[Graham Boak]

Thanks, but I think we can still differ on the term "significant".

Can we place some numbers into this discussion? Turning to "Putnam's Hawker Aircraft since 1920" - purely for convenience, I'm sure other sources will do - we find the Typhoon quoted at an empty weight of 8,840lb, and a loaded weight of 13,250lb with 2x1000lb bombs. So for the Typhoons chasing Fw 190 Jabos we have a maximum weight, full fuel, of around 11,000lb. The fuel capacity of the aircraft is 140 gallons (actually quoted for the Tornado, so if anyone knowns different?) which will give a fuel weight of some 1120lb, using the specific gravity of kerosene not gasolene, but near enough I think.

So the total fuel weight is close to 10% of the total aircraft weight. Given that no aircraft will continue fighting without reserves and fuel to get home, nor without expending fuel to reach the combat area, we have a realistic weight range of about 5% of the total aircraft weight. (Obviously slightly more for a P-51 that has just dropped its tanks)

The induced drag, the only part affected by weight, is some 15% of the total drag at maximum speed, sea level - and that may be slightly generous. You'll have to trust me on that, but given a set of aircraft characteristics you can calculate it, and it won't be far off. So we have a range of 5% of 15%, or a total of 0.75% of drag due to the variation in combat fuel weights. The speed change is proportional to the square root of the difference in drag - so we are looking at perhaps half a percent of speed - less than 2 mph top.

This is less than the effect of a poor coat of paint, or that snazzy non-standard rear-view mirror, or a badly-fitting engine cowling. Certainly less than aircraft-to-aircraft (or engine-to-engine) variation.

I know that every little helps, especially for a low-fuel Fw 190 running for home with a fuller Typhoon behind it, but I don't think that's significant.