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On monoplane wings the balance point can usually be defined as between 25 and 30 percent of the average chord of the wing, but the ideal value could vary according to the wing-section used and other variables. A simple way

The theory is that the lift generated by the wingsection when totalled has a resultant at approximately 30% of the average chord of the wing. This means that the force generated by the lift is exerting an upward pressure at this point on the wing, opposed by the weight of the model which is centred at the same point and resulting in a total force which is then either upward, downward or constant.

If these two forces are not opposed ie. nose-heavy or tail-heavy, the model's flight charecteristics will change to the extent that it may become totally uncontrollable. A nose heavy model with a balance point forward of 25% of the average wing-chord will have a tendancy toward a nose-down attitude, while a tail-heavy model would have a tendancy toward a nose-up attitude which would result in the wing stalling. For example: a paper-plane which is nose-heavy tends to start pointing it's nose toward the ground as soon as it is released and hit the ground, while a tail-heavy paper-plane would have the tendancy to point it's nose upward until it stalls, recover and then start pointing it's nose upward again.

On monoplanes this theory is relatively simple to implement, simply calculate the mean aerodynamic chord and then 25 to 30 % of this value to get the ideal balance range.

The mean aerodynamic chord or average chord of a wing is simply put, the average width of the wing between leading and trailing edge. The mean aerodynamic chord of tapered wings can be most easily calculated by using the method shown below.

To simplify things somewhat here is a balance point calculator which will simplify these calculations for you:
Balance point calculator

On biplanes and other multi-wing models, the calculation of the balance point changes changes, with more than one flying surface, one has to calculate the average chord of each of the wings individually and the balance point for each of these wings, and then the average of all of the balance points to come to a final balance point.

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Maiden Flights - by Warren Gardiner

Firstly go through your preflight checks, as prescribed by your local model flying club or Model flying organisation. A simple checklist will look like this:

• Make sure that all control links are secure,
• all servos are fitted and sturdy
• all controls are working correctly,
• all hinges are fitted securely and won't pull out in flight,
• the undercarriage is secure and sturdy,
• the engine is mounted solidly, and all screws are tight and wont't rattle loose,
• no control slop, all flying surfaces are strong and sturdy,
• no metal to metal linkages which could cause interference,
• the batterypack and receiver are packed in foam and won't move around at all,
• the prop is balanced and right for the engine

If in doubt about anything on your model consult a qualified instructor or your local hobbyshop.

The first flight of your brand new model is probably the most nerve-wracking and possibly dangerous flight of all. If you are not comfortable maidening your own model, you should definitely ask your local flying club's instructor or some other capable person.

If maidening your model yourself, first get comfortable with your transmitter, making sure that you will easily be able to reach the trims while flying if necessary(usually). Once you're comfortable with your model and transmitter, double check that all the controls are the right way around and you're ready for the first flight.

Start the engine and make sure that the engine is set up correctly, hold the model in a vertical position with the engine running full throttle for a few seconds, if it dies, the engine is too lean, if not and it sounds the same while running with the model horizontal the engine is probably set up right. If you have a new engine in it, first run it in as specified in the engine's instruction manual or ask you local hobby shop.

First taxi around a bit to get to grips with the ground handling and once comfortable line up into the wind with the engine on idle. Open the throttle slowly to full throttle, and steer the model down the center of the runway. Once the model is at full speed and about 2 thirds of the runway, whichever comes first, feed in a little up elevator, and it should slowly lift off. At this point you have to be pretty careful, the model might be in need of trim in that it needs either up or down trim, so slowly release the up elevator. If the model dives, pull up until the model is at the right attitude, and keep that amount of up held until you are at a safe height at which time you can release the elevator and feed in some trim. On the other hand, the model might be in need of some down trim, in that it takes off prematurely, or keeps climbing. If this happens, feed in some down until it comes to the right attitude, be sure to not overcorrect, the model might point itself directly down into the runway, destroying your beautiful new model. At a safe height, the down elevator can be released and trimmed to fly straight and level. If the trim tabs are not sufficient for your model to fly straight and level, close the throttle, keeping the model at a straight and level attitude, and land as soon as possible, this is extremely difficult if the model requires down trim, since then you have to push the stick forward to fly straight and level and release it to flare for a landing which is almost directly opposite to conventional landings where you release the stick to fly straight and level and pull back on the stick to flare.

The flight checklist for a new model's maiden flight should look like this:

• Trim the model to fly straight and level.
• Test that the control movements are enough by doing some flat figure eights.
• Fly a few circuits to get used to the model.
• At a safe height, slow the model down by closing the throttle to idle and get accustomed to it's low-speed handling charecteristics and glide.
• Do a few landing approaches.
• Land.

In the event of a sudden engine cut, the first thing to do is to inform the pilots around you(if any) that you have a deadstick and make sure that the runway is clear. Glide directly toward the start of the runway, if you are at a reasonable height, do a small circle or two to lose height and make sure that you will not overshoot or not reach the runway. Glide in and land, but be sure not to slow the model down too much and stall, even on idle an engine supplies enough power to prevent a stall at the same speed as landing deadstick. If you don't make it to the runway, simply level out in a clear area and handle it as any other landing, the model won't be totally destroyed and only a minimum of damage can be expected.

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Undercarriages - by Warren Gardiner

Many problems caused on take-off and landing are usually as a result of undercarriage problems, particularly so in the case of taildraggers.

On of the biggest problems concerning taildraggers is ground-looping, where the model suddenly spins around and is difficult to control on take-off, landing and during taxying. The cause of this is the general lining up of the wheels, if the wheels are both pointing slightly in, it is called toe-in, when they are pointing away from each other it is called toe-out.

The best option on a taildragger model is to intentionally put in some toe-in on the wheels, this helps the model run straight on the runway. This is because that when the model goes slightly off course, eg. to the left, the right wheel will cause more friction (because it is at an angle to the direction of travel) than the left which is running straight and true now. This action swings the model back in the opposite direction helping it to keep tracking straight.

The placement of the undercarriage on your model is also important. On tricycle undercarriages the mainwheels have to be behind the center of gravity to keep it on all three wheels, however it is best to keep them as near as possible to the center of gravity. This is due to the elevator having to work harder to lift the nose of the model and rotate the model when the mainwheels are further back.

The placement of the undercarriage on taildragger models is also important and this also has to be as close as possible to the balance point of the model, conventionally as the model picks up speed, the tailwheel lifts off the ground and as soon as the model is at it's flying speed it will lift off either by itself or with a little up elevator fed in. With a more forward undercarriage the wind over the tail is not enough to lift the tail into the air because of the lever effect caused by the distance between the balance point of the model and the mainwheels. Moving the mainwheels nearer the balance point minimises this lever effect and the tail lifts into the air more easily.

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Hinges - by Warren Gardiner

The right hinges and fitting of hinges are a very important part of your model. Always choose a good well-known brand of hinges and the right hinges for the job,

There are many types of hinges available as well as hinging methods: ranging from standard nylon or plastic pinned hinges to CA hinges and surface hinges. For club models and general sport models pinned nylon hinges and CA hinges are the norm. For information on the types of hinges available and the correct use thereof speak to your local hobbyshop or members of your flying club in the know.

The first thing to do when fitting hinges is cutting the slots in which your hinges will fit, the slots will have to be of the same thickness as the hinges being used. There are many commercial tools available such as hinge - slotting kits and electric tools but these are not always available or present in the average workshop. For nylon hinges a simple method is to use an old junior hacksaw blade from which the pin has been removed and the point sharpened.

Fortunately CA hinges(Cyano Acrylate hinges) are relatively thin and generally require nothing more than a sharp blade cut by a hobbyknife for a slot.

The next step is to fix the hinges in place, CA hinges are so named because that is how they are affixed, simply fit the hinges once the model is covered and drop a few drops of superglue on the hinges and they're permanently stuck.

Nylon pinned hinges usually require a little more effort. Be careful of using superglue to affix pinned hinges, the superglu is most likely to end up in the hinge joint and end up jamming it, so it's best to use some epoxy squeezed into the hinge slots and wiped clean and then fit the hinges. Another option is to use pins right through the control surface and the hinge and cut off flush with the surface, but epoxy is usually a safer long-term option.

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