Jet aircraft turbines- how do they handle water (rain)?

Question

I undestand that they operate on the principle of compression- the vanes compress air, fuel is injected and ignited = boom. My question is this- water is incompressible, so how does a heavy rain affect a jet engine?

Answer 1

Water doesn't hurt them at all. Many older jet engines used water injection to boost takeoff power. The J-57 engine used on both the KC-135A and B-52s up through the D model were excellent examples.

Although water is incompressible, jets use a series of fans to compress the air, not a sealed cylinder and piston. The water just flows through the engine harmlessly and actually improves performance a bit in some cases.

Answer 2

Contrary to first thought, light rain/mist actually will boost power output of a turbine, the compressed air in the high pressure compressor will evaporate the water causing a cooling effect which makes the air denser and the engine can make more thrust.

Heavy rain every now and then is a good thing it that it can clean the compressor and make it work more efficeintly . Other than that I don't know what else to tell you, When they certify engines for flight they literaly take fire hoses and measure how much water an engine can ingest and still make power. All a pilot may do is turn on the ignitors which normaly are off.

Best answer may come from an airline pilot. But here again by common sense and prudent practice pilots don't go around looking for trouble in the form of severe storms.

Answer 3

I think it is due to difficulty of mounting a high bypass turbofan cantilever on the side of a fuselage compared to hanging under a wing. Noise and vibration? Yes the back of a 727 is loud compared to a modern A320, but what about a compared to a contemporary aircraft like the 737-200 with its nozzle sticking out the back of the wing next to the aft passengers? Much louder than the 727. And the front of the cabin is so quiet you have to check instruments to make sure the engines are running (even with a gutted cargo interior). Weight and balance better? Then why could they stretch the DC-9/MD-80/MD-90 to more than twice its original length and stretch it more forward than aft? You can't do that with a conventional plane. The 727 will sit on its tail only if there is no fuel in the center tank and no load. I worked on cargo 727s and there was no special way of loading it. Catastrophic engine failure easier to manage? Well, in a airplane with wing mounted engines I guess there is no mistaking which engine failed. In the 727, you have an indicator on the dash that tells you an engine has failed because otherwise you don't know. There is no dangerous yaw like aircraft with wing mounted engines have and less drag since you don't have to use rudder and bank to correct the yaw. All jet engines have fuse pins (including United 232, it was a maintenance error that caused the engine to separate) and a rear engine departing the aircraft would cause no damage to the lift surfaces. Easier maintenance access? Okay I'll give you that one, but everything on the 727 was just a scissor lift away from access. Assymetrical thrust more efficient than the rudder? First off, you don't use the rudder on a jet in normal flight, the spoilers take care of adverse yaw. Second, on the ground, you use the tiller wheel, not differential thrust like little bug smasher. Plumbing? Who cares. Modern jets with triple and quadruple redundant hydraulic systems have much more plumbing than the 727 with redundant manual reversion flight controls. Deep stalls were an early problem with the BAC 111 and Trident, but after modifications these aircraft and every other T tail aircraft have never had problems with deep stalls. Oh yeah, the Challenger 600 prototype had a deep stall as well, but the basic design has obviously been a major success. All business jets have rear mounted engines. I still think it is just the problem of mounting a large engine on the side of the aircraft, but it was far easier to do on the MD-90 than the 737.

Answer 4

A really good bunch of answers, but no one has mentioned that in high bypass turbofan engines like are used today 60- 80 percent of what goes in does not go through the engine. It is bypassed by the same ratio as the air that enters. Actually the particle separators may by pass even more. Pure jets, which are few and far between on passenger craft today are more likely to flame out due to the fact that everything that goes in the intake comes out the exhaust.

Answer 5

Most of the people here response are correct being that it won't hurt it, and actually help cleans the turbine and compressor blades. On our Pratt & Whitney PT6 we have an optional water spray directly above the intake to increase power and/or to clean the compressor blades which can get really dirty in low flying conditions or dusty conditions. In pistion type engine the older types used a water and menthonal solution to boost the horsepower output. So flying thru a severe thunderstorm or rainstorm poses no threat. The only reason the aircraft trys to avoid them is because of the static electricty build-up (think lightning) which will damage critical electronic sytems.

Answer 6

Bostonian and Citation X have the best answers. However there is a limit to the amount of water which an engine can ingest before it loses its efficiency. As an airline pilot, I have flown through very tremendous amounts of tropical rain storms and have experienced no adverse affects. However I am sure there is a limit.

Answer 7

Up to a certain amount the water evaporates as it is compressed and heats up, so it actually cools the engine, this allows a bit more fuel to be burned, if the engine controller allows, and that gives you a bit more power.

Answer 8

Despite all the confidence shown above, when the rain turned to hail in New Hope, GA in 1977, both engines of a DC-9 flamed out. Details at
http://www.ntsb.gov/ntsb/brief.asp?ev_id=55832&key=0

Answer 9

Your common sense suggestion is a correct one. Jet engine performance is adversely affected by droplets in the engine intake ducts, and also by the ingestion of the much larger droplets encountered in extremely heavy, tropical style rain storms. The latter have a major effect in the descent-idle (minimizes fuel while descending at enroute airspeed...like coasting downhill in a car) and in some extreme cases can cause a flame-out.

Answer 10

It does not harm the engine,when running tests on Donald Campbells Bluebird engine we threw buckets of water into the the engine it had no effect on performance.