airboat propulsion and drive

http://www.prime-mover.org/Engines/Torsional/contact1/contact1.html

I think this link can explain it bether than me.

I think the problem might be reduced if you use reduction trough v-belts since I think they would absorbe some off the vibration from the engine.

To keep the rpm down you could chose a Diesel. I think aluminium auto turbo diesels are not that hard to find in scrapyards annyome. Opel, VW or some japanese.

 

steve, i ,miss your reply, u mean i dont need a reduction gear? in this case, i will a gear assembly( or sprocket assembly ) to transmit the power the prop,
then can i have this assembly , with proper ration as to limit the prm of the prop?

 

stianM,
this is a good article, thanks. but i think the chain system is better and secure than the v belt system in the marine situation as we drive airboat in the water rather than air? what do you think?

 

I think a v-belt wont corode like a chain drive, but I think a more omportant factor is that a v-belt in rubber would transfere less vibrations from a engine.

I would think the guys like Steve know this bether than me since I'm no expert on propulsion in air.

 

Jxing,

I can not say if you need a reduction gear, it is going to depend on a few things. Many auto engines will not rev much with a propeller in direct drive so unless the engine has the ability to over rev it is not needed. There are a few simple ways to keep the engine from over speeding the prop with direct drive. A company here in the USA called MSD sells a rev limiter that installs on their ignition system that slows the engine when it reaches the limit by miss firing the spark plugs. This works to keep the engine at the speed you want with out too much effort. On most diesels the governer can be set to the speed you want to use and several newer petrol engines have a rev limiter that can be reset to do the same thing.

In using a car engine you may have to use a reduction gear if the engine is not very powerful. A propeller uses a lot of torque to drive it, an aero engine of 180 HP is 6 liters and a 300 HP aero engine is 9 liters. These engines are slow for petrol engines as well most only rev to 2700-2800 RPM normally. An auto engine is about the displacment of an aero engine of equal horsepower and in the last few years getting much smaller. A newer auto engine is making 80-100 HP per liter without supercharging. The low torque may demand a reduction gear to drive the propeller but a lot will depend on your engine. Do you have large displacement engines that you can use? For your airboat the bigger the engine the better, you don't have to use all the power all the time but having the torque of a big engine will be of great help.

V-belts may work but a better choice is a timing belt. You don't have to worry about miss match and they last a long time.

Steve

 

do you come across any airboat using v belt? although timing belt type is more feasible and less vibrant too , this i totally agree with stianM, however, in open sea, wind can come in any direction and may come from behind the airboat that will create, i think , a opposite thrust to the prop and hence the v belt, then , will it create a slippage on the v belt assembly?
i was thinking to operate the airboat in coastal area of south china sea, and the condition of the wave and wind in s.c.sea have to be considered?? though the hull design of the airboat is usually flat bottom, where people use it in the swamp area or lake, but my situation is , this airboat is to operate in river region but sometimes will have to operate near coastal area, or maybe the airboat is not the type i need?
the engine easily available here is mostly used auto engine and for diesel and petrol one it is around 3 liters. does this capacity enough for airboat? or i will have to import from usa for bigger capacity engine!?
i also heard of the ready made v blet assembly sold in usa, right?
steve mention about the low torque will demand a reduction gear, why? and how to decide whether the engine is low torque?
thanks

 

Unless you need to operate in 6 inches of water choked with grass , you dont want an airboat.

FF

 

sorry fred, i mislead you, sorry for my poor english!
i mean most of the time i need to operate in the shallow river where there are small rock, sand and mud , the this will create problem for outboard engine i think, so i prefer to use airboat where the proplusion is locate topmost.
but, there are occasions i will need to tranfer the airboat to nearby region which i will drive across s.c.sea. however, this will spend only 1 hr in the coastal area before i reach the other region. thanks.

 

I think jack frost proposed a vw engine. After some thinking I think this would be a great engine since it weight close to nothing and are cheap and not to hard to get some extra power out off. Reduction should provide the torque neaded.

Since Fred don't think airboats are the moust economical way of transportation just get a outboard to power it and you can tilt it up once you get into the shalow water and start your airprop.

I gues there is thousands way to do this. A more expensive sulution would be a inboard with a clutch making you able to chose by a outboard drive and the proppeler where the outboard drive can be tilted up entering rivers.

You ben waking my dream to build a howercraft. Who here is a howercraft owner? I remember someone having it as signature.

 

Hi, just noticed this one. The boat I am building is going to use a 489 CID Big Block Chevy. I am going to use it on the river so I am using 12 gauge steel for the hull and it will have a total width of 8 feet wide and 16' long. Air boats can be built either direct drive of with a reduction gear, normally do not have neutral or reverse although some people have used automatic transmissions but they are heavy. I am using a "Rotator" box with a 2.68/1 ratio that directly bolts on to chevy and Caddy engines. 3000 RPM max prop is a realistic limit however with the 2.68 and the right propeller my max prop rpm will be 2200 RPM and will be as quiet as possible. Should be able to cruise at around 50 KPH at about 2800 RPM, other people I have talked to suggest fuel burn of 3 miles per gallon. The ammount of HP would depend if you want to haul those 6 people across dry ground or up hills, the modern airboat is more of an all terain vehicle. There are a number of Propeller manufacturers that build either wood or composite props. The advantage of composite is that they are ground adjustable for pitch so the normal trend is to pitch to the max prop or engine rpm you want to run. A light Diesel direct drive would probably work pretty good as long as you want to keep the boat in the water. I'm going for show for my first one on antisipation of starting a sucsesfull company.

 

here Is some video of a small block chevy reduction boat! Lots of information and links on this website! http://www.southernairboat.com/photopost/data/526/Movie_0011.wmv

http://www.southernairboat.com/photopost/member.php?uid=88&protype=1

http://www.southernairboat.com/photopost/data/526/88Movie_0007.wmv

www.southernairboat.com

 

Nice link, $5,000 aircraft engine? The other ones I've seen have been $30,000.

 

That's me, I'm the hovercraft guy. If there is another on the board I'd like to meet them.

More hover info here:
http://www.hoverclubofamerica.org/

I don't think an old VW aircooled engine is going to power much of an airboat. You can use that engine with a hovercraft because the power requirements are much less and hovercraft are much better on fuel than airboats. Airboats are real brutes and inefficent as other's have pointed out. On the up side, no skirt to wear out or tear.

 

How mutch power is neaded to lift a howercraft? kw/kg.

I gues the power neaded for forward movement is quite low since it only nead to combat the resistance off air.

 

When an aircraft engine "times out" it can be purchased at very low cost , as the cost of a rebuild , by a licensed wrench to make it flyable again is HUGE.

To find out the power required , simply mount enough weight in the boat to represent the engine , passengers operator and load,and borrow an outboard .

When you are cruising at whatever speed you enjoy , measure the fuel consumption.

1 GPH is about 10 hp and about 20 lbs of thrust.

If 4 gph (about a 40 hp outboard) is fast enough an air propeller that produces 40hp x 20lbs thrust is about 800lbs of thrust.

That would require an air prop that can put about 160hp X 5thrust =800thrust.

So a well done 200hp car engine and reduction gear with the correct prop will get you going.

FF