tigris72

Not sure if this is the right section but thought I would try as I can't find an answer anywhere else.

I am a teacher, not a pilot but was wondering if anyone had the technical knowledge of aircraft to answer a question I have.

In my lessons we are learning about the property of flight and have covered the science behind how an airline takes off with airflow etc over the wings. However, we have become stuck on what actually changes on the aircraft when a plane reaches a speed where the plane is rotated. We have visited our city's domestic and international ariport which has excellent viewing areas and watched planes land and take off and we were unable to notice anything that changes at rotation. We are specifically talking Boeing / Airbus planes ie A320, 737, 767 etc.

Firstly, does a pilot pull back the yoke or side stick and if so what does this actually do to change the angle of attack on the wings and make the aircraft airborne?

Thank you for any comments that will help my classroom.

TonyWilliams

What age are the students? Knowing that might determine how technical the answer will be.

But, yes, the aircraft, on the takeoff roll is "configured" for takeoff. The flaps (attached behind the wing, pointed aft and slightly toward the ground) are set per a schedule of runway performance that includes thrust used for take off, weight of the aircraft, and wind. If nothing is done, except advance the engine power to take-off thrust, the airplane would just roll off the end of the runway at a very high speed. Bad day.

So, at a calculated speed called VR (Velocity of Rotation), the "Pilot Flying" (PF) pulls back on the control stick / yoke at a steady 3 degrees pitch up per second until reaching the target pitch, which might be 10 to 18 degrees. You should see the elevator / stabilator on the trailing edge of the rear most edge of the aircraft, usually also the highest point on the aircraft, defect UPWARDS.

It won't move much to the naked eye at the distance you'll be from the aircraft to view, unfortunately.

The aircraft will lift off when lift becomes greater than the gravitational pull against mass.

Hope this helps.

SunDog

The pilot pulls back on the controls, which causes the elevator to produce a downward force at the tail, which in turn causes the nose to rotate up.

when the aircraft nose rotates upwards, the angle of attack of the wings (relative to the air flow) increases and more lift is produced.

other than control surface deflection, (or poor technique) there are no physical changes to the aircraft. were you perhaps confusing "angle of attack" with "angle of incidence"?

the FAA has a good free book: Pilot's Handbook of Aeronautical Knowledge
in particular look at chapters 3 and 4.

rickair7777

The amount of lift generated by the wing increases as airspeed increases, it also increase with angle of attack. On the takeoff roll the lift increases as the airplane accelerates.

As the lift approaches that needed for the airplane to fly ( > than the weight of the airplane) the pilot rotates the nose up slightly, which increases angle of attack providing a sudden boost in lift which pulls the airplane off the runway.

If you just kept accelerating without rotating the airplane would also eventually takeoff when the lift got high enough but it would require a longer runway and would not be elegant...the airplane might bounce down the runway a little bit first.

Most of the lift comes from the airspeed, the rotation is just done to provide a clean and decisive takeoff point and reduce runway length..

TonyWilliams

I'm not so sure every plane will do that !!!! How long of a runway? Would the drag of the wheels on the ground be enough to never allow many / most jet planes to ever reach the "non-rotation" lift off speed?

But, I get the point you're trying to make.

mswmsw

Aerodynamics can explain why a barn door will fly or how your hand can "fly" while outside your car window zipping down the highway. But do your kids a favor and teach them what really makes an airplane fly...... money.... and lots of it!

snippercr

One thing I never really understood until I almost got my CFI (Certified Flight Instructor) was the difference between how an airplane produces "Lift" and how an airplane "climbs."

Lift (To counter gravity) is primarily generated by the wings and is dependent on air speed, angel of attack, air density, surface area, etc.

Climb performance is based on the engine and how well the engine performs.

When I am really trying to make sure my students fully understand this fact I show a video of an F-16 in a vertical climb. I ask them what is the angel of attack of this jet vs us when we are cruising out to the practice area? If they say "The same" I go onto the next lesson. If they say "MUCH greater" than I know I have a little more work to do.

tigris72

Thank you everyone, I am very grateful for your replies. The explanations have really helped. I teach middle school kids 11-15 Year old so I will be able to use a lot of this in my next lesson.

msmspilot

Realizing that you said you're primarily looking at big airplanes, you might change tactics slightly to make the "change" more visible.

If you know someone who is a pilot, call them up, and take a field trip out to your local small airport. Small airplanes fly for the same reasons big airplanes do, and it's easier to see the elevator deflection when you can get a little closer to it. If you don't know a pilot, find a local flight school or independent Flight Instructor. I did field trips to the airport for various school groups, day cares, Boy Scouts, and some stuff with Civil Air Patrol. Most good flight instructors are interested in helping spread interest in aviation.

Planespotta

Excess thrust directed upwards helps, too. Don't forget that.