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Author Topic: Odd Propeller Model  (Read 712 times)

Offline taildragger

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Odd Propeller Model
« on: December 02, 2017, 02:42:46 am »
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?

Offline kitnut617

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Re: Odd Propeller Model
« Reply #1 on: December 02, 2017, 07:05:38 am »
could it be an experiment for a 'slotted' propeller blade   ???
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Offline Sundog

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Re: Odd Propeller Model
« Reply #2 on: December 02, 2017, 08:11:28 am »
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.

Offline taildragger

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Re: Odd Propeller Model
« Reply #3 on: December 02, 2017, 10:20:06 am »
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.

Offline Trident

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Re: Odd Propeller Model
« Reply #4 on: December 02, 2017, 12:10:07 pm »
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 !
   ;)
« Last Edit: December 05, 2017, 02:58:57 am by Jemiba »

Offline Tonton-42

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Re: Odd Propeller Model
« Reply #5 on: December 02, 2017, 01:03:45 pm »
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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Offline taildragger

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Re: Odd Propeller Model
« Reply #6 on: December 03, 2017, 10:36:43 pm »
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.
« Last Edit: December 04, 2017, 01:30:26 am by taildragger »

Offline kitnut617

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Re: Odd Propeller Model
« Reply #7 on: December 04, 2017, 04:50:42 am »
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)
« Last Edit: December 04, 2017, 05:52:57 am by kitnut617 »
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Offline DWG

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Re: Odd Propeller Model
« Reply #8 on: December 04, 2017, 06:48:07 am »
I think we can rule out a contraprop based on blade clearance.

Offline dan_inbox

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Re: Odd Propeller Model
« Reply #9 on: December 04, 2017, 05:59:24 pm »
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.

Offline kitnut617

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Re: Odd Propeller Model
« Reply #10 on: December 05, 2017, 02:35:36 am »
A-ha! right --- thanks for that
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