Delamination cause for Concern?

[Gabriel]

I’m considering purchasing this propeller. I’m dealing directly with the vendor and not the auction sites on which it appears, however it is still expensive given the price of similar propellers recently.

My concern is the cracking around the propeller hub/boss. Thoughts or opinions welcome on whether it looks like an issue at the moment, or will become one in the future - and if so what can be done about it.

[Gabriel]

And here’s another one from the top showing a bit more detail.

[Dbahnson]

For a display propeller that's not an issue. It's an unavoidable consequence of the joinery at the hub, where wood grain expands and contracts perpendicular to the wood grain laminations. It would certainly be an airworthiness issue, but that's not the case for this one. (See another example at the bottom of this page.)

The photo doesn't show it well, but has this prop been shortened? The tips look squared off, but that may just be the projection of the photo. It should measure around 90 1/2 inches from tip to tip.

[Gabriel]

Thanks for the background info on end-to-end laminations and how they suffer. From memory, the majority of two blade propellers I've seen don't suffer, but four blades do, I guess that's a function of how the laminations are laid up.

Regarding this specific prop, I don’t think it’s been shortened (although I must admit, I haven’t measured it).

Here’s another photo from a different angle.

[Dbahnson]

The angle of a photo that doesn't aim "straight down the middle of the center bore" is almost always misleading, but it wouldn't hurt to check the measurements before a purchase.

[Bob Gardner]

Gabriel,

The data on your prop is translated below.

G64 N61 A batch number issued by the Air Board in late 1917. A batch contained 100 propellers of which yours is number 61.

The data on the hub translates as:
T28096 The propeller drawing number, where the letter T indicates the Royal Aircraft Factory, which designed both the prop and the aircraft.
D2362 the diameter in mm
P3340 The pitch described in mm
200 Hispano The French aero-engine designed by the Spanish and French team in France. 200hp.

I have seen this prop several times before and have listed it in my database. I agree with Dave Bahnson, who founded this forum, that it looks odd in your photograph. Send me a link by PRIVATE MESSAGE so that I can see the dealer's website and the prop more closely.

The movement in the laminations of the hub are the result of it being stored in dry conditions. Humidity causes wooden props and wooden furniture to expand and shrink. If you buy it, keep a saucer or dish of water near it to maintain humidity.

There has been an unexpected increase in the asking price for such propellers. I thought the centenary four years of WW1 would lead to an escalation in early wooden prop prices but in fact there was little movement. This is merely my impression, not the result of detailed analysis. But for the last year or two, prices have risen, particularly for four-bladed props. But usually such props remain for sale for months at a time which indicates that no one is prepared to buy at the asking price. So when one does sell, the buyer will probably have obtained a considerable discount, bringing joy to both him and to the dealer, who has at last recovered some money.

With kind regards,

Bob

[Gabriel]

Hello Bob,

Thank you for your kind offer.

I've sent you a PM.

[JR44]

Would someone have doctored the tips and then re covered them in linen again?
The linen looks period.
In fact there is one for sale on 1st dibs in a restored condition allegedly sold by you Bob, and it looks the same.

[Dbahnson]

Whenever you take a photo from any angle other than from the center, it distorts the blades. Note how no two blades look the same, and looking at the center bore you can see that the camera was above and to the left of the center of the prop, so I'm guessing that the photo is just very misleading. When it's taken looking down the center of the center bore, all blades should appear to be identical.