|By Jim Van Namee
Whenever we fly, we should be concerned about flying the appropriate airspeed for the event involved. For example, many pilots fly a final approach airspeed they’ve become accustomed to regardless of its impact on where the airplane will touch down on the runway. They have become fond of a particular airspeed, regardless of its suitability. I’d like to challenge you to use a final approach airspeed closer to that which the airplane was certificated. I’m going to use the term Vref in place of “final approach speed.”
General aviation airplanes are certificated to Vref airspeeds 30% above stall speed in the landing configuration. With the landing gear down and flaps deployed, this is known as 1.3 times Vso. Unless there are performance charts for specific airplane weights, POH Vref airspeeds are normally based on Maximum Gross Weight (MGW). For example, a Cessna-182 POH indicates Vref, flaps down, of 70-80 knots at MGW. This is quite a speed range to enter the flare. However, the C-182 POH states that Vso is 49 knots. Therefore, at 1.3Vso, Vref can be 64 knots, a far cry from a span of 70-80 knots. Could the difference be a “lawyer thing”?
There is a rule of thumb that says that for each knot above Vref over the runway end numbers, the touchdown point will be an additional 100 feet down the runway than stated in the POH. Assuming the rule of thumb is correct and you are flying at POH Vref of 70-80 knots, instead of 64 knots, then you are landing 600 – 1600 feet farther down the runway than the performance charts in the POH indicate.
As I said, unless otherwise indicated, the POH numbers are based on MGW. When was the last time you landed an airplane at MGW? If you come up with an answer in the affirmative, keep it to yourself since you took off over-gross. How does one determine Vref when landing after a long flight? There are two ways to ballpark this. First, another rule of thumb is that Vref reduces approximately .8 knots for each 100 pounds under MGW. You can do the math on this one. Another way is to climb to a minimum of 3000’ AGL in your local practice area, set up a 500 FPM descent, using normal approach power settings, at different weights and flap settings. Pull up into a stall and note the airspeed, not the horn, at stall. Multiply these airspeeds by 1.3 and make a Vref performance chart of your own for different flap settings at different weights. You might want to do this with another pilot in the right seat to take the notes.
On a calm day, I regularly fly the C-182 at 65 knots on final with full flaps; 70 knots (1.3 times flaps up stall speed (Vs) of 54 knots) with 20 degrees flaps. Touchdown is consistently within 200 feet of my aim point. I make a habit of doing this each and every landing so that I don’t loose this skill in case I really need it on a very short field.
Try this technique and see how you like it. I predict that eventually you‘ll come to terms with the higher nose attitude than the one you’ve gotten comfortable with. Now I’m going to offer a technique for your “bag of tricks” that can help maintain Vref from base all the way to the flare.
You’ve probably noticed ads in some aviation magazines for Angle of Attack (AOA) Indicators. As a Naval Aviator the AOA indicator was one of my key instruments. I made the most of AOA in take-off, climb, cruise, air combat maneuvering, descents, and landing. You, in your GA airplane, can have a “poor man’s” angle of attack indicator every time you fly.
But first, let’s review what AOA is about. AOA is the angle between the chord line and the relative wind. The chord line is an imaginary line that connects the leading edge of an airfoil with the trailing edge. Relative wind can be viewed as the opposite of the airplane’s flight path. Visualize the flight of the aircraft during a descent and recognize that the descending flight path defines relative wind.
Angle of Attack controls airspeed in steady state flight and the throttle controls the ability of the airplane to climb or descend. If you have any doubt about this, go fly a glider. You’ll quickly note that you use attitude (angle of attack) to control your airspeed and, with no throttle available, you accept whatever rate of descent you get with that airspeed. The majority of your everyday flying is in steady state flight – takeoff, climb, cruise, letdown, and approach to land.
Lift, a by-product of AOA, is brought about by three factors:
1. For every action there is an equal and opposite reaction – Newton.
2. When air speeds up going over the top of an airfoil, pressure drops, causing a low-pressure area on the top of the wing – Bernoulli.
3. HIGHS always fill a LOW - The Weather Channel.
If you hark back to the dark ages of basic flight training you may recall the expression “Pitch + Power = Performance.” This means that for each power setting and pitch attitude you will produce a specific performance. For example, a setting of 10-11 inches MAP with 20 degrees of flaps provides a 500-600 FPM descent rate and Vref in certain airplanes.
Now, let’s put these concepts into use. Fly to your practice area at an altitude that gives you ample elevation for an extended descent. Simulating downwind in the pattern, configure the airplane with gear down, zero flaps and slow to 20 knots above Vref. Note the power setting required to hold this speed and the pitch attitude required to maintain level flight. Reduce the power approximately 3-5 inches MAP or 300-500 RPM (whatever it takes to hold a 500 FPM descent), set initial approach flaps, and hold altitude. Allow the plane to slow to Vref. Trim to Vref. As the plane approaches Vref, lower the nose about 5 degrees. Use power to maintain a 500 FPM descent and pitch attitude to maintain Vref. When you have a stabilized power setting for a 500 FPM descent and a stabilized pitch attitude holding Vref make a mental note of the pitch attitude in relation to the horizon. If altitude permits, make 90 degree turns, left and right, while maintaining the pitch attitude the at about the same point on the horizon. Practice until you can maintain Vref and a 500 FPM descent while straight and level and in turns. Perform this exercise several times at different configurations to obtain solid power settings and pitch attitudes for the various configurations.
Once you have gotten the feel of this technique, go back to the landing pattern and try it. Establish 20 knots above Vref on downwind. Set power (as determined in above paragraph) and initial approach flaps abeam the runway numbers. Trim to Vref. Hold pattern altitude until reaching just a few knots above Vref and then set the stabilized attitude that you determined earlier to sustain Vref. Set flaps as desired after rolling out on base and final approach flaps when the runway is guaranteed. Maintain that attitude all the way around the pattern right into the flare. Adjust power to continue a normal rate of descent. I strive for 500 FPM in still air. Fly a normal ground path in the pattern. Try a few passes at zero flaps, then approach flaps and, finally, at full flaps. See if this keeps you close Vref all the way to the flare.
Oh, what is the “Poor man’s AOA Indicator?” It’s pitch attitude relative to the horizon when using the proper power setting for the performance desired. That’s fine, you say, but what about flying the pattern at night with no horizon available? While practicing this technique, note the pitch attitude on the attitude indicator (AI). As long as you set the AI in a consistent manner prior to take off, it will provide pitch attitude feedback while on downwind, base, and final. Keep in mind, it’s impolite to stare, so keep the AI in your scan.
Remember, airspeed is controlled by pitch attitude and rate of descent by power. Weight, bank angle, temperature, and density altitude will vary every flight. But, even with these variations, pitch attitude and power settings you ascertain from practice sessions will be close and, with practice, you’ll determine the minor changes required from flight to flight.
Jim Van Namee, CFII and owner of Silver Eagle Aviation, LLC, operates at Taos Regional Airport (KSKX) in Taos, NM. He retired as a Naval Aviator with over 6000 flight hours and loads of carrier landings. He is the New Mexico Pilots Association Director of Mountain Flying Instruction and a Designated FAA Aviation Safety Counselor. He can be reached at firstname.lastname@example.org or 505-377-6786.