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Cobra S - free plan

Old 02-02-2016, 07:13 AM
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Originally Posted by Hydro Junkie
Looks to me like the boat is better than the driver. It's probably a good thing the boat is built heavy. One other thing I saw is that the prop isn't going to last long if it keeps hitting the water. Molded props tend to splinter if they strike things thicker than air very many times


On the red - usually wood props are bad karma on an airboat run on water. Wood props can shatter. Plastic moulded props like APC or Master Airscrew are typically used/recommended but any plastic prop works.
Old 02-02-2016, 09:35 AM
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You are right about the boat being better than the driver ;-) It's pretty boring driving around the middle of a lake though, one needs obstacles to dodge (or in my case, to collect).

The prop is a plastic APC, or was, it snapped from a collision with the jetty long before any indication of damage from water strikes. I expect that could be different if the motor had more juice though.

One of my earlier designs had a 3rd channel to tilt the motor upwards, which helped it generate lift and climb out of the water before tilting forwards (the prop usually only strikes the water when going too slowly to plane which, due to the anemic motor, happens a lot)
Old 02-02-2016, 09:48 AM
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APC props don't break from hitting water alone. I've flipped enough boats using APC props and never had one get any damage. Flipping on dry ground will do damage though. If you chip an APC prop, throw it away and get a new one. Master Airscrew props are more durable, but horribly less efficient and flex more.
Old 02-07-2016, 06:25 AM
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Shouldn't this thread be linked to http://www.rcuniverse.com/forum/rc-a...-underway.html?
Old 04-26-2016, 04:29 AM
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these front prop boats seem underpowered,.....probably due to the fact that the prop has to be cut to a much smaller diameter for clearance. an air engine's "power", comes from the outer areas of it's prop diameter and in order to be used on a design like that, the most efficient part of the prop must be eliminated. to me it doesn't make sense t do that.
Old 04-26-2016, 05:10 AM
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Agreed, that is one of the biggest challenges. I think a multi-bladed prop is a good workaround though, but they are not easily available (at least within my budget).

As far as making sense.... well, I never build RC models to make sense, I build things that intrigue me, which means they are usually unusual, and generally impractical. I do enough sensible design in my day job :-P

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