P51 service ceiling

[GScholz]

Are you using auto-climb? If so, are you changing the climb speed during the climb? The default is the best climb speed only at sea-level.

[J_A_B]

I don't know about the OP, but when I tested it myself I flew the airplane manually and used manual trim control to achieve best results.  You have no choice but to do it that way--the automatic settings don't work right up that high and will give you a best altitude of about 37K.  Note that I did this a little over a year ago.  If there's been some major revision of the Aces High P-51D flight model since then my knowledge would be out of date, but I know of no such revision.

Manifold pressures observed during climbs:

20k.......67
21k.......67
22k.......67
23k.......67
24k.......64
25k.......62
26k.......58.7
27k.......56
28k.......53.2
29k.......51
30k.......49
31k.......47
32k.......45.2
33k.......43
34k.......41
35k.......39.5
36k.......37.5
37k.......36
38k.......34
39k.......33

Here are altitudes I was able to achieve at various weights:

75% fuel, 6 guns, full ammo (combat load): 38,600
75% fuel, 6 guns, no ammo: 39,100
50% fuel, 4 guns, no ammo: 39,250

I did these tests offline and in the final test was very low on fuel by the time I reached 35K-plus.

I did speed tests as well, but seem to have deleted that file.  My recollection is that speeds were generally in order, though perhaps a hair (5-7 MPH or so) optimistic for a P-51 running at only 67'' MAP.

J_A_B

[GScholz]

How do they compare with the real-life tests over at wwiiaircraftperformance.org ?

[J_A_B]

Neat site, it compiles a great deal of research into one place--thanks for showing it to me.

As I noted in my first post, flight tests at military weights for V-1650-7 powered Mustangs indicate a ceiling in the vicinity of 41K.  A climb rate of about 1500-1600 FPM could be maintained at 30K versus the ~1100 achieved in AH.  In general the Aces High P-51D's performance falls off at altitude more quickly than that of the flight tested airplanes.

Using the site you linked as a reference, V-1650-7 engined mustangs are shown in a couple different flight tests as maintaining around 54-55 inches MAP at 30,000 versus the 49'' my own test in-game maintained at the same level.  This largely correlates to the difference in rate of climb between the modeled plane and the flight tests.

The Aces High performance, as I noted, closely correlates to an estimate North American drew up around the end of the war which is also posted on that site you mentioned.  This estimate was not directly based on flight tests.

I made no tests in the mid-altitude (~15K) "dead zone" range for this airplane.  I tested level speeds, but no longer have the file I made.

J_A_B

[GScholz]

If I'm not mistaken, the tested aircraft were B-models.; could that be the cause? Although I admit the difference in manifold pressure seems very large.

[J_A_B]

Good hypothesis, so I checked it.  On the site you posted the flight tests include both -B and -D models with the 1650-7 engine.  Climb performance for the two types appears essentially equivalent as would be expected.

Also note that the AH performance chart on the AH wiki agrees with my own testing so I don't believe I flubbed my in-game tests of the performance we have.

Upon reflection the manifold pressure difference can likely (almost certainly, actually) be attributed to ram effect.  It might be possible to push the manifold pressure in the Aces high P-51D over 50 inches at 30K by getting it fast enough.  Therefore this does not correlate to observed variations in climb rate after all.

The site you linked me has much more detailed info than my own personal sources.  I've been going through it all evening.  One flight test of a P-51D shows a climbing speed manifold pressure of 46.4 at 30K alt, but the plane still climbing at 1700 FPM.  Another involving P-51B's also show MAP in the upper 40's at that elevation but also show a climbrate of ~1600 FPM.  Therefore the number on the Aces High manifold pressure dial is probably about right for that speed.

What I can't wrap my head around is the sustained climb rate and ceiling discrepancy.  In all flight tests the -7 engined planes (be it a B or a D) plot something in the vicinity of ~1600 FPM at 30K and could stagger up to around 41K.  Mostly they plot about ~600 feet per minute or so at the 38-39K range where the AH P-51D doesn't even want to climb anymore with a military load.

On the other hand there's still that NAA-estimated report that puts the P-51D right as it performs in AH.  If you believe that report, then AH is spot on.

For my part in several years of on-and-off researching and testing I never have been able to come to a conclusion that I find entirely satisfactory which is why I never posted on this subject myself.


J_A_B

[GScholz]

I guess they use the NAA-estimated report then.

[drgondog]

Remember that if take off is a military load you probably will draw down at least 80-90 gallons getting to ceiling for the 1650-7 which was spec'd at 41900

[Brooke]

In 8th AF scenarios, lots of P-51 fights are above 30k (and up to 34k).



Here, bombers are at 25k.

[Chalenge]

Upon reflection the manifold pressure difference can likely (almost certainly, actually) be attributed to ram effect.  It might be possible to push the manifold pressure in the Aces high P-51D over 50 inches at 30K by getting it fast enough.  Therefore this does not correlate to observed variations in climb rate after all.

The only problem with this idea (if it did anything) is the airspeed required would be so high it would fool the supercharger into thinking it was at low altitude and your power would disappear instead of increase. Fortunately the airspeed required is well beyond the capabilities of the P-51.

I think you missed where I pointed out the B-model in AH does not have the same engine as the D. At least, according to the performance charts it cannot.

[J_A_B]

I'm well aware that the Aces High P-51B is an early production variant with the V-1650-3 powerplant.  I'm not sure why you think I missed that or what real relevance it has anyhow; the core of the discussion relates to the Mustangs equipped with the V-1650-7 engine.  If Ram effect cannot make up the manifold pressure difference I noticed then that wouldn't affect the bottom line anyway:  Bottom line is that at high altitudes the Aces High P-51D climbs more slowly than any flight-tested Mustang with the same engine and doesn't reach the same maximum altitudes.  Performance only correlates to a pen-and-paper estimate drawn up by NAA of suspect accuracy.

Were the Aces High P-51D changed to better reflect flight test data, the game's P-51B (unchanged) would still have a superior high altitude climb rate as well as a higher ceiling.

My ongoing interest is academic only since I haven't played this game online since before you even registered on the forum.

J_A_B

[Chalenge]

If Ram effect cannot make up the manifold pressure difference I noticed then that wouldn't affect the bottom line anyway

This is exactly why I thought you did not know the difference, because ram effect will not make the difference at that altitude. How long you have been posting here and absent from the game makes no difference.

Now that I know you are a troll only. Ignored.