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Author Topic: How to replace racing-type props on RTR Bismarck/Smasher/Challenger?  (Read 2810 times)

Edward Pinniger

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In short: How (short of fitting new prop shafts) would I go about replacing the props on the RTR Bismarck with smaller, more in-scale (and non-racing-type) ones?

These two photos show the existing props + shafts (apologies for the condition of the hull, it hasn't been repainted yet and the metallic red paint on the lower hull "stains" badly in contact with liquid poly glue):





Last year I started a conversion project based on the RTR Bismarck hull (I didn't want to build yet another Bismarck and thought 1/350 was a bit small for a working model, so decided to convert it into an earlier, smaller ship, working out at about 1/200 scale). This involved some major reshaping of the hull around the bow area (which turned out quite well) and a completely new deck, but when I gave the rebuilt hull a test run, I got rather discouraged by the model's completely non-scale performance on the water - hence the model has sat on the shelf gathering dust for the last 6 months.

The basic problem is that it has two-bladed "racing" props (I think these are the surface-piercing type, but not sure), which even at low power give a ridiculously overscale speed for 1/350 or even 1/200 scale (with the supplied ni-cad pack, they virtually break the scale sound barrier!) The "Smasher" and "Challenger" (Sovremenny and Kiev) RTRs have the same problem, but I managed to get my "Smasher" to run at a reasonable speed by fitting a lower-voltage (4.8v) battery pack. The Bismarck appears to have more powerful/higher RPM motors, as doing the same still gives far too high a running speed. This is with the basic RTR radio gear, but I suspect that if I fit a new radio and ESC, I would need to run at the lowest speeds possible to avoid speedboat-like performance.

The difficulty with replacing the props is that rather than the usual threaded fitting, they have a notch which fits into a peg on the shaft, and are held in place by a brass nut on the end of the shaft. (See the photos above). I think this is what's called an "Octura" type prop (am I correct?) and the only replacement props I can find of this type are all racing-type ones.

The motors and prop shafts appear to be decent quality, good enough for a model this size, and the prop shaft + coupling installation is also neatly done - I don't really want to have to strip out and replace all the running gear, even if the radio needs replacing.

Any ideas? I don't really want to continue with the project (or invest in a decent radio to replace the RTR one) until I can sort out the prop issue.
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Shipmate60

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Re: How to replace racing-type props on RTR Bismarck/Smasher/Challenger?
« Reply #1 on: April 29, 2010, 09:49:33 pm »

I would suggest you get new shafts machined with a 4 mm thread on the external end.

Bob
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tobyker

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Re: How to replace racing-type props on RTR Bismarck/Smasher/Challenger?
« Reply #2 on: April 29, 2010, 10:41:35 pm »

On my Smasher, I just bought a couple of brass 3-bladed props 30 or 35 mm, sawed the cones off the back, drilled out the threads to fit the Smasher shaft, filed a slot to take the Smasher prop driver, and put the original nut back on the end of the shaft. I might even have posted a photo on the old "Chinese destroyer" thread.  It's all quite simple to do with a piercing saw, drill and needle files.
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Edward Pinniger

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Re: How to replace racing-type props on RTR Bismarck/Smasher/Challenger?
« Reply #3 on: April 30, 2010, 01:55:24 pm »

On my Smasher, I just bought a couple of brass 3-bladed props 30 or 35 mm, sawed the cones off the back, drilled out the threads to fit the Smasher shaft, filed a slot to take the Smasher prop driver, and put the original nut back on the end of the shaft. I might even have posted a photo on the old "Chinese destroyer" thread.  It's all quite simple to do with a piercing saw, drill and needle files.

Thanks for the suggestion - I was wondering if this would be possible to do. I'll try it out with plastic props first, as I don't want to risk ruining expensive brass ones (reasonable quality threaded plastic props would probably be OK for a model of this size anyway)
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Shipmate60

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Re: How to replace racing-type props on RTR Bismarck/Smasher/Challenger?
« Reply #4 on: April 30, 2010, 05:01:24 pm »

The plastic props usually have a brass insert for the thread.
This would give the basis for a strong bond and can be worked relatively easily.

Bob
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