FreeFlight Advice: VG use when landing
Posted on FreeFlightAdvice.com December 28, 2013
Q: I’m H3 flying a S2-175 @ 193lbs I fly with 75-100 VG all the time but always back it off on landing. Several vintage pilots were advising that I land with full VG, it seems to me that low and slow before the flair you want all the control possible but would this fly more like a high performance wing in landing configuration?
A: There are a number of ways to answer this question: I could tell you what I prefer on landing, or why; I could tell you to consult the Sport 2 owner’s manual and do as it recommends; or I could run through the pro’s and con’s of VG so you can make your own educated decision.
The short answer to VG and landing the Sport 2, from the owner’s manual:
We recommend that you make your approach with the VG set between full loose and 1/3 on. A full loose VG setting will reduce glide performance, making it easier to land on a target or within a small field. It will also ensure maximum control authority during the approach, and especially when flying very slowly on final. At VG full loose, however, there is some loss of aerodynamic efficiency and flare authority, For this reason, in very light winds, at higher wing loadings or at higher density altitudes, it is recommended that a setting of VG 1/4 be used.
Steve Pearson and Mike Meier (Wills Wing glider designers and the authors of the manual) are some of the most knowledgeable and experienced folks in the world of flex wing hang gliders. They know the trade-offs of VG use as well or better than anyone, and I find it very hard to make any recommendation contrary to what they recommend.
What I can do, though, is help you arrive at your own conclusion through education (and bet it’ll be about the same as theirs above)… also from the manual:
The Sport 2 VG system uses a reduction system of pulleys both inside the sail behind the crossbar center, and also inside the right downtube. Tightening the VG increases the spanwise tension which the airframe places on the sail, reducing the spanwise twist and the sail elasticity. The result is an increase in L/D performance and a reduction in roll control authority and roll control response. The VG is activated by pulling laterally on the VG rope and then moving the rope to set the rope in the V-cut knife cleat. The recommended procedure for increasing VG tension is to grasp the rope firmly at the cleat, and pull straight across the basetube. VG full loose is for maximizing roll control authority and roll rate. Due to the slightly slower trim and increased pitch pressures at VG full loose, you may find that total effective control is actually improved in some conditions at slightly tighter settings up to VG 1/4. VG settings between VG loose and VG 1/3 are recommended for working lift when any significant degree of turbulence is present, or when you are in proximity to terrain or other gliders. Between VG full loose and VG one half, the glider retains good lateral control authority and response. Tighter than VG one half, the glider’s roll pressures increase significantly and the roll rate becomes significantly slower. Tighter VG settings are recommended for straight line gliding, or for flying in smoother conditions when well clear of both the terrain and of other gliders. The stall characteristics of the Sport 2 at tighter VG settings are more abrupt and less forgiving and the glider is more susceptible to spinning. Full breaking stalls and accelerated stalls at tighter VG settings are not recommended.
In simpler language: more VG = less twist. Less twist = less forgiving stall characteristics.
If you read our previous entry about the landing round out and ground skim, I touched on the concept of a “1/4 loop” flare. If this is how you land, then more VG would mean a more efficient transfer of energy (airspeed) into direction change (altitude) before the entire wing stalls. With the VG tighter your are still more likely to have one tip stall before the other, but in light winds dropping a tip during a full flare landing isn’t much of an issue.
If you are NOT using the “1/4 loop” style flare, however… more VG will mean the onset of stall is more sudden, with less “mushing” as the wing transitions from flying to… uhh… not flying. Flare timing remains relatively unchanged, but you may get less feedback from the glider with higher VG settings. Another handling trait that changes with VG that rarely gets talked about is dihedral/anhedral. Pulling the VG pulls the cross bars back, which pushes the cross bar-leading edge junction further out toward the tips. The length of the side wires remains unchanged. The result is more anhedral, which makes the glider less roll-stable. In a turn the glider will want to roll further into the turn, or at least require high-siding to maintain constant bank. Not exactly a trait we want when landing. With very little VG, we have the least anhedral (or possibly effective dihedral via the washout of the trailing edge), which makes the glider much more roll stable. In smooth conditions you may not notice a difference because a wings-level glider will stay that way either way… but if you get banked by turbulence, it can make a huge difference in how much you get steered off course, or how much input is needed to get it back.
Then there are the more obvious concerns of less lateral control and increased gliding efficiency requiring a larger LZ… if you’re in smooth conditions and have a huge LZ, just adjust your approach accordingly. If you’re good at keeping the glider balanced and flying straight, and always nail the flare timing… why not try landing at a higher VG setting? I might suggest, as with all learning, a progression is the way to go- the more often you can fly the better, and on each landing (assuming calm and predictable conditions) try a little more VG. Maybe move up in 1/4-1/8 increments. It’s not like landing at 1/4 is good, 1/3 is ok, and 1/2 is death… good technique works with any setting, just know and manage the risks and work up to higher settings so you can get a feel for how they differ. Then you can decide where the best balance is for YOU.
As a side note: If you weigh under 200 lbs you are on the very light end of the Sport 2 175. Wills Wing says the optimum body weight for the 175 is 215-260 lbs. That is because it is not just a scaled-up version of the Sport 2 155, but instead built with a much more rigid airframe to better control airframe flex and sail twist under the loads of flying gravity-gifted pilots. It’s actually the only glider I know of that is truly built up to “big guy” standards. And for big pilots, there is no better glider… but for those of us not quite so big, the stiffened airframe really hurts handling. Not that we can’t fly the 175, but it handles like a truck compared to the 155 (for a pilot of our size/weight). I am supremely surprised (impressed even) that you are flying it around at 3/4-full VG all the time!) Please be careful landing at higher VG settings, because those settings combined with your body weight means you will have EXTREMELY LIMITED ROLL CONTROL. Remember, safety is no accident- fly smart!