Yesterday I touched on the theory of the different kinds of climbs. I discussed the best-rate of climb (Vy) and the best-angle of climb (Vx). Today, let’s talk about how we use the appropriate climb speed for given situations.
Most of the time, we operate airplanes off adequate runways. By this, what I mean is, most pilots perform takeoffs on hard surface runways of more than adequate length without obstacles. The pilot’s concern following this sort of takeoff is getting the airplane to the proper cruising altitude as soon as possible. To do this, a pilot should use a Vy climb or a cruise climb, depending on cruise level winds aloft.
To explain further, if the flight plan calls for a tailwind enroute to the destination, most pilots want to take advantage of that wind. Typically, the winds aloft are stronger at altitude; it is to anyone’s best advantage to spend as much time as possible in those high tailwinds at cruise level.
The best way to do this is to climb the airplane into those tailwinds as quickly as possible. The climb speed for this is Vy. Again, this speed most effectively uses all available excess horsepower and provides for the fastest climb to altitude.
On the return trip when the pilot has to deal with a headwind, the trick is to keep out of the high winds as much as possible. More than likely the flight plan will require a much a lower altitude where the winds are not as strong. However, the pilot is still dealing with a headwind component. The less time spent with a headwind, the better. This is where the “cruise climb” is most appropriate for climbing to altitude.
There are two advantages to using a cruise climb when dealing with a headwind. First, the higher airspeed used in the cruise climb will allow for a greater distance traveled during the climb. Secondly, the pilot will reach altitude further downrange from takeoff. This allows for less time spent cruising against the headwind.
The proper use of the third type of climb, Vx, is to clear obstacles. Typically, this means getting beyond the 50-foot tree at the end of each runway as mandated by the FAA. However, all joking aside, in mountainous terrain you may have to use a Vx climb for an extended time to get over a nearby ridge.
In clearing an immediate obstacle at the airport, the appropriate method is to keep the angle-of-attack on the wing reduced during the initial takeoff roll. This allows a faster acceleration on the aircraft due to the reduced drag of the lower angle-of-attack as opposed to the drag created by the higher angle-of-attack of a normal takeoff.
Once the airspeed reaches a few knots less than Vx, the pilot then rotates the airplane to an attitude that results in a steady Vx airspeed. The pilot needs to consider two aspects of this climb. The first and most important is to avoid over-rotating; if he or she brings the nose too far up, the airspeed will be considerably low. An overly aggressive pilot may even pitch the airplane into a stall less than 100 feet above the surface.
The other consideration for performing this takeoff is not being aggressive enough. In other words, if a pilot fails to pitch appropriately in the climb to avoid the tree at the end of the runway, the pilot might just fly the airplane into the tree.
Stalling out 100 feet above the ground or flying into the tree is unacceptable.
This is what makes the short field takeoff so challenging. Of course as I mentioned in the second paragraph, most of us today perform our takeoffs from hard surface runways of more than adequate length. Indeed, most pilots today shy away from any runway less than 2000 feet long.
There are a few grass runways less than 1500 feet long scattered throughout the land. These are the airports I enjoy the most.
© 2011 J. Clark