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jan.de.jong(at)xs4all.nl
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nwcmc(at)tiscali.co.uk
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 Posted: Fri Dec 15, 2006 3:32 am Post subject: Vne Speed |
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| Quote: | In Don Dykin's booklet about Europa aerodynamics he says that the flaps
take just about half of the plane's weight at top flap speed. With
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aerodynamic forces increasing with speed squared I wouldn't want to rely
on
the flaps not failing before the wings, which have been tested to 10g
after
all!<
I assume that this statement is with the flaps extended. One presumes
that the load taken by the flaps is much less when they are retracted.
Nigel Charles
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wdaniell(at)etb.net.co
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| Posted: Fri Dec 15, 2006 8:36 am Post subject: Vne Speed |
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Someone also told me that the Vne sometimes has to do with elevator
effectiveness - that is to say that above a given speed the elevator ceases
to work...
Anyone else heard this is it BS.
Will
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robh(at)hyperion-ef.us
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| Posted: Fri Dec 15, 2006 9:46 am Post subject: Vne Speed |
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It's not BS. For a detailed discussion on the subject see
http://www.auf.asn.au/groundschool/flutter.html and scroll down to "control
reversal." Generally this is not a factor below around Mach 0.3 (OK,
that's about 200 KIAS).
Best regards,
Rob Housman
A070
Airframe complete
Irvine, CA
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rparigor(at)suffolk.lib.n
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| Posted: Fri Dec 15, 2006 10:34 am Post subject: Vne Speed |
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Hello David
"In Don Dykin's booklet about Europa aerodynamics he says that the flaps
take just about half of the plane's weight at top flap speed. With
aerodynamic forces increasing with speed squared I wouldn't want to rely
on
the flaps not failing before the wings, which have been tested to 10g
after
all!"
Were the XS short wings really tested and held up to 10 Gs, or was it
closer to 6 before failure?
I think the glider wings are stronger, and perhaps 10 on them?
What I was getting at, is with flaps down you have a wing that kinda sorta
has 30 degrees washout. Go much faster than max flap extension speed and
the tips are pushing through at a negative angle of attack, and the area
near flaps at a positive angle of attack. The net needs to be enough to
keep the plane in the air. There is this twisting and each half of the
wing fighting each other that is a very awkward.
Can this fight I speak of overload the wing in the middle and break it?
Can this fight I speak set up for flutter and break it?
Can this fight I speak of set up flutter in the ailerons?
Will the flaps flutter and depart?
will the flaps overload the attachments and depart?
Don't know exact, but the drag and lift bars double convinced that
exceeding max. flap down speed is not a good idea, evil begins full
hearted when you do.
Ron Parigoris
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davidjoyce(at)doctors.org
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| Posted: Sat Dec 16, 2006 12:13 am Post subject: Vne Speed |
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Ron, Somewhere I have seen a picture of the wings loaded up with sandbags to
a total of 10g - presumably the biological bits fail well before the wings.
I did understand that you were talking about the outer sections effectively
developing negative incidence when the flaps are down at high speed. However
since the inner section of the wing (& principally the flaps) have to
provide lift equal to the weight of the plane plus any negative lift being
developed by the outer wing (& possibly the fuselage) my bet is on the flap
brackets failing well before the wing, & and while I would be relaxed about
going a bit above Vne I would not want to exceed flap speed significantly.
Regards, David Joyce, G-XSDJ
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karelvranken(at)hotmail.c
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| Posted: Sat Dec 16, 2006 11:53 am Post subject: Vne Speed |
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Ron,
Is it possible to make a long final at Vno and at 50' above the figures pull
up for a nearly perfect loop around the setting sun. Then in the 3th quarter
setting out the wheel and flaps before Vna and landing on the figures
without bumps? You better try this than breaking your wings.
Karel Vranken.
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h&jeuropa
Joined: 07 Nov 2006
Posts: 635
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| Posted: Tue Dec 19, 2006 10:30 am Post subject: Re: Vne Speed |
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Vne
Wow, thanks for all the replies. I've learned a lot from this discussion!! That’s what makes this forum so valuable!! Here is what I have concluded - much of this information is from www.auf.asn.au/groundschool/umodule2.html#flight_envelope
Vne is defined by regulations as “the indicated airspeed (IAS) which should never be intentionally exceeded in a dive or other maneuver in smooth air”.
However, “unlike the performance airspeeds which are also specified as indicated airspeeds, Vne is related to those structural characteristics and limitations associated with bending, twisting and aeroelasticity which affect stability , control and structural integrity. Often Vne is related to flutter phenomenon which tends to be excited by dynamic pressure which increases exponentially with velocity, but Vne could be associated with other factors; for example bending of the fuselage.”
“Indicated airspeed really reflects dynamic pressure rather than airflow velocity so if the structural limitations which define Vne for an aircraft type are particularly associated with the distribution of forces associated with velocity then the specified indicated Vne has to be decreased as altitude is increased to adjust for the increase in true airspeed with altitude.”
The article goes on to state that some aircraft (especially those being operated at altitudes above 12500 ft) may have a Vne/altitude table which converts Vne to IAS as a function of density altitude. I imagine that high aspect ratio wings, like those on gliders, are susceptible to failure that is associated with velocity and gliders certainly operate at high altitude when possible, hence the caution in glider training manuals to convert Vne for density altitude.
I'm still curious as to what is Vne for the MG?
Jim Butcher
N241BW
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