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I was watching James May's Toy Stories, particularly the one where they try to fly a glider across the English Channel. In the middle of the episode they mention a glider that was used for training in the RAF during the 1950s. It was called the Slingsby Swallow, and it looks like this:

enter image description here

When I saw those pieces of metal coming out of the wings I was...surprised. At first I thought they were split flaps but then I found another picture and became even more confused:

enter image description here

The devices are clearly coming out of the top and bottom of the wing, not the trailing edge.

Does anyone know what these are and what they are used for on the Slingsby Swallow (or any other aircraft the employs a similar device)? My only guess is that they are some sort of spoiler that may reduce lift to help get the glider on the ground...but I'm uncertain.

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  • $\begingroup$ @FreeMan I just wish he'd make more! There are only, like, 10 as far as I can tell. $\endgroup$
    – Jae Carr
    Commented Jul 13, 2015 at 16:28
  • $\begingroup$ TheTvDB lists 12 episodes from Dec '05 - Dec '14. 6 "Regular Series" episodes, and 6 "Special" episodes. +eleventy on making more! But... we're wandering waaaaay off topic... $\endgroup$
    – FreeMan
    Commented Jul 13, 2015 at 16:51
  • $\begingroup$ Just a clarification because it is not mentioned explicitly in the answers: every single glider built in the last 70 years has them. $\endgroup$
    – Martin Argerami
    Commented Mar 11, 2016 at 1:29

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You're correct -- they're speedbrakes, often referred to as spoilers, and are retracted when striving for efficient flight, but are generally extended in the landing pattern so that you have correction available if you start to get slightly low. Also frequently extended when the glider is left on the ground to reduce the effect of gusty winds & the likelihood that they would lift a wing.

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  • $\begingroup$ Should that read "generally retracted in the landing pattern..."? That way you can extend them to help slow down if needed. I'm not a glider pilot so I might be wrong here :-) $\endgroup$
    – Padraig H
    Commented Jul 13, 2015 at 2:50
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    $\begingroup$ @aviationstats I'm not a pilot of any kind, but I think the post is correct -- if you plan to land with them extended, but get low, you can retract them to return to the planned flight profile. $\endgroup$
    – Jeffrey Bosboom
    Commented Jul 13, 2015 at 3:02
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    $\begingroup$ @aviationstats Not a typo in my answer -- "generally extended in the landing pattern" is what I meant to post. In a glider, you have various ways of getting rid of energy (extend downwind, use spoilers, sideslip), but no way to create it. So you plan your pattern to start at "this" point & "this" altitude, fly with partial or full spoilers, turn base "here," and everything will work out. Then, if you find you're a bit low, you retract the spoilers until you determine that you're back on path. $\endgroup$
    – Ralph J ♦
    Commented Jul 13, 2015 at 3:45
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    $\begingroup$ To clarify, I agree with @RalphJ but I was taught to normally not use the spoilers on final turns, etc as you can lose height very rapidly! (OK in exceptional cases though.) Ideally a perfectly judged circuit would be finishing final turn in a position to use half spoiler for the final approach - you can then use less or more as necessary. It's also OK to use them anytime on downwind or base leg if high in the circuit. $\endgroup$
    – Andy
    Commented Jul 13, 2015 at 10:44
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    $\begingroup$ @RalphJ Interesting analogy is when sailing through a crowded mooring field with lots of anchored boats I was always taught to aim a course at the stern of a moored boat. The boats point into the wind & a sailboat has several ways to fall away from the wind but it's much harder to sail closer upwind. If you try to pass an anchored boat close to the bow of an anchored boat & have to adjust course it can get very hard to adjust course upwind. $\endgroup$
    – curious_cat
    Commented Aug 30, 2015 at 18:28
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If you observe the image below, in the marked areas, you'll see a rectangular patch (it's very faint): Slingsby Swallow LR by Borderglider - Own work. Licensed under CC BY 3.0 via Wikimedia Commons

These are the places over and below the wing where the "Devices" you mentioned are housed. These devices are called Dive Brakes. They are used as spoilers to increase the drag while flying so as to lose altitude by increasing the drag (and hence the name). These can be retracted when not required, and deployed when required. The patches in the image are the housings where these are actually deployed from and retracted back to. And from Ralph J's answer, they can be left deployed when the plane is on ground, as its a very light plane and gusts and winds can actually cause the plane to lift if enough drag is not there.

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    $\begingroup$ I don't think I've ever heard them being called “dive brakes” on anything else than a dive bomber. They are called “spoilers” or “air brakes”. The later is more general term; “spoilers” extend from the upper wing surface, “air brakes” may extend on other places as well. And note that most “dive brakes” actually are not “spoilers”, because “spoilers” spoil lift and a dive bomber is going to need a lot of lift to pull out of the dive. $\endgroup$
    – Jan Hudec
    Commented Jul 13, 2015 at 12:13
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    $\begingroup$ I researched a bit and the wiki article clearly states this. :( $\endgroup$
    – Victor Juliet
    Commented Jul 13, 2015 at 12:28
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    $\begingroup$ Interesting to note the Slingsby Swallow's wikipedia page does use the term "Dive brakes". I've never heard that term used on any glider, though if Slingsby used that name there may be documentary evidence... Note "Spoiler" and "Airbrake" tend to be used casually by pilots regardless of the actual effect of the device. Properly, spoilers don't reduce speed much but disturb airflow (especially above the wing) and reduce lift, increasing the descent angle. They are used for pinpoint landings, not speed limiting. True spoilers might not reduce speed very much in a near vertical dive... $\endgroup$
    – Andy
    Commented Jul 13, 2015 at 14:06
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    $\begingroup$ I own a Swallow and in the book of data that comes with it from Slingsby they do use the term dive brakes. Apparently the glider will not exceed Vne with them fully extended. $\endgroup$
    – user10023
    Commented Aug 30, 2015 at 6:13
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    $\begingroup$ Nice high-viz color scheme-- $\endgroup$
    – quiet flyer
    Commented Jan 19, 2021 at 21:05
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When I saw those pieces of metal coming out of the wings I was...surprised.

I don't think anyone has pointed out yet that those spoilers/airbrakes/dive brakes are constructed mostly of out wood, not metal. As is the rest of the Slingsby Swallow.

Some gliders (e.g. Schweizer 2-22/ 2-33/ 1-26) use a different style of spoiler/airbrake where the surface is hinged on its leading edge, and lays down flat in a slight recess on the wing when not in use, rather than rising vertically up out of a deep "well" or slot in the wing.

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