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Hammerhead (Stall) Turn
Now let's take a look at the Stall Turn. Here's the description directly from the Competition Regulations. The ellipsis (...) indicates that the part of the description dealing with rolls, as done in the higher classes, has been omitted.
||Model executes one-quarter (1/4) loop to a vertical track, performs a stall turn through 180 degrees, then recovers with another one-quarter (1/4) loop to level flight in the direction. ... The length of the vertical segment is not a judging criteria. Downgrades:
- Model not level at start and finish.
- Track does not become exactly vertical.
- Model not vertical at start and finish of ... stall turn.
- Return path not parallel to entry path.
- Exit not at same altitude as entry.
- Pivot radius greater than 1/2 wingspan.
- Pendulum movement after stall.
- Loop segments not round with same size and radius.
- There is more to this maneuver than meets the eye, so let's take a close look at this it, one section at a time.
- Model not level at start and finish. As with every maneuver, the Stall Turn starts and ends with STRAIGHT AND LEVEL FLIGHT! You're probably getting tired of hearing me say those words, but get used to it. They are probably the most important words you'll read on these pages. If your entry is not straight and level, the rest of the maneuver will fall apart rapidly. It's also a downgrade. Get it right!
NOTE:The one-quarter loop begins on the center line! This is vitally important. It is easy for the judges to see where center is, and just as easy to provide downgrades when you miss starting the 1/4 loop there.
- Track does not become exactly vertical. First, let's review the definition of TRACK: the trajectory or flight path of the center of gravity of the aircraft over the ground. Notice that it doesn't say anything about the attitude of the aircraft. They will be identical in no-wind conditions, but otherwise will be different to compensate for wind drift. Many new pattern pilots try to make the
attitude of the plane vertical. If there is any wind, the plane will drift back in the downwind direction. This will bring immediate downgrades from the zebras -- oops, I mean judges. Sorry, too much football today.
Note that we are flying in three dimensions, so there is also an excellent possibility that the plane will try to drift left or right as well as backward. I don't know about your field, but the wind is seldom down the runway at mine. Left or right drift is corrected with Rudder. You know, the other control over on the left stick with the throttle. Use as much rudder as needed in the opposite direction from the drift to stop the drift. In other words, if the plane is drifting to the
left (looking at the top of the plane), apply right rudder. One of my pattern cronies here on the Prairie was having trouble with his Stall Turns last summer and asked me for help. Every time he'd start to drift left, I'd say "Right Rudder!" He'd just keep drifting left, so I repeat my "Right Rudder" suggestion. After several attempts he finally said in exasperation, "I've got right rudder in it!" I told him "Put in some more!" Use whatever type
and amount of control input it takes to correct the problem as quickly as you can, because it will only get worse if you don't.
Another possible culprit that causes right or left drift is our old friend and nemesis, wings level. If your wings aren't perfectly level when you start the 1/4 loop, the plane's heading will be off in the direction of the low wing. You've violated the "track being vertical" rule even before your start the maneuver. Remember, the track needs to be vertical, not the attitude.
||A word here about the loop from your friendly webmeister. Use a nice large radius on your loop. This will allow you and the judges to get a good look at the TOP of your plane during the vertical segment. This is very important in seeing any wind drift as soon as possible -- so you can correct it at soon as possible. It also presents the maneuver to the judge in a much clearer manner, and allows better timing of the stall turn.
- Model not vertical at start and finish of the ... stall turn. This may seem a little strange, especially since the maneuver must be wind corrected. However, just before the stall turn, the model must be put into a perfectly vertical attitude relative to the ground! I know it sounds difficult, and it does require some timing and practice, but it can be done. The airplane must remain vertical throughout the 180 stall turn, then wind
correction is reapplied as necessary.
- Return path not parallel to entry path. The track of the airplane on the downward leg following the stall must be parallel with the upward track prior to the stall. Wind correct as required. If the wind is down the runway, down elevator will be required.
- Exit not at same altitude as entry. Sounds elementary, but it is often overlooked. Following the 1/4 loop at the end of the downward line, the exit altitude must be the same as the entry altitude.
- Pivot radius greater than 1/2 wingspan. When executed perfectly, the airplane should pivot about it's own Center of Gravity. The worst case allowed with downgrade is for the plane to pivot around its wingtip (radius of pivot = 1/2 wingspan). This requires some technique. There are two basic problems usually associated with stall turns. The first is the flop, caused by waiting too long before applying rudder, allowing too much airspeed to bleed off.
Problem two is flying through the stall, not pivoting. This is caused by applying rudder too soon!
Here are two things that will help you with your stall turns.
- Add a little throttle during the Stall Turn. There are several ways of doing this. One is to use the stick to give a couple of clicks of throttle just before the stall turn. Another is to set the throttle trim to a high idle during the maneuver. This is your webmeister's favorite, and it's particularly simple if you have a computer radio. Simply mix Throttle into Throttle and control it with a switch -- just flip the switch to high idle during the turnaround preceding the stall turn
and flip it back to low idle during the next turnaround. That let's you maintain the low idle setting needed for takeoff and landing, but still give the extra boost needed for the stall turn. Both of these methods will cause airflow over the rudder during the stall, increasing it's authority and giving a much cleaner stall.
- Practice, Practice, Practice!!! There is no other way to get the timing correct than to practice it until you can do it right every time.
- Pendulum movement after stall. This occurs because the rudder stick is released and snapped back to center after the stall. There are two remedies for this condition. Try both and see which one works best for you.
- Hold the rudder in until the stall is completed and the airplane is heading down, then release it slowly! This will hold the nose of the plane slightly past vertical after the stall, but at least the tail won't waggle.
- Release the rudder during the stall. After the plane starts to pivot, approximately when the nose of the airplane is horizontal, start releasing the rudder. All of the rudder should be released when the nose of the plane reaches vertical. This is your webmeister's favorite, and has been for many years.
- Loop segments not round with same size and radius. This should be a no-brainer. Both the 1/4 loop at the beginning and at the end of the stall turn must be the same size. It's harder to do than the say, so get out there and burn some fuel.
Developed by Geistware of Indiana© ., 1999.
Updated December 1, 2000