Lil Amigo (oz14790)

About this Plan

Lil Amigo. Radio control sport trainer model. Wingspan 45 in, for 12 to 20 engines and 3 or 4 and 3 channels.

Note the Lil Amigo and the Amigo Baby (oz14789) both appeared in the same article in AMI, May 1996.

Quote: "Moderately sized at 45 ins wing span, the Lil Amigo can be used as a basic trainer or sports model. Ailerons are optional, as is a tricycle undercarriage arrangement.

Designed originally as the 'Three Amigos' the two smaller versions, 'Lil' and 'Baby' are presented here as your PREMIUM FREE PLANS.

Training models for R/C flying should ideally be fairly large, but not everyone has the facilities, or cash, to build large. The Lil Amigo is certainly big enough to be used as a basic trainer, given reasonable weather conditions.

The Amigo Baby is more suitable as a fun sports model, it was thought that it could be used as an indoor flyer and this is not impossible. For indoor use I would suggest 'upping' the dihedral of the wings a couple of degrees (to give better rudder response) and definitely fit the throttle controlled PAW 55 diesel.

Incidentally, the Amigos should make good free flight models, but the dihedral angle should be increased (extra 30 each panel) for this form of flying.

Building instructions are fairly comprehensive, as there will be, hopefully, a number of beginners cutting their modelling teeth on the Lil Amigo. For the same reason there is a variety of building techniques - and control linkages - involved in construction. These traditional built-up structures will not suit all aeromodellers, some will be looking for the short cut to the flying field. For the fly-at-all-costs modeller, and there is nothing wrong with this approach, the ARTF kits offer a better route to their aims.

What about the larger Amigo trainer? It is under construction and if there is sufficient demand we will introduce it into our Plans Section. But you can always have the present drawings enlarged (the Lil Amigo x 1.33 will give a handy size for around 30 sized engines).

Construction notes generally refer to the Lil Amigo, but the Amigo Baby follows similar methods - just smaller materials and engines.

Basic trainer considerations: I have frequently stated that, for trainer aeroplane designs, there is no point in being different just for the sake of being different. This doesn't mean that all trainers have to look exactly the same but they will have the same essential elements with regard to basic aerodynamics and, to a lesser degree, structure. Cosmetic changes can make a tremendous difference to the looks of a model, even when that design incorporates the 'simplification factors' of a box type fuselage, parallel chord wing and a flat plate tailplane.

Designing a trainer results in a series of compromises between the best aerodynamic answer, the attractive appearance of the model and the practical aspects of the construction and structure. There is no one 'perfect' aerodynamic design, it will depend on the aptitude of the student, the flying site conditions, whether he has good and continuous instruction (possibly with a 'buddy-box' system) and whether the building of the model gives as much satisfaction as the flying.

Aerodynamically we certainly want a model that is as light as possible to fly slowly and, for this reason, I dislike the use of veneered foam wing and moulded GRP wings for trainers. They may be strong, but this is of little consequence if it results in more crashes. Don't be fooled into thinking that built-up balsawood and plywood structures are weak, previous trainers have proved just how tough this form of structure can be, they are capable of surviving many hundreds of flights.

Rightly or wrongly - and the customer is always right, nearly - beginners like a trainer to look like a 'real' aeroplane. As a designer of a score or so of training models I have stopped trying to argue with this desire and the Amigo designs do have a cabin, albeit painted on the fuselage.

All of the airframe components are built on the building board and, providing that is flat and true and you take reasonable care, you should finish up with a straight and warp free airframe. The fuselage has a mainly straight lower edge so that the sides can be joined over the plan and the fin slots positively into the fuselage.

To improve the appearance there is an engine cowling and you have the option of mounting the engine upright or 'sidewinder'. The latter looks better but some modellers prefer the upright location.

Also on option is the tricycle undercarriage or 'taildragger' location. For tarmac or short grass operation the trike' is suitable, or even the 'de luxe' version with spats, but for longer grass the basic two wheel system is probably the better answer. For really long grass situations you could remove the undercarriage totally and rely on hand launching and belly landings.

Enough of general descriptions, let's make a start with the preparation for building.

Before construction can commence we have to make a number of decisions so that the airframe can be built correctly. For the beginner a standard two-stroke engine of 0.15 capacity (0.20 for the aileron version) is perfectly adequate. When you have selected the engine to be used you can sort out the engine mount, the retaining bolt locations and whether it is to be installed upright or side mounted. The engine should run equally well in either position, it is only with an inverted engine location that you might find it a little more difficult to start the engine and a greater risk of a 'flame-out' at low rpm. With a side mounted engine you will want to go for the lower fuel tank position and ensure that the silencer clears the silencer. Draw on the plan the position of the engine carburettor and the throttle linkage to the servo. Mark the formers Fl and F2 for the route Of the linkage and drill holes accordingly.

Whether to go for the three function (no ailerons) version or the full four function model will depend on your preference and, if it is for use as a basic trainer, how you are to learn the gentle art of R/C flying. Note that the wing dihedral for the rudder version is twice that of the model with ailerons fitted. 'Bike or trike' is another decision which must be resolved, the undercarriage vertical doublers must be situated for the legs sloping back or forwards. The same shape doublers are used, they are simply positioned to suit the undercarriage arrangement. Obviously, with the bicycle (taildragger) layout the sub-fin (common to both types) must be fitted with a tailwheel leg.

Mark on the location of your radio equipment on the drawing. Note that there is quite a reasonable space beside the fuel tank or, in the case of the high mounted fuel tank, underneath the fuel tank floor. These areas can be used for locating the battery and provide alternative positions for the battery to achieve the correct balance point of the completed model.

Take a good look at the drawing to make sure you understand all of the areas of construction and you are ready to go. These instructions refer to the Lil Amigo but building the Amigo Baby is essentially similar.

Material selection and adhesives: Balsawood varies in density, strength and bendability to a considerable degree. For the wing spars and fuselage longerons we are looking for a 'stringy' (not short grain) balsawood of med/hard density and for wing ribs a quarter grain or similar non-flexible wood. In contrast, the leading edge wing sheeting does need to flex, so that it will bend around the aerofoil curvature.

Fuselage sheet parts need to be firm, as do the uprights, cross-pieces and diagonals; the tailplane has a 'soft centre' with firm leading and trailing edge pieces..."

Direct submission to Outerzone.

Supplementary file notes

Article pages, thanks to RFJ.

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