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Debunking Glider Spoiler Turns Causing Spin Thinking



 
 
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  #131  
Old January 6th 18, 12:48 AM posted to rec.aviation.soaring
[email protected]
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Default Debunking Glider Spoiler Turns Causing Spin Thinking

On Friday, January 5, 2018 at 1:32:08 AM UTC-5, wrote:
I think the issue was made murky by stipulations. Any aircraft IN A TURN that stalls is prone to spin - much more so if it is uncoordinated. The turn to base or final is the last place you want this to happen. Not adding flaps while turning was part of my pilot training in the 70's. The combination of turning (higher G loading) increases stall speed, and if you add drag while doing it, you can inadvertently loose too much airspeed for the bank angle, add to this the possibility of an uncoordinated turn. To error is human, to error close to the ground offers the answer to one of mankind's greatest debates; what happens to your soul when you die!

In the USA a pilot must consistently recover from a stall with less than 50ft altitude loss in order to get a license. Do we do stalls at 150ft? Heck no; we do them at 2000ft. We know a mistake close to the ground will kill us. The same is true for screwing with the aircraft while it is in a turn.


Could you please provide the reference from which you got the 50 foot standard.
UH
  #132  
Old January 6th 18, 01:09 AM posted to rec.aviation.soaring
SoaringXCellence
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Default Debunking Glider Spoiler Turns Causing Spin Thinking

As a currently appointed glider DPE I can say with some certainty the there is no documented minimum altitude loss in the current US FAA Glider Practical Test standard.

The current standards were published in 1999, prior to that time there were many elements that are no longer tested or for which the tolerances have changed.

Mike
  #133  
Old January 6th 18, 06:17 AM posted to rec.aviation.soaring
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Default Debunking Glider Spoiler Turns Causing Spin Thinking


NOTE: Entering a stall/spin does not require the airbrakes being extended, nor does having them extended increase the likelihood of a stall/spin (because we all know that stall speed increases when they are extended).

In 10 years of flying gliders in the U.S. in everything from 2-33's, 1-26's, Blaniks, Grobs, Krosnos, Discus, PW-6, Duo Discus, Pegase, HpH304, ASG-32 and others with a wide variety of instructors at a wide variety of soaring sites, whether flying with me or giving a pre-flight checkout, the only mention of airbrake use during landing I ever heard from a CFI-G was to check them on downwind to ensure they were working. This started when I was a student with my first glider flights. I have and do use the airbrakes during landing (including during my biennial checks and area checkouts with no comments from any CFI-G about this) - in downwind, base, and final - in all these gliders with no adverse effects. The basic training mantra was airspeed, airspeed, airspeed, along with coordinated turns and TLAR) - the airbrakes were secondary and used to control rate of descent regardless of position in pattern to help maintain TLAR - and that was what I was taught, and how I use them - (and that does not require much use once the pattern is established (but there are those gusty, shear laden days with surprises ...)). Position in the pattern is not a factor - airspeed, coordinated turns, and TLAR were the gospel preached to me. There are times to come in high and get down fast, and times to come in low and hold off - the airbrakes are an integral part of handling a variety of (out)landing situations - but all depend on maintaining adequate airspeed, and coordinating turns.



  #134  
Old January 6th 18, 08:30 AM posted to rec.aviation.soaring
Sig_ZA
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Default Debunking Glider Spoiler Turns Causing Spin Thinking

I was taught that there is nothing inherently dangerous in using spoilers in the circuit, provided that the correct speeds are maintained.

With spoilers out, even just cracked open, during base and finals turns safe speed margins are reduced, i.e. inside wing flying slower, reduced lift from deployed spoilers and wind shear (again inside wing flying slower).

However, I was advised NEVER to use them on the base and finals turns (unless absolutely necessary and me paying full attention) and here is why:

Imagine that you normally use spoilers during these turns, with no problems at all, but one day you are returning from a 9 hour cross country flight, it’s been a long final glide and energy is low. Also the weather has changed and the wind is gusting from an approaching storm front.

So you are fatigued, the glider is in a low energy state and wind is gusting. The holes in the cheese line up and you crack the spoilers during a steep base turn with speed too low. The end.
  #135  
Old January 6th 18, 09:37 AM posted to rec.aviation.soaring
Andy Blackburn[_3_]
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Default Debunking Glider Spoiler Turns Causing Spin Thinking

I haven't read every comment in this thread from the beginning, so maybe someone has observed this previously. If so, apologies for the repetition.

There's nothing inherent about turning that will cause a stall or spin. There's nothing inherent about deploying the spoilers that will cause a stall or spin. There's noting inherent about putting out the landing flaps that will cause a stall or spin. There's noting inherent about turning low that will cause a stall or spin. There's nothing inherent about doing them all at once that will cause a stall or spin. But, the more moving parts there are in your approach maneuvers the more attention it will take to keep everything in proper order. A few examples:

Turning below a few hundred feet presents the pilot with a very different peripheral scene because the inside wing tip traces a circle against the ground that is in the direction of travel rather than the opposite direction at higher altitudes. This tends to make it feel as though you are slipping and over-ruddering the turn can become a risk. Not a problem if you fly the airplane properly.

When you deploy the spoilers two things happen. First, you spoil the lift on the portion of the wing spanned by the spoiler (that's why they're called spoilers). This means to maintain unaccelerated flight the rest of the wing needs to produce more lift, which the pilot may compensate for by increasing angle of attack. Not a problem if you fly the airplane properly, but if you are too close to the angle of attack for stall, you can end up on the wrong side of the Cl vs alpha curve.

Second, deploying spoilers increases drag so the descent angle needs to increase to keep from bleeding off airspeed. The net effect between loss of lift and increase in drag depends a bit on the glider and the airspeed and g-load, but suffice to say that airspeed and AOA will have additional influences inflicted on them. Not a problem if you fly the airplane properly, but a bunch of rates and angles are going to change when you tug on the spoiler of flap handle.

I, for one, try not to change too many things too quickly all at once in the pattern, or if I do, I tend to push the nose over a bit in case I get distracted by, you know, looking out the window. Can you yank aggressively on all the handles at once and not create a problem? Absolutely, but it helps to pay good attention if you do.

The FAA preaches stabilized approach for a reason:

https://www.faa.gov/news/safety_brie...opic_16-11.pdf

Andy Blackburn
9B
  #136  
Old January 7th 18, 04:01 AM posted to rec.aviation.soaring
John Foster
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Default Debunking Glider Spoiler Turns Causing Spin Thinking

On Saturday, January 6, 2018 at 1:38:02 AM UTC-7, Andy Blackburn wrote:
....
Second, deploying spoilers increases drag so the descent angle needs to increase to keep from bleeding off airspeed. The net effect between loss of lift and increase in drag depends a bit on the glider and the airspeed and g-load, but suffice to say that airspeed and AOA will have additional influences inflicted on them. Not a problem if you fly the airplane properly, but a bunch of rates and angles are going to change when you tug on the spoiler of flap handle.

....
Andy Blackburn
9B


This, I believe is the key that people are not considering. The physics of it is such that when the air brakes/spoilers are deployed, they disrupt not only the lift, but increase the drag. As such, if you kept the aircraft in the same attitude, you would increase the AOA and are more likely to stall.

However, if you maintain your airspeed, to do this and deploy the spoilers, you would need to change the attitude of the aircraft into a more nose-down position. This would decrease the AOA, thus compensating for the decreased lift and increased drag, and the net effect would be no significant change to the stall speed, whether you are turning or flying level wings. The AOA remains the same, and IAS and stall speed also remain the same.
 




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