AirBoat build

[Chop]

Hello everyone,

I have had a small electric air boat for a couple of years now. I bought it used (when it was in beautiful shape), and have beaten the hell out of it (Avanti, don’t look at the photo!). I really like to play with this in the winter when all the water around here is solid. Its beating is in part, due to my handing the controls over to the kids in the neighborhood and letting them play (trying to get some future enthusiast’s).

I would like to build another, larger air boat that can handle the irregularities that a snow surface presents (the micro Gator disappears in a boot print). And yes, I also want it to be water worthy.

Considerations:
• CHEEP!!! Money is very tight due to the plant closing - I haven’t had a job in over a year. But I have time to build.
• Electric I have several 380 and 540 size motors that could be used, along with ESC’s. I’ll get specs on them soon.
• Material The bottom must be able to take the abuse of running on a hard surface, I have a piece of 12”x 24”x1/32” (30.48 x 60.96 x .7937 cm) birch ply that might be used for that, and balsa for the rest of the hull.

The rest, well that’s what I’m here for. Some of you “experts” have forgotten more about boats than I know – and the things that you have forgotten weren’t worth remembering.

I’m all ears.
Chop

[screwball]

this looks really cool! i built one a couple of months ago out of foam but it didnt turn out that great lol

[Chop]

Thanks screwball. I'm hoping for some help here because Ive never built one from scratch.

[Jesse J]

I like the styrene sheets for the bottom - no treatment and pretty slippery. I'll be watching, cool stuff.

[tth]

Sweet looking little boat. I started into the boat side of RC when I took apart an RC car, built a wood hull and installed all of the components to make an airboat. That was my very first venture into electric boating 16 years ago.

PS- Notice I left off the fast before electric in my paragraph, the boat was a TURD! But it was mine and nobody else had one.

[j.m.]

I made one a few months ago that used a GWS ducted fan on top of a 3/4" thick piece of blue foam from HD covered in packing tape. Light and bounce resistant. Ran it with a 3s 800mah pack. It was pretty fast. I rounded the bottom corner of the foam on the front and sides so it would go up and over things, and kept the rear bottom corner square.

Ply would be too heavy, you have to keep it light so it will 'float' on the cushion of air under it from forward motion.

[Chop]

I am thinking of using the 1/32" (.7937cm) ply for the bottom. I know that it is pretty thin but since I am running it on snow/concrete/asphalt (snow covered streets and driveways sometimes have bare spots) I will probably fiberglass it. Any scratches or gouges can be repaired with epoxy.

[Chop]

Work on the AirBoat has begun.

I'm trying to keep this as economically stingy (cheap!) as possible so I'm using as many "scraps" as I can.

Plans came off of a Airboat site named "Gator RC AirBoats" or something to that effect.

Pic 1 - I drew out the parts on the ply, and cut the pieces.
Pic 2 - Frame is assembled
Pic 3 - Parts are glued in place. I added blocking down the middle and along the sides. I want to be able to use a 12" x 24" piece of HDPE on the bottom and the only real practical way to attach it is with mechanical fasteners.
Pic 4 - Deck is in place, "foam in a can" sprayed into the empty chambers for added flotation. Rudders temporarily installed.

Now, my question: What size motor & prop to use to power it? The bottom of the hull measures 11" x 24" and as shown in the last picture it weighs 3# 10oz (1.644 Kg).

I have a few 540 size motors available, Feigao 7L, 8L, 8XL, 10XL.

Thanks for any help.

[j.m.]

A 540 sized motor is going to be massively overpowering.

540 sized neu motors are used (with props) on gliders with 8+ foot wingspans. This is with a more than 1:1 power to weight ratio.

For a motor, i'd use this:

http://www.hobbycity.com/hobbycity/store/uh_viewItem.asp?idProduct=8483&Product_Name=Turnigy_3639_Brushless_Motor_1100kv

Do you have room for a 12" prop? B/c that's what that motor's meant to spin on 3s. That's a high power option.

Here's something a bit tamer:

http://www.hobbycity.com/hobbycity/store/uh_viewItem.asp?idProduct=8502&Product_Name=Turnigy_2632_Brushless_Motor_1000kv

Again on 3s, but with an 8" prop.

[Chop]

When everything is installed (motor, ESC., Batteries) the boat will weigh close to 4 pounds (1.814 Kg). Keep in mind that this has the friction of being pushed across the ground too.

I have to look around, I know I have a few 380 size motors lying around. That doesn't rule out buying a more appropriate motor though.

J. M., this is EXACTLY the kind of information I'm looking for here, thanks.

[j.m.]

Inrunners are better at high rpm applications. Spinning a boat prop is one of these.

However, air props are much more efficient at low RPM, say around 8000. And to spin a big prop at low RPM, you need a motor with a lot of torque. This is where outrunners come in.
There's lots of cheap aircraft power systems available, but if you insist on using an inrunner, you should easily be able to find a suitable EDF. (electric ducted fan)

[j.m.]

So are you looking for a 1:1 power ratio?

For the sake of not having a 12" prop singing around, i'd go with the EDF. And you already have the motor. Do you have any spare 100 amp speedos?

[Chop]

I have a few Mystery 100A ESC's, might even have a 200A. My only concern with using a Feigao motor: will the airflow over the motor provide adequate cooling?

Also, if I do go ahead and get an outrunner, could I go with a 3 bladed prop and cut down on the diameter? It is 5" (12.7cm) from the deck to the motor platform, there is also a 3/4" (1.9cm) recess in the in the deck below the motor platform.

The supports for the platform are 4" (10.16cm) apart so putting a 3.5" (8.89cm) ducted fan underneath it might be cleaner looking.

[j.m.]

That's what im thinking... I have a little airboat with a small brushed GWS EDF, and it's really low profile and safe. No cutty-cutty on your fingers.

The motor would do fine if your not on full throttle all the time (which will be insane btw), but you could put a small heat sink on the back part of the motor.

http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXTC78&P=7

This would be right in the airflow.

EDIT> this would be even better:

http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXJD94&P=7

[Chop]

Okay, I hit the brakes on the forward progress because I decided to go with the ducted fan suggestion.

I did some demolition and reworked the motor mounting area.