DESO interview questions

[eljopito]

Hi guys,

In browsing old threads I have come across a few questions without the answer being given that left me puzzled.
Care to help me (and maybe others) out?

Sometimes to increase the TO weight we have to reduce TO thrust, how does that work?
(Something to do with reduced V1 and Vmcg?)

If winglets decrease induced drag, why doesn't the 777 have them?
(something to do with the fact that the 777 has a best wing design to date?)

Thanks!!

Jopito

[energie]

If winglets decrease induced drag, why doesn't the 777 have them?
(something to do with the fact that the 777 has a best wing design to date?)

This is all over the board, you would find several different reasoning by searching

basically, one of the components that causes induced drag are wing tip vortices. These are eddies that gathered at the end of the wing tip. Winglets decrease induced drag because they will diffuse these wing tip vortices as they are collected at the end of the wing tip in motion.

B777s don't have them because they simply don't need them. the 777 is the first plane to be completely designed by computer, so their wings already have the optimal dimension and shape(ie raked wing tips)

good luck

[betaboy]

To very basically answer the first question: some operations are Vmcg limited, as you may be if you had a very short runway. If that were the case, you could reduce the thrust moment for the engine failure case by reducing the thrust. So you would set a "derated" take-off thrust. You would be unable to firewall the thrust in the event of an engine failure, but it would allow you to increase the gross takeoff weight.

Plenty of more complete answers in this forum and the Tech Log.