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-   -   Prop choice, gas airboat. (http://www.rcuniverse.com/forum/rc-airboats-246/6667157-prop-choice-gas-airboat.html)

RhesusMinus 11-24-2007 04:13 PM

Prop choice, gas airboat.
 
I built an airboat a few years ago, but I got tired of the whole project so I put it away for five years or so. The boat is 58"x23" and weighs in at 16-17lbs. I converted a Ryobi 31cc engine, that I have modified for more power. I´m more into gas boating, so I havent got a clue about air propeller, this is where I need some help. I just brushed the dust of the boat and would like to get it finished, at last. I testran the engine on a bench yesterday, and it ran 8600 with a MAS classic 18x8 (only prop LHS had in this size), pulled my heavy workbench over the floor, scared the crap out of me, never expected that. Any idea what kind of thrust this setup is delivering? I have been told that the Ryobi should stay below 7500 because of the week conrod and crank, so I guess I have to get a bigger prop. 18 is the biggest prop that I could use, so I guess it have to be an 18x10., or any other suggestions, or other prop brands recommended? Do airboats need a high pitch prop, or do they like more thrust? What kind of speeds are you seeing from airboats of this size and power ratio?

89ram 11-24-2007 10:14 PM

RE: Prop choice, gas airboat.
 
could you lower your rpms slightly with some linkage adjustment to keep it from over-revving?

TERBObob 11-24-2007 10:39 PM

RE: Prop choice, gas airboat.
 
Since its an older Ryobi , that prop you used at first , would be my choice . Gotsta remember ... an airboat requires a bit more power than an airplane AND personally , even as your thoughts about what planes would do , an airboat is different . My fear for you might be that it might get too hot ( too much strain ) , not of over rev'ing .
And that "myth" about the con rod is basically just that . Granted , the con rod used ( if you want to call it that ) is nothing more than a bunch of THIN con rods joined together for thickness ... But , I have replaced the Ryobi coil with one from a Homie ( not R's restricted like the Ryobi's are ) and have not had an issue yet .
I built TWO different gasser airboat with Ryobi's and again , not a single issue ( granted , one of them , in addition to changing the coil , I also changed the carb to a big bore - 11.7 venturi , gutted the muffler , lightened the piston , and opened the transfer ports and widened the intake and exhaust mannies as well )
One the modded engine , I even used a 16X10 MA pusher and she ran GREAT ... LOTS of power !


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