Lomcovak

Agli inizi degli anni 60, durante uno dei più importanti raduni acrobatici
Il Lockhead Aerobatic Trophy , Ladislav Bezàk, capitano della squadra cecoslovacca stupì tutti gli osservatori presentando una manovra che sembrava sfidare tutte le leggi di aerodinamica e di gravità.
Il Lomcovak.
Anche se in America fu subito ribattezzato "headache" e in molti paesi europei quali Francia, Svizzera , fu conosciuto per molti anni come l'homme slovaque, in realtà il suo nome deriva da una parola Polacca che significa "Ubriaco"

(nota di colore)
La manovra fu subito ripresa dai piloti russi che iniziarono a sperimentarla sugli Yak 18.
Dopo diversi problemi strutturali riscontrati sul castello motore di vari velivoli, dall'alto arrivò l'ordine di non eseguire tale manovra, pena l'immediato cambio di residenza presso qualche lussuoso e confortevole gulag siberiano.

Contrariamente a quanto si possa pensare, il lomcovak non è una vite rovescia o una manovra incontrollata e casuale.
Sopratutto non è una singola manovra, piuttosto un'insieme di manovre che hanno un ben preciso inizio e fine.

Il segreto del Lomcovak è che il controllo dell'aeroplano è soggetto a quattro forze aerodinamiche anziché le tradizionali tre.
La quarta è rappresentata dal precessionamento giroscopico del disco dell'elica, controllato tramite la manetta del Gas.

Esistono cinque versioni base di Lomcovak; ciascuna delle quali possiede diverse varianti.
In ogni caso tutte sono eseguite sotto "G" negativo.

Maneuver Description:

The 45 ° Up Lomcevak begins with an aggressive pull to the 45° up line "A".
Once established on the 45 ° up line, the aircraft is smoothly rolled to the left knife-edge position "B".
With little or no hesitation in the knifeedge position the aircraft is then yawed approximately 70 degrees off of the normal flight path while the control stick is simultaneous shoved fully forward creating a tumbling end-over-end-over-end negative-G gyroscopic condition "C".
The aircraft is recovered to the inverted 45 ° nose low position "D" and a recovery is accomplished, in this case, by pulling the aircraft through the vertical down position to a recovery in the opposite direction to the original entry heading "E".

The one most commonly seen, the "main" Lomcevak, is entered from upward inverted flight.
As the airspeed decays to near zero, the pilot initiates an outside snap roll ("flick roll" for you Brits).
The aircraft comes to zero airspeed while rotating about all three axes, and proceeds to perform three end-over-end negative "g" tumbles, each tumble 45 degrees to the plane of the last.
The maneuver ends when the aircraft begins falling with enough speed for the airflow past the tail feathers to stop the tumbling.

There is another category similar to the "main", but entered from knife-edge flight. This one is particularly violent.

The "cap" Lomcevak starts out much like a hammerhead turn, but as the fuselage rotates to horizontal at the top, a combination of precession and down elevator cause the aircraft to pivot about the wing in a perfect pirhouette.
The wing remains vertical during the maneuver.

In the last two categories, the "positive conic" and "negative conic", the aircraft sweeps out the shape of a cone while pointed nose-upwards, with the bottom of the wing tangent to the surface of the cone during the entire maneuver.
In the positive version, the nose is the apex of the cone, while in the negative version the tail is the apex.

Lomcevaks are terribly disorienting but otherwise fairly gentle for the pilot.
The same CANNOT be said for the aircraft!
All sorts of strange loads appear on the airframe, ones that were probably never conceived of in most aerostructures texts, such as high centrifugal forces on the wings.
The worst effects seem to be reserved for the engine mounts, crankshaft and prop. +
There have been quite a few cases of major damage to these components during Lomcevaks entry heading "E"


video

What is a lomcovak
During the 1950s there was a wonderful event called the Lockheed Aerobatic Trophy, which attracted pilots from all over Europe.
The contest consisted of an exact five minute period in which one had to extract the maximum from the pilot/aeroplane combination, and where competitors were encouraged to "paint a picture in the sky", and the chief judge put it.
Five minutes is not a very long time when it comes to demonstrating everything that one can do (or thinks one can do) in an aerobatic aeroplane, yet the contest was extremely popular, perhaps because the atmosphere was so relaxed.
The first day was devoted to practice flights over the airfield, and we all turned out to watch the Czechs practice in their Zlins.
What happened that day left us dazed with disbelief.
We saw all the laws of aerodynamics and gravity refuted.
We saw aeroplanes flying backwards, sideways, tumbling and rotating about all three axes, at zero airspeed, and still apparently under full control.
By our standards, what we were watching was completely impossible !
But the culmination of it all came when one Zlin described three consecutive forward somersaults, the plane of each circle being at 45° to the one before it;
and all with apparently no forward speed at all.
This, we were told, was a lomcovàk.
From that moment on, the Czechs knew no peace.
Gone were any ideas we may have had about placings in the contest;
all we wanted to know was how they did it, and whether it could be done in any other type of aeroplane, for at that time the club was equipped with Stampes.
But it was all very confusing, because everyone we talked to seemed to have a different method of executing the manoeuvre.

Not until much later did I realise that there are at least five basic lomcovàks, each with several derivatives.
At the outset we concentrated on the type known now as the "big" or "main" lomcovàk, which is initiated from a nearly vertical climb.
We struggled through the competition, watched the Czechs dazzle pilots and judges alike, and flew back to our base full of ideas and enthusiasm.
Our early attempts at carrying out a lomcovàk were undoubtedly hard on both pilot and aeroplane,because we made the mistake of just applying full control in the appropriate direction and hoping for the best.
In fact one has to "play" the controls much as a fisherman plays a fish on the end of his line - give a little, take a little.
My first attempt left me more confused than I had been before I started.
I entered the manoeuvre from the inverted and pushed up towards the vertical, using full power , at which point I applied the controls to initiate an inverted flick roll.
The world exploded into a juddering, whirling, kaleidoscope of green and blue;
something hurtled out of the cockpit, narrowly missing my head in the process.
I still have no real idea of what the aeroplane did that day, but when I got it sorted out, the entire “P" compass was missing !
We never found it.

This made us realise that if we continued the bull-in-a-china-shop technique something was going to break. So for several years I experimented, proceeding by very slow steps, until I could produce a spectacular, safe, figure with very low g forces.
But still I could never predict with 100 per cent accuracy where the aeroplane would finish.
I always refused to tell people how I entered the manoeuvre, because I still didn't understand fully what was going on, and I knew by this time that there was the very real possibility of badly overstressing the aeroplane.
The figure I was flying, though it looked spectacular, was evidently not a real lomcovàk, because once I had initiated it I no longer had any real measure of control, whereas I was certain that the Czechs' manoeuvres were controlled.

Then came the breakthrough, when I had the opportunity to talk to and fly with the ex-world champion, Ladislav Bezàk of Czechoslovakia, who was originally responsible for conceiving the lomcovàk.
He explained the more common types to me, and demonstrated them in the air.
Initially I used the Stampe, but when I tried some lomcovàks in a Zlin I could see instantly why the Czechs had been able to control this strange figure so precisely.
More than that, when the manoeuvre is flown correctly, it is incredibly gentle !

Compared with our earlier efforts, everything seems to happen in slow motion, with the exception of the figure I had been trying to fly for so long, the "main" lomcovàk.
This one is a multiple turn figure and I have not found it necessary to change my technique very much:
but I have decided that I will only fly it with an aircraft equipped with a wooden propeller, as I feel that the
gyroscopic forces involved are too high if a metal propeller is fitted.
Also, for the general safety of the aeroplane I feel that these manoeuvres should not be entered at an angle of more than 45° from the vertical climb, otherwise the dissipation of airspeed is not sufficiently high before the rotation builds up, and the chain reaction from this can cause damage to the aeroplane.
All these manoeuvres can be entered from a speed equal to the maximum straight and level speed in a biplane, or 85 per cent of the maximum straight and level speed in a monoplane.
However,it should be remembered that most of the so-called aerobatic aeroplanes today are really only semi-aerobatic, and therefore should not be subjected to these manoeuvres.

The "main" lomcovàk is entered from a climb which is slightly over the vertical, the level speed before the climb having been as described above.
If the propeller turns anticlockwise as seen from the cockpit, the inverted flick roll is initiated with left rudder, and stick forward and to the right.
At this point the flightpath becomes vertical.
The yaw and roll resultant then precesses owing to engine/propeller gyroscopic forces, and the aeroplane reaches a state where all the rotation is about the lateral axis in a forwards direction, this axis being vertical with respect to the earth.
At this point one has the option of leaving full power on and continuing the "main" lomcovak, with the lateral axis itself precessing after the first turn until it is again horizontal;
alternatively,one can use the throttle to achieve a "cap" lomcovàk.
In the first case, if the entry has been fast in terms of control application, it can produce three complete turns;
the last being a forward loop on the spot with nil airspeed.
It can also cause damage to the aeroplane, so I personally restrict it to two turns, by entering the figure more gently.
One can also finish up in an inadvertent tail-slide, with fully deflected controls.
By leaving full power on, a steady roll around the longitudinal axis of the aeroplane can be maintained:
this is not due to the ailerons because airspeed is almost zero.
In the case of the "cap" lomcovak the intention is to make a forward loop of 360° with the lateral axis vertical to the earth;
therefore the engine is used smoothly as an extra aerodynamic control to prevent any further roll around the “A" axis once the “B" axis is perpendicular.

Since the rotational force for the complete manoeuvre comes from the engine, throttling down will slow the pitch rate almost to zero, and this should be reached after one complete rotation.
In our aircraft as described above the right wing will be towards the ground.
The stick is pulled fully back and full left rudder is applied:
this initiates a sideslip to the right, just enough so that when the rudder is reversed and power applied, one exits in the same manner as from a stall turn to the right.
If this rudder reversal technique is not used, the aeroplane wilt roll onto its back and sink out of control.
The "cap" lomcovàk can also be entered from a climb just short of the vertical, but this time using right rudder.
Of all the lomcovàks, the “conic" lomcovàks are by far the prettiest and cleanest.
The positive "conic" is inclined at 15° to the vertical, with the nose of the aircraft acting as the focal point and the tail describing a horizontal 360° circle.
The path traced by the fuselage is cone-shaped - hence the name.
The negative "conic" is 15° beyond the vertical, and this time the aircraft's tail is the focal point, while the nose describes the circle.
The exit from the positive “conic" is a stall turn or tail-slide, while the exit from the negative "conic" is by tail-sliding or simply pitching over into a vertical dive.

Perhaps the most difficult thing about flying lomcovàks is the need to use the throttle, not as a "go faster" lever, but as an extra aerodynamic control.
This is why the "conic" lomcovàks are easier than the others, in that there are only two required positions for the throttle - open or shut.
In the case of the positive "conic" the throttle is closed as soon as rotation starts, and is opened to recover, while in the negative "conic" the throttle is left wide open until the moment of recovery, when it is closed.
Needless to say, the latter is the more violent.

During these lomcovàks, initiated from a near vertical attitude, there is considerable pilot disorientation.
All lomcovaks are flown under negative g regardless of the type of entry, so that one is subjected to very high rates of rotation often in three planes simultaneously, while subjected to an inverted loading.
This can make it quite difficult to think coherently.
Since the pilot is sitting somewhere near the C.G. he is not very far from the centre of rotation, so that after the initial peak of negative g he may be in a very low g environment during the steady rotation.
It is as well to consider what is going on at the extremities of the aeroplane, especially in terms of the gyroscopic forces at the propeller when the engine is at full power.

Another type of lomcovak which is rather hard on the aeroplane, unless great care is taken, is the lomcovak from sliding knife flight in a 45° climb.
The further the angle from the vertical, the more violent the manoeuvre.
This one is started as an inverted climbing flick roll, and progresses to the state of the "main" lomcovak.
It is the only time I ever saw an aeroplane going upwards, backwards !
Several Zlins have lost their propellers during this manoeuvre, though it can be done safely, if one is
prepared to throttle back.

There is only one variation of the lomcovak which can be started from anything less than a 45° climb and that is the "tumble", which is entered from inverted horizontal flight, but at a very low airspeed, in fact very near to the inverted stalling speed.
Even so, unless one throttles back in the early stages of rotation, the yaw rate accelerates dramatically, and damage usually results.

In this figure, the aircraft quickly goes from an inverted flick roll into a horizontal inverted flat spin, which is fully developed by the end of the first turn, resulting in the aircraft pointing vertically upwards.
Since it is still yawing rapidly, the last 180° of rotation is the same as a stall turn, as far as the recovery goes,
except that with the stick fully back the ailerons may be used in the outspin mode to augment recovery, but only after the accelerometer begins to give a positive reading.
If the throttle is not closed after this manoeuvre commences, besides the danger of severe disorientation, and engine damage, there is usually heavy airframe buffet present in some types.
The safety of the manoeuvre depends entirely on a low entry speed and an early throttle closure.
The smaller the aeroplane, the wilder and more spectacular will these manoeuvres evidently be.
They will also be less controllable and less pretty to watch.
The combination of a very small aeroplane with a very large engine will give the most uncomfortable
ride imaginable, since the manoeuvre is primarily a gyroscopic one.
For the same reason an aeroplane fitted with a metal propeller will probably produce more prolonged rotation than an identical aeroplane fitted with a wooden propeller.
Although the lomcovak is widely used throughout the world in freestyle flying and in displays, it is not really understood.
Pilots talk about "the lomcovàk" as though there were only the single manoeuvre, but as we have seen, the term can cover a wide variety of gyroscopically controlled figures.
They do not appear in the Aresti dictionary because they have hitherto not been regarded as properly controlled manoeuvres, except, perhaps in Czechoslovakia, where they define the lomcovak as "A rapid negative roll executed in that direction towards which the torque of the propeller is helping in rotation."
The real origin of the name lomcovak conles from the Slovak slang'expression for a large, stiff drink.
A Czech pilot once likened the sensation to the result of consuming rather too much plum brandy
- I can well believe it !

Aerobatic, Neil Williams