Go / no go - how to calculate obstacle clearance

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Vatso
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Re: Go / no go - how to calculate obstacle clearance

Postby Vatso » Fri Jun 01, 2012 5:42 pm

I think the answer is allot less complex then all the hard work people have put into the calculations

lets go back to basics!

when we take off the most important thing is speed and not how quick we can climb trying to climb to quick with engine failure will result in a bad day for all!!

so what one needs to do is know your trike! if you are airborne in 200meters @ 50mph & are climbing at max 200ft per min that will tell you what you can clear ahead of you. that is if there is no wind! if you take off into wind you GS is slower so you travel less in 1 min that gives us a "quicker" climb

hope this helps ?
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Re: Go / no go - how to calculate obstacle clearance

Postby Bundy » Mon Jun 18, 2012 8:15 am

Hi chaps,

In particular to John.com....thanks for taking the time to give us your points and share your methods of calculation. One can spot an Engineer quite easily it seems :lol: I admire the way you go to great lengths to ensure you take into account as many factors as you can in making your decisions. (^^)

This is a highly complicated topic, with many factors to consider. The one I didnt see mentioned is RUNWAY CONDITION/SURFACE.... Very important! It is amazing how this affects take off distances.

A quick question: How many trike pilots can honestly say that they know (to the meter) their take off distances (solo, dual, full fuel load, etc.)?

What you wrote above made me think....and I admit to not knowing this exactly..... :wink: Something I will definately have to remedy as they say. puff

I admit that I am extremelly nervous of short (300m and less) strips with any obstacles. I take a lot of what you have written into account when making decisions to TO and land, and after reading through what youve written, this list will definately get longer too.

One thing I am extremelly scared of (after a very bad experience!) is Vertical Windshear. The day this happened, I was taking off from ML 03. Wind sock was hanging flat calm, on this day, I had no obstacles to clear and there was ample length 400m. A normal TO on any given day in other words. Weather was cold, and wind predicted was 14knts 180. I had no visual evidence of this at the time though. Cloudless sky...looked like a beautiful day. With the sock still hanging "dead" I started my TO roll down 03. I rotated no problem.....then as I started to climb out, was prob about 25ft off the deck I experienced severe sink. I brought the bar back in to increase speed (I was allready at full rev's) and managed to level off. Eventually I slowly managed to initiated a very slow climb.... Why was it scary? Because I cleared the fence at the bottom of the runway (400 m long) by about 10ft :shock: The biggest mistake I made that day was that I did not realise that the 14 knt wind was in fact there!..... Just was not right on the deck.... If this had happened on runway 21 I would have ended up in the wires or worse. :shock: BIG LESSON LEARNT!

Vertical and Horizontal WS affects all your calculations...and must be taken into account especially for what you may think is a minor tailwind.

Anyway, thanks for a very informative post. I learnt a lot. (^^)
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John.com
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Re: Go / no go - how to calculate obstacle clearance

Postby John.com » Tue Jun 19, 2012 9:47 am

Bundy wrote: One thing I am extremelly scared of (after a very bad experience!) is Vertical Windshear. The day this happened, I was taking off from ML 03. Wind sock was hanging flat calm, on this day, I had no obstacles to clear and there was ample length 400m. A normal TO on any given day in other words. Weather was cold, and wind predicted was 14knts 180. I had no visual evidence of this at the time though. Cloudless sky...looked like a beautiful day. With the sock still hanging "dead" I started my TO roll down 03. I rotated no problem.....then as I started to climb out, was prob about 25ft off the deck I experienced severe sink. I brought the bar back in to increase speed (I was allready at full rev's) and managed to level off. Eventually I slowly managed to initiated a very slow climb.... Why was it scary? Because I cleared the fence at the bottom of the runway (400 m long) by about 10ft :shock: The biggest mistake I made that day was that I did not realise that the 14 knt wind was in fact there!..... Just was not right on the deck.... If this had happened on runway 21 I would have ended up in the wires or worse. :shock: BIG LESSON LEARNT!

Vertical and Horizontal WS affects all your calculations...and must be taken into account especially for what you may think is a minor tailwind.

Anyway, thanks for a very informative post. I learnt a lot. (^^)
Hey Alan, thanks for sharing this "windshear" experience! Noted . . . BUT . . . . how does one "predict" such windshear when the windsock is "pap"? "Not easy" is the answer I am anticipating! I mean, the big airports use Doppler radar to "see" windshear and to warn aircraft of the impending risks!

Anyone with some advice out there? (^^)

Thanks, John.com
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Re: Go / no go - how to calculate obstacle clearance

Postby BeanCounter » Tue Jun 19, 2012 1:32 pm

John.com wrote:Hey Alan, thanks for sharing this "windshear" experience! Noted . . . BUT . . . . how does one "predict" such windshear when the windsock is "pap"? "Not easy" is the answer I am anticipating! I mean, the big airports use Doppler radar to "see" windshear and to warn aircraft of the impending risks!

Anyone with some advice out there? (^^)
Maybe we should start carrying small bottles of helium and party balloons :lol: After preflight you go to the middle of the runway and send a couple skywards to see what happens! Alan, if I had your experience coming up 21 I'm not sure what I'll do, plant the plane back down or try to do a low turn over the sprinklers before you reach the wires?? (**) I guess a runway is like fuel, you can't have too much of it!
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Re: Go / no go - how to calculate obstacle clearance

Postby Bundy » Tue Jun 19, 2012 1:55 pm

BeanCounter wrote:
John.com wrote:Hey Alan, thanks for sharing this "windshear" experience! Noted . . . BUT . . . . how does one "predict" such windshear when the windsock is "pap"? "Not easy" is the answer I am anticipating! I mean, the big airports use Doppler radar to "see" windshear and to warn aircraft of the impending risks!

Anyone with some advice out there? (^^)
Maybe we should start carrying small bottles of helium and party balloons :lol: After preflight you go to the middle of the runway and send a couple skywards to see what happens! Alan, if I had your experience coming up 21 I'm not sure what I'll do, plant the plane back down or try to do a low turn over the sprinklers before you reach the wires?? (**) I guess a runway is like fuel, you can't have too much of it!
21 is always a bit scary....not my favorite :wink: I usually start turning east immediately after establishing the climb. (I'm sure merv and fanie have shown you the same :lol: ) Just gives you more options in case of "whatever".

Nowadays, after my little scare, I spend a lot of time during my preflight etc just staring at the clouds (if any) and especially the birds....they both give us huge clues as to what the conditions are like 100ft or so above the deck. What happened to me that day was that I took off in calm surface conditions and climbed into a heavy tail wind....I had no cloud cover to guide me in my runway decision, but..... had I paid more attention to the birds I could have seen what was in store for me.... School fees. :wink:

Oh and one last thing.....if the birds are walking....DONT FLY! ## :lol:
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Re: Go / no go - how to calculate obstacle clearance

Postby jj le roux » Sat Aug 04, 2012 1:01 pm

Thank you this is a very useful thread. Gives one a lot to think about. Would be great to see more of this type of thing doing the rounds.

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