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What is a "short field" for a PA28-181



 
 
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  #1  
Old November 18th 04, 03:34 AM
Roy Page
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Default What is a "short field" for a PA28-181

I have been trying to determine the length of a runway that would be
considered a "short field" for my Archer II.
The two instructors that I work with on occasions disagree on the amount of
flaps to use for takeoff at gross weight.
One guy says my airfield with a 2,800ft runway is a "short field" and I
should use 25deg flaps as per the POH for takeoff at gross weight.
The other says 2,800ft is not a short field and I should use 10 deg flap at
gross weight and that 25 deg increases drag too much.
It does not help that the instructors have a low opinion of each other.
The POH is clear about using 25 deg for a short field but I have failed to
find what runway length puts in a short field category.
These guys also instruct in a PA28-140 based here and you can guess that
some students are using 1 notch of flap, while the other set use 2 notches.

So the question is.
How long is a "short field" for a PA28-181 ? And for that matter how does
that relate to a PA28-140 with 30 less horses.

--
Roy
N5804F - PA28-181


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  #2  
Old November 18th 04, 04:14 AM
zatatime
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On Thu, 18 Nov 2004 02:34:16 GMT, "Roy Page"
wrote:

One guy says my airfield with a 2,800ft runway is a "short field" and I
should use 25deg flaps as per the POH for takeoff at gross weight.

In the summer, heavily loaded I'd say he's right. In the summer with
obstacles at the end of the runway I'd also say he's right.

The other says 2,800ft is not a short field and I should use 10 deg flap at
gross weight and that 25 deg increases drag too much.

In the winter, or fall with a headwind I'd say he's right. At a field
with no obstacles and fields beyond the end of the runway, I'd also
say he's right.



There is no cut and dry answer to this. You need to learn your
airplane. Look at the POH and make a determination of what you feel
is appropriate for your skill level. It's pretty obvious these two
are fighting for fighting sake since they are arguing over something
that is situationally dependant, and one of the "finer" points of
flying. If you're completely in doubt use the 25 the POH says and you
should get close to what the charts depict for short field performance
assuming a descent engine and airframe.

HTH & Good luck with those two.

z
  #3  
Old November 18th 04, 04:45 AM
BTIZ
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Look at the POH and determine what the take off distance is over a 50ft
obstacle, normal take off (no flaps) Then compute the landing distance over
a 50ft obstacle. This will give you a very conservative Accelerate / Stop
distance estimate. If the runway in use is shorter than that, then you may
not be able to accelerate to rotation speed, chop the throttle and safely
stop. I would use the short field take off procedure.

If the POH does not list take off data for 1 notch of flaps, and states to
use 2 notches for a short field. Then I would use 2 notches and not pay
attention to the instructor that says to use only one notch.

With no data in the POH for a "modified short field technique", then you are
a test pilot and only can reasonably estimate that the required distance to
clear the 50ft obstacle is somewhere between the no flap (normal) departure
and the prescribes short field (2 notch) departure.

I can read the NTSB report now, pilot attempting take off from a short field
did not follow the prescribed takeoff procedure and failed to outclimb the
obstacle on departure. Causal factor: Pilot error.

jmho
BT

"Roy Page" wrote in message
nk.net...
I have been trying to determine the length of a runway that would be
considered a "short field" for my Archer II.
The two instructors that I work with on occasions disagree on the amount
of flaps to use for takeoff at gross weight.
One guy says my airfield with a 2,800ft runway is a "short field" and I
should use 25deg flaps as per the POH for takeoff at gross weight.
The other says 2,800ft is not a short field and I should use 10 deg flap
at gross weight and that 25 deg increases drag too much.
It does not help that the instructors have a low opinion of each other.
The POH is clear about using 25 deg for a short field but I have failed to
find what runway length puts in a short field category.
These guys also instruct in a PA28-140 based here and you can guess that
some students are using 1 notch of flap, while the other set use 2
notches.

So the question is.
How long is a "short field" for a PA28-181 ? And for that matter how does
that relate to a PA28-140 with 30 less horses.

--
Roy
N5804F - PA28-181




  #4  
Old November 18th 04, 05:51 AM
Blanche
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And don't forget density altitude!

  #5  
Old November 18th 04, 06:22 AM
Jim Burns
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Try taking the landing and take off distances over a 50 ft obstacle and
doubling them. Anything at or under those distances I'd consider using the
short field techniques.

I just grabbed an old Archer II POH and ran my finger across the table I
come up with a rough guess short field take off over a 50 ft obstacle
distance of 1500 ft from a dry paved runway with 25 degrees of flaps at
standard conditions. Double that and you get 3000 ft. Under 3000 ft I'd
use the short field technique. Flaps up, same conditions takes 1850 feet.
Double that and you get 3700 ft.

Between 3700 and 3000 ft of runway, it would depend more on the
circumstances and conditions.

I'd apply the same rule of thumb to landings.

These numbers may sound way to conservative, but they give you a lot of
fundge factor on the safe side and I'd rather be safe than sorry. Most of
us don't fly factory fresh airplanes and most of us aren't test pilots.

Jim



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  #6  
Old November 18th 04, 03:26 PM
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Roy Page wrote:
: So the question is.
: How long is a "short field" for a PA28-181 ? And for that matter how does
: that relate to a PA28-140 with 30 less horses.

I fly a Hershey-bar PA28-140 with a 180hp engine, so it's probably somewhere
between the two. If your POH is anything like mine, I understand your apprehension
about what the "true numbers" are. Piper was particularly awful in the older books
WRT some things. For instance, I routinely fly my plane on grass strips with
3000-4000' DA, but I have no guidance from the POH on grass. I would also like
partial loading characteristics, since I almost never fly at gross (for a -180).
Neither of these are present.

I think that the poster who suggesting adding the takeoff (w/ or w/o obstacle
clearance) + the landing distance ground roll makes a very reasonable, yet not overly
conservative estimate. For mine at 3000' DA, that'd be 2200+600 over a 50' obstacle
from a paved runway. Given the safety factor of generally being under gross by
200-300 lbs, that's a very reasonable number.

WRT 1 notch or two, the decision is clear. You're either doing short field
by the book or you're not. While adding 1 notch may help some, you have no
substantive reason to know how much... thus, I wouldn't do it where I wasn't
comfortable with a normal takeoff.

All that said, from what I've gathered by looking through a number of POH's
(not Pipers') and other references, I've come up with the following "rules of thumb"
to keep from being overly aggressive/conservative:

"good" grass: adds 10-20%
"bad" grass: adds 20-30% - not yet tried...
10% under gross: decreases 10%
nonstandard DA: By the book

YMMV
-Cory


--

************************************************** ***********************
* Cory Papenfuss *
* Electrical Engineering candidate Ph.D. graduate student *
* Virginia Polytechnic Institute and State University *
************************************************** ***********************

  #7  
Old November 18th 04, 04:37 PM
Mike Rapoport
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The problem with this logic is that the 50' obstical distance is genarally
greater with the short field flap setting. Only the ground run is shorter.

Mike
MU-2

"BTIZ" wrote in message
news:[email protected]
Look at the POH and determine what the take off distance is over a 50ft
obstacle, normal take off (no flaps) Then compute the landing distance
over a 50ft obstacle. This will give you a very conservative Accelerate /
Stop distance estimate. If the runway in use is shorter than that, then
you may not be able to accelerate to rotation speed, chop the throttle and
safely stop. I would use the short field take off procedure.

If the POH does not list take off data for 1 notch of flaps, and states to
use 2 notches for a short field. Then I would use 2 notches and not pay
attention to the instructor that says to use only one notch.

With no data in the POH for a "modified short field technique", then you
are a test pilot and only can reasonably estimate that the required
distance to clear the 50ft obstacle is somewhere between the no flap
(normal) departure and the prescribes short field (2 notch) departure.

I can read the NTSB report now, pilot attempting take off from a short
field did not follow the prescribed takeoff procedure and failed to
outclimb the obstacle on departure. Causal factor: Pilot error.

jmho
BT

"Roy Page" wrote in message
nk.net...
I have been trying to determine the length of a runway that would be
considered a "short field" for my Archer II.
The two instructors that I work with on occasions disagree on the amount
of flaps to use for takeoff at gross weight.
One guy says my airfield with a 2,800ft runway is a "short field" and I
should use 25deg flaps as per the POH for takeoff at gross weight.
The other says 2,800ft is not a short field and I should use 10 deg flap
at gross weight and that 25 deg increases drag too much.
It does not help that the instructors have a low opinion of each other.
The POH is clear about using 25 deg for a short field but I have failed
to find what runway length puts in a short field category.
These guys also instruct in a PA28-140 based here and you can guess that
some students are using 1 notch of flap, while the other set use 2
notches.

So the question is.
How long is a "short field" for a PA28-181 ? And for that matter how does
that relate to a PA28-140 with 30 less horses.

--
Roy
N5804F - PA28-181






  #8  
Old November 18th 04, 04:39 PM
Mike Rapoport
external usenet poster
 
Posts: n/a
Default


"Roy Page" wrote in message
nk.net...
I have been trying to determine the length of a runway that would be
considered a "short field" for my Archer II.
The two instructors that I work with on occasions disagree on the amount
of flaps to use for takeoff at gross weight.
One guy says my airfield with a 2,800ft runway is a "short field" and I
should use 25deg flaps as per the POH for takeoff at gross weight.
The other says 2,800ft is not a short field and I should use 10 deg flap
at gross weight and that 25 deg increases drag too much.
It does not help that the instructors have a low opinion of each other.
The POH is clear about using 25 deg for a short field but I have failed to
find what runway length puts in a short field category.
These guys also instruct in a PA28-140 based here and you can guess that
some students are using 1 notch of flap, while the other set use 2
notches.

So the question is.
How long is a "short field" for a PA28-181 ? And for that matter how does
that relate to a PA28-140 with 30 less horses.

--
Roy
N5804F - PA28-181


Keep in mind that the short field settings shorten the ground run but
generally increase the distance to clear a 50' obstical.

Mike
MU-2


  #9  
Old November 18th 04, 04:55 PM
Mike Rapoport
external usenet poster
 
Posts: n/a
Default


"BTIZ" wrote in message
news:[email protected]
Look at the POH and determine what the take off distance is over a 50ft
obstacle, normal take off (no flaps) Then compute the landing distance
over a 50ft obstacle. This will give you a very conservative Accelerate /
Stop distance estimate. If the runway in use is shorter than that, then
you may not be able to accelerate to rotation speed, chop the throttle and
safely stop. I would use the short field take off procedure.


This is indeed conservative! it is probably twice the accelerate/stop
distance.

Mike
MU-2

jmho
BT

"Roy Page" wrote in message
nk.net...
I have been trying to determine the length of a runway that would be
considered a "short field" for my Archer II.
The two instructors that I work with on occasions disagree on the amount
of flaps to use for takeoff at gross weight.
One guy says my airfield with a 2,800ft runway is a "short field" and I
should use 25deg flaps as per the POH for takeoff at gross weight.
The other says 2,800ft is not a short field and I should use 10 deg flap
at gross weight and that 25 deg increases drag too much.
It does not help that the instructors have a low opinion of each other.
The POH is clear about using 25 deg for a short field but I have failed
to find what runway length puts in a short field category.
These guys also instruct in a PA28-140 based here and you can guess that
some students are using 1 notch of flap, while the other set use 2
notches.

So the question is.
How long is a "short field" for a PA28-181 ? And for that matter how does
that relate to a PA28-140 with 30 less horses.

--
Roy
N5804F - PA28-181






  #10  
Old November 18th 04, 05:33 PM
Dave Butler
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Posts: n/a
Default

Mike Rapoport wrote:
The problem with this logic is that the 50' obstical distance is genarally
greater with the short field flap setting. Only the ground run is shorter.


I don't have any documentary evidence, but this is counterintuitive and contrary
to my unquantified experience. The Cherokees feel like they go up at a much
steeper angle with the flaps. Is it an illusion?

 




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