Tuesday, June 26, 2012

MABRA Racer Forced to Use Arms in Flight Attempt


As most of us know, the energy requirements for riding a bicycle are incredibly small--we ride the most efficient mode of transportation on Earth.  We're also aware that flying is, in terms of energy cost, quite expensive.  Drive a hybrid all year, take one flight, and all that energy frugality is cancelled out.  Better to have driven a Hummer.


Because flight requires so much energy, the human body would seem to be too weak and heavy to hold itself in the air (yes, even you, ambitious fred).  One would think.


A teammate of mine recently was given the chance to prove this notion wrong.  Dennis Bodewits, a Cat 2 racer with District Velocity Racing (shown above), is a faculty member at University of Maryland, and, now, one of a handful of people on Earth who has hovered using only the power of his own body. Dennis is one of three pilots chosen to fly Gamera II, a project to claim the Sikorsky Prize.  As you can see from the picture above, the design of the machine not only requires significant power output from the legs, it also requires that the arms do something other than sustain the torso.


Dennis was kind enough to take the time to answer some of my questions about what it feels like to ride on air:
(1)Tell us how you got the opportunity to be involved in Gamera II?  Was it your brains or your brawn?


The previous Gamera was flown by Judy Wexler. When she left the University of Maryland, she posted an announcement at the MABRA listserv that the team was looking for new pilots. Since I work at the university, I thought this would a nice combination of work and hobby and sent them an email. The had me run a couple of test on an ergometer to see if I could run the power required to lift the helicopter (8 W/kg) for longer than a minute – one of the requirements for the Sikorski prize.

(2) We can watch videos and look at pictures of the machine, but the structure isn't totally clear.  It looks like they're using a lot of lightweight trussing for the structure, and the wings look to be clear plastic over some kind of forms.  What kind of materials and structures stand out?
 The structure is one of the amazing feats of the Gamera II design. It has the span of a Boeing 737 but weighs only 75 lbs, 30% lighter than the previous version. It is entirely made of carbon fibres, handmade by a small army of engineering students in a workshop on campus [photo above]. The blades are amazing, too, and much improved since Gamera I. For stiffness, they use a carbon skeleton that looks a lot like the micro trusses. They further consist of a mylar hull around a balsawood frame. 
[See the structure here.]

(3) Gamera 1 looked like a similar overall design, but there are notable differences--the wings, for instance, are much more rigid on Gamera II.  What other differences are there?
There were many small improvements, but for me frame, rotors, and cockpit design stand out. The new frame design, while being much lighter allows for heavier, more powerful pilots. The new cockpit is much more ergonomic thanks to advice from Scott Epsley (below). If you look at videos of Judy's world record attempts you can see that the drivetrain was very jerky, and no doubt a lot of power was lost. Gamera II has a large flywheel in the cockpit and is much smoother and more efficient. 

Physio Scott Epsley examines the cockpit of Gamera II



(4) As a scientist yourself, you have some insight into the machine you're flying--you're not just the engine.  What about it is most impressive?  I mean, if we were considering a Gamera II vs. a SuperSix Evo, how does it compare in terms of weight, aerodynamics, and handling?

The trusses are open and not aero at all. Vertically, the Gamera is very responsive but to control where you are going is more like steering a ship. You can direct it, but it takes a while before it moves. It fits my riding style; fast climbing, slow corners.

(5) What are the challenges that the team faces?
The Gamera is very fragile, and the room we're testing in is a little bit to small. We have about 10ft on each side and have to be really careful not to crash into the walls. The team itself is amazing. They’re 40 students that have worked incredibly hard on this for one or two years. I can only imagine what it would be like to have a team like this design the ultimate time trial bike for you. I’m sure it would rock.





(6) If you could make an ideal human-powered helicopter pilot, would he be like Fabian Cancellara?
Joe Dombrowski! Probably way below the150 lbs pilot weight that the frame can currently support, with incredible power to weight. I’m sure he would crush every possible world record in human powered flight.


(7)  Tell us about your flights:  How many times have you done it?  What are the wattage demands of the task?  Is it strange to use your arms along with your legs?
To get off the ground, I need to provide about 8 W/kg at a cadence of 100 rpm, ~500 W in my case. I think the machine is a little more efficient than was previously thought. I think this is amazing - this is small amount of power to get a human hovering above the ground, less than half the power of a vacuum cleaner!

My wife was really excited about the prospect I was going to do work outs with my upper body. It took some effort to get used to the feeling and we’re still learning on the optimal phasing between arms and legs. Power tests on the ergometer indicated that by adding arm cranks the pilot would yield 15% more power than with legs-only.

(8) This is the question I really am hoping you'll go into--what does it feel like like to spin those huge blades and to hover?  That has to be incredible!
That is simply beautiful. The Gamera really wants to fly and within a couple of strokes you're up in the air. It feels like you're sitting on a pillow of air (the ground effect). You spin a little more and it goes up immediately. Sitting in the center of these huge blades is a weird experience though - everything around you is rotating. 






(9) Is there ever a possibility that this could be more than an experiment?  Is human-powered or -supplemented commuting possible?
  I'm already commuting on it. Amongst the pilots, there is a fierce competition who gets to take it home. All joking aside, the guy who developed the Gossamer Albatross, which was the first human powered airplane to cross the English Channel, used his experience to develop solar powered aircraft and ultralight airplanes that can fly into the stratosphere. There are many applications to the engineering challenges that had to be overcome in this project. 




(10) What I mean was, can you win Lost River with this thing?
I think the pack would really appreciate the gentle breeze from the giant blades. 
Thanks to Dennis for answering questions.  First dibs on Gamera production model.  Can't wait to hit the first goon ride with that baby.

1 comment:

Brian said...

Good reporting. I love this.