WWII question

mike_baram · 2 December 1998, 06:37 AM

Why I dredge up these arcane subjects from the depths of my memory is beyond me, but here goes....
I remember reading in WWII aviation novels ("A Yank in the RAF", etc.) that in order to escape a pursuing ME-109, the pilot would inject water into the cylinders of his engine.
Possible? Impossible? Pure fabrication?
If it's real, what's the principle involved?
(Cripes! The things I lose sleep over!)
Mike

Billy_Bishop · 2 December 1998, 07:24 AM

Water injection was indeed one of the ways to boost power. I don't know the details but it was used by the DB601-605 in the Bf-109 fighters.

Barrett · 2 December 1998, 07:48 AM

A water-methanol solution was available in mid- to late-war fighters to cool engine temps for short periods (c. 5 minutes) at high manifold pressure/high rpm. However, even safe use of same could result in engine damage and some squadrons had a policy prohibiting use of water injection offensively--only to get out of Deep Serious.
The Spit/109 situation in the BoB didn't involve water injection but carburetion. Spit Mk II didn't have fuel injection like the 109E, and hence the Merlin tended to cut out when inverted or under negative G. The Daimlers had no such trouble and thus gained an advantage.

2 December 1998, 10:02 AM

The F4U Corsair also had such a system. The throttle had a copper wire that would allow the pilot to "Push through" the wire to go beyond the max throttle setting. There is one example of a F4U driver being pursued by two Zeros after an attack somewhere in the Solomon islands. Heading out to sea (the wrong direction from his base) the Zeros had swung out to both sides, so he couldn't turn left or right and were closing to gun range. The pilot was forced to use the water injection system provided for such an emergency.
What happened in the end? With the realization of his situation, legs shaking and panic starting to set in, he knew he must do something quick, as the miles to his base were increasing fast. The extra horsepower from the injection allowed him to pull away enough to throttle back and crank the Corsair through a turn. The zero pilot to the side he turned to was caught off gaurd and tried to turn with him, hooked a wing tip on the water and crashed. The other was far behind now and never caught up. When the pilot crawled from his plane exhausted, he noticed his sweat soaked flying suit had turned green, probably from the adrenalin.

Billy_Bishop · 2 December 1998, 10:14 AM

About mid-way to late in the war most aircraft had some sort of power boost system. Though even early war aircraft had what was known as a "war-emergency-power" setting. In a lot of aircraft this amounted to exceeding the recommended maximum sustained manifold pressure.

Generally this couldn't be done for very long or damage to the engine would ensue. The water-methanol system was one of the ways devised to enable WEP to be used longer without damaging the engine. On some aircraft (FW190) this only really helped it at high altitudes. On most others it would help at any height.

mike_baram · 2 December 1998, 10:47 AM

Kirchner,
You'd think that the Corsair, with a top speed of 417 mph would be able to outrun and outclimb the Zero, which had a speed of 330 mph, without resorting to emergency measures.
Mike

2 December 1998, 01:19 PM

Mike,
Does seem unlikely that a Corsair couldn't pull a Zero. I think I still have the book and can get more details and respond on Monday. Thanks for the input. - D.K.

2 December 1998, 03:28 PM

Ya,it's true,water injected-cooled engines

Barrett · 2 December 1998, 08:01 PM

Kirchner's example sounds like an event recorded by LT Ike Kepford of VF-17. It wasn't that an F4U couldn't outrun an A6M--it's that the angles were all wrong. I knew the skipper, Tom Blackburn, and engineering officer, Butch Davenport, for years. Both are deceased; both wonderful gents. Kepford was in fact headed away from base and the Zekes had the angle on him, hence his speed advantage of c. 25 knots at low level was no big help. He had to pull big G's in the turn but got away with it. Kepford also is long gone now.

2 December 1998, 08:27 PM

Mike, The "principal" of water-methonal injection was to boost engine manifold pressure in an emergency situation. It worked by super cooling induction air to the engine, and was introduced downstream of the pressure carb. In addition, a fuel derichment valve reduced fuel flow at a comparable volume so that the engine would coninue to run at a correct mixture. The whole system sort of worked as a poor man's supercharger.