Debunking Glider Spoiler Turns Causing Spin Thinking

And if the L/D ratio IS really poor, the increase in stall speed with increasing bank angle is even less. S

On Friday, June 26, 2015 at 12:36:00 PM UTC-7, wrote:
Ditto the above question-- unless the L/D ratio is really poor, the stall speed in a 45-degree banked turn ought to be about 1.189* the stall speed in the same configuration in wings-level flight. S

This is probably an unneeded addition, but for the sake of completeness, I would change "45-degree banked turn" to "45-degree banked LEVEL turn in still air". Lots of us fly 45-degree banked turns in thermals without pressing the stick back much.

On Friday, June 26, 2015 at 7:57:19 PM UTC-7, Jim Lewis wrote:
On Friday, June 26, 2015 at 12:36:00 PM UTC-7, wrote:
Ditto the above question-- unless the L/D ratio is really poor, the stall speed in a 45-degree banked turn ought to be about 1.189* the stall speed in the same configuration in wings-level flight. S

This is probably an unneeded addition, but for the sake of completeness, I would change "45-degree banked turn" to "45-degree banked LEVEL turn in still air". Lots of us fly 45-degree banked turns in thermals without pressing the stick back much.

Is there some suggestion here that the glider behaves differently in an updraft? Surely not.

Re "level"-- in a glider? If the flight path is horizontal with respect to the airmass, you are decelerating, not in a steady-state situation. To maintain horizontal flight, you'll have to keep moving the stick aft at a certain rate, as the airspeed bleeds off. Will the glider reach the stall angle-of-attack at a different airspeed than if you just ease the stick ever-so-slowly aft, so that the rate of deceleration is negligible, and you stay very close to a steady-state glide?

At any given instant of time where the glider is at some given angle-of-attack, the L/W and Na/W values (Na=Net Aerodynamic Force) will be slightly smaller in the steady-state glide than in decelerating level flight, so the airspeed at the stall angle-of-attack will be slightly less in the steady-state glide than in decelerating horizontal flight, but the difference will be trivial for normal sailplane L/D ratios. In the decelerating level flight case, the L/W value will be the same as it is on the top line (infinite L/D) of the table I posted on June 25, and the Na/W ratio will be slightly larger. For any given glider at some given angle-of-attack, the ratio between L, D, and Na will be the same in the decelerating level flight case as in the steady-state glide case. Looking at the table I posted June 25, for glide ratios of 10:1 or better you can see that there is no discernible difference between L and Na. There's also no discernible difference between the value of L, or Na, at a 10:1 L/D, and L, or Na, at an infinite L/D. So I'd say there's no way you'll be able to tell the difference between the stall speed at the slow deceleration rate required to maintain exactly horizontal flight in still air, versus the extremely slow deceleration rate you'd use to reach the stall angle-of-attack while staying very close to a steady-state glide.

S

On Monday, June 1, 2015 at 9:09:34 PM UTC-6, wrote:
Either a large majority of us are unaware that we are on the verge of death every time we adjust our spoilers while landing, or some people are being taught this and causing them to unnecessarily fear spoilers and using them to their full degree of helpfulness and effectiveness.

Here's a video I made trying to demonstrate what happens when you use spoilers while turning...nothing! I was a little bit of a punchy mood while taking the video - sorry for being a little bit snarky.

https://youtu.be/tC-Yqp-uHo0

Here is the description of the video:
I had been flying gliders for almost 20 years before someone on the internet wrote to me that adjusting spoilers while turning to land can kill you. What?!?! Supposedly, because your inside wing is flying so much slower than the outside in a turn, a little spoiler can spoil the whole day. I have been freely adjusting my spoilers as needed during landing my entire flying career. Why have none of the glider manuals I have ever read warned about this?

I've asked multiple CFI-G's (glider instructors) and they are also baffled this is being taught to students. I've now heard from 4-5 different people (all pilots outside of USA) that have been taught this by their instructors. Time to try to debunk this. Glider is an ASW-27B flown dry at the time of this video out of Cedar Valley, Utah.

Thanks for your insights and comments to try to help clarify the confusion.

On Tuesday, June 2, 2015 at 7:52:00 AM UTC-7, Bill D wrote:
On Monday, June 1, 2015 at 9:09:34 PM UTC-6, wrote:
Either a large majority of us are unaware that we are on the verge of death every time we adjust our spoilers while landing, or some people are being taught this and causing them to unnecessarily fear spoilers and using them to their full degree of helpfulness and effectiveness.

Here's a video I made trying to demonstrate what happens when you use spoilers while turning...nothing! I was a little bit of a punchy mood while taking the video - sorry for being a little bit snarky.

https://youtu.be/tC-Yqp-uHo0

Here is the description of the video:
I had been flying gliders for almost 20 years before someone on the internet wrote to me that adjusting spoilers while turning to land can kill you. What?!?! Supposedly, because your inside wing is flying so much slower than the outside in a turn, a little spoiler can spoil the whole day. I have been freely adjusting my spoilers as needed during landing my entire flying career. Why have none of the glider manuals I have ever read warned about this?

I've asked multiple CFI-G's (glider instructors) and they are also baffled this is being taught to students. I've now heard from 4-5 different people (all pilots outside of USA) that have been taught this by their instructors. Time to try to debunk this. Glider is an ASW-27B flown dry at the time of this video out of Cedar Valley, Utah.

Thanks for your insights and comments to try to help clarify the confusion.
Bruno - B4

This is what I told Bruno earlier in a phone call.

Opening spoilers increases the stall speed something like 4 knots. Most flight manuals provide specific guidance to this effect.

A moderately banked turn sets up a speed difference across the wing span (the outside wing tip is going faster than the inside tip in a turn). This difference is in the range of 10 knots. This can be determined mathimatically from airspeed and bank angle.

So, with the inside wing tip flying at roughly 5 knots less than the ASI says and the spoiler on that wing increasing the stall speed roughly 4 knots, you have reduced your stall margin on the inside wing tip about 9 knots. That can be significant.

Whether that matters depends on the airspeed. A low airspeed turn to final with spoilers open can put the inside wing right on the edge of a stall. If you fly patterns at the speed your instructor taught you to, you'll have adequate stall margin even with the spoilers open. Pull the speed down below the yellow triangle in that turn and you could be in trouble. Add gusty winds and it gets much worse.

So, it is correct to teach "no spoilers in a turn"? I think that's an over reaction based on a misunderstanding. A better approach is to teach airspeed control and using that control to maintain at least 1.5 x Vso + 1/2 the gust speed until stabilized on the final approach with wings level. Only then can airspeed be safely reduced to the yellow traingle approach speed..

That's my $0.02

I would never fly a pattern at so slow a speed that opening the spoilers (or 4 knots error in airspeed) would cause a stall. If you do so, some day you are very likely to stall or spin, spoilers or no spoilers, in anything but perfectly calm conditions. Are 4 knot gusts so uncommon in the world?

That's a pretty good $0.02, Bill.

There's a trend to teach people to stay out of trouble by being overly
conservative rather than to teach proper theory and practice.
Disappointingly this leads to a bunch of mediocre pilots and, I believe,
more accidents.

As to using dive brakes, I open them as I begin my final turn (a
descending 180 deg turn to final) and I use them during the turn as I
see fit. Once on final I use them less, maybe 1/2 to 3/4 until just
before touchdown when I open them fully. I pick my touchdown point on
downwind and fly to that point. Never do I fly to a landmark and then
make a turn to base, fly to another landmark and turn to final. That's
just asking for trouble.

My $0.02.

On 6/2/2015 8:51 AM, Bill D wrote:

On Monday, June 1, 2015 at 9:09:34 PM wrote:
Either a large majority of us are unaware that we are on the verge of death every time we adjust our spoilers while landing, or some people are being taught this and causing them to unnecessarily fear spoilers and using them to their full degree of helpfulness and effectiveness.

Here's a video I made trying to demonstrate what happens when you use spoilers while turning...nothing! I was a little bit of a punchy mood while taking the video - sorry for being a little bit snarky.

https://youtu.be/tC-Yqp-uHo0

Here is the description of the video:
I had been flying gliders for almost 20 years before someone on the internet wrote to me that adjusting spoilers while turning to land can kill you. What?!?! Supposedly, because your inside wing is flying so much slower than the outside in a turn, a little spoiler can spoil the whole day. I have been freely adjusting my spoilers as needed during landing my entire flying career. Why have none of the glider manuals I have ever read warned about this?

I've asked multiple CFI-G's (glider instructors) and they are also baffled this is being taught to students. I've now heard from 4-5 different people (all pilots outside of USA) that have been taught this by their instructors. Time to try to debunk this. Glider is an ASW-27B flown dry at the time of this video out of Cedar Valley, Utah.

Thanks for your insights and comments to try to help clarify the confusion.
Bruno - B4
This is what I told Bruno earlier in a phone call.

Opening spoilers increases the stall speed something like 4 knots. Most flight manuals provide specific guidance to this effect.

A moderately banked turn sets up a speed difference across the wing span (the outside wing tip is going faster than the inside tip in a turn). This difference is in the range of 10 knots. This can be determined mathimatically from airspeed and bank angle.

So, with the inside wing tip flying at roughly 5 knots less than the ASI says and the spoiler on that wing increasing the stall speed roughly 4 knots, you have reduced your stall margin on the inside wing tip about 9 knots. That can be significant.

Whether that matters depends on the airspeed. A low airspeed turn to final with spoilers open can put the inside wing right on the edge of a stall. If you fly patterns at the speed your instructor taught you to, you'll have adequate stall margin even with the spoilers open. Pull the speed down below the yellow triangle in that turn and you could be in trouble. Add gusty winds and it gets much worse.

So, it is correct to teach "no spoilers in a turn"? I think that's an over reaction based on a misunderstanding. A better approach is to teach airspeed control and using that control to maintain at least 1.5 x Vso + 1/2 the gust speed until stabilized on the final approach with wings level. Only then can airspeed be safely reduced to the yellow traingle approach speed.

That's my $0.02


On 6/2/2015 8:51 AM, Bill D wrote:
On Monday, June 1, 2015 at 9:09:34 PM UTC-6, wrote:
Either a large majority of us are unaware that we are on the verge of death every time we adjust our spoilers while landing, or some people are being taught this and causing them to unnecessarily fear spoilers and using them to their full degree of helpfulness and effectiveness.

Here's a video I made trying to demonstrate what happens when you use spoilers while turning...nothing! I was a little bit of a punchy mood while taking the video - sorry for being a little bit snarky.

https://youtu.be/tC-Yqp-uHo0

Here is the description of the video:
I had been flying gliders for almost 20 years before someone on the internet wrote to me that adjusting spoilers while turning to land can kill you. What?!?! Supposedly, because your inside wing is flying so much slower than the outside in a turn, a little spoiler can spoil the whole day. I have been freely adjusting my spoilers as needed during landing my entire flying career. Why have none of the glider manuals I have ever read warned about this?

I've asked multiple CFI-G's (glider instructors) and they are also baffled this is being taught to students. I've now heard from 4-5 different people (all pilots outside of USA) that have been taught this by their instructors. Time to try to debunk this. Glider is an ASW-27B flown dry at the time of this video out of Cedar Valley, Utah.

Thanks for your insights and comments to try to help clarify the confusion.
Bruno - B4
This is what I told Bruno earlier in a phone call.

Opening spoilers increases the stall speed something like 4 knots. Most flight manuals provide specific guidance to this effect.

A moderately banked turn sets up a speed difference across the wing span (the outside wing tip is going faster than the inside tip in a turn). This difference is in the range of 10 knots. This can be determined mathimatically from airspeed and bank angle.

So, with the inside wing tip flying at roughly 5 knots less than the ASI says and the spoiler on that wing increasing the stall speed roughly 4 knots, you have reduced your stall margin on the inside wing tip about 9 knots. That can be significant.

Whether that matters depends on the airspeed. A low airspeed turn to final with spoilers open can put the inside wing right on the edge of a stall. If you fly patterns at the speed your instructor taught you to, you'll have adequate stall margin even with the spoilers open. Pull the speed down below the yellow triangle in that turn and you could be in trouble. Add gusty winds and it gets much worse.

So, it is correct to teach "no spoilers in a turn"? I think that's an over reaction based on a misunderstanding. A better approach is to teach airspeed control and using that control to maintain at least 1.5 x Vso + 1/2 the gust speed until stabilized on the final approach with wings level. Only then can airspeed be safely reduced to the yellow traingle approach speed.

That's my $0.02

--
Dan Marotta

I noted in one of the responses to Bruno's video, and I'm paraphrasing
here, that you should never use spoilers in the base turn unless
something unusual happens, i.e., an unexpected thermal. I submit that
doing something only seldomly in an unusual case is more dangerous than
doing it all the time and being well-practiced.

On 6/2/2015 9:47 AM, Dan Marotta wrote:
That's a pretty good $0.02, Bill.

There's a trend to teach people to stay out of trouble by being overly
conservative rather than to teach proper theory and practice.
Disappointingly this leads to a bunch of mediocre pilots and, I believe,
more accidents.

As to using dive brakes, I open them as I begin my final turn (a
descending 180 deg turn to final) and I use them during the turn as I
see fit. Once on final I use them less, maybe 1/2 to 3/4 until just
before touchdown when I open them fully. I pick my touchdown point on
downwind and fly to that point. Never do I fly to a landmark and then
make a turn to base, fly to another landmark and turn to final. That's
just asking for trouble.

My $0.02.

On 6/2/2015 8:51 AM, Bill D wrote:
On Monday, June 1, 2015 at 9:09:34 PM wrote:
Either a large majority of us are unaware that we are on the verge of death every time we adjust our spoilers while landing, or some people are being taught this and causing them to unnecessarily fear spoilers and using them to their full degree of helpfulness and effectiveness.

Here's a video I made trying to demonstrate what happens when you use spoilers while turning...nothing! I was a little bit of a punchy mood while taking the video - sorry for being a little bit snarky.

https://youtu.be/tC-Yqp-uHo0

Here is the description of the video:
I had been flying gliders for almost 20 years before someone on the internet wrote to me that adjusting spoilers while turning to land can kill you. What?!?! Supposedly, because your inside wing is flying so much slower than the outside in a turn, a little spoiler can spoil the whole day. I have been freely adjusting my spoilers as needed during landing my entire flying career. Why have none of the glider manuals I have ever read warned about this?

I've asked multiple CFI-G's (glider instructors) and they are also baffled this is being taught to students. I've now heard from 4-5 different people (all pilots outside of USA) that have been taught this by their instructors. Time to try to debunk this. Glider is an ASW-27B flown dry at the time of this video out of Cedar Valley, Utah.

Thanks for your insights and comments to try to help clarify the confusion.
Bruno - B4
This is what I told Bruno earlier in a phone call.

Opening spoilers increases the stall speed something like 4 knots. Most flight manuals provide specific guidance to this effect.

A moderately banked turn sets up a speed difference across the wing span (the outside wing tip is going faster than the inside tip in a turn). This difference is in the range of 10 knots. This can be determined mathimatically from airspeed and bank angle.

So, with the inside wing tip flying at roughly 5 knots less than the ASI says and the spoiler on that wing increasing the stall speed roughly 4 knots, you have reduced your stall margin on the inside wing tip about 9 knots. That can be significant.

Whether that matters depends on the airspeed. A low airspeed turn to final with spoilers open can put the inside wing right on the edge of a stall. If you fly patterns at the speed your instructor taught you to, you'll have adequate stall margin even with the spoilers open. Pull the speed down below the yellow triangle in that turn and you could be in trouble. Add gusty winds and it gets much worse.

So, it is correct to teach "no spoilers in a turn"? I think that's an over reaction based on a misunderstanding. A better approach is to teach airspeed control and using that control to maintain at least 1.5 x Vso + 1/2 the gust speed until stabilized on the final approach with wings level. Only then can airspeed be safely reduced to the yellow traingle approach speed.

That's my $0.02


On 6/2/2015 8:51 AM, Bill D wrote:
On Monday, June 1, 2015 at 9:09:34 PM wrote:
Either a large majority of us are unaware that we are on the verge of death every time we adjust our spoilers while landing, or some people are being taught this and causing them to unnecessarily fear spoilers and using them to their full degree of helpfulness and effectiveness.

Here's a video I made trying to demonstrate what happens when you use spoilers while turning...nothing! I was a little bit of a punchy mood while taking the video - sorry for being a little bit snarky.

https://youtu.be/tC-Yqp-uHo0

Here is the description of the video:
I had been flying gliders for almost 20 years before someone on the internet wrote to me that adjusting spoilers while turning to land can kill you. What?!?! Supposedly, because your inside wing is flying so much slower than the outside in a turn, a little spoiler can spoil the whole day. I have been freely adjusting my spoilers as needed during landing my entire flying career. Why have none of the glider manuals I have ever read warned about this?

I've asked multiple CFI-G's (glider instructors) and they are also baffled this is being taught to students. I've now heard from 4-5 different people (all pilots outside of USA) that have been taught this by their instructors. Time to try to debunk this. Glider is an ASW-27B flown dry at the time of this video out of Cedar Valley, Utah.

Thanks for your insights and comments to try to help clarify the confusion.
Bruno - B4
This is what I told Bruno earlier in a phone call.

Opening spoilers increases the stall speed something like 4 knots. Most flight manuals provide specific guidance to this effect.

A moderately banked turn sets up a speed difference across the wing span (the outside wing tip is going faster than the inside tip in a turn). This difference is in the range of 10 knots. This can be determined mathimatically from airspeed and bank angle.

So, with the inside wing tip flying at roughly 5 knots less than the ASI says and the spoiler on that wing increasing the stall speed roughly 4 knots, you have reduced your stall margin on the inside wing tip about 9 knots. That can be significant.

Whether that matters depends on the airspeed. A low airspeed turn to final with spoilers open can put the inside wing right on the edge of a stall. If you fly patterns at the speed your instructor taught you to, you'll have adequate stall margin even with the spoilers open. Pull the speed down below the yellow triangle in that turn and you could be in trouble. Add gusty winds and it gets much worse.

So, it is correct to teach "no spoilers in a turn"? I think that's an over reaction based on a misunderstanding. A better approach is to teach airspeed control and using that control to maintain at least 1.5 x Vso + 1/2 the gust speed until stabilized on the final approach with wings level. Only then can airspeed be safely reduced to the yellow traingle approach speed.

That's my $0.02

--
Dan Marotta

--
Dan Marotta

On Tuesday, June 2, 2015 at 9:55:37 AM UTC-6, Dan Marotta wrote:
I submit that doing something only seldomly in an unusual case is
more dangerous than doing it all the time and being well-practiced.


Do you stall the aircraft on final frequently so you can be good at it?

An aircraft recovers from a stall at any altitude, in the same manner
and with the same loss of altitude, given the same initial conditions
and recovery controls.Â* Of course, closer to the ground a pilot is more
inclined to pull harder on the stick as the ground rushes up, preventing
recovery.Â* Practicing at altitude will train the pilot to use the
correct amount of pressure, minimizing altitude loss.

Of course, practicing NOT stalling is more beneficial.Â* Learning how far
you can push your aircraft without stalling is, in my opinion, the
better way.Â* And, to address the subject line, I use spoilers throughout
the turn as needed.Â* I think a pilot who applies a particular amount of
spoiler and holds that throughout the pattern to landing is leaving a
lot of performance on the table.

On 1/4/2018 11:35 PM, wrote:
On Tuesday, June 2, 2015 at 9:55:37 AM UTC-6, Dan Marotta wrote:
I submit that doing something only seldomly in an unusual case is
more dangerous than doing it all the time and being well-practiced.

Do you stall the aircraft on final frequently so you can be good at it?

--
Dan, 5J

On Tue, 02 Jun 2015 09:47:50 -0600, Dan Marotta wrote:

Never do I fly to a landmark and then make a turn to base, fly to
another landmark and turn to final. That's just asking for trouble.

Surely that can only work for a pilot who never has and never will land
anywhere but his home field.

UK training specifically warns against that trick.

My 2p.


--
martin@ | Martin Gregorie
gregorie. | Essex, UK
org |