How proficient are you in slow flight? Knowing where the slow flight range is for your aircraft, and how it feels, is more important than many pilots realize.
Slow flight is the speed range between the airspeed for flight for endurance and the stall. The recognition features of slow flight are the recognition features for an approaching stall. The aircraft nose attitude is nose high in comparison to the relative airflow, the airspeed is low, the flight controls feel “mushy”, and the stall warning light or horn will be on as we approach the stall. By the time the stall warning comes on, it is time to leave slow flight to avoid a stall.
Every time we go flying, we are likely to fly in slow flight for at least a little while. Let’s take one model of the C-172 as an example. The endurance speed for the C-172 is about 60 knots and the stall is 51 knots with the flaps up and 46 knots with the flaps down. The POH states that the nose wheel should be lifted for take-off at 55 knots. The aircraft will get airborne at about 60 knots, right at the edge of slow flight.
If we complete a soft field take-off, we will get airborne in ground effect at 48 to 50 knots and we will have to transition through the slow flight range. The best angle of climb speed is 60 knots. This is right on the edge of slow flight. A very slightly too high nose attitude will put us into slow flight.
The final approach speed with flaps down for a C-172 is 65 to 70 knots (61 knots for a short field approach). So with full flaps, most of our final approach will be close to slow flight. As we flare for landing and the airspeed decreases, and we hold the aircraft off for that nice slow soft landing, we will be approaching the low end of the slow flight range.
There are times when we have to perform an overshoot when in the final stages of a landing. An overshoot may be because of problems with a gusty wind or a cross wind, or because of something on the runway. We are now required to make power, pitch and bank changes while in slow flight and very near to the ground.
Add gusty winds, cross winds or a little turbulence to slow flight and we can see why so many of our accidents occur in the take-off and landing phases of flight.
How many of us actually practice slow flight? Likely very few of us.
When we do practice slow flight we usually pick an airspeed like 55 knots and we practice straight and level flight, maybe a few gentle turns, and then the recovery to normal flight. This is good practice, but we should be practicing exercises that simulate real life.
Exercise 1: Slow the aircraft (C-172) to 50 knots with 10 degrees of flaps (the flap setting for a soft field take-off) while maintaining altitude. Then initiate the recovery while maintaining heading and altitude (simulating flying over the runway and remaining in ground effect). Force yourself to maintain altitude within 35 feet above the simulated ground until you have attained at least the best rate of climb and then climb away.
Exercise 2: Configure the aircraft (C-172) for a full flap final approach and set the aircraft at a short field final approach speed of 61 knots. Set an altitude as the simulated ground. When 50 feet above the simulated ground, flare and hold the altitude at just above the simulated ground until the airspeed has decreased to 50 knots and then overshoot. Maintain heading and altitude to simulate flying over the runway in ground effect. Force yourself to maintain altitude within 35 feet above the simulated ground until you have attained at least the best rate of climb and then climb away.
Before we practice any slow flight exercise, we should perform a “HALT or HASEL check. We will be near the stall with a nose high pitch attitude. We must make sure the area around us is clear of other traffic and that we are at a safe altitude, at least 2,000 feet above ground.
These are difficult exercises at altitude, but when mastered, will make slow flight at ground level much safer.
These exercises require large power increases which will cause the aircraft to want to pitch up, or pitch down in the case of above the fuselage mounted pusher props. A pitch up may result in a stall. A pitch down may result in sudden contact with the ground.
While performing these exercises, we must be very conscious of our use of the rudder. Most of us have become lax in rudder use and in normal flight in most modern aircraft we can get away with it. In slow flight, lack of rudder input or improper rudder input can result in a spin.
Remember adverse yaw. In a turn to the left, the left aileron goes up decreasing the angle of attack on that wing and the right aileron goes down increasing the angle of attack on the right wing. The increased angle of attack results in increased drag, which causes yaw away from the turn.
The slower we fly, the more aileron deflection is required to initiate the turn. This results in more adverse yaw and the need for more rudder in the direction of roll to correct for it. Adverse yaw must be corrected for. The differential or Frise that is designed into some flight control systems will partially correct for adverse yaw. The rest is up to us. We are very close to a stall while in slow flight. If we do stall with adverse yaw uncorrected for, we will spin.
The practice of slow flight exercises in realistic scenarios will improve our pitch and yaw control in slow flight. This will make soft field take-offs, obstacle clearance take-offs and all full flap landings safer. A safe flight is an enjoyable one.
Dale Nielsen is an ex-Armed Forces pilot and aerial photography pilot. He lives in Abbotsford, B.C., and currently flies medevacs from Victoria in a Lear 25. Nielsen is also the author of seven flight training manuals published by Canuck West Holdings.
Got an aviation safety story to tell? Dale Nielsen would like to hear from pilots who have educational aviation experiences to relate. Excerpts from these stories will be used in upcoming safety articles. Dale can be contacted via e-mail: firstname.lastname@example.org