Hi,

It is the first time that I enter this forum (I even did not know that they are called "airboats") and would like to build my first boat.

I am skilled with RC planes (building and flying) but have no idea about boats.

I went through this forum, but haven´t find any plans . There are tons of plans and tips for aiplanes on RCU, but not so much for boats. Maybe it is just that I did not have a look at correct post.

My intention is to make a fast and easy build:
- blue foam (I have hot wire cutter)
- flat bottom (I am open to another concept)
- electric (I am planning to run it in the city park lake and noise of a glow engine would be not acceptable)
- I have brushless engine Tower Pro 2408 (with 8x4 prop) which I would use for this project.

Is there any proven design which you could recommend?


If no: Could anybody give me basic key data for design?
(I just know that CG should be in 1/3 of hull, sides rake about 30%, and CG as low as possible due to stability) What more?

Regards,

Marian

the width should be 1-3 inches larger than the width of the prop. the length should be about 2-2.5 times the width. ei, 10Wx24L. foam is a good medium for a start(easier to work with and quicker) if your overall shape/design works, then try balsa wood or something more durable. make sure your Rx and esc are protected from water. you dont want it do die in the middle of the lake!

Go to www.rcairboats.net/phpBB/index.php you`ll find lots of info there.

welll even u could build with depron thats what ive used and loved it other thatn the fact if a hammer falls of the rack and hits it theres a huge dent

Hi,

Thank you for your responses. Last night I have spent hours reading about airboats on RCU and another forums. Unfortunatelly did not find "ultimate plans for simple foam boat", so I started to cut blue foam board making estimations.
If the boat ... (please help me. I am used to say "my plane flyes in this or that way", but what is correct verb for boat (??) ... good, I will make simple plans in Acad.

The first bet is the overall size. (if the engine I have is not enought, I will purchase another from Hobbycity, they are very cheap there).
Lenght: 42 cm
Width: 24,5 cm / 15,5 cm
Rake: 30º

Thickness of the hull: 3,5 cm (maybe too little, but this is what I found in my workshop).

Next steps:

Engine mount:
I will set engine incidence to 0º, the vertical position is limited by prop diameter, but I can move it forward or backward. How does it influence caracteristics of the boat?

Rudder:
I think I will go with double rudder.
How do you estimate the size?
What about throws?

Regards,

Marian

Hi,

I have made a paper model of what should be the engine mount and rudder.

Experienced guys:
Is the size of the rudder about OK?
I can still move the engine mount a little bit backward (inside of rudder frame). Does it make sense?

Marian

no the moter mount looks fine and rudders well ive had a boat with huge rudders and it still never compared to how my small rudders work on my boat and on my friends boat yours look ok maybe just a bit taller

mr. ilikehelp,

I am not sure if I understand you correctly. What you are saying is, that I should make the rudders a bit taller?

Regards,

Marian

looks like a solid design. you shouldnt need a motor much larger than the tower pro you already have. its going to be a small quick boat for sure.!

Hi Marian, one easy way to get fast results is to buy a "body board" and add your equipment in a simple way. Attach photos of mine.....hope this helps..Cheers/Harald

Wow. These things are huge ... I have temptation to take a "body board" of my daugther and install engine over it (it is yellow, decoration "Tweenies" ).
I can imagine it on a beach here in Spain: full of people, suddenly an engine is started and the board running crazily here and there. It would be shocking ...

Which size of engines do you use on these airboats?

Regards,

Marian

Marian, both these use .40 engines. Mine to the left has a piped OS.40FSR and the one on the right has a MDS.40. Front spoilers are needed to keep them from flipping over at higher speed. These boats are NOT for high speed but rather for sliding around in water or on grass........Cheers/Harald

I would angel the sides in a bit more the norm is 45* also if you are not going pusher set-up I would connect the rudders to the motor mount this will stiffen both up and make the build simpler. You can angel the rudders in at the top if you wish this may help in the terns by making the boat lean more like flaps on a plane. I think the Wright size of boat is about 2"or 3" wider then your prop diameter and 2 to 2.5 times the diameter in length (8" prop 10"x16" ) so your dimensions look good. A lower CG is not always a good thing with an airboat all the thrust is up top so the lower the CG the more force is on the front of the boat. This happens because the prop force is farther out of alignment with the CG and after that you add in the friction form the water on the hull. This is just something to keep in mind I would simply put the batteries and everything on the deck of the boat instead of in it, the rudders also help the boat to lean in a corner more with a higher CG. The best improvement to handling is to drop the prop thrust down as much as you can
Anyway just my 2c hope it helps

Also make sure the bottom of the hull is not bode in (concave) this creates suction on the water and your boat with not plane off. Looks like you may have a bit of one if so just need to sand it out

Marian, I added a video demonstrating the effect of a spoiler to keep nose down on my body board airboat. Gives you an idea of how it performs....Cheers/Harald

http://rcuvideos.com/item/5J893GJF03KTZ6TZ

Canardlover, the video is cool. It runs nicely with that engine. But, my home is full of airplanes and I cannot dedicate space for such a big airboat. By the way: coutryside is very nice. Where is it?

Pinky, on the second model I will join the rudder and the motor mount (angeled in). For this one I have already made these parts. I will use the same shape of the engine mount and make it longer (the engine would stay in the same position as it is now).

Good point about the CG.


I am going to install el. equipment.

I thing that if I put the ESC and the battery to the waterproof box (together with servo and receiver) they will generate too much heat.

Could you tell me how do you solve this issue?

Regards,

Marian

Marian, video is taken at the very northern tip of the Baltic Sea, outside Kalix between Luleå and Haparanda. Nice area but lots of mosquitos and rather much cooler than Madrid....Cheers/Harald
http://www.hitta.se/MapPage.aspx?Sho...x&SearchType=4

Hello,

RC instalation: I did not find a tupperware box of correct size, so I have made it from lite ply. Half is inserted into the hull (I used router for it) and the second half is covered as it shoven on the pics.

As nobody responded if it is good idea to put all equipment into the box, I have decided to make it as big as possible. Hopefully the temperature will not rise too much inside.

it loks like that box cover is screwed down that might be hard to get the batteries and stuff out

Hi,

The boat is finished and I have spent several nice afternoons with my kids riding it. On 2S LiPo it is acceptable but on 3S it "flyes". When it is fully charged it is way too much power, but a lot, LOT fun ...


Some photos:

This thread is called "Basic concepts of airboat" because I would like to learn them from you, more experienced guys.

My experience with this boat:
1. It is pretty fast
2. In curves it slides nicely, no intention to flip over even at top speed
3. When it slides at top speed, sometimes it is stopped suddenly, as if it hitted something laterally. The rake is 30º. SHOULD I INCREASE IT A LITTLE BIT? I do not want to flip it over.
4. Sometimes happen (when the boat is moving relatively slowly): if too much rudder is applied, the boat starts to turn around (without moving forward) and DIVING the inner front corner. I see two possible causes: A/ The hull is too low (only 3,5 cm)
B/ The rake below the front part is too long (see picture below)
Your opinion?
5/ Never happened on 2S battery, but sometimes on 3S battery: If the boat is quit and full throttle is applied, the nose dives and the boat goes almost as submarine. Easy reply would be (Do not apply full throttle when the boat is quiet ..)
I think that the causes are the same as in the point 4.

I am asking this because would like to make a V2. I consider:

- maintain the lenght and width
- make the hull higher (how much?)
- Rudder sensitivity is OK, even they could be smaller. What effect would have if I make them lower (and the same lenght). As it is now, the boat leans correctly inside the curve.

Rudder:
Pinky, could you explain more on "You can angel the rudders in at the top if you wish this may help in the terns by making the boat lean more like flaps on a plane" ?

Instead of having your rudders strait up and down when looking at them form the back like l l angle the top in like /\
What this will do is the one rudder when turned will force part of the thrust form the prop down and the other rudder will force some of the thrust from the prop up.
This creates a torque in the hull from back to front making the hull lean into a corner more, working similar to a plain if one flap was up and the other down creating a barrel role effect.

The sudden stop when turning you mention is form the sides of the hull catching the water a more angled side would stop this

Thank you for your comments.

How should I prevent diving of the front inner corner at low speed?

What size props are you using? They look like they run pretty good.

At the end I let the engine which I mentioned in the beginning of this thread in the airplane and bought new equipment for this project:
Engine 2410 -08 and Supersimple 20A regulator. Both things for less than 14 USD in hobbycity ...
The propeller I use is 8x6.

This boat "flies" with 3S lipo.

Marian.

PS. Any suggestions on improvements? I need your help ...