I've gotten 2 minutes, but my times are very inconsistent do you guys have any idea why?
2012 Events
State: Shock Value - 8th place
Nationals: Helicopter Egg Drop - 6th place 2013 Events
Regionals: Helicopters-2nd place Rotor Egg Drop-3rd place
State: Helicopters:-5th place Rotor Egg Drop-5th place
Nationals: Helicopters:-17th place Rotor Egg Drop-46th place
What was the ceiling height on some of these posted times? Our team could try the 24 foot ceiling and loose their helicopter or 9 foot dropped ceiling. We played it safe after seeing two other teams loose their helicopters.
Word on the street is that there have been some wicked times (1:20+) in lower ceilings because the copter somehow hits the ceiling and 'sits' there, if I understand. In a larger ceiling that it won't reach, the same copter will come down faster. I don't entirely understand why that is, but that's what I am told.
This is a debate that has gone on since Helicopter was introduced. At first, it was attributed to pointy ceiling bumpers somehow 'sticking' into the ceiling and holding the helicopter up when the rotors did not provide enough lift to hold up the copter. Alternatively some claim that somehow stopping one rotor, without it hanging up vertically, and transferring power to the other rotor in some way that's more efficient than two rotors and increasing efficiency. Some claim that ES are not properly recognizing when a helicopter is hung on something and not self supporting.
The pointy ceiling bumper discussion resulted in the round disk at the top of your copter rule. Sticky substances on the disk have been banned when recognized.
One rotor stopping (without providing vertical support) doesn't match reasonable aerodynamic theory. L is proportional to velocity. Drag is proportional to velocity squared. All other things (form, area, temperature) being constant (as they are in a single copter). If two rotors have to spin at x rpm (translates to velocity x1 at the tips), one rotor will HAVE to spin at 2x to give the same lift, creating 4x drag. The rubber CANNOT spin twice as long. Never believed that theory.
There is a 'theroretical' possibility if BOTH rotors keep spinning. A wing flying closely above a horizontal surface gains lift above the normal due to interaction with that surface, something called ground effect and very demonstratable. I'm sure a wing would also interact with a surface above it, though I haven't seen the math/data which says whether it helps or hurts lift. If it helps, that might explain longer flights when touching the ceiling. But as long as all teams have access to that same smooth ceiling, I don't see a problem with that. Though frankly I haven't seen it demonstrated in practice
Now, before we added the disk, I saw no reliably reported data that did not either fit the stuck in ceiling probe, or ES not recognizing a copter was not supporting itself.
Oh, in a site with raftered AND smooth ceilinged areas we did see that competitors could wind harder if they flew in the smooth ceiling areas (even with a lower ceiling) and get longer flights than if they flew in the raftered areas because there was no way to avoid hanging up and stopping the flight if they wound that hard in rafters. In fact, last years nationals winning teams exploited that knowledge.
If you are seeing reports of this, the rules writers would appreciate reliably and carefully described first hand examples so we can see if a new rule is needed, or if students have somehow discovered a valid aerodynamic behavior and exploited it.
Oh, I'm not sure 1:20 is all that wicked a time. 2 minutes has been posted on this list, and seems reasonable given this years design constraints.
Jeff, I propose the following reason why stopping the top rotor gives longer times;
The typical helicopter with 2 rotors has more than enough lift to reach the ceiling and would probably continue to climb for a very high distance without the obstruction. To maintain the altitude requires far less lift. If the top rotor is stopped, the bottom rotor has enough lift to keep the helicopter at the ceiling for a much longer amount of time since the top rotor is not using the winds. Once the bottom rotor slows and cannot hold the helicopter it usually falls away from the ceiling. At this point, the top rotor will generally start turning again and the combination of the 2 rotors quickly use the remaining amount of winds.
sparkchaser wrote:What was the ceiling height on some of these posted times? Our team could try the 24 foot ceiling and loose their helicopter or 9 foot dropped ceiling. We played it safe after seeing two other teams loose their helicopters.
I assume (for various reasons) that you went to the Auburn University Regionals. If so, that was my copter that you saw stuck in the rafters. -_- (to be fair, we did both runs on the tall ceiling, lost only one copter, and still ended up getting third).
9 foot ceiling time: 32 sec with good copter
Higher ceiling time: 54 sec with good copter (I really cannot build)
That was the only reason we chose to take a risk.
The 1st and 2nd place times at Regs were 1:34 and 1:21. Both did them on the low ceiling. (I watched them, and also, the kids were on my team, only not on my competitive team.)
Physics is difficult for 99% of the world's population because they don't understand it. The other 1% know too much.
