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Starlionblue
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V-speed Definition Question

Thu May 31, 2012 8:08 am

I'm reading "Handling the Big Jets" and Davies defines V3 and V4 as follows:
- V3 - The all engines screen speed; the speed at which the aeroplane is assumed to pass through the screen height with all engines operating on take-off.
- V4 - The all engines steady initial climb speed; the speed assumed for the first segment noise abatement take-off procedure.

However Wikipedia and other sources say:
- V3 - Flap retraction speed.
- V4 - Steady initial climb speed. The all engines operating take-off climb speed used to the point where acceleration to flap retraction speed is initiated. Should be attained by a gross height of 400 feet.


Which one is correct? Yes I realize Handling the Big Jets was last revised in 1971.  
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egph
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RE: V-speed Definition Question

Tue Jun 05, 2012 12:41 pm

The Wikipedia article to which you refer cites a current Transport Canada webpage as its source for V3 and V4 definitions. So it comes down to whether you trust a current Transport Canada source or a book last reviewed before some of today's pilots were even born.
 
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Starlionblue
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RE: V-speed Definition Question

Tue Jun 05, 2012 12:58 pm

Quoting egph (Reply 1):
So it comes down to whether you trust a current Transport Canada source or a book last reviewed before some of today's pilots were even born.

Fair point. But basically then we're saying this is about various regulatory authorities language interpretation? 

BTW said book also calls "angle of attack" "angle of incidence", said I have heard describe the angle of mounting of the wing.
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Fabo
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RE: V-speed Definition Question

Wed Jun 06, 2012 12:58 am

Poteyto potahto...

V3 and V4 are not universally used like 1 and 2. They dont quite need the same stringent definition.
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vikkyvik
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RE: V-speed Definition Question

Wed Jun 06, 2012 5:07 am

Quoting Starlionblue (Thread starter):

That's interesting - so by the Wikipedia definition, you'd reach V4 before V3?

Quoting Starlionblue (Reply 2):
BTW said book also calls "angle of attack" "angle of incidence", said I have heard describe the angle of mounting of the wing.

Interesting - I've never heard AoA refer to anything but the angle of the wing with respect to the freestream flow. Similarly, I've never heard AoI refer to anything but the mounting angle of the wing.
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David L
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RE: V-speed Definition Question

Wed Jun 06, 2012 9:12 am

Quoting vikkyvik (Reply 4):
Quoting Starlionblue (Reply 2):BTW said book also calls "angle of attack" "angle of incidence", said I have heard describe the angle of mounting of the wing.
Interesting - I've never heard AoA refer to anything but the angle of the wing with respect to the freestream flow. Similarly, I've never heard AoI refer to anything but the mounting angle of the wing.

I've seen this come up in discussions before. While I don't remember anyone justifying it, I think the general reaction was to cut him some slack because the context makes it clearer and because of the quality of the work - i.e. you just have to "power through" that aspect.
 
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Starlionblue
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RE: V-speed Definition Question

Wed Jun 06, 2012 10:08 am

Quoting David L (Reply 5):
Quoting vikkyvik (Reply 4):
Quoting Starlionblue (Reply 2):BTW said book also calls "angle of attack" "angle of incidence", said I have heard describe the angle of mounting of the wing.
Interesting - I've never heard AoA refer to anything but the angle of the wing with respect to the freestream flow. Similarly, I've never heard AoI refer to anything but the mounting angle of the wing.

I've seen this come up in discussions before. While I don't remember anyone justifying it, I think the general reaction was to cut him some slack because the context makes it clearer and because of the quality of the work - i.e. you just have to "power through" that aspect.

Truth be told, I'd never heard the terms used for anything else either.

The book is more or less legendary and certainly the gentleman writing it seems to have been quite a character. I can't find any records on him easily googlable but I bet he was flying during WWII and then went on into flight test without ever raising his voice once. The way he describes what must have been quite harrowing flight tests in passing and with withering understatement is a pure pleasure. This was way before CFD and all that so who knew what would really happen. This is truly writing from before the PC age, when men were men and women were secretaries. No excuses, no pandering to sensitivities, just a clear message.

I'm with David. The book is so good that I suppose cutting the man some slack for archaic terminology is warranted. As someone on PPrune said (I paraphrase): "You have no idea how hard the man worked to make the craft you are flying safe."
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