LiveATC Discussion Forums
Air Traffic Monitoring => Listener Forum => Topic started by: mhawke on May 22, 2007, 12:26:26 AM
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I realize this is not a ATC communication question, but has been a curiosity of mine for some time as I travel quite often for business.
During takeoff at rotation, the A320 planes (at least as flown by Northwest) shake quite noticably for a few seconds, at least until the landing gear is retracted. I am curious as to why.
A former commercial pilot has told me he thinks it may be a company policy to not apply brakes after rotation. He said many times a pilot will apply brakes to stop the wheels and keep them from spinning after leaving ground. He is suspicious that Northwest may have a company policy not to do that which may be allowing wheel spin to cause the vibrations once the wheels are off the ground.
Any Northwest pilots or A320 pilots care to offer an answer to a frequent business traveler?
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The 'shudder' you feel is basically just the gear and probably the wind surfaces shaking during take off. I fly the A320 and there is no procedure that tells you to apply brakes after take off. Actually other than our small piper P-28 that I trained on in flight school, I have never apllied, or been asked to apply brakes after take off.
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A former commercial pilot has told me he thinks it may be a company policy to not apply brakes after rotation. He said many times a pilot will apply brakes to stop the wheels and keep them from spinning after leaving ground. He is suspicious that Northwest may have a company policy not to do that which may be allowing wheel spin to cause the vibrations once the wheels are off the ground.
On the A320 the movement of landing gear doors sequence the normal braking system to AUTOMATICALLY apply the brakes to stop the main wheels from turning during retraction, as well there is a brake band in the nose gear wheel well that stops the nose gear as the door closes. There is no need to apply manual brakes to stop the wheels turning. I've flown in the back of the A320 many times and haven't noticed any different vibration compared to other types ?
DJ
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Jetscan1 Is correct. The normal braking system (Green hydraulic system) takes care of the main gears after t/o where as a strip takes care of the nosewheel. The reason is that the nosewheel does not create any centrifugal force as it retracts, also there is no braking for the nosewheel anyway. The main wheels will, however, so they need to be stopped from rotating to reduce the forces as it retracts.
I hope that helps.
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Thanks for the answers. Just a curiosity of mine anyways.
Like I said, I have only noticed this on Northwest flights. Specifically on the Minneapolis to Bozeman, MT route which is the only route I fly Northwest regulary. I wonder too if there is a higher takeoff speed for Bozeman because of the high elevation and that may make the wheels more prone to cause vibrations once they clear the ground.
Oh well, just curious, thanks for the answers.
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altitude, temperature, pressure, and wind affect the take off speeds
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I noticed that shuddering past week, mhawke. A320 from MSP to SAN had that shuddering thing before gear up. Didn't get that on the A320 leaving SAN for DTW yesterday.
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When the 320 first came out Airbus found out the elevator bearings would wear at a higher rate than expected. This is not a safety issue, but feeling the flutter caused concern and led Airbus and the FAA to issue an AD to have the bearings replaced. For a while 320 operators climbed at a slower airspeed than programed by the flight computer inorder to keep the stabilizers "loaded" and prevent the vibrations. It is hard to say if the vibrations you experienced were caused by premature bearing wear. Usually it is worse in the cockpit area.
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Elevator bearings wearing out would suggest that there is an aerodynamic cause... a low frequency vortex?
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Don't you think you are implying something next to vudo.
There is always a vortex any time lift if produced. Flutter has been known ever since the Wright brothers.
I think you are on the wrong forum.
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Don't you think you are implying something next to vudo.
There is always a vortex any time lift if produced. Flutter has been known ever since the Wright brothers.
I think you are on the wrong forum.
Yep, discussing airplane aerodynamics is drifting into off-topic area.
I have had my share of fluid dynamics and I am only suggesting a mechanism that may explain the vibrations... vortexes may be created at every surface edge with a pressure gradient; not just at the wingtips.