throttle system for dual turbofan.

[thepax]

Im building a jet of my own and i was trying to make a throttle system that uses only manual pullys with no electrical systems to minimize weight.

i was just wondering how they get both turbofans on the huge commercial airliners to give the same amount of thrust at the exact same time.

:] any answers?

 

[MikeHalloran]

They don't use 'throttles' that throttle air flow; they use 'fuel controls' that ... are connected to 'throttle handles', but that's not what they do.

I think they _can_ synchronize fuel flow with computers, but the primary synchronizer is the guy with his hand on the (independent) throttle handles... and his feet on the rudder pedals.



Mike Halloran
Pembroke Pines, FL, USA

 

[thepax]

yea but those bring on so much wieght, im looking for an allternate way of controling fuel so the thrust is symetrical with only coming to a totall of a few pounds.

i was thinking a hand crank that could pull a wire that pulls a fuel controller of some sort that puts more fuel into the combustion chamber.

or something like that, very very simple.
im not to familiar with the fuel input system of a turbofan. and any extra info on the GE 90 whould help too.

 

[FieldTeam]

707 uses four throttles rigged at the same angle. The engine fuel controls are set at part power, where all the throttles are rigged for this setting.
The engines are trimmed at part power to produce the same power (P&W charts dictate the EPR setting conditional on barometric pressure and temp).
This way, at any given power setting, each throttle will be producing the same amount of thrust (within the limits of the trim porcedure and indicating system tolerances).
In effect, on a properly rigged and trimmed aircraft, you can select any power setting and all four throttles will be aligned.

Acceleration is dependant on each engines poerformance characteristics (within the accepted limits). You can have one engine reaching TRT in 6 seconds and another engine reaching TRT in 8 seconds.....you will feel the the 2 seconds in acceleration, but once at power the throttles will align.

If you are using more than one engine, I would assume that both (or more) engines are the same and therefore have the same fuel controls. Find the reference power setting for fuel control adjustment (part power) and adjust them to the same values. With the throtles rigged the same and the motors trimmed the same, they should produce equal thrust at equal throttle settings.

 

[thruthefence]

Do you have the faintest idea what a "GE 90" turbofan costs?
Engines of this class are normally carried on a separate lien from the airframe,(or leased from the manufacturer ) because of the expense.
It produces something on the order of 100,000 lbs of thrust, and you are trying to save weight by rigging a "hand crank" pulling a "wire" for the fuel control?

 

[thepax]

haha no i wasnt going to use the full size GE90 that whould be rediculous if i was trying to save weight for that huge of a engine.

im just trying to make my jet suitble enogh for a human to carry, and fuel controls easy for an instant takeoff.

i was intrested in the GE 90 because of its thrust/weight ratio, if you made a smaller model like say 1/100 of its size, my question is would it be suitable to carry about 100-300 pounds? or a little more?

 

[KENAT]

You probably wouldn't get the same thrust to weight ratio on a smaller engine, even using the same basic technology.

I'd look at some of the small engines used in cruise missiles if you're just looking at sizing a concept.

KENAT, probably the least qualified checker you'll ever meet...

 

[thepax]

"I'd look at some of the small engines used in cruise missiles if you're just looking at sizing a concept. "

you mean a rocket. im building a jet. thanks for everyones help

 

[IRstuff]

No, he meant turbofans.

TTFN

FAQ731-376

 

[KENAT]

thepax, no offense but do you know what you're doing?

This is starting to sound like a school project or home build or something, which isn't really what this website is about.

Cruise missiles are generally jet powered with the more modern/larger ones often making use of small turbofans.

http://en.wikipedia.org/wiki/Cruise_missile

KENAT, probably the least qualified checker you'll ever meet...

 

[MintJulep]

would it be suitable to carry about 100-300 pounds?

Yes, thrust and weight are both measured in pounds. But you do understand that the thrust produced by the engine is not the same as the load carried by the plane, right?

 

[KENAT]

Not necessarily Mint, if we're talking VTOL then there's a close correlation, just need to add in the mass of the engine & airframe etc. Something like:

http://en.wikipedia.org/wiki/Williams_X-Jet

However, you make a fair point that every cruise missile I can think of weighs a lot more than 100-300 lbs and the little jets work just fine.

http://en.wikipedia.org/wiki/Williams_F107

http://adg.stanford.edu/aa241/propulsion/smallfan.html

KENAT, probably the least qualified checker you'll ever meet...

 

[MintJulep]

With an efficient airframe, you can maintain steady level flight with remarkably little thrust.

Just for rough numbers, consider a standard class sailplane. L/D around 40:1, weight in the neighborhood of 1000 lbs. That puts the drag at a measly 25 pounds.

 

[KENAT]

I wasn't dismissing your point Mint, I knew what you meant and you're correct, however given thepax posts I wasn't sure he got it and was just playing up.

Given his other post I now suspect something like the X 48B.

http://www.google.com/search?hl=en&sa=X&oi=spell&resnum=0&ct=result&cd=1&q=X+48B&spell=1

KENAT, probably the least qualified checker you'll ever meet...

 

[Surestick]

I'm picturing something like this:

http://www.coolorwhat.net/blog/archive/2005/05/13/758.aspx

 

[KENAT]

OK, now I want one;-)

KENAT, probably the least qualified checker you'll ever meet...

 

[MiketheEngineer]

Cute - but probably a good way to die....

 

[IRstuff]

The scale RC planes with microturbines are pretty awesome, but you don't get to sit in the cockpit, though...

TTFN

FAQ731-376