320DRIVER
5th Feb 2011, 13:52
This is a link (http://www.boeing.com/Features/2010/10/bca_787_test_limits.html) to the B787 VMU test (only a short excerpt shown...) and has the following text attached to it.
In the velocity minimum unstick test or VMU, pilots carefully drag the 787's tail on the runway to determine the lowest speed needed to leave the ground.
This test establishes the lowest speed the airplane can leave the ground and requires putting the tail on the runway. “You don’t want to hold the tail on the ground because that’s actually a big brake. It will slow the airplane down and you’ll never get up to take-off speed but then again you can’t let the tail come up because then you’re missing your data. So the idea is to get the tail down quickly, smoothly and just hold it on the ground, just, just hold it on the ground and then hold that altitude and then you have to fly away.”
It seems that the tail was held on the ground very very briefly compared to other VMU tests for other types. Is the "big brake" explanation really the issue or was there a worry of the effects of a tailstrike on the composite structure?
In the velocity minimum unstick test or VMU, pilots carefully drag the 787's tail on the runway to determine the lowest speed needed to leave the ground.
This test establishes the lowest speed the airplane can leave the ground and requires putting the tail on the runway. “You don’t want to hold the tail on the ground because that’s actually a big brake. It will slow the airplane down and you’ll never get up to take-off speed but then again you can’t let the tail come up because then you’re missing your data. So the idea is to get the tail down quickly, smoothly and just hold it on the ground, just, just hold it on the ground and then hold that altitude and then you have to fly away.”
It seems that the tail was held on the ground very very briefly compared to other VMU tests for other types. Is the "big brake" explanation really the issue or was there a worry of the effects of a tailstrike on the composite structure?