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4 Answers

Overcoming increased angle of descent in a strong headwind

Asked by: 3363 views Student Pilot

Hi,

 
I'm a recreational pilot, but currently in the process of converting to GA, & would like some clarification on the following questions: 
 
To overcome a strong headwind on base leg, my briefing notes specify that you need to increase power as well as adopt a high nose attitude.
 
1. Is the above method based on: Performance (IAS) = Attitude + Power
 
2. As a result of the headwind, will a new/different attitude be required on base leg?
 
3. As a result of the headwind, will a new/different IAS be required on base leg?
 
4. Am I correct in assuming that each of IAS, TAS, & GS, will reduce if the normal (non-headwind) control inputs (for a C172SP), i.e. 75 Kt, 1500 RPM, & the approximate half windscreen attitude, were adopted?
 
5. For this exercise, which of: (i) increased power or (ii) higher nose attitude(s) are more useful for overcoming increased angle of descent, or should I apply a combination of both?
 
Cheers,
 
Ben 

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4 Answers

  1. Best Answer


    Patrick Flannigan on Apr 30, 2012

    Ben, it sounds like you’re falling into the trap of over analyzing the flight. The important thing is to use whatever pitch and power setting it takes to maintain proper approach speed and stable descent. For a 172, that’s probably going to be in the 70-75 knot range and 400-500 foot per minute on base. Look out the window and fly the plane.
     
    With respect to your questions:
     
    1. According to the Instrument Flying Handbook, performance is controlled by managing attitude and power, so I would venture to say that all phases of flight are based on this. Sure, it’s a factor, but it’s not particularly relevant here.
     
    2. Assuming a constant wind, your pitch attitude should not change from downwind to base. Think about it this way: the airplane is not “attached” to the earth. It’s floating around in the atmosphere which is moving along past the airport. As far as the airplane is concerned, there is no headwind or crosswind – that stuff only affects your ground track and ground speed. 
     
    3. The great thing about IAS is that it is pretty constant regardless of what’s going on. You should fly the same reccomended indicated airspeed regardless of wind or altitude. An airplane will stall at the same IAS in no wind as it does in a 30 knot headwind. It’s probably the most accurate and useful number the instrument panel can give you.
     
    4. When you turn downwind to base, IAS and TAS will not change. Groundspeed may decrease because of the headwind componenet. This has nothing to do with how the airplane flies, but it will affect the length of your base leg.
     
    5. When landing light airplanes, power controls altitude, pitch controls airspeed. So if you’re descending too fast, increase power to shallow the descent. Likewise, if airspeed increases, you should pitch up to slow down. That’s the theory anyways, but practice and experience will show you that it really takes a combination of both.
     
    Try not to overthink it. You’ll find it’s a lot easier (and more fun) to just fly the airplane and make small corrections as needed to stay on profile.
     
    Good luck, and I hope this helps.

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  2. Bob Watson on Apr 30, 2012

    Patrick summed it up nicely.
    Remember that your performance formula is for level flight. For any particular attitude and airspeed, if you have more power than you need for level flight, you climb; less power, you descend. On final , you have less power than you need for level flight, so you descend. If that descent angle won’t get you to the runway (e.g. due to a headwind) you add power, but keep the attitude and airspeed constant.
    Ditto on the overthinking. Just maintain your attitude and airspeed and look out the window. If you’re sinking faster than you want, add power. If you’re not descending fast enough, reduce power. But look at the runway, not the tach to do this.

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  3. Nathan Parker on Apr 30, 2012

    “For this exercise, which of: (i) increased power or (ii) higher nose attitude(s) are more useful for overcoming increased angle of descent, or should I apply a combination of both?”
     
    Ben:  Increasing power will produce a higher nose attitude, because your flight path will flatten out with respect to the atmosphere.  None of your airspeeds will change.
     
     

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  4. Bob Reser on May 01, 2012

     
    Maneuvering is controlling the aircraft attitude away from engine thrust sustained, straight and level, constant indicated-airspeed flight.
    At takeoff, the aerodynamic flight controls become effective as acceleration attains sufficient encountered airflow.  Total engine thrust is causing acceleration.
    Upon becoming airborne, the rudder, aileron, and elevator-pitch controls aerodynamically steer the direction of engine thrust.  The throttle controls the extent of engine thrust effect, but there is no more acceleration, the engine thrust now sustains the liftoff elevator-pitched indicated-airspeed of continued flight, and the excess thrust-component lifting is causing climb angle.
    The elevator-pitch trim previously set for takeoff has set the angle-of-attack of airmass encounter for the indicated-airspeed the aircraft will fly.  Manual elevator control overrides angle-of-attack pitch allowing any necessary adjustment of indicated-airspeed.
    In climbing or level flight, the throttle is the control of altitude and elevates with engine thrust.  The elevator position controls the angle-of-attack frontal plate area allowing the indicated-airspeed the aircraft will fly. 
    In descent, things change.  With power reduction below level flight sustaining thrust, that portion of tractor-engine thrust-component lifting contributing to angle of attack reduces allowing a small acceleration.  Control with power and power changes below level flight sustaining thrust now require continuous coordination of elevator or elevator trim to maintain a constant indicated-airspeed.
    http://safe-flight.net

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