Strange hub construction / repair / restoration

[pmdec]

Hi,

All is in the title and the pics:





The markings are:
Side 1:
G.833 N.38
Blade foot:
AID/N97 [x4] with the classic arrow and letter A
Side2:
AB 7031
200 HB.BHP SIDDELEY
D.27[3 or 5, probably 5]0 .P.2530

So, except for the faulty B of HB (had to be HP), it is standard markings for Admiralty drawing 7301 and there are 9 bolt holes. But, IMHO, this kind of "repair" can't be airworthy. But the markings font seems the right ones, except for the G which looks too large.

I am waiting for the exact length (first given is 278 centimeters, wich is 30 millimeters too much).

Any advice?

Regards,
PM

[Dbahnson]

Hmmmm . . . . Looks like it might be a "stamping transplant" to me. Is it possible that someone used a propeller with damaged tips to "harvest" the stamped numbers from that hub and insert them into a propeller with either no stampings (as in a factory reject) or one with undesirable stampings?

I don't know . . .

[pmdec]

Hi,

Hmmmm . . . . Looks like it might be a "stamping transplant" to me..../...

And I did thought the same ... until I took a closer look!
- Some markings are half on dark wood, half on adjacent clear,
- the dark pieces are quite perfectly symetric from one side to the other.
Could it be a prop using laminations made for 4-bladed prop, some of them turned upside down, and the mortises "filled" with a darker wood? Just perhaps a stupid idea!

Regards,
PM

[Dbahnson]

Hmmmmmm ..... 2

Could be. I don't know exactly how 4 bladed props were mortised, but it seems to me that if they were half-mortised it would be done on each lamination, not every other one as it seems to be there.

But you may be on the right track.

[Bob Gardner]

Bonjour mon Ami,

I received an email yesterday from a Belgian gentleman about this propeller.

Firstly for the benefit of other forumites, the hub data translates as;

AID N97 (four times in a square). The airworthiness stamp applied after four separate inspections during manufacture.
An A with a pointer. A indicates the Army; the pointer is the War Office broad arrow, indicating that it is Government property.
G.833 N.38 G833 is the batch number and N38 indicates the 38th out of 100 in the batch. This batch can be roughly dated to mid 1918.
AB 7031. The Air Board drawing number indicating it was made for the DH4 and DH9 aircraft.
200 HP.BHP SIDDLEY The 200hp Siddeley engine made by Beardmore, Halford & Pullinger.
D 2730 P.2530 Diameter 2730mm, pitch 2530mm

This propeller was made in 1918 for the Airco DH4 and DH9 aircraft. There was a shortage of the Rolls Royce Eagle engine of 275hp intended for these aircraft and thus many were fitted with the almost obsolete BHP engine of only 200hp, for which this propeller was designed. It was listed as the standard propeller for this airframe/engine combination. The prop was two bladed.

In 1918 there was a shortage of wood for aircraft propellers. The Germans suffered most because the blockade by the Royal Navy prevented woods being imported. But Britain too had to use woods other than the preferred walnut and mahogany. Substantial wastage resulted from the need for laminations to be in one piece from tip to tip. Two makers came up with solutions to use the offcuts and planks which were shorter than required.

In normal four-bladed propellers the laminations in the hub have half lapped joints. WD Oddy devised a system of staggered butt joints. This made a stronger propeller and I don't think it saved wood but I mention it because these hubs look like PM's.

In 1917 HC Cleaver devised a method of making props which made economic use of scarce timber, which in essence was gluing bits of wood together to make a lamination. In 1925 he received £1200 GBP from the Government for his invention and patents. £1200 in 1918 was a large sum which would buy a large country manor house. I have not seen an example of his work.

I have seen several props with hubs like PM's. I'm sure it is genuine. I believe it resulted from the two themes above caused by shortages of wood and the need to strengthen hubs but I don't yet know who devised this particular design.

Avec le Respect, (PM; Have I got this salutation correct?)

Bob

[pmdec]

Hi Bob,

Thanks a lot for your very knowledge post (as usual!) It explains perfectly the "strange" look of the hub... It makes this prop very interesting and sweeps away my suspicions!

Just a very little detail: the prop length is probably 275 centimeters and not 273 and the stamped digit half a five and not half a 3: this 275 length is what is written in your book "Propellers Makers of WW1 Part One" page 55.

About Avec le Respect, I think that the usual writting is Respectueusement ("respectfully").. more complicated so more French!

Best regards,
PM

[Bob Gardner]

Pierre-Michel,

QUOTE: About Avec le Respect, I think that the usual writing is Respectueusement ("respectfully").. more complicated so more French!

Vive la difference. Et aussi l'entente cordiale.

https://upload.wikimedia.org/wikiped...le_dancing.jpg

Respectueusement.

Bob

PS: My wife has just made coffee. I'll look at the diameters when I get back to the Office!

[Bob Gardner]

Ah! I see what you mean. It should be 2750mm. Mis-typing by me!

Bob

[pmdec]

Hi,

The French thread about this prop is there: http://forum.aviation-ancienne.fr/t8372-helice-en-bois

Hope there is no harm having posted an extract of your book!

Regards,
PM