Differential Spoilers & Full House Wing


Flying Wing

Normal Flying-wing aircraft uses two control surfaces as Elevons to control pitch and roll. In some cases, rudders are added to the winglets to control yaw. Differential spoiler takes advantage of splitting elevons into 4 independent control surfaces: normal elevon functions are reserved for pitch and roll control, but yaw control is done by using two surfaces on one side of the wing to create drag force thus controlling yaw motion, emulating rudder control. If calibrated correctly, it will ensure pilot has smooth yaw control via rudder input during take-off and landing as well as allowing the pilot to compensate for slip/skid compensation during turning (similar to differential aileron).

Left Yaw by inducing drag on left wing:

Right Yaw by inducing drag on right wing:



The amount of rudder input into the differential spoilers is controlled by DSPOILR_RUD_RATE. A value of 0, totally disables this feature. The default is 100(%). Conventional planes and gliders will probably want to change this.


Gliders can utilize differential spoilers to implement flaperon style functions but with the option of crow brakes. Crow operation is shown below, where the inner and outer spoiler panels on a wing side are moved in opposite directions to implement the crow brake, but move together as aileron panels. The inner panel can be extended further than the outer to provide flap effect. This allows aileron, flap, and crow action to be implemented from the two control surfaces on each side of the wing.

../_images/crow.jpg ../_images/diffspoilers.gif


To use differential spoiler function, the airframe is required to use have 4 control surfaces (2 on each wing).


Now setup your 4 channels using the SERVOn_FUNCTION parameters:

Function Name

Function Number


Differential Spoiler Left 1


This should be set to the outer left servo

Differential Spoiler Right 1


This should be set to the outer right servo

Differential Spoiler Left 2


This should be set to the inner left servo

Differential Spoiler Right 2


This should be set to the inner right servo

You can adjust the direction of each servo using the SERVOn_REVERSED parameters, and swap channels to get the right movement direction for elevons and rudder. Flap operation is also possible. The weighting of flap input to the movement of the outer and inner control surfaces can be set using DSPOILER_CROW_W1 and DSPOILER_CROW_W2 respectively. The default value of “0” for each parameter is no flap action.


manual flap control is controlled by any RC channel whose RCx_OPTION is set to “208”.

Differential Spoiler options

DSPOILER_OPTS parameter gives several options that can be used to tailor the dspoiler functionality to your aircraft. They can be used to setup a ‘full house’ wing on a glider. DSPOILER_OPTS is a bit-mask each, bit enables different functionality.




Pitch control, this bit enables or disables pitch control output using the differential spoilers. 1 uses elevons as source for use with a flying wing, 0 uses ailerons as source for use with a traditional plane


Full span ailerons, 1 uses both the inner and outer control surfaces for roll control 0 just used the outer control surfaces


Progressive crow, 0 gives crow brakes - the inner control surfaces are moved down and the outer surfaces moved up at the same time 1, for 0 to 50% flap only the inner surfaces are moved down then from 50% to 100% flap the outer surfaces are moved up, this gives traditional flaps first then crow brakes

Defaults are bit 0 and bit 1 set to 1. Conventional planes and gliders will probably want to change bit 0 to “0”.

DSPOILER_AILMTCH allows the downwards travel of the inner surfaces to be limited to a percentage of their full downwards travel. This only affects the travel when the control surfaces are used as full span ailerons or for differential yaw. Using this parameter a flap control surface with lots of downwards travel can still be utilized for full span ailerons. Upwards travel of the control surfaces is unaffected.

Crow Mode Switch

If Differential Spoilers are used, setting an RCx_OPTION channel to “87” will allow the control of CROW aileron (outer spoilers) operation.

  • HIGH position: No change to CROW deflection amount or use of progressive crow.

  • MIDDLE position: force progressive crow, assuming DSPOILER_CROW_W1 is non-zero, even if DSPOILER_OPTS bit 2 is zero.

  • LOW position: effectively sets DSPOILER_CROW_W1 to zero. Only inner spoilers move with FLAP channel, ie normal flaps.

This allows live changes to CROW operation on approaches so that speed braking and descent rates can be changed during the approach.