PROGRAMMABLE MIXES: A TRADE-OFF
Mixing out unwanted tendencies during knife-edge is widely practiced, but like most things in aviation, there are tradeoffs to consider. Programmable mixes let you automatically mix another control with your primary input to reduce or eliminate some of the unwanted tendencies associated with certain inputs and maneuvers.
When you apply a lot of rudder to sustain knife-edge flight, for example, most planes tend to gently roll in the direction in which the rudder is being held. Although pilots routinely mix opposite aileron with rudder to cancel out the rolling tendency during knifeedge, the mix may prove contrary to what’s needed during another maneuver or end up causing a deviation somewhere else.
Many “tendencies” are held in check at higher speeds and only show up when the plane is flying more slowly. Some tendencies show up at high-throttle settings but not when the throttle is low. This means a lot of mixes are only appropriate at certain airspeeds and throttle settings. This partly explains why those who look to mixing as a substitute for developing better flying skills often find it difficult to advance beyond the initial success they had when the mix was first introduced.
In fact, you can travel across the country and observe fliers involved in an endless cycle of trying to “dial” into their radios the corrections that they could easily be making only to have to repeat the process each time conditions change, a new maneuver grabs their interest, or they fly a different airplane. You might think that programming the radio has become their hobby! Unless the only maneuver you intend to fly is knife-edge, the most efficient and effective use of programmable mixes is to limit your mixes to no more than 5 to 10 percent (15 percent max). If the tendency that you want to correct is slight, try a 5 percent mix; if it is more noticeable, try a 10 percent mix. Limiting each mix to 5 to 10 percent will help make flying easier without having too much impact on other maneuvers or causing you to do a lot of backtracking as your repertoire expands.
CLASSIC KNIFE-EDGE MIXING Exhibit A: Holding in left rudder during knife-edge flight results in the airplane also gently rolling left. Mix solution: A little right aileron mixed in with your leftrudder input cancels the roll tendency during knife-edge.
fourth points of a 4-point roll. Remember that although the rudder is applied in the opposite direction that the airplane is rolled during the first point, the rudder is applied in the same direction the plane is rolled during the third point. Another way of looking at it is that the rudder is applied “the other way” at the third point compared to the first.
When you perform a 4-point roll, first emphasize rolling to precise 90-degree points, with opposite rudder at the first point, a push at the second, and the same rudder at the third. Also keep in mind that the amount of rudder required during the brief knife-edge points in a point roll is much less than what’s needed to maintain altitude during sustained knife-edge flight.
Here again, the most common mistake is to neglect the elevator inputs at the start of the maneuver and during the inverted portion, and instead using a lot of rudder to hold altitude. You’ll get a better result from blending in a little up-elevator pressure at the start of the first 90-degree roll and forward-elevator pressure when rolling from inverted to the third point. Consequently, less rudder is needed during the knifeedge points, resulting in a cleaner roll with less tail movement and one that is likely to remain linear.
THE TAKEAWAY
A sensible amount of mixing can help make knife-edge flight a little easier, but your flying skills have the biggest impact on how well you perform. It’s true that developing better flying skills is challenging at times, causing some pilots to claim that they’re content where they are. But let’s face it: flying is much more fun when you’re doing it well and making progress.