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Old 10-25-2009, 08:48 PM   #1
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Default WW1 French 100hp Gnome Monosoupape Prop

A few weeks ago I posted the following inquiry:

My Dad has an old all wood prop he would like to have help identifying. He's had this for at least 50 years. Even then it was old. He guesses that it is from the 1920s, & is probably from the USA. It has 8 bolt holes, is 98 1/2" long, 5 5/8" thick at the center. It is comprised of 7 pieces of wood laminated together. Some numbers/markings on it as far as he can tell include: DG70D112 100 HP Mono P20. Thanks for your help!

Bob Gardner replied:
Hello Charles,

Welcome to our forum.

Your Dad's prop dates from about 1915 in the first World War.

It was built to a design of the Integral Propeller Co. The drg no in full reads IPC 70. It was also made, probably, by the British Integral Propeller Co although other people also made the prop under sub-contract.

The diameter of your prop is 2500 mm and the phrase 100hp Mono refers to the French 100hp Gnome Monosoupape rotary engine. Monosoupape translates as one-valve.

This prop was fitted to the de Havilland DH2, a pusher aircraft which helped eliminate the Fokker scourge of 1915 where the German Fokker E III etc was initially able to shoot down every British aircraft at will.

Your Dad's prop is a valuable artefact from World War One and certainly something he should look after (which translates as preserving it as it is and not cleaning or revarnishing it).


Iíve returned with some amateur pictures of this prop. My Dad is interested in knowing its value.

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Old 10-26-2009, 06:57 AM   #2
Bob Gardner
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Thank you for these photographs.

The letters IPC at the top of the data indicate the Integral Propeller Company.

It has the typical shape of Lucien Chauviere who owned the company and designed the props, which is that the trailing edge forms a straight line from one blade to the other through the hub.

Please ask your Dad if there are any small squares on the prop, each square about the size of the little finger nail; usually in a group of four, with the letters AID in each and a number; and usually on the flat sides of the hub.

If these are readable, often not, please let me know the numbers. A typical square will have AID at the top and a number such as 21J underneath.

These are the airworthiness stamps of the Aeronautical Inspection Department. I'm gradually compiling a database of known numbers which might in several years time be good enough to identify who the subcontractor was who made the prop. In this case the letters IPC indicate that Integral made it.

Value at auction here in England would be in the bracket of 1200 GBP to 1600 GBP, about 2000 USD to 2600 USD. I suspect it might sell for less in the States but Dave will be a better judge.

With kind regards,

Bob Gardner
Author; WW1 British Propellers, WWI German Propellers
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Old 10-26-2009, 07:34 PM   #3
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Mr. Gardner,
Thanks once again for your timely response and shared expertise!
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Old 10-31-2009, 01:12 PM   #4
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Default To be offered for sale.

We are choosing to offer this prop for sale but need some advice since we've never sold a prop before. Of course how to offer and safely close the deal where both parties experience a smooth transaction is a must. I've made purchases on Ebay and have sold on Craigslist, but that is about the extent of my experience this type of internet sales.
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