Metal Prop Blade manufacture

The turning over process was done by a massive machine which held the blade whilst a mandrel swaged the blade end material over, much like the process of sheet metal spinning but on a much heavier scale…

That must be something to behold; thanks for the explanation!

I’ve got the (sheared-off) root of a Short Stirling blade which is incredibly heavy and strong; it is difficult to imagine the size of any machine-tool that would have the ability to form the blade-root in such a way.

Bent 109 prop

That photo only goes to prove that the pilot of that 109 had his engine at idle (a sensible action, or he had had engine failure and the prop was windmilling) just before he forced landed.

If it had happened under full power i.e. at take-off and, for arguments sake, the gear had been retracted too soon then the blades would be bent forward.

Another instance is aircraft at high power flying too low over the sea. This certainly bends the blades forward.

Anon

You will note the prop on the 109 is bent back, that indicates it was not pulling power, a driven prop will bend fwd as the blade curves fwd when producing thrust and when it hits the ground it bends that way.

Turning over

The turning over process was done by a massive machine which held the blade whilst a mandrel swaged the blade end material over, much like the process of sheet metal spinning but on a much heavier scale.

Imagine a potter with a clay vase running his fingers around the inside and forcing the clay out to make an open neck. Just like that only, as I say, with a very powerful roller. The root (butt) end then, afterwards, being shaped on a lathe to fit the hub.

All the 109’s had metal blades until, like the Dora 9’s, Ju88’s etc and He111’s late in the war, went over to a very broad chord design which was made of wood/laminate, presumably to help save valuable metals.

de-H didn’t produce wooden blades. This was left to Rotol who, like H-S with metal, perfected the process for all different power applications. Therein lies another story.

A fascinating and little-known subject:)

Anon.

Augsburgeagle, Discovery Channel series how its made did a piece on aircraft props.

Seen here:Metal props

Wooden props

Martin

Thanks for all the replies guys, some very interesting points and it appears quite a few different ways of producing metal props. I would be very interested to see more details of the pantograph method.
As to 109’s and props i’ll see what I can remember:
I think that Black 6 had its metal blades fitted originally, they were then damaged at Benson while running through soft turf, after that it was fitted with a Hoffman Wooden prop which it flew with untill it was crashed in 1997, it is now fitted with the original straigtened 9-12087 metal blades again. The exfoliation corrosion that the Metal VDM props is susceptible to is something to behold!

Red 7 has always used a Composite Hoffman prop and it can be seen here, the hub does not require alteration to fit the Composite props

During the war 109’s wore metal props as illustrated below

This is a VDM 9-12159A prop

The Vs-11 prop of the 190D’s was a massive wooden prop

Matt

Yup sensenich machine there’s from a preshaped billet but I think Mcauley roll theirs….. Some eastern Europeans used to as said grind it down or did from a block… We do still twist them, blades can in use lose some of their twist, so they retwist them, you can set a fixed pitch prop as a climb or cruise pitch, de
Ending on what you need.

Back in the late 1980’s I was invited to the PZL factory in Warsaw, to see the production line of the Koliber 150. This was a licensed copy of the French Rallye 100ST, but with a Lycoming 150 hp engine.
I had ordered two for the British register and was there to see the build quality.
At the propellor section I saw them start from an aluminium block and shape it, as Anon describes. It was fascinating to see it turned into what was a pretty standard blade, but also to talk to the one and only Polish worker in charge of the whole process.
I was informed that he had learned the skill from his father before him, who had worked at the PZL factory before, during and after World War 11.
He was their only ‘prop’ man, and his job was to totally form, polish and balance each blade for production delivery to the aircraft.
It was a hand skill to watch, and something I shall probably never see again.

You could be right about the crash of ‘Black 6’; I’d forgotten about that.

Any idea what the ‘turning over’ process actually is?

Turning over

As I said, the bearing rings are installed and then the base is turned over.

Regarding Black 6, didn’t it go over on its back and wreck its prop at Duxford? I would wager that if it didn’t have a (modern) Hoffmann before the incident it probably got one afterwards to replace the original unit.

That begs the question: do the German types now flying use their original VDM’s, which may have corrosion issues and next to zero spares support, or do they usually remove the original and fit a modern unit to make certification and maintenance easier?

Also, with a modern Hoffmann composite job on, for instance, a 109, is the original hub used and just the blades replaced?

Anon.

…probably a modern Hoffman (German) composite job.

Probably not…..on ‘Black 6’ at Hendon! 😉 I could be wrong but original wartime blades…..anybody? :confused:

I’m interested in the ‘turning over’ process that you mention; is this a second forging operation. The critical point being that the solid bearing rings (or races) do not fit over the base (or the blade) of the blade so they must be fitted before either the blade or the base is formed to (near) its finished dimensions…

…I’ve always wondered how that was done.

Prop blade manufacture

Earlier metal blades were twisted from flat dural plate but later, and with the recognition that mass-production of blades would be required, the Hamilton Airscrew company of America established and refined the process of blade production in the early 1930’s which set the “standard” for the future.

The blade blanks (of Al/Cu alloy or magnesium) were produced by rough forging to establish a spanwise granular structure for strength then set in a pantograph-type machine where a stylus was tracked over a specially designed former (which embodied the characteristics required of the blade) and, in turn, manipulated a cutting head which shaped the blade.

The base (or butt, as the Americans referred to it) of the blade had the bearing rings installed and was then “turned over” to its characteristic mushroom shape before then being turned to the correct profile in a special lathe. This turning over being essential to hold the blade in the hub.

Hamilton Standard, as they later became, refined this process and led the world for years in airscrew blade manufacture licensing out production all over the world. Interestingly, a big licence-producer of HS (and many of their own in-house) designs, de-Havilland Propellers, had two of these original 1930’s American pantograph machines at their manufacturing facility at Lostock, near Bolton, Lancashire right up until they closed the factory in the early 1990’s. They were sold back to the US!

There were many other airscrew/blade producers but none achieved the huge production figures of Hamilton Standard. Curtiss tried hard but the inherent unreliability of some aspects of their designs meant they never managed to get near their rivals in terms of sheer numbers. They went for a sheet steel welded design, which saw reasonable success.

That’s, broadly, how they were produced. I can’t say how the Germans did it though the one in your picture, Augsburgeagle, is probably a modern Hoffman (German) composite job.

Anon.

It is a good question, especially when you consider some are hollow and others have deicing equipment. Some of the American prop blades had air discharge ducts in the tips.
I’m sure I’ve seen reference to some hollow prop blades being made up from two pieces of steel, ie the inner & outer faces, being formed in their cambered profiles before being joined together.

good question really coz ive never even thought about it myself. you would think they are tempered like a sword to withstand all the forces put upon them.

cool photo by the way