Japanese landing gear

[AvisQueMetallum]

I've heard many claims that Japanese landing gear was unreliable, particularly on the N1K1-Ja and Ki-84. Were there common aspects between these devices?

 

[GregP]

In the case of the N1K1 the floatplane had a mid-wing and the landplane's landing gear had to get shorter as it retracted. The mechanism proved unreliable.

In the case of the Ki-84, there was nothing inherently wrong with the landing gear. Late-war attack made it hard to get the landing gear delivered, and late war manufacturing sometimes produced poor heat treatment of steel, resulting in landing gear failures. If the gear made it to the plane and if it was heat treated correctly, there were no landing gear issues. The two issues above are not a design issue; they are related to constant air attack..

 

[Shinpachi]

Yes, the N1K1's landing gear was famous for its own mechanical trouble because it had to suck out oil from the oleo strut to shorten before retracting.

I haven't heard of the strength issue.
Any test or accident reports ?

 

[GrauGeist]

In the case of the N1K1 the floatplane had a mid-wing and the landplane's landing gear had to get shorter as it retracted. The mechanism proved unreliable.

In the case of the Ki-84, there was nothing inherently wrong with the landing gear. Late-war attack made it hard to get the landing gear delivered, and late war manufacturing sometimes produced poor heat treatment of steel, resulting in landing gear failures. If the gear made it to the plane and if it was heat treated correctly, there were no landing gear issues. The two issues above are not a design issue; they are related to constant air attack..

Good point, Greg.

Both Germany and Japan were having serious problems with quality as their factories were being bombed.

They had to effect repairs to the factory as quickly as possible, meaning salvaging what equipment and parts they could in order to get the assembly process underway. In many cases, they had to relocate, creating a gap in the supply line that forced shortcuts in order to meet demand.
They also had to replace any skilled workers who may have been killed with persons unfamiliar with the process. Some machining and related methods that would have required several steps were shortened - example: compare the fit and finish of the early war Arisaka rifles with ones made late war. Night and day.

 

[GregP]

I think they were also very short of alloying metals like tungsten and others. We had a pretty good embargo going via submarine by mid-1944. After that, it was tough to get a lot of raw materials and they didn't have all that many to start with.

I have read of heat treat issues, but have not seen specific event first-hand reports of same. It could be the case or it might be a case of saying it in print and then repeating it. Either way, I have read of heat treat issues with Ki-84 landing gear. I make no claim either way myself on any personal research.

Many quality issues crept up in the late war, and I think most were due to raw material shortages or constant bomb damage rather than lack of any skilled labor or anything like that. The Axis in general and the Japanese specifically did NOT make bad airplanes. Neither did the Germans. You can ask any Ploiesti survivors if the Romanian IAR-80s and -81s were bad fighters - nobody who made it would say that was true!

 

[Shinpachi]

I heard a lot of guesses and generalizations about Japanese myths since I joined this forum in 2008 but -

1. Aged planes were used for the Kamikaze purpose.
2. Brand-new ones were secured for the coming homeland battle.
3. The Allied forces could have had few chances to check actual landing gear troubles.
So, I am interested in reports of which I have not ever heard.

 

[GregP]

I'd be interested in reading the translations of those, too.

 

[Shinpachi]

Sorry, Greg.
I'm asking you such reports if you should have any.

I can't speak English better than this.

 

[Ivan1GFP]

You can ask any Ploiesti survivors if the Romanian IAR-80s and -81s were bad fighters - nobody who made it would say that was true!

I don't suppose the ones who didn't survive would be claim that the enemy made bad fighters either!
(If they could still talk.....)

 

[GrauGeist]

You can ask any Ploiesti survivors if the Romanian IAR-80s and -81s were bad fighters

Just for the record, the Romanians fielded the IAR 80B in defense of Ploesti, along with Bf109s and Bf110s. The Bulgarians mauled the departing bombers with their Bf109s and B-534s.

The IAR 81s were committed to the Eastern Front to perform long-range sweeps and ground attack.

 

[GregP]

Your English is WAY better than my Japanese! I do not have the reports, and would love to read them, too.

Up to now, all I have seen are references to landing gear heat treatment issues in several books, all by western authors, with no endnotes or other references to Japanese reports or documents.

 

[BiffF15]

Your English is WAY better than my Japanese! I do not have the reports, and would love to read them, too.

Up to now, all I have seen are references to landing gear heat treatment issues in several books, all by western authors, with no endnotes or other references to Japanese reports or documents.

We must read all the same books. I was under the same impression regarding late war gear problems being oriented towards metallurgy.

Cheers,
Biff

 

[mokyme]

Besides the Ki-84 low oil pressure in engine problem, which wasn't satisfactorily solved even by war's end, the issues with the landing gear are described by many authors in English language texts. Just Google: Ki-84 landing gear and select Books from menu and see about 8 hits which describe that problem.

The attached pic is a text capture from the Leszek A. Wieliczko book "Ki-84 Hayate" published by Kagero, 2005, which describes the landing gear problems.

To summarise, the Hayate's landing gear problems were caused by:
1. manufacturing problems relating to strength of landing gear legs
2. pilot inexperience as shock absorbers unable to cope with heavy landings
3. over-inflation of tyres

I haven't checked any Japanese language texts such as FAOW to see if they are in agreement.

Darryl

 

[chuter]

Besides the Ki-84 low oil pressure in engine problem, which wasn't satisfactorily solved even by war's end, the issues with the landing gear are described by many authors in English language texts. Just Google: Ki-84 landing gear and select Books from menu and see about 8 hits which describe that problem.

The attached pic is a text capture from the Leszek A. Wieliczko book "Ki-84 Hayate" published by Kagero, 2005, which describes the landing gear problems.

To summarise, the Hayate's landing gear problems were caused by:
1. manufacturing problems relating to strength of landing gear legs
2. pilot inexperience as shock absorbers unable to cope with heavy landings
3. over-inflation of tyres

I haven't checked any Japanese language texts such as FAOW to see if they are in agreement.

Darryl

As a career aircraft mechanic I kind of cringe at that attached description as it sounds like someone with a very limited mechanical, let alone aircraft, background. "The low quality of thermal processing" is strange-speak for poor heat treatment. And "too weak shock absorbers" doesn't mean anything specific as he's talking about oleo struts. Is the stroke too short or the oil too thin/metering orifice too large? Does the plane bounce too much or the gear bottom out too easily? Does he even know? The "even a slight excess of pressure in the tires" line is particularly odd, I can't even imagine how that would work. Maybe if he actually means the strut, then, yeah, that might make sense as a bit too much pressure might blow seals when bottomed out. The Frank at Freeman Field, Indiana (T-2 302) was one of the most reliable aircraft there, once the exhaust stacks had been repaired, and in the T-2 report on it no mention was made of any unusual or difficult characteristics of the type as far as landing and takeoff regimes were concerned. It actually says it was quite good in those areas but notes that both three-point visibility and the brakes are poor so the pilot can't be lazy. Offhand then I'd guess that the problems the Japanese experienced could be largely be chocked up to the steel and its heat treatment (an industry-wide problem) and poor pilot training (and, maybe, the airfields used?).

 

[GrauGeist]

As a career aircraft mechanic I kind of cringe at that attached description as it sounds like someone with a very limited mechanical, let alone aircraft, background. "The low quality of thermal processing" is strange-speak for poor heat treatment. And "too weak shock absorbers" doesn't mean anything specific as he's talking about oleo struts. Is the stroke too short or the oil too thin/metering orifice too large? Does the plane bounce too much or the gear bottom out too easily? Does he even know? The "even a slight excess of pressure in the tires" line is particularly odd, I can't even imagine how that would work. Maybe if he actually means the strut, then, yeah, that might make sense as a bit too much pressure might blow seals when bottomed out. The Frank at Freeman Field, Indiana (T-2 302) was one of the most reliable aircraft there, once the exhaust stacks had been repaired, and in the T-2 report on it no mention was made of any unusual or difficult characteristics of the type as far as landing and takeoff regimes were concerned. It actually says it was quite good in those areas but notes that both three-point visibility and the brakes are poor so the pilot can't be lazy. Offhand then I'd guess that the problems the Japanese experienced could be largely be chocked up to the steel and its heat treatment (an industry-wide problem) and poor pilot training (and, maybe, the airfields used?).

That was an excerp from a translated document.

The "slight excess of tire pressure" means the tires were over-inflated, which can have adverse effects on landing gear (and quality of landing) as it makes the tires too firm.

 

[fubar57]

This is from Aircam Aviation Series...

 

[GregP]

I have seen these, but with no reference to any Japanese documents addressing same. Looks like only the author's words. Alas, I didn't check the notes the last few times I read that to see the sources, if there were any sources referenced.

 

[chuter]

That was an excerp from a translated document.

The "slight excess of tire pressure" means the tires were over-inflated, which can have adverse effects on landing gear (and quality of landing) as it makes the tires too firm.

Well, that is exactly what I thought was meant by a "slight excess of tire pressure" and I still am not sure how that is supposed to be detrimental to the airframe or landing gear. The tires being slightly too firm would be the equivalent of a slightly harder landing with normal tire pressure. It's like saying slightly too high tire pressure in your car tires could damage your car's suspension. That shouldn't affect the shock strut, trunnion or wing spar fatally, on its own, which is why I speculated that maybe he meant the strut instead of the tire. If the seals of the struts are at their limit at full compression of the strut at the specified pressure then overfilling the strut could blow the seal. The problem with this theory is that strut seals generally have a relatively high safety margin which make this unlikely. But this may be a unique case.

PS. On reflection it seems as if the slightly too hard tires was being blamed for snapping the poorly heat treated legs. I would simply chock the broken strut up to the poor heat treatment in that case rather than the crutch of tire pressure as the bad leg is a time bomb all by itself.

 

[GrauGeist]

Tires, especially aircraft tires, have a specific operating pressure and there is a reason for that.

I have been in a Cessna 172 that had over inflated tires and on landing, there was a massive jar to the aircraft and we bounced up about 6 feet with what should have been a soft touch-down - and this was a light civil aircraft.

Over inflated tires do not allow a cushion or rather, a margin of energy absorption, when the aircraft sets down and that energy is transferred to the main-gear struts. If the struts are fatigued or mis-tempered, or the Oleos are faulty, this shock will aggravate an existing condition.

The Bf109's landing gear was at it's optimum on a grass field with a moderate tire pressure. If that Bf109 had high air pressure in it's tires, it became a handful, to the point of ground-looping or worse.

So appropiate air pressure in the main-gear's tires is a serious factor and is actually part of an aircraft's engineering.

 

[Shinpachi]

An internet article explains the Ki-84's landing gear issue like this.

着陸速度160kmという高速と4t近い重い機体を、整地能力の低さからデコボコな滑走路に着陸させるのは未熟なパイロットには荷が重く、着陸時にバウンドさせよく脚を折った。無論熟練パイロットであればなんの問題もなく着陸できるのだが、疾風のころは促成教育された未熟なパイロットばかりになっていた。設計者も誰でも着陸できるようもっと脚を丈夫にすべきだったと戦後語っている。

It was a hard job for the immature pilots (of Ki-84) to land such a heavy aircraft close to 4 tons at a high speed of 160 km(/hr) on the bouncing ground. They often broke the landing gear. Of course, experienced pilots could do it without problem but they had gone and immature pilots filled in. In the postwar, a Nakajima designer recalled that Nakajima should have designed the landing gear stronger so that newbies could land without worry.

Source: 四式戦 疾風 - 艦隊これくしょん -艦これ- 攻略 Wiki* (the middle of the page)


Mechanic of World Aircraft vol 7 for Hayate (Ki-84) also confirms above episode in page 175.

PS: Corrected "a heavy duty" to "a hard job".