The Lancaster as a potential nuclear bomber in 1945

[Koopernic]

Historical bombing altitudes were ~32000ft and 29000 ft (Nagasaki)

Lancaster VI service ceiling is 28500ft at 65000lb TO weight. However, at weapon release, the aircraft will have burnt off about 1500-1800 IG of fuel (~11000 to ~13000lb from 72000lb TO weight) and weight will be 61000-59000lb with a consequent increase in service ceiling. However even at 28000ft a Lancaster would have been safe from the ~21kt yield of a FAT MAN bomb as was proved by Bockscar dropping at ~29000ft. The LITTLE BOY bomb only had a yield of 13kt.

i think that's slightly optimistic.

I calculate a reduction in air density of 17% (ie 83%) between 23500ft and 28000ft which would reduce lift by 17%. In addition as the engines are above FTH the power would also drop 17%. A 12000lb reduction in weight from 72000lb to 60000lb is also a reduction of 17% however the reduction you refer to is from 65000lbs to 59000lbs is only 10%. There is a slightly reduction in parasitic drag. Although I can't see the operational ceiling (500 fpm) going from 23500 to 28000ft I can see it going to half way there, maybe 26000ft but the aircraft would reach 28000ft with maybe a climb rate of only 200fpm. This means the aircraft is hanging on the very edge edge of a stall with the engines at maximum power. This is a problem for an aircraft whose main escape was a corkscrew that generally lost enemy night fighters, The "silver plate" Lancaster VI would no doubt have fishpond for its H2S radar and village inn radar for its tail gunner and have the dorsal turret deleted. I think the Lancaster could drop little boy. Incidently the first atomic bomb to go off was little boy over hiroshima. There was no prototype test so yield could have been higher. Nitrous Oxide was used on single stage Merlin Mosquitos and we know the two stage used them so a nitrous oxide supply was a possibility. I think 26000ft is a good enough altitude and if done at night stood good chances of evading interception.

Air Pressure at Altitude Calculator
(assuming boyles law on PV = constant

 

[nuuumannn]

he above states .95 AMPG at mean mission weight of 66500lb = 2850 miles with 3000IG of fuel.

And if you increase the fuel load you have to decrease the warload, which pushes it below the value of even the Little Boy bomb. Trials carried out with the Lancaster fitted with overload saddle tanks showed that with a max take off weight of 72,000lb calculated from a standard 2,154gal internal fuel load, plus the saddle tank fuel load the radius of action was 1,500 miles with a 6,000lb load.

With the saddle tank, the maximum range was 3,154 miles, but again the warload was 6,000lbs.

Range or load? Can't have both.

Don't know if this will help any:

Nice drawing, but it only shows the diameter of the bomb body, not the fins, which equates to a box of the same diameter as the body, of 1.5m each flat side. That cannot be carried internally - the width of the bomb fins is wider than the internal bomb bay walls. It would have to be suspended below the fuselage level. Let's also consider for a minute what impact that will have on drag, not to mention loading on the bomb itself whilst in flight. No aerodynamicist nor engineer would certify that at all. Even if it were enclosed by purpose built doors, what impact does that have on clearance? We are talking a completely fictional scenario that has too many impracticalities written into it.

This all simply boils down to whether the Lancaster, with reasonable modifications, could act as a 1945 nuclear bomber. Not what would be the best nor issues of nationality nor if it were actually considered for it.

Correct, but nationality was on the cards, both Groves and Arnold wanted an American bomber.

 

[RCAFson]

i think that's slightly optimistic.

I calculate a reduction in air density of 17% (ie 83%) between 23500ft and 28000ft which would reduce lift by 17%. In addition as the engines are above FTH the power would also drop 17%. A 12000lb reduction in weight from 72000lb to 60000lb is also a reduction of 17% however the reduction you refer to is from 65000lbs to 59000lbs is only 10%. There is a slightly reduction in parasitic drag. Although I can't see the operational ceiling (500 fpm) going from 23500 to 28000ft I can see it going to half way there, maybe 26000ft but the aircraft would reach 28000ft with maybe a climb rate of only 200fpm. This means the aircraft is hanging on the very edge edge of a stall with the engines at maximum power. This is a problem for an aircraft whose main escape was a corkscrew that generally lost enemy night fighters, The "silver plate" Lancaster VI would no doubt have fishpond for its H2S radar and village inn radar for its tail gunner and have the dorsal turret deleted. I think the Lancaster could drop little boy. Incidently the first atomic bomb to go off was little boy over hiroshima. There was no prototype test so yield could have been higher. Nitrous Oxide was used on single stage Merlin Mosquitos and we know the two stage used them so a nitrous oxide supply was a possibility. I think 26000ft is a good enough altitude and if done at night stood good chances of evading interception.

Air Pressure at Altitude Calculator
(assuming boyles law on PV = constant

The Lancaster VI service ceiling at 65000lb was 28500ft (100ft/min climb rate) and absolute ceiling was ~29800ft.

A Lincoln with a Merlin 85 engines had it's service ceiling increase from ~30000ft at 69500lb to 32500ft at 63500lb so I think we could predict a similar increase in combat and service ceiling for a Lancaster VI, as per your calculation. However another way to look at the problem, is that of how much fuel is required for a flight from Hiroshima (630 miles)/Nagasaki (490 miles) to Okinawa? I would guesstimate that 800IG would suffice and would provide for at least 900 miles even with a high speed cruise, given the reduced weight. Therefore we can afford to have burned ~2100 IG at ~20min prior to weapon release for a weight of ~57000lb and an increase in combat ceiling to ~27000ft and service ceiling to ~33500ft and therefore only another 3-5 minutes from 27000ft to 29000ft for Hiroshima, which is still well below the service ceiling. For a Nagasaki mission we can return to Okinawa with 700IG remaining at 20min prior to weapon release and about 55000lb for a combat ceiling of ~29000ft.

Of course it is convenient to use the historical Lancaster VI, as an "off the shelf" solution, but the Merlin 85 is really a medium altitude rated engine and a Lancaster VI variant could be fitted with a high altitude rated Merlin such as the Merlin 86, which increases the FTH by ~6000ft ( 16000ft to 22250) over the Merlin 85.

As per earlier data presented by GREYMAN, removing the top turret increases Vmax on the Lancaster VI by about 12mph and IIRC, removing the front turret would add another 4mph.

 

[nuuumannn]

It's also worth mentioning that at a max take off weight of 72,000lbs the Lancaster was a beast to fly. The A & AEE recommended that only the most skilled pilots fly it, the engine oil temps were at their maximum safe level at less than max rate climb and any speed over 260mph provoked severe vibration throughout the airframe. Cruise was restricted to below 170 to 180mph. Flying at that speed over Japan in 1945?

It's worth remembering that the Lancaster VI suffered vibration and overheating during A&AEE trials resulting in the loss of an airframe during testing, with thankfully no loss of life. Performance figures were an improvement, but the decision was made to not pursue the type, and as posted previously, it was withdrawn from service in November 1944.

Regarding in-flight-refuelling, Lancasters were used in trials in late 1944 and these were promising, but no in service examples were so fitted by August 1945.

 

[GrauGeist]

Again, Okinawa cannot be used as an Atomic staging base.
It was under constant attack by the Japanese and would put the atom bomb program in jeopardy.
Aside from the fact that there was a limited supply of atom bombs, if one of the bombs was destroyed by a Japanese bomb, there would be the issue of radioactive debris.

 

[RCAFson]

And if you increase the fuel load you have to decrease the warload, which pushes it below the value of even the Little Boy bomb. Trials carried out with the Lancaster fitted with overload saddle tanks showed that with a max take off weight of 72,000lb calculated from a standard 2,154gal internal fuel load, plus the saddle tank fuel load the radius of action was 1,500 miles with a 6,000lb load.

With the saddle tank, the maximum range was 3,154 miles, but again the warload was 6,000lbs.

(1)Range or load? Can't have both.



(2)Nice drawing, but it only shows the diameter of the bomb body, not the fins, which equates to a box of the same diameter as the body, of 1.5m each flat side. That cannot be carried internally - the width of the bomb is wider than the internal bomb bay walls. It would have to be suspended below the fuselage level. Let's also consider for a minute what impact that will have on drag.



(3)Correct, but nationality was on the cards, both Groves and Arnold wanted an American bomber.

Tiger Force was formed to drop conventional bombs on Japan and these bombs used a large volume of the bomb bay especially incendiaries and the Tallboy/Grandslam. Therefore to increase fuel load they needed to add extra internal tanks by extending the upper fuselage as a saddle tank. However the saddle tank fuselage mods were heavy and so overall not an efficient aircraft and the saddle tank design was discarded. It has been pointed out to you, repeatedly, that during the Operation Catechism Tirpitz raids from Scotland, that Lancasters loaded with 2560IG (2160 + 400IG) of fuel flew a 12000lb Tallboy mission an average of 2400 miles (return) to destroy Tirpitz with a Lancaster TOW of 68500lb. One Lancaster returned from Tirpitz with a hung up bomb . Max TOW of the Lancaster was increased to 72000lb, which along with the more compact and balanced Atomic bombs would have allowed for additional fuel via internal aux bomb bay tanks. So a Lancaster could carry ~3000IG of internal fuel and a ~10000lb Little Boy or Fat Man bomb.

2) Again Fat Man width was 60.25in or less while the Lancaster B-B was 61in wide by 38in deep. So some protrusion, similar to the existing radome. This is assuming that no mods can be made to the ceiling of the bomb bay.

3) irrelevant.

 

[nuuumannn]

Max TOW of the Lancaster was increased to 72000lb, which along with the more compact and balanced Atomic bombs would have allowed for additional fuel via internal aux bomb bay tanks. So a Lancaster could carry ~3000IG of internal fuel and a ~10000lb Little Boy or Fat Man bomb.

Again though, this is entirely fictional. If you add extra tanks in the bomb bay plus max internal fuel load and warload, you have exceeded your maximum take off weight. And again, can't carry Fat Man at all.

 

[RCAFson]

Again, Okinawa cannot be used as an Atomic staging base.
It was under constant attack by the Japanese and would put the atom bomb program in jeopardy.
Aside from the fact that there was a limited supply of atom bombs, if one of the bombs was destroyed by a Japanese bomb, there would be the issue of radioactive debris.

Okinawa was used to stage Bockscar to Tinian after the Nagasaki mission.

 

[RCAFson]

Again though, this is entirely fictional. If you add extra tanks in the bomb bay plus max internal fuel load and warload, you have exceeded your maximum take off weight. And again, can't carry Fat Man at all.

Catechism raid = 12000lb Tallboy plus 2560IG of fuel and a TOW of 68500lb on a 2400 mile mission. Hypothetical Hiroshima raid = 10000lb bomb plus ~3000ig (extra 440IG = 3170lb plus ~330lb for the aux tank = 3500lb) of fuel for a TOW of 70000lb or 2000lb less than the allowable TOW of 72000lb.

 

[FLYBOYJ]

Okinawa was used to stage Bockscar to Tinian after the Nagasaki mission.

Staged? Visit? Irrelevant!!! The fact is the mission STARTED from Tinian!!!!

 

[RCAFson]

Stage? Visit? Irrelevant!!! The fact is the mission STARTED from Tinian!!!!

Yes, as I previously stated, Bockscar's actual Nagasaki mission staging = Tinian->Nagasaki->Okinawa->Tinian. This would be the staging plan for a Lancaster mission.

 

[FLYBOYJ]

Yes, as I previously stated, Bockscar's actual Nagasaki mission staging = Tinian->Nagasaki->Okinawa->Tinian. This would be the staging plan for a Lancaster mission.

Bockscar should have gone Iwo Jima, that was the emergency landing field. Okinawa was NOT part of the plan! There were many mistakes made during the Nagasaki mission but nothing that would justify the use of an inferior aircraft to complete the same mission!

 

[wuzak]

2) Again Fat Man width was 60.25in or less while the Lancaster B-B was 61in wide by 38in deep. So some protrusion, similar to the existing radome. This is assuming that no mods can be made to the ceiling of the bomb bay.

The ceiling of the bomb bay was the centre wing section.

I can't find the dimensions of the H2S radome at this time. However, I doubt it sat as low as the Fat Man bomb would.

As nuuumannn said:, the box tail of the Fat Man bomb was as wide as the bomb diameter - 60in. Which means that the biggest part of the bomb within the actual bomb bay was 60" wide, leaving only 1" extra room, or 0.5" per side. Doesn't seem practical, especially if you want to use some sort of bomb door.

 

[FLYBOYJ]

The ceiling of the bomb bay was the centre wing section.

I can't find the dimensions of the H2S radome at this time. However, I doubt it sat as low as the Fat Man bomb would.

As nuuumannn said:, the box tail of the Fat Man bomb was as wide as the bomb diameter - 60in. Which means that the biggest part of the bomb within the actual bomb bay was 60" wide, leaving only 1" extra room, or 0.5" per side. Doesn't seem practical, especially if you want to use some sort of bomb door.

I was thinking the same thing. Anyone consider the bomb rack in the equation?

 

[RCAFson]

It's also worth mentioning that at a max take off weight of 72,000lbs the Lancaster was a beast to fly. The A & AEE recommended that only the most skilled pilots fly it, the engine oil temps were at their maximum safe level at less than max rate climb and any speed over 260mph provoked severe vibration throughout the airframe. Cruise was restricted to below 170 to 180mph. Flying at that speed over Japan in 1945?

It's worth remembering that the Lancaster VI suffered vibration and overheating during A&AEE trials resulting in the loss of an airframe during testing, with thankfully no loss of life. Performance figures were an improvement, but the decision was made to not pursue the type, and as posted previously, it was withdrawn from service in November 1944.

Regarding in-flight-refuelling, Lancasters were used in trials in late 1944 and these were promising, but no in service examples were so fitted by August 1945.

I'm sure that an A-bomb mission will be assigned to skilled pilots, but the aircraft will lose ~10,000lb minimum during the cruise outbound from Tinian before begining their cruise climb prior to entering Japanese airspace..

This is from page 102 of Mason's The Secret Years Flight testing at Boscombe Down :

In January 1944 the first Lancaster with Merlin 85
JB675, was delivered and given full handling and cooling
trials; the latter indicated that the radiator was
unsatisfactory in the cruise. ND479, also re-engined with
Merlin 85s, was engaged on stick force tests, but on 26
April 1944, the port outer engine oversped to 4,000 rpm
and could not be feathered; the extreme drag could not
be controlled and the aircraft crashed, but without
casualties. A third aircraft with Merlin 85, ND558, arrived
in June 1944 with tests concentrated on the propeller
constant speed unit. After lengthy climbs to 30,000 ft,
the engines were set at 2,700 rpm (90% maximum) and
plus 2 psi boost and the aircraft dived, reaching 350 mph
(indicated) at about 25,000 ft (equivalent Mach No 0.72).
Apart from the escape hatch disappearing, nothing
untoward happened. Asymmetric handling with the
higher power of the 85s confirmed failure of the port outer
as the worst case on take-off. With full rudder and aileron
combined with significant bank, 130 mph (indicated)
could just be held; without bank, 155 mph was the
minimum.

Typical teething issues but we then have a Lancaster VI achieving Mach .72 at 25000 ft and no engine problems in June 1944.

 

[GrauGeist]

Bockscar ONLY landed at Okinawa as an emergency measure.

All of the 509th CG's bombers were to transit from Tinian, to target and back to Tinian. This was to preserve security of the missions and the chain of secure data gathered on board.

Bockscar broke security protocol by landing at Okinawa due to a faulty fuel transfer pump AND excessive loiter time over both targets.

There was a secure emergency field at Iwo Jima but there was not enough fuel to reach it. As it was, Bockcar's engines were shutting down from fuel starvation AS it was landing at Yontan field.

So the actual flight for Bockscar was:
Tinian to Rendezvous Point at Yakushima
Loitered at Yakushima 30 minutes
Yakushima to Kokura
Loitered at Kokura 50 minutes (3 bomb runs - unable to bomb)
Kokura to Nagasaki
Orbited Nagasaki
Bombed Nagasaki
Nagasaki to Okinawa

 

[FLYBOYJ]

Typical teething issues but we then have a Lancaster VI achieving Mach .72 at 25000 ft and no engine problems in June 1944.

Any by July 1944 the Japanese homeland was being bombed by B-29s

 

[RCAFson]

The ceiling of the bomb bay was the centre wing section.

I can't find the dimensions of the H2S radome at this time. However, I doubt it sat as low as the Fat Man bomb would.

As nuuumannn said:, the box tail of the Fat Man bomb was as wide as the bomb diameter - 60in. Which means that the biggest part of the bomb within the actual bomb bay was 60" wide, leaving only 1" extra room, or 0.5" per side. Doesn't seem practical, especially if you want to use some sort of bomb door.

Fat Man would protrude about 22-24in. The Radome extends about 1/4 of the height of the max aircraft fuselage height so they seem quite comparable

Roy Chadwick said it was practical.

 

[FLYBOYJ]

Roy Chadwick said it was practical.

Practical vs probable.

 

[wuzak]

Fat Man would protrude about 22-24in. The Radome extends about 1/4 of the height of the max aircraft fuselage height so they seem quite comparable

Roy Chadwick said it was practical.

Did he say it was practical for the final Fat Man bomb, or for a provisional design that may have had different dimensions?