Referring to Lusche’s latest WEP chart (

http://bbs.hitechcreations.com/smf/index.php/topic,386482.0.html) - based on HiTech’s previous data (

http://bbs.hitechcreations.com/smf/index.php/topic,383002.msg5097338.html#msg5097338). I noticed an inconsistency which I suspect must an error in the ‘total time’ of WEP. There is a pretty obvious inconsistency with some of the other aircraft. Well, three to be specific.

The Ki-84's WEP was achieved in real life through water / methanol injection. Many of the German V12s used a very similar system. Let’s just call that MW for convenience (I know the exact constitution varied subtly but it's not relevant).

A quick comparison then of MW tank capacities and total AH WEP durations from three examples:

Bf109K-4 - 43 minute total WEP time. MW-50 tank capacity - 118 litres (31.2 US liquid Gallons).

Fw190D-9 - 43 minute total WEP time. MW-50 tank capacity - 115 litre capacity (30.37 US liquid Gallons).

The American Technical Intelligence report (T-2 Report on Frank-1 (KI-84), T-2, Serial MO. 302, Interim Report NO. 3 (Project NO. NAD 25 - Release Date November 1946) Page 3 - 'factual data' states the water and methanol tank of the Ki-84 had the capacity of 42.2 gal. Which is 159.74 litres. Total WEP time in AH: 10 minutes.

To recap:

Bf109K-4 - 43 minute total WEP on 118 litres (31.2 US liquid Gallons) of MW.

Fw190D-9 - 43 minute total WEP on 115 litres (30.37 US liquid Gallons) of MW.

Ki-84 - 10 minute total WEP on 160 litres (42.4 US liquid Gallons) of MW.

The displacements of the engines are comparable:-

Daimler-Benz DB 605 - 35.7 litres.

Jumo 213E - 35 litres.

Nakajima Homare 21 - 35.8 litres.

All three engines used direct fuel injection. The German engines are 12 cylinder while the Nakajima an 18. Additionally the Nakajima 2-valve head, German V-12s 4 valve heads. All were supercharged. The Nakajima was air / oil-cooled, German ones liquid-cooled. The Ki-84 is heavier than the 109 due to a heftier structural construction, slightly larger size and the hydraulic system - don’t know about the 190s.

Even conceding some drop in efficiency to allow for the above factors the Nakajima has 36% and 39% more supply of WEP juice than the Fw190 and Bf109 respectively. Yet the new total WEP scheduling suggests the following relative rates:-

43 minutes x 60 = 2580 seconds of WEP total for the Bf109K-4 - That’s

**2.7 litres per minute** consumption of MW alone (fuel & air aside).

10 minutes x 60 = 600 seconds of WEP total for the Ki-84 - That’s

**16.0 litres per minute** of MW alone (fuel & air aside).

I can’t give actual WEP consumption rates because that information is lost but making inferences from the K-4 seems sound given how similar in execution it was and how well documented the German engineering was / is. Intuitively, just considering cylinder displacement, revolutions, power cycles and fuel mixtures from other engines it looks likely the Homare couldn’t possibly consume

**petrol** (avgas) at that rate, let along

**petrol PLUS the MW**. At the consumption rate AH now models that is 4 (US) gallons per minute, of liquid additive alone!

I am aware there is a lot of rumbling in the AH jungle about the WEP modelling of many aircraft. I don’t know enough detail about other types to comment. Obviously a balance has to be struck for aircraft in which pilots were instructed to only go to a point for so long to preserve engines and some throttles had breakable wires etc. In AH we’d likely be there all the time. If however you are going to model the consumption of a finite medium, then surely it cannot be done with any semblance of realism without carefully considering the capacities and consumption rates.

I hope this post therefore makes a convincing argument that the total WEP time for the Ki-84 ought to be corrected to somewhere considerably closer to the K-4 end of the spectrum.