precision landing championship – Achtung, Skyhawk!

By me
All photos me too, copyrighted

Looking back on it (even though it still has a month and a bit left to run), this year has, aviation-wise, been almost a complete joke. One of the rainiest years since record keeping began in Croatia some two centuries ago, it has produced no less than three major floods, interspersed with unusually frequent (and surprisingly violent) cyclones and depressions that had – in some cases – dumped a year’s worth of rain in just a few weeks. Scenes such as this and this had kept most of our grass airfields closed and flooded for days on end, trapping all of our money-making aircraft and rendering them unable to flee to the paved safety of the country’s major airports…

Likewise, man-made disasters had conspired against us as well, with the country’s long-standing economic crisis now running into its seventh consecutive year – with very little light only dimly visible at the end of the tunnel. Apart from a general reduction in life standard, spanners thrown into Croatia’s GA works include soaring fuel prices, increased maintenance costs – and, not least of all, stepped-up efforts by several operators of popular paved airports to collect increasingly exorbitant fees and charges in order to alleviate their own financial difficulties.

An yet, despite all of this, the local GA scene is operating like there’s no tomorrow (likely because if the weather continues like this, there probably won’t be 😀 ), with a new bizjet, new skydive Cessna, new glider and towplane all having arrived in country within the past few months. Flying clubs are on a roll as well, with mine already having beaten its previous flight time high, set – ironically – in 2013 :). Skydive flights, airshow performances, panoramic flights, private rentals… all seem to be coming back on track despite the worsening living standard (with only flight training letting the side down).

Much of the same could have also been seen during the 24th Zagreb Cup precision landing championship, held at Lučko Airfield (LDZL) on Saturday 11 October :). A yearly small-town event whose sole purpose is to have some good-natured fun (and enjoy a good BBQ afterwards 😀 ), the competition had this year attracted an all-time record in aircraft and competitors, numbering at four Cessna 150s, three Cessna 172s and 24 competing pilots respectively. While this doesn’t sound like much compared to some of the larger and more formal competitions held elsewhere in Europe, it is still of one of the main aviation (social) events of the season, and had this year easily topped the 2013 competition, where we had a showing of only five aircraft and just 18 pilots.

A handy visual guide to everything you need to know about the competition. Closest to me is the landing field used for the purpose, drawn up in lime powder on the right side of RWY 28L. 72 meters long in total, it is marked off in several 5 meter wide grids, plus a two meter wide “zero mark” that represents the ideal touchdown point. For 20 meters on either side, the grids are further split into one meter wide segments – as shown here – to aid the judges in determining the exact point of contact. Further back behind the field are three of the seven competition aircraft – parked on RWY 28R – with the competitors monitoring progress on the runway’s edge.

As nearly every year so far, the competition had been blessed with beautiful summer-like anticyclonic weather, sporting clear blue skies, temperatures of around 25 degrees Centigrade – and lighting conditions to die for. The only thing missing compared to last year was a stiff 15 knot crosswind, replaced this time by a light, variable and refreshing breeze – quite welcome when standing in the sun for several hours 😀 .

Even though this meant we’d miss out on the visually attractive landings of 2013, my shutter finger was not left to stand idly by, with my role as assistant judge allowing me the occasional opportunity to play around a bit… 🙂

The first group of competitors (minus C150 9A-DMI standing to my left) prepares for take-off down RWY 28L. Since they were departing individually, for reasons of safety the lead ship had to be the fastest of the group – C172 9A-DFH – with the three slower C150s at the back sequenced by their pilots’ precedence on the competition roster. Of note, since the competition field took up half the width of the runway, all competitors had to take off from an intermediate position – roughly 200 meters from the threshold – to avoid blowing the flags and lime away…

To avoid running over the above – and the occasional judge – on the way to the intermediate position, the competitors had to taxi past the field on the left side of the runway, which had conveniently brought them to within a few meters of my position – thus allowing me plenty of opportunity to play with various compositions as they rolled by. One of these had inadvertently ended up being a study of the minute differences and options available on the Cessna 150 during its production run…

*One of life’s rare opportunities to stand in front of a (slowly) taxing aircraft on the primary runway of a (somewhat) busy airfield with a camera in one hand and a cool beverage in the other!*

A crowd on final like we’re at a proper airport! Even though the competition specified a separation standard of one and a half minutes between successive aircraft – enough to have four machines evenly spaced around the circuit all at once – different piloting techniques and approaches had invariably eroded it from time to time…

“Caution wake turbulence”. They may not be fast jets and there’s no smooth tarmac under their tires, but it nevertheless makes one happy to see them! Interestingly, by the time CCG had turned onto the crosswind leg, the lead ship of the group – Cessna 172N 9A-DHL – was already turning final…

Even though it happens only rarely, it is not unseen for contestants to have occasional tailstrikes during these sorts of competitions. Thankfully, in this case the actual strike was very light and brief, with only the tail tie-down ring making contact with the ground. Had it not been there to kick up the grass, we likely would have never noticed…

Deja-vu from 2013… even though there was almost no wind for the entire duration of the competition, occasionally some of the contestant had made a hash of their final “no flaps, no power” approach, forcing them to stretch their glide as much as possible and plonk the aircraft down on its last few Newtons of lift. While this does look somewhat dramatic, the competition rules allow it up to a point, provided the wheel in the air is at a height less than its diameter and not for more than 5 meters horizontal distance.

By me
All photos me too, copyrighted

If any further proof was needed that the weather patterns in Zagreb have a mind of their own – something the author has been shy to mention in the past 😀 – one needs to look no further than Lučko’s annual Zagreb Kup precision landing championship, held this year on 20 October. One of a number of seasonal sporting events at the field (and the only one that manages to get us all together in the same place), the championship is nearly always blessed with sunny skies, moderate temperatures and generally all-round fine flying weather – often a curiosity among the month’s frequent rains, low clouds and general dreariness.

The 2013 event was – unsurprisingly – more of the same, with beautifully clear skies, uncharacteristically high temps and weather more suited to that of September. The odd man out though was a strong, gusting, 15 knot southwestern wind that had been blowing for a better part of the week – and which, coming in nearly perpendicular to Lučko’s runways 28L and R, had promised quite the spectacle 🙂 .

Tall tales of short approaches

However, while said spectacle was a delight for the photographer, for the pilots taking part it had represented a whole different kettle of fish. The more obvious – and more immediate – issue facing them was the heading correction necessary to compensate for the sideways motion of the air. While this is a perfectly straightforward procedure in level flight (especially when using a few neat mental formulas to calculate the exact correction needed), on a “competition” approach it does present a few interesting challenges 🙂 . Chief among these is the need to increase the heading correction as speed is decreased in order to provide the same level of compensation and stop the aircraft drifting away. By default, competition approaches imply low speeds* (to give the pilots time to judge their rate and angle of descent), which in turn translate into relatively large corrections necessary. Indeed, at 60 knots – a good approach speed for a Skyhawk – every knot of crosswind component has to be parried by a heading correction of one degree. At 15 knots then – conditions similar to those prevailing on 20 October – you would be looking at a 15 degree crab angle.

* however, it is not uncommon for contestants to dive into the ground effect and progressively bleed of excess speed there. Floating just a few inches off the ground, this allows them to set the aircraft down suddenly, quickly and precisely – but often requires impeccable timing and a very good feel for the specific aircraft being flown

Angles of this magnitude produce a distinctly visible sideways drift across the ground (especially in the last few hundred feet of the approach), which can play havoc with one’s perception of the aircraft’s true direction, speed and motion. An additional factor – albeit a smaller one – is the reduced forward visibility from the cockpit. With the nose swung over to the side, the pilot no longer has the luxury of staring at the landing spot straight down the nose; depending on the direction of the wind, he/she now has to either look out of the curved windshield side panels (in the case of a wind from the right), or worse, across the diagonal of the cowl with a wind from the left. Both of these effects combine to measurably influence the pilot’s depth perception – consequently affecting his/her ability to correctly judge the aircraft’s height and proper angle of descent.

A more subtle issue is the slight – but still noticeable – increase in the aircraft’s angle of descent. It is important to note here the difference between the angle of descent and the rate of descent. The rate of descent – grouped under the term “vertical speed” in everyday parlance 🙂 – is a measure of how much altitude the aircraft has lost in a unit of time (feet and minutes respectively being used in the West, and meters and seconds in the lands of the former USSR). The angle of descent on the other hand effectively shows the distance the aircraft has covered per unit of height lost.

To complicate matters further, these two measures are never on the same page when wind is concerned 🙂 . Consider an aircraft flying in still air at a constant 60 knots ground speed and descending at 500 feet per minute. Starting out at an altitude of 10,000 ft, it would need 20 minutes to reach the ground, during which time it would cover 20 nautical miles of horizontal distance. Fine. But now let’s set same aircraft flying into a 20 knot headwind, reducing its ground speed to 40 knots. Since it is still descending at 500 ft per minute, it’ll still need 20 minutes to get down; but the horizontal distance it will cover in that time will now be only 6.67 NM. So, while its rate was constant, its angle had increased dramatically 🙂 (to complicate things EVEN further, the “angle” does not refer to the aircraft’s pitch – which is the same in both cases – but rather to its flight path)*.

* when viewed “in reverse”, this also explains why aircraft have two distinct airspeeds for the climb: the best rate of climb speed (Vy) and the best angle of climb speed (Vx). Vy gives you the quickest time to altitude – that is, the highest vertical speed. Vx on the other hand gives you the highest increase in altitude per unit of horizontal distance covered – that is, the greatest flight path angle – and is used immediately after take-off to clear close-in obstacles 🙂 .

The same mechanism is at work during competition approaches. While I may say that the contestants faced “a crosswind” out of pure brevity, very few crosswinds are exactly 90 degrees on – most of the time there’s a headwind component (however small) reducing the aircraft’s ground speed by a few knots. While this hardly sounds like the end of the world (especially knowing you have an engine to compensate), the effect is still there and can be particularly troublesome on the competition’s second and third approaches which prohibit use of the throttle – and consequently decrease room for error in terms of flight path perception and aircraft control. Come in too low or too far out – like you would in still air – and you might not even make the landing zone, let alone the zero mark… 🙂

All of these effects – despite being almost negligible and easily compensated individually – had come together in force on 20 October, culminating in visually the most interesting (but also most exciting and challenging) competition we’d had in years… 🙂