High School SMILE Meeting
1999-00 -- 05-06 Academic Years
Airplanes and Helicopters

29 February 2000: Bill Shanks (Joliet Junior College)
raised the question, What makes things fly? Following the usual textbook explanation, he sketched a wing cross-section, said that the air over the top of the wing had to travel farther than that on the bottom, and so had to move faster, resulting in lower pressure at the top wing surface than on the bottom - and so providing lift on the wing a la Bernoulli. But then Bill sketched a flat-looking wing (supersonic aircraft?) and pointed out there would be very little difference in path over top and bottom. Same for a kite. No asymmetry - no difference - no lift! But then Bill pointed out that - assuming a wing inclined upward relative to the air stream - air striking the bottom surface would be deflected downward. Then the change in its momentum would be downward, corresponding (Newton's 2nd Law) to a downward force on the air by the wing. But the air must be exerting an equal and opposite force (Newton's 3rd Law) on the wing, which would be upward - resulting in lift! So where does that leave Bernoulli? (or those who invoke his "law"?) Refreshing, Bill!  For more information see the websites  http://www.allstar.fiu.edu/aero/airflylvl3.htm and http://www.amasci.com/wing/airfoil.html.

09 December 2003: Don Kanner (Lane Tech HS Physics Teacher)      Helicopter Whirligigs
At our last meeting John Scavo was wondering how the number of blades on a propeller related to airflow and Richard Goberville had propeller whirligigs for all of us to take and experiment with. Don had collected all of the whirligigs from the other Lane Tech teachers at SMILE and modified them in an attempt to answer John's question. Here is the data table:

Helicopter Whirligig Data
Number of Blades Mass / grams   Result
4 blades  11.3 hovers
2 blades 11.3 hits ceiling  
2 blades 5.8 hits ceiling
2 blades 4.0 hits ceiling
2 half-blades   9.5 halfway up
1 blade (balanced) 9.5 hovers
It was shown that while a four blade whirligig would only hover, the two blade reached the ceiling. With the speculation that the mass of the whirligig was the factor, a second two blade was prepared by adding mass to match with the four blade. Surprisingly, it also reached the ceiling. Thus, we have good reason to believe that two blades move more air than four blades. However, rotational speed was not controlled. Christopher Jarr, a student at Lane Tech, suggested that the whirligigs might be slipped over the shaft of a drill bit on an electric drill to produce a constant speed for each. Lane Tech Earth science teachers pointed out that hand-held anemometers were available in most of the science supply house catalogs.

21 March 2006: Bill Shanks (Joliet Central, retired)                   Whistle Balloon Helicopter
Bill shared with us a favorite physics toy -- the Whistle Balloon Helicopter http://www.costumes4less.com/products/kb125/Whistle_Balloon_Helicopter. It is also available as the Neato Balloon Helicopter.  It is great for illustrating Newton's Third Law. A balloon is inflated and attached to a little nozzle on a rotor with three blades. As the air comes out of the balloon, it causes the rotor to spin and you get a little helicopter that flies up. Look for it at toy stores or museum stores.
And off we go! Thanks, Bill.