|
kijangnim
trailing edge will extand .5 to 1 degree during flight to move the c of g, the bird is magic |
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? :8 |
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 |
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? |
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. 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..:p XPM |
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 |
Thank you all. Makes more sense now. :cool:
|
'
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. |
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. |
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 |
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. |
| All times are GMT. The time now is 03:30. |
Copyright © 2024 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.