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Christchurch and District Model Flying Club
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Dynam Catalina, improvements to handling on water

by Adrian Sharpe

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 Unfortunately it is not uncommon for ARTF models to have a few niggling faults which need to be sorted by the flyer to achieve enjoyable flying sessions.

 The Dynam Catalina has been reviewed in the Modelling press and some of its shortcomings have been highlighted. My Catalina has logged up several hours over Longham Reservoir and I have found that whereas the model was pleasant to fly it needed a few modifications to improve is handling on water.

 The main challenge the model presented was its tendency to ground loop either on take-off or after returning to the water.  I made two changes to the model to reduce this tendency. The first was to fit LH and RH pitch propellers so that there was no torque reaction and non-symmetrical airflow over the model to induce a ground loop. The second modification was to raise the wing floats by some 20mm.

 In its original state the wing floats dragged in the water even when the model was planing during take-off or returning and with the wing was almost level. As a consequence any amount of bank on the model during take-off or return would result in one wing float creating significantly more drag in the water than the other precipitating quite a sharp swing.

 By raising the floats 20mm they can be flown clear of the water at quite low air speeds allowing the model to kept straight and true as it moves onto the plain during take-off or slowing from planing to displacement on returning to the water.

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The final change to the model was concerned with the water rudder.  The original Dynam water rudder was too small to be effective when trying to manoeuver at low speed on the water. It was also quite fragile and impossible to repair.

 My new water rudder is a clear Perspex/Celluloid extension to the air rudder, it is about one square inch in size, very effective and cannot be seen once the model is airborne.  I have used a similar water rudder made from clear plastic material on my Robbe Seabee. DSCF1892

 My Catalina now takes off and returns to the water in a reasonable fashion and when flying, it is not aerobatic but good for gentle circuits and fly-bys.

Adrian Sharpe

 

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