Written by Mark Christy Thursday, 04 February 2010 01:33
Paddles ...what they are.. why we have them.. and how flybar weights and flybar lengths come in to play.
Back in the dark ages when we first started making model helicopters the designers had 2 types of rotor head control mechanisms to try from the full size counterparts, Bell or Hiller.
With the Bell system there were either weights or hydraulics on the head to create a form of damping. The controls directly controlled the main rotor blades with the weights/hydraulics making the responses sensible.
On the Hiller system there were mixing levers and paddles much like our models to create the damping effect. The controls connected directly to the paddles/flybar and this in turn controlled the main rotor blades. For the historians out there there was also the Lockheed system.. but that was quite complex.. and not relevant here.
The Bell system was typically quite fast in response but low in over all control power.
The Hiller system was slower in its responses but had better control power.
Model designers soon realised that a pure Bell system wasn't completely workable at our small scale and we soon ended up with the system we have today which is a mix of Bell and Hiller. On 90% of models out there we control the main blades directly as well as the paddles.
At this point I would like to point out that I haven't mentioned stability once. Paddles have no effect on the models stability. Paddles affect the response rate (to either pilot input or external inputs) and control power of the rotor system not the stability of the rotor system.
Now back to the Hiller system.. as I mentioned earlier the controls affect the paddles and the paddles in turn then affect the main blades. Therefore the paddles have quite a large part in the control of your rotor disk. e.g. your roll rate!
There are 4 things you can do with paddles to change how they control your rotor disk:
4) Distance (flybar length)
I'll deal with them in that order.
As they are aerodynamic devices then clearly as you increase the size of the flybar then the more powerful it will become. For example something like Stubz paddles need you to have your control deflections set to maximum because they are so small and need all the help they can get.
The heavier something is the more effort is needed to move it. Heavier paddles have a lower response rate and lower overall power.
A paddle with a thin sharp section will "grab" the air more and hence accelerate more quickly. A fat blunt paddle will be more gradual in its response.
The further away from the rotor head you put the paddle the more air it is moving through and therefore as it is an aerodynamic device the more power it will have.
I would say the only type of paddle you really want to stay away from are those with a very thin section and long leading edge as they are so aggressive that the model will experience lots of "pitching" effects in fast forward flight as the section "grabs" the air.
As paddles control how the rotor system responds to inputs (both pilot and external..eg. wind..) we ideally want a system that responds to external inputs with an equal and opposite output. In simple terms a gust of wind should not make the model move off the spot it is hovering (in an ideal world). If when your machine is hit by a gust of wind it moves down wind away from the gust then your flybar is not responsive enough. If your model moved forward into the wind then it is over responsive. Clearly you can control these by changing the factors listed above.
Note. Changing the section of the paddles will not change the overall control power of the paddles but just the initial control response.
Generally paddles designed for 3D are light weight with a sharp section to give a fast and powerful response.
Paddles designed for F3C are large and heavy with a blunt section. This gives them good control power but a slower response rate.
Flybar weights can be used to tune the paddles. They have exactly the same effect as changing the weight of the paddles themselves. The more weight the slower the response rate and the lower the control power. In conclusion.. if your roll rate is too low then lighten your paddles or fit a longer flybar. If your model is "pitchy" on the elevator in fast forward flight then change to paddles that are fatter in section. Generally I leave flybar length as per the original manufacturer design as it's probably the least effective of all the options. Weight and size are the prime candidates for changing.
( 44 Votes )