Aerodymamics...

Why do many Ruskie Airliners have low wings with Anhedral?

Does that make them more maneuverable?

[edit on 26-10-2006 by PisTonZOR]

Uhh - which aircraft are you referring to in particular?


I haven't seen one with anhedral yet. If your looking at a picture of the aircraft on the ground, perhaps wing droop is making you think its got wings with anhedral

Originally posted by PisTonZOR
Why do many Ruskie Airliners have low wings with Anhedral?
Does that make them more maneuverable?

Hi, friend!
As my knowledge, that anhedral wing be stted on most Cargo or Passenger aircraft just is in order to defend that boundary layer rolling up to wing, if boundary layer get upward to wing that will be dicrease the lift that wing given. Also anhedral can not stop the phnomenon completely, so you can see there is small vertical wing usually be stted on wingtip, thus also for the same reason.
Cheers

I have more questions about the dynamics design for Fighter.

1) I knew what is flaperon and what is aileron, but yesterday, I saw a cutaway of a fighter, that the place where other cutaway show in should be flaperon wherease showing as elevon. So what is elevon? What's the different between elevon and flaperon or aileron.

2) What the different effection between leading-edge slat and leading-edge flap? The leading-edge flap seem to be used by F-16, the leading-edge slat surely be used Mirage2000

3) I looked around recent generation fighter, then found only F-16 and Su-27 only be designed as no aileron, whereas others has. I got strong sillness why such high maneuverability fighter has less control rudder planes then others? Think anout MiG-1.44 has so many moving plane to gain over maneuverability, which give me profound image.

[edit on 29-10-2006 by emile]

Hehehe, guys, I'm studying this stuff at school right now. It's my minor area of study in aerospace engineering. Almost all high angle manuvers mean your airfoil is stalled. Most stall above about 15 degrees angle of attack, fighter wings may take a little longer. They are of course designed to have a very soft stall, in other words not lose as much lift as many other wings. If you look at a Liebeck airfoil, it has the worst stall characteristics I've ever seen in my life. If you enter stall with a Liebeck... you're dead. Where as if you enter a stall in a fighter you'll likely be fine. A note about dihendral, anhedral, and horizontal tail position. If it's too high, you can enter what's called a deep stall. This can occur with T-tails... frequently... even if you're careful. This is where the stall air (turbulent, separated flow) from your wings envelops your horizontal tail. This means you're stuck in stall because you can't apply power to get out of it and it's likely to induce a spin at which point you're F***ed basically. You can recover but you need a TON of altitude.

For those who don't know I'll go over some basics. Flaps are for landing, they're used to increase lift so you can land at a lower speed. Ailerons are used for roll control, they are outboard of the flaps. Elevators are at the back of the airplanes and are used for pitch control. The tail induces yaw (left and right in the horizontal plane of the aircraft) and roll.

Emile, a few things. I believe the term flaperon is just a funny term used when the aileron and flaps are combined. This is done a lot of times on smaller wings because it means its a larger control surface and can generate more lift when deflected. I imagine elevons would be when ailerons and elevators were combined, basically means a canard delta wing configuration. This would be because the roll and pitch would be controlled with that surface.

Another note on control surfaces. You want to push them away from the center of gravity. That way when you deflect a surface it creates a larger moment on the aircraft because of the larger moment arm. At least you want that for fighters. That's why the tail is positioned at the back. You'd have some major other problems if you tried to place it forward, it would cause downstream issues.

To whoever was asking about variable geometry, some of the lift is based on aspect ratio and sweep angle. This being said, drag is therefore also based on these things. You're changing the wingspan of the aircraft and the chord length of the airfoil going into the wind. These change the aspect ratio and the sweeping of course changes the sweep. I've got the equations somewhere, but I don't feel like getting the book out right now. Also, sweeping also has major implications for when you start shocking. The shocks (especially on the F-111 which is really friggin' fast) will envelop the tips of the wing causing some major problems. The sweep brings the tips back inside the shock cone. And no, I won't solve the oblique shock equation in cylinder or god forbid spherical coordinates for kicks. That is pain, I'll get one of my programs to do it for me.

By the way, Boiler up!

Originally posted by emile
Hi, friend!
As my knowledge, that anhedral wing be stted on most Cargo or Passenger aircraft just is in order to defend that boundary layer rolling up to wing, if boundary layer get upward to wing that will be dicrease the lift that wing given. Also anhedral can not stop the phnomenon completely, so you can see there is small vertical wing usually be stted on wingtip, thus also for the same reason.
Cheers

I have more questions about the dynamics design for Fighter.

1) I knew what is flaperon and what is aileron, but yesterday, I saw a cutaway of a fighter, that the place where other cutaway show in should be flaperon wherease showing as elevon. So what is elevon? What's the different between elevon and flaperon or aileron.

2) What the different effection between leading-edge slat and leading-edge flap? The leading-edge flap seem to be used by F-16, the leading-edge slat surely be used Mirage2000

3) I looked around recent generation fighter, then found only F-16 and Su-27 only be designed as no aileron, whereas others has. I got strong sillness why such high maneuverability fighter has less control rudder planes then others? Think anout MiG-1.44 has so many moving plane to gain over maneuverability, which give me profound image.

[edit on 29-10-2006 by emile]

In your first paragraph I believe you are reffering to spanwise boundary layer flow, if the lift distribution of the wing is badly concieved, or the wingtips poorly designed, then spanwise boundary layer flow will result in a large loss of lift. Early fighter designs like the MiG 15 overcame this with the vertical fences. Later designs had better wingtips and wing twists to overcome this without the need for fences. Anhedral/Dihedral are purely for stability.


1. LoB answered it

2. A slat will increase the angle of attack a wing can go to before stalling, a flap will increase the lift coefficient without having to change the angle of attack.

3. Not sure what you mean, the F-16 and Su-27 both have flaperons and LE slats... The advantage of only having one control surface on the TE of the wing is reducing the mass of the wing, which reduces the lateral polar moment of inertia, which gives faster roll response.

Originally posted by kilcoo316

Originally posted by emile
........
2) What the different effection between leading-edge slat and leading-edge flap? The leading-edge flap seem to be used by F-16, the leading-edge slat surely be used Mirage2000

3) I looked around recent generation fighter, then found only F-16 and Su-27 only be designed as no aileron, whereas others has. I got strong sillness why such high maneuverability fighter has less control rudder planes then others? Think anout MiG-1.44 has so many moving plane to gain over maneuverability, which give me profound image.

.........
2. A slat will increase the angle of attack a wing can go to before stalling, a flap will increase the lift coefficient without having to change the angle of attack.

3. Not sure what you mean, the F-16 and Su-27 both have flaperons and LE slats... The advantage of only having one control surface on the TE of the wing is reducing the mass of the wing, which reduces the lateral polar moment of inertia, which gives faster roll response.

2) Goood post, veeery good! I should know it originally, but you reminds me of it.

3) Yeah, I am suspicious of F-16 and Su-27 suing flaperon to both. What I mean is why do they didn't be designed as using flap and aileron? I think,obviously, that using flap and aileron separatly would be more efficient than only using flaperon.
Still waiting for your teaching.

[edit on 29-10-2006 by emile]

Originally posted by emile

3) Yeah, I am suspicious of F-16 and Su-27 suing flaperon to both. What I mean is why do they didn't be designed as using flap and aileron? I think,obviously, that using flap and aileron separatly would be more efficient than only using flaperon.
Still waiting for your teaching.

[edit on 29-10-2006 by emile]

Why should it be more efficient?


What they have done is made a larger aileron that can double as a flap - it should provide more roll control than a conventional smaller aileron. The compromise may be in flap performance, but that is not so important for those two particular fighters.

I think if that has outboard tranditional aileron, that will be longer force moment of roll control, so that lead to faster rolling turn rate.

[edit on 30-10-2006 by emile]

The Valkyre was capable of Mach 3, at least!!! (Never believe the officials ) This was possible due to the incredible wingtips wich were variable on the outer ends. This made it possible for the plane to use something called compression lift (if I recall right).

When the plane reached Mach 1, with the wingtips positioned in a (wrong term but I can't really figure out a better one) ahedral way. (The outer end of the wing was lower than the part close to the fuselage.) The energy wich was "released" when the plane reached the speed of sound, was trapped between the fuselage and the outer ends of the wing-tips, thus creating more lift and generating more speed. The obvious problem here is heat caused by friction. For the concept to work properly it would demand good and expensive materials to be used. But I have a feeling we've came a long way since the Valkyre first flew, and such materials could be made today.

Am I totally of the chart with this? My second question lies more around modern aircraft engineering. Why isn't this used more? I understand it hasn't found its place in the figher industry. But I could imagine the bomber, perhaps even civil aviation benefit a great deal of this, reaching Mach 3. That'll give the jumo jet designers something to think about

Oh, sorry about my poor english, I haven't spelled educatedly for a while now

[edit on 28-4-2007 by Figher Master FIN]

I can understand what do you want to express, but sorry, I have no ablility to help The question also is what I need to know.

On the XB-70:


Supersonic lift generation is fundamentally different to subsonic generation.

Subsonic lift comes from a higher dynamic pressure above the wing (relative to the underside) resulting in a lower static pressure above the wing. This is a result of the bound vortex system.

At supersonic speeds, the bound vortex disappears as the pressure perturbuations cannot transmit back upstream - so lift results from the geometric angle of the surfaces to the freestream (both top and bottom of the wing).


At hypersonic speeds, newtonian lift theory is valid and the upper surface can be neglected.


Anywayz - these changes in lift generation result in changes in the wing aerodynamic centre (the imaginary point that a single force could act through and represent the loading of all the wing) position moves, usually backward.

When the aero centre moves backward, it can cause the nose of an aircraft to tuck (pitch nose down), and there is f__k all the pilot can do about it. The Me163 had such a problem. The wingtips on the XB-70 were designed to rotate to prevent such a problem.


With the wingtips down. Shock interactions could have increased the local angle of incidence to the lower surface, increasing lift - but I don't think this was the case.


Having the wingtips down also increased the vertical surface area, aiding lateral stability.

text removed, wrong place.

[edit on 30-4-2007 by waynos]

Originally posted by Figher Master FIN
When the plane reached Mach 1, with the wingtips positioned in a (wrong term but I can't really figure out a better one) ahedral way.

Sorry, who are willing to teach me what does Ahedral mean? English dictionary never published this word, but I am sure I'd seen this word somewhere else before but lose it.

Check the very first page of this thread emile.


Why do aircraft fly?

That's my question. As simple as it sounds I've came to the conclusion that very few actually know how "heaveier than air" -flight works. I am not talking about the Bernoulli explanation (The longer path explanation) nor the Newtonian explanation because they are faulty and don't represent the truth. So if anyone knows the "real deal" please post, it would be highly appriciated.

Now what I do think I know, without lieing, is that aircraft fly because of higher pressure beond the wing than above it. We have the formula for pressure wich is p=F/A and if we divide the equation with A we get F=p*A. Where the p is the pressure and A is the area of the wing. The larget the pressure is (in other words the faster the plane goes) the more lift we get, and the bigger the wing is the more lift you get. This due to the F=p*A formula. The force grows when p and A grow. The aircraft lifts when the force under the wing (aimed upwards) is larger than the (downwards) aimed force (G=m*g) where m is the mass of the plane and g is a constant (9.81 m/s2). I believe this is true. However, if it's faulty please correct me. For me everything falls on the whole "why is the pressure larger under the wing than above it??" So if anyone can answear this I'd be greatful. You tell me that and you made my day. Thanks you in advance.

Your question if I gather correctly is if pressures play a part (not the only) part in how a wing generates lift? The simple answer is yes they do play a part. I also noticed that you mentioned that bernoulli's principle is flawed. I was wondering if you could point out to me where the flaw is? As far as I know the wing acts as half of a venturi tube with the venturi effect being part of the bernoulli principle. The top half of the wing creating the lower pressure do to the need for the air mass on top of it to meet the mass on the bottom at the same point. its the increase in speed due to shape that creates the low pressure. With the low pressure above the high pressure and the high pressure acting upon the bottom of the wing you get lift. now I'm not sure if I told you anything to new but I want to sorta serve for you as someone else who appears to be under the same style of thinking as your self. EH

Originally posted by Figher Master FIN
I am not talking about the Bernoulli explanation (The longer path explanation)



For me everything falls on the whole "why is the pressure larger under the wing than above it??"



nor the Newtonian explanation because they are faulty

1. The longer path explanation is crap, ignore it.

A wing in flight has a vortex system around it (we'll just ignore the starting vortex for simplicity), there is a bound vortex, and the two wingtip vortices.

Here, suprisingly managed to find a diagram with all this, thank god for NASA eh?




OK, now, it is the bound vortex that results in the airspeed differential between top and bottom, (as the vortex velocity component acts with the airstream above the wing, but against it under the wing). This vortex system is the result of pressure perturbations (variations) along the wing surface (not normal to it) - uhh, maybe it is better explained as pressure variations around an aerofoil slice of the wing, but only in the direction parallel to the surface.


Below around Mach 0.3, airflow can be considered incompressible, even up to around Mach 0.7 compressibilty effects are still less than 20% (IIRC). Thus here Bernoulli does apply.




2. So, anyway. The total pressure on any surface point is given by:

Ptotal = Pstatic + Pdynamic

Pstatic is just atmospheric conditions, from the international standard atmosphere, Pstatic is 101325Pa at sea-level.

Pdynamic is given by - (MINUS) rho* V^2


So when the dynamic pressure increases, total surface pressure decreases (if the flow is parallel to the surface - to avoid explaining stagnation points).




Note: At supersonic speeds, the pressure perturbations/variations which form the bound vortex can no longer travel upstream, breaking the bound vortex. Thus, the lift generation mechanism at supersonic flight is entirely different from subsonic flight.




3. Newtonian lift does exist - the lift generation mechanism at hypersonic speeds is straight Newtonian theory (slightly different from supersonic lift).

So the Bernoulliprincipal is correct up to mach 0.7-0.9 area after that this vortex lift take over?

No. Bernoulli lift is a result of this vortex system. The system is what creates the velocity differences between the top and bottom of the wing.




Traditionally above Mach 0.3, the flow is no longer treated as incompressible, which means Bernoulli's theory does not tell the whole story (there is the effect of compression to be considered), although the general principal is still the same - raise speed = raise dynamic pressure = lower total pressure.


Above Mach 0.7, compressibility effects begin to have serious effects, so Bernoulli is not the driving factor, although still a major factor.


I can't find a graph of compressibility vs mach number online, so cannot check the numbers at home, but I think at 0.3 Mach the flow is around 3% "compressible", but at 0.7 Mach its around 16% "compressible".

[edit on 5/6/07 by kilcoo316]

This is really great. Thanks heavens there are people like you.

Great info Kilco, there's alot here to understand. I was just wondering, in the dynamic pressure formula "V" stands for velocity right. But "rho" is that now density or what??

And when you count with static pressure (101.325 kPa) How many significant figures do you use when you calculate? I've always thought that it's enough 101.3, but then again I don't do this for a living.

Canada, here's an extract for why the Bernoulli explanation isn't totally correct.

Why is it not entirely correct?
There are several flaws in this theory, although this is a very common explanation found in high school textbooks and even encyclopedias:

1. The assumption that the two air particles described above rejoin each other at the trailing edge of the wing is groundless. In fact, these two air particles have no "knowledge" of each other's presence at all, and there is no logical reason why these particles should end up at the rear of the wing at the same moment in time.

2. For many types of wings, the top surface is longer than the bottom. However, many wings are symmetric (shaped identically on the top and bottom surfaces). This explanation also predicts that planes should not be able to fly upside down, although we know that many planes have this ability.

Originally posted by Figher Master FIN
Great info Kilco, there's alot here to understand. I was just wondering, in the dynamic pressure formula "V" stands for velocity right. But "rho" is that now density or what??

And when you count with static pressure (101.325 kPa) How many significant figures do you use when you calculate?

V is velocity, rho is density.

I use 101325, its as handy to stick that in as 101.3kPa to be honest.

Originally posted by Figher Master FIN
Canada, here's an extract for why the Bernoulli explanation isn't totally correct.

No guys, your still getting mixed up.


Bernoulli explains (correctly) the variation of dynamic pressure for incompressible flows. So Bernoulli does correctly explain the variation of pressures on surfaces for incompressible flows.


The incorrect part is the reason given for the flow speeds being different top and bottom of the wing (the travel path explanation). Its this part that is rubbish. The real reason for the different speeds top and bottom is the bound vortex, as explained earlier.