---------------------------------------------------------- Kolb-List Digest Archive --- Total Messages Posted Sat 05/29/10: 13 ---------------------------------------------------------- Today's Message Index: ---------------------- 1. 04:01 AM - Re: drag conundrum (Thom Riddle) 2. 06:35 AM - Re: Re: drag conundrum (Dana Hague) 3. 06:54 AM - Re: drag conundrum (Thom Riddle) 4. 07:08 AM - Re: Re: drag conundrum (Jack B. Hart) 5. 09:13 AM - Re: Re: drag conundrum (Eugene Zimmerman) 6. 09:23 AM - Re: drag conundrum (Thom Riddle) 7. 10:52 AM - Re: Re: drag conundrum (robert bean) 8. 12:55 PM - Re: drag conundrum (John Hauck) 9. 02:26 PM - Re: Re: drag conundrum (John Hauck) 10. 03:23 PM - Re: Re: drag conundrum (Jack B. Hart) 11. 04:10 PM - Re: Re: drag conundrum (John Hauck) 12. 06:03 PM - Re: Re: drag conundrum (Jack B. Hart) 13. 07:13 PM - Re: Re: drag conundrum (John Hauck) ________________________________ Message 1 _____________________________________ Time: 04:01:07 AM PST US Subject: Kolb-List: Re: drag conundrum From: "Thom Riddle" Jack, Thanks for your input. I know and expected that the loss of drag at the lowest point of the aircraft in flight will(did) necessitate the addition of nose down trim. However your assumption that the CG would move forward with the loss of weight from lighter tires is incorrect, since the main wheels are well forward of the CG range. My empty weight CG location moved aft by .63 inches and my typical loaded CG moved aft by .25 inches. My yaw string behavior did not change. I think that my fuel consumption rate is down after changing tire size but won't be certain until after I've flown a few hours at my normal cruise rpm. My surprise was that the same rpm did not result in higher airspeed at same fuel burn rate, rather than reduced fuel consumption at the same airspeed. But the more I think about it, I can see how reduced drag could have either result or some combination of the two. Why one and not the other is still a mystery to me, but if I get less fuel consumption at same speed, then my original goal has been accomplished. -------- Thom Riddle Buffalo, NY (9G0) Kolb Slingshot SS-021 Jabiru 2200A #1574 Tennessee Prop 64x32 I am always doing that which I can not do, in order that I may learn how to do it. - Pablo Picasso Read this topic online here: http://forums.matronics.com/viewtopic.php?p=299246#299246 ________________________________ Message 2 _____________________________________ Time: 06:35:07 AM PST US From: Dana Hague Subject: Re: Kolb-List: Re: drag conundrum At 08:58 PM 5/28/2010, Thom Riddle wrote: >Dana, > >As I read your post I was almost convinced you were right when you said... > >At the same rpm and the same airspeed, the engine should be putting out >the same amount of power, since the same amount of air is moving through >the prop, at the same speed. > >Then I started thinking about the amount of work being done. If the drag >is less then the work being done by the prop at a certain rpm and >traveling at the constant airspeed, must be less. Less work means less >power and less fuel consumption. If I had a very precise vernier throttle >with a precise scale, I would speculate that I'm getting the same airspeed >with the same rpm but at a smaller throttle opening. I almost thought your were right too, at first :) Consider: At constant airspeed and constant rpm. the same amount of air is flowing through the prop, at the same speed, as you say. This means a constant blade AOA, thus constant blade drag, constant torque on the prop shaft, and thus constant HP... and constant thrust. Change any one thing and at least one other thing has to change; they're all interrelated. If the drag is less, then the thrust is also less... but it can't be, under the same conditions, as described above. Either the aircraft accelerates until the drag increases until it equals thrust (which by this time will be a little less since at constant RPM the blade AOA will decrease with increasing airspeed), or you have to reduce thrust (RPM) until it equals drag, to maintain a constant airspeed. Less drag = go faster at the same rpm, or less thrust (less RPM) at the same airspeed. 5% drag reduction gives 5% lower fuel consumption with a reduced power setting at the same airspeed, but only 2.5% higher airspeed at the same (original) power setting. I still suspect in this case instrument error in the ASI or tach or both, or varying atmospheric conditions, or all three. -Dana -- A .44 magnum is the world's only usable point-and click interface. ________________________________ Message 3 _____________________________________ Time: 06:54:09 AM PST US Subject: Kolb-List: Re: drag conundrum From: "Thom Riddle" Dana, I agree with your explanation. Perhaps my measurement accuracy is off enough to not be able to detect the change, whatever it is. As John Hauck noted, he could not detect any difference in cruise speed when he changed from 600x6 to 800x6 tires. The change, though real, is probably within the measurement inaccuracy range or differences in atmospheric conditions. However, if over the next few hours of flight at my normal cruise rpm I see measurably lower fuel consumption at similar density altitudes, then I'm inclined toward thinking my throttle opening for this condition is less than with the larger tires. The significantly lower drag has to show up somewhere. I wish I had a fuel flow monitor or at least a manifold pressure gauge which is a better proxy for power than rpm alone on a fixed pitch prop. -------- Thom Riddle Buffalo, NY (9G0) Kolb Slingshot SS-021 Jabiru 2200A #1574 Tennessee Prop 64x32 I am always doing that which I can not do, in order that I may learn how to do it. - Pablo Picasso Read this topic online here: http://forums.matronics.com/viewtopic.php?p=299256#299256 ________________________________ Message 4 _____________________________________ Time: 07:08:24 AM PST US From: "Jack B. Hart" Subject: Re: Kolb-List: Re: drag conundrum At 04:00 AM 5/29/10 -0700, you wrote: > >However your assumption that the CG would move forward with the loss of weight from lighter tires is incorrect, since the main wheels are well forward of the CG range. My empty weight CG location moved aft by .63 inches and my typical loaded CG moved aft by .25 inches. > >My yaw string behavior did not change. > Thom, In my case I have to plead a brain fart. Once in a while humble pie is good for me. When flying gliders, I used yaw strings. But one must remember that yaw strings indicate the direction of the local air flow over a small portion of the plane. In our case of a pusher powered aircraft with a little power factor present, one side of the prop swing will give a greater bite that the other side. Therefore the yaw string will indicate no slip when the plane is actually slipping. Also, if you are used to using a yaw string and always fly with the string centered, why would you expect for it to change indication? A ball slip indicator indicates what the total plane is doing. It might be worth your time to borrow a ball indicator from someone and recheck your trim. I hope this makes better sense. Jack B. Hart F004 Winchester, IN ________________________________ Message 5 _____________________________________ Time: 09:13:49 AM PST US From: Eugene Zimmerman Subject: Re: Kolb-List: Re: drag conundrum Hey guys, It appears that you guys are not getting the the appropriate dose of air-time to prevent the airplane hypochondria syndrome. ; ) | _____|_____ *=======================R=======================* \ / ^ \ / ( /---\ ) \___/ / \ () () Eugene Zimmerman On May 29, 2010, at 9:30 AM, Dana Hague wrote: > At 08:58 PM 5/28/2010, Thom Riddle wrote: >> Dana, >> >> As I read your post I was almost convinced you were right when you >> said... >> >> At the same rpm and the same airspeed, the engine should be putting >> out the same amount of power, since the same amount of air is >> moving through the prop, at the same speed. >> >> Then I started thinking about the amount of work being done. If the >> drag is less then the work being done by the prop at a certain rpm >> and traveling at the constant airspeed, must be less. Less work >> means less power and less fuel consumption. If I had a very precise >> vernier throttle with a precise scale, I would speculate that I'm >> getting the same airspeed with the same rpm but at a smaller >> throttle opening. > > I almost thought your were right too, at first :) > > Consider: At constant airspeed and constant rpm. the same amount of > air is flowing through the prop, at the same speed, as you say. > This means a constant blade AOA, thus constant blade drag, constant > torque on the prop shaft, and thus constant HP... and constant > thrust. Change any one thing and at least one other thing has to > change; they're all interrelated. > > If the drag is less, then the thrust is also less... but it can't > be, under the same conditions, as described above. Either the > aircraft accelerates until the drag increases until it equals thrust > (which by this time will be a little less since at constant RPM the > blade AOA will decrease with increasing airspeed), or you have to > reduce thrust (RPM) until it equals drag, to maintain a constant > airspeed. > > Less drag = go faster at the same rpm, or less thrust (less RPM) at > the same airspeed. 5% drag reduction gives 5% lower fuel > consumption with a reduced power setting at the same airspeed, but > only 2.5% higher airspeed at the same (original) power setting. > > I still suspect in this case instrument error in the ASI or tach or > both, or varying atmospheric conditions, or all three. > > -Dana > > > -- > A .44 magnum is the world's only usable point-and click interface. > > ________________________________ Message 6 _____________________________________ Time: 09:23:18 AM PST US Subject: Kolb-List: Re: drag conundrum From: "Thom Riddle" Gene, I'm on honey-do duty today but tomorrow BB and I are planning on meeting up and fly to a not-very-distant b-fast, in a flight of two Kolbs, probably arriving to great yawns and someone hollering "Look at them ultralights coming here. Sure hope they know how to land without hitting my real airplane." That would be from someone whose real airplane is not actually flying because it costs too much to feed and maintain. When is the last time you flew your Kolb to a fly-in and the crowds flocked around the 8th C172 to land? I love Kolbing. do not archive -------- Thom Riddle Buffalo, NY (9G0) Kolb Slingshot SS-021 Jabiru 2200A #1574 Tennessee Prop 64x32 I am always doing that which I can not do, in order that I may learn how to do it. - Pablo Picasso Read this topic online here: http://forums.matronics.com/viewtopic.php?p=299274#299274 ________________________________ Message 7 _____________________________________ Time: 10:52:46 AM PST US From: robert bean Subject: Re: Kolb-List: Re: drag conundrum quite right Eugene. And I'm one of the deprived. Strange how a guy can be retired with no responsibilities but a dog and STILL doesn't get around to flying something he spent hours/weeks/years building. Thom, that new float valve appears to have done the trick.. No more fluctuating idle. I reset the mixture and will live with the 1400 rpm idle. (divide by 2.26 for prop) Should be good for launch tomorrow morning. re: prop rpm..... I don't know how many of you guys are so used to grass that when you get on busy pavement, especially if it's downhill slightly, that you wish your brakes were slightly better :( If I get in a dicey situation I shut down the motah to zero out any thrust. I usually like to park away from the crowd. -and while I'm rambling here.... it sure bugs me when folks at a fly in seem to think it's ok to open the door on your plane and even let kids climb in. -with no invite. Lotta nerve. Follow them back to their car and climb in the back seat while they're leaving. BB grump mode off do not archive On 29, May 2010, at 12:13 PM, Eugene Zimmerman wrote: > Hey guys, > > It appears that you guys are not getting the the appropriate dose of air-time to prevent the airplane hypochondria syndrome. ; ) > > | > _____|_____ > *=======================R= ======================* > \ / ^ \ / > ( /---\ ) > \___/ > / \ > () () > > Eugene Zimmerman > > > > On May 29, 2010, at 9:30 AM, Dana Hague wrote: > >> At 08:58 PM 5/28/2010, Thom Riddle wrote: >>> Dana, >>> >>> As I read your post I was almost convinced you were right when you said... >>> >>> At the same rpm and the same airspeed, the engine should be putting out the same amount of power, since the same amount of air is moving through the prop, at the same speed. >>> >>> Then I started thinking about the amount of work being done. If the drag is less then the work being done by the prop at a certain rpm and traveling at the constant airspeed, must be less. Less work means less power and less fuel consumption. If I had a very precise vernier throttle with a precise scale, I would speculate that I'm getting the same airspeed with the same rpm but at a smaller throttle opening. >> >> I almost thought your were right too, at first :) >> >> Consider: At constant airspeed and constant rpm. the same amount of air is flowing through the prop, at the same speed, as you say. This means a constant blade AOA, thus constant blade drag, constant torque on the prop shaft, and thus constant HP... and constant thrust. Change any one thing and at least one other thing has to change; they're all interrelated. >> >> If the drag is less, then the thrust is also less... but it can't be, under the same conditions, as described above. Either the aircraft accelerates until the drag increases until it equals thrust (which by this time will be a little less since at constant RPM the blade AOA will decrease with increasing airspeed), or you have to reduce thrust (RPM) until it equals drag, to maintain a constant airspeed. >> >> Less drag = go faster at the same rpm, or less thrust (less RPM) at the same airspeed. 5% drag reduction gives 5% lower fuel consumption with a reduced power setting at the same airspeed, but only 2.5% higher airspeed at the same (original) power setting. >> >> I still suspect in this case instrument error in the ASI or tach or both, or varying atmospheric conditions, or all three. >> >> -Dana >> >> >> -- >> A .44 magnum is the world's only usable point-and click interface. >> >> >> href="http://www.matronics.com/Navigator?Kolb-List">http://www.matronics .com/Navigator?Kolb-List >> href="http://forums.matronics.com">http://forums.matronics.com >> href="http://www.matronics.com/contribution">http://www.matronics.com/co ntribution >> > > > > ________________________________ Message 8 _____________________________________ Time: 12:55:30 PM PST US From: "John Hauck" Subject: Re: Kolb-List: drag conundrum roger/gang save some fun for me. i use the the yaw string to calibrate my slip/skid indicator. basic adjustment can be made with airframe, on the ground in level flight attitude, but the yaw string in flight is the instrument to fine tune the slip/skid indicator. typed left handed, index finger. ;-) john h Roger @ the Rock House ________________________________ Message 9 _____________________________________ Time: 02:26:54 PM PST US From: "John Hauck" Subject: Re: Kolb-List: Re: drag conundrum jack, Also, if you are used to using a yaw string and always > fly with the string centered, why would you expect for it to change > indication? > i don't know. why? > A ball slip indicator indicates what the total plane is doing. It might > be > worth your time to borrow a ball indicator from someone and recheck your > trim. > > Jack B. Hart F004 yaw string indicates relative wind. mount the string bottom center windshield. i used a short piece of safety wire for standoff and no lateral drag. if you are concerned of prop influencing string, shut down the engine. out of trim situations have insignificant effect on kolbs. i flew 17,400 mile flight in my mkiii at 1/2 ball out of trim. later doubled size of rudder trim tab. mkiii flies ball centered, feet off the rudder pedals. flew 10,000+ mile flight trimmed up, ball centered. performance figures for both flights nearly identical. yaw string, properly mounted, more accurate than slip/skid indicator. take care, john h ________________________________ Message 10 ____________________________________ Time: 03:23:24 PM PST US From: "Jack B. Hart" Subject: Re: Kolb-List: Re: drag conundrum At 04:25 PM 5/29/10 -0500, you wrote: > >jack, > > Also, if you are used to using a yaw string and always >> fly with the string centered, why would you expect for it to change >> indication? >> > > >i don't know. why? John, I thought I was asking the question. > > >yaw string indicates relative wind. mount the string bottom center >windshield. i used a short piece of safety wire for standoff and no lateral >drag. > >if you are concerned of prop influencing string, shut down the engine. It is a little difficult to maintain altitude following this procedure. > >out of trim situations have insignificant effect on kolbs. i flew 17,400 >mile flight in my mkiii at 1/2 ball out of trim. later doubled size of >rudder trim tab. mkiii flies ball centered, feet off the rudder pedals. >flew 10,000+ mile flight trimmed up, ball centered. > >performance figures for both flights nearly identical. > Since you compensated for built in skid or slip by use of a tab on the rudder, one would not expect to see any drag reduction or any performance improvement. My Kolb FireFly, must be an exception, in that by trimming out p-factor, and offsetting the thrust line to fly straight in level flight and not using trim tabs, it has shown definite improvement. >yaw string, properly mounted, more accurate than slip/skid indicator. The slip/skid indicator indicates coordinated, lower drag, and more economical flight. A yaw string indicates as you said relative wind and I use it the most on taxiing out to detect what the cross wind is doing. Jack B. Hart FF004 Winchester, IN ________________________________ Message 11 ____________________________________ Time: 04:10:49 PM PST US From: "John Hauck" Subject: Re: Kolb-List: Re: drag conundrum > The slip/skid indicator indicates coordinated, lower drag, and more > economical flight. A yaw string indicates as you said relative wind and I > use it the most on taxiing out to detect what the cross wind is doing. > > > Jack B. Hart FF004 > Winchester, IN jack, yaw string and slip/skid indicator provide identical information, whether the aircraft is trimmed in yaw, is slipping or skidding. when trimmed in yaw, the aircraft is trimmed into relative wind. when i line up the string with the center line of the airframe, it indicates i am trimmed in yaw. how does a slip/skid indicator indicate coordinated, lower drag, and more economical flight? realize you were asking question. i don't have an answer. reason i asked why. only time i have ever been concerned with pitch trim was shooting 2,75 inch rockets from the AH-1G Cobra in VN. i use the wind sock when taxiing. how precise is your instrumentation? probably same as mine. a slip/skid indicator with ball centered indicates relative wind. flying from my bed which needs a yaw string to keep me trimmed with the meds i am taking. ;-) john h ________________________________ Message 12 ____________________________________ Time: 06:03:59 PM PST US From: "Jack B. Hart" Subject: Re: Kolb-List: Re: drag conundrum At 06:09 PM 5/29/10 -0500, you wrote: > > >jack, > >yaw string and slip/skid indicator provide identical information, whether >the aircraft is trimmed in yaw, is slipping or skidding. > The yaw string only gives an indication of relative wind over one spot of the aircraft. This works very well on a sailplane or glider, because one does not have to counter propeller torque, thrust and gyroscopic effects. When under power and if one trims for the most used or a desired flight speed, one must trim the roll to counter the propeller torque and adjust the horizontal stabilizer to establish hands off level flight. Under this condition, the plane more than likely will skid due to the fact the roll trim requires one wing to carry a little more load than the opposite side. In this case the ball will be out. Before slapping a tab on the rudder to bring it in, it is best to washer the engine to check for p-factor and adjust to bring the ball in as far as it will go. Then what ever ball is left can be brought in by sliding the thrust line side to side or a tab on the rudder. To ignore the p-factor means that you are just tossing money away due to inefficient use of thrust. If you do all of the above and you want to check it with a yaw string, then I will agree that the yaw string is as good as a slip/skid indicator. > >when trimmed in yaw, the aircraft is trimmed into relative wind. when i >line up the string with the center line of the airframe, it indicates i am >trimmed in yaw. > If you have not addressed cruise p-factor you will be using excessive trim on the rudder and creating an overall higher drag condition. > >how does a slip/skid indicator indicate coordinated, lower drag, and more >economical flight? > If the plane is properly trimmed out, the ball centered position will always give the lowest drag configuration. > >i use the wind sock when taxiing. > Not all fields have wind socks. > Jack B. Hart FF004 Winchester, IN ________________________________ Message 13 ____________________________________ Time: 07:13:24 PM PST US From: "John Hauck" Subject: Re: Kolb-List: Re: drag conundrum > The yaw string only gives an indication of relative wind over one spot of > the aircraft. that is all you need. the rest of the airplane is permanently connected to that spot. when you center the yaw string you are trimmed for yaw and roll. when you center the ball, you are trimmed for yaw and roll. both instruments accomplish equal roles. p factor at cruise is probably not measureable. how do you calibrate your slip/skid indicator? what kind of slip/skid indicator do you have? we have adverse yaw as the result of the way the prop wash hits the tail section, especially high horse power and large prop combos. this is quite evident on my mkiii. only the left side of the upper and lower vertical stabilizers are hit. right sides stay clean. top of left horizontal stab and elevator are also hit by prop wash. there is a lot going on back there. remember when you were going to tuft the tail section to see if prop wash was hitting elevators? i knew it was and i recommended standing behind the airplane with the engine running, stick your hand down there and feel the air? lot quicker than tufting. 23 years ago i experimented with thrust line of my firestar. up, down, left, and right. no change in performance, yaw, or pitch. I have experimented with leading edge upper vertical stab, leading edges horizontal stabs when i built and tested my mkiii 18 years ago. found the sweet spot for horizontal stabs. vertical stab a waste of time. i have an airplane that performs well throughout its entire performance band. for off site landings with no wind sock i use basic pilot skills to determine wind direction. there's lots of ways to do that. if i had an open cock pit, the wind on my face. if not, the airplane gives me very definite feed back when taxiing. john h still flying my bed, but no adverse yaw or roll. ------------------------------------------------------------------------------------- Other Matronics Email List Services ------------------------------------------------------------------------------------- Post A New Message kolb-list@matronics.com UN/SUBSCRIBE http://www.matronics.com/subscription List FAQ http://www.matronics.com/FAQ/Kolb-List.htm Web Forum Interface To Lists http://forums.matronics.com Matronics List Wiki http://wiki.matronics.com Full Archive Search Engine http://www.matronics.com/search 7-Day List Browse http://www.matronics.com/browse/kolb-list Browse Digests http://www.matronics.com/digest/kolb-list Browse Other Lists http://www.matronics.com/browse Live Online Chat! http://www.matronics.com/chat Archive Downloading http://www.matronics.com/archives Photo Share http://www.matronics.com/photoshare Other Email Lists http://www.matronics.com/emaillists Contributions http://www.matronics.com/contribution ------------------------------------------------------------------------------------- These Email List Services are sponsored solely by Matronics and through the generous Contributions of its members.