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Top of the White Arc - Airspeed

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  • Top of the White Arc - Airspeed

    Ok...it's unclear from the regs what the top of the white arc, or Vfe, should be. Is it the speed where you can use full flaps (65mph) or the speed where you can apply the first notch of flaps, (100mph)? I'm inclined to go with 100mph and have a placard as to the speed for each notch of flaps below 100mph. Thoughts?

  • #2
    I think you are right Paul. Top of white arc should be 100 mph. Mark

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    • #3
      I didn't have the benefit of Mark's answer above when I was setting mine up, and I set the high speed end of the white arc for the second notch speed. So far it has been working out, though for me the white arc really only applies to another pilot who might be flying the airplane, since I'm not usually using it as a cue to decide when to extend the flaps. In most cases I'm listening to the noise level in the cabin, since my eyes are outside of the windows judging the position and energy of the plane. Another cue is that the second notch speed is also pretty close to where my prop reaches the low pitch stop (where I can advance the knob without having a change in RPM) so I'm usually doing that before I start wanting to have the drag of extended flaps. The advantage of having a higher start to the arc would be most apparent in a case where you are high and/or fast and want to get the flaps down to create drag, and this is especially an issue in slippery airplanes that really need the drag of the flaps to slow down. I find that our Bearhawk has enough drag that I can bring the throttle to idle, hold altitude, and see the speed come down to second-notch flap speed pretty quickly, even with the prop control still back, so it hasn't been an issue to have the arc start lower. Contrast this to an RV or similar type, where 150 knots on the downwind is going to make for a very extended pattern. Lower flap extension speeds might also reduce the stress on the flaps and flap system, and reduce the pitching moment during extension. Under normal circumstances, I'm not going to be indicating much more than 120 knots on the downwind in a high-speed scenario, and usually I'll be closer to 100 if I'm on the normal profile, so I don't have much speed to lose. Mark and the other big-engine guys might be going a little faster and need the drag, so that's something to think about. I added a placard on the panel for each setting, and the FAA inspector didn't have anything to say about flap speed markings.

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      • #4
        I used the second notch. The first notch of flap does basically nothing (<1") ....

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        • #5
          In the C90 (pays the bills) there is a little white triangle on the A/S for the first notch (approach) of flaps at 184 KIAS then the white arc for final or landing flaps at 148 KIAS. Maybe a tic of some kind at 100 and an arc starting at 85?

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          • #6
            The newer 172s has two speeds for flap extension called out. You can put in 10 degrees at 110 kias, and full flaps at 85kias. As a point of reference, the white arc stops at 85. From cessna I would infer that the white arc is full flap.
            Stan
            Austin Tx

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            • #7
              Vfe the top of white arc is the max speed at which flaps may be used. The aircraft is designed for max extension at this speed. Above this speed there is potential for damage.

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              • #8
                I went ahead and made the top of the arc at 100mph and will put a placard next to the indicator for the speeds for the subsequent notches. I agree with Jared that it mainly applies to those that may fly the airplane. It will be part of the briefing if that ever occurs.

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