Turboshaft Outboard - Jetboating for Gentlemen!

[Johansson]

Firstly YES I am building one and secondly YES I must be retarded to start a new project when I have the bike to finish.



I´ve been planning for this build for quite some time now and with the family still away and the bike frame delivered to the painter I realised that I had an entire sunday to do what I wanted with, so I started on this build. It should be a fairly quick project and I aim to have run it before the end of summer.



I am using my AMT Pegasus MK3 as the gas producer, it is so small compared to the JU-01 but still capable of producing 30hp (edit: closer to 25 most likely) in a turboshaft configuration. I have to make a new engine cover since the original one is leaf thin and to well made for me to hack it to pieces, I started making a new cover from 1.5mm stainless sheet instead.



The idea is to make an axial power turbine, a set of angle grinder gears is on its way and a gearbox housing for them has to be made. The output shaft is pointing downwards so beneath the engine I will put a chain drive from the output shaft to the propeller shaft, a brake caliper will be fitted over the secondary chain sprocket so I can stop it while shifting or picking up fancy ladies at the docks.



A thick stainless ring was turned down to a sliding fit around the turbine cover just like the original engine cover, any minor air leaks there will go into the NGV and through the power turbine so it won´t be completely wasted.



The cover about to be welded together with the turbine ring.



A 30mm long sleeve was fitted to the cover where the freepower section will be connected, I considered a ring of M4 threaded holes around the turbine ring but the heat would only seize the damn screws.



Not too shabby, left to fit is the glowplug but that is easy since the original cover has a threaded fitting for it so I only need to drill a hole and fit it with the special nut from the inside of the cover.



I´ll try to find some numbers for the Pegasus to do some calcs for the freepower turbine from, at this point I just want something in the ball park preferably a bit on the large side to keep the temps down. After all it isn´t speed I am after as much as annoying people at the lake, and the slower it runs the more time I have to annoy them! *LOL*



Cheers!
/Anders

[stoffe64]

Fantastic...a new build,this one gonna be interesting!
Cheers/stephan

[metiz]

Because OF COURSE you just happen to have a turbojet lying around:)

30hp, that's quite a lot for such a small engine. Hook up the output of 2 of these engines together and run them to two ducted fans - "jet"pack!
Seriously though, cool project for "in between", and with 30 or so hp you should still get there fast!

[Johansson]

This will be great fun, just imagine taking it to a fishing contest.

I don´t think I´ll be able to get 30hp out of it, I will keep the freepower revs down since the turbine wheel will be made from thick sheet stainless, later I can make a more sturdy one to squeeze the last pony out of it but right now a third of that would be enough.

[Johansson]

I just remembered that in my livingroom bookshelf I have the rotary assembly of an old Holset truck turbo, a set of calcs I´ve done for the engine says that a radial freepower turbine needs to have a 3.2" exducer and this one is darn exactly 3.2 inch!



Some numbers for you calc punchers out there:

Pegasus MK3: 57.2mm inducer = 0.62lb/s mass flow and an estimated 11.3kg thrust which is in the ball park of the official rating.

The jet pipe area is 25.5cm2 and the radial turbine inducer area is 47.5cm2.

I´ll set the throttle stop after the EGT so in case it tends to run a bit hot at higher revs I´ll just back off on the throttle a bit and leave it at that.

Cheers!
/Anders

[Johansson]

That is exactly what I had in mind for the radial, a sheet metal snail housing, a simple lubricated bearing tunnel and the gocart sprockets driven from it!

Is this guy hanging around here? It would be interesting to know how the internals of the power turbine housing looks like, the design of the guide vanes etc.

[stoffe64]

I have seen this One before on youtube i think he calls himself jet A1 terminator

[enginewhisperer]

excellent project!

[Johansson]

Indeed, one only needs to get properly dressed and the success amongst female bystanders will be total. *grin*



Today I bought a set of ball bearings for the freepower shaft and turned it down to 17mm in the lathe after truing it.



Bearings test fitted on the shaft, they will be lubricated by bleed air and oil which will dribble down on the chain sprocket as chain lubrication once passed both bearings.



The freepower shaft with bearings, the spacer tube, primary sprocket and a shaft nut.



I must be on the right track with this build since Olov and I giggled like a pair of schoolgirls while discussing the layout of the engine package. *LOL

Cheers!
/Anders

[Richard OConnell]

Haha, this sounds like an entertaining project. turbochris the AMT almost looks like it would fit on the pocket bike, eh?

[miuge]

Another great project Anders!
Idea is absolutely fantastic, we were thinking the same too, replacing my friend's electric motor with our turbine one.. Would be a slight difference in sound

[turbochris]

heh heh heh to pick up fancy ladies

[Johansson]

Been at the build from time to time now and it is slowly starting to look like an engine, the shaft housing is made in aluminum and the rest of the scroll is 3mm mild steel since it won´t get overly hot in there.



Threading and cutting the turbine shaft.



Here the shaft is in place with the chain sprocket fitted.



A turbine cover was made to fit the turbine wheel.



Here the parts are mocked up so I could figure out how to make the scroll, my first plan was to make a circular segmented scroll like the one Mikko made and threw in the scrap bin but it was to much work so I settled with a much simpler flat sheet scroll instead.



Last night I got this far, I need to roll and weld an edge around the housing and make a transition between the scroll and engine exhaust. The scroll inlet area is a bit marginal but it´ll do, if temps get a bit high at full throttle then I´ll simple lower the revs a bit and leave it at that.



Cheers!
/Anders

[miuge]

That doesn't look bad at all! Shouldn't weight more than 5kg as you used aluminium in the CHRA.

[Johansson]

No it is pretty lightweight, I would love to have a circular scroll but it would take forever and I don´t have much time to spare since I need to get the turbine bike on the road this summer.