SHP (shaft horsepower) and not EHP (effective horsepower) which adds the effect of the jet exhaust thrust, which would raise the power somewhat (7.5% for a TPE331, less for a PT6). I presumed it was Jet-A fuel.

So at 200 HP in cruise flight (think 67% power for an IO-550 that makes 300HP at sea level) this will burn 16.8 GPH?

At say 7500’ MSL?

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 Post subject: Re: Low cost turbine....
PostPosted: 09 Feb 2021, 11:59 
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Username Protected wrote:
So at 200 HP in cruise flight (think 67% power for an IO-550 that makes 300HP at sea level) this will burn 16.8 GPH?

As the engine gets larger, the fuel specifics will improve, so maybe 16 GPH for a 200 HP version? That would be 0.54 lbs/hp/hr which is good in that size class. A good piston engine is around 0.40 lbs/hp/hr for comparison.

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At say 7500’ MSL?

Generally, turboprops reach peak efficiency right where torque and temp limits meet. That could be at 7500 MSL depending on the derating employed. Higher temps mean higher efficiency.

Mike C.

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 Post subject: Re: Low cost turbine....
PostPosted: 09 Feb 2021, 15:01 
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Another thing that took me by surprise as I did the back-of-a-napkin calculations for fuel burn for a long range idea was how much more diesel makes sense the longer the range. Up to about 5hrs range, a gas engine's light weight is a better choice for overall weight savings, but after that, despite Diesel-engines much higher weight, the savings in fuel burn make them lighter than gas engines. The longer the range or endurance, the more diesel makes sense.

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 Post subject: Re: Low cost turbine....
PostPosted: 09 Feb 2021, 17:43 
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Username Protected wrote:
Another thing that took me by surprise as I did the back-of-a-napkin calculations for fuel burn for a long range idea was how much more diesel makes sense the longer the range. Up to about 5hrs range, a gas engine's light weight is a better choice for overall weight savings, but after that, despite Diesel-engines much higher weight, the savings in fuel burn make them lighter than gas engines. The longer the range or endurance, the more diesel makes sense.


that is the basic result I get especially if you look at the comparative installed weight and not the bare engine weight.

diesels tend to have more stuff on them like radiators, intercoolers, turbo's and more sophisticated controls so they weight more especially on smaller engines.

the other thing to consider, is that depending on most peoples risk tolerance, most aircraft take off with 4 1/2 to 5 hours of fuel for a 3 hour flight. so if you assume that you always need to tanker a little fuel for reserves, on average a three hour or longer flight is where the diesel is a better solution.


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 Post subject: Re: Low cost turbine....
PostPosted: 27 Jul 2022, 21:42 
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This is a very interesting thread and I'm way late to the discussion. I just wanted to add one thing.

If a plane with an IO-550 is producing 250hp @ 15k and a RR250 is producing the same HP at 15k, the RR250 plane will still cruise faster than the piston plane by a decent amount. The reason being is that the drag caused by the much bulkier nose of the IO-550 plane will be quite large in comparison to the RR250 plane.

All of my numbers are hypothetical of course. Just making a point.


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 Post subject: Re: Low cost turbine....
PostPosted: 27 Jul 2022, 22:27 
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Username Protected wrote:
This is a very interesting thread and I'm way late to the discussion. I just wanted to add one thing.

If a plane with an IO-550 is producing 250hp @ 15k and a RR250 is producing the same HP at 15k, the RR250 plane will still cruise faster than the piston plane by a decent amount. The reason being is that the drag caused by the much bulkier nose of the IO-550 plane will be quite large in comparison to the RR250 plane.

All of my numbers are hypothetical of course. Just making a point.

Uh, no, horsepower is horsepower. If both planes are making the same power at the same altitude, they’ll fly at the same speed.

A nose redesign to package a turbine probably won’t buy much, as the cross-sectional area of the fuselage isn’t changing, the airframe wetted area is probably identical, and exhausting the turbine to the free stream might actually increase drag.


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 Post subject: Re: Low cost turbine....
PostPosted: 27 Jul 2022, 23:18 
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Username Protected wrote:
Uh, no, horsepower is horsepower. If both planes are making the same power at the same altitude, they’ll fly at the same speed.

A nose redesign to package a turbine probably won’t buy much, as the cross-sectional area of the fuselage isn’t changing, the airframe wetted area is probably identical, and exhausting the turbine to the free stream might actually increase drag.

Two words: "cooling drag".

A significant amount of power is being used to push air through the piston engine for cooling. That is why some setups have cowl flaps, to reduce that drag.

The turbine also has jet thrust. Typically, this is about 10% of the power output, so the effective horsepower is 10% larger when the shaft horsepower is the same.

For any given shaft horsepower, the turbine airplane has much lower drag and higher effective output power.

Mike C.

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 Post subject: Re: Low cost turbine....
PostPosted: 27 Jul 2022, 23:19 
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I don't think that is clear. You see an airspeed change with cowl flaps even though the cross section changes very little. It does take aerodynamic power to cool a piston engine.

Username Protected wrote:
This is a very interesting thread and I'm way late to the discussion. I just wanted to add one thing.

If a plane with an IO-550 is producing 250hp @ 15k and a RR250 is producing the same HP at 15k, the RR250 plane will still cruise faster than the piston plane by a decent amount. The reason being is that the drag caused by the much bulkier nose of the IO-550 plane will be quite large in comparison to the RR250 plane.

All of my numbers are hypothetical of course. Just making a point.

Uh, no, horsepower is horsepower. If both planes are making the same power at the same altitude, they’ll fly at the same speed.

A nose redesign to package a turbine probably won’t buy much, as the cross-sectional area of the fuselage isn’t changing, the airframe wetted area is probably identical, and exhausting the turbine to the free stream might actually increase drag.


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