Plan file details
Classic Trim Trainer. Free flight sport trainer for .040 diesel or similar. Uses an all-sheet Jedelsky type wing.
Quote: "Learn flight trimming with this 34-1/2 in span basic free flight model, powered by the MP Jet Classic .040 diesel. Trim Trainer, by David Boddington.
All too few aeromodellers these days take the opportunity of learning to properly trim out their models. It doesn't matter that the model is radio controlled, it will only fly well if it is accurately built and assembled - and correctly trimmed. To be able to flight trim the model you have to understand the basics of aerodynamics. In days gone by (yawn, yawn!) modellers learned these lessons as a result of having to trim out free flight models - the only alternative being a series of crashes. Nowadays, it is straight into radio control flying, with poorly trimmed models made to fly by applying controls electronically to the model - and not always the correct ones. The cause and effect of the different control surfaces, balance point positions and incidence settings are rarely fully understood.
Let me give you an example. The other summer I was watching a lad of about 14 years old flying an aerobatic R/C model at our local flying field. He was a very competent pilot and carrying out quite advanced aerobatics, but the model was not flying absolutely true, it obviously had some cross controls on rudder and ailerons. Right, I thought, let's see how much this lad knows about aerodynamics, and whether he can make the necessary trim corrections. 'What makes the model bank to the left', was my opening question, 'This', says the lad, pushing the right hand transmitter stick over to the left. I smiled and left him to his flying, perhaps he was happier in his ignorance.
A little knowledge? It would be irresponsible to suggest that the science of aerodynamics is any easy subject, it is highly complex and the more you become involved in attempting to understand it, the more you realised how little you know. However, that is no excuse for not at least learning some of the basics and giving you the chance of applying the lessons in a practical manner and allow the model to be flown better. Although the 'Classic Trim Trainer' is a means to this end, it is a fun model too, so build it, learn some trimming techniques and enjoy the flying at the same time.
Cut away. If the trainer is to do its job, it must be built as accurately as possible and be consistently aligned each time it is assembled - this design reflects these aims. You will note that separate aileron, elevator and rudder trim tabs are fitted, hinged with small pieces of lithoplate, the holes for the engine bolts (the MP Jet Classic has a two bolt fixing) are slightly over large to allow a certain degree of down thrust adjustment. Using 8 ba or 2 mm fixing bolts helps to give this flexibility.
Cut out the wing ribs and pin to the plan, with the root rib angled for dihedral. Plane and sand the top surfaces of the 3/16 in leading edge section, cut the wing tips shape and sand away some of the tip underside to remove the 'solid' look. I prefer to grain-fill both sides of the front and rear wing surfaces before gluing them to the ribs... "
Trim Trainer, Model Flyer, July 2001.
Direct submission to Outerzone.