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Legioneod

P-47 Flight Model Discussion

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Posted (edited)

I'll be adding to this post over the next few days/weeks but I just wanted to get a discussion started on the FM of the P-47, and on what is correct vs inaccurate with the current model.

 

Things I'd like to discuss, either to confirm or deny their accuracy in the current FM. (I'll add to this over time as the discussion progresses)

 

-Engine Model (engine power limits, damage model, etc)

-Dive Performance (structural integrity in the dive, dive acceleration, compressibility, maximum dive speed, etc)

-High Speed Maneuverability (Elevator effectiveness, roll, high speed stall, etc)

-Low Speed Maneuverability

-Climb

-Zoom

-Speed Performance (Top speeds at various altitudes, power settings, and weight)

 

The first thing I will be going over is the engine model and the dive performance. It's late so I'll probably just continue filling this out in the morning.

 

I know its kinda pointless to start a thread without any information but I'll continue with this later.

 

 

Edited by Legioneod
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Posted (edited)

Engine Limits

(Propose and increase of WEP limit to allow for full 15 min use in order to get a more accurate depiction of what was available to real world pilots.)

Spoiler

Currently the P-47 has a maximum WEP time of 5min before you need to reset. This limited amount of time is a huge handicap to the aircraft, and isn't accurate to what was used in actual combat.

 

The P-47 has a water injection system that allows operation at War Emergency Power for the duration that the water is available.

The P-47D-28 has around 30 gallons of water at its disposal which would allow for a WEP time of 15 min at 64" MAP.

Currently we can only use around 5 min of water effectively before we have to reduce power, this is detrimental in combat and can easily lose you the fight.

 

Real world pilots did not have this concern and were able to push their engine to the full limit without fear of failure.

 

Here's a document showing a 7 1/2 hour WEP test for the R-2800. This test was conducted over a period of time but it does show that the engine can endure long periods of WEP use without damage or maintenance.

2800 WEP Test.jpg

 

Below is an excerpt from the P-47D manual dated 1945 which states that water injection can be used unhesitantly at War Emergency Power for the duration that water is available.

Water Injection was NOT for military power, a real world pilot wouldn't think about wasting water on a power setting lower than War Emergency.

1413688262_P-47WEP.PNG.bfc6a768c56a1ff0cb8c8f057b09a656.PNG

 

 

 

Structural Integrity in a dive and maximum dive speed. (WIP)

Proposal: Increase P-47 structural integrity up to or around it's maximum Mach of around Mach 0.83. 

Loss of structure should still occur under certain circumstances (previous damage, high g) but in a stable dive no loss of structure should occur.

(Keep in mind I'm not talking about the P-47s critical mach in this section but the structural integrity and maximum possible speed in a dive. I will go over critical mach and compressability later on)

Spoiler

Currently in game the P-47 has a dive limit of around 560 mph IAS, this is due to the loss of structural surfaces at speeds at or in excess 560-570 mph. Structural loss at these speeds is incorrect to the actual dive capability of the P-47 and should be changed.

 

The P-47 should not lose any structural surfaces in a dive (even up to it's maximum speed) apart from being damaged before entering into the dive or excessive G on pullout.

 

Structural damage to the P-47 in a dive was pretty much unheard of and the only documented reports of it happening (as far as I'm aware) was on the early fabric covered tail surfaces of the P-47.

 

The fastest capable dive speed of the P-47 is around Mach 0.83 (around 630 mph give or take, not 100% sure) 

Below and up to this speed the P-47 had very little chance of structural failure and could safely recover from dives up to its maximum mach.

 

Loss of structure due to high speed dive is incorrect for the P-47 and should only occur under certain circumstances (damage being the primary cause)

 

Edited by Legioneod
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Legioneod - do you have the book America's Hundred Thousand?

 

I've got it and can post some info from that - it goes pretty in-depth on all US Fighters.

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Posted (edited)
40 minutes ago, CUJO_1970 said:

Legioneod - do you have the book America's Hundred Thousand?

 

I've got it and can post some info from that - it goes pretty in-depth on all US Fighters.

 

Unfortunately I don't. I've been doing most of my research from things I already know and from first hand accounts or test reports.

 

I'll be updating the post over time. Next post will probably be about compresability modeling and some of the problems with it in-game.

Edited by Legioneod

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Dive performance

My tests have established that the P-47's dive acceleration is on par with that of the the Spit 9, irrespective of dive angle. Only when the Spit reaches it's redline does the 47 start to pull away. We got the same results in our Fw190 vs. Spit 9 comparison. Both comparisons contradict wartime reports.

 

I don't think it's the 47's fault. In game, planes with better weight-to-drag ratios seem to have zero benefit from that when it comes to dive acceleration and zoom performance. Instead, lighter fighters like the Spits and Yaks have tremendous dive and zoom performance.

 

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Posted (edited)
18 minutes ago, JG27_PapaFly said:

Both comparisons contradict wartime reports.

 

Not sure that is completely true.   Historically the Spitfire should out-accelerate the 109 & 190 in the first part of the dive then quickly get overtaken.    A spit V chasing a 109 will gain on it for the first 15 seconds then start dropping back so it loses the gain after 20 seconds then soon after is left behind.   The practical effect of this is that diving away from a spitfire that is in gun range wont gain you anything for 20 seconds and wont take you out of his effective gun range for at least 30 seconds by which time anyone diving in a straight line thinking their superior dive speed will save then will probably be dead and the next thing they will do is come into the forum complaining that the spit kept up with them throughout the whole dive.   20-30 seconds is a very long time to be within an enemys gun range!    Yes the YAk also historically had a good initial acceleration.

Edited by 56RAF_Roblex
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Posted (edited)
Just now, 56RAF_Roblex said:

Not sure that is completely true.   Historically the Spitfire should out-accelerate the 109 & 190 in the first part of the dive then quickly get overtaken.    A spit V chasing a 109 will gain on it for the first 15 seconds then start dropping back so it loses the gain after 20 seconds then soon after is left behind.   The practical effect of this is that diving away from a spitfire that is in gun range wont take you out of his effective gun range for at least 30 seconds by which time anyone diving in a straight line thinking their superior dive speed will save then will probably be dead and the next thing they will do is come into the forum complaining that the spit kept up with them throughout the whole dive.   30 seconds is a very long time to be within an enemys gun range!

 

That's not what happens in the game. The Spit can follow the Thunderbolt whole way in a dive. It's only when both planes level and start to decelerate the P-47D can gain distance.

Not only that but 109s/190s will out-pull the P-47D in recoveries from very fast dives. The Jug tends to lose parts first, too.

Edited by Ehret

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1 hour ago, 56RAF_Roblex said:

Historically the Spitfire should out-accelerate the 109 & 190 in the first part of the dive then quickly get overtaken. 

Now here's the catch: in our tests, the 190A5 was on par with the Spit9 in level acceleration between 250 and 400 kph, where the A5 started to accelerate faster. You'd expect the 190 then to outaccelerate the Spit from the very beginning of a dive. That would also be in line with war reports and with the head to head comparison flown by Capt. Brown.

 

Check following tests in the vid:

 

@13:00 min: Fw190A5 vs Spit9 flown at 15lbs boost to replicate Brown's dive test.

 

@14:20 min: Fw190A5 zoom vs Spit9 15lbs zoom comparison

 

@15:05 min: Fw190A8 dive vs. Spit9 18lbs

 

@17:00 min: P47 vs Spit9 18lbs dive test

 

We have more than anecdotal evidence that high weight-to-drag ratio planes are outclassed in diving and zooming by the lighter planes.

 

 

Spit9_P-47_DiveTest_6000m.thumb.jpg.d865f144664f7873630b9af33ab0dec1.jpg

These are the graphs of the Spit9 18lbs vs. P47 dive test from 6000m. The Spit is absolutely equal to the 47 up to 850 kph.

 

 

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2 hours ago, JG27_PapaFly said:

Dive performance

My tests have established that the P-47's dive acceleration is on par with that of the the Spit 9, irrespective of dive angle. Only when the Spit reaches it's redline does the 47 start to pull away. We got the same results in our Fw190 vs. Spit 9 comparison. Both comparisons contradict wartime reports.

 

I don't think it's the 47's fault. In game, planes with better weight-to-drag ratios seem to have zero benefit from that when it comes to dive acceleration and zoom performance. Instead, lighter fighters like the Spits and Yaks have tremendous dive and zoom performance.

 

Yep, lighter aircraft seem to be better for some reason. I've noticed the P-47 can't get away from anything in the dive despite reports stating it accelerated quickly and overshot everything it dove against.

 

Here's a report from some tactical trials.

http://www.wwiiaircraftperformance.org/p-47/p-47c-afdu.html

Dive

16.            The P-47C dives very fast. Its initial acceleration is good an it quickly reaches its limiting figures (520 m.p.h., I.A.S. at 10,000 feet, 450 m.p.h. at 20,000 feet). At these speeds the recovery needs several thousand feet and can only be effected by careful use of the trimming tab. There is no tendency to recover fiercely from the dive, but a large amount of left trim is required on the rudder to hold the aircraft straight.

 

P-47C v. Spitfire IX

 

24.     Dive – The P-47 is able to out-dive the Spitfire quite easily.

 

51.            The P-47 dives very fast, its initial acceleration being particularly good. (para.16)

 

2 hours ago, Ehret said:

 

That's not what happens in the game. The Spit can follow the Thunderbolt whole way in a dive. It's only when both planes level and start to decelerate the P-47D can gain distance.

Not only that but 109s/190s will out-pull the P-47D in recoveries from very fast dives. The Jug tends to lose parts first, too.

 

Which it shouldn't be able to do, none of these aircraft could outdive the P-47, and it was said the P-47 would overshoot them and have a much better angle of pullout. We don't see this in-game at all and 109s and 190s have a much easier time pulling out of dives and can stay with the P-47 in most or all of it's dive.

 

P-47 loses it's structure around 560 mph (190 seems similar) but the 109 loses structure around 580-590 mph and can still pull out of dives much easier than the 47 past 400 mph.

This contradicts wartime reports of 109s and 190s locking up and diving straight into the ground while the P47 was still able to pull out of the dive.

 

wade-dive.jpg

 

Another interesting thing I've seen but I'm not 100% sure how to read it is the roll comparison.

 

Rates of Roll

The ability to roll rapidly is vital to a fighter, and throughout the War continuous efforts were made to increase the rate of roll particularly at the higher speeds, where some aircraft tend to become unmanageable. Here again it is impossible to state categorically that any one particular type has the best rate of roll, as so much depends on the speed, and to a much lesser extent the altitude at which it is carried out.

For example, the Tempest V is not so good as the Spitfire between two and three hundred miles an hour, but above this speed, in common with the Thunderbolt it will out-roll anything, including the Thunderbolt, particularly at over 400mph.

 

Looking at this chart it seems to show the P-47 with a roll rate of around 110-120 deg a sec at speeds over 300-400 mph which is much faster than what we see in-game.

I know this isn't meant to be accurate but it still shows the roll being faster than in game.

wade-roll.jpg

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On 4/11/2019 at 5:25 PM, JG27_PapaFly said:

Dive performance

 

... In game, planes with better weight-to-drag ratios seem to have zero benefit from that when it comes to dive acceleration and zoom performance. Instead, lighter fighters like the Spits and Yaks have tremendous dive and zoom performance.

 

 

I think we put our finger on the big concern of the flight models ...

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1 hour ago, Arsenal53 said:

I think we put our finger on the big concern of the flight models ...

 

I think the big concern is that most people fail to understand that weight to drag matters little in a short, steep dive and that a Yak is not an aircraft with a bad weight to drag ratio to begin with. As long as you accelerate sharply while converting altitude into speed (as in a dive) or vice versa (as in a zoom climb), weight cancels out and things are about power/drag ratio to a large degree.

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54 minutes ago, JtD said:

 

I think the big concern is that most people fail to understand that weight to drag matters little in a short, steep dive and that a Yak is not an aircraft with a bad weight to drag ratio to begin with. As long as you accelerate sharply while converting altitude into speed (as in a dive) or vice versa (as in a zoom climb), weight cancels out and things are about power/drag ratio to a large degree.

Not quite. In gliding, pilots fill water ballast into their sailplanes in order to make them heavier. We do it for two reasons:

1) Better L/D at higher speeds

2) Better zoomclimb (energy retention) when we pull up in order to slow down so that we can thermal.

 

None of the above effects is noticeable in-game. AND we see equal dive and zoom performance from planes that are roughly equal in level acceleration (measure of trust-to-weight), but have significantly different mass.

The core of the issue might well be missing trim drag in-game.

In gliding it makes a hell lot of difference, and nobody in his right mind would attempt a speed task without water ballast on a decent day.

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Posted (edited)

So, have you tested the same aircraft with a dead engine and different loading? Say full ammo and fuel vs. none? What are the margins you see in gliders, what do you observe in game? I of course don't know which glider(s) you fly, but if it's a fairly modern it will have glide ratios factor three to four higher than a WW2 fighter, even with a prop feathered. So small changes will have a larger impact on glider performance than on ww2 fighter performance. On the bottom line, I'd expect a couple of percent, if measurable.

 

And then I don't get that if I say it's mostly about POWER/drag - you come up with gliders, which have a power of ZERO. Obviously, if you eliminate the largest factor, secondary factors are far more noticeable.

 

Why would you want to see different dive and zoom performance from aircraft with roughly equal level acceleration but different mass?

Edited by JtD
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Posted (edited)
1 hour ago, JtD said:

What are the margins you see in gliders, what do you observe in game?

Here's one example: a medium performance two-seater with and without water ballast. Exactly the same aerodynamics, just different wing loading.

ZFmN6.jpg.e0837229bf50dd6ab411916ecd42576d.jpg

 

By increasing the wing loading by 50 percent the L/D ratio almost doubles at 180 kph. As you see, the lighter plane must sink with 3 m/s to maintain the speed, while the heavier plane sinks with 1.75 m/s at the same speed. And the difference gets even bigger as the speed increases.

 

Regarding dive acceleration and zoom performance: trim drag increases drastically for a plane with low wing loading in high-speed flight. That's why, in a dive, the heavier plane will start to out-accelerate the lighter one long before the lighter one approaches is level-flight top speed. IMO that is consistent with war reports. Otherwise I'd expect the Mustang to be an absolute pig in that regard.

Edited by JG27_PapaFly
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1 hour ago, JtD said:

Why would you want to see different dive and zoom performance from aircraft with roughly equal level acceleration but different mass?

 

Because that's how it was irl? In some cases. 190 vs 109 is a decent example, both accelerated at roughly the same rate (from what I gather) yet the 190 had a better dive and zoom iirc.

 

The 109s had much better acceleration than P-47s but pilots from both sides state that the P-47 was the better in zoom and dive.

P-47 also had slow level speed acceleration but is said to accelerate very quickly in the dive, and would outpace other aircraft.

 

Why is it that the P-47 in-game can't outdive or really overtake anything in a dive yet in reality it was said to overtake pretty much everything in a dive save for the tempest.

 

Another good example is the Spitfire vs P-47 dive. Spitfire in game can easily stay right next to a P-47 in a dive where in reality the P-47 easily outpaced the Spitfire to a large degree.

 

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3 minutes ago, Legioneod said:

Another good example is the Spitfire vs P-47 dive. Spitfire in game can easily stay right next to a P-47 in a dive where in reality the P-47 easily outpaced the Spitfire to a large degree.

 

Early mock fights between P-47s and Spits ended very badly for the former; there were few fatal stall incidents because Jugs tried turning fights with Spit. Only when then diving-zooming tactics were adopted the P-47 was able to become an effective fighter.

 

From here:

"Initial mock dog-fights between Thunderbolts and Spitfires seemed to confirm these feelings—we lost four Thunderbolt pilots in rapid succession, spinning in from low level, while trying to match Spitfires in turns. In the end our headquarters issued an order banning mock dog fighting in Thunderbolts below 8,000 feet.

    Gradually, we learned how to fight in the Thunderbolt. At high altitude, she was a hot ship and very fast in the dive; the technique was not to mix it with the enemy, but to pounce on him from above, make one quick pass and get back up to altitude; if anyone tried to escape from a Thunderbolt by diving, we had him cold."

 

Now compare that to what we have in the game...

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35 minutes ago, JG27_PapaFly said:

Exactly the same aerodynamics, just different wing loading.

 

At 180km/h the DG-1000 at 28kg/m² produces 12% more drag than at 42.8kg/m², due to significantly worse parasitic drag. Find a WW2 fighter that does the same, and you'll have the same results. However, WW2 aircraft were optimized for other speeds so that this is not possible. A Fw190, for example, utilizing the same lift coefficients as the Dg-1000 at 180km/h, will produce about 7% less parasitic drag, and even at extremely high dive speeds it's just about 2% more for a light version. Over the speed range of a dive, a heavy Fw190 will produce more drag than a light Fw190 - and is therefore different from a DG-1000.

 

15 minutes ago, Legioneod said:

Because that's how it was irl?

 

A6M52 vs. P-47D, pretty much as much light vs. heavy as possible:

 

Acceleration test level flight 10k feet: The P-47 rapidly accelerated away from the A6M, after a minute it was about 500 yards ahead.

Dive acceleration test from 10k feet: The P-47 was about 100 yards ahead 30s after beginning the dive.

I don't see the heavy aircraft gaining on the light in excess of what it gains in level flight. And I see marginal differences to begin with. No magic instant separation.

 

At 25k the P-47 gained somewhat more in the dive, 300 yards.

 

These dives were carried out from 320 km/h to 520 km/h indicated, at 10k therefore to about 600 true air speed, at 25k to about 700, so no prolonged dives.

 

Fwiw, Smallest difference in level flight in these tests was the P-38 at 25k feet, which gained 250 yards in a minute. 30s after the start of the dive from the same altitude, it was a whopping 75yards ahead.

 

 

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1 hour ago, Ehret said:

She was a hot ship and very fast in the dive; 

 

People must stop using quotes like this as scientific proof... 

 

Cheers, Dakpilot 

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Maybe we could ask Holtzauge to make a simulation with a P-47 and say a Bf 109 G-14 to see what are the results. But I guess it will be a similar case to what he has said before: that while X plane is a better diver than Y it still needs to have enough initial separation because gaining distance takes time (and maybe the lighter plane gains on it initially)...which is too much time when you are in guns range and being shot at.
 

 

 

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Posted (edited)
2 hours ago, Ehret said:

 

Early mock fights between P-47s and Spits ended very badly for the former; there were few fatal stall incidents because Jugs tried turning fights with Spit. Only when then diving-zooming tactics were adopted the P-47 was able to become an effective fighter.

 

From here:

"Initial mock dog-fights between Thunderbolts and Spitfires seemed to confirm these feelings—we lost four Thunderbolt pilots in rapid succession, spinning in from low level, while trying to match Spitfires in turns. In the end our headquarters issued an order banning mock dog fighting in Thunderbolts below 8,000 feet.

    Gradually, we learned how to fight in the Thunderbolt. At high altitude, she was a hot ship and very fast in the dive; the technique was not to mix it with the enemy, but to pounce on him from above, make one quick pass and get back up to altitude; if anyone tried to escape from a Thunderbolt by diving, we had him cold."

 

Now compare that to what we have in the game...

That's what I'm saying, what we have in-game doesn't match the testing.

 

1 hour ago, Dakpilot said:

 

People must stop using quotes like this as scientific proof... 

 

Cheers, Dakpilot 

Yes but it is backed up by flight trials and testing.

 

During combat trials the P-47 "easily" outdove the spitfires and could catch it in a zoom climb. This is how the P-47 did best in combat by using dive and zoom.

Currently in-game there is no difference in diving ability of the Jug vs Spitfire, the Spit stays right alongside the Jug all the way through the dive. I haven't tested it at steeper angles but maybe it's different then.

 

EDIT: Anyone want to do some testing between Fw-190 and P-47? I think it's the bet place to start since we have actual trails between the two aircraft and can get an idea on if the dive is performing as it should..

Edited by Legioneod

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Just now, Dakpilot said:

People must stop using quotes like this as scientific proof...

 

Say what you want but IRL Thunderbolts weren't able to match Spitfires in turns. In the game we can. The diving tactics of the P-47 had great results in IRL. In the game it will get you shot-down. That's is exactly the inverse what happened historically according to tests, results of mock fights and pilots notes.

 

Perhaps then Devs (or you) should "enlighten us" and show the strict data showing that the P-47D had been flown like it's in the game. Go ahead - if you really think that's is correct provide what you call a scientific proof.

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Posted (edited)

Here's some testing criteria if someone wants to test dive performance and see if it' in the ballpark.

 

P-47 vs Fw190 A

 

Loadouts:

P-47

-Full fuel

-Extra Ammo for guns

 

Fw-190

-wing cannons (not pods)

-full fuel (not 100% sure but might as well use full fuel)

 

Altitude 10,000ft

250 mph when entering dive 

65 deg dive angle

Don't touch throttle in the dive but keep it at the same setting.

Fw190 should be a bit faster in the beginning but the P-47 should overtake it at around 3000 ft with much greater speed.

 

Full power dive would be different and I'd expect the P-47 to perform a bit better.

 

Edited by Legioneod

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As JtD said, if you want to see the effect of weight on dive performance - or anything else - you need to test in game by varying only weight. Same plane type, full fuel vs almost empty etc. Then measuring exactly what happens. Work out from that whether the physics makes sense.

 

I cannot see the developers being motivated to change anything by people saying that plane A should be "a bit better".

 

7 hours ago, Ehret said:

 

Say what you want but IRL Thunderbolts weren't able to match Spitfires in turns. In the game we can. The diving tactics of the P-47 had great results in IRL. In the game it will get you shot-down. That's is exactly the inverse what happened historically according to tests, results of mock fights and pilots notes.

 

Perhaps then Devs (or you) should "enlighten us" and show the strict data showing that the P-47D had been flown like it's in the game. Go ahead - if you really think that's is correct provide what you call a scientific proof.

 

If your first point is correct that may be because stalls and their recovery are rather benign in BoX. Your previous post mentioned losing several P-47s turning at low level. 

 

I suspect that people often misinterpret the "diving away" anecdotes. My read on this is that if you had a formation of fighters diving on another formation they could "dive away" after a single firing pass because they were already at very high speed and their targets were not: indeed if the targets had turned to meet the attack they might be slow and nose up. Of course you can get separation in that context.  109s used exactly this tactic against Spitfires during the RAF's cross channel operations in 1941-42. 

 

  Anyway,  the long standing understanding here is that the developers make their best efforts and it is up to us to prove them wrong if we can, with quantitative analysis and source documents. JtD's diving tests done a while ago illustrate the relative unimportance of weight - IIRC unless both planes are already at or near maximum speed and over a long dive.

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Posted (edited)
3 hours ago, unreasonable said:

you need to test in game by varying only weight.

 

It appears folks cant be bothered to test and post results when something contradicts their predetermined errors in the flight model or a preconceived truth about flight physics...End of rant, test results:

 

In game, P-47 gliding test. The 180 km/h example PapaFly chose for the DG-1000 is about twice best glide ratio speed or two thirds maximum permissible dive speed - to put it into the same ballpark for the P-47 I chose to glide at around 320mph indicated. With that speed I dove past 10k feet, and dove down to 5k, increasing speed to 335 indicated, to compensate for denser air, in an attempt to not let true air speed drop too much. Engine at idle, prop pitch set to 0%.

 

P-47 config 1: Full fuel, extra ammo for 8 guns.

P-47 config 2: 10% fuel, no ammo.

 

Should make a difference of somewhere around 1.3 tons, or 20% the aircraft weight.

 

Not knowing the polar of the P-47 in detail, lets assume there's no difference in parasitic drag, and at these speeds we can ignore the difference in induced drag. Total drag will vary within a couple of percent. This means, about 20% extra weight should give us 20% less sink rate for the heavy version. In theory. What does the game make of it?

 

Config 1: 56 seconds from 10000 to 5000 feet, maintaining speed.

Config 2: 48 seconds from 10000 to 5000 feet, maintaining speed.

 

17% lower sink rate for the heavy version. Flight model physics proven correct in that regard. Again.

 

Feel free to repeat more accurately, in particular with a more constant true air speed than I went for.

Edited by JtD
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Excelent! But the million dollar question remains unanswered: why is the Spit9 identical to the P-47 until it starts to fall apart? I'm sure Johnson and others who tested the planes head-to-head would have mentioned that, instead of insisting on the P-47 being superior in dive and zoom.

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What were the exact conditions of the anecdotes you mention - power level, submodels involved, condition of the aircraft, atmospheric conditions, altitude dived from and to, angles dived at, angles zoom climbed at, start and end speeds? Within these variables, I can produce any result you would like to see. In game and real life.

 

In addition, if I look at your charts I immediately realize that the Spitfire is lower than the P-47 throughout the dive. So it has converted more altitude into speed and should be faster, if all other things were equal. This is because it enters the dive quicker, even if a little bit later. If you move the charts so that say 5km altitude happens at the same time, say add about a second to the Spitfire line, you'll find the P-47 to be as fast or faster at all altitudes, even if only marginally initially. But then actual tests have shown differences to be about a few hundred yards. Best would of course be a speed over altitude chart, to get rid of testing inaccuracies, plus an integrated speed distance to illustrate separation.

 

Also next time level out or at least reduce the dive angle, make use of the high speed in the P-47. You can't expect the aircraft to magically gain a huge separation within a few seconds, and you can't expect it to gain anything if you don't make use of its strength.

 

And a better comparative testing procedure would be similar to what I did gliding the P-47 - find a high speed, maintain it, compare altitude loss between P-47 and Spitfire.

 

All that said, the P-47 is not a particularly low drag aircraft. It needs 2200+hp to achieve the speed of a Spitfire at 1600-hp. 40% more drag, and just 80% more weight. That's just 9% more speed when there is no acceleration. At best. About 20m/s at high diving speeds, 200m separation after 10 seconds, maybe, in the late stages of a dive, or after levelling out. Far less (close to nothing) as long as there is significant acceleration involved in the early stages of a dive.

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Posted (edited)
2 hours ago, JtD said:

What were the exact conditions of the anecdotes you mention - power level, submodels involved, condition of the aircraft, atmospheric conditions, altitude dived from and to, angles dived at, angles zoom climbed at, start and end speeds? 

Pay attention to the vid, the settings are listed. The map is irrelevant, since the test was flown head-to-head by JG27_Kornezov and me.

BTW we tested a shallow and a step dive, with identical results.

 

2 hours ago, JtD said:

In addition, if I look at your charts I immediately realize that the Spitfire is lower than the P-47 throughout the dive.

Where in god's name do you see that? Don't mix up pitch and altitude. The pitch angles are slightly different because of the vastly different wing loadings. The altitudes are spot on.  And we dove from 6000m for 60 seconds. Get your facts right before you criticize.

Look again:

Spit9_P-47_DiveTest_6000m.thumb.jpg.246b003d1623ff46929c1f49c36d1734.jpg

Edited by JG27_PapaFly

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I dont understand how weight has anything at all to do with dive speed. Someone correct me if I am missing something, but acceleration due to gravity is constant irrespective of mass. So woudlnt dive speed and acceleration just be a function of drag and thrust? My guess would be that the faster diver would be the plane with the highest level top speed not counter structural limits. 

 

Am I wrong?

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11 minutes ago, Fumes said:

I dont understand how weight has anything at all to do with dive speed. Someone correct me if I am missing something, but acceleration due to gravity is constant irrespective of mass. So woudlnt dive speed and acceleration just be a function of drag and thrust? My guess would be that the faster diver would be the plane with the highest level top speed not counter structural limits. 

 

Am I wrong?

fig_28-05.gif
In a dive, resultant forces in the longitudinal axis would be
F = Thrust + Weight * sin(a) - Drag

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10 minutes ago, Fumes said:

I dont understand how weight has anything at all to do with dive speed. Someone correct me if I am missing something, but acceleration due to gravity is constant irrespective of mass. So woudlnt dive speed and acceleration just be a function of drag and thrust? My guess would be that the faster diver would be the plane with the highest level top speed not counter structural limits. 

 

Am I wrong?

 

There is the drag/weight ratio to consider. When you descend you gain KE from potential energy loss. If you have better drag/weight ratio then your plane should benefit more.

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Posted (edited)
39 minutes ago, JG27_PapaFly said:

Pay attention to the vid, the settings are listed.

 

I don't see Johnson and others who tested the planes head-to-head in that vid. Let alone what they did. You keep referring to them as the benchmark, so I need to know what it is.

 

39 minutes ago, JG27_PapaFly said:

Where in god's name do you see that?

 

In the middle chart, with the "altitude" label on it.

 

39 minutes ago, JG27_PapaFly said:

we dove from 6000m for 60 seconds.

 

I see about 42 seconds of diving before the Spitfire chart ends. And about 24 seconds of diving before the P-47 is faster than the Spitfire, even though it's still about 100m higher (that's worth roughly 15km/h at that speed).

 

39 minutes ago, JG27_PapaFly said:

Get your facts right before you criticize.

 

Got my facts right, and I don't criticize. Just interpreting data the way I see it.

 

16 minutes ago, Fumes said:

Someone correct me if I am missing something, but acceleration due to gravity is constant irrespective of mass. So woudlnt dive speed and acceleration just be a function of drag and thrust?

 

Exactly. Things change, however, when you don't accelerate any more, then it's conversion of potential energy (i.e. altitude*mass*g) vs. drag. The longer the dive, the less acceleration, the more you benefit from a higher mass.

Edited by JtD
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3 minutes ago, JtD said:

 

I don't see Johnson and others who tested the planes head-to-head in that vid. Let alone what they did. You keep referring to them as the benchmark, so I need to know what it is.

 

 

In the middle chart, with the "altitude" label on it.

 

 

I see about 42 seconds of diving before the Spitfire chart ends. And about 24 seconds of diving before the P-47 is faster than the Spitfire, even though it's still about 100m higher (that's worth roughly 15km/h at that speed).

 

 

Got my facts right, and I don't criticize. Just interpreting data the way I see it.

 

 

Exactly. Things change, however, when you don't accelerate any more, then it's conversion of potential energy (i.e. altitude*mass*g) vs. drag.

Im not trying to be contrarian here, just confused.

 

If you stop accelerating why would any changes matter, since speed is now constant? If you have two P-47 shaped rocks, one of 8 tons and one of 8 ounces, do they not fall at exactly the same speed? so if I add a propeller to each, would I not just have the same two rocks plus whatever speed the prop adds?

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2 minutes ago, Fumes said:

If you have two P-47 shaped rocks, one of 8 tons and one of 8 ounces, do they not fall at exactly the same speed?

 

I know this is true in a vacuum, ie with wind resistance removed,  and on the face of it you would think that two rocks of the same shape would have the same drag but...    If that was the case why would scientists go to the trouble of building a giant vacuum chamber to demonstrate that everything falls at the same rate?   A sheet of lead does not fall at the same rate as an identically sized sheet of paper.   Perhaps with sheets it is down to teh paper bending and affecting the airflow but two balls? One of Lead and one of hollow plastic?     

I don't know the answers.  Just wondering what I am missing 🙂

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Aerodynamics is always much simpler if you neglect the forces the air exerts on the body moving through it. ;)

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15 minutes ago, Fumes said:

Im not trying to be contrarian here, just confused.

 

If you stop accelerating why would any changes matter, since speed is now constant? If you have two P-47 shaped rocks, one of 8 tons and one of 8 ounces, do they not fall at exactly the same speed? so if I add a propeller to each, would I not just have the same two rocks plus whatever speed the prop adds? 

 

Roll a ping-pong ball and a golf ball down a slope, see which is down first. If you want to simulate an engine, blow them down with a hair dryer to see the effect.

 

I'm pretty sure someone's already done that and posted a youtube video, if you don't have a slope, a hair dryer and two balls yourself.

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Posted (edited)

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.

 

Overlay screenshot with P-47 data on top. First column time, second altitude, third dive distance and fourth TAS.

 

Quick delta at 37.99 s gives that the P-47 should be ahead by about 200 m.

 

 

SpitMk9at18boostP47at65inch.png

 

Same conditions as above but at 20 degree dive angle instead. This brings the total dive in the C++ simulation time closer to the test done in BoX.

 

Now the P-47 pulls ahead even more: At 66 s the the P-47 is ahead by around 450 m.

 

 

SpitMk9at18boostP47at65inch20deg.png

Edited by Holtzauge
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Posted (edited)
On 4/15/2019 at 9:35 PM, -=PHX=-SuperEtendard said:

Maybe we could ask Holtzauge to make a simulation with a P-47 and say a Bf 109 G-14 to see what are the results. But I guess it will be a similar case to what he has said before: that while X plane is a better diver than Y it still needs to have enough initial separation because gaining distance takes time (and maybe the lighter plane gains on it initially)...which is too much time when you are in guns range and being shot at.
 

 

 

 

Did the simulations before I saw your post. ☺️

 

But you are quite right: The higher T/W fighter will pull ahead initially, especially if you start off at lower speeds. First time I did these type of simulations I thought I had made a mistake in the modeling but then it dawned on me that the heavier fighter will only start to benefit from the higher weight once T<D which can take a looooong time if you start off at low speeds. So a P-47 that drops down in speed will be caught by a Spitfire Mk9 unless he starts off with sufficient speed and separation because initially the Spitfire will actually gain closure.

Edited by Holtzauge
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Posted (edited)
4 hours ago, 56RAF_Roblex said:

 

I know this is true in a vacuum, ie with wind resistance removed,  and on the face of it you would think that two rocks of the same shape would have the same drag but...    If that was the case why would scientists go to the trouble of building a giant vacuum chamber to demonstrate that everything falls at the same rate?   A sheet of lead does not fall at the same rate as an identically sized sheet of paper.   Perhaps with sheets it is down to teh paper bending and affecting the airflow but two balls? One of Lead and one of hollow plastic?     

I don't know the answers.  Just wondering what I am missing 🙂

 

In a vacuum with no air resistance everything falls the same speed. In an atmosphere things are different because you have air resistance, heavier objects can usually fall faster in atmosphere than lighter objects. It takes more time to get the heavier object going but once it does it will go faster than the lighter object.

 

 

This is pretty much what we see with the P-47 in reality, the P-47 is slower at first but once it starts accelerating it'll pick up speed very quickly and overtake the aircraft it's diving against, this is stated in nearly every single dive test done with the P-47.

 

One thing I really want to do is the Fw190 test I posted above, it gives us everything we need to see how dive is working in-game.

Edited by Legioneod

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20 minutes ago, Legioneod said:

 

...It takes more time to get the heavier object going but once it does it will go faster than the lighter object...

 

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...

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