Patches. A/2 contest glider.
Quote: "US Nats winner & National record holding A/2 glider. Patches, by Glenn C Kinney.
First A/2 glider in our knowledge to qualify for the eighth round in any A/2 contest run to the FAI system of progressive fly-offs, Patches set up the enviable record of 22 minutes in seven consecutive maximum flights at Wiilow Grove last July. It introduces many new features to the experienced glider enthusiast and is certainly not for the novice; though study of the design detail in reduced plan below will reward many beginners with ideas for warp-free wing and tail structures.
THE PLANFORM AND dimensions of Patches are typical of A/2 designs flown by the New England Wakefield Group (NEWG). Many of its features show the influence of the designer's tutor and flying buddy, Jim Daley. Wing structure was suggested by Gerry Moss of Luton, Beds, during his visit in the summer of 1960. The design emphasises rigidity, strength and flight stability in the hope that the result would hold trim adjustment under rough contest conditions and in spite of any maltreatment short of actual breakage. That something of this sort was achieved seems evident from its performance at the '61 National Championships.
Just before noon the model was given two short test flights in order to check the trim in the hot, windy weather, and to rehearse the flyer and launcher (the latter is Glenn's 12 year old son who two days earlier had taken first place and set a new national record in Junior A/1). During the next six hours, the model was flown to seven successive maxes in a two-man, seven flight fly off, (there were five maxes of three minutes, one of three and a half minutes, and one of four minutes) and was disassembled and retrieved by strangers three times. In every case, the model was simply reassembled, checked visually, and flown for official time. No additional test flights or hand launches were made, and every tow was identically straight and overhead. On the last flight, Patches won over a keen competitor and second place winner, Dan McDonald of Pennsylvania, and was lost in the woods. It appears to be a successful model, and some of its design features and the reasons for their selection may be of interest.
Certain features, such as the simple tow hook and auto-rudder mechanisms, the tailplane design (except, perhaps, for the angled ribs), the D/T arrangement, and several aspects of layout and fuselage design are Daley influences reinforced by personal experience. The double finger, plywood, wing tongue deck prevents sharp bends in the wing under heavy loads, and the wide tongue provides accurate keying of wing to fuselage.
Cap stripping yields a smooth profile by keeping the tissue off the spars, and by allowing less unattached tissue, adds to the rigidity of the double I-beam wing structure. The wing layout, with its rectangular centre section and straight taper from dihedral break to tip, can be easily and accurately jigged for construction.
Neither wing nor tailplane warped in months even though they were always stored loose in the basement. They were not pinned down when sprayed or doped (Japanese tissue and thinned plasticized, clear nitrate dope were used).
The fuselage is straightforward, and one need not fuss with exact size of stringers, cross-section, nose shape, etc., since none of these is critical. The rugged boom and 12 gramme tailplane led to a longer nose and the forward mounted timer in order to achieve the 50 per cent chord balance without prohibitively excessive weight. The pine nose provides a solid mounting for the tongue, the wing, the tow hook and the timer.
The very soft balsa blocks for wing and tailplane tips are light, strong and simple. The machine screw stops for tailplane and auto rudder are reliable, adjustable over a wide range, and easy to use.
The model as shown in the plan is one and a half ounces overweight. If one wished, the best way to save weight, perhaps, would be to use a smaller wing tongue, to punch holes in the plywood tongue deck, to substitute hard balsa for pine in the fuselage nose, and to build a lighter fuselage boom. However, the extra weight probably has a negligible effect on performance, and while the long nose is unpopular, it is harmless. In any event, it seemed wiser at the time not to reduce strength and rigidity.
Aerodynamically, the design choices are more difficult to handle. While personal tastes and prejudices cannot be discounted, some thinking and testing did occur. As was mentioned above, the general dimensions have been satisfactory in several other models. The wing profile is a Davis modified slightly to suit timber sizes. It has been used many times before and seems to be as good as others of comparable thickness. The wing dimensions, dihedral and washout were provided in an attempt to ensure that if the model were upset in flight along any axis, it would be quick to recover with small loss of altitude.
The fin is underneath because that's where it ought to be in order to avoid blanking out the airflow to it during all flight altitudes, especially when towing. The fin area was mated to the rest of the model by adjusting it in test flights until it was just large enough to prevent Dutch Roll.
The turbulator has little effect in calm weather, but in bumpy weather the modle flies much better and trims less sensitively with the thread simply doped on as shown in the plan. The model was trimmed to turn to the right in the glide, but it should fly equally well to the left.
Building the model presents no special problems, except perhaps for the time required by the large number of pieces. The designer builds two jigs out of wooden box ends to prop up the wing tips with correct tip dihedral and washout. The spars and trailing edge are blocked up at proper height from the working surface, and all possible pieces are assembled from the top before the wing is removed from the building board. Correct alignment of all surfaces is easy to achieve, however, and Patches has presented no other problems, other than that of chasing it, yet.
The fuselage was sanded and clear doped for smooth finish, then painted with black pigmented dope. Fin and rudder were sanded and clear doped for smooth finish, then covered with lightweight, white Japanese tissue. The tailplane was covered with lightweight, white Japanese tissue, given three coats of thinned, plasticized, clear nitrate dope. The wing was covered with standard weight orange Japanese tissue, and given 5 coats thinned, plasticized, clear nitrate dope. The carpet thread turbulator was doped on after the wing was finished."
Patches, Aeromodeller, April 1962.
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