That's a rocket, jets are different.
if the jet exhaust is not faster than the rest of the air (all speeds measured relative to the craft), the engine is imparting drag, not thrust.
there's a small amount of rocket effect from the fuel, but jet exhaust is mostly air.
-- \_(?)_
f
But you had to burn a lot of fuel to get the reaction mass up to near orbit al speed before you ejected it. Jet engines aren't rockets. They collect on e and a half O2 molecules from static air(48 atomic mass units) which they combine with one carbon and two hydrogen atoms to spit out one CO2 molecule and one water molecule (62 atomic mass units). There's a lot of nitrogen i n there that rides along.
The plane that carries the jet engine stays aloft by accelerating air downw ards (which is what the wings do) so there's extra momentum being bled out there.
It's aerodynamics rather than rocket science.
-- Bill Sloman, Sydney
After-burners are hideously inefficient - which is the only way the tail-pi pe can survive. In practice the combustion temperature inside the engine is limited to about 2000 C, and a substantial part of the air coming out of t he compressor isn't burnt, but rather routed through the exhaust turbine to cool the turbine blades below about 1300 C.
By creating shock waves at the intake. "Mostly" is a weasel word here.
-- Bill Sloman, Sydney
Sure. Except that the SR71 was on afterburners the entire time. Otherwise the exhaust wouldn't have been not enough. Maximum exhaust temperature is a key metric for rockets and afterburners.
Taking stationary air and getting it into an engine that's moving at Mach 3.6 is going to be a bit violent, obviously. But that shock
*decelerates* the plane, which is not what you were getting at originally.Not at all. I was making the exact same distinction you were--the intake air was initially supersonic, but there was a shock boundary partway into the intake. The rest of the SR71 engine was 100% subsonic.
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
On Mon, 17 Aug 2015 01:43:12 -0700 (PDT), Bill Sloman Gave us:
Wings stay aloft from lift, not downward forced air. You're an idiot.
John S prodded the keyboard with:
What ! You mean that you have never heard of the V1 or Buzz bomb !
--
Best Regards:
Baron.
On Mon, 17 Aug 2015 20:25:10 +0100, Baron Gave us:
Neither of which utilized a scramjet. They were both slow as molasses. Get a clue.
On Tuesday, 18 August 2015 01:12:36 UTC+10, DecadentLinuxUserNumeroUno wro te:
I'm afraid the idiocy is all yours. Lift is a complex phenomenon, and there were experts in hydrodynamics that asserted that it couldn't occur in a pe rfect fluid, but the force that holds the plane up is generated by accelera ting air towards the ground. What confused the hydrodynamics experts was t hat this generated trailing vortices, which can't be created (or destroyed) in a perfect fluid. Thompon thought that atoms might be vortices in the et her.
-- Bill Sloman, Sydney
Sure. But the 4000 C temperature isn't reached until the air is outside the engine. It would melt any tail-pipe. That's why the after-burner is hideou sly inefficient, because it works by raising the pressure in the tail pipe, and thus the exhaust mass, rather than the exhaust velocity.
.Seems unlikely. The air was supersonic when it went into the engine,and it' s been heated and expanded to some tune when it emerges. The speed of sound in a 2000 C airstream would be about 2.8 times higher than in a 300 C air- stream, but we are talking about a Mach 3 aircraft, so the exhaust has to b e travel faster than the local speed of sound as it goes out the tailpipe.
None of this validates David Eather's original claim, that you can't get a supersonic shock wave out of a fuel-air mixture. Scram-jets depend on exact ly that.
-- Bill Sloman, Sydney
Strange. For years I've been reading that lift is generated when the air on the upper surface is forced to move faster than the air on the bottom surface thereby creating a low pressure area on top of the wing.
Vortices are caused by the air moving from the bottom of the wing to the lower pressure area on the top of the wing at the wing tips. Winglets have been added to reduce this effect.
OK, I can wear that.
FFS NO! The air was STATIONARY when it went into the engine! The engine was moving at supersonic speeds.
,and
My claim (which I have repeated but you have ignored) was an unconstrained fuel air explosion would not produce a supersonic shock wave. You're the prat who wrenched a simple comment out of context.
END
On Mon, 17 Aug 2015 17:58:09 -0700 (PDT), Bill Sloman Gave us:
No shit, SlowBoy.
Gasses act differently than fluids.
The vacuum created above the wing in the gaseous lattice cause the lift, and that cannot be demonstrated in a fluid experiment. Fluids demonstrate laminar flows and do not exhibit the pressure differentials found in a gas lattice.
So it is NOT "fluid dynamics" at work. Hydrodynamics experts are wrong.
Helicopters get lifted into the air, not pushed up. Fixed wing aircraft get lifted through the airstream not pushed away from their rake angle in it.
On Mon, 17 Aug 2015 23:09:37 -0500, John S Gave us:
The mistake the "experts" made was using fluid dynamics in an attempt to describe something which occurs in a gaseous latticework.
They didn't make a mistake. They just didn't have the tools that let them tackle the problem in a useful way from that point of view. The tools have come on a lot since then.
-- Bill Sloman, Sydney
Gases are fluids.
Fluids exhibit laminar flow for Reynold's numbers lower than 2100. Above that turbulence sets in, sometimes quite a bit above that.
A minority opinion.
You may think so, but you are AlwaysWrong.
-- Bill Sloman, Sydney
t
d
You are the prat who made a stupid claim and continues to assert it without adducing any evidence to support it.
As Phil Hobbs has pointed out, burning jet-fuel in air can raise the temper ature of the combustion products to 4000 C, which increases the volume they occupy by about a factor of 14. It doesn't take much of a compression wave to Joule-Thompson heat the air in the vicinity of the fuel to it's ignitio n temperature, so you've got a propagating ignition front, which can propag ate faster than the local speed of sound.
or more explicitly, see pages 37 and 38 of
-- Bill Sloman, Sydney
pulse jets involve supersonic combustion?
-- \_(?)_
Newton's third law says your're wrong as usual.
-- \_(?)_
That vacuum pulls down on the air mass above causing brief downdraft resulting in vortices.
Next you'll be telling they don't cause a massive downdraft, and are unsuitable for drying sportsfields.
Lift is the side effect of pushing or pulling air downwards.
-- \_(?)_
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