747-400XQLR

The 747-400XQLR — Quiet Long Range — was announced at the Asian Aerospace show in Singapore in 2002, and was supposed to enter service in 2004. It never did. Development was abandoned and the effort was redirected into what became the 747-8.

The X in the name marked it as a variation on the 747-400 rather than a new aircraft.

Where it came from

The QLR was the survivor of a larger effort. After the 747X programme was terminated — a much more ambitious plan involving an entirely new 777-derived wing — Boeing kept studying what could realistically be improved on the existing aircraft without that expense.

The QLR was the answer: better range, less noise, no new wing.

What was proposed

Range. 7,980 nmi (14,800 km) — further than the 747-400ER.

Noise. New acoustic liners in the engines, and chevron-shaped cowlings around the fan and core exhausts. The claimed result was a 20 percent reduction in noise area level on takeoff and 40 percent on landing against a standard -400.

Those chevrons are the serrated trailing edges now familiar from the 787 and 747-8. They work by smoothing the mixing between the exhaust flow and the surrounding air, which is where much of the low-frequency noise of a jet is generated.

Fuel. Extra storage in the horizontal tail tank, with gross weight rising from 910,000 lb to 921,000 lb.

Wingtips. Raked wingtips in place of the -400’s upright winglets, similar to those on the 777-200LR/300ER and the 767-400ER.

What became of it

The QLR did not reach production, but almost nothing about it was wasted. Its features were carried into the 747 Advanced study, which Boeing launched as the 747-8 in November 2005.

The connection is direct and visible. The 747-8 has raked wingtips instead of winglets, chevron-edged engine nacelles, and a noise footprint about 30 percent smaller than the 747-400’s — the QLR’s three headline claims, delivered by a different aircraft.

The noise work in particular mattered commercially. Boeing said the 747-8 would be able to operate at London Heathrow around the clock, where most aircraft face a night curfew on noise grounds.