GrauGeist
Generalfeldmarschall zur Luftschiff Abteilung
The Jetstream literally passes over Japan as it heads west over the Pacific, the only time it's going to hinder/help a B-29's flight, is when it's close to landfall.
Fighter Escorts of B-29's over Japan & Pacific
- Thread starter Zipper730
- Start date
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Dash119
Senior Airman
First, I think the Jet Stream will hinder/help based more on the altitude and heading of the B-29 rather than it's position relative to landfall.
Second, even though the B-29 is not flying directly into the Jet Stream, flying into it 45 degrees off the nose will burn more fuel to get to the target than would otherwise.
The jet stream doesn't blow in straight lines and constantly varies in strength / altitude, it had an effect on fuel consumption and navigation but completely screwed up any idea of bombing accurately from 30,000 ft.
MIflyer
1st Lieutenant
By the way, the P-47N flew only one B-29 escort mission to Japan.
GrauGeist
Generalfeldmarschall zur Luftschiff Abteilung
The point being, is that the bulk of the B-29's flight time to the target area as well as the return flight to base is outside of the Jetstream's zone of influence.
Once the B-29s get within proximity of the Home Islands, will they come under the influence of the Jetstream.
So even when the Jetstream shifts to an extreme southerly course during the warmer months, the B-29s flying from the Marianas wouldn't encounter it until roughly halfway to Japan proper.
Once the B-29s get within proximity of the Home Islands, will they come under the influence of the Jetstream.
So even when the Jetstream shifts to an extreme southerly course during the warmer months, the B-29s flying from the Marianas wouldn't encounter it until roughly halfway to Japan proper.
- Thread starter
- #26
Nothing to do with jetstreams, the B-29 stayed at low altitude for the cruise portion of flight to and from the target because of engine stresses (heat/cooling), they were only getting 100 hours out of engines at the time before being scrapped. Keeping the engines cool was the Achilles heel of the B-29 operations, such was the problem that on take off the run was started with the gills fully open and as the aircraft accelerated the engineer progressively closed them, if during the taxi or at the intended start of take off if the CHT had reached a certain figure the flight was to be aborted.
GrauGeist
Generalfeldmarschall zur Luftschiff Abteilung
It wasn't until the lower daylight raids that the B-29s were flying below 25,000 feet.
And even at mid altitudes, the B-29 (and any other type) would cruise more effectively in the thinner, cooler air.
And even at mid altitudes, the B-29 (and any other type) would cruise more effectively in the thinner, cooler air.
33k in the air
Staff Sergeant
- 1,356
- Jan 31, 2021
Not exactly what you are asking for, but the following might be of interest. It comes from the Tactical Mission Report for mission #58 conducted by XXI Bomber Command on April 7, 1945. Times are in hours:minutes, fuel quantity is in U.S. gallons, weights are in pounds.
MISSION #58 (73 Wing)
Flight Data
Avg. Time at Low Altitude: 7:00
Avg. Time of Climb to Bombing Altitude: 0:27
Avg. Time at Bombing Altitude: 1:01
Avg. Flying Time: 15:22
Avg. Distance Flown (Nautical Air Miles): 2,959
Fuel Consumption
Consumed to Target: 3,906 avg. (min. 3,560 max. 4,369)
Consumed from Target to Base: 2,300 avg. (min. 2,048 max. 2,588)
Total Fuel Used: 6,189 avg. (min. 5,805 max. 6,667)
Total Fuel Remaining: 547 avg. (min. 133 max. 909)
Avg. Gallons Consumed Per Hour: 402.7
Avg. Gallons Consumed Per Mile: 2.09
Weight Data
Avg. Basic Weight of Aircraft: 74,977
Avg. Weight of Bombs Loaded: 10,275 (5 AN-M66)
Avg. Weight of Fuel Loaded: 40,572 (avg. fuel load of 6,762 gallons)
Avg. Misc. Weight: 7,401
Avg. Gross Weight at Takeoff: 133,225
The Tactical Mission Reports, along with other primary source documents, can be found at the website I mentioned earlier in the thread.
Incorrect I'm afraid during the war. You need to read the tactical bombing reports linked to previously. The data 33k provides in the previous post is typical, total flight time 15:22, time at bombing altitude 1:01, time at low altitude 7:00 (inbound to target), the leg back to home was made in a continual descent from the bombing altitude and hence reduced power. Engine cooling in the cruise at high altitude meant running at high temperatures which was detrimental to longevity.
33k in the air
Staff Sergeant
- 1,356
- Jan 31, 2021
That apparently was adopted later. The Tactical Mission Report for Mission #59 (April 7, 1945) says this in the section about the cruise back to base in its mission summary:
Return to Base: Return to base was made at altitudes between 8,000 and 25,000 feet, no particular return procedure proving to be definitely superior to others.
The Tactical Mission Report for Mission #174 (May 14, 1945) says this in the section about the cruise back to base in its mission summary:
Return to Base: The most economical return to base was made using a constant letdown of approximately 30 feet per minute. Headwinds encountered at return altitudes cost slightly more fuel than predicted..
There is a wealth of information in these Tactical Mission Reports, they are excellent primary source documents, so I would encourage anyone interested to view them online or download them for easier reading.
GrauGeist
Generalfeldmarschall zur Luftschiff Abteilung
Sorry, but wrong.
Economical cruise is achieved at altitude, the atmosphere is thinner and the temps are typically below 32°F.
Even today, commercial carriers traverse comparable altitudes for the exact same reason.
33k in the air
Staff Sergeant
- 1,356
- Jan 31, 2021
The XXI Bomber Command, in its wartime operation of B-29s, found otherwise for the purposes of the missions it undertook. The data and statistics are right there in its Tactical Mission Reports. Fuel usage and flight time figures were included for most of them.
GrauGeist
Generalfeldmarschall zur Luftschiff Abteilung
So you're saying that XXI command didn't operate at higher altitudes because of poor fuel economy and engine overheating?
33k in the air
Staff Sergeant
- 1,356
- Jan 31, 2021
I would refer you to post #30 and the flight time data. Nearly half the total mission flying time was at low altitude, with that on the cruise out from base. If you would like further examples from the Tactical Mission Reports, I can post them.
GrauGeist
Generalfeldmarschall zur Luftschiff Abteilung
I am FULLY aware of the operations and the mission profiles.
I appreciate your enthusiasm for the mission details although I find it surprising that as absorbed as you seem to be in the mission details, that you don't seem to be aware of how the B-29 functioned as a machine.
The B-29 (or any other aircraft) will operate more efficiently higher altitudes both in fuel consumption and engine load demand.
The B-29 bombing and mine-laying campaign against Japan was a fluid operation, making adjustments as conditions dictated as well as compensating for the base of the combat radius of those sorties.
And post #30 is about range in response to Zipper's query.
33k in the air
Staff Sergeant
- 1,356
- Jan 31, 2021
Sure. But operationally something other than purely high altitude cruising was used, for various reasons. This difference between best case and actual usage is worth noting.
Joe Broady
Airman 1st Class
- 106
- May 30, 2019
Have you got B-29 performance numbers to demonstrate the mileage vs altitude relationship? Unfortunately I have no data, at least for the B-29. But let's look at cruise performance of another turbocharged heavy bomber designed for sustained high altitude flight: the B-36. I chose a weight of 320,000 lb (about 80% of max useful load) as a representative outbound cruise condition. Power settings and speeds are selected for optimum fuel mileage at each altitude. The jet pods are not used.
0 ft, 190 mph EAS, 190 mph TAS, 35.0 nm/klb, 1800 hp
5000 ft, 186 mph EAS, 200 mph TAS, 35.5 nm/klb, 1870 hp
10000 ft, 185 mph EAS, 215 mph TAS, 36.0 nm/klb, 1980 hp
15000 ft, 178 mph EAS, 224 mph TAS, 35.5 nm/klb, 2050 hp
20000 ft, 175 mph EAS, 240 mph TAS, 31 nm/klb, 2200 hp
25000 ft, 175 mph EAS, 261 mph TAS, 26 nm/klb, 2400 hp
Best mileage ("nm/klb" = nautical miles per thousand pounds of fuel) is at 10,000 feet, though there's little difference from sea level to 15,000. But cruise at 20,000 and above causes a serious drop in fuel economy, though the power per engine is still acceptable for continuous operation. As you climb from sea level to 25,000 the best mileage airspeed does yield a steady increase in true airspeed, but the engines must be pushed harder too. Cruise at 30,000 with no jets is possible but not recommended since the best mileage speed is uncomfortably slow. It also requires 2500 hp/engine.
If you run two jets at 87% then 30,000 feet is no problem as long as 24 nm/klb is acceptable. With jet help only 2230 hp is required from each reciprocating engine. By running all four jets at 85% you can cruise at 35,000 (same weight) but mileage drops further to 23 nm/klb, though you enjoy a true airspeed of 314 mph.
Data for the B-36H (not the Featherweight version) from AN 01-5EUG-1, the 1953 flight handbook.
GrauGeist,
I have flown T-37, T-38, F-15, B757 / 767, A319 / 320, plumbed the DC-10, DC-8, and B727. All of those work as you described above. Higher is better for fuel mileage. I've also flown the OV-10 & RC-26 (Swearingen Metroliner) and neither of those planes operated on those principles. Unfortunately I no longer own the flight manual for either (Dash 1), however I do remember being taught in the OV-10 that should we need to divert from a missed approach to climb to MEA (Min Enroute Altitude) and no higher, as any fuel used in the climb would not be made back in the criuse / decent flight portions. I specifically asked the instructors in the RC-26 what was the min fuel divert procedure and all basically said the same thing (climb to MEA and no higher). The RC-26 flight manual didn't even have the fuel burn charts to answer this question.
While I can't speak to piston engined planes, I can to turbine powered and the only thing I can see that is different is props. Hopefully Bill will chime in using the P-51 as an example, or explain to the masses the why's of prop efficiency as compared to jet.
Cheers,
Biff
