Thoughts on the Nakajima Ki-84 and Kawasaki Ki-100

[SaparotRob]

I hope I look as good when I'm 79.

 

[VA5124]

I hope I look as good when I'm 79.

Just dont get parkson's like morgan shepard

 

[SaparotRob]

Unfortunately, we don't get a choice.

 

[VA5124]

Unfortunately, we don't get a choice.

Morgan doesnt even have his team anymore they went bust when the virus broke out

 

[BlackSheep]

The only wood I know of in an A6M5 Model 52 is the handle on the throttle. Everything else is aluminum or a small bit of steel in some areas (main landing gear and maybe a few things like engine mount and control cables), with some fabric on the control surfaces thrown in and maybe some other material for the instrument panel top cover. Maybe aluminum ... maybe not. There are standard cable pulleys of G10-type material and rubber seals and tires. But make no mistake, it is a metal airplane, reasonably well-built.

This ain't no paper airplane! It's a real, live warbird complete with a 2-row radial engine and a prop made from Hamilton-Standard drawings by Sumitomo for Mitsubishi / Nakajima.

The Planes of Fame Zero, number 61-120, is the 2,357th A6M5 off Nakajima's production line. it was delivered in May 1943 and was assigned to the Japanese Naval Air Corps on Honshu. It moved to Iwo Jima and was later assigned to Asilito Airfield on Saipan. On 18 June 1944, Alilito Airfield was captured by the U.S. Marines with a number of intact Zero fighters. They were shipped to NAS North Island in San Diego.

61-120 was ferried to Patuxent River, Maryland on 23 Aug 1944 for use in the 1944 Fighter Conference flyoff, during which it was flown by Charles Lindberg, among others. It was ferried back to Dan Diego on 11 Jan 1945 where front line pilots were given a chance to fly it. Altogether, 61-120 logged some 190 hours of flying time before being declared surplus after the war. In 1950 it was acquired by the Museum. it was restored in 1978 with help from both Mitsubishi and Nakajima (now called Fuji Heavy Industries ... today they sell us Subarus).

R/Woosh
I hope you realize no one was seriously inferring that the Zero was really made of paper. I apology for my part in getting this thread off track.

 

[DarrenW]

The J2M likely has such a large cockpit because the radial engine is much bigger than a Sakae, but I just don't know the actual reason the cockpit is so large

The J2M had a wider cross section than all the R-2800 engined fighters. However, it possessed an aerodynamically clean nose section but I think this attribute was mostly nullified by the extra wide airframe. But then again, the wing section looks thinner than those found on F6F and F4U and similar to the P-47 (concerning T/C).

 

[GregP]

It does NOT give the impression that it is small when you are standing next to it. That is likely largely due to the wide fuselage. It is sort of like a Zero designed by the Granville Brothers of GeeBee fame. Kind of reminds me of a streamlined Zero GeeBee. Sort of like below, only without the pinched fuselage.

 

[Conslaw]

Where do you get the tires for these restorations?

 

[GregP]

You have to look at sizes only. In WWII, the U.S.A. had it so all the manufacturers had a different tread pattern. Firestone, for instance, had diamond tread pattern (a bunch of diamond-shaped lugs). Goodyear had plus signs (+), others had circles, etc. Today, you can still get original tread patterns for some, but a diamond tread wears out quickly on pavement, so you look for tires sizes only.

By way of example, the Planes of Fame has a Hispano Ha.1112 Buchon, and the entire airframe is basically Bf 109 G-2 with a Merlin on the front. Can't get WWII German tires easily or cheaply, but the tires for a MiG-15 fit perfectly, and are WAY cheaper ... AND they are not turf tires, so they last longer on pavement.

Another example: The tires for P-38 main gear are used on only two aircraft ... the P-38 Main wheels and the B-24 nose wheel. When you need them, they are EXPENSIVE. You need to have the tire molds and then convince a tire manufacturer to make a custom run of them after contacting all the owners who might need tires. Tires and brakes can get very effort/money-intensive. Try finding new disks for an F-86F!

A bearing set for the slats on an F-86 costs $5,000 USD!

Cheers.

As a cheaper example, Yanks Air Museum is currently restoring a Grumman Mallard. We need new floorboards, so we are cutting them from interior-grade plywood and using indoor-outdoor carpeting that gets contact-cemented on using aviation contact cement. A gallon of it is $100! But these floorboards are CHEAP compared with most aircraft items. An aircraft-grade USB port, for instance, is almost $100 USD alone. By aircraft-grade, I mean FAA-approved. What THAT means is that if it catches fire, it doesn't emit toxic fumes that disable or kill the pilot while he or she is dealing with the emergency. Using the proper approved items likely isn't cheap, but it IS safe.

 

[special ed]

About 30-35 Years ago while I was still active with old cars, my father complained he would have to buy two new trailers because he couldn't get the original car tire sizes they came with. The newer US sizes to replace 6.70x15 and 7.50x14 were too wide to fit in the fenders/frame space. I told him no problem, I would get him two of each. The original sizes for my 1948 Plymouth were 6.70x15 and the 1957 Ford originally had 7.50x14. I went to my secret wholesale supplier who supplied the other wholesalers and ordered them. He said it might be quite a while before he found them. Months later, the 6.70x15 came in marked "made in Australia" and were from the original Goodyear molds. The 7.50x14 he apologised for as they were truck tires rather than passenger car tires. I forget where they were from. I can only sympathize with finding tires for old aircraft. Back then a friend had an N3N and had 24 inch Sears car tires on it.

 

[MiTasol]

I have seen others fix that problem with longer studs and spacer rings. Seemed to work okay though I expected the bearing loads and axle bending forces to be significantly different.

 

[Clayton Magnet]

using aviation contact cement

1300L?

 

[GregP]

will have to check the can when I get home from vacation. Don't recall offhand. I only use it every few years since I'm mostly doing aluminum or wood, not attaching carpet to wood or rubber rub strips to cowling pieces as we have been doing. It's right in the Aircraft Spruce catalog with contact cements.

But somehow, "1300" sounds right. It's yellow, as has been most contact cement I have used. Cheers.

 

[Spindash64]

If Wiki is correct the Homare was a 2187 cu in engine, It already used a rather high compression ratio in the cylinders, which may have helped cruise settings but hurt max power settings.
The main problem with air cooled aircraft engines is getting rid of the heat.
The water alcohol helps with this in several ways, one is as an internal coolant that absorbs some of the heat and carries it out the exhaust. another way is by lowering the peak temperatures in the cylinder.

Getting around 1,900hp on less than 100 Octane fuel and that displacement is genuinely impressive to me, even with the Water Injection. The R-2600s maybe could run that much later war, but that's with American factories and fuel. Obviously, the R-2800 was making 2,000hp years earlier, but that's again with US factories and a MUCH higher displacement.

 

[GregP]

I followed everything you wrote except why higher compression may help in cruise but hurt max power. Is that do to cruise power being close to max power in a higher compression example or is it do to heat rise?

Cheers,
Biff

Hi Bifff15.

You can only compress gasoline so much until it detonates from either pressure, temperature, or both. The ONLY reason you can run 140" MAP on a racing "Merlin" (not really a Merlin) at Reno is because the compression ratio (CR) is about 5.0 : 1. They'd try 4.0 : 1 if they could make it start.

If the CR is 6.0 / 6.5 : 1 as in a stock engine, you cannot get to 140", even with 150 PN fuel. It detonates first. You could maybe get to 80" / 90" max, and then you'd be right at the detonation limit.

 

[BiffF15]

Hi Bifff15.

You can only compress gasoline so much until it detonates from either pressure, temperature, or both. The ONLY reason you can run 140" MAP on a racing "Merlin" (not really a Merlin) at Reno is because the compression ratio (CR) is about 5.0 : 1. They'd try 4.0 : 1 if they could make it start.

If the CR is 6.0 / 6.5 : 1 as ina stock engine, you cannot get to 140", even with 150 PN fuel. It detonates first. You could maybe get to 80" / 90" max, and then you'd be right at the detonation limit.

Greg,

Okay I understand that the racers want lower compression engines, to begin with, versus stock. I also get you can't get an ultra low compression ratio motor to fire off. What I don't get is why higher compression will help at cruise but hurt at full power or vice versa. I'm probably missing the obvious due to not understanding something fundamental about gas engines so I apologize in advance.

Cheers,
Biff

 

[Spindash64]

Hi Bifff15.

You can only compress gasoline so much until it detonates from either pressure, temperature, or both. The ONLY reason you can run 140" MAP on a racing "Merlin" (not really a Merlin) at Reno is because the compression ratio (CR) is about 5.0 : 1. They'd try 4.0 : 1 if they could make it start.

If the CR is 6.0 / 6.5 : 1 as ina stock engine, you cannot get to 140", even with 150 PN fuel. It detonates first. You could maybe get to 80" / 90" max, and then you'd be right at the detonation limit.

I suppose it's no coincidence those are the quoted manifold pressure limits on War Emergency Power for the V-1650-9. Granted, the -9 uses Water Injection, which I would ASSUME changes those numbers, but the basic principle remains

 

[GregP]

When you reach the detonation limit, you can't move any more air through the engine, and a piston engine is an air pump. They use a compressor and higher rpm to move more air. So, if your stock engine is supercharged and turns at 3,000 rpm (think Merlin or Allison), you have to creep up on more rpm carefully. A racing Merlin or Allison (if anyone but Joe Yancey ever raced one recently) can turn 3,400 / 3,600 rpm and not blow up. All that is left to move more air is compression. It so happens that if you drop the compression ratio to 5.0 : 1 on a Merlin or Allison, you can get to about 140" MAP with a 2-stage supercharger (Merlin) and maybe 110" to 120" with a single-stage (Allison).

The last Allison we raced was in the Yak Full Noise flown by Graham Frew in 2017. When I say "we" I mean Joe Yancey and Graham Frew. I helped a small bit. It was a G-series engine and nose case with an F-series supercharger section. All they could get was about 110" MAP, and that was enough for about 2,200 hp. It won Bronze, won Silver, and transferred into Gold, at which time they had an issue with the race engine and swapped it out for the stock engine and finished last in Gold. Wish they could have tried the Allison out in Gold, but his speeds weren't Gold-winning speeds. He was averaging 420 mph or so (fast for an inline-powered Yak), and that wasn't fast enough to win Gold anyway. Still, we had fun.

The number 35 in the side was the number of Burt Munro (World's Fastest Indian motorcycle).

Here's a pic of Full Noise at Reno:

Here's a video.

 

[Shortround6]

What I don't get is why higher compression will help at cruise but hurt at full power or vice versa.

I will give this one a try.

With higher compression you get more power from each pound of fuel burned.

The cylinder peak pressure will be higher and thus the average pressure (or mean pressure) acting on the piston crown will be higher.

But there is a limit to the peak pressure, that is a combination of the intake manifold pressure and the compression ratio.

With a lower compression ratio you can use more boost which allows you to cram more fuel and air into the cylinder for each firing cycle. You get more total power but you don't get the same power per pound of fuel burned.

Max Cruise for a Merlin was around 2650-2700rpm at 7-8lbs of boost (US and British didn't always rate them the same.)
Range cruise could be a lot lower.

The Merlin ran at 6 to 1 compression unless experimental?
The Allison ran 6.65 compression ratio and got about 8-10% more power at similar rpm and boost (cruising). There were a few other differences.
A few late model Allisons were made with 6.0 compression ratio to get more power (higher boost) while sacrificing a bit of economy.

Boost from increased compression was not linear.

 

[BiffF15]

I will give this one a try.

With higher compression you get more power from each pound of fuel burned.

The cylinder peak pressure will be higher and thus the average pressure (or mean pressure) acting on the piston crown will be higher.

But there is a limit to the peak pressure, that is a combination of the intake manifold pressure and the compression ratio.

With a lower compression ratio you can use more boost which allows you to cram more fuel and air into the cylinder for each firing cycle. You get more total power but you don't get the same power per pound of fuel burned.

Max Cruise for a Merlin was around 2650-2700rpm at 7-8lbs of boost (US and British didn't always rate them the same.)
Range cruise could be a lot lower.

The Merlin ran at 6 to 1 compression unless experimental?
The Allison ran 6.65 compression ratio and got about 8-10% more power at similar rpm and boost (cruising). There were a few other differences.
A few late model Allisons were made with 6.0 compression ratio to get more power (higher boost) while sacrificing a bit of economy.

Boost from increased compression was not linear.

View attachment 682008

Okay, let me see if I understand. The lower CR allows more fuel / air to be pushed in via the supercharger / turbo. With higher CR (too much pressure in the combustion chamber) the supercharger/ turbo is unable to push more in due to "no room in the combustion chamber "?

The "boost devices" cram fuel / air into the cylinder, and the lower the CR the more they can squeeze in?

I understand too much compression or heat causing detonation (premature ignition), or as diesels use compression ignition normally and or Mazda is using spark controlled compression ignition in its new skyactive engines (gas compression ignition) however it uses super high CR and a supercharger.

On top of that, making more power does not translate into a more efficient engine at optimum cruise due to the CR / boost trade off in WW2 aero engines.

Irregardless is that the gist of it?