Springtime spells changes in turbulence

Please tell what happened and how it might have been avoided. Names should be ommitted. This forum should help others learn from mistakes that caused or nearly caused a mishap.
greblo
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Springtime spells changes in turbulence

Post by greblo » Sat Mar 31, 2007 7:41 am

As we would expect this time of year, we're beginning to see some launch and landing events that are pretty serious. Our departure from the generall smoother flying conditions associated with winters low sun angle and shorter period of daytime solar heating, brings us into a more turbulent and gusty time of year.

Spring has a generally more unstable airmass and in the past week we've seen 100 + hour pilot get turned back into the mountain just after launch, and we just had a 100 hour pilot unable to make the landing area due to heavy sink. He landed south of the bridge and between the 2 sets of powerlines (pretty scary). He didn't remember there were two sets and was pleased to see he made it over the first set.

Learning to predict when and where winds and turbulence may be is an important pilot skill. Reading and learning about weather, understanding the sources and causes of turbulence, and attending weather classes like the one Hungary Joe is having next week is a good idea for all pilots.

Two tips in the meantime may help. Before launching and landing, try to get a good feel for the any of the sources of turbulence that might exist in front of launch and during the approach, and fly through it with an angle of attack low enough to prevent a turbulence induced stall. You can never prevent the disruption to your wing that the turbulence will create (unless you can avoid the turbulence), but you can make sure that you have a wing that's controllable when you enter turbulence near the ground by avoiding the impending stall. The stronger the "potential turbulence" the faster you should fly.

Also, if you encounter easterly winds when you arrive over the l/z, consider setting up a much higher approach with a base leg that's higher and further back towards the bridge. This way you will can deal with the strong drift caused by the east winds, and descend through the turbulent layer when you are on final with your wings level, rather than entering it during your turns to base or final. Also, come in much faster to avoid control loss.

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stebbins
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Post by stebbins » Sat Mar 31, 2007 1:02 pm

What is the aviation rule for airspeed on final? If I remember right, it is:

1 1/2 times your stall speed + 1/2 the wind speed.

And that's for airplanes with motors and aerodynamic controls. We have neither, so should perhaps fly even faster than that on final! Especially in stronger conditions and at Kagel in East (rotor) winds.
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JBBenson
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Post by JBBenson » Sat Mar 31, 2007 2:45 pm

Is the rule: the more turbulence, the faster one should fly?

I have heard it said that in extreme turbulence one should not fly very fast, as it can over-stress the glider?

Is this true?

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Post by abinder » Sat Mar 31, 2007 6:42 pm

stebbins wrote:What is the aviation rule for airspeed on final? If I remember right, it is:

1 1/2 times your stall speed + 1/2 the wind speed.

And that's for airplanes with motors and aerodynamic controls. We have neither, so should perhaps fly even faster than that on final! Especially in stronger conditions and at Kagel in East (rotor) winds.
At least when I was flying single engine planes, the landing speed generally was a specific landing speed that the manufacturer specified; airspeed is airspeed, not ground speed. (at least that was with the pipers and cessnas that I flew.)

Now in extreme turbulence, the manuvering speed was definitely less than the cruising speed but greater than the landing speed.

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stebbins
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Post by stebbins » Sat Mar 31, 2007 7:25 pm

abinder wrote:
stebbins wrote:What is the aviation rule for airspeed on final? If I remember right, it is:

1 1/2 times your stall speed + 1/2 the wind speed.

And that's for airplanes with motors and aerodynamic controls. We have neither, so should perhaps fly even faster than that on final! Especially in stronger conditions and at Kagel in East (rotor) winds.
At least when I was flying single engine planes, the landing speed generally was a specific landing speed that the manufacturer specified; airspeed is airspeed, not ground speed. (at least that was with the pipers and cessnas that I flew.)

Now in extreme turbulence, the manuvering speed was definitely less than the cruising speed but greater than the landing speed.
Landing speed is not necessarily the same as approach speed. I was talking about approach speed. (I called it speed on final, but I meant from several hundred feet until you are in ground effect.) Clearly you don't do your full approach at landing speed or you'd have serious issues....Usually called crashes.

Joe was talking about approach speed as well. He even used that term.
Fly High; Fly Far; Fly Safe -- George

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stebbins
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Post by stebbins » Sat Mar 31, 2007 7:32 pm

JBBenson wrote:Is the rule: the more turbulence, the faster one should fly?

I have heard it said that in extreme turbulence one should not fly very fast, as it can over-stress the glider?

Is this true?
In some sense, yes. But only in the sense that you shouldn't fly REALLY REALLY fast in turbulent air. If your glider is going to break (or get "over stressed") because you flew a reasonable approach speed, you need a new glider!

Do the math. Stall speed on a Litespeed (depending on pilot weight) is around 22? With a 10mph wind that gives: 1.5 * 22 + 0.5*10 = 33 + 5 = 38mph. Maybe more if turbulent. That isn't all that fast for a topless glider. If your glider will have stress issues at that speed, you've got other problems besides turbulence.... You can do the math for your own glider/pilot/wind combination.

Personally, I think that (with a few exceptions) it is better to be 5mph too fast on approach than 5mph too slow. Heck, 10mph too fast is better than 5mph too slow....

Think of it this way: For every pilot whose glider has broken up (or been "over stressed") because they flew too fast in turbulence on approach there are probably a hundred who have crashed because they flew too slowly and stalled or lost control due to lack of airspeed. Of course, you really shouldn't be flying your glider at 70mph near the ground in turbulence. That is a whole other kettle of fish...

By the way, that 1/2 the windspeed part is important. Think "wind gradient" and you'll understand why.
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Post by abinder » Sat Mar 31, 2007 10:10 pm

stebbins wrote:
abinder wrote:
stebbins wrote:What is the aviation rule for airspeed on final? If I remember right, it is:

1 1/2 times your stall speed + 1/2 the wind speed.

And that's for airplanes with motors and aerodynamic controls. We have neither, so should perhaps fly even faster than that on final! Especially in stronger conditions and at Kagel in East (rotor) winds.
At least when I was flying single engine planes, the landing speed generally was a specific landing speed that the manufacturer specified; airspeed is airspeed, not ground speed. (at least that was with the pipers and cessnas that I flew.)

Now in extreme turbulence, the manuvering speed was definitely less than the cruising speed but greater than the landing speed.
Landing speed is not necessarily the same as approach speed. I was talking about approach speed. (I called it speed on final, but I meant from several hundred feet until you are in ground effect.) Clearly you don't do your full approach at landing speed or you'd have serious issues....Usually called crashes.

Joe was talking about approach speed as well. He even used that term.
I as well meant approach speed. usually in small single engine planes, the speed that you maintain in the pattern is the same as you fly at while descending toward the ground until you have to level off. This pattern/approach speed is specified by the manufacturer of the plane and is generally followed regardless of the wind speed.

Again, airspeed is airspeed; not ground speed.

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stebbins
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Post by stebbins » Tue Apr 03, 2007 7:42 am

abinder wrote:
stebbins wrote:
abinder wrote:
stebbins wrote:What is the aviation rule for airspeed on final? If I remember right, it is:

1 1/2 times your stall speed + 1/2 the wind speed.

And that's for airplanes with motors and aerodynamic controls. We have neither, so should perhaps fly even faster than that on final! Especially in stronger conditions and at Kagel in East (rotor) winds.
At least when I was flying single engine planes, the landing speed generally was a specific landing speed that the manufacturer specified; airspeed is airspeed, not ground speed. (at least that was with the pipers and cessnas that I flew.)

Now in extreme turbulence, the manuvering speed was definitely less than the cruising speed but greater than the landing speed.
Landing speed is not necessarily the same as approach speed. I was talking about approach speed. (I called it speed on final, but I meant from several hundred feet until you are in ground effect.) Clearly you don't do your full approach at landing speed or you'd have serious issues....Usually called crashes.

Joe was talking about approach speed as well. He even used that term.
I as well meant approach speed. usually in small single engine planes, the speed that you maintain in the pattern is the same as you fly at while descending toward the ground until you have to level off. This pattern/approach speed is specified by the manufacturer of the plane and is generally followed regardless of the wind speed.

Again, airspeed is airspeed; not ground speed.
Not near the ground it isn't. If you think so, you are asking for a crash.

Imagine this scenario. You are landing into a 20 mph headwind and are at 100 feet. You fly your normal speed for an approach. Say, 25mph. As you approach the ground, the wind slows to 5 mph. Remember the gradient? You are now flying at 10 mph. Or more specifically, you are stalled. At a low altitude. Ouch.

I once had a 20mph headwind on final. As I approached the ground, the wind dropped to a 5mph tailwind. If I had been flying at even 30mph, I'd have crashed. (The wind change happened below 50', not enough time to recover from that severe a stall...) Strangely enough, I encountered the same conditions the next day at another spot 80 miles away. Go figure. Windspeed is not groundspeed, it is true. But near the ground, you darned well better keep BOTH in mind.

Your comments about plane manufacturers "fixed" airspeed on approach make perfect sense for faster aircraft. When you are landing at 150 mph, a 10mph wind is pretty much irrelevant. When you fly at 25 mph, 10mph is VERY relevant near the ground. Ignore this at your peril. My comments about "general aviation rule" above clearly meant slower flying airplanes. Those manufacturers either tell you to include the windspeed, or are negligent IMO.

Ask Hungary Joe if he flys his Dragonfly near the ground without considering the windspeed.
Fly High; Fly Far; Fly Safe -- George

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Chip
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Maybe I'm just dense?

Post by Chip » Tue Apr 03, 2007 3:45 pm

Imagine this scenario. You are landing into a 20 mph headwind and are at 100 feet. You fly your normal speed for an approach. Say, 25mph. As you approach the ground, the wind slows to 5 mph. Remember the gradient? You are now flying at 10 mph. Or more specifically, you are stalled. At a low altitude. Ouch.
I don't get it ..... If you were flying 25 into a 20 you have 5mph over the ground. Now if you are flying 25 into a 5 wouldn't that mean you are flying 20mph over the ground, not 10?

If you are flying 25mph and the wind is blowing 20, you're not making much headway (GS wise) and on your LS you're near stall already (stall being 22 as stated).

Now if the wind drops to 5mph and you keep flying at 25, well you're making some headway and you're still near stall speed with a lot more groundspeed that you'll need to deal with (by running or using that bad flaring technique that Greblo is educating pilots away from :wink: ).

Sure you need to consider the windspeed when you're landing, I guess mainly so you know how high and how far back to start your approach. Oh .... and which direction to make your approach too :o

A little extra speed on your approach once you have it all lined up "usually" isn't a bad thing
Last edited by Chip on Wed Apr 04, 2007 1:29 am, edited 1 time in total.

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Post by JBBenson » Tue Apr 03, 2007 4:55 pm

Also, the windspeed generally does not drop precipitously, thus the term "gradient".

If it goes from 25 to 5 suddenly there is something else going on, which is not what we are talking about.

In a headwind, as the windspeed drops your groundspeed will pick up, (in inverse proportion), given fixed airspeed.

Isn't theory fun? If only it were so easy... :|

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Post by Christian » Wed Apr 04, 2007 11:48 am

I think Joe's talking mostly about turbulence-induced stalls. He says that with spring weather, weird and unpredictable stuff happens on final approach. Since we have no choice but to fly through this stuff in order to land, we need extra airspeed to ensure control.

Every stuent learns that in class, but there are several factors that make it easier said than done, at least for me, with 70 hours.

--When turb is kicking your butt on short final, it feels physically harder to keep pulling in, especially on a double surface. There is a psychological tendency to relax and slow down so things quit happening so fast.

--When necessary to set up a crab angle to keep on course, you still have to keep pulling in equally hard. That's two things to do at once, and one hand is probably on the speedbar.

--On short final, areas of pop and sink challenge the whole beautifully constructed landing plan. The touch-down point shouldn't matter, fly down through the junk and land soon as possible.

--When I have trouble in these conditions I can usually trace it back to the point I entered the pattern to begin with. If I got that right, the final approach works out. If I got it wrong, the rest is a bunch of last-minute corrections and prayer.

Your mileage may vary--and I hope it's better than mine!

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Post by stebbins » Sat Apr 07, 2007 6:03 am

"Wind speed doesn't drop off that fast, hence the term Gradient". Well, that's usually true. But it only takes once to ruin your day. My experience is that there are quite a few times that the wind will drop at lest 10 mph in a couple of seconds on final. Gradient, wind shadow, turbulence, whatever. It happens. If you don't have your airspeed up, you will get pounded.

And as for your glider responding by keeping it's speed constant, that's groundspeed. When the wind drops off, your airspeed does too. It takes time for it to speed back up. That energy comes from diving. If the ground is near by, then boom.

I will be off-line for a whiile. See you all later. Fun discussion.
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Post by abinder » Sat Apr 07, 2007 12:09 pm

stebbins wrote:

And as for your glider responding by keeping it's speed constant, that's groundspeed.
I think that you're getting ground speed and airspeed mixed up.
You talk like you have lots of aviation experience. Have you ever had a private pilots license?

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Post by Greg Kendall » Sun Apr 08, 2007 4:50 pm

George is accounting for the inertia of the glider. It’s true that if a glider (or airplane) flying at constant trim encounters a reduction in headwind, it will tend to accelerate (with respect to the ground) to maintain airspeed. However, this acceleration doesn’t happen instantly and it doesn’t happen for free. In George’s example, the glider will have to trade 10 or 15 feet of altitude to accelerate from a groundspeed of 5 mph to a groundspeed of 20 mph. You might ask why going from an airspeed of 25 mph to an airspeed of 25 mph constitutes an acceleration. The reason is that the air can’t be used as an inertial reference because it accelerates.

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Post by abinder » Sun Apr 08, 2007 10:36 pm

Greg Kendall wrote:George is accounting for the inertia of the glider. It’s true that if a glider (or airplane) flying at constant trim encounters a reduction in headwind, it will tend to accelerate (with respect to the ground) to maintain airspeed. However, this acceleration doesn’t happen instantly and it doesn’t happen for free. In George’s example, the glider will have to trade 10 or 15 feet of altitude to accelerate from a groundspeed of 5 mph to a groundspeed of 20 mph. You might ask why going from an airspeed of 25 mph to an airspeed of 25 mph constitutes an acceleration. The reason is that the air can’t be used as an inertial reference because it accelerates.
nothing happens instantaniously; not even in a power plane.

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Post by Christian » Mon Apr 09, 2007 9:07 am

When foilks plop down in the middle of the runway and dig the nose in, it can look fairly instantaneous. Wha' happened, the wind stopped?

Sounds like a whuffo joke but essentially that is what happens. Drops you a couple feet and nothing left to flare with. Stay hot ín ground effect and in doesnt happen.

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Post by abinder » Mon Apr 09, 2007 2:12 pm

Christian wrote:When foilks plop down in the middle of the runway and dig the nose in, it can look fairly instantaneous. Wha' happened, the wind stopped?

Sounds like a whuffo joke but essentially that is what happens. Drops you a couple feet and nothing left to flare with. Stay hot ín ground effect and in doesnt happen.
Most of the time it's people trying to flair before they land; land first, then flair; much easier. Do power planes stop and then land? No, they land first and then stop.

And don't use the excuse "I can't run fast enough". Joe had Phil demonstrate one time for someone that used the excuse "I can't run fast enough"; Phil came in hopping on one foot and then flaired. So the excuse of "I can't run fast enough" doesn't hold up one bit.

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Post by Christian » Mon Apr 09, 2007 3:56 pm

Its true that with airplanes, settting up a constant airspeed and sink and angle of attack is the gold standard for approaches. Get it right ten miles out and read a magazine down the ILS.

But I don;t find that the lesson transfers to landing a hang glider in anything but sled-ride conditions. We have so little mass that mid-day thermals and sink and crosswinds are relatively huge forces. So we speed up on final as insurance against turb induced stalls. (If you did that in an aeroplane you'd float forever.)

But little planes teach the same speed lesson when the wind is up. I've landed a Decathlon (no flaps) in a 30 knot 45-degree crosswind. We came in parallel to the runway on the downwind side, headed 45 across the runway, slammed the plane down like a carrier landing and stood on the brakes.

Well, I flew most of it, anyway--until "Duke" took the controls as we leveled off and just slammed the plane onto the tarmac in a three-pointer so hard I thought the wheels would come off.

"Basically, you're crashing it," he said. "No way youre flying along in this shit, put it on the ground."

Hang gliders are much harder to land, in my opinion.

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Post by abinder » Mon Apr 09, 2007 10:51 pm

Christian wrote:Its true that with airplanes, settting up a constant airspeed and sink and angle of attack is the gold standard for approaches. Get it right ten miles out and read a magazine down the ILS.

But I don;t find that the lesson transfers to landing a hang glider in anything but sled-ride conditions. We have so little mass that mid-day thermals and sink and crosswinds are relatively huge forces. So we speed up on final as insurance against turb induced stalls. (If you did that in an aeroplane you'd float forever.)

But little planes teach the same speed lesson when the wind is up. I've landed a Decathlon (no flaps) in a 30 knot 45-degree crosswind. We came in parallel to the runway on the downwind side, headed 45 across the runway, slammed the plane down like a carrier landing and stood on the brakes.

Well, I flew most of it, anyway--until "Duke" took the controls as we leveled off and just slammed the plane onto the tarmac in a three-pointer so hard I thought the wheels would come off.

"Basically, you're crashing it," he said. "No way youre flying along in this shit, put it on the ground."

Hang gliders are much harder to land, in my opinion.
hmmmmmmmmmm.......................

Never did have the luxury of having an ILS 'guide' me in, so I've never experienced the "Get it right ten miles out and read a magazine down the ILS".

I actually feel that the experience that I've had flying Cessna 152s in cross wind conditions has helped with my landing hang gliders.

Never flew a tail dragger before (that is was a Decathlon is isn't it?). I was flying into Apple Valley airport one time with a flight instructor in crosswinds that were definitely greater than what the 152 was rated for but he still wanted to land anyways. He took the controls just before we touched down (as he had stated that he would). I had slipped it in most of the way and then when he touched down we seemed to roll what seemed like forever on the windward wheel (I think that he just wanted to see how long he could do that!). He was a young 'crazy' flight instructor but I learned alot from him!!!!!

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Post by Greg Kendall » Tue Apr 10, 2007 7:41 am

nothing happens instantaniously; not even in a power plane.
Gusts and turbulence can happen instantly. The glider (or power plane) can't accelerate instantly in response. This can result in dangerous airspeed excursions, which was the original point of this string.

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