Avoiding Stalls

Red bug at 55 kts is Vref marker
During every biennial review, we must demonstrate recovery from a stall. But as J. Mac McClellan writes in the June, 2016, issue of Sport Aviation, that process evidently has not helped reduce the number of fatal stall/spin accidents. 

 He compares the practicing of stalls for general-aviation pilots with the ironclad rule of the airlines according to which airspeed may not go below Vref, defined as 1.3 times the stall speed. No wonder the airlines have virtually no stall/spin accidents!

 So why not adopt this same rule for our small planes? One may argue that this cannot be done since Vref depends on the configuration of the aircraft and payload. But there is a conservative approximation where we take max weight and consider the stall speed without flaps and with flaps in landing configuration. In each case, the stall speed is multiplied by 1.3 and the resulting value is marked on the airspeed indicator. This produces one mark for enroute flying and another lower one for landing. 

 Bug Speed

 In our case, it's even simpler, since our Zenith 601HDS does not have flaps. Stall at gross weight is somewhere around 41 kts, and 1.3 times 41 gives 53 kts. We have rounded this up to 55 kts, and have added a bug on the airspeed indicator; see above photo. Let's call 55 kts the bug speed for our plane. 

 Whenever we fly, we tell ourselves that we are not allowed to ever go below the bug speed unless we are right over the runway and ready to flare for touchdown.

 GPS Safe Speed

 There is a second rule. We learned it from Barry Schiff's article "Maintain Thy Groundspeed," published in AOPA Pilot some years ago: When winds at an airport are gusty, maintain the landing speed according to the GPS and not as shown by the airspeed indicator. This conservative rule has served us well in nasty weather conditions. In connection with the bug speed, this means that GPS speed is not allowed to fall below the numerical value of the bug speed. Let's call this GPS safe speed. 

 Turns to Base and Final

 There is a third consideration. The turns from downwind to base and from base to final are made at reduced speed. Make gentle turns while pushing the nose down a bit to unload the wings. That way, there is no significant increase of stall speed. 

 Stall Avoidance

 Here is the gist of stall avoidance: (1) Never fly below the bug speed; (2) when landing in gusty winds, never fly on final below GPS safe speed; (3) in the pattern, make gentle, descending turns to base and final. It's that simple.

Comments

  1. IcarusJune 27, 2016 at 3:38 PM

    ... and always keep the ball centered when turning in the pattern.
    About 35 years ago, i flew a friend's C150A from Buffalo NY to visit you in Dallas, Klaus. I started the takeoff roll from this tiny field near Buffalo, focusing on the end of the short runway and the elevated train tracks off the end of it. Acceleration felt normal but i glanced at the airspeed indicator anyway to make sure. The airspeed read zero (0, nada). In the second or two it took for my brain to process the meaning, i had traveled far enough that I didn't think I could stop in time, so i continued the takeoff and the plane behaved as usual. Shaken, but not deterred, I climbed to pattern altitude and went around to land. Fortunately, by then I had been a flight instructor for a while and had lots of time in the C150, so I had a feel for whether i was going fast or slow. nevertheless, it was very scary to make the turns in the pattern and then slow down on final to what i thought was the correct speed for landing. I was judging the speed by the resistance on the control yoke. obviously i made it. i landed and a friendly mechanic helped me disassemble the pitot tube to remove the large spider nest.
    -John

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