Simviation Forum - why are jets faster then props?

Reply #30 - Feb 9^th, 2003 at 11:39pm

SilverFox441 Ex Member

Jet engine turbines don't stall because of the configuration of the intakes. The intake is designed to slow the incoming airstream and increase it's pressure.

Some aircraft (like the SR-71) have variable geometry intakes that allow this effect to be maintained over a wider speed range. You should note that the SR-71 and the F-104 (which had a similar intake style) both suffered from "unstarts" which is basically a compressor stall caused by allowing supersonic airflow into the engine.

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Reply #31 - Feb 10^th, 2003 at 12:44am

Deputy Offline
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Hillsboro, Oregon

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Which would cool the air enough that it couldnt cause thrust right? I should know this, but I don't.

-Brad

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Reply #32 - Feb 10^th, 2003 at 10:02am

Felix/FFDS Offline
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Without going into details, combustion turbines (i.e., gas turbines, but considering they can operated on fuel oil, propane, natural gas, ....) are designed to operate at a certain range of inlet air mass/pressure - too much or too little air flow and your turbine won't turn over...

(analogy -stand in the airflow of a table fan - if it's turning fast enough, you won't be able to breathe properly... too much air for you to handle, so you have to take it in "gulps; get on a high mountain, where there's lower air pressure ("thin air") and you can't breathe either - you'll welcome that table fan!)

This is one of the reasons you have variable inlets - to control the airflow into your turbine

The air temperature is important - the compressor takes in the inlet air, increases the pressure and by pressurizing it, increases the temperature so that when it goes into the combustion chambers, and fuel is injected and ignited, a more efficient combustion takes place...more *work* is generated to turn the turbine blades which turn the compressor.....

In a pure tubojet engine, the thrust provided by the exhausted gases (the jets) provides all the force.

In high bypass engines, the "fans" up front provide most of the "thrust"

You can generalize up to a certain point - all combustion turbines "suck, squeeze, bang, and blow" - its the how they do it that drives engineers nuts...(who have to start with)

Quote:

Which would cool the air enough that it couldnt cause thrust right? I should know this, but I don't.

-Brad

Felix/FFDS

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Reply #33 - Feb 15^th, 2003 at 10:24am

Fly2e Offline
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Yeah, I agree with

and

and

and

! Thanks for info. I am going back to the garage and make a few adjustments to the jet engine I am building! Now, if only I could find where I put those directions! LOL Wink

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Reply #34 - Feb 15^th, 2003 at 2:36pm

Deputy Offline
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Hillsboro, Oregon

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Quote:

Without going into details, combustion turbines (i.e., gas turbines, but considering they can operated on fuel oil, propane, natural gas, ....) are designed to operate at a certain range of inlet air mass/pressure - too much or too little air flow and your turbine won't turn over...

(analogy -stand in the airflow of a table fan - if it's turning fast enough, you won't be able to breathe properly... too much air for you to handle, so you have to take it in "gulps; get on a high mountain, where there's lower air pressure ("thin air") and you can't breathe either - you'll welcome that table fan!)

This is one of the reasons you have variable inlets - to control the airflow into your turbine

The air temperature is important - the compressor takes in the inlet air, increases the pressure and by pressurizing it, increases the temperature so that when it goes into the combustion chambers, and fuel is injected and ignited, a more efficient combustion takes place...more *work* is generated to turn the turbine blades which turn the compressor.....

In a pure tubojet engine, the thrust provided by the exhausted gases (the jets) provides all the force.

In high bypass engines, the "fans" up front provide most of the "thrust"

You can generalize up to a certain point - all combustion turbines "suck, squeeze, bang, and blow" - its the how they do it that drives engineers nuts...(who have to start with)

Oh thanks, that makes me feel smart. . .

-Brad

Bad boys, bad boys, whatcha gonna do? Whatcha gonna do when I come for you?&&&&Iustita Omnibus&&Justice for All&&&&Women are: attractive, single, mentally stable. Pick two.&& &&Yes, we drive on the right-hand-side of the road. Yes, I parked on the left-hand-side of the road. Yes, I blocked traffic for a picture. &&&&&&

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Reply #35 - Feb 19^th, 2003 at 5:39pm

torquestripe Offline
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Because the air speed indicator says so!!! Jeez Loweez.
Save your brain cells for the HARD questions like why is the grass green or why is the sky blue.

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Reply #36 - Feb 19^th, 2003 at 11:04pm

Professor Brensec Offline
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Can't you give me a couple
more inches, Adam?
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As you see, the comment has been completely removed.

Thanks, no harm. Grin

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Reply #37 - Feb 19^th, 2003 at 11:05pm

torquestripe Offline
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Reply #38 - Feb 19^th, 2003 at 11:12pm

Professor Brensec Offline
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Can't you give me a couple
more inches, Adam?
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Quote:

OH gosh almost forgot, could you please direct me to one of the more enlightened forums.

Pretty much any of the others. This one is unique, in that it's populated almost exclusively by people with IQ's Higher than "cretin"

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Reply #39 - Feb 26^th, 2003 at 3:46am

Redsunfox Offline
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Hi All,

The only stupid question, is the question you don't ask.

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