DAVE 858 wrote: ↑
Mon Nov 13, 2017 6:25 pm
Im seriously interested in how a figure 8 approach is a better choice than a DBF, BF or straight in approach. Specifically how it can be more accurate and precise than a DBF approach.
A good place to start this might be in talking about the most effective ways of using figure-8 style approaches- because I see above you said "straight in approach". I don't care if a pilot does a DBF, 8's, S's, or flips around randomly to get themselves into an LZ... a straight final is an integral part of LANDING... so a more accurate way of thinking of the approach is everything leading up to the straight final. And before someone goes apeshit, yes I am aware there are occurrences where landings don't involve, or literally can not involve, a straight final... but that's like .1% so let's not go there please.
The purpose of an approach is to position your aircraft where it "needs" to be, in order for you to land where you want to land. Needs is in quotations because we're human, flying small lightweight gliders in an active invisible medium... striving for perfection is encouraged, but also recognizing that where your glider needs to be is a soft concept, it's a general area kind of thing. Hopefully everyone understands glide slope- where being close to your target and low when you start your final gives you a short final, and being higher and farther away can give you a longer final but still land you in the same exact spot... if your distance-to-altitude stays along that glide slope angle.
How someone gets themselves onto this glide slope angle is a bit irrelevant to the landing itself, as long as they do it... hopefully we can agree on that, right? So- why figure-8 instead of DBF?
Someone already commented on how their DBF went all wonky when they found themselves landing in way more wind than they were accustomed. Humans are creatures of habit, and while a pilot SHOULD be constantly monitoring position and judging ground speed on the downwind and estimating how that shifts the ideal glide angle positioning steeper (closer to the desired touchdown spot)... we also easily fall into routine. If your downwind leg takes 45 seconds or more most flights, it's surprisingly easy to get caught off guard when circumstances call for it to be like 10 seconds, or possibly even less! This is if you start at about the same geographic staging point to start your DBF. If the pilot recognizes early how windy it is, they might start their DBF farther upwind in order to still have that 45-second (I'm making these numbers up, never actually timed a traditional DBF haha) downwind leg. But at some point this gets pretty impractical, gliding way upwind... presumable way past the LZ from where you originated... just to box it and come back again.
Which brings up- there is a minimum altitude required to perform a DBF. If someone gets to the LZ too low to fly upwind first, then downwind alongside their LZ, then fly a base leg, and finally... a final. That might turn into more of a downwind to BaFinal, where the base and final are really just a single 180 degree turn. If you don't like the idea of doing 90-120 degree heading changes in a figure-8 approach, I doubt you support flying downwind and doing a 180 turn back into the wind. Not to mention much of the adjustable nature of the DBF is lost in that case.
So maybe getting to the LZ low someone is disciplined and aware enough to let go of their DBF plan BEFORE they try flying upwind, creating the need for that 180 BaFinal thing. Maybe they fly to the side of the LZ in a way that they can basically drop in to a DBF without the D... they just fly the Base and Final. Well again, a lot of the adaptability in the DBF is lost. In fact, doing just a base leg and turn to final is the same as doing one leg of a "figure 8" and turning final. It's just a crosswind heading and a turn into the wind.
Speaking of A TURN INTO THE WIND... a figure 8 approach can have many turns into the wind. A DBF has ONE. An advantage of figure 8's is that the pilot can exit the eights on either end, or cut one short and turn into the wind and into the LZ. If someone gets a DBF wrong, they find themselves with some serious last-minute decision making to do! Should I land into the wind, somewhere else... or land in the LZ, but it might be downwind, or maybe I can at least get cross-wind... maybe. If you've ever been there you probably remember the feeling of helplessness as you're on the wrong side of where you wish you were... it's quite memorable!
Obviously this means someone messed up their DBF... and for fairness we should discuss how so many people mess up a figure 8 style approach, too. It's called a figure 8 because, in no wind, the pilot needs to fly a figure 8 pattern over the ground. This is often seen as undesirable because that means the pilot is turning a bit away from their LZ again and again in order to do those 8's. What happens a lot is people, being imperfect humans again, don't want to or aren't comfortable with turning away from the LZ enough to keep themselves over one area of ground while they figure 8... so they end up flying more like a series of "S" shapes, where they are getting lower like they want, sure, but also getting closer to their desired landing spot... and effectively they are following a glide slope line into the LZ... all the while staying above where they want to be, and steadily inching lower and forward and always staying over that slope angle they want to get into.
The more wind there is, the less of a challenge this is- because with the drift of the air moving over the ground, it becomes less and less necessary to actually point the nose of the glider away from where you want to land. And so, in wind, it's fair to say figure 8's become easier to perform correctly, or said similarly it gets harder and harder to fly "S"'s and inch your way in rather than getting lower until you're on that angle to turn final and head in... and like I said earlier, a figure 8 approach can present a lot more opportunities for when to turn in... whereas a DBF requires you to have an idea of if you are too high or a bit low while you are still upwind, or while traveling downwind, or while flying that base... although options are decreasing by the second at that point... too low cutting base early means landing a bit off the wind line, and too high means doing essentially a figure 8 type turn before final... so I hope it's a skill that's there when needed!
One more thing about a DBF vs figure 8 approaches. Well, I'm sure there are other things I'm not thinking of right now... but this one more thing is a big one, and I saved it for last on purpose.
When flying a DBF, a pilot is more or less flying flat and level, initiating a turn, leveling out, etc. In figure 8 typed approaches, the glider is almost always banked. Does that matter? Yep... well, sometimes anyway! Turbulence tends to be more vertical and horizontal. Either thermals are rising and other air is descending to take it's place, or air is flowing over hills or mountains or trees or houses or whatever. Maybe the airflow gets shifted a bit left or right, but generally turbulence is felt the most when you're flying flat and level, and the least when you're banked. Also, when you're banked and turning, the forces created are actually multiplying your wingloading. If I recall correctly- and don't kill me if I'm mixing up my numbers- I think in a 30 degree coordinated turn you're pulling 1.5G's, right? So if I hook in at say 200 lbs, and my glider is 144 sq ft, I have a wingloading of ~1.39 lbs/sq ft. When I'm in that 30 degree bank coordinated turn, the glider is feeling 1.5x my weight, so my 200 lbs feels like 300! Glider didn't get any bigger, so now I'm rocking ~2.08 lbs/sq in. In case anyone hasn't connected the dots yet- we're flying weight shift hang gliders, so more weight is more control.
In either approach there is the concern of being bumped off course by turbulence, and it's never a great thing in either approach. Getting bumped off course in your downwind leg can mean extending that leg unintentionally, requiring shortening the base or possibly the base and the final. Getting bumped off course in a figure 8, although less likely, can simply mean one loop of your 8 is really big, or your 8 starts looking like a three-leaf-clover, or an experienced pilot might think quick enough to go with that bump and take a quick 360 rather than fighting it and trying to stick with the 8's plan... but whatever happens, if you suddenly lost some time/altitude, no big deal, that just means one less "8" leg. As long as the plan is to always exit the approach for a nice long final, the argument about getting dumped out of a figure 8 downwind and hitting the ground with a drastic ground speed is no more relevant than getting bumped and turned downwind on the base leg of a DBF.
With all of that said- and advocating that everyone (eventually) get proficient in performing both types of approaches- I'll confess that I also prefer a DBF over figure 8's for most people, most times. But that doesn't mean I don't see the value or the strengths in figure 8's etc. And hopefully now you can understand how, sometimes, a figure 8 approach can very well be a wiser choice than a DBF... assuming you've got the skills and experience to perform it well.
In any event, the safest approach is going to be the one you're good at over the one you're not... so if you've practiced and worked hard to get really good at one, that is excellent- and yes definitely use that one when things are "interesting". But when things are mellow, why not start practicing and training the 8's... or some variation therein... dial it in on those flights when you could DBF it in your sleep. Who knows, there might come a day where the site, or the conditions, or the traffic, or whatever suit the figure 8 style approach... and bam, whip that skill out of your bag o tricks and land like a boss. I have had a few times when I was truly glad it was something I learned to do in addition to a DBF!
And responding to Dietch... I will NOT stop trying to win! Winning, to me, would be every glider sold from hereon out would have the same downtubes it came with from the factory. Winning would be when people come to an LZ to "watch dem crazy kite peoples" land... they see an entire community of skilled aviators, not a bunch of "arrivals" where they appear lucky to have smacked into the right field at least. If I didn't know hang gliding didn't have to be like that, and I saw pretty much any average day at an LZ like Ajax... hell no would I even consider hang gliding! Crashing doesn't look COOL or FUN! So, yea... I'm gonna keep trying to win. Anyone that wants to win with me is welcome, and there are a lot of people I've helped along the way that will attest to what I'm all about (and what I'm not- re: bullying or intimidating people?). As for arguing... that's exactly why I was asking if Dave really wanted to know... 'cause there was a time when I came to hg.org for entertainment, and while I never argued anything I didn't believe in, I absolutely welcomed a good debate for the sport of it. A lot of times you were my Huckleberry... so again I find it funny you saying you try not to argue. You would just go on and on insisting you will never land well, it's not something you are personally capable of, it can't be done in never-seen-before fields, and can't be done in those conditions... and it wasn't just me, you had lots of people saying they flew the same gear, higher, hotter, rowdier places, longer durations and distances, and still had nice landings... and you'd come at it again and again. I know that to this day you feel I was beating you over the head like a whack-a-mole every time you'd post yet another video with a seismic landing... or another flight where the camera battery died or card was full right when you turned final I truly just wanted you to wise up before you got hurt! The irony that you broke your neck AFTER you got wise and practiced and put some polish to your landings... just fuking sucks. That is SO not the positive reinforcement that should follow such a long overdue wise decision!!! Despite what you may think, I was not at all happy to hear of that incident. And I can even say I am glad you are still out there getting after it and flying... that's an inspirational tale. I just wish you weren't still holding that chip on your shoulder from the 10 years I spent trying to get you to listen, and weren't here needling at me while I'm taking the time to try to help educate (again). No good deed I guess..........
Shut up and fly.