Today I showed a group of high school kids, teachers, and parents around Hanscom Field. They are planning to build a human-powered helicopter, hoping to hover for 60 seconds, and wanted to see a conventional helicopter. We ran into a U.S. Air Force colonel. I introduced him and told the kids to feel free to ask him why we weren’t able to win any of our current wars. Then I asked if it violated any Air Force policy to be both an officer and a member of Al-Qaeda. He said “I’d have to check. Apparently it is okay in the Army.” We continued out on the ramp where I cautioned them against walking over what I call the “red line of death” that outlines the sterile area for scheduled airline flights (policy and badges remain in place despite the airline having shut down two years ago). I showed them the flight school planes that remained on the ramp in the middle of a beautiful Sunday morning (most of the fleet having dispersed with renters to Maine, the Cape and Islands, etc.). The two Cirruses were parked on the ramp; customers prefer the less expensive Piper Warrior. I told them that Angelina Jolie flies the same kind of plane. The fathers were excited, but not the students.
When we got to the Robinson R44, I showed them how the flight controls worked. They had the typical layperson’s misconception that the cyclic tilts the rotor system (the cyclic changes the blade pitch as the blades rotate around the disk, generating unequal lift, which causes the rotor system to fly itself into a new position; the helicopter hangs from the rotor system and follows). They were very interested in the engine/belts/driveshafts/transmissions. Once we had the inspection panels buttoned up we walked past the corporate jets into Signature Flight Support where they treated themselves to the free cookies and we had a question and answer session in the conference room. Not believing in my friend Dirk’s maxim that “pilots are notoriously stupid”, they asked me all kinds of questions about the best materials to use for their helicopter.
One of their ideas was to lift a transmission from an old helicopter and use it for their design. I reminded them that the Robinson transmission was designed to go 2200 hours without more than a tiny risk of failure, which meant that it was going to be hugely overengineered and therefore heavy. I reminded them of Colin Chapman’s statement that “the perfect race car falls apart as it crosses the finish line.” They needed a transmission that could run reliably for a few minutes in a hover, not one that could transfer 200 hp for 2200 hours.
The kids talked about various ideas for rotor systems and whether they should have more than one human power source. I told them that I thought the best design might be two counter-rotating rotors as seen in the Chinook (designed in 1957). With one bicyclist working each rotor they would not have the weight and complexity of a transmission. A conventional helicopter design wastes a significant amount of power driving the anti-torque tail rotor. In a Chinook-style helicopter, both rotor systems are producing useful lift.
Before and after the show-and-tell I taught a couple of helicopter instrument flying lessons in near-perfect conditions.
If I’m not mistaken there is an axle between both rotorsystems to make sure they are synchronized. I seem to remember to prevent the tips of the aft rotor to hit the forward rotor.
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Andreas
Just a suggestion from the world’s only batwinged unicyclist:
Expanding on Philip’s double rotor thought – start with a tandem bicycle add two rotors and following the Wright Brother’s first success, ride it downhill utilizing gravity to help lift off. While such a stunt drastically violates Sikorsky’s rules, it offers an achievable alternative that may lead to flat land success.
Is this even theoretically possible? I can envision a stored-energy rotor hopping to 3 meters, but not sustaining flight.
As far as blade timing on a tandem, it should be fairly simple with a chain. I’m wondering if a coaxial arrangement like a kamov might not be easier from an engineering standpoint particularly weight minimization.