Squirrel, did you miss this paragraph?

Squirrel,
You are right, I didn't include a punchline!

Thepower increase is only when the aircraft is up against engine power limits (of course) and also only when the engine is temperature limited. It is quite possible to get 5 to 10% pure power boost with injection, which means for a few pounds of gear (water tank and sprayer) you can get 10% mre gross weight, and maybe 20% more payload.

Thanks for the reply Nick - so if WMI is a panacea for power boosting, why isn't it utilised more in helis ?

Because it involves carrying water that might not be used - at 10lbs weight per imperial gallon.

I've often thought that certain heavy lifting helis could use the water/alcohol windscreen washer fluid as required to:

A) Boost engine power for certain flight regimes / tasks.

B) Carry out a self compressor wash, to save the balls-ache of having the engineers come out at the end of the day to do it for us.

Or, C) If all else fails, wash the windscreens.

Just to add to what Nick said...

The main benefit of water injection is to cool the air/fuel charge entering the engine, whether piston or turbine. Water injection is normally only used where air is compressed before the air/fuel charge is burned, as in a piston engine with a turbo or supercharger, or a gas turbine.

By cooling the air charge, destructive detonation (caused by high fuel temp) can be delayed in the boosted piston engine, and a destructive TOT can be lowered in the turbine engine. The main benefit for both engine types, is that a larger air/fuel charge can be feed into the engine and burned without causing damage, while the water injected cooling is taking place. The burning of this larger air/fuel charge (made possible by the water injection cooling) is where the extra power comes from.

The tank was really only good for around three takeoffs, and because the tank was pressurised by bleed air (while the system was armed), it was inconvenient and sometimes dangerous to open the tank to top it up during a hot refuel if you were doing repetitive tasks like fire bucketing.

And if you forgot to disarm the system after takeoff, the continual pressure in the tank could bleed the contents overboard, so you had nothing left when you needed it.

Ahhhh.... but remember that sweet smell when you stood downwind of an alcoholically-assisted takeoff. Better than being downwind of me after a night on the turps.:ugh:

Nick:
Thanks for clarifying that for me. It has been > than 20 years since I studied piston engines. One of my aviation regrets is that I never got to operate a BIG Round engine like the Wright 3350 Turbo Compound with Water/Meth or one of the BIG Pratts. My biggest piston is a Turbo Charged Continental 520.

I do now it is all about temperature in the Allison 250 Engines though. Flying the Straight L with water /meth was fun and it made a significant difference in performance. I often thought that it would have been a neat mod on the S76A.

http://www.pilotfriend.com/aircraft%...evelopment.htm

We have used water injection on airplanes used for crop dusting. We use a 28 gallon tank mounted to the firewall and fill with distilled water. It is good for most of the day (30-40 takeoffs). We don't mix anything with the water and can expect a 50 to 70 degree drop in EGT which is a considerable increase in horsepower. The water increases the air density as if the day was much cooler. According to Honeywell, the engine can handle a little over 100 gallons of water per hour and not flame out. Sure is a kick in the pants for the few seconds it takes to get in the air.

Barryb

L performance charts
 

Water alcohol never delivered same relative performance boost for turbines as pistons.
The main claim to fame for turbine rotorcraft was to allow basic L model to take-off at MGW (4000 pounds) above Sea Level.
The WA system was only certified up to 10K PA, and after that really did not give any performance gain anyway.
Standard engine was barely able to TO at MGW on hot day temp limit at Sea Level.
Water Alcohol raises TO limit to 3000 PA for same temp.
At higher PA the difference in performance is usually about 100 to 125 pounds more payload.
I seem to remember the WA kit weight was about 25-30 pounds plus weight of water mix?

http://tinypic.com/2anpqq

http://tinypic.com/2anpsy