Wirral Radio Control Flying Society

Plans

There are hundreds of plans available, for practically any sort of model. You can buy them from specialist publishers such as Nexus, who have a catalogue of designs from many different designers; from individual designers who specialise in one type of model, such as scale; and many modelling magazines publish free plans, complete with a guide to construction. Many people like this start-to-finish approach but it does require a higher degree of constructional skill. Beginners are also less likely to have wood or accessories already to hand and will have to buy everything needed: these items may be specified on the plan but if not then you will have to choose and source all the necessary parts yourself.

Kits

One step up from a plan is a kit. There ar two types of kits available; semi-kits and complete kits. A semi-kit is a plan plus some of the parts required to build it. Usually it includes moulded and plywood components, but you are left to buy the remainder of the wood and parts required to complete the model. The advantages are that you are then free to use the materials and hardware, hinges, engine mounts and so on, of your choice. For experienced modellers this can be a cost saving as they have probably built up a stock of components from other projects, as well as leaving them free to use their judgement on their preferred type or brand of equipment; the beginner will of course have to buy everything new. For the new starter the complete kit with all the hardware required to complete the model is the best option.

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Used Models

Buying a used model is probably the quickest and cheapest way of getting started, but as for the purchase of any second-hand item, there are pitfalls. Trainers, by their very nature, lead a hard life and any prospective purchase will need to be inspected very carefully. The best course of action is to ask a trusted and experienced club-mate to examine the model for you. You can often pick up a good deal for a model and engine combination, and sometimes even the radio equipment if the seller is upgrading to a more sophisticated set. The advantage to this is that all installation problems will have been dealt with, and the model should be flight proven and trimmed. You need to look out for repairs - if these have been done properly then there should be no problem, but repairs are an indication of a crash and there could be other, undiscovered problems besides the repaired ones.

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Almost Ready To Fly

ARTF models are a very fast and successful method of getting into the air, with most of the work done for you by the manufacturer, but consequently they are the most expensive way to do it. The range of models available is huge, from simple trainers to sophisticated scale aerobatic types. If you buy ARTF, look for the availability of spare parts, sometimes the construction methods do mot lend themselves to home repair and you may find yourself needing to buy a new wing or other part. When you first arrive at our flying field an experienced instructor will inspect your model for airworthiness and unfortunately this is where most newcomers get their first knock back due to assembly errors which are not their fault but the fault of the kit importer who hasn't put proper instructions in with the kit.

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Assembly

First thing on the list is the wings. When you buy the kit the wings are usually in 2 pieces and need to be joined. To do this you need to use Epoxy glue (Araldite or similar) and you must ensure that the centre brace in the wing and all the other contact areas are thoroughly coated in glue. Make sure that all covering material is removed from the area to be joined so you are joining wood to wood only. When you bring the 2 pieces together they should butt up with no gap between them. When dry this will produce a wing that will be very strong and won't break in flight (yes we have snapped a few)

Next we will fix on the Tail surfaces of your Plane, first of all these must be perfectly aligned or your plane will not fly correctly. To align the tail when you are gluing it in place, Fit the wings to the model and using a piece of string measure the distance between the edge of the tail and a corner of the wing on each side and adjust the tail so that the distance is equal on both sides. The Tail should also be level with the wings when viewed from behind. When gluing on the Tail of the Plane also use Epoxy and ensure that all covering material is removed from join areas otherwise your Tail could come off in flight (Yes it has happened) remember wood to wood joints only .Follow the same procedure for all flight surfaces.

If you are required to fit the hinges to any of the control surfaces, these must be glued into place using either a contact adhesive or epoxy. Dry fit the surface first with the hinges and ensure that it can move freely in either direction without binding or pulling on the hinges. Remove the control surface and the hinges from the slots and coat one half of each hinge with adhesive (also try to get a bit in the slot), then fit the hinges into the wing, tail or fin and allow to dry. When dry repeat on the other side of the hinge and fit the control surface. You should be able to give the control surface a strong tug without it trying to pull out. If in doubt you can also peg the hinges into place by inserting and gluing a piece of cocktail stick through the hinge as well

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Radio

When installing Servos all of the supplied inserts for the servo mounting lugs (look like a small piece of metal tube with one end belled over) should be inserted into the rubber grommets from below. This stops the mounting screws from crushing the lugs on the Servo and the little bell stops the tube from digging into the mounting rail. This provides maximum insulation from vibration. All Servo output arms should be at 90deg to the pushrod when at neutral position so you have an equal amount of movement available each side of neutral.

The Receiver and batteries should be wrapped in sponge and firmly secured in the fuselage as the last thing you want in flight is weight shifting around or something getting disconnected. The sponge is very important as we need to protect our Radio equipment from vibration which could cause it to fail.

The Fuel Tank also needs to be well insulated from vibration and should be held firmly but not packed solid with sponge. Try to avoid the tank actually touching any of the wooden structure if necessary cutting some away with a sharp knife. The Tank should be mounted in the best position possible, which is with the centre line of the tank inline or approximately 1cm below the main needle valve of the engine. If this is not possible then mount the tank as close to this guideline as you can.

With the throttle trim on the Transmitter in the middle and the stick pushed fully forward the carburettor should be fully open. With the trim in the same place and the stick pulled right back the barrel should be open approximately 1mm to 2mm. With the trim pulled right back the barrel should be completely closed. If necessary adjust the throttle stop screw on the carburettor to prevent the Servo from hitting it and stalling (humming)

The biggest problem with most trainers is that they are provided with steer-able nose legs. These are no use on grass and will probably damage the Rudder servo so you will need to lock this up in the straight ahead position and obviously not connect it to the servo.

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Engine

One of the things that puts a lot of people off this hobby is an unreliable engine. The local Model Shop will probably try and sell you a cheaper engine with your Plane i.e. MDS. Now while there is nothing wrong with these engines in the hands of an experienced modeller (I have several myself), there is nothing more frustrating to the beginner than the engine constantly cutting out in mid air with the result that you only get short stabs at the controls and spend the rest of the time walking to and from the pit area starting your Engine. So I would recommend that you spend a little extra and buy a good quality engine that will give you years of good service and enjoyment. Some examples are Irvine, O.S. and Super Tiger.

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Center of Gravity

A number of important factors, such as wing area, wing loading, and tail volume percentage, make an airplane fly well; however, most airplanes can fly with many of these parameters out of norms. So, how do you figure out the CG? It’s pretty easy, actually. Acceptable CG ranges for almost all airplanes is between 25-33% of the Mean Airfoil Chord (MAC) so the hardest part of figuring CG is the “mean” part. On an airplane with a constant chord wing, such as a Cub (see Figure 1), the MAC is easy to figure since the chord of the wing is constant. Just measure the back 25-33% of the chord from the leading edge and that’s where the airplane should balance. If the chord is 10 inches, the airplane will be in balance if the CG is between 2.5 and 3.3 inches back from the leading edge.

Not all wings have constant chords and that is where the “mean” part starts to get complicated. Figure 2 shows a wing with a leading edge taper so the chord at the root is considerably larger than the chord at the tip, causing the “mean” chord to be somewhere in between the two. To figure the MAC, measure back 25-33% at the root and mark it. Then measure 25-33% at the tip and mark that. Connect the two marks with a dotted line. Now, measure the wingspan from the center of the wing to the tip (include the part of the wing that is covered by the fuselage). Go half that distance to get the mean point on the wing. Do the same for the other side of the wing and draw a line between the two points. Now you have the balance point of the airplane. Notice that the balance point at the tip is nearly at the leading edge of the wing so it’s critical that you mark where the balance point is. If you just measure back 25% from the leading edge at the tip, the airplane will be nose-heavy. Although Figure 2 only shows a tapered leading edge, this method also works with trailing edge taper and even wings with both leading and trailing edge taper.

Figure 3 shows a wing with sweep, and once again, figuring the CG is a simple matter of finding the 25-33% point at the root and tip, then finding the point at half span and drawing a line between the two. Notice that the CG is well ahead of the tip leading edge and with more sweep, can actually be behind the root trailing edge. Once again, it’s important that you know where on the wing you’re going to balance the airplane.

The most complex wing design you’ll encounter is shown in the next diagram (Figure 4). This wing has a constant chord section, a tapered section, and sweep, so how do you figure the MAC? Interestingly enough, it’s just as simple as any of the other types of wings. You find the MAC of the constant chord section and the MAC of the swept and tapered section. Then you find the mean point on the wing. The only thing that could get you in trouble here is forgetting to include the part of the wing covered by the fuselage. The sweep angle in Figures 3 and 4 is exactly the same, but you’ll notice the CG line is further forward on the wing with a constant chord section. This is the effect of the constant chord area reducing the total area of the swept section.

How does this work with a biplane and two wings? Once again, the answer is simple. Figure 5 shows the wings of a biplane (bottom and middle ovals) looking from the tips of the wings. To figure the MAC on a biplane, just consider both wings as a single wing for CG purposes and measure from the leading edge of the forward wing (usually the tip wing) to the leading edge of the aft wing. Consider the span to be a single wing (shown by the top oval in Figure 5. Then, use the 25-33% of that total as the CG location. Notice that the balance line is well aft of the 25% of the top wing and well forward of the 25% of the bottom wing.

Only one wing type will not work with this system—a delta wing. This type of wing has considerable aft shift of the center of pressure so using this method will result in the CG being much too far forward. There must be some chord at the tip for this to work

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