So you built a lovely model and after covering and adding all the servos/batteries etc you find that the CG is 3/4" back from the ideal designed position and you want to add some weight to bring the CG to correct position without ending up with lots of trials and errors. This is what you do:

• Weigh and note the weight of the model (say it weighs 130oz)
• Locate the designed/required CG and measure from rearward CG position to designed CG (say it's 3/4")
• Identify the the exact location where you intend to secure your ballast/weight
• Now measure the distance from the designed/required CG position to where you are going to fix the ballast (say it's 7")

For our calculations we will call the weight of the model "W"=130oz next we will call the distance between the rearward CG to designed CG "D"=3/4" We measured from the designed/required CG position to where we need to secure our weight and we will call that "F"=7"

So to calculate the exact amount of ballast required to shift the CG forward by 3/4" we need to calculate as follows:
W x D
   F

130 x 3/4 = 14oz of ballast required to balance the model correctly
    7

Information researched By Alan Hirji from Radio Control Scale Aircraft by Gordon Whitehead (RM Books Ltd 1980)

Does it seem that the small bits in your newly purchased radio control outfit are getting smaller, or are your fingers just not as nimble as they used to be.

I find it very difficult, these days, to properly engage the little bushes into the holes in the rubber anti-vibration mounts on the servos. After one rather harrowing session, where I seemed to drop every bush I was fitting to a servo and spending ages looking for them on the messy garage floor I happened to be looking along my tool rack and spotted a most useful bush insertion tool.

It was my trusty old bradawl. You simply place the bush on the pointy end of the bradawl, now my dedicated bush insertion tool, and present it to the rubber anti-vibration mount centring the point of the brad in the hole, a little pressure and forward movement and you will find that the bush slips in like a dream.

Allan Bell

Laser engines are fitted with Irvine carburettors. The Irvine carburettor will be anodised purple or black. Before 1995 the Laser-120, 150 and 300v were fitted with Super Tiger carburettors. All other Laser engines were fitted with Super Tiger carburettors before 1996. The Super Tiger carburettor is cast aluminium

Irvine and Super Tiger carburettors are both twin needle types.

All Laser engines are bench run and the carburettors set before they are despatched. The carburettors will need to be to be finally set in your model to suit your fuel and installation.

Initial setting of the slow running needle

Fit a piece of fuel tubing onto the fuel nipple so that you can blow into it. Open the main needle about 4 turns. Close the throttle barrel down to the idle position, the barrel will be open about 1mm. Blow into the tube, you should hear air escaping. If you do not, open the slow running needle. Screw in the slow running needle until you hear the note of the air change. This will be near the correct setting. Final tuning must be with the engine running.

Setting carburettors on Laser Twins.
The linkage should be set so that the throttle arms are parallel at mid opening. The carburettors must be set to close to the same point. Use a piece of 1mm wire as a gauge so that each carburettor has exactly the same idle position.

The slow running position can be set as detailed above.
Altering the setting on one needle may affect the setting on the other carburettor so it is important to follow the procedure. Set the main needles at about 4 turns open and start the engine. Let the engine warm up and run to full throttle. Set one main needle to give maximum rpm. Next set the other main needle. Check the setting on the first needle and then again for the second. Repeat until the maximum rpm is reached.

The same procedure should carried out for the fine-tuning of the slow running needles.
The slow running needles can be finally set with the cowl removed. The main needles must be set with the cowl fitted, as the cowl will affect the airflow to the carburettors. If the main needles are set without the cowl fitted it is normal to find that one carburettor will be rich and the other lean when the cowl is fitted.

General notes

It is essential that the open tank vent is faced forwards into the air stream. The condition of the glow plug will also affect the running of the engine. If in doubt, fit new plugs.

An on board glow system can be used and this will often smooth out the slow running. The on board glow can disguise the correct setting of the slow running needle so it should be switched off when the needles are being set. Running up to full power with the plug energised can destroy the glow plug. Nitro methane will make settings even less critical.

With the Laser twins each cylinder should be regarded as a separate engine with separate fuel tanks and fuel supply. It is possible to use a single fuel tank and even a tee piece. If this is used and does not work then revert back to separate fuel tanks.

There is a spring that holds the throttle barrel against the cam screw, you should be able to push the barrel in and feel this. Also make sure that the linkage is not pushing the barrel in.

With Super Tigre carburettors it is possible for the slow running needle to be fitted outside the hole in the spray bar, make sure that it is engaged in the hole. Also note that the jet hole should be assembled facing into the inlet port and then rotated approximately 45 degrees in a clockwise direction. This places the jet at an angle from the port.

Dirt in the carburettor will cause a blockage, congealed castor oil will cause the same problem. The carburettor should be dismantled and cleaned by blowing carburettor cleaner through.

The cam screw on the Irvine carburettor must be 'Locktited' using 'Nutlock' or similar. The fuel nipple cannot be rotated on the Irvine carburettor, it is a drive fit in the body and should not be removed.

Contributed by: - Neil Tidy of Laser Engines.