Spin Training Video

Recently my friend Bill Weber, an aerobatic pilot and flight instructor, took me up for some spin training in my Cessna 172. I will post a more detailed post at some point on spins, but in the meantime, the video below of my lesson will give you at an indication of how dramatic spins can be, with large losses in altitude even with prompt recovery control inputs. In the video, Bill first demonstrates a spin to the left and then to the right. My job as the student was to talk him through the maneuver. On the first attempt, I was too panicked flustered to get my words out. At one point you may hear me utter “Wow!” Bill was kind enough to recover the aircraft anyway. Thank you, Bill. For the last two spins, I was at the controls.

The thing that is hard to discern in the video is the relatively high g-loads in the pull up. Spins are only approved in a Cessna 172N when the weight is low enough — and the center of gravity far enough forward — to allow the aircraft to be operated in the utility category, in which case the aircraft can safely sustain a limit load of up to 4.4g. Below a critical airspeed, called the maneuvering speed and denoted by V_A, the aircraft wings will stall before the limit load is reached, protecting the aircraft from catastrophic failure. For the weight we were operating at (2000 lb), the maneuvering speed would be

(1)   \begin{equation*} V_A = V_s\cdot\sqrt{W/W_{\mbox{max}}}\cdot\sqrt{4.4} = 50~\mbox{kt} \cdot \sqrt{2000/2300} \cdot \sqrt{4.4} = 98~\mbox{kt} \end{equation*}

Above maneuvering speed, however, one can exceed the limit load and potentially destroy the aircraft. (There is, in principle, an additional factor of safety of 50% before the so-called ultimate load is reached.) Because the latter part of the recovery puts the aircraft in a near vertical position, and because the aircraft is aerodynamically clean, speed can build rapidly past maneuvering speed, and one must exercise extreme caution not to exceed the limit load in the pull up.

You will note that in the four spins in the video — watch the altimeter — we lost between 500 to 1000 feet of altitude. This is one reason inadvertent spins are so dangerous; inadvertent spins usually happen at low altitudes while landing or taking off, with too little altitude available for a safe recovery.

Look for a more complete blog on spins in the near future. In the meantime, see this interesting guest blog post by Bill Weber on his experience with an inadvertent spin in a Cessna 188 AGwagon.

The Teacher

[Editor’s note: This is a special guest column by Bill Weber, an aerobatic pilot and flight instructor, on the perils of inadvertent spins and the lessons we can all learn from his experience.]

Cessna C-188 Agwagon.
Cessna C-188 Agwagon.

Entry from Pilot Logbook #2:

  • Date: 11/1/90
  • Make and Model: C-188 Agwagon
  • From/To: Local
  • Remarks: Power on & power off stalls.
  • Duration of Flight: 0.7 hours

The logbook entry gives no indication that this flight was a pivotal moment in my flight training. I had 424 hours in powered aircraft and some glider time as well. However, most of those hours were quality hours. I had my commercial single, multiengine, and glider ratings. My weekends were spent flying, and my vacations were centered around aerobatic training at various schools around the country. Continue reading “The Teacher”

Cruise Performance Charts

I fly a Cessna 172N, which comes with a POH with lots of information. One of the more useful tables is the Cruise Performance table shown below (Figure 1). The chart gives the fuel flow rate and true airspeed for various combinations of pressure altitude, temperature, and engine percent power. Unfortunately, the table only provides data at the max gross weight of 2300 lbs. Furthermore, my aircraft recently had an Air Plains modification, replacing the existing 160 hp Lycoming O-320-D2G with a 180 hp O-360-A4M, with a commensurate increase in max gross weight from 2300 to 2550 lbs. The Supplemental Airplane Flight Manual has a Cruise Performance table similar to the one provided in the original POH, but it does not include cruise airspeeds! Furthermore, I often fly around at gross weights less than 1900 lbs. What will be the impact on airspeed and fuel consumption with the higher horsepower engine at reduced gross weights? Continue reading “Cruise Performance Charts”