ConcordeBoy
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Water/rain-ingestion Affect Engine Performance?

Fri Mar 19, 2004 2:35 am

While I've seen the videos of Boeing dumping hundreds to thousands of gallons of water into a revving PW4077, and watching it pump out thrust seemingly unaffected..... I'm curious as to whether any considerations must be taken into affect when planning takeoff performance (et al).

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Is the effect negligible?
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UAL Bagsmasher
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RE: Water/rain-ingestion Affect Engine Performance?

Fri Mar 19, 2004 3:44 am

Humidity/precip. generally has a negligible impact on turbine engine power output. That being said, systems such as continuous ignition come into play in heavier precipitation to prevent flameouts, etc.
 
mt99
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RE: Water/rain-ingestion Affect Engine Performance?

Fri Mar 19, 2004 4:53 am

Water ingestion was the main reason that TACA 737's engines flamed out during approach to MSY in the mids 80's.
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Okie
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RE: Water/rain-ingestion Affect Engine Performance?

Fri Mar 19, 2004 6:56 am

I saw a video of the Boeing 777 doing the water ingestion test on the engines possibly the one Concordeboy is referring to. I did notice that the water distribution was towards the bypass areas of the engine but then again there is more area as you get away from the center and you would be trying to emulate evenly distributed rainfall. Needless to say it was still a impressive video. I would also suspect that centrifugal force the fan would instill on the water droplets that hit the blade would tend to push the water away from the core like a centrifuge. One would think that putting that much water into an engine would have a tendency to reduce the EGT (takes 970 btu per lb of 100c water to convert to steam) and slightly increase exhaust gas velocities due to the expansion of the water vapor.
Since newer engine functions are set to N speeds or EPR, I suspect that the FADEC would just cut back on the fuel logging and the thrust would just remain the same but then that's just a guess. I know that on the older engines the fuel was basically mechanically controlled/metered to the engines and some had water/methanol injection to increase thrust for take off but was time/temperature limited.

Maybe the Skipper can help us out here. Would the EPR's or N speeds jump when you hit those turbines with water/methanol?

Okie

Okie
 
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RE: Water/rain-ingestion Affect Engine Performance?

Fri Mar 19, 2004 7:30 am

Takeoff performance (and engine power) changes with water/rain are negligible...
Quoting the books from Boeing... NEGLIGIBLE...
It is recognized that braking action (V1 aborted takeoff) should be considered.
Engine power, not whatsoever...
xxx
I took off in heavy rain storms... call it Bangladesh... monsoon rains.
Engines quit, like a fraction of a second, they take "their turn"... ignition is ON... immediate relight.
xxx
In real life, heavy rain... I knock down 10 knots on V1... be conservative...
And for weight, my pencil reduces max takeoff weight by 5,000 kg...
I am "paid" to make these educated corrections.... ha ha...
Nobody would question them.
xxx
Happy contrails  Smile
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timz
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RE: Water/rain-ingestion Affect Engine Performance?

Fri Mar 19, 2004 7:32 am

I thought that Southern DC-9 crash (attempted landing on a highway) was due to double flameout due to heavy rain.
 
Okie
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RE: Water/rain-ingestion Affect Engine Performance?

Fri Mar 19, 2004 8:10 am

Timz
The official report said massive amounts of water, hail and thrust lever movements on your Southern DC-9. I would suspect the hail did enough damage that the engines could not auto relight.

Then again some of the first reports on Three Mile Island sort of implied all that was needed was a mop and a bucket to clean up some spilled water in the containment building.

Okie
 
SlamClick
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RE: Water/rain-ingestion Affect Engine Performance?

Fri Mar 19, 2004 12:31 pm

Southern 282 had lots of problems relating to their weather encounter including a shattered windshield.

I saw a presentation by a Pratt & Whitney rep at a seminar at McDonnell Douglas when the MD-80 was a new airplane. The subject was the Southern DC-9 crash near Atlanta in 1978. The amount of water ingested was firehose stuff. The compressor stall began deep in the engine, perhaps at the 13th stage and was so severe that the blades were flexed forward to strike the stators in front of them - shelled out the engine. I don't remember, and probably did not fully understand all the reasons, but there was not much the pilots could have done as either reducing or increasing throttle would both have aggravated the condition.

And Okie it was also said that if you sat in the middle of the reactor building area at TMI the radiation encountered was about the same as watching color television at a distance of three or four feet as many children do. Hard to know what to believe.

But Skipper is dead right about it. The water ingestion from any rainstorm we are likely to be flying in (on purpose at least) is not a factor in performance or engine operation. Standing water on the runway is another matter. Big factor there.

There was once an engineering study once (and the FAA bought into it completely for a short while) that proved that an airplane would not fly in any amount of rain. The reason? Picture a high-speed strobe photo of raindrops striking a wing and making those little corona-like splashes. Well the computer model treated those splashes as if they were solid as metal. Well of course, no wing that rough would fly!
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IMissPiedmont
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RE: Water/rain-ingestion Affect Engine Performance?

Fri Mar 19, 2004 1:46 pm

Normal rainfall does in fact, help the performance of any fuel burning engine. This is offset by the fact that water creates drag though. But throwing several thousands of gallons water into any intake is not a good idea.
The day you stop learning is the day you should die.
 
Okie
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RE: Water/rain-ingestion Affect Engine Performance?

Fri Mar 19, 2004 2:40 pm

Your correct there SlamClick, I should have looked that up. When you mentioned the 13th stage it jogged my memory about it being deep in the engine.

Basically there was a greater volume of water going in the intake than would fit out the exhaust, essentially turning an air pump into a hydraulic pump. Best I can remember they had never seen that type of turbine damage before.

They had bad weather brief from company dispatch from the start and things just kept going down hill from there.

Okie

 
Moolies
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RE: Water/rain-ingestion Affect Engine Performance?

Fri Mar 19, 2004 11:56 pm

BA stuck "mud flaps" on their concordes to stop water being kicked up from the wheels and going into the engines.
 
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Starlionblue
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RE: Water/rain-ingestion Affect Engine Performance?

Sat Mar 20, 2004 1:14 am

They also stopped stray pieces of tires lying around runways. But that's a whole other story.
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ConcordeBoy
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RE: Water/rain-ingestion Affect Engine Performance?

Sat Mar 20, 2004 6:42 am

BA stuck "mud flaps" on their concordes to stop water being kicked up from the wheels and going into the engines.

Both airlines utilized these.


They also stopped stray pieces of tires lying around runways

Deflectors had nothing to do with stopping tire FOD.
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Starlionblue
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RE: Water/rain-ingestion Affect Engine Performance?

Sat Mar 20, 2004 5:27 pm

Getting off topic but aren't these the same deflectors of which one was missing on the ill-fated AF Concorde?
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ConcordeBoy
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RE: Water/rain-ingestion Affect Engine Performance?

Sun Mar 21, 2004 4:45 am

No.

The auto-alignment spacer for the left front bogie was missing... the deflector was in place.
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Starlionblue
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RE: Water/rain-ingestion Affect Engine Performance?

Sun Mar 21, 2004 8:03 am

Ok, I get it now. Thx ConcordeBoy.
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Moolies
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RE: Water/rain-ingestion Affect Engine Performance?

Mon Mar 22, 2004 11:25 pm

yes i think it was those ones what were missing on the ill fated concorde. but that is what i heard from a guy at BA
 
ConcordeBoy
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RE: Water/rain-ingestion Affect Engine Performance?

Tue Mar 23, 2004 3:31 am

...course, that was only one of the myriad factors that lead to this crash... albeit an extremely significant one  Sad
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brons2
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RE: Water/rain-ingestion Affect Engine Performance

Tue Mar 23, 2004 3:53 am

Basically there was a greater volume of water going in the intake than would fit out the exhaust, essentially turning an air pump into a hydraulic pump. Best I can remember they had never seen that type of turbine damage before.

Interesting.

Kind of like hydrolocking a reciprocating engine. (ie, you get water in the combustion chamber and things like connecting rods tend to bend or break when the cylinder goes up) I'd never heard of that on a turbine though. Would seem like this would be less of a problem in a higher-bypass engine.
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ConcordeBoy
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RE: Water/rain-ingestion Affect Engine Performance?

Mon Apr 05, 2004 7:28 am

I thought that Southern DC-9 crash (attempted landing on a highway) was due to double flameout due to heavy rain.

Though they were in heavy precipitation (so severe that the meteorologic equipment of that time couldn't accurately process it), the crash has since been contributed to copious hail ingestion, not liquid water.
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