Moderators: richierich, ua900, PanAm_DC10, hOMSaR

 
convair880mfan
Topic Author
Posts: 223
Joined: Fri Jun 25, 2021 12:33 am

Size of speed brakes[spoilers] on airliners?

Wed Aug 25, 2021 3:28 pm

It might just be an optical illusion, but as a passenger looking at a wing from inside an airliner, it seems like the speed brakes[spoilers] on Boeing jetliners are much larger than those on some McDonnell Douglas jetliners. The DC-10 and MD-11 may be exceptions to this.

I haven't flown enough on Airbus jetliners to have an opinion about those aircraft. The speed brakes[spoilers] on the various DC-9 and MD-80 series aircraft seem to have less height when they are extended. I think the DC-8 might have this too?

I wonder how engineers determine the size of these panels?
 
User avatar
AirKevin
Posts: 843
Joined: Wed Apr 26, 2017 2:18 am

Re: Size of speed brakes[spoilers] on airliners?

Wed Aug 25, 2021 4:28 pm

One other one I would like to add is they don't all deploy at the same time or at the same angle, either. On the 747, for instance, out of the four outboard spoilers on each wing, the two inboard spoilers deploy first, followed by the two outboard spoilers. On the 777, not only do they all deploy at different times, but there's the one spoiler panel on each wing that deploys at a smaller angle compared to the rest. I wonder how they determine that.
 
User avatar
BWIAirport
Posts: 1089
Joined: Thu Jun 23, 2016 10:29 pm

Re: Size of speed brakes[spoilers] on airliners?

Wed Aug 25, 2021 5:27 pm

AirKevin wrote:
One other one I would like to add is they don't all deploy at the same time or at the same angle, either. On the 747, for instance, out of the four outboard spoilers on each wing, the two inboard spoilers deploy first, followed by the two outboard spoilers. On the 777, not only do they all deploy at different times, but there's the one spoiler panel on each wing that deploys at a smaller angle compared to the rest. I wonder how they determine that.

That's a good question, just like the one outboard spoiler on the 737NG and Max that deploys higher than the rest. Almost seems random, although I'm sure it's not.
 
User avatar
Horstroad
Posts: 597
Joined: Thu Apr 08, 2010 8:19 pm

Re: Size of speed brakes[spoilers] on airliners?

Wed Aug 25, 2021 6:35 pm

AirKevin wrote:
On the 777, not only do they all deploy at different times, but there's the one spoiler panel on each wing that deploys at a smaller angle compared to the rest. I wonder how they determine that.

I can't tell you what they were thinking... but the spoiler/speedbrake schedule is actually quite wild on the 777.


For spoiler operation there are 4 schedules.

Spoiler panels 1, 2, 3, 12, 13 and 14 can deflect up to 63° for ground speedbrake operation and 47° for all other operations.
Spoiler panels 4 and 11 deflect up to 45° at all times. They are the mechanical backup in case FBW fails.
Spoiler panels 5 and 10 can deflect up to 63° for ground speedbrake operation and 47° for low speed lateral control. They are not used for high speed lateral control or as inflight speedbrakes.
Spoiler panels 6, 7, 8 and 9 can deflect up to 63° for ground speedbrake operation, 15° for inflight speedbrake operation and 22° for lateral control.

When the speedbrake function is inhibited, for example when the pitch attitude is more than 2° or the first 1.25 seconds after WOW, spoiler panels 2, 5, 10 and 13 do not deploy. 6, 7, 8 and 9 are limited to 20°. Spoiler panels 4 and 11 are always deployed to full 45° when the speedbrake lever is >54°.


So in summary:

For roll control all spoilers operate corresponding to the control wheel inputs up to 47°. Except the two inboard spoiler panels on each side, they can deflect only up to 22°. And except the ones one position further outboard, they do not deflect at high speeds (depending on altitude the cutoff is between 160 and 275 knots). And except one position even further outboard... they deflect only up to 45°.

For speedbrake control in flight, all spoiler panels deflect up to 47° corresponding to the speedbrake lever position. Except the two inboard spoiler panels on each side, they deflect only to 15°. And except the ones one position further outboard, they do not deploy at all. And except one position even further outboard... they deflect to 45° when the speedbrake lever is >54°.

For ground speedbrake control in the first 1.25 seconds the two inboard spoiler panels on each side deploy to 20°. One position further outboard does not deploy. One position even further outboard deploys to 45°. The next one deploys to 63°, the next one does not deploy, the outermost one deploys to 63°. After 1.25 seconds all spoiler panels deploy to 63°, except the ones right in the center of each wing, as they are limited to 45°.
This can be seen here: https://youtu.be/KA_igkOnxT0?t=17


Of course this is all in normal mode. It's a bit different in secondary and direct mode.


The spoiler panels are counted 1 through 14 from left to right.

LH outbd               LH inbd      |      RH inbd                        RH outbd
1   2   3   4   5          6   7         |         8   9          10   11   12   13   14





btw, the spoiler panels are 1.1m x 2.0m for the inbd spoilers and 0.7m by 2.0m for the outbd spoilers.
 
hitower3
Posts: 240
Joined: Fri Oct 21, 2016 9:55 am

Re: Size of speed brakes[spoilers] on airliners?

Wed Aug 25, 2021 7:35 pm

Highly interesting topic indeed!
To contrast with the complexity of the 777 spoiler system, here is the observed control logic in the Fokker 70/100:
When weight on wheels: all spoilers up.
No speed brake or aileron augmentation functions to my knowledge.
There is a speed brake in the tail cone though.
 
User avatar
BWIAirport
Posts: 1089
Joined: Thu Jun 23, 2016 10:29 pm

Re: Size of speed brakes[spoilers] on airliners?

Wed Aug 25, 2021 8:12 pm

Horstroad wrote:
AirKevin wrote:
On the 777, not only do they all deploy at different times, but there's the one spoiler panel on each wing that deploys at a smaller angle compared to the rest. I wonder how they determine that.
.

Thanks for an excellent write-up. Certainly validates and quantifies everything I've noticed about the complex spoiler system on the 777.
I must say, I did not believe you for a second when you said the outboard spoilers were 2 feet, 3 inches tall. Until I went and got a tape measure, watched a video of a control surface check on YouTube, and compared it for myself.
 
User avatar
Horstroad
Posts: 597
Joined: Thu Apr 08, 2010 8:19 pm

Re: Size of speed brakes[spoilers] on airliners?

Sat Aug 28, 2021 11:04 am

BWIAirport wrote:
I must say, I did not believe you for a second when you said the outboard spoilers were 2 feet, 3 inches tall.

For comparison, the MD11 spoilers are 0.67m by 1.85m (26.5" x 73") for the outboard spoiler panels (4 on each wing) and 0.47m by 3.05m (18.5" x 120") for the inboard spoiler panels (one on each wing).
On the 777 that's 5.21% of the total wing area (5.32% without raked wing tips), on the MD-11 it's 3.79%. It would be interesting to so figures for other airliners for comparison.
 
LH707330
Posts: 2513
Joined: Fri Jun 15, 2012 11:27 pm

Re: Size of speed brakes[spoilers] on airliners?

Sat Aug 28, 2021 4:15 pm

Horstroad wrote:
BWIAirport wrote:
I must say, I did not believe you for a second when you said the outboard spoilers were 2 feet, 3 inches tall.

For comparison, the MD11 spoilers are 0.67m by 1.85m (26.5" x 73") for the outboard spoiler panels (4 on each wing) and 0.47m by 3.05m (18.5" x 120") for the inboard spoiler panels (one on each wing).
On the 777 that's 5.21% of the total wing area (5.32% without raked wing tips), on the MD-11 it's 3.79%. It would be interesting to so figures for other airliners for comparison.

It'd also be good to look at spoiler area/ton of GW to get a measure of how much spoiling work they're expected to do. The A350-1000, for example, has a lower ceiling than the -900 in part because the wing is mostly the same but the plane is heavier, so meeting the emergency descent criteria was trickier. Similar story with the 747-8: more weight, same spoiler size, lower-drag reprofiled wing.
 
trent768
Posts: 209
Joined: Wed Feb 03, 2016 5:32 pm

Re: Size of speed brakes[spoilers] on airliners?

Mon Aug 30, 2021 9:59 am

Horstroad wrote:
AirKevin wrote:
On the 777, not only do they all deploy at different times, but there's the one spoiler panel on each wing that deploys at a smaller angle compared to the rest. I wonder how they determine that.

I can't tell you what they were thinking... but the spoiler/speedbrake schedule is actually quite wild on the 777.


For spoiler operation there are 4 schedules.

Spoiler panels 1, 2, 3, 12, 13 and 14 can deflect up to 63° for ground speedbrake operation and 47° for all other operations.
Spoiler panels 4 and 11 deflect up to 45° at all times. They are the mechanical backup in case FBW fails.
Spoiler panels 5 and 10 can deflect up to 63° for ground speedbrake operation and 47° for low speed lateral control. They are not used for high speed lateral control or as inflight speedbrakes.
Spoiler panels 6, 7, 8 and 9 can deflect up to 63° for ground speedbrake operation, 15° for inflight speedbrake operation and 22° for lateral control.

When the speedbrake function is inhibited, for example when the pitch attitude is more than 2° or the first 1.25 seconds after WOW, spoiler panels 2, 5, 10 and 13 do not deploy. 6, 7, 8 and 9 are limited to 20°. Spoiler panels 4 and 11 are always deployed to full 45° when the speedbrake lever is >54°.


So in summary:

For roll control all spoilers operate corresponding to the control wheel inputs up to 47°. Except the two inboard spoiler panels on each side, they can deflect only up to 22°. And except the ones one position further outboard, they do not deflect at high speeds (depending on altitude the cutoff is between 160 and 275 knots). And except one position even further outboard... they deflect only up to 45°.

For speedbrake control in flight, all spoiler panels deflect up to 47° corresponding to the speedbrake lever position. Except the two inboard spoiler panels on each side, they deflect only to 15°. And except the ones one position further outboard, they do not deploy at all. And except one position even further outboard... they deflect to 45° when the speedbrake lever is >54°.

For ground speedbrake control in the first 1.25 seconds the two inboard spoiler panels on each side deploy to 20°. One position further outboard does not deploy. One position even further outboard deploys to 45°. The next one deploys to 63°, the next one does not deploy, the outermost one deploys to 63°. After 1.25 seconds all spoiler panels deploy to 63°, except the ones right in the center of each wing, as they are limited to 45°.
This can be seen here: https://youtu.be/KA_igkOnxT0?t=17


Of course this is all in normal mode. It's a bit different in secondary and direct mode.


The spoiler panels are counted 1 through 14 from left to right.

LH outbd               LH inbd      |      RH inbd                        RH outbd
1   2   3   4   5          6   7         |         8   9          10   11   12   13   14





btw, the spoiler panels are 1.1m x 2.0m for the inbd spoilers and 0.7m by 2.0m for the outbd spoilers.

Thank you so much for this! Do you know why they have to delay the full deployment? Because I thought that if they were to be deployed fully right away, the increased drag would probably reduce the landing distance.

Also, what's the deal with the A380's outermost spoileron? I noticed when we were reaching a certain speed during approach, the spoileron started to move individually in a very complicated way, like a wiggling fingers. My hypothesis is that by dividing them in several sections, they could adjust the banking rate more smoothly or efficiently when compared to a one large piece spoileron. But wouldn't it be simpler mechanically if they just move in unison? The programming and engineering for those spoilerons must cause a lot of headache!
 
CeddP
Posts: 53
Joined: Sat Feb 23, 2013 12:04 am

Re: Size of speed brakes[spoilers] on airliners?

Mon Aug 30, 2021 3:31 pm

Keep in mind that for cruciform tailplane, the stabilizor is in the wing slipstream. Often these weird spoilers settings have to do with buffet on the horizontal tailplane. On Airbuses you'll often see outer spoilers deflecting more than inners to limit buffets. Boeings have a flight and ground detent on the speedbrake lever for this reason as well. On some aircraft, the buffeting problem is so acute that spoilers deflection is very limited in flight (hence inefficient) despite dimensions of spoilers appearing to be "normal" (yes, I'm looking at you 737 !!). On others (eg 787), despite small size, they are very efficient.

trent768 wrote:
Also, what's the deal with the A380's outermost spoileron? I noticed when we were reaching a certain speed during approach, the spoileron started to move individually in a very complicated way, like a wiggling fingers [...] The programming and engineering for those spoilerons must cause a lot of headache!

They did! The behaviour results form a wing elasticity issue. During flight test they discovered that during roll command, wings would oscillate at 2 specific frequencies which would sometimes resonate leading to huge discomfort, especially noticeable in the aft of the aircraft. They programmed this function to neutralize them and called it VDA for "Valse Des Ailerons" (= Ailerons Waltz) and which, in its final iteration, would result in having the inner aileron to deflect 2,5x the amount of the outer one, with the middle one following the inner with a 350ms delay.
Something similar was designed for the rudder, called VDR (Valse Des Rudders).

Comes from Claude Lelaie's book, "The A380 flight test campaign, a pilot's view", highly recommend it.
 
User avatar
Horstroad
Posts: 597
Joined: Thu Apr 08, 2010 8:19 pm

Re: Size of speed brakes[spoilers] on airliners?

Mon Aug 30, 2021 3:57 pm

trent768 wrote:
Do you know why they have to delay the full deployment? Because I thought that if they were to be deployed fully right away, the increased drag would probably reduce the landing distance

I can only guess.
To my understanding the main purpose of the ground spoilers is to destroy most of the lift after touch down, so the risk of the aircraft bouncing back up is reduced. After all the aircraft still has enough energy and lift to fly at touch down, so the risk of unintentional lift off would be quite high without a reduction of lift force.
I assume the partial deployment results in a smoother touch down as not "all" of the lift is removed immediately, but the lift force is decreased in two steps. The effectiveness of the ground spoilers can be seen in this video. The aircraft sinks quite noticeably after the spoilers deployed:
https://youtu.be/7aM3rmMJQMY?t=158

CeddP wrote:
in its final iteration, would result in having the inner aileron to deflect 2,5x the amount of the outer one, with the middle one following the inner with a 350ms delay.

I always wondered why the ailerons of the A380 sometimes point in different directions. Thanks for the explanation.
 
LH707330
Posts: 2513
Joined: Fri Jun 15, 2012 11:27 pm

Re: Size of speed brakes[spoilers] on airliners?

Mon Aug 30, 2021 8:33 pm

Horstroad wrote:
trent768 wrote:
Do you know why they have to delay the full deployment? Because I thought that if they were to be deployed fully right away, the increased drag would probably reduce the landing distance

I can only guess.
To my understanding the main purpose of the ground spoilers is to destroy most of the lift after touch down, so the risk of the aircraft bouncing back up is reduced. After all the aircraft still has enough energy and lift to fly at touch down, so the risk of unintentional lift off would be quite high without a reduction of lift force.
I assume the partial deployment results in a smoother touch down as not "all" of the lift is removed immediately, but the lift force is decreased in two steps. The effectiveness of the ground spoilers can be seen in this video. The aircraft sinks quite noticeably after the spoilers deployed:
https://youtu.be/7aM3rmMJQMY?t=158

CeddP wrote:
in its final iteration, would result in having the inner aileron to deflect 2,5x the amount of the outer one, with the middle one following the inner with a 350ms delay.

I always wondered why the ailerons of the A380 sometimes point in different directions. Thanks for the explanation.

Adding my speculation, I could see 3 reasons to deploy the 777 spoilers as they do:

1. Hard-landing protection: if you plant it down hard and you're close to bottoming out the strut, you don't want the spoilers to max out and to keep driving it in. Dump just enough lift until the shock is absorbed and the plane doesn't bounce, then add more downforce to aid deceleration. 1.25 seconds is probably about the time it takes to absorb most of the downward acceleration, at which point a static downforce becomes more welcome. I wonder if going full spoiler right at WoW would actually encourage bouncing and thus lengthen the ground roll.
2. Pitch/derotation: because the spoilers are behind the CL, they might make a slight nose-up pitching moment after touchdown, which you'd want to either limit or control somehow. Having a phased spoiler deployment probably helps smooth this out.
3. Aileron effectiveness: the spoilers next to the flaperon don't move as much, probably to strengthen roll authority in crosswind landings. I imagine that a crosswind over a spoiler could make a downwind flaperon less effective and make ground control harder.

Again, I'm making educated guesses here, it'd be good to know from someone who was more involved in it.
 
User avatar
AirKevin
Posts: 843
Joined: Wed Apr 26, 2017 2:18 am

Re: Size of speed brakes[spoilers] on airliners?

Tue Aug 31, 2021 1:15 am

So here's an interesting one. On the 737-800, the spoiler deflection was increased with the short-field performance package. This puts the spoiler deflection angle in line with the outboard spoiler panel at 60 degrees, compared to those without the short-field performance package which were limited to 33/38 degrees. So why wouldn't they just have them at 60 degrees from the start.
 
User avatar
Starlionblue
Posts: 20805
Joined: Fri Feb 27, 2004 9:54 pm

Re: Size of speed brakes[spoilers] on airliners?

Tue Aug 31, 2021 1:22 am

AirKevin wrote:
So here's an interesting one. On the 737-800, the spoiler deflection was increased with the short-field performance package. This puts the spoiler deflection angle in line with the outboard spoiler panel at 60 degrees, compared to those without the short-field performance package which were limited to 33/38 degrees. So why wouldn't they just have them at 60 degrees from the start.


Wild arsed guess: Additional wear on the components.
 
LH707330
Posts: 2513
Joined: Fri Jun 15, 2012 11:27 pm

Re: Size of speed brakes[spoilers] on airliners?

Tue Aug 31, 2021 2:55 am

Starlionblue wrote:
AirKevin wrote:
So here's an interesting one. On the 737-800, the spoiler deflection was increased with the short-field performance package. This puts the spoiler deflection angle in line with the outboard spoiler panel at 60 degrees, compared to those without the short-field performance package which were limited to 33/38 degrees. So why wouldn't they just have them at 60 degrees from the start.


Wild arsed guess: Additional wear on the components.

...or sandbagging so they could upsell the SFP later :D

Who is online

Users browsing this forum: 113312, thepinkmachine and 16 guests

Popular Searches On Airliners.net

Top Photos of Last:   24 Hours  •  48 Hours  •  7 Days  •  30 Days  •  180 Days  •  365 Days  •  All Time

Military Aircraft Every type from fighters to helicopters from air forces around the globe

Classic Airliners Props and jets from the good old days

Flight Decks Views from inside the cockpit

Aircraft Cabins Passenger cabin shots showing seat arrangements as well as cargo aircraft interior

Cargo Aircraft Pictures of great freighter aircraft

Government Aircraft Aircraft flying government officials

Helicopters Our large helicopter section. Both military and civil versions

Blimps / Airships Everything from the Goodyear blimp to the Zeppelin

Night Photos Beautiful shots taken while the sun is below the horizon

Accidents Accident, incident and crash related photos

Air to Air Photos taken by airborne photographers of airborne aircraft

Special Paint Schemes Aircraft painted in beautiful and original liveries

Airport Overviews Airport overviews from the air or ground

Tails and Winglets Tail and Winglet closeups with beautiful airline logos