Large compressor blade with forked root · 26 cm

The largest blade in this find: 26 centimetres, a broad twisted aerofoil, and at the root a fork with two slots and a fitted brass bush.

This blade was not slid into a groove but hung on a pin: the forked root straddles a lug on the disc and a pin passes through it. The fitted brass bush is the bearing for that pin. You find this design on large compressor and fan blades of older engines — more elaborate than today's dovetail, but it lets each blade be replaced on its own.

At this length the purpose of the profile becomes visible: the leading edge is rounded, the trailing edge runs out thin, and the aerofoil twists noticeably over its height — steeper at the root, flatter at the tip. That is not styling but the answer to the tip travelling faster than the root. Stood upright it carries itself and needs no base.

Which engine this came from is not known. There are no papers with it, and apart from its shape nothing identifies the type. The material cannot be named without testing either: compressor blades use titanium, steel or a nickel alloy depending on the stage. What is certain is in the key facts — the rest stays open.

• Length 26 cm
• Forked root with two slots
• Brass bush as pin bearing, firmly seated
• Broad, markedly twisted aerofoil
• Metal, alloy undetermined
• Stands upright without a base

Used. The surface is matt with fine running marks, and there are a few tiny dents along the leading edge — ordinary service, none of it deep. No crack, no distortion. The brass bush is tight and clean.