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#11
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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
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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 --- 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 |
#13
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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 --- 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 |
#14
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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 --- 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 --- 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 |
#15
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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 * ************************************************** *********************** |
#16
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#17
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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
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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 --- 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 --- 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 |
#19
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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
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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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