Best angle, best rate, normal, or cruise?
I once indulged my interest in sports-car racing by buying an expensive how-to videotape. The hands-on driving shots were cool, but the thing that made the greatest impression on me was something that was said in the introduction. "A racer can only make his car do four things," the narrator said: "Accelerate, brake, turn left, and turn right. It's how well you coordinate and execute those four things that determines the outcome of your race." I realized that the same is true of airplanes, except for one significant difference: Airplanes operate in a third dimension as well. Like cars, airplanes accelerate, slow down, turn left, and turn right, but they also climb and descend. And therein lies an interesting set of challenges. Let's talk about the climbing part.
But as soon as the airplane climbs higher than about a wingspan above the runway, ground effect and its benefits disappear. Now it's decision time: Climb at an airspeed that will result in best angle, best rate, normal climb, or cruise climb?
No, that's not quite right. The time to decide on the climb profile is not when I start climbing, but before I take off. Remember the mantra-plan my flight and fly my plan.
If I'm taking off from a runway with obstacles on the departure end, I'll want to quickly get to best angle of climb speed. That should get me up and over the obstacles in the shortest distance. My climb rate may be better at a higher indicated airspeed, but with obstacles I'm not much interested in how quickly I can get to a safe altitude. My objective is to reach that altitude in the shortest horizontal distance. So what if it takes a few seconds longer?
But there are no obstacles anywhere near my home airport. It's in southwest Florida, where the land is as flat and as low as the current stock market index. What I am facing on my flight today is low-level turbulence, thanks to a strong cold front that blew through a day ago. It's beautifully clear and bright, but other pilots have reported that the air is washboard-rough below about 3,000 feet above ground level (agl). I'd sure like to get through that nastiness and into more comfortable smooth air as quickly as possible.
In this case I'm more interested in minimizing time rather than distance, so in my preflight planning I decide that I will climb at best-rate airspeed. That should get me to my cruising altitude at the highest possible climb rate, and therefore in the shortest amount of time.
Best-angle and best-rate airspeeds aren't my only choices for the climb profile. Last week I had a trip that departed early in the morning, and as is often the case at that time of day the air was supple and smooth from the surface on up. The sun had not yet had a chance to warm the ground, the roads, parking lots, rooftops, and everything else on the surface, so there were no pesky thermals to jab at the wings. In the late afternoon and evening it's like that, too, as the sun retreats to the horizon, the Earth begins to cool, and the air settles down.
When the air is uniformly smooth I can choose either a normal climb speed, or a cruise climb speed. The differences are subtle. In The Advanced Pilot's Flight Manual, the late William Kershner, noted author, instructor, and test pilot, defined normal climb as "the best rate of climb possible without overworking the engine." That's a simple, good explanation. Some airplane manufacturers cite a normal climb speed in the pilot's operating handbook (POH), information manual, or airplane flight manual (AFM); some don't.
For example, the POH for a Cessna Skylane 182P says that the obstacle-clearance climb speed (best angle) is 57 knots indicated, the best rate is 80 knots indicated (decreasing to 73 knots indicated at 10,000 feet), and the normal climb speed is 90 knots indicated.
Many manufacturers seem to prefer the term cruise climb or en route climb to normal climb. Cruise climb or en route climb is an indicated airspeed that strikes a compromise between climb rate, over-the-nose visibility, and forward speed. The idea is to go fast (relatively speaking) and have a good over-the-nose view of oncoming traffic while still climbing at an acceptable rate.
Unlike best-angle and best-rate airspeeds, which are hard numbers determined by the manufacturer during certification test flights, other climb speeds-normal, cruise, and en route-are more general in nature. You don't have to peg the airspeed indicator on the normal climb speed cited in the POH. A few knots, or miles per hour, above or below that speed will yield much the same results. Consider the manufacturer's normal, cruise, or en route climb speed as a recommendation rather than a rule.
Next time you have a flight that involves a sustained climb to altitude, spend some time testing various climb speeds. Start with a best-angle speed right after takeoff (if you haven't done it in awhile you'll be surprised at the steep angle of attack), then at about 400 feet transition to best-rate climb.
Hold that speed until reaching about 1,500 feet agl, then transition to a normal, cruise, or en route climb speed. See how the relationship changes between the climb rate on the vertical speed indicator and ground speed on the GPS or DME, if the airplane is so equipped.
Try a few different climb speeds, preferably over several flights. If the weight of the airplane varies between flights, so much the better. That will give you a good feel for the effect of weight on climb performance.
The objective of this experiment is to get a better feel for how the airplane you usually fly behaves in the climb phase under various conditions, primarily weight and density altitude. Find a speed you are comfortable with, taking into consideration forward speed, visibility, and climb rate. That will be your personal normal climb speed.
One other consideration to factor into your climb plan is to look at winds. If you'll be flying into a good headwind, you can minimize its groundspeed-robbing effects by climbing at normal or cruise-climb speed. If it's a good day and you'll be flying with a generous tailwind, climb at best rate to get to cruise altitude quicker. The tailwind will boost your groundspeed, so you'll have the best of both worlds-a more-rapid climb rate, with a good groundspeed.
Once you have the climb part figured out, it's time to concentrate on the descent. We'll look at that next month.
Mark Twombly is a writer and editor who has been flying since 1968. He is a commercial pilot with instrument and multiengine ratings and flies a Piper Aztec.
