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Author Topic: Skimming along  (Read 564 times)

GG

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Skimming along
« on: February 10, 2020, 01:14:59 pm »

The latest model has been "wrung-out" now with out encountering any problems, well apart from the weather (so foggy I couldn't see the other side of the lake one day) and a reduced voltage battery pack on another outing!


It's based on the two previous air-boat design for Speed 400 and 500 motors.  I came across a forgotten brushless motor and whilst pondering a new aircraft for it, realized it was December with poor weather and a very soggy flying field (almost liquid mud!).  So an air-boat model seemed to be a better bet, at least it could cope with water, snow, ice and even wet grass.


Compared with the other air-boats, the design was slightly enlarged and modified to cope with the extra power.  Construction of the hull was from balsa and plywood giving a ready to run weight of around 36 ounces (1 kg).


Same characteristics as the previous models, runs fast and flat with only the rear part of the flat bottom in contact with the water which makes little disturbance as it zips along.  The single air rudder has maximum deflection of 35 degrees both ways.  This is way more than needed at full speed but very handy when you use very low motor speeds, it can turn tightly and get out of embarrassing situations (the ESC has no reverse being intended for model aircraft).


At full speed you need to drive it with modest rudder commands to keep it on a straight heading, just like a high model boat or aircraft, definitely not one for the people who like to turn their heads and chat to the person standing next to them whilst sailing!  High speed turns require steady progressive application of the rudder, the model will yaw into the turn with the bows pointing into the center of the turning circle.  If the model is traveling on the desired path you simply learn to ignore this yaw which might make you think it's not turning and add any more rudder.


If too much rudder is applied then the corner between the hull sides and bottom, which is kept sharp to make the water break away cleanly at speed, will "dig-in".  This has never been a problem will all three of my air-boat models, they just come to a sudden stop and are now pointing at 90 degrees to their original path.  This creates lots of spray and, because my throttle stick is spring loaded to the "Off"" I have already stopped the motor.  Just let the spray fall back into the water and, assuming the model is pointing in a safe direction, apply full power and skim off again.  With practice you can learn to reduce the throttle when turning a shade too tightly for full power,


Easy to build, good performance and great spectator appeal to boot!  BUT it need to be driven with full attention to both where it is at any moment and, perhaps more importantly?, where it will be in a few second time.  Not a model for the inattentive or casual characters....!


Glynn
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TheLongBuild

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Re: Skimming along
« Reply #1 on: February 10, 2020, 01:19:40 pm »

Like it, need to get mine out of dry dock..  Also mine also worked when upside down  %% , just not as fast..


What battery are you using with this ?.

GG

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Re: Skimming along
« Reply #2 on: February 10, 2020, 03:58:42 pm »

TheLongBuild,
                I started out with a six cell Nimh pack and intended to then try one of the Lipo packs I fly with.  But, it's so damn fast with the Nimh pack I've stayed with that.  To be honest the thrust/weight ratio is not far short of 1 as it is so with the lighter and higher voltage Lipo packs, it might be rather hairy...?
Glynn
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