Could anyone help with this prop

[David Bathe]

Hi everyone. Have this wooden propeller in my procession.
Great condition, this is what I know: British, Type fitted to a Sopwith Camel/similar.
Thats it.
Any more information would be great.

[Mtskull]

Nice propeller.

Drawing Number 644 confirms that it is for a Sopwith Camel.
In theory it should be possible to determine manufacturer and approximate date from the batch (G) number but that is the province of those with access to greater resources than mine; however the very existence of the G number does determine that the propeller dates from the second half of 1917 or later.
The D and P numbers refer to diameter and pitch in millimetres.
There is a curious anomaly: A propeller made to Drawing Number 644 should have a diameter of 2590mm, whereas yours is stamped 2650. This is the same as the pitch measurement, which makes me wonder whether it was simply mis-stamped it during manufacture. Obtaining an accurate measurement of diameter would settle that question.

I hope this is of interest.

[David Bathe]

Thanks, Great Info! Just checked the diameter and it is in fact 2650 give or take a couple of millimetres. What's that about I wonder?
So what you're suggesting is the Number: G297 NO96 relates to production date/batch number etc? Interesting.

[Dbahnson]

Can you post a photo of the entire prop?

I agree with Mtskull's assessment, and have to believe that it was just stamped incorrectly. Bob Gardner had determined a while ago that mis-stamping was a fairly common occurrence among British manufacturers and attributed that to the hiring of lesser skilled workers for that step of the manufacturing process.

Curiously, there was also an "AB 644" Camel propeller with the same diameter and pitch. I owned this one previously.

(P.S. If you can take a picture of the whole prop, it's best to position the camera in such a way that the view passes directly through the center bore, which then appears as a perfect circle. Because of the change of blade angle along its length, propellers can appear quite distorted if photographed from almost any other angle.)

[David Bathe]

I've jigged up the blade and taken a measurement. It's same as stamped on the hub. 6cm / 2.36222 difference./ possibly some mm larger. I'll try and take some pictures over the next couple of days. Not easy as you say, even less so on an iPhone.
BTW, The hub has the number 205 stamped into the front. and ideas what that referees too?
Also there are a couple of small icons, initials inside a square frame. One on the hub face and two others one the prop surface each side of the hub. Would you know what it says/represents?
BTW... Really appreciate your assistance gentlemen, I've had the prop in my possession for decades and never found a satisfactory answer to the markings.

[Dbahnson]

The stamps you describe are typically inspector's stamps, and I think the number 205 is probably inconsequential, and most likely production number that was superseded by the G and N number once the inspection was complete.

Small discrepancies in length can occur with wood expansion/contraction and/or some "dressing" of the prop tip with wear or minor tip damage.

[Mtskull]

So what you're suggesting is the Number: G297 NO96 relates to production date/batch number etc? Interesting.

To clarify: G297 refers to the batch number and No96 is the number of the propeller within that batch.
As I understand it, each batch number refers to a specific order placed with a manufacturer for a certain number of propellers.
Records were kept from which it should be possible to determine date and manufacturer but I suspect that it would require a great deal of detective work to access them.

[David Bathe]

UPDATE:

From the pictures you can see the prop is marked:
A.D. 644. R.H
130. H.P. CLERGET
D.2660 . P 2650
G 297 NO 95
From you help we now know its produced for a Sopwith Camel, the production date, Batch number, Lot number and the Pitch...
but the eagle eyed amongst noticed diameter anomaly which we presumed was a production mistake.
I can now categorical state that the number stamped on the hub is actually 2660 and not 2650 as was first presumed from the low quality picture. Please see closeup.
I have now carried out extensive measurements of the complete jigged propeller and that figure is indeed spot on!.
So obviously this isn't a mistake.

Im guessing the extra dimension was ordered to combat the engine slightly over reving due to certain unusual combat conditions, cold weather operation, very low level combat sorties etc.
Anyone out there with additional inside? I'm looking forward to your input.

[Dbahnson]

In Bob Gardner's British Aircraft Propellers of WW1 (the first of SIX British propeller volumes that he published) on page 64 there is reference to the Aeronautical Inspection Department, or AID, having to inspect so much material that they allowed the manufacturers to use their own inspectors approved by the AID. Here's a quote from that page:

"A conundrum faced by the AID was that failure to maintain a high standard could imperil an aircraft and its crew, but severity in rejection could reduce output. An example of common sense can be seen in the diameter of WW1 propellers, where a leeway of several millimeters was allowed in the actual diameter of a prop. Sometimes this is recorded so that a prop listed as of 2750m diameter will be stamped for a diameter of 2745mm."

So my guess is that this propeller is an example of that allowance, even though it's a full centimeter difference.

[David Bathe]

Nice find. Thanks.
We're looking at a full 7cm, (2.3/4") difference. Could that be possible? Possibly.
It would appear strange to me that such a deliberate error, would be stamp marked with such pride.
We'll possibly never know.

[Dbahnson]

Oops. I was looking at the discrepancy vs. the stamped pitch. My mistake.

If you add 7 cm to a drawing, where does that come from in the drawing? Continue a taper at the tips? Add to the root near the hub? It seems to me that it would require a new drawing, which would typically mean a new drawing number.

[David Bathe]

Exactly, that was my original question.
Having spent 48 hours measuring, studying , analysing and drawing the propeller I've become particularly intimate with the design, construction and thus the hands/mind set of the people who made it.

Using Occam's razor, I would deduce the simplest, fastest, most cost efficient way of testing or supplying a prop for a special purpose is to simply extend the one we already have by a few centimetres. Everything stays the same, the tooling, jigs, incidence, profiles etc... just add 35mm extra teach tip before making the cut... and then just sand it out to fit.
I believe I can see it with my eye's although it could be an optical illusion as I don't have a standard prop for reference. When I feel the tip with my fingers though, it definitely feels flattened out.

Having built and flown IC powered radio control airplanes since 1972 I'd say I'm reasonable qualified to offer a guess. Anyone who has operated these models in freezing conditions will notice a remarkable increase in engine performance over normal/hot weather conditions. This is due to the carburettor breathing in far a more condensed, oxygen rich air than normal. I could go up in prop diameter or reduce the explosive content in the fuel say from 30% to 15/20% that was the level of difference. Of course I always changed the prop and enjoyed the free energy and performance increase on offer. Back in 1917, I guess they'd be having a similar experience and thoughts or at least a desire to experiment.

[David Bathe]

Exactly, that was my original question.
Having spent 48 hours measuring, studying , analysing and drawing the propeller I've become particularly intimate with the design, construction and thus the hands/mind set of the people who made it.

Using Occam's razor, I would deduce the simplest, fastest, most cost efficient way of testing or supplying a prop for a special purpose is to simply extend the one we already have by a few centimetres. Everything stays the same, the tooling, jigs, incidence, profiles etc... just add 35mm extra teach tip before making the cut... and then just sand it out to fit.
I believe I can see it with my eye's although it could be an optical illusion as I don't have a standard prop for reference. When I feel the tip with my fingers though, it definitely feels flattened out.

Having built and flown IC powered radio control airplanes since 1972 I'd say I'm reasonable qualified to offer a guess. Anyone who has operated these models in freezing conditions will notice a remarkable increase in engine performance over normal/hot weather conditions. This is due to the carburettor breathing in far a more condensed, oxygen rich air than normal. I could go up in prop diameter or reduce the explosive content in the fuel say from 30% to 15/20% that was the level of difference. Of course I always changed the prop and enjoyed the free energy and performance increase on offer. Back in 1917, I guess they'd be having a similar experience and thoughts or at least a desire to experiment.

[pmdec]

Hi,

It could be very interesting to have pictures of the last side of the hub (the one not shown yet) and of the whole prop (as already requested).

The sherry on the cake would be to have the pitch measured... It's extremely easy with a tape and an iPhone (there is a built-in clinometer).

Regards,
PM

[David Bathe]

Take a look: