Go Back  PPRuNe Forums > Flight Deck Forums > Tech Log
Reload this Page >

787 First Flight - Signs of Trouble Ahead?

Tech Log The very best in practical technical discussion on the web

787 First Flight - Signs of Trouble Ahead?

Old 23rd Dec 2009, 14:25
  #61 (permalink)  
 
Join Date: Feb 2005
Location: flyover country USA
Age: 82
Posts: 4,579
Likes: 0
Received 0 Likes on 0 Posts
kijangnim
trailing edge will extand .5 to 1 degree during flight to move the c of g,
How's that again?

the bird is magic
Ahhh, maybe that explains it...
barit1 is offline  
Old 23rd Dec 2009, 14:34
  #62 (permalink)  
 
Join Date: Jul 2003
Location: Cheshire
Posts: 191
Likes: 0
Received 0 Likes on 0 Posts
I think he means centre of lift. Altering the camber of the wing to effectively "trim" the aircraft, if you can call it that?

More to the point, what are the going to call these devices? Flaperators? Flims?
BigHitDH is offline  
Old 23rd Dec 2009, 18:46
  #63 (permalink)  
 
Join Date: Jan 2005
Location: north
Posts: 319
Likes: 0
Received 0 Likes on 0 Posts
Boeing calls it Cruise Flap. One increases camber to reduce drag.

For a better understanding of the theory behind it, some reading
up on Supercritical Airfoils might help.

XPM
XPMorten is offline  
Old 23rd Dec 2009, 19:44
  #64 (permalink)  
 
Join Date: Feb 2005
Location: flyover country USA
Age: 82
Posts: 4,579
Likes: 0
Received 0 Likes on 0 Posts
I can readily accept the advantage (within limits) of a bit more camber.

The question then becomes: Why operate without said camber? In what flight regime is it an advantage to have less camber?

Boeing may have all the answers, but are they disclosing them to we peons?
barit1 is offline  
Old 23rd Dec 2009, 20:52
  #65 (permalink)  
 
Join Date: Jan 2005
Location: north
Posts: 319
Likes: 0
Received 0 Likes on 0 Posts
Cruise flaps are trailing-edge flaps operated at small deflection
angles for the purpose of reducing drag at offdesign conditions.
The deflection of a cruise flap results in a shifting of the low-drag
region (bucket) of the drag polar for an airfoil, as shown in Fig. 1.
Flap deflection moves the leading-edge stagnation point, which
affects the pressure distributions along the airfoil upper and lower
surfaces. Figure 2 shows that for natural-laminar-flow (NLF) airfoils,
there is a small region at the leading edge in which it is most desirable
to locate the stagnation point [1,2]. Doing so results in favorable (or
less adverse) pressure gradients over the upper and lower surfaces,
even at offdesign coefficients of lift. Without the cruise flap, either
the upper or lower surface would have experienced loss of laminar
flow at these offdesign conditions. Thus, when scheduled correctly, a
cruise flap can result in a large range of Cl values over which low Cd
is achieved
. For this reason, several NLF airfoils have been designed
with cruise flaps [3–5]. Cruise flaps have also been successfully used
on high-performance sailplanes for several decades.
So basicly, automated cruise flap ensures that the wing STAYS inside
the low drag bucket for a larger portion of the flight reducing drag.
I would guess the main advantage would be whenever you are
above or below your optimum altitude or airspeed. In other words, most of the time..

XPM
XPMorten is offline  
Old 23rd Dec 2009, 21:11
  #66 (permalink)  
bearfoil
Guest
 
Posts: n/a
Cruise Flap permits the addition of drag (lift) aftward of the CL, effectively displacing the cg aft, allowing the Tailplane to load, with attendant reduction in angle of attack, which reduces overall drag.

bear
 
Old 23rd Dec 2009, 23:56
  #67 (permalink)  
 
Join Date: Feb 2005
Location: flyover country USA
Age: 82
Posts: 4,579
Likes: 0
Received 0 Likes on 0 Posts
Thank you all. Makes more sense now.
barit1 is offline  
Old 24th Dec 2009, 05:24
  #68 (permalink)  
 
Join Date: Mar 2000
Location: Arizona USA
Posts: 8,571
Likes: 0
Received 0 Likes on 0 Posts
'


Cruise Flap permits the addition of drag (lift) aftward of the CL, effectively displacing the cg aft, allowing the Tailplane to load, with attendant reduction in angle of attack, which reduces overall drag.
Hoot' Gibson tried this with a TWA 727 years ago, didn't work out so well when the FE stuck his oar in the water, and the result was a wild ride down....way down.
411A is offline  
Old 25th Dec 2009, 13:29
  #69 (permalink)  
 
Join Date: Jan 2005
Location: north
Posts: 319
Likes: 0
Received 0 Likes on 0 Posts
A bit more details.
The system will be moving the trailing edge through a 3 deg arc,
with the edge deflecting up and down by as much as 1,5 deg either side
of a neutral setting position. It will move in 0,5º increments.
In addition, the spoilers will droop up/down to adjust the airflow around the
slot between the flap and spoiler.

It will save drag equivalent to about 450 kg weight.
XPMorten is offline  
Old 28th Dec 2009, 10:34
  #70 (permalink)  
 
Join Date: Nov 2000
Posts: 645
Likes: 0
Received 0 Likes on 0 Posts
Yesterday ZA001 had it's second flight. This source claims it was cut short by around three hours. Weather looked CAVOK.

Boeing 787 beginnt reguläre Flugerprobung - FLUG REVUE
Kerosene Kraut is offline  
Old 29th Jan 2010, 07:37
  #71 (permalink)  
 
Join Date: Dec 2001
Location: what U.S. calls ´old Europe´
Posts: 941
Likes: 0
Received 0 Likes on 0 Posts
As can be seen in this picture of the second prototype, Boeing is now using aileron droop in the high lift configuration (meaning the ailerons are slightly deflected down to support the flaps in delivering the lift needed for take of and landing). This is how it is done for Airbus from A319 to A380, this is how everybody expected the 787 to be designed. Load alevation in the high lift configuration by deflecting both ailerons up as some posters assumed would not make any sense.

So finally we have learned, that the unusual upward deflection of the ailerons during first flight was an additional safety measure to have more margins for any unforseen events and is not a standard 787 design feature. The structure obviously is also capable of taking the bending moment in the high lift configuration with aileron droop. (and Boeing is confident in this by now)

case closed.
Volume is offline  

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service

Copyright © 2024 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.