Why was P-36 so successful in the battle of France?

tomo pauk said:

How good was the MS.410?

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It fixed the worst of the MS 406 problems and got it up near D 520 speeds, but the D 520 was also improving.
The 410 used four 7.5mgs in the wing and so had the same armament as the D 520.
The Swiss pushed it rather far.


A Swiss D3801

A D3803. used a Saurer 1500hp engine.

Wild_Bill_Kelso said:

The P-40s did 520 mph in dives, but the manuals started out at 460, then 480, then 485, then I think maybe they got up to 500.

No matter how strong the aircraft is, very high speed dives are quite dangerous. In the P-40 getting over 400 mph also meant using a lot of rudder trim and / or having a very strong leg. Less experienced pilots should beware, you don't want to go into a spin at 450+ mph. Going down at 500 mph you get close to the ground very quickly and pull out always takes some time (and space).

There is always some gap between the recommended limits in the manual (and in training) and what the more experienced combat pilots (or company test pilots) figured out they could do in an emergency in the field.

I don't have any real primary source or even good secondary literature on the Hispano or D.520, but the Wiki on the D.520 says the plane was twitchy in general but handled well at high speed.

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I have two manuals. One says 480 and the other says 485 mph IAS. These speeds aren't "suggestions." They are "Do Not Exceed" speeds. Past the recommended speeds, you are looking at dynamic pressure and flutter limits. I seriously doubt 525 mph dives in a P-40.

I have some experience with a P-40N, and it had flutter issues when the elevators got painted with a new paint scheme. They had to be rebalanced to get flutter margins back.

All of the above doesn't mean there was no P-40 that went 525 mph in a dive. It means you definitely should not do so unless you are a very confident test pilot with some manual entries or calculated indicators saying it is safe to go that fast.

Well, there was a Curtiss test pilot, Herbert O Fisher, who noted several times that on his routine checkout flights with new P-40s he always put them to "500 mph+" in a dive. Every time. So I would call that fairly routine.

"The standard procedure for an acceptance flight was a one-hour check of all major systems. Fisher had a specialty, he would take an aircraft up to "20,000, strain the engine upward, then go inverted, throttle full forward, and nose it over, losing 10,000 feet or more at 500mph+."

Several wartime pilots mentioned going over 520 mph in dives in P-40s, and the only complaint was that it took a lot of rudder trim. Less in the later "long tail" models than the earlier.

For that matter, in spite of it's alleged fragility compared to a P-40, another Curtiss test pilot put an H-75 to 575 mph in a dive, at least according to newspaper reports.

Wild_Bill_Kelso said:

Well, there was a Curtiss test pilot, Herbert O Fisher, who noted several times that on his routine checkout flights with new P-40s he always put them to "500 mph+" in a dive. Every time. So I would call that fairly routine.

"The standard procedure for an acceptance flight was a one-hour check of all major systems. Fisher had a specialty, he would take an aircraft up to "20,000, strain the engine upward, then go inverted, throttle full forward, and nose it over, losing 10,000 feet or more at 500mph+."

Several wartime pilots mentioned going over 520 mph in dives in P-40s, and the only complaint was that it took a lot of rudder trim. Less in the later "long tail" models than the earlier.

For that matter, in spite of it's alleged fragility compared to a P-40, another Curtiss test pilot put an H-75 to 575 mph in a dive, at least according to newspaper reports.

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"Aviation experts, who declined to be quoted directly, estimated that the speed might have exceeded 600 miles per hour, compared with the normal falling rate for a 170-pound man of 150 miles an hour." I wonder why they declined to be quoted.........

SaparotRob said:

Even Greg from Planes, Trains and Automobiles (whatever) has issues with Lindy Beige.

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Actually, I would consider that a compliment.
But for sheer comic value Lindy Biege is hard to beat.

elbmc1969 said:

Sorry, are you arguing that I'm wrong, or just providing information for general interest?

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General interest......you'll know when I'm arguing....

With all this talk about these aircraft going crazy fast in dives and with some of the references quoted, did anyone research to see if these claims were based on indicated or true airspeed? Were these airspeeds based on aircraft instrumentation or was there external telemetry equipment recording these speeds?

Good question

Wild_Bill_Kelso said:

Well, there was a Curtiss test pilot, Herbert O Fisher, who noted several times that on his routine checkout flights with new P-40s he always put them to "500 mph+" in a dive. Every time. So I would call that fairly routine.

"The standard procedure for an acceptance flight was a one-hour check of all major systems. Fisher had a specialty, he would take an aircraft up to "20,000, strain the engine upward, then go inverted, throttle full forward, and nose it over, losing 10,000 feet or more at 500mph+."

Several wartime pilots mentioned going over 520 mph in dives in P-40s, and the only complaint was that it took a lot of rudder trim. Less in the later "long tail" models than the earlier.

For that matter, in spite of it's alleged fragility compared to a P-40, another Curtiss test pilot put an H-75 to 575 mph in a dive, at least according to newspaper reports.

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P-40s aren't aerodynamic enough to go 575 mph ... perhaps in a fairy tale.

Wild_Bill_Kelso said:

Well, there was a Curtiss test pilot, Herbert O Fisher, who noted several times that on his routine checkout flights with new P-40s he always put them to "500 mph+" in a dive. Every time. So I would call that fairly routine.

"The standard procedure for an acceptance flight was a one-hour check of all major systems. Fisher had a specialty, he would take an aircraft up to "20,000, strain the engine upward, then go inverted, throttle full forward, and nose it over, losing 10,000 feet or more at 500mph+."

Several wartime pilots mentioned going over 520 mph in dives in P-40s, and the only complaint was that it took a lot of rudder trim. Less in the later "long tail" models than the earlier.

For that matter, in spite of it's alleged fragility compared to a P-40, another Curtiss test pilot put an H-75 to 575 mph in a dive, at least according to newspaper reports.

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Unfortunately, I didn't save the story but I've read that after considerable study, flight test engineers determined that the initial estimate made by extrapolating from the line running off the graph and then returning was in error and the actual speed was less than 575 mph. I believe that part of the error was said to be caused by the rapid change in actual ambient pressure during the dive versus the pressure in the static system.

Wild_Bill_Kelso said:

Less experienced pilots should beware, you don't want to go into a spin at 450+ mph. Going down at 500 mph you get close to the ground very quickly and pull out always takes some time (and space).

There is always some gap between the recommended limits in the manual (and in training) and what the more experienced combat pilots (or company test pilots) figured out they could do in an emergency in the field.

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Generally an aircraft will hit its structural limits (failure) long before its stall when operating at high to very high speeds. Is there something about the P-40 in particular or WW2 aircraft in general that they could stall & spin at high speed and not structurally fail first? Realize that a spin at those speeds would most likely induce wing fuselage and or empanage separation.

In regards to the gap between book limits and actual aircraft limits realize that the company test pilot is flying brand new planes, not war weary birds that may have been over stressed numerous times and maintenance done in a combat environment. To over speed the latter is much more risky than the former.

GregP said:

P-40s aren't aerodynamic enough to go 575 mph ... perhaps in a fairy tale.

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That anecdote (and news story) was about a Hawk 75 / P-36

P-36 had a higher drag index than the P-40, so the P-36 was not aerodynamic enough either.

re P-40 dive speeds "British Full-Scale Wind-Tunnel & Turbulence (i.e. why they thought the Beaufighter could do 370 mph)"

BobB said:

Unfortunately, I didn't save the story but I've read that after considerable study, flight test engineers determined that the initial estimate made by extrapolating from the line running off the graph and then returning was in error and the actual speed was less than 575 mph. I believe that part of the error was said to be caused by the rapid change in actual ambient pressure during the dive versus the pressure in the static system.

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I believe you, I have my doubts that a P-36 got that fast, for one thing their structural strength is considerably less. But I remembered the news story.

ThomasP said:

P-36 was not aerodynamic enough either.

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"I don't make the news, I just report it"

You replied too fast, while I was adding an edit to my post above.

BiffF15 said:

Generally an aircraft will hit its structural limits (failure) long before its stall when operating at high to very high speeds.

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That is basically what I was getting at. I've read numerous P-40 pilot accounts of combat in which they described going "over 500" or "past the 500 marker" (because on some of these planes anyway the speedometer only went to 500).

But! And here's the kicker - they all mentioned (Russians, Brits, Americans, Australians) that the aircraft was hard to control in 'terminal velocity'. There was even a running joke about the leg of a P-40 pilot. This was a problem because their escape maneuver, usually an outside roll or split S followed by a full throttle dive, was constantly putting them in this situation. Once they actually were in very high speed, I assume a loss of control or a spin would be catastrophic. Some of them do mention going into a Spin though and some even just used that as a way to get out of the vicinity of enemy fighters. Presumably they hit the spin before they were going dangerously fast.

The Canadian Ace James "Stocky" Edwards thought it was a big enough deal that he had his turn coordinator instrument put in the center of his control panel so he could keep the ball in the center more easily.

BiffF15 said:

Is there something about the P-40 in particular or WW2 aircraft in general that they could stall & spin at high speed and not structurally fail first? Realize that a spin at those speeds would most likely induce wing fuselage and or empanage separation.

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WW2 fighters tended to be stressed for high G loads, obviously, and the P-40 in particular was stressed for 10Gs. That is one of the reasons it was a bit overweight. But also contributed to it's reputation for durability and ability to handle high speed dives.

All that said, I don't think a 500 or 520 mph dive is all that unusual or strange, it's not unique to a P-40. I think the other big issue as WW2 aircraft get up to that speed is really more compressibility, and P-40s didn't seem to suffer from that very early, the way some other fighters did. P-51D reached 505 'indicated' in this test during a dive. This was 0.8 mach, and beyond that they were restricted due to the risk of compressibility, except in 'extreme war emergencies' in which case they were permitted to go to 0.83 mach. The report says they were suffering damage and various control problems at 0.85.

BiffF15 said:

In regards to the gap between book limits and actual aircraft limits realize that the company test pilot is flying brand new planes, not war weary birds that may have been over stressed numerous times and maintenance done in a combat environment. To over speed the latter is much more risky than the former.

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True but those are also being passed to training units and so on after a few months of getting 'worn out' on the front line. Generally when they were getting into a maximum velocity dive in a combat area it was because they were in big trouble and contending with the imminent possibility of being torn apart by 20mm cannon shells from a pursuing aircraft... so it's a matter of balancing risks.

If the company test pilot thought a 500+ mph dive would damage the aircraft during a checkout flight I doubt he would put that stress on it.

ThomasP said:

You replied too fast, while I was adding an edit to my post above.

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Sorry!

Wild_Bill_Kelso said:

Well, there was a Curtiss test pilot, Herbert O Fisher, who noted several times that on his routine checkout flights with new P-40s he always put them to "500 mph+" in a dive. Every time. So I would call that fairly routine.

"The standard procedure for an acceptance flight was a one-hour check of all major systems. Fisher had a specialty, he would take an aircraft up to "20,000, strain the engine upward, then go inverted, throttle full forward, and nose it over, losing 10,000 feet or more at 500mph+."

Several wartime pilots mentioned going over 520 mph in dives in P-40s, and the only complaint was that it took a lot of rudder trim. Less in the later "long tail" models than the earlier.

For that matter, in spite of it's alleged fragility compared to a P-40, another Curtiss test pilot put an H-75 to 575 mph in a dive, at least according to newspaper reports.

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I wouldn't call it routine at all. Maybe for that test pilot and maybe position and compressibility errors were getting the best of his ASI. It happened to most WWII fighters, even the ones created well AFTER the P-40 was designed.

The P-51D has Cdo = 0.0151. The P-40E has Cdo = 0.0173. That is 14.5% higher for Cdo.

The flat plate drag area of a P-51D is 4.30 sq feet. The flat plate drag area of a P-40F (closest I can get to a P-40E) is 5.12 sq feet. That's 19.1% more flat plate area for the P-40F.

In combat use, do you really think a P-40 was faster on the way down than a P-51D? I'd doubt that, and the P-51D had a VNE of 505 mph, with the dynamic pressure limit being a factor past that speed. It is STILL a factor today for Strega and Voodoo, and is still at that speed. So, they have to choose the weather for speed record runs VERY carefully to avoid dynamic pressure limits at more than 505 mph IAS.

I'd comment on the P-40 speed here, but nobody is trying to set world records in one. They lap Reno at 320 mph MAX while Strega and Voodoo lap it at 510 mph when needed, assuming higher temperatures than standard. Despite the racing wings not being stock airfoils, the dynamic pressure limit is the same as wartime since the airfoils are modified with caulking and not internal structure. So, they aren't any stronger than stock airplanes, as far as dynamic pressure limits go. I don't know for sure right now, but I'd bet the dynamic pressure limit of a P-40 is about the same or below that of a P-51D.

I suppose a P-40 COULD be a stronger airframe than a P-51D. I've never seen a study that details the P-40 at high speeds and the manuals I have seen don't go above 485 mph as the limiting speed. Vd (design dive speed) is generally a bit above Vne (never exceed speed), but not by much.

Vd , by rule, must be 40% above design cruise speed, and predicted flutter must be at least 1.2 Vd. Vdf is the demonstrated dive speed in actual flight, and the FAA comes along and paints a red line on the ASI at 90% of Vdf, and calls it Vne (redline). So, the redline is set at 10% less than the fastest the airplane has ever flown, and that was in a new aircraft. We pilots don't know if the aircraft is limited by structure strength (dynamic pressure) or by flutter speed; they don't tell us. Basically, they have given you a buffer so you don't have to convert IAS to TAS in-fight on a moment's notice. But, make no mistake. If you exceed Vne, you are a test pilot rapdily after your airspeed needle does past the redline.

You might have a good day and you might not.

I'm well aware a Mustang is much faster in level flight, but I don't think drag is really the issue with either aircraft. I definitely don't think the P-40 is structurally more weak than the P-51.

The issue and limitation for both aircraft in a dive are compressibility effects, which comes down to a mach number. My understanding with the Mustang is that the 505 mph IAS limit is at 0.8 mach which is the 'normal' limit but they were allowed to go up to 0.83 in a 'war emergency' so a bit faster. That's in the document I linked.

How a given airframe reacts to compressibiity is a bit unpredictable unless you are using a computer model. But going strait down at full power I think most mid to late war fighters could get going fast enough to get themselves in trouble pretty quickly.