FreeFlight Advice: RLF (Restricted Landing Field) Techniques
Posted on FreeFlightAdvice.com January 26, 2015
Q: Got any tips for RLF and/or landing downhill? Any info you have and/or video would be great.
A: I’ll start with the easy answer, which is that landing downhill sucks. If it’s a really gentle slope, then it can be done… but plan for a really long ground skim, especially on high performance equipment. When it comes time to flare, a climbing flare is not advisable. Because the ground is dropping away as you progress forward, your height above the ground is increased through the climbing flare, and the strain on your back, hips, knees, and ankles is increased. A full-on moonwalk landing is not advised either, because with the slight slope you’ll be moonwalking forever and it won’t really stop you very well. Instead a smooth flare, like you would for a 2-3 step landing on flat ground, works well. Because of the slope, be mentally prepared to take more than the usual 2-3 steps that flare might yield.
Anything more than a gentle downhill slope, and it’s probably better to land across the slope, which is presumably cross-wind. If the slope is steep enough that flying wings-level across it endangers you in catching your uphill wingtip on the slope, then it’s probably better to land uphill… even if it’s downwind. For more depth on uphill/downwind landings, see our previous article about Fly on the Wall Landings.
The reason landing downhill is such a struggle, is one of simple mathematics. The glide slope of our gliders has gotten better and better of the years… and today even a mellow slope is a challenge, because we glide so well. Anything that can be done to degrade the glide slope of the glider, enables landing on that much more slope.
And- on the topic of degrading glide- we can talk about RLF, or Restricted Landing Field, techniques! The USHPA’s RLF sign-off requires demonstrating a landing using a downwind leg, base leg and a final leg approach where the entire base leg, final and landing occur within a 300′ square. The important thing to notice is that it isn’t just a definition of landing zone size, but also available approach area. Landing in a small field, with an unlimited approach area, is just a fancy spot landing after all. Spot landings are a function of carefully crafted and very accurately executed approaches… which are ALSO a key principle in RLF landings. So, focus on your spot landings before turning your focus on honing RLF skills. There is lots of spot landing info out there, so I won’t get into that right now. Here is a video that shows a typical downwind/base/final approach, with some advanced glide-slope adjustments during the final (more on those advanced techniques at the end of this article)
Beyond setting up your approach, a huge factor in successful RLF landings is how you turn on final. When you turn final is important; as is how much airspeed you have when you do- because more airspeed means a longer groundskim, and therefore more runway needed. But HOW you execute the turn to final matters most… Especially on high performance gliders.
We have written before about yaw- what it is, and where it comes from. To keep things simple, let’s just say a general rule: the bigger the roll input, the more adverse yaw. A really-quick-but-really-big input will have more yaw associated with it than a small input held for a longer period, achieving the same desired roll of the wing. Being smooth is crucial here. Also, stretching out that turn to final- so that your glide path makes a nice curved turn rather than a sharp 90 degree kink.
The reason minimizing adverse yaw in your turn to final is key in an RLF situation, is because it allows us to approach slower. Speed, you see, equates to TIME spent in ground skim. And TIME is what is needed for the yaw from our roll inputs from our turn/level-out on final to dissipate. If we’re not so good at being smooth and minimizing the adverse yaw, we’d better carry a little more speed so that we have a long enough ground skim for the wing to oscillate back and forth a few times before you need to flare. If you can carve a really smooth turn, with almost no yaw, you don’t need much time at all after leveling out before flaring… and perhaps your flare could even be attached to the end of your leveling input. Worth mentioning that there are OTHER risks associated with flying your approach very slow, and even more risks with maneuvering near terrain slow. Right now we’re just discussing airspeed required due to yaw issues.
Here is a fun video my friend Tom Lowe posted a while ago, of a few pilots landing in a pretty small field:
The first landing is a kingposted glider, probably a U2. Compare his approach and landing placement to the second landing, on a topless. Despite the higher performance glider, the second pilot carried less speed through the approach, and was able to land considerably shorter. Not quite as easy to compare, because he lands in a different direction, is the third pilot. His turn to final is lower because he is not limited by the treeline, but yet he appears to have the longest ground skim, because he was carrying the most speed. I don’t blame him, because turning that low is risky, and turning that low, AND being super-slow, is death. But the video is a good demonstration of how airspeed = runway required.
Besides these maneuvering nuances, anything that deteriorates your glide performance (Lift/Drag) will help you land in a small area. Immediately people usually envision a drag/drogue chute to accomplish this, and that’s certainly one good way. Drag chutes are an added complication, with added things that can go wrong without proper diligence… so if you’re going to use one, study up on the technique, practice deploying it hanging in a simulator, and then do it first in as ideal and controlled a situation as you can create for yourself. The one thing I will say about using drag chutes, which is often overlooked, is that the drag chute is connected to your body, so any drag created is pulling your body back. This might not be enough force to ACTUALLY change the CG of the glider much, but it certainly changes the bar-pressure feel around “trim”. Basically, hands-off “trim” becomes a tad slower than without the drag chute deployed… and without consciously considering and being ready for that, trouble can arise.
Simpler solutions like getting your body upright and presenting as much surface area to the airflow as you can (use the boot of your harness too if you can) will help a lot, especially at faster airspeeds. In the ground skim, dragging your toes has saved many-a-pilot from overshooting a short field.
One other, extremely advanced, technique is to alter the performance of your glider by reducing your airspeed to a “mush”. Because of the twist and sweep in hang gliders, the onset of stall is progressive- meaning the whole wing does not stall at the same time. The root (middle) is at a higher angle of attack, and will stall sooner than the tips. Because VG reduces twist, letting the VG completely off (on gliders so equipped) is important. Since glide performance is lift divided by drag- stalling part of the wing both reduces lift AND increases drag… so it can make a really drastic change in glide slope. Of course, flying around semi-stalled isn’t considered entirely “safe”. First, there’s the loss of lateral control at such low airspeeds. Even minor turbulence can result in catastrophic heading changes. Also to be considered is the effect moving our CG aft has on pitch stability- it reduces it. Getting dumped out of a thermal or dust devil is more likely to result in tumble the more aft your CG is, and the less airspeed you have. And there are also concerns such as wind gradients, where if you are riding the edge of a full-stall, and you descend into a layer with less headwind, your inertia resists accelerating and you end up STALLED, not mushing. It would be kind of like flaring at 50+ ft. Ouch.
My good friend and legendary sky god pilot Joe Bostik decided to demonstrate said mushing technique during a landing clinic I did at Andy Jackson Airpark. I did not know it was Joe, or that he was intentionally flying around stalled (if you don’t know Joe, he’s a little crazy sometimes!)… so ignore the running commentary. But watch the glide performance. Even if you are not familiar with that LZ, you can see he brought that T2C in using less space than most single surface gliders consume. Impressive, albeit risky. Joe did say he got a little too greedy trying to demo the technique and did not pull in soon enough to get the glider fully flying again before flaring, which is why the end of the landing was less than graceful. But it was pretty soft… and I think everyone can see how he could have gotten things flying and had a nice snappy flare.
We could keep rambling, but that’s probably already more thorough coverage than most pilots are looking for.
And please remember- train and practice RLF skills in a larger space, giving you margin for mistakes. Knowing how it’s done is great, but it’s not the same as being able to do it when you need to. It’s a great skill to have, so I’d urge all H3+ pilots to develop their ability to RLF… but do so progressively.
Happy (RLF) landings!