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Exceeding Vno, where is the danger?
Curious as to how others approach exceeding Vno, into the yellow arc on the ASI. The normal cautions are to only be in that regime when in smooth air, but what defines smooth air?
Can I use my g-meter to measure the cutoff between smooth and non-smooth air? For example, if I experience turbulence that shows up on my g meter, say .5 to 1.5, should I be slowing down to Vno? What about if it displays 0.0 - 2.0? Or greater? Can I safely pull 3 g's in a loop when exceeding Vno if I am in "smooth" air? Or perform a roll where positive g's are maintained and do not significantly exceed 1.0? Can someone provide an understanding of the aeronautical engineering process that goes into determining Vno? |
Google "V-g diagram".
Vno is set where the load limit is reached in a instantaneous 30 ft/sec downdraft. (Old definition. I believe there is a revised standard which applies the force in a not-instantaneous fashion, but gives similar results). |
Otherwise known as a "design gust."
A design gust is significantly stronger than you think. It's enough to exceed a -3 acceleration, which is probably the kind of turbulence that's serious enough to just keep you on the ground, rather than be in the air wondering what speed you should be flying at. Also note that the yellow arc has nothing to do with Va, the speed at which full control deflection exceeds the aircraft's maximum load factor. That seems to be a point of confusion among some pilots I talk to, so it's worthy of note here. - mark |
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FYI, my Rocket has a Vno of 160 knots. My normal cruise at 23 squared, 3000 ft ASL, LOP, is >170 knots. This seems to be the airplanes happy place. I sometimes get into a bit of light chop, especially when crossing converging valleys, and get to wondering - when should I pull the power back? At the onset of any bumps at all? |
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https://www.dropbox.com/s/zztwztfpdj...20CAT.mp4?dl=0 I was just cruising along at 140 KIAS (in the yellow arc) in smooth air when I hit some CAT. The engine hesitated and I thought something vital had departed the aircraft, but everything smoothed out again. No damage was done, other than to my skivvies. |
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If you want to fly faster than Vno, without your airplane coming apart, you need to be aware that the strength of gust you can cope with is now reduced. Given that you can't tell when and how strong the next gust will be, you had better be damned careful when you encouter any turbulence at speeds higher than Vno. |
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I sincerely value your input. |
Turbulence definitions: NOAA
Scott pretty much hit it on the head. The only thing I would add regards the significance of that 30 FPS gust.
NOAA defines light turbulence as gusts 5-19 FPS and moderate turbulence as gusts of 20-35 FPS. So, that 30 FPS gust is close to the upper end of moderate turbulence. Everybody has a different tolerance for risk, but it would not be too smart to fly into an area of forecast moderate turbulence above Vno :D NOAA Reference |
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Would be really interesting to know if there is any correlation between gust levels and what a person is likely to register on a g-meter, assuming an RV-like aircraft. Light chop always seems to show up on my g-meter as an extra +- ~0.5 g. |
The current requirement for Vno is to withstand 50 fps gusts (https://www.law.cornell.edu/cfr/text/14/23.333), which according to the NOAA document linked above, corresponds to extreme turbulence.
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