Tornado 'Combat' Power Throttle Setting

[Obi Offiah]

Hello :)

For some time I've been wondering about the nature of the Combat setting on the Tornado throttle panel and thought I'd finally ask.

In US aircraft such as the F-15, the throttle has above idle detent points that represent 'Mil' (UK Max Dry Thrust) and 'Max AB' (UK Max Reheat). The big question for me is what the Combat setting provides in the Tornado? Is its function similar to the Vmax switch in PW-220 equipped aircraft?

Thanks
Obi

[talk_shy_tall_knight]

A big question indeed and one that has also troubled me for yonks. Any ideas anyone?

Also can anyone tell me how long the pipe is on the Chinook piss tube?

[charliegolf]

Also can anyone tell me how long the pipe is on the Chinook piss tube?

It's 10". But even though thats small for Puma crewmen, they'd be equally worried that the diameter were big enough.:ok:

CG

[Secretsooty]

On the Tonka RB199 engine, the engine is controlled by either an analogue control unit (MECU) or digital (DECU). In dry range, the engine's primary controlling "loop" at max dry is temperature, measured via optical pyrometers. Selecting combat effectively raises the control point by around 26? degrees. I can't remember the exact figure off the top of my head, but that is the principle.

[Phil_R]

Er, doesn't that mean that the engine will produce less thrust when the ambient temperature is higher?

I appreciate that on paper this is inevitable, but a twenty-six degree difference between two settings seems, well, slim. So slim that trying to select the higher level on a warm day might effectively make no difference. Presumably I am misunderstanding something.

[Kitbag]

Phil R is correct, gas turbines do produce less thrust at high ambient temps, hence the requirement for hot and high trials to prove performance when the air is hot and thin. Fortunately temps generally reduce when you are in free air and as altitude increases, it tends to be hot on the ground because of reflected heat etc.
The increase in temperature of the controlling loop is sufficient to provide about 10% extra thrust, but at a cost- all the hot end components get cooked and stressed out which eats into the engine life. At the temperatures we are talking about which have reduced from the combustion chamber temps by the time the gas flow gets to the blades (on RB199) or thermocouples in the jet pipe the energy in the fuel is being released more efficiently.
A gas turbine designer wants to burn fuel as hot as possible, but he is always limited by materials technology, at high temps metals do some very strange things. Most modern engines have gas flows hotter than the melting point of the metals immersed in them and it only clever cooling designs that stops everything going quiet suddenly.

[Genghis Couldn't]

10% is a bit optimistic in practise. It won't work in the dry range (failure free) as the setting itself requires the throttles to be at the top of the reheat range (there is a switch that has a similar effect, but it's not the 'combat' setting - IIRC it raises the temp 36 deg ish at the cost of engine life). Going from Max Rht to combat has a barely perceivable effect but it 'feels good' psychologically as it's another detent!

GC

[cornish-stormrider]

IIRC Ghengis, going to combat removed some of the other controlling loops in the lowest fuel wins argument therby allowing the 199 to run nearer to its own redline. The DECU datum switch raises the temp by 34 ?? and combat by 26 kelvin??. with them both you get more noise but also remember the 104's as fitted to the Bear/Backfire chaser get more thrust wet than the mud movers 103, it's due to an extended m15 and the fact it doesnae look like its been chasing parked cars........

remember less volts = more fuel but no volts = big bill. An in case my old chiefy is on here the lugs on the front of the m10 shaft are not oil ways!! as you told the AOC.......

[Genghis Couldn't]

I remember seeing a 'no volts' panto - I have never seen fat people run so fast (the skinny people were doing some knots too..).

I think the 'brickodynamics' of the GR were more crippling than the smaller motors ;-)

GC

[Duncano]

The reheat fuel is also increased when in 'Combat' to maintain the pressure differential across the HP Turbine otherwise just increasing TBT would cause the engine to overspeed and/or blow out the reheat.

[Obi Offiah]

So the combat setting is similar to the PW-220 Vmax switch. With Vmax FTIT is increased by 22 degrees, with a 2% increase in RPM. Fuel flow and thrust increases by 4%.
I'm curious as to what restrictions are placed on the Combat setting. Vmax is a non-peace time, guarded switch setting that can only be used for 6 minutes and requires engine inspection after use. If the Combat setting is simply a detent away from Max reheat, I guess there is less of a restriction in its usage?

Obi

[mary_hinge]

On the Tonka RB199 engine, the engine is controlled by either an analogue control unit (MECU) or digital (DECU). In dry range, the engine's primary controlling "loop" at max dry is temperature, measured via optical pyrometers. Selecting combat effectively raises the control point by around 26? degrees. I can't remember the exact figure off the top of my head, but that is the principle.

IIRC, in the early 1980's also refferd to the War and Peace switch. Selecting COMBAT raised the max TBT by 26 degrees, which also lifted the dry thrust by 28%. Problem was that in the "peace" setting, the engine was unable to obtain the MITL figure so was locked into the higher setting.(on the GR1s anyway)

Also the Throttle had a "Combat detent", again added ex degrees to the TGT and another 20% plus of thrust level at Max Re-heat.

Always fun on an EGR timing the engine through 65% NL to Combat power

[Obi Offiah]

Cheers zero/zero

I must say I'm a little surprised that there is limit imposed on max reheat usage also. Having said that 20 minutes is plenty of time.

[Phil_R]

Apropos of nothing - is the reheat actively ignited or does it simply rely on the EGT to set fire to it?

[mary_hinge]

is the reheat actively ignited or does it simply rely on the EGT to set fire to it?

A "ball" of fuel is released upstrem to the HPT,(Hot Shot Relay!!) the HPT would then ignite the fuel ball which would then pass into the re-heat section. This would then ignite the fuel in the "trough"

[Backwards PLT]

There is confusion here between the datum/low switch which is:
1. Wire locked
2. Increases temperature and therefore thrust in dry power
3. Only very rarely used as the engineers/sooties get grumpy
4. Don't know if it gives extra on top of combat pwr (I spy a good staneval question!)??

Combat power is:
1. A detent post max reheat
2. Gives a bit more thrust
2. Can be used whenever you like (5 mins yadayadayada)
3. Rarely needed as the Tornado has so much thrust and great aerodynamics.

Hope that helps.

Please note that one of the above statements is a lie. If you can't work out which one, you should log off PPRuNe Mil forum immediately. zero/zero I fear this may apply to you!;)

[BluntM8]

Does that give you a transient T6 or TPT overheat? Any long term effect on the engine? And if there is a need to maintain a px gradient across the turbines, what happens when you deselect reheat? Do you suck the engine out? And what exactly happens during a "burner pop"?

So many questions...

Blunty.

[Backwards PLT]

I think both increase TBT/T6/whatever (temperature downstrem of combustion pre reheat!). The 5 min limit prevents any issues, AFAIK its not logged anywhere (the Tornado isn't that clever!) but if the wirelock is broken you will use the higher temp everytime you are near max dry - which could damage the engine, but only life, it isn't going to disintegrate if you use it for 20 mins airborne.

A burner pop is when you deselect reheat, then the reheat goes out, leaving a little fuel in the pipe, then you reselect reheat again (less than 3 secs?) this causes quite a decent bang and can look quite good from outside. Doesn't damage the engine apparently. Did it on the threshold once and someone in a car waiting to cross said it looked very impressive (for a Tornado).

As for the other questions, bluntm8, the engine is totally care free handling, slam the throttles where you like and it will just get on with it. Even know people who have flown backwards and the jet just flops out and the engines cope.

[Phil_R]

I've worked with tiny model aircraft engines where having Ts 1, 2 and 3 was a luxury. Where on earth is T6?

P

[HallamPilot]

You only get 'Burner Pop' or Reheat Surge if there is a blanking plate in the reheat purge line on Mk 103 ECU's (controlled by MECU's).

On Mk 104's (controlled by DECU's) you can quite happily Reheat Surge them without the plate, and this usually resulted in a phone call from 'The Management'.

In fact, we used to do it every now and again and use the stopwatch to time how long it took the J Eng O to ring down! :E

The blanking plates were fitted as a mod during GW1 as deselection of reheat created a large white cloud of fuel vapour behind the jet.

You lot got all panicky about advertising your whereabouts to the baddies!!!



P.S. You can lift the roof off the test bed doing such stunts. :*

[BluntM8]

Phil,

T6 is the turbine inlet temperature - if it is too high you can easily cook the HP turbine into an unuseable mess!

For interest, the general list is (IIRC):

0 - Ambient air.
1 - Air at compressor inlet.
2 - Air at exit of LP compressor.
3 - Air at exit of HP compressor.
5 - Combusting gases in chamber.
6 - Gas at HP turbine inlet.
7 - Gas at LP turbine inlet.
8 - Exhaust Gas.

Where Tn refers to the temperature and Pn refers to the pressure.

Don't be confused with N1 and N2, which are also refered to as NL and NH - the percentage rotation speed of the LP/HP spools.

T6NL caption, anybody?

Blunty (ready to be corrected!)

[flipflopman RB199]

Blunty,

That list is slightly different for Tornado, but I'll not be so pedantic as to attempt to correct you here!! :p

As I remember, the 34 Deg K at Datum/Low and 26 Deg K at Combat are entirely correct. With the DECU controlled 104, 25 Deg K TBT also equates to a 1% NH increase, and this is used when re-datuming the DECU to the ECU test bed figures. I remember on Post Inst runs ensuring that the TBT registered around a 25 Deg rise upon selection of Combat.

As goes the Datum/Low switch, the only time I can ever recall messing about with that, was during Post Insts on the 101 engined GR1's where the switch was left in the datum position for everyday use. As goes the worry of cooked engines, bear in mind that the engine was designed to operate safely and reliably with the DATUM position selected, and LOW is simply a cheap and easy way of stretching a little more life from the engines.

T6NL? Adour, if I'm not mistaken :ok:

Hallam Pilot,

I remember the blanking plate mod well, Also the subsequent mod to drill a 3.2mm hole in the centre, to try and alleviate the burst spray manifolds that began to occur!! :E



Flipflopman

[Obi Offiah]

There is confusion here between the datum/low switch which is:
1. Wire locked
2. Increases temperature and therefore thrust in dry power
3. Only very rarely used as the engineers/sooties get grumpy
4. Don't know if it gives extra on top of combat pwr (I spy a good staneval question!)??

Combat power is:
1. A detent post max reheat
2. Gives a bit more thrust
2. Can be used whenever you like (5 mins yadayadayada)
3. Rarely needed as the Tornado has so much thrust and great aerodynamics.

Hope that helps.

Please note that one of the above statements is a lie. If you can't work out which one, you should log off PPRuNe Mil forum immediately. zero/zero I fear this may apply to you! ;)

So the Datum/low switch is similar to the Vmax switch which is also wired guarded. The exception is that Vmax only comes into effect when in Max AB and supersonic.

Judging by its name, Combat power I guess would only be needed when evading defences and during heavy take-offs, so I assume the restrictions are ok.

I wonder, has the triple spool layout of the RB199 been a factor in allowing the aircraft to have a Combat setting?

BTW Combat power point 3 is the most
accurate statement:p

[Obi Offiah]

This question doesn't apply specifically to the RB199, but does anyone know why at times a flame ring (like a very low power, low energy afterburner) can be seen deep within the combustion chamber, looking in from the rear (of course)?

Also what is a "blanking plate"

Cheers
Obi

[HallamPilot]

Also what is a "blanking plate"

Upon deselection of reheat, the priming, dump and shut-off valve (PDSOV) is closed, isolating the fuel system from the manifolds, but residual fuel in the manifolds is dumped over board on shut-down.

The blanking plate was a square piece of metal inserted between the joint of the reheat purge line.

This effectively blocked any fuel from being dumped overboard on deselection of reheat, thus stopping the plume of tell tale vapour.

This left residual fuel in the pipework and on a rapid reselection of reheat the residual fuel would ignite and cause a reheat surge.

As flipflop stated, this also caused the manifolds to start bursting due to the pressure on the system.

To stop this happening, some clever sort came up with the modification to drill a 3.2mm hole in the centre of the blanking plate. This allowed the fuel to trickle into the purge line, not so much to cause the plume, but enough to stop the surge.

[cornish-stormrider]

The triple spool was thought of to make a more effiecent and lighter engine, also having the contra rotating spools was thought to decrease the gyroscopic effect. In reality it was a much longer pain in the arse to rebuild, unnecessarily complicated, and still had that god-awful eyetie M12 with the interstage ring and the thermocouple wiring that was too difficult for the dog-lovers to deal with.

My training on the interstage ring was having several goes at it and my chorpscrawl slinging it in the bin -

I got there in the end though, the trick was making into a work of art.

[Kitbag]

The triple spool was thought of to make a more effiecent and lighter engine


And compact, look at other engines of the same period and power output and they are larger. The pressure rise across the compressor was also pretty impressive.

[BluntM8]

also having the contra rotating spools was thought to decrease the gyroscopic effect.

I believe, and no doubt JF will be able to elaborate, that the major design triumph of the RR Pegasus engine is that the HP and LP spools have identical angular momentum, although in opposing senses. Therefore, whilst the harrier is in the hover and gyroscopic effects caused by attitude change are competely cancelled out within the engine. Clever or what!

Blunty

[Obi Offiah]

Thanks for the responses.:ok:

Obi