Can a high by pass turbine be made?....

[FCBrosius]

OK, I just got off of the phone with my son who is an A&P mechanic. I asked him “BASICELY” how dose the High By Pass work. He says that a P&W (I think he said) use the first stage to turn the FAN and Rolls Royce use the 3rd stage to turn the FAN. He said the Rolls may be the better way to go he thinks.

I saw a turbine at the Jet rally that could not have been any bigger then 1 ½ X 3 inches. The question is simply this, why can't someone design a small turbine that powers a 75 – 120mm ducted fan? Would that in short be a High by pass fan then. A longer shaft out the front of the turbine then the DF then the starter! Sounds good to me but would it work? As he says most turbines are only running at 70 – 80% max power on the real planes anyhow…(passenger)

[pmackenzie]

Check out this (http://cpl.usc.edu/eschuste/) site for a high bypass turbofan:
http://cpl.usc.edu/eschuste/turbofansmall.jpg
Pat MacKenzie

[FCBrosius]

I have seen this plane before, I was wondering about something smaller to replace brushless motors and use the VIOJET FAN or something like that… could that be done?

[mcjustis]

FCBrosius,
to answer your question about putting a shaft out the front of the turbine, won't work. Unless it's geared and running off a secondary turbine wheel. With a turbine as small as you are asking, you couldn't just run straight off the shaft, something that small would turn upwards of 250,000 rpm. Doubt you'll find any fan that could handle that kind of rpm. Besides, you'd be better off just using the turbine as a turbo jet for something that small, you'd never be able to overcome the weight you'd add by making a turbo fan. In other words, the plane would be way too heavy and extremely overly complex. An engineering marvel none the less, but doubt it'd work.
Later...
Martin

[downunder]

All fan engines use the last stage of turbines to drive the fan. The problem is that the fan is free turning, it's not governed by fuel flows like the core engine and the only thing restricting its speed is the back pressure in the tailpipe so exhaust area is critical. This is why an afterburning turbofan has moveable nozzles. They vary the area to keep the tailpipe pressure constant so the fan keeps the same speed. Just for interest's sake, if the nozzle happens to snap full open at full dry (military) power then the fan section of a TF-30 will acclerate at a rate of 100,000 revs/second!

The setup in the original post is more like a turboprop (without the gearbox) but even a turboprop uses a free spinning low speed turbine to drive it. I guess it could be done but you'd need a turbine designed to extract more power than normal from the combustion chamber(s). And a ducted fan unit that could handle the revs :)

[Ossie]

Seen this ???

http://www.gtba.co.uk/gallery/turbofans/index.html

Quite a bit of info there on minature GT engines if your interested.........

[FCBrosius]

Ossie: THX for the help in photos! Now that is what I'm talking about, only a bit smaller?

Leave it up to our over seas friends to pull this off as they always look to be ahead of us in the modeling field...