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Rapid Descent

Old 20th Sep 2023, 14:37
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Rapid Descent

I have just watched a video of a dead-stick landing into Teterboro by a C152. The Pilot managed it quite easily by circling the airfield to reduce altitude, and was able to use any runway because of his emergency status. He seemed to be constantly flying at about 70 knots to make his glide approach. ( Vx..?)
I tried this same rapid descent scenario in a C172, and found that with full flaps and a high speed, the height came off quite rapidly. (about 2000ft/min.) I limited the speed to just below Vf as I didn't want to exceed that. Once the height was suitable then I could continue with the slower 65-70 knots approach speed, but this only made -600ft/min., as it is closer to the minimum part of the drag curve.
I was never taught this manoeuvre, but it could be useful one day.
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Old 20th Sep 2023, 21:44
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FWIW in the event of engine fail here we're taught to adopt Vbg 'till closer to chosen field and then fly a standard pattern as much as possible.

Once I was past my training and was able to research and think for myself I came across the military 'circling approach' methodology for engine failure. In my view this has a lot to recommend it and may give a pilot a greater chance of achieving a landing on the site they desire. OTOH I guess there is a higher risk of stalling in the turn so YMMV.

There have been various discussions on this in the past, complete with some fairly strong views around the 'best' way to deal with a forced landing. I'm not sure that there is such a thing, and that each situation/pilot will differ, however what would be good is to be proficient with both Vbg and how to bleed of speed/height as necessary (side-slipping, s-turns, flaps if available etc).

FP.
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Old 20th Sep 2023, 22:04
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Flying as a passenger in a Hunter we did a PFL from FL160.
Reduce speed to 240kts at 500ft/min rod until height equals range from touchdown and when it does so, increase rod to 1000ft/nm by lowering the gear.

Last edited by chevvron; 21st Sep 2023 at 13:12.
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Old 20th Sep 2023, 22:15
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Why would anyone be in a hurry to land after engine failure unless on fire?

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Old 21st Sep 2023, 13:56
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Well 'On Fire' is one good example. Another reason would be that you don't want to spend half an hour descending from FL180 at 600 ft/min.

To reduce your energy by flying in a high drag configuration, means you either have to fly close to Vs, or just under Vf with flaps deployed, or between Va and Vne without flaps. All of which needs to be done with caution. I think that just below Vf is the safest way, and may result in the most amount of drag.

edit.. Just thought of another reason for a fast descent, maybe only applicable to larger aircraft... Loss of Cabin Pressurisation, at higher FLs.... Usually these wings have Speed-Brakes, which help a lot to achieve a high RoD.

Last edited by scifi; 21st Sep 2023 at 14:19.
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Old 21st Sep 2023, 14:55
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Originally Posted by chevvron
Flying as a passenger in a Hunter we did a PFL from FL160.
Reduce speed to 240kts at 500ft/min rod until height equals range from touchdown and when it does so, increase rod to 1000ft/nm by lowering the gear.
A "One in One" approach...?
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Old 21st Sep 2023, 15:44
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Originally Posted by ShyTorque
A "One in One" approach...?
Correct. Amazing how well a Hunter glides with the throttle shut.
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Old 21st Sep 2023, 23:08
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One of the wise ones who has now passed away, but used to generously share his knowledge here would say: "If it quits, point it to where you think you can crash it, and don't crash when you get there.". Yes, trimming for Vbg with an engine failure is a good first action. If a forced landing is a certainty, I'm quite content to pick a closer spot, and quick descend myself to a good place on short final. I don't mind giving up gliding capacity, if I don't need to "make" a far spot. I would rather slip down final to dump excess height/speed, and position myself more precisely over the fence, than to have mis judged, and undershoot. You're better going off the end of your selected spot, having touched down too fast, and decelerated on the ground, than to hit the fence because you misjudged. This is particularly a thought if you're flying a type in which your recent practice forced approaches are few, and your precision may not be great.
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Old 22nd Sep 2023, 18:43
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With 40 flap in C-172 or 150, you can point the nose where you want to land with not much risk of exceeding VFE. Since drag increases with the square of airspeed, you can get a steep approach. Best to practice ahead of dire necessity.

​​​​​​Once you have a field made, likely using best glide to reach that point, a steeper approach can give you a longer ground run once you have made very sure you will clear the wires. Flying gliders, I've dropped in to several fields. Assume there's always wires (look for the poles) and plan your approach accordingly.
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