Flyangle Article & Plans
March 1970 American Aircraft Modeler
Bill Hannan was a prolific designer of and author of magazine articles and books about free flight models. His contributions spanned more than fifty years. Many of his designs, like the Flyangle, targeted beginners. His goal was to present models that were easy to build and that were constructed in such a manner as to virtually guaranty success. Based on the inherently rigid, warp resistant triangular features of the AMA's Delta Dart, Hannan's Flyangle introduces a built-up fuselage with a triangular cross-section. It is the next logical step up from the Delta Dart. Airplanes and Rockets website visitor Ray M. wrote to request this article. It's nice to know there are still purists out there building these models.|
FlyangleFor added realism this rubber-powered cutie is a slightly advanced version of the basic Delta Dart.
Probably the most influential simple model of this decade has been the Delta Dart. Designed by AMA Technical Director Frank Ehling, the model was published in the much-lamented "Sig Air-Modeler" magazine during 1966. It was known at the time as the "AMA Racer." In April of 1967, American Aircraft Modeler featured plans under the name "Delta Dart," which seems to have been the most widely accepted name for the species. A modified version kitted by Sig Mfg. Co. is called the "AMA Cub." A larger, glow-engined variation called "Oily Bird" appeared in the Oct. '68 issue of American Aircraft Modeler, and in fact, full-size plans for it are still available through Sudden Service Plans.
Off it goes into the wild-blue yonder, the North Pacific Sleek Streek prop churning away on one loop of 1/8" rubber. The intent aviatrix demonstrates just-right launching.
It has its good points - all over the place. Delta Dart-type wings and tail minimize dangers of warps in the surfaces. That's important if it is to fly successfully.
Simple wing mounts and rubber-band attachment show clearly here. Wing slides back and forth for making necessary corrections in balancing. Article describes how to adjust model.
Wing frame is built directly on covering paper, as with Delta Dart. The wing mounts are 1/16" sheet balsa with 1/16" dowels attached. Rubber bands wrap around dowels and body.
Even the fuselage has a triangular motif. Because it has a flat top, it can be assembled inverted on your board. Nothing can be simpler. Rubber is inserted with a stuffing stick.
"Flyangle" represents an effort to produce a slightly advanced version of the basic idea, incorporating a fuselage and other items intended to add a degree of realism. While the model is not as simple to construct as the Delta Dart, anyone who is willing to work carefully should be able to produce an attractive, flyable aircraft.
Materials: Medium-hard balsa can be used throughout, with the exception of the fuselage longeron, nose block, and wing mounts, which should be made of hard balsa. When selecting wood for the job, choose straight, warp-free pieces, which may be found by sighting down each strip from end to end.
Construction: Build the model on a flat surface in order to prevent any built-in warps. Spend a few minutes looking over the plans and photos to be sure that you understand the relationship of the parts. Since the plans are printed full-size, you may build directly over them. A sheet of waxed paper or clear plastic food wrap will keep glue from sticking to the plans.
Fuselage: Cut the fuselage top panel from 1/16" sheet balsa, and sandpaper the edges lightly to remove any roughnesses. Mark the position of each triangular fuselage former on the panel, using a soft pencil or ballpoint pen. Next, cut out the various formers. Since the fuselage is constructed upside down, the top panel will actually be on the bottom during the building stage, and may be held flat against your building board with straight pins.
Glue each former in its correct location, checking that all are vertical for proper alignment. Allow the formers to dry, then add the 1/16" sq. hard balsa longeron, which will need to be cracked at the rearmost F2 former, in order to permit the change in angle at that point. Cut out and install the triangular rear rubber-peg retainers. It is easiest to make only a pin hole where the peg fits in each retainer, at first. Then, enlarge the holes to proper size after the retainers are installed and have dried. This will assure correct peg alignment. Add a second coat of glue to the former and peg retainer joints, as they are subject to strain when the motor is fully wound.
After the fuselage assembly has dried, remove it from your building board and sandpaper any rough places. By using a small sanding block or emery board, it is easy to blend in any edges or corners that may protrude. The time spent in doing this will make the task of applying the covering much easier.
Landing gear: The landing gear legs are bent from a piece of .025-diameter music wire, using needle-nose pliers. The wheels used on the original model were plastic, but could just as well be wood. The size is not too important, and anything from about 1/2" up to 1" diameter should prove satisfactory. The wheels are retained by bending the axle ends upward. For good ROG (rise off ground) starts, the wheels should revolve freely. Note that the landing gear legs are bent slightly to the rear to provide propeller clearance.
The landing gear wire is sandwiched between F1 and F1-A using plenty of glue. A clothespin or two can be used to clamp the assembly together while the glue dries.
Noseblock and prop: The nose block can be made from a 3/16" -thick piece of hard sheet balsa, with a 1/8" hard balsa sheet triangular plug glued on, or the block may be laminated from 1/16" hard balsa sheet. In either case, the nose plug should be a snug fit into F1, so that it will not fall out during flight. The prop shaft bearing is a short length of 1/16" -diameter aluminum or brass tubing. Note that it is mounted in a slanted hole to provide 4-5 degrees of down-thrust. Roughen the outside of the tubing with a file or sandpaper, and glue it into the nose block. Be certain to clean out any glue that may find its way into the inside of the bearing.
The prop shaft may be formed from a piece of music wire, with the aid of needle-nose pliers. Any suitable plastic prop from 5" to 6" in diameter may be employed, but a North Pacific "Sleek Streek" prop was used on the prototype. Add enough small washers or sequins to the prop shaft so that the propeller will clear the corners of the nose block. Also, apply a drop of oil to reduce friction.
Wings: The wing panel is constructed directly over the plan from 1/16" -sq. medium-hard balsa strips, which are held down while drying, with straight pins. Do not puncture the strips with the pins, as that would weaken them. After the wing panel has dried, it may be removed from the board, and a second one exactly like it may be built.
The wing mounts are cut from hard 1/16" balsa sheet, and glued to 1/16" -diameter hardwood dowels. These may be obtained at low cost from a drug store, by asking for "swab sticks." The rear rubber peg is also made from one.
Tailplanes: The tail parts are made from 1/16" balsa strips in the same manner as the wing panels. Note that there is an extra piece of 1/16" sq. at the lower front part of the fin. Cut the small triangular sub-fin (which also serves as a tail skid) from 1/16" sheet balsa.
Covering: There are several approaches to covering a model with tissue, but our favorite is as follows: Apply several coats of clear dope to each part of the structure where the tissue will be secured. The use of a plasticized dope, such as Sig "Litecoat" will reduce the chance of warping. Also, even though the wings and stab are only covered on the top side, it is a good plan to dope both sides of the structure to minimize warping, caused by the action of the dope drying. The small amount of additional weight is more than offset by the efficiency of good, true flight surfaces.
After the dope has been applied (usually two or three coats are required), cut a slightly oversize piece of tissue paper and place it over the framework to be covered. Using a small brush, flow some dope thinner through the tissue, along the previously doped structure. The thinner will penetrate the tissue and soften the clear dope film underneath enough to render it sticky. Do only a few inches at a time, and press the tissue firmly against the structure. If the tissue develops a bad wrinkle, apply thinner, pull it off, and try again. Work your way around the entire outline, then put the part aside to dry for ten or 15 minutes. The excess tissue may be neatly trimmed from the structure, with a sharp razor blade. Check for any areas that may have popped up or worked loose. A light application of thinner and/or dope should take care of them.
It is only necessary to cover the two fuselage sides, but we elected to cover the top also to achieve a more uniform color scheme. The wing and stab, as mentioned earlier, are covered on the top side only. The fin would only need to be covered on one side, but its appearance is much better when covered on both sides. The forward cockpit portion of the fin is covered with cellophane. Don't forget to put the paper pilot inside first.
The fuselage covering may be lightly shrunk with water, but the wing and tailplanes are left alone and not shrunk or doped.
Assembly: Glue the fin onto the exact center of the stab and check to be sure that it is vertical as viewed from the rear. After the fin has dried, the tail assembly may be glued onto the fuselage. For greatest strength, a small amount of tissue should be removed from the fuselage if the top has been covered, so that the glue can grip wood rather than paper.
Sand a small flat into the rear portion of the fuselage longeron so that the sub-fin can be solidly attached.
Glue the two wing panels together at the centerline, raising one tip 4" off the board for dihedral purposes. A block of wood can be used to hold the tip up while the glue joint dries, preferably overnight. When dry, add the wing mounts. The rear (short) mount glues on the underside of the wing trailing edge, while the front (tall) mount glues on the underside of the small crosspieces just aft of the wing leading edge. After the mounts have dried, put a little extra glue into the crack along the bottom side of the wing dihedral joint.
The wing is held in place on the fuselage with two rubber bands. CAUTION: Do not use excessively strong rubber bands, or the lower longeron may be broken. Only a small amount of tension is needed to hold the wing securely in position.
Flying: Check the wings and tail surfaces to be sure that they are not twisted. Happily, the nature of triangular planforms is such that warps do not cause as serious a problem as would the same amount of deflection on a normal wing design, but severe warps or twists should be eliminated.
The power requirements of individual models vary, depending upon the choice of propeller, and the weight. Ours performed well on a single loop (two strands) of 1/8" flat brown rubber, but it is recommended that you try different sizes and brands until you arrive at the best combination for your particular aircraft. A stuffing stick is the easiest way to insert the rubber motor. It consists of a hard balsa 1/8" -sq. strip about a foot long, with wires bound and glued on one end. With it, the rubber loop can be inserted from the front of the model. If this system does not work well for you, you may prefer the old-timer's approach of leaving one fuselage space uncovered behind the rubber retaining peg. A small weight on a piece of thread may then be used to pull the rubber loop through the fuselage.
Since the model is rather light, test flying should be performed on a calm day, and if possible, over a soft landing field of some sort. Even an ordinary lawn is more gentle to models than such unyielding surfaces as asphalt or concrete! When gently launched from shoulder height in a slight nose-down attitude, the model should neither dive nor stall. If it does dive, slide the wing forward on the fuselage. If the model stalls, slide the wing toward the tail. A 1/8" movement should be enough to make a noticeable difference. If the model tends to fall off on one wing, a simple cure is to affix a small lump of modeling clay to the opposite wing tip.
When a fair glide has been achieved, try winding in 50-60 turns of the prop and giving the model a gentle hand launch. It is likely that a little right-thrust may be needed. This is obtained by inserting a sliver of wood between the nose block and F1, so as to point the propeller slightly toward the right, as viewed from the rear of the model. Additional down-thrust might also be needed, and a sliver of wood at the top of the nose block will provide it. As power is increased, small changes in the wing position and/or thrust shims may be indicated. Perform only one adjustment at a time, so that you will know what not to do, if things get worse! Once your adjustments are just right, it is suggested that the thrust shims (if any) be glued permanently in place, and that a mark be drawn on the fuselage to record the best location of the wing. This is so that if the wing is shifted or dislodged, it can be returned to the correct position.
Remember to give "Delta Dan" part credit for your good flights - you can tell by his nose that he is a sharp pilot!
(The plans for the Flyangle are available from the AMA Plans Service for $3.)
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Posted October 21, 2012