In addition to what @what_next said it is less demanding to have a rotation speed in initial training when the student can see that his action leads to a reaction of the aircraft. Flying with minimun speed in ground effect and letting the aircraft accelerate to Vx or Vy (or to what ever you chose to climb with) is more demanding than letting the aircraft take off with a speed with which you can fly her out of ground effect. Later, when the student has internalised the basic principles of flying and has some experience the proper procedures for short and soft field takeoffs can be taught in addition to the standard takeoff procedure. I have found that this is much easier when the student is advanced enough to really understand and feel the differences in takeoff techniques.
The same is true for landings. Before teaching a STOL landing with a 1.1 Vs0 approach or dog-legging the short final or flying an approach with an idle engine, the student has to be proficient in normal landings and be able to understand the differences.
In general it helps if you teach one consistent procedure (favourably one that allways works) until the student is proficient in them and only then teach deviations from these procedures.
Neil wrote:
Why keep a single engined aircraft on the ground until an arbitrary speed then yank it off?
Sometimes it does help in a crosswind to keep the nosewheel a little longer in contact with the ground to help with directional control.
But that’s about it. An aircraft needs to fly when it wants to fly. So let it fly.
Archie wrote:
An aircraft needs to fly when it wants to fly. So let it fly.
So that the lightest gust can bring it down again? Really?
Archie wrote:
An aircraft needs to fly when it wants to fly. So let it fly.
an easy demonstration of this – what is exact value of Vr for aircraft you fly? If you fly only single aircraft, there is a chance you know. but if you fly more types, you´ll hardly know. You just let it fly when she wants to fly.
I guess there is only one exception – short field take off, it makes sense to check POH…
Michal wrote:
You just let it fly when she wants to fly.
Depending on the trim setting (and for a lot of types independently of the trim setting) many aircraft do not start to fly on their own. They will continue to accelerate along the runway until either the tyres burst or it runs at high speed into whatever comes behind the runway. There are even types with a nose-low ground attitude which can not be rotated after passing a certain speed. So better have a look into the POH of every aircraft one intends to fly…
I agree; with the standard trim setting the TB20 will go to at least 90kt before it starts to float off. One does have to do a positive pull… But that’s just one and almost the only type I fly nowadays.
One of the benefits of flying light tailwheel aircraft is that their intrinsic yaw instability on the ground and light wing loading (i.e. gust sensitivity) gets you in the mode of flying the plane, not operating by wrote. Rotation speeds and the like have little meaning on that kind of plane, and you don’t stare at the ASI on the take off roll because you’re keeping the plane going in a straight line by nailing the nose visually on a distant point and dancing lightly on the rudder, particularly when on a hard surface. Meanwhile in pitch you use the right technique and feel the plane into the air, holding the nose down a little longer if the controls are moving around to counter gusts. After you’re airborne you sense the airspeed by climb rate and elevator feel, if necessary gaining a little more speed in ground effect. All done mostly by feel, except I like to check the ball right after liftoff to make sure some unintended yaw isn’t harming the initial climb rate.
Likewise on my nose wheel plane, I don’t like to use a high pitch rate to achieve the combination of AoA and airspeed that causes lift off. Perhaps a little more abrupt pitch control on a short runway, but mostly that’s unnecessary and rough, so why do it. Also the nose gear leg is stiff, it’s a poor design, and the plane bounces around if you leave the nose wheel on the ground too long. Elevator power is no problem from very low speed, so I like to ease the nose off the ground when the rudder is effective, but before the stiff nose gear becomes an issue, then continue with the nose airborne until I feel the airspeed rising through the controls, then ease up to a higher AoA with the aim of attaining takeoff AoA at the same time as takeoff airspeed. Meanwhile, as with a taildragger, I’m rolling on the main gear and keeping the nose nailed on a point with the rudder.
That’s fun, it’s even fun to write down! Jets and jet flying techniques are conversely associated with traveling for work, which for me is the opposite of fun.
Archie wrote:
An aircraft needs to fly when it wants to fly.
But an aircraft doesn’t “want” anything. It will attempt to lift off when it reaches a speed that it’s configured to lift off at. If an aircraft will lift off at X kts, then trim a bit more nose up, and it will lift off earlier; Trim a little less nose up, and it will wait until a higher speed before starting to lift off.
Through a badly configured trim, which was missed on pre take off checks, it could well try to lift off at a speed that it can’t accelerate at.
Personally, I prefer to lift off at a speed that gives me a little margin that if I get a gust that reduces headwind at the wrong moment, I won’t find myself unceremoniously dumped back on the runway! So for me this means taking charge over the lift off speed, rather than leaving it to chance on how accurately I set the trim.
what_next wrote:
So that the lightest gust can bring it down again? Really?
Yes.The lightest gust won’t bring it down, because you are applying full take-off power and accelerating even quicker as the wheels leave the ground. Really.
what_next wrote:
Depending on the trim setting (and for a lot of types independently of the trim setting) many aircraft do not start to fly on their own. They will continue to accelerate along the runway until either the tyres burst or it runs at high speed into whatever comes behind the runway.
But an aircraft doesn’t “want” anything. It will attempt to lift off when it reaches a speed that it’s configured to lift off at. If an aircraft will lift off at X kts, then trim a bit more nose up, and it will lift off earlier; Trim a little less nose up, and it will wait until a higher speed before starting to lift off
And yes, the aircraft wants to fly. I can tell you when it doesn’t: below Vs1 for the weight. Have you learned to listen to your aircraft?
Archie wrote:
Have you learned to listen to your aircraft?
You mean when it say: “Pull up, pull up pull up” 
I also think airline thinking applied to small aircraft is crazy. But I don’t think the aircraft “wants” to do things, it’s more that whatever I do, will enable the aircraft to do certain things.
