Harrier water injection

[tartare]

Halfway through the superb book on the Pegasus.
Can any bona jet drivers (or others who may know) clarify something about water injection.
I read on wiki that it cooled the outlets, allowing running at higher power and outlet temperatures for 90 secs max.
I assume it was sprayed on the inside of the outlet in some sort of mist and that the rear hot exhausts simply dumped super-heated steam overboard as part of the jet efflux?

[Engines]

Tartare,

The distilled water was injected into the combustion chambers to provide a temporary reduction in turbine temperatures and higher thrust. No steam out of the engine, as I remember it from the deck.

The water injection manifold was located very close to the fuel manifold, and wrapped around the engine. The water tank was located just aft of the engine between the aft nozzles. Water was injected at a high rate using a special pump located up in the main wheel bay.

'Wet' operation of the engine was strictly limited, and whether for launch or recovery, was closely monitored.

Hope this helps

Engines

[tartare]

Thanks engines - my question answered and from no better a source!
I'd thought the water injection might also temporarily increase the mass and thrust of the efflux, but then deduced if that was the case, then all supersonic aircraft would probably have water afterburners...;)

[H Peacock]

I think as well as slightly reducing the turbine inlet temperature, water injection does also increase the mass-flow rate and hence thrust! The drawback is that you need lots of water, so water injection tends to be limited to the brief periods when maximum thrust is needed, ie take-off or, for the Harrier, hovering at high auw.

[MSOCS]

Tartare,

To add to Engines reply, water injection sprayed de-mineralised water, at pressure, onto the HP turbine blades and reduced the Jet Pipe Temp (JPT) by 23-25C. This temperature suppression allows increased fuel flow (and therefore RPM under certain conditions). The net effect of higher RPM and increased mass flow is more thrust - Harrier only had 90 sec of aggregate water flow.

The 'wet' and dry engine lifts were governed by a number of factors such as water switch position and gear/PLAU positions, not by the contents of the water tank. You could be in a position where you might be operating the engine to the higher 'wet' limits but if you didn't have water (I.e. you had run out) you would be fatiguing the engine per second like billy-oh. Hence, there was some (but not necessarily crucial) priority to get the jet landed before the water was gone.

Importantly, you didn't always need water to hover (low ambient temp, high atmospheric pressure), but if you did - and ran out mid-hover - there were fortunately only a few conditions where you would actually descend whilst at max throttle position.

[Vzlet]

In everyday use, was there a different water loading procedure (https://flic.kr/p/fShWun) than this?

[PDR1]

Tartare,
To add to Engines reply, water injection sprayed de-mineralised water, at pressure, onto the HP turbine blades and reduced the Jet Pipe Temp (JPT) by 23-25C. This temperature suppression allows increased fuel flow (and therefore RPM under certain conditions).

This is an almost universally misunderstood field. The following is a standard answer that was prepared by one of the gas turbine design specialists at RR:

Are you sitting comfortably? Good, then we shall begin ....

First of all, gas turbine water injection is a thrust augmentation device. The concept of injecting water into a gas turbine has got sod all to do with cooling the engine as one of the advantages of a gas turbine is that they are self cooling – ponder the extensive use of such beasts in stationary applications, such as on oil rigs, pipelines and for powering ships.

Now we’ve got that one nailed – just how can you increase an engine’s thrust by injecting water? At first glance, it seems an absurd thing to do. Well, it’s simple really, and there are three different ways of doing it:

1) Add the water at the front of the compressor
2) Add the water directly to the combustion chamber
3) Add the water immediately before the turbine section or just before the propelling nozzle.

Taking each one in turn:

1) Injecting water at the compressor face has the effect of lowering the temperature of the inlet air, (assuming the water is at a lower temp than the ambient temp, of course, but seeing as you will generally be using water injection on hot days, that's taken as read). Remember the old maxim of 'It's fookin' difficult to compress cold air and vladimir impossible to compress hot air' and you soon realise that lowering the inlet air temp allows you to get either:
a) the same level of pressure rise as before but from less power offtake or
b) more pressure increase for the same shaft power requirement.
Both of these effects give you greater thrust (via less power offtake or through higher pressure ratio respectively) but option 1b) is usually the one used. In a nutshell, you are fooling the engine into thinking the ambient temperature has suddenly gone down and gas turbines work best at low temperatures. Because you have lowered the inlet air temp then obviously you are lowering the compressor outlet temp as well. This allows you to add more fuel and gives you a greater delta t across the combustor. You are also putting more mass flow through your engine (because you've added the water and water is more dense than air), giving you greater thrust because thrust is directly related to mass flow. Additionally, you can utilise a water/ethanol mix if you so desire, with the ethanol being burnt in the combustor giving you even more bang.

From point 1b) you can see the problems that occur with gas turbines at high ambient air temperatures: Higher air temp = lower compressor efficiency = lower pressure ratio = less efficient combustion = lower resultant thrust because the turbine is using up all the available power to run the compressor = you ain't going nowhere.

2) Adding water directly to the combustion chamber is one for the theoretical physicists. What you are trying to do is induce blockage and temporarily reduce the volume of the chamber, thus increasing the pressure inside the combustion chamber as the efficiency of the combustion process is increased at higher pressure. It also has some other peculiar effects such as increasing the air flow speed which is not detrimental. This type isn't used much as it's difficult to model and understand and can lead to combustion instability, which is a bit of a bad thing (tm)

3) Adding water at the turbine face or just before the nozzle simply works by adding mass flow to the engine's exhaust thus giving you more stuff out the back = greater thrust.

Option 3 is the simplest and most straightforward whereas option 1b will most probably give you the greatest thrust increase. Sometimes you will get a water injection installation that gives you both compressor and nozzle injection to get even more increase at the expense of plumbing complexity.

If anybody ever says that water injection is for 'cooling the engine', just ask them exactly what a couple of gallons of water is supposed to do to a raging inferno at 1,200 degrees centigrade travelling at 200 meters per second. You should get a few blank faces in return...

[longer ron]

Vzlet - In everyday use, was there a different water loading procedure than this?

Taken during a holiday on the cruise ship 'Vincible' some years ago :)

http://i695.photobucket.com/albums/vv316/volvosmoker/Dunsfold/fillingwatertankoninvincible.jpg

Back at sunny Dunsfold we had a small diesel powered bowser for the Flight Line and a similar but elec powered one for Hangar use.

Edit just realised it is the same S Harrier as in your link Vzlet :) (just a few years later )

[Vzlet]

Good to see the use of adequate sun protection! Use of a dedicated water source does seem much more efficient.

Interesting coincidence indeed with XZ439. Here on the US east coast, we're fortunate to benefit from its regular performances at air shows. The owner, Art Nalls, also now has T.8 ZD993

[AutoBit]

I don't think MSOCS was trying to say that water injection cooled the engine. He's saying that, among other effects, it resulted in a 25C drop in JPT. He's absolutely correct in that statement.

[PDR1]

Interesting coincidence indeed with XZ439. Here on the US east coast, we're fortunate to benefit from its regular performances at air shows.

439 was one of the FA2 development batch (the other being 195 IIRC) which were part way through being converted for the JTIDS upgrade at the time the FA2 was taken out of service. IIRC this included some structural mods in the rear equipment bad and of course the replacement of the old BCIU (80186-based mission computer) with the vastly more powerful "Core Computer" (I think it was a box full of PowerPC604s, but that was a long time ago!).

I don't think the Core Computer was ever given a flight clearence (hardware or its OFP) so I've always assumed Art's flying is on purely mechanical instruments with no HUD. That in turn probably means no IMC clearence because I remember that all the SHARs had an IMC clearence that required HUD and mechanical instruments to be both serviceable and in agreement with eachother.

PDR

[sandozer]

For those with further interest on the Pegasus engine. .

The book "Pegasus, The Heart of the Harrier" is still available on Amazon for the bargain price of 99 pence :ok: Kindle edition of course.

[longer ron]

PDR1 - 439 was one of the FA2 development batch (the other being 195 IIRC)

Spot on PDR - ZA195 was the other development SHar.

[MSOCS]

PDR, as my colleague Autobit says, I never said it cooled 'the engine'. It cools the turbine blades, resulting in a temp drop (oh, yes I'm afraid, it DOES!)

I have personally invoked this phenomena over 1500 times in my Pegasus-propelled flying career, and watched the JPT drop almost every time (except where the water pump failed or the tank was empty) I also gave account of the increased mass flow you mentioned in your cut-and-paste reply.

So, as I stated previously, there are a combination of factors that increase the thrust in the Pegasus: the cooling effect is real (on ~700C Turbine blades, not in the chamber at >1000C!); the drop in temp permits more fuel/RPM (about 3% in fact); the higher mass flow gives higher thrust for the same RPM; and the digital engine control system re-datums to provide higher 'wet' limits for constrained times (15 seconds or much lower at times)

[Haraka]

Reading the Kindle "Peggie" book as well. I would suggest that it is very desirable reading for ex-Harrier Force mates .

[Nozzle Nudger]

PDR1 on this one I'm afraid you're wrong. The primary reason the Harrier and the Pegasus use water injection is to cool the turbine section of the engine so that in cooler weather you have a lower JPT for the same thrust or in warmer weather you do not lose thrust due to the engine TGT limiting.

I speak from experience with over 1000 hrs on the ac and an A2 QFI rating. I've got countless <90 second "Press Up" sorties in the log book in the back of the T Bird and the reason for this is because they could not achieve jet borne flight without the cooling effect of the water. Given that the 500 lbs of water was used in 90 seconds that gave you about 40 seconds in the hover which made instructing "interesting"!

The other thing to consider is that the thrust that comes out of the Hot and Cold Nozzles is totally different! The front cold nozzles are at about 200 degrees C and the air that is coming out has not gone through the combustion process, it has only been accelerated by the front fan. The rear hot nozzles are at about 700-750 degrees C and the air/water has. If the Water Injection were to increase the mass flow and thrust then this would only have an affect on the rear ones which would cause a nose down pitch effect when the water flowed and I can assure you this did not happen!

Finally if you ran out of water you did not lose thrust, the JPT simply rose by 25 degrees. Provided this was still below the short lift wet temp limit of 755 degrees nothing happened, you just put more Life Counts on the engine. If it did go above 755 the DECS would trim the fuel flow to maintain 755 degrees and you would lose thrust. You would not crash though as you could "Trip the Limiters" which muted the JPT signal into the DECS and the engine limited purely on RPM.

As a pilot of the Carbon Fibre Death Provider you had to have a VERY intimate knowledge of the engine logic or you were in trouble. We used to have a "Weeds Brief" on a regular basis to refresh us to keep us out of those weeds!!!!!!!!!!!!!!

Oh what happy days! Oh what an AMAZING aircraft built by pipe smoking and tea drinking legends! :ok:

[Wetstart Dryrun]

Please excuse defective memory banks.

Maybe, Short Lift Dry was 103%, 715Deg C for 10 seconds

Possibly, Short Lift Wet was 107% 745Deg C, also for 10 seconds.

The reality was 10 gallons used on a wet take off, leaving 40 gals for recovery to VL. Sometimes the water injection would slow the engine accel, possibly giving a water stagnation at about 95%. The fix was to select water on as the motor hit full power.

You only need wet Thrust (107%) on short TO or VTO and the TGT sort of caught up later as you turned it off. Hovering for a VL was temp constrained to avoid cooking the engine. 670C dry or 695c wet. ...but not quite that simple because you were burning 400lb/min petrol and 400lbs of water in the same minute - so all a lot lighter, all a bit easier.

The equation was only spoiled by gentle yellow lights as you approached limits and more unpleasant red flashes as you porked it. Resultant hypertension would lead to a bit overc0ntrolling which increased TGT as engine bleed to the puffers put in a bit more fuel.

Only feel sorry for the poor QFI in the bargelike T4 that was nearly always water dependent as the FNG hovered over the field site. 'You blew down all the soddin tents,Sir! You had to weave to do that.'

[bvcu]

Quite common a few years ago , water methanol on the Andovers RR Darts , on the early 747 with P&W JT9's and a few others i believe

[rogerg]

Quite common a few years ago , water methanol on the Andovers RR Darts , on the early 747 with P&W JT9's and a few others i believe
The 11-1s I used to fly had it as well.

[tartare]

A broader question.
The common layman's view was that the Harrier was very difficult to fly, prone to yaw in the hover, etc.
Hence only the best of the best were selected to fly it.
Certainly the P.1127, Kestrel and first Harriers broke new ground exploring the VTOL envelope, thanks to Messers Farley et al.
Yet the Pegasus book seems to suggest that once flight protocols were developed it was relatively benign to handle, even in VTOL flight.
Is that an accurate view - or was it still a handful that could bite you badly?

[Lima Juliet]

Water Injection?

It reminds me of a conversation once upon a time that went a bit like this when I was Duty Auth and in swaggered a visiting JJF&HHST* mate asking "Have you any de-ionised water?"
Quick as a flash the Rects Chief said with a smirk "Did you bring your travel iron with you, Sir? I can ask the Mess if they can help?" To which I added "He'll need more than a small iron to bring the creases out of those ridiculous flaps on his boots, Chief!"
The Harrier jock looked most unamused and said "No it's for my engine!". Then the JEngO chipped in hardly looking up "We normally put AVTUR in engines mate".
Off he toddled shaking his head "I'll take that as a No then..!"

*Jump Jet Fanny & Her Hawker Siddley Tw@t

[MSOCS]

Ah, those halcyon old days Leon. The fighter pilots of today don't quip as much though...probably because they actually go on operations these days, and stay on them.

[RedhillPhil]

I had a SaaB 900 Turbo circa 1984 that had water injection.


Didn't the Vietnam era B-52s have water injection fitted to those smoky things hanging off the wings?

[AutoBit]

Yaw had to be carefully controlled during the decel to the hover as getting out of balance, and inducing large side slips by decel'ing out of wind for example, could result in Intake Momentum Drag (IMD) which would induce a extreme, and normally uncontrollable, yaw and roll which was nearly always unrecoverable unless caught very early on. We had what was basically a small weather vain on the nose of the aircraft and so long as you kept the vain straight i.e into the relative wind you were fine.

Once in the hover later generations of Harrier, with SAAHRS (akin to helicopter stabs although I've probably got the abbreviation wrong, it's been a while) where fairly comfortable to fly, but I would say it was never easy and required you to always be on your game. As you correctly observe the Harrier could bite, and bite fast and could very quickly go from all fine to 'Oh S&@t!!' especially for junior guys new to the jet.

As for did the best pilots go the Harrier.......absolutely! ;)

[riff_raff]

The R-R Pegasus used distilled water injection at the combustor to keep turbine inlet temps within acceptable limits during hover. The injected water reduces gas temps thru latent heat of evaporation. Since the injected water is inert, it does not contribute to the combustion process, but it does absorb heat which reduces the gas temp at the start of combustion, and thus allows a greater mass of fuel to be added to the existing airflow without exceeding turbine inlet temp limits.

Technically, the water injection does not "cool the engine". It simply lowers the temperature of the compressed air flow at the start of combustion. Gas turbine engines are typically limited by turbine inlet temps, or basically peak combustion cycle temps. So reducing gas temp at the start of combustion allows for a larger temperature rise during combustion. This means more fuel can be burned, and more heat energy added to the exhaust gas.

[Not_a_boffin]

*Jump Jet Fanny & Her Hawker Siddley Tw@t

Thems were the days..

http://66.media.tumblr.com/936a312c834f82cc3253de292f651493/tumblr_mzvar11yMh1s8su8go1_1280.jpg

[tartare]

Christ!
Was there just a little bit of bitterness and competition between yer average fastjet mate and the harrier blokes?!

[Wetstart Dryrun]

Chill, Tart.

It's knowing that they're the B-team that makes them so mad.

[H Peacock]

I've known a great many Harrier drivers over the years. Most of them were good, but I'm sure most of them would reluctantly admit they did take themselves/life much too seriously. The banter at Gutersloh between the guys on 230 Sqn and Harrier mates was simply fantastic to observe! The youngsters didn't stand a chance against Messrs Carpenter & Blackie!

[Lancman]

Shackletons had water/methanol injection 65 years ago.

[AutoBit]

Good to see this thread has degenerated into the usual Harrier pilot slagging off match.

By the way Leon J, if I was the Duty Auth on a sqn that treated visiting aircrew in the rude, discourteous and unprofessional manner that you boast about I would have been embarrassed.....not bragging about it.

[SammySu]

Tartare

Actually not very difficult to fly - with the nozzles aft it was a big Hawk, in the VSTOL regime handling was slightly more challenging but no black art.

The problem was how close to the edge you were in the VSTOL regime - very black and white between all going fine and nope I've crashed. Mostly down to the balance of fuel water and performance and a few minutes/seconds of criticality to work to - particularly from the deck with few outs. In most other jets there is a bit more grey - if I've screwed it up a bit I'll still get it back under control minus a few heartbeats.

Autobit

Indeed, but then you weren't aggressively low average....😉

[charliegolf]

Chill, Tart.

It's knowing that they're the B-team that makes them so mad.

I was told that they were the 'top pick' at role dispersal. No?

CG

[Wetstart Dryrun]

Oh dear, I must write more clearly, with exactitude and precision.

The B-team refers to those not blessed with the title of Bona-mate. - a pathway to camping in swamps, crapping in Field toilets and digging jets out of
bogs when they slip off the tin. Jealousy is a dreadful thing.

[Art E. Fischler-Reisen]

Harrier pilots had to get helicopter pilots to teach them how to hover. IIRC, they were given 5 hours at Shawbury, during my QHI'ing time there.

Most were probably unaware that teaching them to hover a Gazelle at Harrier hover heights (in the avoid curve) wasn't a particularly happy time for their QHIs. Obviously, "Bang seat let down" in the event of an engine failure wasn't an option.

Having been given the opportunity to fly the T4 from Gutersloh, I can say that it was quite stable in the hover compared to most helicopters. The approach on the braking stop was a bit weird, I have to admit, being very used to nose up to decel a helicopter.

[MSOCS]

I seem to recall flying the helicopter during the Shawbs Harrier course as:

a. Great fun
b. Of no practical or relevant use to prepare for Harrier STOVL
c. Quite easy to get to grips with

Like most things, the devil is in the detail and I wouldn't presume to apply the ease of hovering in a field near Ternhill to landing a Lynx on a bucking Frigate deck, or infil-ing an SF team into a compound at night, lights out on NVG, with little power margin. Similarly, one shouldn't discount that STOVL was a means to an end and, though it was unquestionably challenging at times, there was often a mission between take off and landing events.

The key delineator in ability was the prospective Harrier pilot's skill to consistently produce a safe, textbook VL or Slow Landing at the end of a very busy sortie. Those that couldn't, didn't last. Those that could, earned their place.

[Wetstart Dryrun]

The Shawbury helo course was known as the 'walkabout course' because it involved wandering about until a chap said get in this helicopter and do it. ... and they certainly said it was an unhappy envelope corner, but they could have been sergeant pilots.

No checks, no navigation, no airmanship at all, just watching a speedo drop to nothing and then persuading a clattering heap of aluminium on to the ground.

I was told that the ab initio Bona-mates ablity to pick up helicopter skill quickly in this unloaded environment led to the helo course being changed to reflect this style of syllabus.

Helos are pleasingly responsive in the hover, harriers have a sluggish inertia, T4 harriers are sluggisher, heavier and usually with about 2 minutes of fuel to practise with. ..and a QFI in the back to complain.

[Lima Juliet]

Autobit

http://www.thetimes.co.uk/tto/multimedia/archive/00499/a58d63e8-73af-11e3-_499536b.jpg

[George Richardson]

Beverley's also had water methanol injection 1955/6!

[AutoBit]

There we go Leon, you're catching on. At least thats quite funny.

[charliegolf]

Beverley's also had water methanol injection 1955/6!

They went so slowly people thought they were in the hover!

CG

[lsh]

Don't suppose anyone is interested in hearing about my Hillman Imp, with it's failing head-gasket, producing more power?

Thought not!

lsh
:E