Turbulence penetration question
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Re: Turbulence penetration question
Okay so we have an instructor in the sim... he has very little operation experience, but by his accounts a large amount of experience as a test flight engineer for Denel. He insists we fly all the descents in all conditions below Va. Which for our machine is 70-80 kts below the barbers pole. His point of view is that turbulence can occur at any time, so we should always be below Va. But then we are often in the cruise way above Va. What I continue to see is that turbulence penetration varies massively based on the aircraft type, when it was certified, where it was certified. Turbulence penetration is surely a speed at which you enter an area where you expect turbulence!
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Re: Turbulence penetration question
Interesting - thanks Burner. Wasn't this guy's point that you can still hit turbulence when you don't expect it, and must therefore be at a safe speed?Burner wrote: ↑Thu Feb 13, 2020 3:17 pmOkay so we have an instructor in the sim... he has very little operation experience, but by his accounts a large amount of experience as a test flight engineer for Denel. He insists we fly all the descents in all conditions below Va. Which for our machine is 70-80 kts below the barbers pole. His point of view is that turbulence can occur at any time, so we should always be below Va. But then we are often in the cruise way above Va. What I continue to see is that turbulence penetration varies massively based on the aircraft type, when it was certified, where it was certified. Turbulence penetration is surely a speed at which you enter an area where you expect turbulence!
Ha ha ha - I suppose that this is not an economically viable precaution for ALL operational flying.
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Re: Turbulence penetration question
In a light aircraft, absolutely! But in many high performance turbines and jets, you are usually cruising well above Va in level flight. Especially at lower altitudes. My argument is then surely all aircraft should NEVER be above Va, and Va should be treated like Vne. Of course this is totally impractical! Would I descend above Va in a 210 going through 10000 feet on a hot summers day... of course not!jimdavis wrote: ↑Thu Feb 13, 2020 11:08 pmInteresting - thanks Burner. Wasn't this guy's point that you can still hit turbulence when you don't expect it, and must therefore be at a safe speed?Burner wrote: ↑Thu Feb 13, 2020 3:17 pmOkay so we have an instructor in the sim... he has very little operation experience, but by his accounts a large amount of experience as a test flight engineer for Denel. He insists we fly all the descents in all conditions below Va. Which for our machine is 70-80 kts below the barbers pole. His point of view is that turbulence can occur at any time, so we should always be below Va. But then we are often in the cruise way above Va. What I continue to see is that turbulence penetration varies massively based on the aircraft type, when it was certified, where it was certified. Turbulence penetration is surely a speed at which you enter an area where you expect turbulence!
Ha ha ha - I suppose that this is not an economically viable precaution for ALL operational flying.
jim
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Re: Turbulence penetration question
Okay got it - that makes perfect sense, thanks Burner.Burner wrote: ↑Thu Feb 13, 2020 11:45 pmIn a light aircraft, absolutely! But in many high performance turbines and jets, you are usually cruising well above Va in level flight. Especially at lower altitudes. My argument is then surely all aircraft should NEVER be above Va, and Va should be treated like Vne. Of course this is totally impractical! Would I descend above Va in a 210 going through 10000 feet on a hot summers day... of course not!jimdavis wrote: ↑Thu Feb 13, 2020 11:08 pmInteresting - thanks Burner. Wasn't this guy's point that you can still hit turbulence when you don't expect it, and must therefore be at a safe speed?Burner wrote: ↑Thu Feb 13, 2020 3:17 pmOkay so we have an instructor in the sim... he has very little operation experience, but by his accounts a large amount of experience as a test flight engineer for Denel. He insists we fly all the descents in all conditions below Va. Which for our machine is 70-80 kts below the barbers pole. His point of view is that turbulence can occur at any time, so we should always be below Va. But then we are often in the cruise way above Va. What I continue to see is that turbulence penetration varies massively based on the aircraft type, when it was certified, where it was certified. Turbulence penetration is surely a speed at which you enter an area where you expect turbulence!
Ha ha ha - I suppose that this is not an economically viable precaution for ALL operational flying.
jim
jim
"PPL Manual"
"Flight Tests"
"So Others May Live"
"Flying in Africa" Vol 1
"Flying in Africa" Vol 2
Look inside these books, or buy them at: www.jimdavis.co.za.
"Flight Tests"
"So Others May Live"
"Flying in Africa" Vol 1
"Flying in Africa" Vol 2
Look inside these books, or buy them at: www.jimdavis.co.za.
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Re: Turbulence penetration question
Why Va? Judging by those speeds, that is a transport category aircraft, so should have a published Vb (turbulence penetration speed) - which is lower than Va.Burner wrote: ↑Thu Feb 13, 2020 3:17 pmOkay so we have an instructor in the sim... he has very little operation experience, but by his accounts a large amount of experience as a test flight engineer for Denel. He insists we fly all the descents in all conditions below Va. Which for our machine is 70-80 kts below the barbers pole. His point of view is that turbulence can occur at any time, so we should always be below Va. But then we are often in the cruise way above Va. What I continue to see is that turbulence penetration varies massively based on the aircraft type, when it was certified, where it was certified. Turbulence penetration is surely a speed at which you enter an area where you expect turbulence!
So by picking Va, you are flying at some arbitrary speed (which has no relationship to gust loadings), which is lower than your still air limit, but still higher than the turbulence limit.
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Re: Turbulence penetration question
B1900?Burner wrote: ↑Thu Feb 13, 2020 3:17 pmOkay so we have an instructor in the sim... he has very little operation experience, but by his accounts a large amount of experience as a test flight engineer for Denel. He insists we fly all the descents in all conditions below Va. Which for our machine is 70-80 kts below the barbers pole. His point of view is that turbulence can occur at any time, so we should always be below Va. But then we are often in the cruise way above Va. What I continue to see is that turbulence penetration varies massively based on the aircraft type, when it was certified, where it was certified. Turbulence penetration is surely a speed at which you enter an area where you expect turbulence!
GR III C210 B1900 YDKWYDK
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Re: Turbulence penetration question
Indeed. Whilst I'm all for the idea of flying conservatively, higher performance aircraft often are flying at speeds above Va and Vb(turbulence penetration). To descend at 170 kts indicated on an aircraft that in many cases at lower altitudes is 50-60kts above this at level cruise indicated, makes zero sense. I see speeds above Vb as the yellow arc. It's where the speed must come back to when there is predictable turbulence.Slam and Go wrote: ↑Fri Feb 14, 2020 4:24 pmB1900?Burner wrote: ↑Thu Feb 13, 2020 3:17 pmOkay so we have an instructor in the sim... he has very little operation experience, but by his accounts a large amount of experience as a test flight engineer for Denel. He insists we fly all the descents in all conditions below Va. Which for our machine is 70-80 kts below the barbers pole. His point of view is that turbulence can occur at any time, so we should always be below Va. But then we are often in the cruise way above Va. What I continue to see is that turbulence penetration varies massively based on the aircraft type, when it was certified, where it was certified. Turbulence penetration is surely a speed at which you enter an area where you expect turbulence!
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Re: Turbulence penetration question
In this type I was taught to slow to 160KT in the cruise before top-of-descent and maintain this speed during descent. Would anyone with B1900 experience care to chip in?
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Re: Turbulence penetration question
Turbulence penetration speed provides the safest possible margin below the structural speed, and above the stall speed.
As previously mentioned, it is that speed at which a full and abrupt pitch input will see an aircraft stall before it breaks (overly simplified).
Va is max manouver speed.
Vb is turbulence penetration speed
Turbulence penetration speed need only be used in severe turbulence, during air transport operations. Severe turbulence is when it’s difficult to read the instruments.... Not when one thinks it’s going to be bumpy!
This is not to say that one shouldn’t slow down a little in turbulence. What it is saying, is this should be done appropriately.
Flying under IFR (Airways), at 160 KIAS from ToD, is unnecessary, and puts one in conflict with ATC planning.
A B1900 should easily be able to fly 210 to 15nm, 180 to the GS intercept, and 160 to 5nm.
As previously mentioned, it is that speed at which a full and abrupt pitch input will see an aircraft stall before it breaks (overly simplified).
Va is max manouver speed.
Vb is turbulence penetration speed
Turbulence penetration speed need only be used in severe turbulence, during air transport operations. Severe turbulence is when it’s difficult to read the instruments.... Not when one thinks it’s going to be bumpy!
This is not to say that one shouldn’t slow down a little in turbulence. What it is saying, is this should be done appropriately.
Flying under IFR (Airways), at 160 KIAS from ToD, is unnecessary, and puts one in conflict with ATC planning.
A B1900 should easily be able to fly 210 to 15nm, 180 to the GS intercept, and 160 to 5nm.
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Re: Turbulence penetration question
In smooth air, the 1900 is absolutely fine 10 kts below the barbers pole all the way down. I spent more than a few years flying in Afghanistan, Kandahar specifically where I was told to keep the speed up and land deep. My gripe is that Va and Vb are very important when the conditions dictate. Flying in the Sahara in summer, before I hit 10000 feet, i slow down to below turbulent penetration speed, because I know there will be "lumps and bumps". In a sim scenario, to blanket ban any flying above 170 on a 1900 is pathetic and shows a lack of understanding how to balance theory I the real world.Slam and Go wrote: ↑Fri Feb 14, 2020 4:56 pmIn this type I was taught to slow to 160KT in the cruise before top-of-descent and maintain this speed during descent. Would anyone with B1900 experience care to chip in?
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Re: Turbulence penetration question
Turbulence penetration speed is misunderstood by many pilots (esp airline pilots) to be the speed that gives the smoothest ride. I am so glad it has been given some attention here. Hope it gets lots of coverage.
Smoothest ride although related, is a different conversation.
Smoothest ride although related, is a different conversation.
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Re: Turbulence penetration question
Bit of a generalization there regarding the airline pilots... I guess there are some who do not read the material provided to them.Dragon wrote: ↑Sat Feb 15, 2020 6:25 pmTurbulence penetration speed is misunderstood by many pilots (esp airline pilots) to be the speed that gives the smoothest ride. I am so glad it has been given some attention here. Hope it gets lots of coverage.
Smoothest ride although related, is a different conversation.
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Re: Turbulence penetration question
It would be interesting to know why people use speeds other than the recommended VRA. Are they:
- Concerned about fatigue implications?
- Find a slower speed more comfortable?
- Are worried about the effect of turbulence on control ability?
- Concerned about fatigue implications?
- Find a slower speed more comfortable?
- Are worried about the effect of turbulence on control ability?
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