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

2. 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.

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

4. Spar
Motor
Hooks
Rib
Chord
Parts of a Helicopter

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

6. 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.

7. 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

8. 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!

9. 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.

10. 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

11. 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

12. 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

13. 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

14. 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.

15. Torque Meter

16. 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

17. Sample Torque Curves
Thrust < Mass

18. 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.

19. 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 - ed_files/torqueMeter.pdf

20. 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

21. Basic Helicopter Template
Print on card stock

22. 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

23. 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 ” 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.)

25. Cut out and fold templates

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

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

28. Lightly tape spars to template (I use drafting tape)

29. 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

30. 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.

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

32. 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).

33. 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)

34. 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).

35. 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.

36. Thrust Bearing (Pigtail) –
Cut two pieces of hardened music wire in order to make a thrust bearing. Follow directions at:

37. 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!)

38. Assemble and fly the finished helicopter!

39. Links
Supplies - Covering material, Teflon washers, winders, various tools:
Rubber:
(buy 1/8” stock unless you have a rubber stripper)
Various tools:
Bulk Balsa: