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Thursday, 06 June 2013 00:00

On the Shoulders of Giants Featured

Written by  Daniel Ventura González Alonso / Aero Club Barcelona-Sabadell / Fundació Parc Aeronàutic de Catalunya
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Trener Master y Akrobat

At Sabadell Airport we have the good fortune of combining two aspects of aerobatics: the present and the historical.  The present in the aerobatics section of the Barcelona-Sabadell Air Club, and the historical under the direction of the Parc Aeronàutic de Catalunya Foundation, which has been able to recover authentic gems from the aerobatics of yesteryear.

 

Two of the most well-preserved pieces from the FPAC collection of planes in flight are two Zlin that belonged to the Spanish Team of Aerobatic Flight during the era in which Castaño, Ugarte, Negrón, and Aresti (who, by the way, was also an instructor at the Aeroclub Barcelona-Sabadell - Spain) were declared world champions of aerobatics (1964 in Sondica, Bilbao), both as individual (Captain Castaño) as well as teams.

The Foundation's two Zlin are the Trener Master, two-seater version, EC-AXA, which was flown in the world championships, and the Akrobat, one-seater, EC-BDS, which came to the Spanish team with the championship already in pocket, and charmed the Spanish public with its displays.

The planes vary in performance and in manner of flying from those of the present.  From a metallic structure, retractable gear, and great complexity, its flight is composed of long lines and delicate rotations, gently bringing to mind the movement of a sailboat.

Having flown them, it is surprising that it was precisely in those planes that a figure like the Lomcevak was "invented," since one might think that it had already been accomplished in smaller, and apparently more agile planes, like the Pitts Special.

 

Flying the Zlin

An external review reveals some of the differences in this plane model with respect to other, more modern aerobatic planes. To begin with, the retractable gear with an electric engine, with “legs” that fold back and leave part of the tires in view (very practical for landing without gear, as the pilots of Yak-52 will know.)

We continue with the variable pitch propeller that has a curious system that makes the air pressure over the propeller hub automatically determine the two-blade propeller's pace.

Trener Master EC-AXA

And finally, the mechanical actuation flaps that cannot be seen from the cabin.

Once inside, we should check that the nitrogen pressure is at green arc, nitrogen, which signals that the primary spar is intact.  This indicator was added as a result of Neil Williams' accident, who is famous for being able to land a Zlin Akrobat while maintaining the integrity of the wing flying upside down until just a few meters from the ground.

The management of the 180hp inverted Walther engine is very simple, operating only on the throttles (we have already said that the propeller pitch is automatic), with fine adjustment of the mixture in order to cruise at a high altitude and little more.  The engines are fairly cold, so in winter a permanent deflector is installed that reduces the entry of air into the engine.

Taxing is simple thanks to the control that we have over the taildragger and brakes which, although they have a tendency to stick intermittently with use, are effective and reliable.

The take-off is two-points with a rotation around 100 Km/h. With the plane in the air, the position of the nose during the whole climb is maintained at below the horizon (like the rest of the flight), with a very high rate of climb.

The cruise is around 180 to 200 Km/h, although for aerobatics we will need to reach 250 Km/h, always with incredible visibility, given that the plane flies with a position of a very low nose.

The roll is quite smooth, compared to a CAP-10B, with a much more sensitive elevator control and heavy pedals (typical of the Zlin).  In every case, the maximum elevator imput is quite limited.

Basic aerobatics is easy and uncomplicated except for the derivatives of the wingspan, with quite a bit of adverse yaw.

The Trener Master has a black legend of unrecoverable spins, although it has not been demonstrated in what situations this could occur. The fact that these planes carry gasoline in the wings (a tank in each wing, connected) added to the size of the wings can complicate the recovery from a flat spin depending on the load and the center of gravity position.

The fact is that in countries in the east, a great many planes were destroyed for this reason.

Curiously, the Spanish aerobatics team of the 1960s never had this danger, given that due to an error on the part of José Luís Aresti, they thought that they should be flown from the front seat, which made for an extremely heavy nose...so much so that they had to modify the compensator to convert it into a handle that they had to actuate constantly in order to be able to perform aerobatic figures.

After they won the world championship, in which the Czechs made them see their error, they began to fly as he touched.

Both planes have an alarm that turns on at 4Gs to prevent pilots from overload Gs with the plane during a maneuver.

Akrobat EC-BDS

The Akrobat Zlin and Trener Master have feeding systems to fly inverted, but it is recommended to only use them with the gases totally forward, since otherwise the motor will cough.

The approach is pretty simple thanks to the excellent frontal visibility. Beneath 150 Km/h we lower the landing gear (it is recommended that you give a small bump of gases to help the electric engine) and beneath 140, lower a flaps point.

Approach 140 Km/h with 10º and 120 Km/h with 20º, however it is recommended to not deploy the flaps at its maximum deflection if there is cross wind, given that the plane has a tendency to raise the wing closer to the wind.

The flare is in two parts, looking first for the horizontal position and losing energy while looking for the landing position. Otherwise, because of the large wing surface, the plane will fly up into the air with great ease. 

In the case of the Akrobat, the nose is very heavy, and we must put pressure on the stick despite having the whole plane compensated nose up.

The default landing is three-point, since the retractable gear bend back and it is not convenient to work directly upright, as would occur in a wheel landing.

In summary, we are dealing with planes whose elegance in flight is difficult to match, from simple piloting and an enviable visibility, but limited at the aerobatic level compared to any modern model.

This makes it even more surprising that it was in these planes that figures like the Lomcevak were invented, from a violence apparently far from the figures of long and delicate lines that the plane seems to elicit by its long wings.

Like Newton, I have had the pleasure of flying "on the shoulders of giants," truly appreciating the talent of great pilots like Captain Castaño, Quintana, Negrón, or Ugarte.

It is in their honor that I hope these planes continue flying for many years.

 
 
 
 
 
Read 2946 times Last modified on Monday, 06 March 2017 08:48
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