Quanto tempo já foi gasto em discussões nos aeroclubes e escolas de aviação mundo afora sobre qual é a melhor aeronave para treinamento – ‘convencional’ ou triciclo? Talvez milhares de anos… Então, para que possa sobrar mais tempo para discutir outros assuntos – Boeing ou Airbus? Aeroclube X ou Escola Y? PP pode trabalhar como piloto?? etc. – leiam esse artigo da Airfacts que o nosso amigo Beto Arcaro indicou, que explica praticamente tudo o que interessa sobre o assunto:
Why you must fly a taildragger
Training Squadron (where I teach) is a “stick-and-rudder” school. We teach flying fundamentals–either from scratch for our ab-initio pupils or as “modification of behavior” for our more experienced ones. All our aircraft happen to have tailwheel, a.k.a “conventional gear,” but we are not bigoted against tricycle gear aircraft. Not every aircraft needs to have a tailwheel; in fact it may be preferable to have a nosewheel for many reasons–not the least of which may be increased margin of error for various conditions that may be encountered while flying that aircraft.
I was prompted into writing this article because of two events. One, the crash of the Asiana Boeing 777 at San Francisco airport, which is about 20 minutes flying time from where we are based, and the second was the publication of an article by Budd Davisson in Sport Aerobatics magazine entitled “The Pitts as a (Basic) Trainer.”
The first event brought into sharp focus the need for basic flight skills (airspeed – altitude – flightpath) even in an highly automated and complex airplane like the Boeing 777. The second provocatively posed the question about whether our trainers are too “dumbed” down to be effective.
Basic Flight Skills still needed
Tailwheel airplanes like the Cub demand an awareness of speed, altitude, energy and flight path.
Landing an aircraft in daylight should be a basic skill, even with the advent of automation. Awareness of speed, altitude, energy and flightpath should be so basic that it should be instinctual. My hypothesis is that conventional training aircraft with tricycle gear do not help a student pilot gain these instincts and taildraggers /tailwheel /conventional gear aircraft do.
Budd Davisson pretty much echoes my hypothesis. Quoting from his article: “…nosedragger trainer really does not care how you put it on the ground… the result is PPL pilots with weak basic skills… The Pitts won’t let you get away with ignoring the basics.”
Easy to fly, hard to fly well
My father was 19 years old and had only ever ridden a bicycle before he was plunged into Air Force flight training in the mid-1950s. The first airplane he flew was the Percival Prentice. The aircraft was very easy to fly and he sailed through basic flight training without a hitch. But according to him, he really learned to be a pilot when he started flying the famous North American T-6 Texan/Harvard “Pilot Maker.” The T-6 was quite a handful–it would swap ends if landed with any drift, would drop a wing on final if the speed got too low and had all kind of torque effects that had to be compensated for. Landings had to be without drift, on speed, with the right amount of crosswind correction and with the right rate of descent or else the poor flight cadet was in for the ride of his life! Elimination loomed large for a number of the cadets. (And then you had to do it all over again at night!)
However, all those who mastered the T-6 found that they had the basics down, and as far as flying airplanes was concerned they could rely on the hard won skills built on the T-6. The Prentice was too easy to fly and too easy to fly well (my father thought they would make good “civilian” aircraft!). The T-6 was easy to fly and was an honest airplane but made you work hard to fly well. The great trainer aircraft were all like that–this was true of the JN-4 Jenny, Stearman, etc.
Modern trainers such as the Cessna 150, Cherokee and Cessna 172 are all too easy to fly and they do not penalize the pilot who does not fly them well. This is mostly due to the “anyone can fly” message that the manufacturer wants to send. The characteristics that make them easy to fly include nosewheel gear, limitation of adverse yaw, offset tails and tilted motor mounts to minimize P-factor and heavier, stable control feel.
Downwind to touchdown showcases all the skills
Are modern trainers like the Cessna 172 too easy to fly?
We will concentrate of the skills needed for landing. From downwind to touchdown all the flying skills that you need are compressed in time. Attitude changes, altitude changes, speed control, turns, glides, descents, alignment, power changes, trim, flightpath control, energy management all come into play from downwind to touchdown. The idea is to get the airplane to the touchdown point in the “sweet spot” in ground effect just before the wheels touch. Flying the aircraft well in all phases of flight is important of course, but the proof of the pudding is in the downwind to touchdown phase.
If you fly the downwind to touchdown phase with a few errors, that is not important to a nosewheel airplane. Being slightly off alignment, having a slightly higher rate of descent or not being in a full flare attitude isn’t going to cause one much grief. One might not even notice those, and a solid landing can still be made. This is what inhibits the development of the basic skills needed. According to Budd, “[the lack of basic skills] is not a hyper serious problem, and is generally barely noticed. Until they strap on a Pitts, that is.” I would add, “Until a situation is encountered where those skills are needed.”
I am not advocating that aircraft be difficult to fly, and that modern aerodynamic, human factors and systems improvements not be incorporated into GA aircraft. I am concerned however when I see a lot of people being trained in aircraft like the Cessna 172 and the Cirrus. They are marvelous aircraft for what they are intended to do–but do not make the kind of trainer that teaches basic skills that are a foundation of flying skills.
So assuming that teaching basic skills are important:
- What are they?
- What characteristics do trainers need to have to develop the “basic flight skills?”
- Why are we claiming that taildraggers tend to have traits that tend to develop “basic flight skills” and nosedraggers do not?
I’ll try and answer those questions in the rest of the blog.
What are the basic skills?
The basic skills are:
- Angle of attack control
- Balanced flight control
- Total energy control (including the use of power and drag)
- Attitude control
- Flightpath control (including trajectory and alignment control)
- Control of interactions (between 1-5)
While all pilots need to have at least some level of skill in all aspects of control, a nosedragger will tolerate a lesser degree of control in each and will also take care of some of the interactions automatically. A tailwheel airplane will require a higher degree of control and of the interactions between them.
I will use a concrete type, the Bellanca Decathlon rather than an abstract “tailwheel airplane” for two reasons:
- Because it’s a lot easier to talk authoritatively about something real rather than in hypothetical terms
- The Decathlon is the trainer we use for both our starting students and those converting to tailwheels, so we have the most recent experience of the type
Angle of attack control
Controlling angle of attack is critical for tailwheel pilots.
Controlling the angle of attack of an airplane is vital. There isn’t a dial in the cockpit that tells you what the angle of attack is and a surrogate has to be used–which is airspeed. Airspeed is a good enough indicator for most situations, if it is clearly understood the angle of attack and not airspeed is what makes a airplane fly (after money is factored in!). In a taildragger, landing entails being close to the stalling angle of attack (when doing a three point landing). If the angle of attack varies more than little in a taildragger on touchdown, the aircraft will “bounce.”
A bounce if not corrected for will result in a wild ride! Even if the bounce is benign, the taildragger pilot is aware that the touchdown wasn’t at the right angle of attack. In a nosedragger one can touch down within a wide safe range of angle of attack, and the landing will even feel right. Teaching full flare landings, where the aircraft lands at the slowest possible speed with the nose high is optional in nosedraggers, but essential for taildraggers.
The taildragger pilot also has to be aware of the lift margin available from the wing in order to reduce the rate of sink in the roundout and flare. Since the typical 3 point tailwheel landing demands that the aircraft be stalled or semi-stalled when touchdown occurs, a tailwheel pilot will constantly play with the lift vector from the wing so that at the moment of touchdown the maximum lift is being generated at the slowest speed, while the aircraft is descending a very slow rate. This level of “feel” is not required in a nosedragger and a perfectly acceptable landing can be made with the wing nowhere near its maximum lift and slowest speed.
What this translates to is the fact that tailwheel pilots will develop an acute feel for angle of attack which will not be developed easily in nosewheel pilots.
Balanced flight control
Every control has an effect and then has a further effect. Ailerons are no exception, and with the primary effect of roll they produce yaw. In most nosewheel aircraft the ailerons are engineered to minimize the adverse yaw effect. This means that nosewheel pilots can move their ailerons without needing to worry about using rudders to cancel out the adverse yaw. Since the close association between aileron and rudder is not needed all the time, most nosewheel pilots do not develop the keen awareness of balanced flight that tailwheel pilots do. This means that in some situations where correct use of rudder is called for, such as in climbs or abrupt pitch ups, they tend to let the aircraft wander directionally. This can prove deadly in slow flight near the ground–since a spin can develop from a stall if there is an unbalanced yaw force.
The Bellanca Decathlon has tons of adverse yaw. Most tailwheel airplanes do –since a lot of them were designed or are based on designs in the 1930s/40s or are aerobatic airplanes that do not want to mask the roll/yaw effects. It also will roll very readily with rudder application. To fly it balanced requires close coordination of the stick and rudder. The adverse yaw effect is so pronounced that it cannot be missed. This is even more so during the roundout and flare stages of a touchdown–since the fuselage needs to be aligned with the direction of motion and any drift sideways on touchdown is rewarded with a swerve. If the stick is moved to level the wings, it will produce a sideways motion that will lead to a sideways drifting touchdown–UNLESS the rudder is moved in anticipation of the adverse yaw to keep the drift from developing.
The tailwheel pilot is very sensitive to the ball (and to differential butt pressure!) and will instinctively put in rudder when it is needed. This includes when P-factor is a factor, such as when the tail comes up for the takeoff run and when power is added in the flare. The nosewheel pilot does not need to be as sensitive to the ball, since a little sideways motion will be corrected by the forces on the nosewheel during touchdown in this situation.
Total energy control
A smooth touchdown in a tailwheel airplane requires an understanding of the airplane’s energy state.
When making landings in a tailwheel aircraft, the pilot has to be very aware of the total energy of the aircraft. Total energy is the sum of kinetic energy (speed) and potential energy (height). A three-point touchdown must be made so that the aircraft touches down in a certain narrow attitude range at a certain narrow speed range within a narrow range of rate of descent. This means that excessive speed and excessive height need to be dissipated while leaving enough energy to flare. The rate of change of angle of attack in the roundout and flare depends on the rate of descent. This means that the tailwheel pilot is always aware of his/her “energy budget.” Any error in estimating the total energy will lead to a “bounce” (excess energy at the moment of touchdown) or a hard landing (a deficit of energy at the moment of touchdown).
In a nosewheel aircraft as long as the aircraft is at a reasonable speed and reasonable rate of descent, the touchdown will be fine and the energy can be dissipated after touchdown. This does not encourage fine-tuned sensing of total energy.
The use of power to control total energy is also fine-tuned in wheel landings in a tailwheel. In a wheel landing, the airplane touches down in a level attitude on just the mainwheels. This is done for multiple reasons, including better visibility, better crosswind control, better braking due to heavier weight on the wheels. In a wheel landing, like in a three point landing, a touchdown must be made so that the aircraft touches down in a certain narrow attitude range at a certain narrow speed range within narrow range of rate of descent. Only now the attitude, speed and rate of descent required to make a good two-point landing are different from the combination required for a three-point landing. This provides even more fine tuning of the feel for total energy.
The Decathlon does not have flaps and most tailwheel trainers do not either (most Citabrias, J-3 Cubs, Champs and Taylorcrafts don’t have them). This means that slipping is a primary maneuver for them! The Decathlon isn’t particularly an easy slipping airplane, I find that it tends to speed up or slow down during a slip. This means I have to be aware of the drag on the aircraft at various speeds, and I find it more effective to slow to 70 mph to come down faster. Using the back side of the drag curve for generating more drag is something that is much more dramatic in the Decathlon. In a typical nosewheel trainer with flaps, the rate of descent can be very easily controlled with flaps and one doesn’t need the fine-tuned “drag” sense.
As an aside, I found the Pitts much easier to bring in for an approach; I would tend to be high throughout the approach and on final pulled the power to idle pretty close in. The high drag of the biplane configuration and the ease with which the Pitts could be confidently slipped meant a high rate of descent towards the threshold, which I could easily modulate without the use of power. The Pitts also have low wing loading and huge excess of lift so that even a very steep descent could be stopped without the use of power and the flare made with attitude alone. Not so with the Decathlon, it is very slippery and doesn’t like to come down very easily. The pattern has to be planned from downwind and precise speeds flown so as not to be too high or too low on approach. A steep rate of descent typically requires the use of a little power to slow down the rate of descent. I think the Decathlon is a better trainer for it since it develops that sense of total energy throughout the pattern!
A taildragger pilot has to be aware of their attitude to a far more critical degree than nosewheel pilots. It starts with the takeoff, which starts with lifting the tail to a precise attitude. Too high or too low on the tail has an impact not only on the total runway used but also the directional stability of the airplane. In the Decathlon being a little tail low (i.e. nose too high on the horizon) will result in a premature liftoff. If the tail is raised too abruptly to the takeoff attitude, then gyroscopic precession will swing the aircraft to the left (for US aircraft with clockwise turning propellers). This is in contrast to a nosewheel aircraft in which the gyroscopic precession when the nose is lifted acts against the left turning tendencies and tends to stabilize the takeoff. So tailwheel pilots need to be aware not just of the attitude but also the rate of change of attitude.
On approach, the attitude is important for maintaining the correct speed on approach. Like most tailwheel trainers, the Decathlon does not have flaps, so to “go down one has to slow down.” The attitude is nose high but the aircraft is descending. This reinforces the difference between attitude and flightpath, something which doesn’t come across so clearly in a Cessna 152/172 or Cherokee.
While landing attitude control is paramount, since in three point landings the “three point attitude” has to be held within a narrow range otherwise the aircraft will either bounce or have a hard landing. This narrow range is even narrower while doing a “wheel landing” in which the taildragger is landed on the front wheels only in a level attitude. The attitude has to be held at a low rate of descent and any excessive rate of descent will result in the aircraft “bouncing” due to the wing being forced into a higher angle of attack (as a result of the CG being aft of the mainwheels). This attitude is held until the aircraft slows down with progressive forward stick. This level of awareness of attitude is not required in a nosewheel aircraft.
Controlling the flightpath is much more critical for a tailwheel pilot especially at landing. I have already touched upon some the adjustments that need to be made. These include:
- Steepness of the flightpath–this effects how early the flare starts and how much modulation of the angle of attack will be required before touchdown (either 3 point or 2 point).
- The flightpath in the flare–keeping the flightpath such that the touchdown is made at a certain attitude at the lowest speed for that attitude. The flightpath will need to be finely modulated from the point of roundout through the flare all the way to touchdown, staying parallel to the ground if the energy is high to dissipate the energy, and adding power or increasing the angle of attack quicker to shallow the descending flightpath when energy is low. Gusts can also change the flightpath and these have to be accounted for while still meeting the conditions of good two point or three point landing.
- Keep the flightpath direction along the runway without drift using the appropriate amount of aileron and rudder. Even a slight drift that would be corrected on touchdown by the stabilizing action of a nosewheel aircraft can result in a divergent trajectory if not corrected forcefully and accurately.
- Flightpath control without auxiliary devices such as flaps (that are common in nosewheel training aircraft but not so common in tailwheel training aircraft) requires better planning and a better sense of the drag characteristics of the aircraft.
Control of interactions
It is challenging enough controlling one aspect of control as outlined above, but adding interaction effects makes it a lot more complicated. The interaction effects are also more challenging in a taildragger, because the margins if these effects are ignored are very narrow compared to a nosewheel airplane. Some salient interaction effects are:
- Any slip in a Decathlon increases the rate of descent dramatically, which is why even a mild crosswind is challenging. The rate of descent increases when the wing down method is used and rudder is used to side slip the aircraft while keeping the fuselage aligned with the runway. This rate of descent has to be compensated by either adding power or starting the roundout/flare a little early. In a nosewheel airplane the rate of descent is not as critical and for most slip angles only small adjustments need to be made for a decent landing.
- Adding power in the a nose high approach attitude and high effective angle of attack (due to lack of flaps) causes a left turning tendency due to P-factor. This has to be immediately corrected in the Decathlon and most tailwheel trainers. Most nosewheel trainers have flaps and their effective angle of attack is lower in the approach (due to the higher camber of the wing, more lift is produced at the same angle of attack)–and adding power doesn’t have the same dramatic effect.
- In a gusty crosswind not only must the alignment with the runway be maintained, but a close watch kept of the attitude and the rate of descent within far more narrow margins than in a nosewheel aircraft. Any change in power, side slip conditions, airspeed and attitude results in changes of rate of descent and flightpath and all those interactions have to be compensated for. In most nosewheel aircraft, keeping the aircraft reasonably aligned and keeping the rate of descent and touchdown attitude within a broad range will provide a reasonable landing.
On reading the exposition above if you come to the conclusion that tailwheel aircraft need the same skills needed to fly a nosewheel aircraft, just within narrower margins (which translates to more control by the pilot)–you would be right. Since wonderful inventions make it easy for us to fly modern trainer aircraft, being human, we tend to be lazy. When flying with more control (or within narrower margins) is forced upon us, soon it becomes a habit. That is why it took one of my students only 2 hours to be a safe pilot in a G1000 Cessna 172 (even before soloing our Decathlon) whereas most experienced pilots who come to me for a tailwheel endorsement need 8-10 hours before they can fly a taildragger safely. We need something to keep us honest–and I think a tailwheel trainer fits that bill.