Screen Height

[George Yogi]

what is so special about the number 35 (for jets) or 50 (for piston engine aircraft). Why is screen height not any other convenient number like 100ft or 50 meters? Thanks in advance

[john_tullamarine]

50ft originated in the early days of US military aviation when Curtiss provided a demonstration at an Army base (the name of which eludes my memory searches). The parade ground from which the demonstrations occurred was surrounded by trees approximately 50 ft high. There were more than a few finger in the wind rules raised in the early days to start the regulatory ball rolling.

Source - course about 25 years ago at which one of the instructors was a rather aged ex-CAB engineer and who was a boy in the office at or about the time.

35ft, as I recall from conversations with somewhat older certification folks, came about in the early days of jets when 50ft was found to be too limiting and a bit of equivalent safety horse trading was the salvation.

[MarkerInbound]

My understanding is Boeing got the jet requirement lowered from the prop 50 foot because the early 707s couldn't make 50 feet on the runways available.

Remember it's your takeoff distance. Most people think of takeoff as breaking ground. Requiring runway and clearway to allow you to get to 100 feet would make the aircraft performance numbers look bad. The manufactures would probably like the end of the takeoff to be 5 feet. "See, you can weight xxx,xxx and still get off a 6000 foot runway."

[bucks_raj]

Even lower for a wet runway

[HazelNuts39]

Special Civil Air Regulation no. SR-422 of 1957 was preceded by the Final Report of ICAO's Standing Committee on Airplane Performance of 1953. The US authorities participated in the SCOP and adopted part of its recommendations.

The screen height of 35 feet is equal to the NFP obstacle clearance that must be maintained after the end of the takeoff distance.

[aterpster]

bucks raj:

15 feet.