Li Lightning (oz426)

 

Li Lightning (oz426) by Doug Joyce 1976 - plan thumbnail

About this Plan

Li Lightning. 1-2A odd canard gas free flight.

Update 03/04/2020: Added article, thanks to RFJ.

Quote: "This is an 'it went thattaway' design that is a top competition machine. It has been built in many sizes, and is well tested and refined.

Li' Lightning was designed primarily as a simple-to-build plane to introduce modelers to a fully-developed canard arrangement. This is not an experimental, one-of-a-kind canard, but a fully-developed plane capable of competition, with innovations in aerodynamics, fuel system, and VIT. The design is simple and lightweight, the original being constructed in about one week and weighing in at 7 ounces, ready to fly.

Why is the Li' Lightning different from other canards? First, it is aero-dynamically refined, particularly the matching of the two wings with respect to airfoil and aspect ratio. The front wing has greater camber and a higher aspect ratio than the main wing, and incorporates an efficient turbulator to give good performance in the subcritical Reynolds number range in which it operates. The front wing will usually limit the glide, since it is smaller and more heavily loaded. The rear wing, being four times as large as the front wing, has the greater influence on the climb, and was designed accordingly. To minimize drag during the climb, the airfoil is thinner and has no undercamber.

Secondly, Li' Lightning was designed for competition, not as an experi-ment like most of my previously published designs. This plane was not intended to be different, but rather, to win meets.

The third and most important feature of Li' Lightning is its performance edge. It climbs like a plane with 290 square inches, and glides like one with 380 square inches. The unique zig-zag turbulator on the front wing was developed from the triangular turbulator design reported in Frank Pearce's article in Zaic's book (1959-60). The performance improvement provided by this turbulator is remarkable, as it not only improves the glide performance, but also greatly aids consistency of the glide trim. Once set, it is not necessary to retrim the glide, except to open or close the turn, depending on the field and the wind conditions. In addition to the practicality of this turbulator, it is also easily installed with the aid of a simple template.

The superiority of the pen-bladder tank is unquestionable with regard to the way the engine runs. However, its use does present some unpleasant drawbacks; such as the squirt in the eye and the cramped fingers when filling the tank and getting the engine started. Also, the mess the flood-off makes of the plane as it dumps, not to mention the flooded engine for the next start, are other problems of this design. The design of the Li' Lightning canard provides a simple solution to one of these problems. The solution is to dump the fuel overboard, rather than into the engine. This operation is just as positive as a flood-off, and the fuel is thrown clear of the plane. Also, the cut-off is much cleaner than that obtained with a pinch-off.

A conventional flood-off timer is used in this design. A second line from the tank is routed through the timer, but instead of the line going to the Venturi as per usual, it is routed down-ward. When the timer is actuated, the pen bladder is emptied very quickly and the engine stops. This innovation was a necessity for Li' Lightning since it was being ruined by the dousing of raw fuel on the wing and wing mounts during each flight.

WINGS: The construction of the wings has a new twist. Namely, the main full-depth spar is built up first. In this manner, each joint may be fitted exactly with the overlapping tapered splices, thereby making the usual dihedral joint doublers unnecessary. Most of the usual stress concentrations are also eliminated, and the amount of dihedral is accurate, which is most important for a canard.

The panels of the wings are built one at a time, using Titebond in the usual manner. A simple way of making the ribs is to strip the 1/16 inch C-grained sheet to the depth of the wing spar (ie 1/2 inch). The rib can then be accurately cut to length and fitted, and then cut to shape.

A simple trick to try when constructing the wing is to reglue each joint with Hot Stuff. This will harden the balsa around the joint, thereby increasing its strength and also waterproofing the Titebond..."

Supplementary file notes

Article.

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Li Lightning (oz426) by Doug Joyce 1976 - model pic

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