Realistic shaft horsepower expectations

[noshell]

Hey all
Ive had an idea...
Ive allways wanted a jet bike, now i realise it is a huge untertaking. However i think ive figured out good way to go about it.
Id plan to build a turboshaft engine, and have it run through the gearbox of a 125... Clutch and everything.

I figure id need something like a 5:1 reduction onto the crank. Advantages of this over building something from scratch is that you could just leave the bike in neutral and it would charge the battery. Also you could spool the engine and launch it with the clutch, even go through the gears with it. Meaning you shouldnt need a crazy powerful engine.

Anyway... Step 1 is to build a turbocharger based engine.
Step 2 would be a freepower unit. I figure i could use a turbo hot housing and some gear reduction, i could mount it all where the cylinder used to live.

What kindof realistic shaft horsepower could i expect from a 47mm inducer engine?

I think 15-25hp would be nice in a 125 crosser/adventure bike frame

[racket]

15-25 HP is realistic from a 47mm inducer , but I wouldn't be happy about leaving a freepower in "neutral" , also you need to remember a freepower has a torque multiplier effect , your 125 clutch might not be up to the job .

[noshell]

Thanks for the reply. Can you explain what you mean by the freepower has a torque multiplier effect?
I figured the torque would be very low and it would need a lot of gear reduction. I think the drag of the gearbox and running the stator would keep it at a sensible rpm at idle in neutral.
Im guessing at WOT the freepower unit will spin at something like 50k? Im pleased you think 20hp would be achievable.

[noshell]

To be honest id probably want the clutch to be a bit slippy because if i ever locked the rear wheel up, something needs to give.

Edit: This sounds like im being argumentative haha.
I appreciate your expertise. Im a dyno technician by trade. So my knowledge of engines and power systems is very good. But i really am in the dark when it comes to turbines. Its very helpful to be able to ask this kind of stuff.

Speaking of random questions... How does a helicopter engine work? Do they even have a freepower unit? Or is the output just geared off of the main shaft. Looking at diagrams and stuff i cant work it out.

[racket]

Have a look at this jetandturbineowners.proboards.com/thread/1260/turbine-torque

Yep heli engines have freepower turbine stages , we use the 3rd and 4th stages from the Allison 250 engines for our bike freepowers .

Anders used the 4th stage in his jetandturbineowners.proboards.com/thread/53/landspeed-bike-diy-gas-turbine for 0 to 304 kph with a single speed gearbox .

I used the 3rd stage jetandturbineowners.proboards.com/thread/1366/tv84-turbine-bike.

and a different way to go jetandturbineowners.proboards.com/thread/40/2-shaft-turbine-kart-build

If you want a safety device for any potential lockups , theres plenty of options .

Cheers
John

[noshell]

Very interesting stuff there John. If you were to make your kart again, would you use a turbo housing for the freepower and just have additional gear reduction instead of the high AR?
I say that simply because of the difficulty you mention in making your sheet metal housing.
Cheers, Dan

[racket]

Hi Dan

Theres "issues" with chains , the racing karting chain can be used to 20,000 rpm , whereas larger sized chain has lower rpm but can handle more torque/power , so unless the gearing is fairly large , theres not much point in going to the trouble of a gearbox , even with our fairly large engines using the 4th stage Allison freepower which has a max rpm limit of ~30,000 rpm we still need a gearbox with ~6:1 ratio , I used a 4.8:1 on my bike because thats all I could source at the time , but for the 10/98 engined bike jetandturbineowners.proboards.com/thread/34/motorcycle-project I made a suitable gearbox .

When we consider the sized freepower you'll be needing to use , then rpm will be maybe 45,000 max, so something with an 8:1 gearbox would have an output rpm that the normal motorcycle chain would handle .

A standard turbo turbine stage would be easier to use than the one I made , even though the cast iron one would be heavier , and for your sized engine the Cummins ST/VT50 turbo would be OK to use for the freepower with a "tight" scroll A/R and a suitable gearbox.

LOL................Don't know about making another kart .......but I already have the "perfect" karting turbine engine sitting on my shed floor imgbb.com/FKvB9fB ;-)

Cheers
John

[noshell]

Cheers John.
Your new engine looks awesome.

[racket]

Hi Dan

Its slowly getting there , just minor issues to sort out , the main components seem to be spinning around safely , its still very early days in its development :-)

Cheers
John

[noshell]

How does adding a freepower unit affect the design of the jet engine itself?

The turbocharger im basing all this on has a slightly oversized hot housing.
Intuitively this seems optimal as the exhaust side will have some added restriction anyway from the freepower unit.
Hows my logic?

[racket]

Hi Dan

Our gas producer can't tell the difference between a jet nozzle or a freepower turbine stage , all it feels is a backpressure , as long as both are the same it doesn't matter .

When you say an "oversized hot housing" is that from an auto perspective , autos generally run "undersized" turb stages from a gas turbine perspective .

Cheers
John

[noshell]

As in, oversized even by our standards.
My turbine exducer is something like 70mm and my compressor inducer is only 47.

[racket]

LOL.....That is a "tad" oversized , its gunna be hard to fill the scroll unless its very tight , any idea of its A/R ??

What size is the inducer of the turb wheel ??

Cheers
John

[noshell]

The turbine housing has "1.00" in the casting and is twin scroll.

Maybe that would be better used as the basis for my freepower unit and instead make another more optimal gas producer.

Most turbochargers im trying to find to make a gas producer with are variable vane... This seems like it would flow well but i think the vanes might melt?

[racket]

1.00 is the A/R and is at the upper end , you'd have problems most likely .

the variable vanes won't melt before your turb tip fly off