jet drive impeller

[Byron Rees…(Ron)Participant @byronrees-ron]

Hi Ashley,

I too have played with jet drives etc. and even though your project may be on the back burner some basic info that I discovered may get those little grey cells fired up again.

My prototype units were based around plumbing pipes both copper and plastic and then further tidied up by making silicone moulds and casting the parts in resin.

Some research and experimentation was done with the impellors and restricting the diameter of the expansion area, where the impellor is, down to the outlet to increase pressure.

I tried Kort type props and they were not bad. I also had in my scrap boxes some Graupner Jet drive impellors. The smallest one is very basic indeed, only two blades, square ended and twisted almost 45 degrees to the hub, with no curve in them at all.

These were easy to recreate in brass by cutting a brass sheet circle of whatever diameter you needed, a fairly close fit to the tubing used. A centre hole drilled (4mm) and a 4mm plain aluminium alignment rod used to hold Brass wheel collets one each side. These were soft soldered in place before bending the blades to the 45 degree angle needed.. A little fettling was done to their edges but no sharpening. A 43mm diameter impellor like this was tested using a 3530 x 1500 kv B/L motor on an 11.1 li-po and it worked extremely well. Another similar test was done using a 33mm dia prop of the same shape on a 2830 x 1250 kv B/L motor on 11.1 volts and it was even better!. The nozzle reduction was about 10 to 15 % smaller than the expansion area in each case.

This was all meant for another of my silly articles in MB but really needs a boat to test it out for the photos. I started building a Pibber, Vietnam twin Jet drive model for two of the small ones but other things got in the way and they too are sitting on the 'Back Burner'

So…yes, the home made system can work well. Impellors from water pumps (Metal) would be OK if the right shape, but the brass ones are easy to make. Sorry no photos, I just cannot get my PC to manipulate photos for this or the Mayhem sites!!!…………Not the technologies fault, just my stupid brain………..Love your posts.

Regards………..Ron Rees.

PS Computer Fans (Small ones) are almost the right shape but have too many blades. The maximum I found was about 4 or they just self destruct…..All part of the fun though.

[ashley needhamParticipant @ashleyneedham69188]

Ron. Thanks for those thoughts. The project at the time would have involved a jet style system, and I thought there may be some rules-of-thumb out there to get the best from them.

The Alvis Stalwart I made uses cast 25mm three blade props in a close fitting tunnel and this seems to work very well. From subsequent investigation, it looks like high pitch props, fitting very closely in the pipe and driven at high speed seem to be the thing.

The project I was thinking of at the time is still on the list and may well be built later on.

Ashley

[Byron Rees…(Ron)Participant @byronrees-ron]

Hi again Ashley,

You mentioned 3D printing could be the way to go and I can go along with that, John Parker, from Australia, who writes for MB….and his mates down under have had some success with 3D printed props. I don't know if he writes on this forum but some of his pictures of them were promising. Of course you can make almost anything you like with that technology but it is tricky trying to get the printed plastic to encapsulate a metal insert. When I had a go at it I tried turning up some 4mm threaded brass ferrules and used a straight knurling tool before cutting them to length. These were then pressed into a hole in the prop with a little jig. Radio Active glass nylon props were made in the same way, and they never came apart.

The down under brigade ended up making 'Dog Drive' type props on the printer with a cutout for a pin in the shaft and this was successful, certainly an easier way to get over the problem.

If you watch 'You Tube' much, there is a film clip on there of a guy making a water pump which really goes, using what looks like a 500 size motor. The flat tin disc is cut across nearly to the centre and these are folded up at 90 degrees!!! It squirts a jet of water out of a 1/2 inch pipe about 50 feet, amazing. I'll try and find it again and sent you the site. If not a Jet drive then a monster bow thruster!!.

Happy Boating…

Ron.

[ashley needhamParticipant @ashleyneedham69188]

Thanks for that Ron. Dog drive props are easy to mount on a length of plain rod as you can get the dog drive collars very cheaply, and they just slip over the rod, with another collar to keep the prop falling off. Actually very useful for odd applications without hunting for threaded end rod, or attempting to thread some yourself. I have converted some S and X props for dig drive by the simple expedient of filing out the thread, cutting the end of the boss off and filing a notch to match the drive. They lasted OK for testing.

I would dearly love to have a lathe but not sure if I would get much use from it, just "now and then". You can get small hobby ones of course which are less expensive and don't take up much room… unimat for instance…

Ashley

[Byron Rees…(Ron)Participant @byronrees-ron]

Hi Ashley,

I think if I was a kit builder and had almost everything I needed in the box then I wouldn't really need a lathe, but a bit like me you enjoy playing with things and coming up with new ideas. As 'sort of experimenters' a lathe is just so incredibly useful and I don't know how I would manage without one now.

I've been experimenting lately, building drive units which house a brushless motor which runs totally immersed in the water. The casings, couplings and even the props in some cases have all been made by turning bits of S/H hardwood on the lathe and then making silicone moulds of them. Also, it's so easy to cast in resin gears and bevel drives etc. and use the lathe for making alterations. Saves a fortune too.

I used to be a Technology teacher and am used to using such equipment, I even have a big old school workshop lathe down the garden in the shed which I got when a local school closed down but its too cold in winter and I do most work in a little 10×8 insulated shed by the house. I decided to splurge out 2 years ago and bought an 18 inch between centres one, one of the cheap imports through Axminster Tools. The same lathes are imported by loads of engineering shops like Chester,Warco and others and they had some pretty good deals last January at the ME Exh. at Ally Pally.

Unimats, Cowells and other small machines fetch more than they are worth I think, maybe another MB Forum reader has one he wants to sell, I hate being in a bidding war on Flea-Bay. Put an 'I want a……on the blog, see what happens!!.

I think for someone with your flair a small lathe would be used to hell and back.

Cheers…….Ron.

I'm not sure which area you are from but there is a firm at Leytonstone, London who does some really good deals inc. delivery. Several members at my club have bought them. About £350 for everything, they are really good machines and brand new.

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