Just found out from a friend of mine that SAA B747-200's with PW engines used to do water injection take off's


Apparently their aircraft were specifically modified for the job and there would be a 30s window during take off to inject the water to provide extra thrust that was required.


I have never heard of this before.

Can somebody explain the theory/ops etc etc?

Wikipedia explains it a little: http://en.wikipedia.org/wiki/Water_injection_%28engines%29

[Edited 2010-05-14 03:15:46]

Roughly speaking, the concept of water injection (with or without methanol) in a gas turbine is to reduce the temperature of the air entering the combustion zone. This achieves beneficial things like a more dense inlet flow, cooler inlet flow and greater mass flow. The cooler inlet flow was particularly helpful in the "G O Ds" when materials technology wasn't as well developed as now. The methanol is generally added for anti freeze, not extra cooling - think Metro which needs it for a potential 1EI missed approach in many places.

How it works is that water is injected into the diffuser case at the end of compression to cool the air. Compression causes considerable input of heat - as I recall it, the JT9 series diffuser case air temps run about 200*C at T/O power - so the water cools it. This means that combustion starts from a lower temp, so the turbine inlet guide vanes get a bit of relief - not much I grant you, but when they're so close to the limits of the materials every little bit helps. Also the water has mass, which is accelerated through the engine increasing mass flow. In the case of the JT9D it uses 600Kg per engine in 2.5 minutes.

The down side is that the system is rather complex and weighs quite a bit. From an operator's point of view, the complexities of the performance calculations were a veritable mine field given that we used it rather infrequently.

Thanks

Just heard the BAC 1-11 had an option for it?

Wonder if anyone on these forums has used it in anger.

The tanks were located behind the landing lights in the space fwd of the front spar and behind the leading edge, saw the tanks but the system was deactivated, was a 100 or 200 P&W.

This very complicated water injection system could be used with the following JT9D engines on the 747 :

JT9D-3A, Dry T/O rating 43.500 lbs. Wet rating 45.000 lbs.
JT9D-7 and -7H, Dry T/O rating 45.500 lbs. Wet rating 47.000 lbs.
JT9D-7A and 7AH, Dry T/O rating 46.150 lbs. Wet rating 47.670 lbs.
JT9D-7F, Dry T/O rating 46.750 lbs. Wet rating 48.650 lbs.

On the DC10-40 :
JT9D-20, Dry T/O rating 44.500 lbs. Wet rating 47.500 lbs.


Water alone is specified and should contain no more than 10 (ppm) parts per million impurities. Use of water is limited to takeoff operation up to an altitude of 8,000 feet for D-3A, and 10,000 feet for D-7, -7H, -7A, -7AH, -7F and -20, at the minimum ambient temperatures of 32oF. Take off using both water injection and dry takeoff power is
limited to a maximum period of 5 minutes including operation with water injection for not more than 2 1/2 minutes
(JT9D-3A, -7, -7H, -7A, -7AH, -7F) and 5 minutes (JT9D-20).


On the 747-100/200 two water tanks were each built in the wing roots (left and right) and extra piping was installed for transportation of the water to the four engines (one tank for 2 engines at the same wing.) Also piping for waterfilling and draining of residual water after T/O was installed. Four high capacity water pumps were feeding the engines with water.
Each engine had an adapted fuelcontrol to cater for extra fuel when the system was activated.

System operation (747) :

- When a wet rating was needed min. 2300 kgs of water was uplifted. (standpipe level was 2450 kgs)

- During Taxi-out, just before entering the runway, the system was switched on (F/E panel), the four water pumps were momentarily giving a flow indication (four green lights), check all water low press lights out. Most frequent failure at this moment : water pumps start to operate but the water shut off vlv is still (partly) open. This is called a "steam out" or "piss out" . The relevant engine (still at idle) gets the full water flow and stops operating and has to be restarted, after switching off the waterinjection system.

When entering the runway the system is now armed.

After advancing the powerlevers at approx. 1.25 EPR the system comes in, four green water flow lights illum (pilots annunciator panel), the watershut off valves are open. Carefull monitoring of the EGT indication is crucial (one engine can suddenly revert to no water (pump failure), but still with the high (wet) fuelsetting.
After 2.30 minutesa or just before water run out (indicators on F/E panel), the system is switched off, 2.30 minutes dry rating is still available when needed.
Switching off was the most tricky part of the operation, because of the low usage of the system frequently failures occured.
The most dangerous was that the waterpumps stopped and shut off vlv's closed but one engine fuelcontrol stayed at the wet fuel rating. Before you could blinck an eye the EGT exceeded the T/O limits and an expensive boroscope check or even an engine change was required.

[Edited 2010-05-14 11:02:04]

[Edited 2010-05-14 11:04:14]

Quoting BALandorLivery (Reply 2): Wonder if anyone on these forums has used it in anger.

Used it all the time in the old A-frame...



We were Gods - we made water burn!

Quoting Qantas744ER (Reply 1): Roughly speaking, the concept of water injection (with or without methanol) in a gas turbine is to reduce the temperature of the air entering the combustion zone.

On typical turbine water injection systems, the water is injected directly into the combustion chamber via a combined water and fuel nozzle. The water cools the flame temperature (not the incoming air temperature) thus reducing the turbine inlet temperature. More fuel can be then be added until the engine TIT limit is reached. The increased mass flow through the engine results in the increased power. I do not know of any water injection systems (Other than industrial applications) where water is used to cool air entering the combustion chamber.

Quoting kl671 (Reply 6): The water cools the flame temperature (not the incoming air temperature) thus reducing the turbine inlet temperature.

Water cools the flame temperature *by cooling the incoming air*.

Flames are a gaseous reaction, they don't "see" liquids. The temperature rise due to combustion is also pretty fixed (the water injection doesn't alter the fuel/air ratio much). The only way for water to interact with the flame (at the quantities we're talking about) is to vapourize. This sucks a ton of heat out of the air, lowering the air temperature. You've now got colder air participating in the combustion reaction...colder inlet air with constant temperature rise means colder outlet products.

Tom.

Quoting tdscanuck (Reply 7): Water cools the flame temperature *by cooling the incoming air*.

Wrong. Water injection into a combustion chamber is used to cool exhaust gasses, not intake air.

Quoting tdscanuck (Reply 7): Flames are a gaseous reaction, they don't "see" liquids.

Injecting water into a combustion chamber results in steam. Steam is a gas at the temperatures and pressures found in a combustion chamber.

Quoting tdscanuck (Reply 7): The only way for water to interact with the flame (at the quantities we're talking about) is to vapourize. This sucks a ton of heat out of the air, lowering the air temperature.

Perhaps a more accurate statement would be "This sucks a ton of heat out of the products of cumbustion, lowering the turbine inlet temperature"

Quoting tdscanuck (Reply 7): The temperature rise due to combustion is also pretty fixed

Not when you inject water to lower the temperature rise.

I stand by ny statement. "The water cools the flame temperature"

Quoting tdscanuck (Reply 7):

Quoting kl671 (Reply 8):

Very interesting topic! As far as I can tell, the phase change of the water from liquid to gas removes large amounts of heat from the working fluid as it passes through the engine core. One can then burn more fuel before reaching the limiting turbine inlet temperature (TIT). The question is where would the best location be to inject the water?

I suppose this can be done in the compressor or diffuser section, or directly in the combustion chamber (CC). Nonetheless, wouldn’t the overall effect be the same? Cooling the air prior to entering the CC allows more fuel to be burnt before reaching the limiting TIT. Burning more fuel in the CC and then cooling also allows more fuel to be burnt without exceeding the limiting TIT.

Thermodynamically, I seem to think injecting prior to the CC more be more efficient, as this increases the heat difference across the engine, which is a key method of increasing thermal efficiency. However, I suppose the primary concern with water injection is increasing thrust, not efficiency, thus, both processes should result in the same outcome. The only difference is the order of processes. Injecting prior to the CC cools and then heats, whereas injecting directly into the CC heats first, then cools.

Quoting Qantas744ER (Reply 1): Also the water has mass, which is accelerated through the engine increasing mass flow.

I wonder whether it is an increase in mass flow, or the increased acceleration (or both?) that provides the additional thrust? One other mechanism that may be beneficial is the phase change of the water from liquid to gas.

Water in the gas phases occupies much more volume compared with the liquid phase. This rapid and significant expansion would surely be beneficial, as the expansion of the working fluid is a key to improving the performance of a jet engine.

Regards, JetMech

Quoting kl671 (Reply 8): Quoting tdscanuck (Reply 7): Water cools the flame temperature *by cooling the incoming air*. Wrong. Water injection into a combustion chamber is used to cool exhaust gasses, not intake air.

There's no difference...cooler reactants leads to cooler products.

Quoting kl671 (Reply 8): Quoting tdscanuck (Reply 7): Flames are a gaseous reaction, they don't "see" liquids. Injecting water into a combustion chamber results in steam. Steam is a gas at the temperatures and pressures found in a combustion chamber.

Exactly. The the energy to convert the liquid to steam results in a temperature drop in the incoming air (and the outgoing too, if the evaporation isn't complete before the flame front passes).

Quoting kl671 (Reply 8): Quoting tdscanuck (Reply 7): The temperature rise due to combustion is also pretty fixed Not when you inject water to lower the temperature rise.

There isn't enough water mass to appreciably alter the temperature rise *of the combustion*. The only way you can do that is to alter the fuel/air ratio or the fuel. This is sort of a philosophy question though...it depends if you write the entire process (combustion + evaporation) as a single reaction or a series. It doesn't matter which order to you do the series though (or if you do it all as a single reaction), the end products are the same.

Quoting kl671 (Reply 8): I stand by ny statement. "The water cools the flame temperature"

No argument there. We're quibbling over the mechanism, not the result.

Quoting jetmech (Reply 9): The question is where would the best location be to inject the water?

For maximum effect, you'd want to do it at the LP compressor inlet to provide the most time for evaporation (it functions roughly like an intercooler if you do that). But lots of liquid water and compressor blades may not get along...given that you've already got a nice injection system in the combustor, I suspect the combustor inlet is the most practical spot.

Quoting jetmech (Reply 9): I suppose this can be done in the compressor or diffuser section, or directly in the combustion chamber (CC). Nonetheless, wouldn’t the overall effect be the same?

Mostly, yes. The farther you put it upstream, the greater the intercooler effect in the compressor, but I suspect that's pretty small compared to the bulk temperature drop's impact on turbine inlet temperature.

Quoting jetmech (Reply 9): I wonder whether it is an increase in mass flow, or the increased acceleration (or both?) that provides the additional thrust?

Both. Since the flow area is fixed, you can't get more mass flow without also increasing acceleration. The only way to get more mass flow is to increase velocity, which requires the spools to spin faster, which means higher pressure ratio, which means more acceleration.

Quoting jetmech (Reply 9): Water in the gas phases occupies much more volume compared with the liquid phase. This rapid and significant expansion would surely be beneficial, as the expansion of the working fluid is a key to improving the performance of a jet engine.

This increases the outlet velocity of the engine (same flow area, more volume flow rate), hence the thrust hike.

Tom.

Quoting BALandorLivery (Thread starter): BALandorLivery

Well, I've never heard about those 30 sec window but 747classic explanation was pretty accurate.

I've seen B747's with single tank installation (bladder type 700 USG capacity) located in a dry bay above the keel beam centre wing section and with two integral tanks built into the leading edge structure.
The system included individual hardware for each engine: Water injection water pump, shut off valve, regulator, pipping, nozzles (part of the fuel nozzle - 20 x engine) and drains.
As explained above, when the system was armed the water (under high press) was against the (spring loaded) closed injection shut off valve. Moving the thrust levers to T/O range allowed high pressure bleed air to enter the valve, which then open if the water and the bleed air was above certain threshold.
The injection shut off valve automatically close if either water or bleed air pressure drops below a certain value. (Now way I'll remember that!!)
From the shut off the water flows to the regulator (which send a signal to the FCU for a higher governor setting) and to the manifolds/nozzles.
The operation is stopped by placing the pumps to off or retarding the thrust levers (bleed air press drops)
Right after T/O remaining water had to be drain: The drain mast was electrically heated and with a vortex generator for inflight draining.
Max operating time in no flow was 10 min.
Max operating time at rated flow was 2.5 min. and was not supposed to be used below -18 C or above 8,000 feet PA.

...and no A/P engagement until water injection pumps are off...

Regards,

B747FE.

On the JT9D the water is injected via the twenty (20) fuelnozzles into the combustion chamber.
From the longitudial section drawing of the JT9D-7(W) engine the following is stated :
"Each nozzle is connected to primary and secondary fuel manifolds and to the watermanifold".

In my archive I found the following test stand parameters : (From the F/E expanded 747-AOM section)

Operating Particulars .................JT9D-7 Dry...............JT9D-7 Wet

Total thrust T/O Thrust(lbs)..........45.500.......................47.000
Fan thrust (lbs),..........................34.600.......................35.500
Prime Thrust(lbs)........................10.900.......................11.500
EPR..........................................1.54...........................1.59
Fuel Flow (kg/hr).........................7520..........................8475
TSFC (lbs/hr/lb thrust).................0.364.........................0.398
N1 RPM (3600 = 100%)..............3325(92.4%)...............3370 (93.6%)
N2 RPM (7800 = 100%)..............7580(97.2%)...............7575 (97.1%)
Total airflow (lbs/sec)..................1520..........................1540
Fan airflow (lbs/sec)...................1265...........................1280
Prime airflow (lbs/sec).................255............................260
Bypass ratio...............................4.9.............................4.9
Compressor ratio........................23.0...........................23.9

Conditions : Static test stand, sealevel, 29.92 "Hg, OAT 26.7 degr C, no bleed, no accessory power extraction, Take -off power.

Remarkable is the lower N2 RPM in wet condition (typo ?) or somebody can explain this.

[Edited 2010-05-15 02:14:55]

Quoting 747classic (Reply 12): Remarkable is the lower N2 RPM in wet condition (typo ?) or somebody can explain this.

Decreased working pressure from the additional fuel/water in the combustion area?

Okie

Quoting kl671 (Reply 6): any water injection systems (Other than industrial applications) where water is used to cool air entering the combustion chamber

I assume you are talking about turbine engines only? Water injection kits are available for many turbocharged internal combustion engines; Aquamist is one of the more popular manufacturers. I have one on my car. It uses a pressure switch to activate a pump connect to a single spray nozzle that injects a mix of water and isopropyl alcohol just before the throttle body when the boost pressure exceeds the specified value. I have it set to 7psi. It increases the density of the charge air, which provides more power. It also cools the charge, reducing pre-detonation at high boost levels. Some systems allow a second nozzle to mist the front side of the intercooler.

Fantastic and fascinating info.

Thanks 747Classic for your detailed explanations.

Quoting tdscanuck (Reply 7): Flames are a gaseous reaction, they don't "see" liquids. The temperature rise due to combustion is also pretty fixed (the water injection doesn't alter the fuel/air ratio much). The only way for water to interact with the flame (at the quantities we're talking about) is to vapourize. This sucks a ton of heat out of the air, lowering the air temperature. You've now got colder air participating in the combustion reaction...colder inlet air with constant temperature rise means colder outlet products.

Also, while the bulk products temp stays the same (or is reduced if fuel isn't added to achieve the same turbine inlet temp) the flame becomes more homegenous and hot spots within the flame are reduced. While this could be a good thing from a materials longevity perspective, in practice the water flashing to steam can fairly dramatically shorten the life of the combustor. The 'balancing' of flame temperature does reduce NOx production dramatically and is why industrial combustion turbines are quite often water injected. Another down side, as seen from the values noted in reply 12, is that SFC increases due to the energy required simply to flash water to steam.

Quoting tdscanuck (Reply 10): Mostly, yes. The farther you put it upstream, the greater the intercooler effect in the compressor, but I suspect that's pretty small compared to the bulk temperature drop's impact on turbine inlet temperature.

In the applications I'm familiar with, the effect per unit of water injected is much greater when injected into the compressor. For industrial versions of the CF6, for NOx reduction we inject ~45 gpm into the combustion chamber (using application-specific fuel nozzles) and see roughly a 2% increase in power. We also inject ~18 GPM into the LPC but see about 8.5% more power.

Quoting 747classic (Reply 12): Remarkable is the lower N2 RPM in wet condition (typo ?) or somebody can explain this.

My guess is that because LPC airflow is higher feeding the HPC, to preserve HPC surge margins not all the possible fuel is added back in (i.e. turbine inlet temp is run somewhat lower than when operated dry).

Mike

So what did it feel like to take off with one of these systems?

Quoting DocLightning (Reply 17): So what did it feel like to take off with one of these systems?

The passengers likely couldn't't tell. The wet takeoff was used under heavy or hot conditions. More likely the passengers would notice if it weren't used! As it would be a slow lazy takeoff.

It was like the "Black Power" takeoffs we used to use on the DC-1030ER YYZ-NRT, almost every caution light in the cockpit was illuminated ... but to the passengers is was a normal take off.

Quoting DocLightning (Reply 17): So what did it feel like to take off with one of these systems?

Quoting Longhauler (Reply 18): The passengers likely couldn't't tell. The wet takeoff was used under heavy or hot conditions. More likely the passengers would notice if it weren't used! As it would be a slow lazy takeoff.

In my memory passengers could hear the difference.

I made a lot of Wet Take Off's between 1978 and 1990 on KL 747-206B aircraft.
Most of them on the AMS-LAX and AMS-IAH stretches, nearly always with also airconditioning switched off to obtain the last drop of thrust from these engines. All three in the cockpit were always fully aware that in fact this aircraft was underpowered and the engines required a lot of extra attention during these kind of Take Off's.
The engine sound of the 4 P&W JT9D-7W changed to a very low growling sound when the waterinjection came in at approx. 1.25 EPR powersetting. Most of the time we let the brakes a little longer applied to gain some runway length and checked that all four green waterflow lights were illuminated.
After the"Water on" call the brakes were released.
With four growling engines it took a very long time before Vr was reached. It always looked very close to the end of the runway. Slowly climbing with mostly MTOW (351.000 lbs) we climbed away until the water was almost running out or 2.30 minutes was reached.
Now "water off" was called by the F/E to warn the pilots for the impending thrust decrease. P/L's were retarded a little bit, before actual stopping of the waterinjection system on the F/E Panel. This was done to prevent an overboost during transition to the dry setting. Now GA or CLB was selected at the engine mode selectpanel and, depending climb out procedures, GA or CLB thrust was set.

Especially after selecting the waterinjection off and setting CLB thust it became very quite in the aircraft, so sometimes the captain warned the passengers before take off, that after take off the engines were only retarded and not shut off !!!!.

747classic, thank you for the detailed explanation and the interesting details! Must have been a great time to work at KLM.

Did all the KL 747 classics have water injection or only the early ones? I was always convinced that only the very early turbojets/fans required water injection.

Quoting 747classic (Reply 19): Especially after selecting the waterinjection off and setting CLB thust it became very quite in the aircraft, so sometimes the captain warned the passengers before take off, that after take off the engines were only retarded and not shut off !!!!

Seeing how some people turn pale when Climb thrust is selected on modern airliners I can imagine this must have been quite the experience!

[Edited 2010-05-16 08:53:12]

Quoting TravelAVNut (Reply 20): Did all the KL 747 classics have water injection or only the early ones? I was always convinced that only the very early turbojets/fans required water injection.

Only the first 7 (PH-BUA till/incl.-UG) were powered by JT9D-7W engines with waterinjection. The first were delivered with JT9D-3W engines, but quickly converted into the Dash 7W variant.

All other 13 KL 747-206B/306 aircraft (PH-BUH until/incl -UW) were powered by General Electric CF6-50E or CF6-50E2 engines . Later all were brought on -50E2 standard.

Quoting Longhauler (Reply 18): The passengers likely couldn't't tell. The wet takeoff was used under heavy or hot conditions. More likely the passengers would notice if it weren't used! As it would be a slow lazy takeoff.

Quoting 747classic (Reply 19): In my memory passengers could hear the difference.

Could those aft of the wing see the steam?

Quoting DocLightning (Reply 22): Could those aft of the wing see the steam?

No, AFAIK.

Quoting 747classic (Reply 12): Remarkable is the lower N2 RPM in wet condition (typo ?) or somebody can explain this.

It seems realistic to me.

The compressor ratio is increased from 23.0 to 23.9. That will make the HP compressor "work harder", which - everything else equal - decreases N2 RPM.

But everything else isn't equal. Since EPR is increased from 1.54 to 1.59, then the HP turbine will also works harder, increasing N2 RPM.

So we have two factors affecting N2 RPM in opposite way. It seems realistic to me that the end result can be an N2 RPM decreased by a fraction of a percent (for the JT9D-7 0.1%).

On another engine type, or under slightly different test conditions, the end result could be the other way around. But in any case, we have two factors working in opposite direction regarding N2 RPM.

But of course N1 RPM increases substantially (JT9D-7 1.5%). It is affected only by the increased EPR, not by the increased HP compressor ratio.

And BTW, that 1.5% N1 RPM increase is the greater part of the whole game since it is responsible for roughly 1,000 lbs of the 1,500 lbs thrust increase.
((1.015 ^2) * (some 30-35,000 lbs fan thrust)) - (some 30-35,000 lbs fan thrust) = roughly 1,000 lbs

I like rough numbers. Remember Charley Brown, six years old school boy of last century, now retired. One evening he couldn't fall asleep, but had instead an exercise in philisophy:

- If I make one mistake each day and get 80 years old, then I will produce roughly 30,000 mistakes.

- When calculating my mistakes it is best to use rough numbers.

Quoting tdscanuck (Reply 10): The only way to get more mass flow is to increase velocity, which requires the spools to spin faster, which means higher pressure ratio, which means more acceleration.

Quoting 747classic (Reply 12):

Fair enough, that makes sense, and going by 747classics's information, it is exactly the mechanism that occurs for a water injected take off. However, could we also increase mass flow rate and thrust with a constant working fluid velocity? If we take in denser working fluid at a fixed velocity, mass flow rate will increase and in theory thrust will also rise.

Quoting tdscanuck (Reply 10): This increases the outlet velocity of the engine (same flow area, more volume flow rate), hence the thrust hike.

The phase change of water from liquid to vapour results in a significant volume increase, but I suppose the downside is the copious amounts of heat one would need to add to achieve this   .

Regards, JetMech

The gaseous form of water, water vapor, is invisible.

Quoting LTC8K6 (Reply 26): The gaseous form of water, water vapor, is invisible.

But i'd figure that it would tend to condense to visible steam pretty quickly on exiting the rear of the engine, especially on a cold day.

Left photo :

PH-BUE, equipped with original JT9D-3AW engines, with blow-in doors for additional airflow during (wet) T/O power settings.
For noise and fuel economy reasons the nacelle was later changed to a "Quiet nacelle type", without blow-in doors.

Right photo :

PH-BUD : F/E panel, just above the clock the waterinjection panel is visible, with the following switches, dials and warning lights :
Top row 4 water press lights (amber)
Underneath : one water low press light (amber)
Lefthand switch (with white cover) = start switch.
Guarded switch (with guard open) = water drain vlv.
Water quantity indicator. (left and right in one dial)

View Large View Medium Photo © Miguel Snoep

View Large View Medium Photo © Walter Van Bel

[Edited 2010-05-16 23:56:18]

Quoting 747classic (Reply 12): Conditions : Static test stand, sealevel, 29.92 "Hg, OAT 26.7 degr C, no bleed, no accessory power extraction, Take -off power.

I've never seen such a higher EPR value at standard pressure.
Normally we got below 1.3 part power wet and below 1.5 T/O wet...On-wing off course. I guess the difference is due to the power extraction for accessories.

Quoting 747classic (Reply 12): Remarkable is the lower N2 RPM in wet condition (typo ?) or somebody can explain this.

Quoting okie (Reply 13): Decreased working pressure from the additional fuel/water in the combustion area?

Reduced work of compression per pound of air.

Quoting DocLightning (Reply 27): Quoting LTC8K6 (Reply 26): The gaseous form of water, water vapor, is invisible. But i'd figure that it would tend to condense to visible steam pretty quickly on exiting the rear of the engine, especially on a cold day.

Not on the JT9D.

747classic Nice pic of the office!! 


Regards,

B747FE.

Last time I used water injection was in the summer 2006 on L-410-UVP-E model with Walter 601E engines.
When performance limited due to high temperature and short runway, we were able to carry cca. 2 additional passengers when using the water injection. Water used was demineralised or simply distilled water, which was easier to buy (in the local shop..). On L410, there are three possible settings for quantity and duration of injection system, which sprays water directly into compressor inlet, with a possibility to dump remaining water to prevent freezing at higher levels (as the tank is in the right main wheel well). Cockpit controls include press buttons for starting and stopping the water pump and toggle switch for drain valve.
Operation is fairly simple - at cca. 60% TRQ, copilots presses the start button and ITT on both engines drops by approx. 20deg C, which enables higher TRQ (and fuel flow) for the same ITT. Simple and reliable system, quite unique for an airplane this small (17pax).



Spray ring is vertical installation in front of the intake mesh.

Quoting bri2k1 (Reply 14): just before the throttle body

A bit more on car engines - I saw a sprinkler system which sprayed water on the face of the intercooler.

Quoting BALandorLivery (Reply 2): Just heard the BAC 1-11 had an option for it?

DanAir operated a fleet of 1-11s (among other types) from the UK to Mediterranean destinations (among others). It was common to see 6 or 8 barrels of water-meth loaded in the aft hold (at the forward bulkhead) for use on the return flight. The barrel was translucent plastic in a metal "cage", approx 80 cm high and 50 cm diameter IIRC.

The fact that they were carrying barrels for the return flight (often from hot and/or short runways) implies there was already water in the tanks on departure from the UK. For some reason I don't remember ever seeing water-meth pumped into the aircraft at Gatwick, and always assumed the long runway made it unnecessary.

I seem to recall the water-meth filler point was near the starboard wing trailing edge root.

There must be someone out there from that era who was paying more attention than I was - I look forward to clarification!

Regards - musang

In our 747 operation it was stricktly prohibited to uplift water in station A and then carry it to destination B for a wet T/O.
The issue was freezing of the water in the watertanks (leading edge of the wing) during the transit flight.
Always, after T/O the drainvalve had to be opened, as stated on the after T/O checklist.
I recall, that we had asked for permission to uplift water in MEL for a wet T/O in SYD for the return leg, but it was not granted by our tech/ops department, despite the short flying time between the two airports.

[Edited 2010-05-23 02:04:17]

Does anyone know why it is allowed to use 110% torque on a TPE331 installed on a Metro when using water injection? We used a lot of time to discuss it ay my module 15 turbine ngine course.

/Lars

I guess the Martini is going to my head but I have a couple of questions:
- On the 747-200, was all the water used, or simply as much as would be needed until the "set climb power" point?
- Is there a time limit on wet power, similar to the time limit on take-off power?
- Assuming it was not all used, how much would be left? Was this a safety margin?
- Say you're doing a wet take-off and one engine fails just as you climb out. Would all the water then be used in order to get all possible power out of the engines?

Quoting Starlionblue (Reply 34): On the 747-200, was all the water used, or simply as much as would be needed until the "set climb power" point?

Normally after 2.30 minutes (max. certified "wet"thrust time) the waterinjection was switched off. Approx 150 kgs were left and were drained with the folllowing After T/O checklist item : Drain vlv....... open.
Sometimes the two water quantity indicators (Left for engine 1&2, Right for engine 3&4) approached zero BEFORE reaching the 2.30 minutes time limit. The waterinjection was now switched off (all engines) to prevent unequal reversion to the dry setting of the engines.

Quoting Starlionblue (Reply 34): Is there a time limit on wet power, similar to the time limit on take-off power?

Certified : 2 and a half minutes, if needed followed by another 2.30 minutes dry thrust (GA setting).

Quoting Starlionblue (Reply 34): Assuming it was not all used, how much would be left? Was this a safety margin?

Approx 150 kgs. Standpipe level for filling the watertanks was 2450 kgs. Needed normally 2300 kgs. This was a safety margin, to avoid unequal reversion to the dry settings.

Quoting Starlionblue (Reply 34): Say you're doing a wet take-off and one engine fails just as you climb out. Would all the water then be used in order to get all possible power out of the engines?

Normally not, after 2.30 hrs normal reversion to GA thrust.
When the trees are really come close, you can try to extend the wet thrust time as long as possible in concert with the Pilot Flying. But avoid not equal thrust settings of the three remaining engines, because the Pilot Flying doesn't want additional yaw changes in a N-1 situation, when not needed.

[Edited 2010-05-23 07:12:53]

Thanks. Very informative!
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A bit off topic, but bad things happen when you fill the water injection tanks with kerosene.

http://aviation-safety.net/database/record.php?id=19710906-0

Quoting 747classic (Reply 32): The issue was freezing of the water in the watertanks

I should have thought of that.

Thanks! - musang

Quoting Larshjort (Reply 33): Does anyone know why it is allowed to use 110% torque on a TPE331 installed on a Metro when using water injection? We used a lot of time to discuss it ay my module 15 turbine ngine course.

Having not flown a Metro or any other 'Single Redline' equipped TPE331 aircraft, I don't know the details. However, I found in a Honeywell TPE331 Pilot Tips book a brief exlanation of Engine Perfomance Augmentation Systems. It states that the "Water-Methanol Injection System can be used to A) recover lagging torque resulting from unfavorable ambient conditions, and B), in the event of an engine failure on take-off or landing, to augment power on the opposite engine."

The manual goes on to explain that (depending on installation), the water-methanol injection system lowers combustion temperature; additionally, you can increase max allowable ITT for a given amount of time. Consequently, If you were already at max torque on takeoff, engaged the injection system following an engine failure, and then advanced the power levers to the 'new' ITT red line, you will have a new torque value in excess of 100%. From what I gather, the amount over 100% varies depending on which 331 varient we're talking about.

Additionally, the TPE331 can have at least two other performance reserve systems: an Automatic Performance Reserve system, and a Continuous Performance Reserve system. APR allows for a higher ITT; CPR starts water injection to allow for increased power settings.

Of those three systems, only one is installed on any particular engine installation.

Quoting 747classic (Reply 35): Sometimes the two water quantity indicators (Left for engine 1&2, Right for engine 3&4) approached zero BEFORE reaching the 2.30 minutes time limit.

Was the system on the 747 split between left and right? On the KC-135, the water came out of one tank (in the starboard main gear well) but one pump fed the inboard engines and one pump fed the outboards. Apparently, when first designed, one pump handled engines 1&2, the other 3&4, but after a few incidents where they lost water on one side (and at least one crash, I believe) the system was changed to inboard/outboard.

Quoting moose135 (Reply 40): Was the system on the 747 split between left and right? On the KC-135, the water came out of one tank (in the starboard main gear well) but one pump fed the inboard engines and one pump fed the outboards. Apparently, when first designed, one pump handled engines 1&2, the other 3&4, but after a few incidents where they lost water on one side (and at least one crash, I believe) the system was changed to inboard/outboard.

I stand corrected. When reading your reply, I began to doubt (twenty years after the last wet T/O).
I checked my old 747 Aircraft Operational Manual (AOM) and you are fully correct.
The LH tank contained two separate water pumps to feed engine 1 & 4, the RH tank supplied engines 2 & 3.

[Edited 2010-05-25 10:11:04]