AvNerd-Dispr t1_isqe7ix wrote
Reply to comment by ChuckChuckelson in TIL: Airplanes take off and land into the wind. They takeoff into the wind to reduce the groundspeed required to lift and land into it to reduce groundspeed when landing. by Key-Code-4296
Incorrect. Headwinds improve performance, short distance required, and lower the Vr (speed at which rotation is initiated). Tailwinds, even for big jets, have HUGE performance penalties.
Nokneemouse t1_isqkbmc wrote
They rotate at a given airspeed, which doesn't change, they just have a head start getting there due to wind speed.
AvNerd-Dispr t1_isqn86d wrote
As a pilot and someone who plans these numbers for dozens of flights on passenger jets everyday at work, I can confirm that the Vr is not static. It changes based on weight, flap/slat configuration, headwind/tailwind, temperature, ambient pressure, location of the CG… all of it affects the V speeds and they do very much change.
Nokneemouse t1_isqomm7 wrote
I mean that the VR is set for a given configuration of the aircraft.
son_et_lumiere t1_isr2whw wrote
Who or what does all the calculations that tells you how fast you have to go within what distance?
Good-Cardiologist679 t1_isr920e wrote
A flight planner, it’s someone’s job to crunch numbers for the pilot, but now pilots use ipads and etc and they have flight planning apps like foreflight that tell you all the info you need.
son_et_lumiere t1_israjdd wrote
I would have to assume the flight planner is in the cockpit with them, to account for changing variables in real time? Also, do they still exist in case like the iPads break or malfunction or something?
Good-Cardiologist679 t1_israwnc wrote
No. A flight planner is in a remote location. Theres a pilot and co pilot. Theres 2 tablets and the plane has built in gps, weather radar, navaids etc in it. Anything in the air is up to the pilots flying to make decisions
AvNerd-Dispr t1_issgdu0 wrote
For a commercial operation, the aircraft dispatcher. For a private pilot flying on their own, the pilot is responsible. Charter operations vary, its the pilots responsibility but some choose to hire flight planners and/or dispatchers as well and the responsibility is delegated to them.
The numbers and charts are found in the airplane manual for small aircraft, for commercial jets a separate manual is generally produced for the performance charts; my airline calls it the Operations Data Manual, or ODM. Our engineering team has gone through the ODM and coded all of the numbers into our flight planning system, so that as we plan the flight and update items like passenger count and the weights for checked bags and cargo, the system automatically updates and displays the numbers for those conditions for us to cross check and verify.
ChevExpressMan t1_isqiapw wrote
You mean only for takeoff. Otherwise tailwind help the jet in flight.
ChuckChuckelson t1_isqf33b wrote
you are right I meant to point out its less important for jets hat have two mile of runway
AvNerd-Dispr t1_isqjf6t wrote
Depends on the jet and how much payload and fuel it’s carrying. Also depends on the airport, altitude, temperature, obstacle clearance requirements, etc. I have planned and dispatched 777’s off 13000’ runways where we were bumping cargo to other flights due to poor takeoff performance.
Runway length is only 1 piece of a very complicated formula for determining payload allowed, its called Runway Allowable Takeoff Weight, or RATOW - this number can be higher than structural, in which case structural would be the weight limit, or it can be much lower depending on a whole host of factors, in addition to the length of the runway and the amount of headwind or tailwind.
Good-Cardiologist679 t1_isr8lxy wrote
Jets can take off with less than a mile of runway.
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