Flight Technique/Master Cross-Box Combinations

Using crosswinds to your advantage

Using crosswinds to your advantage

When you watch really good aerobatic fliers, you’ll notice that they take advantage of all the airspace within the aerobatic box by performing maneuvers both parallel (X axis) and perpendicular (Y axis) to the runway, and consequently they enjoy greater flexibility and far more options when flying aerobatics. The “aerobatic box” is the airspace in which a pilot performs his maneuvers with good visibility. To remain in the box, a contest sequence will often feature a set of “cross-box” maneuvers on the Y axis to reposition the plane for an upcoming maneuver, to achieve a different viewing perspective, and (most important) to reposition the airplane in the event a strong crosswind forces the plane too close or too deep within the box. The practice of sequencing two turnaround maneuvers together will certainly prove helpful for intermediate-level sport fliers as well. Therefore, the objective this month is to highlight some of the turnaround-maneuver combinations on the Y axis that will enable you to use crosswinds to your advantage, rather than having to fight or fear them.

HAMMERHEAD INTO A HUMPTY BUMP

The most common Y-axis turnaround combination is the hammerhead into a humpty bump, and vice versa. This combination is ideally suited to set up any center-box maneuver that starts from a lower altitude and requires a moderate to high entry speed. This combination also works well to reposition the airplane to either the front or rear of the aerobatic box, depending on which direction the plane is rolled in the first maneuver. When the hammerhead is the first maneuver, start parallel to the runway and pull to vertical near the end of the box. If you’ve been following this turnaround series, you know that there are several crucial points pertaining to vertical uplines, starting with the importance of pulling up to the vertical with the wings level. If the upline is not perfectly vertical at the start, everything that follows becomes much more difficult. Therefore, you must pull up to the vertical with the wings level, as well as neutralize the elevator at the exact instant that the plane points straight up to have a chance at performing a good hammerhead pivot and a good half loop on top of the humpty. The throttle position should be high, and all pulls to the vertical should be smooth but completed quickly to establish the upline before losing too much speed. The uplines then need to be maintained until sufficient altitude has been achieved to perform the subsequent downlines without feeling rushed.

When the altitude is right, reduce the throttle below 1⁄4 leading up to the hammerhead pivot and work to maintain the vertical line as long as possible, as if you were trying to hover. When the plane approaches zero airspeed at the top of the upline, pivot into the wind, using full rudder to achieve a nice tight pivot. The secret to performing good hammerheads is maintaining some power approaching the pivot to generate enough propwash over the tail to keep the controls effective throughout. As a consequence, you’ll likely need to apply a little right rudder to counter the left-turning effect of the propeller slipstream (propwash) as the airplane slows along the upline. The exceptions are when you need left rudder to correct for wind or when the upline wasn’t truly vertical.

The right balance of power and timing is the key to performing nice tight pivots. When the airplane performs a wingover rather than a tight pivot around the wingtip, the pivot was initiated too early while still climbing and/or the throttle was too high. Wait until the airplane comes to a stop before pivoting and/or use a lower power setting (but not to idle or the ability to consistently control the pivot will be lost). On the other hand, if the airplane is hesitant to pivot or slides backward, you waited too long to initiate the pivot and the power setting was too low; correct this by better timing and using a higher power setting.

THE SECRET TO PERFORMING GOOD HAMMERHEADS IS MAINTAINING SOME POWER APPROACHING THE PIVOT TO GENERATE ENOUGH PROPWASH OVER THE TAIL TO KEEP THE CONTROLS EFFECTIVE THROUGHOUT.

Near the end of pivot, idle the engine to slow the descent and start smoothly taking out the rudder the instant the airplane points straight down. Be careful not to completely neutralize the rudder all at once or the sudden disappearance of the rudder force will cause the tail to pendulum and deviate from vertical.

The next step after establishing the downline is to perform a 1⁄4 roll to orient the plane to pull out on the Y axis (into the wind). Make sure that you establish vertical lines before and after the roll long enough to give yourself time to think about which way to roll the airplane and what altitude to pull out at. If you feel like you don’t have time to think on the downline, you’ll have to extend the upline longer/higher.

In competition, all maneuvers must start and end in level flight. Along with being an important competition requirement and a stamp of proficiency, establishing level flight between maneuvers affords you time to anticipate what you’re going to do next. As a rule, the stronger the crosswind, the farther you should fly across the box before pulling into the humpty bump. The humpty will require full throttle to maintain positive control over the top. So again, you’ll likely need right rudder to correct for propwash nearing the top of the upline. When you pull into the loop, considerable P-factor (asymmetric propeller thrust) will try to yaw the airplane to the left, so more right rudder will be needed to keep the loop tracking straight until you idle the engine on the back side of the loop. Ultimately, the ease of the loop will reflect whether the preceding upline was vertical or not. If the upline wasn’t vertical, the loop will likely magnify the deviation. On the other hand, a perfect vertical line ensures a successful loop over the top every time. The role of the rudder is simply to perfect it.

The loop will tend to elongate once the nose points down and the plane starts accelerating, resulting in a low finish that shortens the amount of time you’ll have to complete the downline. To keep the loop round, you will have to steadily increase the elevator input as soon as the airplane has passed the top of the loop. Around the same time you start increasing

ULTIMATELY, THE EASE OF THE LOOP WILL REFLECT WHETHER THE PRECEDING UPLINE WAS VERTICAL OR NOT.

the elevator, reduce the power to idle to slow the descent and start getting ready to quickly neutralize the elevator at the instant the airplane points straight down. Now establish the downline long enough to give yourself time to think about which way to roll so that the pullout brings the airplane back to center box.

HUMPTY BUMP INTO A HAMMERHEAD

The Y-axis turnaround combination that starts with a humpty bump followed by a hammerhead makes a great impression. The humpty is entered parallel with the runway near the end of the box. This time, perform a 1⁄4 roll on the upline in the direction in which you intend to loop over the top (into the wind). Pull over the top and perform a half roll on the downline to set up the pullout on the Y axis. To be certain that the all-important upline starts out and remains truly vertical, maintain the initial upline for at least a few seconds before performing the 1⁄4 roll and then continue the upline after the roll until it matches the length of the line before the roll. The standard method for matching the length of the lines is to count “one-two” along the line before the roll, and then add an extra beat to the upline after the roll to account for the steady loss of airspeed during the climb. This technique will not only reinforce consistency but also buy you the altitude you’ll need to perform the later downline without feeling rushed. The objective is to pull over the top of the humpty into the wind, and that’s set up by the direction you roll on the upline. A simple technique for judging the 1⁄4 roll is to input the roll in the direction that you plan to loop over the top (into the wind). Put another way, perform the 1⁄4 roll so that the top of the plane is facing into the wind.

After you complete the pull over the top, reinforce consistency along the downline using the counting method. However, because planes tend to build speed quickly pointing straight down, you may need to abbreviate the count to “one-two” leading up to the roll and just

THE OBJECTIVE IS TO PULL OVER THE TOP OF THE HUMPTY INTO THE WIND, AND THAT’S SET UP BY THE DIRECTION YOU ROLL ON THE UPLINE.

IT’S MUCH EASIER TO OVERCOMPENSATE FOR THE WIND AND THEN LET THE WIND DRIFT YOU BACK THAN IT IS TO DISCOVER THAT YOU HADN’T COMPENSATED ENOUGH.

“one” after the roll prior to pulling out. When you’re getting ready to enter the hammerhead on the Y axis, keep in mind that despite your best efforts, some amount of wind drift will likely occur during the maneuver; it’s better to start farther upwind than not far enough. It’s much easier to overcompensate for the wind and then let the wind drift you back than it is to discover that you hadn’t compensated enough for the wind and you’re left fighting against it to get where you want to be.

During the hammerhead, you have the option to place the 1⁄4 roll on either the up or downline. Or you could instead fly a second humpty bump and push over the top just to make it more interesting. This is where a small handheld model will be immensely helpful to visualize how these turnarounds fit together before you fly. If you don’t have a pretty good idea what to do before you take off, what are the odds that you’ll figure it out while speeding around the sky at 75mph? A little planning goes a long way to ensuring some level of success right away.