Using a moped engine to power a rc-powerboat with a outrigger hull.

What do you mean by weight and by displacement? Displacement = mass = weight. Or in some cases displacement = weight + load, but what would be the load in this case. Fuel?

Or do you think displacement = total volume? That's not a common definition.

 

Well, I was thinking about the total volume yes - guess I formulated that poorly =/

I've given some more though into the design and it's much smaller, total volume is about 30-50 liters.





Having a prop and a high powered engine would surely make this thing a rocket What changes should I make to the design?

I also tried to find suitable propellers, but that wasn't easy - is there any shops carrying these kind of high speed propellers?

 

I use Vespa Ciao motor as it has fan & shroud.

Air cooled motors need airflow at all times and are prone to overheating otherwise.

My moped mechanic says the constant forced fan cooling solves a lot of problems.

I think this is a bigger factor on goofy projects than in their intended use on mopeds, because the first thing that happens with goofy projects is you get the motor running but then need to fiddle with other stuff for a few minutes.

Plus, the Ciao motor seems much more compact with the carb very snug to the rear of the motor, rather than at the end of a intake tube. You only need to mount the crankcase, and a support for one exhaust mounting.

An Indian company called "Kinetic" makes a Ciao clone, but I here they are very low quality.

Ciao's have 65CC and 75CC kits for more power.

 

I've never been involved hydroplanes. You should seek for much more information before building it. You should carefully design the angles of the outriggers and the position of them.

I would think, that you need a very different bow from. The one you designed will make it fly when speed increases.

Here are some links to start with:

http://en.wikipedia.org/wiki/Hydroplane
http://www.hydropoker.com/history-hydroplanes-poker.html
http://findarticles.com/p/articles/mi_qa3918/is_200208/ai_n9141727/
http://www.rcboataholic.com/hulls/hullshydro.htm

 

With the dimensions and weight you have given I expect you could get it to fly with the power you have so I want to correct my earlier comment on this.

If it is designed to fly then the primary consideration is aerodynamics. The hydroplaning aspect is a means to an end.

A scaled up version of the flying model you provided in the video clip should be possible.

A correctly size air propeller for this application can achieve an efficiency well above 80%. The best you will achieve with a cavitating prop is 70% and of course a water prop does not allow you to fly. Whether you can fit a prop large enough to get the high efficiency is something that needs investigating. The faster it will go the smaller the prop but you need to have enough thrust to get it up to speed on the water.

I now understand the reason for your symmetric nose. You are really considering it as a wing section.

As far as marine props go I have seen the ones linked here referenced before:
http://www.cmdracing.com/updated/prop_picks.htm
I have not checked if they have any large enough for you hydroplane but they are the biggest I have seen for RC boats.

Rick W

 

hot motor might crack on contact with water.

they can take rain drops, but if that thing flips and dunks a hot engine....

 

I'm not using a aircooled engine, it's watercooled with a separate system so that I don't need any water intakes. The original stock radiator will be swapped for a ligthweight aluminium Intercooler that I'll rebuild to use with water.

Also, Ciao's aren't as good as the vertical minarelli engine and certainly doesn't have the accessabillity to tuning parts that minarelli does. Aircooled engines doesn't achieve the performance levels watercooled does

Definitely some nice links there, thanks

I'm abit scared of the thought of flying that thing really, so I think I'll start off making it fly on water.

I do not quite know what speed I should go for, 60 kn? 70 kn? 80? it should be doable with some careful conciderations when it comes to the aerodynamics? The propeller choice is to me the hardest part

At this time I haven't decided what prop to use.

It's all aluminium, and the outer casing of the cylinder is not much over 130-140 degrees - the main problem will be cleaning out the water from the engine I'd say.

 

I think an air prop will be a lot scarier than a water prop with an RC boat/plane of that size. There are issues with thrust line and weight distribution with the air prop as well.

You will certainly get the best speed with an air prop but a lot of factors to account for.

Rick W

 

Yea, I can see where this is going really -> water prop. Even though the air prop will get me better efficiency - it will probably add 4 kg just in gearing and sprockets and prop mountings to make it solid. (abit exaggerated, but ok )

I've been searching around for someone doing something similar, but I haven't found anyone with a air prop.

As I see it, the goal is to build a as aerodynamically stable vessel as possible while minimizing drag. I have some plans of how to tune it in nicely by trial and error - then to make the final welds on the offriggers.

I will try to make some more detailed drawings later - but atm my exams are coming up so I'll have to focus on them. I hope to start building just over christmas and have it finished by the time summer comes in may

 

There was a thread started for a PWC with an air prop and one is pictured on the thread:
http://www.boatdesign.net/forums/boat-design/planning-two-seater-pwc-air-boat-hybrid-30016-2.html
See post #23. I do not know how well it works.

You also see there are some pretty slick airboats that are not all that big:
http://www.youtube.com/watch?v=h-nQyldySmE
There are plenty of smaller RC airboats. Some are close to the configuration you have in mind:
http://www.youtube.com/watch?v=i9PCPr2hQtI&feature=related

I guess what you are working on is at the upper end of RC and lower end of piloted.

Rick W

 

Well - in size, it is

There was some outrigger designs in that first tube video there yep - but the thing is scalabillity. Their propeller and motor was quite small compared to the hull - it would take a pretty big hull for me to do the same.

The fact that a water propeller would enable my boat to go in my car would be a huge plus, so size just got abit more important atm. Also a outrigger brings the huge plus that it could be built so that it can be taken apart easyer.

#23 was interesting, but engine brackets and everything will be much more complex compared to a water prop.