B25 mitchell question

[peter]

Hello Guys
B25s are as foreign to me as they get but I do like reading about them etc etc. I was wondering why some B25s have many small fairings on the cowlings and some dont?

[Matt Gunsch]

the small fairing cover exhaust stacks. on the wartime models, all the cylinders had individual stacks, hence fairings all the way around the cowls. After the war, B-25s that were kept in service underwent overhaul and came out with a combination of individual stacks and half collector ring.

[Larry Kraus]

From what I've read about B-25's,the individual short stacks were the only arrangement that worked for flame dampening for night flying.The A-26 used flattened finger stacks for the same purpose,but they were on R2800's and apparently didn't work on the R2600's used on B-25's

The main problem with short stacks is that they are very loud.with no muffling qualities at all.Another problem is that the exhaust nuts loosen up from vibration.We had a similar problem on High Gross Beech 18's which had an extractor exhaust system that used various lengths of relatively short stacks.

The #7 stack (I think it was) ended up as a single short stack.I've had a few of those either rattle the exhaust nuts loose,or break at the flange weld and fall off in flight.You can tell when you taxi in by the popping noise from the open exhaust port.I wondered where the stacks ended up.Think "The Gods Must Be Crazy".

Super PBY's and PB4Y's that were used as air tankers were modified to use surplus B-25 QEC's.These had partial collector rings along with some remaining short stacks.From what I understand,post-war B-25's had the partial collectors installed for muffling properties,as the short stacks closest to the fuselage caused fatigue on both the airframe and aircrew.

The Super PBY's used to "Hot Load",or fill with retardant with the engines running,as they were mounted so high as to not cause a safety problem to the loaders.After two or three minutes at idle,the combination of a rich mixture and short,very hot exhaust stacks made it sound like a fire-fight was taking place.Also,the co-pilot usually carried a sawed-off broom handle during post flight inspection and stuck it in the stacks and wiggled it around to check for loose or missing exhaust nuts.

[B25PBYGUY]

This is all correct. The post war Hayes and Hughes conversions sported a collector ring for the upper seven cylinders for noise and ease of maintenance, while the lower seven had the individual Clayton "S" stacks.
The Super Cat sported either the Claytons on all cylinders, or all 14 cylinders tied to 2 collectors. Of the six 25's I've flown, only one was fully equipped with Claytons. Very loud indeed. But, quintessential in appearance. A workload if a stack stud was pulled on an upper cylinder though.

[Jerry O'Neill]

This is all true for the B-25's that are currently in existence, but I believe the early models, A's, B's, C's and D's had complete top and bottom collector rings with a single outboard exhaust. Only retro fitted ealry model B-25's had the short stacks in any combination.
Some of you B-25 guys out there could correct me if I'm wrong.
Jerry

[RickH]

The CWH B-25 is the only one that I've seen that had a collector top and bottom.

[Jack Cook]

but I believe the early models, A's, B's, C's and D's had complete top and bottom collector rings with a single outboard exhaust.

Ds had the short stacks.

Capt Austin Eivers 42nd BG 1943

The CWH B-25 is the only one that I've seen that had a collector top and bottom.

That's a strange one-of-a-kind set up. Looks like 2 half rings with a dual instead of a single exhaust dump.

Last edited by Jack Cook on Mon Dec 11, 2006 3:10 pm, edited 1 time in total.

[N3Njeff]

Kermit Weeks "Apache Princess" and the Mid Atlantic air museums "briefing Time" have the short stacks all the way around.

[needle]

As does Cavanaughs "How Boot That!"

[Jack Cook]

As does Cavanaughs "How Boot That!"

and Axis nightmare.
Here's another question................
How many B-25s still have the low profile carb intakes??

[Jerry O'Neill]

How many B-25s still have the low profile carb intakes??

The New England Air Musem's B-25H, "Dog Daize", still retains the low profile intakes.
Jerry

[peter]

I kind of figured it was config of the exhaust but wasnt sure.. now i know.

[sledge39]

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.....Ds had the short stacks.....

....is that photo reversed or did some B-25 props turn the wrong way?...

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[sledge39]

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........that looks better...

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[B25PBYGUY]

Pacific Prowler has the "low profile" carburetor air intakes fabricated to fit the post war installation Bendix Stromberg PR48A4 carburetor. During wartime the R-2600 had Holley carbs. By the way the low profile Holley carb intakes are termed "Carter" intakes.
Yes, the early A & B models only had the collector ring. It was determined that the exhaust flame was overly visible a night. Hence, the Clayton S stacks.
I had a B-24 pilot CBI veteran explain that at night, the Japanese fighters would target the center of the exhaust, since they couldnt see the airplanes. They would fly a loose formation with the bomber, behind and below and attempt to lob rounds into the bombers. This particular pilot, Bob Chambers, once entered a shallow descent toward the outline of mountainous terrain, narrowly clearing the ridge line. The Japanese pilot, focused on maintaining firing position behind the 24's exhaust plume, flew into the terrain. True story, as this pilot provided me with a written narrative of all his missions.