Vintage Instructor THE
BY Steve Krog, CFI
The lost art of slips
hile recently attending the 25th Annual Sentimental Journey Fly-In held at Piper Memorial Airport in Lock Haven, Pennsylvania, my friend Mark Stewart and I were watching airplanes and their pilots hopping rides and demonstrating their piloting techniques doing takeoffs, landings, and flybys. Most every airplane, when on the approach to land, employed a forward slip to achieve a touchdown on the numbers and make the first turn-off comfortably and safely. Mark turned to me and commented, “The slip really is a lost art and a maneuver many pilots really don’t understand or use today.” I agreed. The slip, when implemented correctly, is a useful and safe tool for pilots young and old, provided it is practiced with some regularity. But with the introduction of flaps it has become a lost art, even though pilots flying flap-equipped airplanes should understand the slip and be able to perform it when needed. Ask yourself these questions: “When was the last time I performed a slip, and how often have I practiced slips?” When conducting flight reviews I frequently ask the individual to demonstrate a 50-foot obstacle short-field landing using a slip. The pilot will often look at me and state, “I haven’t done a slip in a long time!” “Sure you have,” I’ll reply, “you just didn’t realize it. How do you set up your approach for a crosswind landing? Each time you make
34 AUGUST 2010
a crosswind landing, you’re executing a side slip.” There are two types of slips: the forward slip and the side slip. In the simplest of definitions, the forward slip is used to lose altitude, while the side slip is used for runway alignment. Let’s take a look at their respective similarities and differences. The forward slip is often em-
“When was the last time I performed a slip, and how often have I practiced slips? ployed when a pilot has set up for the final approach to land and has excess altitude, when making obstacle landings (especially at short fields), or when making a spot landing. A forward slip allows for the aircraft to maintain a straight-line track over or on the runway centerline while on approach. However, when maintaining the track, the nose of the airplane is not aligned with the runway and needs to be realigned before landing. The side slip is often employed when making a crosswind landing or to align the airplane with the runway centerline. The nose of the airp lane (long itudin al axis) remains aligned with the runway centerline.
How to Practice Forward Slips The next time you make a pleasure flight, climb to an altitude of about 2,500 feet above ground level (AGL). Level off and align your airplane with a straight road that is also aligned with the surface wind. If the wind is generally from the south, fly south over a north/ south road. Reduce the power to the setting used on final approach to land and establish the final approach glide speed. Apply left aileron, lowering the left wing about 10-15 degrees (similar to a shallow bank turn). The airplane will want to turn left. Now apply opposite, or right, rudder using just enough rudder that the airplane continues to track in a straight line over the road. The airspeed will give you erratic readings whenever doing slips, so it is more important to focus on maintaining the correct descent or glide attitude. You may need to apply very slight forward pressure on the stick or yoke to do so. Continue the descent and track for 1,000 feet of descent; then return to cruise flight by slowly taking your foot off the right rudder and bringing the left wing back to a level-flight attitude. If you haven’t done a slip in a while, setting up for and holding the forward-slip attitude will feel awkward at first, as will the return to level flight. A few repetitions will significantly increase your comfort and coordination. Now try executing the forward slip with the right wing down and
applying left rudder. Hold your descent attitude and track over the road for 1,000 feet and then return to level-cruise flight. A forward slip to the right will often feel more awkward than the forward slip to the left. Try practicing the forward slip from a safe altitude a few more times, increasing the wing-down angle a little more each time. You’ll soon find that you will reach a point where you run out of rudder and cannot hold the straight line track. Now you know how far you can go with the slip in your airplane and still have full directional control. Congratulations! You’ve just acted as a “test pilot” and found the limits of your airplane in a slip. If your aircraft is equipped with a vertical speed indicator (VSI), note the rate of descent while holding the plane in the forward slip. Compare it to the normal rate of descent used when flying your final approach. Once comfortable entering and exiting the forward slip, you’re ready to give it a try in the traffic pattern. Fly a normal pattern, but intentionally maintain some excess altitude. If you normally turn final at approximately 500 feet above the ground, maintain altitude and turn final at 800 feet above the ground. Once established on final approach with power reduced and normal glide attitude established, enter into a forward slip to eliminate the excess altitude. Do not hold the airplane in the forward slip all the way to your normal level-off altitude. Rather, discontinue the slip at about 50 feet above the ground, giving you plenty of time to focus on and establish the proper landing attitude.
How to Practice Side Slips As mentioned earlier, the side slip is generally used for a crosswind landing. Even though you’ve
been making crosswind landings for a long time, you may want to practice the side slip. Again, climb to an altitude about 2,500 feet above the ground. Level off and align your airplane with a straight road that is perpendicular to the surface wind. If the wind is generally from the south, fly over an east/west road. Reduce the power to the power setting used on final approach to land. Establish final-approach glide speed. If the wind is from the left, apply
left aileron, lowering the left wing about 10-15 degrees (similar to a shallow bank turn). The airplane will want to turn left. Now apply just enough opposite, or right, rudder so that the nose of the airplane—or longitudinal axis—remains aligned with the road. Add a little power, perhaps 100 rpm. The airspeed will give you erratic readings whenever doing slips, so focus on maintaining the correct descent or glide attitude. You may need to apply very slight forward pressure on the stick or yoke to do so. Continue the descent for 1,000 feet, maintaining alignment with the road; then return to cruise flight by slowly taking your foot off the right rudder and bringing the left wing back to level flight. Turn the airplane 180 degrees and again align it with the road. This time the crosswind is from the right. Lower the right wing 10-15 degrees and apply just enough left
rudder to maintain alignment with the road. Add 100 rpm and continue with the side slip for 1,000 feet of descent. Then level off and resume cruise flight. If you’ve allowed the airplane to drift away due to the wind, add a bit more wing-down aileron, causing the airplane to move back to the road. Once over and aligned with the road, adjust the amount of aileron and rudder to remain over the road. After trying the side slip both left and right several times and reaching your comfort level, it’s time to give it a try in the traffic pattern. If you are truly landing with a crosswind, some level of the side slip will need to be maintained throughout the approach and landing. In a tailwheel airplane the main gear wheel most into the wind will touch down first, followed by the other main gear. This is necessary to maintain airplane alignment with the runway centerline. Then the tail wheel will touch down. From this point forward, follow through with the normal crosswind landing inputs. The slip is one of the basic maneuvers that, when understood and practiced, will give the pilot an added tool for safely putting the airplane exactly where he or she wants on the approach to land. A slip can be put in, taken out, or adjusted as needed to modify the rate of descent or runway alignment (when landing with a crosswind).
The descriptions for establishing and practicing forward and side slips described in this article generally apply to fixed-gear aircraft with no flaps. However, slips can be used in most flap-equipped aircraft. Consult the pilot’s operating handbook for flap-equipped aircraft before practicing slips, as they may recommend not doing slips when flaps are extended beyond the halfflap setting.
VINTAGE AIRPLANE 35