One of the joys of flight is the ability to maneuver vertically, rather than be restricted to the two-dimensional playground of earthly pursuits. This is new territory for beginning pilots, who must be taught the right—and wrong—ways to manage ascent and descent.
As with all airplane maneuvering, proper altitude changes are based on the foundational formula “power plus attitude equals performance.” If maximum performance is desired, an airspeed or angle-of-attack recommended by the aircraft manufacturer is established by adjusting pitch attitude, paired with the optimal power setting. For climbing, full or recommended climb power is usually employed, and for descent or landing approach, a power setting that produces the desired descent rate is selected.
When discussing climb technique, it’s easy to confuse high power setting with increasing lift. It’s the wing that generates lift, not the engine. However, excess propulsive thrust, over that needed to maintain level flight, can be utilized to either increase speed or climb to a higher altitude. In climbing, we point the nose up and let the engine pull us up the hill. If we want to get to altitude as quickly as possible, we set the wing’s angle of attack to its most efficient increment, commonly with reference to the airspeed indication.
This climb speed is determined by minimizing the two sources of drag acting against the airplane. If speed is too low, meaning angle of attack is too high, induced drag builds up, as the wing is working extra hard to make lift. If speed is too fast, parasite drag becomes excessive, created from the increased wind resistance. At the Goldilocks speed both drag producers offer their least input, we achieve our best climb performance.
The aircraft manufacturer’s testing and computing have usually resulted in two airspeed targets for climbing. VX, or best angle-of-climb speed, produces the most altitude for a given amount of forward motion. We want to clear that 200-foot pine tree off the end of the runway by going up, not moving rapidly toward it, so flying at VX, found close to stalling speed but still well away from it, is our best option.
In the absence of any obstacles ahead, we’re more interested in reaching cruise altitude as soon as possible, where we can level off and use that excess engine power to pick up speed. VY, or best rate-of-climb speed, is the speed that gives the most altitude for a given unit of time, found somewhat higher than VX on the airspeed scale, but not so fast as to get into parasite drag rise.
It may be that we’re not in a hard-pressed hurry to get up to altitude as soon as possible, being primarily interested in getting farther down the road toward our destination. So, we may adjust pitch attitude downward and pick up a bit more speed, termed a “cruising climb” procedure, employed as soon as we’re high enough to no longer mash our noise footprint against sensitive ears on the ground. This cruiseclimb may not decrease the rate of climb as much as you think, because increased airspeed generates more lift from the wing and, in the case of a fixed-pitch propeller, the engine rpm may rise to add horsepower. Although optimum, VY is simply in the middle of a fairly broad lift-over-drag curve. Added speed also brings better engine cooling and a wider view of the traffic ahead as the nose is lowered.
Power Management
Engine power is our altitude producer, so any thrust reduction during our climb should have a purpose, in light of its negative consequences. There’s rarely any reason to pull the throttle back from full when climbing with a fixed-pitch propeller.
Most F/P props are a compromise between takeoff and cruise performance and, given that most of our time is spent at cruise, they’re usually biased more toward cruise pitch. At low speed during climb, the engine is probably generating about 70 percent of rated power, so engine wear is hardly a consideration.
Constant-speed propellers, on the other hand, allow the engine to achieve full rpm and all available horsepower from the get-go, greatly enhancing takeoff acceleration and climb rate. High propeller rpm generates noise, so it’s common practice to reduce rpm as soon as any obstruction threats are below the flight path, perhaps preceded by nudging back throttle to a matching manifold-pressure number if you’re a traditionalist. The resulting climb at 75-80 percent of rated horsepower may not match POH max-performance numbers, but the engine and airport neighbors are happier.
Optimizing climb performance requires paying attention to small matters, like leaning the mixture to a best-power setting to avoid an overly-rich mixture at altitude, which would rob horsepower. Another frequent cause of lost climb rate is keeping your feet flat on the floor. P-factor is then offset by holding right aileron to keep the heading constant, and the slip indicator is out of center by a quarter or half of the ball or marker, showing that the airplane is flying sideways in the climb. The resulting drag increase slows climb rate. Putting your right foot on the rudder pedal and neutralizing the ailerons cancels the drag and the VS1 goes up a little more.
If you’re flying in thermal turbulence, you can get to altitude quicker by pausing in the updrafts and minimizing time in the downdrafts. Using a slower-than-VY climb speed when you’re being pushed upward in free lift can briefly double the normal rate of climb indication. Conversely, resist the temptation to yank the nose up and slow down in sinking air. Instead, fly at VY or more to quickly get through the downdraft and back into neutral or rising air.
Topping Out
Most beginner pilots level off their climb by immediately pulling the throttle back to a cruise power setting, leaving the nose high and airspeed struggling to build up from VY. The airplane then sinks back down, requiring time and effort to bring it back to the target altitude.
Learn to lead the level-off by about 10 percent of the climb rate (400 fpm means you start the push-over about 40 feet under the altitude you want to capture). Add power to maintain cruise speed and allow the preset trim to raise the nose back to level flight. Then set cruise power and fine-tune the trim and mixture.
Once you’ve settled in at cruising altitude, consider that you’ve made an investment in stored energy. That potential energy represented by thousands of pounds of airplane parked a mile or so above the Earth can be used when it’s time to come down. You can either save fuel by coasting downward with reduced power, maintaining cruise speed, or shorten the flight by picking up 10 knots or more in a shallow dive at cruise power, or maybe a little of both. Either way, you can put that hard-won altitude to work for you.
Let It Down Easy
The object should be to begin the descent at a point that will allow it to continue without further power adjustment all the way to the landing pattern.
The usual maximum descent rate for passenger comfort is about 500 fpm—or less if they’re not used to the pressure changes of flying. Even if your GPS doesn’t offer a top-of-descent or rate-of-descent reminder, you can easily figure two minutes per thousand feet needed for the letdown, and crunch that time-to-go number with your ground speed to establish a start-down mileage point.
There are some variables to be considered during descent. If you choose to pick up extra speed on the way down, the ensuing faster ground speed requires an earlier beginning for descent. Conversely, if you must slow down to reduce the strain of rough air at lower altitudes, you’ll need to lessen the descent rate. The wind vector may change during the descent as you drop out of a tailwind or encounter a beam wind.
Remember that your target is not the airport but a point in space at traffic pattern altitude a comfortable few miles short of the field, giving you time to slow down for flying the pattern.
If it becomes necessary to level off at an intermediate altitude, don’t pull back on the yoke to arrest the descent. Instead, add power to maintain cruise speed and trim to raise the nose to level flight. Begin a gentle level off about 50-100 feet above the target altitude so as not to press the passengers into the seat cushions.
Don’t forget that you had the mixture leaned for a higher cruise altitude, and it must be enriched for the traffic pattern and possible go-around. The engine may be running fine at low power, but if the throttle is pushed back up, you could encounter a rough-running engine from the overly-lean mixture. Go to full rich on the downwind leg or short final, unless you’re landing at a high-altitude field.
With practice, you can trim off your excess descent airspeed as you level off outside the traffic pattern, entering the circuit at a safe, slow speed to follow other airplanes, leaving the power at a slow-cruise setting. The needs of air traffic control may take precedence, however, and you might have to stair-step your way down at times, but it’s a satisfying achievement to manage the airplane’s stored energy all the way to touchdown.
Going up or down are fundamental skills that are frequently neglected in a training regimen that concentrates on cross-country navigation and pattern work. Proper three-dimensional control of the airplane should be emphasized from the beginning of flight training and during all transitions to new aircraft types.
