Propeller Identification Help Please.

[JohnBrowning]

So my wife got me this propeller for my birthday since she knows I love old aviation stuff. However I have been unable to identify it and the estate sale people she got it from had what I believe to have misidentified it as from a JN-4.

The estate belonged to a pilot, possibly retired military from the Northwest Florida area.

It appears to be mahogany, scimitar shaped, and has four bolts (two of them with it has castle nuts so they can be wire locked) in a diamond pattern. There is not a hole in the middle but it looks like it had a circular plate on it before there was the diamond plate. There is also thin metal on the leading edges of the prop tips. It is I believe 78" long.

Any help is appreciated.

[Dbahnson]

Pictures are not viewable.

What is the length of the prop from tip to tip?

[JohnBrowning]

Pictures are not viewable.

What is the length of the prop from tip to tip?

78" I think. Pictures posted up again. Photobucket didn't like the pictures for 3rd party hosting. Sorry.

[Dbahnson]

It's certainly NOT from a JN 4. It's too short, it has a left hand rotation, and the hub drilling is not consistent with any of the engines that powered the Jenny. The absence of any stamped data makes positive identification impossible, and it's always possible that it is home made.

In addition, the hub pattern is not consistent with any certificated or early aircraft that I'm aware of. It is more consistent with an ultralight application or perhaps not even an aviation purpose.

Also, on the photo below you'll note that there is a circular "witness mark" underlying the imprint created by the diamond shaped hub plate. This implies that at some point a round hub plate was used, but the absence of a center bore indicates that however it was mounted it was not mounted onto a crankshaft the way virtually all certificated props are mounted. I don't know what that means except that its appearances suggests more than one mounting method, none of which are common on regular aircraft engines.

[Bob Gardner]

This is an exciting find!

The pattern of bolt holes is typical of a Rupp fastener, devised by Albert Rupp circa 1916. He was Swiss but conducted his business in Germany until 1919 when he returned to Switzerland. He may have got the idea from Lucien Chauvière via the Imperial Propeller Works which prior to the outbreak of war in 1914 existed as the German subsidiary of the French Integrale Company.

The device was a quick release fastener. The propeller was fastened to the crankshaft by a central nut. The four holes are actually blind conical holes for locating studs. There is no requirement for a central hole for the crankshaft to slide onto. It was also made in a three-locating-hole format for lower powered engines.

Hermann Goring, when commanding the Richthofen Jasta in 1918, saw its potential for quickly replacing a damaged prop on a returning fighter. It was fitted to the BMW IIIa of 200ps, amongst others and Axial, Heine, Reschke and Wollf all made propellers for this fitting.

In 1919 Rupp returned to Switzerland and his device was introduced into the Swiss Air Force. In the 1920's Rupp returned to Germany and his device came into use in both the Luftwaffe and Civil aviation; examples are the Focke-Wulf FW44 Goldfinch Trainer and the Junkers F13 airliner introduced in 1919.

The look of this prop suggests it is from an aircraft such as the FW Goldfinch, which dates it from 1928 to 1945.

I describe the device in fifteen pages in Part Three of my series on German WW1 Propeller Makers which will be published in a few weeks time and can send the owner of this prop the relevant pages now, should he so wish, or the complete book in a few weeks time. If so contact me via the Private Message box which is top right on this screen.

Your propeller is extremely rare and very interesting and I congratulate you on finding such a thing and on showing it on this website.

With kind regards,

Bob

[Dbahnson]

Interesting point, Bob. I forgot about the Rupp idea, even though I had a propeller with that set-up once. Do we know that these holes are only partially drilled, rather than drilled through? I thought that the drilling for Rupp fasteners were always partially drilled.

Also, what do you make of the diamond shaped plate - decorative only? And what about the absence of any stamped information?

[Bob Gardner]

'Afternoon Dave,

I too glanced over this post several times before the name of Herr Albert Rupp sprung to mind.

All the stud holes in Rupp hubs that I have seen have been both tapered and blind. Perhaps John can tell us if his are blind as well. And most or all of them had considerable ovality, much more so than on ordinary conventional bolt holes. As the ones on John's prop appear to be perfectly round we might assume that his prop is unflown.

I have always assumed that a German prop with no data stamped on it is one that was not accepted by ZAK (the Zentrale Abnahme Kommission) which had two main offices in Berlin-Charlottenburg and Adlershof airfield with 46 subsidiary offices, one at each major aviation factory, referred to as Bau Aufsichts Amt (Manufacturing Inspection Offices).

I don't know what the diamond-shaped plates are for. The holes appear to match those in the hub and the witness marks on the hub appear to match
the shape of the plates.

I have not seen anything similar in connection with a Rupp Hub. I wonder if this means that a previous owner has drilled the stud holes through to the other side to allow bolts to be fitted. I hope not. I despair of the innocent unintended sacrilege of these rare artefacts.

With kind regards,

Bob

[pmdec]

Hi,

@JohnBrowning: Is the shielding metal? If true, wich one? And could you post a very clear close up of its fitting to the prop (on the picture it seems there are things like stapples)?

@Bob: The patent from 1919 shows a central hole
(https://patentimages.storage.googlea...S1318805-1.png ) and I can't understand how it could work without.

Best regards,
PM

[Bob Gardner]

Bonjour Mon Ami !

A plate was bolted or fastened to the end of the crankshaft. It had the four tapering studs mounted on it and a protruding shaft with a large nut on the end, which held the propeller tight. You are correct that a hole in the prop was necessary. I think about 6cm in diameter, much smaller than the hole in a conventional propeller hub.

Shall I email you the fifteen pages from my book?

With kind regards,

Bob

[JohnBrowning]

Hi,

@JohnBrowning: Is the shielding metal? If true, wich one? And could you post a very clear close up of its fitting to the prop (on the picture it seems there are things like stapples)?

@Bob: The patent from 1919 shows a central hole
(https://patentimages.storage.googlea...S1318805-1.png ) and I can't understand how it could work without.

Best regards,
PM

The shielding is metal and appears to be thin sheet metal. Along the wood it appears to be nails similar to brad nails and there are larger nails on other parts of the shielding.

I'll try to get some pictures outside which might show the details better.

[pmdec]

The shielding is metal and appears to be thin sheet metal. Along the wood it appears to be nails similar to brad nails and there are larger nails on other parts of the shielding.

I'll try to get some pictures outside which might show the details better.

Yes, a clear close up of the shielding could help understand how it is fitted to the wood.
Thanks by advance,
PM