There are several factors at work here, but the basics are related to drag, propeller efficiency, and top speed.
The two big types of drag are induced drag and parasitic drag. Induced drag decreases with speed, and parasitic drag increases with speed. Also related is propeller efficiency, which decreases with speed. At some speed the combination of parasitic drag and decreased prop efficiency stops a plane from going any faster.
Now lets apply that. I am in my trusty Jug, and I just dove after a 190A8. We are both diving to above our top level speed. He slams it to the deck, and begins deccelerating to his max level speed. At the same time, I begin a very gentle climb, at just under my max level speed. After a while we will both be at our max level speeds, but I have several K of altitude I have gained, and in addition my TAS is probably slightly higher due to altitude. I can then begin a gentle dive to increase my speed above my max level speed, and begin gaining on the bogey.
As you can see, at a 3k higher altitude, my TAS will be as much as 15 Mph faster than it would be at sea level. That is fairly significant and accounts for some of the difference right there. The TA152 is similar:
The rest is simply the difference between one plane slowly gaining energy in a very gentle climb, and the other staying static at it's top speed. Of course, we are also assuming all the other possible factors such as fuel load, WEP state, and that sort of thing which were equal. Starting energy states also play a big role here.
This is really the opposite case to the one BadBoy is talking about. In this case we are talking about planes diving above their max level speed, while Badboy is discussing planes accelerating to that speed. Based on the graphs I've looked at in Shaw's Fighter Combat, there is possible a sweet spot with prop fighters where induced drag may decrease faster than prop efficiency and before parasitic drag starts to ramp up. We'll see.
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Sean "Lephturn" Conrad - Aces High Chief Trainer
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