Helicopters SOSI 2013 CeAnn Chalker ceann@chalker.org Pictures & Construction info by Matthew Chalker chalker7@gmail.com

Disclaimer This presentation was prepared using draft rules. There may be some changes in the final copy of the rules. The rules which will be in the published Rules Manual will be the official rules.

Parts of a Helicopter 2 Rotors (4 Blades) Fuselage/Motorstick Thrust Bearings Parts of a Helicopter

Spar Motor Hooks Rib Chord Parts of a Helicopter

Two Overall Components Helicopter(s) up to 2 in competition Flight Log

Construction Parameters Rotors Maximum Rotor Diameter – 25.0 cm Any number of blades No chord size maximum Students must construct rotors Minimum Overall Weight – 3.0 g No Boron Filaments on helicopter Any other Material may be used - Glue, wire, clay for ballast, plastic, tape, etc.

Construction Parameters cont’d Rubber Powered rubber weight doesn’t contribute to overall weight No mass or size limit on the rubber itself Rubber lubed before or after check in Flat Balsa Wood Disc – upper most part of helicopter Design - May use published plans, kits, and/or student designs Helicopter must be Labeled

Flight Log Minimum of 10 Entries Minimum of 6 Data Points Motor size before windup any of these - Mass, width, length, etc. Number of turns before flight Flight Time Any three other Most important part of practice and competition!

Competition Flight Period for Official Flights – 8 minutes Starts with 1st Official Flight Official Flights – up to 2 using 1 or 2 helicopters All flights within a Team’s Flight Period are official unless declared a trim flight prior to launch.

Timing Start – when helicopter leaves student’s hand End - Any part of the helicopter touches the floor (including pieces that break off) Rotors no longer support the weight of the helicopter Judges determine the flight to be over

Scoring Longest single flight aloft (+/- Bonus or Penalties) wins Ties broken by longest non-scored flight Bonus – Each single-bladed rotor assembly (up to 3) receives a 10% bonus added to that helicopter flight time (max 30%) Penalties -10% flight time deduction for incomplete log, 30% deduction for none (off of each flight) Construction & Competition violations for a helicopter are ranked below all other teams

Flying - Basics Wind rubber motor Attach one end to each hook Pay attention to winding direction! Attach one end to each hook Check the ceiling Make sure you launch in a clean/clear spot Let Go of Helicopter! Record Data! Be prepared for repairs Don’t grab a flying helicopter from the air

Flying – More Advanced Critical Parameters affecting duration Turns on motor Torque of motor Pitch and Diameter of rotors Weight of overall helicopter (motor and airframe) Drag Rubber Motor is the most easily adjustable factor Thickness Length Batch

Flying – Torque More advanced Torque can be fairly converted to Thrust Torque is the rotational form of force, if you apply more force on something, it will move faster. If you have more torque on your rubber band, the rotors will turn faster and you’ll have more thrust. Thus, knowing how much Torque the motor outputs, you essentially know how much Thrust the helicopter has. A Torque Meter is the most essential tool to increasing flight times.

Torque Meter

Creating a Torque Curve Wind a thick motor with one end attached to the torque meter Initially the meter will quickly jump several numbers Meter will hold steady for a period of time Meter will quickly jump until the motor breaks Counting the winds, record at each interval: Number of winds Number on the torque meter Plot on the graph Repeat the process with a thin motor

Sample Torque Curves Thrust < Mass

Using the Torque Curves Make a flight with the thick motor wound until just before it breaks (or close) At end of flight, take motor off and check remaining torque on the meter Mark that spot on the Torque Curve for that motor Any winds left on the motor are wasted turns (always will have some left) Idea is to find the correct combination of motor size to each helicopter that gives you the least number of winds left at the end of the flight.

More Torque info Thrust is needed to counter the weight of the Helicopter Thrust > Mass = Climbing Thrust = Mass = Hovering Thrust < Mass = Descent For Helicopters, it is important to be powered for the whole flight Building a Torque Meter - http://www.soinc.org/sites/default/files/upload ed_files/torqueMeter.pdf

Construction – General Tips Anticipate building many helicopters throughout the year Priorities 1 - Build quality/trueness/straightness 2 - Strength 3 - Weight 4 - (and a distant number 4) Design

Basic Helicopter Template Print on card stock

Adjusting Basic Template Rotor Pitch – Increase pitch by lengthening the fold up triangle flaps at the ends of the template Rotor Diameter – Increase or Decrease the width of the template

Supplies Balsa Music Wire – One 36” piece of 0.020” music wire Four sticks of ~40 cm long 1/16” x 1/16” (rotors) (can be stripped from sheet stock) One 1/8” x ¼” x ~15” balsa (motor stick) One ~3”(wide) x 1/16” sheet balsa (ribs & disc) Music Wire – One 36” piece of 0.020” music wire Covering Material (condenser paper, mylar, tissue) Glue (Titebond, use superglue extremely sparingly), 3M 77 spray adhesive Tools (templates, razor blades, rulers, pliers, etc.)

Cut out and fold templates

Trim long sticks to required length for spars (longitudinal supports). Mark spars in 6 equal lengths with marker (rib locations)

Using curved template (can be cut from soda cans, French Curves, sheet metal), slice curved balsa ribs from 1/16” sheet stock

Lightly tape spars to template (I use drafting tape)

LIGHTLY dip one end of rib in a small puddle of glue LIGHTLY dip one end of rib in a small puddle of glue. Just enough dipping to cover the tip (I can’t emphasize how much glue is overused). Place the glued end on the lower spars, resting the rib on the top spar. - Do not use curved spars for center posts, use a piece of 1/16” x 1/16” stick

Allow the lower glue to dry (it should not be long if you are using the right amount). Cut the scrap end of the ribs off at the spar to miter the joint. Apply a similarly small amount of glue, using a scrap piece of wood as a brush.

Once dry, you have a completed rotor frame! If covering with paper, cut a piece a bit larger than the section to be covered.

LIGHTLY dust the area to be covered on the frame with 3M Super 77. Roll frame on covering to firmly attach paper. Trim excess with a brand new razor blade(the sharpest you can find).

Cut a piece of music wire ~4” long for the motor hook. Bend a complete circle on one end. Bend base of circle back to make the rotation symmetrical. Bend a small flare on the end of the wire loop to allow motors to attach (not pictured)

Cut two pieces of ~1/8” square to 3 cm long. Mark the center. Pierce the pieces with the motor hooks Bend the wire as shown to latch onto the stick Glue the sticks and wire to the center of the spars (the top spar for the bottom rotor, the bottom spar for the top rotor).

Cut a stick of 1/16” x 1/16” x ~2” long balsa Cut a stick of 1/16” x 1/16” x ~2” long balsa. Attach a disc larger than a dime atop. Glue assembly to top rotor.

Thrust Bearing (Pigtail) – Cut two pieces of hardened music wire in order to make a thrust bearing. Follow directions at: http://www.youtube.com/watch?v=y8YL3kYLTVk

Attaching the Thrust Bearing to the Fuselage - Cut the 1/8” x ¼” piece of wood to ~15” (this is something to play with a lot) Cut a notch in each end Glue the thrust bearings into the notches (make sure the center thrust line is perfectly straight on each side!)

Assemble and fly the finished helicopter!

Links Supplies - Covering material, Teflon washers, winders, various tools: www.f1d.biz www.indoorduration.com www.a2zcorp.us/store www.freedomflightmodels.com Rubber: www.faimodelsupply.com (buy 1/8” stock unless you have a rubber stripper) Various tools: www.indoorspecialties.com Bulk Balsa: www.nationalbalsa.com www.Lonestar-balsa.com