Here I am, sitting on the loggia at the Taos Regional Airport (KSKX) watching folks perpetrating takeoffs. It’s fascinating to see the same make and model airplane, with similar loads and flap configurations, lift off at different locations far down the runway. And, usually, to the left of the centerline stripe. Evidently, diverse pilot techniques are at work; many of them revealing more about the pilot implicated than the technique itself. No matter the training provided, eventually all pilots get out there and develop individual techniques.
Unfortunately, there is a body of gullible “wisdom” accepted by the trusting that contributes to these private techniques being detrimental to an airplane’s performance. For example, some less than astute sages enlighten trusting pilots proclaiming additional indicated airspeed should be added when taking off at full gross weight or when flying out of high altitude airports. “Add a few for spouse, kids, and dog.” Let’s try to dispel some of this folklore.
Preparing beforehand for take off requires making allowances for the plane’s weight, airport density altitude, type of runway surface, obstacles, and wind velocity and direction. All of these variables should be familiar subjects and the proficient pilot will know how to deal with them. But, why be casual when it comes to rotation speed, take off distance, and side of the runway to use? The following narrative assumes a no wind situation.
Rotate at the POH stated take off velocity (Vr). Unless there is a table in the performance section for various weights, Vr has been established for a maximum gross weight (MGW) plane and allows for acceleration to climb speed at full power. If you continue to roll down the runway beyond recommended Vr then you are exposing yourself to added risk. On shorter runways, you’ll rotate at a point that may not allow a landing on the runway surface should an engine quit immediately after take off. Continued acceleration while on the ground will cause the plane to “wheelbarrow” on take off roll. This means that the elevator lifts the plane’s tail, followed by the main tires leaving the ground with you continuing the take off roll on the nose wheel only. Loss of control follows just before or after the propeller strikes the runway surface. As another sage, Charlie Nelson, once said, “If you can’t afford to do something right, than be darn sure you can afford to do it wrong.” And you’re stressing your tires; they’re not NASCAR approved. Hangar trivia – Vr is in the order of 1.1 times the plane’s stall speed with flaps retracted.
Keep the plane‘s longitudinal axis (the cabin) aligned with the centerline stripe with right rudder pressure. The plane has a predisposition to turn to the left when power is applied on take off roll. P-factor (more lift on the right propeller blade as is rotates down), slipstream effect (propeller blast against the left side of the vertical stabilizer), and gyroscopic effect (let’s not go there – that concept usually vanishes 3.5 milliseconds after the FAA written exam is completed) all come into play on take off roll. Keep yourself in the middle of the runway using rudder. Once airborne, three more items come into play:
• Additional P-factor as the angle of attack of the downward blade increases adding additional lift to that prop’s performance.
• Additional gyroscopic effect caused by rotation of the nose.
• Loss of friction produced by the tires on the runway overcoming the side loads of the plane’s attempt to ease left.
Add a bit more right rudder upon rotation. Keep the rudder pressure in and fly straight towards the point on the horizon you picked as the extended runway centerline so you don’t drift into another aircraft’s pattern. A crosswind may help or hinder your efforts.
Now that you are off the ground, what type of climb schedule are you going to bring into play? If you have to clear the FAA standardized 50’ impediment, then climb at best angle speed (Vx). Otherwise, a normal climb to a reasonable altitude is usually accomplished at best rate (Vy), then cruise climb to your target altitude. What is cruise climb? A rule of thumb is to take the difference between Vx and Vy and add that number to Vy for cruise climb airspeed. If Vx is 63 knots and Vy is 73 knots, the difference is 10 knots. Add 10 knots to the Vy speed of 70 and climb at 80 knots.
Let’s thrash out Vx and why it’s used to clear an obstacle. Vx allows you to obtain the maximum altitude in the minimum distance over the ground. It permits a climb at a steep angle in order to clear a barrier at the end of the runway. Using Vx you clear the FAA standard tree in a shorter distance than by using any other airspeed. Usually, this take off technique is accomplished with a POH stated flap setting. Using flaps gets you off the ground ahead of a no flap take off resulting in a climb that starts earlier. With the earlier lift off and the steeper angle the net outcome is a gain of altitude in the minimum distance. Any other airspeed changes the angle and thus the clearance between you and the obstacle. A really short field exodus with high density altitude and obstacles presents a probability of survival equal to the angle of departure. Hangar trivia – Vx is in the order of 1.2 times the plane’s stall speed with flaps retracted.
A note about Vx and flaps. As I stated, flaps allow you to lift off early. However, the plane’s climb and descent performance is superior with a clean wing (no flaps). When at cruise if you have to climb over a mountain range, or forgot about that minimum crossing altitude, use Vx if necessary and no flaps.
Vy provides for maximum altitude gain in the minimum time. Your climb angle is less than Vx, but with no obstacle to worry about, you’re more interested in climb rate than angle. Reducing airspeed below Vy increases angle of attack, thus increasing induced drag, with an ensuing reduction of climb rate. Increasing airspeed above Vy increases parasite drag, resulting in a reduced climb rate. Consequently, climbing at any other airspeed than Vy reduces your rate of climb. Hangar trivia – Vy is in the order of 1.4 times the plane’s stall speed with flaps retracted.
The Vx and Vy speed in your POH may be listed with only one airspeed for each performance condition. If so, they are for maximum gross weight (MGW) at sea level. Some manuals do list different airspeeds for distinct altitudes, and possibly other gross weights. Nevertheless, there are some rules of thumb for your non-turbocharged GA aerospace vehicle that can be applied to assist you in discovering the airspeed closest to the one required. For each 1000’ of increase in density altitude from sea level, reduce Vy climb speed by one percent. Or, make a reduction of one knot per 1000’ of density altitude gain and you’ll be close. For Vx, increase your climb speed one-half of one percent for each 1000’ increase in density altitude. Now you can apply the weight rule of thumb – both Vy and Vx speeds increase approximately one knot for each 100 pounds below MGW.
Using these rules of thumb, along with your POH, develop an unofficial Vy and Vx climb schedule for your airplane. Next, go out and test fly your personal climb schedule and make what adjustments are necessary. Keep in mind, the POH climb schedule and airspeed, although official and FAA approved, was formulated in a new plane, with a new engine, and may not have all the additional drag inducing antennae that you have subsequently installed. Perform your test flight on a calm morning to mitigate the influence of convective thermals or gusty winds. Climb rate will diminish as you climb. An engine puts out less power as you climb. Another aviation rule of thumb is a loss of approximately 3.5% of non-turbocharged engine power for each 1000’ of altitude gained.
If all this is frustrating (“Why can’t I just go out and fly?”) just remember, if God wanted you to climb out serenely, he would have given you enough money for a Turbo-Bonanza.
Jim Van Namee, CFII and owner of Silver Eagle Aviation, LLC, carries on in the skies above and around the Taos Regional Airport (KSKX) in Taos, NM. He is the New Mexico Pilots Association Director of Mountain Flying Instruction. A retired Naval Aviator with over 6000 flight hours and bunches of carrier landings (more than 150 at night – that’s why he doesn’t have a real job), he is also an FAA Designated Aviation Safety Counselor. He can be reached at silvereagleav@taosnet.com or 505-377-6786.
