B-29 True Max Speed?

SpicyJuan11 · May 17, 2023

I'm getting conflicting reports, most sources report 357 mph, but this SAC manual that I found on this site from 1950 claims 383 mph with 20,000 lbs of bombs. At first I thought that the 1950 document was the B-50 with 3,500 hp Pratt & Whitney R-4360-35's, but the document clearly shows it's for the 2,200 hp Wright R-3350-23. What gives?

ThomasP · May 17, 2023

Hey SpicyJuan11,

The info I have from the 1945 pilot's manual (dated June 1945) - for the B-29A at a flying weight of ~100,000 lbs - says Vmax was:

405 mph TAS at 31,000-32,000 ft
380 mph TAS at 25,000-26,000 ft

This is with the R-3350-57/-57A running at 2500 BHP. The ratings for the engines as of June 1945 were:

2500 BHP WEP for 5 min
2350 BHP Military for 5 min
2000 BHP Normal continuous
2200 BHP for TO

EDIT corrected 2200 BHP Military to 2350 BHP, sorry, typo.

daviemax · May 23, 2023

The 357 mph figure is for an aircraft with guns and turrets mounted. The higher figures are for aircraft without the two dorsal and two ventral turrets.

Dave

Alan Stevens · May 24, 2023

I recall reading that the 509th B-29s reached 450 mph in their diving 155 degree turn after releasing the atom bomb at 31,000 feet.

This maneuver was designed to put as much distance as possible from the blast.

It also strained the airframe to the max and was near the limits of breaking it.

ThomasP · May 24, 2023

The speeds I posted above are for aircraft with full gun armament.

The B-29A SAC (Standard Aircraft Characteristics) dated 9 March 1949 gives the same basic speeds with full gun armament (ie 12x .50 cal and 6000 rounds).

The Flight Operating Instruction Charts (ie fuel vs range vs Vcruise) in the manual give a maximum cruise on the way to the target, using Normal power, of 353/359 mph at 30,000/35,000 ft at a flying weight of 120,000-110,000 lbs - which would be after the aircraft had burned off ~1/2 fuel (TOGW of 140,000 lbs with 47,000 lbs fuel and 10,000 lbs bombs).

drgondog · May 24, 2023

ThomasP said:
The speeds I posted above are for aircraft with full gun armament.

The B-29A SAC (Standard Aircraft Characteristics) dated 9 March 1949 gives the same basic speeds with full gun armament (ie 12x .50 cal and 6000 rounds).

The Flight Operating Instruction Charts (ie fuel vs range vs Vcruise) in the manual give a maximum cruise on the way to the target, using Normal power, of 353/359 mph at 30,000/35,000 ft at a flying weight of 120,000-110,000 lbs - which would be after the aircraft had burned off ~1/2 fuel (TOGW of 140,000 lbs with 47,000 lbs fuel and 10,000 lbs bombs).

What was cruise data for max combat radius with 10.000 pound bombload?

ThomasP · May 24, 2023

Hey Drgondog,

If I am looking at this right, using the Long Range Cruising Charts and approximately the same loading as in my posts above (140,000 lbs TOGW with 47,000 lbs fuel and 10,000 lbs bombs) with ~7,000 lbs fuel (used for WUTTO, Climb, Combat, Safety Allowance) not available for range:

To Target Area
210 - 200 mph IAS at altitudes upto 20,000 ft (FGW of 140,000 - 120,000 lbs)

Increase Power and Climb to 35,000 ft Altitude, Increase Speed, Drop Bomb, Run Away AFAYC
FGW of 100,000 lbs after release of 10,000 lb A-bomb

To Home
195 - 180 mph IAS at altitudes upto 25,000 ft (FGW of 110,000 - 80,000 lbs)

Here are the relevant charts

drgondog · May 25, 2023

ThomasP said:
Hey Drgondog,

If I am looking at this right, using the Long Range Cruising Charts and approximately the same loading as in my posts above (140,000 lbs TOGW with 47,000 lbs fuel and 10,000 lbs bombs) with ~7,000 lbs fuel (used for WUTTO, Climb, Combat, Safety Allowance) not available for range:

To Target Area
210 - 200 mph IAS at altitudes upto 20,000 ft (FGW of 140,000 - 120,000 lbs)

Increase Power and Climb to 35,000 ft Altitude, Increase Speed, Drop Bomb, Run Away AFAYC
FGW of 100,000 lbs after release of 10,000 lb A-bomb

To Home
195 - 180 mph IAS at altitudes upto 25,000 ft (FGW of 110,000 - 80,000 lbs)

Here are the relevant charts

Hi ThomasP- Thanks for this.

If you go to page 7 for 100K-90K for 3500 gal, the extremes for cruise speed TAS at 25000 feet
Far Left for Range of 1000 statute mi
354mph TAS at Max Continuous 43.5" MP, auto rich, and 1020 gal per hour
Far Right for Range of 2250 statute mi
301mph TAS at 33" MP auto lean, and 518 gal per hour.

Zipper730 · Aug 4, 2023

T ThomasP

ThomasP said:
The info I have from the 1945 pilot's manual (dated June 1945) - for the B-29A at a flying weight of ~100,000 lbs - says Vmax was:

405 mph TAS at 31,000-32,000 ft
380 mph TAS at 25,000-26,000 ft

This is with the R-3350-57/-57A running at 2500 BHP.

Wow, that's pretty good. What were the listed max be around 110,000-120,000 lb?

The Flight Operating Instruction Charts (ie fuel vs range vs Vcruise) in the manual give a maximum cruise on the way to the target, using Normal power, of 353/359 mph at 30,000/35,000 ft at a flying weight of 120,000-110,000 lbs

And this would be pushing up the speed a bit to minimize time over target correct?

ThomasP · Aug 5, 2023

Hey Zipper730,

The 2500 BHP was a War Emergency power in June of '45. i think this may have been only for the Silverplate B-29s as of that date. There is no Vmax listed in the manual for other altitudes and weights at that power setting. The later B-29A SAC do not list the 2500 BHP War Emergency settings, only the Military power setting of 2200 BHP.

Based on the Military and Normal power settings vs the weights, the speed would be 12 to 15 mph less at 110,000-120,000 lbs GFW.

re cruise speed

Higher speeds would of course help decrease time over target. Depending on the weight of the aircraft over target, the higher power setting might also be necessary to operate at a higher altitudes to evade FlaK and/or fighters. If I am reading the charts correctly, the B-29A would have to be operating at Normal power to bomb at 30,000 ft with a weight over target of ~120,000 lbs. At ~135,000 lbs the Service Ceiling at Normal power is only 20,000 ft. Fuel burn at Normal power was 1020 USgal/hr.

B-29 True Max Speed?

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