Putting it (very) simply, drag is about the shape of the object, its physical size and frontal area and how it moves through the air. Other complexities include the viscosity of the air, the speed of the object etc. With an increase in speed comes an increase in drag, which correspondingly reduces acceleration and increases workload to maintain specific values. Basically, the faster you go, the greater the amount of resistant force on the aircraft and therefore the greater the amount of work required to maintain those values. Acceleration decreases and the engines have to work harder, which means a higher fuel consumption as the aircraft accelerates on take off and into establishing the climb. With aircraft that are heavily laden, around 20 percent of their total fuel load is used just to get off the runway (a value roughly calculated in a class exercise using a 747, its total fuel load and its MTOW versus its speeds and acceleration).
Yes, I'm familiar with the "speed squared law" as it applies to drag, as well as the different types of drag: form, induced, friction, parasitic.
By even fitting a streamlined bulge to the underside covering the Fat Man would be like increasing the frontal area of the Lancaster by nearly twice its value since the bomb is almost the same diameter as the aircraft.
How did you work out that carrying a Fat Man would double the frontal area of a Lancaster? Yes, the bomb is almost the same diameter as the Lanc...but the Lanc fuselage was racetrack-shaped and had a depth of 8ft 2in. If we add the canopy onto that (let's say 8in which is not unreasonable), then you have an (approximate) flat-sided oval of height 9ft and width 5ft.
Also bear in mind that 50% of the Fat Man will fit into the standard Lanc bomb bay, which means only 50% of the bomb is exposed to the airstream. This is based on the fact that the 4000lb Cookie had a diameter of 30in and that fitted into the Lanc bomb bay without bulged doors...although there's an assumption that any Fat Man bomb shackle didn't add more distance between the weapon and the bomb bay ceiling than was the case for the 4000lb Cookie.
All of the this ignores other sources of form drag...minor things like the wings, engines, propellers, tail surfaces etc. Given the above, carrying a Fat Man wouldn't come near to doubling the frontal area of a Lancaster.
Oh and Mark, as an engineer as you've pointed out, since you don't know the exact content of what Ramsey revealed to Chadwick, it's best not to presume until you do.
I'm not presuming. I'm working on a balance of probabilities. Another poster commented that "of course Chadwick would say the Lanc could carry the weapon." I'm afraid I just don't see that as a realistic scenario. You have one engineer, Ramsey, asking another engineer, Chadwick, an engineering question. Even if Chadwick did make the claim without doing calculations, would Ramsey have accepted it...as an engineer? The far more likely scenario is that Chadwick did some rough calculations, based on data provided and some agreed assumptions, and that Chadwick confirmed, to Ramsey's satisfaction, that the statement about the Lancaster's ability was sufficiently solid.
In all reality, we'll probably never know exactly what information was exchanged. It's highly likely details of bomb size and weight were provided verbally, that any calculations were done pretty quickly and then immediately destroyed. I simply find the idea that 2 engineers would discuss an engineering problem without diving into the mathematics somewhat ridiculous.
For all the criticism of the "Lancaster Unicorn" (and, trust me, I fully accept that the Lancaster would need extensive modifications and acknowledge that performance would absolutely be affected), let's not swing the other way in seeking for nonsensical arguments just to prove a point. I think arguments about what information Chadwick may or may not have obtained fall into that category and can never be positively resolved because the records likely don't exist. Weight clearly wasn't an issue so the only question is whether an adequate carrying shackle could be designed to accommodate Fat Man's girth given the Lancaster's fuselage width. We're into a balance of probabilities but, ultimately, the Lancaster's chief designer said the weapon could be carried and, unless there's evidence that Chadwick ever was economical with the truth, he should get the benefit of the doubt.
We also need to bear in mind that when Chadwick was asked the question, the targets for the weapons hadn't been selected. We do need to be careful of not applying the retrospectroscope and automatically applying the same Silverplate mission profile to the Lancaster. Again, with no B-29 in the mix, the decision calculus changes fundamentally. However, there were engineering solutions already in play as early as September 1944 to allow Lancasters to reach Japan.
At the Quebec Conference in September 1944, Churchill proposed to transfer a force of forty bomber squadrons to the Far East, of which 20 would act as airborne tankers. The tankers would use the Cobham AAR technique had been successfully trialed in 1935 - this was proven, rather than emerging, technology. Frankly, the last few pages of discussion on how much fuel gets burned during engine start-up and take-off are irrelevant. Tiger Force planned to use AAR so why overload a nuke-carrying aircraft on the ground? Much safer to keep the weight down for take-off then refuel in the air.
Roosevelt accepted Churchill's offer because, at that time, it was still unclear who long the war would continue. Ultimately, the RAF bombers weren't needed because the US was able to roll over Japanese defences and muster sufficient combat power on its own. However, if the B-29 programme had failed, Lancaster-based options were certainly available. It would have involved more aircraft and certainly would have been more complicated, with consequent increase in risk. However, I have no doubt it could have been done...had it been needed.
For me, there are 2 critical unanswered questions regarding the Lancaster's ability to successfully complete a nuclear weapon mission, and both are related to safe release of the weapon:
1. Could the Lancaster have attained sufficient altitude to drop the weapon?
2. Could the Lancaster have escaped the target area sufficiently quickly to protect the crew from the blast?
and couldn't see the obvious error in that statement.
