Ryanair uses all the runway.
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As self loading freight carried in and out of Bristol, I do wonder whether your post underlines the concerns raised by some posting here.
It has been suggested by some with a better technical understanding than me, that the likely reason that the aircraft shown in the video made full use of the limited runway at Bristol was because it was using reduced thrust.
If a decision had to be made on this aircraft to delay the rotate call to avoid a large flock of birds crossing the runway, what would have been the consequence?
It has been suggested by some with a better technical understanding than me, that the likely reason that the aircraft shown in the video made full use of the limited runway at Bristol was because it was using reduced thrust.
If a decision had to be made on this aircraft to delay the rotate call to avoid a large flock of birds crossing the runway, what would have been the consequence?
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The thread has crept somewhat but throughout my longhaul career I was fairly certain that most of the so-called safety margins were very marginal but could somehow be justified on paper. Max weight (over?) 747-100 departures from Caribbean islands were usually a matter of holding your breath just after rotation and hoping that the gear didn't hit anything on the boundary. Similarly at very low temperatures out of Anchorage trying to accelerate and climb.Or Nairobi with runway temperature quoted in 1/2 degrees to fiddle the book figures. 3 engines shortly after V1 would have been interesting. Fortunately the first generation of 707 and 747s IIRC didn't have the added potential for cockups of reduced thrust take-offs. As a young F/O on a very hot and humid Lourenco Marques departure I called rotate, the a/c lifted off briefly and then settled back on the r'way. The second attempt succeeded-just...
Last edited by Lodems; 19th Oct 2017 at 12:40. Reason: typo islands
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Despite comments in this thread to the contrary, meaningful metrics can be collected from cell phone video.
In this case, I am looking at the shadow of the wing to judge the relative position of the 737 at it crosses runway landmarks.
Here's is what I note:
2:11 Early edge of taxiway H. About 1475 meters of runway remaining.
2:21.5: Middle of retired taxiway. About 780 meters of runway remaining.
2:27: End of bar at outside edge of runway. About 356 meters of runway remaining.
So, in that last stretch, the 737 crossed 424 meters in 5.5 seconds. Averaging 77 meters per second or 150 knots.
That's averaging roughly 150 knots.
At that point, he still had 350 feet on runway in front of the wing - but did not rotate for another second.
So as best I can tell, this was a delayed rotation.
In this case, I am looking at the shadow of the wing to judge the relative position of the 737 at it crosses runway landmarks.
Here's is what I note:
2:11 Early edge of taxiway H. About 1475 meters of runway remaining.
2:21.5: Middle of retired taxiway. About 780 meters of runway remaining.
2:27: End of bar at outside edge of runway. About 356 meters of runway remaining.
So, in that last stretch, the 737 crossed 424 meters in 5.5 seconds. Averaging 77 meters per second or 150 knots.
That's averaging roughly 150 knots.
At that point, he still had 350 feet on runway in front of the wing - but did not rotate for another second.
So as best I can tell, this was a delayed rotation.
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Do you know Vr?
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.Scott:
Surely, before any information from shadows can be included you must know the height of the sun above the horizon, its position relative to the aircraft etc. also, just minor movement of the hand holding the smartphone will change the picture. Throughout this thread assumptions have been made without knowing any of the relevant trigonometry which has just been ignored.
In this case, I am looking at the shadow of the wing to judge the relative position of the 737 at it crosses runway landmarks.
Surely, before any information from shadows can be included you must know the height of the sun above the horizon, its position relative to the aircraft etc. also, just minor movement of the hand holding the smartphone will change the picture. Throughout this thread assumptions have been made without knowing any of the relevant trigonometry which has just been ignored.
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So i had some snarky remarks but i'll cut it out.
How many meters would you guess is the shadow from the wing? If you say less than 10 than that's easily good enough to know where the airplane is.
He only used the shadow to get relative positions so speeds estimated are as accurate as possible. The change of sun angle during takeoff is negligible.
Regarding the angle described in an earlier post, there is some distortion but the analysis isn't nearly as bad as you make it out to be.
Instead of just disregarding what they did maybe use some trigonometry to approximate the errors made using their techniques.
How many meters would you guess is the shadow from the wing? If you say less than 10 than that's easily good enough to know where the airplane is.
He only used the shadow to get relative positions so speeds estimated are as accurate as possible. The change of sun angle during takeoff is negligible.
Regarding the angle described in an earlier post, there is some distortion but the analysis isn't nearly as bad as you make it out to be.
Instead of just disregarding what they did maybe use some trigonometry to approximate the errors made using their techniques.
Surely, before any information from shadows can be included you must know the height of the sun above the horizon, its position relative to the aircraft etc. also, just minor movement of the hand holding the smartphone will change the picture. Throughout this thread assumptions have been made without knowing any of the relevant trigonometry which has just been ignored.
a) the aircraft tracking more-or-less along the runway centreline up to the point where it rotates and becomes airborne, and
b) the sun staying in the same position in the sky for the duration of the takeoff roll
The point at which the aircraft rotates and becomes airborne can be readily discerned from the change in the angle that the wing L/E subtends with the horizon, the position of the wingtip/winglet relative to the runway edge marking and the distance between a point on the wing and its corresponding shadow on the runway.
Minor movements of the camera will have a negligible effect on any of those.
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I see the aircraft rotate right after the 1,000 marker, and it seems like a very mild rotation. Some pilots rotate like an aerobatic maneuver, and others do it like they are taking a child's hand. I am guessing this pilot is the latter.
Well, if the pilot rotated at Vr at a rate of one degree per second, he or she would have chewed up a lot f runway before the wheels lifted compared to a normal flight where the rotation rate is approx 2.5 degrees per second.
Rough figures, at 150kts you're using 250ft of runway a second.
The aircraft leaves the ground at about 11 degrees nose up.
At the normal rotation rate it is 4.4 seconds from beginning the rotation until airborne.
At 1 degree per sec it is 11 seconds.
That's an extra 6.6 seconds on the ground with the slower rate.
6.6 seconds = approx 1600ft of extra runway used.
Kinda explains everything really ( assuming the estimated rotation rate is correct).
Edit; I just had a look in the FCOM and lift off at flap 5 is 8 degrees, not 11, so the slower rate uses an extra 1200ft of runway, not 1600ft.
Rough figures, at 150kts you're using 250ft of runway a second.
The aircraft leaves the ground at about 11 degrees nose up.
At the normal rotation rate it is 4.4 seconds from beginning the rotation until airborne.
At 1 degree per sec it is 11 seconds.
That's an extra 6.6 seconds on the ground with the slower rate.
6.6 seconds = approx 1600ft of extra runway used.
Kinda explains everything really ( assuming the estimated rotation rate is correct).
Edit; I just had a look in the FCOM and lift off at flap 5 is 8 degrees, not 11, so the slower rate uses an extra 1200ft of runway, not 1600ft.
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.Scott:
Surely, before any information from shadows can be included you must know the height of the sun above the horizon, its position relative to the aircraft etc. also, just minor movement of the hand holding the smartphone will change the picture. Throughout this thread assumptions have been made without knowing any of the relevant trigonometry which has just been ignored.
Surely, before any information from shadows can be included you must know the height of the sun above the horizon, its position relative to the aircraft etc. also, just minor movement of the hand holding the smartphone will change the picture. Throughout this thread assumptions have been made without knowing any of the relevant trigonometry which has just been ignored.
Oh dear...
The formula for constant acceleration is v = 2 * d/t - final velocity is twice the average
However acceleration during a jet takeoff is not constant as thrust from a jet increases non linearly as speed increases. Drag generally does not offset thrust increase while on the runway during takeoff.
As for shadow angle from the wing, corrections could be applied for earth rotation and latitude-longitude change as well as wing flex. Note that on the runway the sun is lined up close to the wing axis. The wing tip shadow stays in a constant relative position to the outer flap canoe until liftoff. A beer says any correction would be less than 10 cm. Etkin in Dynamics of Atmospheric Flight states that earth rotation and latitude-longitude change effects are negligible until in high mach flight.
Like the original poster I have had a similar view of the opposite end piano keys departing on a hot day and still wonder how things would have turned out had we had a V1 cut.
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Fair enough all you naysayers, wiedehof, neila83/David Reid, yet more assumption without a single figure of data to back it up, just your own guess work, take it all to an enquiry, or a court if you like, and see how far you get 
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The next question is that given that the runway was dry, what relevance does the screen height of 15 feet for wet runways have to do with the issue raised here?
That would be akin to saying that because emergency vehicles in the UK are exceptionally permitted to disregard the normal traffic rules when responding to an emergency providing the blue flashing lights and sirens are used, drivers of such vehicles could rely on that exception when not responding to an emergency.
That would be akin to saying that because emergency vehicles in the UK are exceptionally permitted to disregard the normal traffic rules when responding to an emergency providing the blue flashing lights and sirens are used, drivers of such vehicles could rely on that exception when not responding to an emergency.
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The cameraperson is on their seat with a seatbelt on, so given the distances involved, camera movement is sure to be neglible - and the window size restricts the possible viewpoint variation even further. I did assume the aircraft staying on the centerline. The height of the observer can be judged by the height of the horizon with respect to the runway, as long as the airplane remains above the center.
The horizon isn't always visible (obscured by scenery and a small elevation), so I judged rotation by comparing it with the angle of the runway edge, which remains unchanged as the airplane is on the ground, but may vary as the plane lifts off, due to perspective and lens distortion. I've now confirmed the value of 6° rotation over the threshold by attempting to line up the horizon, see attached image. (Lining the first image up by the edge of the green or the treetops, the difference is about 0.3°.)
Takeoff was 1:30, I believe, so on BST the sun should be almost to the south, on a takeoff due west. That means the shadow position changes minimally with wing height over the runway (the point of contention being that the plane is low over the threshold); 10' height change with the sun 12° off-axis equals 2' lateral position change (sun 191°az 29°el at 1:30 BST). The shadow shape will narrow <1% as the wing rotates 6°.
I've looked at the distance from the blue dot at the bottom of the wingtip to the tip of the wing shadow to determine wingtip height. Assuming[1] the bottom of the winglet is at 13.5' over the eastern threshold marker, it rises as the wing flexes with lift and is around 15' over the center of the runway, up to the aiming point. Rising slowly (~60 ft/min), it exceeds 17' at the final touchdown marker and shows from 19 to 20.5 feet over the threshold marker (~300 ft/min). Runway end 22.5', 400'/min. This checks with the wingtip positions on the image I posted at #192.
I believe that takes care of Dave's suggestions (thank you!).
[1] http://www.boeing.com/assets/pdf/com.../acaps/737.pdf p.46 (p.50 in the PDF), row K.
The horizon isn't always visible (obscured by scenery and a small elevation), so I judged rotation by comparing it with the angle of the runway edge, which remains unchanged as the airplane is on the ground, but may vary as the plane lifts off, due to perspective and lens distortion. I've now confirmed the value of 6° rotation over the threshold by attempting to line up the horizon, see attached image. (Lining the first image up by the edge of the green or the treetops, the difference is about 0.3°.)
Takeoff was 1:30, I believe, so on BST the sun should be almost to the south, on a takeoff due west. That means the shadow position changes minimally with wing height over the runway (the point of contention being that the plane is low over the threshold); 10' height change with the sun 12° off-axis equals 2' lateral position change (sun 191°az 29°el at 1:30 BST). The shadow shape will narrow <1% as the wing rotates 6°.
I've looked at the distance from the blue dot at the bottom of the wingtip to the tip of the wing shadow to determine wingtip height. Assuming[1] the bottom of the winglet is at 13.5' over the eastern threshold marker, it rises as the wing flexes with lift and is around 15' over the center of the runway, up to the aiming point. Rising slowly (~60 ft/min), it exceeds 17' at the final touchdown marker and shows from 19 to 20.5 feet over the threshold marker (~300 ft/min). Runway end 22.5', 400'/min. This checks with the wingtip positions on the image I posted at #192.
I believe that takes care of Dave's suggestions (thank you!).
[1] http://www.boeing.com/assets/pdf/com.../acaps/737.pdf p.46 (p.50 in the PDF), row K.
Last edited by Musician; 20th Oct 2017 at 10:55.
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.Scott:
Surely, before any information from shadows can be included you must know the height of the sun above the horizon, its position relative to the aircraft etc. also, just minor movement of the hand holding the smartphone will change the picture. Throughout this thread assumptions have been made without knowing any of the relevant trigonometry which has just been ignored.
Surely, before any information from shadows can be included you must know the height of the sun above the horizon, its position relative to the aircraft etc. also, just minor movement of the hand holding the smartphone will change the picture. Throughout this thread assumptions have been made without knowing any of the relevant trigonometry which has just been ignored.
Of course, you may want to know distance from the end of the runway to a particular spot on the plane - such as the nose or the landing gear. And I do not have those offsets.
As other posters have noted, since the sun angle does not appreciably change during the take off roll, and the wing stays approximately the same distance above the surface during that time, the shadow makes for a good indicator. It is moving with the plane.
As far as the distances are concerned: I used a runway map, compared it to photographs of the airport to verify that it was true, downloaded it to my computer, brought it up in paint, and examined it at the pixel level.
Then I used the 2011 meters and the runway end markers to establish the exact scale. All other measurements were based on that.
Perhaps the biggest contributor to error was the timings. If I had downloaded the video, I could have stepped through it frame by frame and gotten timing good to about 70 milliseconds. But since I viewed them from the web, those timing were probably only good to about 200 ms.