Re: Effects of wing loading
- It's true that wing loading, even in ultralights, sometimes doesn't matter much. If you takeoff by aerotow and fly only in good lift, you can fly a little faster and make wider turns with no discouraging penalties. Glide performance, stability, and control will not be reduced by flying faster, and may in some ways even be improved (better headwind pennetration, for instance).
The problem is that in light conditions or during critical takeoff and landing situations, the need to fly even just a little bit faster becomes a serious handicap. A glider that cannot slow down and turn tight will not stay in the air with the others in light conditions, and will be unsatisfying. If it always needs an extra strong wind to launch off a hill with a good margin of confidence, then it will be impractical for roll launching. If it can't slow down enough to land gently on rough ground or in bushes, it will be under repair too much of the time or will be limited as to where it can fly.
For hang gliding, the guideline I accepted was "fly the biggest wing you can handle". The hang glider wing loadings (about 1.7 lbs. of gross weight for every square foot of wing area) have been relatively constant in recent decades, despite many attempts to fly heavier. I accept this as an evolutionary answer to what a good upper end wing loading might be for a pilot flying in the open. Wing loading is fate.
Mike Sandlin.....San Diego California
--- In Airchairgroup@yahoogroups.com, "Dayhead" <crash_corbin@...> wrote:
> A builder of a Bug 4 wants to increase the span because he is heavier than average.
> It has been my experience in 34 years of hang gliding that wing loading doesn't make that much difference, in terms of sink rate and best glide angle, or L/D.
> Of course, with weight-shift control there can be a very noticeable difference in "handling", or control response, especially about the roll axis.
> Some of the HG's I've flown were produced in 3 sizes. My weight puts me on the middle sized one. I've had the pleasure of flying all three sizes.
> While I do notice a difference between the smallest and largest sizes, the difference was mostly in the handling qualities.
> Not too long ago I flew a "small" size modern high performance HG. The hill wasn't steep, and there was no wind to be found. The glider easily lifted off with only a few steps.
> The modern gliders have more span efficiency than ever before.
> I expect than Bugs and Goats also enjoy a good level of span efficiency.
> So anyway, I'm wondering if some of you mathematically inclined fellows would like to compute the actual differences in stall, min sink, and best glide speeds for the range of possible pilot weights we might see amongst airchair builders. I just wonder how much the difference might be for a 100# lady and a 300# teamster.
> In the meantime, I think that with wheeled launch and landing capability there is probably no need to modify the Bug, unless of course the pilot expects to regularly use a short launch slope in no wind conditions. Just my $.02
- Got the reasons - thanks!
I will look at the math and make some decisions as to size / strength / spacing.
--- In Airchairgroup@yahoogroups.com, "LR" <lincolnr@...> wrote:
> I meant to mention that increasing the wingspan a little can increase loads on the wing, so even if the structure was overbuilt before, it might not be adequate after a stretch. This is beyond the increase from more weight.
> The stall speed will be approximately proportional to the square root of the wing loading, though Reynolds number effects might change things a little bit.
> The turning radius I figured from a=v^2/r, equivalent to r=v^2/a. a is constant for a 45 degree banked turn in steady flight at 1g in the horizontal direction. However, you have to account for the increased speed, because the wing has to provide a total of 1.414 g's. So you can take the square root to get the new velocity.
> a = acceleration
> v = velocity
> r = radius
> 1g = 32 feet/s^2