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Airspeed is King: A Christmas Gift from an Old Duster Pilot

by Jeremy Cox 1. December 2009 00:00
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Since it is impractical for me to send each and every one of you an individual Christmas gift, I felt that instead I could at least give you some of the wisdom that I had learnt many years ago, which I hope might actually save your life if ever you decide to get low amongst the killer trees and wires that dot much of our landscapes.

How am I qualified to impart this knowledge you may ask? Well I once taught crop flying techniques to students from around the World, and during this period of my life I can tell you that I ran the ragged-edge many a time, with luck somehow staying with me in the cockpit so I am able to write this article for you today. So without much further ado here is your Christmas present:

The absolute number-one fact that does truly shadow the importance of everything else that I will tell you in this piece is this: "Airspeed is King." Trust me. Regardless of what tomfoolery you might be attempting in your aircraft, if you do not have sufficient airspeed to make it through the manoeuvre, you will snap, slip, slide, flip or stagger and fall out of it. This is okay if you are three or four hundred feet above the ground, but at two hundred feet and below there are no two ways about it; you are going to hit the deck and it is highly likely that you will not be able to walk away from it.

What do I mean by "Airspeed is King"? Well when you fly more than a couple of hours every day, you will quickly develop a sixth sense that stems from multiple physical forces that are acting upon your body and brain. I will cover this later, but with experience in feeling your speed through your controls and your bottom you will instinctively know without ever having to look at your airspeed indicator that you are 'on-speed.' If you haven't developed this sense then you really shouldn't be flying close to the ground. But if you are so foolhardy to do this based on your instruments instead of your buttocks and hands, then you had better at least keep your speed in the green arc; and that's with your wings-level. I don't want you cranking in the bank and having to rely on an indicator to tell you if you are above the increased stall-speed that comes with steep angles of bank. If the controls start getting sloppy and you feel some burbling in the tail, then you are on the ragged edge, and the old girl that you are slapping through the air is ready to blow you a kiss that you definitely won't want. Push her beyond these sensations and "BAM!" Trust me; I've done it at altitude using a flat cloud as my simulated ground deck and found that regardless of how nice your bird stalls wings level with a steady even pull till the break comes, you whack some bank in and get her turning for your return swath path back down the field, and this lady is going to snap you upside down. This is okay with sufficient height to recover but when you are only at one hundred and fifty feet or less, which is about where you crank the bank in to return your path inbound back to the end of the field after climbing out and away, the aircraft may not even have time to get to inverted, and instead you will likely cartwheel in. Always remember that your wing will stall at the same angle for the given speed that you have fed in, so be gentle on the controls whenever you are slow.

The next fact of survival is this: "Never make a Downwind Turn." How do you know which way the wind is blowing? Well first; shame on you for not knowing! Mother Nature is an easy book to read if you know where the chapters begin and end. Before you ease your aircraft below five hundred feet you should have read the surface of any water that you have passed over. You will see which direction that the fine patterns of ripples are travelling. If there are no ripples because there is no water along your route, then look for any smoke that you can espy within your panorama. Which way is it drifting? Failing this, then look at which way the leaves on the trees are turned. Are they trembling? Follow their bend from stem to tip; you will see what great windsocks they really are if you learn to read them correctly. No leaves, then how about the grass? The same observations apply to their blades as they do for tree-leaves.

Once you begin to relate reported wind speeds to the movements in nature, you will soon be able to judge wind speed very accurately as well. If you are really unlucky and have absolutely no references to read from because you are flying over a featureless desert or snow-scape, you will just have to run a quick diversionary course along a shadow or stain on the ground, just like you would if you were checking your compass deviation. Make at least three runs at the same speed and height (the more the better), but on different headings and watch how and where you drift. You are looking for a rate and direction of your drift over this point-of-reference line.

Okay back to downwind turns. Do you remember the concept of relative wind back in your flight school days? Well there is no real mystery here except for the fact that you might feel comfortable at a speed heading into wind, but change the dynamics by heading away from and with the wind while you are slow and close to the ground, then I promise you that you will very quickly feel the controls go slack and wobbly, which a dead giveaway for letting the king lose his head (remembering that "Airspeed is King.")

So what about the distraction caused from hitting a tall weed, a brush-pile, a down-draft, a wasp sting, smoke in the cockpit, chatter on your radio, or whatever? How do you make sure that you don't turn your head after losing your concentration during your run and the ground quickly sucks you into her wicked embrace? The easiest and no-cost insurance is found in your trusty trim wheel. Okay so you might make your arm ache by the end of a long day but in no time your muscles will quickly adapt and grow to accommodate the force. What am I blathering on about? It's this: Wind-in some 'nose-up' trim before you leave the safety of a five hundred foot AGL height. If anything happens to either you or your steed while you are both close to the deck, the natural overriding force that is now naturally in-play is that the climbing trim that will safely lift you out of trouble without you having to think about it. Don't crank enough in that will make you do a ground level loop; but do dial enough in that will have you climbing at a good one hundred and fifty feet per minute, or more. You can thank me later for this tip after it has saved your life, which it will if you are buggering about close to the ground.

So what about trees or hills, or whatever? I won't talk about buildings here because you shouldn't be dropping chemicals or fertilizers near them, and if you are not working for a farmer or government agency, then you are busted for being somewhere that you don't belong, and even though you may not get caught this time, you still have it on your conscious. No, what I am talking about is how close can you get before pulling up and over them? Well airspeed is the answer to this question combined with how heavy you and your lovely winged date are, as a couple. You have a hopper full of stuff and the lady will act like she has made too many trips to the buffet by moving very slowly, so account for this fact by easing her up early. As she sheds her weight by you metering it off and out onto the field that you are working, you will eventually be yanking up and over instead of easing up above them. I have measured as few as three fuselage lengths before a hard pull when I've been close to depleting my payload. Weight increases inertia, or what I mean to say is that you will experience 'mushing' before the controls bite and change your trajectory. With less weight onboard will result in less mush. Fir trees can present a tall obstruction to zap over, but they are fairly safe obstructions because they are ordered and somewhat slender beings. Oak trees are a different story because they can have all sorts of errant and disorderly branches that might reach up and snatch at your main undercarriage, tailwheel, wing leading edges or tail feathers. If the branch is meaty enough, you might find yourself staggering into the tree-line instead of sailing over it.

Lastly never forget that trees are the nesting place of choice for birds, and I have seen some bloody great birds launch themselves out of a tree canopy. Getting a crane or heron through your windscreen while low and slow might make that day your last. Practice, judgement, more practice, all at varying weights will go hand-in-hand with your sphincter, in telling you how close you can get before you need to pull-up and over.

What about wires then? Please read this, and re-read it until you can recite this in your sleep: "All Wires Kill!" How do they kill you may ask? Well if you don't know that they are there, then they will kill you for certain. A survey of the field from the ground will save your life; but I will cover this later on. What I am trying to impart to you is that if you fly through a wire and it doesn't sever, and instead it grabs you like an arrester cable on an aircraft carrier, you will sadly and immediately see the 'Game-Over' sign flash in your head as you are smacked down.

Now let's consider all of the rest of the wires that populate our planet. These are the nice ones that don't want to kill you, because you have already been introduced to them on the ground and therefore have met before (see field survey later.) These almost charming wires are now just a minor inconvenience for as long as you keep their presence at the forefront of your thoughts, as you streak across the crop rows. The only decision required with these friendly wires is whether you are going over, or under them. You can only decide this if you have seen them while you have been standing safely and firmly on the ground. Without a survey the only decision that you can make is that you are going over them, period-no compromise.

If you have determined earlier that you are going under them then what technique must you use? Well there is no secret here other than that you must follow the golden rule of never fixating on the wire itself. Set up your traversing height as you make the approach, but keep your eyes ahead without looking at the wire and instead feel it through your sixth sense as it slides overhead. Keep the poles in your peripheral vision especially if they closely spaced, making sure that you don't catch one on either of your wing-tips.

Apart from the points made above, flying under a wire, or any other ground feature is really a non-event. Please don't ever do this on a blustery day though, because I guarantee you that even friendly wires will immediately revert back to their natural psychopathic nature.

Another issue that might kill you is fuel starvation. If you don't know how much your girl drinks during a typical sortie, then you are as good as a walking corpse. Start out with the certainty of how much fuel you have got and that it is enough for the planned operation. Set and live by it like your life depends on it because really it does. A fixed pull-up and return to base time is an absolute that you cannot deviate from. Once you have established this parameter; and it must be done before you crank your engine you then must write you're 'start-time' and the pull-up time, down on your hand so you cannot forget it. This may sound unnecessary to you, but I promise you that as soon as you get into the mesmerizing groove out in the field, running back and forth laying a swath, your mind will wander. Without those critical times written on your hand you might be forced to experience the terror of pulling up over a tree line and feeling your aircraft coughing and settling into a glide because you have run out of go-juice.

Okay so what about this mystical business of developing a sixth sense? There is no mystery here either because once you start wearing your aircraft instead of being perched within; you will naturally develop this feeling that the aircraft is an extension of your own being. Your eyes, ears, sense of smell, the palms of your hands, the bottom of your feet, your shoulders through the straps, the hairs on the back of your neck, your sphincter, and lastly the 'seat of your pants'...your buttocks, will all develop an acutely heightened sense of feeling. Every rise, fall, acceleration, deceleration and angle shall become apparent to you. You will be able to feel your buoyancy in the air, which ultimately lets you instinctively know just how much lift you have in reserve that can be called upon for your next manoeuvre. The days of needing to look at your slip/skid indicator ball are long gone once you reach this nirvana. You will instantly know when your trajectory whether straight, curved, rolling or turning, is in perfect balance and is harmonized like it is supposed to be. If it is not, you would have instinctively pressed on the appropriate rudder pedal to bring your lady straight, regardless of where you are heading, or in what flying state that you are pushing her through.

What's that; you don't really know how to use the rudder? Well it is about time that you did! The best way to learn this is to keep pressure on your pedals at all times. In a way you are bracing yourself, but in truth you are setting the correct triangulation connection up between you and your interface with your aircraft. If you are used to doing a lot of high-altitude flying on autopilot with your feet planted on the floor and not resting on your pedals, then I am afraid to say that except for the controlled crashes that normally call landings, I must plead with you to please stay away from the ground as much as possible when you fly.

I will end this article with an insight into the required planning and subsequent field manoeuvres that are all required to be accomplished by a 'duster pilot' to properly and safely treat a field with a payload.

Before ever getting in the aircraft you must plan the sortie. You must have a detailed map of the field which has been marked and double-checked by the person that has asked you to treat the field. It would be a disaster to work the wrong field. Apart from being upsetting to everyone involved, you can actual cause property damage or even worse depending on what you have in your hopper. Now go out to the field and survey it from the ground; preferably on foot. The height of the tree line, wires, barns and hills must be fixed in your head, and a flight profile properly planned. Fly every swath with your mind's eye, and identify any problems before they become disasters. This is because once you are dropping into the field on your first run, this is definitely not the first time that you should be seeing an irrigation pump or standpipe out in the middle of the field. Talking of which, these fixtures love to tear undercarriage legs off the aircraft that is flown by an ill-prepared pilot.

Now that you have the lay of the land sorted out in your head, and you have scrawled sufficient notes directly onto your map, you may now go back to your office and figure out the load quantities and fuel requirements. With all of this work done and the calendar window of when you will make the application onto the field has been agreed upon, then all you will have to do is wait for the appropriate weather to arrive. When you are spraying a liquid, a windless or near windless day provides the best conditions for you to make your runs. When dropping solids like a fertilizer, the wind is less of a factor however you will probably find that your busiest times come during the very early morning and the late afternoon of each suitable spraying day.

You are now airborne and you have already read all of natures signs on the ferry-ride over to the field that you will be working. Please don't immediately swoop down and go to work as soon as you arrive at your worksite, though. First it is imperative that you make a survey of the field again, but this time it will be made from the air. Obviously this so that you can make certain that you are about to treat the correct field, but also more so that you can scope out any topographical changes that may have taken place since you last visited the site while on the ground. Wires may have been strung that were not there before, or any other structural feature may have been changed. You will only know this by surveying from a safe height, both flying the perimeter and the middles of the field. Two hundred feet above ground level works pretty well for this, but any height will do just as long as you make sure that you remain above all terrain and structural obstructions until you are absolutely ready to make your entry into the field on an actual money run.

If you have difficult areas like tall tree lines and the like, I suggest that you get the majority of the field treated and then when you are lighter, you can clean up and tackle these tricky areas more safely. When beginning a field, always start at the downwind end and work your way across it upwind, so you stay out of the drift from your swaths. Your runs should be evenly spaced appropriate to your wingspan and the spread from your delivery system. At the end of each run you will add power, pull up initiate your turn to about forty five degrees downwind of your direction of run (yes, I did say downwind, but you did this fast with plenty of airspeed) then you will make your slowest but level and balanced turn into wind looking for the 'roll wings level point' on the centre of your next swath run. At this point you 'come down the hill' from your turning height to cross over the fields' boundary. You have reduced the power that you added to leave the field, and then some to enable your round-out at the optimum height at the start of the next row. As you regain the groove for your path across the field just over, or slightly after passing the boundary, you feed in the necessary power to make a uniform delivery run. When I did this in the Piper Pawnee I always flew the field runs at 100 MPH. My target wheel height above the crops was three feet. My right hand held the stick while my left hand worked the throttle and the delivery valve, which when spraying I would refer to as 'booms' (it controlled the spray booms on the trailing edge of both wings.) The movements into and out of a run went as follows: Left Hand - Power then Booms; Right Hand - simultaneously Round-Out and set height. My Feet kept me true and on line depending on the strength of my crosswind. On leaving the field I did the same as I did for entry with some slight variation: Left Hand - Power then Booms; Right Hand - simultaneously ease up to safe banking height, set-up a climbing 45 degree track. My feet keeping my turn perfectly balanced. Then the into-wind turn to the field entry point projection line. Left Hand - reducing power; Right Hand and Feet setting up my alignment, then the same as before on my last field entry.

Anyhow that's how you should do it, and unless I have completely confused you; by following the methods that I have outlined above, should keep you and your aircraft in one piece for many years of low-level flying to come.

Now that I have given you the proper "hand and cheek" techniques of tree top flying I know that many of our readers have a few tails (sorry had to put that in) to tell and if you are so bold to tell us the outcome I am sure we will all gain in our experience at flying on the deck.

Merry Christmas to you all!

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Jeremy Cox


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