Mechanical mind bender.

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Old 07-08-15, 08:36 AM
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Mechanical mind bender.

Its been a while since I have been on the forum. Been pretty busy with school, side business, etc.
Had a mind bender come out of an r&d discussion and thought I would see what you guys came up with.

Prop propelled (air) vehicle, all things considered equal and space was not a huge concern, variable speed drive (adjustable transmission) and fixed pitch prop vs. fixed drive (motor to prop) with a variable pitch prop?

Its a theoretical system at the moment, target is speed and fuel efficiency (like everything motorized).
 
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Old 07-08-15, 09:11 AM
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Well, I'm no engineer...but I would think something like a CVT to a fixed prop would be easier and more efficient. You can keep the engine in it's efficient RPM range with a CVT. Variable pitch props have advantages (reversing for instance) but the system is kind of complicated in my experience. The ones I've dealt with were hydraulic/mechanical.

CVT's are what many car manufacturers have gone to for efficiency, but I think they are still limited on their strength and require advanced electronics.

Is this a wheeled vehicle, boat, or a plane? Problem with a plane would be the additional weight of the trans vs the variable pitch system.
 
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Old 07-08-15, 09:33 AM
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Planes also have heavy restrictions on what can be used.
I am thinking the same with the CVT and being prop, it doesn't require any clutching so zero slippage.
 
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Old 07-08-15, 12:58 PM
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Nice to see you again Northern Mike it has been a long time. Your question is kind of out of my league my father was the mechanic in the family and my interests are mainly computers. Still though this interests me because it is something different do you have any diagrams or videos to show what you are talking about? I probably wouldn't understand everything so I can't really offer any ideas but it is interesting.
 
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Old 07-08-15, 12:58 PM
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Are you building an aircraft or an air boat? In both cases weight and horsepower are fighting for the number one position. And, I can speak from personal experience on both accounts that either vehicle is not good to have a breakdown. An air boat is slightly better but if you've ever hiked out of a south Florida swamp on foot you'll learn a new respect for simplicity and reliability.
 
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Old 07-08-15, 04:26 PM
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hedgeclippers;
I'll see if I can remember to draw something up for you.
Pilot Dane;
Leaning towards and air boat design. Planes are too regulated to be able to mess around with the output drive and space is a bit too confined.
 
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Old 07-08-15, 05:10 PM
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For airboats I like airplane engines. They are simple, light weight, don't require a reduction drive and very reliable. Their big drawback is they are limited to the lower power end with about 250 hp the max. To push a bigger boat you are into a rare (very expensive) aircraft engine or a V8 with a reduction drive.

What size boat/vehicle are you planning? Without knowing I'd say prepare to need twice as much power as you think. 80-100hp is good for a very small, lightweight hull on water for one or two people. 150-180 hp is a good area for average construction and carrying two people on water. 225-250hp for sturdy construction and two or three people on water and enough to push one person and the boat across level land or up a mild incline. Then you ramp up quickly in power if you want to climb steeper hills or banks or want to carry more load.

In all cases it's a fixed pitch prop. On the ground there is just not much benefit in a variable pitch prop as speeds change quickly and frequently. So it's big, fixed pitch paddle blades.

Oh, and everything is very, very, very loud! Big engines with straight pipes and big propellers operating close to structures like bracing & the hull. You burn lots of fuel and 75% of it seems to be converted to noise.
 
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