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Old 10-10-2016, 07:48 AM
  #1
Paulekins
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Default wont turne left

hi all my air boat wont turn left but will turn right on a six pence
both rudders have independent servos but the servos are matched and run off a y lead to one servo control
both rudders move left and right the same amount
i am running a pusher prop which rotates anti clockwise
any one got any idea's
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Old 10-10-2016, 10:15 AM
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How much throw do the rudders have?
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Old 10-10-2016, 04:35 PM
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Pusher prop torque will make an airboat turn right easier than left. Looking at your build, your rudders are too small for that big prop. They should be taller and wider to deflect more air. As stated above they also may need more throw. How strong are the servos?



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Old 10-11-2016, 07:33 AM
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hi all
the servos i cant remember what they were (they are painted now )
i do know that they are both rudder servos off a couple of old Morley helicopters and they were a matching pair
they both will turn at full throttle so no shortage of power or slipping gears
the trow in both directions is 125%
i will try bigger rudders the reason they are that size is i was told they only need to be 1/2 the size of the prop but i will put bigger ones on
and we will see how it goes
thanks
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Old 10-11-2016, 08:31 AM
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The endpoint percentage means nothing. How far from centered do they "throw" - maybe a picture would help in addition to a good idea of the angle? Pictures are worth a thousand words - especially on custom built/one-off stuff.

I found with a recent boat build that it would turn right well but not left. Turns out the size of the rudder made all the difference requiring almost tripling the size of the rudder from what the plans called for.
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Old 10-11-2016, 11:52 AM
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here are some pics for the left and right rudders
i hope you can make out the angles but they all seem to be about the same give or take a degree
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Old 10-11-2016, 12:17 PM
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If you're getting 45 degrees of throw and it doesn't turn well in both directions, then the size and/or shape of the rudder is the problem. That is if the servo/linkage/rudder isnt deflecting at all from the force of the prop blast.
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Old 10-11-2016, 01:15 PM
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hi there are no linkages as such they are connected directely to the servos

i will make up some new rudders this week and see how they perform
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Old 10-12-2016, 04:10 AM
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Rudders on airboats work by deflecting airflow from the prop. The more air they deflect, the more effective they are. First off, your rudders are too far apart. In a right turn the right rudder is deflecting very little air, so most all the work has to be done by the left rudder - which is too small. Look at the boat from the rear and you will see that the rudders are not covering much of the prop thrust cone.

First I would try larger rudders (2x current area) in their current location, that is a lot easier if it works. If that isn't enough, re-mount the rudders closer together so that at full deflection the trailing edge of one rudder overlaps the leading edge of the other. If needed, get an extension for your starter motor like the EDF guys use.


.

Last edited by Got RPM; 10-12-2016 at 04:13 AM.
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Old 10-12-2016, 07:44 AM
  #10
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this is frustrating as in my original build log you can see i started out with bigger rudders (see pic)

but as every one now is saying i need bigger rudders
i will make a new set this week end and see what happens
thanks for your comments
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Old 10-25-2016, 12:09 AM
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well i made some bigger rudders and hay the boat turns both ways equally now
thanks all
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Old 11-01-2016, 09:25 AM
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Your prop is a pusher prop, you may want to turn it over and remount it so the printed label is facing fwd.

Last edited by controlliner; 11-01-2016 at 09:26 AM. Reason: spelling
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Old 11-01-2016, 09:51 AM
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see previous post above
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Old 11-01-2016, 10:03 AM
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Quote:
Originally Posted by Paulekins View Post
see previous post above
The airfoil on the prop will put out more thrust if it is installed on the right way. Your boat will perform better with more speed.
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Old 11-01-2016, 10:19 AM
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ok the engine is facing backwards and from the reverse the prop is on the correct way around with the writing facing towards the rear of the boat

Last edited by Paulekins; 11-01-2016 at 10:21 AM.
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Old 11-02-2016, 09:16 AM
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The writing on any prop faces the direction of travel of the boat/plane. Yours is on backwards and is much less efficient than if it was installed correctly.



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Old 11-02-2016, 09:28 AM
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The propeller is installed correctly when the thickest part of the blade is the leading edge in normal engine rotation. If the thinnest part of the blade is the leading edge in normal engine rotation, it's backwards.
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Old 11-02-2016, 11:24 AM
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Quote:
Originally Posted by Got RPM View Post
The writing on any prop faces the direction of travel of the boat/plane. Yours is on backwards and is much less efficient than if it was installed correctly.



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don't forget this is a pusher prop so it goes the opposite direction of travel
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Old 11-02-2016, 11:29 AM
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Quote:
Originally Posted by 1QwkSport2.5r View Post
The propeller is installed correctly when the thickest part of the blade is the leading edge in normal engine rotation. If the thinnest part of the blade is the leading edge in normal engine rotation, it's backwards.
the thickest part is on the leading edge
dont know how we ended up talking about prop direction i have no problems with the amount of puff the blade gives my original prob was wont turn left which has been sorted by putting bigger rudders on and now all is well in the world
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Old 11-02-2016, 11:40 AM
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Quote:
....don't know how we ended up talking about prop direction i have no problems with the amount of puff the blade gives my original prob was wont turn left which has been sorted by putting bigger rudders on and now all is well in the world
Well we are trying to help you get the most out of your boat. Doesn't matter if it's a reverse prop or not, it is on backwards. But if you're okay with much lower thrust out of your engine, I'm fine with it too. Don't worry about me bothering you again with any advice.


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Old 11-02-2016, 12:05 PM
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Quote:
Originally Posted by Got RPM View Post
Well we are trying to help you get the most out of your boat. Doesn't matter if it's a reverse prop or not, it is on backwards. But if you're okay with much lower thrust out of your engine, I'm fine with it too. Don't worry about me bothering you again with any advice.


.
the prop was never on the wrong way to start with
well that's according to the diagram that came with the prop and also the members of my local flying club
the only problem i was having was that it wasn't turning properly and that was down to the fact that i was told by members on this forum
that my original rudders were too big so i made them smaller which caused the turning problem once i put bigger rudders back on it now handles perfectly
the power of the prop was never a problem

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Old 11-02-2016, 04:21 PM
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Quote:
Originally Posted by Paulekins View Post
the prop was never on the wrong way to start with
well that's according to the diagram that came with the prop and also the members of my local flying club
the only problem i was having was that it wasn't turning properly and that was down to the fact that i was told by members on this forum
that my original rudders were too big so i made them smaller which caused the turning problem once i put bigger rudders back on it now handles perfectly
the power of the prop was never a problem
The picture in post #8 shows the prop on backwards. The engine turns counterclockwise as looking at the front of the engine. So with the prop mounted the way it is in post #8 turning CCW, Got RPM is right - the prop is mounted backwards. An efficiently operating prop puts more air to your rudders and makes it turn better and will also make the boat a bit faster too.
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Old 11-03-2016, 05:37 AM
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Instead of doing a 90 degree left turn you could always do a 270 degree right turn
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Old 11-03-2016, 09:20 AM
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if i put the prop on the other way around the taper of the hub would be tapering towards the nose cone ant not the engine plus the back of the prop is hollow
so if i put the prop on the other way around there would be nothing to lock the nut down onto
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Old 11-03-2016, 09:22 AM
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Quote:
Originally Posted by rgburrill View Post
Instead of doing a 90 degree left turn you could always do a 270 degree right turn
but i can now do circles in both directions now
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