As a bit of light relief
from discussing the relevance of the Geneva Convention to military aviators parachuting into insurgent territory they had recently bombed, having been shot down by fighters from a neighbouring country (Military forum), can someone answer the following question:
At what stage did BOAC decide to ban the use of Flaps 14½° for take-off? Could it have been in reaction to the BEA Trident accident on 18/6/72?
AFAIK, Flaps 14½° was first introduced into service in autumn 1964, when BUA introduced its first VC10 - a "standard" Type 1103 with the chord-extended "super" wing (G-ASIW). BOAC's 12 standards (Type 1101) retained the standard wing, and - for reasons unclear to this writer - the Flaps 14½° facility was not retrofitted. BOAC took delivery of its first Super VC10 (Type 1151) about a year later. Did the airline ever make use of its Flaps 14½° option for take-off, or simply as an intermediate setting above 400 ft for the initial climb?
For readers not conversant with the history of the Anglo-American fight for supremacy in the post-Comet, 1960s jet-airliner market, the VC10 was already struggling for sales against developments of the B707 and DC-8. The VC10's main mission to provide decent payload-range out of hot-high-shortish runways in the former colonies (Lusaka-City being a classic example) had quickly been marginalised by the fact that most other capital cities are situated at low altitude, and governments were rapidly extending their runways to accommodate the early, under-powered 707s and DC-8s (and Rolls Royce was providing by-pass Conways to transform their field performance, while Pratt & Whitney's JT3D turbofan was in the pipeline).
By introducing the option of Flaps 14½° as an addition to the basic Flaps 20°, Vickers/BAC were able to offer an RTOW increase of up to about six tonnes (see my previous posts) at very-hot or hot-high airfields where the runway was long enough to permit the higher V1, VR and V2 speeds involved. Flaps 20 would continue to be the better option on short runways. (I once carried 150 charter passengers from Bournemouth to Tenerife, a 4-hour flight off Hurn's [at the time] 6000 ft runway. You couldn't do that on a B707-320.) On our a/c, restricting take-offs to Flaps 20 would have involved no RTOW penalty at sea-level up to +39C. Despite Entebbe's elevation of 3782 ft, Flap 20 was the better option on its short, 7900 ft runway (until the mid-1970s, when a 12000 ft runway was opened).
But at Nairobi (elevation 5327 ft), as previously mentioned, the 13500 ft runway immediately enabled the benefit of Flaps 14½ to be fully exploited, and the same would have applied to the long runways at Johannesburg (elev. 5557 ft), Addis Ababa (elev. 7625 ft) and (from 1967) Lusaka International (elev. 3779 ft).
I infer that, ironically, the BOAC/BA Super VC10 was used mainly for routes between low-altitude airfields, where its unused Flaps 14½ capability would rarely have been an advantage in terms of performance (but might have reduced wear-and-tear). The hot-high airfields on the company's network seem to have been mainly operated by its Type 1101s, which only offered Flaps 20. No doubt East African Airways, like BCAL, took full advantage of Flaps 14½ on its (Super) VC10s.
Hi
finncapt,
Yes, and the B707-320C MTOW was 151011!
No wonder the hard drive was nearly full after nine a/c types and their variants, despite futile efforts to delete data that was no longer relevant...
Quote:
"I have often wondered how much better performance could have been obtained had separate flap and slat retractions been possible."
But would BOAC/BA have used them?
Actually, as you know, the tied-together levers could be separated, but IIRC the slat lever had no detents of its own. From January 1972, BCAL started sim-training for double-engine failure on take-off. (BOAC may have considered the same contingency?) The zero rate-of-climb figures on our a/c with Flaps 20 were said to be 133T (ISA, sea-level), 123.5T (ISA+20, sea-level) or 115T (ISA+20, 5000 ft). I'll not relate the whole procedure in this post, but one segment of the acceleration involved retracting flaps to zero while leaving the slats extended. (The slats lever was pulled and held fully aft, while the flaps lever was selected forward.)