Wilcharl From United States of America, joined Jun 2000, 1170 posts, RR: 3
Reply 2, posted (14 years 4 months 6 days 2 hours ago) and read 4068 times:
i know the early 747's had them but does anyone have a photo of a water injected take off on a -100 also anyone know how many gallons were dumped in or the specifics of the JT-9D water injection system? Were these inoped on the a/c equiped with it? where were the tanks? were they serviced similar to potable water?
TimT From United States of America, joined Jun 2001, 168 posts, RR: 0
Reply 3, posted (14 years 4 months 6 days ago) and read 4056 times:
Every JT9 I've seen has an adjustment point for the water injection on the fuel control. All deactivated and the adjuster sealed with RTV. 747-200, DC-10-40. Engine models JT9-7,-7A,-7AH thru -7Q and -20 and -20J. The 747-200's TWA had still had the water lines in place, but the tanks were deactivated. No idea of capacity.
LZ-TLT From Germany, joined Apr 2001, 431 posts, RR: 0
Reply 5, posted (14 years 4 months 4 days 4 hours ago) and read 4005 times:
Bio15, I'll try to give it a go:
On piston engines, water injection was used since the mid 30's(actually, it started with aviation engines and was then accomodated to the high-tuned dragster and competition car engines). With a piston engine, water injection has several effects:
- increasing: the pressure in the cylinder (water damps add their partial pressure to the whole, so without increasing the compression ratio, you get a higher-compressed combustible fuel/air mix)
- cooling effect: Water is injected in liquid condition and evaporate in the cylinder. Since the evaporation is an endergonic process(consumes external energy), it "consumes" part of the heat in the cylinder.
However, running a water-injected recip engine on low/middle rpm's didn't pay off - you have to spray just a small amount of water(or else you'll end up with water condensing in the cylinder) and the benefits are fairly marginal. It pays off only on high-rpm regimes(ie dragsters and other racing cars). As a matter of fact, many of the WWII fighters were equipped with the so-called "emergency combat power unit" which was a water-injection system. The Mustang in particular has this feature.
I'm not that common with jet engines, but I imagine, water injection could help to produce a higher combustion pressure as well, as long as cooling the combustion chamber at the same time. What my sources say, I must agree with JETPILOT - the early 747's had water-injected engines.
Remember the PanAm 747 which struck the approach lights taking off from SFO - this one apparently had water injection and had used it during its ill-fated takeoff to get the extra power needed.
TomH From United States of America, joined May 1999, 960 posts, RR: 2
Reply 6, posted (14 years 4 months 3 days 4 hours ago) and read 3981 times:
Thanks for the info, guys, you were correct. I finally got time to look at some print references and indeed, early 747s had it. I would imagine the reliability of the available power from the JT9Ds led to permanent deactivation of the system after a short time in service-but I'm guessing here.
Real nice explanation. I know with piston types it was usually a combination of distilled water (for purity) and alcohol. Many piston engines used this system to boost power, and it was found on a high percentage of combat types by war's end. Into the postwar years airliners had it (Martin 2-0-2 and, I think the Convair 240, as well as others). Most second-generation American jet engines such as the JT3 series featured optional water injection.
I'm surprised to find it was used in conjunction with the early turbofans. I thought they replaced water injected engines immediately because of greater available power, but apparently it was felt there was a need for both systems, at least for a time. Thanks for the help.
Prebennorholm From Denmark, joined Mar 2000, 6881 posts, RR: 54
Reply 8, posted (14 years 4 months 2 days 8 hours ago) and read 3960 times:
If my rusty memory doesn't fool me, then many years ago I read in some magazine that a vintage generation B-52 bomber with straight J-57 turbojets (D og G model?) used roughly 1500 gallons water for a take-off. It was all gone in less than two minutes, so they hardly got the gear up before the water tanks were dry. But it did allow a considerably higher fuel load to be lifted off a given runway, especially on hot days of course.
Can somebody confirm or correct that? There must be a lot of people out there with first hand experience on for instance KC-135A.
Best regards, Preben Norholm
Always keep your number of landings equal to your number of take-offs