Just Junior (oz2925)

About this Plan

Just Junior. Radio control (or free flight) sports model, a 75% scaled-down 48in span version of the original 63in vintage free flight KK Junior 60 (oz9995) originally by designed by Albert Hatful. For 1 - 1.5cc engines.

Quote: "Go Mini vintage with this month's full-size plan! Just Junior by Paul Hoey.

EARLY IN 1986 I built a Majestic Major - an enlarged Junior 60 - powered by a Laser 61. Between them Messrs Hatfull, Buckle and Tidey produced a most remarkable combination of aircraft and engine. It therefore seemed logical to build a reduced size version for an Elfin 1.49cc engine that my father had passed on to me. This engine couldn't have been run for at least 20 years, but no problem; it started almost instantly when tested.

Plans were drawn up and the original was built over a two-month period with the constant eneouragernent of Richard, my four-year-old son who was hoping I would teach him to fly. It seems the norm for the writers of articles relating to plans to acknowledge that readers skip the construction details and turn to the flying report. If this is so, and I'm no different to anyone else, let's move straight to the interesting bits!

Flying field fun: The original was test flown on a damp, overcast day which led to a somewhat dramatic first flight. After test glides and radio checks to establish that all was reasonably well, the engine was fired up and the maiden flight commenced; this being where the problems really began. The take-off was rapid to say the least; the ensuing climb out being a steep upward spiral to the left despite down elevator being applied with increasing panic. As the model went up I swear the clouds descended. Fortunately the engine cut just as the model was about to be engulfed.

Subsequent flights have exploited this lively performance, an average flight time of five minutes being obtained from a 100-second engine run. Richard, to his delight, is learning to fly the miniature Junior. He is making good progress and should soon be landing it without my intervention. We tend to fly it as a 'guided free flight' model which in itself demonstrates the stability of the design and its ability to handle a surfeit of power. A Mills 1.3cc would be absolutely ideal.

Back to the basics: Now that your appetite is whetted there seems little to say other than construction is very straightforward, but I am rather making the assumption that readers of Aeromodeller know how to make a traditionally-constructed airframe. I always purchase most of my wood from the Balsa Cabin, using their excellent competition grade balsa as much as passible. Only the fuselage longerons, tail-plane and wing spars need to be medium-hard balsa; wing ribs are cut from quarter-grain sheet. The strength of this kind of open construction lies in good joints!

It is important to keep the tail end light. The original needed no nose weight to balance but this may not be the case if you choose to fly without R/C gear. Modern glues are excellent; the use of one of the new flexible cyano glues will save weight, should speed construction and probably will be as strong as any other glue except for epoxy, which should be used where specified.

The difference between an average model and a good one is usually 'attention to detail', it is worth spending extra time making a nice cowling and sanding the nose to a well-rounded shape. Trexler airwheels with the hubs sanded, polished and then fitted with recessed washers improve the appearance, as do window frames which also add to the strength of the cabin..."

Note: This plan was published as having a 42in wingspan, and the subtitle: "A 42in span sports model" is printed on the plan itself, but the actual measured span is 48in. Presumably that was an error made by the publisher Aeromodeller in 1987.

Update 17/05/12: Tri-pacer mailed in to say: "Another error on the plan (not yours) is the center section rib and the main rib: It appears they have them backwards. Either that, or they have one strange airfoil for the main ribs!"

Update 26/01/2015: Have edited the text on this plan in a couple of places, to fix the original printed typos. So the quoted wingspan at top left on sheet 1 now appears as 48in (not 42in), and the labelling of the two different wing ribs shown at bottom of sheet 2 has been switched around (centre section rib, main rib).

Supplementary file notes

Article page, text and pics.

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