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#1
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Flap Settings
I understand, a wing will perform optimally when the flap is set at
the proper angle for the airspeed ... any mismatch of flap to airspeed will result in some performance losses vs. the correct setting. Of course, we have a couple of compromises here ... the flaps are set at fixed increments and the airspeed varies continuously ... so by design, you will rarely have the flap and airspeed matched up perfectly. I remember seeing a story where one of the German schools modified an LS-3 with springs, etc. so it automatically put in the correct amount of flap for the airspeed ... did this result in a measurable improvement? Along the same lines, I have heard some pilots say they put the flap in a position where they feel no pressure ... does this work? I myself tend to go negative quicker or maintain a negative setting longer ... then pulling in positive flap ... thinking being too positive is more costly then too negative ... is this valid? KK |
#2
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Flap Settings
Good, question. I'll follow this thread with interest.
I can make one comment. My Nimbus 2C has a complex set of trim/flap interconnect springs and gas struts that probably to more to effect the "feel" of the flap handle than aerodynamic forces. Even so, the neutral force point on the flap handle "seems" to be about right. Most of the time I keep my left hand on the flap handle with the setting at some intermediate position between detents that "feels about right". The only time I use the detents is when I need to use my left hand for something else. I expect the only way to know for sure the flap setting is right is to install a "drag meter" pitot rake on the flap trailing edge. Bill Daniels "Ken Kochanski (KK)" wrote in message ups.com... I understand, a wing will perform optimally when the flap is set at the proper angle for the airspeed ... any mismatch of flap to airspeed will result in some performance losses vs. the correct setting. Of course, we have a couple of compromises here ... the flaps are set at fixed increments and the airspeed varies continuously ... so by design, you will rarely have the flap and airspeed matched up perfectly. I remember seeing a story where one of the German schools modified an LS-3 with springs, etc. so it automatically put in the correct amount of flap for the airspeed ... did this result in a measurable improvement? Along the same lines, I have heard some pilots say they put the flap in a position where they feel no pressure ... does this work? I myself tend to go negative quicker or maintain a negative setting longer ... then pulling in positive flap ... thinking being too positive is more costly then too negative ... is this valid? KK |
#3
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Flap Settings
I'm reaching back a bit in my memory here so apologies
to the real practitioners if I miss anything. I believe optimal flap settings are a function of angle of attack, not airspeed, though obviously there is a relationship between the two if you adjust for weight, density, etc. Second, the 'feel' on the flap handle is determined by the hinge moment on the flap/flaperon. Again, minimum hinge moment does not necessarily correspond to minimum drag, maximum lift coeficient or maximum L/D. You might want to optimize for any one of these at a given airspeed. Each would require a different flap setting I think. 9B At 16:24 10 July 2007, Bill Daniels wrote: Good, question. I'll follow this thread with interest. I can make one comment. My Nimbus 2C has a complex set of trim/flap interconnect springs and gas struts that probably to more to effect the 'feel' of the flap handle than aerodynamic forces. Even so, the neutral force point on the flap handle 'seems' to be about right. Most of the time I keep my left hand on the flap handle with the setting at some intermediate position between detents that 'feels about right'. The only time I use the detents is when I need to use my left hand for something else. I expect the only way to know for sure the flap setting is right is to install a 'drag meter' pitot rake on the flap trailing edge. Bill Daniels 'Ken Kochanski (KK)' wrote in message oups.com... I understand, a wing will perform optimally when the flap is set at the proper angle for the airspeed ... any mismatch of flap to airspeed will result in some performance losses vs. the correct setting. Of course, we have a couple of compromises here ... the flaps are set at fixed increments and the airspeed varies continuously ... so by design, you will rarely have the flap and airspeed matched up perfectly. I remember seeing a story where one of the German schools modified an LS-3 with springs, etc. so it automatically put in the correct amount of flap for the airspeed ... did this result in a measurable improvement? Along the same lines, I have heard some pilots say they put the flap in a position where they feel no pressure ... does this work? I myself tend to go negative quicker or maintain a negative setting longer ... then pulling in positive flap ... thinking being too positive is more costly then too negative ... is this valid? KK |
#4
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Flap Settings
Unfortunately we do not have A of A meter. I have come to the
conclusion that using the flight manual for specific flap setting and speeds and wing loading is the way to go. For example: At a gross of 800 lb and a flap setting of +20 the optimum speed range is about 5-7 kt, about the same in a 45 deg. bank with the needed extra speed added for that bank. But in level cruise the minimum drag has a range from about 70 kt to 95 kt at zero flap and 800 lb gross. You will feel the aft loading of the airfoil in climb at the Flap handle , but no load in cruise. Due to friction this " flap handle feel", as an indicator is unreliable and depending on the airfoil also misleading. I can speak from practical experience. On my past projects I had to calculate the speeds for each flap setting as well as wing loading In case of that airfoil it had a very narrow speed range in each flap setting to maximize performance but it comes at a cost of having to pay attention to the flaps to get the most out of each setting. Udo On Jul 10, 11:49 am, "Ken Kochanski (KK)" wrote: I understand, a wing will perform optimally when the flap is set at the proper angle for the airspeed ... any mismatch of flap to airspeed will result in some performance losses vs. the correct setting. Of course, we have a couple of compromises here ... the flaps are set at fixed increments and the airspeed varies continuously ... so by design, you will rarely have the flap and airspeed matched up perfectly. I remember seeing a story where one of the German schools modified an LS-3 with springs, etc. so it automatically put in the correct amount of flap for the airspeed ... did this result in a measurable improvement? Along the same lines, I have heard some pilots say they put the flap in a position where they feel no pressure ... does this work? I myself tend to go negative quicker or maintain a negative setting longer ... then pulling in positive flap ... thinking being too positive is more costly then too negative ... is this valid? KK |
#5
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Flap Settings
On Tue, 10 Jul 2007 08:49:17 -0700, "Ken Kochanski (KK)"
wrote: Along the same lines, I have heard some pilots say they put the flap in a position where they feel no pressure ... does this work? Indeed this works for most gliders with the FX62-K... (ASW-20, LS-6 etc.) and FX-67-K...x (Nimbus-2, LS-3, Pik-20 etc.) airfoils, but most later airfoils (ASH-25, ASW-27 etc.), need a firm "push" towards negative settings. Bye Andreas |
#6
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Flap Settings
Ken Kochanski (KK) wrote:
I understand, a wing will perform optimally when the flap is set at the proper angle for the airspeed ... any mismatch of flap to airspeed will result in some performance losses vs. the correct setting. Of course, we have a couple of compromises here ... the flaps are set at fixed increments and the airspeed varies continuously ... so by design, you will rarely have the flap and airspeed matched up perfectly. I remember seeing a story where one of the German schools modified an LS-3 with springs, etc. so it automatically put in the correct amount of flap for the airspeed ... did this result in a measurable improvement? Along the same lines, I have heard some pilots say they put the flap in a position where they feel no pressure ... does this work? I myself tend to go negative quicker or maintain a negative setting longer ... then pulling in positive flap ... thinking being too positive is more costly then too negative ... is this valid? Its well worth digging out Dick Johnson's reports on flapped gliders and looking at the combined polar he plots - the one showing polars for all flap settings. The polars for the ASW-20 blend quite nicely except at the ends of the speed range for each setting and the available speed range gets smaller for each setting at more positive settings. The implication, I suppose, is that selecting the right flap is more critical at lower airspeeds. The same may apply to other gliders too: I haven't looked. -- martin@ | Martin Gregorie gregorie. | Essex, UK org | |
#7
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Flap Settings
On Jul 10, 11:49 am, "Ken Kochanski (KK)"
wrote: I understand, a wing will perform optimally when the flap is set at the proper angle for the airspeed ... any mismatch of flap to airspeed will result in some performance losses vs. the correct setting. Of course, we have a couple of compromises here ... the flaps are set at fixed increments and the airspeed varies continuously ... so by design, you will rarely have the flap and airspeed matched up perfectly. I remember seeing a story where one of the German schools modified an LS-3 with springs, etc. so it automatically put in the correct amount of flap for the airspeed ... did this result in a measurable improvement? Along the same lines, I have heard some pilots say they put the flap in a position where they feel no pressure ... does this work? I myself tend to go negative quicker or maintain a negative setting longer ... then pulling in positive flap ... thinking being too positive is more costly then too negative ... is this valid? KK Hi Ken - It depends very much on the glider. The Antares manual specifically says "do not let the flap handle move to the position of no force, as you will have the wrong flap setting" (I'm on the road so that's an approximate quote). In other gliders I've flown this is sort-of the correct flap setting (but far from exactly right). Factors include the mechanics of the flap system, any trim spring interconnect to flap, airfoil, etc... To your second question, correct flap setting depends on CL not airspeed. Again, the Antares manual specifically warns against pulling the flap down during a pull-up. Because of the flat polar and consequent high cruise speed, you would end up with the flaps down way too soon and incur much extra drag during the pull-up - more so than older designs. Hope that helps, Best Regards, Dave "YO" |
#8
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Flap Settings
On my want to do list is to build a flap controller for my HP16T. I have been using PIC Microprocessers and pressure sensors that could easily be adapted to do this. My initial Idea was to install a drag rake that the microprocesser would read the pressure difference from and would adjust the flaps accordingly. Alternate ideas are to connect directly the the Pitot/Static system or build an AoA Sensor. All are pretty easy to do but good low pressure sensors are in about $100 range and so far my budget hasn't made it to that. I really hadn't considered AoA sensors until reading this thread, That might be a cheaper way of doing this. Brian Case HP16T N16VP. On Jul 10, 11:25 am, Udo wrote: Unfortunately we do not have A of A meter. I have come to the conclusion that using the flight manual for specific flap setting and speeds and wing loading is the way to go. For example: At a gross of 800 lb and a flap setting of +20 the optimum speed range is about 5-7 kt, about the same in a 45 deg. bank with the needed extra speed added for that bank. But in level cruise the minimum drag has a range from about 70 kt to 95 kt at zero flap and 800 lb gross. You will feel the aft loading of the airfoil in climb at the Flap handle , but no load in cruise. Due to friction this " flap handle feel", as an indicator is unreliable and depending on the airfoil also misleading. I can speak from practical experience. On my past projects I had to calculate the speeds for each flap setting as well as wing loading In case of that airfoil it had a very narrow speed range in each flap setting to maximize performance but it comes at a cost of having to pay attention to the flaps to get the most out of each setting. Udo On Jul 10, 11:49 am, "Ken Kochanski (KK)" wrote: |
#9
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Flap Settings
I've noted that there are AoA probes that use two pressure ports on 45
degree faces. Such as: http://www.cgmasi.com/aviation/index.html although this one is also a pitot probe. I've wondered if pressure ports on the top and bottom of the fuselage nose where the nose contours are at about 45 degrees to the airstream wouldn't give about the same pressure diferential that could be used to compute AoA. Bill Daniels "Brian" wrote in message oups.com... On my want to do list is to build a flap controller for my HP16T. I have been using PIC Microprocessers and pressure sensors that could easily be adapted to do this. My initial Idea was to install a drag rake that the microprocesser would read the pressure difference from and would adjust the flaps accordingly. Alternate ideas are to connect directly the the Pitot/Static system or build an AoA Sensor. All are pretty easy to do but good low pressure sensors are in about $100 range and so far my budget hasn't made it to that. I really hadn't considered AoA sensors until reading this thread, That might be a cheaper way of doing this. Brian Case HP16T N16VP. On Jul 10, 11:25 am, Udo wrote: Unfortunately we do not have A of A meter. I have come to the conclusion that using the flight manual for specific flap setting and speeds and wing loading is the way to go. For example: At a gross of 800 lb and a flap setting of +20 the optimum speed range is about 5-7 kt, about the same in a 45 deg. bank with the needed extra speed added for that bank. But in level cruise the minimum drag has a range from about 70 kt to 95 kt at zero flap and 800 lb gross. You will feel the aft loading of the airfoil in climb at the Flap handle , but no load in cruise. Due to friction this " flap handle feel", as an indicator is unreliable and depending on the airfoil also misleading. I can speak from practical experience. On my past projects I had to calculate the speeds for each flap setting as well as wing loading In case of that airfoil it had a very narrow speed range in each flap setting to maximize performance but it comes at a cost of having to pay attention to the flaps to get the most out of each setting. Udo On Jul 10, 11:49 am, "Ken Kochanski (KK)" wrote: |
#10
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Flap Settings
Bill Daniels wrote:
I've wondered if pressure ports on the top and bottom of the fuselage nose where the nose contours are at about 45 degrees to the airstream wouldn't give about the same pressure diferential that could be used to compute AoA. The factory AOA meter in my DG-600 uses cross-connected pairs of fuselage static ports just above the wing root, one set just aft of the leading edge, and another at roughly 50% chord. The meter appears to be a slightly modified electronic vario. Marc |
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