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Legioneod

P-47 Flight Model Discussion

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image.thumb.png.eeb299a20995aa254493f93d82ff73b0.png

 

Interestingly the Brits found no limiting airspeed for the Thunderbolt. Even the Tempest is listed as 550.

 

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They didn't list it in that table, as with several others. Manuals give limiting speeds as low as 250mph indicated at 35+k feet. Basically it's 500 up to 10k and then -50 for every 5000 feet.

 

An early report says 520 indicated up to 10k, and NACA says they tested a configuration at 600mph true air speed in flight (that would roughly be 500 indicated at 10k).

 

They don't lose ailerons, though, they just get a nose down attitude, which makes dives hard to recover until you reach lower altitudes (and apply power). Mach drag raise starts at figures of about 0.7 already, so you can't really expect to exceed 0.8 by much. Which again is roughly 600 true at sea level, less as you go up. I've read about 0.78 in flight tests at the most, though reaching maximum Mach was not the point of these tests.

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Posted (edited)
4 hours ago, Talon_ said:

image.thumb.png.eeb299a20995aa254493f93d82ff73b0.png

 

Interestingly the Brits found no limiting airspeed for the Thunderbolt. Even the Tempest is listed as 550.

 

 

Interesting to note that the Brits had a higher limiting speed for the Thunderbolt than the Americans. 520 iirc vs 500 mph

 

2 hours ago, JtD said:

They didn't list it in that table, as with several others. Manuals give limiting speeds as low as 250mph indicated at 35+k feet. Basically it's 500 up to 10k and then -50 for every 5000 feet.

 

An early report says 520 indicated up to 10k, and NACA says they tested a configuration at 600mph true air speed in flight (that would roughly be 500 indicated at 10k).

 

They don't lose ailerons, though, they just get a nose down attitude, which makes dives hard to recover until you reach lower altitudes (and apply power). Mach drag raise starts at figures of about 0.7 already, so you can't really expect to exceed 0.8 by much. Which again is roughly 600 true at sea level, less as you go up. I've read about 0.78 in flight tests at the most, though reaching maximum Mach was not the point of these tests.

 

Exactly this. They don't lose surfaces in a dive irl. The limiting factor on P-47 dive limit was compressability and control in a dive. Structurally the P-47 could hit it's maximum mach (0.83) and be fine. I wouldn't expect to reach these speeds much though, the chances of surviving them are low due to compressability.

Edited by Legioneod

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46 minutes ago, Legioneod said:

Interesting to note that the Brits had a higher limiting speed for the Thunderbolt than the Americans. 520 iirc vs 500 mph

 

Could be the British had razor-backs and Americans tested the newer bubble-canopy models? Or they had different standards measuring this?

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The 520 is a US figure which the British used. It's not that every US manual says exactly the same.

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Posted (edited)
51 minutes ago, Ehret said:

 

Could be the British had razor-backs and Americans tested the newer bubble-canopy models? Or they had different standards measuring this?

Brits just had a higher allowed speed listed. Americans used a larger safety margin.

 

29 minutes ago, JtD said:

The 520 is a US figure which the British used. It's not that every US manual says exactly the same.

Nearly all American manuals list the safe dive limit of the P-47 as 500 mph IAS the only exception is later P-47s like the N with a safety limit of 560 mph IAS.

 

 

EDIT:

Was reading through some documents and it states synchronized guns weren't provided on the P-47 (at least that's the way I read it.)

Based on this I think synchronization should be removed for the P-47 and replaced with a more accurate ballistic model.

 

234144533_sunchroguns.PNG.49af238f5ebad7840862450d466494b4.PNG

Edited by Legioneod
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37 minutes ago, Legioneod said:

Was reading through some documents and it states synchronized guns weren't provided on the P-47 (at least that's the way I read it.)

Based on this I think synchronization should be removed for the P-47 and replaced with a more accurate ballistic model.

 

Some time ago I posted a video showing P-51D firing her guns on the ground where the free-firing was apparent.

There is no point of any synchronization for wing batteries of 0.50" caliber guns at all if the bullets don't pass through a propeller disc. Just none.

The only possible justification could be the game has an optimization of some kind which doesn't compute every round path individually but do the whole volley as something like a converging line. If that's the case then... well.

(it could explain few things but I hope that's not the case)

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10 minutes ago, Ehret said:

The only possible justification could be the game has an optimization of some kind which doesn't compute every round path individually but do the whole volley as something like a converging line. If that's the case then... well.

(it could explain few things but I hope that's not the case)

 

It's actually super simple - the game fires a gun when the gun switch is pushed. There's simply no delay simulated from gun to gun.

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5 minutes ago, Talon_ said:

It's actually super simple - the game fires a gun when the gun switch is pushed. There's simply no delay simulated from gun to gun.

 

Then where is the problem to implemented it..! The program must keep cycling rate variables already; just set them with some spread the way the left and right sides have the same cumulative rate. Shouldn't be too hard to do... actually should be very simple comparing to all other stuff (like 3d graphics) the game has to compute.

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Actually all guns have a delay. In case of WW2 guns, it's set to 1 ms ingame (it's 2 ms for the WW1 guns of FC). So it's easily possible to create a desynchronized behaviour by copying the guns and changing the delay for each gun. Then editing the plane files to use those different guns. Takes less than 5 minutes.

 

I suggested it a few years ago for the P-40.

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3 minutes ago, Matt said:

Actually all guns have a delay. In case of WW2 guns, it's set to 1 ms ingame (it's 2 ms for the WW1 guns of FC). So it's easily possible to create a desynchronized behaviour by copying the guns and changing the delay for each gun. Then editing the plane files to use those different guns. Takes less than 5 minutes.

 

I suggested it a few years ago for the P-40.

Need's to happen. Especially since the P-47 (or most American aircraft iirc) didn't have synchronized .50s.

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3 minutes ago, Legioneod said:

Need's to happen. Especially since the P-47 (or most American aircraft iirc) didn't have synchronized .50s.

 

All 3 US planes in the BOBP should have free-firing guns. I'm not completely certain about the Spitfire and the Tempest but I'd bet that they have free firing guns, too.

11 minutes ago, Matt said:

Actually all guns have a delay. In case of WW2 guns, it's set to 1 ms ingame (it's 2 ms for the WW1 guns of FC). So it's easily possible to create a desynchronized behaviour by copying the guns and changing the delay for each gun. Then editing the plane files to use those different guns. Takes less than 5 minutes.

 

I suggested it a few years ago for the P-40.

 

Well... that's both interesting and (very) bad to hear. :(

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Another way to unsychronize would be to give each (or each pair) of guns different rates of fire, after all the variability of the AN/M2 was 750-850 rpm

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1 minute ago, =362nd_FS=RoflSeal said:

Another way to unsychronize would be to give each (or each pair) of guns different rates of fire, after all the variability of the AN/M2 was 750-850 rpm

Could work and be an easier way to model desync.

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That would be just as easy. Same method really, because by changing the firing delay and without changing the rechamber time, the rate of fire would automatically change as a result. But then you would always have the same guns/pairs running out of ammo sooner/later than the rest. Not a big issue, but probably not necessary.

 

As for the maximum dive speed which has been mentioned above, since the official speed limit is around 600 mph TAS and taking into account that most (maybe all?) planes in BoX are modelled with a maximum dive speed above the official dive speed limit (some up to 100 kph  or more above official limit), there really shouldn't be anything falling off the P-47 in a dive.

 

I was happy to see that the Me 262 doesn't have any such thing as ailerons falling off when exceeding dive speed and i hope that kind of modelling gets carried over to the P-47 and other planes in the future.

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4 hours ago, Matt said:

That would be just as easy. Same method really, because by changing the firing delay and without changing the rechamber time, the rate of fire would automatically change as a result. But then you would always have the same guns/pairs running out of ammo sooner/later than the rest. Not a big issue, but probably not necessary.

 

As for the maximum dive speed which has been mentioned above, since the official speed limit is around 600 mph TAS and taking into account that most (maybe all?) planes in BoX are modelled with a maximum dive speed above the official dive speed limit (some up to 100 kph  or more above official limit), there really shouldn't be anything falling off the P-47 in a dive.

 

I was happy to see that the Me 262 doesn't have any such thing as ailerons falling off when exceeding dive speed and i hope that kind of modelling gets carried over to the P-47 and other planes in the future.

I wonder if they can make it cycle with each pull of the trigger? That way you wouldn't get the same exact rate of fire per pair each time, it would be more random. This way you don't have the same pairs running out of ammo earlier/later each time.

 

Another way they could do it is have the guns fire at the same time with the first pull of the trigger then have them desync as the trigger is held, this would happen within a few rounds being fired. It's not much different from the above method, a bit more realistic though I think.

 

As far as the dive limit I really hope it gets updated in the future for all aircraft. Not every aircraft should lose parts and not every aircraft should be able to dive to the max without losing parts, it'd should be a characteristic of each individual aircraft model.

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How much drag did the bubbletop cause? I've been doing some test to see the differences between the overall performance of the Razorbacks and the Bubbletops for the same weight/power.

I'm finding that the bubbletops are significantly slower than the razorbacks for a given weight/power settings.

 

 

Another thing I've noticed is that the water pressure gauge doesn't show any decrease in pressure when the water runs out, it stays in the "on" indicator with no loss of pressure. Once water runs out the gauge should drop in pressure and probably show the "off" indicator. I also didnt notice any loss in performance once the water runs out, the aircraft behaves as if it still has ADI which is incorrect.

 

Another thing is the turbo and the position of lever needed to turn it on. Based off the manuals it seems the turbo is activated as soon as you start to move it forward but in-game we have to move it 80-90% of the way forward in order to activate it.

 

 

One last thing. Why don't we have the Curtis Prop on the D-28? It was standard from the factory and all the performance figures are with the Curtis Electric Paddle Prop.

 

658564695_p-47prop.PNG.8cab06544b9b532b7ccd810b87a481d0.PNG

Edited by Legioneod

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21 hours ago, Legioneod said:

How much drag did the bubbletop cause? I've been doing some test to see the differences between the overall performance of the Razorbacks and the Bubbletops for the same weight/power.

I'm finding that the bubbletops are significantly slower than the razorbacks for a given weight/power settings.

 

 

Another thing I've noticed is that the water pressure gauge doesn't show any decrease in pressure when the water runs out, it stays in the "on" indicator with no loss of pressure. Once water runs out the gauge should drop in pressure and probably show the "off" indicator. I also didnt notice any loss in performance once the water runs out, the aircraft behaves as if it still has ADI which is incorrect.

 

Another thing is the turbo and the position of lever needed to turn it on. Based off the manuals it seems the turbo is activated as soon as you start to move it forward but in-game we have to move it 80-90% of the way forward in order to activate it.

 

 

One last thing. Why don't we have the Curtis Prop on the D-28? It was standard from the factory and all the performance figures are with the Curtis Electric Paddle Prop.

 

658564695_p-47prop.PNG.8cab06544b9b532b7ccd810b87a481d0.PNG

 

The turbo issue is that turbines generate the majority of their power band once they are past about 60-70% RPM. Before that, not much happens. 

 

On the ADI, what power setting are you testing it at? In the N manual it mentions that the flow rate is dependent on boost. When I tested it last year, I do recall it running dry, but I was using, I think 60" and 2550 RPM to get it to got for 15m+.

 

I'm actually wondering if we can get significantly longer boost times by running the Water at 54" 2700 RPM, but have not had time to test it. That at least would be a book power rating, if only for 100 octane. 

 

On the RS Johnson dive story, I believe Greg's Airplanes and Autos references some things from his autobiography, that it sounds like he and his crew chief had worked with one of the Republic engineers to get his P-47D-5 modified to do 72" boost on British 130 octane. Given that the R-2800 was later rated for that with, I believe, only adding bigger cooling fins, I find it plausible, and that may explain the reported dive performance. 

 

Also, 300 yards, even though we do stuff at that range all day, is a very long way off. Olympic Riflery is only a 50 yard sport, and many rifle ranges are only 100 yards deep. The target is really far off.

 

Looking at the gun convergence article on Wikipedia, not having done much additional research on it yet, it looks like the convergence range was often recommended to be a close as 100 yards of less, though apparently later in the war, convergence a stretched bacon out to the 300 yard range.

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1 hour ago, Voyager said:

 

The turbo issue is that turbines generate the majority of their power band once they are past about 60-70% RPM. Before that, not much happens. 

 

On the ADI, what power setting are you testing it at? In the N manual it mentions that the flow rate is dependent on boost. When I tested it last year, I do recall it running dry, but I was using, I think 60" and 2550 RPM to get it to got for 15m+.

 

I'm actually wondering if we can get significantly longer boost times by running the Water at 54" 2700 RPM, but have not had time to test it. That at least would be a book power rating, if only for 100 octane. 

 

On the RS Johnson dive story, I believe Greg's Airplanes and Autos references some things from his autobiography, that it sounds like he and his crew chief had worked with one of the Republic engineers to get his P-47D-5 modified to do 72" boost on British 130 octane. Given that the R-2800 was later rated for that with, I believe, only adding bigger cooling fins, I find it plausible, and that may explain the reported dive performance. 

 

Also, 300 yards, even though we do stuff at that range all day, is a very long way off. Olympic Riflery is only a 50 yard sport, and many rifle ranges are only 100 yards deep. The target is really far off.

 

Looking at the gun convergence article on Wikipedia, not having done much additional research on it yet, it looks like the convergence range was often recommended to be a close as 100 yards of less, though apparently later in the war, convergence a stretched bacon out to the 300 yard range.

 

I'll have to do more test to check water pressure gauge again. As far as using water below 64" imo it's useless and the added power from it is minimal. Only point in using water is to get 64"-70"(with 150 fuel) WEP,  thats all it was for,  running it below WEP rating is a waste of water imo.

 

As far as the turbo goes I was wondering why the turbo doesn't even turn on unless we push the lever 80-90% of the way forward, it doesn't even register on the rpm gauge unless nearly full forward, only exception to this is when throttle is full and turbo is used to control manifold.

 

In regards to Johnson I don't recall reading anything about a dive, I just remember him mentioning it was a great diver. The test I refereed to were from Herbert O. Fisher. He did over 100 dive test in the P-47 to test it's mach limits. My main gripe with P-47 dives is not with the overall performance in a dive which is ok I guess, but with the structural integrity in a dive. P-47 loses parts when it shouldn't.

 

Officially the P-47D was only rated for 70" with 150 fuel though I have read that Johnson and Gabreski both used 72" at one point before the official rating was released. P-47N and P-47M were rated at 72".

 

Convergence was around 300-400 yds on the P-47 as standard. Pilots may have adjusted it but I don't know. Also they aren't all converging at the same rang, theres different convergence range for the pairs of guns, depending on what pattern was set.

P-47_gun_harmonization_-_two_types.jpg

 

I'm still curious about the drag caused by the bubble canopy, I'm not getting anywhere near razorback speed when flying at the same rating and weight.

Edited by Legioneod

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@Legioneod So I've confirmed that the WI gauge is not working. You can test this by setting the RPM to 2550 rpm turning on the boost and setting the engine to 50" of manifold pressure. The engine will run for 30m+ so long as you control the thermals. 

 

That said, I believe the water draw *is* modelled. At about 15m into the test the engine thermals suddenly spiked and I had to go from 0% Cowl and 20% oil radiator to 100% oil radiator and 50%+ cowl flaps to keep the oils from going past 90c.

 

I also noted that I could also go into full 64" boost after this, but could only keep it going for about 3m before the oil temperature a completely ran away. 

 

The turbo is just behaving super wierd. Apparently you do need the waste gates at >50% closed before the turbo starts spinning, and closing the main throttle doesn't crash it. That's just not right. 

 

Interestingly, adjusting the intercooler seems to marginally impact the engine temperatures, but I was only doing that after I believe the water had run out, so might now be relevant. 

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11 hours ago, Voyager said:

@Legioneod So I've confirmed that the WI gauge is not working. You can test this by setting the RPM to 2550 rpm turning on the boost and setting the engine to 50" of manifold pressure. The engine will run for 30m+ so long as you control the thermals. 

 

That said, I believe the water draw *is* modelled. At about 15m into the test the engine thermals suddenly spiked and I had to go from 0% Cowl and 20% oil radiator to 100% oil radiator and 50%+ cowl flaps to keep the oils from going past 90c.

 

I also noted that I could also go into full 64" boost after this, but could only keep it going for about 3m before the oil temperature a completely ran away. 

 

The turbo is just behaving super wierd. Apparently you do need the waste gates at >50% closed before the turbo starts spinning, and closing the main throttle doesn't crash it. That's just not right. 

 

Interestingly, adjusting the intercooler seems to marginally impact the engine temperatures, but I was only doing that after I believe the water had run out, so might now be relevant. 

Thermals shouldn't have spiked when only running at 50" as water isn't needed to keep the engine cool when running anything below WEP power.

 

Turbo damming and pulsation isn't modeled in-game but I agree the turbo does seem to behave oddly.

Edited by Legioneod

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11 hours ago, Voyager said:

Interestingly, adjusting the intercooler seems to marginally impact the engine temperatures,

It doesn‘t do that. This is correct.

 

What it does, it allows you to cool the mixture temp to both get more power and prevent pre detonation (at the top MAP range) as well as keep a certain minimum temperature for lead not separating from fuel. (You have to close the intercooler once you see temps unduly low, depending on the situation).

 

The above is not modeled in the sim in its entirety, for the purpose of flying in the sim just keep temp near the orange and you get most power. In the least, don‘t let it go into the red part of the arc, there be less power.

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been away from il2, how is the modelling currently on the p47?  Its honestly the only reason i would fly il2 so any  fixs and or improvements on the level of sim...

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38 minutes ago, MercCrom175 said:

been away from il2, how is the modelling currently on the p47?  Its honestly the only reason i would fly il2 so any  fixs and or improvements on the level of sim...

I have a friend who had a P47 for real, apart from P51s and many other warbirds.

He tried it in VR in IL2 and said performance and handling was pretty realistic, he was impressed.

Although he didnt dive it at high speeds or turned it real slow with flaps because he did not do that in real life.

The cockpit and sounds are real nice in Il2.

 

With that being said, the damage model is fragile, engine is fragile, wings are fragile, so in that respect a disappointment.

Many topics about the P47 DM in the forums.

Edited by SCG_motoadve
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3 minutes ago, SCG_motoadve said:

I have a friend who had a P47 for real, apart from P51s and many other warbirds.

He tried it in VR in IL2 and said performance and handling was pretty realistic, he was impressed.

Although he didnt dive it at high speeds or turned it real slow with flaps because he did not do that in real life.

The cockpit and sounds are real nice in Il2.

 

With that being said, the damage model is fragile, engine is fragile, wings are fragile, so in that respect a disappointment.

Many topics about the P47 DM in the forums.

I have a friend who had a P47 for real, apart from P51s and many other warbirds.

He tried it in VR in IL2 and said performance and handling was pretty realistic, he was impressed.

Although he didnt dive it at high speeds or turned it real slow with flaps because he did not do that in real life.

The cockpit and sounds are real nice in Il2.

 

With that being said, the damage model is fragile, engine is fragile, wings are fragile, so in that respect a disappointment.

Many topics about the P47 DM in the forums.

Ya that was my initial thought aswell, as this game having a pretty good and or indepth ish damage model i expected to be limping the 47 home all beat up.  But having wings snap off is literally just like seriously?  Im sure its been said before but real ww2 pilot cases of ripping a wing off hitting a tower or a tree and still get home.  Now that Rhineland is out the urge to crush trains and convoys is at its highest but the Jug is way to fragile to participate and its a shame.

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Something that came up on the side - I checked the take off distance of the P-47. This was tested IRL on a Thunderbolt Mk.I at 14130lb weight. The P&W take off setting was 2700rpm and 51.5" boost. The prop used was a Hamilton 13" (which is good, because it offer decent low speed thrust, so real life results are not conservative).

 

Take off runs were tested mostly with a 30° flap setting. The report contains seven runs made by three different pilots. The lowest take off speeds are 90mph IAS and 93mph TAS. The shortest take off distance corrected to standard condition and zero runway slope was 425yards. Average were 95mph IAS, 99mph TAS, and 565yards.

 

In game tested on the Lapino Autumn map from QMB, the solo flight airfield, with 91% fuel, full throttle but no water injection, flaps to 70%. I average at 390 yards and can manage 320 yards. I need 440 yards to take off at 100mph IAS. Compared to the real life data I'm accelerating too fast, and can easily take off at a way too low speed (80 some being possible). I have to assume that on a computer I'm willing to take higher risks than the real life guys, and can take off at a lower speed, which explains my extremely short minimum take off run. But still, my average is easily safe, good enough for real life, and I'm way too fast after 440 yards.

 

This means that for certain low speed thrust is too high. Plus it indicates that with that flap setting, power on lift is somewhat high.

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34 minutes ago, JtD said:

This means that for certain low speed thrust is too high. Plus it indicates that with that flap setting, power on lift is somewhat high.

This is my feeling as well. Nice that you made those tests. Thrust on our current P-47 is such that it is not likely to pass "coffin corner" in an approach (once you get too slow, all power you have will not be sufficient to keep you from entering a stall) as you can yank your ride always out of a dire situation by going full power. It takes a lot to become a passenger, and this is quiet against any sensible advice for flyung a Jug that I've ever come across.

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3 hours ago, JtD said:

Something that came up on the side - I checked the take off distance of the P-47. This was tested IRL on a Thunderbolt Mk.I at 14130lb weight. The P&W take off setting was 2700rpm and 51.5" boost. The prop used was a Hamilton 13" (which is good, because it offer decent low speed thrust, so real life results are not conservative).

 

Take off runs were tested mostly with a 30° flap setting. The report contains seven runs made by three different pilots. The lowest take off speeds are 90mph IAS and 93mph TAS. The shortest take off distance corrected to standard condition and zero runway slope was 425yards. Average were 95mph IAS, 99mph TAS, and 565yards.

 

In game tested on the Lapino Autumn map from QMB, the solo flight airfield, with 91% fuel, full throttle but no water injection, flaps to 70%. I average at 390 yards and can manage 320 yards. I need 440 yards to take off at 100mph IAS. Compared to the real life data I'm accelerating too fast, and can easily take off at a way too low speed (80 some being possible). I have to assume that on a computer I'm willing to take higher risks than the real life guys, and can take off at a lower speed, which explains my extremely short minimum take off run. But still, my average is easily safe, good enough for real life, and I'm way too fast after 440 yards.

 

This means that for certain low speed thrust is too high. Plus it indicates that with that flap setting, power on lift is somewhat high.

Perhaps the excessive low-speed thrust is responsible for some of the flaps issues? i.e. the amount of power and airflow over the wings from just the engine increases lift and counters the drag from the flaps, enabling it to turn quickly without losing too much airspeed?

Also have you made any attempt to test takeoff distance with other aircraft? we see people managing to take off from historically too-short airfields in the Me-262 and I wonder if takeoff acceleration is just globally too fast in the flight model...

Also also how did you measure the takeoff distance? I'd like to try some tests myself if I can.

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I have to finally admit to myself that I would have been a really bad P-47 pilot. I am awful in the Jug in here....but I've been awful in it in every single sim I've flown that has had the airplane. The Spitfire, Mustang, Lightning, all work for me. I'm useless in the P-47. Well...I can drop bombs in it, but air to air combat in the P-47 Thunderbolt is something I can't seem to do.

But I'm trying not to feel too bad about it. It seems that I'm in good company. I was just reading Robert Dorr's "Air Combat: An Oral History," last night. 354th Fighter Group ace ,Glenn Eagleston, said that he , very much, disliked the P-47. It couldn't climb, couldn't turn. At least it could take punishment. But he thought that the P-51 was a greatly superior airplane. He thought that it was great that the P-47 could take so much damage...but he'd rather be flying an airplane that was so good that it didn't have to TAKE so much damage!

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19 hours ago, ZachariasX said:

This is my feeling as well. Nice that you made those tests. Thrust on our current P-47 is such that it is not likely to pass "coffin corner" in an approach (once you get too slow, all power you have will not be sufficient to keep you from entering a stall) as you can yank your ride always out of a dire situation by going full power. It takes a lot to become a passenger, and this is quiet against any sensible advice for flyung a Jug that I've ever come across.

 

In terms of thrust, at least in level flight, I don't think many WW2 fighters actually had a real "coffin corner". I think for most it was a matter of maintaining control. For instance, the Fw190A8 developed around 20000N of thrust, maximum. Which is roughly the induced drag you produce at 70km/h. You'll never get there and at realistic stalling speeds, you'll still have pretty much the same thrust, but only produce a fraction of the induced drag (and parasitic is not that high at low speeds).

 

I'm pretty sure you'd flip over and land cockpit first frequently if you were to suddenly apply full power at low speeds, though.

 

16 hours ago, RedKestrel said:

Perhaps the excessive low-speed thrust is responsible for some of the flaps issues? i.e. the amount of power and airflow over the wings from just the engine increases lift and counters the drag from the flaps, enabling it to turn quickly without losing too much airspeed?

 

It is part of my testing around the flaps down performance(s) in game. It was the best real life test I have on gauging low speed thrust on the P-47. And I think thrust and airflow are the main culprits.

 

16 hours ago, RedKestrel said:

Also have you made any attempt to test takeoff distance with other aircraft? we see people managing to take off from historically too-short airfields in the Me-262 and I wonder if takeoff acceleration is just globally too fast in the flight model...

Also also how did you measure the takeoff distance? I'd like to try some tests myself if I can.

 

I once tested the Fw190A, which was OK. I don't recall having tested and compared to real life data any other aircraft, mostly for lack of interest, but also for lack of sources to compare against.

 

I measured take off distance by counting the tiles on the runway, watching the track. It's easier if you make a mission in the Editor and place some objects near/on the runway that mark distances, so you don't need to count several dozen tiles but only a handful. Or not at all, if you put a marker every 10m, which I was too lazy for.

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On 11/13/2019 at 8:42 AM, JtD said:

Something that came up on the side - I checked the take off distance of the P-47. This was tested IRL on a Thunderbolt Mk.I at 14130lb weight. The P&W take off setting was 2700rpm and 51.5" boost. The prop used was a Hamilton 13" (which is good, because it offer decent low speed thrust, so real life results are not conservative).

 

Take off runs were tested mostly with a 30° flap setting. The report contains seven runs made by three different pilots. The lowest take off speeds are 90mph IAS and 93mph TAS. The shortest take off distance corrected to standard condition and zero runway slope was 425yards. Average were 95mph IAS, 99mph TAS, and 565yards.

 

In game tested on the Lapino Autumn map from QMB, the solo flight airfield, with 91% fuel, full throttle but no water injection, flaps to 70%. I average at 390 yards and can manage 320 yards. I need 440 yards to take off at 100mph IAS. Compared to the real life data I'm accelerating too fast, and can easily take off at a way too low speed (80 some being possible). I have to assume that on a computer I'm willing to take higher risks than the real life guys, and can take off at a lower speed, which explains my extremely short minimum take off run. But still, my average is easily safe, good enough for real life, and I'm way too fast after 440 yards.

 

This means that for certain low speed thrust is too high. Plus it indicates that with that flap setting, power on lift is somewhat high.


I shared your post with Gavrick and he wrote this reply:
 

Quote

Last winter, I already answered about the run and flaps, so I will translate and leave here:

About the take-off run.
So.
Yes, the plane is heavy. However, do not forget that he has a large wing area and very effective flaps, as well as a large screw. To begin with, we will check whether the take-off is related to the available sources. Takeoff data can be found in the flight manual:

5.jpg.c93f47e6087776686e2c7f1197af1ad4.j

We will take off with a boost of 52 inches, RPM 2700. Throttle - 95% (when the Throttle is completely forward given off at the ground, the boost is ~ 54 inches, this is a feature of the boost control unit at low altitudes on this aircraft). Flaps are retracted.

Check all three cases.
A weight of 14,200 pounds is 94% fuel load, in the simulator the takeoff run is 680 ... 750 m, according to the manual- 655 m.
Weight 16,000 pounds - this is a 100% fuel loading, additional ammunition and 2,500 pound bombs. In the simulator, the take-off run turns out to be 920 ... 1100 m, according to the manual- 1061 m.
The weight of 18,000 pounds is a 100% fuel load, and full loading with bombs, rockets and increased ammunition (it will turn out about 17970 pounds). In the simulator, the run turns out to be 1420 ... 1550 m, according to manual - 1524 m.
In general, the take off distance with manual converges very well.

Now let's move on to the flaps. Fowler flaps were installed on the P-47. This is one of the most effective types of wing mechanization among those that are found in our simulator. In one of the test reports you can see the following entry:
4.jpg.b95f4586942f8ffc16624f1e3d468d82.j
That is, Cl maximum, judging by the purges - at least 2.12. Technically, given the large wing area with a flap (about 65% of the wing area) and the type of flap, such a figure can really be obtained.
Now let's count a little. Take the weight of the aircraft 14,200 pounds, or approximately 6400 kg, as in the test above. The characteristic area is 27.87 m. With the flaps removed, the Cl at take-off angle of attack is approximately 0.92. With this Cl, the take-off speed can be estimated as approximately 228 km / h. Actually, the plane comes off at 210 km / h - the calculation does not include blowing the wing with a propeller.
Now let’s release the flaps. We have Cl ~ 1.9 and the estimated Vtakeoff = 159 km / h. The difference with the “clean wing” is almost 70 km / h, that is, you can expect the plane to come off at a speed of maximum 140 km / h. And again, this is an overestimated estimate, because with the flaps extended, the effect of blowing will be even more noticeable.
Check in the simulator.
With a weight of 14,200 pounds and with the flaps released, the takeoff speed is about 120 km / h, the takeoff run is 220 m. That is, the estimate we made above is fair.
In winter, and with an empty airplane, the take-off run will be even shorter.

And i summarize:

-At the “clean wing” the plane corresponds to the flight manual,
-Judging by available sources, the plane had a very high Cl with flaps released, and, in principle, technically this is quite possible and permissible,
- Due to this, the take off speed, and, consequently, the take-off length, significantly decrease, and the estimate of the take off speed by calculation correlates with the result in the simulator.
-I did these take off tests last winter. If something is going wrong now, and results of my tests above is wrong - let me know.


 

Edited by -=PHX=-SuperEtendard
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13 hours ago, -=PHX=-SuperEtendard said:

I shared your post with Gavrick and he wrote this reply

 

Thank you, also to Gavrick for his reply. I'm interested which report he found the 2.12 in. Can he tell us or should I bother him with a separate PM?

 

I find his numbers high, but not completely unbelievable and I agree that the take off run without flaps is pretty accurate. What I don't see is the jump to 120km/h power on being OK (I tested 110km/h). It might even be OK in terms of backwards airflow, but then it may not come without the related control problems, caused by the propwash spiralling around the aircraft.

 

NACA tested the stall speed flaps down power off 100mph, power on (not really controllable) somewhere near 85mph, about 15-20mph higher without flaps. Oddly enough, they exactly match the P-47 manual with 100mph and 115mph for flaps down and up. Gives 1.8 power off flaps down, 1.4 power off flaps up. To me, that's perfectly reasonable, given that the wing of the P-47 is not a perfectly shaped and smooth airfoil and that near 15% of the 300sq feet of the wing area are actually fuselage.

(Position error correction is not available for these speeds, but based on the take off trials, the IAS is a little on the low side, so if any correction is necessary, we'd have even lower cl's.)

 

Edited by JtD

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The 2.12 is from the lateral control test. It is taken from a 1/6 scale model wind tunnel test, flaps down, power on. It may not representative for the actual aircraft. However, using it with the P-47 as flight tested at 13210lb in the same configuration, leads to a stall speed of 90mph, which might be a little higher than what was achieved in the test (slightly below 90mph, wing only partially stalled). So the ~2.2 range for the power on stall is reasonable.

 

Now we only need to clarify why in game the aircraft still flies at 73mph under these conditions, with a cl of 3.2, and why it is possible to achieve a cl of 2.2 with engine idling (1.64 from wind tunnel test, ~1.8 from flight tests).

 

FWIW, looking at the 300sq feet wing, I'm getting about 100sq feet without flaps, 150 with flaps and 50 fuselage. If you look at airfoil data, you'll get clmax of about 1.7 no flaps, 2.8 with flaps. From that you'll have to subtract about 0.2 for practical things like imperfect surface, leaks or wing guns (or wheel wells when gear is down). So in theory you'd end up at about (100*1.5+150*2.6+50*0)/300 = 1.8. Which (surprisingly, given the crudeness of the approach) is exactly as flight tested.

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Maybe the P-47 is even more exceptional than the other BOX planes but I think the low speed performance is in general better than IRL in BOX and as has been pointed out above, it’s not totally clear if it’s a flap or thrust issue.

 

Speaking for the latter, the legacy Maddox Il-2 had an issue with prop efficiency at low speeds that was quite marked since you could fly much slower than best climb speed and climb just as well. This was tuned and got very much better but my gut feeling is that it is still a bit better than it should be. Also, I had a long discussion with a developer about the P-51’s prop efficiency in the DCS forum a few years ago and the early Me-109 K4 there could really hang on its prop before this was tuned. Moving back to BOX, I remember with fondness Monostripzebra’s slow speed videos (unfortunately removed from YouTube) showing Il-2’s helicoptering onto Stalingrad rooftops and P-40’s and I-16’s prophanging STOL-like takeoffs and landings, bouncing up and down on runways at crazy aoa’s etc.

 

So it seems it’s difficult to get the low speed handling and performance right in flight simulators in general and not just in BOX. OTOH this is hardly surprising: Considering theoretical aerodynamics and flight mechanics I would say that if you were to draw a diagram with modelling difficulty on the y-axes and speed on the x-axis you will get a so-called bathtub curve: High on the ends and lower in the middle. Why? Well on the high end you have compressibility effects: Subsonic drag rise, Mach tuck and buffeting etc. while on the low end you get larger and larger regions with major flow separation affecting both lift and drag and in addition, prop efficiency is very difficult to predict. Personally I have spent a lot of tuning effort on both ends of the “bathtub” in my C++ model and while I can afford the luxury of waiting while the numbers are being crunched this is for obvious reasons not an option in BOX where everything needs to be calculated within ms. So maybe there is a limit to what can be done here but without knowing any details about the exact nature of the BOX modelling I’m guessing these parts (high and low speed characteristics) have some sort of script overlay on the basic (I’m guessing panel based) FM. As an example, I would be very surprised if the FM models the Mach tuck effect by modelling a shock wave gradually developing in the inner wing section leading to a flow separation which in turn reduces the downwash on the stabilizer/elevator leading to a nose-down pitching moment. I would rather guess that it is some sort of rule overlay on the basic FM just as I’m assuming that the stick forces, control column shaking and aileron falling off due to flutter have all not been modelled in detail but are rather rule based meaning they can be tuned. I would guess that this also applies to the low end range of speed so that it should in theory be possible to tune the in-game prop/lift/flap efficiency somewhat. Of course it’s difficult to deliver solid proof that some of the slow speed antics we see today in-game are not also possible IRL but I have to admit that there are some video clips like those Monostripezebra posted that I find hard to accept as being possible to replicate IRL.

 

That being said I agree with YIPPEE that the most import thing is to get the relative speed, climb and turn rate between the planes right but here my impression is that BOX has made great strides lately so this does not stick out as a big issue anymore as far as I can tell. In addition, now that the AI are far better behaving and have been weaned of their propensity for prophanging with full flaps all the time I think the low end speed handling is of less importance but OTOH I sympathize with the MP players where I can only guess that whatever low speed “exploits” there are will be found and used so I’m all for a tuning of this and based on the input in this thread so far a guess on my part is that a reduction in slow speed propeller efficiency and maybe also the wing/flap lift & drag would be a step in the right direction.

Edited by Holtzauge
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Appreciate the detailed looks. Something generally is off and it should be addressed. While we probably will never have sim nirvana, constant improvement can be an achievable goal. 

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S!

 

 Flap flopping is still a very much used "combat tactic" in BoX. In over 90% of cases engaging any pilot, they drop flaps. It is more a normal thing than anything else. It just fights against all the memoirs and reports where pilots stated avoiding using flaps in combat. There were exceptions of course, but general consensus seemed to be no flaps outside landing or take-off. Interesting read by JtD and Holzauge :)

Edited by LLv34_Flanker
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1 hour ago, LLv34_Flanker said:

S!

 

 Flap flopping is still a very much used "combat tactic" in BoX. In over 90% of cases engaging any pilot, they drop flaps. It is more a normal thing than anything else. It just fights against all the memoirs and reports where pilots stated avoiding using flaps in combat. There were exceptions of course, but general consensus seemed to be no flaps outside landing or take-off. Interesting read by JtD and Holzauge :)

I honestly can't remember the last time I saw an enemy pilot drop flaps in a fight, but I fly mostly Allied... Maybe a few months ago, against a 190? He turned sharp and slowed down really fast in a climbing turn and I set him on fire. Didn't really help him much :D

Do you mean just P-47 pilots? I know the 'standard advice' I get when flying that plane is to drop 20 degrees of flap to turn hard, but I don't bother. It takes so long to deploy the flaps and it costs you so much speed that its really just a temporary solution anyway. The P-47 takes so long to accelerate under anything other than boosted power that costing yourself speed in order to turn hard doesn't seem like that great an idea, when the P-47's fantastic roll rate is right there and ready for you to evade with a rapid barrel roll or a flat scissors that will force an overshoot, rather than a hard turn that will just make your enemy go vertical, retain or increase their energy and then nail you.

 

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1 hour ago, LLv34_Flanker said:

Flap flopping is still a very much used "combat tactic" in BoX. In over 90% of cases engaging any pilot, they drop flaps. It is more a normal thing than anything else. It just fights against all the memoirs and reports where pilots stated avoiding using flaps in combat. There were exceptions of course, but general consensus seemed to be no flaps outside landing or take-off.

General consensus among whom? LW pilots? Idk about 109 or 190 but the P51 had combat flaps that could be used at pretty much any speed. Also, many Japanese planes (Ki-43, Ki-44, N1K1, N1K2, Ki-84) had fowler style flaps specifically designed to be used in combat. Some even had flaps that would automatically extend during tight turns (N1K1, N1K2). Also you have to remember that the average sim pilot is much more experienced than the average wartime pilot in terms of aiming and dogfighting, so ingame ppl know how to push their aircraft to the limit better than actual wartime pilots. That said, here's a few examples of P51 pilots using flaps in combat: 

 

 

1st Lt. Louis H. Norley, 8 April 1944, 4th FG                         "Three (3) Fw 190's destroyed. "I dropped 20 degree flap and easily out turned him."
1st Lt. Paul S. Riley, 22 April 1944, 4th FG                            "Letting down 20° of flaps, I could get on the inside of the turn and pull deflection."
2nd Lt. Grover C. Siems, 12 May 1944, 4th FG                     "Observing that I was overtaking too fast, I pulled up over the right e/a and dropped flaps."
2nd Lt. Frank E. Speer, 24 May 1944, 4th FG                        "I had to put down 20° flaps to keep from overrunning him, indicating above 500 m.p.h."
1st Lt. Thomas D. Shank, 19 September 1944, 55th FG     "I dropped full flaps and placed myself directly astern of the e/a on the extreme right of the formation."
1st Lt. Frank E. Oiler, 14 January 1945, 78th FG                   "I got into a Luftberry at 1100 feet with the FW 190, and with the use of flaps I got on his tail in two turns."
1st Lt. Chris J. Hanseman, 10 June 1944, 339th FG           "I cut my throttle and turned inside of him, dropping 20 degrees of flaps."
2nd Lt. Chris J. Hanseman, 24 May 1944, 339th FG            "…dropped 20 degree flaps…"
Harold W. Scruggs, 24 May 1944, 339th FG                          "I lowered about 10 degrees flaps and made two 360 degree turns in which I gained rapidly on the E/A…"
Capt. Bradford V. Stevens, 12 September 1944, 339th FG    "…I was able to turn inside the Me 109 after dropping 20° flaps."
2nd Lt. Myer R. Winkelman, 6 August 1944, 339th FG         "I put down 20° flaps and got on his tail."
2st Lt. S. K. Moats, 29 July 1944, 352nd FG                           "I dropped 20 degrees flaps and after 2 more turns I was closing on the tail of the E/A."
Lt. Glennon T. Moran, 27 May 1944, 352nd FG                      "We fought for about 20 minutes and it was necessary for me to put down combat flaps three times in order to turn with him."
Major George E. Preddy, 21 June 1944, 352nd FG               "He turned into me and I dropped 20 degrees of flaps, out turning him."
1st Lt. Arthur C. Cundy, 14 January 1945, 353rd FG            "With throttle pulled back and full flaps down, I overshot this 190."
1st Lt. William J. Cullerton, 2 November 1944, 355th FG    "I started to overshoot so I dropped full flaps and gave him another long burst just as he was leveling off to land."
Capt. Walter V. Gresham, 15 August 1944, 355th FG           "I downed 40 degrees of flaps and got in another burst which hit him hard."
Capt. Fred R. Haviland, 21 June 1944, 355th FG                   "At 1,000 feet, I dumped 20 degree flaps and made a turn inside him and started to get within firing range, when the E/A made an   abrupt turn, snapped over and crashed into the ground, exploding as he hit the ground."
2nd Lt. Esward Moroney, 2 November 1944, 355th FG         "...I put down full flaps and closed on the E/A."
1st Lt. Harold W. Spencer, 16 August 1944, 355th FG         "I dropped full flaps to keep from overrunning and fired from dead astern at about 100 yards and as I went over him, the Jerry popped his stick forward and crashed."
Capt. Clarence E. Anderson, 30 April 1944, 357th FG          "By using 20° flaps and full throttle I pulled around on their tails in one turn and started firing…"
Capt. Leonard K. Carson, 2 November 1944, 357th FG        "I chopped my throttle and dropped flaps."
1st Lt. Leonard K. Carson, 30 May 1944, 357th FG               "I dropped flaps and turned back behind him."
Capt Robert W. Foy, 18 November 1944, 357th FG               "I lowered flaps and gave E/A a short burst."
Capt. Robert W. Foy, 25 July 1944, 357th FG                         "He suddenly pulled into a sharp right turn and I put down 20° flaps and followed giving several bursts with about two radii lead."
1st Lt. Gilbert M. O’Brien, 27 May 1944, 357th FG                "I slid right up beside him with my flaps down. He bailed out as I was alongside of him, at about 12,000 ft. His chest was covered with blood and he hit the rudder."
Capt Richard A. Peterson, 6 October 1944, 357th FG            "In the ensuing combat I was unable to turn inside the E/A until I dropped 10 degrees of flaps."
F/O Boyd N. Adkins, 24 October 1944, 359th FG                    "I dropped flaps and slid in trail with him at close range."
1st Lt. George F. Baker, 11 September 1944, 359th FG         "I dropped flaps to stay astern of E/A."
Capt. William C. Forehand, 30 May 1944, 359th FG               "I dropped twenty degrees of flaps and cut my throttle and closed in behind him firing from approximately 100 ft.”
1st Lt. Frank O. Lux, 16 August 1944, 359th FG                      "I closed on him, dropped about 10 degrees of flap, and started to fire."
1st Lt. James L. McCubbin, 2 December 1944, 364th FG     "The e/a then dropped his wheels and I dropped 20° flaps to stay behind."
Lt Elmer A. Taylor, 24 August 1944, 364th FG                         "I dropped 20° Flaps and outturned him." 

 

 

So yeah, with the exception of P-47 and maybe couple other planes, there's nothing wrong or unrealistic about using flaps in dogfights. It's weird though how there has long been this notion on many different flight sim forums that using flaps is somehow unrealistic or even immoral lol.

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I think we really need to make a difference between flaps at low settings and flaps at full settings. Aerodynamically, low settings i.e. a combat setting makes sense if you want to turn quickly, and if it wasn't used historically then it had much to do with tactics and possibly reliability or robustness of the system. What does not make a lot of sense are full settings, which create a lot (really, a lot) of drag and which would only be used as the great exception in combat. We also have to remember that many fighter aircraft only had systems that allowed flaps on and flaps off, or had them automatically retract above certain speeds. For instance, I doubt you'll find a lot of Spitfire pilots stating the same as the above P-51 pilots.

 

Btw., did you have that collection ready or did you just manually collect them?

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1 hour ago, JtD said:

I think we really need to make a difference between flaps at low settings and flaps at full settings. Aerodynamically, low settings i.e. a combat setting makes sense if you want to turn quickly, and if it wasn't used historically then it had much to do with tactics and possibly reliability or robustness of the system. What does not make a lot of sense are full settings, which create a lot (really, a lot) of drag and which would only be used as the great exception in combat.

Yes, of course. Low flap setting when you want to turn quickly. The only situation where dropping full flaps would be useful in combat would be at low speed when you are trying to prevent an overshoot; sliding behind someone or during scissors. Of course getting that slow in a furball is not a good idea because you could always get bounced by another plane which is probably why there's only a handful of reports that mention using full flaps. 

 

1 hour ago, JtD said:

We also have to remember that many fighter aircraft only had systems that allowed flaps on and flaps off, or had them automatically retract above certain speeds. For instance, I doubt you'll find a lot of Spitfire pilots stating the same as the above P-51 pilots.

Yea, there are big differences between different aicraft. P-51 could use 10 degrees of flap up to 400 mph according to the flight manual, 500mph according to one of the pilot reports above. Don't think I've ever heard about a Spitfire pilot using flaps in combat, probably because the spit is a really good turner even without flaps and because it had only 2 flap settings, and the flaps were limited to 160 IAS. Also the Spitfires 90 degree split flaps don't help with turning nearly as much (if at all) as say fowler flaps would.  Again, IMO only time they would be useful is when trying to prevent an overshoot at low speed. Doesn't mean they couldn't be used in combat, just probably not wise to get that slow in a furball. 

 

1 hour ago, JtD said:

Btw., did you have that collection ready or did you just manually collect them?

I found them here http://www.wwiiaircraftperformance.org/mustang/combat-reports.html

Edited by Ruthless_Killer

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