Rotor Egg Drop

1. Rotor Egg Drop By Jeff Anderson MSO Executive Director Sometimes National Event Supervisor Ford Motor Company Engineer jander14@ford.com janderson@twmi.rr.com 313-805-6108

2. Overview • What the event is about • Critical takeaways • Resources • Building • Record Keeping • First flights, initial trim

3. What Rotor Egg Drop is about • Due to tiering, it is about NOT breaking the egg. • As this is a new event without a public corrolary (like the flying events) design WILL be important. • In addition to design, data collection will also be critical!! • Note, the design, test and eval elements will give you a lot of surprising opportunities to explore math and science at all stages of building and flying!

4. Critical takeaways • Rule 1, build the rotor system as light as you can!! Extra mass means extra lift needed that could have slowed the egg more. • Rule 2, make sure your system doesn’t weigh too much • Rule 3, go back and read rules one and two! • Rule 4, build accurately, spend time preparing materials, making jigs & patterns, etc. Build fast. • Rule 5, take LOTS of data, which means fly lots! • WARNING: the helicopters are fragile, you will break it, others will break it even easier if you let them, sometimes you break it intentionally, GET OVER IT!

5. Resources • Where to find help? • Everything I cover here and more is on the internet somewhere, the National SO page is a good starting point • I monitor several discussion boards on the net and respond to e-mail questions • Check you local AMA clubs, especially those focusing on free flight. While this is not an event they participate in, their unique skills and knowledge will be valuable

6. Resources • Building Tools, must have • A flat building board, able to take pins and covered with wax paper, I use foam insulation board • Sharp knives with lots of spare blades • A good metal edge rule/straight edge • Lots of pins & scrap balsa blocks • A good scale accurate to 0.01 gm, cheap (less than $20) electronic ones available on the net or build your own for less • Wire cutters and pliers

7. Resources • Building tools, nice to have • Precision micro super glue applicator, two pins stuck through a stick at an angle to come together at their ends • Balsa stripper • Mat board, tablet backs or foamboard, not poster board, for jigs • ¼ inch thick balsa sheets for jigs • Misc square blocks for jigs

8. Resources • Building materials • A complete kit, easy way to get everything to build 1 or 2 helicopters, costly • OR… • Balsa, 1/32, 1/16, and ¼ inch thick sheets, or suitable width sticks, light to medium density • Covering, indoor mylar, tissue, grocery store bags • Glue, Superglue (also called: cyanoacrylate or CA) or balsa cement • If using CA, instant setter • Wire, 0.020 diameter • Prop hanger

9. Resources • Flying • Necessary: • Stop watch, NOT your cell phone, you’ll get DQ’d • Your flight LOG and a pen/pencil! • A good carrying/storage box • Darned Nice to have: • Stooge to hold the device when not in use, remember, they break • Repair Kit, CA, setter, knife, spare covering, spare balsa

10. Building • Overview • Develop a plan/design. Look at Helicopter duration for ideas, but KEEP IT SIMPLE to start. • Gather and prepare materials • Make jigs • Make rotor frames • Cover rotors • Make Egg support.

11. Things to consider in a design • Comment: Unlike Helicopter Duration, I’m sure there is NO well accepted ‘GOOD’ design. • More blades provide more lift, but also more drag, and weigh more. But, not all at the same rate. There is an optimum out there you need to find it. • Another key factor will be rotor pitch. • Flat pitch will have more lift, but take longer to start spinning (ie drop further). OK for a high launch, not so much for low. • Steeper pitch spins up faster, but doesn’t slow things as much. MIGHT be worth it for short drops.

12. MORE Things to consider in a design • Have some theoretical understanding about what factors are important, make sure the students focus on those FIRST. • The most important factor is weight. You don’t want it, you always need to be aware of it. Heavy things don’t fly well, and this thing SHOULD be flying. • Next is probably number of rotor blades and their area. • Followed closely by pitch or angle of the blades. • Make sure you have a way to hang the egg that does not add friction! • Much further down the list are things like outline of individual blades, aerodynamic profile of the blades, etc. DON’T spend a lot of time on these until you have the first three right! • Ultimately, DATA talks, opinions walk • I’m frequently amazed how often students ask what I THINK works best. • While I might be an expert, and OK starting point, teach them to quickly move to testing and evaluating their ideas. • New things come from finding out where the expert is WRONG. But its not about THINKING something is wrong, its about having DATA to SHOW something is wrong.

13. Rotor Construction • Three basic approaches • Straight, offset, twisted spars with ribs connecting, covered by light material, what I’ll be showing today. • Formed props, possibly most efficient, solid or built up, attached to a center spar see: http://www.indoorduration.com/INAVHobbyShopper.htm or http://www.indoorduration.com/F1DPropConstruction.htm a simplified version of this prop can use flat paddle blades. • Carved Rotors, see: http://www.gryffinaero.com/models/ffpages/tips/propcarve.html or http://www.hbrf.org.nz/joomla/index.php?option=com_content&view=article&id=101:carving-a-balsa-propeller-35&catid=40:general-articles&Itemid=59

14. Select Plans: The Drawing

15. Select Plan:Bill of Materials

16. Prepare materials • Select straight parts from your sticks or strip your own from sheet to match plan, make sure you check weight against the bill of materials, stiff and straight, cut slightly long • Cut ribs, lots, select the best that weigh the bill of materials amount • Cut covering with a one inch margin • Cut multiple motor sticks, select the best, stiffest, to weight on bill of materials • If building on plan, tape to building board, cover with wax paper, otherwise just cover board with wax paper. • Have glue, pins, scrap blocks to hand

17. Cutting Ribs

18. Prepare Jigs • You can build without jigs, just not as well or as fast. • Spending time on accurate jigs greatly speeds building good planes

19. Prepare Jigs

20. Prepare Jigs

21. Build rotor frame • Pin spars to plan or jig. DON’T pin through balsa! • Dry fit ribs in position • Check rib position for accuracy • Glue with CA using microapplicator • Let dry or apply accelerator. • Remove from building board

22. Cover Rotor While example is tissue, this approach works for any covering Any spray glue works Once you drop it, don’t try to move it!

23. Cover rotor Smooth down one edge Roll down Smooth down second edge edge Trim, use a fresh, sharp knife

24. Make up Motor Stic

25. Trials and Record Keeping • If you don’t have data, you can’t say ANYTHING about your design! • Is it better than the previous one, or worse? • What should I try next? • What change made a difference? • Science & Engineering Design are PRIMARILY about data collection and evaluation. • Unlike helicopter duration, flight logs are not required. • But if you don’t have one, you will NOT succeed.

26. Students: Orville Wright Wilbur Wright Samuel Pierpont Langley Middle School

27. Thoughts on optimizing the design • Be organized, collect data carefully, DOCUMENT it. • Select variables you plan to explore • Organize your experiment to test alternatives effectively. • Measure and analyze results. Multiple trials to minimize errors. • Repeat as necessary.

28. Thoughts on optimizing the design • For my design, variables to explore: • Area -- Pitch -- Differential pitch