My attempt at an air boat!

While I wait for my hospital appointment, I thought I might as well start on my air boat. This is built on a Mobile Marine Models ABS moulded hull. I have fitted some plastic strips to take the plywood deck. It will be powered by a brushless motor and forwards only ESC. The motor I will start with is a 1650Kv, but I have others. I intend to start with a 2S LiPo, but have a 3S also which the motor will take.
Not having experience of model aircraft finding a propeller was a bit hit and miss The motor says a 6 or 7 inch, which don't seem to be very common. Then you have to decide if you want a slow fly or regular prop I have a couple of slow fly a 6" and a 7".
The motor will be mounted on a piece of 20mm square timber. I intend to mount the ESC on the stick as well - plenty of cooling air

Here is where I've got to at the moment. The deck has so far had two coats of Easy Kote and will get another couple at least.

Barrie

I see your boat has a V at bow at a similar angle to mine Barrie.
6, 7, 8 " props are standard sizes and come in 4, 5 & 6" pitches The 2 i'm using are 6x5" and 9x5"

That looks good Barrie, I was going to build another one as mine is getting a little worse for ware, but seeing the price of that hull I couldnt buy the wood for that. Think I will have to get one..

Going by your set up it is going to fly, the motors go OK upside down for recovery, but I don't know about ESC mounted outside unless it is fully waterproof.

Don't tell me you wont flip it. If you don't flip it your not trying hard enough



Alan

Alan,

The ESC outside was for two reasons - to provide some cooling if its needed, and to save having to extend the ESC to motor leads at this point in time. If it goes OK then I will look at mounting it in a waterproof container with the other items which need protection.

Damien

This hull has a V down most of its length. The bottom of the hull is also ribbed for most of its length. I could only find one prop less than 7", most were 8 and 9" at the two on-line suppliers I looked at. I am starting with the 7" and have a 6" to try also, but these are the "slow fly" types.

I'm still trying to decide how to mount the motor in relation to the vertical I'm also not sure if I will need any weight in the bow. I think with most of the weight in the stern its going to sit with the bow out of the water - is this normal?

Barrie

I've no idea of the balance characteristics i'd take a guess at fairly neutral buoyancy and play with it until they both sail well.

Thanks Damien! I have now found that I can fit the ESC below decks without extending the leads. Only managed a short spell this morning as I need to go shopping for my wife who's in hospital. I hope to get the motor post installed tomorrow. I am trying to make it so I can vary the angle to see which runs best.

I've also to make the rudder. I have laminated two pieces of 1/8th balsa, and I have some 3mm and 4mm brass tube which are a sliding fit. Just trying to decide if I can leave the rudder as a loose fit, or it should be fixed to the inner tube somehow!

Barrie

Here is where I've got to. I've made a mount for the motor which I think will allow me to vary the angle to the vertical; the rudder is still under construction - balsa with tissue covering using Easy Kote. The hatch lid is held by magnets. As you can see it sits with its bow in the air. I will have to try it in the test tank before I fix the deck as it looks as though it will need some weight forward.

Barrie

The rough balancing point for an airbout is about one third from the transom, so if you put a round piece of tube at this point and then move your battery untill it balances, this should give you a good starting point on your first sail.

An airboat should be kept as light as possible, so adding weight to balance is a no go.

Just my thoughts.

Alan

Thanks Alan - I may need to use a heavier battery then. The LiPo I planned to use is quite light.

Barrie

I expected to be in hospital by now, but as I am not, I have finished my airboat - apart from painting. It will get an outing tomorrow morning. The deck is well sealed, so the paint is only cosmetic I do need to work out how to build a cage around the prop - tomorrow I'll just be extra careful

I plan to start with a 7.4v LiPo, but will take a 7.2v NiMh in case I need the extra weight. The prop is 7x6, and I have a 6" as well.

Barrie

Good luck, looking forward to hearing how it goes, any chance of a vidio



Alan

Alan,

I don't think I can manage the boat and a video camera It will have to wait until my wife is fit enough to come with me as camera woman! She only came out of hospital yesterday, so it may be a week or two, by which time it should be painted.

Since I took the photo I have added a rubber band to hold the hatch. I wasn't quite satisfied with the magnets.

Barrie

No maiden voyage yesterday The weather was perfect but I wasn't.

It will give me a chance to paint it before getting it wet

Barrie

Today I was perfect ( well that's relative ), but the weather wasn't as kind, however I did manage to test the Air Boat. I started with a 1400Kv motor on 7.4 volts, which went pretty well, but then put in an 11.1volt battery, and it flew (not litteraly ). Balance seems to be about right, but I think I need more rudder area as the turning circle is huge. I will try extending upwards so more of it is in the airflow.

No photos or video I'm afraid as I needed both hands for control!

Barrie

Interested to see what she goes like barrie

i would also lower the motor mounting pylon , so the prop is spinning closer to the deck , plus an increase in the rudder height to the full swept area of the prop .

Thanks for that tip! I wasn't sure how big a prop would be required which accounts for the height, but now that I know the 7" prop is adequate I could indeed lower it.

Barrie

i made a few airboats last spring / summer , from the free plan in one of the model magazines , ( the skimmer ) ,running on standard brushed 400 motors , a 6" prop is normally enough to give a good turn of speed , , unfortunatly theey wernt powerfull enough to push my sailing yachts out of the seaweed they ere being caught in ! good fun as a model on their own running over the weeds but as posted elsewhere do have a tendancy to flip over , so you need to seal all electronics below the deck ! the hull your using looks good , how thick is the hull ?

Not sure if you mean the thickness of the material which will be 1.5mm plastic as that is what MMM use for their vac forming. We have a couple of air boats in the club which also use brushless motors, but on ply hulls.

Barrie

it was the thickness of the vac form , ive found the link to mobile marine , those hulls are much cheaper than any of the materials needed to build your own ! , my last airboat was a 1.5mm ply coated in polyester resin / matting , . although i now have a rowing boat for model recovery im also working on a waterjet drive dory hull for use in the shallows and around the seaweed !