VH1943-1950

 

                Not all appreciate what a tremendous jump in technology the B-29 represented for it's time. It began with AF & Boeing planners anticipating the need for a very long range aircraft that would carry very heavy loads. The story of this early development is very well written in the chapter Eddie Allen and the B-29 by Boeing experimental test pilot Robert M Robbins and published as part of Chester Marshall's book The Global Twentieth  Vol III. Robbins story tells of how the B-29's aerodynamics, it's wing and flaps came about. The wing had to be low drag, thus a wing loading of 69 lb/sqft, actually as high as 80 lb/sqft in actual use in the Marianas. The large Fowler Flap made it possible to lift heavy loads on takeoff yet have the low drag wing for sustained long flights. The heavy wing loading made it more difficult to fly, the C-1 Auto Pilot being all the more appreciated, taking some of the strain from long flights. Except sometimes it failed, the Pilot killed, causing the AC already stressed by events in the cockpit, to manually fly from Japan to Saipan. Ref the story The Buddy System by AC John Cox in this same book by Marshall. (Marshall was Pilot on John's crew, John & I worked together on the B-1B in 1980 to 1985 period often comparing it with the B-29).

                Test pilot Robbins story reveals the engine problems & fire which took Eddie Allen’s life and the resultant near collapse of B-29 flight testing at this most critical time of development. At that stage of development many of the problems were with the aircraft and the installation of engines & superchargers in the aircraft. The Wright built R3350 was a big jump from the Wright R1820 which powered the B-17 and a jump from the Pratt Whitney R2800 which was also developed during the war. The R2800 powered the P-47, B-26, C-46, F4U, P-61; it had a service life of about 1000 hours, benefiting from a 1.5 years lead relative to the R3350.

                It's a classic Systems Engineering problem: bring together the products of multiple contractors such as Wright, GE, Hamilton Standard & Boeing. Wright had no problem with cooling their engines during shake down tests. GE had evolved a highly reliable supercharger based on efforts for the P-38, B-17, P-47. Hamilton Standard Propellers were poven to be very reliable. It fell upon Boeing to package the AF procured subsystems & place them in a low drag nacelle. Boeings Flight Test Program was to prove the items they designed. Each prime prime contractor was doing his job, the engine problem fell through the crack, it should have been the AF responsibility, between Air Force Flight Test and Wright Field, to track down the cause and solution to the problem. The right people were not there at the right time -- post WW II proceedures did not permitted such a problem to linger or be blamed on Hot Kansas Summers. Our nation was very hard pressed for experienced engineers, the Manhattan Project and others soaked up almost all available resources, and many engineering students were pulled from college to fill the needs for large numbers of navigators and similar tasks.

                Hamilton Standard propellers did not come equipped with cuffs used for extra thrust and engine cooling. The cuffs of FiFi's props were not on operational B-29's, these were added later.

                Driving super chargers with exhaust gas from the engines placed an extra burden on the engines, this back pressure caused the temperatures at the cylinder exhaust ports to go up.

                The exhaust valve was larger than the intake valve and was filled with metallic sodium which became liquid when hot and sloshed heat from the red hot valve head to the valve stem for removal via the valve guide. This heat to be carried away by lubricating oil and by air from the rocker arm region, was a very concentrated heat load. Of the fuel being burned in the pistons, 1/3 of the energy was delivered as power via the crankshaft to the propeller, 1/3 carried out the exhaust as waste heat, and 1/3 into the engine structure to be carried away by cooling air. Supercharger loads elevated the exhaust valve port temperature and obstructions between propeller and cylinders blocked the cooling air.

                I've since found that those operating out of Saipan in the early phase and those later out of Guam used different engine settings and fuel-bomb loads. Aircraft for early missions out of Saipan were equipped with a 640 gal bomb bay tank. This was because Iwo was not available as a refueling stop and they were flying in formation from Saipan or sometimes joining in formation at high altitudes of 30,000 feet just off Japan for their bomb runs. Gen Hansell, initially in command on Saipan, began operations based on experiences in Europe, high altitude and formation flying. The B-29 had been designed for high altitude flying with pressured compartments and ability to supercharge engines to deliver full power at 30,000 feet. Flying in formation and reaching high altitude consumed excessive amounts of gas and this was compounded by the unanticipated Jet Stream, sometimes blowing planes backward until making adjustment to a different altitude and approach to the target. Experience was a great teacher but it took time to experience and learn.

                LeMay took over from Hansell, benefiting from what had been learned and applied a new strategy of low level bombing with incendiaries. Hansell had done a magnificent job of planning Air Force needs for General Marshall, but things did not work as anticipated, they seldom do. LeMay began as a navigator then a B-17 Pilot & sent to England. Crews had become fearful of being hit by flak if staying on a bomb run. LeMay applied what he'd learned from ROTC artillery to determine odds of being hit by flak when staying on a bomb run; odds were much better than thought so orders were to stay on bomb run to hit target and not waste missions. He had also evolved formations of B-17's so gunners could pool their fire on enemy craft. He was sent to the Pacific to see what could be done. Results to date had been terrible, a poor return on the huge investment in the 20th AF. Hansell & LeMay wrote Essays for the Historical Society book set called IMPACT. It is a collection of WWII  IMPACT magazines produced by the Air Corps and released as Confidential Documents at the time plus essays by persons in key positions. For those interested these books were published in 1989 by National Historical Society 2245 Kohn Rd, Harrisburg, PA, 17105. I highly recommend you obtain a set.

                An Impact story of a B-29 mission had said the Flight Engineer had closed the Cowl Flaps for takeoff, I sure hope all real Flight Engineers knew better! They were partially closed to 3 inches.

                LeMays essay said 20th AF used Production Line Maintenance methods as a reason for success. I didn't know of any PLM methods used on B-29's till after the war. I was assigned to set up the only one there was on North Field Guam after the war. The success that was achieved was due to ground crews being dedicated to their airplane and those who flew it, that's why they'd stay up all night if need be to have their plane ready.

                Operations on Guam seldom used bomb bay fuel tanks because Gen LeMay changed most missions to be flown at night singly, cruising and bombing at low altitudes below 10,000 ft. Daylight formation missions were flown as single ships at low altitudes enroute to a redezvous point near the coast where squadrons joined in formation and then climbed to their assigned bombing altitudes of 15,000 to 22,000 feet, much lower than the previous altitudes above 30,000 feet. Also, Iwo Jima became available for emergency fuel if needed. Thus the bomb loads went up, the maximums depending on distance to the target, forecast winds and types of bombs used.

         Tech Order bomb loads by type

Number

Bomb weight

Total weight

80

100

8000

56

300

16800

40

500

20000

12

1000

12000

12

1600

19200

8

2000

16000

4

4000

16000

                The Tech Order table reveals there is much difference in takeoff weight depending on load.

                One bomb bay fuel tank weight could be 4232 lb allowing 500 lb for the tank, 640 gal per tank and .70 specific gravity for gasoline. Consuming 1/4 bomb bay capacity it would be about 85% of a max load.

                You could carry a 3/4 load of 500 lb bombs, or 500 lb incidiary clusters which would mean maximum loads with one bombbay tank would be 19232 lb.

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                Vern Chandler wrote as follows:

                It is impossible to reconstruct our bomb loads precisely. The type of bombs was specified for the target by 21st Bomber Command and given to Wings for flight planning. Wing and Group Commanders wanted to put maximum tonnage on the target to win the war and also because that gave them a better report card and promotion! A few years ago, B/Gen Roberts commented to me that "We out carried those groups across the runway." So you can see there was competition.

                On receipt of the target directive, Wing & Group Operations, Navigator and Flight Engineer computed a detailed flight plan considering:

                1. Gross Weight 140,000 lbs. (I was surprised one day with a load to 142,500 lbs, but with the confidence of youth (age 27?), just went!)

                2. Initial cruise and bombing altitudes specified by Wing.

                3. Forecast enroute winds

                4. Takeoff performance based on runway temperature, humidity and wind. (I recall one mission when the load was decreases in order to take off down wind. The problem was a light wind from the southwest, but either Wing or 21 Bomb Cmd didn't want to chance crashing a B-29 somewhere near Hwy. !, Army Hospital or, Heaven Forbid, 21 Bomb Command. We therefore took fewer bombs in order to take off downwind to the northeast.)

                5. Computed fuel load needed. If within wing and center tank capacity, all bomb shackles were available, 20 each bay for 500 lb G.P., and 500 lb incendiary cluster, or 100 lb napalm hung with small adapter cables six per shackle. (Great in turbulence to watch them bounce on their tethers!)

                6. Add crew and ammunition weight.

                Compute bomb load for types specified by directive.

                Now, a technicality arises because the bomb types did not weigh their common number:

                                500 lb General Purpose                        = 450 lbs actual

                                500 lb Incendiary Cluster                    = 450 lbs actual

                                500 lb Fragmentation                                           = ?? (Don't recall, but think about 450 lbs.)

                                100 lb Napalm                                                       = 80 lbs.

                There were even some variations among these with subtle differences, but I don't know where to find the data now. The above weights are my best memory and at least compute for my maximum loads of 18,600 lbs.

                You can see my bomb loads on the attached personal Mission Record. I count:

                                14            Night Incendiary Single ship

                                2              Night G.P or Flare Single ship

                                4              Day Incendiary     Formation

                                8              Day G.P.                                 Formation

                                1              Show of Force, Aug 29, 1945, no bombs.

                We did not carry a bomb bay tank on any night mission so 40 bomb shackles wore open. Usually, we loaded one bomb bay with napalm and the other with 500 lb clusters and one 500 lb Fragmentation. I count my higher bomb loads in round figures of:

                                15,000 lbs               5

                                17,000 lbs               2

                                18,600 lbs               2 (max load available with this combination.)

                I cannot now account for the smaller night loads except for light loads on the early missions to compensate for inexperience. On day missions, we made night takeoff and cruised at assigned low altitudes of 3,000 to 8,000 feet to a specified rendezvous point, joined formation, then climbed to our bombing altitude and thence to the Initial Point for the bomb run. In rare instances when enroute weather interfered, we rendezvoused at a point on the Jap coast at bombing altitudes. The 45 minutes more flight time and higher bombing altitudes of 15 to 22,000 feet reduced bomb loads on day missions. Bomb bay tanks were used on only the longest day missions, I am sure less than half, but have no record.

                Regarding running out of incendiary bombs:  That was after the initial March series of five, but didn't affect subsequent missions because we were needed to bomb Kyushu airfields in support of the Okinawa invasion.

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                Planes taking off from Guam were already 600 feet above sea level at takeoff, those from Saipan 200 feet, but those from Tinian only 15 feet. Thus there was less margin for error with a Tinian takeoff. Some obviously used the extra height to gain speed or cool engines, all appreciated any extra margin of safety in the event of less than full power.

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                Vern Chandler wrote as follows:

                The technique of 'diving over the cliff' was done by some but not the experienced pilots. A basic flying instruction is to maintain a gradual climb after takeoff. I for one never dove for airspeed, but after gaining 100 feet to clear obstacles, leveled to gain airspeed to the climb speed of 190 mph. We had no trouble with engine over heating, but if encountered I would simply retard the throttle enough to reduce the cylinder head temperature. After several months on Guam, Capt Keough came to me one day saying that he had observed that I did not dive over the cliff and that they also noted that our B-29 M-2 (Dan Sidelco crew chief) did not require nearly so many engine changes. He postulated that the gradual speed increase for cooling might be better than a sudden cooling which could strain the metal of the valves or cylinders. It seems like the stories of wild dives to sea level increase with the years as does the quantities of whisky taken over seas and consumed!

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            Recollections of Engine Power Settings vary; depend on what kind of engine, what airplane, what period of the war, where from, where to, what loads and extenuating circumstances. The B-29 Tech Order indicates Military Rated HP as 2200 at 2600 rpm and 48 inches of mercury manifold pressure. It defines Take Off HP as 2200 at 2800 rpm & 48 inches. If a manifold pressure of 48 inches is maintained at an increases from 2600 rpm to 2800 rpm then delivered power would increase from 2200 HP to 2369 HP. If used at take off, those overheated exhaust valves becoming hotter yet!.

B-29 Engine Operating Limits Chart, from Operators Training Manual

 

            There were also changes in the airplanes. For example a surviving Tech Order shows 1367 gallon each for # 1 & 4 outboard engines and 1436 each for #2 & 3 inboard engines, a total of 5606 without bomb bay tanks. This is true for early B-29s delivered to the 58th Bomb Wing and flown to the CBI theater without Center Wing Tanks. However, later deliveries to all Wings included a Center Wing Tank with 1300 gallons for a total internal fuel except for B-29As built at the Renton Plant which had 200 gallons less in the Center Wing Tank. (Note: Based on Pilot Training Manual, AAF manual 50-9, 1 Feb 1945 in V. Chandlers library. “my second airplane, 44-0103, M-7 replacement was one of these from Renton.)

            Radar systems also changed, the 315th Wing B-29's on NW Field Guam having a wing-shaped radar antenna and a much improved radar set for precision Bombing.

            Bombay doors were either operated by electric motor actuators or by compressed air actuators. On my trip to look into FiFi's aft bomb bay I noticed it was equipped with electrically operated bomb bay doors. I made the comment that FiFi must have been one of the earlier B-29's as it had electrically operated doors. A fellow nearby responded, "Oh No, the electric doors replaced the air operated doors!" When I repeated that I recalled it the other way around, he was very emphatic to the contrary, certain he was right. I didn't say more. My recollections were of problems with the electrically operated doors on M-11, one of the older planes whose fuselage had been distorted, probably during one of the incendiary raids when crews were startled by the severe up drafts and buffeting they experienced.

            The newer planes such as M-15 came with air operated doors, they were much preferred by the flight crew. They were quick opening and closing and were connected through the bomb sight to open just seconds before ‘Bombs away’ and to close immediately afterward. This decreased drag with loss of airspeed on a long bomb run.