Screen Height

[Pete O'Tube]

Hi Folks,

Just doing a bit of book bashing and can find loads of references to Perf A, one engine out screen height of 35 ft.
The only reference I can find to 50 ft is when a turn of more than 15 degrees is required.

Now am I getting mixed up with other Perf Cat's or does Perf A normally have an all engines operating screen height of 50ft.

Call me stupid, daft but my minds gone blank and can't find a reference.

Thanks

[Genghis the Engineer]

For an airliner the answer is at

http://www.jaa.nl/jar/ihs_data/frame...6435/46435.htm

For a smaller aircraft, it's at

http://www.jaa.nl/jar/ihs_data/frame...5865/45865.htm

And for a yet smaller aircraft it's at

http://www.jaa.nl/jar/ihs_data/frame...0511/50511.htm


I'm not honestly sure why transport aircraft such as are in parts 23 and 25 use 35 feet, and "very light aeroplanes" use 15m (49ft). Anybody else know ?

G

[Pete O'Tube]

Thank you Gengis,

seems like a good web site that

[john_tullamarine]

It is my understanding that the original 50 feet height was somewhat arbitrary, dating back to the early US days of aviation. It was based on the height of trees around a particular military compound which in turn was relevant to a particular military aircraft marketing demonstration (if my recollection is correct, by Curtiss).

A number of the early rules were plucked out of the air on the basis of engineering judgement to get the US civil rule making machine started.

I have never seen a certification justification for it but, if you do the sums for, say, the 707/DC8 - ie the early jets in vogue when the present ruleset took wing, with 15 degrees bank the outer pod drops down around 15 feet so I have always presumed something along those lines to have been the basis for the 50 feet turning clearance to the net flight path.

As such the original screen heights are not, in any way, sacrosanct, just historical ...

[ 30 November 2001: Message edited by: john_tullamarine ]

[411A]

If you look back far enough...you would notice that this all (more or less) changed when CAR4b became FAR25...in the mid-1950's.
Also suspect that, due to the rather poor airfield performance of the early jets (no leading edge devices, non-fan engines, ie: early B707) many could not make a 50' screen height. If many junior guys got into one of these aeroplanes today, they would wonder how they were ever certificated.
And...high altitude handling was no bargain either.

[m&v]

My understanding too.With the pistons,cert'data referred to the 50'limit with the advent of turbojets ,35'the only reference.CAA(bcar) circa the late 70's introduced the 'wet'15' compromise(adopted be JAR's)and hopefully to be Harmonized by the FAA.