Turbulence penetration question

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Re: Turbulence penetration question

Unread post by Burner » Thu Feb 13, 2020 3:17 pm

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

Unread post by jimdavis » Thu Feb 13, 2020 11:08 pm

Burner wrote:
Thu Feb 13, 2020 3:17 pm
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!
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?

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

Unread post by Burner » Thu Feb 13, 2020 11:45 pm

jimdavis wrote:
Thu Feb 13, 2020 11:08 pm
Burner wrote:
Thu Feb 13, 2020 3:17 pm
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!
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?

Ha ha ha - I suppose that this is not an economically viable precaution for ALL operational flying.

jim
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!
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Re: Turbulence penetration question

Unread post by jimdavis » Fri Feb 14, 2020 5:17 am

Burner wrote:
Thu Feb 13, 2020 11:45 pm
jimdavis wrote:
Thu Feb 13, 2020 11:08 pm
Burner wrote:
Thu Feb 13, 2020 3:17 pm
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!
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?

Ha ha ha - I suppose that this is not an economically viable precaution for ALL operational flying.

jim
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!
Okay got it - that makes perfect sense, thanks Burner.

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Re: Turbulence penetration question

Unread post by heisan » Fri Feb 14, 2020 9:31 am

Burner wrote:
Thu Feb 13, 2020 3:17 pm
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!
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.

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

Unread post by Slam and Go » Fri Feb 14, 2020 4:24 pm

Burner wrote:
Thu Feb 13, 2020 3:17 pm
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

Unread post by Burner » Fri Feb 14, 2020 4:46 pm

Slam and Go wrote:
Fri Feb 14, 2020 4:24 pm
Burner wrote:
Thu Feb 13, 2020 3:17 pm
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!
B1900?
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.
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Re: Turbulence penetration question

Unread post by Slam and Go » Fri Feb 14, 2020 4:56 pm

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

Unread post by Richard Smit » Fri Feb 14, 2020 9:42 pm

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.
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Re: Turbulence penetration question

Unread post by Burner » Fri Feb 14, 2020 10:18 pm

Slam and Go wrote:
Fri Feb 14, 2020 4:56 pm
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?
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.
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Re: Turbulence penetration question

Unread post by Dragon » Sat Feb 15, 2020 6:25 pm

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.
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Re: Turbulence penetration question

Unread post by Caravan Driver » Sat Feb 15, 2020 9:30 pm

Dragon wrote:
Sat Feb 15, 2020 6:25 pm
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.
Bit of a generalization there regarding the airline pilots... I guess there are some who do not read the material provided to them.
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Re: Turbulence penetration question

Unread post by StressMerchant » Sun Feb 16, 2020 2:36 pm

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?
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