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Beginner’s Guide to Constructing an RC Helicopter

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The single most important thing you can do when assembling your RC helicopter is to follow the instructions. This may seem obvious at first, but it is the single biggest factor in determining whether the construction of your model is successful.

I can speak from experience on this. When I was building my first model I rushed through the construction, taking many shortcuts. This leads to me spending the entire flying season undoing the damage I did to get it to fly. The moral: do not let this happen to you. Take your time, read the instructions before starting, and if something doesn’t make sense, ask before going any further.

Now that we have clarified that, I will show you the general guidelines for building your first RC helicopter model.

The first thing to do when your RC helicopter kit arrives is to not open the box. Do not open the box until you are completely ready to start construction. All of the parts will be packed neatly and efficiently, so if you take them out, you are likely to lose them. Find a place to work on your rc model where it will not be disturbed by dogs, cats, or small children. The work surface should be flat, and large enough to set out all of the rc helicopter components neatly. Refer to the article titled “Basic Tools for RC Helicopter Repair & Maintenance” for a list of the tools you will likely need. Once you have the place, time, and tools to work on your model, you can begin construction.

As you proceed through the instructions, check off each step after you complete it. This way you will not lose your place when you come back. Nuts used in the RC helicopter sometimes have an insert in them that prevents them from vibrating loose while the model is in flight. If they don’t, use blue Loctite to secure them. Be sure not to confuse this with red Loctite, which is permanent. It is very easy to strip the heads and threads of the different screws that you will be using during assembly. Getting a stripped screw out of its hole is not an easy task, and it is better to simply not over-tighten them in the first place.

Ensure that the engine cooling fan is balanced because if it’s not, the resulting vibration will affect the entire RC helicopter. If it isn’t perfectly balanced when you get it from the manufacturer, you can correct it with a small amount of sanding. Once installed, make sure that this fan runs true.

It is critical that the mesh between the main gear and the pinion gear is correct. If it is too tight, friction will waste power and wear out both gears. If the mesh is too loose, then the gears will rattle back and forth, causing vibrations and wear in the system. Some rc helicopters are made to such a low tolerance that there is no way to adjust the mesh of the gears. If the RC helicopter allows it, move them in or out until they turn freely, without either friction or excessive play.

When assembling the smaller components of the head, swashplate, and washout unit, be careful to do it accurately. Use Loctite to secure all of the bolts, and do not overtighten. Make sure that the resulting parts have freedom of movement and that the control is not sloppy.

Constructing the tail rotor gearbox requires special care. The gears must mesh properly, for the same reasons mentioned above. Align the position of the setscrews so they tighten against the flat spots on the shafts. Some gearboxes provide a way to lubricate the gears after construction. If yours does not, then you will have to lubricate it well before it is sealed. The gears will wear out quickly if you do not apply enough lubricant.

Balancing the tail rotor blades is also important. To do this, mount the blades on the center hub and place the system on a high point balancer. Adjust the balance by sanding, or adding blade covering material. When installing the tail rotor blades, make sure that they are not too loose or too tight. This is essential for smooth operation. They should be tight enough to not fall under their own weight, and loose enough to move freely.

The tail boom can be secured to the fuselage with a small bolt, inserted into a hole drilled into the boom and the main frame. This can prevent the boom from coming loose if its attachment to the main frame fails. The horizontal fin does not affect the flight characteristics of the helicopter in any significant way, but the vertical fin does. The vertical fin contributes to the helicopter yaw stability, and it is important to have a large one while learning to fly your model. You can make one with light plywood, but be sure to fuel-proof it. If the fin extends below the tail rotor and can help protect it.

Fuel tanks are mounted differently between models, but here are some points to consider when mounting your tank:

  • Protect the tank from vibration with foam rubber, to prevent the fuel from foaming with small vibrations.
  • The clunk in the fuel tank should be able to move freely, and should also reach the bottom of the tank.
  • Fuel filters are good, they can be either attached to the fuel system, or the fuel can be filtered before use.
  • Pressurize the fuel tank by attaching one line to the muffler, this will increase fuel flow.
  • Adding an extra, or header tank is also fine, but it does not affect the fuel flow to the engine.

The blades for your RC helicopter will need to be balanced. This is one of the cheapest and easiest ways to do it:

  1. Find the spanwise center of gravity by balancing the leading edge of each blade on a pencil, and then mark the center of gravity.
  2. Determine if the balance points on each blade are the same by lining them up. If the balance points match, then no further adjustments are necessary.
  3. If the balance points do not match up, then add electrical tape to the tip or root of the blade as required.
  4. Mount the blades on a blade balancer to determine their relative weights. These need to be equal, so if they are not, add electrical tape to the center of gravity of the light blade, until the balance is achieved.

The blades of the RC helicopter will have to be made visible, while in flight. You will need to tell between the two different blades and see the rotor disk. The former can be accomplished by placing different colors of tape on the ends of each blade. The former can require strips of blade covering material, in a color that contrasts the rotor blade, to be applied to both rotor blades.

After the assembly process is complete, you should have a finished model that you can be proud of. Make sure that everything looks right, and enjoy flying your new RC helicopter.

RC Helicopter Pre Flight Adjustments

After building your RC helicopter, you will need to make several adjustments before flying. This is a critical step, small errors here could lead to a crashed RC helicopter later on. Be sure to carefully follow the instructions that came with your model while making these changes. We will explain one or two things that probably differ from your instructions, but follow these general tips, and you will have an RC helicopter suited to learning to hover.

We talked about the set-up of the throttle in the article titled “Best RC Helicopter Transmitter – How to Get the Right Radio System for You“. You will need to ensure that every control moves freely. Do this by disconnecting the linkage from the servo, and move it back and forth. If it moves with little resistance and moves the control surface as much as it needed, then it’s fine. Match the throttle servo arm to the throttle by adjusting the throw of the servo, or the length of the servo arm.

Make sure that the throttle is neither completely closed on idle, or overdriven when open. Make these adjustments with the throttle servo disconnected, so as not to overdrive it accidentally. The throttle arm should be 90 degrees to the body of the servo when at idle, to improve the effectiveness of the trim. When the throttle stick and the trim at idle positions, the carburetor should be closed. This will turn off the engine, and it is important that you be able to do so in an emergency. When the throttle trim is increased fully, it should move 1/8 of an inch. This movement should allow the idle of the RC helicopter to be adjusted, and the engine to turn off.

The tail rotor will need to be adjusted so that the blades have a small positive angle of attack when the rudder servo is neutral.

The gyroscope will need to be adjusted so that it controls one-quarter of an inch of the rudder movement.

Collective pitch can be adjusted until the movement is from 0 to 5 degrees. This aids in making the RC helicopter more controllable when learning how to hover. Having a negative pitch available can allow the rc helicopter to descend very rapidly, and a large positive pitch can make it climb higher than is desired while learning how to hover.

The collective pitch can be set using the pitch gauge using the following method:

  1. Turn the radio system on.
  2. Level the swashplate using the elevator trim tab on the transmitter.
  3. Attach the pitch gauge to a rotor blade, making sure to keep the tail boom, flybar, and swashplate level.
  4. Using the transmitter, move the collective pitch to its upper and lower maximums, and note the pitch on each.
  5. The pitch range is the difference between the upper and lower pitch limits, we want a window of 5 degrees.
  6. The window can be adjusted by changing where the push rod attaches to the servo. Moving it in will cause the window to decrease, and moving the pushrod farther away will decrease the window.
  7. The maximum pitch needs to be 5 degrees, do this by altering the length of the rod from the head to the swashplate
  8. Repeat steps 3 to 7 for the other rotor blade.

By following these simple procedures, you can prepare the RC helicopter for its first flight, and reduce the chances of a crash.

by Graham Longacre

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