130 mm
Notes on trimming and running characteristics
If a racing boat is to attain as high a speed as possible, combined with safe handling on the water, it is essential to align
the power system correctly and set the appropriate Centre of Gravity. Naturally this applies to the “Spitfire”.
Experts refer to these inter-related adjustments as the boat's “trim”. There are two levels of these settings: the “base trim”,
which represents an efficient starting point, and the “situation trim”; the latter will vary depending on water and wind
conditions, and may differ more or less significantly from the “base trim”. It can also take into account the driver's personal
preference and habits.
Trim
Before adjusting any trim settings it is advisable to place the model on a level surface (table top, workbench, bench seat at
the lakeside), so that you can view it easily from the side at eye-level.
Adjust the height of the outboard motor so that the centre of the propeller shaft is exactly in line with the hull bottom at the
model's stern. The angle of inclination of the outboard motor, which directly affects the thrust angle, should initially be set
to neutral, i.e. the outboard motor is tilted neither forward nor back.
The next step is to set the Centre of Gravity: install all the components in the boat so that it is ready to run, i.e. including
the batteries and - if you wish - the dummy driver.
For the boat's “base trim” the Centre of Gravity should be exactly 130 mm forward of the transom. Measure this distance
using a tape measure or ruler, and mark this point on the side of the hull, e.g. with a small piece of adhesive tape or a
pencil line. If you now place the bottom of the hull on a square wooden strip at the marked position, the hull should remain
exactly horizontal when viewed from the side, i.e. it should not tip forward or back. If the hull inclines forward or back,
adjust the position of the movable internal components in the hull until the Centre of Gravity is correct.
Example: bow tips down = move batteries and / or dummy driver further aft in the model.
Bow rises = move batteries and / or dummy driver further forward in the model.
If it is not possible to set the CG correctly by re-positioning the internal components, you must
add lead ballast to the hull. Add ballast in small increments, and be sure to secure it carefully
using glue or double-sided adhesive tape.
With this CG position your “Spitfire” is set up to run efficiently when the water is calm and
there is little wind. The boat “planes” on the last third of the hull, with the bow and midship
sections out of the water. This gives high speed combined with good steering response and
reliable running characteristics.
If the wind is a little stronger and / or the water is slightly choppy, you will need to push the
bow down onto the water to avoid the boat jumping (pitching): this is achieved by tilting the
outboard motor slightly back, as shown in the drawing. Viewed from the side, the propeller
shaft is now inclined slightly down at the rear, and the revised thrust line presses the bow
down onto the water.
If you want to extract even more speed from the model in calm conditions, then you can try
tilting the outboard motor forward slightly. Viewed from the side, the propeller shaft is now
inclined slightly up at the rear. This raises the bow and midship section further out of the
water, and the boat 'planes' on just the last few centimetres of the hull. The effect is to
increase the boat's speed, but at the expense of slightly more difficult handling and steering
characteristics. In this guise the boat demands experienced hands on the transmitter.
Summary of Contents for Aeronaut
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