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P-47 vs P-51/P-38

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7 hours ago, JtD said:

It absolutely should, both by span/area effected and by power going into it. FWIW, the lift coefficients for both planes were in excess of what I get in a power off stall, so prop wash definitely plays a role.

 

I'm not saying propwash doesn't play a role, I'm saying it isn't really going to play more of a role for the P-38 than it does for the Fw190 in terms of percentages which is what matters,  esp. if we start considering wing reference area taken up by fuselage & engine nacelles. Furthermore the propwash intensity produced by the Fw190 is over the covered area is going to be higher.

 

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I disagree. All I need to do for the P-38 to achieve the relative performances I tested in game in clean condtion is to give it a 9% higher lift coefficient than the Fw190. That's well within the realms of possible, for several reasons mentioned above, and that means the overall advantage doesn't need to be with the Fw190D. In particular as I tested at sea level, which is the best possible altitude for the Fw.

 

At 7940 kg vs 4270 kg you would need about a 11% higher Cl to achieve the same load factor, which I don't see as realistic flaps up all things considered. 

 

From an AR of 6 to 9 you usually don''t see more than a 7.5% increase, and that's with less reference wing area taken up by fuselage & nacelle structure.

 

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You pick the plane and fly it in circles, while keeping speed and altitude constant. Then you look at a watch. It doesn't really get more simple than that.

 

I prefer a more precise method, like measuring the sustainable load factor :)  Otherwise I'd have to record my turns, rewatch them and then trust in the ASI etc, which I guess is possible but not usually how I'd do it :)

 

 

Anyway IMHO the P-38 should not be outturning the Fw190, P-51 or P-47 flaps up, it can possibly match them, but that's it IMO. As for the 109, and esp. the Spitfire, not a chance.

Edited by Panthera

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It seems propwash affects a signficant part of the wing area... over half of it? Just judgding by whats behind the propeller arcs, I don't know if the propwash effect extends away from them or if it's constrained a bit inside the propeller circumsference.

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Eitherway while the P-38 is fairly popular in multiplayer currently, it is mostly becuase of it's high bombload capability. It doesn't seem to be "breaking" MP stomping the 109s and 190s... more like the contrary to be honest 😅 many take the 38 with bombs and end up quickly dispatched in transit or after dropping them on the target. Some good players do rather well in it but it seems that you can be more effective in other planes for each particular combat style (P-51, Spit, Tempest). Currently it seems to be one of the lesser performing allied planes in regards to kill/death ratio.

Edited by -=PHX=-SuperEtendard
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There is also a venturi effect over the central wingspan due to the interaction of the engine and cockpit nacelles. This increases the speed of the airflow over the center span and if I am not mistaken should increase lift at subsonic speeds relative to other planes without this effect at the same speed.

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13 hours ago, Panthera said:

if we start considering wing reference area taken up by fuselage & engine nacelles

 

If we do, we should also consider other elements like landing gear, wing gun mounts and generally hatches and panels, so that we can arrive at a certain wing quality figure.

 

FWIW, I tested the P-38 flaps fully down and managed 17.9s sustained at 240km/h. I pretty much failed to stall the aircraft even with stick fully back. That's an issue, two issues actually, as far as I'm concerned.

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3 hours ago, JtD said:

FWIW, I tested the P-38 flaps fully down and managed 17.9s sustained at 240km/h. I pretty much failed to stall the aircraft even with stick fully back. That's an issue, two issues actually, as far as I'm concerned.

 

Have you tried the same with SpitIX in-game?

Edited by [DBS]TH0R

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12 hours ago, -=PHX=-SuperEtendard said:

It seems propwash affects a signficant part of the wing area... over half of it? Just judgding by whats behind the propeller arcs, I don't know if the propwash effect extends away from them or if it's constrained a bit inside the propeller circumsference.

 

It does, but percentage wise it's about the same for both aircraft, and the effect is indeed significant. However as I mentioned before a larger part of the P-38's wing reference area is taken up by fuselage & nacelle structure, and thus you run into the problem of less percentage wise area optimally shaped for generating lift.

 

 

6 hours ago, JtD said:

 

If we do, we should also consider other elements like landing gear, wing gun mounts and generally hatches and panels, so that we can arrive at a certain wing quality figure.

 

FWIW, I tested the P-38 flaps fully down and managed 17.9s sustained at 240km/h. I pretty much failed to stall the aircraft even with stick fully back. That's an issue, two issues actually, as far as I'm concerned.

 

For sure, I totally agree.

 

Yes, I see no reason why you shouldn't be able to enter an accelerated stall with the flaps down, esp. since this will actually lower the critical AoA of the wing. 

Edited by Panthera

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The P-38 flaps behaviour mentioned above seems consistent with issues we've seen with using flaps in combat with other aircraft - most notably the P-47 but also in other craft. Flaps appear to have some kind of global issue in terms of reducing stall speeds too much and granting unrealistic turn rates.

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On 10/28/2019 at 9:47 AM, RedKestrel said:

The P-38 flaps behaviour mentioned above seems consistent with issues we've seen with using flaps in combat with other aircraft - most notably the P-47 but also in other craft. Flaps appear to have some kind of global issue in terms of reducing stall speeds too much and granting unrealistic turn rates.

 

Note that that is only in turns or under high power loads. I did the glide slope test on the P-47 flaps earlier this year and they did appear to be behaving as described in the flight manual. Recall, the flight manual has you gliding into the land, not coming in with power. It even notes to be sure to run up the engine for a moment early in the glide slope just to be sure the engine hasn't carboned up and would actually run up if you needed to abort. 

 

The high power loads, I suspect is a problem with expectations rather than the model. Climb is the difference between power required to sustain level flight at that speed and the available power, and while the power required does go up as the speed goes below a certain point, many of these planes have a *lot* of excess power. That's how things like modern muscle bi planes are able to do those high AoA knife edge take offs. 

 

All that leads me to wonder if there is another aerodynamic effect that we only see in turns that's not being accounted for. Perhaps there is a span-wise flow effect that's not usually considered when measuring flap behavior? 

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7 minutes ago, Voyager said:

 

Note that that is only in turns or under high power loads. I did the glide slope test on the P-47 flaps earlier this year and they did appear to be behaving as described in the flight manual. Recall, the flight manual has you gliding into the land, not coming in with power. It even notes to be sure to run up the engine for a moment early in the glide slope just to be sure the engine hasn't carboned up and would actually run up if you needed to abort. 

 

The high power loads, I suspect is a problem with expectations rather than the model. Climb is the difference between power required to sustain level flight at that speed and the available power, and while the power required does go up as the speed goes below a certain point, many of these planes have a *lot* of excess power. That's how things like modern muscle bi planes are able to do those high AoA knife edge take offs. 

 

All that leads me to wonder if there is another aerodynamic effect that we only see in turns that's not being accounted for. Perhaps there is a span-wise flow effect that's not usually considered when measuring flap behavior? 

I see. I rarely glide in with power off - I usually have a little power to the engine and use a lower flaps setting, rather than the recommended full flaps down glide in...I just find it harder to land that way, but i should probably keep trying to do it the by-the-book way. 

I haven't  used the flaps in combat or under high power settings really at all...as they were not able to be used that way IRL as I understand, I just haven't used it that way. When I fly the P-47 that way it behaves the way I would expect it to. I have received the common advice of dropping 20 degrees of flaps in combat as a way to turn better but I haven't bothered to do it, except once as a test when I was doing a familiarization flight, and once by accident when I forgot to raise my flaps after takeoff. It takes so long to drop and retract the flaps that I feel I'm better served using the roll and dive characteristics than trying to force the jug to turn fight, plus it just feels more realistic to me. 

I don't have anything more than a basic layperson's understanding of aerodynamics but I think you are likely correct - there is something going on with flaps in combination with high engine settings. 

Could it be that the propeller at high throttle settings is giving enough airflow over the wings that when flaps are deployed, it can generate a too large amount of lift?

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Finally got the P-38 J Lightning modeled in C++. Here are results for stationary turn rate:

 

Time to do a 360 degree turn at weight 7332 Kg (16149 lb):

 

No flap: 20.6 s @ 339 Km/h

 

Combat (8 deg) flap: 19.3 s @ 319 km/h

 

45 degree flap: 16.8 s @ 270 Km/h

 

So quite close to the numbers in the turn time charts JtD posted earlier and also quite in line with the in-game 45 degree flap turn test as well. So as far as I can see the current BOBP modeling seems close and the Lightning with 45 degrees Fowler flap should turn quite fast with a small radius. Question is do you want to go there? However, if you do find yourself at low speed in a knife fight it certainly looks like the Lightning delivers! ;)

Edited by Holtzauge
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@HoltzaugeIve been a way a while, but did you run that type of model analysis for the P-47D-28 with flaps? I was able to test the glide slope a while back and it seemed reasonable, but never had the background to dig into the turn performance beyond finding the asymmetrical issue. I'm very curious what the results would be. 

 

I also found out later that the P-47 flaps are more slotted flaps than Fowler style. Still better than plain or split, but not quite Fowler flaps. 

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1 hour ago, Voyager said:

@HoltzaugeIve been a way a while, but did you run that type of model analysis for the P-47D-28 with flaps? I was able to test the glide slope a while back and it seemed reasonable, but never had the background to dig into the turn performance beyond finding the asymmetrical issue. I'm very curious what the results would be. 

 

I also found out later that the P-47 flaps are more slotted flaps than Fowler style. Still better than plain or split, but not quite Fowler flaps. 

It's a fowler flap due to the mechanism and how it deploys, same with the P-38.

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@Voyager & @Legioneod: I have the P-47 D-30 modeled and at sea level with 65" boost 45 deg flap I get 18.2 s for a 360 deg turn at @ 242 Km/h assuming about 50% fuel (ca 12000 lb) so it looks like the Thunderbolt should turn pretty well at low speed if you drop the flaps and don't carry a full fuel load. That being said I have done no tests myself so I don't know how the P-47 is behaving in-game but I have seen complaints. What kind of turn times are people getting in-game then that they think are too good?

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1 hour ago, Holtzauge said:

@Voyager & @Legioneod: I have the P-47 D-30 modeled and at sea level with 65" boost 45 deg flap I get 18.2 s for a 360 deg turn at @ 242 Km/h assuming about 50% fuel (ca 12000 lb) so it looks like the Thunderbolt should turn pretty well at low speed if you drop the flaps and don't carry a full fuel load. That being said I have done no tests myself so I don't know how the P-47 is behaving in-game but I have seen complaints. What kind of turn times are people getting in-game then that they think are too good?

With 50% fuel P-47 in game 65inches with max flap manages 22.1deg/s sustained at 217kph.

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OK, well I get 21.1 s at 212 Km/h so close enough. 😉

 

BTW: Did you try going faster? For me the corner speed is around 240 Km/h which was why I posted the 18.2 s because that was the lowest turn time I got.

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4 hours ago, Holtzauge said:

@Voyager & @Legioneod: I have the P-47 D-30 modeled and at sea level with 65" boost 45 deg flap I get 18.2 s for a 360 deg turn at @ 242 Km/h assuming about 50% fuel (ca 12000 lb) so it looks like the Thunderbolt should turn pretty well at low speed if you drop the flaps and don't carry a full fuel load. That being said I have done no tests myself so I don't know how the P-47 is behaving in-game but I have seen complaints. What kind of turn times are people getting in-game then that they think are too good?

At 100% flaps and around 50% fuel I'll outturn nearly everything, I even stuck on the six of an I-16 and a Spitfire with little trouble.

I'm not saying it's too good (though they do seem a bit too floaty), if the P-47 could use flaps in combat irl it very well may have been an excellent turner but I've never found any accounts of the P-47 being able to use flaps. I've only ever read that the flaps had a tendency to deploy asymmetricaly so they weren't used in combat.

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So maybe all this time the unrealistic flaps were only unrealistic in that they deploy symmetrically in game?

 

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Asymmetric flap deployment is a very serious issue if this was a common thing I would think there would be more information on this (very dangerous) flaw. 

 

Some investigation into to the  flap operation and method of actuation should easily prove this. Most aircraft have some sort of flap interconnect. 

 

Asymmetric flap deployment on a high performance aircraft such as this would be a killer. 

More info and corroboration is needed 

 

Cheers, Dakpilot 

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On 11/3/2019 at 5:56 PM, Holtzauge said:

Finally got the P-38 J Lightning modeled in C++. Here are results for stationary turn rate:

 

Time to do a 360 degree turn at weight 7332 Kg (16149 lb):

 

No flap: 20.6 s @ 339 Km/h

 

Combat (8 deg) flap: 19.3 s @ 319 km/h

 

45 degree flap: 16.8 s @ 270 Km/h

 

So quite close to the numbers in the turn time charts JtD posted earlier and also quite in line with the in-game 45 degree flap turn test as well. So as far as I can see the current BOBP modeling seems close and the Lightning with 45 degrees Fowler flap should turn quite fast with a small radius. Question is do you want to go there? However, if you do find yourself at low speed in a knife fight it certainly looks like the Lightning delivers! ;)

 

Well that's 608 kg lighter than in my calcs so that certainly changes things, but out of interest how does the Fw190D9 compare with a similar fuel percentage and 2071 hp in your C++?

 

Btw don't think I ever asked this before, but does your C++ program take into account the increase in Cl with a higher AR ? Would be interesting to plug the Ta152H into it.

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8 hours ago, Dakpilot said:

Asymmetric flap deployment is a very serious issue if this was a common thing I would think there would be more information on this (very dangerous) flaw. 

 

Some investigation into to the  flap operation and method of actuation should easily prove this. Most aircraft have some sort of flap interconnect. 

 

Asymmetric flap deployment on a high performance aircraft such as this would be a killer. 

More info and corroboration is needed 

 

Cheers, Dakpilot 

You are not supposed to deploy flaps in the P-47 when going faster than 195 mph. If you do so, one of the two flaps is gonna break first. If you have one flap stuck, the only thing you can do is deploy the other in the same way *and go for landing immediately*. The flaps are not interlinked beyond the hydraulics. 314 km/h as max allowed speed for flaps is very slow.

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9 hours ago, Dakpilot said:

Asymmetric flap deployment is a very serious issue if this was a common thing I would think there would be more information on this (very dangerous) flaw. 

 

Some investigation into to the  flap operation and method of actuation should easily prove this. Most aircraft have some sort of flap interconnect. 

 

Asymmetric flap deployment on a high performance aircraft such as this would be a killer. 

More info and corroboration is needed 

 

Cheers, Dakpilot 

I had read it stated explicitly somewhere, but couldn;t remember where, so I did some digging. On this page it says that:

"6.              The controls for the hydraulic system for undercarriage, (all wheels retract), flaps and cowling gills are accessible, but there is also a flap equalizing valve which must be operated to ensure that the flaps will come down evenly, making one more control for the fighter pilot to remember."

From this I concluded that the flaps often deployed unevenly, causing serious issues - the solution was the secondary control in the cockpit to equalize the flaps. But this was for the P-47C. Looking at later manuals like this one here on pg 35, it seems that this valve was only included on variants P-47D-10 and earlier. Presumably they solved the issue in later variants, and since we have the D-28 it shouldn't be a concern. 
 

44 minutes ago, ZachariasX said:

You are not supposed to deploy flaps in the P-47 when going faster than 195 mph. If you do so, one of the two flaps is gonna break first. If you have one flap stuck, the only thing you can do is deploy the other in the same way *and go for landing immediately*. The flaps are not interlinked beyond the hydraulics. 314 km/h as max allowed speed for flaps is very slow.


So if the flaps risk uneven deployment unless I use a second control (at least on earlier models), and they can't be used above 195 mph without fear of damage, then I can't imagine they were very tactically useful in real life.

It is a little reassuring to see that perhaps the flap behaviour itself isn't incorrect. But I would like to see flap damage from improper deployment at high speeds for sure. Dropping flaps during a 250 mph dogfight in a P-47 should cripple your aircraft, not give you a turn advantage.

I don't believe this is currently modeled - I don't think I've ever damaged flaps through misuse in-game, but then I tend to only use them on takeoff and landing, not during dogfights.

 

Edited by RedKestrel
Edit: Cited my sources better
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Naca report 2899, pg 61 shows how the flaps deploy over time and the pilot stick inputs to compensate for it on the P-47D-30. The pilot ends up needing 4-5 degrees of roll input in each direction to keep the plane lined up as the flaps deploy. I'll need to read through the report to be sure if that was 5 degrees of aileron deflection or 4-5 degrees of stick deflection. 

 

Essentially, they did not really bother to fix it, and pilots just learned how to deal with it. If you know it's coming, and you are wings level, it's not necessarily a big deal, but if you are turning under G's I can see how it could cause an accelerated stall. 

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3 hours ago, RedKestrel said:

Dropping flaps during a 250 mph dogfight in a P-47 should cripple your aircraft, not give you a turn advantage.

The flaps speeds on the airplanes are not necessarily going to break the flaps linkages. Some planes simply didnt have that sort of thing listed, and instead only have the range of speeds the flaps are meant to be used for landing. The actually speed they break it would be much higher. For example, max flaps speeds on a 109 are listed as being similarly low, but you can open them well above this. Take note that for neither the 47 or 109 are there are indications of what amount of flaps can be opened at the speed limit. This is because it is just a generic indicator of when to put the flaps down.

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To expend on that, it will depend on the mechanism used. The F4F Wildcat, for example apparently used some sort of pneumatic system that really didn't care what speed you lowered the flaps at; if you were to fast the wind pressure simply kept them up until you slowed down. Apparently that plane has no operational red lines, no Vne, or anything like that at all. I think it was Greg's Airplanes and Autos who was joking that he wasn't sure if that was a testament to its construction or a condemnation of its aerodynamics... 

 

I haven't really looked into what the failure mechanism would be for deploying flaps in the P-47. Since they are hydraulic, I'm thinking you could either blow a piston, detach a mount or warp the wing. I believe the F-14 also used hydraulic pistons for its flaps, and if deployed to fast they could jam in position. 

 

It would be an interesting addition for hydraulics failures to enter the damage model. 

 

It would also be interesting to start seeing the planiform specific high AoA characteristics begin being modelled too. From the FAA Pilot's Handbook, apparently different wing planiforms stall differently. The Elliptical planiform used by the P-47 and Spitfire apparently had a delayed, but abrupt stall with little warning, and tended to stalk all at once so you had less aileron control, while the moderately tapered wing (P-51, Bf-109) tended to stall at the root first and left much more aileron control, but the extreme tapered wings (Yak's) could actually stall at the wing tips first and lose most of the aileron control before they fully stalled. 

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Now that we have the career and can fly longer missions, I am even more impressed by the P-38. It will cruise at close to 300 mph with a 2,000 lb. bomb load (2550 rpm/43") and with just a bit of pitch trim, you can practically fly hands off. Perfect for AG missions where you want to get in and out quickly.

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