Shortround6
Major General
We may have three problems here.
1. The single stage supercharger just doesn't work that well over 20,000ft now matter how many gears or what gear ratio you use or drive it with. The late model Allisons used higher pressure ratios at take off than the early versions (mainly becaue they could use improved fuels), the -73 vesion in P-40K ran at 51in of boost for take off and 1325hp and 60in of boost at war emergency for 1550hp at sea level for pressure ratios of 1.7 and 2.0 respectfully. going to even 20,000 feet at those power levels means you need pressure ratios from your supercharger of either 3.4 or 4.0. The higher the pressure ratio the more power it needs to drive it AT ALL altitudes and throttle settings. Two stage superchargers can give the same pressure ratios with less power input and less heating of the intake charge. Or even more boost for the same drive HP.
2. Increasing compression gets more work or power from the same amount of fuel. Great for cruising or for engines without superchargers. An engine running at 60in of MP is putting 20% more fuel and air through the engine per minute than an engine running at 50in of MP. so 20% more gross power, deduct the extra power needed to run the supercharger at that level and you have your net or propellor HP. ANYTHING that gets in the way of getting the MAXIMIUM amount of fuel and air through the engine per minute is going to hurt PEAK power. AN 8 to 1 compresion ratio would seriously limit the ability to use high manifold pressure. Allison themselves dropped the Compresion ratio of the later two stage engines.
3. Can the P-40 ever be made competitive with the Me 109? the basic weight of most P-40s (the E through Ms) is about 6900-7000lbs? That is no guns, fuel, ammo, pilot etc. vrs the normal loaded weight of the 109 at just about the same 6900-7000lbs. Loaded the P-40 is going to go about 1500lbs more. even allowing the P-40 a bit less becasue of it's larger full tanks that is a lot of extra weight to try to compesate for. even Calling the 109 at 6900lbs and the P-40 at 8000lb for combat weight you are going to need 1677hp at altitude to equel the power to weight ratio of the 109G. Yes the P-40 may have some advantages but it was never going to have the straight line speed and climb of the 109. unless it had an egine with much,much more power.
If you can get a copy I would strongly suggest "Vee's For Victory!" by Daniel Whitney. See if yoiu can get it from a library if nothing else.
I used the early Allison and Merlin engines as an illistration of effects of different setups because at the time there was little difference in the performance of the superchargers on the two engines. Later superchargers with much differnt pressure ratio capabilities and efficiencies would tend to cloud the results.
1. The single stage supercharger just doesn't work that well over 20,000ft now matter how many gears or what gear ratio you use or drive it with. The late model Allisons used higher pressure ratios at take off than the early versions (mainly becaue they could use improved fuels), the -73 vesion in P-40K ran at 51in of boost for take off and 1325hp and 60in of boost at war emergency for 1550hp at sea level for pressure ratios of 1.7 and 2.0 respectfully. going to even 20,000 feet at those power levels means you need pressure ratios from your supercharger of either 3.4 or 4.0. The higher the pressure ratio the more power it needs to drive it AT ALL altitudes and throttle settings. Two stage superchargers can give the same pressure ratios with less power input and less heating of the intake charge. Or even more boost for the same drive HP.
2. Increasing compression gets more work or power from the same amount of fuel. Great for cruising or for engines without superchargers. An engine running at 60in of MP is putting 20% more fuel and air through the engine per minute than an engine running at 50in of MP. so 20% more gross power, deduct the extra power needed to run the supercharger at that level and you have your net or propellor HP. ANYTHING that gets in the way of getting the MAXIMIUM amount of fuel and air through the engine per minute is going to hurt PEAK power. AN 8 to 1 compresion ratio would seriously limit the ability to use high manifold pressure. Allison themselves dropped the Compresion ratio of the later two stage engines.
3. Can the P-40 ever be made competitive with the Me 109? the basic weight of most P-40s (the E through Ms) is about 6900-7000lbs? That is no guns, fuel, ammo, pilot etc. vrs the normal loaded weight of the 109 at just about the same 6900-7000lbs. Loaded the P-40 is going to go about 1500lbs more. even allowing the P-40 a bit less becasue of it's larger full tanks that is a lot of extra weight to try to compesate for. even Calling the 109 at 6900lbs and the P-40 at 8000lb for combat weight you are going to need 1677hp at altitude to equel the power to weight ratio of the 109G. Yes the P-40 may have some advantages but it was never going to have the straight line speed and climb of the 109. unless it had an egine with much,much more power.
If you can get a copy I would strongly suggest "Vee's For Victory!" by Daniel Whitney. See if yoiu can get it from a library if nothing else.
I used the early Allison and Merlin engines as an illistration of effects of different setups because at the time there was little difference in the performance of the superchargers on the two engines. Later superchargers with much differnt pressure ratio capabilities and efficiencies would tend to cloud the results.