Debunking Glider Spoiler Turns Causing Spin Thinking

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?