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Pano roof exploded

Discussion in 'New A3/S3 (8V Chassis)' started by number3, Mar 7, 2014.

  1. cuke2u
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    cuke2u Well-Known Member

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    [Mar 10, 2014]
    I meant air exhausts of course and they are normally hidden behind the rear bumper side trim or in the rear door shuts. Not sure where they are on the A3....
    Last edited: Mar 10, 2014
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  2. veeeight
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    veeeight Well-Known Member

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    [Mar 10, 2014]
    The waffle is behind the rear bumper side trim.
    #42
  3. Belfin
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    Belfin Active Member

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    [Mar 10, 2014]
    Oops, I think I've stumbled into the wrong forum - I was looking for Audi-Sport.net!

    (While I'm here, can one of you pilot types explain to me how a wing is supposed to create lift by it's shape, yet an aircraft can remain airborne whilst inverted?)

    Cheers, Paul.
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  4. veeeight
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    veeeight Well-Known Member

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    [Mar 10, 2014]
    Oh dear, you've opened up a can of worms with that request !!!

    I'm not a pilot type, but will answer from a fluid dynamics perspective.

    How wings generate lift depends on many factors, and depending on what stage of flight the aircraft is in, depends on which factor is the most dominant at that moment in time.

    For the specific example you quoted above, if we say that that aircraft is a powered stunt/acrobatic aircraft (which usually have symmetrical wing shape, rather than an aerofoil) - then the dominant factor in this instance is "Angle of Attack", and Newton's 2nd & 3rd law of motion. Very similar to when you put your hand out of the car window while going along, and shape your hand at an angle to the oncoming air.

    Even if the wing of this stunt/acrobatic plane is a traditional aerofoil shape, flying upside down is still possible, given enough power (thrust) and angle of attack. But stunt/acrobatic planes tend to have symmetrical (non-aerofoil) wing shapes precisely to enable inverted flight without excessive thrust and angle of attack.
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  5. cemerson
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    cemerson Well-Known Member

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    [Mar 10, 2014]
    Basically, the question arises from the misunderstanding of how a wing works that veeeight was talking about. The shape of the wing helps the air flow over it very efficiently and adds to the effect of air rushing faster over the top, but actually it's the angle the wing makes with the airflow (called the 'angle of attack') that matters. Even a barn door held at the right angle will act as a wing - just in the same way that putting your hand out the window of a moving car and angling it will, even though it's not aerofoil shaped.

    Wings actually throw a lot of air downwards (they have to - newton's third law says so!), and the low pressure on top of the wing actually serves to 'drag' a lot of air from the front of the wing up and over the top, speeding it up as it goes in a strange self-sustaining kind of way.

    Wings work upside-down in the same way - by having an angle of attack with the airflow. Because of the way a wing is mounted on the aircraft to provide an angle of attack without tipping the plane's nose up too much (the angle the wings are mounted on the plane is called the angle of incidence), when it flies upside-down, the nose is actually pretty high anyway. The shape of the wing isn't exactly helping the effect. It doesn't counteract anything, it's just very inefficient at flying upside-down! Aerobatic planes usually have a symmetric aerofoil, which looks the same the right way up and upside-down. Not as efficient as a normal wing where the trailing edge points downwards (called 'camber'), but much better at flying upside-down.
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  6. cemerson
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    cemerson Well-Known Member

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    [Mar 10, 2014]
    If you want to read more, this site has a very good section on how aerofoils work (and still barely scratches the surface!)

    Airfoils and Airflow
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  7. veeeight
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    veeeight Well-Known Member

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    [Mar 10, 2014]
    Haha snap :)

    My explanation of your second paragraph goes into the Kutta Condition at the leading and trailing edges (which explain the behaviour of the vortices leading to the air travelling faster over the top of the aerofoil) and the Coanda effect (much less so, but still a factor).

    I still don't know for the life of me why they teach the equal transit time theory b0110cks at school, and even university.
    #47
  8. Belfin
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    Belfin Active Member

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    [Mar 10, 2014]
    Thanks Veeeight and Cemerson! (I admit that I just had to Wiki Newton's laws of motion!)


    *Edited because of posts overlapping as I replied!
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  9. cemerson
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    cemerson Well-Known Member

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    [Mar 10, 2014]
    Easier to understand I guess. The reason the air flows faster over the top is more complicated than the average school student would understand! University though should be better...
    #49
  10. cemerson
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    cemerson Well-Known Member

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    [Mar 10, 2014]
    I don't know much about the coanda effect, but that's described as a fallacy also by the link I pasted above... and as I understand it the Kutta condition basically says 'air likes to flow cleanly off a trailing edge'
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  11. veeeight
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    veeeight Well-Known Member

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    [Mar 10, 2014]
    I wouldn't say Coanda is a complete fallacy, but it does apply to specific wing types, especially those that have a forced jet design, with a plenum chamber in the leading and trailing edges.

    It's used extensively for changing the stall speed by changing the stagnation points on advanced aerofoils, but I guess on general commercial aircraft this design has yet to see widespread adoption.

    Also - current circulation theory doesn't really take into account viscosity, and this is where Coanda plays a part.

    Here's a reasonable pitch as to why Coanda is pooh-poohed by many at present, but this will change in the next 10 or so years.

    Why is Coanda effect considered controversial in explaining flow around airfoils? Why is it not quoted much? - Yahoo Answers India



    edit:

    A more useful way to (simplistically) think about the Kutta condition, is that at the point where the Kutta condition occurs, 2 stagnation points on the
    aerofoil occur, and it is because of these stagnation points, that the velocity of the air below the aerofoil is slower than the air going over the top - thus giving you the lift. The Kutta condition occurs most effectively with a sharp trailing edge.

    Last edited: Mar 10, 2014
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  12. cemerson
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    cemerson Well-Known Member

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    [Mar 10, 2014]
    Gliders have been at the forefront of all this... there are 1970s glider designs with forced jets to force early separation of the boundary layer in order that it rejoins by the trailing edge and flows off cleanly. I think winglets were either developed on, or adopted by, gliders a long time before they were on commercial aircraft. Construction techniques that are only just becoming commonplace on commercial aircraft (certainly passenger jets) were in use in gliders ~ 40 years ago. Maximum performance from a wing is key in competitive gliding, so there are a lot of developments there. The latest gliders use carbon fibre wings with aramid / Kevlar spars, very high aspect ratios, winglets, turbulator tape (preferred to the 'forced jet' style these days) and much more. You even see retractable 'bug wipers' on modern competition gliders that move along the wing cleaning the leading edge with a thin nylon wire and are then retracted back to housings in the wing root, just to gain every bit of efficiency possible from them!

    Anyway, we appear to have taken this thread somewhat off topic...
    #52
  13. s33nyboy12
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    s33nyboy12 Well-Known Member

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    [Mar 10, 2014]
    Yeh absolutely mate....... I was asking to see if you were still inside the warranty period, it's still a pretty bad thing to happen you know you can go out and buy a ten year old audi and have no problems with it over 45k miles but you spend your hard earned cash to buy a new car and have problems like this with it! Bloody annoying, I almost don't care how much dealer does to sort the problem out the problem shouldn't occur in first place........ I'm sure you will get it sorted and then be dying to get rid of it??

    Hope alls well ends well mate.

    Sean
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  14. JohnnyM100
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    JohnnyM100 Active Member

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    [Mar 11, 2014]
    Number3 - hope you get your roof sorted and let us know how you get on.

    Veeeight & cemerson. As someone on the periphery of understanding some of the basics, thanks for your clear explanations of a v complex topic. Seriously thanks.

    John.
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  15. Twizzler
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    Twizzler Member

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    [Mar 11, 2014]
    Given that the car in question was returned to the dealer twice for sunroof rattles I would wonder if something had been tightened down to try and overcome the problem and had put the glass under stress. Following that you may not need much in the way of flexing to cause breakage.
    I'm old enough to remember the Austin Allegro. Affectionately known by many owners as the All Aggro. Jacking the front caused many to have their windscreen break.
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  16. alistairm1
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    alistairm1 Member

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    [Mar 11, 2014]
    Austin Allegro also had the first FBSW
    #56
  17. warren_S5
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    warren_S5 Moderator Staff Member Moderator VCDS Map User

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    [Mar 11, 2014]
    Pretty flat; granted!...
    [​IMG]

    Makes you wonder why the UK car industry hit a sticking block back then, I mean just look at it...
    [​IMG]
    #57
  18. alistairm1
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    alistairm1 Member

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    [Mar 11, 2014]
    Steel wheels, skinny tyres, "Starsky and Hutch" styling stripes.
    What's not to like?

    :laugh:
    #58
  19. number3
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    number3 Active Member

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    [Mar 12, 2014]
    Ok well Audi "Germany" has come back to the dealer. Long story short, which included statements of stones and stone chips strong enough to shatter a window but invisible to the eye, must be ninja stones !!!! they have left it to the dealer to decide on an action to take, as it's inconclusive !

    Luckily the dealer has confirmed they are going to sort it through as a warranty item :) not sure what I was really hoping for to be honest, in regards to an answer from them as to the cause should just be happy they are fixing under warranty.

    Should have the car back within a week, it wasn't being worked on until Germany had come back to them.

    Am still a bit pee'd off that I had to spend most of the day in the tow truck due to the confusion as to whether to send a car directly to me, it turns out that regardless of fault if the car is un-drivable they will!! ...... Unless it's glass damage!!!! And they don't currently have an option for pano roofs, so computer said no!! Even though not safe to drive.

    The other thing that is still niggling in the back of my mind , was that the roof was worked on regardless of what they did or didn't do! And there seems a similar issue on q5's which have a recall.

    Just want the car back and sorted then really will be just see how it goes !!
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  20. Rexus
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    Rexus Member

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    [Mar 12, 2014]
    Glad you've got a dealer who will pay for the repair. It's all right Audi talking about some bizarre stones that drop down onto the roof with such force as to shatter it, (load of nonsense), but why do they fit non-laminated glass above the occupants heads in their cars?!!!
    I wonder if it's possible to stick a plastic sheet on the glass inside of the roof to stop it shattering and having flying glass pieces in such instances.
    #60
  21. warren_S5
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    warren_S5 Moderator Staff Member Moderator VCDS Map User

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    [Mar 12, 2014]
    #61
  22. Rexus
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    Rexus Member

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    [Mar 12, 2014]
    Sounds good, will have to give them a call, thanks.
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  23. andy203
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    andy203 181 BHP

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    [Mar 12, 2014]
    #63
  24. PilotAudi
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    PilotAudi New Member

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    [Mar 12, 2014]
    I remember driving one of these awful things around Goodwood many years ago. Also an 1850 SSS in lovely brown with a beige vinyl roof!

    However back to the OP.. The roof issue is worrying. We have had 4 Pano roofs (3 on 8p) and the new one. Last 8p had a rattle in hot weather eventually fixed by a new roof, and on an 08 model a rock hit front panel (non opening) and shattered the toughened glass. I wouldn't expect to see laminated glass in the roof nor would I expect it to shatter unless hit by something.

    The amateur aeronautical observation s are generally sound IMHO .

    Watching with interest for an Audi response but generally happy with new roof even though it's not so big a glass area as the old 8p open sky double roof.
    Last edited: Mar 13, 2014
    #64

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