Motor and propeller advice for a home made hovercraft

Tribal-Warrior · 22 Sep 2019 at 05:42

I'm planning to build a very basic version of a hovercraft with a leaf blower inflating a tarp 'skirt' wrapped around a sheet of plywood. There a number of youtube videos featuring DIY hovercrafts like these. However, I would like to take it a step further and add a petrol motor with a propeller from an rc plane for forward movement like in these two videos:

https://www.youtube.com/watch?v=1CoH2Jl80DI

https://www.youtube.com/watch?v=7EvQ4TXsxY0

Problem is I am clueless about motors. I am considering getting this one for my upcoming hovercraft build:

https://www.ebay.com.au/itm/253031141216

Though how would I mount or attach the propeller? Obviously, this kind of motor wouldn't be designed specifically with a propeller in mind. And the other question is whereabouts would I mount it? I'm guessing that a propeller might be attached to something spinning like a fan? It looks like there are two circular things on this motor in the pictures but I'm not sure if one of them is a fan or not.

Additionally, would anyone have any idea what size / pitch etc of propeller would be suitable for a motor like this?

And looking at the motor, would it be possible to get an idea of the start up sequence? For example, all I know is that you'd have to pull a cord to start the motor. After that, would it be in idle or neutral or something like that? And then would there be throttle control and some kind of release for the acceleration?

I guess it's pretty obvious from my questions that I am clueless about motors / engines etc. However, if I can get working with something like this, I think it will improve my knowledge in this area which would be beneficial for me later down the track for different types of projects and tasks. So I think it would be a valuable learning experience.

red eye · 23 Sep 2019 at 20:59

I’d run the prop though some sort of gearbox. You can get an adapter machined up from your local machine shop.

I would build a little rc hover craft, less stress a lot cheaper and you won’t kill your self

Tribal-Warrior · 24 Sep 2019 at 00:13

Thankyou for the advice. I'll check out some machine shops and see if they can come up with an adapter. With regards to the gearbox, I guess I'd also have some adjustment of the speed from the throttle control though that's just an assumption. Just having the bare motor on it's own - I'm hoping to have some kind of throttle control. Out of curiosity, whereabouts on the motor would be the best place to attach the propeller?

I'm very keen to have a full size version for myself to ride in. Should be loads of fun. I used to ride a dirt bike (motorcycle) on a farm. And the motor I'm planning to install is suitable for a childrens entry level dirt bike so it's unlikely to turn out to be a speed demon. Plus from what Ive read, a hovercraft will be slower than a motorbike when the same equivalent motor is used. Additionally, I'll mainly be riding the hovercraft on sand at the local beach. I am reluctant to try it out in water as that would be risky.

ezekial · 24 Sep 2019 at 09:46

While I don't have much advice in the way of building a hovercraft, I will say that this is awesome and that you should definitely try it over water.

HRL · 24 Sep 2019 at 14:31

Shallow water!

This thread needs pictures.

SimonCHere · 24 Sep 2019 at 14:32

I'm a little concerned that you are trying to build a hovercraft to actually move yourself on and don't know the most basic of how a throttle works on an engine.
Anyway. Behind the black plastic bit without the air holes in it has the output shaft and a gear set of some sort to step down (or up) the motor output to the gear output that you can see in some of the pictures. That would then go to the gear/clutch system of the bike/buggy/whatever. You could mount the motor on the deck of your hovercraft and then run a chain up to the drive shaft of the propeller on some type of A frame. Then of course you can build your guard cage around the A frame and propeller so you don't dice anyone up.

As for props. Well that's a whole other thing. In my model plane days I spent ages, and loads of money, buying different pitches and diameter props for my small electric planes to see which one was best. Now with my quads I just pick up ones recommended for my motors and try them.
Probably best to find a hovercraft forum and ask in there.

Simon

Tribal-Warrior · 24 Sep 2019 at 18:44

SimonCHere said:
Anyway. Behind the black plastic bit without the air holes in it has the output shaft and a gear set of some sort to step down (or up) the motor output to the gear output that you can see in some of the pictures. That would then go to the gear/clutch system of the bike/buggy/whatever. You could mount the motor on the deck of your hovercraft and then run a chain up to the drive shaft of the propeller on some type of A frame. Then of course you can build your guard cage around the A frame and propeller so you don't dice anyone up.

It is certainly an elaborate system they have. At what time in the video do the gears appear? That handle they have near the seat wouldn't be the gear control, would it? I like the throttle and kill switch cable idea that's readily accessible. Ive changed my mind about the 49cc motor I linked to before. I am now considering using a lawnmower motor instead. And yea I'll definitely have a guard cage. Do you reckon chicken wire would be adequate to wrap around the frame of the cage or should I go for something stronger?

SimonCHere · 24 Sep 2019 at 20:27

Didn't watch the vid earlier sorry. My comments were about the engine.
As to the video. The first one you link has very detailed information about the build. I would suggest watching it.
The handles are for steering they move the rudder at the back.
The throttle is on the hand grip.
There are no gears like a car would have in this setup.

No chicken wire is not up to the job. You need a duct. The orange circular thing around the propeller and wire mesh strong enough to stop bits of wood travelling at high speed if the prop breaks

Tribal-Warrior · 24 Sep 2019 at 20:40

SimonCHere said:
As to the video. The first one you link has very detailed information about the build. I would suggest watching it.

Ive watched the video several times. I'm asking about clarification of certain aspects of the video. That is the reason why I posted it.

SimonCHere said:
The handles are for steering they move the rudder at the back.

I know they're connected to the rudder. I'm not referring to those handles. I'm referring to the black handle / handgrip.

Since Ive been referring to various aspects of the video, what makes you think that I haven't watched the video?

SimonCHere · 24 Sep 2019 at 21:15

Tribal-Warrior said:
Ive watched the video several times. I'm asking about clarification of certain aspects of the video. That is the reason why I posted it.

I know they're connected to the rudder. I'm not referring to those handles. I'm referring to the black handle / handgrip.

Since Ive been referring to various aspects of the video, what makes you think that I haven't watched the video?

OK perhap watched but not taken it in.
At 5:18 on the video it says "the throttle cable and kill switch were run to the pilots seat".
The kill switch looks like a clothes peg with copper contacts which is on the black handle. Must go to the electrical system in the engine.
The throttle can be seen on the pilots left at 6:14, will just be a cable attached to the throttle on the engine and that red knob handle on the ratchet. You can see him increase the engine running speed from idle at 6:48.

Good luck with the build and if you ever get it running post a vid I'd be very interested in it. For now though, I'm out.

Nomisf · 24 Sep 2019 at 21:52

Head over to YouTube and look at Paramotors , their engines are very close to your requirement. Small, light, geared for propellors with the right mounting faces already in place, a clutch so the engine can idle without spinning the prop, and a hand throttle with kill switch. Maybe a junk "non airworthy" paramotor or just its engine from eBay would be a good shout ...?

Tribal-Warrior · 28 Sep 2019 at 10:35

Nomisf said:
Head over to YouTube and look at Paramotors

Those things look really cool. It would be great to fly one of those one day.

SimonCHere said:
The kill switch looks like a clothes peg with copper contacts which is on the black handle.

I know. Combined with the throttle control. That was obvious to me every time I watched the video. Though I admit it looked different in appearance when it was put to use with the black handle - hence why I didn't recognise it as the same thing later on in the video. Though no matter how many times I watched the video, I still couldn't see the gears that you were referring to. Though I guess you were referring to gears from another source and not the video.

Regardless, although these kinds of basic hovercraft should provide lots of fun, they do have a number of limitations. They are nowhere near as versatile as a conventional hovercraft which can be ridden just about anywhere. One thing Ive noticed from watching many videos is that the basic leaf blower hovercrafts cannot be ridden over grass. They'll come to a complete stop as soon as they reach grass. And Ive actually been wondering with conventional hovercraft whether it's the power of the motor providing lift or the design of the skirt or a combination of both that allow them to ride over grass successfully. I recently came across this video of a fairly basic home made hovercraft riding over grass with no issues:

https://www.youtube.com/watch?v=QncK_cwmaqk

And the skirt looks like a single sheet design rather than segmented so it looks quite similar to the basic skirt designs generally used on the DIY hovercrafts with leaf blowers. You'll note too that as the guy rocks back and forth on his hovercraft, parts of the skirt get squashed temporarily and then return to their original shape. That squishing is a characteristic that I have noticed in some videos of leaf blower hovercrafts where a basic skirt design was used (single piece of plastic or tarpaulin covering the bottom of the wood with a central plate and multiple small holes surrounding that plate.) Alternatively, it could be a bag skirt like some conventional hovercraft use though I'm not sure if they exhibit that squishing behaviour. At first, I thought that 6.5hp motor may be diverting some of the air flow into the skirt but I don't see any pipes etc linking it to the deck. There could be another motor specifically used for lift inside that wooden box at the back. Whatever it is, it must be a fair bit more powerful than a leaf blower to allow riding over grass.