Cadet (oz14802)

About this Plan

Cadet (AMI Cadet). Radio control sailplane model.

Note article also includes drawing of optional power pod for Cox TD .049 engine.

Quote: "63 inch wing span, two channel, all-Purpose Towline and Slope Sailplane with power pod option. Cadet, by Len Whalley.

This is a model that can be used as an introduction to RC flying so we will be covering some fundamentals. Your decision which version to adopt will depend on the flying field available to you. If you have room to stretch a bungee (plus a bit) you will want to fit the tow hook, whereas a hill top launch is a safe way of testing the abilities if you have such a site available. The power assist version can be flown out of a patch the size of 2 football fields but space is not the only consideration and you should allow a nuisance margin of up to 500m.

Building priorities: CG: The intended Centre of Gravity (balance point) is shown on the plan and it is of paramount importance that the model does not balance further back than this point (up to 1/4 inch in front is OK for starters). Remember to keep the materials in the rear end fairly light. 1/2 oz saved there saves 1-1/2 oz in the nose and the total 2 oz saving is really worthwhile. It is of less importance but the two wing halves should be about equal in weight.

Twists: The Wings and Tailplane are Flying Surfaces and if these twist by more than 2mm from end to end then the effects will need to be offset by control input. Larger distortion can become impossible to handle. It would be nice if the fuselage and fin too were kept as straight as possible during construction. All warps increase their effect as flying speed increases, so we would rather not have the problem! Build straight, and cover open areas with equal diagonal pressure. The tailplane should align with the central wing panel or this too will cause the model to veer towards the side which is high.

Outlines: If you ignore the Leading and Trailing edge shaping on the Flying surfaces, then the efficiency is reduced and performance will suffer severely. Hinge gaps should be close-fitting or air-tight and yet move freely.

Flying priorities: Check that your frequency is clear before you switch on.

Controls: Your model will fly at least 12 to 15 mph so remember that the elevator/rudder tend to resist movement at that airspeed. If the full movement (throws) of each surface are a bit too much, they can easily be reduced. The opposite is not always true. For precise authority over elevator, the link onto an elevator horn should be as far from the hinge line as possible whereas a reduced throw at the servo end provides even more power to the linkage but reduces movement. Try out the variations and feel the resistance to the control movement on each surface by hand.

Trimming: This term describes all the adjustments which need to be made to improve the model's handling. After you have gone through the full set of checks (including CG location) but before you actually fly, switch on and support the model above your head, holding the nose end, in the smoothest airflow you can find and 'feel' for any strong tendency. Walk it into wind if the breeze is not strong enough. If there is a consistent pull to one side then use opposite trim to correct and try again. Even the elevator setting can be tested in this way.

Once this is done, move the servo centre by one spline or adjust the clevis links as necessary. A hand launch is risky option you may wish to take. That's up to you. Assuming that it is built straight, this model is very stable in smooth air. Your enemy when first trying to master these skills is turbulence, either in the air flow across the flying field caused by trees or from other obstacles such as uneven ground. On the hill, turbulence is formed by your hillside or protruding spurs and plantations upwind. Avoid risk areas such as busy roads. Assume that the worst CAN happen. Inspect your landing site before you launch.

Construction notes: You will already have learned to respect the sharp blades used to cut and shape balsa, but cutting thick ply is particularly difficult and quite hazardous. It actually produces a better job if, for example, 1/8 ply parts are made from two equal shapes of 1/16 glued together. This is easier to cut and also means there is one variety less in the materials list.

Your FLAT Building Board must be able to accept firm pins. Cover your plan with a clear plastic sheet during any construction on the board. It will protect the plan and the job comes away easily when the glue has set.

Adhesives: Two types of glue should be used; White PVA (or preferable an Aliphatic PVA) for the majority of jobs, and 2-part epoxy at high stress areas such as fin base and for joints between ply and hardwood. 'Super-glue' is not suitable.

Construction: FUSELAGE: The sides (ONE Left and ONE Right) are cut out first and the longerons and wing seat strip are fixed close against the outline. The doublers are marked up for the former positions and fitted between the longerons, allowing for the sides to curve in slightly at the nose end by packing under say 3 mm from building board.

Now glue the formers F3 and F4 in place and support the complete fuselage on its top surface while these set. Make sure that the rear ends will line up when they are pulled together or you could build a twist into your fuselage. The underside of the wing curves up to the LE and the wing seat is shaped to match. F2 is assembled over the plan. Mark the centre-line on each former if this will help, then add F1 and F2 and the tailplane platform in turn, making sure that the fuselage does not become twisted or bent to one side.

Leave the rear underside open for installation but add all other fuselage sheeting etc. and fit servo bearers and such. Drill for dowels. There is no need to glue the wing and tail band dowels in position..."

Cadet from Aviation Modeller International, May 1996.

Direct submission to Outerzone.

Supplementary file notes

Article pages, thanks to RFJ.

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