Jet Engine Help?...I want electric!

No.

Others are better at this than I am, but from what I know a turbo-fan is not a "jet engine", nor is it a rocket engine.

Suck, bang, boom is a jet engine.

Theoretically you may be able to ride lightning, though I have strong doubts that you would like where you ended up.

New studies out of Duke University suggest you might go straight up, though typically you run right into the ground.

As far as #3, it sure sounds untrue to me.

I may be wrong, but I think Q4 shows that you don't understand how a jet engine works.
All the rotating stuff is a sideshow...It's the burning of fuel which produces the 'jet' which produces the thrust.

Just using electricity you could drive a propellor or a ducted fan...but you wouldn't have a jet untill you compress an air fule mixture and ignite it.
Del

As per as other questions are there

First- common sense- the blades of turbofan can not cross the sound speed, it will simply disintegrate- so there goes.

Second - detailed design calculations, and may be hours of data churning by software.

Third- most likely - the turboprops are the propeller driven by turbine, so the motion is by propeller - which you are calling secondary flow, but isn't it actually primary flow? (I may be wrong, not in the aviation business)

Q4- Del: You may be right but who knows- it may be a PMM ?

http://www.youtube.com/watch?v=oPaiH19j3UI&eurl=http%3A%2F%2Fwww.navyaircrew.com%2Fblog%2F2009%2F07%2F18%2Fsuck-squeeze-bang-and-blow%2F&feature=player_embedded

Ok... So the 'jet' only gives 20% of the thrust, but it provides 100% of the power, because the energy of the jet is used to turn the fan at the front end...
Like I said...without the jet you just have a ducted fan....
Del

A final tip: the numbers are large..

_{Yeah but you can always use a smaller font}
Del

thanks bhrescobar. I suspected I was a off in some regard, and was fastened on airliner engines such as the turbo fans on a 737, while forgetting the designs for something like the Blackbird. Learned something. Thanks.

You're welcome. But keep in mind that even airliners like the B-737 do observe transonic and supersonic flows in some regions in the fuselage. Actually, the CFM56 engine also do take advantage of the shock wave between the nose cowl and the fan spinner.

And you're right: the blackbird is a great example. As it travels at mach 3+, it has to provide means to at least three distinct zones of shock wave in the engine inlet. That's why its spinner is movable forward and aft according aircraft speed.

There are some presentations of this effect over the net, I remember have seen something like this...

Regards.

I did actually have the pleasure of speaking with a pilot who had flown the SR71.

He told me that it went so fast that he actually had to keep downward pressure on the yoke to prevent it, and himself, from going off into outerspace, and not returning.

I am sure that he said he had had it up to Mach 6, and then said he would have trusted it to Mach 10.

I myself had rejected an electric powered turbofan out of hand, which I ought not have.

Our engineering hero, and the great inventor Tesla if put on it would have probably come up with something astounding.

"If you want to see the future, go to a toy store." is a quote from somebody that seems true to me.

In answer to the question I have started to wonder what the most powerful and lightest generators are, and how to mate that with the lightest and most powerful electric motors and props.

-not to mention airframes and even light fuels like alcohol.

Reality does impose some limits, but using multipules of motors run from one generator, with a very light airframe, hi aspect wings, it may well be possible to make a practical aircraft that utilizes electric motors.

In my mind I do have doubts about at which point the numbers break down, and also still suspect this craft may not ever be as fast as the OP might want, but do accept the idea now as possible to achieve.

GA. Wish you were here, Ky.

bhrescobar you were very good in providing the details but i suspect that u confused turbo fan with bypass engine?

bypass engine are those in which some of the fresh air is bypassed form the combustion chambers and mixed with the combusted air. It is done in heavy planes as in 737 in order to provide more thrust for take off. As the hot gases reduces the density of the air so the push is not good, here comes the role of bypass air which is relativly cold and helps in thrust.

No.

A turbofan engine is a jet engine that uses a fan to provide thrust along with the gases from the power section itself. The power section main function is to provide torque to drive the fan, and not a jet stream to provide direct thrust by the power section exhaust.

In the current engines development, the fan driven air stream is the main responsible for thrust. Its not mixed to the hot air, neither is a booster to make the air cooler to provide thrust. Well, it will be mixed, but after engine exhaust, so, it does not count.

Unless you are talking about some specific model. B-737 CFM56 series work just this way.

you are right about turbo fan as i know that only 10% combusted gases and 90% fan is responsible for thrust. but in your post you said "A fan engine (I believe you are talking about high-bypass fan engines) is commonly used in transonic and supersonic flights." so i am asking is turbofan and bypass engine same thing?

ok bro i am going to post the exact saying of encarta 2009 about turbofan or bypass engine. turbo fan and bypass is the same thing. what ayou are talking about is the turbo prop engine. hope it will help in improving your understanding of the topic. dont take the correction negatively plz

Oh, well mentioned! Maybe the original post refered to turboprop engines. Well, the quality of the response is a reflect of the quality of the question...

A turboprop engine is a bit different indeed. The concept is really close. Both use shaft power to drive a propeller or a fan, that are the elements responsible for the thrust.

But a propeller is not able to work at that high speeds, or at that high altitude in low density conditions. Its open architecture lacks the ability to work in transonic or supersonic flow conditions. Well, there are researches for open fan developments that are a mix between fans and propellers, but they are not around and not applicable to the same conditions.

Regarding power for thrust, in a turboprop unit, for example, in a commercialy widelly-used engine, for a shaft power output of 1800hp, the associated reaction thrust due to the power section exhaust would count for only 120hp.

Turbo fan or Bypass The turbofan engine is an improvement on the basic turbojet. Part of the incoming air is only partially compressed and then bypassed in an outer shell beyond the turbine. This air is then mixed with the hot turbine-exhaust gases before they reach the nozzle. A bypass engine has greater thrust for takeoff and climb, and increased efficiency; the bypass cools the engine and reduces noise level. In some fan engines the bypass air is not remixed in the engine but exhausted directly. In this type of bypass engine, only about one-sixth of the incoming air goes through the whole engine; the remaining five-sixths is compressed only in the first compressor or fan stage and then exhausted. Different rotational speeds are required for the high- and low-pressure portions of the engine. This difference is achieved by having two separate turbine-compressor combinations running on two concentric shafts or twin spools. Two high-pressure turbine stages drive the 11 high-pressure compressor stages mounted on the outer shaft, and 4 turbine stages provide power for the fan and 4 low-pressure compressor stages on the inner shaft. An example of an engine of this type is the JT9D-3 jet engine, which weighs about 3850 kg (about 8470 lb) and can develop a takeoff thrust of about 20,000 kg (about 44,000 lb). This is more than double the thrust available for the largest commercial planes before the Boeing 747. Current research in turbojet and turbofan engines is largely directed to achieving more efficient operation of the compressors and turbines, to devising special turbine-blade cooling systems to permit higher turbine-inlet temperatures, and to reducing jet noise. Microsoft ® Encarta ® 2009. © 1993-2008 Microsoft Corporation. All rights reserved.

turbo prop engine In a turboprop engine a propeller mounted in front of the jet engine is driven either by a second, or free, turbine or by additional stages from the turbine that supplies power to the compressor. About 90 percent of the energy of the expanding gases is absorbed in the turbine portion that drives the propeller, leaving only about 10 percent to accelerate the exhaust jet. The exhaust jet, therefore, contributes only a small fraction to the overall propulsive thrust. Turboprops have certain advantages for small and medium-sized planes at speeds of up to about 480 to 640 km/h (about 300 to 400 mph). They cannot compete, however, with turbojets or fanjets for very large planes and for higher speeds. Microsoft ® Encarta ® 2009. © 1993-2008 Microsoft Corporation. All rights reserved.

If you go through the equations (and I haven't for a very long time) you will find that the most efficient propulsion for an aircraft is a function of speed.

High speed requires a high speed body of air, low speed a low speed, high mass body of air.

This is the rationale behind high by pass turbo-jets.

When you look at some of them, so much air is bypassed that you wonder if they are a jet or a ducted fan. At this point it is basically semantics.

For subsonic flight, the high bypass engine provides a large mass of comparatively slow air to efficiently propel the aircraft.

At supersonic speed, you need a low bypass ratio. Most military jets work on 20% bypass and less, whereas the subsonic commercial jets are around 80%.

At higher mach numbers, the bypass is eliminated entirely, so propulsion is by a small, high speed jet, frequently with additional speed added to it by means of an afterburner.

When speeds get higher still (as eg in the SR71), most air is bypassed around the working parts of the engine and ram compression is used, so it becomes more and more of a ramjet.

In answer to your original question:

1. Fan jets are not efficient at supersonic speeds.

2. Torque required can be approximately calculated using the equations in any reasonable thermodynamics text book. You need to know the compression ratio and the total air mass flow rates, as well as the bypass ratio.

3. The ratio of bypass thrust to jet thrust is a function of bypass ratio and will depend on the design of the engine.

4. The turbine exists to power the compressor. The thrust developed is provided by the mass and velocity of the air thrown out behind the engine.

If, eg, you had a nuclear power plant on board producing great gobs of electricity, you could power the compressor electrically. Power involved is huge as you find in gas turbine power plants where the power to drive the compressor can be larger than the output of the power turbine. Thermodynamically, this is referred to as a small work ratio and the implication is that small variations in efficiency of either turbines (power and compressor turbines) or compressor will give large variations in overall efficiency.

By contrast, a steam cycle has a large work ratio and is reasonably insensitive to minor variations in component efficiencies.

Hope this clarifies rather than confuses.

... and besides, in a steam power plant, you don't have to worry about TOGW... or available cargo volume...

Dear bhrescobar,

I feel that some of the go around here on this thread is comparable to some physics go arounds I've between Jorrie and Roger Pink, I've tried to keep up with and understand about physics.

Could you explain a bit more what exactly "Bypass" means in relation to these engines?

Possibly if we grasp more fully what that term is really referring to, all here will have a better grasp of the forces involved.

It would appear that we have drifted far from the original posters desire to make a fast electric motor powered aircraft.

I myself don't see how you could make one without using either a recip, or jet engine to generate electric power that then powered the electric motors that powered props.

Still with the right combinations of motors and jet engine and genset, this may be viable. Certainly it would not be supersonic, but might well be viable.