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50FT Obstacle landing.
Posted: Sun Feb 25, 2018 10:28 pm
by TopGun1234
When landing with a 50ft obstacle, is there a rule of thumb that states how high you should clear the obstacle? I'm in a C172. The FTM doesn't list a specific height.
Thanks,
Re: 50FT Obstacle landing.
Posted: Mon Feb 26, 2018 7:54 am
by Schooner69A
I'm not sure anything is specified. Your comfort zone, I guess.
I did a check out in a 172 years ago and in overflying a real obstacle (trees short of the runway) during a short-field landing demonstration, my "examiner" noted "You were pretty close to the tree tops". To which I replied: "If I'd have been in a helicopter, the skids would have been IN the tree tops"...
John
Re: 50FT Obstacle landing.
Posted: Tue Feb 27, 2018 4:23 pm
by Blackdog0301
Back when I was instructing, I’d usually give them a height ASL (which was roughly 50AGL) that I wanted them to cross the threshold at. If they were right bang on their altitude, I couldn’t really tell them they were off, but I did point out the fact that they probably scratched some paint on the belly as a result. So obstacle +50 feet on the altimeter is what I’d usually teach. Seemed to work very well.
Re: 50FT Obstacle landing.
Posted: Tue Feb 27, 2018 4:32 pm
by photofly
The point of the exercise is not to clear the obstacle by any fixed amount, but, to “select the most suitable touchdown zone and specify a touchdown point;” then clear the obstacle safely and “touch down at the specified touchdown point (+200/–50 feet)”.
It’s about predicting your own performance and matching your flying to your prediction, and not about aceing the shortest touchdown over the obstacle in history.
Re: 50FT Obstacle landing.
Posted: Tue Feb 27, 2018 10:24 pm
by ahramin
Well the 50 foot obstacle landing distance in your POH is based on clearing a 50 foot obstacle by 0 feet.
Re: 50FT Obstacle landing.
Posted: Wed Feb 28, 2018 10:24 am
by CpnCrunch
For the flight test, the examiner just wants you to imagine there is a tree or something similar at the threshold...so as long as you're somewhere in the region of 50ft that's fine. If there is an actual obstacle, just leave as much of a gap as you're comfortable with.
height ASL (which was roughly 50AGL) that I wanted them to cross the threshold at
I'm not sure it's a good idea to be looking at your altimeter on short final, and it probably isn't going to be accurate enough anyway.
Re: 50FT Obstacle landing.
Posted: Wed Feb 28, 2018 1:05 pm
by lownslow
photofly wrote: ↑Tue Feb 27, 2018 4:32 pm
It’s about predicting your own performance and matching your flying to your prediction, and not about aceing the shortest touchdown over the obstacle in history.
It's been a while since I did trig but on a 3* glide path you should be at fifty feet AGL just under a thousand feet before your aiming point. Since a VFR circuit is more courteous with a little steeper approach you'd probably be around fifty feet AGL maybe 800 feet prior to your aiming point then a bit of float and touch down smoothly after about a two hundred foot flare, but monitor your own performance to hone your consistency then as photofly said just pick your aim point accordingly.
Re: 50FT Obstacle landing.
Posted: Wed Feb 28, 2018 7:29 pm
by Blackdog0301
CpnCrunch wrote: ↑Wed Feb 28, 2018 10:24 am
height ASL (which was roughly 50AGL) that I wanted them to cross the threshold at
I'm not sure it's a good idea to be looking at your altimeter on short final, and it probably isn't going to be accurate enough anyway.
Well yes, but simply imaging a 50ft obstacle that isn’t there isn’t easy for a new pilot either. It was more about picking an aim point, fly an approach (at as constant of a descent as possible) and then just as you’re coming up to where your imaginary obstacle is, take a quick peak down to see where you sit. Never had a student fail that exercise with this method.
Re: 50FT Obstacle landing.
Posted: Wed Mar 28, 2018 2:17 pm
by C.W.E.
Where do you look to judge your height at 50 feet?
Re: 50FT Obstacle landing.
Posted: Sun Apr 01, 2018 9:31 am
by dpm
lownslow wrote: ↑Wed Feb 28, 2018 1:05 pm
photofly wrote: ↑Tue Feb 27, 2018 4:32 pm
It’s about predicting your own performance and matching your flying to your prediction, and not about aceing the shortest touchdown over the obstacle in history.
It's been a while since I did trig but on a 3* glide path you should be at fifty feet AGL just under a thousand feet before your aiming point. Since a VFR circuit is more courteous with a little steeper approach you'd probably be around fifty feet AGL maybe 800 feet prior to your aiming point then a bit of float and touch down smoothly after about a two hundred foot flare, but monitor your own performance to hone your consistency then as photofly said just pick your aim point accordingly.
If you have an actual obstacle, then as long as it appears to be moving slightly downwards in your windshield, you'll clear it with a bit of a margin (modulo any windshear or downdraft). If you're carrying ~10% over stall, you'll be able to zoom 10–20ft to clear if you do encounter that downdraft or shear. I agree with other posters that short final is no place to be fixating on your altimeter or counting runway markings—it's the time for basic stick and rudder flying.