A6M2 engine and negative G load

[GrungyMonkey]

The Akutan Zero's engine would cut out under negative Gs. 

Because of this, several historians and books have cited this as a weakness of the plane.

On the other hand, I've heard that this was actually due to a mistake while repairing the Akutan Zero, and that the real thing had no such issue.

The Zeros were also known for attacking bombers upside-down down to speed up their break-off. This seems unlikely if their engine couldn't stay on. But this could still be an issue with just the early models, like with the Spitfire.

As a side note, modern Japanese media portrays the Zero as perfectly capable of flying inverted.

Is there a good way to know which is true? It'll be important to the sim to get this right.

[Boba Fett]

I don't own it but this book is getting excellent reviews over on Amazon

 

https://www.amazon.com/Japanese-Aero-Engines-1910-1945-Mike-Goodwin/dp/8365281325/ref=sr_1_2?crid=WB4UPSZOQ3S4&keywords=japanese+wwii+aircraft+engines&qid=1696692892&sprefix=japanese+wwii+aircraft+engines%2Caps%2C86&sr=8-2#customerReviews

[BlitzPig_EL]

When the captured Zeke was repaired, the technicians made a mistake with the carb, causing negative G issues.  A6Ms in service with the IJN had no such issue.

[wheelsup_cavu]

Learned something new today.

 

Wheels

[GrungyMonkey]

1 hour ago, BlitzPig_EL said:

When the captured Zeke was repaired, the technicians made a mistake with the carb, causing negative G issues.  A6Ms in service with the IJN had no such issue.

That's what I think too, but I read that on War Thunder. It felt weird disagreeing with actual historians with that as my source lol

[ZachariasX]

Eric Brown flew that Zero and he doesn't mention any carb cutting out and he had his fun with that plane. But the carb cutting out is mentioned in other places as well, but I find those sources more doubious. The Zero was one of Browns most enjoyabe rides, despite some shortcomins in control like shifting trim over the speed range and relatively poor ailerons. But 4500 ft./min climb is respectable in 1941...

[ZachariasX]

Ask ChatGPT:

Q: Does the A6m Zero fighters engine cut out during negative g maneuvers?

ChatGPT: Yes, the A6M Zero fighter's engine could cut out during negative g maneuvers. The aircraft's carburetor was not equipped with a float chamber, which meant that during negative g maneuvers, fuel flow to the engine could be disrupted and cause the engine to stall. This was a significant disadvantage for the Zero compared to other aircraft of its time.

😆

[busdriver]

Just to add to the confusion. 

The first A6M2 Model 21 Zero-sen fell into Allied hands in China on November 26, 1941. On a reinforcement mission (to serve as escorts for G4M1 “Betty” bombers operating against the British forces in Burma and Malaya) from the IJNAF airfield at Tainan, in Taiwan, to Saigon, two A6M2s of the Tainan Kokutai strayed from their formation and encountered fog at low altitude. Zero-sen construction number 3372 (tail code V-172) was flown by PO1c Shimezoh Inoue, while the other fighter (tail code V-174) had FPO2c Taka-aki Shimohigashi at the controls. En route to Hainan Island to refuel, the two Zero-sen pilots had drifted apart from the primary formation and now found themselves in quite a predicament as they were running out of fuel and their aircraft lacked radios in an attempt to boost the A6Ms’ range. Relying solely on their compasses for guidance, Inoue and Shimohigashi pressed on until the dense fog lifted, whereupon they spotted a lengthy beach near a town that appeared to be suitable for an emergency landing. Within minutes they had both landed on the beach on the Leichou coastline, where the pilots and their aircraft were captured by Chinese troops. Although Inoue’s fighter was virtually unscathed, Shimohigashi’s Zero-sen had suffered extensive damage upon landing and had to be written off. Inoue’s A6M2 was later repaired by US engineers at Kunming airfield, in China, with a section of the forward fuselage just aft of the engine cowling boasting a new improvised covering that featured specially designed ventilation/cooling slits.

Chambers, Mark. Wings of the Rising Sun: Uncovering the Secrets of Japanese Fighters and Bombers of World War II (pp. 53-54). Bloomsbury Publishing. Kindle Edition. 

It took ~6 months to get the airplane off the beach and up to Kunming and reassembled. The 23rd FG's evaluation says they didn't have the facilities to do a detailed inspection. But they were only able to get 2075 rpm, clearly rendering their comparative performance numbers invalid.

Without knowing whether somebody knackered the reassembly of the engine to the airframe (taking an undamaged carburetor apart and putting it back together), the USAAF guys reported a problem with negative g engine cutout.

Some folks will say, there are no reports of A6M2 pilots commenting on this ergo it wasn't an issue. Sure we know about Spitfires and Hurricanes having this problem because we read and speak English. But how many memoirs of Zero pilots exist? If a pilot knows about the limitation he flies in a manner to negate the problem. It seems to me that highly experienced (and superior) IJNAF pilots would know not to unload or pushover, rather they would fly like Hurricane and Spitfire guys.

My point is that with two different captured A6M2 Model 21s there are two different reports about the negative g cutout of the engine. What I would like to see is a contemporaneous document saying, oops we f*cked up and reassembled the carburetor incorrectly. I would like to see something other than anecdotal evidence from 20+ years after the fact.

Y'all got anything like that?

FWIW, the list of repairs for Koga's airplane.

 

 

 

 

 

 

 

[Ludo]

I stumbled on this twitter thread by Justin Pyke, I discovered him on some Youtube videos by Drachinifel about the Zero.  In his twitter thread He quotes one of his contacts that states the carburetor was not well maintained on the captured Zeros, hence the engine cuts.

https://www.youtube.com/watch?v=ApOfbxpL4Dg

https://www.youtube.com/watch?v=r1sn-1ZCmDg

https://twitter.com/CBI_PTO_History/status/1161126022521036800

https://twitter.com/CBI_PTO_History/status/1161263927788892160

https://twitter.com/qaz1300 He seems to have a lot of information about japanese planes from primary sources, as he can translate them.

https://ww2aircraft.net/forum/threads/the-a6m-could-not-do-negative-g-maneuvers.48892/ This forum has a lot of information about WW2 planes also.

 

 

 

Edited April 20 by Ludo

[Props]

Yep, Justin is definitely a master on the Zero, as he mentioned that he is a intelligence analyst as well as a historian I take his word over many armchair experts. Great vids I've watched them all repeatedly.

[busdriver]

The first YT video, at the 1:17.:38 mark, the guest Justin Pyke provides an explanation accompanied by a diagram. That's a good find @Ludo. 👍

The A6M Naval Carrier Fighter

Edited April 20 by busdriver

[ZachariasX]

Great finds @Ludo!

So they got their own and a tad more elaborated version of a Shilling restrictor without having to find out beforehand. One might add that this contraption does not permit prolonged inverted flight, as the chamber in the carb will be empty rather quickly. But it should compensate for some maneuvering. Then again, even fuel injected engines in the Bf-109 didn't permit inverted flight as such, as while inverted the oil would not be recovered again by the pump and the engine, while being fed happily with fuel, will blow due to insufficient lubrication. Prolonged negative g maneuvers were not on anyones mind obviously.

It is actually funny that the Brits tried to make a negative g tolerant carb after the disaterous consequences of mounting regular float type carb to a fighter aircraft engine became obvious even to them, and miserably failed at it. And this at a time where it was more than obvious that fuel injection is in many way drastically superior. They had to find out that a Merlin engine that just had makeshift standard injectors drilled in the cylinder heads would already make equal power to the regular carburated version.

It is just sad that Beatrice Shilling had developed a working fuel injector system even back in the late 20's (IIRC) for the RAE, but fuel injection was not His Majesty's way to feed an engine. And since then, one of Britains greatest engineers is just remembered for nothing but a little disc with a hole in it.