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does this sound right

J

josh_2562

Well-known member
OK I'm think about putting a motorcycle engine on a mini. this will be the first air boat i have ever messed with. if i got this right let me know if not correct me. the ideal is to swing the bigest prop you can and stay where your engine make hp am i right or wrong? lets say i had a 3./1 reduction and a prop with a 3000rpm max does that mean i could turn the engine up to 9000rpms? What i was think is i could get a porp with a lot of pith and use the gears on the engine to get it moveing then use the gear on the engine to get it to a safe crusie rpm. do you thank this would work? thanks for the help
 
I don't think I would try using the shift gears I can picture problems with that , to reduction question yes in theory small gear in the engine and larger gear on the prop at 3:1 if the prop speed is 3000 rpm's then the engine would be 9000rpm You want the maximum torque hp is just a benefit
 
sounds bad dont listen to what i say i just joined this website and dont know much about airboats but i would think u want throttle responce on an air boat incase u need to turn or something or if u actualy want to take off... if your props so big u have to use your first gears to get it moving and get it up to speed at your top gear its gona take off so slow right ?

-randy

im just learning with you so dont take my comments wrong i hope u can make this work i'd love to see anything new and neat
 
I had thought a while ago about using a 2 speed tranny on a boat instead of a reduction box. Run the first gear at 2.6 : 1 or there abouts and then run a second gear at 1.5:1 or there abouts so once you got up on plane and had the prop moving you could drop into second gear and cruise and drop your RPMs a ton. One problem I have noticed though is that big ol prop catching wind unwinds pretty darn fast. Of course I have never seen a prop clutched to see how it acts in free wheel.
It'd also interesting if someone clutched race boat. Wonder how a hub would stand up to a 6k stage clutch dump.
I am like a lot of you fairly new to airboating so imagine there is a reason why this stuff isn't done. It would be hard for me to believe it hasn't been tried already.
 
The ideas are neat but I hope you know that it won't work. Instead of setting a prop at a single angle of incidence and shifting it to get different gear ratios you should just install a constant speed prop. With the constant speed prop you can change your blade angles to get the most out of the prop at different RPMs. I'm surprised no one has tried that. Combine that with a clutch and a tranny and build a big boat to float it all. This build would be great on youtube.
 
well with the down shifting alone I see broken belts or gear maybe a crank etc. form trying to stop he mass of the spinning prop think about riding a four wheeler and running full throttle down the trail then dropping to first gear all of a sudden now image a prop sinning at 3000 Rpm and doing that :shock:
 
It mite take som tweeking but I think it could work. There was a pic on here some where of a boat with a turbo 400 tranny on it,used first to get the prop turning and it would shift to second when it had enough rpm.And Ive talked to a few guys who have had this set up and they say it works.my opinion is,if ya allready got it,use it,worst that can happen is it won`t work 8)
 
Gave it to huntnfish for the cost of shipping,was tierd of it being in the way.He was nice enough to give a little extra witch was a bounus for me 8) Says it woke his motor up though
 
goldhunter_2":1lwtaofe said:
well with the down shifting alone I see broken belts or gear maybe a crank etc. form trying to stop he mass of the spinning prop think about riding a four wheeler and running full throttle down the trail then dropping to first gear all of a sudden now image a prop sinning at 3000 Rpm and doing that :shock:
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why would i need to drop it all the way to first? the way I'm think is like ride a street bike or even driving a car. If I'm cruising along and need some more prop speed i could just drop it one or two gears it would be just like in a car when you go to pass some one you drop a gear and go. when you down shift the engine the prop speed should stay the same but the speed of the engine will go up where it can make more power. that is how I'm thinking of it.


you guys may talk me out of this ideal. so if you do what do you think about a ROTAX 600 engine from a snow mobile.
 
Josh I am thinking the same its not like going from 5th to 1st in a car cause your gear isn't going to be that far apart. it would be like giong from 5th to at most 3rd. I just am not sure you could keep the prop spinning fast enough for the time it took to change gears to make it effective. I was also thinking if you did it this way you could use a drive shaft and put the motor low and in the middle. This is just my non-mechanical mind thinking though. I should be the last one your taking advice from :lol:
 
jpatter123":1f60pxnh said:
Josh I am thinking the same its not like going from 5th to 1st in a car cause your gear isn't going to be that far apart. it would be like giong from 5th to at most 3rd. I just am not sure you could keep the prop spinning fast enough for the time it took to change gears to make it effective. I was also thinking if you did it this way you could use a drive shaft and put the motor low and in the middle. This is just my non-mechanical mind thinking though. I should be the last one your taking advice from :lol:
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well once you get the prop going you don't have to use the clutch to shift gears so i'm sure i could change gears fast. I'm not sure how I would mount the engine yet still work on if i should try it or not
 
yeah I'd wait to find someone who has already done it unless you just have a lot of time on your hands to fiddle fart around with it and some money in case you break somethin.
 
josh_2562":1grx36zd said:
goldhunter_2":1grx36zd said:
well with the down shifting alone I see broken belts or gear maybe a crank etc. form trying to stop he mass of the spinning prop think about riding a four wheeler and running full throttle down the trail then dropping to first gear all of a sudden now image a prop sinning at 3000 Rpm and doing that :shock:
Click to expand...

why would i need to drop it all the way to first? the way I'm think is like ride a street bike or even driving a car. If I'm cruising along and need some more prop speed i could just drop it one or two gears it would be just like in a car when you go to pass some one you drop a gear and go. when you down shift the engine the prop speed should stay the same but the speed of the engine will go up where it can make more power. that is how I'm thinking of it.


you guys may talk me out of this ideal. so if you do what do you think about a ROTAX 600 engine from a snow mobile.
Click to expand...

the dropping to first gear was to highlight point and I do see what your saying but i am thinking you have this huge mass spinning around (prop) and when you drop a gear even one it is going to try to slow that prop down several hundred rpms all at once in my mind something is going to give pretty quick.
Not trying to talk you out of the engine , i am a firm believe in using what you have or can find and make it work but I think if it where me I would do away with the transmission idea and use a straight reduction unit
if you have the rotax snowmobile engine laying around that would work also
 
I also am not that mechanically inclined. I know just enough to be dangerous. I have seen a gyrocopter with I believe a Subaru engine with a clutch. I think it was somewhat automatic like the old Honda QA-50's. When it idled the prop did not turn, but when he hit the gas the prop would spin. It also had an adjustable prop that could be changed from the control seat. He could turn the blades far enough to back up and could also adjust in-flight.
 
I don't know squat, but it sounds the same or worse than flying a helicopter but only in two dimensions. Pretty busy with the feet and hands.

A CS prop like Des Moines brought up, I think would be alot simpler.
 
do they make them in a pusher for an airboat? I have heard guys say they had adjustable on the fly props out of aluminum but I haven't ever seen one.
 
jpatter123":1iswsqki said:
do they make them in a pusher for an airboat? I have heard guys say they had adjustable on the fly props out of aluminum but I haven't ever seen one.
Click to expand...

The cessna O-2 had a tractor and a pusher, but that's an aircraft engine.
 
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