airboat propulsion and drive

[jxing62]

i was thinking of building my own airboat , for the airboat hull i think it is not a problem but i dont have any information about the propulsion and the drive, i mean the transmision, the mechanical part from the engine to propeller. can anyone kindly give me some advice. thanks.

[StianM]

http://www.dair.co.uk

Reduction and damper is from what I understand build into the engine.
I have no experience with airboats and have no idea what kind off power you nead, but a 100hp should be enough.

[Frosty]

Well I dont think they have a transmission. I think a VW engine is popular or can be used and the prop is connected straight to the crank --start and go-.

I am pretty sure I have seen converstion kits to do this on the internet somewhere.

Where in malaysia are you?

[StianM]

Originally Posted by jack frost

Well I dont think they have a transmission. I think a VW engine is popular or can be used and the prop is connected straight to the crank --start and go-.

No reduction gear? You then would nead to keep the prop diameter quite low not to brake the sound barier. If you runn a engine at 5000rpm the propeler diameter could not become larger than 1,2-1,3m befour the tip are traveling at Mach1.

Is there not also easier to get grip in the air with a larger diameter proppeler?

[jxing62]

i also believe it should have some sort of gearbox/transmission, one that is a must is forward and neutral gear. otherwise you are not possible to park the airboat.
stainM mention abot the mach1, can you describe more detail about the mach1, not really understand it.and what is the normal diameter of the prop in airboat, and is it true peoples are using the airplane prop in airboat?

[jxing62]

sorry i forget about jack frost, i am living in east coast of malaysia - kelantan, which is very close to thailand. yes, ialso agree that vw engine is suitable for airboat as it is aircooled. i also heard gm engine is used in airboat also,right?

[Steve in SoCal]

With a VW engine swinging a prop pitched for the engine, at 0 speed you will not be able to get amywhere near full RPM. As the speed rises the RPM will rise also to around 3000RPM. 3000-3200 is about max speed for a two blade prop in the size needed for a WV. You can also use a small inline engine. I have seen Air Boats with everything from Chevy V-8's to BMW motorcycle engines. You may want to look at Honda and Toyota, a water cooled enginge will run better. You dan't need reduction gear, you do need to limit the RPM to max prop RPM. At idle the thrust is low most boats have a kill switch to stop quickly. A reversing prop is going to be really expensive and I have never seen a prop with "Beta" in that small a size. Air Boats use airplane props.

Steve

[StianM]

Originally Posted by jxing62

i also believe it should have some sort of gearbox/transmission, one that is a must is forward and neutral gear. otherwise you are not possible to park the airboat.

I'm no expert, but flying with smal 2 motor aircrafts along the Norwegian coust I think some off them have cp proppelers.

Originally Posted by jxing62

stainM mention abot the mach1, can you describe more detail about the mach1, not really understand it.and what is the normal diameter of the prop in airboat, and is it true peoples are using the airplane prop in airboat?

Mach1 is braking the sound barier(330m/s) If you have a prope spinning at 5000rpm at a diameter off 1,2-1,3 your in the area where the tip off the proppeler is working at this speed's.

I'm no aviator, but I would asume this would include alot off noice and vibrations.

I'm shure there is someone in here that can explain it behter and more profesjonal then me. They have this huge junkjards out in the desert in the US (atleast that is what I see on movies) where they chop up old airplanes. A nice prop could probartly be bought for a good price if you have a good friend over there. I hear from a friend off mine that is a flight mecanic that moust parts is in good shape, but has too manny hours on it to be alowed to fly.

[Steve in SoCal]

A propeller that has a tip speed near Mach 1 has a harsh buzz sound. It is hard to relate but do you guys remember the planes of WWII in dives the noise the props made? That is the sound of a tip at or near Mach I. You don't want to turn the propeller that fast, all the propellers are designed to turn at around 2700-3000 RPM max, do not over rev the prop or it could break and tear the engine off the boat.

You can buy used propellers that have been cut down because of tip wear that can't be used on airplanes for not too much. Call an airplane propeller shop, I have a bent prop in my garage but it is too big for your needs. Shipping from the US is going to e costly. Try to find something local first.

Steve

[Frosty]

[quote=Steve in SoCal;142086 do you guys remember the planes of WWII in dives the noise the props made? That is the sound of a tip at or near Mach I. [/QUOTE]


Are you kidding?

[Steve in SoCal]

No, The high pitch buzz you hear from propeller airplanes is the prop tips

Steve

[FAST FRED]

The problem with air boats is they need huge HP , and are fuelish.

A prop in the air will make about 5 lbs of PUSH from a HP.
7lbs is theoretical max.

A crapy outboard will give 20lbs of push , for the same HP.

Some tugs with kort nozzels claim 30lbs / hp.

So as a minimum you need to feed 4 times as many horses with an air driven boat as a water driven boat.

Fine if you need to go over Sawgrass as the South FL boats do, but pretty expensive for other applications.

FF

[Steve in SoCal]

Jack, I am not saying do you remember them in person. Movies and old film footage, many airplanes can make that noise with the propeller at high RPM. I just use that as because I thought everyone would recall the noise of a dive bomber, from a war movie

Steve

[jxing62]

hi friends,

from the above discussion, the propeller rpm should be maintain below 3000 rpm for practical reason, and the most economic available engine is autoengine while this auto engine can make up to 5000 rpm, so i think i will need to have a reduction gear or transmmison to control the speed of the propeller,so that it not exceed the 3000 rpm bearer, right?
and what s damper btw?

[jxing62]

fast fred,
if i am building a 6 pax air boat then how much hp engine i need?