Blue afterburner?

[Phoinix]

One question for all russian hardware specialists. How come russian suhoi fighters have blue flame afterburner compared to all other fighters which have ornge flames shooting out the back.
Is it better burning, higher air/fuel ratios, different introduction fuel to air?

http://www.jetphotos.net/img/1/3/4/3/53284_1186946343.jpg

http://i29.photobucket.com/albums/c257/garfildka/MAKS%202007/SUN_4978.jpg

[ZH875]

And the Brits thought that Natural Gas would be no use for Fast Jet fuel...:)

[Phoinix]

Yeah, looks like kitchen stove :rolleyes:

[scopey]

Do they have Pimp My Ride in Russia? :8

[Phoinix]

http://www.metacafe.com/watch/384526/pimp_my_ride_the_russian_version/


... just like they do in america... raptor powerplant


http://static.howstuffworks.com/gif/f-22-raptor-12.jpg


Come on guys. Let's get real smart ass stuff in this thread.

[Capt Pit Bull]

Well, I'm no combustion expert, but the general physics of the matter is that the hotter something is, the higher the frequency (bluer) the light is.

pb

[peppermint_jam]

Gratuitous reheat photo, apologies for the quality, I don't have the best camera in the world!

http://i51.photobucket.com/albums/f372/robstuff/Tonka079Medium.jpg

[Razor61]

I'm going to look really stupid now....
But isn't the reheat blue while stationary or just starting the take off run because there is a limited amount of cold air being sucked in while on the ground... whereas in the air, cold air is literally forced in rapidly which could in effect cool down the burner slightly to make it an orange colour as you see it when it's airborne and whizzing about the sky.

[Phoinix]

In flight photo:

http://i29.photobucket.com/albums/c257/garfildka/MAKS%202007/SUN_4823.jpg

Thank you guys. Blue flame is in deed higher temperature. I'm guessing its better fuel introduction and more air left out from main combustion chamber.

[Arcanum]

Seeing the picture of the F3 doing a ground run in full reheat, I'm reminded of a story I heard years ago about a Lightning doing a ground run back in the 60's that ended up getting airbourne with one of the ground crew in the hot seat.

Any truth?

[The Helpful Stacker]

Any truth?

Yes.

It was at Lyneham when it had 33MU (who serviced Lightnings) based there.

W/Cdr Walter Holden, whilst carrying out engines runs to trace a fault in XM135, found himself in full reheat running allong a runway at Lynham. Forced to lift it off the ground, without canopy or flying equipment (to avoid a fuel tanker I think), he managed to put it down after four attempts, with only minor damage to the tail.

[Focks 2]

The 'colour' also depends when the photo is taken. In the image below the top burner has just been lit. Raw fuel v fuel/air?

http://s178.photobucket.com/albums/w251/stevel_03/Brunty%2006/?action=view&current=_MG_0666_2030.jpg

Click image for full size.

[Razor61]

Not all Sukhoi Flanker variants have blue burners.... this one is airborne with orange burners
http://www.globalsecurity.org/military/world/russia/images/su30_01.jpg

[Kitbag]

Must be because of all the extra stores its carrying

[greycoat]

possible (and boring) answer is to cast your minds back to the Bunsen burner flame: blue = hottest due to max amount of air being admitted through the air inlet/collar and complete combustion occurring whereas yellow indicates least efficient/insufficient oxygen to burn the gas

[Phoinix]

I'm thinking of the same principle. Blue afterburner at it's max efficeincy.

[FAAjon]

beat me to it:}

[Arcanum]

Hate to be a smartass... but that's not an F3

My bad - shouldn't have assumed it was an F3 from the picture.

Thanks, Helpful Stacker, for the answer on the Lightning.

[Phil_R]

I think you'll find it's largely a photographic artifact concerning when and how you shoot them. At night they almost always look blue or blue-pink, but it's not very luminous and generally invisible in daylight. Also they tend to be blue when they're just starting up and the fuel/air mix is very lean. Video cameras tend to see it whiter than stills cameras since they tend to have less IR filtering on the sensors.

Must admit, I'm never quite sure why it's useful to be throwing all that flame out the back, since if it's burning outside the engine it surely can't be all that propulsively useful.

Phil

[N Joe]

"it surely can't be all that propulsively useful"

Not useful? Ask any FJ mate how he'd feel about taking off in dry power!

N Joe

[kokpit]

The RB199 was, I thought, the first engine to double its thrust when in reheat.

However, MTU are showing 41Kn to 72Kn Max Dry to Reheat, quite propulsively useful I'd say ;)

[splitbrain]

The propulsive usefulness of reheat (as a measure of the increase in thrust gained through its use) is a function of the change in temperature that is achieved between the dry value and the wet value, not the amount of flame coming out of the exhaust :}

[Phil_R]

Of course reheat increases thrust...

What I'm talking about is the fuel that's being burned outside the engine, which is presumably not doing much.

Phil

[splitbrain]

The fuel is actually being burned at the reheat manifold. It is the velocity of the exhaust gases that carries the flame outside of the propelling nozzle. Yes, it would probably be more efficient (in terms of heat transfer) to retain the flame inside the exhaust system, but I'm not sure its possible simply because of the way the system has to work.

[L Peacock]

It's well known that reheat isn't an efficient means of developing thrust. Around 10 times the fuel flow to double the thrust. Handy when required though.

[BigEndBob]

And why do we see the 'dancing Diamonds' i think they are called, is that a photo or video effect.

[N Joe]

PR does have a point. Most FJ aircraft just have convergent nozzles meaning much of the expansion energy is wasted outside the engine. It would be most efficient to have a large convergent-divergent nozzle (like the main engine nozzles on the back of the shuttle) which would capture the thrust generated by the full expansion of the exhaust gases behind the aircraft. However, the drag and weight would be excessive when not in reheat (90%+ of the time). Latest generation FJ engines have (variable) con-di nozzles but even then, the limited diameter means that they still can't recover all of the expansion energy.

N Joe

[N Joe]

The diamonds are due to the shock-waves in the expanding supersonic exhaust flow. Gases at different pressures/temperatures have different refractive indexes so bend the light differently. Same principle as shimmer in air over hot tarmac etc, except that the changes though the shock-waves are much sharper.

N Joe

[Focks 2]

And why do we see the 'dancing Diamonds' i think they are called, is that a photo or video effect.
Shock diamonds:

http://www.aerospaceweb.org/question/propulsion/q0224.shtml

[Stitchbitch]

To confuse matters, if you watch a Tornado take off during the day it's AB is orange, at night it appears to be blue...:O

[Synthetic]

Or striations.:cool:

[ehwatezedoing]

http://i165.photobucket.com/albums/u45/kartoon67/AirlinersNetPhotoID214029.jpg

Orange, blue....Blue or orange.

It's all related to Vodka quality.

:}

[Phil_R]

> at night it appears to be blue

Yes. What you're seeing is the blue flame after it's exited the engine and encountered a whole load more oxygen. It's very dim. During the day it's invisible and all you can see is the rich-mixture area inside the, er, whatever you call the adjustable nozzle.

Phil

[Red Snow]

Watch an F-15E take off - you can tell if it's an older one with Dash 220 engines (yellow a/b) or a newer one with 229 IPEs (blue a/b).

I'll get my anorak.