Lesson 5: Approaches and Departures
Last time we discussed basic movement of controls for the helicopter in the context of cruise flight. We also took the opportunity to combine climb/descent and turns. Mastery of these basic maneuvers is essential to proper helicopter flight, and we will combine them further here for some more useful operations: approaches and departures. In case you are wondering why we have not discussed hovering, lets start with a short story.
When I was learning to fly my first two instructors would complete each lesson with hovering practice. To the ground observer, it was obvious why the FAA imposes strict rules against flying under the influence of intoxicating substances. To me, it was obvious why one should always wear clean underwear. I was completing my first lesson with my third instructor (an interesting character taking the winter off from flying in Alaska) and asked if we would do some hovering when we got back to the airport. He responded that it seemed ludicrous to waste my money on that since I hadnt mastered the basic controls while away from the ground. Instead, what he had me do was shoot approaches (a maneuver to a landing) and as we neared the ground we would slow to an airspeed and then depart. The next time around, we slowed further. This continued several times until ground speed slowed to zero and I found myself in a hover.
Helicopter operations can be defined in several categories, the most noticeable of which are enroute operations and ground reference maneuvers (which includes hovering). Just about anything you do with the aircraft will fall into one or the other of these categories. Enroute operations stress use of the aircraft instruments and looking outside the cockpit to ensure you are going where you want. Ground reference maneuvers are just that: keeping eyes outside the aircraft (except for the occasional scan of the engine instruments) to keep from striking the ground. Other examples of ground reference maneuvers include sideward flight, air taxi, pedal turns, and turns about the tail rotor.
Fundamental to doing approaches and departures is understanding what is expected (typically by other pilots, who need to understand your intentions, but also by your instructor) of you while operating near the airport. Assuming you are flying from a departure, the four legs of the pattern are the crosswind, downwind, base leg, and final. The crosswind leg follows your first turn after departure, and may be a climbing turn. You may still be climbing when you turn the downwind leg to be parallel to the runway. In the course of your downwind leg, you should begin your descent, and turn for the base leg toward your final approach leg, appropriately called the final. All turns should be 90 degrees, and to avoid fixed wing traffic, helicopters often fly a right hand pattern (all turns to the right). Consult the rules for operation at the airport of your choice. Sometimes airplanes fly right patterns, and sometimes helicopters fly left patterns. Either way, you should be avoiding airplanes, and this can be accomplished by staying inside the airplane pattern (staying closer to the airport and making tighter turns) and/or flying at a lower altitude. For this exercise, we should aim to be 600 feet above the airport elevation and within one half mile of the runway in the course of flying the pattern. Airspeeds should be 60 to 80 kts, unless it is obvious to have the aircraft at another speed. By the way, if you feel particularly inspired, try shooting your approaches to a taxiway or a grass strip adjacent to the runway.
Lets begin the flight where we left off last time and you are enroute in level flight. Get close to an airport and set yourself up to be parallel to the runway with the rabbit lights coming toward you. You should be a half to a quarter mile away, 600 feet above the field, and at 80 kts. Continue in that direction until you are abeam (directly opposite) the approach end of the runway (not the lights you want the tarmac). Slowly lower the collective until the aircraft begins to settle (lose altitude), and then decelerate to 60 kts while maintaining altitude.
When the aircraft reaches 60 kts, again lower collective until you are in a comfortable rate of descent (maybe 500 fpm). Dont forget to add right pedal as you change power settings.
When the aircraft begins to descend, start a 90 degree turn to the right. Maintain your descent and airspeed. Anticipate your turn to the runway.
When appropriate, begin a 90 degree turn to the right to line up with the runway. Again, maintain your descent and airspeed. Select a spot on the runway (or taxiway or grass strip) for landing. At this point, your spot should be near the approach end of the runway, but dont be too afraid to overshoot if you have to. Adjust collective to keep this spot centered in your exterior view. As your selected spot begins to loom large in the windshield, begin decelerating. Keep adjusting collective and cyclic to keep the spot where you want it (yeah I know define that it will come with practice). The goal is to be at 5 feet and 30 kts. As you approach 5 feet, be prepared to apply up collective to avoid hitting the ground.
If you get to 30 kts before you get to 5 feet, keep this airspeed. At 5 feet, move the cyclic forward. There should be no need to add collective unless you really are heading straight for the ground. Accelerate to 60 kts, pull back a bit on the cyclic, and begin climbing, while maintaining this speed. Feel free to add a little collective here to ensure an adequate rate of climb.
If you get to 5 feet before you get to 30 kts, move the cyclic forward and accelerate to 60 kts and depart as above.
As you cross 300 feet above the field, begin a 90 degree turn to the right, continuing your climb and maintaining airspeed. Maintaining airspeed here is essential to safe operation in case your engine quits. If you get to 600 feet before the point where you feel comfortable turning downwind, level off. If not, enter your downwind leg and continue climbing to 600 feet. Once established in the downwind leg accelerate to 80 kts.
In practice, pattern work is about exciting as doing the Indy 500 in a Ford Escort, but practice is what is required here. Continue in your downwind leg and repeat the pattern as before. Reduce your final speed to 20 kts, then 10, then 5. When you are comfortable cruising at 5 feet and 5 kts, consider slowing to a hover. If you want to make it a little easier, set the wind to be 10 kts and right down the runway.
Once you feel comfortable shooting an approach to a hover, you can begin departing from a hover. Again, just lower the nose by moving cyclic forward a bit to accelerate, but avoid adding collective. You can try beginning your climb once you have reached 15 to 30 kts, but make sure that you continue to accelerate as you climb until you reach 60 kts.
Effective Translational Lift
Effective translational lift (ETL) describes part of the phenomenon of the power required being greater in a hover than in forward flight. ETL kicks in at about 15 kts when the power to required begins to lessen, and typically results in a slight vibration in the aircraft when you hit this transition. ETL will also be effective if the aircraft is stationary but the headwind is 15 kts or greater. This is why you dont have to add power to depart from a hover: the power is already there and you just take advantage of the increased performance for climb and acceleration by speeding up.