B-29 Fifi & Doc Engine Question

[Dan Jones]

I'm assuming that "Doc" is running engines similar to those fitted to "Fifi", and I'm wondering if those engines are a low altitude only variant, or if they could operate up around 30 000 ft? Also, though I know that these two fly unpressurized, how was a B-29 pressurized? EDC's?

[Brad]

Both have the same engines. Neither have turbos now so they won't make the high altitudes. I had FIFI at around 10,500-11,000 or so a few years back and she was really working hard. If I had the props turning a a few more rounds she would have gone a little further up. I'd say 12,500 would be pretty close to the limit. Originally the air for pressurization came from the inboard turbos on #2 and #3.

[CAPFlyer]

Having just spent a bunch of time on researching the L-049/C-69 Constellation, it's interesting to note the performance of the hybrid engines. The L-049 with 2-speed supercharger usually switched to "high blower" around 13,000 feet as that was about where you ran out of throttle to hold 32" MAP. The original single speed engines fitted to the first few C-69s however maxed out at only 8000', limiting the airplanes to a service ceiling of just 14,000 feet. It seems that with their new power and fixed blower, the B-29's power is somewhere in between considering the power available on 100LL. I wonder what you'll be able to get out of them once 100UL is available.

[JohnB]

Brad...
-At 11,000 were you on oxygen?
-Do the superchargers automatically come on at various altitudes?

[B-29 Super Fort]

Both have the same engines. Neither have turbos now so they won't make the high altitudes. I had FIFI at around 10,500-11,000 or so a few years back and she was really working hard. If I had the props turning a a few more rounds she would have gone a little further up. I'd say 12,500 would be pretty close to the limit. Originally the air for pressurization came from the inboard turbos on #2 and #3.

Great information Brad, thanks for sharing!

[Dan Jones]

Thanks for the info, Brad. How much power can you pull on takeoff with them? 42 inches or so?

[Brad]

Thanks for the info, Brad. How much power can you pull on takeoff with them? 42 inches or so?

44" and 2400 RPM is full power in this configuration. That is the standard for takeoff. We have used 40" before and she just hops off the ground. With shorter prop blades we could get more RPM because we have a lot of inches left in the engines.

[bdk]

Brad...
-At 11,000 were you on oxygen?

"You have to use supplemental oxygen if you fly more than 30 minutes at cabin pressure altitudes of 12,500 feet or higher. That at cabin altitudes above 14,000 feet pilots must use oxygen at all times. And that above 15,000 feet each occupant of the aircraft must be provided supplemental oxygen. All of this is spelled out in Federal Aviation Regulations Part 91.211."

https://www.aopa.org/training-and-safet ... n-aviation

[Dan Jones]

Brad...
-At 11,000 were you on oxygen?

"You have to use supplemental oxygen if you fly more than 30 minutes at cabin pressure altitudes of 12,500 feet or higher. That at cabin altitudes above 14,000 feet pilots must use oxygen at all times. And that above 15,000 feet each occupant of the aircraft must be provided supplemental oxygen. All of this is spelled out in Federal Aviation Regulations Part 91.211."

https://www.aopa.org/training-and-safet ... n-aviation

Twenty-five years or so ago (back when I was still immortal) I used to be able to fly all day at 12 500', unpressurized, and smoke a pack of cigarettes while doing it. Ahh youth...

[bdk]

Twenty-five years or so ago (back when I was still immortal) I used to be able to fly all day at 12 500', unpressurized, and smoke a pack of cigarettes while doing it. Ahh youth...

You meant 12,499' right?

[b29flteng]

In FIFI and Doc at about 12,000 feet we can pull about 30 inches manifold pressure with the throttles wide open. With the throttles wide open, the carburetor is operating at peak efficiency.

Neither aircraft is pressurized anymore.

[gemmer]

I seem to remember reading that a poorly designed front exhaust collector ring contributed to the overheating problem. Can anyone elaborate on that? Also, did the B-32 use an improved version of the 3350 compared to the B-29? I've never read of any engine problems with the B-32, although granted, they weren't around very long.

[CAPFlyer]

The early R3350's had 2 collector rings for the exhaust, one for the front row and one for the back row. The front row's collector ring was mounted in front of the cylinders. Wright's idea was that because the engine was intended for the next generation of high altitude aircraft, they thought the forward position would help provide heat into the engine during cruise to keep it from getting too cold.

With the B-29 though, the desire for extreme high altitude efficiency meant that it had very close fitting cowls and because of it, there was a serious airflow deficiency at low altitudes and speeds. This led to overheating. There were also metallurgy issues that exacerbated the problem.

I don't know if the B-32 had the same problems, but I also know that the L-049/C-69 which used the same engines didn't have the problem as bad because it had bigger cowlings which allowed more airflow. It wasn't a full fix, the rear row of cylinders still had heat issues that had to be watched when operating at high power settings, but it didn't have the same issue with overheating while idling.

Oh, and it's also important to note that the R4360 had the same problem on the B377, KC-97, and B-50 as well. In hot weather, if the cowl flaps weren't fully open or you got enough of a tailwind, the engines would overheat just as quickly as the R3350.

[b29flteng]

With the new engines on FIFI and Doc we don't have a temperature problem. We had to remove some baffling to bring the cylinder head temperatures up a bit.

[b29driver]

The early R3350's had 2 collector rings for the exhaust, one for the front row and one for the back row. The front row's collector ring was mounted in front of the cylinders. Wright's idea was that because the engine was intended for the next generation of high altitude aircraft, they thought the forward position would help provide heat into the engine during cruise to keep it from getting too cold.

With the B-29 though, the desire for extreme high altitude efficiency meant that it had very close fitting cowls and because of it, there was a serious airflow deficiency at low altitudes and speeds. This led to overheating. There were also metallurgy issues that exacerbated the problem.

I don't know if the B-32 had the same problems, but I also know that the L-049/C-69 which used the same engines didn't have the problem as bad because it had bigger cowlings which allowed more airflow. It wasn't a full fix, the rear row of cylinders still had heat issues that had to be watched when operating at high power settings, but it didn't have the same issue with overheating while idling.

Oh, and it's also important to note that the R4360 had the same problem on the B377, KC-97, and B-50 as well. In hot weather, if the cowl flaps weren't fully open or you got enough of a tailwind, the engines would overheat just as quickly as the R3350.

If proper procedures were followed there was no problem on the ground with the 4360's on the K-97.