jet drive impeller

[ashley needhamParticipant @ashleyneedham69188]

I am considering, for the next model, a jet drive. Thing is, I want to make this myself as it will be too difficult to fit a commercial unit due to the design constrains I am imposing ! Large-ish diameter about 40mm – without having yet finalised plans.

 

Question is…what shape is the impeller?? I cant find a picture of the Graupner one anywhere..or have been looking in the wrong place.

 

Does it need to be like a Kort prop, or will an “X” type do, or even an ordinary brass one or Hydro type??

 

Any suggestions plse thanks.

 

Ashley

[ashley needhamParticipant @ashleyneedham69188]

[Dave MilbournParticipant @davemilbourn48782]

http://www.jet-drive.de/index.php?option=com_virtuemart&page=shop.browse&category_id=8&Itemid=17

Have fun, Ash – and good luck, mate!

Dave M

[ashley needhamParticipant @ashleyneedham69188]

Cheers Dave. The one picture shows a sort of X prop clipped at the edges on the website.

 

I think I may end up making a test rig of duct and shaft by my reconing about 40mm should do it, and try different props. Its not going to be a fast machine, I just want a reasonable thrust.

 

Ashley

[TelstarParticipant @telstar]

Hi. Ashley many years ago I made a simple (crude) jet drive using 1.5 in ‘waste’ pipe and bend, It was powered by a OS19 I/c fitted with a 30mm red plastic (Marx I think) prop.

It performed very favorably against a similar hull fitted with conventional drive and same size engine. My only problem (mistake) was the unit was slightly too high in the hull, and at low speed (rpm) much of the prop was out of the water and didn’t pick up very well when throttled up again. Later mods included putting reducers in the outlet giving a better ‘jet’ and improving top speed.

 

I suppose I should use metric! 40mm bend and pipe reduced to 32mm

 

cheers Tom

[ashley needhamParticipant @ashleyneedham69188]

Tom, thanks for that. Useful stuff,plastic plumbing!

 

I have a suspicion that almost any sort of prop in a tube , with minimal clearance and, as above, underwater, will produce thrust of some sort.

 

The question is of course which is best. The link from Dave has a prop as I described, but I suspect that this is a high speed item. I only need reasonable speed so I think a kort type prop may be best, even if it will be driven a bit quicker than on a tug, for instance.

 

Unless there are more post from home made jet drive persons I forsee an amount of experimentation..

 

Ashley

 

 

[Dave MilbournParticipant @davemilbourn48782]

Ashley

I always reckon that in a jet boat it’s not the prop which directly provides the thrust; it’s the force of the water coming out of the nozzle. This needs to be pretty fast if you’re to obtain any decent speed. Think of the “prop” more as an impeller i.e. high speed and high pitch are mandatory.

Dave

[Bob Abell 2Participant @bobabell2]

Hello Ashley

 

Your water spout device is not that easy, thinking about it!

 

For the simple reason of the water source?………Not forgetting the motor either?

 

Will you post some design ideas, please

 

Bob

[ashley needhamParticipant @ashleyneedham69188]

Dave, good point there.

 

Bob. Its one of my little “projects” without being melodramatic. The design is fixed by the look of the craft, and so things like propulsion have to fit in with this. A bit like the Triumph Herald..you know what it has to look like, and then have to translate this into a working model.

 

The Propulsion in this case has to be out of site, so as not to spoil the look of it, and will be mostly underwater. So a jet drive is, or seems to be, the answer. Having decided, on a jet drive then I need to know what to do to make one effective.. as Dave says,, high impeller speed is one of those things and so this will affect my choice of motor and so on.

 

The designs for my oddities really do get sketched on the backs of envelopes…all those little things and good ideas that you have suddenly. It pays to think ahead on this sort of thing..and the last thing I want is to install something and it doesnt work (as we all know!!)

 

Ashley

[ashley needhamParticipant @ashleyneedham69188]

Sorry…to continue, at some stage I shall most certainly be making a test-rig to try out some ideas on the propulsion front and will post drawings or pictures as I go.

 

Ashley

[Dave MilbournParticipant @davemilbourn48782]

A cheap brushless motor and forward-only ESC might be a good starting place? I’ve no doubt there are folk who understand KV figures………………

DM

[ashley needhamParticipant @ashleyneedham69188]

May be the way to go, a tube of the size envisaged would need a heap of power to get the impeller spinning quick enough.

 

Ashley

[Dave MilbournParticipant @davemilbourn48782]

O, they do! Graupner usually recommend the Neodym versions of their Speed series motors – ultra-fast and very, very expensive. They also eat amps like nothing else I know – except, perhaps, for electric fires and brushless motors…….?

(“Heads down! Incoming!!”)

DM

[josh nicholasParticipant @joshnicholas98718]

now this might be out of the blue for me but im thinking of making my own jet drive too, but i need mine to be 60-65mm OD (outside diameter) with a wall thicknes of 2-3mm question is,

Where can i get an impeller around 58-63mm in diameter? any suggestions please?

How did you get on with yours BTW Ashley? i know you posted this back in 2011 but is there any update?

[ashley needhamParticipant @ashleyneedham69188]

Josh. I have built two craft with tunneled drives, the Lotus sub and the Stalwart. However these are not particularly high performance "jet" drives,

The Lotus uses brass three blade props filed down on their ends to be a good fit inside the tubes, and the Stalwart ones are 25mm 3 blade cast props (of a nice shape) running in 26mm tubes.

​The fit of the prop is important, with minimal running clearance. In your size I would be tempted to use an S or X pitch two blade prop in a close fitting tunnel, reducing at its outlet a bit to provide more jet speed. Acrylic tube is good stuff to fiddle with as it comes in a good range of sizes. Altering the props is very easy using a drill and sandpaper at the most basic level.

Ashley

[Dave MilbournParticipant @davemilbourn48782]

Josh

This is not going to be cheap. I suggest you contact Simon Higgins at Protean Design. He was the man behind PropShop and knows more about the science and the practical aspects of producing propellers than anyone I can think of. I've sent you his contact details by PM.

Dave M

[Paul TParticipant @pault84577]

Ash

A couple of years ago I played around with a home made jet drive using a computer cooling fan as the impeller and 1.5 inch plastic waste pipe. It worked quite well but it never went any further than a prototype test rig as I lost interest in the system.

Paul

[Dave MilbournParticipant @davemilbourn48782]

Yes – I wondered about a cooling fan impeller but at that size (63mm) they seem rather insubstantial to withstand very high revs in water. The pitch might also be too fine.

DM

[ashley needhamParticipant @ashleyneedham69188]

As DM says, building a proper jet drive will not be cheap as the impeller is the vital part.

​HOWEVER, depends what you want… If you want a jet drive simply to get a shallow draught or to be able to be a bit more weed free, then a tunneled prop is quite achievable along the lines wot I have spoken of.

Ashley

[Paul TParticipant @pault84577]

Dave

The cooling fans worked well on Thor when I went daft and fitted them as forward facing propulsion, they provided decent thrust as they compressed the water and forced it out of the shrouds narrow exit.

This is a pic of the prop shrouds before and during construction.

You are correct about the fans not being very good at high revolutions, I tried using them as lift fans in a hovercraft but they spun themselves to bits.

Ashley

What kind of 'project' is the jet drive for?

Paul

 

Edited By Paul T on 15/02/2017 16:33:59

[josh nicholasParticipant @joshnicholas98718]

Thank you all for your replys,

DM – i can make them cheap my dad works in a place where he can get stainless pipe and bends etc… of different diameters for free and he is able to weld all the joints and as he is an engineer hes fairly good at working with metal, i could even go with aluminium i know the benefit with aluminium is that its lighter than stainless steel but as its going to be used in salt water and on the beach etc id prefear stainless etc…

Only problem i have is making it the correct size for my model as the hull is 4ft long and a width of 16 1/2 inch and the hull on its own is 4.390KG – so i figured the best size would be a 63mm stainless pipe with a wall thickness of 2mm leaving enough room for a 61mm diameter prop (if i can find one)

I can get a decent brushless motor from hobbyking to spin FAST but i need to know the best starting point for the pitch as i want the model to be able to pull alot of waight but not be dead slow,

my idea is that when the model is finished i want to rig it up with FPV and rig a Rescue system up so i can go out in a pond and bring other models back in if they stop working,

i have a robotic arm to put onto the model to turn models that my be upside down the right way up…

[ashley needhamParticipant @ashleyneedham69188]

Josh. If the o/d of the pipe is 63mm and the wall thickness is 2mm the I/d is 59 if I have thought it through correctly.

A 4 foot boat equipped with a conventional twin drive of X55 props and decent motors for say 8000 rpm would provide power in plenty. Props are the biggest cost, jet drives tend to have smaller rather than larger props driven at high speed, as far as I know, however Tunnelled props or Kort type nozzles do provide better low speed power but at more modest prop revs.

​Finding a prop and matching the tube to it would be the way I would go. A 1 mm clearance would be needed…an X60 if you can get one could have the very tips sanded off 0.6mm (!!!) for instance. In theory this would not be good practice but I think it makes little practical difference….

Ashley

[Stewart McCarthyParticipant @stewartmccarthy89466]

Hi Ashley, have a read of this thread.

http://www.modelboatmayhem.co.uk/forum/index.php/topic,56939.0.html

I am nearing completion of the latest version fitted to an actual vessel rather than a washing up bowl……lol.

Stewart

[Bob Abell 2Participant @bobabell2]

Hi Ashley

Just spotted your thread and knowing your requirement……..Have you thought about a vacuum cleaner impeller?

Plenty of impellers out there

Bob

[ashley needhamParticipant @ashleyneedham69188]

Hi Stewart and thanks for that link. Very interesting. 3D printing is the way to go in the future.

Bob. Impeller, yes there are loads out there, however I have settled on something else now. The issue as I saw it would be connecting a commercial impeller to a model sized motor, and of course sealing it against water ingress.

The original question I posed was for a project now on the back burner for a while.

Ashley

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