turbo-prop?

[jaredyates]

Dave, thank you for coming around to clarify and answer questions!

[Mark Goldberg]

And all the best to you on your project. For Patrols and 4 place Bearhawks in different places in the world where avgas is hard to find - your engine would be a good option. Good luck. Mark

[TurbAero]

Jared and Mark, thanks for your support.

I shall give a brief description of recuperator technology as it is a little known technology.

To derive power from a turbine engine, in basic terms, a certain mass flow and turbine inlet temperature (TIT) are required. For a fixed mass flow, the power is proportional to the TIT. In order to reach a specified TIT, a certain amount of fuel is required to raise the temperature of the air coming into the combustor from the compressor to the required TIT after it is burnt.

I shall put some arbitrary numbers in to be an example. Let’s assume that the air from the compressor entering the combustion chamber is at 200 degrees celsuis and the TIT required to produce 100hp is 900 deg.c. Enough fuel needs to be injected and burnt to raise the temperature 700 deg.c.

Now let’s assume the exhaust gas temperature is 500 deg.c. If we have a recuperator, it acts as a heat exchanger which uses the hot exhaust gas at 500 deg.c. to heat the compressor air which starts at 200 deg.c. but after the recuperator, it may now be at 400 deg.c. before it enters the combustion chamber. Instead of adding enough fuel to raise the temp 700 deg.c., the temp now only has to be raised 500 deg.c. to achieve the TIT of 900 deg.c. to develop the required power. This means that to develop the same 100hp, we need to add less fuel. This is how a recuperated engine can offer up to 40% better fuel efficiency over an identical unrecuperated turbine engine.

The challenge is to develop a recuperator that is compact enough to be suitable for an aircraft engine, but also offer the effectiveness to reduce the fuel consumption to an acceptable level. We are confident that we have the required solution, but testing will confirm this. Recuperators have been done before for non-aviation turbine applications (Capstone) and even for a few aviation applications and testing has verified the results of those programs, but there is not a lot of publicly available literature about it.

For those that are concerned about us taking people deposits, I say again that all deposits are held in escrow. We do not have access to those funds until the deposit holder chooses to actually purchase the engine. He may obtain a refund of his deposit at any time. His money is secure and if we go under, his funds are safe and will be returned to him at his request and if we succeed, he will have one of the first affordable, efficient small gas turbine engines to put into his aircraft. All the decisions rest with the buyer. I don’t think we could be fairer or more ethical than that.

Dave

[Battson]

Jared and Mark, thanks for your support.

I shall give a brief description of recuperator technology as it is a little known technology.

To derive power from a turbine engine, in basic terms, a certain mass flow and turbine inlet temperature (TIT) are required. For a fixed mass flow, the power is proportional to the TIT. In order to reach a specified TIT, a certain amount of fuel is required to raise the temperature of the air coming into the combustor from the compressor to the required TIT after it is burnt.

I shall put some arbitrary numbers in to be an example. Let’s assume that the air from the compressor entering the combustion chamber is at 200 degrees celsuis and the TIT required to produce 100hp is 900 deg.c. Enough fuel needs to be injected and burnt to raise the temperature 700 deg.c.

Now let’s assume the exhaust gas temperature is 500 deg.c. If we have a recuperator, it acts as a heat exchanger which uses the hot exhaust gas at 500 deg.c. to heat the compressor air which starts at 200 deg.c. but after the recuperator, it may now be at 400 deg.c. before it enters the combustion chamber. Instead of adding enough fuel to raise the temp 700 deg.c., the temp now only has to be raised 500 deg.c. to achieve the TIT of 900 deg.c. to develop the required power. This means that to develop the same 100hp, we need to add less fuel. This is how a recuperated engine can offer up to 40% better fuel efficiency over an identical unrecuperated turbine engine.

The challenge is to develop a recuperator that is compact enough to be suitable for an aircraft engine, but also offer the effectiveness to reduce the fuel consumption to an acceptable level. We are confident that we have the required solution, but testing will confirm this. Recuperators have been done before for non-aviation turbine applications (Capstone) and even for a few aviation applications and testing has verified the results of those programs, but there is not a lot of publicly available literature about it.

Dave

The "recuperator" principle is common in ground-mounted power turbines, where they are commonly used to generate steam or run a binary cycle for heat recovery. I suspect there are good reasons why they are not commonly used in aircraft.

While this device might add efficiency to the open cycle turbine, surely this will reduce maximum power output and add an unacceptable weight. The exhaust gas mass flow is enormous and any heat exchanger capable of dealing with the flow and temperatures needs to be large and heavy.

[svyolo]

The company doesn't have an operating prototype anywhere near the efficiency they are claiming. It is still "a dream". So they are taking real money deposits, for an engine that doesn't exist.

Ethical? More ethical would not be soliciting deposits, until you are ready to sell engines. That is a gigantic red flag. That one fact makes me lose total interest.

If you were posting videos of an aircraft flying with your engine, I would be extremely interested.

I have seen this movie many times before. It always ends the same.

[Rollie]

I have been waiting for someone to make a turbine engine or an electric motor for GA planes. Things like that don't happen overnight. It's funny how we complain that the available engines are all based on antique designs but then poo poo anybody who is trying to make an advancement. Sure lots of people have lost deposits in the past, but if they didn't recognize that they were investing in an idea as much or even more than in a purchase, they were rather foolish. Most of the people who are trying to invent new things for aviation are either individuals or small companies who need some kind of investors. The main way to attract investors is to show that they have a market for their product. That is done by showing how many people have put down deposits.

As for the recuperator heat exchanger thing being big and heavy, how big and heavy are we talking? Bigger and heavier than the engine? That might be ok. I've thought about trying to figure out how to repurpose a helicopter turbine into an airplane, but ran into a couple big issues right away (cost and figuring out a reduction gearbox) but then another issue is weight and cg. They are very light. The Turbomeca Ariel that The AS-350 A-Star runs puts out close to 1000 shp and only weighs about 245 lb. An engine that produces an appropriate hp for our planes would probably weigh a little over 150 lb. If it had another 150lb of heat exchanger on it, it would still weigh less than an O-320 or 360. I'd be ok with that.

My bigger concern would be how you could produce turbine blades at such close tolerances required to produce a reliable, long lasting engine for a low enough cost to make an affordable engine. It's my understanding that that is one of the bigger hurdles to producing a low cost turbine engine.

[svyolo]

I wish I was an inventor or a visionary. I am neither. I was probably born an engineer, self educated, and formally educated, myself as such. But I had a dream of flying. The dream worked out. I was only an engineer for 3 years.

I still look in awe at the inventors and visionaries. The ones that can invent something new. The ones that can see where the world is going, and get there with a product that the public didn't even know they wanted.

But 56 years on this earth have made me skeptical. I am mostly skeptical of those who sell a dream, but want real money now. Aviation didn't invent this business model, but I think we perfected it. There are always new suckers who will fund the R&D project.

If the new company was a real project, and needed money, they would put together a business plan, outlining their knowledge and ability to execute on a technical level. That is a minimum. If they could convince someone to invest, the investor would bring to the table the ability to bring to production and marketing. And capital. For that they would want a return on investment of some type. A percentage of ownership in the company, or a really high interest rate.

Soliciting deposits before the pre-production phase is........well, use whatever 4 letter expletive you want. For the company, it is an interest free loan. If they were legit, and had a real game changer of an idea or product, they would solicit investors, not suckers to loan them money.

Deposits put in escrow? I was going to type in "escrow.com better business bureau". Before I got to "be" google predicted what I was looking for. Most of the predictions were not very positive for the safety or security of the deposits. I will leave it at that.

The vast majority of my flight time is turbine. I would love to buy a turbine to fly behind for my own plane. Sell me one, And I will gladly eat crow.

How many new engine projects have I heard about in almost 40 years? I have forgotten most of them. In 5 years, I am pretty sure this one will be purged from my memory as well.

[TurbAero]

While this device might add efficiency to the open cycle turbine, surely this will reduce maximum power output and add an unacceptable weight. The exhaust gas mass flow is enormous and any heat exchanger capable of dealing with the flow and temperatures needs to be large and heavy.

A recuperator does not restrict the maximum power output. A specific target power output is specified for the engine in the design phase, and the recuperator, turbo machinery components etc are designed to the necessary parameters to achieve the required engine power.

As Rollie correctly points out, if we don’t achieve a weight of say 180 lbs, but we end up coming in at 300lbs to facilitate a recuperator that gives our engine the required efficiency, our engine is still a better weight proposition than an O320/O360. For our recuperator, we have options available to us in relation to configuration, architecture and materials. We can achieve our target size, but the trade offs are weight against cost. We could have a 160lbs recuperator that has a favourable cost, or we could have a 50lbs recuperator that costs significantly more. There are options that are in between those extremes. The decision to be made is whether to offer a heavier but cheaper engine, or a lighter but more expensive engine. The decision we make will be evident when actual specifications are released publicly following testing.

Dave

[TurbAero]

... Most of the people who are trying to invent new things for aviation are either individuals or small companies who need some kind of investors. The main way to attract investors is to show that they have a market for their product. That is done by showing how many people have put down deposits.

As for the recuperator heat exchanger thing being big and heavy, how big and heavy are we talking? Bigger and heavier than the engine? That might be ok. I've thought about trying to figure out how to repurpose a helicopter turbine into an airplane, but ran into a couple big issues right away (cost and figuring out a reduction gearbox) but then another issue is weight and cg. They are very light. The Turbomeca Ariel that The AS-350 A-Star runs puts out close to 1000 shp and only weighs about 245 lb. An engine that produces an appropriate hp for our planes would probably weigh a little over 150 lb. If it had another 150lb of heat exchanger on it, it would still weigh less than an O-320 or 360. I'd be ok with that.

My bigger concern would be how you could produce turbine blades at such close tolerances required to produce a reliable, long lasting engine for a low enough cost to make an affordable engine. It's my understanding that that is one of the bigger hurdles to producing a low cost turbine engine.

Hi Rollie,

i have abbreviated your first paragraph in the quote above. You have identified a primary reason for instituting a reservation program. Having 10,000 people say they will buy your engine will not necessarily translate into actually making a single sale. Having people put down $500 gives a more serious indication of intent to buy an engine which is a positive indicator to investors that there is tangible interest in the product. In our case, and I stress this again for svyolo’s benefit, all our deposits are non-binding on the buyer, and we do not have access to those deposits. They are certainly not an interest free loan to us as we do not have access to those funds. They are being held in escrow and belong to the deposit holder, until such time as they release them to us, the seller. If they want their deposit back, they advise escrow.com and their funds are returned to them.

As I indicated on my response to Battson above, we have recuperator options ranging from 50-160lbs, depending on materials and architecture. With either recuperator option, we would have a sub-300 lbs 200hp engine which is still smaller in size than the 200hp piston engines. The cost to manufacture the recuperator will be a consideration in our decision which option to incorporate into our engine.

Manufacturing techniques that produce accuracy that is very precise are readily available now, even for the materials that we will incorporate into our engines. This aspect of our program is not a problem that needs to be solved as it has been solved already. Having precision components manufactured at a price point that allows us to deliver an affordable turbine engine to the market is challenging but is achievable.

Dave

[TurbAero]

If the new company was a real project, and needed money, they would put together a business plan, outlining their knowledge and ability to execute on a technical level. That is a minimum. If they could convince someone to invest, the investor would bring to the table the ability to bring to production and marketing. And capital. For that they would want a return on investment of some type. A percentage of ownership in the company, or a really high interest rate.

Soliciting deposits before the pre-production phase is........well, use whatever 4 letter expletive you want. For the company, it is an interest free loan. If they were legit, and had a real game changer of an idea or product, they would solicit investors, not suckers to loan them money.

Hi svyolo,

I’m not really sure where I should start with my response to your comments but I will keep it brief.

I would like to start by thanking you for your business advice in the first paragraph of the quote above. Your advice has validated our own approach to the business because that is what we have done and will continue to do moving ahead.

In relation to the second paragraph above, I say again, all our deposits are non-binding on the buyer and we do not have access to those deposits. They are certainly not an interest free loan to us as we do not have access to those funds. They are being held in escrow and belong to the deposit holder, until such time as he releases those funds to us. Their deposit may be returned to them at any time by requesting them from escrow. We cannot and do not wish to stop any one from receiving a refund of their deposit if they want it back. We set the program up this way to protect the buyer and his funds.

I suspect that our current deposit holders would not appreciate being called suckers who are loaning us money. They have had the interest and the foresight to place a small amount of money to ensure that they are one of the first to receive an engine that they desire for their aircraft. If we don’t deliver for any reason, they get their money back and they can then go and buy that traditional offering. I would classify our deposit holders as true enthusiasts who are excited about the opportunity to obtain a long sought after engine product and who are willing to set aside a little of their overall project budget to ensure that if that product becomes available, they will be amongst the first to have one.

So for those on this forum that are valued customers of ours, I’d like to thank you for your support. To svyolo, I will look forward to receiving your order and delivering that engine to you, once our product has been demonstrated and proven to your satisfaction.

Dave

[Battson]

A recuperator does not restrict the maximum power output. A specific target power output is specified for the engine in the design phase, and the recuperator, turbo machinery components etc are designed to the necessary parameters to achieve the required engine power.

As Rollie correctly points out, if we don’t achieve a weight of say 180 lbs, but we end up coming in at 300lbs to facilitate a recuperator that gives our engine the required efficiency, our engine is still a better weight proposition than an O320/O360. <abridged>

Dave

I do note your point about a theoretical recuperated turbine being a comparable engine to an ICE, also noting that I am not aware of any such aero-turbine flying today. I didn't mean that a recuperator restricts the maximum theoretical output you can design for, I meant that the design is bound to restrict the output from any given engine. Unless I am mistaken, an aero-turbine recuperator heats the inlet air stream after it's passed through the compression stages and before it reaches the combustion chamber. In which case, such a heat transfer device is bound to restrict the mass flow or cause a considerable pressure loss which reduces power output and power to weight ratio, in favour of fuel efficiency comparable to an ICE.

[Bdflies]

I truly appreciate Dave’s contributing to our forum! Takes a bit of moxie to play the target on here! I’ve seen some "pre-production deposit" schemes go badly, but it seems that the concept described is about as sterile and fair as could be designed.

It occurs to me that some of us are focusing on turbine engines in a historical frame of mind. As mentioned before, I don’t come from an engineering background. But I've gotten good at reading the readily available materials. Frankly, I had to do some reading to learn what a recuperator was. I agree with Battson, that I don’t think I’ve ever seen or heard of such on an aircraft engine. I will, however, challenge the concept of comparing a turbine to an ICE. As I understand it, a gas turbine is an ICE (internal combustion engine). From the sound of this discussion, it seems that we all agree that such an engine doesn’t currently exist in a package suitable for aircraft use.

How about we just accept that and think of it a different way. Let’s discuss the idea of a new 200hp engine, in a package smaller than an O-320, capable of burning alternative fuels. Let’s say this engine employs only a few major moving components, uses proven technology to produce reliability and has fuel consumption comparable to similar horsepower piston engines. Yeah, it’s a turbine. But it operates differently than what we’re used to seeing. The design goal isn’t to produce as much power as possible, damned the fuel burn. His goal is to produce 200 hp in a package that compares favorably to existing 200hp aircraft engines, burning similar amounts of more readily available fuel. I find it exciting that Dave’s team is thinking a bit outside of the box! Plenty of us moan about the antiquated technology of our Lycomings and Continentals. I just can’t bring myself to moan about dinosaurs and shoot arrows at this new way of thinking.

No doubt, a bunch of new aircraft engines have flopped in the past. This one might follow suit. At some point, SOMEONE is going to hit the right idea at the right time and revolutionize our planes. Dave might be the guy! Employing the concept of "You Only Live Once", I'd hate to be known as the guy who preached to Burt Rutan that it was ludicrous to think of building a plane out of fiberglass...

As usual, my $0.02

Bill

[Bdflies]

So, how would a common engineer describe a Wankel?

[TurbAero]

Thanks Bill. You’ve expressed things very well in your post and I believe that your thoughts echo those of our supporters.

[James]

Yeah Dave - I don't know much about GA aircraft, or experimental engine design, but I do know that I want to keep flying my bearhawk 10 - 20 years from now, when Avgas is no longer available in Australia. Whether it runs on diesel or JET-A1, is a piston engine or a gas-turbine, any aircraft engine that can burn a range of heavier fuels will be a winner going forward. At the very least, think about the USDF "single fuel" policy, and the future market for mass-produced light engines for drone aircraft etc, all CAD-designed and 3-D printed. These last two factors alone completely change the market dynamics and the economy of scale problems that have plagued every other engine design that has gone before.

This is the promise - not sure if Dave's engine will be the answer or not, but at the very least I'll reserve judgement and give the benefit of the doubt to those people out there giving it a go. The deposits are in a holding account, so it's not like they're based in the Cayman Islands or something (you're not, are you?)

Good on you mate

James

[svyolo]

If we were talking steam turbines, or some form where a medium is heated by some other means, I could see a recuperator working. On a combustion engine?

Maybe I will go try it. I will take my cars' turbo intercooler off the top of the engine where it is currently, and remount it on the exhaust pipe where I can recuperate exhaust heat. Bingo - 30% better gas mileage. I can't believe Honda and GM didn't think of this

Most turbo cars already have a recuperator. They just mounted it in the wrong place.

I apologize to the forum for the sarcasm.

FWIW, I hope it works. I will finally have a great engine for the BD-5 sitting in my garage for 35 years.

[Battson]

If we were talking steam turbines, or some form where a medium is heated by some other means, I could see a recuperator working. On a combustion engine?

Maybe I will go try it. I will take my cars' turbo intercooler off the top of the engine where it is currently, and remount it on the exhaust pipe where I can recuperate exhaust heat. Bingo - 30% better gas mileage. I can't believe Honda and GM didn't think of this

Most turbo cars already have a recuperator. They just mounted it in the wrong place.

I apologize to the forum for the sarcasm.

FWIW, I hope it works. I will finally have a great engine for the BD-5 sitting in my garage for 35 years.

Svyolo, perhaps you are missing the subtly.
The ICE (class one, fixed volume piston) compresses and ignites in the same chamber. You want coldest possible air jammed tight into the chamber, then to heat it as cheaply as possible. There is not a simple way of recovering any heat energy from the exhaust and transferring it into the piston at the right time, after the valves are all closed for the compression stroke. On a turbine, such a possibility exists theoretically. Whether it can be done practically, who knows.

[zkelley2]

If we were talking steam turbines, or some form where a medium is heated by some other means, I could see a recuperator working. On a combustion engine?

Maybe I will go try it. I will take my cars' turbo intercooler off the top of the engine where it is currently, and remount it on the exhaust pipe where I can recuperate exhaust heat. Bingo - 30% better gas mileage. I can't believe Honda and GM didn't think of this

Most turbo cars already have a recuperator. They just mounted it in the wrong place.

I apologize to the forum for the sarcasm.

FWIW, I hope it works. I will finally have a great engine for the BD-5 sitting in my garage for 35 years.

That's an incredible flase equivalency.