Chapter 7

 

Chapter 7

Getting aloft

The big moment arrives when you emerge from the shelter of your workshop to put theory into practice. To get off to a good start, make it a point to bring along the right equipment and a predetermined testing procedure. For any model more complex than a hand-launched glider or balsa ROG, the first necessity is a good flying box, containing a few well-chosen tools and supplies, so you can make necessary adjustments and minor field repairs without having to retire to the workbench, which is sometimes miles from the flying field.

A metal fishing-tackle box can be easily adapted for the modeler's use, or you can build a simple plywood box, like the one shown in Figure 33, with room for everything needed.

Here are the items you shouldn't be without to be prepared for any kind of flying:

Fuel (diesel or glow, to suit your engine), 1-1/2 volt battery (for glow engines), Battery leads with alligator clips on both ends, Fuel pump, (a hypodermic syringe with 1/16" O.D. needle ground square is good), Extra fuel tubing, three sizes, Spare glow plug with washer, Glow plug wrench, 6-inch adjustable crescent wrench, Long engine-mounting bolts and nuts, Small wood screws (for emergency mounting of engine), Spare engine (or rubber motor) to fit model.

Propellers and reamer if needed to make it fit shaft, Fuel tank for testing or emergency use, Razor blades and/or pocket knife, Slip-joint pliers, Small screwdriver, Sheet lead or strip solder for weights, Fast-drying fuelproof cement, Straight pins, Clear dope - 4 oz. bottle, Brush-flat 1/2", Thinner - 4 oz., Spare needle-valve assembly complete, Hacksaw blade, Rubber bands in several sizes - plenty of them. A lump of modeling clay (wrapped in waxed paper) for weight.

Sandpaper in two grades, Thin aluminum sheet for trim tabs, 1/8-inch plywood for emergency firewall repair, etc. Balsa, a few strips of each thickness, Sheet balsa 3" x 12" in several thicknesses. One sheet of light-weight tissue (in waxed paper envelope) for patching, Spare control lines, Spare handle, Spare wheels to fit model, Spool of fine copper wire, Small package of tissues or soft cloth, 1/16" and 1/8" drill bits - use as augers to make emergency mounting holes.

Some modelers carry more than this - but these items will cover most field emergencies. Adapt the list to fit your situation; if you use only glow engines, diesel fuel is unnecessary - except to lend to a pal in need. The diesel flyer won't need batteries, and a rubber-power fan can get along without fuel - but he needs a spare rubber motor. Get duplicate tools and equipment for your flying box, rather than use your regular workshop equipment, so you won't have the job of making up the kit each time you go out to the flying field.


fig.33
fig.33
 

The next consideration is a place to fly. This would be first, but for the knowledge that a modeler armed with a ship that's ready to fly will inevitably find a place to fly it. If you live in a small city or town, or in a rural area, this may seem an unimportant consideration. The big-city dweller may find it quite a problem - but it can be solved. If you fly only C/L, you won't need a great deal of space, but it will be necessary to have the permission of the owner of the site and an OK on the noise from any near neighbors. To non-modellers, engines make quite a racket. The use of small engines and mufflers helps on this point.

Your C/L site should be at least half again as broad as the diameter of the flight circle; i.e., 60 feet square for 20-foot lines, 210 feet square for 70-foot lines. This will allow room for a few bystanders, and space to maneuver if the lines go slack in a gust. Be sure to warn your audience (you always have an audience) to stand well back, and keep the model above head-level when in flight - lines have been known to break, though rarely both at once.


Night flying - C/L scale model.
Night flying - C/L scale model.
 

For free-flight you'll need a generous field, at least several acres in extent, even for modest-sized rubber jobs. If your model stays aloft for just one minute and a light breeze is blowing at ten miles per hour, the ship will drift one-sixth of a mile, even though it flies in a perfect circle. It's ground travel that counts, not air miles. Pick a field without trees, fences, buildings, etc. and try to find one not bordered by steep roofs, TV antennae, or tall trees. If your ship flits past the cleared area, its going to be hard to find in that sort of jungle.

The perfect F/F flying site is an abandoned or little-used airport. Some fields with only one or two scheduled flights per day will allow modelers to use the runways between flights. Once you have gotten permission to use a field, don't abuse the privilege; observe whatever rules or limitations the owner imposes, and see to it that other modelers do the same. A good flying site is too valuable to lose by carelessness.

Once on the field (pick a calm day for testing) with your flying box, run through a preflight check. If the model is a free-flight, rubber or engine powered, look at the flying surfaces (wing, tail assembly) to make sure you have no unintentional warps. If you discover a warp, you'll have to correct it before you can fly successfully.' For an all-balsa surface, simple twisting may do the trick. Bend the warped member strongly against the direction of warp, and hold it for thirty seconds. If this doesn't work, wet it with water or clear dope and prop it in position until dry.

For a doped tissue-covered wing, brush on thinner and hold a reverse twist until dry. Recheck these surfaces after a flight or two, to be sure the warp hasn't crept back in.

With all surfaces flat, look the model over for alignment; the wing and elevator should be parallel, both from top and front views, with the rudder at right angles and on center. Be sure the engine has the proper thrust angle. You can check side-thrust by setting the propeller horizontally and measuring back from each tip to the rear of the fuselage. Most free-flight ships require down-thrust and offset to the right. For pylon models the latter rule is reversed, because of the prop wash against the pylon, which tends to turn the model to the right.

If no balance point was shown on your plans, assume one at the one-third point of the wing. If the model doesn't assume a level position when supported at this point (or near it), you'd better add some weight to the proper end to start with. The first test glide will show whether it's needed. If you have removable wings and tail, be sure they're adequately held down. It's better to use short rubber bands stretched well out, than longer ones with less tension.

For test glides, remove the propeller and substitute an equal weight; props tend to break easily on nose-overs, dives, etc., which are to be expected at first. Gliding over tall grass is a good way to minimize this kind of damage. Cover all engine openings with masking tape to keep dirt out. Aim the model into the wind, slightly down to avoid starting off in a stall position, and toss the model lightly forward toward a spot on the ground about twenty feet away. The idea is to give the ship flying speed and the proper flight angle; it may help you to trot into the wind with the model until you feel it beginning to lift, then let it slide forward. Throw it as you would a light spear - not a baseball.

If the model is properly trimmed fore and aft, it will continue at the angle at which you started it off, flattening out as it nears touch-down (Fig. 34). If the model bores steadily downward and smacks the ground head first, it's nose-heavy - or else you threw it too weakly to give it flying speed. You can overdo it, too. By hurling a nose-heavy model at high speed you can make it whistle along in a flat glide, until drag slows it down. But we're assuming you've done your homework and are gliding the model properly. Put an incidence block under the leading edge of the wing, or the trailing edge of the elevator to correct nose heaviness (Fig. 35). This is where the balsa strips in your flying box came in handy. Start off with a thin strip and increase as needed.


fig.34
fig.34
 

The point at which many beginners become confused is with a stall in the test glide, because, although a stall results from tail heaviness, the model will still hit nose first. But the condition is easy to distinguish from nose heaviness. If the model dips in its glide, starting out flat or even climbing a bit - then dropping its nose and descending suddenly - that's a stall. The heavy tail causes the nose to move up, putting the model in a mushy attitude, with wings and elevator at an angle to the direction of flight. This extra drag slows the ship below flying speed. The flying surfaces become no better than dead weights, the weight of the nose asserts itself, and down toward the earth the plane goes - bang!

A stall is cured by placing an incidence block under the trailing edge of the wing or the leading edge of the elevator. Be very careful not to set up a negative angle between the wing and elevator, with the leading edge of the wing relatively lower than that of the elevator (Fig. 35); under power this will cause a spectacular power dive.

If you need more correction of trim than you can get with a reasonable amount of added incidence, start adding weight to the appropriate end of the model. Clay packs easily into any space available, and bits of lead can be embedded in it as needed. Once the balance is established, cement some balsa over the ballast to hold it in position.

After three or four glides and some juggling of incidence and weight, you will have arrived at a satisfactory initial trim. If any marked turning tendency has shown up, correct it by offsetting the rudder tab slightly away from the direction of turn. If this isn't enough, set the wing at a slight angle, as viewed from above, with the tip toward which the model has been turning slightly forward (Fig. 36). An alternate method is to block up one side of the elevator; this will cause the model to turn toward the high tip (see the Adjustment Check List at the end of the chapter).

Now comes the moment you've been waiting for - the first powered flight. Whether your ship is powered by rubber or an engine, all your power testing and preparation should have been done at home before coming out to fly. You'll have plenty to occupy you with adjusting the ship without also having to tinker with a cranky engine or make up a rubber motor. For your first tests with a rubber job, a hundred or so turns without stretching out the motor will do. If you use a glow engine, run it as rich (needle valve open) as possible with steady running. A diesel can be throttled back by slacking off the compression. Position the prop on the shaft so that it will rest horizontally as it begins to come up against compression. Put a little fuel in the tank, start up and launch the model just as for a test glide. This low-power flight will give you a much better opportunity to observe your model's flight habits. Here is where a turn is likely to show up. If it is not too pronounced, leave the rudder setting as is until you see how it looks under full power. Correct any power stalling or diving by adjusting the angle of thrust of the engine. In most cases, the trouble if any will be stalling, and a washer under the proper engine mounting bolts (or for rubber, a wedge under the thrust button) will correct the situation.


fig.35
fig.35
 

With only a few turns, a rubber model will probably land with the prop still turning, so you won't be able to study the glide until you try more power. An engine-powered job will stay in the air as long as the motor turns, and give you a chance to watch a longer glide down. Make any further glide-trim adjustments now to achieve a smooth flat glide with a gentle turn. Be careful about adding left turn at this point, since with engine torque it may add up to a spiral dive under high power. A right turn is preferable, canceling out torque effects. Some turn is not only inevitable, it is highly desirable to keep the model in the vicinity of the modeler. Lost models and long chases are not generally the result of a straight fly-away, but of wind, which causes the circular flight path to move away in toto. That's why you shouldn't try to fly in a wind of more than about 10 mph. The wind also tends to buffet the model about and makes for hard landings. To combat wind drift, fly from the upwind end of the field, and launch the model crosswind, slightly into the wind; so that its natural turn will bring it into the wind. Of course, it will continue around and make a dash downwind before coming around into the wind again, but it will have gained its altitude and used up some motor run bucking the breeze, and won't be so likely to be a quarter of a mile downwind when power cuts.

Now you can hazard a flight under full power. Use only enough fuel for a five-to-ten-second motor run, and be certain there is no unexpended fuel from a previous motor run in the tank. An engine running a little off proper setting may quit early several flights in a row, then perversely burn it all on the next flight and end up in the next county. Even a low-powered sport model gets upstairs fast under full power, and it's amazing how quickly your model can dwindle away to a mere speck in the sky. Any time your model seems to be headed away from home don't hesitate to take off in pursuit in a hurry. Keep an eye on the model, and if it disappears from view behind an obstruction, stop and study the situation; fix in mind the position and direction of the ship as last seen. Then head for the spot where you calculate it should be, and start hunting. Most contest-type models use a de-thermalizer to bring the ship down abruptly but safely after a specified time. Commonest is the pop-up elevator, released by the burning of a timer fuse.


fig.36
fig.36
 

The chief risk on the first full-power flight is a spiral dive, or loops ending in a nose-up power cut-off and a subsequent failure to pull out. The spiral dive is sometimes the result of excessive torque (assuming your glide is correct), and you can remedy this by using a lower-pitch prop and by offsetting the engine farther. More down-thrust will cure the loops. If the loops are straight-away, a little turn will convert a loop into a nice climbing spiral.

Use the tissue or soft rag in your flying box to wipe the model carefully after a motor run. Even fuelproof finishes can soften up some if fuel is allowed to remain on them indefinitely. By taking a moment to clean the ship, you'll save a lot of time later in scraping off sticky paint and embedded dirt. Recheck all settings and incidence blocks after each flight, and shake the tank dry, just in case. Be careful about preflighting the ship, and you'll save most of your crack-ups and flyaways.

Control-line test procedures are simpler, since you rely much less heavily on built-in flight patterns. Start by laying out and checking your lines. Use lines that are heavy enough, but don't load the ship down with oversized ones.

For small C/L jobs No. 30 linen thread is heavy enough. Single-strand steel wire, available at hobby shops, should be used for the bigger models. Stranded steel cable is needed for the biggest monsters, and for high-powered speed ships. Don't let steel lines get kinked, and try to keep spectators from walking on your lines; something they seem to love to do, claiming they can't see them when they're laid out in the grass. The audience also needs to be discouraged from stepping on models, kicking over fuel cans, and testing fabric ("Ooh, I didn't know it was only paper!"). Next, check the balance of the model. Most C/L jobs balance at about the leading edge of the wing. This nose-heavy condition gives the pilot better control; you don't want your tethered job to start floating like a F/F while the lines hang slack.

Usually both an offset rudder and a weighted outer wing tip are used to keep the model out on the lines. Engine offset helps, too. It is customary to fly counterclockwise, but there is no reason not to install your controls so as to fly clockwise if you prefer - and you'll have torque helping to hold the model out. After a few flights, when you have the feel of the model, you may want to reduce your rudder and engine offset to increase efficiency.

If you're a novice at flying on lines, try to get an old hand to test-hop the ship for you. When he's satisfied all is well, you try it.

If possible, a C/L ship should be allowed to take off under its own power so as to enable the flyer to get the feel of the controls and lift the ship at will. For the initial flight, it's wise to set the control linkage for minimum control surface movement - particularly down - since the chief danger is overcontrol with an unfamiliar ship. After a few practice flights, set them as sensitive as you want them, but don't forget you've done so.

Make a last-minute, but very important, check of your controls to be sure up is up, have your crew chief start the engine (with a modest fuel supply - you may get tired), and let her go. Hold the controls neutral until the ship is skimming along ready to rise. If it's sluggish about getting up on the main gear, try just a little down elevator to get the tail up - then neutral again as it picks up speed. When you're ready, and not before, give a touch of up, and back to neutral. (Be prepared for the model to take off before you give it any control, by the way; it may not wait for that touch of up.)

Once in the air and flying straight and level, cautiously try a delicate maneuver or two. Of course, if your ship is a bit tail heavy, or overly responsive, you may already have your hands full trying to keep it flying level; in this case, omit the maneuvers.

C/L models can't fly or be blown away, but a high wind can cause the ship to come in, on the upwind leg of the circle, so be prepared for this when you try flying in breezy weather. If you back-pedal in a hurry, you can keep the lines taut. This is where that extra room counts.

When the engine begins to change tone preliminary to stopping, bring the model down about waist high, and hold it in level flight. Let it glide in naturally, with a little up only if obviously needed. A big stall at this point can wash out the model. Give the ship full up as soon as it touches the ground firmly, to avoid a nose-over. As you become more practiced, you'll find you can whip the model around after the engine cuts and set it down at any point you wish.

The average sport model is capable of doing a wide loop; trainers usually are not, unless a bigger power-plant is installed. A true stunt model can do consecutive tight loops, and almost anything else you can think of. Work your way into these stunts carefully, and don't try maneuvers that are beyond the model on the lines. It's a lot more fun to watch your ship perform properly, doing what it was designed to do, than to see it laboring to do the impossible. Sport models don't climb like contest jobs; C/L trainers aren't noted for stunting. The real thrill of flying your ship is in obtaining correct, controlled flight - when you make that assembly of inanimate parts behave almost as though it had life and intelligence of its own.

Even if you're a solitary type, you'll find there's more pleasure in flying with other modelers. They're a congenial bunch for the best of reasons; a genuine common interest in the sport. It's always interesting to see what the other guy has built, to see other models and engines in action, to learn new angles and tricks to help your own flying. Then, too, it's nice to have a little help with a cranky engine, or getting a C/L job aloft, or chasing a runaway. Don't be stingy with your own time and help, either. You can even carry extras in your flying box, including some items you don't use yourself, just in case somebody needs them. He'll pay you back when you're about to be grounded for want of a mounting bolt or a spare prop some day. Like flyers in the early days of aviation, modelers stick together.

If there's a club in your vicinity, join it. Clubs frequently have good flying sites, quantity purchase arrangements, and other advantages to offer, in addition to the company of other modelers. If the city fathers (or cranky citizens) object to flying in the park or on a vacant lot, a club can present a better case for a change of heart than an individual. Often the local hobby shop or department is the sponsor of a club. If yours isn't, suggest it. The more the merrier!

Businesses with large parking lots, like supermarkets, can often be persuaded of the public relations value of letting the club use the paved area for C/L flying on Sundays. Don't be bashful; scout around and get things lined up for more flying fun.

The Society of Model Aeronautical Engineers is the national organisation for aeromodelling in Britain. It has an average annual membership of 4,000 active aero-modellers and conducts a very active contest programme which runs from March to October each year. About 150 clubs are affiliated to the SMAE and this collective representation is responsible for the facility of using Royal Air Force airfields. For details of membership, contact the Secretary (a voluntary post, there is no permanent paid official) of the SMAE, c/o Royal Aero Club, 116 Pall Mall, London, SW1Y 5EB. A feature of SMAE activity is the regular National Championships held over each Spring Bank Holiday (Whitsun).

While some model builders think in terms of free-flight endurance competition as the only real measure of a model, the great majority of modelers fly for the pleasure of making something with their hands, tinkering with engines, watching their jobs buzz around, and associating with other modelers. While staying up ten minutes on a fifteen-second motor run is an interesting trick, it depends completely on the presence of thermals; the best model will glide down in a minute or so without a rising air current. There are other feats a model can perform that are at least as difficult - realistic take-offs, flying a predetermined pattern, spot landings, free-flight speed - the possibilities are endless. Try out all the ideas you can think of, and if bad luck strikes and you clobber in - it'll happen now and then - head back to the old drawing board philosophically; that's part of the challenge and the sport of modeling.

ADJUSTMENT CHECK LIST

Glide:

Model dives -

• increase positive incidence in wing

• increase negative incidence in tail

• add weight to tail

• lighten nose Model stalls -

• decrease positive incidence in wing

• decrease negative incidence in tail

• add weight to nose

• lighten tail

• increase turn

Model wavers and falls off on one wing -

• check for warps in wing or elevator

• increase rudder area Model turns too sharply -

• offset rudder in opposite direction

• warp up trailing edge of wing on side to which turns

• offset wing (from top view) - tip opposite turn to rear

• tilt elevator - raise side opposite turn Model yaws or flips over -

• lower center of gravity

• increase rudder area

• increase dihedral

Power:

Model dives -

• raise thrust angle

• increase positive incidence in wing and add weight to nose

Model stalls -

• increase down-thrust

• increase engine offset for more turn

Model spiral dives -

• reduce engine offset

• use lower-pitch prop

• add rudder area below fuselage Model turns too sharply -

• reduce engine offset and increase down-thrust if necessary

• use lower-pitch prop

 
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