The Straight Dope on P-47 Dive Speed By Greg’s Airplanes

[Rattlesnake]

Apparently the P-47 had a problem with aileron reversal at 545mph IAS. Meaning they remained attached at that velocity.

P-47 Thunderbolt Part 2 Dive Speeds and Mach Numbers

[Legioneod]

Not sure if control reversals are modeld but either way the Jug shouldnt lose ailerons in a dive anyways, it simply didnt reach the speeds that it encountered structural failure.

Edited November 24, 2018 by Legioneod

[Rattlesnake]

4 minutes ago, Legioneod said:

Not sure if control reversals are modeld but either way the Jug shouldnt lose ailerons in a dive anyways, it simply didnt reach the speeds that it encountered structural failure.

Yes, that is implied

[Legioneod]

3 minutes ago, CMBailey said:

Yes, that is implied

Of course it's top speed want 545 IAS either though but eventually it did plateau and couldnt go any faster.

[-=PHX=-SuperEtendard]

In game you start to lose ailerons when you reach around 565 mph .

[Rattlesnake]

The 500mph IAS airspeed limitation was apparently purely to stay well away from aileron reversal. The British cleared it to dive to 520. The P-47M/N had a fix for this problem that raised the max allowable speed to 565z

Edited November 24, 2018 by CMBailey

[DSR_A-24]

14 minutes ago, CMBailey said:

The 500mph IAS airspeed limitation was apparently purely to stay well away from aileron reversal. The British cleared it to dive to 520. The P-47M/N had a fix for this problem that raised the max allowable speed to 565z

What was the fix?

[Rattlesnake]

From video, chart rendered from documentation.

[Legioneod]

11 minutes ago, DSR_T-888 said:

What was the fix?

Dive flaps. Also implemented on the D-30.

 

The dive limitations on P-47s were for compressibility reasons and had nothing to do with structural stability in the dive. The P-47 could dive well over it's limits without structural failure.

Edited November 24, 2018 by Legioneod

[Talon_]

New wing on the N, compressibility recovery flaps on D-30 and M-1-RE

[Rattlesnake]

50 minutes ago, Legioneod said:

Dive flaps. Also implemented on the D-30.

 

The dive limitations on P-47s were for compressibility reasons and had nothing to do with structural stability in the dive. The P-47 could dive well over it's limits without structural failure.

You are of course right about the P-47 structural strength, but the video specifically mentions the aileron reversal problem being fixed on these two planes. Which implies that the wing was stiffened somewhat to avoid being warped by the ailerons at high speed, but it doesn’t say exactly. The video also points out that the N didn’t have dive flaps (needed more room for fuel) and IIRC  the M doesn’t either. But I could be wrong there.

Edited November 24, 2018 by CMBailey

[Legioneod]

2 minutes ago, CMBailey said:

You are of course right about the P-47 structural strength, but the video specifically mentions the aileron reversal problem being fixed on these two planes. Which implies that the wing was stiffened somewhat to avoid being warped by the ailerons at high speed, but it doesn’t say exactly. The video also points out that the N didn’t have dive flaps (needed more room for fuel) and IIRC  the M doesn’t either. But I could be wrong there.

Aileron reversal didnt cause warping of the airframe, it cause the controls to reverse control input.

 

M had the same exact wing as the D model so there is no difference between the two.

[Garven]

N model had "clipped" wings.

[Legioneod]

3 minutes ago, Garven_Dreis said:

N model had "clipped" wings.

They were also longer than on the D model.

Edited November 24, 2018 by Legioneod

[Rattlesnake]

3 minutes ago, Legioneod said:

Aileron reversal didnt cause warping of the airframe, it cause the controls to reverse control input.

 

M had the same exact wing as the D model so there is no difference between the two.

Aileron reversal is caused by the forces on ailerons twisting the wing tips at high speeds. Spits had a problem with it also.

Greg here was saying the M had a new wing with a new higher dive limitation vis a vis the aileron issue. He could have it wrong I suppose.

[Talon_]

The M has the D-30 wing with brakes.

[Legioneod]

19 minutes ago, CMBailey said:

Aileron reversal is caused by the forces on ailerons twisting the wing tips at high speeds. Spits had a problem with it also.

Greg here was saying the M had a new wing with a new higher dive limitation vis a vis the aileron issue. He could have it wrong I suppose.

 

M had the same wing as the D-30 and the D-30 had the same wing as all other D blocks, with the addition of dive recovery flaps.

 

Structurally nothing really changed.

Edited November 24, 2018 by Legioneod

[HR_Zunzun]

Yes. The new wing was introduced with the N.

I read somewhere that it raised the critical mach number to something like 0.8.

[Rattlesnake]

2 hours ago, HR_Zunzun said:

Yes. The new wing was introduced with the N.

I read somewhere that it raised the critical mach number to something like 0.8.

 Gonna have to watch the video again when I get home, but I believe the creator found that the Brits discovers the 47D could dive to .8 also. The lower recommendations in the manual were for margin of error. Again, IIRC.

2 hours ago, Legioneod said:

 

M had the same wing as the D-30 and the D-30 had the same wing as all other D blocks, with the addition of dive recovery flaps.

 

Structurally nothing really changed.

Bottom line it seems like the D Jug should structurally be able to dive to 565 also, just be hard to control.

[Legioneod]

2 minutes ago, CMBailey said:

 Gonna have to watch the video again when I get home, but I believe the creator found that the Brits discovers the 47D could dive to .8 also. The lower recommendations in the manual were for margin of error. Again, IIRC.

Bottom line it seems like the D Jug should structurally be able to dive to 565 also, just be hard to control.

 

Like you said, In reality it would be able to dive those speeds, it would just suffer from control issues until entering into thicker atmosphere.

 

Not trying to derail the thread but whats the mach number of the 109? And what were it's structural limits? The reason I ask is becasue currently the K4 can maintain quite a bit higher speeds than the P-47 in a dive and without losing any control surfaces, it also seems to have more control but that could be my imagination. 

[Bremspropeller]

Ailerons flying off are not realistic on several airframes. Among those is the Fw 190.

 

19 minutes ago, Legioneod said:

Not trying to derail the thread but whats the mach number of the 109? And what were it's structural limits?

 

Critical Mach was around .75-.78 for both the Fw 190 and Bf 109. That's as much as or greater than the critical Mach of the P-47.

 

IIRC max dive was 750kph IAS on the 109 due to aileron limitations.

There wasn't a structurally limiting diving-speed of the 109 per sé.

Dynamic pressure of flutter was not an issue on the Bf 109, the Fw 190 or any american or british fighter.

[HR_Zunzun]

1 hour ago, CMBailey said:

 Gonna have to watch the video again when I get home, but I believe the creator found that the Brits discovers the 47D could dive to .8 also. The lower recommendations in the manual were for margin of error. Again, IIRC.

Bottom line it seems like the D Jug should structurally be able to dive to 565 also, just be hard to control.

 

 

The critical match indicates the speed at which the first shock wave is formed over some part of the wing. Higher is better but It is not an ultimate indication of the maximum speed at which the plane can be dived. It indicates at which speed the compressibility effects are going to start being noticed.

Both p38 and p47 had more modest mach number but also a very high acceleration in the dive. Both conditions meant that if happening at the wrong angle of dive could make the recovery impossible. That´s why the dive flaps were introduced. In the case of the Jug, it never was a tactical limitation. On the contrary, diving was a tactical strength.

[Voyager]

I'm wondering if the aileron ejection is a side effect of wings being modelled as rigid structures? As I understand it, aileron reversal is caused by the forces in the ailerons being so much that the whole wing twists against the aileron, rather than the ailerons deflecting the airflow, but I'm guessing the wings are assumed to be rigid bodies in the physics of this game, and rather than the wing twusting, all that energy is getting a hunted back in to the ailerons and off they go instead? 

 

Does this sim have high speed aileron reversal in it? I snagged Battle of Moscow during the sale, but haven't had a chance to get that far in to trying things out yet. 

[Legioneod]

43 minutes ago, Voyager said:

I'm wondering if the aileron ejection is a side effect of wings being modelled as rigid structures? As I understand it, aileron reversal is caused by the forces in the ailerons being so much that the whole wing twists against the aileron, rather than the ailerons deflecting the airflow, but I'm guessing the wings are assumed to be rigid bodies in the physics of this game, and rather than the wing twusting, all that energy is getting a hunted back in to the ailerons and off they go instead? 

 

Does this sim have high speed aileron reversal in it? I snagged Battle of Moscow during the sale, but haven't had a chance to get that far in to trying things out yet. 

 

As far as I can tell aileron reversal is not modeled. The compressibility model is still a very earl wip I assume so who knows what we'll see in the future.

 

At the very least we need mach tuck, aileron reversal, flutter, and control stiffening in order to get a good high speed model. Two of these are already in-game I believe (control stiffening for sure and I think flutter is as well)

[Voyager]

I will say, if they do introduce high speed aileron reversal, they're going to have to have a dedicated community reap once person on the forums to deal with people completely freaking out the first time they encounter it.

 

Control reversal problems generally result in a quick fiery end when ever someone hits them. I know I'm probably going to crash the first dozen or so times I hit that. 

[Legioneod]

23 minutes ago, Voyager said:

I will say, if they do introduce high speed aileron reversal, they're going to have to have a dedicated community reap once person on the forums to deal with people completely freaking out the first time they encounter it.

 

Control reversal problems generally result in a quick fiery end when ever someone hits them. I know I'm probably going to crash the first dozen or so times I hit that. 

As long as you know how to deal with it theres no reason you should crash or have any serious problems getting out of the dive.

[Bremspropeller]

On 11/24/2018 at 5:12 PM, Legioneod said:

Aileron reversal didnt cause warping of the airframe, it cause the controls to reverse control input.

 

Nope.

Just like Greg says in the video: The aileron acts like a trim-tab to the wing and twists it so much that the net roll goes in the opposite direction.

 

Fun-fact: Wing-twist used to be the common thing for roll-control before ailerons became standard.

[danielprates]

11 minutes ago, Bremspropeller said:

 

Nope.

Just like Greg says in the video: The aileron acts like a trim-tab to the wing and twists it so much that the net roll goes in the opposite direction.

 

Fun-fact: Wing-twist used to be the common thing for roll-control before ailerons became standard.

 

It was how the Wright brothers did it, until Curtis patented ailerons to circumvent their own patent, wasn't it? 

 

Wing warping remained a serious issue further on. From memory, I recall the B-47 or the B-52 (or both?) suffering from in in some speeds. You use the ailerons thinking the plane will roll to one side, it rolls to the other, since the aileron is actually twisting the wing to the opposite direction and, well, the wing has more area than the aileron, so the wing's countertorque is actually higher than the aileron's torque.. the net torque vectoring to the other (wrong) direction. 

[Voyager]

1 hour ago, Legioneod said:

As long as you know how to deal with it theres no reason you should crash or have any serious problems getting out of the dive.

That's the rub: you have to know that it is control reversal, rather than some other effect, and know how to counter it, otherwise the instinctive response sends the plane further out the intended flight path. From the pilot's perspective, they have suddenly and inexplicably lost control of the aircraft.

 

And given this will happen on different aircraft at different speeds, and would likely be used by savvy pilots to either gain advantage in high emotion engagements it's very easy for people to mis-atribute to malice what was merely a new dynamic they weren't aware of. 

 

Better to be ready for it and answer it early and consistently than to let it fester unchecked. 

[Bremspropeller]

Roll-reversal airspeeds should generally* be unobtainable unless you're coming in from outer space.

 

___

* P-47, Fw 190, P-51, etc.

[Legioneod]

9 minutes ago, Bremspropeller said:

Roll-reversal airspeeds should generally* be unobtainable unless you're coming in from outer space.

 

___

* P-47, Fw 190, P-51, etc.

How so? I've read reports that say it was a problem for the P-47 at high speed dives (550-600mph)

[Bremspropeller]

...which was not an airspeed attained on a daily basis.

 

Edit (for those interested):

NACA report 868 has aileron reversal airspeed for the P-47C-1-RE "around 540mph IAS".

That's hauling some pretty decent butt.

Edited November 26, 2018 by Bremspropeller

[Legioneod]

4 minutes ago, Bremspropeller said:

...which was not an airspeed attained on a daily basis.

 

Clearly but in-game those speeds are common and the player will push the aircraft as far is it can go.

[Bremspropeller]

Depends if you're a gamer or a simmer ?

[Legioneod]

3 minutes ago, Bremspropeller said:

Depends if you're a gamer or a simmer ?

Wouldn't make a difference imo, if I was in combat I'd take every advantage I can get and do everything I could to stay alive, even if it meant diving crazy high speeds.

Edited November 26, 2018 by Legioneod

[Bremspropeller]

Yes it would.

A big part in staying alive is not wrecking the airplane in the first place.

The boundary between pushing it and digging in was pretty thin.

 

The way people fly airplanes in combat sims is competely unrelated to the real deal. Bostly because you don't die for real. And because it's more fun. And because the crew-chief won't floor you after coming home with a bent airframe for the third time.

[[TWB]Sauerkraut-]

On 11/26/2018 at 12:11 PM, danielprates said:

 

Wing warping remained a serious issue further on. From memory, I recall the B-47 or the B-52 (or both?) suffering from in in some speeds. You use the ailerons thinking the plane will roll to one side, it rolls to the other, since the aileron is actually twisting the wing to the opposite direction and, well, the wing has more area than the aileron, so the wing's countertorque is actually higher than the aileron's torque.. the net torque vectoring to the other (wrong) direction. 

 

An intuitive way to think about it is that the ailerons essentially become trim tabs (or, more accurately servo or "flettner" tabs in this case) for the entire wing that function in the same way that the rudder tab on late 109's worked.

Edited November 29, 2018 by itsthatguy