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Vfr screen height

Old 22nd Feb 2021, 23:27
  #21 (permalink)  
 
Join Date: Sep 2020
Location: Melbourne, Australia
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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

Takeoff.

...................
(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.

David J Pilkington is online now  
Old 23rd Feb 2021, 04:03
  #22 (permalink)  
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Initial and early amendments of FAR 23.51 that requirement only applied "For airplanes of more than 6,000 pounds maximum weight"
Yes, which is why I referred to "applicable". Lighter planes are sometimes (for my experience testing them) even more susceptible to difficulty gliding safely from a Vx climb, so I consider the "more than 6000 pound rule" suitable to apply to less than 6000 pound airplanes also, as they don't have a prescriptive performance standard. I find that this characteristic of airplanes is poorly appreciated by many pilots (though very well appreciated for helicopters by helicopter pilots), so I'm more cautious when demonstrating design compliance during testing modified planes (floatplanes, in particular), and more likely to train it to unfamiliar pilots.
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Old 23rd Feb 2021, 17:47
  #23 (permalink)  
 
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There was an accident to a Beagle Pup, a British certified Single Engine Piston aircraft, a couple of years ago. Here's the link to the Air Accident Investigation Branch report:

Beagle Pup Report

Turn to page 11, where the results of some test flying examining the flare characteristics at various speeds is laid out. This engine failure happened about 300' after takeoff so not quite what we're talking about here but I think the results of the test flying are very revealing. I'm now teaching EFATO with a BIG push, to 'light in the seat', even at Vy. The Captain's Brief prior to lineup emphasises the best glide speed (which happens to also be the Vy we use).

Whilst we're here, we teach recovery from a sudden, catastrophic loss of power, both on takeoff and in the cruise. The worst accidents seem to happen with a subtle gradual loss. Our examiner is very keen that we train for this from the cruise, but we don't do too much after takeoff. We encourage people to set an attitude first, then verify performance by checking the speed. Of course we don't want people to be 'heads in' so what else can we do? Engine note is good to learn in a fix pitch prop aircraft, but less so in a VP.

TOO
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