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



 
 
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  #11  
Old November 18th 04, 06:07 PM
Mike Rapoport
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"Dave Butler" wrote in message
...
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?


I think so. The Helio Courier flight manual gives different flap settings
for minimium ground run vs. minimiunm 50' obstacle clearance with a lower
flap setting for the obstacle clearance distance. These airplanes have more
sophisticated flaps than a Cherokee (single slotted fowler flaps on the
Helio) so I assume that the Cherokee is even more disadvantaged as the flaps
are deployed since they are creating relatively more drag for each increment
of increased lift. Of course, if the runway is not hard and dry, anything
that reduces ground roll will likely reduce the obstacle distance.

Also, the maximium performance takeoff in a Super Cub is to accelerate with
the flaps retracted and then deploy full flaps to break ground, then to
reduce flaps while accerating in ground effect to Vx and then to climb at
Vx. It is impressive to see someone do this well.

You will need more pitch with the lower flap setting.

Perhaps someone with a newer Cherokee could look in the manual and see if
there are obstacle clearance charts for the different takeoff
configurations?

Mike
MU-2


  #12  
Old November 18th 04, 06:38 PM
Jim Burns
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The one I looked at was an Archer II POH.

25 degrees of flaps, standard conditions, dry, paved, level runway was about
1500 ft over 50 ft obstacle

0 flaps, same conditions takes about 1850 ft over a 50ft obstacle

Those were the only two configurations given.

I didn't compare ground roll distances but that would indeed be interesting.

And you are correct, the Super Cub is impressive. I did my tailwheel
checkout in a SC. We never used the flaps off, flaps on, flaps off
technique, but even so, once you break ground you can pull the stick back as
far as you want and it just goes UP!

Jim


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  #13  
Old November 18th 04, 06:51 PM
Mike Rapoport
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Thanks. Are both takeoffs to Vx?

Mike
MU-2


"Jim Burns" wrote in message
...
The one I looked at was an Archer II POH.

25 degrees of flaps, standard conditions, dry, paved, level runway was
about
1500 ft over 50 ft obstacle

0 flaps, same conditions takes about 1850 ft over a 50ft obstacle

Those were the only two configurations given.

I didn't compare ground roll distances but that would indeed be
interesting.

And you are correct, the Super Cub is impressive. I did my tailwheel
checkout in a SC. We never used the flaps off, flaps on, flaps off
technique, but even so, once you break ground you can pull the stick back
as
far as you want and it just goes UP!

Jim


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  #14  
Old November 18th 04, 07:55 PM
Jim Burns
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I thought of that question also and I'll check tonight when I get home. I
would think that a "normal" takeoff would be to Vy and a short field to Vx.
But then again sometimes "normal" has many definitions!

Jim

"Mike Rapoport" wrote in message
hlink.net...
Thanks. Are both takeoffs to Vx?

Mike
MU-2


"Jim Burns" wrote in message
...
The one I looked at was an Archer II POH.

25 degrees of flaps, standard conditions, dry, paved, level runway was
about
1500 ft over 50 ft obstacle

0 flaps, same conditions takes about 1850 ft over a 50ft obstacle

Those were the only two configurations given.

I didn't compare ground roll distances but that would indeed be
interesting.

And you are correct, the Super Cub is impressive. I did my tailwheel
checkout in a SC. We never used the flaps off, flaps on, flaps off
technique, but even so, once you break ground you can pull the stick

back
as
far as you want and it just goes UP!

Jim


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  #15  
Old November 18th 04, 07:55 PM
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Mike Rapoport wrote:
: Keep in mind that the short field settings shorten the ground run but
: generally increase the distance to clear a 50' obstical.

Isn't that the *point* of short field technique... to get off and over in the
shortest distance? There would appear to be a logical flaw to that statement.

I would agree that it will take more *time* to get to a given altitude at
(e.g. 50' obstacle clearance)... Short field performance is defined to give the best
obstacle clearance per *distance*. I would agree that soft-field technique will
increase distance, but short is short.

Am I missing something?

-Cory



--

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

  #17  
Old November 18th 04, 08:35 PM
xyzzy
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BTIZ wrote:

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.


I fly a warrior. If I am not doing a short field technique I usually
take off with one notch of flaps. This was suggested by an instructor
and I find that with 1 notch the plane "unsticks" and climbs to 50 feet
much easier. I don't think it improves the performance signficantly but
it's a much smoother and comfortable takeoff.

short field is 25 degrees and 52 kts. And it does get off and clear an
obstacle in less distance that way.


  #18  
Old November 18th 04, 08:41 PM
xyzzy
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This is for a pa28-161, so don't know how different the -181 would be
but the answer is no for the -161: Vx is 63 kts. Short field takeoff
technique is with 25 degrees and climb at 52kts, which is also the short
field rotation speed.

Jim Burns wrote:

I thought of that question also and I'll check tonight when I get home. I
would think that a "normal" takeoff would be to Vy and a short field to Vx.
But then again sometimes "normal" has many definitions!

Jim

"Mike Rapoport" wrote in message
hlink.net...

Thanks. Are both takeoffs to Vx?

Mike
MU-2


"Jim Burns" wrote in message
...

The one I looked at was an Archer II POH.

25 degrees of flaps, standard conditions, dry, paved, level runway was
about
1500 ft over 50 ft obstacle

0 flaps, same conditions takes about 1850 ft over a 50ft obstacle

Those were the only two configurations given.

I didn't compare ground roll distances but that would indeed be
interesting.

And you are correct, the Super Cub is impressive. I did my tailwheel
checkout in a SC. We never used the flaps off, flaps on, flaps off
technique, but even so, once you break ground you can pull the stick


back

as
far as you want and it just goes UP!

Jim


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Checked by AVG anti-virus system (http://www.grisoft.com).
Version: 6.0.788 / Virus Database: 533 - Release Date: 11/1/2004






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  #19  
Old November 18th 04, 08:42 PM
Mike Rapoport
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wrote in message
...
Mike Rapoport wrote:
: Keep in mind that the short field settings shorten the ground run but
: generally increase the distance to clear a 50' obstical.

Isn't that the *point* of short field technique... to get off and over in
the
shortest distance? There would appear to be a logical flaw to that
statement.

I would agree that it will take more *time* to get to a given altitude at
(e.g. 50' obstacle clearance)... Short field performance is defined to
give the best
obstacle clearance per *distance*. I would agree that soft-field
technique will
increase distance, but short is short.

Am I missing something?

Maybe :-) If the short field takoff is using a higher drag, higher lift
configuration (more flaps) to get off the ground at a lower speed (shorter
roll) it then takes longer (in both time and distance) to make the climb
over the obstacle because of the higher drag configuration. I hope this
makes sense.

In the Helio, the shortest ground roll is with 40 degrees of flaps but the
shortest distance over a 50' obstacle is with 30 degrees of flaps.

Mike
MU-2
Helio Courier


  #20  
Old November 18th 04, 08:53 PM
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Mike Rapoport wrote:
: Maybe :-) If the short field takoff is using a higher drag, higher lift
: configuration (more flaps) to get off the ground at a lower speed (shorter
: roll) it then takes longer (in both time and distance) to make the climb
: over the obstacle because of the higher drag configuration. I hope this
: makes sense.

: In the Helio, the shortest ground roll is with 40 degrees of flaps but the
: shortest distance over a 50' obstacle is with 30 degrees of flaps.

: Mike
: MU-2
: Helio Courier

OK... I'll buy that. My experience with performance charts is with a 172 and
a PA-28. The latter is sorely lacking in much relevant detail. I would imagine much
more precision and other ways to figure how to eek out the maximum poop from your
Helio POH... that's what the plane's FOR!

My PA-28 book makes no distinction. Just says, "Max effort, 25 degree flaps
over 50'" It might not matter, but I don't info one way or the other.

-Cory


--

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

 




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