Air boat fever

[Basstronics]

With the onset of winter I have come to realize I wont be able to run boats. I would however like to build a fun and fast air boat to be able to run in the snow and the water.

I built one out of wood awhile back and shes kind of a hog (heavy). Shes pretty fast but unstable.

I see those 3 points which are pretty basic, but I kind of like the simplistic design. However Im a bit different and want something more unique.

Enter the air boat cat.

Basically what Im going to do: 3 main pieces of wood. Two larger uprights which will form the inside of the sponsons/tube and provide the uprights for mounting of motor/fins. They will key into the flat top deck which will form the other part of the sponsons. The actual sponsons will be made of foam which I will cover with light ply/glass. The center tub section will have foam added to hold battery, esc and servo. I will utilize the HK "Swamp dog" fins and lower mount. These seem to be the hardest part to build... I got a good size out runner and 8" props.

I will be posting plans/assembly drawing in the near future.

[SirBudman32]

I can see some racing coming

[Fluid]

Sounds like good fun. I've built quite a few airboats over the years, although I've only run them on water. IME the main things to avoid are too much weight, too much frictional area in contact with the surface you're running on (probably less important on snow), and using too much rpm with the motor/prop. Most FE motors have an excessive Kv, I found best results with: Kv x nominal volts = 10,000 to 15,000 rpm. The upper rpm limit is usually the prop tip speed: 145,000/diameter = maximum rpm. More rpm usually results in much lower efficiency and wasted power. There are many air prop calculators to use to compare different props maximizing thrust and speed with amps. I run under 100 amps continuous, usually around 75 amps.

Prop diameter is also important. More diameter is your friend (again on water, snow may be different) as it creates more thrust. Pitch is important too for top speed, although too much will stall the prop and you effectively go nowhere. I have had good success with ~800 Kv motors, 4S and 12" to 13" props on ~34" boats, although 6S with the same motor required 10" to 11" props and wasn't as much faster as I had anticipated. Hull design doubtless plays a role. Wood props are a no-no on water, but they may work well on snow. My current airboat is in pieces for some maintenance, once it's together I'll take a photo.





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[Basstronics]

Thanks for the tips. I wanted to go cat style to reduce the ammount of friction in the water but keep the stance as wide as possible. It will also allow me the freedom to adjust ride pads.

My first venture ended in disaster as I tried using a 3000Kv motor on 3s. I forget the Kv off hand but I think it puts me around 15,000 / or slightly under.

I think the overall design will be easy enough if it works well others might build it too. I just need to come up with a radio box to hold electrics/battery.

[Fluid]

Here is the latest airboat I built this year. It was a proof-of-concept model for a design dating back to the 1940s. The original used a jet engine and air plane floats, but no photos of it were ever found and only third-hand descriptions of how it ran. This was a simple way to see if the idea was practical. On a model scale it was, but I doubt that jet engine power available back then would have worked. Anyway, here is my rendition, with what the original probably looked like. While it was not my intent, it also looks like some other vintage race boats (final photo). This is a fun boat to run, but like the original it was not meant to turn sharply. That's fine, I have plenty of pond room.

Floats - 34" for a .40-sized plane
Motor - Scorpion 4020-8
Props - 13x6.5 and 13x8
Voltage - 4S1P/5000 mAh
ESC - Castle ICE100

[Basstronics]

I finally got my 3D CAD software installed tonight. I got the turn flaps and motor/prop assembly drawn up. Tomorrow Im going to start on the hull portion.

I need to source a radio box thats cheap, water proof and easy/quick on/off.

[Basstronics]

Ended up ordering the fiberglass radio box from Zipp kits. I want to work this into the design.

Im keeping my modeling semi-simplistic. In my mind I balance whats worth doing and whats not, going overly detailed is a fruitless labor...

Looking for ideas on the sponsons, how to shape and how much flat ride surface it needs in the rear.

[Fluid]

What length and weight will the boat be? Need that info to give you sponson size estimates. You don't need to have wooden up-rights for the insides of the sponsons if they are going to be made of foam covered in plywood. Just glue the sponosn to the deck after covering the foam with 1/32" ply. Weight is the enemy here.

An 8" prop won't move much air. You need thrust to get an airboat up to speed and pitch speed to keep it there. It depends on the motor you have, but even at 18,000 rpm an 8x6 prop only gives 5.2 pounds of thrust at around 60 amps. A 9x6 at 17,000 rpm gives 7.3 pounds at ~85 amps. A 10x6 at 14,500 rpm gives 8.1 pounds at ~75 amps. The 13x6.5 prop I use gives 8.5 pounds at ~65 amps. The latter will lift my airboat off the ground if I hold it pointed straight up (not recommended!).


IMG_0192.jpg

[Bduncan]

Cheap airboat build.

http://youtu.be/iKWhYKbDeYg

Built this out of a kids kick board alum flashing pvc spare parts. Neu heli motor MM esc. 11x8 3 blade prop

With the onset of winter I have come to realize I wont be able to run boats. I would however like to build a fun and fast air boat to be able to run in the snow and the water.

I built one out of wood awhile back and shes kind of a hog (heavy). Shes pretty fast but unstable.

I see those 3 points which are pretty basic, but I kind of like the simplistic design. However Im a bit different and want something more unique.

Enter the air boat cat.

Basically what Im going to do: 3 main pieces of wood. Two larger uprights which will form the inside of the sponsons/tube and provide the uprights for mounting of motor/fins. They will key into the flat top deck which will form the other part of the sponsons. The actual sponsons will be made of foam which I will cover with light ply/glass. The center tub section will have foam added to hold battery, esc and servo. I will utilize the HK "Swamp dog" fins and lower mount. These seem to be the hardest part to build... I got a good size out runner and 8" props.

I will be posting plans/assembly drawing in the near future.