X-120. Control line stunt model.
Quote: "An unusual stunt job for 3.5 - 5 cc engines. The X-120, designed by Ralph Hart.
STUNT models generally tend to follow a well defined pattern, but X-120 is a model with a difference. Let it be quite clear this difference is not in the performance, for this model will fly the stunt schedule as smoothly and as well as any more orthodox design, but on the score of looks X-120 is really eye-catchingly different. The originals (there are four) have been variously powered with glo-plug 19's and 29's and a 9 x 6 prop has been found to give the best results.
Construction. The wing should be built first as it must be finished and covered before being installed in the fuselage. The actual construction is quite straightforward and is clearly shown on the plan, but it should be remem-bered that pushrod No. i must be soldered in place before the wing is covered.
Now for the fuselage, and here, contrary to usual practice, it is best to start at the rear and work forward. The first step is to cement the 'rudder' parts, and former C together as shown on plans - allow to dry thoroughly. The motor mounts may be glued to the fuselage sides at this time. In step No.2 the fuselage sides are cemented to former C and to the rudder portion. A small clamp may be placed at the top of C and another just above the tail pipe portion, so that the inverted V formed by C is formed from the tail pipe forward only. When dry, the temporary tail pipe former and the 1/4 in horizontal member may be added.
Step No.3 which is the installation of formers A and B is by far the most difficult. Before beginning this step a small clamp should again be placed at the top of former C to ease the strain there, and some arrange-ment should be devised for clamping the fuselage sides to A and B. I have found that two pieces of 1/4 in plywood about 5 in square, connected by 3 in bolts through each corner, are best for this purpose. Former B is put in place first and the fuselage sides are clamped in until they close on former A. To accomplish this the sides must be bent gradually, using a slight amount of steam if necessary. Care must be taken to get the fuselage square with the rudder. A slight warp in the fuselage to act as offset is incorporated, but be careful not to use more than shown on the plan.
The engine should be temporarily installed next (not offset) and the mounting nuts firmly attached to the top of the motor mounts. The tank may be installed now. I use a stunt tank arranged so that both filler and vent tubes are brought through the lower firewall to avoid external openings.
The control system is unorthodox and a great deal of patience is some-times required when installing it. Pushrod No.3 should be linked to the elevator control-horn and the stabiliser glued in place. The L bellcrank is then installed temporarily and the rest of the control system soldered up as accurately as possible. The control system may then be adjusted by shifting the L bellcrank. When you are satisfied with the behaviour of the control system the L bellcrank rod may be securely attached to the fuselage sides by means of balsa blocks and glue. A small amount of oil on the L bellcrank assembly is sometimes helpful..."
Update 14/11/2018: added article, thanks to RFJ.
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