VC10s vs late-model B707s
Quote from Slats One:
The lighter, less powerful 707-336 had more range and could do the LHR- USA west coast hop in one go- which was one of the 707s few advantages of the VC10. Having said that of course, no 707 (nor 747!) could leave Nairobi at full load on a hot day and fly non stop to London or Frankfurt - the VC10 could of course.
[Unquote]
You’ve summarised it nicely, but I think it was the VC10 that had the “few advantages”. As one who was posted from RHS Standard VC10 to RHS B707-320C(advanced), when BCAL sold our last ‘Ten’ (G-ASIW) at the end of 1974, it was not long before I operated to both LAX and NBO in the Seven-oh.
On the 707, LGW-LAX (~10:30) was pushing it with a charter load, but easily done with 140-150 pax. I think the longest flight-time on a laden Standard VC10 was little over 9hrs, retaining reserves.
Out of Nairobi, our under-powered 707s − operated under the conventional take-off techniques of the day − were limited to about 129T (tonnes), about 22T below structural. Our Standard VC10s (with the droop-snoot wing tips to enable FL430), could manage about 142T (only ½T below structural). This didn’t handicap the 707 quite as much as it seems, because the Boeing was a lighter airframe and burned much less fuel at a given gross weight. But it certainly couldn’t carry a decent payload NBO-LON (which we ex-VC10 pilots were well advised not to point out, if we wanted a smooth conversion course in that cramped, uncomfortable cockpit…).
This embarrassing situation was ameliorated in 1975/6, when we managed to increase the Nairobi RTOW to about 136T: partly by a dispensation to over-boost the engines; but mainly by introducing the increased-V2 technique − now the norm − to improve second-segment climb gradient, taking advantage of the 13000-foot runway. By that time, however, our slots on the route had been given to BOAC in exchange for somewhere else, so it was only the occasional freighter that benefited.
Yet again, the ubiquitous 707 had been “tweaked” to improve its performance and profitability. The VC10s that we flew were among the first 20 off the production line; the 707s nearer the thousandth. The “Ten” design never had a chance to mature.
Once the 707 is above the safety altitude, its configuration makes it inevitably more efficient than the VC10. The “Ten” is also heavily over-engineered. By the 1970s the Conway by-pass engine, far superior to the JT3C turbojet on early Seven-ohs, had been bettered in efficiency − though notably not in power − by the JT3D turbofan of later 707s. Presumably, no suitable replacement engine was available. If the VC10 had been re-engined with two big turbofans like the RB211, CF6 or JT9D − all available by the mid-1970s − it might have been a (stretchable?) improvement, but long-haul twins were non-existent in those pre-ETOPS days. And I can’t imagine any VC10 derivative being able to carry 39T of tomatoes from Las Palmas to Schiphol.
It was all BOAC’s fault, apparently, in insisting on short-hot-high runway performance…
But what a beautiful thing she is.