Airboat reduction gear

Been done in experimental aircraft field for ages.

The even 2:1 ratio could (very likely) cause harmonic problems. A better choice would be a fraction off - 2.25 to 2.58 : 1.

The next problem would be getting the belts to take the load equally rather than one overloading and failing - causing the other to overload and fail.

One Gates Polychain belt sized to the load might be a better way to go. Find somebody who can cut the elliptical tooth wheels.

FWIW

Richard

The prop will act as a flywheel - whether you want it to or not. (Large rotating mass with inertia)

But the problem with multiple belts is simply getting them to load equally. with high torque loads like this it's really hard to do.

That's why...

DL

Could you use two spring loaded tensioner pulleys? As long as you werent using the prop as a flywheel I dont see why you could't.

n airboat and plan on putting a 4 cylinder engine on it

The prop hub will be about about 2 feet above the engine as I would like to keep the center of gravity low. I can't picture what you are suggesting with the timing chain? Could you explain more. Thanks

airboat and plan on putting a 4 cylinder engine on it

The timing chain turns the cam shaft.

No real torque load.

The prop you are planning to use will absorb all of the available engine power.

Do you know what the rpm / torque output of the engine is?

an airboat and plan on putting a 4 cylinder engine on it

I was thinking of a K-car engine. 2.5 liter inline 4cylinder, it has approx. 100hp/135ftlbs torque

Some time ago, Ted Edwards made a reduction pully set for a homebuilt on his 3-in-1. A search of the dropbox may find the description and pictures.

Kevin Gallimore

:59=A0pm, mark wrote:> I am building an airboat and= plan on putting a 4 cylinder engine on it

The timing gear sprockets would give a 2/1 ratio but you would have to reverse the crank and cam sprocket. The timing chain would be too short however some of the older chains had removeable links and several chains could be spliced together. Probably too much trouble and expense.

A belt system from some motorcycles might give you a better setup and more choices in gear ratios.

DL

airboat and plan on putting a 4 cylinder engine on it

Whatever you set up will have to handle that much torque and rpm.

A timing chain or a couple of belts just isn't got to get it done.

Ever seen the blower belt on the old dragsters? THAT was just to turn the blower! You will be running 100 hp through this thing.

That's why the gearboxes are so much more successful...

Ricahrd

Might work, but you are going to go through a lot of belts. Get Pulleys for Gates toothed belt. Put small pulley on crankshaft (bolted to flywheel. Mount 1/2" +/- thick aluminum plate to the engine (bell housing bolts and by bracket to the head) and use an automotive wheel bearing/hub assy to fasten the big pulley - bolted to the plate with slotted holes to tension the belt. I have friensa flying aircraft with the same setup and it works.

Automotive heavy duty timing chains (like on a BB Chevy) can handle up to 50 HP but they need to be in a sealed shell to keep them oiled.

airboat and plan on putting a 4 cylinder engine on it

If you want the prop up and the engine low you can't beat a harley final drive belt system.

As for the blower belt, just how much (or little) horsepower do you think the blower on a 1200 HP blown fuel dragster absorbs?

Would you believe in excess of 400 in some cases!!!!!!! Yup - that 1200 HP fuely would be over 1600 if it didn't need to power the blower.

For simplicity and reliability for his app, you can NOT beat a polychain, or even the older gates style toothed belt.

What kind of belts, and how big is the smallest pulley?

The original "helio-plane" had a vee belt drive between the engine and the propeller - approved by the FAA.

It is quite a common configuration. I installed a 125 HP diesel driving four (IIRC) 6 ft. cooling fans (propellers) for a heat exchanger setup.

One point - the belt people have charts which specify how many horsepower a belt can transmit - RTFM before you start building :-)

Cheers,

Bruce (bruceinbangkokatgmaildotcom)

I think either Schweizer or Hughes produced a certified helo with a belt drive also. The large V belts will transfer a lot of HP with a large enough driven pulley.

Another factor here is the fact it's a boat. You could add another 50-75 lbs of flywheel weight and greatly reduce the belt loading from torsional vibration.

snipped-for-privacy@4ax.com...

Are polychain belts and sprockets commonly available the way V belts pulleys, weld on hubs and belts are. What about cost, would 2 sprockets and a belt be $100, $1000...ballpark? You guys are great, I posted this same question in a airboat forum and not one response.