Spiteful F.15; has anyone tried to make a contra-prop work

[kitnut617]

I've got a new project on the go, it's a 1/48 Trumpeter Supermarine Spiteful.  I've decided to build the F.15 and F.16 versions of this aircraft and first up is the F.15.  This was supposed to be a contra-prop version of the F.14 and in the book Aircraft of the Fighting Powers-Vol.VII it shows what it could have looked like.

What you see here is how it more or less comes out of the box (apart from the rocker cover fairings)




But it's going to look like this




But I've taken it a step further, I've made the contra-prop work --- sort of. If you turn the front prop the rear one rotates in the opposite direction by itself, here's what I did to get it to do that.

[deathjester]

That's awesome!   

[Dizzyfugu]

Very cool, and surprisingly compact arrangement. 

The only OOB kit I know which features such a (funtional) contraprop gearbox is Bandai's 1:72 "Skyly" kit, from the "The Sky Crawlers" anime.

[The Rat]

 

[perttime]

I'll be watching this...

Somewhere, it was mentioned that carb intakes were switched around quite a lot on Spitefuls and Seafangs. In addition to the contraprop, the "chin intake" mostly seen on Seafang photos makes me prefer the Seafang look.

[PR19_Kit]

Blimey, that's ULTRA-tricky, wel done inded. 

The Lindberg 1/48 Convair XFY- Pogo has a similar arrangement to make both of its props rotate when you turn one of them, but as the Pogo has such a GINORMOUS  spinner they manage to fit all the gears actually inside the spinner itself!

[sandiego89]

Brilliant, would appreciate any more details on the contra gear set up, source etc- unless they are a "trade-secret"! 

[kitnut617]

This project is basically a practice run for some upcoming projects I have in the works, all involving large aircraft with contra-props.  It originally start in a quest to find some propellers that were of the diameter I needed in 1/72 scale, and the 1/48 Wyvern propeller fits my requirement to a 'Tee', it working out to about 18'-0" diameter in 1/72 scale.  The idea then expanded to having the contra-prop working and this came about and to save me some money having to buy a Trumpeter Wyvern just for the propeller, my friend Jeffry Fontaine loaned me parts from this kit of the prop assembly and also a couple of other kits he had.  If my future projects pan out I have about twenty contra-prop assemblies to build and I working on how to reproduce the propellers for them.

As Kit mentions, there's the Lindberg 1/48 Pogo, here's a pic giving a comparison between the The Spiteful and the Pogo prop parts.  The Pogo prop is huge so there's a lot of room inside the spinner to accomodate some mechanism.



Then there's another 1/48 Pogo kit made by Microscale Models, this has a similar parts arrangement as the Lindberg kit.



The system that these kits use is that there's one shaft with two little perpendicular shafts sticking out of it.  These little shafts are for the idler gears and then the front and rear spinner are slid along the main shaft from either end. The shaft is then glued to the kit fuselage and so the two spinners then turn in opposite directions.

There's recently been another kit in this club of working contra-props, the 1/48 Trumpeter Wyvern.  This uses a two main shaft system with the gears attached to the ends of the inner and outer shaft.  here's a pic of the assembled parts and a pic from off the box of how the gearing works.





As you can see my system is much smaller than any of these.

[kitnut617]

I decided then that none of the systems really worked for what I want to do, as the space I will have to work in is about the same as the Spitefuls even though the projects are in 1/72 scale.

Now some of you know that my scale is 1/72, and you might ask why am I building a 1/48 kit.  The simple answer is that the 'Plan' changed --- slightly     Over the years I have acquire a half dozen or so 1/48 kits, either from the Airfix Club offering or because at the time there was only a 1/48 kit of an aircraft I wanted to build (Tamiya Grand Slam Lanc to be exact), then in the Airfix 617 Sqn. Commemorative set, the Tornado was a 1/48 kit.  Well, I decided to make just a very few kits of my absolutely favorite aircraft in 1/48 scale, and the Spiteful is one of them.  And I just happened to be building one of the two Spiteful kits when I decided to try and make the contra-prop work in this kit. 

The prop comes from Heritage Aviation's 1/48 Seafire FR.47 conversion set (the extended air intake that comes with the set will go on the other Spiteful to create the Mk.F.16), but I got stuck on what to use for the gearbox.  It was then that I remembered something when I was swapping the rear end axle assembly of my truck last winter, I had it up on blocks and I was turning one wheel when I saw the other wheel rotating in the opposite direction.  Well this gave me a clue what to do, see if I could find a differential gear set that was small enough.  When I was at the LMS picking up my own 1/48 Wyvern kit (story about that some other time), I visited the RC side of the shop and found there was available right off the shelf, differential gears replacement sets, so I bought a couple of them (they were quite cheap C$6.00).

In this pic, you can see two sets, the one on the left has the large gear about 21mm in diameter and the set on the right, the large gear there is 10mm in diameter.  I used the small gear set for the Spiteful

[kitnut617]

Here's a couple of pics of the gearbox I made up,




First though I had to figure out a way to support the two idler gears, I started by working out how to do this.  I cut a generous bit of styrene card which was about the thickness of the idler shafts, the tiny pins you see in the pic in th eprevious post. Then starting with a hole for the inner prop shaft, I carefully cut out some slots to hold the idler gears after measuring the small face of the large gear for spacing.  Then I carefully cut some notches in the long sides of the slot to hold the pins in place. Then I glued a couple of strips of styrene to hold the pins at the inner end which also serves as a spacer to keep the large gears at the correct distance apart (also re-enforces the main bit of styrene).  I then attached one of the large gears to the inner propshaft, and one to the outer prop shaft.  This pic shows the parts un-assembled.



You then slide the inner propshaft through the hole in the card,



Then slide the outer propshaft over the inner propshaft from the other end,



And basically that's it, then it was the job of sanding and filing away at the main bit of card to get it to fit inside the cowling.  The white tubing on the outer propshaft is just a spacer to keep the gear in place once it's installed in the model, I'm going to do another practice run using my Airfix Seafire FR.47 (yes, another of my all-time favorite aircraft -- ) and I'll refine the whole thing.

[kitnut617]

I went with the gears and system because the gear parts are easily found and are off-the-shelf at the RC shop.

[kitnut617]

That's why I don't claim to have invented anything, I just came up with this to fit into a really tight spot.

[FAR148]

Very Cool!

Steven L 

[NARSES2]

Nice miniature engineering

[Rheged]

Nice miniature engineering

I agree,  it is an extremely impressive piece of work.