Slightly Odd question regarding connecting to the shaft...

[FirmamentFX]

Hi all,

Just a hypothetical - it might be totally off radar but go with it before you tell me it's a c%&p idea :rolleyes:

Would it be possible in theory, if the turbines were totally overspecified (to account for the loss of energy and therefore thrust), to attach a small gearbox-type mechanism to front of a turbine which can then power:

a) a miniature generator (for eg: http://www.sullivanproducts.com/GenesysMainFrame.htm ), and
b) a large ducted fan (which could be shaped to avoid air being thrust into the turbine, just around the outside.

The reasons for this are to generate power (obviously), and to firstly make the engine fan look more realistic, and secondly provide a cool air bypass which can be used for reverse thrust.

Could be a crazy idea, but what do you think?

M

[Boomerang1]

Yes, probably, in theory. BUT, people who no doubt know more about these things than you or I, have made available turbines that are 'soft coupled' using the exhaust to spin another turbine attached to a gearbox which then powers whatever you want. I'm sure if the direct connection was better and/or more practical that's the path they would have followed.

Check out the Wren website http://www.wrenturbines.co.uk/index.php

Included in the galleries section are a locomotive, a bicycle and turbo prop aircraft. - John.

[FirmamentFX]

Hi John,

Yes I see - they are more turboshafts though. I was thinking more in terms of still using the jet exhaust to provide thrust for the aircraft, while using a coupling on the front to connect to the generator, and a fan to provide the cool air high pressure "bypass" to power the thrust reversers...

Martin

[mcjustis]

Martin,

If you want to use a jet engine, in this case as the core engine, as a turbo shaft, turbo prop, or turbo fan, you wouldn't really want any thrust coming out the back. You would want that secondary turbine wheel to use all the energy it receives from the primary turbine wheel. If you are getting much thrust out the back, the secondary wheel isn't taking all the 'juice' from the exhause flow. Also if you couple directly to the main shaft out the front of the core engine you will be turning way to high an rpm on any type of fan. Kurt Schreckling has a good book on building a turbo prop, In the book he goes into a little detail about a turbo shaft and turbo fan. Both would have to be used off a secondary turbine.
You would be surprised how small the core engine can be to power a very large prop or fan. If you want to learn all about small turbo props, I'd check out Schrecklings book.
Hope this helps some,
Martin

[FirmamentFX]

Hi Martin,

Thanks for the reply. I actually don't want to use the jet engines to drive a prop. I'm looking to do 2 things:

a) connect a generator to the shaft to provide electrical power generation while the engine is on.
b) make the engines look more realistic but having a large fan on the front (even if the fan doesn't do anything useful like provide thrust!)

I still want to keep the jet exhaust as the primary means of thrust.

Martin

[mcjustis]

Turbo prop, fan, or shaft, it all uses the same core engine and basically the same design theory. If you just want the fan on the front for effect put it on a shaft on bearings in a bearing tube and let it free wheel. Why would you go to the complexity of making a turbo fan just to see it spin??
As far as the generator goes, how do you plan to couple that to the turbine itself? The genesys you talked about looks like it peaks at 15000 rpm. That's extremely slow for a straight coupling to the main shaft. Not to mention if you did that you'd just bog the turbine down and probably have some EGT issues.
Good luck,
Martin

[mr_matt_II]

Hi all,

Would it be possible in theory, if the turbines were totally overspecified (to account for the loss of energy and therefore thrust), to attach a small gearbox-type mechanism to front of a turbine which can then power:

a) a miniature generator (for eg: http://www.sullivanproducts.com/GenesysMainFrame.htm ), and



On the industrial line (used for UAVs and researc), JetCat already mounts a generator to the front of the compressor. It runs at full shaft speed (just over 100,000 RPM) and generates about 800 watts of power.

The turbine does not even know it is there, like a squirrel riding on an elephant.