Taking A Wrong Turn
In a level turn, the number of “gees” a pilot pulls (which is also known as the “load factor”) is as we know related to the angle of bank (actually it’s the reciprocal of the cosine of the bank angle). Just as important as the increased load imposed upon the wings from the turn is the resulting increase in stall speed, which goes up by a factor of the square root of that reciprocal . However, there is actually one way that a pilot can yank and bank at will, and not impose any airframe stress or suffer any increase in stall speed. Just what is that?
- by accelerating downward (steadily increasing downward pitch) while turning
- By pitching downward at one third of the bank angle in a gliding turn, stall speed will not increase (although load factor still will).
- There actually is no way to return the load factor and stall speed increase ratio back to unity. This is a trick question.
- With a downward pitch of two-thirds the bank angle, both stall speed and load factor will remain unchanged from level flight.
Answer: A. Most people would consider it intuitively obvious that stall speed will not increase during a gliding turn, as it will during a level one. Actually though, during a stable gliding turn (that is, at a constant sink rate), the effect upon stall speed is exactly the same as it is in level flight! To prevent the stall speed from increasing, one must unload the wings. A way to do that would be by accelerating downward while turning. If one used a calibrated g-meter and carefully pulled some negative gees to counteract the previous load factor so that the accelerometer again read one gee, it could probably be matched fairly closely. As long as sink rate is increasing, stall speeds will fall as well. (Eventually though, you might run out of altitude.) And as you stop the drop and sink rate is reduced back to level flight (i.e., zero), stall speed would again rise according to whatever bank angle you still had. But since few of us fly with accelerometers in our panels, and negative gees are hard for most of us to judge accurately, proving this little physics factoid is best approached with caution!
Handy Hints For When Your Back Is To the Wall
For those without fuel injection, what is the wisest thing to do first, if the carburetor on your reciprocating engine ices up?
- Immediately select a full rich mixture and apply full carb heat
- Immediately trade airspeed for altitude until you reach best glide speed.
- Immediately lean the mixture.
- Apply carburetor heat.
- As soon as practical, surrender your license, because you weren’t paying enough attention to the atmospheric conditions in the first place, nor to the dropping rpm or manifold pressure to notice the problem before things really got out of hand.
Answer: C. Ice in the venturi of your carburetor will block some of the incoming air, resulting in a richer than optimal mixture. Yes, apply carburetor heat, but before it takes effect, your mixture will still be too rich, and leaning the mixture to better match the reduced air flow (as well as adding full power) will expedite your being able to help your engine return to normal. The engine will most likely falter momentarily as it ingests water, but afterwards it should return to normal operation (assuming you remember to readjust the mixture for your altitude).
Time And Tide
When landing at an airport near the seashore, why might you care what the tide tables say?
- Offshore winds often accompany high tides, and there are very often onshore winds during low tide. This can be helpful information for choosing which way to land.
- Birds are more numerous at low tide. You have a greater chance of avoiding a bird strike at high tide.
- Lacking a calendar, you can use the highest high (spring) tides to predict the next full moon, when planning a night flight.
- At low tide, you will have more beach available as an emergency landing site.
Answer: B. Aside from a storm surge, there is little correlation between wind direction and level of the water at the shoreline. There is a correlation between tides and lunar phases of course, so this might be a plausible application of one’s knowledge of the physical sciences, but these days, who doesn’t have a calendar? Don’t even think about landing on a beach at low tide, unless you’re either on fire or you know for certain that it will be deserted and without hidden hazards.