Turboshaft Racecar?

[rcman50166]

Hi everyone,

I'm new to the forums. Some background about me. I am an NDE technician for a major jet engine manufacturer (I don't care about disclosing this information, but they might). I have a mechanical engineering background and I'm a car enthusiast. I've joined the site to seek more advanced concepts to jet engine theory and design. I'm also looking for good places to start researching my project.

So what is it? Well the title pretty much says it all. I want to make a turboshaft powered race car. I mean driven wheels. This is by no means practical or economical so I'd rather not hear about how there are cheaper alternatives. It's something I've wanted to do since seeing vehicles like the helicopter powered minivan (one of your own), the Howmet TX, and turbine assisted vehicles like the Mannic Beattie. The scope is autocross or SCCA track day type stuff. The vehicle will be built from the ground up to accommodate the engine. It will likely be a small RWD, mid engined, open wheel car.

So what engine should I use? I'm looking for something in the 200-1000hp class. I want a low maintenance, low cost engine. I'd prefer single stage compressor and turbine with a separated power turbine. Blisk/centrifugal architecture is preferred. Looking around a Pratt and Whitney PW200 or something similar would be perfect. This is where my knowledge is lacking. I am unaware of what the big manufacturers make or how easy they are to get. Quantities produced greatly affects how many trickle into the private owner arena. I am also unaware of where any private citizen gains access to such equipment. This is knowledge I hope to gain from this forum. So any help in this area would be greatly appreciated.

Other talking points:

-Engine maintenance cycles and costs
-Power transmission to driven wheels
-variable guide vanes for power turbine
-throttle response and how to translate a throttle pedal into acceleration
-oil system
-fuel system
-gyroscopic influence of a jet engine
-chassis to engine vibration mitigation
-hot section metallurgy
-flow design and jet turbine architecture

[smithy1]

Hi RCman,
Welcome... and indeed an interesting project you are proposing.

I believe there were some turbine powered race cars which graced the Indianapolis race track in the mid-late 1960's from a few different manufacturers. They were exceptionally fast but also horrendously thirsty, I understand they had to pit nearly twice as much as the normal piston engine cars due to their thirst for fuel. Although their HP wasn't much to talk about, they had a prodigious amount of torque.

Another thing which hurt them was their dislike of slowing down and accelerating back up to speed, they much preferred a constant speed. Throttle response is not something a turbine is good at. I understand there was talk of other race teams deliberately slowing down and speeding up the race pace to give these cars grief and making their fuel consumption even worse.

Cheers,
Smithy.

[racket]

Hi

Welcome to the Group .

You want a low maintenance and low cost engine , turbines are low maintenance relatively speaking , but low cost they ain't unfortunately , and if you break a part it'll cost lots to fix , engines can be found on Ebay occasionally

Power transmission is pretty straightforward , but be aware of the torque multiplication ( 2 to 2.5 times) of a stalled freepower wheel with gas producer at 100% , this could overstress the engines inbuilt gearbox as there'd be very few aero engines that would encounter a stalled freepower , the prop/rotor will normally be spooling up with the gas producer .

Variable NGVs for the freepower , can't think of any engines with them , some of the auto turbine engines had them .

Throttle response is poor with larger engines , gets better with smaller lighter rotatives, but still kinda poor compared to an IC engine , throttle pedal would work normally , as all we are doing is adding more fuel .

Oil and fuel systems will vary between engines , so an operation manual required .

Gyro effects ...........have no idea .

Some normal rubber engine mounts should take care of vibrations getting back to the engine.

Hot section metallurgy , generally nickel based

Flow design and jet turbine architecture ..............now thats too broad field for a simple answer.

And one other thing ...............we need massive brakes , turbines tend to "run on" after lifting the throttle as they use heat in the metal parts for "fuel" until they cool down .

Cheers
John

[Johansson]

This sounds like a fun project!

Here in Sweden the Caterpillar/Boeing 553 turboshaft engines can be found for sale relatively cheap (2000-3000USD) from time to time, 500-ish HP. We used them in a turret-less tank a couple of decades ago.



You can also get a Rolls Royce Nimbus for the same kind of money, Chris Krug with the turbine van use such an engine. 700-ish HP.

The downside with a Nimbus compared to a Boeing 553 is that it is build for a helicopter and not a land based vehicle so it has its exhaust pointing backwards and is in general a less compact engine than the Boeing. I´ve never actually seen a Nimbus next to a 553 though so please correct me if I am wrong.

Throttle lag will be a problem just as Smithy and John has pointed out, but it can be overcome at the expense of an even worse fuel consumption. I remember reading about a turbine race car that had its engine running close to 100% RPM all the time and controlled the power output by a simple exhaust bleed valve on the interstage duct.

Best of luck!

[racket]

Hi Anders

Yep , I'll second your choice of engine :-)

Not too big , not too small , just right , and the main thing is it was designed for land based use , so hopefully a bit more "heavy duty" , they didn't need to watch the weight quite as closely for a tank engine as an aero unit .

Cheers
John

[rcman50166]

Thanks for the information, everyone. Throttle lag is a recurring topic so I thought I might share my idea. It's a pie in the sky solution with no design background or precedence.

I would design and build a power turbine with nearly no deflection angle and minimal gas surface radius. There would be variable guide vanes that would direct turbine gasses at various angles into the power turbine to create variable loading on the output shaft. This way, the gas generator section of the engine runs at full power the whole time and the power turbine's torque output can be instantly adjusted. If the guide vanes have enough control authority, the power turbine could even be run in reverse at reduced output. I can add a small illustration later today to help visual describe what I want to do. The huge waste gate idea used in the Howmet TX would be the backup plan.

As for fuel consumption, I am not worried. The scope of the project accommodates for poor fuel consumption as autocross courses are under a minute and track days are timed laps no longer than a few minutes per lap.

[racket]

Hi

If you want to do that with the freepower then you'll need to be able to separate the gas producer from the freepower stage as there probably won't be sufficient axial distance for the variable vanes.

Checkout the Chrysler turbine en.wikipedia.org/wiki/Chrysler_turbine_engines which was equiped with variable vanes .

Cheers
John

[rcman50166]

Thanks for that information. I knew the Chrysler turbine existed, but was unaware of the engine development/architecture. Very cool to read about.

The Cat engine looks good, but upon a cursory search about it, it seems like a pretty old design that isn't manufactured anymore. Am I correct in that? I'd generally want to avoid retired engines because of included cost of rebuilding them.

Another thought pops into my head. What if I were to combine multiple automobile/industrial turbo chargers together with a shared combustor? The engine would have the throttle response required because of the lower inertia of a few impellors/turbines rather than one larger one. Any thoughts on doing something like that? The only real problem I see is horrible efficiency and power to weight ratio. Does anyone know the shaft horsepower of those DIY engines?

[Johansson]

You can´t really find a low cost engine that is still being used in aviation, the only way a person with an average paycheck can afford a factory built gas turbine engine is to source an outdated model that is out of production. Like the Boeing 553, RR Nimbus or a handful of other models.

On top of that, more modern engines are heavily computer controlled so you would probably need most of the helicopter electronics in order to operate it. The older engines are more mechanical with direct driven pumps and such.

Building a turbocharger based car engine that can safely produce 500-1000hp is probably not the most sane choice, you´ll need a school bus to fit the cluster of turbochargers needed.

Cheers!
/Anders

[rcman50166]

I figured it might be something ridiculous. Power output rarely scales linearly with combustion engines and size. Are those DIY engines a couple of HP each? What about compounding turbo chargers? For example. Turbocharger A's compressor stage feeds into Turbocharger B's compressor stage feeding into Turbocharger C's compressor stage. Turbocharger C's compressor output goes to a combustor which powers C, B, and then A's turbine stage. Assuming a triple in the compression of the first stage, double of the second, and then 1.5 of the third, you'd be left with a 9:1 compression ratio with combustor inlet pressures around 130 PSIG. Case pressures and combustor temperatures are a concern with this design, but a few of those setups might get into the usable power regime.

[racket]

Hi

All a high Pressure Ratio does is basically reduce fuel burn rates , there are some gains in HP over a lower PR engine but its not huge .

As for HP from our homemade engines , my old Garrett TV84 turbocharger ( 1.8 lbs/sec mass flow) based engine produced 115 rear wheel HP on the dyno , this was my first engine build which began its life back in ~1991 but took more than a decade to finally get finished , reasonable performance for a total bike plus rider weight of ~ 370 kgs - 815 lbs www.youtube.com/watch?v=P-5PgWqgIJo with a single gear ratio, no clutch .

Anders current bike engine is producing >150 HP just going by its speed performance which is steadily approaching 300 kph, and would probably be similar if fitted to a lightweight race car , his new JU-02 engine jetandturbineowners.proboards.com/thread/734/building-ju-02-gas-producer should produce >250 HP.

Smithies GT6041 turbocharger kart gas producer jetandturbineowners.proboards.com/thread/568/again-gt6041-powered-green-beast would produce close to 200 HP from a freepower wheel .

This latest turbo from Garrett turbobygarrett.com/turbobygarrett/turbochargers/gtx5533r-gen-ii would make an interesting engine considering its 5:1 PR capability and relatively lightweight componentry .

I wouldn't consider a compounded arrangement , too much complication for a race car , remember the only engineering truth..... " KISS" .

I've had a lot of correspondence over the years on the merits or not of compounding so please don't go there .

As Anders has already explained, its only possible to use relatively outdated aero derived engines , their big concern is parts as you've recognised , but also costs , a single bearing will be very expensive to replace , thats why we make our own engines , they cost less than that bearing :-)

Cheers
John

[Johansson]

A word of advice from a DIY gas turbine racer might be in place.

If you decide to buy an industrial manufactured engine you can focus on the actual racing business, with a homemade engine running at full throttle a handful of inches away from you 95% of your concentration is spent watching gauges and worry about increasing temps etc.

I hardly notice when I cross the standing mile finish line in >250km/h since I am so focused on what is happening to the bike engine.

So, if you are interested in racing you should buy an engine. If you look forward to spending a decade or two designing engines you should build one. Simple as that.

We´re here to support you no matter what.

Cheers!
/Anders

[racket]

Hi Anders

Yep , those red hot bits spinning around close to ones "family jewels" certainly focuses the mind ;-)

Cheers
John

[smithy1]

Dec 5, 2016 18:19:46 GMT -5 racket said:

Hi Anders

Yep , those red hot bits spinning around close to ones "family jewels" certainly focuses the mind ;-)

Cheers
John

LOL...Not much difference for me....my "family jewels" were "fixed" years ago...LOL You can now call me "Christmas Balls", they're just hanging there for decoration..!

Cheers,
Smithy.

[racket]

Hi

I did some numbers for that big Garrett turbobygarrett.com/turbobygarrett/turbochargers/gtx5533r-gen-ii , the turbine stage is just too small to flow the compressors potential output :-(

My thoughts for a reliable DIY gas turbine gas producer is a trusty old GT6041 with its nice big turbine stage , but do some mods to the compressor stage , there are upgrade billet comp wheels with better aero potential as well as higher PR potential from lower Trims.

A simple "sore thumb" combustor fitted with a high pressure spray nozzle to complete the engine.

With a lower Trim wheel , roughly same sized inducer , maybe a mm or two bigger , the comp map would extend up into the >4:1 PR range with > 3lbs/sec flow at reasonable efficiency and potential for >250 HP from a freepower wheel .

Cheers
John