Debunking Glider Spoiler Turns Causing Spin Thinking

On Tuesday, June 2, 2015 at 8:15:06 AM UTC+1, Kevin Neave wrote:
Hi John,

If you're having to use the airbrakes everytime have you considered opening
up the circuit? Or is there something at Portmoak that prevents this?

I'm quite happy to use (or have my pupils use) airbrakes during final turn
if they were using them on base leg. Less happy for pupils to open them
during the turn. The final turn probably takes about 5 seconds so why not
wait 'til wings are level and the picture has stabilised before opening the
brakes. Why increase the workload for the sake of a few seconds?

KN

I respect the standard teaching for pupils and it is a sensible approach for them and for low performance gliders and others with very powerful airbrakes - but take a look at pictures of experienced pilots in high performance gliders turning onto finals and see how many of them have the airbrakes cracked open. I am not alone. BTW I didn't say I opened them during the final turn - for me on a normal circuit pattern the height judgement and adjustment starts somewhere on the base leg. During the final turn my attention is devoted to airspeed and lookout rather than height as I have already been thinking about that. I believe that is a safer practice for me.

JG

I was taught to open the airbrakes to a certain point ⅓-½ at the right time in the pattern to not change the setting , unless of course necessary. If you fly a power plane, do you pump the throttle in the pattern?

On Tuesday, June 2, 2015 at 2:42:53 AM UTC-5, Surge wrote:


The "no spoilers during turns" rule makes sense if you're flying the turn too slowly and not taking the increased stall speed into account.

Example: According to the POH, a 650kg (1430lbs) Twin Astir stalls at about 90km (49 knots) with spoilers fully deployed. Add a 45 degree bank and the stall speed increases to 126 km/h (68 knots).
This is usually above the normal approach speed flown during circuits so I can conceive that a pilot who is not "ahead of the glider" could possibly fly too slowly during the turn. Throw in an uncoordinated turn and things could go wrong very quickly depending on glider type.

This is just the expected % increase in stall speed due to the loading imposed by the turn, right? But remember, the turn doesn't really "impose" the extra loading. The extra loading (lift) is imposed by either an increase in airspeed (safe), or by the pilot moving the stick aft to try to maintain the old airspeed (unsafe). If the pilot doesn't move the stick aft as he increases the bank angle, it will take a bit of time (a few seconds) for the airspeed (and loading) to increase, but there will be no risk of stall. During these few seconds, the flight path will curve slightly downward because the wing is not producing the full load "required" by the bank angle. The same would happen if the pilot opened the spoilers while holding a constant (or zero) bank angle-- the wing won't stall unless the pilot increases the angle-of-attack.

I guess what I'm trying to say is-- one of the key points of Tom Knauff's books is that turns aren't unsafe as long as you don't move the stick aft. The same could be said of spoiler usage. Opening the spoiler won't produce a stall as long as the pilot doesn't move the stick aft to increase the wing's angle-of-attack.

Banking and opening spoilers aren't completely analogous though. As you increase bank angle, you must move the stick further aft just to hold the SAME angle-of-attack that you had at a shallower bank angle. To actually increase the angle-of-attack, you have to move the stick even FURTHER aft. This is a point in the pilot's favor, in terms of avoiding accidental stalls, so long as the pilot has some awareness of what he is doing with the stick. Again this comes up in Knauff's books and seminars. This has to do with the curving nature of the airflow in a turn, and the resulting change in airflow at the tail. The same is not true when you increase loading per unit wing area in other ways-- like by adding water ballast, or by "removing" part of the wing (opening spoilers).

I guess there's another factor that could be relevant. In some gliders, opening the spoilers creates a large trim change, forcing you to move the stick just to hold the same angle-of-attack that you had before opening them. If you have plenty of airspeed-- no problem. If you have less airspeed and you are going by the theory that you won't stall because you aren't doing the wrong thing with the stick, maybe you could have a problem. Even if angle-of-attack tends to stay constant as the spoilers are opened, the resulting downcurve of the flight path could tempt a pilot to haul back on the stick to arrest it. At the end of the day I guess you'd better have plenty of airspeed if you are making radical changes in spoiler setting.

S

Hmmm.... never heard of this either. Flying for ~40 years (in sailplanes) & a CFIG for 8 years.
Maybe the "original issue" was sailplanes that had a noticeable pitch attitude change with change in spoliers/dive brakes (add spoliers, nose pitches up, thus slower/higher AoA?). Rather than point that out, the decision was made to not use them in a turn.

Kind of like training that, "Go fast in the pattern so you don't stall/spin", rather than stall/spin training & recognition.

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 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 |

On Tuesday, June 2, 2015 at 9:47:56 AM UTC-6, 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 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.