A6M Zero Wings Would Snap Off in A 6G Turn?

[contrails16]

Hi all, on my last thread someone mentioned that there was an interview with a USN veteran who said in a 6G turn the wings of a zero would bend and snap off the plane. This sounds strange to me. Does anyone else have anything to add to this? Thanks all

 

[drgondog]

Seriously doubt it. A6M designed to nearly same ultimate load factors US Military standards. The Zero was just ruthlessly stripped of weight. As mission weight creeped over design gross weight loading - ALL fighters reduce their G load safety factor. As an example - the P-51/Mk I had design load of 8000 gross weight for 8G Limit/12 G Ultimate. That said, at takeoff max GW of 11,600 pounds for P-51D, the Limit load reduces to 5.5G Limit, 7.7G Ultimate

 

[Shortround6]

The book "Zero" by Robert C. Mikesh says that some of the early Zeros (late 1940 and early 1941 production.) were limited to 250kt dives and 5 G pullouts until they received modifications. Apparently there was a wing flutter problem that was made worse by the installation of balancing tabs on the ailerons. The tabs had not been used on the prototypes or very early production. By May of 1941 production aircraft were getting
1. increased thickness outer wing skin.
2. longitudinal stringers to increase torsional strength
3. added external balance weights to the ailerons until modifications of the internal weights could be worked out.

However once fixed the limits would have gone back to normal. The book makes no other mention of low "G" load limits.

 

[contrails16]

Seriously doubt it. A6M designed to nearly same load factors as US Military standards. The Zero was just ruthlessly stripped of weight. As mission weight creeped over design gross weight loading - ALL fighters reduce their G load safety factor. As an example - the P-51/Mk I had design load of 8000 gross weight for 8G Limit/12 G Ultimate. That said, at takeoff max GW of 11,600 pounds for P-51D, the Limit load reduces to 5.5G Limit, 7.7G Ultimate

You see I was thinking the same thing and wanted the opinions of others on this matter as well. I was going to ask the op to site his source but he did in the original post. Idk, just seemed highly unlikely to me. Thank you

 

[contrails16]

The book "Zero" by Robert C. Mikesh says that some of the early Zeros (late 1940 and early 1941 production.) were limited to 250kt dives and 5 G pullouts until they received modifications. Apparently there was a wing flutter problem that was made worse by the installation of balancing tabs on the ailerons. The tabs had not been used on the prototypes or very early production. By May of 1941 production aircraft were getting
1. increased thickness outer wing skin.
2. longitudinal stringers to increase torsional strength
3. added external balance weights to the ailerons until modifications of the internal weights could be worked out.

However once fixed the limits would have gone back to normal. The book makes no other mention of low "G" load limits.

How is the book? I'm currently reading Eagles of Mitsubishi right now and am loving it!

 

[GregP]

As I understand it, the Zero was not quite designed to the same load factors as a U.S. fighter. The Planes of Fame operates an original A6M5 Model 52 and our zero was restored in the late 1970's with the help of Jiro Horikoshi, the original designer. The Museum has the design documents.

Most U.S. fighters were designed with an 8 g normal load factor with a 50% safety factor for an ultimate load factor of 12 g. That is, you can pull 8 g without damage. If you pull anywhere between 8 and 12 g the aircraft will not fail, but will likely sustain damage of some sort. The severity of the damage goes up as the g-load goes up. If you exceed 12 g, the structure could fail.

The Zero was designed with a 6 g normal load factor and a 100% safety factor. So, you can pull 6 g all day with no damage. If you pull between 6 and 12 g, the aircraft should do it but will likely sustain damage. If you exceed 12 g, the structure could fail.

So, the Zero has the same ultimate load factor as a U.S. fighter, but is basically a 6 g airplane rather than an 8 g airplane. That is not much of a disadvantage since WWII fighters didn't have enough excess power to sustain a 6 g turn indefinitely anyway. I see the 6 g load limit as a tactics factor in dive pullouts, but not in dogfighting. At 180 - 280 mph, the Zero was King of the heap. Above 300 mph it was starting to get out of its element and was quite vulnerable. Above 325 mph, the Zero was, for practical purposes, pretty much done as a super fighter, and was not very maneuverable. The A6M5 Model 52 had higher dive limits than earlier Zeros due to slightly shorter span and slightly heavier wing skins, but the control system was essentially the same.

By the way, the P-51D load factor at 8,000 pounds was 8 g. But the formula for the load factor is: LF = 64,000 / weight [edit: I said g-load, but was just thinking about that. It's weight] . so:
1) 8,000 lbs --> 8 g
2) 8,500 lbs --> 7.53 g
3) 9,000 lbs --> 7.11 g
4) 9,500 lbs --> 6.74 g
5) 10,000 lbs --> 6.4 g
6) 10,500 lbs --> 6.1 g

Standard "clean" combat weight of a P-51B was 9,680 lbs., where the normal load factor was 6.61 g, assuming you didn't have a lot of fuel in the aft tank. The P-51D had a "clean" combat weight of 10,100 lbs for a 6.34 g load factor. Again, that assumes not much fuel in the aft fuselage tank. So ... how much of a dogfight disadvantage was the 6 g normal load factor for the Zero? Not much, if any at all.

 

[Admiral Beez]

Did any piston-powered, single-engine, single-seat, monoplane fighter tear off its wings under loads that the pilot could physically sustain?

 

[GregP]

Probably not unless it had sustained battle damage. I doubt there was otherwise a genuinely weak fighter out there.

They'd find that in testing, don't you suppose? Not a sarcastic answer. I don't think anyone fielded a weak airplane classified as a fighter.

That assumes the tremendously ugly, fragile, and short-lived LWS Zubr wasn't a fighter ...

 

[drgondog]

Did any piston-powered, single-engine, single-seat, monoplane fighter tear off its wings under loads that the pilot could physically sustain?

Yes - the P-51B suffered structural failures due to a.) gear uplock failure in a high AoA mode - with gear opening door fairing and creating a huge asymmetricload on the wing due to major loss of lift on that wing, and b.) high speed rolling pullout causing asymmetric load again on the empennage due to a combination of yaw and torque forces palced on rudder and both elevators.

The addition of the DFF, Gear uplock improvement and Reverse Rudder Boost tab cured most of these issues. The P-51D-5 emerged from early production line with same issues but by the time they arrived in the ETO/MTO the kits had been released.

 

[DarrenW]

Standard "clean" combat weight of a P-51B was 9,680 lbs., where the normal load factor was 6.61 g, assuming you didn't have a lot of fuel in the aft tank. The P-51D had a "clean" combat weight of 10,100 lbs for a 6.34 g load factor. Again, that assumes not much fuel in the aft fuselage tank. So ... how much of a dogfight disadvantage was the 6 g normal load factor for the Zero? Not much, if any at all.

I fully agree. Even F6F-5 (which is often thought of as being a far stronger-built airplane that the A6M5) had a maximum positive combat loading of 6.6 G (at an 'overload' weight of 12,740 lbs). Flight limitation charts found in pilot's manuals limit it to +7/-3 G at 12,000 lbs but that's relying on manufacturer recommendations so it's hard to compare different aircraft side-by-side as to which one could actually handle the most aerodynamic stress in fight without causing physical damage to the airplane.

For example, according to the pilot's manual the F4U-1D had a do not exceed load factor of +7.5/-3.4 G ( up to 12,600 lbs) but no one would could ever claim with a straight face that the Corsair had any real structural strength advantage over the Hellcat. In practice the US Navy limited both airplanes to +7 G at 12,000 lbs but did allow the F4U-1D an extra 0.4 G in negative acceleration at this same weight.

 

[DarrenW]

It is weird that you brought this up as I watched a pretty good video last night that delves deeply into the structural strength of the the A6M and other aspects of the fighter as well.

 

[Admiral Beez]

It is weird that you brought this up as I watched a pretty good video last night that delves deeply into the structural strength of the the A6M and other aspects of the fighter as well.

Interesting, the IJN pilots were ripping the radios out of their Zeros because the radio was rubbish.

 

[pbehn]

Did any piston-powered, single-engine, single-seat, monoplane fighter tear off its wings under loads that the pilot could physically sustain?

Mosquitos killed a few test pilots in early dive tests, undercarriage or doors bursting open as I remember.

 

[Shortround6]

Interesting, the IJN pilots were ripping the radios out of their Zeros because the radio was rubbish.

I believe it was a combination.
Poor shielding on the engine ignition system and not the best radio.

I would note however that a number of aircraft had radio problems and the First P-47s to go into service in Europe did so with British radios (the American ones were pulled out and British ones installed) after a several weeks of trying to get the US radios to work properly.

 

[GregP]

The early Typhoon had several failures of the tail section, resulting in rear fuselage external stiffeners being riveted on.

Several aircraft revealed structural issues in development but, once sorted, were not weak, including the Typhoon.

The Zero was also not weak, but it could sustain much less physical damage than a contemporary U.S. fighter before becoming weak due to thin aluminum skin and structure in the name of saving weight. If undamaged, it was as strong as required to be a fighter. The skin inside the gear wells, for instance, is either .020" or .025", I now forget which, but we put in a new one when we overhauled the Planes of Fame A6M5 Model 52. The person who installed it was Alex of Fighter Rebuilders.

 

[cherry blossom]

There were reports of structural failure with early Ki-43 Oscars. Could the veteran have not known the type of plane suffering the failure?

 

[contrails16]

As I understand it, the Zero was not quite designed to the same load factors as a U.S. fighter. The Planes of Fame operates an original A6M5 Model 52 and our zero was restored in the late 1970's with the help of Jiro Horikoshi, the original designer. The Museum has the design documents.

Most U.S. fighters were designed with an 8 g normal load factor with a 50% safety factor for an ultimate load factor of 12 g. That is, you can pull 8 g without damage. If you pull anywhere between 8 and 12 g the aircraft will not fail, but will likely sustain damage of some sort. The severity of the damage goes up as the g-load goes up. If you exceed 12 g, the structure could fail.

The Zero was designed with a 6 g normal load factor and a 100% safety factor. So, you can pull 6 g all day with no damage. If you pull between 6 and 12 g, the aircraft should do it but will likely sustain damage. If you exceed 12 g, the structure could fail.

So, the Zero has the same ultimate load factor as a U.S. fighter, but is basically a 6 g airplane rather than an 8 g airplane. That is not much of a disadvantage since WWII fighters didn't have enough excess power to sustain a 6 g turn indefinitely anyway. I see the 6 g load limit as a tactics factor in dive pullouts, but not in dogfighting. At 180 - 280 mph, the Zero was King of the heap. Above 300 mph it was starting to get out of its element and was quite vulnerable. Above 325 mph, the Zero was, for practical purposes, pretty much done as a super fighter, and was not very maneuverable. The A6M5 Model 52 had higher dive limits than earlier Zeros due to slightly shorter span and slightly heavier wing skins, but the control system was essentially the same.

By the way, the P-51D load factor at 8,000 pounds was 8 g. But the formula for the load factor is: LF = 64,000 / weight [edit: i said g-load, but was just thinking about that. It's weight] . so:
1) 8,000 lbs --> 8 g
2) 8,500 lbs --> 7.53 g
3) 9,000 lbs --> 7.11 g
4) 9,500 lbs --> 6.74 g
5) 10,000 lbs --> 6.4 g
6) 10,500 lbs --> 6.1 g

Standard "clean" combat weight of a P-51B was 9,680 lbs., where the normal load factor was 6.61 g, assuming you didn't have a lot of fuel in the aft tank. The P-51D had a "clean" combat weight of 10,100 lbs for a 6.34 g load factor. Again, that assumes not much fuel in the aft fuselage tank. So ... how much of a dogfight disadvantage was the 6 g normal load factor for the Zero? Not much, if any at all.

That is awesome, I am actually finishing up his book on the Zero, Eagles of Mitsubishi, great read. I kind of assumed the person that said the wings would snap off at 6 g was full of it, but I just wanted further verification. Thank you for the informative post Greg. So I have to ask, did you ever get a chance to see their Ki-84 before it was given back to Japan, or was that before your time? I cannot remember the year it was brought to Japan. Once again, thanks for the information

 

[contrails16]

There were reports of structural failure with early Ki-43 Oscars. Could the veteran have not known the type of plane suffering the failure?

possibly, but I am not sure.

 

[slaterat]

The early KI 43 1's with the two bladed prop and the longer wingspan were known to be structurally weak in the wings. There is a well known incident described in Terence Kelly's "Hurricane Over the Jungle", in which a KI 43 loses's it's wings pulling out of a dive after bouncing some landing Hurricanes over Sumatra in early 42. Hurricane pilots were known to practice high speed high G pullouts for this reason.

Nakajima's Fragile Falcon

 

[GregP]

Hi Contrails 16.

I have seen films of it, but never the actual aircraft. That particular aircraft had a very slightly bent propeller blade and could not fly at full power due to vibration, but there was no chance of getting a new propeller.

At the time, there was absolutely no interest in a flying Japanese fighter at U.S. airshows, so it was eventually sold to a Japanese museum. It was transferred to the Arashiyama Museum in Kyoto in 1973 for display. With unsupervised access allowed to the aircraft, parts were stolen from the Ki-84, and coupled with the years of neglect it could no longer fly. Following the museum's closure in 1991, the aircraft was transferred to the Tokko Heiwa Kinen-kan Museum, Kagoshima Prefecture, where it still is displayed to this day. When they came to get it, they cut the wings off with a chain saw (!) and re-assembled it with non-flyable repairs. It is the only surviving Ki-84.