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V-n Diagrams



 
 
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  #1  
Old August 26th 04, 01:33 PM
john smith
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Default V-n Diagrams

I have been playing around making V-n diagrams for the various airplanes
I rent from my flying club.
I made one for our P28T-201RT and was looking for the numbers on the
PA32-300.

The one item for the PA32-300 that would not follow the formula for
calculating the lift line was Va. The book shows it as 132 kias, but the
formula generates a speed of 103 kias for the intercept of the 3.8
load limit line.

Can anyone explain this discrepancy?

It is interesting to note that Piper does not allow any negative
maneuvers in the Normal catagory, on 3.8 positive. (Cessna does, -1.52.
Another reason to own a high-wing! ;-)))
Another interesting item was that both have a Vne of 192 kias and Vfe of
108 kias.

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  #2  
Old August 26th 04, 03:05 PM
Bob Moore
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Default

john smith wrote

The one item for the PA32-300 that would not follow the formula for
calculating the lift line was Va. The book shows it as 132 kias, but
the formula generates a speed of 103 kias for the intercept of the
3.8 load limit line.


When is 3.8g not 3.8g? When it is 4.5g or some other number.
Remember, 3.8g is a minimum figure for the normal category.
I have seen V-N diagrams for aircraft where the 3.8g line was
extended upward to accomodate the gust loading envelope at Vno.
Observe the gust envelope in the diagram at this web site:
http://adg.stanford.edu/aa241/structures/vn.html


It is interesting to note that Piper does not allow any negative
maneuvers in the Normal catagory, on 3.8 positive.


This is contrary to the required limits in FAR 23

Bob Moore
  #3  
Old August 26th 04, 03:25 PM
Mike Rapoport
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The load limit for normal catagory isn't always 3.8G. In a 747 it is around
2G and a MU-2 is 3.25G.

Mike
MU-2


"Bob Moore" wrote in message
. 6...
john smith wrote

The one item for the PA32-300 that would not follow the formula for
calculating the lift line was Va. The book shows it as 132 kias, but
the formula generates a speed of 103 kias for the intercept of the
3.8 load limit line.


When is 3.8g not 3.8g? When it is 4.5g or some other number.
Remember, 3.8g is a minimum figure for the normal category.
I have seen V-N diagrams for aircraft where the 3.8g line was
extended upward to accomodate the gust loading envelope at Vno.
Observe the gust envelope in the diagram at this web site:
http://adg.stanford.edu/aa241/structures/vn.html


It is interesting to note that Piper does not allow any negative
maneuvers in the Normal catagory, on 3.8 positive.


This is contrary to the required limits in FAR 23

Bob Moore



  #4  
Old August 26th 04, 03:33 PM
Bob Moore
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Default

"Mike Rapoport" wrote

The load limit for normal catagory isn't always 3.8G. In a 747 it is
around 2G and a MU-2 is 3.25G.


Too early for you Mike? :-) 747s aren't certificated in the
Normal Category...how about the Transport Category?

Bob Moore
  #5  
Old August 26th 04, 03:35 PM
john smith
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Default

Bob Moore wrote:
john smith wrote
The one item for the PA32-300 that would not follow the formula for
calculating the lift line was Va. The book shows it as 132 kias, but
the formula generates a speed of 103 kias for the intercept of the
3.8 load limit line.


When is 3.8g not 3.8g? When it is 4.5g or some other number.
Remember, 3.8g is a minimum figure for the normal category.
I have seen V-N diagrams for aircraft where the 3.8g line was
extended upward to accomodate the gust loading envelope at Vno.
Observe the gust envelope in the diagram at this web site:
http://adg.stanford.edu/aa241/structures/vn.html


Yes, where the lift line intercepts the 3.8 load limit line is Va. Some
V-n diagrams then show another linear lift line extending from the load
limit line to Vno linearly back down then back down to Vne line.

Va=(33*sqrt(wing loading)).
But for the PA32-300 this calculation yields 145 kias, higher than book
value, 132 kias.
Vno is 149 kias.

For other aircraft the formula and book values coincide, but for some
reason, the PA32-300 numbers do not.

I have been using this formula to generate the lift line:
n=(V/Vs)**2
then plotting n (y-axis, rise) against V (x-axis, run)

It is interesting to note that Piper does not allow any negative
maneuvers in the Normal catagory, on 3.8 positive.


Should read "... only 3.8 positive."

  #6  
Old August 26th 04, 03:41 PM
john smith
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Default

Bob Moore wrote:
The load limit for normal catagory isn't always 3.8G. In a 747 it is
around 2G and a MU-2 is 3.25G.


Too early for you Mike? :-) 747s aren't certificated in the
Normal Category...how about the Transport Category?


Must not have to know that for the ATP rating. :-))

  #7  
Old August 26th 04, 03:55 PM
Mike Rapoport
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Well it is pretty early here...MU-2 is normal catagory though

Mike
MU-2


"Bob Moore" wrote in message
...
"Mike Rapoport" wrote

The load limit for normal catagory isn't always 3.8G. In a 747 it is
around 2G and a MU-2 is 3.25G.


Too early for you Mike? :-) 747s aren't certificated in the
Normal Category...how about the Transport Category?

Bob Moore



  #8  
Old August 26th 04, 03:59 PM
Mike Rapoport
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Default


"john smith" wrote in message
...
Bob Moore wrote:
The load limit for normal catagory isn't always 3.8G. In a 747 it is
around 2G and a MU-2 is 3.25G.


Too early for you Mike? :-) 747s aren't certificated in the
Normal Category...how about the Transport Category?


Must not have to know that for the ATP rating. :-))


Fortunately for me!

Mike
MU-2


  #9  
Old August 26th 04, 04:04 PM
john smith
external usenet poster
 
Posts: n/a
Default

Mike Rapoport wrote:
The load limit for normal catagory isn't always 3.8G. In a 747 it is
around 2G and a MU-2 is 3.25G.


Too early for you Mike? :-) 747s aren't certificated in the
Normal Category...how about the Transport Category?


Must not have to know that for the ATP rating. :-))


Fortunately for me!


Sorry Mike, I hit the send key too quickly.

I am reading a paper about "Radial G" and the next paragraph is:
"By the same logic a large aircraft certified under FAR 25.337(b) with
the minimum allowed limit load of 2.5 would be restricted to a 1.65-g
rolling pull up. To keep things in round numbers, the "rolling" Va, as
calculated for the aircraft weight, would be about twenty percent less
than the symmetrical Va."

  #10  
Old August 26th 04, 04:50 PM
Tom S.
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Default


"Mike Rapoport" wrote in message
k.net...
The load limit for normal catagory isn't always 3.8G. In a 747 it is

around
2G and a MU-2 is 3.25G.



3.28g for the TC 690/695 series as well.

Tom


 




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