The thread drift trade winds seem to have arrived for what was an OP on soft field take offs. Propeller aircraft (well the vast majority) have positive wing incidence and straight wings, so will naturally lift off, and arguably a safe take off speed is equivalent to Vlof. Teaching a jet concept such as Vr seems pretty harmless but is arguably a misnomer. Taking this to a mechanistic level, can and does lead to wheelbarrowing accidents with take off departures as students try and keep their nose drag puddle jumper on the runway to speeds above Vlof.
The soft field technique might logically require a higher angle of attack in a rolling take off to ensure the nose wheel does not dig in, which is expected to result in a Vlof which is below normal lift off speed, and requires acceleration in ground effect. If you attempt to fly out of ground effect at such a high AoA the jump in lift dependant drag (over 50 %), at speeds way on the back side of the drag curve will result in either a stall or no climb at all. The only way out of this is lowering the nose to reduce AoA and come down the drag curve. Low level wind shear also applies for the transition to flying out of ground effect.
ATP students are expected to understand these concepts from their PoF paper, for example the need for positive rotation on a swept wing jet, and the different thrust curves between turbo fans and propeller aircraft, Not sure how a straight wing slowtation behaves, but expect it lifts off naturally without the need for a positive rotation?
Some instructors believe that flying with just a compass and oil pressure gauge might improve how students listen to what the aircraft is trying to tell them.
RobertL18C wrote:
The thread drift trade winds seem to have arrived for what was an OP on soft field take offs. Propeller aircraft (well the vast majority) have positive wing incidence and straight wings, so will naturally lift off….Most of my flying experience is in C172 and PA28 aircraft. In my experience, C172’s do indeed fly off by themselves while PA28s need a positive rotation. At least they do for short field take-offs — which are the majority for me since I am based on a shortish grass field.
Teaching a jet concept such as Vr seems pretty harmless but is arguably a misnomer. Taking this to a mechanistic level, can and does lead to wheelbarrowing accidents with take off departures as students try and keep their nose drag puddle jumper on the runway to speeds above Vlof.
Not if you use the correct Vr for the takeoff mass.
@RobertL18C Nobody advocates forcing the aircraft on the ground. If you do a gentle rotation to consiously pitch to liftoff attitude it is much gentler as ripping the aircradt off the ground at minimum speed and then accelerate in ground effect, at leat for a new student. After the student has gained some feel for the aircraft you can show the other options… And when training ATPL you expect them to follow procedures right away. It is a pity but the industry doesn’t pay for their pilots to become aviators.
Not sure how a straight wing slowtation behaves, but expect it lifts off naturally without the need for a positive rotation?
No multiengine Cessna I have flown so far (prop and jet) lifts off by itself. They all need to be positively rotated. I have done grass field takeoffs with the C421 where even strong bounces above stall speed would not make it fly on it’s own.
what_next thank you, they have no incidence while sitting on the ground is my guess and presumably don’t have a tendency to wheelbarrow?
mh agree no one advocates forcing the aircraft on the ground until you achieve a certain speed, at the same time a soft field take off has nothing to do with ripping the aircraft off the ground, the aircraft just flies off the ground at minimum speed – if you do not ease forward at lift off then the aircraft will mush. The soft field take off used to be a PPL PTS but doesn’t seem to be required in Europe, I think it still is required Stateside.
RobertL18C wrote:
Some instructors believe that flying with just a compass and oil pressure gauge might improve how students listen to what the aircraft is trying to tell them.
I entirely agree! I delight in having my trainee pilot fly the Super cub from the back first, so they can’t see any instruments anyway. Once they show some skill there, I’ll move them forward.
No multiengine Cessna I have flown so far (prop and jet) lifts off by itself. They all need to be positively rotated.Quote
I see the point being made with this statement, multi engine Cessnas are more “airliner” than single engine GA aircraft in the way they handle slow speed flight. However, every single Cessna I have flown, from the 140 through to the Caravan responds nicely to flying itself off. If a positive pitch attitude is held (meaning pitch control back pressure for the tricycles) from the early stage of the takeoff roll, the plane will fly off on its own at an appropriate speed. It would be impossible to safely control a tricycle Cessna which was being “held onto” the runway to greatly excess speed. It would wheelbarrow horribly, and you would groundloop it. I know of this being done during landings. It does not work.
I do not accept the argument that the nosewheel of a Cessna should be left (or worse, held) in contact to enable “steering” to maintain directional control. Once the airflow over the tail is adequate to affect the pitch attitude (and enable you to lighten the nosewheel), the directional control is accomplished entirely with the rudder, the nosewheel is just along for the ride. I fly a 300HP C 182 which has only free castoring “steering”, so the pilot does not use nosewheel steering at all to control direction. The rudder is solely and entirely effective with takeoff power set, from speeds of about 15 knots onward. I teach at all times to consider the rudder as the means of steering, and get the third wheel early (Tomahawks excepted). If third wheel steering were necessary for directional control at speed, during takeoff or landing, the very common tailwheel locks would be counter to that, and every plane with a free castoring nosewheel would be off the side of the runway. But theses types work entirely well. Similarly, every seaplane has no directional control reacting to the surface after takeoff power is applied, and can be precisely directionally controlled. Note that all tricycle Cessnas have steering springs, so that if the application of rudder control is in conflict with the castoring steering angle, the nosewheel will trail straight anyway – it saves scrubbing the nosewheel tread (much), as is unfortunately more possible in aircraft with direct nosewheel steering (Twin Otter).
To overcome my concerns about crosswind takeoff and landing directional control in a rather challenging taildragger I own, I spend an afternoon in a 20 knot wind, flying on and off the ice of a local lake. Zero traction whatever – glare ice. I worked my way around to flying landings and takeoffs directly against the wind with no difficulty with directional control, until the plane slowed to less than 10MPH, at which point it would weathercock, for lack of rudder effectiveness. Otherwise, it was entirely controllable. What I learned was that at speed, the rudder was fully enabling the control I required.
So from this, I will always teach that the third wheel is to be held light as early in the takeoff as possible, unless there is a specific reason to not do so. Tomahawk, or specified POH technique required). For the past three decades or more, most every takeoff I have flown in a single has been more or less the soft field technique, unless there has been a reason to do otherwise. Using this technique has meant more than 3000 hours flying my tricycle Cessna with never a need for nosewheel/oleo repair – simply the specified maintenance. It works for me, so I teach it!
No it is part of training but in initial flight training (read: The first 20..30 takeoffs) it is easier to have an aircraft that won’t mush along once airbourne. Lifting off at minimum speed requires max AOA and with some aircraft and loadings it is entirely possible to move along past that on the main wheels and Stalling the aircraft on the ground.
So basically normal procedure is letting the aircraft roll, make a contious rotation to achieve a flyable AOA and let it lift off at or around Vx. No wheelbarrowing or pushing the aircraft on the ground would be required for that.
mh wrote:
So basically normal procedure is letting the aircraft roll, make a contious rotation to achieve a flyable AOA and let it lift off at or around Vx. No wheelbarrowing or pushing the aircraft on the ground would be required for that.
For a typical GA tricycle (excluding Tomahawk), I follow a different approach. I have noticed that when a pilot decides (apparently based upon indicated airspeed) that it is time for the aircraft to fly, they expect it to fly. This means a rather short duration transition between wheel borne, and (hopefully) airborne. In this situation, everything is happening at once, and it can get busy. Pilots are not so good at instantly assessing the fact that maybe the aircraft is not ready to fly just yet, and instead of waiting in that attitude, will pull more. Or, the possible crosswind suddenly becomes apparent as drift, which must be wholly corrected right away. It will work, but is more “notchy” flying.
If a Cessna (as my example type) is pitched up so as to reduce by half, whatever view the pilot has of the runway over the cowl, and held at that attitude as it accelerates, the possible affect of a crosswind will gradually become apparent, and can be compensated, and at that attitude, the plane will simply fly off with no other pitch change, or worries about stall or light gusts. It’s not being hauled off the ground below stall speed, and hanging in ground effect, and it’s certainly not wheelbarrowing down the runway.
I agree that some GA flight manuals refer to a “rotate” speed. I simply find this unfortunate. Yes, it works, but it leads to pilots who are looking at instruments to determine how a plane is to be flown, rather than allowing aerodynamic forces to act when the desired equilibrium is achieved. For heavy and multi engined aircraft, this has a place. Much less so for light singles…
Pilot_DAR wrote:
I have noticed that when a pilot decides (apparently based upon indicated airspeed) that it is time for the aircraft to fly, they expect it to fly. This means a rather short duration transition between wheel borne, and (hopefully) airborne. In this situation, everything is happening at once, and it can get busy. Pilots are not so good at instantly assessing the fact that maybe the aircraft is not ready to fly just yet, and instead of waiting in that attitude, will pull more. Or, the possible crosswind suddenly becomes apparent as drift, which must be wholly corrected right away. It will work, but is more “notchy” flying.
I think that’s a great description. Unless a very short runway forces you to transition from lowest drag rolling attitude to takeoff attitude in the minimum amount of time, there are a lot of good reasons to do it another way, with details often depending on type.
Pilot_DAR wrote:
… but it leads to pilots who are looking at instruments to determine how a plane is to be flown, rather than allowing aerodynamic forces to act when the desired equilibrium is achieved.
The instruments are a mirror image of the aerodynamic forces acting upon the aircraft. Not every pilot has the experience or the ability to “gut feel” those forces, therefore instruments are fitted for him. Instruments don’t fool anybody, “gut feelings” do sometimes. If one can fly his aeroplane be feel – good for him. But this is nothing I can teach anyone in the assigned number of flying lessons.
RobertL18C wrote:what_next thank you, they have no incidence while sitting on the ground is my guess and presumably don’t have a tendency to wheelbarrow?
No wheelbarrowing at all!
