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This item is discontinued. GREAT PLANES SHOESTRING ARF
SPECIFICATIONS RCM PROTOTYPE SUMMARY
When Jim Pearson called, it didn't really surprise me, I had just received the September issue and Cliff Weirick's memorial was in that issue, so I thought he was calling to make sure I'd seen it. I was, however, totally taken by surprise when Jim asked if I'd like to do a product review of the Great Planes Shoestring 60 ARF. Let's see, the workbench is piled high with Cliff's stuff, but this is an ARF, and there's that huge hole in the hangar where the Big Laser was stored until I let a friend fly it just last Sunday. I'm sure Tami won't mind if I use the dining room table just this once ... besides I've always liked the Formula I "style." Formula I was established in 1947 as an alternative to the outrageously expensive Unlimited class and is the oldest continuously operated airplane racing class in existence. The Formula I specification originally imposed rigid airframe compliance and a maximum engine size of 190 cubic inch displacement. The Continental four cylinder air-cooled engine of 188 cubic inches was rated at 85 horsepower; it was economical, compact for its time, readily available, and had an excellent reputation for reliability degrees it soon became the standard power plant for Formula I. With the passage of years, the Continental C-85 engine went out of production and with ever-limited availability by the mid-60's, it became necessary to amend the specification and permit use of the newer and slightly larger piston displacement engines of 200 cubic inches. This was done on January 1, 1968, and the 190 Cubic Inch Class officially became the Formula I Class. It is interesting to note that this has been the only significant change to the rules for Formula I in its 50-year history. Today NASA technology has allowed these small racers to reach top speeds approaching 300 mph on the same engine that powers a Cessna 150 to barely 100 mph. The 9" x 15" x 43" box arrived with no shipping damage and everything in the box was neatly packed and protected, and all loose parts that could do damage were sealed in separate boxes, ensuring nothing would rattle around. I fished out the instruction manual, made myself a large decaf mocha and sat down to read the manual and get a feel for building the Shoestring. Instruction manuals have been getting better over the last few years, but WOW, this is one of the best I've ever seen, 24 pages with 58 pictures and 11 diagrams that not only give directions on how to build the airplane but is chock full of tips to make building easier and "straighter" and covers everything from how to inventory the parts to first flights and even includes phone, fax, and an e-mail address for technical support, a nice touch. After reading the manual twice it's finally time to get parts out of the box. Great Planes advertises that the Shoestring can be built in 14-20, hours so let's glue some parts together and find out.
Construction: The wing goes together in typical ARF fashion and everything matches nicely. I dry-fit everything, then wrote "up" on the top of the wing halves and the dihedral brace just to make sure it would be right when glue started getting hard and I was in a hurry. For some reason Great Planes wants you to put the aileron servos in before the wing halves are joined. I wasted a good half hour of the allotted time trying to figure out if there was some special reason for this, and finally concluded there wasn't. I didn't want the servos sticking out of the bottom of the wing to hit the table and affect the dihedral angle while the glue was drying, or the servo wires getting in the way when I was trying to mate the wing halves, so I decided to wait until after the wing was a single piece before installing the servos. Just cut the covering on the holes for the servo wires and move the pre-installed strings from the root rib to the bottom of the wing. The wing is very well constructed and the halves fit together with no misalignment. It is possible to "rock" the trailing edge a small amount even with the dihedral brace in; so to ensure there was no twist when the glue dried, I put a small piece of masking tape around the trailing edge joint to hold it in alignment while the epoxy cured. The instructions call for you to drill two holes and poke a number of pinholes in the aileron where the control horn will mount and then to saturate the area with thin CA to harden it. I recommend you actually mount the control horn and carefully draw around it with a pencil, top and bottom, then take the control horn off prior to doing the hole punching and CA hardening. This does two things, it keeps you from getting overzealous and poking too many holes in too big an area, spoiling the looks of the aileron, and more importantly it requires you to get the screw holes for the control horn in alignment while the wood is still soft, which is a bear to do right once the area is CA hard (ask me how I know). This is also where I ran into the first problem. The instructions call for #2 x 1/2" screws to mount the aileron control horn, and that's what's provided in the hardware package. Unfortunately, the leading edge of the aileron is considerably thicker than 1/2" and there's no way the provided screws are long enough. I had some 1 inch #2 screws in my shop; if you don't, you're done with the wing until you can get to the hobby shop and purchase the correct screws (#2 x 1 inch). If you follow the instructions it's almost impossible to get the tailfeathers out of alignment. The slot for the horizontal stab on my kit was just a hair off, but 1 lb. of lead on the high side while the glue cured had everything in alignment. I did try to cut the covering to leave the 3/32" flaps per instructions to cover the joints on the horizontal stab after it was installed, but it's just more trouble than it's worth. The flap gets shoved in one side and could cause the covering to be ripped off the other side when you install the stab, and glue gets all over the flaps so you can't iron them down anyway. I also tried the "Expert Tip" of using a soldering iron to cut the covering off the stabs and fin where they glue to the fuselage and didn't find it to be particularly helpful. It could possibly be done well that way, but after trying twice on scrap, it takes a practiced cut with a good soldering iron to get even mediocre results. A metal ruler and #11 X-Acto work fine with no practice required and no burnt wood or melted covering. With the tail feathers on, it's starting to look like an airplane. The construction, fit and finish of the parts is some of the best ARF construction I've seen to date. The fiberglass cowl and wheel pants are of excellent quality and much preferred over ABS plastic parts, and the paint even matches the MonoKote. Covering: The airplane comes professionally covered in MonoKote and the glass parts are pre-painted with matching paint. The manual lists the names and stock numbers to ensure you get the right colors should you need to make repairs (can't beat that for thinking ahead for the eventual dings and pokes). Engine: The Shoestring calls for either a 2-stroke .61 or a 4-stroke .91. I've been putting off this decision until I had to install the engine. It's a bigger airplane than I expected and I'd like to put my .91 Surpass in it, but the manual warns that even with an O.S. .61FX 2-stroke, the prototype required tail weight, and I didn't want to have to add weight to the tail to balance the heavier Surpass; so based on that I finally decided to use my experienced Super Tigre .61. I was briefly confused when it came time to install the engine. The manual starts with "cut out the template on page 23 and use it to locate where to drill the holes in the firewall." I cut out the template and as I'm looking at the firewall with four holes pre-drilled with blind nuts pre-installed, I'm trying to figure out what I'm supposed to do with the template. I finally figured out that the pre-drilled holes and blind nuts are a recent change and I could ignore the template steps. I had intended to use the stock Super Tigre muffler, but that cowl looked so good I just couldn't force myself to cut the huge hole that would've been required to fit it in, so I bought a Bisson Pitts muffler which keeps everything completely hidden in the cowl. The provided engine mount must be relieved a little to make room for the muffler, but the manual provides directions and an illustration on how to do it right. The 14 oz. fuel tank is provided and fits the hole pre-cut in the front of the fuselage. It's a tight fit and I was a little worried about vibration as there's no provision, or room, for foam rubber to isolate the tank from the airframe. Radio: I used an Airtronics Vision with a 6-channel Airtronics receiver, 732 servos on flight controls and a 322 on throttle. There's more than sufficient space in the fuselage for the elevator, rudder, and throttle servos with the servo mounting plate pre-cut for standard size servos and the control rod tubes pre-installed. I glued some spruce hardwood rails to the bottom of the ply plate prior to installation just to give the servo screws more bite. I used the two aileron template on the Vision and plugged each aileron into a separate channel so I can mix flaperons or differential later, as I get used to the flight characteristics, but you can fly this airplane with a simple 4-channel radio using a "Y" harness for ailerons. Finally with the construction complete, control throws set (both high and low rate called out in the manual) and C.G. checked, WHAT! Tail heavy. That was unexpected, but moving the battery from behind the receiver to in front of the receiver had the C.G. dead on without adding any weight. It's time to go flying. Total time from a box on my front porch to ready to fly was 18.5 hours.
Flying: The engine has been run and everything checks out, so there's no more excuses. The high speed taxi test shows that the Shoestring tracks well at high speed and requires minimal effort on the rudder to keep it straight. Back to the take-off end of the runway, line up and slowly go to full power. The Shoestring accelerates rapidly and leaps into the air. Some down elevator has the nose down and under control, so I fly a few circuits to get the trim right. Aileron and rudder trim are right on, but elevator requires considerable down trim for straight and level flight. Inverted flight and power changes prove to me that the C.G. is right on and the wild pitch-up on take-off was not due to a tail-heavy airplane, so I continue the flight. Rudder and elevator throws are just right, full aileron gives rolls in excess of 400 degrees per second and is way too high for scale flight and I'll reduce it later. Trims are set and I've tried some basic maneuvers, so time to land and check everything out. The manual warns that the Shoestring doesn't slow down easily and requires care while landing, and they're right. I make a long approach and with judicious use of throttle, manage a nice three pointer (and still run off the end of the runway). I use the subtrim function to re-center the elevator trim and the elevator has a noticeable nose down angle, so I pull out the manual and check C.G. again and it's right by the manual and flies like the C.G. is right on, so will check later to see if the horizontal stab has any incidence built into the fuselage mounts. (A later check at home with my trusty Robart incidence meter shows everything in perfect alignment and the airplane flies great as set up even with the noticeable "down elevator" position at neutral trim.)
On the second flight I wring it out a little. This is one fine flying airplane. It'll do all the scale maneuvers the Shoestring is capable of and it really looks great down low doing knife-edge pylon turns, which, with that huge fuselage side area requires no rudder and shows no tendency to drop the nose no matter how hard you pull the elevator. The .61 Super Tigre provides plenty of power for large vertical maneuvers and gives moderately fast speeds, just like "real" Formula I racers. The manual warns that three-point landings should be performed and that wheel landings usually result in bouncing. In order to explore the full flight envelope (okay, so I couldn't get it slowed down and forced the landing anyway) I tried a wheel landing on the second flight. Final count was five bounces and cracked both wheel pants at the mount. Slow, nose high landings are a must, but with the light wing loading and fuselage shape, this is easily done if you use good glide path and airspeed control on final. Subsequent flights just continue to get better. All flight controls are crisp and the airplane responds with no coupling in any axis seen to date on any maneuver. The Shoestring snaps rapidly at high throttle settings, but snaps at slow speed are slow and "floppy." Knife-edge requires minimal rudder and is arrow straight with no elevator mix to keep it on a line. Flying the Shoestring is just fun, there's enough variation between the high and low speed flight characteristics to keep you on your toes and who couldn't use an airplane that forces you to work on your landings. Oh, and did I mention how great it looks down low doing pylon turns around the number 2 pylon. Conclusion: The Shoestring is extremely easy to build, but it's definitely not a beginner's airplane. You should have two or three other airplanes under your belt and, due to the landing characteristics, at least one of the prior airplanes should've been a taildragger. The airplane goes right where you point it. Due to the low drag, racing configuration, it does not slow down on final like the more "draggy" airplanes you may be used to, and requires good throttle and attitude management to land well. If you're looking for a well built airplane that looks aggressive, flies superbly, and still provides some challenge, the Great Planes Shoestring would be an exceptionally good choice. Special thanks to Tom Murray and Dick Doucet for taking flight photos. A Short History of Number 16 In the latter years of "Golden Age" air racing there began to be some concern over the high cost and unacceptable accident rates that were beginning to threaten the existence of air racing through impending regulation and reduced numbers of aircraft and teams on the flight line. In 1939 the Technical Committee of the NAA proposed a class of small racers powered by inexpensive engines to create an economical race class, but alas WWII got in the way. Immediately after the war the Professional Race Pilots Association completed the specifications for this "midget" class and in 1947 it was given a significant boost when the Goodyear Aircraft Corporation sponsored three annual trophy races with a purse of $25,000, and thus the Goodyear class was born.
Rodney Kreimendahl worked at Lockheed where there was an ongoing effort to develop a Lockheed racer to compete in the Goodyear, but the Lockheed team had all the design members they needed so Rodney started his own team. Kreimendahl's team did not have the resources that the factory teams had, so to finance the project the team members each kicked in $1 a week of their own money. The Lockheed design ended up being called Cosmic Wind and when Rodney asked his wife what they should call their new racer she dubbed it "Shoestring" because it was built on a shoestring budget. In 1965 Ray Cote was reading Trade-a-Plane when he announced that he'd found the airplane he wanted to buy and ended up in possession of an 18 year old Midget Racer named Shoestring. Ray raced Shoestring for another 16 years, winning 41 races including nine National Championships. In 1981 Ray donated Shoestring to the San Diego Aerospace Museum in Balboa Park, where it remains on display to this day. When Ray retired Shoestring after 34 years of racing he declared it "the aircraft with the most wins in aviation history."
Three days after I took these pictures, 71 year old Ray, and Phyllis, his wife of 50 years left for Reno where Ray continues to race Formula I in an Owl Racer named Alley Cat in which he once again won the National Championship in 2000 at 245.181 mph. Good luck this year Ray. Photos by Jerry Neuberger. Reprinted with permission.May, 2002 R/C Modeler Magazine Editor: Patricia Crews
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