About the Author

My photo
Southport, Manitoba, Canada
Steve Pomroy is a professional flight instructor and aviation writer. He has been teaching since 1995 and holds an Airline Transport Pilot License, Class 1 Instructor and Aerobatic Instructor Ratings, military QFI, and an undergraduate degree in Mechanical Engineering. He's written and published three flight training books through his company, SkyWriters Publishing, and has several other books under development. Steve currently teaches RCAF pilot candidates on their Primary Flight Training course.

Wednesday, July 13, 2011

Turning Steeply

Well, I meant for this post to be about corner speed. But somehow it got transmogrified along the way into a post about steep turns. I guess corner speed will have to wait!

Early in training, every pilot learns how to do a "steep turn". Unfortunately, we don't often get taught the full maneuver. The Flight Test Guide (in Canada) specifies that the steep turn be conducted at 45° angle of bank. So that tends to be where the training ends (I've whined about this phenomenon in previous articles: Einstein's Razor and Multi-Engine at Night).

Properly done, the steep turn can be a much more comprehensive exercise than a simple 45° bank, 360° turn (not that this isn't a good starting point, it's just that it makes a very poor finishing point). Turning at other angles of bank should be included, as well as descending steep turns (and climbing is your airplane has the horsepower), and steep turns off of a 360° line (90° or 180° turn).

The steep turn itself is done mostly as a coordination exercise. Proper and timely use of all four primary controls (pitch, roll, yaw, power) is required to make the maneuver work. However, as a coordination exercise, it can be much more effective if we vary the angle of bank and roll-in/roll-out rates, and include a turn reversal (the CPL flight test now includes a reversed steep turn, which is a step in the right direction, but it is still limited to 45° of bank).

Further to improving the value of the steep turn as a coordination exercise, some attention should be given to the practical use of the steep turn. Three uses come immediately to mind: Collision Avoidance, Canyon Turns, and Cloud Breaking.

Using the steep turn as a collision avoidance maneuer, do we roll gently to a precise 45° AOB, turn 360°, and then gently roll out? Nope. If the collision geometry is such that a turn is the way out (it isn't always), that turn should be very aggressive—using a rapid roll rate to the highest useable AOB (limited by airspeed, limit load factor, and power available). In most cases, the turn should cover about 90° of direction change, but sometimes 180° makes more sense. In many cases, the less we need to turn, the higher the AOB can be. This is becasue many light aircrat are underpowered in steep turns and will bleed off airspeed rapidly—preventing a full 360° of turn without a stall, but allowing shorter turns without difficulty.

A canyon turn is exactly what the name implies. The technique is used during mountain flying, and serves as a way out if we take a wrong turn into a box canyon and find ourselves approaching a cumulo-granite wall that we can't outclimb. Assuming your aircraft has enough power to maintain altitude and airspeed, the canyon turn should be conducted at your corner speed (this is the link, I went from a post about corner speed to a post about steep turns here). In brief, your corner speed is just the right speed for a maximum-load-factor-minimum-airspeed turn, which will give you the smallest possible turn radius. More on the corner speed (and it's relationship to other useful speeds, such as Vo and Va) in a future post.

Cloud breaking is a use of steep turn to descend through an opening in cloud after inadvertently getting stuck on top. It's not an ideal solution (a much better one being not getting stuck on top in the first place!), but it can get you out of a jam if you don't have an instrument rating, or if your aircraft is not equipped for instrument flight. In order to conduct this maneuver safely, you need to be able to execute a stable steep descending turn without letting it evolve into a spiral dive or stall/spin scenario. If you can do that and find a hole in the cloud big enough for your airplane, you can descend visually to full visual flight underneath.

Another example of where we might see a steep descending turn is during a turn to final. Sure, we normally try to stay away from higher angles of bank during such a critical phase of flight, but steep turns to final can be conducted safely if they are planned and executed well. The ability to do this is especially important in cases such as an engine failure, where you may have to choose between a steep turn to a beautiful landing spot, or flying straight and landing in trees and rocks. If you aren't proficient with steep descending turns, this may not be a choice at all—trees and rocks under control are better than a nice landing strip in a stalled/spinning condition.

The bottom line to all of this chit-chat is that the stepp turn is a much more comprehensive exercise than typical PPL/CPL training would lead us to believe. This is unfortunate, and detrimental to overall student performance. If you are a flight isntructor, consider adding to your steep turn training program. If you are a student, pester your instructor for more thorough steep turn coverage.

Happy Flying!

No comments:

Post a Comment