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Pipistrel Virus I-B939 doing 245kt

Steve6443 wrote:

If I recall correctly, the issue with Va is not the fact that you see traffic and haul back on the stick – in such an instance, the plane will stall before the airframe experiences any damage. The issue is negative G. If you push the stick forward, the wings are more susceptible to damage due to negative G hence the relatively low limit in Va.

Yes in many aircraft bellow VA has stall protection from pull on the elevator VA vs VS*SQRT(G) for positive G and but yes it will get highly restrictive on negative G, there is more than just total G/Lift in a turn, the bending moment on wings when applying full ailerons and full elevator also matters, while total lift is mainly determined by G, you may have more lift on high wing and less on low wing, some structures are designed to take a lot of load (Lift_Left+Lift_Right) = Weight*G but one wing may snap when the torsion (Lift_Left-Lift_Right) moment is really high

This has been cited as factor in few deadly series of Piper Malibu/Mirage in-flight breakup in the 90’s, but most involved flying faster than VA anyway due to pilot loss of control, so it does not matter what comes first: flutter, max G, VNE, VA or max torsion…

Last Edited by Ibra at 15 Oct 11:55
Paris/Essex, France/UK, United Kingdom

Wow

This bit made me smile “Ko sta pilot in potnik izstopila iz letala sta ugotovila da sta v Sloveniji.

Have I understood it correctly that non-one knew they were in difficulties? Bovec is the back end of nowhere and they were lucky to land in a valley and not up a mountain.

EGHO-LFQF-KCLW, United Kingdom

I went to look for the original accident report for this one. I found one link but it is dead.

The reg is I-B939. ASN.

Found it eventually – local copy

Administrator
Shoreham EGKA, United Kingdom

Ibra wrote:

Pipistrel SW had reinforced structure and all speeds were raised: VA from 75kts to 95kts, VB from 75kts to 130kts and VNE from 135kts to 165kts but I still think it’s VA is way too low, imagine you suddenly see a traffic in 140kts cruise?

If I recall correctly, the issue with Va is not the fact that you see traffic and haul back on the stick – in such an instance, the plane will stall before the airframe experiences any damage. The issue is negative G. If you push the stick forward, the wings are more susceptible to damage due to negative G hence the relatively low limit in Va.

EDL*, Germany

Wow Pipistrel is slick & fast but this one just went faster than the Acclaim or PC12…

I wonder if they end up deep IMC why not cut power, trim for slow speeds and use air-breaks to slow the speed in the IMC decent? (that’s what BRS does anyway)

While there are so much assumptions in flight envelope design, it’s fair to assume if you lose control past VNE it’s 100% game over, in controlled “wing level” flights, you can exceed VNE by holding your teeth and you can exceed Gmax if you stay awake, in uncontrolled dives, VNE & Max G may not even matter, you can even snap one wing way bellow maxG & VNE simply by full ailerons twist & full elevator pull above VA !

Pipistrel SW had reinforced structure and all speeds were raised: VA from 75kts to 95kts, VB from 75kts to 130kts and VNE from 135kts to 165kts but I still think it’s VA is way too low, imagine you suddenly see a traffic in 140kts cruise?

Last Edited by Ibra at 14 Oct 09:12
Paris/Essex, France/UK, United Kingdom

Vne has very little to do with flutter. Vne/0.9 is the max speed the aircraft is designed to fly at. Above that speed anything can happen. Reversal of aileron control due to wing twist, overloading of the tail, break up of structures (fairings, panels, cowlings etc).

Then the aircraft must be tested at Vne (or above) for odd effects. Flutter is just about the only thing to test, because you cannot manouver or do anything with the aircraft at that speed. Flutter itself isn’t a difficult thing to deal with if needed.

The elephant is the circulation
ENVA ENOP ENMO, Norway

We might be a little more careful in our evaluation: The quote above is from a marketing publication of the chute manufacturer. Has anyone read the original accident report with a more neutral representation of the facts?
The link in the marketing statement doesn’t work and my Slovenian is too nonexistent to search it myself on the Slovenian government page…

The plane was overstressed and disintegrated – so far a normal behavior of any mechanical structure. To judge if this is what any plane would do or if this is really a sign of exceptional design one needed to have much more information, e.g. how long the loads were at which magnitude.
With respect to excess airspeed: It is completely normal that an airplane doesn’t suddenly fall into parts when Vne is exceeded. Typically such designs are flutter limited and flutter catastrophes take some time. In addition, the high wingload is actually in favor of overspeed stability, as flutter is much less likely at high wing loads (i.e. it may well be that the wing survived the 220-240kt for some time not despite but because the wing load at that time has been 6g…).

Germany

Well, two things are sure :

1. The Pipistrel engineers must receive an annual present from all onboard
2. While sitting in a car in a parking lot, my pucker factor went from 0 to 6 reading this.

This is like nothing I’ve ever heard before.

@dublinpilot exactly! Reading it I was wondering the same… They must have been reaching for it, but 6g to 10g to 0g, like how do you make your arm move the direction you want in that hellstorm?!

Also, how is this not a movie?
Even a short film.
No one would believe it, but those people know stuff we don’t!

dublinpilot wrote:

Amazing that after exceeding 10G they were still conscious enough to be able to pull the chute!

I guess the 10Gs were very momentary. As soon as the wings snapped, it would be 0G…

ESKC (Uppsala/Sundbro), Sweden

If the data is correct, that’s a big tribute to the build strength of pipistrel.

Video
https://www.galaxysky.cz/data/video/grs-rescue-slovenia-2015-10-3.mp4

The accident occurred, after the aircraft, which is not approved for flying under Instrument Flight Rules and/or in Instrument Meteorological Conditions, stalled inside clouds and departed controlled flight.

always learning
LO__, Austria
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