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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 |
#2
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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
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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 |
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And don't forget density altitude!
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#5
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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 --- Outgoing mail is certified Virus Free. Checked by AVG anti-virus system (http://www.grisoft.com). Version: 6.0.788 / Virus Database: 533 - Release Date: 11/1/2004 |
#6
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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
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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:2VUmd.106033$bk1.85623@fed1read05... 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
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"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
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"BTIZ" wrote in message news:2VUmd.106033$bk1.85623@fed1read05... 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
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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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