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Old 04-16-2019, 03:31 PM   #11
Bob Gardner
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I'm sure you are correct, Pierre-Michel.

As I mentioned, having suggested originally that the prop might be for a Hisso engine, I began to have doubts, and I knew I had a photo of a similar prop somewhere. I found the photo in one of my books, in the chapter on Lang Propellers where there is a photograph that is of French design for a 110hp Le Rhone engine, but made in Great Britain for the Nieuport Scout by the Lang Propeller Co with the drg number LP3420. Now I can rest easy.

My observation is only that the British Lang propeller made for a 110hp Le Rhone with drg number LP3420 for a Nieuport Scout is very similar to the shape of the prop in the photo. I believe that Nieuport Scouts bought for the British Admiralty came with two spare propellers. I have long thought that these were copied by Lang who was the prop maker for the Royal Navy.

I have been horrified all day by the recurring news film of the fire in Notre Dame and am much relieved that the outer shell of the Cathedral remains intact. I used to visit Notre Dame after attending NATO conferences twice a year at Quai D'Orsay circa 1984-85.

with kind regards,

Bob
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Old 04-16-2019, 07:19 PM   #12
pmdec
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Hi Bob,

Thank you for your kind words about Notre-Dame!

The BrokenWing prop is a left handed pusher: look at his pics "06" and "07". The side of the hub we are seing is the intrados side. The center hole is not tappered, so it can't be placed against the engine. Thus, it is the other side of the hub which was against the engine and then it is has to be a pusher prop. But I stand to be corrected!

Best regards,
PM
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Old 04-16-2019, 11:17 PM   #13
Dbahnson
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I'm not quite positive that it's a pusher, although it's certainly likely. But the SPAD 13 used a 200 hp Hisso engine that was geared, so the rotation was reversed in a tractor configuration.



I agree that one would expect the "engine side" of the propeller to be rounded for easier mounting on the crankshaft, but was that always the case?
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Old 04-17-2019, 06:52 AM   #14
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Hi,

If the data from Gorrell's are right, the Levasseur serial 540 was 272 cm long and has a 155 cm pitch. This pitch is way too low for a geared engine. BUT, from BrokenWing measures, the length is only 254 cm and the blade tips don't seem reshaped. So... Reading (or guessing!) the markings could be the only way to know...

About the "rounded" central hole: it is not there to improve the implementation of the prop but to fit the shape of the metallic hub. Some props have both central hole ends rounded, but the only props without any side rounded I have seen are the front prop from two-pieces four-bladed or not finished props (but then, there is no airworthy stamp).
BUT I can't be sure there is not somewhere a prop of the WW1 era without rounded central hole: I would be pleased to see one!

Levasseur made a prop for the geared HS of SPAD 13: the serial 586. Length 255 cm, pitch 230 cm, blade width 182 mm, central hole 80 mm (rounded on intrados side), hub thickness 175 mm. I can post pictures.

Regards,
PM
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Old 04-17-2019, 07:27 AM   #15
Dbahnson
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Here's a photo of a Chauviere prop for the geared SPAD. Regrettably, I loaned this to a person years ago so he could make a copy and I never got it back.
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Old 04-17-2019, 03:39 PM   #16
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Hi Dave,
I have pics of the same Chauvière serial 2223, but made later (around 1920) than yours:


@Dave and Bob: What is the right word to explain that the hole end is like on the engine side of a prop?

@Brokenwings: Can you post a clear pic of the "other" side of the hub? Even if you don't see anything? Some faint marks may be enough...
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Old 04-18-2019, 10:24 AM   #17
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Cher Pierre-Michel,

I'm not aware that there is a specialist term. I would describe the curved edge of the central bore hole in the prop shown above as bevelled or as rounded.

With kind regards,

Bob
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Old 04-18-2019, 10:30 AM   #18
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The tool to make it is a quarter rounding bit, so I too just call it rounded, but I like the description "intrados", which is an architectural term applied to arches.

But I think architecturally the "extrados" refers to the top of the arch rather than the other side of the arch. In other words, when both sides of the center hole are rounded, they would both be "intrados" and the outside of edge of the hub would be "extrados".

I was mistaken in my belief that the purpose of the rounding was to make it easier to attach to the shaft of the hub. As PM has pointed out, it's actually to accommodate the metal fill where the center shaft is joined to the hub plate (welded, I presume).


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Old 04-18-2019, 05:02 PM   #19
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Hi,
Thank you for the words to be used. And about my words, sorry to not to be more explicit: "intrados" and "extrados" were just referring to the side of the blades (using same words that ones for wings) , to show that on this tractive prop the "straight" central hole was on the extrados and the rounded one on the intrados so it was not possible to use the prop on a pusher.

The joined pic is a French metallic hub from the WW1 era and it shows what Dave explained: the rear plate and the central part are joined with a "rounded" part to avoid cracks. The technical wording is perhaps "fillet"? In French, it is "congé" (same letters that the word for hollidays)

In France, until the 20s, only one side of the props central holes are rounded, so it is easy to know if they are from a tractor or a pusher. But after around 1924-25, many props have both ends of the central hole rounded.

The "rounding" (?) could be made to ways by using the concave OR the convexe part of this tool: but on quite all the props I have seen, the concave tool was used. I suspect the central hole of the first propellers was made using a hand tool, perhaps a file. The second joined pic is from a Régy serial 54 for a Blériot XI fitted with a 80 HP Le Rhône (same prop as the one of Meaux Grande Guerre museum http://www.pyperpote.tonsite.biz/lis...1111%20(1).jpg , unfortunatly without its decals).

Regards,
PM
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Old 04-19-2019, 07:46 AM   #20
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Chamfered offered by Dave is probably the best term in the Anglo-Saxon aviation litany for the shaping of the central bore-hole in the hubs of wooden propellers.

I have also followed Pierre-Michel's use of the terms intrados and extrados with interest. They describe curves on propellers. I have never seen their use in British aviation literature. Pierre-Michel's use of them always reminds me of reredos which describes a screen in a church.

I collect, in a minor way, technical books from early aviation but intrados and its reciprocal do not appear in Alfred Schlomann's astonishing book Das Illustriete Technische Worterbuch from 1932. The German text is 300 pages long and the translations into English, French and Italian account for another 550 pages, a total 850 pages, but nary a mention of intrados.

With kind regards,

Bob
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