billswagger
Airman 1st Class
- 256
- Mar 12, 2009
With supercharger gear ratio used in the engines on the "N" aircraft a WER rating of 1410hp was available at 9,500ft (without ram?) which gives the aircraft it's speed of 378mph at 10,000 or 10,500ft? but as the plane climbs above that hight the supercharger looses the ability to supply the extra air and power falls until there is only 1125hp available at 15,500ft. It is at 15,000ft that the "N"s were rated at 343-348mph. This is about 15mph slower than an "E" at the same hight and "E" had even less power at 15,000ft. It's engine maxed out at 11,700ft at 1150hp and lost power above that hight. (it was good for 1490 hp down at 4,900ft though).
Comparisons are also hard to nail down because sources often quote figures where aircraft are tested on different days, giving different ratings and different speeds.
I found a direct comparison of the P-40E to N, putting the N 1000lbs less with the same load (save 30 gal fuel and 6x20lb bombs) as the E.
It noted that the P-40E was made of aluminum alloy, while the N was made of alclad. It had some parts removed such as a pair of 50 cals, but what i found interesting is that the N had an armor protected cooling system, something not found on the E.
They also used different engines but the rated height of the E was considered 15,500 while the rated height of the N was 17,300.
This put rated top speeds of the E at 338, and the N at 364mph at their rated heights.
It is one of the more detailed comparisons that put the N considerably ahead of the E in both speed and climb at rated power.
WER, still becomes a mystery but you can look at engine charts to see the available horsepower at their respective heights and RPMs.
The Allison could shell out 1700+ horses at 3200rpm under 3500ft.
GE also found their Allison F3R (P-40E) and F4R engine could muster as much as 1700 hp at considerably higher altitudes.
My guess would be that the Allison performed generally the same from block to block, but variants differed to accommodate supercharging and reduction gearing as well as propeller types.
The reason WER info is not available to the same extent as other aircraft may have something to do with the lack of any ADI or Water injection system.
Pilot accounts mention running above rated manifold pressure (obviously under FTH) but only pushing the throttle until knocking was heard, and in some cases no knocking occured at all. Pilots reporting 55-60".
I only add to the tangent after reviewing more P-40 data.
This article shares more differences between the variants, and probably uses the same base article I'm referring to as a reference
http://www.adf-serials.com/research/Part2-P40.pdf
Bill