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Old 22nd Feb 2021, 22:27
  #21 (permalink)  
David J Pilkington
Join Date: Sep 2020
Location: Melbourne, Australia
Posts: 34
Originally Posted by Pilot DAR View Post
The design requirements for many GA planes do not require that a glide landing be possible from Vx. When applicable, the requirements ris that a glide landing be possible from Vx + 5 MPH:

(my bold)
Sec. 23.51


(2) Upon reaching a height of 50 feet above the takeoff surface level, the airplane must have reached a speed of not less than--
(i) 1.3 ; or
(ii) Any lesser speed, not less than VX plus 5 miles per hour, that is shown to be safe under any condition, including turbulence and complete engine failure;

Any GA planes for which I've looked it up, have a Vx which is noticeably slower than the best glide speed. In a draggy plane, the effect suddenly slowing down with sudden power loss is greater.
Initial and early amendments of FAR 23.51 that requirement only applied "For airplanes of more than 6,000 pounds maximum weight". For less than that it was simply
"(1) The takeoff may not require exceptional piloting skill;

(2) With takeoff power, there must be enough elevator control ..." my example airplane below.

Originally Posted by oggers View Post
But Vx is a safe speed to flare from. There is no need to accelerate to best glide, let alone Vy, for a safe flare. The 50 foot speed in a max performance take-off will be equal or less than Vx and yet it is certified “safe under all reasonably expected conditions including complete engine failure” and “not requiring undue skill”.

here are some POH figures:
C-172: glide 65kts; landing without engine power 60kts. (Vx = 59)
PA-28: glide 73kts; “when the field can be easily reached slow to 63 knots for the shortest landing”. (Vx = 63)
M20K: glide 90kts; EFATO 75kts flaps down. (Vx = 79)
My FAR 23 certified Super Decathlon has glide 75 mph "landing whenever power is still available but if a complete power failure considered imminent 75 mph recommended 70 mph minimum" (Vx = 58 mph) and stall speed is 56 mph. Short field take-off "maintain the folllowing speed until clear" 58 mph plus a warning that injury or death may result in the event of power failure "must be pitched forward to a safe power-off speed". From the applicable FAR 23.51 "The takeoff may not require exceptional piloting skill". Short field landings at 60 mph require power per the manual with the warning that at speeds below this "landing flare can only be assured with an application of power" suggesting to me that Vx + 5 (63 mph) might be enough to walk away from.

My trainees and myself are far from exceptional yet CASA's tailwheel endorsement standards require achievement of book distances using those speeds. Landings also.

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