Bell Kingcobra

[rogerwilko]

Noticed on youtube the 12 exhaust stacks on each cylinder bank on it's Allison engine. Is this exclusive to Kingcobras? Also wikipedia states the russians were'nt to use these aircraft against the Germans??? Why on earth not?

 

[rogerwilko]

No takers?

 

[wuzak]

I believe in the US the exhausts were done by the airframe manufacturer.

 

[Siddley]

If the Wikipedia entry on the sky claimed it was blue in colour I would go outside and look, just to check for myself

 

[MiTasol]

No - Bell P-39Q also had twelve stacks per side

 

[MiTasol]

If the Wikipedia entry on the sky claimed it was blue in colour I would go outside and look, just to check for myself

Unfortunately Wiki is written by everyone and unscrupulous companies monitor their wiki pages and instantly remove facts they do not want the public to know - For example Qantas has an appalling accident rate (no big ones recently but 10 incidents and 1 minor in last year plus the Jetstar subsidiary's 8 incidents in same time) yet on Wiki appears to have had no accidents
That said Wiki has a lot of good info and some photos that are hard to find elsewhere so it is a good resource so long as you verify its accuracy elsewhere

 

[wuzak]

I was just told that the P-82/F-82 had 12 exhausts on some of the Allison versions.

http://www.cloud9photography.us/Mil...litary airplane picture, by W T Larkins-L.jpg

 

[rogerwilko]

Thanks. Seems the later Allisons started using them.

 

[GregP]

Neither the P-39 nor the P-63 had 12 exhaust stacks per side. Each "pair" is part of one "stack" that is fed by one cylinder. The V-1710 is a V-12, not a V-24. It may look that way from a distant photo but, up close, you can see the double stack efect is just an illusion caused because you can't see the base of the stack, If you saw one up close and out of the plane, it would be immediately obvious.

 

[rogerwilko]

They had 4 valve heads Greg so logically they had 2 exhaust ports per cylinder.

 

[GregP]

Just one. But you can bolt on an exhaust stack with two holes in it. Not sure why, but maybe it had to do with back pressure for combustion efficiency ... maybe not. Either way. there are six exhaust openings on the side of the engine and the "look" of the exhaust depends entirely on which stacks you use. The weidest are P-82 night fighter stacks that go on one exaust port with 3 - 4 horizontal slits in it to reduce flames at night. The sounds of the engine is almost entirely dependent on the stacks and the configuration. That is, a V-12 can be made to sound may ways depending on the stack and the rest of the xhaust (if so equpped ... like a Lamborghini), but WWII planes almost always have no exhaust system betond the stacks.

 

[wuzak]

There was a separate port for each valve

http://upload.wikimedia.org/wikipedia/commons/4/4c/Allison_V-1710_Engine_1.jpg

Unlike the Merlin, whose ports were siamesed

http://www.thunderboats.org/history/images/history0324_1.jpg

 

[GregP]

There is a single port with a very small center spine Wayne. There isn't enough material for it to be structural, and the same port style has both single seeming and double seeming stacks ... they are interchangeable with the same bolt hole pattern. Any Allison exhaust stack, including a night fighter unti, will fit on any Allison cylinder bank.

 

[Wurger]

I think these pics can help you....

P-39/P-400

Russian P-63 Kingcobra ...

 

[Wurger]

Oh... by the way... the Allison V1710 engine...

with six double exhaust stacks....

with 12 individual exhaust ones...

 

[Wurger]

And here two more of P-39D I found via the net ...

 

[rogerwilko]

Well Greg, however you want to put it, I see 12 separate ports!

 

[GregP]

The Cylinders have a very small divider in what is basically a sinlge opening. It is non structural to the engine block and I have seen some of them removed to create a single port with no ill effects. Even with the 12 openings per side, the side consists of 6 stacks with two openings per side that butt up to the small divider wall. The guys who removed the divider wall also removed the divider between the ports and used single port per cylinder stacks. There was no difference in performance, but the external appearance changed slightly, as you might expect.

Technically you can consider it two ports per cylinder, but they go into the same cylinder. If you look into both, you are looking at the same place. That's why I called it one port. Also, I can stick my index finger into one port and put it into the other port from inside the divider wall, so it doesn't do much except increase back pressure. The exhausts with one opening per stack have a 2-into-1 collector ... except for the custom stacks I saw once where the owner removed the center divider and improved the exhaust flow. Externally it looked very similar to a stock unit, but the footprint was difference where the stack surface seals to the cylinder bank.

So, it's a matter of perspective and I suppose you CAN consider it a double port ... I just don't look at it that way since I installed one stack for one cylinder regardless of how many openings it had.

I've also seen Merlins with two cyinders feeding one exhaust opening and they look like big six cylinder unit because there are only three openings per side. I believe this was prevalent on early Hurricanes ... but the stacks were being fed from 12 cylinders. Then there are the one-opening per cylinder stacks.

A Hurricane, Spitfire, and P-51D or later Mustang all have Merlins, but don't especially sound similar to one another due to stack configuration. a Griffon sometimes sounds like an engine failure about to happen due to the stacks, especially the Fairey Firefly with night fighter exhaust ramps on it. Over here in Southern California, we have one owned by Captin Eddie and it sounds like a real hot rod compared with the Merlins we usually hear around Chino. Hopefully it is approaching flight again after a gear-up landing caused by gear malfunction ... they tried for an hour but couldn't get the gear extended, so they foamed a runway and slid down the foam. The real issue might be finding a new prop!

 

[wuzak]

Greg, no doubt only one flange fits each cylinder.

But the two ports are separate at that flange face.

btw, it is my understanding that Allison supplied the flange, and it was up to the airframe manufacturer (Curtiss, Bell, Lockheed, North American) to build the exhaust system from that.

 

[GregP]

Yes, Allison supplied the flanges. Joe has boxes of them. If he ever built a Reno Allison, he would probably eliminate the center divider to get more flow. I haven't asked him, since it never occurred to me to muck with it.

Most of the stacks Joe has for his existing stock come from the engines themselves, but he CAN make custom stack for people like tractor pullers or boat guys. He starts with the Allison exhaust flanges and goes from there. I still consider it one port ... like the intake port in a Mazda wankel engine. The bridge in the middle is there only to keep the tip seal from being flung into the combustion chamber when it slides by the middle of the intake port. I have "bridge-ported" about 5 Mazda wankels and we went from ~140 HP to ~240 HP while the rpm went from 8,000 to about 10,000 ± a few. You have to pin the gears on the rotor to turn it that fast without the gears slipping in the rotor. In the case of the Allison, I have NO idea why the bridge is there and would remove it if I happened to by running one.

By the way Wayne, you might recall Joe's old, weather beaten 1964 Chevrolet Impala. It was never wrecked and Joe has put together a 750 HP Chevrolet 409 engine and is coupling it it with a Doug Nash 5-speed transmission, and the car has been cleaned up at a body shop. He has all new interior and exterior trim and other items and is building a KILLER Impalla ... and his will have a good frame under it, not the totally ridiculous X-frame it came with. Should look like a show car and SHOULD run down the quarter mile in about 9 seconds flat. His old Camaro with a 454 is already that fast, Last time he went to the dragstrip with it he ran an ET of 8.69 and they threw him out and said to never come back. You are supposed to have a pro license to run thath quick! WHen he is finished, I'll send pics. Joe's engine are very far srom stock, but are still streetable and reliable. If I had the money, I'd commission him to do an engine for me.