Fly Lah!

michyiki wrote:But differnet aspects nds to be consider if the wing stalls at the tip or root. Nwadays commercial airplanes uses geometrically washout and aerodynamically washout to prevent aircraft stall at the wingtip. Becuse if aircraft stalls at wingtip, pilots will be in trouble of rolling the plane by moving the aileron. Correct if i nt mistaken.

yerpp.. you are right. That one if we discuss about 'an early stall' . Then pilot will have enough time to react. I'm sure for airbus nowdays it wont stall at all..there is auto recovery system right?

on top of giving an early stall to pilot, washout is really important for big aircraft with swept back wing because we don't want the wing to 'bend' overlimit due to much lift created on the outboard wing.(More over the outboard of swept back wing has less wing area to that of inboard wing). So by creating the washout , the wing is twisted so that the angle of incident of the tip is lesser than the root.

The basic (exams) questions are on the comparison between rectangular, tapered and elliptical wings, also come the issue of swept wings. But,... true ... manufacturers try to correct the issues by varying washout and other tricks ....

Concerning Airbus it is not recovery systems it is prevention ones (Alpha Floor, Alpha prot....). The attitude of the aircraft is limited, in pitch (but also in roll), Auto thrust is automatically going to TOGA before the speed decreases to the stalling speed...If for some reasons, the aircraft has stalled, it is to the Pilot to recover, the automatisms cannot do it.

This is an extract the A320 Flight manual, (I have used for making a leaflet on this topic (JAR questions - Instrument))

FLIGHT ENVELOPE PROTECTION (FBW )
The introduction of computers in the command chain of flight control and the new flying laws have modified the stall protection systems. Orders are given by the computers overtaking the pilot input.
This is a description of the stall protection on such an aircraft (A 320– extract of Flight Manual)
"STALL PROTECTION
The aircraft resists attempts by either a pilot or the atmosphere to stall it. If a pilot attempts a stall, he feels the aircraft trying to pitch down as speed approaches the amber and black strip. The pilot can resist this tendency until speed reaches the red band (alpha maximum), and then further nose-up control is not available. Between these two points, alpha floor automatically sets go around thrust. The pilot can hold full back stick, if it is needed (see windshear), and the aircraft stabilizes at an angle of attack close to but short of the 1 g stall.
WHEN FLYING AT ALPHA MAX, THE PILOT CAN MAKE GENTLE TURNS, IF NECESSARY. As the aircraft enters protection at the amber and black strip (alpha prot), the system inhibits further nose-up trim beyond the point already reached. Nose-down trim remains available if the pilot pushes the stick forward.
The pilot should not deliberately fly the aircraft in alpha protection except for brief periods when maximum maneuvering is required. If the pilot enters alpha protection inadvertently, he should get out of it as quickly as possible by easing forward on the sidestick to reduce the angle of attack while simultaneously adding power (if alpha floor has not already been activated or has been cancelled). The system will regain the normal load factor law if the stick is pushed forward of neutral, but it will re-enter alpha protection if the stick is released with the angle of attack still greater than the value set for alpha protection,. Thus to exit alpha protection properly, the pilot should reduce angle attack to a value less than the value set for alpha protection.
The PFD (Primary Flight Display) shows this clearly, because the indicated speed is above the black and amber strip.
The pilot should now increase speed above VLS note 1 (clear of the amber strip) as soon as other considerations (ground clearance, for example) allow him to do so.
Alpha floor will usually be triggered just after alpha protection is entered, and go around thrust will automatically be applied. Thus, if the sidestick is held aft, either inadvertently or deliberately, the aircraft will start to climb at a relatively constant low airspeed. To recover to a normal flight condition, alpha protection should be exited by easing forward on the sidestick, as described above, and the alpha floor should be cancelled by using the disconnect pushbutton on either thrust lever as soon as a safe speed is regained.
The aircraft can also enter alpha protection at a high level, where it protects the aircraft from the buffet boundary. The PFD shows that alpha protection is active in the same way it does so at low speed or low level : the amber and black strip rises to the actual speed of the aircraft. As at low speed or low level, if the stick is merely released to neutral the aircraft maintains the alpha for alpha protection. (This value of alpha is not however the same as the value used at low speed : alpha for alpha protection is reduced as a function of Mach so that a typical cruise value is in the order of 3.5° for the A321 or 4.5° for the A320.). Thus the aircraft may climb, stick free, when leaving a turn after entering alpha protection. If the pilot has flown into alpha protection, he should leave it as soon as other considerations allow by easing forward on the stick to reduce alpha below the value of alpha protection while simultaneously increasing thrust or speed as appropriate."

And thus the use of Digital Fly-By-Wire..

maverick
Flight Enveloppe protection is an add-in to the Fly By Wire aircraft system : it is not the main aim.

To understand the evolution of modern aircraft, first the aircraft manufacturer is required to make a gain in productivity around 18%/20% for a new generation of aircraft, if he want to sell his aircraft.
Big challenge! Different research axis but none is apparently sufficient in itself:
- jet engines are arriving at maturity in their evolution,
- reducing the weigth...the interest to use composite materials
- and aerodynamic...somewhere it is absurd to be obliged to develop a negative lift with the tailplane, just to provide stability, because at the same time the drag is increased,
So the idea of unstable aircraft... yes but human cannot fly directly such aircraft, because human are not enough sensitive and it is the derivative of the derivative which must be detected!
Computers until few years (I will say end of the seventies...) were not fast and powerful enough, also the networking technology was in its childish phase. However, militaries were already on this track; fighter aircraft and also the space shuttle are amidst the first unstable aircraft.

In Civil Aviation, a very conservative approach is engaged: reducing step per step the stability; the A320 has been the first sucessful aircraft with reduced stability: this is the reason of the Fly By wire aircraft and the future is there: productivity improvement.

You will fly probably a "Flying Wing" in 15 or 20 years. researches are on going, Boeing as well as Airbus, are working on projects of Flying wings (1,000 passengers, with hydogen engines...)("BWB" as it is named standing for Blended wing Body). Because those designs, at the difference of conventional design, provide a huge volume which is required for stocking hydrogen (volume required 9% more than JET A1).

This is aviation, a passionating evolution is on going... You have already a model flying with NASA, nicknamed the Skyray (X48). I have seen pictures... this aircraft (scaled model) is beautiful. i would like to be younger....

I have post some pictures on image shack

whoaa...rich of infos... tq2

Good post Terengganu01!

Awesome post Terengganu01!.. I've read about the flying wing concept like the B-2 Stealth Bomber, but Hydrogen engines?!?.. That's a whole new level of technology...

But For any aircraft to fly without constant correction it must have directional stability in yaw. Flying wings lack the long fuselage which provides a convenient attachment point for an efficient vertical stabiliser or fin. The fin must attach directly on to the rear part of the wing, giving a small moment arm from the aerodynamic center, which in turn means that to be effective the fin area must be large. This large fin has weight and drag penalties, and can negate the advantages of the flying wing. The problem can be minimised by increasing the leading edge sweepback, as for example in a low-aspect-ratio delta wing, but most flying wings have gentler sweepback and consequently have, at best, marginal stability. In the so called 'ruptured duck' configuration, the wing tip sections are angled sharply downwards (anhedral), increasing the area at the rear of the aircraft when viewed from the side.

The Flying wing may have some directional stability becaust it is not "Flat" but you can have important winglets like the X48B (and I suppose this play a role in the directional stability) or ondulations. The concept of the flying wing is rather old and some have alredy flown. it seems that it is the longitudinal stability which is more critical. To be confirmed.
I am out of station until end of next week but I will post some information about the Flying Wing history.
A conventional aircraft (B747, A3800 cannot store hydrogen in enough quantity, its endurance will be ridiculous.

Terengganu01 wrote:The Flying wing may have some directional stability becaust it is not "Flat" but you can have important winglets like the X48B (and I suppose this play a role in the directional stability) or ondulations. The concept of the flying wing is rather old and some have alredy flown. it seems that it is the longitudinal stability which is more critical. To be confirmed.
I am out of station until end of next week but I will post some information about the Flying Wing history.
A conventional aircraft (B747, A3800 cannot store hydrogen in enough quantity, its endurance will be ridiculous.

Looks like you copied this piece of crap and pasted it rightttt here....

Cheers Mate!..

Maverick wrote:
Looks like you copied this piece of crap and pasted it rightttt here....

Cheers Mate!..

yea,,see,,the sentence,the coma, have space,,not like usuall he type.. :]. . but,,nice information. . ;]