I doubt that the guys in the little planes that drag signs behind them take off with the signs attached. But how do they actually deploy those signs? I’m guessing that there’s only one pilot in those planes. How do they actually do that? And how do they get the signs back on board before they land?
IIRC the banner is laid out on the ground, with the loop at the towed end being supported on uprights. The tow plane flies low and picks up the loop with a hook.
EDIT: This page has an embedded video that shows a banner pick-up.
.
What, and then flies backwards to get it off the hook before they land?
They string the signs out on the ground, with the leading end supported up off the ground. The plane has a special hook attached on the tail end. The plane swoops down low enough so that the hook snags the special loop that is attached to the end of the sign, which is called a banner. Sometimes the plane doesn’t snag the hook the first time around, and has to go around and try again, sometimes multiple times, until they get it. The plane can fly slow enough so that this is possible.
Before they land, they fly down real low to the ground, and remotely release the banner and it falls a short distance to the ground, so that the plane can then land. They don’t land the plane with the banner attached.
This account is based on my having seen it done a number of times.
Great. Thanks. Asked and answered. xo, C.
That seems a lot more difficult than just jettisoning it out the back like a drag racer parachute once airborne. Why do they go to all that trouble?
There’s no place to deploy it from. If it was deployed from the cabin, then there’s the risk that it would foul the control surfaces. Obviously the banners are not very heavy, but if there was some sort of structure added to the rear of the aircraft, it would add to aft-CG (as would the structure). I’m sure there’s an aft-CG moment, but I suspect that it is not as great as it would be if there was a container.
It really is the simplest solution. All you need is a hook on the plane and a couple of uprights on the ground. As far as difficulty, I can’t say from personal experience. But most pilots can land ‘on the numbers’ (all of my landings were right on the spot – in the helicopter! 
), and when you come down to it hooking the banner is just a matter of making a precise landing – without the landing part.
Every summer we have banner towers working out of my neighborhood airport. They do occasionally miss the pickup, but most of the time they hook the banner the first time.
As far as weight - depends on how you define “heavy”. Some of the larger banners are heavier than I can handle on my own. The tow planes are typically stripped down to only the most essential items (for example, these guys usually use hand-held radios instead of the much heavier panel-mounted ones) to allow the airplanes to pick up and drag those banners behind them. Weight and balance calculations are very important. Every decade or two we have tow pilot screw up on that. The result is that the airplane hooks a banner that is either too heavy (or the engine isn’t producing sufficient power - yes, you’re supposed to check that before you pick up the banner!) or the balance with the banner moves too far aft. The usual result is that the airplane stalls. If the pilot is quick enough he can drop the banner and resume flying, if not, the airplane has a disturbing tendency to pancake onto the ground. This is Very Bad for the occupant.
The advantage of the “tail hook” system is that it is mechanically simple and less likely to cause problems than, say, throwing something out of the airplane (as already covered) or installing some sort of deployment system, which would add weight and add the potential for something to jam or break in the system.
Broomstick: You know more about banner towing than I do. Can you describe how weight-and-balance is calculated? I’m only familiar with putting a weight at a position and figuring the moment. Let’s say a banner weighs 40 pounds (pulling a number out of the air). Obviously that would create quite a moment if it were a block of lead bolted to the tail tie-down. But a banner isn’t a weight hanging from a point. There’s a significant drag vector that is perpendicular to the weight vector; so that 40 pounds isn’t pulling straight down on the tail. Since banners vary in size, they must create more or less drag, and so the percentage of weight to be applied to W&B must be different, right? Is there a general formula for applying the weight of banners to W&B? Or is each banner ‘placarded’ (so to speak) with the W&B information? What percentage of the weight is applied to the moment?
How do they keep the banner upright, instead of horizontal, or corkscrewed? Weights along the bottom?
They do not do it much anymore with the cost of fuel being so high but back in the 60’s & 70’s in Oklahoma, more powerful aircraft were used and the banner was pulled directly from the ground.
The banner was laid out backwards and the takeoff run was parallel to it so the plane starts out just pulling a bit of rope at first. Getting the tail up quick so that the first of the banner will be lifted up. Also the aircraft would usually be off the ground by the time the full banner had been reversed and completely streaming behind the plane.
Obviously a big banner pulled by an weak 85HP Camp could not do this but many others did it this way.
Even when doing a fly & snag type pickup the banner is laid out in reverse so that the full load comes on gradual and not all at once.
The downward moment at the point of attachment is not much, but the drag is horrendous. Think of towing a sailplane with the sail plane pilot staying slight lower than the tow aircraft, he’ll get cussed a lot but unless it is a really weak tow aircraft, they will be alright, it just makes it a lot harder. That is what the banner towing aircraft pilot is contending with.
The load of most banners are well known and the type of aircraft need to pull them. You don’t just go out with your C-150 and get a job towing.
A lot of the first flighst of a new banner is trial & error unless a wind tunnel is used and that is too much $$$$$. Use a more powerful plane, have a gauge on the tow line and when in flight compare it to other know banners and they know how much they need to change it or how powerful a plane they need to pull it…
Can prolly do it all on computers now and make it to spec.
How do they keep them oriented vertically?
The rod (at the front) is weighted.
I think Gus gave a more coherent answer than I am capable of at this moment (looooong day at work). My knowledge in this matter stems from observation and occasional questions directed at tow pilots, not from actual experience.
This question has occurred to me more often than the OP’s, so I’m glad it got added to the thread.