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Airboat Construction

Old 07-23-2003, 09:08 AM
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Default Airboat Construction

I am currently building an airboat based on a 1/8 scale hydroplane (1985 Miss Bud I think), with a GMS 61 engine spinning a 12 x 8 prop. I am also using a gyro for pitch stablisation ( the boat has an elevator mounted on the rear wing) and twin air rudders.

Having only build aircraft before I am seeking some advice about fuel and header tanks and turning spikes...

Can I put the main tank in the hull(lower the CoG) and a header tank up behind the engine, this would mean the exaust has to pressurise the main tank and push fuel vertical about 6 to 7 inches into the header tank..

As it is an airboat what do I do about a turning spike/fin...

Cheers
Old 07-23-2003, 10:03 AM
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Default me too

I was thinking of doing the same thing.

I have an extra K&B .61 with perry carb.

Keep me informed, and maybe throw some pictures my way.

Talk Soon!
Old 07-24-2003, 05:41 PM
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Default airboat

Gee,

I would really like to see some pic's.

I have 2 airboats, the RTR aquacraft airforce airboat and just love them. I am also building the wild thing (plans out of RCBM)

I just picked up the flitecraft tempest hull. needs a few things.

I am planning on getting a .61 to put on one of my aquacrafts.

Sporty
Old 07-25-2003, 10:31 AM
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Default Sporty

Sporty,

What is the length of your boats? Do they handle well?
Old 07-25-2003, 02:15 PM
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Default Airboat Construction

I think it handles pretty well, for a airboat. The hull is a little different and that maybe why it has a little better handeling.

31 inches long, 14 wide at the back but narrows some in the front to 10.5. these are aproximate numbers. I measured really quick.

sporty
Old 07-26-2003, 06:54 AM
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Default Airboat Pic

Hi,

Here is a picture of the boat, it has progressed a bit from this stage. The engine (Mag 41) and tank (8 oz) are not the ones used only there for the photo. The boat is 1100 mm long by approx 600 mm wide.

Any info on turning fins would be helpful. Will post more pics as the boat progresses.

Cheers
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Old 07-26-2003, 08:30 AM
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Default Airboat Construction

looks good so far,

did you go from plans ? or a kit ?

sporty
Old 07-26-2003, 08:46 AM
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Default Plans not Kit

This is built from plans (plan 147..RJN 10/85) as found on the newton marine site (http://www.newtonmarine.com/). The materials used so far:

1/4 sheet of 1/4 (6 mm) ply
1/4 sheet of 1/8 (3mm) ply
1/2 sheet of 1/16 (1.5mm) bending ply

qty 9 of 6 mm square x 2400 mm long Tasmanian Oak

Lots of PVA and Cyno Glue.
Old 07-26-2003, 08:58 AM
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Default Airboat Construction

I looked at 147, but did not appear to be airboat. ??

sporty
Old 07-26-2003, 09:04 AM
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Default Correct

You are correct plan 147 is not for a airboat, I am modifing the plan to suit... I have no idea how well it will work but it should be ok as there is alot of surface area in the tunnel and the shape seems right to me. I think the boat will almost fly hence the gyro for pitch stablisation.

Slayer
Old 07-26-2003, 09:10 AM
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Default Airboat Construction

interesting concept,

will have to keep me posted on how it does once you are finished.

sporty
Old 07-26-2003, 09:11 AM
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Default Airboat Construction

take a look at the gator airboat

www.rcstore.com
Old 09-06-2003, 05:47 AM
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Default Airboat Construction Update

Hi all,

The attached pic shows the current state of construction with my airboat. The engine shown is for show only....the boat will run a GMS 61 when complete.

Still to come are the air rudders, the elevator, mounting the fuel tank in the hull below the engine mount.

I will be using a Cline fuel pressure system to move the fuel.

Comments or suggestions welcome ?

Cheers
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Old 09-09-2003, 06:25 AM
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Default RE: Airboat Construction

Hey Slayer, I have been playing with a custom built air boat; it's 18" long and has a 7.5" beam. The base sheeting is birch veneer and is covered with exotic hardwood veneer. I wanted the fuel tank in the hull to keep the CG low and because it would have cleaner lines. I found that there is head pressure is the fuel line that prevents proper flow to the carb.; to solve the problem I bought a check valve (one way valve) and put it between the fuel tank and carb. I found it at Tower Hobbies, it is intended for use with air craft smoker systems but it worked perfectly. Without it I couldn't keep flow to the carb. As for the turn fin I have a tunnel hull that I got tired of turning right all the time so I am thinking of using a center turn fin. In talking to a freind that used to race tunnel hulls it appears that a center fin will allow turning in both directions. Brother Tried to send you a pic but it didn't work, any hints on that?
Old 09-10-2003, 04:01 AM
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Default RE: Airboat Construction

Brother,

From the information I have found, it indicates that either a perry pump or Cline Fuel System will do the job... I guess I will find out.

Still don't know about a turning spike... I'll see how it turns without one first.

As for the pic, I think this forum has a size limit on pics however if is attached straight into an email it should get to me.

Slayer
Old 09-12-2003, 11:00 PM
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Default RE: Airboat Construction

Hey Slayer, I think I got it this time; let's hope so. I have been working on another airboat, this one will be made with a foam core for the hull and be covered with fibreglass. I will try to get some pic's of the progress and send them. It will be considerably bigger than my first one, 14" beam 28" long and 3" to 4" thick. It will be powered by an OS LA 40 engine. anyway talk to you later. Brother
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Old 10-21-2003, 09:28 AM
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Default RE: Airboat Construction Update #2

Here is the latest construction pics for my airboat. The elevators have been trial fitted and appear to be very sensitive with the gyro connected to changes in pitch on the boat……may have to wind down the sensitivity. Had a few issues with rudder authority however that issue is now worked out, just waiting on the engine (GMS 76 running a 12 x 6 prop).

Any Comments welcome

Cheers
Slayer
Old 10-21-2003, 09:23 PM
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Default RE: Airboat Construction

Hi Slayer, your airboat is just downright badd azz!! I love it!

If you still need a turn fin, try this guy:

http://www.barebonesboats.com/Turnfins.htm

He makes them to order. Just ell him what you want or better yet e-mail him a drawing and he will hook you up. Top of the class workmanship and very fair pricing. Be sure to tell him Kmot sent you.

Cheers,
Tom
Old 10-22-2003, 03:50 AM
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Default RE: Airboat Construction

Kmot,

I'll try again with the pics. as the modem dropped out half way through.
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Old 10-22-2003, 01:18 PM
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Default RE: Airboat Construction

Looks sweet, dont just happend to have the plans available to pop in to a scanner and let me have? its not quite what i had in mind but i think it could give me a few hints as for how to build the darn think i was thinking about...

Oh, please show us how it goes... :- )
B!
Old 11-10-2003, 12:34 PM
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Default RE: Airboat Construction

hows this project going?
Old 11-11-2003, 10:09 PM
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Default RE: Airboat Construction

Slayer that boat is so cool! Just keep going and get it into the water!

Some thoughts:
- Do you want the tail of the boat out of the water when you get moving so the air under that big front end has somewhere to go? Little rear sponsons might help.
- Expect the rear end to "sit down" when you come off the throttle when the boat is going fast. The prop disk will act as a brake.
- Will the center of gravity come out well with the engine weight shifted aft? Will you compensate with forward battery placement?
- Will you use a turn fin?

It looks great and I bet you'll make it work! Ya gotta get pics of it in the water for us!
Regards,
Will
Old 11-18-2003, 05:28 AM
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Default Airboat Construction Update

Here is the next instalment.

Finally I have had some time to work on the boat, the engine and cline fuel system are installed, CoG is approx 2/3 from the front, Gyro mount installed, hull has been covered in epoxy and is currently painted red however had a little trouble with some thinners and lost one of the mermaid decals. Refer attached pics however my camera went flat so no pics of the boat painted.

Next.. finish the painted,redo the decals and fix the TX. At this stage I will leave the turning fin off... I guess well see what happens.

After all of this it should finally get to see the water in the next two weeks.

Cheers
Slayer
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Old 11-19-2003, 12:13 PM
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Default RE: Airboat Construction Update

First of all, Good Luck!
I've run various airboats of different sizes for far too many years, so I may have a little experience to share.

On the turn fin issue, it depends on how you want it to handle. If you want it to ride like on rails for oval use, use a turn fin like you would as if it were an inboard. Attach your turn fin to the right (inside) sponson close to the inside chine and angle the bottom of the fin in, towards the center of the hull ( -/ ) like so.
If you will mostly be running around the lake at random, but want more positive steering, approximate the same location, and mount it in the center of the hull (through the hull would be best for strength).
For the most fun, run with out a fin. Power sliding these boats at full throttle is a blast.
Air rudders are not as effective as a water rudder, so planning your turns requires more attention to the amount of room you have. Thats why racing these type of boats is so much fun. A lot of hull slamming usually happens.

To properly trim an airboat for ride attitude, you will have ti have access to the motor mount. Reason being is you may have to add shims to either the front or rear motor mount bolts to angle the motor center line, or thrust line.
With the engine mounted parallel to the hull centerline, it will have a neutral angle of attack. If the hull is perfectly balanced (Very very rare) no adjustment will be necessary.
If the rear of the hull seems to ride too deep in the water while the front rides high, you will need to angle the front of the motor upwards, usually by placing a few washers under the motor flanges on the front bolts. What this does is changes the thrust angle to lift the rear of the hull more. If the front of the hull rides heavy and the rear high, put washers under the motor flanges on the rear bolts. This thrust angle will force the rear of the boat down and the front up.
Trim adjustments do not need to be dramatic, it usually only takes a few degrees of change to show a difference.

As far as the movable elevator, don't bother. The gyro will respond too slow to make any difference in proper attitude. These hulls bounce around a lot, and to have the elevator moving will hamper the performance. By the time the elevator starts to move, you'll already have gone over several more waves so the movement of the rudder will be far behind. Hate to rain on your parade, but it's been tried before, with no appreciable good results. Any other questions, I'll be wathching this posting.
Old 11-24-2003, 05:03 AM
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Default Airboat Construction Update #4

Well it floats - sits rather low at the transom (ie water lapping at the deck), I guess thats what you get for having an engine and fuel tank at the rear although the CoG is about 30% forward of the transom (as it should be according to the research I have done) ... next engine runs once I fix the Tx as it keeps cutting out []..

Until the next update............See ya

Slayer [sm=spinnyeyes.gif]

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