Sweepbacks nose high attitude on approach?

[ckhy]

How would you answer this question in an interview, in a more technical sense?

Why do sweptbacks approach at a much higher nose attitude than traditional straight wing?

any ideas apart from they producing less lift at the same AoA comparing to the other one?

Cheers

[What Traffic]

Because more of the lifting surface area of the wing is farther back on the airplane than a straight wing, requiring a center of gravity farther back as well. As the airplane rotates around that center of gravity, there is more fuselage sticking up forward of the CG?

That's my guess anyway.

[RobinR200]

u might asked urself with such a question: high attitude compared to what?

if u compare it to a straight wing, i guess the answer could be: due to angle at which the wind hits the wing (lateral component, not the vertical one) u got a lesser windspeed than when it hits the wing in a straight manner (as in the case of a straight wing). To compensate for this relative lift loss u have to increase the attitude (if CAS remains the same in both cases).

[Rainboe]

The answer is sweptback wings are optimised for high speed, high altitude cruise flight. At slow speed, they need extensive lift devices to produce more lift. This means leading edge devices and trailing edge flaps to reduce what would otherwise be a high stalling speed and create more low speed lift. The result is a higher nose attitude at the slow approach speeds. The effect of having no extra lift devices operating can mean approach speeds increased by 50 knots for a B737, and danger of tailscrape because of attitude.

[EK4457]

Its all to do with

Lift = Cl 0.5 rho V squared S

Swept wings (as explained above) are designed to reduce drag in the transonic speed range. The down side is that they actually produce less lift at a lower IAS. Hence your light A/C don't have them (and turboprops).

If you apply this to the above equation, with equal air density, speed and surface area, a swept wing requires a higher Cl than a straight wing. This means a higher angle of attack, which (in this situation but not always) means higher nose attitude.

EK

[engineer07]

Well actually they don't all approach at high AoA ! Take the A380 as an example - it has a high wing sweep, but approaches at very low AoA - but this a/c has a very big wing. The other reason why a lot of swept wing a/c approach (and stall) at high AoA's is that they are usaully equipped with leading edge devices (slats, etc). These leading edge devices generate more lift from a given wing area by increasing the stall AoA - and of course the approach AoA with it.

[Rainboe]

The current A380 is not representative. That wing is plainly intended for a longer fuselage which is what the A380 will eventually gestate to! In short, the wing for the current version is too large, so it's approach attitude is not really representative. All the other widebodies do have high atitudes.

[411A]

Older folks may well have operated more 'senior' airline transport jets, such as the B707...DC-8 as well.
It should be noted that these aircraft did not fly a final approach segment at the presently observed nose-high pitch attitudes, as more modern aircraft do.

Why is this, I wonder?

This older pilot knows the answer, but I should allow others to have their considered opinions, first.
Hint: Think B-47 specific design.

[barit1]

Please remember that fuselage attitude (nose high, nose low...) DOES NOT equal AOA. It's a matter of how the angle of INCIDENCE is set by the manufacturer. The BAC-111 and the B-52 are excellent examples of the incidence angle set so high that the fuselage is actually nose-down on final.

[411A]

Please remember that fuselage attitude (nose high, nose low...) DOES NOT equal AOA. It's a matter of how the angle of INCIDENCE is set by the manufacturer. The BAC-111 and the B-52 are excellent examples of the incidence angle set so high that the fuselage is actually nose-down on final.

Number one (of three) primary reasons.
Barit1 clearly has a grasp of the aerodynamic situation, and I would suggest he also knows the other two, if he is old enough...or, has studied the historical situation to any reasonable degree.

[Mad (Flt) Scientist]

Aircraft pitch attitude on approach is a function of glideslope angle, (body) angle of attack and headwind. Assuming the same glideslope and headwind, then the variable is body AoA.

Body AoA is a function of: wing (setting) incidence, approach speed as a factor of stall speed and stall AoA.

If I keep stall AoA unchanged, and keep wing incidence unchanged, then the closer my approach speed to the stall, the higher my body AoA and thus higher my pitch attitude on approach.
Modern aircraft using the 1.23Vs1g rule probably fly closer to the aerodynamic stall on approach, and therefore will approach more nose-high

If I keep stall AoA unchanged and approach speed factor unchanged, then my wing AoA on approach is also unchanged. But if I vary wing incidence I will change my body AoA for a fixed wing AoA
Aircraft with smaller wing (setting) incidence will tend to approach more nose-high

If I keep approach speed factor unchanged, and wing setting incidence unchanged, but increase my stall AoA (by, say, use of slats or the like) then I will fly the same 'distance from stall' but stall is at a higher AoA, therefore I fly at a higher AoA
Aircraft with LE devices will tend to approach at higher AoA

Incidentally, an oversized wing shouldn't be a factor, because you still fly at a stall speed ratio on approach. You would fly slower, but at the same AoA, as a heavier aircraft with the same wing.

[fantom]

I'm gonna come over there and sort you out, Mad FS.

There's no point posting factual, highly scientific and correctly punctuated answers here.

What we want is uninformed garbage postulated by no-brain wannabees in text-speak.

Sorry; you're not welcome in the New World.

joking, of course.

[411A]

I'm gonna come over there and sort you out, Mad FS.

MadFS is correct, as far as he goes.
However, this does not answer the question of why older designs approached at a greatly reduced body angle.

Barit1 had one reason, two more to go.

Further hint...think B-47 wing total configuration.
By the way, the USA was first with this design, for a larger aeroplane.

[Flying Spag Monster]

Don't know about three magic answers but rigger's (sp?) angle is one as mentioned. Some a/c (corsair?) could adjust it for landing allowing the body angle to reduce. Aerodynamically the lift curve of a swept or delta is a lot flatter than non or less swept wing for the same aerofoil section, this is because you are considering the flow that is perpendicular to the leading edge not the total flow over the wing. Meaning, max CL is achieved at a much higher AoA therfore body angle. Some earlier fighter types and swept transports would increase parasite drag on approach to shift the total drag curve up and left, ie total drag was increased but min drag speed was actually lower. This was achieved by using speed brake on approach and even small drag chutes (B 47 I think was one type that used a chute or similar).

[gr8shandini]

I'm not quite sure what you're getting at, 411. AOA, glideslope angle, and angle of incidence will give you pitch attitude in a stabilized descent.

Could you be hinting at the tandem landing gear on the B-47 that requires a more level touchdown, and hence the massive angle of incidence?

And in case anyone's not familiar with '60s fighters, another unique aircraft was the F-8 Crusader. It had a variable incidence wing that was intended to let the pilot maintain visual contact with the carrier when on steep approach.

Edit: Looks like FSM was one step ahead of me, and close, but no cigar. The A-7 Corsair was pretty much a subsonic variant F-8, but it lost the pop-up wing along the way.

[Clandestino]

I'm not an expert on early jet transports... were they perchance hardwings?

[777fly]

411A,

Being an old 'airdog' as well, I think I can remember why, or maybe not.... Our old metal did not benefit from the latest wind tunnel derived super critical wonder aerofoils, capable of lift at impossibly low airspeed. We had to hurtle down the glideslope at relatively high speed just to make them work. High speed=high ROD= low attitude? My new 777 wonderjet flies the same speed at twice the weight, approaches at 1 degree nose up and stops in 2/3 the distance. Technology wins, every time.

Now, about the fuel price crisis, why is nobody talking about fusion reactor technology..........???

[411A]

Our old metal did not benefit from the latest wind tunnel derived super critical wonder aerofoils, capable of lift at impossibly low airspeed. We had to hurtle down the glideslope at relatively high speed just to make them work. High speed=high ROD= low attitude?

Yes, just about right.
These older aircraft did not have especially advanced airfoil sections, and....also did not have leading edge devices nor advanced trailing edge flap designs, so a lower body angle was absolutely needed.
The B-47, just as one example, used quite a clean wing design, no leading edge devices, and single slotted semi-Fowler type trailing edge flaps.
Early B707's...the same.
Later on, with more advanced designs, detailed LED's (and especially, slats) together with double (and triple) slotted Fowler flaps were a great help in keeping approach speeds in check, while at the same time, allowing much greater landing weights, in normal operations.
Higher apparent body angles were the result.

[777fly]

411A,

A true observation, but I think that the high attitude approaches of the 70's and 80's era were simply a result of the hi-tech LE and TE devices which were bolted onto old technology wings, simply to get them to work efficiently. Its all about getting air to work over the wing. These days it all works so well, without brutalising the air to make it happen.

[411A]

A true observation, but I think that the high attitude approaches of the 70's and 80's era were simply a result of the hi-tech LE and TE devices which were bolted onto old technology wings, simply to get them to work efficiently.

Quite true, generally speaking.
The B727 is a perfecrt example of this technique.

An exception is the Lockheed TriStar.
A quite advanced wing design with very effective slats and slotted trailing edge flaps.
A well thought-out design, from the beginning.
Expecially so on the -500 model, with active ailerons.
We can then mention DLC on the 'ole TriStar.
Rock solid constant body angle on the ILS, regardless of weight.