WHACK!!!

[Glenn]

What the hell was all that? I can't even follow it. Are you guys married...to each other? As for George's opinion, I want it and value it. He has a long excellent record of flying successfully and more important, safely. I want us all to have that. I will suck his brain dry.

Anyway, for this discussion the wind is either a headwind, a tailwind or a crosswind period. It's always relative to the pilot's current track.

I still am not convinced there are any negatives to a fast approach that outweigh the dangers of a slower one. We always say the speed should be chosen according to the conditions, but what conditions would warrant a slower approach. In addition, the actual conditions we will encounter are at best a guess, it's often changing by the second. It just seems to me that the faster approach is best to deal with any adverse conditions and causes no real problem if the air stays smooth, so why not fast? What is wrong with an approach that is as fast as possible without struggling or inducing oscillation until rounding out into ground effect? Then, reducing speed is very easy, quick and the only action needed. It eliminates the option of going faster, by making it unnecessary. Wouldn't this approach eliminate most whacks. Most I see involve a loss of control from flying too slow at some point in the approach which then leads to over compensation and whack. What am I missing?

[Don]

Glen, I agree with you "...As for George's opinion, I want it and value it. He has a long excellent record of flying successfully and more important, safely. I want us all to have that. I will suck his brain dry.

If you don't like someone's opinion - just don't read it.

This public Forum is NOT the place for personal attacks!

[stebbins]

Stebbins,

I'm just sick and tired of your "know it all" attitude that always seems to come from you and I have had several other people express the same thing to me.

That's fine. You have the right to that opinion. Heck, I might not even disagree.

But this is not the place for it. This is about making our friends and ourselves safer.

{Other stuff deleted by George because it wasn't about safety.}

[Chip]

Yeah ask him to give you his perspective on what happen in Florida. Should help illustrate that EVEN hang 5's can and will have problems landing from time to time.

Not that I'm immune either. Had my run in with a fence in Elsinore when I opted for a green field (read grass) rather than put it down into a bigger dirt field. I thought I was gonna impale myself on the chain-link fence. I barely made it over and hit my outboard left wing tip and came into the "green" field sideways and took out several tree saplings as well as the stakes holding them up.

Without the speed I would have certainly hit the fence with my torso. I was able to basically convert the speed into altitude to "almost" make it in.

[stebbins]

....

I still am not convinced there are any negatives to a fast approach that outweigh the dangers of a slower one. We always say the speed should be chosen according to the conditions, but what conditions would warrant a slower approach. In addition, the actual conditions we will encounter are at best a guess, it's often changing by the second. It just seems to me that the faster approach is best to deal with any adverse conditions and causes no real problem if the air stays smooth, so why not fast? What is wrong with an approach that is as fast as possible without struggling or inducing oscillation until rounding out into ground effect? Then, reducing speed is very easy, quick and the only action needed. It eliminates the option of going faster, by making it unnecessary. Wouldn't this approach eliminate most whacks. Most I see involve a loss of control from flying too slow at some point in the approach which then leads to over compensation and whack. What am I missing?

I'm not sure you're missing anything.** Yes, you can go too fast. I've seen that too. But for every time I've seen someone go too fast on approach, I've seen dozens (hundreds?) go too slow. We aren't talking about going VNE! We are talking about going fast enough to eliminate the overwhelming majority of gust-induced stalls near the ground. That's why the arithmetic above. Put your own numbers in. Use different gust-factors. (Mine was actually conservative - I've seen lots of 10 mph gusts too, and some larger. But remember, we didn't include gradient and vertical gusts, so any numbers you get are still not quite fast enough.)

If you don't like my analysis, do your own. But figure it out, don't just fly the same old way.

And fly safely, please. I'm tired of losing friends.


** Sometimes in restricted landing areas, you cannot go as fast as you'd like, or you haven't got enough room to land. But that's not the normal situation. And if you are doing such an approach, you are trading one risk for another. That must be done consciously, with full knowledge of what you are doing, or you increase your risk more than is necessary. Or you can just avoid landing in such small fields. I learned this lesson personally. (And several others on the same day. Ouch.)

[stebbins]

Yeah ask him to give you his perspective on what happen in Florida. Should help illustrate that EVEN hang 5's can and will have problems landing from time to time.

Not that I'm immune either. Had my run in with a fence in Elsinore when I opted for a green field (read grass) rather than put it down into a bigger dirt field. I thought I was gonna impale myself on the chain-link fence. I barely made it over and hit my outboard left wing tip and came into the "green" field sideways and took out several tree saplings as well as the stakes holding them up.

Without the speed I would have certainly hit the fence with my torso. I was able to basically convert the speed into altitude to "almost" make it in.

Yep. I messed up. Got cocky. Kept trying to get up after it was time to do landing stuff. Picked a worse field knowing it was worse, because it gave me one last chance to get back up. (Dried up swamp with high grass, random trees, bushes etc.) Then, my knee hit a stump hidden in the grass, just as I flared. If I'd landed in the field across the road, I'd have landed in a cow-chewed pasture. Short grass. Lots of room. Stupid. All for an extra 1/4 mile on one day. Had to bail on the rest of the competition(s) because I damaged my knee that badly. So, that 1/4 mile cost me part of the rest of this meet, and all of the next one. Not to mention the money, pain, etc. Or the risk of worse injury. The way I landed, I could easily have taken the stump in my chest instead of my knee.

[Frederick]

I read results of a study showing the tone of emails was misjudged 50% of the time, and view that as the inharent weaknesses of the text medium.

Thank you, to everyone for their contributions on these important forum topics. I appreciate them.

Greblo and I have discussed a danger of max. speed: it puts you at a higher risk of getting tumbled.

[stebbins]

Email tone: I believe your number. I would have guessed 25%, but am not surprised by 50%. We should all try and keep that in mind. (Yes, that includes me!)

Greblo is right about tumbles. However, I've been flying for 26+ years. I've never heard of anyone tumbling on final (with the possible exception of some guy who was doing aerobatics right to the ground, but that wasn't "getting tumbled", that was a blown loop...) Yet we hear about people crashing because they flew too slowly all the time. As I've said before, work on the HIGH risk problem, not the LOW risk one.

Could you tumble that close to the ground? Sure. But the odds are minuscule, unless your glider is messed up. (Out of certification, damaged, etc.) The day that my nose-cone came off, I deliberately landed slower (but not slow). I did it because the glider "wanted" to pitch down. Pulling in became scary. I balanced the risk by flying fast enough but no faster.

And as we've been saying, nobody here is advocating coming in at VNE! Just come in fast enough that the odds of a stall or other sudden loss of lift is highly reduced and the recovery time is reduced and the recovery margin (airspeed) is there for you to use. The numbers in the table above are a guide, not a hard-and-fast rule. If it is 6 pm in November and there is no wind or lift to be found, then you could come in slower than if it is 2 pm, gusty and thermally in mid-July.

And one side note: The very same conditions that might make you think about tumbling are the ones that would give you the highest odds of crashing because of low airspeed. So I vote for solving the issue that is clearly causing problems, not the one that is theoretical.

All risk is a trade-off. There is no risk-free action. Even non-action is not risk free.

[JT]

Freddy and Joe:

Given the number of times I felt as if someone was jumping on the nose of my glider last Sunday, I'd like to see here some of the discussion concerning tumbling at high speed. I chose to fly at a relatively intermediate speed (for a LiteSpeed) in the strongest turbulence - around 30 to 40mph - thinking that I was at greater risk of a tumble at low speeds, say less than 25.

George: If you're going to chime in, great, just use the short version, I have to work tomorrow.

[stebbins]

It seems to me (and this is just my opinion, I haven't spent time thinking this one through) that manufacturers usually have a "best maneuvering speed" assigned to their gliders. I'd think that, barring other issues, this was close to the safest speed to fly in strong turbulence.

In terms of tumbling, my (limited) reading on the issue would indicate that VG off is safer than VG on or VG part-way on. How that plays into the speed issue is another question. Is best maneuvering speed different VG on vs off? Probably.

I do know that the FEEL of the glider is more stable at intermediate speeds than at higher ones. And it FEELS more stable with VG off. More work, though.

On the other hand, if you are really worried, perhaps discretion is the better part of valor, and the day (or location) is too rough to be flying in. Time to land and get that root beer, Gatorade or other beverage of your choice?

I'd love to hear Joe Greblo's take on this.

Short enough, Jim?

[greblo]

I think there's a misunderstanding here in what I believe. Tumbles tend to be more prominent in situations surrounding high angles of attack, not low angles of attack. There are 5 or 6 reasons why I believe extremely high speed approaches have increased dangers (as a general rule) and should be avoided, unless necessary.
1. Given inadvertent lift on final, there's no good way to steepen your glide slope to keep from overshooting. If you're already pulling in all the way, how can you pull in more if suddenly you get lift on final?
2. Gliders are less stable in roll when operating at high speeds. They are also very sensitive to roll commands. PIO is not uncommon even when there is no turbulence. It's the low to middle speed range that provides the most reliable control on most hang gliders (assuming laminar air). This of course changes as the level of turbulence increases.
3. When flying at high speeds, the distance travelled in ground effect becomes quite large, often eating up smaller landing fields.
4. Impact forces are much, much higher at higher speeds.
5. Pilots who constantly make high-speed approaches, often rely on their fast speed to protect them from stalls. This sense of protection can cause them to fail to learn about the causes and locations of "potential" turbulence that can be encountered during the approach. There is probably no more important skill to develop in hang gliding than the ability to forecast the possibility of and magnitude of turbulence in the "danger zone" (any area where positive command and control is required for safety). This certainly means immediately after launch and during the approach.
One of my most meaningful revelations was when I realized that for many years I was looking at turbulence the wrong way. I was thinking of turbulence as a "disturbing force" on the wing. Of course this is true, but there's another, perhaps more critical side to turbulence. It's the effect that turbulence has on the wings angle of attack. Turbulence can be defined as "any change in the velocity or direction in the relative wind". Relative wind is one of the two components of angle of attack. Change the relative wind direction and you change the A of A. The larger the turbulence, the larger the change in A of A. Since stalls result from high angles of attack, and since hang gliders are basically un-steerable in stalls, it's no wonder we sometimes get turned 90 - 180 degrees when flying slowly in thermals and other forms of turbulence. It's not just because of the force of the thermal, it's also because of the large angle of attack change that the wing sees when encountering a thermal or any form of turbulence.
So, the secret to maintaining steering control in turbulence lies in preventing the stall, as all the weight shift in the world won't do much to correct a turn from a stalled glider. At least not until the glider recovers from the stall, and that can take a couple of seconds. A glider can easily get turned more than 90 degrees in 2 seconds.
I believe that the safest pilots (when it comes to launches and landings in turbulence), are the ones that choose a flight speed that results in a low enough angle of attack to prevent the glider from entering a stall "if and when" it enters turbulence. To do this, they first study the environment they are about to fly into. Next they forecast the potential magnitude of the turbulence that might exist there. Finally, the choose an approach speed that protects them from the change in angle of attack associated with that amount of turbulence. Of course it helps to err on the side of caution, so too much speed is generally safer than too little speed.
If I'm trying to make a point here, it's that every pilot needs to become an expert in identifying where and how much turbulence "might" be present in flight, especially near the ground. Armed with that information, you can then choose an angle of attack that will allow your glider to be steerable if and when it hits that turbulence.

[Glenn]

Ahh, the plot thickens: I was hoping Joe would visit here.
Joe said:

If I'm trying to make a point here, it's that every pilot needs to become an expert in identifying where and how much turbulence "might" be present in flight, especially near the ground. Armed with that information, you can then choose an angle of attack that will allow your glider to be steerable if and when it hits that turbulence.

My concern is: can we really reliably predict the turbulence we will encounter on final to a level of confidence to make every landing safe? If not, then wouldn't extra speed go a long way to compensate for our errors in predicting the final's turbulence. The unexpected gust/sink is the only one I'm really concerned with and how is that best handled when it hits. Isn't it too late after the surprise to try to pick up speed close to the ground. Most other aircraft have enough mass (inertia) and a throttle to maintain the speed. Our low mass means that only our velocity gives us the momentum to maintain our speed above stall. In watching birds land in turbulent air they tend to dive aggressively and flare at the last moment. I'm only trying to get you more experienced dudes and dudetts to consider this fully. Is there one simple thing we could all do from now on that would have prevented both the Richard and Jeff scenarios, assuming they were both caused by turbulence of some kind?

[stebbins]

I'm not sure that Joe and I are disagreeing very much. I specifically said that "high speed" wasn't what I was talking about. And several of his points make the case I was making.

I suspect we are talking past one another on one issue: What constitutes a "High speed approach?" Fully pulled in would certainly qualify! But other than that, I'm not sure I know where Joe draws the line between "sufficient speed to avoid stalls" and "too high a speed." He mentions that too much speed is generally safer than too little. I agree, and the numbers show it.

Glenn: Can we really predict? Yes and no. Can we be 100% sure that there won't be some turbulence? Not under reasonable soaring conditions, we can't. However, we can say that certain days are highly likely to have extra turbulence. We can say that certain wind directions/speeds will likely cause more turbulence in any given LZ. We can say that certain terrain features will likely cause more turbulence. If there is more than a slight breeze, and you are landing in a field surrounded by trees, the odds of turbulence are higher than if you land in a 5000 acre flat, green cow pasture. (The other conditions being equal.) If you got 1000 fpm lift a half hour before you landed, your odds of turbulence in the LZ are different than if you flew for 3 hours and never got more than 150 up. You get the idea. I exaggerate for effect, but the principle is the same.

So, my opinion (probably not that different from Joe's) is that whatever amount of turbulence experience suggests is there should be increased some in your mind and then pick the appropriate airspeed. The table I gave above is a good starting point, but not the be-all-and-end-all. And almost always (there are indeed a few exceptions) err on the side of extra speed. But don't get silly about it. Nobody needs to go 70 mph two feet off the ground in a hang glider, except for showing off. Especially on a bumpy day! And 50 is probably too fast too, usually. But 25-30 in a Falcon isn't too fast. And 35-40 in a Topless isn't either. IMO.

And Joe is very right that learning what causes turbulence can help a lot. Example: Kagel is more turbulent when the wind is significantly from the West or more East than normal. That makes sense, and the reasons are left as an exercise for the student.

[Glenn]

Thanks guys,

From this discussion then my conclusion is that I will make my approaches on the faster side and will reduce only when needed such as a short LZ. My default approach will be faster than what seems just OK for the conditions. I feel speed like altitude is better to have as long as possible until I'm sure I no longer need it. I fly a Saturn, so slowing down is relatively easy. A pilot flying a faster wing may feel a little different.

Thanks again.

[greblo]

Glenn;

I'm glad you're making everyone think here. And I agree with your final conclusions. I'm not sure that my thoughts are what most pilots want to hear, but I found it extremely helpful when I owned up to the fact that weight shift hang gliders are only slightly less limited flying machines than paragliders. Sure they can go faster and don't collapse, but what good is that, if moderate turbulence puts us predictably out of control at times when we need control. Hang gliders are lacking the devices that are necessary to minimize the problems that you are addressing. Aircraft designers, long ago, put rudders on aircraft to give them more control in turbulence. They put on ailerons to make them turn more reliably in turbulence; they put on an elevator to make angle of attack changes quicker and more reliable; and they put on flaps to enable them to steepen their glide slope without significantly increasing their airspeed. Hang gliders are my favorite aircraft, but they have none of these important devices. Nor do they have the weight and inertia of a larger aircraft. Therefore, I can't expect the HG to be as versatile or as safe.
World famous aerodynamicist, world sailplane champion, and hang gliding pioneer, Paul McCready suggested in an article written in around 1975 (when hang gliders were more controllable than they are today) that the physics behind the weight shift hang glider's reliability in winds and turbulence is not very pretty. His conclusions were that hang gliders could not be reliably flown in winds above 18 mph, unless done so in an environment absent the types of turbulence encountered in inland and mountain sites. He cautioned against flying hang gliders in these conditions if one wanted to avoid accidents stemming from control problems.
Pilots don't want to own up to that advice because we want the big climb rates, and the high altitudes, and the long flights. We see others do it safely so we think it's safe. But we can't make flying in strong thermals, gust, and strong winds safe; we can only make a little less dangerous. And to make it less dangerous, we need to understand what we're up against. We're up against the fact that hang gliders are very limited flying machines that don't exhibit much control in turbulence. We need to quit dancing around that fact. I choose to think of a hang glider as a "deficient" aircraft, when flown in turbulent conditions. Just like I think of an indian's canoe as a deficient boat when put in the Pacific Ocean. This doesn't mean that I think the canoe is a lousy boat. It's a fine craft that needs to be kept in the right environment. I'd certainly own one if I lived next to a lake.
Now I agree that most of us are not going to limit our hang gliding to smooth winds of less than 18 mph, light to moderate thermal conditions, and avoid areas of mechanical turbulence. To do so would probably mean limiting our summer flying days to after 5 pm in the afternoon, and giving up XC flying. But if we did, we'd have the greatest possible impact on safety. Instead we will fly in conditions that can and will sometimes render our glider out of control. We can reduce the control loss by flying faster before turbulence hits and your idea of doing approaches faster is part of the solution. But understanding when it's necessary to fly faster and just how fast to fly is the part that's even more important.
Dennis Pagen has a formula for how fast to fly on approaches. Dennis is probably the best known expert in hang gliding and thousands of pilots read and enjoy his books. He says one should fly best l/d speed plus half the wind speed. It's wonderful that he gives pilots a formula with which to adhere, but I disagree with him slightly as it can be consistently proven wrong in certain cases. For example, at Torrey Pines, Fort Funston, Marina Beach, Point of the Mountain, and Dockweiler Beach, you can witness very skilled pilots flying and landing in strong winds of 20 mph or more. According to Dennis, to be safe, these pilots should be approaching the ground at best l/d speed plus 1/2 the wind speed. Let's say their best l/d speed is only 25 mph. Add 10 mph to this and their approach speed should be around 35 mph. But at these sites, you generally see skilled pilots coming in for landing at very slow speeds near minimum sink, often hovering straight down without any forward progress, only to land as softly as imaginable. They do this time and time again and no one bats an eye, even though it's windy. The reason it's safe is not because there is little wind, but because these pilots know that in these conditions there is little to no turbulence where they intend to approach and land.
So the flaw in Dennis' formula is that he's using wind as the important factor to address for control problems, rather than turbulence. He probably does this because wind is often the source of turbulence; but it's not always. A better formula is one that I stated earlier. Before a pilot launches and before a pilot begins his approach, he should study the flying environment that he's about to enter. He should look for any and all clues to the amount of turbulence that might be present. There are many clues to work with, including wind speed, wind direction, gust factors, stability or instability of the atmosphere, cloud cover, amount of cloud shadowing on the ground, thermal strength, thermal frequency, obstacles to the wind, wind shadow potential, presence of vortices, and on and on. Next he should draw a conclusion from his evaluation and then choose a speed that will minimize control loss should he encounter turbulence. Of course I agree that it's a good idea to have a little extra speed above and beyond what you think is necessary.
Finally, you got my attention when you referred to flying faster on "final approach" for safety. Flying faster in turbulence, on the downwind and base legs, is just as important as flying faster on final. Imagine being on downwind at Kagel and getting turned 90 degrees to the right (toward the houses of Santiago Estates). Even if one managed to get his glider turned around before he landed on someone's roof, I guarantee you he would not land anywhere near where he intended to. The entire approach, including downwind and base, require relatively precise flight in order to land where you want to. Flying too slowly on downwind is a sure way to get into trouble.
To summarize, those interested in taking high risks with their lives ought to continue to fly hang gliders in gusty 20+ mph winds. Those who aren't should avoid these conditions. All pilots should try to learn about the causes of turbulence, when it's more likely to be present, and how airspeed and angle of attack affect one's control in turbulence.
Thanks for listening.

[JT]

Back to tumbling. I have a difficulty with what George and Joe are saying. If there is a lesser chance of tumbling with VG off but a greater chance at high A of A, isn't this a conflict? We fly slowly when the VG is off. Do they cancel each other out?

I suspect the problem is that the two parameters take effect at different times. I think Joe is saying that high A of A usually implies low speed when a moment of down-force can more easily pitch the nose of a glider downward. VG off might have a countering effect by causing a downward moment at the rear of the glider, immediately after. Am I close?

So flying at higher speed through turbulence with the VG off is great but lowering the dive recovery systems (sprogs, dive-sticks) with the VG increases the chances of a tumble at any speed? I remember Moyes saying in their LiteSpeed manual not to thermal with VG on. Oops!

Anyone care to set me straight, if I haven't analyzed the above accurately?

And, thanks guys, for keeping those responses short.

Just kidding, I know complex question mean complex answers, right?
Anyone ever heard about a guy named Alex and a knot?

[stebbins]

Great discussion Joe!

One thought: Joe is right about it not just being "final approach" that needs the extra speed. I tried to use the phrase "near the ground" or similar wording everywhere in my post. I know I forgot in a number of places. The key is to fly faster when "out of control" means a safety issue. At 10,000 feet over the ground, it probably isn't much of an issue. At 100 ' over the rim of Santiago Estates on downwind, it certainly is.

So, Joe is right again. Don't just fly faster on "final", but anywhere that there is stuff to hit, or no room to maneuver, or similar issues. At Kagel that means flying faster a bit higher up than some other sites. At Andy Jackson LZ, there (currently) is more leeway until near the end of your downwind leg. You don't need to speed up quite as soon. Each site varies. I usually use 300' above any obstacle as a starting point for extra speed. Less in smooth air, more in bumpy air, and more in stronger winds. But I'm a notorious chicken about such things.

[JD]

…….. If there is a lesser chance of tumbling with VG off but a greater chance at high A of A, isn't this a conflict? We fly slowly when the VG is off. Do they cancel each other out?........

I’ll chime in here for a couple of reasons including the fact that in ~1977, my friend Stuart Soule died when his heavily modified Sky Sports Sirocco tumbled and collapsed while inverted. IIRC he went over the falls while thermalling.

As I understand it:
The tumbling problem crops up at low angles of attack when there is little or no pendulum stability. This can happen when thermalling at low speed and then going over the falls. Even if your nose is level, if you lose the pull of gravity due to strong sink or you hit downward rolling air at the perimeter of a thermal bubble you will become partially or even totally weightless. You are now at the mercy of the positive pitching coefficient of your glider and at the mercy of the rotation of the air you are in. Now if your airspeed is sufficiently low, your nose will drop and your tail will rise and you may rotate downward past vertical. All the while you are still weightless to some degree. If your VG is mostly off, it won’t take too much increase in airspeed before your glider becomes more pitch positive and will try to rotate its nose back up without any input from you. However, if at full VG it will take a greater airspeed to yield enough positive pitching force to overcome the gliders forward rotating momentum as well as the force from the rolling mass of air you are in. So, its possible that the glider in full VG will rotate far enough past vertical that it ends up with a negative angle of attack and stalls inverted, resulting in the pilot’s weight pushing down from what is now above the glider. It may right itself, tumble forward or backwards, or collapse.

Tumbling is different than a lockout or dive past vertical. A glider without enough washout or twist going out toward the tips will become increasingly prone to an unrecoverable dive as its angle of attack becomes lower and the effect of pendulum stability diminishes as the dive steepens. On his website, John Heiney writes about the dangers of pulling in while coming out of a loop. This reduces the centrifugal force of the loop which takes the place of gravity by providing pendulum stability and can result in excessive speed and a collapsed glider.

I hope this helps.

[abinder]

I totally agree with Joe.