Bf-109 vs Spitfire vs Fw-190 vs P-51

[drgondog]

Originally Posted by Strawn

Got it. I can see the difficulty with the need to map over the entire velocity/altitude scale. Am I correct in assuming that boost figures are only necessary when the HP required includes it (i.e., to simplify absurdly, you don't push the RED GO FAST button at 50% throttle)?

Yes - there is a big difference between a 1650-7 at 75" and a 1650-3 at 61" in Bhp. and the 7 was geared differently to achieve max performance at lower altitudes.

[Strawn]

Okaaaaay. Almost sounds like an impossible task, considering the need for HP performance graphs not withstanding the propellor efficiency or 'power-transmission efficiency' (i.e., eta) issues. (As you can see, I am new enough to this field that I have to create phrases to describe some of the concepts, in contrast to using the appropriate terms.)

Which parameters are you 'accepting' estimates for in this modelling?

[drgondog]

Originally Posted by Strawn

Okaaaaay. Almost sounds like an impossible task, considering the need for HP performance graphs not withstanding the propellor efficiency or 'power-transmission efficiency' (i.e., eta) issues. (As you can see, I am new enough to this field that I have to create phrases to describe some of the concepts, in contrast to using the appropriate terms.)

Which parameters are you 'accepting' estimates for in this modelling?

Soren outlined most of the documented parameters (i.e Aspect Ratio, wing/tip efficiency, Wing Area, CLmax, etc) for each of the ships he wants to compare.

The weights, engine boost, actual manufacturer Hp as function of altitude and Flight test speeds for these parameters are next step.

We can probably agree to ignore compressibility effects on Propeller/engine system at speeds >.5 M and just pick a value - say ".82".

From my own perspective I'm ambivalent about normalized KTAS and density variances as we are theoretically going to pick values from Flight Tests - most of which make corrections for standard Temp and Pressure - as those factors go away once we agree on common altitudes from Flight Test plots.

I am hung up in this 'theoretical' exercise simply because a,) Propeller efficiencies are an arcane analysis, and b.) the math behind turn performance is in fact integral calculus.. it is modelling the rate of change over time for the Free Body Force diagram as the fighter changes relative angle of attack to increase the lift to compensate for the bank angle Lift vector required to offset weight (for level flight assumption) -until it can't fly level anymore.

In reality the a/c slows down in the process, so the entire Induced Drag, Parasite Drag calculations, in real world, are also an integration process, because velocity also changes with time...

A friend has developed a nice model that enables plug ins for one weight, AR, Hp and max V for that HP to get the Velocity to G plot of interest but it is good only for that Hp/Vel state and as such is not comparable across all altitudes/Hp/Velocity states. He assumes a THP/SHP ratio of .8 (IIRC)

All of these ships had different strike zones for best performance..

I did this as an exercise in school once, but it was a jet engine and simpler to do.

Candidly I have better things to do than set up a sophisticated model and am toying with Crumpp's spreadsheet to see what I have to do - assuming we get all the plots we need for Hp/Boost/Speed/Altitude relationships - to then plug in altitude related variables..

[Soren]

Bill,

No'one is setting a deadline here, so don't stress over it. Now I might be wrong but I assume you will start your vacation soon, so perhaps then you could look more into this. That is my plan, as soon as I get my 2½ weeks of vacation I will go more into details about this subject.

[drgondog]

Originally Posted by Soren

Bill,

No'one is setting a deadline here, so don't stress over it. Now I might be wrong but I assume you will start your vacation soon, so perhaps then you could look more into this. That is my plan, as soon as I get my 2½ weeks of vacation I will go more into details about this subject.

Soren - there is no stress.

I am actually going to dig into a footlocker I haven't touched in 35 years that may have my MS Thesis and some of the analytics dealing with this discussion. I had about three pages of equations and assumptions when I was doing my Preliminary Design paper on the jet fighter - which I used to program (in Fortran II) on a IBM 1620.

(I doubt anyone on this board remembers programming on 80 column punch cards)

In the final approach I (you/both) could modify Gene's spreadsheet to accomodate the variable list above - it would always serve well as good 'guestimate'.

The bigger issue is gathering the Flight Test/Powerplant data and putting it all in the Tech section that Paul put together - so that we have a common library and source.

[JugBR]

i want to talk about the Bf 109. i have watched that show "dogfights"(here in BR is called "combates aéreos") from history channel. there was that episode about the legend of an airbase in belgium i gess so, there was a scene of a bf 109 being pursued by mustangs and the german guy making the most extreme maneuvers to escape.

of course later he was shot down. history channel wouldnt show a battle when germans wins, its always about the american victories. but considering this, i believe we should figure how manoeuvrable was the Bf 109 and how skilled was the germans.

[Soren]

The Bf-109 turns and climbs a lot better than the P-51 Mustang in reality, however the Mustang rolls faster, esp. at high speed. The Mustang is also generally faster at all alts (Except against the late war 109's which either matched or superceded it in speed at low to medium alt), but esp. at high alt where only the K-4 could fly faster, and this is where the bombers were. The P-51 enjoyed a very nice performance advantage at 25+kft over most 109's.

In short the P-51 was almost ideal for the escort role because of its performance at bomber height.