Mistrial Mk II (oz13052)
About this Plan
Mistrial Mk II. Legal Eagle class rubber model.
Quote: "Legal Eagle Mania! Ready to give 'Legal Eagle' a try? Our author introduces this newest of fun events, gives a rundown of the rules and presents a sample design to get you started. By Dave 'VTO' Linstrum.
Flying Aces member Dave Stott of Connecticut is known as the co-founder of the internationally popular Peanut Scale event, but he's not one to rest on his laurels. Now he's come up with a new event that is spreading like wildfire across the USA.
The premise of Legal Eagle (see the rules elsewhere in this article) is that the plans must be drawn on a single sheet of legal size paper (8-1/12 x 14 inches) with no overlaps or superimposed parts! This strictly limits model size. Foreign fliers can still build US designs, even though metric paper sizes vary.
We first caught Legal Eagle Fever when rules and plans were published in our club newsletter, The Hangar Pilot, edited by Doc Martin. His 'Shapiro Sport' and 'Bristol Barratry' (look that up in your dictionary) designs were inspirational, but seeing a Bostonian-like design by club member John Barker led us to the very light and high performance 'Mistrial.' We built the prototype in Gil Cougl in's shop in Tacoma, and some of his mods are included in the Mk.II version presented here. Light weight is critical to good times indoors; the prototypes came out at 5.4 and 5.7 grams less rubber. Remember, light flies longer!
Devotees of CO2 power can fly this design in competition, but if you choose electric, you should beef up the structure. Both types of power are allowed by the rules, but we believe that the energy of Dolby Tan II rubber will get the longest flights.
Competition scores are the sum of the best three flights. You can also fly Legal Eagles in the great outdoors, but they are subject to OOS flights in thermals! Also, ground turbulence in wind tends to make outdoor flying frustrating. I avoid that sort of frustration by flying with my club, the Miami Indoor Aircraft Model Association, but still hang up in the girders at MacDill AFB Hangars, where balloons are essential!
CONSTRUCTION: Since this is a contest model and not a beginner's bird, we'll assume you have some experience with stick-and-tissue rubber powered models and therefore will only hit the highlights of unusual aspects of building.
Begin by getting a pair of 11 x 17 photocopies of the centerfold plans - one to build on, the other to use as patterns for the rib, prop and matboard tip forms. Glue the copy to a piece of artist's matboard, then cut out. We suggest you 'kit' the model by slicing all of the ribs (use an aluminum or 1/32 ply template) from quarter-grain 1/16 sheet, forming the curved tips and tail leading edge from 2 lams of 1/32 x 1/16 sheet, and forming the prop blades on a wine bottle (we used Cook's Extra Dry Reserve Champagne) of 4-inch diameter. Strip all the 1/16 balsa from light 4-6 pound contest balsa. We suggest balsa from Indoor Model Supply or Model Aircraft Labs - see their ads elsewhere in Model Builder.
Forming laminated tips is easy using a microwave oven. Make your form overlength so you can tape down the ends of the strips, which you soak in very hot water for 3 minutes. Dry them on a napkin, then apply Titebond or Elmer's Carpenter's Glue to one strip and laminate. Tape one end down, then pull the strips around the form and tape. Pop this in the microwave for 1 minute on high. Be sure the edge of the form is waxed with a candle or soap bar. Repeat until you have enough curved parts.
Cut the prop blades from quarter-grain .015 (1/ 64) balsa, with the bottom lam grain parallel to the spar and the top at 45 degrees. Cut a slightly over-size throwaway 'cap' blade from 1/32 sheet. Soak and glue as with the tips - be sparing with the glue! Put a layer of wax paper on the cylinder part of the bottle, then a blade, wax paper, blade, wax paper, and cap. The wax paper keeps the blades from sticking. Align the parts at 17 degrees to the axis of the bottle, then wrap with rubber. Let this dry overnight - do not microwave - then carefully remove. Use a pitch jig to set the blades at 45 degrees on the spar, which is cut from 1/8 sheet, tapered and then rounded like a big balsa toothpick.
We suggest you build the fuselage sides first, on top of each other, with a wax paper separator. Build the wing and stab next, then box up the fuselage. Note the outside dimensions of the fuselage above the side view; the rules specify a minimum 1-inch width at the wing.
One option when adding dihedral is to "overlap splice" the wing spars at the dihedral break. To do this, glue the full-length spars to all but the dihedral break ribs. When dry, cut the spars at the ribs, prop up the tips with the spars overlapped (you'll have to bend the spars a bit) and hit the splice joint with CA. This gives a very strong joint.
Single-cover the wing and tail with pre-shrunk Japanese tissue. Cover the entire fuselage, but then water shrink for tautness. There's no need to cover the prop or nose/tail plugs. Cut the tissue from the cockpit area and cover with cellophane or UltraFilm. We put a small paper pilot, 'Ms Trial,' in our prototype. She's a hot pilot!
Attach the wing carefully with spots of Duco at the LE and TE atop the fuselage. Insert a 1/16-inch OD aluminum tube bearing to give about 2 degrees down and 2 degrees right thrust. Glue the fin onto the stab rib with 1/16-inch right at the TE. This built-in trim will help establish a right climb. Shim up the TE of the stab about 3/32 - 1/8 inch to start. Add clay or solder to the nose as needed to balance.
FLYING: Depending on the model's weight, we suggest .010-.019 (3/32-inch) FAI Tan rubber in a 16-18 inch loop for test flights. We've gone to 25 inches of .010 for competition. Use a blast tube (rolled drafting Mylar, spiral tape wrapped) if you want to protect the frail fuselage from blown motors. Trim for a shallow, loose climb to the right. This model hops right off the floor and should please you with long flights, much like a good Bostonian."
Direct submission to Outerzone.
Supplementary file notes
Legal Eagle event rules.
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