YS 140L Prop size - RCCanada - Canada Radio Controlled Hobby Forum
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Old 04-09-2008, 10:11 PM   #1
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YS 140L Prop size

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need some advice: what size of prop would be best for break-in of YS140L 4 stroke engine.

Op manual states 14x14,
or 15x12 thru 14 ,
or 16 x11 thru 14.

Will fit to a YAK 72 inch once breakin is completed

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Old 04-13-2008, 10:04 PM   #2
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Re: YS 140L Prop size

I do not have one of these engines but here are some interesting facts about props. I would go with the largest diameter low pitch propeller possible for your plane and engine size. Just remember that you cannot lug an engine using a large diameter prop, model engines need to run in their power band..

Here is why larger diameter props are more efficient.

The working efficiency of any propeller, is found by comparing the velocity of the airplane to the velocity of its "backflow" relative to the airplane. If these were the same (an impossible condition, of course), the propulsion would be 100% efficient, and there'd be no slipstream behind the aircraft. The closer we can approach this ideal with a propeller-driven aircraft, the higher its efficiency. Less energy gets wasted in air turbulence -- and in noise generation.

The thrust we need to keep our airplanes flying comes from the reaction that results from accelerating a mass of air rearward. If this mass is low, like that behind a small-diameter propeller, it's got to be accelerated quite a lot to provide appreciable thrust. This produces a fast-moving slipstream, and efficiency suffers. On the other hand, the air mass that a big prop acts upon needs much less acceleration to achieve its thrust output.

Another thing about large-size, low-pitch props is that they minimize variation in their models' airspeeds. At takeoff, hovering, and at low model velocities, as when you are flying an up line with your Yak, they pull hard, just when high thrust is needed.

Try 17x7 or an 18x6, if these lug your engine then go down in pitch, to 17x6 you will get better thrust efficiency that would benefit your Yak’s performance.
You can never have enough power, as you can always throttle back.

Last edited by BoundForHell; 04-14-2008 at 12:24 AM.
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Old 04-15-2008, 08:11 PM   #3
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Smile Re: YS 140L Prop size

Thanks BoundForHell, I will consider your comments......Dave

I read an article that suggested 16x6 for 3D hovering etc.....just didn't want to take a chance that I would over-rev a new engine beyond its maximum RPM . Therefore 17x7 or 18X6 makes sense.


Last edited by DKing; 04-16-2008 at 05:53 PM.
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