War Emergency Power and Japanese aircraft engines

[windswords]

Did Japanese aircraft, especially fighters, use the equivalent of War Emergency Power (WEP) in combat?

I am familiar with the test reports from ATAIU. And I know that Japanese engines were rated at Military Power (MP).

So, does that mean, because of lower octane fuel or other reasons, that Japanese pilots did not push their aircraft in combat above MP to WEP?
Then there is the fact that some fighters had water/meth injection or similar - that would seem to indicate WEP capability or does it?

There is a lot of discussion on other forums about what the true max speed is especially for fighters and the use of computer programs to calculate top speed, but under WEP.

Also: exactly what is the definition of WEP?
I thought it was some type of "over boost" that the one could use for a limited amount of time before it would damage the engine, and sometimes aided by some type of injection. Whereas Military Power is just the full throttle that will not cause any (significant at least) damage to the engine. If that is not the proper understanding, please let me know.

 

[Laurelix]

Did Japanese aircraft, especially fighters, use the equivalent of War Emergency Power (WEP) in combat?

I am familiar with the test reports from ATAIU. And I know that Japanese engines were rated at Military Power (MP).

So, does that mean, because of lower octane fuel or other reasons, that Japanese pilots did not push their aircraft in combat above MP to WEP?
Then there is the fact that some fighters had water/meth injection or similar - that would seem to indicate WEP capability or does it?

There is a lot of discussion on other forums about what the true max speed is especially for fighters and the use of computer programs to calculate top speed, but under WEP.

Also: exactly what is the definition of WEP?
I thought it was some type of "over boost" that the one could use for a limited amount of time before it would damage the engine, and sometimes aided by some type of injection. Whereas Military Power is just the full throttle that will not cause any (significant at least) damage to the engine. If that is not the proper understanding, please let me know.

They did use WEP in form of water/methanol boost but they never state top speed at WEP power but at military power.

For Example Ki-100-I's Ha-112-II horsepower output was sea level was 1270hp and with water methanol boost the engine had 1500 horsepower.

 

[tomo pauk]

The term 'military power' was strictly American, ie. not used by other countries unless they were buying US military-grade engines (and even then that term was not used in all instances).
WEP is again strictly American term.

With that said, there was several Japanese engines that were using water-alcohol mixture in order for overboosting to be allowed.

Also: exactly what is the definition of WEP?
I thought it was some type of "over boost" that the one could use for a limited amount of time before it would damage the engine, and sometimes aided by some type of injection. Whereas Military Power is just the full throttle that will not cause any (significant at least) damage to the engine. If that is not the proper understanding, please let me know.

There was not a single definition for the WEP. For example, there was the 'dry WEP', or 'WER dry', where engine is overboosted just by uing the properties of the hi-oct fuel. 'WER wet' meant that ADI (anti-detonant injection) was used to overboost an engine. Some engines used only one or another type (V-1650-1 or -3 or -5, or mid-war V-1710s used 'dry', R-2800 and R-1820 used 'wet'), while some engines used both (like V-1650-9 or late V-1710s). Most of the time, war emergency power was the max power that specific engine was capable for during the 7hr30min bench test run.

Military power also changed definition and duration during the war, eg. 1st V-1710s used term 'emergency maximum' for what later became 'military power'. 'MP' was, at least some times, a max power that engine was capable for a 100 hr bench test run. Military power was erstwile a 5min rating, later a 15 min rating.

 

[Ivan1GFP]

Did Japanese aircraft, especially fighters, use the equivalent of War Emergency Power (WEP) in combat?

Hello Windswords,

The answer gets a little complicated here and kind of depends on the particular engine. Some engines were a lot more tolerant of "overboosting" than others were. The Nakajima Sakae and its Army equivalents was apparently very tolerant.

The Japanese had a fairly low octane rating for their standard fuel: 91 to 92 octane. They compensated on some engines by using Water-Methanol injection for anything above cruise power settings, so use of Anti Detonant does not necessarily mean "War Emergency Power" for Japanese engines.

As an example here are some settings for the early Nakajima Homare / Ha-45 engine:
1850 HP @ 2900 RPM +400 mmHg Boost Sea Level Take-Off
1680 HP @ 2900 RPM +250 mmHg Boost 2300m Rated Power – Low Blower
1500 HP @ 2900 RPM +250 mmHg Boost 6500m Rated Power – High Blower
1520 HP @ 2700 RPM +200 mmHg Boost 2300m Maximum Cruise – Low Blower
1370 HP @ 2700 RPM +200 mmHg Boost 6300m Maximum Cruise – High Blower
1300 HP @ 2600 RPM +100 mmHg Boost 3000m Economy Cruise – Low Blower
1180 HP @ 2600 RPM +100 mmHg Boost 6900m Economy Cruise – High Blower

A couple things are worth noting here:
Anti detonant injection started at +180 mm boost which is below even the maximum cruise rating.
There is no listing for Emergency power other than for Take-Off.
An evaluation of a later series of engine suggested that sea level Take-Off boost pressures could be maintained up to 17,600 feet, so the higher boost pressures certainly were available even if they were not listed in the manual.

- Ivan.