Pair of opposite-handed props wanted

[steelpillow]

I need a couple of 4-bladed props for a 1:72 scale whiff I am working up. 10ft dia full-scale, so at least 1.67 in (42 mm) dia. at 1:72 scale.
The trick is, I need them opposite-handed, because the whiff uses the props (and engines) taken from the Fairey F.2 but no kit seems to be available.
Does anybody know of a kit or, ideally, aftermarket accessory, which features such a matched pair of props?
If desperate, I could hack a couple of mismatched props to look like a pair.

[kitnut617]

The Special Hobby Spitfire Mk.21 and 24 come with different props, single blade and contra-props. The blades are all individual bits so if you can get four of each of the contra prop you're on your way. Spitfire prop diameters are 10' to 11'.

Also the AMT XB-35 comes with two types of prop, single prop and contra-prop and both with four blades per prop. They're on the large size though, 16'

[PR19_Kit]

Try and find any pair of old white metal 4-bladers, preferably Aeroclub ones, and you can re-twist the blades on one of them, so long as you work slowly and carefully.

I know this because I did exactly that to one of a pair of Beverly props for my Convair-Hawker Osprey VTOL fighter, which needed contra-props. You'll need a biggish spinner to cover up the root area though, as the re-twist is only too obvious there.

As you're building a Whiff anyway, the addition of a spinner shouldn't be a problem. 

[kitnut617]

I did that when I was making this contra-prop   

[NARSES2]

I've a pair of Aeroclub white metal props (item P.044) which I think are Spitfire props only thing is that they come cast with the spinner.

[steelpillow]

Thanks all. Sadly I am a bit too ham-fisted for white-metal twisted. Opposite handed is where I have landed.

Suddenly remembered that the de Havilland Hornet had handed 4-bladed props, although they were 12 ft dia.
Turns out the Frog/Novo kit has integral spinners that I'd need to cut away, while the SpecialHobby one has individual blades that need mounting on their respective backing plates. A couple of others, Magna and Skybird, are rare/expensive and I can't find any reviews.

I assume the SpecialHobby Spit has only six blades per kit so I'd need two kits, which sounds expensive. On the other hand, I might just have a five-blader in the spares box so I could do something good with at least one of them - You Can Never Have Enough Spitfires (TM).

Their Hornet would be the most practical for me so far but, if I am going to be reshaping and reassembling blade by blade, then I do still wonder if there is a cheaper option.

[kitnut617]

I assume the SpecialHobby Spit has only six blades per kit so I'd need two kits, which sounds expensive.

Six for the contra-prop, five for the single prop.

Is your project a contra-prop or a counter prop ?

[steelpillow]

Six for the contra-prop, five for the single prop.

Um. That's eight one way but only three the other. Still one short.
But hey, no need to raid the spares box after all!

Is your project a contra-prop or a counter prop ?

It's twin R-R Falcons in pusher configuration, rotating opposite-handed. Pure fluke that Fairey retired the one and only F.2 just when my protagonist joined the company, it used the only engine around with the right power, which could easily be configured to work left/right and pusher/tractor as required, and had the right props already fitted. In a reality where such an unlikely combination would be almost impossible to come across, all he had to do in fiction was stick the engines and props in a dark corner, mark them "Matched pair. Unsuitable for service. Keep for experimental work," reconfigure the engines per the manual and remount the props back-to-front. And if the man who started the company had not worked in the past for JW Dunne, my protagonist would have gone elsewhere and my plot would have stalled. My fictional world has been constantly bombarded with such happy coincidences. It's harder for me to get the parts than it was for him!

[kitnut617]

Six for the contra-prop, five for the single prop.

Um. That's eight one way but only three the other. Still one short.
But hey, no need to raid the spares box after all!

Is your project a contra-prop or a counter prop ?

It's twin R-R Falcons in pusher configuration, rotating opposite-handed. Pure fluke that Fairey retired the one and only F.2 just when my protagonist joined the company, it used the only engine around with the right power, which could easily be configured to work left/right and pusher/tractor as required, and had the right props already fitted. In a reality where such an unlikely combination would be almost impossible to come across, all he had to do in fiction was stick the engines and props in a dark corner, mark them "Matched pair. Unsuitable for service. Keep for experimental work," reconfigure the engines per the manual and remount the props back-to-front. And if the man who started the company had not worked in the past for JW Dunne, my protagonist would have gone elsewhere and my plot would have stalled. My fictional world has been constantly bombarded with such happy coincidences. It's harder for me to get the parts than it was for him!

The one blade you are missing would be a 'Merlin' engine prop blade as the eight in the box are handed for the Griffon engine. Should be easy to find a Merlin prop blade that can be converted.

Are you building a Fairey F.2 or building something along the same lines ?

[steelpillow]

The one blade you are missing would be a 'Merlin' engine prop blade as the eight in the box are handed for the Griffon engine. Should be easy to find a Merlin prop blade that can be converted.

Of course! Give that man a cigar! Merlin and Griffon are: a) opposite-handed and b) held back in diameter by the shortness of the Spit's undercarriage.
If I can find a decent kit of the Mk XII or Seafire XV or XVII they had a four-bladed Griffon - ready-made solution.

Are you building a Fairey F.2 or building something along the same lines ?

It is very different, a Dunne-type tailless swept constant-chord high-wing monoplane but with a 4- or 6-passenger cabin, wing profile and fins broadly borrowed from the biplanes, and the aforementioned twin engines. Aimed at much the same market as the contemporary Airco (de Devilland) DH.16 conventional biplane. The Dunne monoplanes had suffered from borderline stability in roll and with a single Gnome rotary they needed a "torque flap" adjusting when the engine was cut for landing. Hence my designer's nervousness about torque. Just a fluke that the F.2 engines not only fit the bill but turned up right on the doorstep.
Fuselage and wing stiffeners are coming from a Britten-Norman Islander kit much hacked about, Wing coverings from scored 10 thou plasticard, engine fairings probably scratchbuilt/spares box, u/c still not sorted but probably the same.

[kitnut617]

Keep in mind that if you're going to do a 'pusher', the blades will still have to be turned around on the spinner no matter which prop type you use (Griffon/Merlin). For what it's worth (and I don't know how hard it is to find them) Aeroclub did/does a Spit Mk.XII prop including spinner.

As an aside, sometime ago I picked up a Planet Models Henschel Hs P 87, this was a canard pusher aircraft which had a contra-prop. Nice little model but it got shelved. Reason was the very nice looking contra-prop has the blades all the wrong way around. It's just a 'tractor' prop turned around and stuck on the rear end.  The shape of the blades makes it so you can't fudge it (they're like those big paddle blades Fw 190's had), the shape of the twist to the blade is very pronounced, just like the Griffon blades are, they're just not reversible.

[steelpillow]

Yep. The "Merlin-direction" prop changes to the "Griffon-direction" engine and vice versa. The engines are turned round but the props are not, they are physically mounted back-to-front on the drive shaft, which has moved from behind it to in front of it. My protagonist is way ahead of you there. He is currently ruminating on whether the tips should rotate inwards or outwards at the top, or if it matters on a pusher.

[kitnut617]

Nope! a Merlin direction prop doesn't change to a Griffon direction prop when you turn it around. All you have is a backward facing Merlin prop (they have airfoils just like a wing does so the wrong side of the airfoil is facing forward)

[steelpillow]

Nope! a Merlin direction prop doesn't change to a Griffon direction prop when you turn it around. All you have is a backward facing Merlin prop (they have airfoils just like a wing does so the wrong side of the airfoil is facing forward)

Ah, but an engine reverses its absolute sense of rotation when you turn it round. What rotated clockwise relative to the direction of travel now rotates counter-clockwise. See anecdote below. This causes two problems with the prop.
Firstly, the prop must not be turned round with the engine or, as you observe, its leading and trailing edges would now also be backwards. So the prop has to be removed, the engine turned around, and the prop put back on without being turned round.
Secondly, with the reversal of the engine relative to the plane, the prop would now be giving thrust in the wrong direction (which way round you mount it does not change that, it only affects the efficiency). It needs the pitch and camber of its blades to change sense, "swappiing Merlin for Griffon," so as to provide forward thrust again.

Dunne himself, in the real world, fell for this one. During the development of the D.1 he coupled two low-power Buchet engines together nose-to-nose on a single drive shaft. He could not get both engines to run at the same time, until somebody pointed out to him that one of them would always be forced to turn backwards! They had to be rearranged nose-to-tail. Back in Whiffland, Tanner knew of the infamous incident and was far too wily to fall into a similar trap.

[kitnut617]

I understand what you're planning now