RAAF FA-18 display at Grand prix

[Octane]

During the display I noticed that one of the aircraft throughout the sequence had different coloured flame in the jet pipes. Blue one side, red the other. What would be the reason for this?

Cheers

Octane

[Slezy9]

They add dye to the fuel :)

[Octane]

Surely you jest?!

[A2QFI]

So just one of the aircraft had special fuel used which only burned in one of the two engines? Not even vaguely likely!

[Phoney Tony]

Choke on one engine left on!

Rember call to St Mawgan ops from a concerned member of the great unwashed asking if the Nimrod, which had just overflown his campsite, had left the choke on!

[Octane]

Well it had me thinking (handicapped Petroleum Chemist, 39C here today so replacing the fluids...)
My take on it was perhaps there was a difference in the combustion characteristics of the 2 engines somehow, resulting in different fuel/Air ratio and therefore different temps/flame colour at the tailpipes? Was the case throughout the display.

[Milt]

Bust that Myth

No such thing as fuel/air ratio for combustion in a jet. There is always stacks of unburnt oxygen in the air throughput some of which can then be burnt by the afterburner. Exhaust nozzle maladjustment may explain differences between engines.

[Octane]

Crikey Milt,

I wasn't suggesting the FA-18 has carburettors! I was talking about F/A ratio in the exhaust gases! i.e. ratio of unburnt kero to air actually present in the jet pipe. Ideally I'd thought all should be equal in both jet pipes therefore same coloured flame....

Even Cheerier Octane

(30C at 2230)

[Il Duce]

An air display? At a sporting event? Brian Moore wouldn't like that!

[Truck2005]

Not too sure about F-18 but it was not unusual to have this on the jaguars. I worked on the test bed in the Bruggen days and this could come from numerous causes. A crack in the valour gutter would cause a blue streak in the flame pattern. Pulling back to the PTR limits would also cause a very blue flame due to the different fuel scheduling. No two engines were the same.

My guess is that the two either had their reheat ranges set up at different ends of the range or, quite simply, the pilot did not have both engines at the same settings, (not too sure if that is normal practise but I am not of the superior race).

[TyroPicard]

They were trying to get one green, one yellow (oops, gold, sorry) but had to settle for Union Jack colours...

[Milt]

Octane

I'll stick my neck out and state that there will be NO unburnt fuel through the turbines.

The burning you see out of the exhaust nozzles when afterburning is just that final residual burn of the enormous volume of fuel being sprayed into the jet pipe.

Pilot could have selected afterburners at differing stages for each engine or they were trimmed differently as previously suggested.

How about some comment from the Hornet's nest.

[ShyTorque]

The second engine would have had a more greenish flame, rather than blue. This is so the engineers can check the engines are installed the correct way round. The port engine has a red flame and the starboard one has a green.

This also helps pilots flying in formation in poor visibiity to see which way up the aircraft in front is flying.

[Brian Abraham]

if the Nimrod, which had just overflown his campsite, had left the choke on
Pioneering aviator and seaman Francis Chichester related in one of his books of being over flown by a RNZAF P-3 trailing the obligatory smoke. Took the pilot to task for running his engines rich and not leaning properly.

[Milt]

Good to have some humour emerge.

What about a "valour gutter"? Does a Hornet's engine have one or more of these Truck2005? What is it?

[Truck2005]

The vapour gutter, at least on an Adour, is basically the afterburner installed in the jet pipe. It is a set of 3 rings shaped like gutters with holes in the forward edge mounted in the gas flow with a catalyst ignitor at the centre. When afterburner is selected fuel is fed into these rings and a chemical reaction on the ignitor ignites the fuel as the gasflow/bypass air mixes in the jetpipe. (I think I have got that right. It has been a few years since I worked on fast jets).

I have seen this on some US aircraft but I do know they use a different system on other aircraft

[Mick.B]

I know one of the Hornets was grounded due to a Hydraulic problem at Melbourne airport. Not sure if this is related in any way. It was the single seater. The other 3 were tubs.

[rapiddescent]

The tubs were there so that 'the boys' could fly down and be part of the celebrity circus.

[Ogre]

The funniest part of the weekend for me was when they interviewed a selection of the military crews on stage in the V8 paddock. this area was set up to allow the crowd to see the racing car drivers answer questions and queue up to get autographs signed.

So you have 5 or 6 members of the military, all in flying suits, being asked questions by this bloke who knew loads about cars but nothing about the military. And every 30 seconds or so this bloke would invite the crowd to come up and get autographs. There were no takers except a couple of kids

Perhaps the MOD could learn a thing or two about press conferences.....

P.S. after a weekend of racing cars of different shapes and sizes the best photo I got was of the Qantas 747 doing a dirty fly past!