“So, how fast can you go?”
Ken Shaw aka Greasehopper – taken by Ofer Eppstein
We’ve all heard the question posed hundreds of times and reasonably so when you realize that most folks have a limited frame of reference. Most folks don’t know what travelling 150mph on the Autobahn in a mushy, squishy, loose jointed chunk of Detroit Steel feels like. They honestly believe a 300mph pass in an NHRA Top Fuel Dragster is really, really fast. They have no clue that the commercial airliner at altitude is cruising at over 600 mph. Sometimes, I simply cringe at the realization that I’m about to explain what the color purple smells like. That’s what it feels like when I’m describing the sort of raw acceleration that immediately wipes the mind clear of all clutter, the sensation of leveling off ant hills with the skid pan at over 40 mph, the sort of incredible power one only fully appreciates after surviving that first savage kite loop. I’m trying to put things in a frame of reference that makes sense to someone who has memorized every statistic about the latest Chevrolet Corvette by re-reading the Car and Driver revue in the “library” every morning for the last month. But it does raise a valid query. Just how fast can we go?
Without turning this into a scientific dissertation, let’s look at some of the possibilities. I think we can all agree that even with a moderately efficient wing, we can achieve speeds of two times the base wind speed. Much of that increase is made simply by working the wing through the available wind window while at speed there by creating the phenomena of “apparent wind” flowing across the wing’s surface. Even so, at some point the drag of the flight lines, bridling and the wing itself represent a friction force that prevents the wing from flying any faster. Along with the drag induced by the flight gear comes the wind drag of the pilot, the buggy and the simple friction forces of wheel bearing, tires and the surface itself. In the kite buggy community, we call this “The Wall”. There is no end to the opinions on where the Wall is for any given kite, buggy, tire and surface combination and wind condition but there is no question that the Wall is simply a drag equation. The Flexi boys did some rudimentary testing with a tow line and the assistance of a few Not-X 13 pre-event participants at Red Lake to examine speed decay rates of various buggy/pilot configurations at various initial velocities. One thing I can tell you from peeking at the preliminary data is that as speeds increase, wind drag of the pilot and buggy increases exponentially. What that says is it’s a lot easier to get 20mph speeds out of a 10 mph base wind than it is to get 80mph out of a 40mph base wind for the same pilot and buggy. There is so much more to this and there are folks in the kite buggy community who write professional papers on the subject filled with equations, long division and technical descriptions of the forces involved but little of that has ever helped me explain the concept to our Corvette fan.
But it does bring to light the critical role that the aerodynamics of buggy and pilot play in achieving maximum speed for a given wind condition and the fact that wake turbulence generated by a buggy pilot in an upright seated position has got to be a limiting factor for achieving maximum speed. So, does that say that the Peter Lynn Speed Buggy is the way forward? To a degree, I believe the recumbent pilot position and smoothed aerodynamic skin have taken huge steps in the right direction but I’m not convinced the grotesquely phallic profile is the strict and final answer especially since ground clearance restricts the design to dry lake environs and options for tuning chassis dynamics are extremely limited.
My thoughts lean rather drastically toward tire contact patch management and achieving maximum side bite. By this I mean actively managing the side load on the wheels in such a way as to emulate the kite bike by allowing lateral forces to act on the camber and caster of a four wheel platform in such a way as to redirect that energy into down force which will transfer to the surface through the tire contact patch. This would permit an incredibly light weight platform to work in and on the surface as effectively as a much heavier platform without inducing additional bearing load and subsequent frictional drag. Sound kinda hinky, doesn’t it? Of course that exactly what they said as the state of the art in Indy Racing made the transition from the full framed, front engine roadsters to the stretched sprint car and on to the sleek, mid-engine, monocoque chassis with full ground effects that we see today. I’m just saying, don’t be too eager to throw the baby out with the bath water because it’s been my experience that at some point the baby will find it’s legs, come back in the house and beat you senseless. It happens to me all the time, sometimes daily. All this to say I don’t think we are anywhere near the pinnacle of speed specific buggy design.
Back to the subject of kites and drag, I think we have been lulled into a trance by the even tempered handling characteristics of today’s reflex profile fixed bridle kites. They are forgiving, ideal for circuit racing and a godsend for the novice but in the quest for maximum speed, I don’t think they have a place. Eliminating drag and working the kite as far forward in the window as possible is critical to achieving the desired goal. Unfortunately, high winds always carry with them a degree of punchiness that cries for just the opposite. So, where does that leave us? Some would argue that de-power is the way forward which I feel is partially correct. The ability to modulate angle of attack while in flight is absolutely desirable for speed and may well be the answer to dealing with punchy winds. But, the current modes, twin skins, LEI’s and bridled snow kites all have huge drag factors that limit their application for speed. I think we have walked too far away from the obvious choices in chasing our airfoil dreams. I think we are overlooking the possibility that a high aspect, ridged frame kite might be the answer to several drag problems. I think a kite similar to the Dragonfly that Joe Hadzicki debuted at NotX 13 may be the way forward.
These are just a few of things I’m considering when the discussion turns to speed and the way forward. I hope you take some time to consider these and formulate your own, truly avant garde ideas so we can compare notes at length over a pint, a shot and a big, fat stogie… preferably at Ivanpah, fireside, under a mildly amusing moon. See ya there.