Odd Propeller Model

taildragger

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Here's an odd propeller display model currently for sale on eBay:

https://www.ebay.com/itm/Hamilton-Standard-Airplane-Propeller-Model-USAF-Vietnam-War-Topping-B-35-e58/182940559595?hash=item2a981b68eb:g:mdcAAOSwOA1aIkAu&vxp=mtr

The model is described as having a 14" diameter, so it's probably not a component of an aircraft model but a representation of a Hamilton Standard product. It looks like a contra-rotating airscrew, but the blades all seem to be oriented to turn in the same direction. The hub also shows no sign of a division between contra-rotating parts.
Maybe it's just a contra-prop with a line decal missing from the hub and the blades attached incorrectly.
Any ideas?
 

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kitnut617

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could it be an experiment for a 'slotted' propeller blade ???
 

Sundog

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kitnut617 said:
could it be an experiment for a 'slotted' propeller blade ???
Yes. Or to put it another way, it's a way to make a thick, chord wise, blade, but also delay flow separation, since if it was a single blade with that much chord, of the two blades together, you would get a lot of flow separation. The slot re-energizes the flow, making it more efficient. At least in theory, anyway. They may have found they could get a blade 3/4 the chord of the two together that had close to the same performance at less cost. It would be interesting to see the results of these tests and the possible program application.
 

taildragger

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Would such a device have to be optimized for a relatively narrow set of flight conditions? The model suggests that the blade pitch can be varied, but any adjustment would alter the slot.
Also, wouldn't blade-to-blade contact be a worry with this configuration? Preventing this is apparently one of the challenges of designing large turbofan fan stages.
 

Trident

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Sundog said:
kitnut617 said:
could it be an experiment for a 'slotted' propeller blade ???
Yes. Or to put it another way, it's a way to make a thick, chord wise, blade, but also delay flow separation, since if it was a single blade with that much chord, of the two blades together, you would get a lot of flow separation. The slot re-energizes the flow, making it more efficient. At least in theory, anyway. They may have found they could get a blade 3/4 the chord of the two together that had close to the same performance at less cost. It would be interesting to see the results of these tests and the possible program application.
Kind of a propeller blade with a Fowler flap :) There's a similar solution on the Russian AL-31F fighter engine 4th stage fan stator (more flow turning and hence pressure rise without separation).

EDIT: Would this topic perhaps be more appropriately moved to the propulsion section?


Indeed !
;)
 

Tonton-42

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taildragger said:
Would such a device have to be optimized for a relatively narrow set of flight conditions? The model suggests that the blade pitch can be varied, but any adjustment would alter the slot.
Also, wouldn't blade-to-blade contact be a worry with this configuration? Preventing this is apparently one of the challenges of designing large turbofan fan stages.
Hi !

A picture of a real propeller with "double blade". I found that in my old book "L'aviation d'aujourd'hui" by Jacques Lachnitt - Librairie Larousse - 1968. It was a solution of "variable curvature" for turboengine propellers because at that time the variation of pitch was insufficient between high and low speed (it's clear ? ???) ...

Tonton
 

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taildragger

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My guess is that the model and the installation illustrated above represent proof-of-concept hardware utilizing off-the-shelf components rather than a product. I'd think that a design intended for service would place each blade pair on a common pivot so that pitch could be varied independently of the slot configuration.
It's probably better for aircraft aesthetics that this idea didn't work out.
 

kitnut617

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You can certainly see the size of it in that photo of Tonton's, it's fitted to the nose of a B-17

EDIT:

I would guess this is the same aircraft with the same propeller in flight (photos found on the internet, no idea who's they are)
 

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DWG

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I think we can rule out a contraprop based on blade clearance.
 

dan_inbox

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kitnut617 said:
I would guess this is the same aircraft with the same propeller in flight
Nope. See attached photo of Pratt & Whitney's N5111N with the XT-34 turboprop feathered.

It may well be another of the JB-17 testbeds, though. Just not this one. IIRC there were three JB-17 conversions.
 

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Tonton-42

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Orionblamblam said:
Thank you for these explanations :-* ! It had been more than 40 years since this strange thing titillated me the spirit in a hidden recess of my (young) brain ;) !
 

AeroFranz

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i suggest renaming the thread something like "Hamilton Standard variable camber propeller" or something to that effect.
 

AeroFranz

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FWIW, in urban mobility circles there is a resurgence of interest in something very similar, the stacked coaxial propeller. There is no variable pitch, but it does have two rows of co-rotating propellers not uniformly spaced.
For example you could have two rows of three bladed props, with the rear row being phased only 10 degrees behind the front one.
 

Orionblamblam

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The work apparently continued for some years. From 1969:
 

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