Hi guys...good answers all!
Here's how I would sum up the three charts. First this...in RL, there was a minimum difference below which we considered the data to be irrelevant...meaning, that while the differences can be measured, how those differences played out in actual flight was considered negligible.
This is somewhat true of the zero Ps curves in these diagrams. At sea level, the differences are minimal...are more so at 15M', and become important at 30M'.
I've rounded off liberally when I did my numbers...if you get values that are slightly different, no big deal!
1. Energy vs angles. We begin by remembering that this categorization is always in relation to another plane. There is no such thing as a plane that is always one or the other.
Overall, the Spit has a higher zero Ps curve and relatively about as fast as the 109. Only at S.L. and above 310KTAS does the 109 have an overall speed and Ps advantage, and there the value is too small to be significant.
This leads me to consider the Spit a better angles fighter based upon this data. But that does not mean then that the 109 is the energy fighter. The 109 does not possess better energy (better zero Ps or max speeds) overall...so it becomes a lesser angles fighter. In this matchup, the Spit is simply the more maneuverable fighter.
2. Corner velocities. We know the definition....smallest radius and highest turn rate...it's where the chart peaks...the intersection of the stall line and the max G line. CV is different for each altitude. For the Spit, it varies from 210KTAS at S.L. to 360KTAS at 30M'. The 109 numbers are 230KTAS (S.L.) and 375KTAS (30M').
Please note that these are true airspeeds...not the airspeed that you see on the instrument panel (indicated airspeed).
Zero Ps speeds. Since the zero Ps line extends from the stall line out to the right, there is no such thing as "one" speed. We have to pick a variable such as G and then read the zero Ps speed that is associated with that value. You may choose to look at where the zero Ps line intersects the stall line and use that as a point of reference. If so, you determine that the Spit can fly slower and at a higher turn rate for a given G.
3. Energy bleed. One quick way to look at energy bleed is to look at the slope of the stall line. The more vertical the line, the greater the bleed in terms of change in turn rate and radius. A "flatter" stall line means a slower reduction in rate and radius.
In these charts, the slopes are pretty much equal...the two planes tend to lose energy at similar rates. Note...this does not say anything about specific performance...only that the two rates of energy decay are approximately equal.
4. "Stall Fighting". This one is pretty obvious. The Spit owns a significant area to the left of the 109 stall line at all altitudes. Using any point along the 109 stall line as a reference, the Spit can then fly at that speed and obtain a smaller radius and higher rate...or. and more importantly, it can fly at the same rate and get a smaller radius...this means it can fly INSIDE the 109 turn...and get a lead angle gun solution.
5. Climb performance. The Spit zero Ps curve is "higher" than the 109's. While the difference may not be great, this means that the Spit has excess energy to burn anywhere along the zero Ps line...this can be converted into a climb...if only for a short time. This is a "maneuvering" concept only...and does not necessarily mean one plane has an overall better climb rate.
6. Overall advantage? Goes to the Spit. Why? Overall better positive energy numbers. Go to the 109 zero Ps line where it meets the stall line. Now project that point upwards to the Spit stall line. That vertical difference can be measured and works out to be around 25-30% (rough overall averages of turn rate and radius values). This % gives a good idea of the overall pitch authority superiority that the Spit enjoys over the 109, according to these charts. The same technique can be used to measure the vertical difference between the 109 and the Spit zero Ps lines at a given speed. The overall results will be a smaller % but will still be in the Spit's favor. This technique gives a "snapshot' look at relative energy values.
Which leads me to the most important point. These findings are not "tactics"...they are only relative comparisons of energy performance. They MAY be used to inform the pilot of areas of superior performance, BUT they should not be used as a ruler for the conception and implementation of tactics.
In the final analysis, the pilot puts the plane where it needs to be to kill the bandit...anything else is rubbish. Some German guy said that a long time ago...and it's still true today. Another guy from USN TOPGUN also said something like "no pilot ever won a fight with a Ps chart"...or something like that!!
Read the charts with an educated eye...but fly to win, not to match up to a diagram!
Andy
