AcesHigh Fighter comparison Models

[drgondog]

http://gonzoville.com/ahcharts/index.php

I just looked these over and have a major question to pose.

Why is the performance of the P-51B below the D in both climb and turn? 

The dominant engine for Both versions from April 1943 through the end of the War was the Packard Merlin 1650-7 with zero difference in either blower ratios, reduction ratios or fuel type...

all the Packard Merlin 1650-3 high altitude engines were effectively replaced by late May, 1944 for all the P-51B-5 through -15's, all the entering P-51D-5's were equipped with 1650 from the production lines and remained unchanged with regard to fuel type, engine rating.  By this I mean when 44-1 fuel came to ETO in June, every B/C/D/K used it so there was zero difference in the fuel.  Most of the P-51D-1's and -5's were WW or sent to FG's transitioning from P-47/P-38's by July, 1944.

Summary
The P-51B/C Basic Weight was 7580 pounds, The D/K was 7760 for a minimum difference of 180 pounds (lighter for B?C) primarily because 4x .50 vs 6x.50 guns

Mission weight for full internal fuel and ammo was: Add 2262 for B/C and 2418 for the D/K for a delta difference of 156 pounds in favor of B due to lighter ammo load.

Net - B/C 336 pounds lighter for every similar load out, same powerplant, same airframe and wing, but somehow the D out performs the B??
Why does anybody believe these numbers or the comparisons?

[colmbo]

The wing is slightly different.  The D wing is thicker and has the leading edge wedge next to the fuselage.

[SmokinLoon]

I'll bet it is because the B had more paint than the D.  Wahdya bet? 

There are other factors than what you listed that are beyond us mortals.  Do not lose any sleep over the issue.   

[drgondog]

Colmbo - the difference aerodynamically speaking closely approaches zero - if anything the slightly reduced surface area of the B is to the advantage of the B.  The ONLY difference in the wing is the slighlty elongated root chord of the D to accomodate the new wheel well/wheel door modification by giving that inboard section a more pronounced 'strake angle' from WS 17.5 to WS 61.5 on the D.

Having said that, there is no difference between the A and the K in area, incidence, twist, thickness ratio, span, dihedral, taper ratio, mean chord length, washout, camber, area, aspect ratio, MAC, airfoil section incidence at the root.  Only the H (of production models) had changes to the above data.

Having said all of this relative to physical data - the models to not account for ANY of the above (nor should they) and focus on CLmax (of power on level flight stall), Weight, Aspect Ratio, and HP (at the recorded altitude and speed) to develop Drag - and even with that I wonder if in the case of Merlin P-51s whether the modellers consider the compressibility effects for high altitude/high speed? (Ditto for Me 109K and Spit XVI, etc) - last - does anybody know if exhaust thrust is applied as it ranges from ~ 11-14% 'depending'.

[drgondog]

I'll bet it is because the B had more paint than the D.  Wahdya bet? 

I would bet A LOT.  It would only make a small difference if you compared ALL the P-51B-1 and -5's delivered in camo prior to March 1944 to ALL the P-51D's delivered after May, 1944 - or you assumed that ALL P-51B's were Brit MKIII's and in that case you pull the fuselage tank, fuel and plumbing out of the calcs.

There are other factors than what you listed that are beyond us mortals.  Do not lose any sleep over the issue.   

I seriously doubt it. but that is a natural extension of my question.

What other factors other than Thrust, Drag, Lift, Gross Weight, Wing Area, Aspect Ration, Oswald Efficiency are bagged into the calcs to give the P-51D superior performance with same aeordynamics, same engine, same fuel, but greater weight - mission for mission.

Since most of the destruction by the 8th by the 8th AF of the LW occurred after March, 1944 (in aggragate), and the P-51B started ops attached to 8th AF and the P-51B's arrived in theatre with NMF in March 1944, and all the D's arrived were NMF, in theatre starting  May, 1944 - with only the 357FG maintaining a % of camo on both the B and D... why would you model the B with an extra increment (~70 pounds) - and if you did, the performance calcs relatively speaking still favor a camo P-51B-5 through the -15 over the P-51D for ALL performnce cals.

[FLS]

If you look at the Aces High charts you'll see that the speed and climb rates vary with altitude and which aircraft is faster depends on the altitude. This suggests they were modeled with different engines.

IIRC the P-51B has a better turn rate.

[Lusche]

I want to add that the values shown on that comparison website had been determined by manually testing the planes. Particularly the difference in turning radius without flaps is so small that it's easily within the range of the small (less than 1.5%), but inevitable human operator error. (To determine turning radius the virtual test pilot has to fly a very precise circle at a certain speed & altitude.)

[Krusty]

We JUST had this thread, too. A casual search might turn it up a couple of pages down. It was that recent.

Different engine gearings. That's the answer. Our P-51s do NOT have the same engine.

Lusche: While the turn radius and the acceleration are tested in-game, the climb and speed charts are apparently direct dumps from HTC's charts. Those can also be misleading, based on illogical loaded weights, etc. According to those the 190F8 and the A8 are 100% identical in speed and climb, because they loaded the F8 to the same weight (rather, they just used the existing charts and logically inferred at the same weight they would be the same).

So the lower parts are based on testing, but the speed/climb are not. I learned that the hard way recently. Wanted to share in case anybody else had the same thought.

[drgondog]

If you look at the Aces High charts you'll see that the speed and climb rates vary with altitude and which aircraft is faster depends on the altitude. This suggests they were modeled with different engines.

IIRC the P-51B has a better turn rate.

IMHO the delta of 9 fpm at SL is grossly understating the turn performance as does the inferior climb performance.  It is equivalent to letting one choose between only the Me 109G-2 and the Me 109G-6, deleting the -14 and K-4.  The P-51B at same weight and fuel load out with a 1650-7 engine is a better combat choice as far as manueverability than the P-51D in every respect at every altitude.

The displayed Climb rates at MP were 3000 and 3200fpm SL respectively (D>B) and 3200 and 3450fpm (D>B) at WEP so clearly the AH model uses the 1650-3 at WEP for 61.5" boost at 3000 rpm - a huge difference from the 1650-7 engine that 90% of all P-51B's used in combat, and nearly 100% after March 1944.  This is exactly what you noted.
 Additionally, for the same altitudes where the HP differences are evident, the climb and (to a small degree, with CLmax more important - and the same- the turn) rates will also display significant differences as HP available to HP required will be to the advantage of one over the other in those regions

ALL P-51B's in 8th and 9th AF were retrofitted with the 85 gallon internal tank by end of March 1944 and the 1650-7 by the end of April.  So, if AH models the P-51B-1 and early -5 with the performance of the 61.5" boost WEP for the 1650-3 - it virtually ignores the majority of the P-51B which fought in WWII.

[drgondog]

We JUST had this thread, too. A casual search might turn it up a couple of pages down. It was that recent.

Krusty - I saw it and it caused me to go looking...

Different engine gearings. That's the answer. Our P-51s do NOT have the same engine.

Not quite so simple.  The P-51H had the -9 which had the same gear ratios and blower ratios as the -3 but a completely improved Carb and WI - with 25%+ more HP than the 1650-3 (and it was beefed up to withstand 90" boost).  If you meant reduction gear ratios they were the same (.479) across all -3, -7 and -9 Packard Merlins so there was no difference in Prop RPM

Lusche: While the turn radius and the acceleration are tested in-game, the climb and speed charts are apparently direct dumps from HTC's charts. Those can also be misleading, based on illogical loaded weights, etc. According to those the 190F8 and the A8 are 100% identical in speed and climb, because they loaded the F8 to the same weight (rather, they just used the existing charts and logically inferred at the same weight they would be the same).

So the lower parts are based on testing, but the speed/climb are not. I learned that the hard way recently. Wanted to share in case anybody else had the same thought.

I am definitely not complaining - I don't play the game - but for those that play the game and want to fly the same P-51B that scored the most credits over the LW, you need to get the P-51B's with the 1650-7 engine and operate with same HP, better climb, better acceleration, better turn and sacrice some firepower.

[FLS]

On the other hand we have a P-51B that you can fly in the mid war arena.

[drgondog]

On the other hand we have a P-51B that you can fly in the mid war arena.

I suppose -  but four months of the war (Dec 1943 through Mar 1944) is not much of a 'mid war' period is it?

in that period in which the P-51B was flying combat with only the -3 Packard Merlin, only the 354th (four months) 4th (1 month), the 355th (2/3 month), the 357th ( 1 1/2 months), 363rd (1 1/2 months) of sorties were flown with the 352nd and 339th coming with strictly the -7 in April/early May.  That is effectively 8 months of sorties with one Mustang Group compared to ~  14 Gp-sortie months for just the 8th AF (including temp assignment of 354FG) Mustang Groups between early April through May for all exclusive P-51B operations, with only the 1650-7.   

When you factor the Mustangs deployed to MTO starting in April/May 1944 wahich were also all P-51B until July and realize that as late as Dec 1944 that 8th was still flying with P-51B comprising 20% of 8th FC.

[FLS]

I don't believe the mid war arena is based on a 4 month period to match the early P-51B. There are other considerations. We have an early war arena, a mid war arena, and a split late war arena. If we had the late war P-51B we wouldn't have a P-51 in the mid war arena. Eventually we may see more P-51 variants but it's not a pressing need at this time. Our current P-51B does well enough in the late war arena as it is.

[drgondog]

The principal opponents for the 1650-3 version P-51B-1 and -5 were the Fw 190A-7 and the Me 109G-5 and G-6

Conversely for the 1650-7 engined P-51B-5/7 and -10 and -15 (and all the P-51C's) fought the Fw 190A-7 and A-8 and D-9 plus the Me 109G-6 and G-6AS and G-10 and G-14 and K-4.

So which of the LW fighters are with the P-51B-1 and -5 (w/o fuselage tanks) in the 'middle period"

[Slade]

http://gonzoville.com/ahcharts/index.php

Gonzo's charts page is the bomb.  Sure wish it could be updated with the newer planes.   

I'd be willing to donate to his site to see that happen.  How 'bout you?