Sponsor Message:
Aviation Technical / Operations Forum
My Starred Topics | Profile | New Topic | Forum Index | Help | Search 
Rumble When Speed Brakes Are Deployed  
User currently offlineBio15 From Colombia, joined Mar 2001, 1089 posts, RR: 7
Posted (11 years 2 weeks 3 days 5 hours ago) and read 3007 times:

Hi everyone, I'm back from a 3 month trip. I got the chance to fly several times, and noticed something that I never payed close attention to. When the aircraft used the speed brakes on descent they generated a rumble. I could tell they had just been deployed just by the shaky rumble they generated on the entire aircraft. It's similar to that sound you hear when the gear comes down. My question is, why does this happen?, Has anyone else noticed this? Thanks in advance.


View Large View Medium
Click here for bigger photo!

Photo © Daniel Talbot



-Alfredo

14 replies: All unread, jump to last
 
User currently offlineMjzair From United States of America, joined Nov 1999, 398 posts, RR: 1
Reply 1, posted (11 years 2 weeks 3 days 5 hours ago) and read 2952 times:

What you are hearing is the sound of the disturbed airflow around the wing...

User currently offlineModesto2 From United States of America, joined Jul 2000, 2792 posts, RR: 5
Reply 2, posted (11 years 2 weeks 3 days 4 hours ago) and read 2914 times:

I've noticed this many times...as you said...when speedbrakes and gear are extended. As Mjzair said, extending speedbrakes introduces disturbances to the airflow. Similarly, I'm sure you've noticed the disappearance of the sound as the speedbrakes are stowed.

User currently onlineAaron747 From Japan, joined Aug 2003, 8126 posts, RR: 26
Reply 3, posted (11 years 2 weeks 3 days 4 hours ago) and read 2908 times:

Welcome to the exciting world of drag.  Big grin


If you need someone to blame / throw a rock in the air / you'll hit someone guilty
User currently offlineC172Akula From Canada, joined Mar 2001, 1000 posts, RR: 4
Reply 4, posted (11 years 2 weeks 3 days 3 hours ago) and read 2893 times:

"Welcome to the exciting world of drag."

Indeed! I'll take one serving of Induced and a side dish of Parasitic!  Smile

STOP THE RUMBLE! (stows speedbrakes)


User currently offlineAA61hvy From United States of America, joined Nov 1999, 13977 posts, RR: 57
Reply 5, posted (11 years 2 weeks 3 days 3 hours ago) and read 2884 times:

It's kind of like a plane "down shifting"  Wink/being sarcastic  Laugh out loud


Go big or go home
User currently offlineBio15 From Colombia, joined Mar 2001, 1089 posts, RR: 7
Reply 6, posted (11 years 2 weeks 3 days 1 hour ago) and read 2851 times:

Thanks guys. I had the idea it was something like that. They must slow the aircraft down real quick since they interrupt a lot of airflow. They must kill an important amount of lift also. When the pilots deploy them, is there a lot of sinking of the aircraft?

-Alfredo


User currently onlineAaron747 From Japan, joined Aug 2003, 8126 posts, RR: 26
Reply 7, posted (11 years 2 weeks 3 days ago) and read 2847 times:

Deploying speedbrakes often allows an aicraft to descend at a higher rate without inducing increased airspeed. You'll often notice the nose angle hardly changes at all - that's because trim is taking care of it all Big grin


If you need someone to blame / throw a rock in the air / you'll hit someone guilty
User currently offlineRendezvous From New Zealand, joined May 2001, 516 posts, RR: 0
Reply 8, posted (11 years 2 weeks 2 days 12 hours ago) and read 2740 times:

The speed brake deployment in my photo up the top was pretty loud, but shortly after that they took them up to what I'm assuming is flight detent. Now let me tell you, that was a sound for someone who's like bass!

Something I saw a few months back I never thought I'd see - Virgin Blue 737 with speed brakes deployed along with flap and a 30* bank turn.


User currently offlineMr.BA From Singapore, joined Sep 2000, 3423 posts, RR: 22
Reply 9, posted (11 years 2 weeks 2 days 9 hours ago) and read 2715 times:

"Something I saw a few months back I never thought I'd see - Virgin Blue 737 with speed brakes deployed along with flap and a 30* bank turn."

I think with Boeing spoilers aren't supposed to be deployed with flaps extended no matter at what setting. I think what you say is the spoilerons (which are also the spoilers) coming up as a certain amount of aileron is imput to turn the aircraft. I think you were sitting at the inside of the turn?

Cheers!



Boeing747 万岁!
User currently offlineRick767 From United Kingdom, joined Jan 2000, 2662 posts, RR: 51
Reply 10, posted (11 years 2 weeks 2 days 9 hours ago) and read 2720 times:

The speedbrakes / spoilers issue crops up on here every so often and the search function might help you learn a bit more about their use.

They serve two basic functions in flight, either:

1) To increase the rate of descent whilst maintaining the same IAS
2) To reduce the IAS while maintaining a fixed rate of descent

We can extend the speedbrakes with flaps extended on the 757/767, up to Flap 20. The drag associated with Flap 25/30 settings combined with speedbrake deployment would be very high and the descent rate would therefore be excessive, and the vibration is an issue.

Below 800ft Boeing suggest no spoiler extension whatsoever (with associated warning light) but most airlines round this up to 1,000ft AGL (which is also the common "must be fully configured for landing" point).

On many aircraft there is a "flight detent" on the speedbrakes (a position beyond which the speedbrakes can only extend to when the aircraft is on the ground). On the 757 there are six spoiler panels on each wing, and panels 4 and 9 (inboard spoilers on the outer set) only extend on the ground. On the 767 all panels are used both on the ground and in flight. The speedbrakes extend to a greater maximum angle on the ground than in flight.

Similarly some of the spoilers operate with the ailerons to assist in roll control.

On the ground the speedbrakes are used to "dump" the lift generated by the wings and thereby placing almost all the weight of the aircraft onto the main gear, which reduces landing runway required by increasing friction and allowing the wheels to grip the runway surface better and therefore allowing a higher braking level to be used.

It is a common misconception that the spoilers actually produce aerodynamic drag to slow down the aircraft on the ground. Whilst they clearly will do this, the effect is very minimal in comparison to the primary function described above.

Similarly in flight the actual parasite drag they induce is smaller in comparison to the lift destruction, which is the primary purpose.

Hope this rather long explanation helped you understand a bit more about these things!



I used to love the smell of Jet-A in the morning...
User currently offlineBio15 From Colombia, joined Mar 2001, 1089 posts, RR: 7
Reply 11, posted (11 years 2 weeks 2 days 4 hours ago) and read 2645 times:

Yes Rick, thanks for that one. I had the misconception of the spoilers's purpose on touchdown. I thought the slowing down was accounted on the most part for the drag generated by the spoilers, and also, the lift dump required you talked about, but in equal amounts. It's easy to have that misconception since the spoilers are huge when deployed and block a large amout of air, or at least that's what I see through the window. Thanks again

-Alfredo


User currently onlineAaron747 From Japan, joined Aug 2003, 8126 posts, RR: 26
Reply 12, posted (11 years 2 weeks 2 days 3 hours ago) and read 2637 times:

If you look out the window and see deployment in a turn - don't be surprised -that's just roll assist at work.

One thing I love about coming home to Oakland is that prevailing weather usually has us on the visual to runway 29 - it's virtually a guarantee the crew will be pushing 250-240 KIAS and use the speedbrakes to slow down before the last turn, like in this pic I took:


View Large View Medium
Click here for bigger photo!

Photo © Aaron 747






If you need someone to blame / throw a rock in the air / you'll hit someone guilty
User currently offlineANA777master From United States of America, joined Mar 2004, 126 posts, RR: 0
Reply 13, posted (11 years 2 weeks 1 day 21 hours ago) and read 2569 times:

Its the wind against the metal of the speedbrakes or flaps. The metal itself reverberates and creates the sound.

User currently offlineMusang From United Kingdom, joined Apr 2001, 864 posts, RR: 7
Reply 14, posted (11 years 1 week 4 days 5 hours ago) and read 2368 times:

Are you sure?

I would suggest the vast majority of the disturbance is from the turbulent air aft of the spoilers, impinging on the spoiler itself and the wing behind. Certainly the spoilers themselves are vibrating, but only transmit part of that to the airframe

Regards - Musang


Top Of Page
Forum Index

Reply To This Topic Rumble When Speed Brakes Are Deployed
Username:
No username? Sign up now!
Password: 


Forgot Password? Be reminded.
Remember me on this computer (uses cookies)
  • Tech/Ops related posts only!
  • Not Tech/Ops related? Use the other forums
  • No adverts of any kind. This includes web pages.
  • No hostile language or criticizing of others.
  • Do not post copyright protected material.
  • Use relevant and describing topics.
  • Check if your post already been discussed.
  • Check your spelling!
  • DETAILED RULES
Add Images Add SmiliesPosting Help

Please check your spelling (press "Check Spelling" above)


Similar topics:More similar topics...
Landing With Speed Brakes Deployed posted Thu Mar 3 2005 03:31:30 by Bio15
Speed Brakes On MD-88. What Did I See? posted Thu Apr 27 2006 17:25:32 by Mastropiero
Did The Concorde Have Any Speed Brakes? posted Tue Aug 23 2005 23:00:02 by Aak777
Flaps And Speed Brakes On Landing Question posted Mon Sep 27 2004 05:29:52 by TriJetFan1
Spoilers/speed Brakes Question? posted Mon May 31 2004 07:38:27 by Soaringadi
Rudder Speed Brakes? posted Wed Apr 14 2004 17:26:50 by Alessandro
Use Of Speed Brakes In Icing Conditions? posted Fri Jan 30 2004 23:20:41 by Mr Spaceman
Main Gear Used As Speed Brakes On DC-7s? posted Tue Jan 15 2002 19:55:28 by Mr Spaceman
Speed Brakes posted Sat Nov 25 2000 00:04:56 by Super Em
Approach Speed When Props Are In Front Of Jets posted Sat Oct 19 2002 20:18:29 by Airbus Lover

Sponsor Message:
Printer friendly format