Assisted power take offs

[MJR]

Excuse the lose subject phrase. I remember from ATPL studies that some aircraft have the option to inject water or a more volatile fluid into the engine intake for extra air flow density during take off. I was wondering how often this was carried out and on which aircraft.

cheers

MJR

[approved]

If I remember HS748's and some Metro aircraft have water/methyl injection. It's use is determind by WAT charts etc. (weight/altitude & temp.)

On the Metro II (SA226 TC) it is called CAWI) Continuous Alcohol-Water Injection and is used during takeoff to recover power lost at high-density altitudes. THe mixture used is 40% methyl alcohol and 60% distilled or demineralized water.

Some more basic operation is that the Engine RPM must be above 90%, pwr lever must be approx. 1/8 inch forward (to close the switch) and the water injection swithc must be placed in CONT.

when the above conditions are met the pilot will notice an immediate torque increase of 30-35% and illumination of the AWI PUMP ON lights. AWI fluid is now flowing to the spray manifold at the top of each engine inlet. When the pressure in the maifold reaches a specific value a pressure switch closes and sends a signal to the SRL computer. AWI flow continues until the AWI switch is turned off, the AWI fluid runs out, or the engine RPM decreases below 90%. If one engine fails, it's AWI flow stops when RPM decreases below 90%. Flow continues for the operating engine.

the storage tank holds approx. 16 gals but only 14 is usable.

hope this helps

[Basil]

Military Argosy (RR Dart engines) approach to El Adem one afternoon - couple of little misunderstandings led to being above water-meth cut-in RPM when Flt Eng switched pumps on in landing checklist.. .Quite dramatic moment as VP props tried to cope with sudden but initially unstable injection of additional push-juice! <img src="eek.gif" border="0">

[Captain104]

When I joined our 747 fleet in the mid-seventies, our big birds used water injection. F/E's nursed. .Pratt&Wittney engines with demineralized water.

We had to use that on airports like NBO (high and hot) with MAX TOW. Had 4 green "water flow lights" above other engine instruments, if I remember correctly. They had to light green until 80 knots. If one failed= takeoff aborted. After having past 80 kts, continue. Only problem was, 3 pair of eyes watched fascinated those funny lights, bit irritating. No grey-haired F/E there around, who can assist me?. .BAC 1-11 used also water, if lucky. Once, a german charter BAC (Panavia?) tried a forced landing on the Autobahn (expressway) right after T.O. in HAM. A ground mechanic in Ham had mixed up 2 containers, one filled with demineralized water, the other with some kind of fuel. That's what I ment with "if lucky". Engines overheated, burnt, failed and the crashlanding on the Autobahn ended under a bridge. Some pax and crew survived. . .By the way:RH seat occupied by a lady-pilot, who killed herself and other passengers some years later on an executive jet during VFR-approach in IMC condition east of HAM. We call it destiny? <img src="frown.gif" border="0">

[ 09 February 2002: Message edited by: Captain104 ]</p>

[polzin]

Worked for Wein Air Alaska years ago flying B-737-200's. If we left the APU running during take-off and climb, it could increase the weight 300 lbs. Now that is a real JATO !!!!!

Flew a very old B707 that had water injection. It lasted one minute fifty seconds from start of takeoff till the water ran out. The 11,200 lb. dry engines then put out a whopping 13,500 lbs wet. N735T

[ 01 February 2002: Message edited by: polzin ]</p>