Quote XL391
Yeah, here’s one for you Andy!!
In pictures of 728 (and a few other frightnings) the flame from the lower jetpipe in reheat (is this number2 engine?) always seems to be longer and brighter. Is this because of the way the engines are staggered in the airframe? Or is it just me talking total and complete sh**e??
Quote Bager 1968
Well, since the lower engine was beneath the wing, and the upper engine was behind the wing (therefore closer to the back end)… good question?
Logic would say that the upper engine’s exhaust should be brighter, but the real question is not where the engine itself is located, but rather where the reheat module is located… as this is sometimes mounted on the engine body and sometimes a lengthy exhaust tube is between the two!
Perhaps the lower reheat module is closer to the outer end than is the upper one?
Right chaps I did say any questions didnt I, and you would pick on the most complicated part of any Lightning, so after alot of sitting here wondering how I can explain it in basic terms here goes;
Firstly the Lightning reheat system is and always was a law unto its self.
No two reheats were ever the same even when they were in service being fettled day and night by teams of grubby ‘sooties’.
In a perfect world they should be both the same, the distance from the engines should make no difference as the fuel is ignited at the same point in both pipes, No1 fuel just has further to go down the pipe before it is ignited.
No 1 engine being the lower one below the wing and No2 the upper one which starts just forward of the leading edge an ends below the tail fin.
When reheat is engaged by the pilot (or idiots like me) alot of mechanical/electrical things click into montion (I havent got the time or will power to type it all out here, sorry)
Basicly when the system is all go and the nozzles go to fully open, a ‘hot shot’ of burning fuel is injected into the pipe (which is sometimes visable when you stand well down wind) this ignites the reheat fuel at the burner ring which is in the same place on both pipes, which like I said earlier should give two even flames out the back, but seldon does, as both engines and reheat systems are separate and are both very difficult to harmonize,
many hours were spent on reheat pans trying to do this, I can assure you.
Those of us that do and have done this kind of thing will tesify that you can spend hours getting it all to work perfectly, and the next time out its as though the gremlins have been in and done their worst.
So basily to answer your question yes they should be equal, and some times god willing they are, many a time burners on operational Lightnings were all over the place, some even going out. (when this happens the system automatically closes the nozzle fully to give extra thrust, which is some cases meant the difference between getting off the ground or not)
Now to add another dimension to your question regarding 728, we do have an on going reheat snag that manifests its self as a minimum No2 reheat flame, this is something that just turned up one day about 2 years ago and since that time we have been slowly working though the systems looking at potensial items that could cause this problem, you have to remember this is a Lightning and nothing is easy to get to, also when ever we need to try it to see if we have fixed any item we need the best part of £500 worth of fuel to try the reheat and see if our fix has worked, we also upset the neighbours. :rolleyes:
What we do know is as the nozzle goes to fully open and the burner lites, it then goes to fully closed which cancels out the buner, so what you see is a smaller flame for a few seconds as the aircraft powers away form you.
What it will be is a soleiond valve sticking, but that means No2 pipe out and a good few days work, which at present we dont have time to do (Q shed getting in the way 😀 )
So if you are all still awake, (even Im nodding off) thats about the top and bottom of my answer to your question.
How about some easy ones, I can do them. 😀
Andy B
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