September 28

RC Model Plane Assembly

In this section we cover your rc model plane assembly. The manufacturers instructions should provide all the information you need to bring the parts together using glues and fasteners as appropriate. Be sure to follow their guidelines a closely as possible.

ARF trainer kit (Hobbico)(Courtesy of Hobbico)

Areas to pay particular attention to are:-

Wing Panel joining and attachment.

Stabilisers & Fin installation.

Aileron, Elevator & Rudder Hinge attachment.

Servos, Control Horns and Pushrods installation.

Receiver and Battery Installation

Undercarriage & Wheels fitting.

Propeller installation.

Let’s take these issues one at a time.

Wing Joining & Attachment

In most ARF kits the two wing panels will come separate, requiring joining together using a spar brace to be glued between the two halves.

The three pictures above show different wing and dihedral bracing arrangements. Numbers one and three show metal tube inserts, number two shows carbon fibre tube inserts. These are features of many modern ARF kits. More traditional kits use a plywood tongue as shown in the picture below.

wing joiner ply brace

Although this shows foam venered wings in uncovered state, you will still find some ARF kits of traditional built up format that use this method.

If your plane is constructed from expanded foam materials, it is important to be aware that Cyano adhesives (normal formula) will attack and melt foam, so a “foam safe” formula or epoxy should be used.

Manufacturers who offer the tube arrangement will suggest either permanent fixing using Epoxy Glue or leaving the two halves as sliding fit on the joiners with tape around the joint line, to hold them together, applied before each flight. This option requires less storage space but is less secure in use. Having said that , it is very rare that wings part company using this arrangement under normal training flight stresses. The Plywood Tongue method definitely requires the Epoxy Glue approach to create a permanent bond. Always use a slow setting epoxy (30 minute type is ideal) to allow time for adjustment and positioning of the wing panels for an acurate joint.

Don’t forget to ensure you set the correct dihedral angle as suggested in the instructions provided. With flat bottomed wing halves, this is simply achieved by laying one panel flat on a true work surface, gluing  both sides of one half of the dihedral brace and inserting it into the slot provided in this wing half. Coat both wing root ribs with an even layer of epoxy glue, coat the other half of the dihedral brace on both sides and slide the second wing half on to the brace. Block up this wing tip with a suitable flat object to the correct height to achieve the suggested dihedral angle.  Wipe any excess epoxy off the wing surfaces using rubbing alcohol before applying some pieces of low tack tape to keep the halves in place and prevent them separating during the drying process.

If you go for this approach with tube joiners, the same process applies, although it is not so important to apply the epoxy to the tubes. The glue joint between the root ribs will retain the panels adequately.

Stabilizers & Fin Installation

The correct alignment of the horizontal stabilizer and the fin are essential for an easy flying trainer (or any plane for that matter). The stabilizer must be truly horizontal and the elevator hinge line should be at right angles (90 degrees) to the centre line of the fuselage. 

Stab & fin alignment

The best way to achieve this is to fit the wings to the fuselage, checking that they also sit at right angles to the fuselage centre line (use a set square to check this).

Stab covering cut out

The faces of the stabilizer that is to be glued to the fuselage must  be cleared of covering (see photo above). Check that the mating surfaces of the fuselage are also clear of covering. Now mix a generous amount of slow set epoxy glue and apply to both mating surfaces.

Insert the stabilizer into its correct location. The necessity of using slow set epoxy will now become clear as you now have to make adjustments to its position to ensure a true alignment.  Stabding behind the model, check that the stabilizer is true in relation to the wing. The angle between wing and stabilizer should be the same on both sides of the fuselage. Take a length of cord or a long rule and measure the distance from left wing tip to left stabilizer tip. Now check that the distance from right wing tip to right stabilizer tip is exactly the same. Double and triple check the alignment of the horizontal stab by repeatedly measuring the distance between the right stab tip and the right wing tip, and check that the measurement for the left hand side matches exactly. Once you have this right double check the true level of the stabilizer.

Once you are confident that the stabilizer is perfectly aligned, let the glue cure completely. Don’t forget to remove any excess glue with some rubbing alcohol on a soft cloth before it sets hard.

After the horizontal stabilizer is fully cured, remove any excess covering from the glue faces of the vertical fin. Mix up some more epoxy and set the vertical fin in place. Once again, it is imperative that the fin is absolutely straight with the fuselage and vertical with respect to the wing and horizontal stabilizer. A good trick to achieve this is to take a long elastic band and stretch it between two pins inserted into the stabilizer tips and over the top of the fin. It may be necessary to insert another pin into the top of the fin to retain the band in place. With this band in place, make final adjustments to ensure the vertical orientation of the fin.

Aileron, Elevator & Rudder Hinge attachment

Most ARTF kits come provided with either One Piece Molded Hinges or Two Piece Molded Hinges.

 One piece molded hinges. These are made from stiff plastic with a thin groove in the middle, the actual “hinge”.

Molded 1 Piece Hinges

An alternative to this type is the “fuzzy” mylar strip hinges, designed to be used with thin CA glue, shown here.

Flat Mylar Hinges

A slot is cut into the surface of the hingeline. Many ARTF kits have these slots already cut in the trailing edge of the flying surfaces and the matching control surfaces. The slot can be held open a little using a round tooth pick whilst you drip some epoxy glue into the slot. The hinge piece is inserted halfway into the flying surface slot. Using the same technique, drip some epoxy into the mating control surface slot. The protruding section of hinge is then inserted into this matching slot. The glue is then allowed to dry.

Obviously, if these slots aren’t already cut then they must be cut first, and everything needs to be ready when the second piece is attached. Commercially available slot cutters can be purchased but by drawing a centre line on both sides of the hinge line at the mating positions, a standard craft blade (No. 11) will create the appropriate slots. Needless to say, the slots you cut must match up on both surfaces. All the hinges are glued at the same time. Since the plastic is smooth it helps to scuff it slightly with a piece of sandpaper before inserting into the glued slot.

“Fuzzy Mylar” CA Hinges are made to be installed with Cyanoacrylate (CA) adhesive. They are similar to 1 piece plastic hinges, they have a rough surface and are slightly thinner. After a slot is made and the hinge inserted, CA is “wicked” into the slot on both sides of the hinge, binding the hinge to the surface. They are strong, fairly easy to install, although they do require a slot, it is smaller and can generally be made with No. 11 blade instead of a special “hinge-Slotting” tool.

A two piece molded hinge (pinned hinge) is shown here.

Pinned Hinge

The example shown here is a larger type using a split pin hinging rod. The ones provided in most trainer kits are made from 2 molded plastic pieces with a wire “pin” connecting them. Somewhat heavier than the other types, they are (if properly installed) the most free-moving, and have a very small gap. They usually require a larger slot made with a thicker bladed craft knife ( if not already slotted) and a small “channel” or groove cut around the slot to hide the pin housing. These are glued using epoxy the same as the one piece molded type. Again, the tooth pick trick helps with the insertion of the glue.

Have a wet cloth (water) ready to clean up any excess glue. For pinned hinges, a spot of Vaseline or silicone grease on the ends of the pin will help prevent binding. Except for the “Fuzzy Mylar” types, Epoxy is probably the best all-around adhesive for hinges because of its slower “setting” time.

Security of the control surfaces is absolutely essential so my favoured additional precaution is to turn the wings and fuselage upside down and, using a 2mm drill bit, create a pilot hole through the underside of the control surface and hinge material and  the same in the mating flying surface. Into these holes I insert a small portion of wooden toothpick which I then cut off flush with the surface. I then wick a little thin Cyano (CA) into these pegs to secure them. Obviously the same applies to the rudder hinges. If you are careful not to drill right through the wood, you will only see the end of the pegs from one side of each surface.

Servos, Control Horns and Pushrods Installation

The diagram below shows the conventional arrangement of these three components.

Servo, Control Horn & Pushrod diagram

Servo, Control Horn & Pushrod diagram

 The important points to note here are:-

1) Position of servo control horn at right angles to the servo body for neutral setting.

2) Control surface horn at right angles to the surface.

3) Control horn attachment holes on the hinge line.

This arrangement is fairly typical of a  direct servo to aileron connection where the servo is installed in the wing adjacent to the aileron control surface as shown below.

direct aileron connection

Some trainers use a single servo to drive both ailerons as shown here.

single servo aileron control

Whichever arrangement your kit provides, it is essential that certain conditions are met to ensure security of operation so lets go through them in some detail.

First of all ensure that your servo(s) mounting is secure. Follow the installation instructions to the word. Make sure servo screws are properly screwed home and if rubber grommets and eyelets are provided, use them correctly. Here is a diagram showing the correct way to use these items.Servo mounting gromet

 In this enlarged view you will see that the brass eyelet is inserted into the grommet from the underside so that the servo is completely cushioned by the grommet and does not come into contact with the servo bearer. If the servo mounting bearers or plate have not been pre-drilled with pilot holes then be sure to do this using a drill slightly smaller then the diameter of the servo screw shank. this will prevent the screw splitting the wood or plastic.

Once your servo is in place fit the arm to the top of the drive shaft ensuring that it sits at right angles to the servo casing and the line to the control horn. It is important to check that the servo is centred before fitting the arm. You can do this by temporarily connecting the servo to your receiver along with a receiver battery and, having bound the receiver to the transmitter (2.4GHz), setting the servo to its neutral position.

You may have to fit the control horn to the control surface. The kit instructions should show how this is done and the correct position. Refer back to our first diagram (above) and ensure the holes in the horn align with the hinge line.

I find it helpful to use spring loaded clothes pegs to clamp the aileron to the fixed part of the wing to line up the aileron control surfaces with the wing trailing edge whilst measuring the length of the pushrods. Two small pieces of cardboard under the jaws of the clothes peg will prevent any crush damage to the surfaces.

The provided pushrods will need to be cut to the correct length. most kits provide these rods with one end threaded to take a 2mm clevis. These should be included in the pack of accessories in the kit. They will be either nylon or metal types.

Nylon ClevisesNylon Clevises

pushrod clevises

Steel Clevises

Screw one of these clevises on to the threaded end of the rod so that the thread just protrudes between the jaws of the clevis by a few threads. Fit this clevis to the control horn and lay the rod across the servo arm. Make a mark on the rod about 6mm (1/4″) beyond the holes in the arm. Cut the rod at this mark.

The accessories provided to fix the pushrod to the servo arm will vary depending on the kit manufacturer. Two of the most popular are the pushrod keepers below:-

pushrod keepers

Or  the screw type quick links in this photo:-screw quick links

 The pushrod keepers require a 90 degree bend to be made in the pushrod 6mm (1/4″) from the end. Remove the clothes pegs from the control surfaces and insert this bend into one of the holes in the servo arm. If you have done your measuring and cutting acurately, the control surface should be aligned with the trailing edge off the wing. If not disconnect the bend and turn the rod either clockwise or anti-clockwise to shorten or lengthen it. re-fit the bend to the arm. Keep making small adjustments until the control surface is aligned. Repeat this process for the second aileron.

If the screw type keeprs are supplied, a bend is not necessary in the pushrod.  Push the base peg of the keeper body through one of the holes in the servo arm and push the retaining spring washer on to the base peg. Insert the pushrod into the hole through the keepr body and, providing the servo arm is at its neutral position and the aileron is flush with the trailing edge of the wing, use one of the screws provided to tighten down on to to the pushrod. It is adviseable to put a spot of thread lock on the screw before tightening it.

In the photo of the steel clevises you will see two very short sections of silicone fuel tubing. These should be fitted to both types of clevis to prevent the jaws from opening under load. The last thing you want is for the clevis to part company with the horn in flight. Before screwing the clevis on to the pushrod, slide one of these over the pushrod then fit the clevis. Once the clevis is attached to the control horn, slide the tube over the clevis to prevent it coming adrift from the horn.

clevises & retainersYou will also notice in this picture that there are lock nuts behind the clevises. Although not essential, these add to the security of the system and should be fitted if provided.

The location of the servos for Rudder and Elevator vary considerably. Some kits provide a central fuselage location with rigid  pushrods to the control surfaces or flexible pushrods ( “snakes”) enclosed in an outer sleeve. The kit instructions should explain the correct installation of the type provided. The alternative is for the servos to be installed into rear fuselage locations with short pushrods to the control surfaces.

Once the servos and horns are correctly positioned, use the techniques described above to achieve the servo and horn connections. Be sure to take your time over these installations. The success of all future flights is reliant on the integrity of these connections. DON’T TAKE SHORTCUTS! If you are in any doubt about your ability to complete these connections correctly, please get help from someone with experience.

Receiver and Battery Installation

This next picture shows an overhead view of a typical trainer servo and receiver installation.

Servo & receiver fit

You will see that the receiver is mounted on a pad of loop and hook two part fixing. It is particularly important to isolate the receiver from the airframe in some way in a Glow powered model. Glow engines transfer a considerable amount of vibration to the airframe and this can be detrimental to the receiver and its components. Having said this, do not be tempted to wrap a 2.4GHz receiver in foam insulation material as it can build up component damaging heat if there is no air around it. Isolating the receiver from vibration is not so important in Electric models as electric motors do not produce vibration unless either the propeller or spinner are out of balance. You may need to get help balancing your Propeller and Spinner.

The three servos shown control Elevator, Rudder/Steering and Throttle as this is a glow powered plane (note rear of fuel tank exrtreem right). In an electric plane only two servos are fitted to control Elevator and Rudder/Steering. The throttle is controlled by an Electronic Speed Controller (ESC) which is connected directly to the throttle output of the receiver and is usually positioned close to the motor in the nose of the fuselage).

It is oviously very important for you to familiarise yourself with the receiver outputs so that you can connect the correct servos to their mating outputs. Also ensure that you know which way round the servo plug fits into the receiver outputs.

In a Glow powered plane you will need to fit a NiMH battery to power your receiver and servos. Most trainers use a four cell version giving 4.8Volts.

4.8V NiMH battery_crIt is possible to use a five cell (6Volt) NiMH battery but this is an unnecessary expense so I would recommend sticking with the 4.8Volt version.

Whether you will need a receiver battery in an Electric powered plane depends entirely on whether you use an Electronic Speed Controller (ESC) with an integral Battery Elimination Circuit (BEC) or a separate Universal Battery Elimination Circuit (UBEC). Both of these configurations take their supply from the main power battery, usually a Lipo, and therefore eliminate the need for a separate receiver battery. Refer to the section on ESCs and BECs for further information.

The model manual should advise you on where to locate the main power Lipo in an Electric plane which, as a matter of course, should be securely fastened in place  using the recommended method for the model. The last thing you want is a wayward Lipo battery crashing around inside you fuselage!

Undercarriage and Wheels Fitting

This process will depend very much on the type of model you have purchased. The choices are either Tricycle or  Taildragger.

airplane-undercarriages

Most trainer kits favour the Tricycle version with a steerable nosewheel. For this reason I will explain the installation process for this arrangement first.

The two components you will normally find in the kit are a) Main Leg assembly:-

Trainer Trike maingear

And b) Noseleg Assembly:-

Noseleg (AMA)Courtesy of AMA

The main leg assembly will vary but the one shown is fairly typical and is designed to fit into two slots in the underside of the fuselage. Either side of these slots will be plywood or hardwood blocks into which screws can be located through Metal or Nylon retaining straps. If not already drilled, use a fine drill smaller than the screw shank to make pilot holes. The straps should be positioned a short way in from the side of the fuselage.

I have included a line drawing of the steerable noseleg for simplicity of your understanding. This assembly will comprise the following components:-

1 x Noseleg,  2 x  Clamps,  1 x Steering Arm,  3 x Brass or Steel collets with grub screws.

Normally your kit will contain a set of wheels of an appropriate size. Providing they are all the same size, it doesn’t matter which you use for noseleg or mainlegs.

By refering to the diagram you can see that the wheel is retained using two of the collets. It is advisable to file a small flat area on the wire of the axle where your grub screws will be tightened. This helps to prevent them sliding loose over time. It also helps to insert a spot of thread lock in the grub screw holes before tightening.

The instructions in your kit should show you the correct location of the two leg clamps on the firewall (The front former of the fuselage). This is normally immediately behind the motor mount. There will also be instructions or a diagram of the correct location of the steering pushrod either from the rudder servo or from a dedicated steering servo. When connecting the pushrod to the servo and steering arm always use a clevis at the steering arm with a silicone tube retainer. At the servo end you will use either a screwed retainer or a pushrod keeper and 90 degree bend.

Again, file a small flat on the wire leg where the grub screw in your steering arm will engage the leg. Ensure that the arm is at 90 degrees to the wheel and on the correct side of the leg to meet the pushrod protruding from its hole either in the fuselage underside or the firewall.

The alternative Taildragger format has two wheels at the front positioned in front of the C of G balance point and a small tail wheel or skid at the rear of the fuselage. The fitting of the main legs will be similar to the main wheel assembly on the Trike version but you will need to follow the instructions for installing the tailwheel or skid. This may or may not be steerable.

Fitting a Propeller

Well, you’re almost there. If you’ve followed the instructions to the book and taken note of the tips and techniques outlined here, your model should be just about ready. So lets complete the job by fitting a propeller.

It’s important to appreciate that you cannot use Glow propellers with Electric Motors or conversely, use an Electric propeller with a Glow Motor. The production and materials are very different and abuse of this rule could prove both dangerous and costly.

Let’s take the Glow route first. The choice of propeller will have been determined from the guidelines of the engine manufacturers manual and possibly having read the section of this site on propeller selection. The first thing to do is check that the hole in the propeller boss is big enough to fit over the engine shaft. It may be necessary to ream the hole to make it fit. This can be done using a pilar drill with the propeller clamped securely in the drill vice with a piece of scrap wood under it to ensure the drill works vertically.

There are special prop reamers on the market which taper to different diameters to enable the correct size hole to be made in any propeller.

prop reamer

Click the image if you would like to order this item on-line in the USA or click “REAMER” here for a UK purchase

Once your hole is the correct size to fit “snuggly” around the engine shaft you are ready to fit it to your engine.

Electric propellers are different. Most types come provided with an oversized hole in the centre and a sprue of different sized inserts to fit into the back of the propeller hub. You have to select the one that fits snuggly over your motor prop shaft.

What happens next depends on whether you have decided to fit a spinner. These are available in various styles and the method of fitting to your engine will depend on the manufacturers chosen construction.

The first of these two is the better option but a little more expensive. The second is obviously cheaper but works adequately on a trainer type model providing it is not badly out of balance.  Spinner number one has a backplate that sits on the shaft between the propeller and the face of the prop driver. So the assembly proceedure is Spinner Backplate followed by the propeller followed by the washer followed by the threaded nut. Tighten this up then slip the spinner cone over the propeller and fix in place with the two screws provided.

Spinner two differs in that the propeller is placed over the shaft first, followed by the spinner back plate then the washer and finally the threaded nut.

It is important to ensure that the blade cutouts do not touch the propeller. You may need to trim these cutouts to clear the blades. If you are unsure how to do this get help from a more experienced modeller. As mentioned previously, it is essential that you check the balance of the propeller and spinner so that your flights are as smooth as possible and the integrity of the glued joints in your plane are not compromised. Once again, this is a skilled job and it would pay you to get the help of an experienced modeller to achieve the correct balance.

At this stage you should have completed your rc model plane assembly and are now just about ready to commit to flight but I beg of you:-

DO NOT TRY TO FLY IT YOURSELF

There are still some things you need to do before you are ready to go flying. So lets go and explore the next step.

Pre – Flight Checks

 


 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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