- Here was one approach considered as a way to increase the range of the B-29 without reducing the bomb load too much. https://oppositelock.kinja.com/cornelius-xfg-1-the-flying-fuel-tank-1791038950
Picture from the Wikipedia article on the XFG-1.
This early attempt at a kind of air to air refueling could have been done far more effectively if it had been done using powered airplanes for the fuel carrier instead of a glider. The glider would have added its towing drag load to the B-29 especially on take off thereby reducing the effectiveness of this method.
Why not use an existing transport airplane? The C-46 for example with its turbocharged engines could keep up with and stay connected to the B-29 up to high altitude. The idea I'm suggesting is still using a linked take off with the B-29 but with the C-46 powering its own take off. This permits the B-29 to take off with a full bomb load but with a partially reduced fuel load. Yep, a formation take off.
The C-46 after powering its own take off stays connected on the long climb out to high altitude with the B-29 "nursing" from the C-46. After all the fuel is transferred from the C-46 the B-29 will be at a more economical for cruise high altitude with more fuel in the tanks (possibly nearly full tanks depending on the weight) as the fuel used up on the climb out was pumped over from the C-46.
This is the sharing the load method. By having the C-46 carry some of the weight of the required mission fuel load for part of the out bound flight path, in particular the heavy fuel burning climb out. By carrying the fuel load in tandem with the B-29 for a much longer period of time then the modern air to air refueling this method is very efficient at increasing the B-29s' range.
After the fuel transfer is complete the B-29 releases its end of the hose. If there is a reel mechanism installed in the C-46 then the hose is reeled in. If no mechanism then the hose is simply dropped. The C-46 crew flies back to their airbase.
Why not just develop modern air to air refueling? That took a few years to develop. This is a faster and more adhoc approach. And it has the advantage of the fuel load sharing function. It would require some careful flying especially in poor weather but the hose length would be long, more than 150 feet, to lessen the difficulty of the formation flying. I think the B-29 hose fitting and connector would be installed just aft of the tail bumper. On the C-46 the same fitting would be on the lower half of the nose.
In WW2 all military pilots had at least some formation flying training. Also a tandem take off and climb out is not too difficult if the two different type of planes take off and climb speeds are similar. The hose would have to be strengthened to withstand a fair amount of tension because there would be some movement in formation. If the hose breaks before the fuel is transferred then the B-29 crew chooses a nearer alternate target.
I think the method I've described could be used for other planes. A good example would be a Tallboy carrying Lancaster. Being topped up after take off and climb out would enable longer ranged missions.
How to extend the range of the B-29 and other Allied heavy bombers.
- Thread starter Draconis
- Start date
Air to air refueling was already in use by the late 1930s Shorts Empire flying boats made 16 Atlantic crossings in 1939 refueled by RAF Handley Page Harrows. The RAF intended to use air refueling to bomb Japan in late 1945.
https://en.wikipedia.org/wiki/Aerial_refueling
https://en.wikipedia.org/wiki/Aerial_refueling
@fastmongrel The one big advantage to this time extended refueling system I described is it shares the weight of the mission fuel load between two airplanes for a longer period than conventional air to air refueling. Which in the lower altitudes and slower speeds before the jet age are a plus. Also this system requires very little extra training for the bomber pilots. The refueling tanker airplane pilots would have to be well trained for this kind of formation flying to avoid putting excessive strain on the hose.
You want 2 fully loaded planes to take off connected by a fuel hose? Are the take off speeds exactly the same? What about take off distance, climb rate, etc.
They would connect together mid flight, rather than staying together.
Errolwi
Monthly Donor
That would be sane, unlike what the OP is suggesting. The additional work/training/risk in connection during the climb is much less than a connected take-off (to a type with a high engine failure rate on take-off, even).
Probably better to modify war-weary B-29 bombers, stripping them of guns and armour and sending them to orbit halfway to the target. They would top-off bombers both outbound and during the return flight.
I was theorizing about a similar inflight refuelling system for RCAF Ferry Command. Have refuelled squadrons based in Newfoundland, Labrador, Greenland, Iceland and Scotland.
Ferrying airplanes would take off from Montreal or Quebec City with temporary refuelling probes and specially trained ferry pilots. They would meet orbiting tankers over the North Atlantic. If they missed a contact, they would still have enough fuel to divert today Greenland, but the goal would be to complete the Atlantic crossing in one hop.
A similar system would see bombers launch from the UK with heavy bomb loads, but only a couple of hours worth of fuel. They would top off from war-weary tankers over the English Channel, then bomb targets in East Germany.
I was theorizing about a similar inflight refuelling system for RCAF Ferry Command. Have refuelled squadrons based in Newfoundland, Labrador, Greenland, Iceland and Scotland.
Ferrying airplanes would take off from Montreal or Quebec City with temporary refuelling probes and specially trained ferry pilots. They would meet orbiting tankers over the North Atlantic. If they missed a contact, they would still have enough fuel to divert today Greenland, but the goal would be to complete the Atlantic crossing in one hop.
A similar system would see bombers launch from the UK with heavy bomb loads, but only a couple of hours worth of fuel. They would top off from war-weary tankers over the English Channel, then bomb targets in East Germany.
Elsewhere on the forum, I described several of the techniques evaluated at WPAFB to extend the range of B-36 aircraft tasked with delivering the massive emergency capability liquid fueled fusion weapons (together with the Dewars containing liquified duterium to compensate for boil-off enroute). Even fuel carrying floating wing extensions (the suggestion of Dr Richard Vogt) as later proposed for the NAA WS-110A submission and leading to the aborted "Tip Tow" program several years later, would not have added enough range.
Other than inflight refueling (which was out of my area) the one concept which would have permitted sufficient range for an out-and-back with this payload was a three ship mission. The weapon carrying ship would be linked, by each wingtip to a tanker "KB-36" each of which would pump fuel into the penetrating ship via in-wing fuel lines with break-away connectors. The aircraft would take off individually, and link-up in flight (later successfully demonstrated with B-29s and F-84s). The flight controls group was confident that strain sensors coupled with the autopilots (and an analog computer) would keep everything together. So here we have an airplane with an aspect ratio of 29.5 and a cruise L/D approaching 20 at high cruise. At some point the aircraft separate, leaving the bomb carrier within perhaps 2000 miles of ground zero with full tanks and overweight payload (considerably above takeoff weight). The two wingtip aircraft return to CONUS while the bomb carrier overflys the target and, much lighter, continues to a landing in the south, or as later computed, with sufficient range to return to South Dakota
A variant of this coupled aircraft mission was later proposed using B-47s- the center aircraft being a drone carrying a proposed very high yield device, beyond any aircraft's ability to escape blast effects.
The concept of fuel in pivoted wing extensions was proposed by Vogt at Blohm & Voss during WW2, and demonstrated by the AF in, I believe, 1955.
Dynasoar
Edit: Correct aspect ratio for span reduction and interwing adapters. Span 645ft.
Other than inflight refueling (which was out of my area) the one concept which would have permitted sufficient range for an out-and-back with this payload was a three ship mission. The weapon carrying ship would be linked, by each wingtip to a tanker "KB-36" each of which would pump fuel into the penetrating ship via in-wing fuel lines with break-away connectors. The aircraft would take off individually, and link-up in flight (later successfully demonstrated with B-29s and F-84s). The flight controls group was confident that strain sensors coupled with the autopilots (and an analog computer) would keep everything together. So here we have an airplane with an aspect ratio of 29.5 and a cruise L/D approaching 20 at high cruise. At some point the aircraft separate, leaving the bomb carrier within perhaps 2000 miles of ground zero with full tanks and overweight payload (considerably above takeoff weight). The two wingtip aircraft return to CONUS while the bomb carrier overflys the target and, much lighter, continues to a landing in the south, or as later computed, with sufficient range to return to South Dakota
A variant of this coupled aircraft mission was later proposed using B-47s- the center aircraft being a drone carrying a proposed very high yield device, beyond any aircraft's ability to escape blast effects.
The concept of fuel in pivoted wing extensions was proposed by Vogt at Blohm & Voss during WW2, and demonstrated by the AF in, I believe, 1955.
Dynasoar
Edit: Correct aspect ratio for span reduction and interwing adapters. Span 645ft.
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Connected take offs and climb outs are happening hundreds of times a day everyday world wide usually without incident.
Ideally the B-29 would have a slightly higher take off and climb out speed then the tanker airplane. This would put a certain amount of towing strain on the hose but it would be built to withstand that amount. By flying with a small amount of towing tension it helps the tanker plane to maintain the full distance from the B-29. The hose should be at least 150 feet long to help ease the formation keeping for the tanker plane.
Since both planes can disconnect their own end of the hose then any problems on take off due to engine failures or other causes mean either crew can separate the connection to deal with their problem. A B-29 losing an engine on take off is likely going to run off the end of the runway. The tanker plane would continue its take off on its own.
This system would not require any extensive training for the bomber crews. Nor would it add much risk to the crew of the bomber. They would fly the take off and climb out to cruise in a familiar stable flight profile. The tanker pilots must be trained to keep proper formation on the bomber. In case of weather or a mistake either crew can separate immediately. And in any event the hose would break if excessively strained.
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Connected take offs and climb outs are happening hundreds of times a day everyday world wide usually without incident.
Ideally the B-29 would have a slightly higher take off and climb out speed then the tanker airplane. This would put a certain amount of towing strain on the hose but it would be built to withstand that amount. By flying with a small amount of towing tension it helps the tanker plane to maintain the full distance from the B-29. The hose should be at least 150 feet long to help ease the formation keeping for the tanker plane.
Since both planes can disconnect their own end of the hose then any problems on take off due to engine failures or other causes mean either crew can separate the connection to deal with their problem. A B-29 losing an engine on take off is likely going to run off the end of the runway. The tanker plane would continue its take off on its own.
This system would not require any extensive training for the bomber crews. Nor would it add much risk to the crew of the bomber. They would fly the take off and climb out to cruise in a familiar stable flight profile. The tanker pilots must be trained to keep proper formation on the bomber. In case of weather or a mistake either crew can separate immediately. And in any event the hose would break if excessively strained.
Are you talking like a KC-135 connected to another aircraft while still on the ground or something? There's a base with a KC-135 wing near me, I've done civilian contractor work there and know several pilots and enlisted. I've never seen a KC-135 or KC-10 physically connected while still on the tarmac, or ever heard it mentioned.
Do you have some references to this?
Yes, I was referring to glider launches by aerotow, which is not so very different from a linked take-off with two powered aircraft. Here's why.
Both require formation flying ability. But the effort to maintain position a couple of hundred feet behind the lead plane is not nearly as demanding a holding position 6 feet off a wing tip. It's such an easy task that amateur weekend pilots do this.
Because both aircraft are large and flying at higher speeds doesn't change the basic flight dynamics of a linked take off. Because the trailing airplane is supplying it's own power for take off doesn't mean that the dynamic of an aerotow can't be applied here. The key being that the take off speed of the B-29 should be a little higher than the tanker plane to avoid the tanker over running the B-29 on take off. For a heavily loaded B-29 that would certainly be the case.
Rather then dangerously extending the B-29s take off run by the brute force hauling of an unpowered fuel tank glider like the XFG-1 instead the tanker airplane powers itself into the air with the tanker planes' pilots controlling their airspeed so as to not close up on the B-29. A strain meter for the hose and the Mark 1 eyeball with experience will help the tanker pilots achieve the optimal airspeed to avoid closing and to avoid slowing too much and straining the hose to the breaking point. Holding position vertically and laterally is not difficult.
Unlike developing the apparatus for air to air refueling and then having to fly training missions the method I'm describing requires no more training for the B-29 crew than a briefing about the flight profile from take off, climb out to the release of the hose. A bit more fuel management task for the flight engineer. And a briefing for the tail gunner ( who would control the B-29s hose release as he has the best view) to release the hose in the event of either aircraft getting too far out of position. The main part of the training would be required by the tanker pilots which would not be too demanding IMO.
Any planned extreme range missions flown would have an alternate set of close range targets in the event there is a problem like a hose break. That way there is no need to abort if the refueling is partially or totally unsuccessful.
Both require formation flying ability. But the effort to maintain position a couple of hundred feet behind the lead plane is not nearly as demanding a holding position 6 feet off a wing tip. It's such an easy task that amateur weekend pilots do this.
Because both aircraft are large and flying at higher speeds doesn't change the basic flight dynamics of a linked take off. Because the trailing airplane is supplying it's own power for take off doesn't mean that the dynamic of an aerotow can't be applied here. The key being that the take off speed of the B-29 should be a little higher than the tanker plane to avoid the tanker over running the B-29 on take off. For a heavily loaded B-29 that would certainly be the case.
Rather then dangerously extending the B-29s take off run by the brute force hauling of an unpowered fuel tank glider like the XFG-1 instead the tanker airplane powers itself into the air with the tanker planes' pilots controlling their airspeed so as to not close up on the B-29. A strain meter for the hose and the Mark 1 eyeball with experience will help the tanker pilots achieve the optimal airspeed to avoid closing and to avoid slowing too much and straining the hose to the breaking point. Holding position vertically and laterally is not difficult.
Unlike developing the apparatus for air to air refueling and then having to fly training missions the method I'm describing requires no more training for the B-29 crew than a briefing about the flight profile from take off, climb out to the release of the hose. A bit more fuel management task for the flight engineer. And a briefing for the tail gunner ( who would control the B-29s hose release as he has the best view) to release the hose in the event of either aircraft getting too far out of position. The main part of the training would be required by the tanker pilots which would not be too demanding IMO.
Any planned extreme range missions flown would have an alternate set of close range targets in the event there is a problem like a hose break. That way there is no need to abort if the refueling is partially or totally unsuccessful.
I was referring to the aerotow launching of gliders which is carried out extensively in many countries. It's the closest analog to the refueling method I'm describing here. And it's easy enough that amateur pilots can do it. I was not intentionally trying to mislead the readers but I wanted to see if anyone would guess where I was leading.
Imagining myself responsible for range extension of the B-29/B-32 program in the late 1942-early 1943 time, and in the absence of mid air refueling, I'd do the following: Abandon efforts to integrate the dismal Curtiss-Wright R-3360 into the long range bomber program, since their management team refused to focus their engineering staff on this engine. Instead, ignoring clearly evident design flaws (some of them quite basic), engineering talent was squandered on the Tornado and R-4020 22 cylinder radial program
Instead, while accelerating the Allison W-3420, I'd concentrate on incorporating the proven and available Pratt & Whitney R-2800. While giving up displacement equivalent to a fifth engine- horsepower with the P&W, particularly on takeoff could actually be somewhat improved over OTL with water/methanol injection. Specific fuel consumption of the turbocharged variant (as used in the contemporary P-47) was better than the C/W engine and the weight savings with P&W could be employed for increased wing tankage. An increase in wing area from a span extension (containing fuel to be consumed last) would improve takeoff distance, rate of climb and service ceiling, without necessarily changing wing bending moments or reducing cruise speed.
If increased speed was desired (as would be available with the Allison Vees) work on the P&W could include both a cooling fan at the nacelle inlet for much less power loss than the propeller cuffs utilized, and a translating ring air outlet to eliminate the climb killing drag of the huge cowl flaps required to try to cool the C/W engine. (Nacelle like the Republic XF-12).
Range improvement if flown at same speed and altitude.... from start of takeoff roll to landing? Probably at least 700 but more likely up to 900 miles.
Dynasoar
Instead, while accelerating the Allison W-3420, I'd concentrate on incorporating the proven and available Pratt & Whitney R-2800. While giving up displacement equivalent to a fifth engine- horsepower with the P&W, particularly on takeoff could actually be somewhat improved over OTL with water/methanol injection. Specific fuel consumption of the turbocharged variant (as used in the contemporary P-47) was better than the C/W engine and the weight savings with P&W could be employed for increased wing tankage. An increase in wing area from a span extension (containing fuel to be consumed last) would improve takeoff distance, rate of climb and service ceiling, without necessarily changing wing bending moments or reducing cruise speed.
If increased speed was desired (as would be available with the Allison Vees) work on the P&W could include both a cooling fan at the nacelle inlet for much less power loss than the propeller cuffs utilized, and a translating ring air outlet to eliminate the climb killing drag of the huge cowl flaps required to try to cool the C/W engine. (Nacelle like the Republic XF-12).
Range improvement if flown at same speed and altitude.... from start of takeoff roll to landing? Probably at least 700 but more likely up to 900 miles.
Dynasoar
thorr97
Banned
Dynasoar,
What? I thought the only reason - and the only way - the B-29 could meet its specs was with those R-3360s. I wasn't aware there was anything else in the same league that could've been substituted! That being the case, why didn't the Army go with the option you described?
What? I thought the only reason - and the only way - the B-29 could meet its specs was with those R-3360s. I wasn't aware there was anything else in the same league that could've been substituted! That being the case, why didn't the Army go with the option you described?
In retrospect I believe they made a mistake going with the Wright R-3350.
https://en.wikipedia.org/wiki/Boeing_XB-39_Superfortress
The Allison V3420 had tons of problems of its own and and although it began development about the same time as the R-3350 (1937) never reached the reliability standards of the R-3350. The P&W 4360 was several years behind the other two it was used in the follow on to the B-29, the B-50.In retrospect I believe they made a mistake going with the Wright R-3350.
https://en.wikipedia.org/wiki/Boeing_XB-39_Superfortress
eral
I have toyed with a storyline where the IFR used by the Empire Flying boats was used in WWII. The problem I see is the number of tankers needed for the large bomber formations (and their associated fighter escort) would be very difficult to coordinate. I see a much more productive use in extending the range of maritime patrol aircraft such as the VLR Liberator and Catalina to close the mid atlantic gap early in 1943. Since these missions were single aircraft at a time there would be less coordination required in cluttered airspace. One patrol aircraft launching with a tanker flying together for a while the tanker tops off the patrol aircraft and returns to base while the bomber now with a full load of fuel several hundred miles into its mission (and after the fuel sucking takeoff and climb) can extend its mission further out or its loiter time by several hours.