Time in the box increases significantly as the Z distance increases. A
good target distance for a two-meter airplane is 150 meters.
Judge guidance for the Sportsman Cobra maneuver. Courtesy of Jim Hiller.
The theme for this month’s Model Aviation is “how-to.” Most of the articles that I’ve written since taking on the “RC Aerobatics” column have been about how to fly the
Sportsman sequence. I should have no trouble fitting that in
with the how-to theme!
In my last column, I left off with the first reentry to the
aerobatic box and one horizontal roll on center, which is
maneuver seven in the sequence. Maneuver eight is a Half-Reverse Cuban 8, which I covered in-depth in my September
2016 column, so I’ll skip ahead to maneuver nine—the Cobra
without Rolls.
I’d like to take a timeout and go back to the basics of how to
fly the aerobatic box because I’ve now sat in the judge’s chair
for the Sportsman sequence on several occasions during the
2017 season, and I have seen many easily corrected centering
errors.
Back to Basics
When you stand at the pilot’s station during an RC Aerobatics
contest, you should see three key guidelines on the runway. One
angles away from you at 60° to your left, another at 60° to your
right, and one extends straight out from where you stand. The
first two extend out to infinity and indicate the left and right
box boundary. All scored maneuvers should happen between
those lines!
Although we tend to be forgiving to Sportsman pilots, you
lose points based on the percentage of a maneuver that takes
place outside of that box. If you fly 50% of the maneuver out
of the box, that’s - 5 points immediately, before the judges start
taking off points for any errors!
There are two factors that you can control to improve your
ability to keep your maneuvers in the box. The first one is your
speed. Virtually every Sportsman pilot I watch is flying way too
fast! A typical Sportsman flight is done in a little more than 4
minutes from takeoff to landing. The goal is to fly well, not get
done fast! The rules allow you 8 minutes; you have almost twice
as much time as what you are using!
The second factor is your airplane’s distance from where you
stand. Consider the accompanying simple sketch that depicts
the view of the box from high above. I’ve drawn in two lines
going across the box, which represent potential Z lines of your
airplane flying parallel to the runway. Note that this creates two
30°/60°/90° triangles with the pilot standing at the 60° vertex
and the box line representing the hypotenuse of the triangle.
If your Z distance is 75 meters, as shown with the red line in
Photo 1, trigonometry tells us that the length of the long side is
130 meters, so the total length of the Z line is 260 meters. If you
push the airplane out to 150 meters, the length of the Z line
doubles to 520 meters—more than half a kilometer!
Now combine the two factors! If you are flying straight and
level at 100 kph ( 60 mph), which is a good speed for a Pattern
airplane, it should take you approximately 18 seconds to fly the
full length of the box if your Z line is at 150 meters. If instead
you fly at 160 kph ( 100 mph), which is not unusual for many
Sportsman pilots, and fly a 75-meter Z line, you’ll traverse the
box flying a straight line in less than 6 seconds. That cuts your
maneuvering and thinking time to a third of what it could be!
In short, slow it down and push it out!
The Cobra Without Rolls
The Cobra maneuver is, in my opinion, one of the most
elegant maneuvers in the Sportsman sequence when it’s done
well. A true Cobra maneuver typically has a rolling element in
the center of the 45° lines, but for Sportsman, we keep things
simple. Pull to a 45° line, push over across the center to a 45°
downline, and as you approach your entry altitude, pull to level.
Simple, right?
As always, be very conscious of whether your wings are level
before you initiate an elevator movement. With two pulls and
the push over the top, there’s plenty of room for you to make a
mistake. If the inside wing is low as you pull the first radius, the
airplane is going to start heading in toward you and your box
will start to rapidly shrink!
118 Model Aviation JULY 2017 www.ModelAviation.com
How to fly the Sportsman sequence
by Peter Vogel
vogel.peter@gmail.com
