Photo Report – Banner Towing Above Zagreb, Feb 2008

By me
All photos me too, copyrighted as usual

Looking back through all the articles I’ve posted here, I saw I’d made quite a few boastful promises about topics that in the end never materialized :). So, still waiting for something to happen here in the present, I’ve decided to clear my topic backlog, starting of with my first true air-to-air photo experience – banner towing :).

1. Fly-by-wire

While banner towing in flight seems – and is – a pretty straightforward affair, down on the ground, getting the thing airborne, is a different story altogether. Despite popular myth, taking off with the banner attached causes more problems than it solves, particularly on uneven grass runways such as at Luฤko – where it would promptly be torn off and shredded, not to mention all the adverse effects it would cause for the unlucky towplane.

To get around this problem, somebody somewhere at some point had borrowed a WW2 method – why not snag the banner inflight? To quote Jeremy Clarkson of Top Gear, “How hard can it be?” :D. The idea is that the banner’s tow cable is suspended between two poles at some height above ground, usually about 2-3 meters. The towplane would then, trailing a hook on another cable, come down low and snag the banner, lifting it off the ground as it climbs away. Those of you who have seen images of Dakotas picking up troop transport gliders during WW2 will immediately see the similarities.

A visual illustration as 9A-DMJ goes down for a snag. Note also the hook cable attachment assembly at the base of the tail. Sorry for poor quality, but for the life of me I can’t find the original, so I had to take this one of my Facebook photo gallery ๐Ÿ™‚
9A-DDD going down for the pickup. The approach is usually flown at about 70 knots and 10 degrees of flaps in the Skyhawk. The speed has to kept at around that figure – any faster and the sudden drag and inertia of the banner will stress the airframe unnecessarily, while any slower means that when the banner yank does come, it can pull the aircraft very near the stall (with the added complication of the engine run-up delay at low throttle settings)
During taxi and takeoff, the hook end of the cable is carried in the cabin by the second crew member. Once airborne, the hook is lowered into the airstream until all the slack in the cable is picked up
A frontal view on a recent mission
Side view. Note the reinforced cable mid-section that acts as a sort of bungee to absorb some of the forces and inertia during pickup
A nice and clean hook up. Sometimes the hook and banner cables can tangle up, with the banner towed not by the hook, but by the tangled cables. This can be quite problematic if the knot untangles in flight – the banner then freely falling away – the reason for which there is always a “ground spotter” with a radio station observing the pickup. If the cables tangle up, the SOP is to jettison the entire thing and start over
Banner snagging being pretty much a visual art, it is not uncommon to miss the banner cable altogether (by anything from inches to meters). In this case a go-around is executed for another attempt

After a successful snag and climb away, the rest of the flight becomes routine – with careful monitoring of the engine temperature gauges that is. Despite most banners weighing not more than 20-ish kilograms altogether, their large surface area creates a lot of drag. This necessitates a higher throttle setting and if not flying fast enough for sufficient engine cooling, it’s not really that difficult to overtemp the engine.

With the mission completed, the banner is then dropped from the aircraft during a slow, low pass. The release itself depends on the hook and tow mechanism, but in our case the whole cable – all the way from the attachment hook below the tail – is jettisoned, to be untangled and separated on the ground. This leaves the aircraft free to perform a normal, unencumbured landing.

Note that the entire cable is released, with only the fixed tail hook remaining in place. For many pilots, hitting an exact bull’s eye with the cable is almost a sport ๐Ÿ™‚

2. A skiing competition, a casino and some fog

While all of the above is fine and dandy, back in the winter of 2008 my aeroclub had gotten a bit ambitious :). The mission was to tow the largest banner ever towed in Croatia, measuring 5 x 30-something meters. Doesn’t sound like much the first time you hear it, but in effect that’s a 150 square meter airbrake – more than three times the surface area of my apartment!

The venue was the Snow Queen skiing competition held on the northern slopes of the Medvednica mountain between 15. and 17. February 2008. And the customer – a large casino near ล entilj, on the border between Slovenia and Austria. Connection – I see none, but it didn’t matter since it got us up in the air with no questions asked :).

Fortunately for our towplane, the temperatures had plummeted during the weekend, down to around -15 Centigrade at the altitude at which we had expected to do our run. (round 2,000 ft) With such a draggy mass behind it, and the requirement to fly at 70-75 knots so people on the ground could actually read what was being towed, engine cooling was a serious issue, so the lower the outside temp, the better.

Now, the original plan was to do a run on the 15th, with DMJ acting as the towplane and DMM – with me on board – acting as the photo ship to immortalize the whole event :). However, even before leaving the ground we had run into a small problem…

Going up! As you can see, the weather was, for our intents and purposes, crap. It was still okay here in the open, but north of Medvednica – where the wind kept blowing moisture up the slope – it was downright awful
Rounding Medvednica from the west near Zapreลกiฤ‡. As you can see, the weather was steadily deteriorating, but undaunted we went ahead to see what’s what ๐Ÿ™‚
In an ironic twist, our 100 HP Cessna 150 turned out to be faster than the 210 HP Reims Rocket, so we had to orbit around a bit to let DMJ gain some distance before our photo run ๐Ÿ™‚
Lining up for another run, showing just how large that banner actually was :). While weighing just under 20 kilograms, its sheer area caused so much drag that DMJ – lightened, with half-full tanks and one person on board – needed to be run at near maximum continuous power
Closeup of DMJ while skirting the northern slopes of Medvednica. The visibility was still good compared to what we hit a few minutes later…

Pretty soon however we ran into problem #2. The ski track which we were supposed to fly over – a track very popular with local skiers – is quite narrow and tucked away between two mountain crests. To follow it, we’d have to fly up the through, climbing continuously, in formation and poor visibility, with one aircraft that was underpowered and another that was barely hauling itself as it was. Realizing conclusively that it would all end in a pretty big accident, we turned round and scurried back toward Zagreb, to try and at least save some of the mission there.

Following one of the city’s fast peripheral roads, with visibility mercifully increasing
Keeping low above town. Though the minimum altitude for flyovers is 2,000 ft – about 1,600 AGL – during banner-towing missions this can be lowered by approval. We may have taken that a bit too seriously… ๐Ÿ™‚
A wide view of the historic city center, with the Cathedral and old Kaptol fortifications easily identifiable

So far so good as far as the towing was concerned, but my photo session was turning into a bit of a mess. The poor visibility and light, coupled with the turbulent downdraft from the mountain, meant I couldn’t really do much with my unstabilized telephoto lens, so to conserve fuel, we turned for home, leaving DMJ to fly two more short runs above town.

3. Cold, cold, cold!

While the results of the first run were mildly disappointing to say the least, the designated god of aviation – Murphy ๐Ÿ˜€ – allowed us to make it all up on the 17th, when the weather finally cleared. Beautifully clear skies, still air, visibility one can only hope for and an even lower temperature were just too good to pass up, so weย  saddled up and full of optimism decided to give it another shot…

A spirited low-level departure above the field to kick off an excellent mission!
Now this is more like it! ๐Ÿ™‚ Shot with the window open – and -17 C outside – with a wide angle to give an impression of size and distance
What a beautiful setting for a photo shoot! Looking north above the northern foothills of Medvednica, with the track right behind us

Because the shoot was going so well, Mr. Murphy decided to intervene again and as we neared the ski track, our coordination sort of broke down :). The problem was that to get good shots, we had to fly to the left, above and somewhat in front of DMJ. This meant that my photopilot couldn’t see DMJ because I was in the way, DMJ couldn’t see us because it’s wing was in the way, and the need to maneuver around hills and keep station above the track meant that our graceful aerial ballet quickly degenerated into a left-footed cha-cha-cha as we tried to keep our little formation together.

My favorite shot of the day, just as DMJ is about to pass below us – without actually seeing us until we were right on top of it ๐Ÿ˜€
A beautiful day, the throaty roar of the engine, and playing catch above the mountaintops. Can it get any better than this? ๐Ÿ™‚

With my hands trembling and my skin cracked from the cold – -17 C at 70 knots in propwash without gloves, absolute genius on my part – and our mission completed (relatively, given there were few spectators out :D), we set course for home. As before, DMJ went to do a circuit of the town, while we proceeded directly to Luฤko, so I could catch a shot from the ground as well ๐Ÿ™‚ (I was having a photo field day).

Turning final for RWY 10 after one of my best photo experiences to date ๐Ÿ™‚
DMJ inbound for release. The angle exaggerates the size of the banner, but it looks cool ๐Ÿ™‚

Unfortunately, getting some “inside” photos from the towplane is a bit difficult and impractical – mostly because both crew are busy with other things… and there’s honestly not much to see; most of the time the banner itself is outside the the crew’s field of view, so it pretty much looks far better from the outside :). I’m also hoping to get a good, systematic sequence of the pickup, but that will have to wait for some warmer weather… ๐Ÿ™‚

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