Forums: Skydiving: General Skydiving Discussions:
Collapses and Turbulence: Article

 

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winsor  (D 13715)

Feb 1, 2006, 10:25 AM
Post #26 of 38 (2056 views)
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Re: [DuckDodger] Collapses and Turbulence: Article [In reply to] Can't Post

In reply to:
Great thread. There is a lot to learn here.

I see you mention manuevering speed and this got me thinking about a question I have had for years. I was a pilot long before a skydiver, maybe something to do with going to Rhinebeck Aerodrome back in '75. That was cool.

Anyway, manuevering speed increases as you increase weight/loading, which to me seems absolutely backwards on the surface. I thought that maybe this had something to do with inertia, that generally, increasing weight made the aircraft more stable, or less likely to move to a critical angle of attack and overstress the wing.

On the other hand increasing weight, should actually increase loading on the wing, so not wanting to stress my little mind, like we seemed to be doing with the wing, I left it there.

A few years later, a good friend of mine said the reason manuevering speed increased was totally dependent on the testing of aircraft. In respect to my friend, I didn't tell him this sounded like crock to me. Then I thought about our dear Gov and thought, maybe so.

Doesn't seem to be much parachute application, other than the thought about inertia, like a more heavily loaded boat crushing through heavier seas. The parachute translates weight to the lines so that sort of makes sense to me, but it might just be acid flashbacks. What do you think?

With my aircraft, the critical factor is not stress on the wings as much as acceleration of the airframe with regard to the engine. If the airframe is abruptly accelerated upward or downward beyond the critical rate, the engine mounts are given to failure. If the engine comes loose, the airplane is unflyable.

Staying close to stall speed allows the wing to stall before it can generate sufficient lift to result in structural failure at the engine mounts when encountering turbulence. Increasing the gross weight increases the stall speed, so your maneuvering speed - with constant margin above stall speed - increases proportionally.

I agree that wing loading would indicate a decrease of maneuvering speed with increased gross weight if the limiting factor was structural failure of the wings. However, with my aircraft at least, it would have crashed long before the wings failed.


Blue skies,

Winsor


rehmwa  (D 12816)

Feb 1, 2006, 11:12 AM
Post #27 of 38 (2049 views)
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Re: [pchapman] Collapses and Turbulence: Article [In reply to] Can't Post

Wow, nice stuff.

I was the one who asked about steady state and did misstate the lift = weight thing. Thanks for fixing that; aerodynamic lift is perp to the airfoil in one definition, perp to the airflow in others (Kallend would be able to say what is in vogue nowadays), not parallel to gravity. But, draw your control volume around the canopy AND the pilot, and you still see that in steady state, it's still one G (I think you did acknowledge that). You are right in that the D and L components opposite gravity balance the W, not just Lift alone. I think Brian is only talking about that miniscule effect of flying over the earth, which is curved, which does result in a loss of G (which is more the faster you fly assuming the same orbit altitude) (but that would be going in perp to gravity, not "going with gravity". BUT, if he can sense that sitting in his harness, then NASA needs to hire out his ass as the most sensitive weighing device in the world. Tongue

Descending canopy having less tension? Yes
Because it's descending and ? I doubt it.
Simpler - Because the faster you descend the more drag your body feels from the air and the breeze is actually supporting you? Yes - the drag of the pilot and the lift and drag of the canopy both hold up the jumper during a fast descent - and the effect on the pilot is more when the descent is faster. (nevermind, you did state that, once I saw you were treating the net drag as canopy +pilot rather than the just the canopy component)

I think he was talking about orbit mechanics, not descent resistance drag of the air on the pilot's body. But maybe that's just because the other thing is more fun to consider.


darkwing  (D 4164)

Feb 1, 2006, 12:16 PM
Post #28 of 38 (2040 views)
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Re: [BrianSGermain] Collapses and Turbulence: Article [In reply to] Can't Post

In reply to:
Nevertheless, I aim to fly at more than One G in turbulence. FLying in smooth, continuous turns allows me to fly faster than full flight, and increases my G Loading. I can increase my wingloading by adding a bit of brakes at the end of the turns to create a high speed positive carve.

DANGER!! An important issue that no one has brought up is the problem of traffic snarl and collisions due to everyone now deciding to do continuous turns when it is turbulent!!


DuckDodger  (D 27017)

Feb 1, 2006, 3:54 PM
Post #29 of 38 (2013 views)
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Re: [BrianSGermain] Collapses and Turbulence: Article [In reply to] Can't Post

That was beautiful. For 20 years I have been wondering about this.

Please keep the good info coming. I realize I need to upgrade some of my practice drills to include being better prepared for a collapse. We fly locally (ATL) at some sites with topography that makes for interesting winds.

Knowledge is the power to stay out of the hospital or worse.

Blues


yuri_base

Feb 1, 2006, 6:36 PM
Post #30 of 38 (1996 views)
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Re: [BrianSGermain] Collapses and Turbulence: Article [In reply to] Can't Post

Brian,

What is your recommendation for a situation when there's a large gradient of windspeed in a thin layer (wind shear) and you need to turn 180 into final approach? E.g. from 25mph downwind layer upwind into 10mph ground layer. Besides the turbulence in the shear layer, there will be a sudden loss of lift caused by the abrupt change in airspeed. What's the best way to handle this sudden dive?

Thanks!
Yuri


Garycal  (A 40806)

Feb 4, 2006, 12:26 PM
Post #31 of 38 (1920 views)
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Re: [BrianSGermain] Collapses and Turbulence: Article [In reply to] Can't Post

Good article hope to see you in hollister again this year.A reveiw never hurt anyone Gary


BrianSGermain  (D 11154)

Feb 10, 2006, 2:42 PM
Post #32 of 38 (1824 views)
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Re: [yuri_base] Collapses and Turbulence: Article [In reply to] Can't Post

In reply to:
Brian,

What is your recommendation for a situation when there's a large gradient of windspeed in a thin layer (wind shear) and you need to turn 180 into final approach? E.g. from 25mph downwind layer upwind into 10mph ground layer. Besides the turbulence in the shear layer, there will be a sudden loss of lift caused by the abrupt change in airspeed. What's the best way to handle this sudden dive?

Thanks!
Yuri

Hi Yuri

The key with such a situation is to carry lots of airspeed, line tension, and most importantly, CALM AWARENESS. You will need to be ready to stab your brakes at any time to bring your flight path back up to it's original trajectory. If you let the wing surge forward on the pitch axis and drop the angle of attack, you will soon be out of time and out of altitude, and will be forced to watch Oprah on the hospital TV. (I still think Oprah is the bomb, but I would rather be in the sky)

It is a matter of quickly applying a little brake OR letting off the front riser(s). Either way you are increasing the angle of attack, which will begin to bring you out of the dive. You can't land with your wing in front of you, so recovering to the angle of attack that flies the correct curve for your final approach is essential for survival.

Does that work for you?

Bri
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(This post was edited by BrianSGermain on Feb 10, 2006, 2:44 PM)


BrianSGermain  (D 11154)

Feb 10, 2006, 5:33 PM
Post #33 of 38 (1804 views)
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Re: [darkwing] Collapses and Turbulence: Article [In reply to] Can't Post

In reply to:
In reply to:
Nevertheless, I aim to fly at more than One G in turbulence. FLying in smooth, continuous turns allows me to fly faster than full flight, and increases my G Loading. I can increase my wingloading by adding a bit of brakes at the end of the turns to create a high speed positive carve.

DANGER!! An important issue that no one has brought up is the problem of traffic snarl and collisions due to everyone now deciding to do continuous turns when it is turbulent!!

Good point. When I say "continuous turn" I do not mean in the same direction all the way to landing. That is called a spiral. I am talking about smooth carving, like a skier or snowboarder, back and forth, continuing in a general direction.

Thanks for helping me clarify that...
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F16Driver  (D License)

Feb 10, 2006, 9:45 PM
Post #34 of 38 (1786 views)
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Re: [BrianSGermain] Collapses and Turbulence: Article [In reply to] Can't Post

I just want to explain the "maneuvering speed" of an aircraft to make it a litle easier to understand. One persons explanation was right, but might be a little complex for others to understand.

MANEUVERING SPEED INCREASES WITH AN INCREASE IN WEIGHT because it is a STALL SPEED.

As you know, an aircraft will stall at a higher airspeed when you increase it's weight. Maneuvering Speed is the max speed at which you can fly where the wing will stall (high speed stall) before it over G's itself. Increase weight there, you also increase the stall speed. By flying at maneuvering speed, you know that you can put the stick right back in your lap and you won't over G the aircraft (aerodynamically impossible).

When going through turbulent air, I fly slower than maneuvering speed. This is because maneuvering speed only gives you protection in the Positive G realm, not the Negative G. Flying a little bit slower puts you closer to the negative G maneuvering speed. So then you can have protection in both directions, since turbulence does the same.

Great article, Brian. Something I think gets neglected a lot is how to identify key areas of turbulence. One DZ I jumped at the peas right next to its BIG hangar. When the wind was from behind the building, I stayed the hell away from the peas, those that went for it, we just sat back and enjoyed the show. The look on everyone's face when they are full flare 10-15 feet off the ground and still descending, is priceless. We told them about it before we left the ground. Luckily, their PLF's were good.

Hope to attend your course in Tecumseh. See Ya!


rehmwa  (D 12816)

Feb 12, 2006, 12:28 PM
Post #35 of 38 (1731 views)
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Re: [BrianSGermain] Collapses and Turbulence: Article [In reply to] Can't Post

In reply to:
(I still think Oprah is the bomb, but I would rather be in the sky)

What's the deal with daytime TV and riggers/jumpsuitmakers?


jumprunner

Feb 26, 2006, 4:10 PM
Post #36 of 38 (1643 views)
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Re: [BrianSGermain] Collapses and Turbulence: Article [In reply to] Can't Post

In reply to:
In reply to:
In reply to:
As for training students to fly in brakes, I am against it. Especially under a huge parachute, we must maintain what little airspeed we have. ...

This is a great thread, havent been skydiving for a while but its got the things you need to know.

A long time ago, when I made the first jumps at Marana, AZ, I was told that if the radio goes out to fly the canopy in at half brakes. Even then, with what limited knowledge I had, I thought this was a bad idea, just had a bad feeling about it.

I had quit skydiving because of my own limited knowledge, and the poor atmosphere of what I encoutered in skydiving instructors and schools. This is not a generalization of skydiving instructors, just the ones I encountered, which gave me a dim view of the sport and made things seem more like you were gambling with your life (from not knowing what to do in a situation).

I can tell you, your kind of information and attitude towards skydiving would have kept me in the air a lot longer. Hope to read more of your articles Cool


(This post was edited by jumprunner on Feb 26, 2006, 4:21 PM)


BrianSGermain  (D 11154)

Feb 27, 2006, 12:12 PM
Post #37 of 38 (1609 views)
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Re: [jumprunner] Collapses and Turbulence: Article [In reply to] Can't Post

Thank you.

It's never too late.
The sky awaits!!!
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Premier fgersch  (D License)

May 29, 2006, 8:03 PM
Post #38 of 38 (1471 views)
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Re: [BrianSGermain] Collapses and Turbulence: Article [In reply to] Can't Post

In Reply To: Helicopter question....

Just a though coming from a non "air technical" background. It seems to me intuitively that the method by which a helicopter generates it's forward
speed and lift would tend to (for want of a better description), neutralize or at least distribute more evenly, any turbulence encountered. I am thinking of this in kind of the same way as to opposing waves (sound/water/whatever) will tended to neutralize one another. A helicopter must generate it's own strong localised waves of air disturbance. I'm guessing that in a somewhat chaotic manner this serves to defeat some of the natural turbulence it may encounter.

If someone knows about helicopter flight. I'd appreciate a reply even if it's to tell me I'm totally off base with my theory.

Cheers

Franz


(This post was edited by fgersch on May 29, 2006, 8:08 PM)


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