Self sufficient turbo charger based engine

[richardm]

Hi !
Anyone having or considering building a turbo charger based jet engineer gas turbine ever thought of making it self sufficient? IE: no external power needed to run the accessories like the fuel pump, oil pump, cooling fan etc? 
That would make the engine more suitable for a vehicle of some kind. Only starting power would be required.

I'm considering two options:

Either a gear box driven by the turbo shaft  or  making the electric starter turn into a generator once the engine is self sustaining.

The gear box option looks to me as the hard way to do it since a very high level of precision and some lubrication would be required due to the high input speed involved.
But that's the way it is done on most real engines.

The "all electric " way implies a starter motor capable of high speed ( 65,000 rpm in my case) . That motor would be permanently attached to the turbine shaft, no clutch here.
It would turn itself into a generator once the stating sequence is over and with the help of some regulator, it would charge the battery and supply power to the needed accessories.

I understand that those options, as any other, would put a load on the turbine at the expense of some power or thrust loss and an higher running temperature.

Any ideas?

[enginewhisperer]

I think a well done starter generator is probably the best system, but won't be easy to do.
It might even make more sense to have a very small generator permanently coupled, and a higher torque starter engaged temporarily.
A high speed generator (brushless motor) can be very small diameter and easily live in the intake area.

Another way people have done it in the past (not sure how successfully) is using bleed air to drive an accessory turbine.

[richardm]

Yes I agree that the starter/ generator option would be the easiest route. Maybe by using a single stage of gears to bring down the speed and lower the torque on the turbine shaft.. Something like a 3: 1 ratio maybe. A brushless motor would obviously be more efficient but also somewhat more complicated to switch from a starter driven by an ESC to a generator. A brushed Dc motor only requires a double pole double trow switch ( or relay ) and a voltage regulator ... I Am not are of how to do it with a brushless motor

[enginewhisperer]

it's actually very easy with a brushless motor. The controller will act as a rectifier and produce DC output when it is not being driven (depending on the controller)

It can also be controlled actively to regulate the output voltage and shaft load.

[richardm]

Really!
Im not familiar with those brushless motors. I'am more of an old school electro mechanical guy, not much into electronic stuff. I better understand what I can see LOL!
I Guess I should start looking and learning about that. From what you're saying that would be the best way to go I guess

[wannabebuilderuk]

I believe this is a self sufficient setup rcdon built youtu.be/EoztC5-8E6s

[richardm]

This is actually a very nice and clean set up! On this one the power is derived from the power turbine/ gearbox combination. I was rather thinking of a pure jet engine on which there would be no such arrangement. So the the accessory power would be provided by the turbo shaft itself. Complications arise from the high rpm involved, somewhere around 60 k rpm..