P-47 Maneuverability or Lack Thereof

[Holtzauge]

There seems to be some confusion about how to compare different Clmax: Clmax may sound like a static but is actually dependent on a lot of things like Reynolds number, Mach, buffeting limits and, what is key in the NACA report being cited (792), if the measurement is taken in sustained or as the report explicitly states in the title, ABRUPT maneuvers.

 

In an abrupt maneuver there is a brief period when a strong vortex is formed on the suction side of the wing which leads to a very short period of significantly higher Clmax than you will see in sustained conditions. So a Clmax in the order of 1.523 or even higher is perfectly possible to attain in abrupt maneuvers even with a Clmax of 1.35 in low Mach, power off conditions. In addition, if you go looking, you may even find a Clmax chart showing that the P-47 has a Clmax of 1.7 in power on conditions. So does this mean you found the proof the P-47 has a Clmax=1.7?

 

No, all this means is that you need to be careful so you don’t compare apples with pears which is easy to do if you look at charts and don’t understand the context and in which situations that particular Clmax is applicable. Usually, if an aeronautical engineer says a certain aircraft has a Clmax of X, he is referring to the power off Clmax for low Mach and mixing in other numbers for abrupt manouvers, power on conditions, or Clmax numbers from wind tunnel trials on small models at low Re is not very helpful.

 

If you google, you will find papers on this effect and I have seen nice smoke tunnel videos on Youtube as well showing what happens when a wing profile is given an ABRUPT change in aoa. This is a very interesting phenomena for sure buts says nothing about the aircraft’s Clmax in a tight turn.

 

Edited December 15, 2021 by Holtzauge

[ACG_Cass]

Thanks @Holtzauge

 

I'll happily admit to being a complete novice on this stuff and understand it's incredibly complex and dynamic. I'm not sure you're insinuating this but just to clarify, no-one is suggesting that the P47 should have a Clmax of 1.7 at low mach. 

 

Super interesting insight around the impact of abrupt manoeuvres. After doing some reading it looks like an incredible complex phenomenon that I have no hope of dissecting and understanding its application in this scenario. 

 

I'm just investigating here and trying to reach at least some consensus so this is something we can hand to the developers on a plate and say "here is how it should be".  Although 792 might have been done in a way that would spike lift during the test, it still ultimately shows how the plane should behave under very strict conditions and that isn't replicated in IL2. I have a sneaking suspicion that IL2 probably doesn't model DSV formation. I'd need to test in DCS whether if that's the reason the FM matches the test, or they have given the plane a too high Clmax. I've no doubt there are issues with the P-47 in DCS, but the fact they have done CFD test and matched them up to IRL tests means the general model is likely to be more correct. 

 

https://www.digitalcombatsimulator.com/upload/iblock/dcc/DCS FM principles plus MiG-29 P-47 F-16.pdf 

Pg. 18 onwards

 

If it's generally agreed that the low mach Clmax is 1.35, that's already a big up tick from 1.2 and puts the P47 closer to its contemporaries. I'd ask - do you agree that as a very rough estimate, exclusive to low mach, are those stall speed corrections likely in the right area?

 

My other main concern is the fact that as far as I can work out at low mach the P47 still has a Clmax of ~1.2 at 6000 feet in IL2 and it seems very strange for it to still have a Clmax of ~1.2 at 214 IAS while running 27", which has got to be somewhere between 7-900 hp and would definitely be considered power on. 

 

On 10/3/2021 at 7:16 AM, ZachariasX said:

What we have here is:

 

[…]

 

D.   Stalling Speeds        Stalling speeds are given in the following table.

 

Wing Flaps	Landing Gear	Shutters	Power	IAS MPH*
Up	Up	Closed	Idling	116
Up	Up	Open	Idling	116
Up	Down	Closed	Idling	114
1/4	Down	Closed	Idling	109
1/2	Down	Closed	Idling	105
3/4	Down	Closed	Idling	101
Full	Down	Closed	Idling	98
Up	Down	Closed	Idling	114
Up	Down	Open	35" Hg. 2200 RPM	107
Up	Up	Open	45" Hg. 2550 RPM	103
Up	Up	Open	35" Hg. 2200 RPM	106
Up	Down	Open	45" Hg. 2550 RPM	104
Up	Down	Open	35" Hg. 2200 RPM	107

 

*This speed is the ship's uncorrected indicator speed, and is effected by attitude of airplane and balance of airspeed lines.   […]   Which is in line with the data I gathered before. I think a Clmax of around 1.3 could be plausible, as the tests are certainly not at sea level and assuming a good pitot arrangement.

 

 

I could be completely misunderstanding what the above is telling us, but I get the same ~1.3 Clmax @ZachariasX gets from the 116 IAS, power off stall. But when calculating the 35" and the 45" stall, I get a Clmax of 1.55 and 1.62 respectively. I could be completely wrong here and am missing something about a condition that needs to be taken into account. But if that's not the case it appears as though we should be seeing a Clmax increase that we don't get. 

 

Again, I'm a complete novice here who's just trying to get something we can put forward so the P47 can be corrected. 

 

Edited December 16, 2021 by ACG_Cass

[ZachariasX]

2 hours ago, ACG_Cass said:

I could be completely misunderstanding what the above is telling us

You did the right thing and you got the right numbers. Even the NACA report above gives those values, but there you have to be aware of what Holtzauge said regarding some of the numbers.

 

As soon as you have the plane almost torquing on foll power, the engine will assist in lift in a way that is not really available to you in normal flight and for our purposes not really relevant.

[Holtzauge]

3 hours ago, ACG_Cass said:

Thanks @Holtzauge

 

I'll happily admit to being a complete novice on this stuff and understand it's incredibly complex and dynamic. I'm not sure you're insinuating this but just to clarify, no-one is suggesting that the P47 should have a Clmax of 1.7 at low mach. 

 

Super interesting insight around the impact of abrupt manoeuvres. After doing some reading it looks like an incredible complex phenomenon that I have no hope of dissecting and understanding its application in this scenario. 

 

I'm just investigating here and trying to reach at least some consensus so this is something we can hand to the developers on a plate and say "here is how it should be".  Although 792 might have been done in a way that would spike lift during the test, it still ultimately shows how the plane should behave under very strict conditions and that isn't replicated in IL2. I have a sneaking suspicion that IL2 probably doesn't model DSV formation. I'd need to test in DCS whether if that's the reason the FM matches the test, or they have given the plane a too high Clmax. I've no doubt there are issues with the P-47 in DCS, but the fact they have done CFD test and matched them up to IRL tests means the general model is likely to be more correct. 

 

https://www.digitalcombatsimulator.com/upload/iblock/dcc/DCS FM principles plus MiG-29 P-47 F-16.pdf 

Pg. 18 onwards

 

If it's generally agreed that the low mach Clmax is 1.35, that's already a big up tick from 1.2 and puts the P47 closer to its contemporaries. I'd ask - do you agree that as a very rough estimate, exclusive to low mach, are those stall speed corrections likely in the right area?

 

My other main concern is the fact that as far as I can work out at low mach the P47 still has a Clmax of ~1.2 at 6000 feet in IL2 and it seems very strange for it to still have a Clmax of ~1.2 at 214 IAS while running 27", which has got to be somewhere between 7-900 hp and would definitely be considered power on. 

 

 

 

I could be completely misunderstanding what the above is telling us, but I get the same ~1.3 Clmax @ZachariasX gets from the 116 IAS, power off stall. But when calculating the 35" and the 45" stall, I get a Clmax of 1.55 and 1.62 respectively. I could be completely wrong here and am missing something about a condition that needs to be taken into account. But if that's not the case it appears as though we should be seeing a Clmax increase that we don't get. 

 

Again, I'm a complete novice here who's just trying to get something we can put forward so the P47 can be corrected. 

 

 

Sorry if you interpreted this as a dig at you since it was nothing of the kind! However, if you have been around these forums long enough you will know that some here dig up all sorts of reports and use that to try to drive FM changes for their favorite ride. This has historically affected especially the Spitfire and Me-109 where you will find all sorts of allegations about what boost they had and their Clmax where some shamelessly use high or low percentile data to drive an agenda so maybe I’m being a bit oversensitive in this case but I think we can all agree that all sorts of data both for the Tempest and P-47 has been posted and the level of relevancy has varied quite a lot.

 

As an example, I found this nice Youtube video showing why NACA report 792 is irrelevant for the Clmax in sustained turning conditions. I enjoyed watching the whole video but if you want to see why abrupt maneuvers give you the wrong results, look at the chart presented around 2:50 min into the video (if you watch it, do give the guy a like for his video, I think he deserves it! )

 

With the caveat that I only looked at that table you posted with the stall speeds (Memo Report No. Eng-47-1774-A), as far as I understand this is giving Clmax calculated using uncalibrated instrument IAS? If that I so it’s basically useless since even if you apply general Mach and other corrections you will still be way off unless you have a position error calibration (PEC) curve since this could add or  subtract as much as 20 mph from those numbers. So even if those Clmax numbers numbers you calculated based on the data all look rather reasonable this is probably just a coincidence since without a PEC the table does not tell you anything about the Clmax: All it tells you is what the pilot should expect to see when he stalls the plane.

 

This is why in most case when the Clmax is determined professionally, you need a so-called trailing pitot system to do this with the needed level of accuracy. The RAE in Britain did this for the Me-109 and Spitfire in the WW2 period and established a Clmax power off of around 1.4 and 1.36 for those aircraft respectively. IIRC then the RAE also established the PEC curve for the Me-109E and it had a very big PEC, around 10-20 mph as I recall, so you can see where that puts you if you were to use that as input for calculating the Me-109 Clmax based in instrument IAS.

 

As far as I know also Il-2 uses the power off Clmax as a base. At least there have been huge discussions for the Fw-190 similar to what is now going on here for the P-47. What happened with the Fw-190 was that an update lowered the Clmax of the Fw-190 down to 1.15 IIRC and the community spent a huge amount of effort to get this corrected. This is why I think it’s important to get the power off, low Mach Clmax for the P-47 right because as far as I can tell, if this is fine in IL-2 then the FM does a decent job of calculating the effects in power on conditions as well. At least this seems to work OK for the other aircraft modeled so I see no reason why It should not also work fine for the P-47.

 

I did a quick run in my C++ code for the Me-109K4 at 50% fuel and 1.8 ata and P-47D30 at 11900 lb with 56” boost at 10 Km altitude and for me they come out needing a bit more than a minute to do a full turn and within a second of each other (109 1 s faster) so basically on par so if the P-47 is taking significantly longer than the Me-109K4 in-game under those conditions then I would agree that something is off but even so it need not be the Clmax in that case since the sustained turn rate is affected by other things like power and propeller efficiency modeling.

Edited December 16, 2021 by Holtzauge

[BCI-Nazgul]

Instinctively, you would expect the P-47 to perform closer to its contemporaries if only because it has huge wings and a huge engine to make up for its huge size.  Proportionately it looks a lot like a giant 190 or Hellcat.  The argument that just because it's big and heavy and therefore shouldn't be good in a dogfight doesn't hold a lot of water with me.   I don't expect it to be a Spitfire, but it seems much more capable in DCS.   Somehow the "magic" 110 seems to do just fine inspite of being "big".

[ACG_Cass]

7 hours ago, Holtzauge said:

As far as I know also Il-2 uses the power off Clmax as a base. At least there have been huge discussions for the Fw-190 similar to what is now going on here for the P-47. What happened with the Fw-190 was that an update lowered the Clmax of the Fw-190 down to 1.15 IIRC and the community spent a huge amount of effort to get this corrected. This is why I think it’s important to get the power off, low Mach Clmax for the P-47 right because as far as I can tell, if this is fine in IL-2 then the FM does a decent job of calculating the effects in power on conditions as well. At least this seems to work OK for the other aircraft modeled so I see no reason why It should not also work fine for the P-47.

 

That makes sense. Thanks for your help on this. I've been linked to the 190 drama a few times. 

 

My concern is trying to find anything concrete on the P47's stall speed and accompanying weight as it's incredibly difficult. I find the standard 115/114mph but with no mention of altitude or weight. The standard weight P47 in IL2 being at 124mph does seem awfully high, there just doesn't seem to be a way to disprove it. 

 

I've got calibrations down to 150-170mph IAS that I can sort of extrapolate, but that doesn't take into account the increase in error that might occur in a higher AoA situation. 

 

http://www.wwiiaircraftperformance.org/p-47/Naca_TN_2675__F-47D-30_Flight_Test.pdf

 

This is particularly frustrating as that data has clearly been put together, I just highly doubt it's out there and findable. A P47N report also mentions using a trailing boon and another plane. 

 

I'll keep digging and see what I can find. Further frustrating this is the fact that quite a few of the NACA P-47 reports still seem to be classified/restricted for some reason.

 

 

 

 

https://ntrs.nasa.gov/api/citations/20090022749/downloads/20090022749.pdf

 

This could maaaybe work. You have weight, altitude and as close as you can get it, IAS. I'll maybe have a stab at trying to get a TAS worked out tomorrow. 

 

 

[Holtzauge]

12 hours ago, ACG_Cass said:

 

That makes sense. Thanks for your help on this. I've been linked to the 190 drama a few times. 

 

My concern is trying to find anything concrete on the P47's stall speed and accompanying weight as it's incredibly difficult. I find the standard 115/114mph but with no mention of altitude or weight. The standard weight P47 in IL2 being at 124mph does seem awfully high, there just doesn't seem to be a way to disprove it. 

 

I've got calibrations down to 150-170mph IAS that I can sort of extrapolate, but that doesn't take into account the increase in error that might occur in a higher AoA situation. 

 

http://www.wwiiaircraftperformance.org/p-47/Naca_TN_2675__F-47D-30_Flight_Test.pdf

 

This is particularly frustrating as that data has clearly been put together, I just highly doubt it's out there and findable. A P47N report also mentions using a trailing boon and another plane. 

 

I'll keep digging and see what I can find. Further frustrating this is the fact that quite a few of the NACA P-47 reports still seem to be classified/restricted for some reason.

 

 

 

 

https://ntrs.nasa.gov/api/citations/20090022749/downloads/20090022749.pdf

 

This could maaaybe work. You have weight, altitude and as close as you can get it, IAS. I'll maybe have a stab at trying to get a TAS worked out tomorrow. 

 

 

 

I only skimmed that report you linked but it looks like the speeds are all in reference to “service IAS” which I would assume is the instrumented IAS which then brings us back to the PEC. Unfortunately most PEC’s I’ve seen and that have been posted in the forum only cover above stall into the cruise and high speed domain which makes sense since they were most likely targeting navigation applications as in aiding the pilot to do dead reckoning navigation. Extrapolating into stall speeds from those is dicey to say the least and will not bring sufficient accuracy to determine Clmax.

 

All aircraft I have come across pretty much follow the rules set by wing loading, span loading and power loading in terms of turn and ceiling which is not strange given that the rules of physics don’t care if there is a cross, roundel or star painted on the wing. In addition, the Republic S-3 is nothing out of the ordinary (very close to NACA 230 AFAIK) which then again suggest that the overall ballpark Clmax is probably in the order of 1.35, i.e. very similar to the Fw-190.

 

In addition, fighters in WW2 were pretty much at the shark stage in evolution, i.e. there was not very much to improve on and you can be sure that everyone else in the industry would have pounced on any opportunity to improve on Clmax while maintaining the other important aspects like low drag and pitching moment if they could. Consequently, if the S-3 had any magical properties it would have been copied immediately. Going off on a tangent, this is exactly why the NACA 230-series was (and still is!) so popular: It’s as close to being magical that seems possible to achieve. Why for example, did Kurt Tank select this “Yankee” profile for the Fw-190 if he had better Teutonic profiles in the drawer?

 

However, don’t let that discourage you and it’s always interesting to see new NACA reports so by all means please keep on digging. However, I would be very surprised if you were to find something showing the P-47 was out of the ordinary in this sense.

 

16 hours ago, BCI-Nazgul said:

Instinctively, you would expect the P-47 to perform closer to its contemporaries if only because it has huge wings and a huge engine to make up for its huge size.  Proportionately it looks a lot like a giant 190 or Hellcat.  The argument that just because it's big and heavy and therefore shouldn't be good in a dogfight doesn't hold a lot of water with me.   I don't expect it to be a Spitfire, but it seems much more capable in DCS.   Somehow the "magic" 110 seems to do just fine inspite of being "big".

 

Note that I'm not saying anything about how accurate the Il-2 high altitude modeling is for the P-47: Just that I don't think it had a significantly higher Clmax than the others.

 

In addition, any info on how aircraft compare between DCS and Il-2 would be interesting: For example, what is the turn time for the P-47 at 11900 lb and the Me-109K4 at 50% fuel at 10 Km altitude in-game in autumn conditions? I posted some simulation results so what do you see in-game?

 

TO THE MODERATORS: WHEN IS THIS DUMB AUTOMERGE FUNCTION GOING TO BE FIXED? PLS MAKE IT OFF BY DEFAULT AND AT THE VERY LEAST SELECTABLE!!!!

Edited December 17, 2021 by Holtzauge

[ACG_Cass]

2 hours ago, Holtzauge said:

I only skimmed that report you linked but it looks like the speeds are all in reference to “service IAS” which I would assume is the instrumented IAS which then brings us back to the PEC. Unfortunately most PEC’s I’ve seen and that have been posted in the forum only cover above stall into the cruise and high speed domain which makes sense since they were most likely targeting navigation applications as in aiding the pilot to do dead reckoning navigation. Extrapolating into stall speeds from those is dicey to say the least and will not bring sufficient accuracy to determine Clmax.

That's effectively what I was trying to say. Everything is useless until we get a condition specified, calibrated stall speed.

 

Just so we're on the same page - I'm trying to find something that shows the plane has a Clmax of ~1.35, not higher.

 

The Clmax of the IL2 P47 according the stats page is ~1.21. That's why I put the below together. The "Corrected" updates the stall speeds to get a Clmax to 1.35

 

 

The stats on those pages line up pretty well with all of the other planes we have in sim.

 

G6

lightest - 1.38

heaviest - 1.40

 

G6L

lightest - 1.38 

heaviest - 1.42

 

P51

lightest - 1.34

heaviest -1.37

 

Spit IX

lightest - 1.34

heaviest - N/A (Maxmum Weight not given)

 

Spit Vb

lightest - 1.34

heaviest - 1.33 (no bombs)

 

A3

lightest - 1.37

heaviest -1.39

 

A6

lightest - 1.39

heaviest - 1.39

 

I understand that the higher clmax at maximum take off weight can usually be attributed to the effect on Cg caused by the bombs and fuel. There's a large disparity between the D22 and D28 there.

 

I'd be ecstatic to get a low mach, power off Clmax of 1.35 in the sim for the P47. Its an almost 10% increase and would likely immediately stop all complaining.

 

We just need to find something that give us a definitive stall speed that says that.

Edited December 17, 2021 by ACG_Cass

[BCI-Nazgul]

6 hours ago, Holtzauge said:

Note that I'm not saying anything about how accurate the Il-2 high altitude modeling is for the P-47: Just that I don't think it had a significantly higher Clmax than the others.

 

In addition, any info on how aircraft compare between DCS and Il-2 would be interesting: For example, what is the turn time for the P-47 at 11900 lb and the Me-109K4 at 50% fuel at 10 Km altitude in-game in autumn conditions? I posted some simulation results so what do you see in-game?

 

TO THE MODERATORS: WHEN IS THIS DUMB AUTOMERGE FUNCTION GOING TO BE FIXED? PLS MAKE IT OFF BY DEFAULT AND AT THE VERY LEAST SELECTABLE!!!!

In DCS: Up high it needs to maintain a high speed or you will still get the dreaded wing stall when you try to turn a bit to sharp.  Below 20K is a different story in DCS.   You can turn quite sharply and it won't stall like your wing got stuck in concrete like it does in IL2.   There's also plenty of warning before a wing stall unlike IL2 where it just goes down instantly.   Also, with the boost on it is quite capable of losing 109s and 190s down low.   It has enough power to drag itself around in very tight turns without stalling and it can out accelerate the Germans when transistioning from a low speed fight to gain some seperation.   Without out the boost it's a bit dicey.  Of course, part two of this is the 8x.50s are deadly in DCS.  When you shoot up an enemy fighter it's not going to bother you again even if it doesn't die immediately.   That's probably at least as important as the manuevering difference between the two sims since the Germans don't get a second chance to win.  It can also take A LOT more damage in DCS and make it home or at least give you flight time to clear the area.   Also, in DCS your pilot doesn't have magic ears that can hear enemy planes coming.   You can't hear anything but your own engine which is realistic unlike in IL2.

 

My biggest gripe about the 47 in DCS is that there are no delayed bombs, so you have to drop from at least 1000 feet with the 1000 lb bombs to avoid blowing yourself up.  That makes really hard to hit things.

Edited December 17, 2021 by BCI-Nazgul

[Denum]

To me the lift seems under modeled. Without question. Even without testing. 

 

Explains why it practically loses its ability to fly with even slight damage. You need to be pretty darn good to do well in the job. Huge skill gap between it and comparable axis birds in its current form. 

 

Could just an honest mistake in the programming, or maybe someone felt the P47 needed to feel really heavy. 

Edited December 18, 2021 by Denum

[Dakpilot]

38 minutes ago, Denum said:

Could just an honest mistake in the programming, or maybe someone felt the P47 needed to feel really heavy. 

 

Why imply that someone on the Dev team would deliberately include false data.... It really does not help

 

Cheers, Dakpilot 

[Denum]

6 minutes ago, Dakpilot said:

 

Why imply that someone on the Dev team would deliberately include false data.... It really does not help

 

Cheers, Dakpilot 

Neither does making asinine assumptions. ?

 

 

In many situations new data can be found after the fact. It doesn't mean someone intentionally did something wrong. The developers work under tight deadlines. We are all well aware they do their very best and can't put every single detail under a microscope. We know they try to, but sometimes time runs short. It's easy for us to pick stuff apart after the fact. It's very difficult to do it with a deadline and eager players waiting for their new toys. 

 

When looking at CL data there's a ton of ways to interpret it. From a short lesson courteous of Yak even where they take the data from, how they take the data can drastically change the end result. In this situation it's looking like (possibly) a 10% discrepancy. 

 

The developers can be factually correct to the source that they had at the time. But on occasion sometimes better data is discovered and it's a win for everyone. 

 

 

[Dakpilot]

1 hour ago, Denum said:

or maybe someone felt the P47 needed to feel really heavy. 

 

No asinine assumptions needed

 

Cheers, Dakpilot 

[Denum]

1 minute ago, Dakpilot said:

 

No asinine assumptions needed

 

Cheers, Dakpilot 

I could go back and quote all the people (and it's quite a few) that suggest the P47 should handle bad because heavy but conveniently ignore the 110s near magic levels of lift. 

 

But I feel that would be a complete waste of effort. 

 

 

[gimpy117]

9 hours ago, Denum said:

I could go back and quote all the people (and it's quite a few) that suggest the P47 should handle bad because heavy but conveniently ignore the 110s near magic levels of lift. 

 

But I feel that would be a complete waste of effort. 

 

 

indeed. you'll get the old "because aerodynamics" vague answer. maybe I missed it, but I've yet to see anyone explain why the 110 gets the treatment it does when compared to other aircraft, especially ones of comparable wing loading power to weight etc. I personally think something is wrong. 

[BCI-Nazgul]

It was a much better plane in the old IL2 not because it could turn tightly, but because the guns were deadly, it had good energy retention, it could climb well, could take a lot of damage, and was fast and handled well at high altitude.  It was the perfect B and Z plane.  In this IL2, none of the above is true.  In DCS most of characteristics are the same as the old IL2, so who is right?  My reading and watching various documentaries tells me that the 47 was not as helpless as it is in this sim.  One other major difference is how devastating a single HE hit of any caliber is to a plane's aero characteristics including the tiny HE charge in the 13mm and 12.7mm rounds.   In DCS you can keep fighting after a close 37mm AA burst or a few 20mm cannon hits and limp home with all kinds of holes in your wings.  In IL2 a single 13mm hit and your done fighting.  If any fighter could take some damage and keep fighting you'd think it would be a P-47, but no.   Something isn't right there.

Edited December 18, 2021 by BCI-Nazgul

[Knarley-Bob]

With all the threads about the P47, one would think they(whom ever that is) would take a good hard look at it. People are just asking for a fair shake. I have heard the the  P47 "was the plane that broke the Luftwaffe's back". How would anyone even be able to claim that when supposedly the plane can't even get out of it's own way? Come on!! Common sense would be that IF that plane was such a 'slug' the USAAF would not have even bothered with it. If the plane crashed and burned by hitting a sparrow at the end of the runway, pilots would have refused to fly them. Yeah , I know anecdotal replies are frowned upon here, but so seems common sense. Implying people are implying, doesn't work either. It seems someone does protest too much.

Edited December 18, 2021 by Knarley-Bob

[Cpt_Siddy]

Have you all forgotten how P-47 could literally VTOL with full fuel and bombload with full flaps?

It could do this at 70 miles IAS at 40deg aoa...

 

I guess something was done to address this and ended up like it is now. 

 

 

Edited December 18, 2021 by Cpt_Siddy

[HR_Zunzun]

14 minutes ago, Cpt_Siddy said:

Have you all forgot how P-47 could literally VTOL with full fuel and bombload with full flaps?

It could do this at 70 miles IAS at 40deg aoa...

 

I guess something was done to address this and ended up like it is now. 

 

 

That is true. But even then the high speed (250-400mph) elevator response was dismal.

[BCI-Nazgul]

27 minutes ago, Cpt_Siddy said:

Have you all forgot how P-47 could literally VTOL with full fuel and bombload with full flaps?

It could do this at 70 miles IAS at 40deg aoa...

 

I guess something was done to address this and ended up like it is now. 

 

 

When?  What sim?

[Denum]

6 hours ago, BCI-Nazgul said:

It was a much better plane in the old IL2 not because it could turn tightly, but because the guns were deadly,

I remember the 1946 110 with the MK108 to be just hilariously deadly 

 

Hard to hit people but when you did. Wow did it mess them up!

[BCI-Nazgul]

13 minutes ago, Denum said:

I remember the 1946 110 with the MK108 to be just hilariously deadly 

 

Hard to hit people but when you did. Wow did it mess them up!

It should.

[Knarley-Bob]

10 hours ago, Cpt_Siddy said:

Have you all forgotten how P-47 could literally VTOL with full fuel and bombload with full flaps?

It could do this at 70 miles IAS at 40deg aoa...

 

I guess something was done to address this and ended up like it is now. 

 

 

And the plot thickens...........So the P-47 USED to perform, beginning to see a pattern........

On 12/18/2021 at 12:08 AM, Dakpilot said:

 

Why imply that someone on the Dev team would deliberately include false data.... It really does not help

 

Cheers, Dakpilot 

Gee wonder why any one would do that?

10 hours ago, HR_Zunzun said:

That is true. But even then the high speed (250-400mph) elevator response was dismal.

250 to 400 MPH huh?

On 12/16/2021 at 2:01 PM, BCI-Nazgul said:

Instinctively, you would expect the P-47 to perform closer to its contemporaries if only because it has huge wings and a huge engine to make up for its huge size.  Proportionately it looks a lot like a giant 190 or Hellcat.  The argument that just because it's big and heavy and therefore shouldn't be good in a dogfight doesn't hold a lot of water with me.   I don't expect it to be a Spitfire, but it seems much more capable in DCS.   Somehow the "magic" 110 seems to do just fine inspite of being "big".

Imagine that...........The 110...........again

 

4 hours ago, Denum said:

I remember the 1946 110 with the MK108 to be just hilariously deadly 

 

Hard to hit people but when you did. Wow did it mess them up!

And again........

How many people have complained about the .50 cals?

I can see a a while ago, the  P-47 that WAS lord of the skies, it handled like it should, fast, rugged with machine guns that shredded everything in it's path. The out cry of the enemy pilots shrieking at the top of their lungs, oh no we can't have this!!! And so something was done...........

 

All one has to do is "Do the math". Why do people on the forum so rabidly defend the way the P-47 is now? I don't wonder too hard.

Edited December 19, 2021 by Knarley-Bob

[HR_Zunzun]

4 hours ago, Knarley-Bob said:

250 to 400 MPH huh?
 

P-47 should struggle at low speed but, at the speed I indicated, before getting into compresibility realm (depending on altitude), it should turn decently well. That is what is being discussed here. Documents that @Yak_Panther, @ACG_Cass and others have brought forward, seems to indicate a lack of Lift and elevator authority.

[Holtzauge]

Having looked some more into this during the weekend, I think I made a mistake to do such a tight connection between the NACA230 and Republic S3 profile: The S3 has a much sharper nose radius and that is a big drawback for attaining high lift coefficients. So if anything, based on this the S3 should have a lower Clmax. This can also be seen in the airfoiltools.com data where the S3 only manages a Clmax of circa 1.25 while the NACA23912 goes over 1.5. However, the data at airfoiltools.com only goes up to Re=1M and I did some runs at Re=5M which would be more in line with the IRL Re. However, the trend persists with the NACA profile managing up to around 1.75 while the S3 only goes up to around 1.45 at Re=5M. This is bad news for those hoping for a high Clmax for the P-47 since this implies that the Thunderbolt will have a lower Clmax than 1.35 on aircraft level since the Fw-190 which uses the NACA230 profile manages 1.35 with a wing profile with a Clmax of circa 1.75 at Re=5M. So unfortunately, this implies that a Clmax of 1.2 on aircraft level for the P-47 is not unreasonable.

 

Finally: Earlier on in this thread allegations about the reliability of results from airfoiltools.com were made with the implication that the data there is unreliable for the Republic S3 profile since it uses a too coarse panel mapping. However, the proper way (and intended) to use Xfoil is to use the coarser coordinate data file to create a finer mesh before running simulations. This has also been done when the L/D-polars for the S3 were generated at airfoiltools.  So doing your own simulations with the coarser coordinate data and based on that disqualifying the results is more a misunderstanding of how the data at airfoíltools was generated and how Xfoil should be used.

Edited December 19, 2021 by Holtzauge

[Holtzauge]

Now that the P-47’s Clmax has been explained with all those NACA charts, I thought it would be good idea to also take a look at the Thunderbolt’s big problems with side fumbling at high angles of attack. How this issue is neatly fixed with the Rockwell Retro Encabulator’s differential gurdle spring is well explained about a minute into the video.

 

Edited December 19, 2021 by Holtzauge

[Denum]

Something with the P47 is still off regardless. I don't feel the CL numbers being out to lunch is off the table yet. But it maybe a more complex situation then I'm currently capable of understanding.

 

The FM feels very different even compared to the heaviest 190s. 

 

The P47 D28 wants to stall at 300mph mid turn. Which seems odd. You can't even get that much stick deflection in before it tries to flip over on you. 

 

Edited December 19, 2021 by Denum

[[CPT]Crunch]

For something so stiff and lanky it sure snaps, flips, and tumbles like a pent up rubberband when it takes a hit.  Physics is out of whack there to an extreme.

[ZachariasX]

26 minutes ago, Holtzauge said:

Now that the P-47’s Clmax has been explained with all those NACA charts, I thought it would be good idea to also take a look at the Thunderbolt’s big problems with side fumbling at high angles of attack. How this issue is neatly fixed with the Rockwell Retro Encabulator’s differential gurdle spring is well explained about a minute into the video.

Absolutely. I mean, the solution would have been so easy. They actually hooked that up with a reciprocating dingle arm to reduce sinusoidal depleneration. They installed this in the American late 80's and it gave them so much more power at only 80 hp thanks to the turbo incabulator. It was the solution of choice for GM's lead engineers to make their cars superior to competing Japanese or German technology.

[Holtzauge]

23 minutes ago, ZachariasX said:

Absolutely. I mean, the solution would have been so easy. They actually hooked that up with a reciprocating dingle arm to reduce sinusoidal depleneration. They installed this in the American late 80's and it gave them so much more power at only 80 hp thanks to the turbo incabulator. It was the solution of choice for GM's lead engineers to make their cars superior to competing Japanese or German technology.

 

Yes, the dingle arm should reduce the tendency for pitch oscillations and maybe dutch roll tendencies as well. Maybe this is why we see the rubber band effect in the Spitfire Mk XIV FM? I mean if the Spitfire's incabulator's dingle arm is out of whack that would explain a thing or two wouldn't it? Maybe also help explains the wing fragility issue we see in FC........

[ZachariasX]

33 minutes ago, Holtzauge said:

 

Yes, the dingle arm should reduce the tendency for pitch oscillations and maybe dutch roll tendencies as well. Maybe this is why we see the rubber band effect in the Spitfire Mk XIV FM? I mean if the Spitfire's incabulator's dingle arm is out of whack that would explain a thing or two wouldn't it? Maybe also help explains the wing fragility issue we see in FC........

I will surely simulate the effect of dingle arm configurations on the Spit XIV. In my Telegram group, they told me it was important that this was done using BF16. Now I have to find out how to make Excel use BF16.

[Ace_Pilto]

Is this a left handed reciprocating dingle arm? I'm not sure that the encabulation is compatible with the European texture set.

[Cpt_Siddy]

12 hours ago, Knarley-Bob said:

And the plot thickens...........So the P-47 USED to perform, beginning to see a pattern........

 

If by preforming you mean being first US VTOL fighter then yes. 

 

The first iteration of P-47 was totally broken, it lost parts in 500mph dive, it could prophang with flaps, if you were empty you could just ignore gravity totally with flaps.

 

It seems that the "fix" to all these problems involved something that castrated the poor thing to the point you can outfight it with Pe-2 at 8km. 

Edited December 19, 2021 by Cpt_Siddy

[ACG_Cass]

6 hours ago, Holtzauge said:

Having looked some more into this during the weekend, I think I made a mistake to do such a tight connection between the NACA230 and Republic S3 profile: The S3 has a much sharper nose radius and that is a big drawback for attaining high lift coefficients. So if anything, based on this the S3 should have a lower Clmax. This can also be seen in the airfoiltools.com data where the S3 only manages a Clmax of circa 1.25 while the NACA23912 goes over 1.5. However, the data at airfoiltools.com only goes up to Re=1M and I did some runs at Re=5M which would be more in line with the IRL Re. However, the trend persists with the NACA profile managing up to around 1.75 while the S3 only goes up to around 1.45 at Re=5M. This is bad news for those hoping for a high Clmax for the P-47 since this implies that the Thunderbolt will have a lower Clmax than 1.35 on aircraft level since the Fw-190 which uses the NACA230 profile manages 1.35 with a wing profile with a Clmax of circa 1.75 at Re=5M. So unfortunately, this implies that a Clmax of 1.2 on aircraft level for the P-47 is not unreasonable.

 

Finally: Earlier on in this thread allegations about the reliability of results from airfoiltools.com were made with the implication that the data there is unreliable for the Republic S3 profile since it uses a too coarse panel mapping. However, the proper way (and intended) to use Xfoil is to use the coarser coordinate data file to create a finer mesh before running simulations. This has also been done when the L/D-polars for the S3 were generated at airfoiltools.  So doing your own simulations with the coarser coordinate data and based on that disqualifying the results is more a misunderstanding of how the data at airfoíltools was generated and how Xfoil should be used.

 

Thanks @Holtzauge

 

Even a modest boost to 1.25 would probably be noticed.

 

It's got to be the lacking elevator authority that is the main culprit then. The stall speeds in DCS at the same weight are almost the same so they're Clmax probably isn't much higher. 

 

Peak G aside, the below shows the elevator authority was very good for the P-47. In game it's certainly in stark contrast to what we have in IL2. 

 

 

 

 

 

 

 

[Holtzauge]

15 minutes ago, ACG_Cass said:

 

Thanks @Holtzauge

 

Even a modest boost to 1.25 would probably be noticed.

 

It's got to be the lacking elevator authority that is the main culprit then. The stall speeds in DCS at the same weight are almost the same so they're Clmax probably isn't much higher. 

 

Peak G aside, the below shows the elevator authority was very good for the P-47. In game it's certainly in stark contrast to what we have in IL2. 

 

 

 

 

 

 

 

 

Well those things should of course also be possible to do in-game but remember those are only transients so you should be able to reach 4.5 g through the effect of the starting vortex but as the histogram implies, you bleed speed quickly and in just a second you are down to 1 g having lost almost 15 mph so nothing sustained about it. In addition, you will not be able to do an instantaneous turn at 4.5 g either since the abrupt angle of attack Clmax is significantly higher than the max that can be sustained for any meaningful period of time. In addition, if you are going fast when you enter the turn there will most likely be buffeting limitations as well. Off the top of my head I remember that Messerschmitt themselves assumed Clmax=1.15 for the Me-109 at higher speeds, probably due to buffeting effects so much lower than the low speed Clmax of 1.4.

 

However, question is if we really can expect things like this to be modeled in-game? These are complex phenomena and I'm impressed by what we have as it is and I think we should be happy if we get the instantaneous and stationary turn rates in the right ballpark. I think expecting Il-2 to model transient effects like have been posted earlier on in this thread is setting the bar too high.

 

OTOH on the plus side, the P-47 at 11900 lb should be able to hold its own in turn even with a Me-109K4 with 50% fuel at 10 Km altitude but then we are nowhere close to Clmax because neither the Me-109 or P-47 has the power to sustain that. I did a quick run in C++ at 10 Km altitude with 65" boost and I get a turn time of around 65 s with the Cl the power can balance out at circa 0.91 so quite a bit below the low speed Clmax even if we assume this in the 1.2-1.25 range.

[ACG_Cass]

2 hours ago, Holtzauge said:

Well those things should of course also be possible to do in-game but remember those are only transients so you should be able to reach 4.5 g through the effect of the starting vortex but as the histogram implies, you bleed speed quickly and in just a second you are down to 1 g having lost almost 15 mph so nothing sustained about it. In addition, you will not be able to do an instantaneous turn at 4.5 g either since the abrupt angle of attack Clmax is significantly higher than the max that can be sustained for any meaningful period of time. In addition, if you are going fast when you enter the turn there will most likely be buffeting limitations as well. Off the top of my head I remember that Messerschmitt themselves assumed Clmax=1.15 for the Me-109 at higher speeds, probably due to buffeting effects so much lower than the low speed Clmax of 1.4.

That's what I meant by "peak G aside". 

 

I'm ignoring that maximum and looking at the rate at which it increases. I think the elevator authority on the P-47 in IL2 are quite a way off it seems. 

 

Here is a full stick pull under the 214 IAS in IL2. This was completed by running the simulation in 1/32 and tracking the G reading every 0.5s.

 

 

Matching the scale and then lining it up with the point at which the force is initially applied. It takes 0.8s to reach full stick back, which lines up with the chart well so I don't think the forces are an issue. What doesn't line up is the onset rate for the forces, which are definitely behind on the IRL test in both rate and time.

 

 

(I'll see if there's a way for me to make the overlay transparent so it's easier to see)

 

 

 

 

Edited December 19, 2021 by ACG_Cass

[DBFlyguy]

Has any of this data been put in the "Technical Issues and Bug Reports" forum so a dev will actually maybe look at it? that's probably where it should go otherwise you all are essentially just talking to yourselves in circles and nothing will be looked at by anyone that may actually be able to address it.

[Denum]

They peek in here every now and again.

 

Currently no one has really nailed down exactly what makes the P47 feel off, 

 

Could be the CL, could be elevator response etc. 

 

 

[Holtzauge]

17 hours ago, ACG_Cass said:

That's what I meant by "peak G aside". 

 

I'm ignoring that maximum and looking at the rate at which it increases. I think the elevator authority on the P-47 in IL2 are quite a way off it seems. 

 

Here is a full stick pull under the 214 IAS in IL2. This was completed by running the simulation in 1/32 and tracking the G reading every 0.5s.

 

 

Matching the scale and then lining it up with the point at which the force is initially applied. It takes 0.8s to reach full stick back, which lines up with the chart well so I don't think the forces are an issue. What doesn't line up is the onset rate for the forces, which are definitely behind on the IRL test in both rate and time.

 

 

(I'll see if there's a way for me to make the overlay transparent so it's easier to see)

 

 

 

 

 

Interesting results but in some sense expected: Granted, I have not flown a WW2 fighter and the hottest ride I have experience with is the Pitts S-2 but most planes I have flown have an immediate response to stick input. For example, the S-2 immediately starts and stops rolling with stick input. Rock solid. No rubber band effect whatsoever. On rails FM.

 

In the early flight sim days people complained about the “on rails” FM and many applauded when the wobbly rubber band FM’s made an entrance since many gamers equate more difficult with more realistic. So maybe we have what we wished for? The “reaIistic” flight sims are then ones that sell? I have no idea if what we see in-game in Il-2 (e.g. Spitfire MkXIV) is the result of a limitation in the FM or if it has been tuned this way? However, fortunately we have people like @ZachariasX here who has flown a real Spitfire and can compare and as far as I understood it from him they are not very similar when it comes to the response to control input.

 

So my question about the result which you posted is this: Is the lag in control input you measured really limited only to the P-47? Is this not how the basic Il-2 FM works? A tad lagging in response and enormous rubber bands that suspend the aircraft in flight?

 

There are numerous videos on Youtube showing cockpit views from WW2 fighters but one of my favourite ones showing the IRL “on rails” FM is this one with a Yak-3. Look at his stick input and how the plane responds rock solid. IMHO the closest thing we have in-game is a Fw-190A3 with 50% fuel. The in-game Spitfire MkXIV? I took that thing for a ride when it was released and now it’s just gathering dust in the hangar……

 

PS: Nicely executed measurements and presentation of the stick response history: Just the thing needed to do worth while comparisons between in-game and IRL.

 

Edited December 20, 2021 by Holtzauge

[ZachariasX]

1 hour ago, Holtzauge said:

So my question about the result which you posted is this: Is the lag in control input you measured really limited only to the P-47? Is this not how the basic Il-2 FM works? A tad lagging in response and enormous rubber bands that suspend the aircraft in flight?

This "mushiness around the center" is something I see on basically all aircraft and all simulators, this and that one as well. It just occurs more or less with each individual simulated aircaft. When they say that "this and that aircraft are very maneuvreable" then to me this implies that the plane acts swiftly upon stick input, meaning it is at least somewhat neutral in pitch axis, whereas on "less maneuvrable" aircraft, you really have to deflect that stick more and with more force, something that is not easily replicated in a sim with a table top joystick.

 

The Spitfire feels so maneuvrable because she feels like you could pull her through a loop with just one finger and on top of that her behaviour seems predictable and precise enough that makes you feel like pulling such a stunt. It has nothing to do with how fast the aircraft actually turns or rolls.

 

I think we are looking at a very basic simulation artifact here.

 

EDIT: As said, I see the relative inefficiancy of control authority in the excessive elevator travel required for a certain pitch moment. In the Spitfire, it is very obvious that the trim does not correspond to the actual aircraft and the stick imput required for a  certain maneuver is also not consistent. It requires way to much deflection at the center and it gets too efficient at large deflections. It is even visible in the FC Dr.I where the difference of forward push between @Chill31's Dr.I and the in-game Dr.I is obvious and has been clearly showed on pictures. I also showed elevator deflection required for cerain flight configurations. We require excessive deflections for common maneuvers in most simulators. These are traits that can make an aircraft feel "less maneuverable".

Edited December 20, 2021 by ZachariasX