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P-47 Flight Model Discussion

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6 minutes ago, AndyJWest said:

 

Not under acceleration due to gravity, it doesn't. Unless you can provide evidence that inertial mass doesn't equal gravitational mass. In which case, congratulations, your Nobel Prize awaits...

 

What I mean is air resistance has a greater effect on the lighter object compared to the heavier one and that the heavier object will fall faster as the dive/fall continues even if at first the difference is minimal.

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2 hours ago, Holtzauge said:

Don't have time to do a chart that would make it easier to read but anyway here is a C++ simulation of a dive history for a Spitfire Mk9 at +18 boost and a P-47 D10 at 65" boost. Start at 6 km 500 Km/h TAS, 35 degree dive angle. Spit weight 3392 Kg, P-47 at 6006 Kg.

......

 

 

thanks for sharing! but 35°, that's not a dive , that's a descent.... 🤣...sarcasm off...

Have you compared your Calculator to real results?...just very curious here...
As it happens, we got the same kind of report as yours (second per second) for the Wurger here and the translation here
It would be nice to see the differences between Factory results and the calculator and as there is question about the wurger's dive in this discussion, it could add the 2 cents...
Thanks.

Kr.

 

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Just now, Legioneod said:

 

What I mean is air resistance has a greater effect on the lighter object compared to the heavier one and that the heavier object will fall faster as the dive/fall continues even if at first the difference is minimal.

Yes, the air resistance has greater effect on the lighter object. Right from the start. Your assertion that " It takes more time to get the heavier object going" is simply untrue, if the only forces acting on the objects are gravity and drag.

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8 minutes ago, AndyJWest said:

Yes, the air resistance has greater effect on the lighter object. Right from the start. Your assertion that " It takes more time to get the heavier object going" is simply untrue, if the only forces acting on the objects are gravity and drag.

It takes more energy to get the heavier object going. Over a short fall both objects will hit the ground pretty much at the same time but if the fall is longer the heavier object will hit the ground first. I think we are agreeing on the same thing but I just worded it wrong?

 

I shouldn't have said time, that was the wrong word to use.

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10 minutes ago, Legioneod said:

It takes more energy to get the heavier object going.

 

Indeed it does. But since inertial mass equals gravitational mass, there is more energy available, in direct proportion to that needed.

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20 hours ago, JV69badatflyski said:

thanks for sharing! but 35°, that's not a dive , that's a descent.... 🤣...sarcasm off...

Have you compared your Calculator to real results?...just very curious here...
As it happens, we got the same kind of report as yours (second per second) for the Wurger here and the translation here
It would be nice to see the differences between Factory results and the calculator and as there is question about the wurger's dive in this discussion, it could add the 2 cents...
Thanks.

Kr.

 

 

Yes well that test was certainly a dive: Up to 80 degrees! Anyway its difficult to replicate for me. I can only do dive at a fixed angle or a dive followed by a zoom with dive and climb angle defined together with the amount of g's used in the pullout with the current code. Looks like in the test you linked that the dive angle varies quite a lot during the dive and I'm not sure how reliable the speed figures are in that test. Anyway, I think the comparison I did probably gives a good idea about the relative performance between the two......

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On 4/16/2019 at 9:38 PM, Holtzauge said:

here is a C++ simulation of a dive history for a Spitfire Mk9 at +18 boost and a P-47 D10 at 65" boost. Start at 6 km 500 Km/h TAS, 35 degree dive angle. Spit weight 3392 Kg, P-47 at 6006 Kg. 

Servus Holzauge, Just out of curiosity: what are your simulations based on? Can you outline your methodology? We came to a different result in our head-to-head tests. Both planes were absolutely equal up to the spitfire's breakup speed.

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A lot of the empiric evidence in the historical charts, eg that the P47 dove better than others, is likely due to pilot hesitancy with some types of machines in exceeding a certain level of speed, and in others, like the P47, pilot confidence in that speed. Regardless of actual “ultimate test” performance levels. 

 

Enemy A/C are not always tested to the extremes of the airframe by the opposing (capturing) forces - imagine how the captured plane’s condition would likely be - so what a document like the comparative historical chart posted earlier likely represents is indeed a comparative evaluation, but one that is an amalgam based partially on combat experience, partially on practical flying abilities of the A/C, and partially on hard data from flight testing.

 

Regardless, when you experience the sorely lacking high speed elevator authority on the P47 in game, it seems hard to believe that any of the three elements above ever came to be in the P47’s favor...

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The drag/weight ratio (or density) rings a bell? Or perhaps it's okay to some of you to have different drag/weight planes to dive just the same like they would be on an atmosphere-less planet?

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Posted (edited)

Lol, that triggered you pretty fast!

All I’m saying is that quickly is a pretty relative term. So unless you provide at least some numerical data with it, it’s like good, bad, slow,

new and old. All kinda relative terms and not helping in anything

but getting your stress hormones up.

Edited by =EXPEND=SchwarzeDreizehn

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You are wrong; I waited 10x longer than before. The next time I will 100x or no at all. Already, lost an incentive to log to your we***** paradise game.

 

Do you want numerical? There is something called potential energy - h * m as simple it gets. In dive the PE has to go somewhere; some will go to drag heat and the rest will add to velocity. The Earth surface acceleration can do a lot of extra work on the heavier plane especially if equip with a big engine.

It's inconceivable that a feather would drop at the same rate as rock on a planet with atmosphere. Drag/weight again. It's inconceivable that in the game the Spit keeps up with the Thunderbolt, especially there are historic tests and notes that the Spit could not.

 

But believe what you want. I don't care much anymore nor I have to.

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Actually, I believe Holtzauge’s Simulation to be the best evidence, in support of your point.

It’s a lot more convincing than hearing the same, “great diver” anecdotes again and again because the simulation actually offers some substance.

But I guess you only hear what you want or expect to hear.

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I provided the link in my previous post to PE related calculations and comparison to other lighter frame. You should read others posts more carefully.

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34 minutes ago, Ehret said:

I provided the link in my previous post to PE related calculations and comparison to other lighter frame. You should read others posts more carefully.

 

No, that’s exactly what you should do because your reply to my first post was in no way related to anything I said.

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Posted (edited)

Having given it some thought I think one could come up with a short numerical example to explain why the P-47 dives faster than the Mk9 at high speed:

 

Beginning with good old: F=m*a in the plane of motion, i.e. the dive angle:

 

T-D+m*g*sin(diveangle)=m*a

 

Dividing both sides with m leaves the acceleration a=(T-D)/m+g*sin(diveangle)

 

However, since g*sin(diveangle) is the same for both aircraft we can remove that from the comparison.

 

This leaves that the acceleration component that differs between the two is proportional to the thrust minus the drag divided by the mass:

a˷(T-D)/m

 

From this follows that as long as the thrust is bigger than the drag then mass is not your friend and a lighter plane (all other things being equal) will accelerate faster.

 

However, as soon as the drag is bigger, i.e. in a fast dive, the plane with the bigger D/m factor will dive faster.

 

Since the dynamic pressure (q) is the same D can be represented with the parasitic drag area Cdo*S (We can discount the induced drag under these conditions)

 

You can probably find a bit different numbers for drag area for both aircraft but in this comparison I’m going to use 5.54 sqft for the Spitfire Mk9 and 6.39 sqft for the P-47. For weight 3392 Kg for the Spitfire and 6006 Kg for the P-47.

 

Comparing the D/m for both, the P-47 has a roughly 53% lower value meaning the acceleration deduction from the maximum vacuum value of g*sin(diveangle) due to drag will be less so at high speed it really should dive better……

 

QED :)

Edited by Holtzauge
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54 minutes ago, Holtzauge said:

Having given it some thought I think one could come up with a short numerical example to explain why the P-47 dives faster than the Mk9 at high speed:

 

Beginning with good old: F=m*a in the plane of motion, i.e. the dive angle:

 

T-D+m*g*sin(diveangle)=m*a

 

Dividing both sides with m leaves the acceleration a=(T-D)/m+g*sin(diveangle)

 

However, since g*sin(diveangle) is the same for both aircraft we can remove that from the comparison.

 

This leaves that the acceleration component that differs between the two is proportional to the thrust minus the drag divided by the mass:

a˷(T-D)/m

 

From this follows that as long as the thrust is bigger than the drag then mass is not your friend and a lighter plane (all other things being equal) will accelerate faster.

 

However, as soon as the drag is bigger, i.e. in a fast dive, the plane with the bigger D/m factor will dive faster.

 

Since the dynamic pressure (q) is the same D can be represented with the parasitic drag area Cdo*S (We can discount the induced drag under these conditions)

 

You can probably find a bit different numbers for drag area for both aircraft but in this comparison I’m going to use 5.54 sqft for the Spitfire Mk9 and 6.39 sqft for the P-47. For weight 3392 Kg for the Spitfire and 6006 Kg for the P-47.

 

Comparing the D/m for both, the P-47 has a roughly 53% lower value meaning the acceleration deduction from the maximum vacuum value of g*sin(diveangle) due to drag will be less so at high speed it really should dive better……

 

QED :)

So really, you can't say that the P-47 out-dives the Spitfire. The P-47s dive performance exceeds that of a Spitfire in certain areas of the flight envelope, i.e. in a high speed dive where drag overcomes thrust.

The Spitfire will accelerate faster in the initial dive, whereas the P-47 really only begins to shine as the dive continues to much higher speeds. 

So the question is then whether the P-47 has enough altitude to reach the point where it will start to do better than the Spitfire, and whether there is enough time/altitude to make up for the separation the Spitfire gained in the initial dive acceleration.

Do I have that straight, or am I completely lost?

 

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33 minutes ago, RedKestrel said:

So really, you can't say that the P-47 out-dives the Spitfire. The P-47s dive performance exceeds that of a Spitfire in certain areas of the flight envelope, i.e. in a high speed dive where drag overcomes thrust.

The Spitfire will accelerate faster in the initial dive, whereas the P-47 really only begins to shine as the dive continues to much higher speeds. 

So the question is then whether the P-47 has enough altitude to reach the point where it will start to do better than the Spitfire, and whether there is enough time/altitude to make up for the separation the Spitfire gained in the initial dive acceleration.

Do I have that straight, or am I completely lost?

 

 

No, you're quite right it does depend on the scenario but you can say that the P-47 should out dive the Spitfire in almost all cases: The exceptions would be a very steep dive where you would be forced to pull out before gaining any meaningful separation or starting from a very slow speed like close to stall from lower altitudes. However, in the test scenario from BoX the planes started off at 500 Km/h from 6 Km and then you pass D>T (i.e. top speed at a given altitude) very quickly and from then on the P-47 should start to pull away.

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Posted (edited)
1 hour ago, RedKestrel said:

So really, you can't say that the P-47 out-dives the Spitfire. The P-47s dive performance exceeds that of a Spitfire in certain areas of the flight envelope, i.e. in a high speed dive where drag overcomes thrust.

The Spitfire will accelerate faster in the initial dive, whereas the P-47 really only begins to shine as the dive continues to much higher speeds. 

So the question is then whether the P-47 has enough altitude to reach the point where it will start to do better than the Spitfire, and whether there is enough time/altitude to make up for the separation the Spitfire gained in the initial dive acceleration.

Do I have that straight, or am I completely lost?

 

 

Just to add that it is not just about altitude, but also about starting speed before the dive. If a P-47 and Spitfire start together at the same cruise speed and then dive while adding thrust, the Spitfire will get ahead first, just as it would if both added thrust while not diving.  The P-47 would catch up and overtake later as they get above maximum level speed, if there is enough altitude.  If they start together at maximum speed, the P-47 will get ahead and stay ahead, since neither has any engine thrust to add.  So if you are in a slow turning fight diving away may not work for you in a heavier (strictly higher m/D)  plane, unless you can also combine it with a direction change the lighter plane cannot match - such as a rapid roll - to help with the initial separation.

 

edit: added before seeing H's last: which I think is the same point: it depends how quickly you can get past maximum level speed.

 

 

Edited by unreasonable
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Yup, but it does seem odd that there seems to be almost no difference in BoX: I think the old simulation results SuperEtendard linked above illustrates the point that

it can take a while to build up separation in some cases but in the BoX comparison PapaFly posted here the P-47 really should pull away since you would pass top speed in a jiffy in that scenario.....

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46 minutes ago, Holtzauge said:

Yup, but it does seem odd that there seems to be almost no difference in BoX: I think the old simulation results SuperEtendard linked above illustrates the point that

it can take a while to build up separation in some cases but in the BoX comparison PapaFly posted here the P-47 really should pull away since you would pass top speed in a jiffy in that scenario.....

 

You could be right, but as a non-engineer virpil I will make no further comment: the Thais have a saying "When elephants fight, the grass gets trampled". ;)

 

     

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I took the following test. Ju-88 vs P-47

Ju-88 100% fuel
P-47 15% fuel

Result: Ju-88 climb more and manages to stay as fast as the P-47

Im wondering if I should make a video about it, I found it bizarre

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7 hours ago, LUZITANO said:

I took the following test. Ju-88 vs P-47

Ju-88 100% fuel
P-47 15% fuel

Result: Ju-88 climb more and manages to stay as fast as the P-47

Im wondering if I should make a video about it, I found it bizarre

 

Whatzzzz?  O quê ? WTF ??????  No way.... Well... on 2nd thoughts, a 744 can climb ( Vy ) better than an A320.... Hmmmm

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8 hours ago, LUZITANO said:

I took the following test. Ju-88 vs P-47

Ju-88 100% fuel
P-47 15% fuel

Result: Ju-88 climb more and manages to stay as fast as the P-47

Im wondering if I should make a video about it, I found it bizarre

 

From what alt? What speed was the dive started at? What engine setting? Which dive angle? At what speed did you start pulling out of the dive? 500TAS? 600TAS? 700TAS? How many G's did you pull to get out out of the dive (because it seems your tests was a dive + climb)? Were your planes trimmed correctly over the whole speed envelope throughout the dive? At what speed did you "end the climb"? How many times did you perform the tests? Or was it a one-time-try? 

 

I mean, your result does raise my eyebrows, but without the context in which you performed the dives and with all its associated side-effects those would entail, it doesn't tell me actually all that much (I'd like to see the vid, that would clarify some of it, like PapaFly's tests). I would say that your test result as you describe it "Ju-88 climb more and manages to stay as fast as the P-47" has understandably zero value in the eyes of the Devs, the persons who you finally are trying to convince that there is something off. Can you explain exactly what were the conditions of your tests (dive angle, engine settings, ....) and quantify your results ("climb more"  : how much more? What was the evolution of velocities?)? I am curious about it and would like to check it for myself.

 

 

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3 hours ago, =FSB=HandyNasty said:

 

From what alt?

6 km

I think I forgot to start the supercharge. I'll do more tests

 Get the experience
6k alt for both. P-47 vs Ju-88 (average) face to face 3km distance

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21 hours ago, Holtzauge said:

in the BoX comparison PapaFly posted here the P-47 really should pull away since you would pass top speed in a jiffy in that scenario

 

It's not the same dive entry. If you go with your simulation and give the Spitfire a 1 s head start (or whatever time necessary so that it is at 5km while the P-47 is still 100+ meters higher), you'll find the P-47 does not start to catch up until the Spitfire reaches terminal velocity either. The pitch of the Spitfire for most of the dive entry phase is about 5° lower than that of the P-47, even though in the steady parts it looks as if the P-47 requires only about 1°-1.5° higher pitch at the same speed for the same flightpath. Effectively, the Spitfire pulls ahead due to a) a slightly better initial acceleration and b) due to entering the dive slightly quicker / steeper. But if you convert a couple of extra % altitude, it is a tremendeous initial advantage and it will take ages to compensate.

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1 hour ago, JtD said:

 

It's not the same dive entry. If you go with your simulation and give the Spitfire a 1 s head start (or whatever time necessary so that it is at 5km while the P-47 is still 100+ meters higher), you'll find the P-47 does not start to catch up until the Spitfire reaches terminal velocity either. The pitch of the Spitfire for most of the dive entry phase is about 5° lower than that of the P-47, even though in the steady parts it looks as if the P-47 requires only about 1°-1.5° higher pitch at the same speed for the same flightpath. Effectively, the Spitfire pulls ahead due to a) a slightly better initial acceleration and b) due to entering the dive slightly quicker / steeper. But if you convert a couple of extra % altitude, it is a tremendeous initial advantage and it will take ages to compensate.

 

What I meant was that in the BoX scenario posted, i.e. a dive from 6 Km at 30-40 degrees dive angle starting at 500 Km/h then the P-47 should pull away from the Spitfire. Of course, if the planes  fly the dive under different conditions then all bets are off…..

 

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23 hours ago, JtD said:

The pitch of the Spitfire for most of the dive entry phase is about 5° lower than that of the P-47, even though in the steady parts it looks as if the P-47 requires only about 1°-1.5° higher pitch at the same speed for the same flightpath.

Don't mix up pitch angle and dive angle. A plane with lower wing loading (Spit) will have a lower pitch angle than a plane with higher wing loading (P-47) up to a certain speed. This is nicely demonstrated in my vid. The motion vectors were in fact extremely close, exactly as in the dive from 3000m, which I included in the vid. The leftmost diagram clearly shows how close the planes were. The Spit was behind the P, in formation and at the same speed when we started. That's why it you split hairs you will argue that the Spit was higher than the P throughout the dive. It was simply locked in formation behind the P. Only from 850kph on did the P start to pull ahead, until it started to disintegrate 100 kph later. Don't you think the wartime comparative reports would be different if the P would have had a dive advantage only between 850 and 950 kph?

Spit9_P-47_DiveTest_6000m.thumb.jpg.a19554b56e3a63174df2ba56d71a9f49.jpg

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Posted (edited)
On 4/24/2019 at 9:06 PM, Holtzauge said:

What I meant was that in the BoX scenario posted, i.e. a dive from 6 Km at 30-40 degrees dive angle starting at 500 Km/h then the P-47 should pull away from the Spitfire.

 

And it does. In fact, in this regard BoX is in a surprisingly good agreement with your calculations (except for break up speeds).

 

21 hours ago, JG27_PapaFly said:

The Spit was behind the P

 

Not in the charts you posted.

 

Edited by JtD
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Posted (edited)

In order to try and visualize it myself I put Holtzauge's dataset into an excel sheet and did a chart of it (see below)

SpitVP47_DiveChart.jpg.3602b44d90b9c7e8a151518f13938d44.jpg 


In Holtzauge's sim, we can see the P-47 gaining speed on the Spit earlier in the dive than we see in Papafly's test. There is a caveat though: Trying to compare Holtzauge's C++ simulation to Papafly's in-game test is a little tricky because there are some questions about how much the conditions really match.

EDIT: This section was incorrect, both tests were from 6km, I misread Holtzauge's post as saying it was from 9km. However, I have to say it would be nice to know the atmospheric assumptions made for this test to see if they are in line with Papafly's test in-game. 

The second factor, and I believe it could potentially be a large one, is that Holtzauge's simulation uses a P-47D-10 (a razorback), whereas in the game we have a P-47D-28 (a bubble canopy). I have heard that the bubble canopy has higher drag than the razorback. If this is the case, and if wartime tests comparing spitfires to P-47s were largely  conducted with Razorbacks (one test above compares the Spit to a P-47C),  we may not have a wartime-era test of the aircraft we have flying against each other. Once again, if this difference is largely irrelevant, please correct me on this. I'm only going by bits and pieces of what I've heard and read regarding bubble canopies.


 

Edited by RedKestrel
I misread a previous post regarding the start height of the C++ sim.
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35 minutes ago, RedKestrel said:

Trying to compare Holtzauge's C++ simulation to Papafly's in-game test is a little tricky 

This is indeed tricky because Holzauge's P-47 dataset is almost equal to the in-game Spit dataset: we achieved a top speed of 925 kph in the Spit, equal to Holzauge's P-47. Holzauge's top speeds are 50 kph lower than the in-game speeds for both planes.

 

@JTD: if you believe you can perform better in a P-47 diving under our test conditions, I'll be happy to follow you in a Spit. I'm available on May 9th.

 

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I believe that if you took your data and displayed speed over altitude instead of both over time, you'd get rid of most of the dive entry differences and could produce a meaningful chart. I've said that 10 days ago, and frankly consider extra testing a waste of time as long as existing data isn't properly evaluated.

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I derived a bit more data from the charts out of curiousity, and to help with visualization.

Here's a chart of acceleration over the course of the dive. I did this by comparing the speed in m/s to the speed in the previous second starting from time 2 (there was no time 1 entry for the P-47 that I could see).

SpitVsP47_DiveAcceleration.jpg.a5525f163155f0180e3f0c82b0aab0f9.jpg

Odd thing about this chart - its been said previous in the thread that the Spitfire should accelerate faster in the initial part of the dive, but the chart shows that the P-47 actually accelerates faster than the Spit at the beginning of the dive, and the spit closes the gap a bit in the middle. At no point does the Spitfire out-accelerate the P-47 in this dataset. Feel free to check my numbers, I may be making some errors here. In any case we can see that near the end of the dive neither aircraft continues to accelerate (we start to see slight deceleration in the last few seconds, and nearly zero for a few seconds before that. As Papafly points out above, the top speeds attained in this simulation are quite a bit lower than those obtained in-game.

I tried to calculate the accumulated closure between the two aircraft over time. How I did this was that I calculated the speed difference in metres per second for each data point, and then took the sum of all the speed differences, reasoning that the speed difference in m/s for any given time would also be the amount of closure occurring in that amount of time. So if the speed difference at second 25 was 7.84m/s, the two aircraft got 7.84 m closer during that second. God I hope this is right, my math skills are rusty in some ways lol. 

Anyway, if we use that calculation, the total closure over the course of the entire 38 second dive is +/-210 m. Pretty close to Holtzauge's estimate when he first posted the data.

If we are to assume that this is a pretty good representation of reality, then I think we're forced to conclude that while the P-47 may have been a better diver than a Spitfire, it was only good enough to actually catch the spitfire if the initial separation between them was minimal. When you put it this way, the P-47's inability to catch the spitfire in a dive in-game wouldn't be that far off from reality, where the gains are minimal and tiny differences in starting speed, timing and altitude would easily wipe out advantages in dive performance. 

Here's a scenario, to put this in perspective: the spitfire dives away from the P-47 in a 30 degree dive from 6000 metres, as in Holtzauge's sim. The P-47 is 1000 m away from the spitfire, and reacts instantaneously to pursue it in the dive. The planes dive for 38 seconds and then level out, with the P-47 moving at 255.07 m/s and the spitfire at 245.81 m/s. At this point, the P-47 has still not closed to a reasonable gun range - its still 790 m away from the spitfire, and its speed is only 9.26 m/s faster than the Spitfire. Assuming it retains this speed advantage, it would need to pursue the spitfire for another 42 seconds to get within a reasonable engagement range of 400 metres. Once the dive speed wears off the P-47 is only faster than the Spitfire at WEP settings at sea level, at combat settings the Spit outpaces the Jug. 

So even though Holtzauge's simulation shows the P-47 diving better relative to the Spitfire than Papafly's test in-game, I still don't think it supports the dive performance many are expecting. People who dive almost 6 km after an enemy are going to be underwhelmed by only a couple hundred metres of closure - depending on how close you are at the beginning, it would look like almost no closure at all!

So either both the game AND Holtzauge's sim severely underestimate the P-47's dive performance when compared to real life, or the anecdotes of its ability to catch its enemies in a dive are somewhat exaggerated. They would have to be almost in engagement range already (less than a km) and you would have to pursue them almost to the deck to catch them. 

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On 4/25/2019 at 1:40 PM, JG27_PapaFly said:

Don't mix up pitch angle and dive angle. A plane with lower wing loading (Spit) will have a lower pitch angle than a plane with higher wing loading (P-47) up to a certain speed. This is nicely demonstrated in my vid. The motion vectors were in fact extremely close, exactly as in the dive from 3000m, which I included in the vid. The leftmost diagram clearly shows how close the planes were. The Spit was behind the P, in formation and at the same speed when we started. That's why it you split hairs you will argue that the Spit was higher than the P throughout the dive. It was simply locked in formation behind the P. Only from 850kph on did the P start to pull ahead, until it started to disintegrate 100 kph later. Don't you think the wartime comparative reports would be different if the P would have had a dive advantage only between 850 and 950 kph?

Spit9_P-47_DiveTest_6000m.thumb.jpg.a19554b56e3a63174df2ba56d71a9f49.jpg

Correct me if I'm wrong, but the test you show in the video is not the test the charts follow right? The test in the video is from 3000m but the chart you show is from 6000m. Do you have video of the other test? I got confused because you said the Spit was behind the P-47, but the opposite is true in the video.

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1 hour ago, RedKestrel said:

Do you have video of the other test? I

I only included the clip of the dive from 3000m in my vid. I didn't want to make it too long and boring. I'd have to look if I have the other vid.

 

Is Holzauge's simulation validated in any way?

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35 minutes ago, JG27_PapaFly said:

I only included the clip of the dive from 3000m in my vid. I didn't want to make it too long and boring. I'd have to look if I have the other vid.

 

Is Holzauge's simulation validated in any way?

I have no idea, I was just trying to put together some charts to get a visual comparison. 

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Posted (edited)

@Kestrel: Good catch with the razorback versus bubble canopy:  I actually have the D30 modeled (which I of course should have used initially as well!) and if you look at the results attached below its just like you say: The D30 does not pull away as fast as the razorback bringing the C++ and BoX results closer together but still, the D30 is ahead by about 275 m at 66 s into the dive. But 275 m in a dive of more than 14 Km is just a difference of around 2% so even in my simulations the anecdotal evidence that the P-47 should leave the competition standing is not really borne out. About the Spitfire accelerating better initially: That is only true if you start off at lower speeds but starting off as high as 500 Km/h then you are into the region where T<D almost immediately.

 

@Papafly: When it comes to the validation of the C++ model: I have under the handle Holtzauge posted results from my simulations for more than 10 years on WW2 aircraft forums and you will have to judge the accuracy in the same way you do BoX: Compare the results with IRL data. I’m quite satisfied with the results so far and have received no feedback indicating any big problems with accuracy. However, that being said, modelling the subsonic drag rise due to compressibility and reduced propeller efficiency due to supersonic tip speeds is no easy task.

 

About the speed difference between BoX and my C++ simulations: I noticed that as well and I don’t know how compressibility is modelled in BoX but in my C++ I have drag creep before the sharp drag rise when you start getting a lot of local supersonic flow and I would guess that the difference is due to different modelling here.

 

Anyway, to conclude, even though the P-47 should be marginally better, the agreement in modelling between BoX and my C++ simulations seems pretty good since while the top speeds reached differ and while in BoX they may be neck to neck the 2% difference I get is not that much of a difference either……

 

 

P47D30at65inch20deg.thumb.png.125cb170948953dcf6dbde969217b0fa.png

Edited by Holtzauge
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Here is a C++ simulation (Overlay P-47 on top of Spitfire, time s, dive dist Km, TAS speed Km/h) for the 3Km at 350 Km/h TAS 20 degree dive in Papafly's video: Notice that in my simulation I get basically the same result: At the end of the dive they are within a hairs breadth. Also notice that at the bottom of the dive the P-47 is a bit faster while at 6 s into the dive the Spitfire is a bit faster: Just like theory would predict and quite in line with the results in BoX! ;)

 

SpitMk9at18boostP47at65inch20deg350Kkn3Km.thumb.png.ca27cc63e5881ccc25307d969a988747.png

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Interesting: in this latter test the point where the P-47's speed exceeds the Spitfire's is 24 seconds!  Accepting the physics of this, and going back to thinking about the tactical consequences, reinforces for me that the lesson from this is not the idea that heavy planes should be able to dive away from a slow turning fight when they find themselves at a disadvantage, which I suspect many players expect, but that they (the high m/D plane) should dive at high speed at a target, take a shot - if they can - and then keep diving away without slowing down significantly, either to the relative safety of your AA zone or with enough separation that you can climb back to altitude.   If they do that there is no way a lower m/D  plane can catch them. 

 

Of course to do that you have to have significant altitude advantage, room below the target, and be prepared to make a fairly low percentage pass, so do not expect to see this done in the game very often.

 

Just as a matter of interest, @Holtzauge , P-47 vs Spitfire is not going to happen in the game, but what happens if you replace the Spitfire with a 109 G or K?  

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