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Radio Requirements

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Radio gear and programming / mixing requirements for Le Fish are relatively modest, but it is important to meet them in order to get the best performance from your plane.

Transmitter RequirementsEdit

Generally speaking, a 6 channel or better transmitter will be required for Le Fish, as most 4 channel radios do not provide flaperon or snapflap mixing, both of which are mandatory for best performance.  Dual rates and exponential are also very important; generally, any transmitter that supports flaperon and snapflap mixing will also feature dual rates and exponential on the primary flight controls (aileron, elevator and rudder).

One inexpensive option is the Turnigy 9X from Hobby King. See the Turnigy 9X Programming Guide for the mixing required for Le Fish.

Minimum transmitter capabilitiesEdit

  • Dual rates for aileron and elevator
  • Exponential for aileron and elevator
  • Flaperon mixing
  • Snapflap mixing

Recommended transmitter capabilitiesEdit

  • 4 Axis reflex/camber control on the flap stick
  • Optional: Ability to add spring centering to flap (throttle) stick for 4 Axis control

Servo & Battery RequirementsEdit

Le Fish requires only four servos, sized appropriately to intended build of the plane. Ultralight builds will be well-served with smaller, lighter servos, while midweight and traditional builds - which will see higher average airspeeds and in-flight surface loads - will require stronger servos. 

Builds of 25oz (700g) or less will be well-served by the Hitec HS-65MG or equivalent.  Heavier builds will benefit from bigger, more powerful servos; the Hitec HS-85MG or equivalent would be a good choice. The original Le Fish prototype was built using inexpensive standard size servos and they worked fine as well.

Metal gear servos are recommended for best durability. The faster and more precise the servos, the better; most builders use a 6V NiMH battery to get the best performance from the aircraft. 6.6V 2S LiFePo4 (also known as LiFe) will also work fine, so long as the receiver and servos can tolerate the higher voltage of those packs. Lithium Polymer (Lipo) and Lithium Ion (Li-Ion) batteries are not recommended for Le Fish due to the rough-and-tumble nature of Le Fish flying and the fire risk a bad crash with Lipos or Li-Ions could cause.

Mixing RequirementsEdit

Besides requiring two aileron servos, dual rates and exponential, Le Fish requires only two mixes for best performance: Snapflaps and 4 Axis. Snapflap mixing is mandatory, 4 Axis is a "really nice to have" and most radios that support snapflap mixing should support 4 Axis as well.

  • Snapflaps aka "Elevator-to-Flap Mixing": This mix is turned on at all times. When you deflect the elevator, the trailing edge moves. If you give up elevator, the trailing edge of the wing droops (camber), if you give down elevator, the trailing edge of the wing raises (reflex). You need very little of this; about 3-5mm each direction is usually plenty. This mix makes a huge difference when turned on and has absolutely no drawbacks unless you use too much or screw up the mix and have the trailing edge moving the wrong direction. There is absolutely no good reason not to use it at all times and you will fail to get maximum performance from the plane without it.
  • 4 Axis aka "Flaperons on a Stick": This mix ties control of the trailing edge to the position of the flap stick (aka throttle stick). Center stick (aka half throttle) is neutral trailing edge. Forward stick (full throttle) is full reflex. Back stick (idle throttle) is cambered trailing edge. We use this at whim to help improve snap/spin figures, to help penetrate (reflex) or float (camber) as needed, and as landing assistance (not so relevant on the ultralights but very useful on the heavier traditional aerobats). Go for as much total travel as possible, as much as the aileron portion of the flaperon movement has (around 40-45º each way).
  • Important: Sometimes people think that snapflap mixing is something we are doing manually with the flap stick, that is not the case at all and would be a hassle. Snapflap and 4 axis are two separate things, the 4 axis allows you to override (cancel out and in fact reverse) the snapflap when doing so is beneficial (i.e. snaprolls).

Snapflap MixingEdit

Snapflap mixing, also known as "elevator to flap" mixing on many radios, is mandatory for achieving the best performance out of Le Fish. Failing to use snapflap mixing will prevent you from achieving full performance from the aircraft, and there are absolutely no drawbacks to using snapflap when it is setup properly. So... use it ;-)

With snapflap mixing (assuming upright flight):

  • When you give a nose up elevator input, the trailing edge of the wing droops down slightly, adding camber to the wing
  • When you give a nose down elevator input, the trailing edge of the wing raises up slightly, adding reflex to the wing
  • In both circumstances above, the net result is that the camber or reflex added serves to generate increased lift in a direction complementary to the commanded elevator input

This results in the aircraft being able to turn / loop harder and tighter while simultaneously maintaining more speed and energy than if snapflap mixing were not turned on.  Snapflap mixing is very commonly used on F3F and F3B planes to maximize turning performance, and aerobatics gliders absolutely benefit from this as well. Many aerobatics airfoils - such as the MG-05 and TP42 - are designed with the expectation that the pilot will use snapflap mixing at all times.

When properly setup, the trailing edge will move only about 3-5mm (1/8" - 1/4") in each direction (measured relative to neutral) when snapflaps are applied. Even though it's such a tiny amount, the effect in flight is absolutely noticeable and you will not achieve maximum performance without it. Conversely, too much snapflap mixing will cause the plane to slow down and lose speed.

Dialing in the mix is an extremely simple process of finding the amount which causes the plane to "bang" a turn - simply increase the mix until the plane bogs down in a turn, then back it off slowly from there till you get the absolute best turn / loop performance.

4 Axis ControlEdit

See the 4 Axis Flying page for more information on how to fly using a 4 Axis setup.

A "4 Axis" control setup refers to setting up the flap stick (throttle stick) with mixing to control the flap portion of the flaperon servo movement. It is a style of transmitter setup that originated in France and has been used with great success on many different types of gliders - though it offers some special advantages for aerobatics gliders.

  • When the flap stick is at the center of its travel, the trailing edge is neutral.
  • When the flap stick is at the forward (upward) limit of its travel, the trailing edge is reflexed (raised).
  • When the flap stick is at the rearward (lower) limit of its travel, the trailing edge is cambered (drooped).
  • Many times, the flap stick is modified with a spring return, so that it self-centers the same as the other stick.

A 4 Axis setup allows you to dynamically and immediately modify the shape of the wing in whatever way seems most advantageous for a given situation.  It absolutely allows an increased degree of control over the aircraft, in much the same way that adding rudder provides a greater degree of control versus aileron & elevator control only.

For aerobatic aircraft, 4 Axis control is used to both augment as well as override / reverse the influence of snapflap mixing. Both scenarios prove vitally important, especially for UltraBatic / VTPR aircraft.

Because snapflap mixing increases the lift the wing generates due to a given elevator input, this can make the wing harder to stall, or make it stall less cleanly, causing snaproll and spin figures to be more difficult to enter and/or less visually appealing.

By using a 4 Axis setup, you can temporarily override the effect of the snapflap mixing and in fact decrease the lift the wing generates. By doing so, you can create a sharper, tighter and more violent stall - which is in fact desired when commanding a snaproll or spin entry.

At the same time, should the lift suddenly die off, you can use a 4 Axis setup to apply a small amount of additional camber - enabling the plane to maintain altitude or even climb out while other planes are forced to land. You could do the same thing inverted, if you liked, by adding reflex - which becomes "camber" when upside down!

Another frequently used application of 4 Axis is in the context of a low altitude "save". For example, you are recovering from a maneuver and realize you don't have quite enough altitude to "pull out" in time. By immediately pulling full camber via 4 Axis - along with your "up" elevator input - the plane will make an extremely tight pull out, thereby preventing the crash that would otherwise be guaranteed. And of course it would work the same way inverted, by pushing full reflex along with your "down" elevator input.

These are just a few basic examples of how 4 Axis can be applied to aerobatics planes. Most radios that support flaperons and snapflap mixing should be able to support 4 Axis mixing as well.

Please see the 4 Axis Flying page for further information.

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