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Thom Riddle

Joined: 10 Jan 2006
Posts: 1597
Location: Buffalo, NY, USA (9G0)

Posted: Fri May 28, 2010 6:17 am Post subject: drag conundrum

Fellow Kolbers,



I recently downsized my Slingshot tires from 800x6 to 15x600-6 for two reasons. One, the soft compound of the 800x6 tires wear fairly quickly on paved runways, like my home airport. They were not worn much yet so they still have a lot of life left in them on grass strips. The 2nd reason was I wanted to reduce drag sufficiently to get a couple more MPH at same cruise power.



Today I flew some test flights to see how my 2nd goal panned out which leads to the drag conundrum on which I'd like some help from you smart guys/gals. In particular, I'm looking for feed back from our resident numbers cruncher and wise man, Jack Hart.



Results of much smaller tires:

1) Zero change in IAS or TAS at same rpm setting. !(at)#$%

2) Good bit of change in pitch trim requirement. Now requires more nose down trim for S&L flight at same RPM than with big tires.



I understand the 2nd result but can't figure out why such a dramatic reduction in drag down low would not result in measurable speed increase. 



Any thoughts on this conundrum will be appreciated, even wise-arse ones, if you are so inclined. 



Per Larry Cottrell's recommendation, my next step will be to fashion some sort of fairings for the long gear legs. Larry said he got about 3 mph increase with his fairings and I believe Richard Pike had similar results. Maybe with the longer legs and higher speed of the SS, I might get that or more with gear leg fairings. After that, I may see what wheel pants will do for me. I already own the pants so all I have to do is figure out how to mount them. On our Rans S6, the wheel pants were worth an extra 4 mph at normal cruise. My goal is not so much faster cruise as more economical cruise, but they are both accomplished by reducing drag.

_________________
Thom Riddle
Buffalo, NY (9G0)

Don't worry about old age... it doesn't last very long.
- Anonymous

by0ung(at)brigham.net
Guest

Posted: Fri May 28, 2010 7:44 am Post subject: drag conundrum

I understand the 2nd result but can't figure out why such a dramatic  reduction in drag down low would not result in measurable speed increase.  



Thom

  

 >>>>>>>>>>>>>>>>>>>>

  

 Thom

  

 when I went from the 15 600 6 tires to 600 6   I  had about a 3 mph reduction in speed.   I cant understand why the  speed would not return when going back to the small tires.

  

 Boyd

 MkIII

  

  

   [quote][b]

Thom Riddle

Joined: 10 Jan 2006
Posts: 1597
Location: Buffalo, NY, USA (9G0)

Posted: Fri May 28, 2010 7:50 am Post subject: Re: drag conundrum

Boyd,



Hence, the conundrum. Does not make sense to me that an obvious reduction in drag, even though it is well below the center of pressure and therefore requiring adjustment of trim, would not reduce the overall drag to the point of improving airspeed measurably.

_________________
Thom Riddle
Buffalo, NY (9G0)

Don't worry about old age... it doesn't last very long.
- Anonymous

Dana

Joined: 13 Dec 2007
Posts: 1047
Location: Connecticut, USA

Posted: Fri May 28, 2010 9:05 am Post subject: drag conundrum

At 10:17 AM 5/28/2010, Thom Riddle wrote:



  	  Quote: 	
		  Results of much smaller  tires:

 1) Zero change in IAS or TAS at same rpm setting. !(at)#$%

 2) Good bit of change in pitch trim requirement. Now requires more nose down trim for S&L flight at same RPM than with big tires.



 I understand the 2nd result but can't figure out why such a dramatic reduction in drag down low would not result in measurable speed increase. 	


 Some thoughts, sheer guesswork since I haven't seen your setup:  First, if the new tires are significantly lighter, it may be a balance thing requiring more down trim.  Second, you're reducing drag from the tires but may be adding additional trim drag from a deflected elevator.  Third, even though the new tires are smaller diameter but a similar width, they]re blunter and so the increase in drag coefficient may be higher than the reduction in area.



  	  Quote: 	
		  ...I may see what wheel pants will do for me. I already own the pants so all I have to do is figure out how to mount them. On our Rans S6, the wheel pants were worth an extra 4 mph at normal cruise... 	


 Depends on the pants.  Well designed pants can reduce drag, but many don't, or even increase it.  On my T-Craft, adding the wheel pants (I took them off each winter and put them back on in the Spring) did absolutely nothing for drag/speed, but they looked nice.



 -Dana

 

 --

  Censorship: The reaction of the ignorant to freedom.    [quote][b]

Thom Riddle

Joined: 10 Jan 2006
Posts: 1597
Location: Buffalo, NY, USA (9G0)

Posted: Fri May 28, 2010 9:43 am Post subject: Re: drag conundrum

Dana,



I know the wheel pants I have will help significantly because these very same pants came off the RANS S6 which gave a 4 mph advantage.



I agree in principle that the change in elevator trim might cause a bit more drag in the tail plane area than before the tire downsize, but can't imagine it being more than the drag reduction from the smaller tires. BTW, the 15x600-6 are nearly 2" narrower at the widest point than the 800x6 tires they replaced. The diameter reduction is nearly 4". Making some rational assumptions I calculated that the net cross-sectional area of the larger tires was about 124 sqin each tire and the smaller ones are about 79 sqin. 



I did some rough calculations to come up with about 2.5 hp savings at 80 mph. Another way to look at it is to let that extra HP deliver more speed, which I calculate to be about 1.5 mph increase. Maybe my baseline data was not accurate enough to see this bit of increase.



Just thinking out loud, here is another way to look at it:

I checked my fuel consumption for this flight and it was down a good bit compared to my previous normal fuel burn rate for steady state cruise at this rpm. PERHAPS, the same rpm is actually less power being produced to yield the same airspeed. This seems reasonable to me since the drag is less and the prop works only as hard as it needs to to give the rpm I dialed in. Thus the same rpm and same airspeed may have been achieved with less horsepower being absorbed by the prop.



I'm beginning to think this last guess may be the key to understanding the change, but I'll have to do some longer distance flying at same rpm and airspeed to get a more accurate fuel consumption figure. If it is true then I may need more prop when I finish with my drag reduction efforts. This experiment is getting interesting.

_________________
Thom Riddle
Buffalo, NY (9G0)

Don't worry about old age... it doesn't last very long.
- Anonymous

Dana

Joined: 13 Dec 2007
Posts: 1047
Location: Connecticut, USA

Posted: Fri May 28, 2010 1:53 pm Post subject: drag conundrum

At 01:43 PM 5/28/2010, Thom Riddle wrote:



  	  Quote: 	
		  I agree in principle that the change in elevator trim might cause a bit more drag in the tail plane area than before the tire downsize, but can't imagine it being more than the drag reduction from the smaller tires... 	


 I agree; I just threw it out as a thought.



  	  Quote: 	
		  Just thinking out loud, here is another way to look at it:

 I checked my fuel consumption for this flight and it was down a good bit compared to my previous normal fuel burn rate for steady state cruise at this rpm. PERHAPS, the same rpm is actually less power being produced to yield the same airspeed. This seems reasonable to me since the drag is less and the prop works only as hard as it needs to to give the rpm I dialed in. Thus the same rpm and same airspeed may have been achieved with less horsepower being absorbed by the  prop. 	


 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.  This is neglecting, of course, other variables such as air density.  I suspect your numbers may be within the noise of your instruments' accuracy.



 -Dana

 --

  "Hiking is just walking where it's ok to pee.....

 Sometimes old people hike on accident....."    [quote][b]

Thom Riddle

Joined: 10 Jan 2006
Posts: 1597
Location: Buffalo, NY, USA (9G0)

Posted: Fri May 28, 2010 4:58 pm Post subject: Re: drag conundrum

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.

_________________
Thom Riddle
Buffalo, NY (9G0)

Don't worry about old age... it doesn't last very long.
- Anonymous

jbhart(at)onlyinternet.ne
Guest

Posted: Fri May 28, 2010 6:52 pm Post subject: drag conundrum

At 07:17 AM 5/28/10 -0700, you wrote:

 	  Quote: 	
		  



Fellow Kolbers,



Results of much smaller tires:

1) Zero change in IAS or TAS at same rpm setting. !(at)#$%

2) Good bit of change in pitch trim requirement. Now requires more nose 

down trim for S&L flight at same RPM than with big tires.
	


 	  Quote: 	
		  

I understand the 2nd result but can't figure out why such a dramatic 

reduction in drag down low would not result in measurable speed increase. 
	


 	  Quote: 	
		  

Any thoughts on this conundrum will be appreciated, even wise-arse ones, if 

you are so inclined. 
	


 	  Quote: 	
		  


	


Thom,



There are a couple of reasons.  First, by reducing wheel weight, you moved 

your CG forward.  This means you must increase tail load to maintain 

straight and level flight.  Every pound increase in tail load means that you 

must off set this load with increased wing lift and wing drag.



Also by reducing the wheel size you are changing the profile drag of your 

plane.  Think about the center of drag and that it must lie above the 

vertical location of the cg.  If this is so, when you reduce the wheel drag 

it will cause a nose up condition about the vertical cg position.



Both of these conditions will cause increased tail load at your normal level 

flight cruise.  In addition this increased load is transferred to the wing.  

One should try to get rid of this additional wing load and drag.  Under your 

normal flight conditions, you need to look at adjusting the horizontal 

stabilizer to get rid of trim.  Then check your slip indicator for power 

factor to see if the ball remains centered.  If not, you may want to washer 

the engine to try and drive the ball back in toward the center.  These two 

changes should bring your plane back into trim, and you should (may) see 

some speed increase.  One can hold altitude and rpm constant, but all those 

other atmospheric influences may mask any early indicators for improvement.  

The most reliable improvement indicator is to calculate your gph rates for 

before and after a change.  



On a very light plane, everything influences everything else.  I ran some 

calculations for the FireFly to figure out what would happen if I moved the 

thrust line.  They can be viewed at:



http://jackbhart.com/firefly/firefly101.html



Jack B. Hart FF004

Winchester, IN

lcottrell

Joined: 29 May 2006
Posts: 1494
Location: Jordan Valley, Or

Posted: Fri May 28, 2010 7:42 pm Post subject: drag conundrum

"First, by reducing wheel weight, you moved 

your CG forward."   

  

 Jack,  This is conventional Kolb gear, correct?   The mains are ahead of the C.G.  Less weight = more aft C.G.  or am I  missing something?

  

  

  

 Roger (at) the Rock House

  

   [quote][b]

_________________
do not archive

Thom Riddle

Joined: 10 Jan 2006
Posts: 1597
Location: Buffalo, NY, USA (9G0)

Posted: Sat May 29, 2010 3:00 am Post subject: Re: drag conundrum

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)

Don't worry about old age... it doesn't last very long.
- Anonymous

Dana

Joined: 13 Dec 2007
Posts: 1047
Location: Connecticut, USA

Posted: Sat May 29, 2010 5:35 am Post subject: drag conundrum

At 08:58 PM 5/28/2010, Thom Riddle wrote:

  	  Quote: 	
		  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.    [quote][b]

Thom Riddle

Joined: 10 Jan 2006
Posts: 1597
Location: Buffalo, NY, USA (9G0)

Posted: Sat May 29, 2010 5:53 am Post subject: Re: drag conundrum

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)

Don't worry about old age... it doesn't last very long.
- Anonymous

jbhart(at)onlyinternet.ne
Guest

Posted: Sat May 29, 2010 6:08 am Post subject: drag conundrum

At 04:00 AM 5/29/10 -0700, you wrote:

 	  Quote: 	
		  



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

Eugene Zimmerman

Joined: 10 Jan 2006
Posts: 392

Posted: Sat May 29, 2010 8:13 am Post subject: 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:

[quote]At 08:58 PM 5/28/2010, Thom Riddle wrote:

  	  Quote: 	
		  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.  	  Quote: 	
		  



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[b]

Thom Riddle

Joined: 10 Jan 2006
Posts: 1597
Location: Buffalo, NY, USA (9G0)

Posted: Sat May 29, 2010 8:22 am Post subject: Re: drag conundrum

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)

Don't worry about old age... it doesn't last very long.
- Anonymous

slyck(at)frontiernet.net
Guest

Posted: Sat May 29, 2010 9:52 am Post subject: 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 andSTILL 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:

 	  Quote: 	
		  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:

 	  Quote: 	
		  At 08:58 PM 5/28/2010, Thom Riddle wrote:

  	  Quote: 	
		  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.  	  Quote: 	
		  



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 [quote][b]

John Hauck

Joined: 09 Jan 2006
Posts: 4639
Location: Titus, Alabama (hauck's holler)

Posted: Sat May 29, 2010 11:55 am Post subject: 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

  

  

 [quote]    

   Roger (at) the Rock House

    

 	  Quote: 	
		  

 	
[b]

_________________
John Hauck
MKIII/912ULS
hauck's holler
Titus, Alabama

John Hauck

Joined: 09 Jan 2006
Posts: 4639
Location: Titus, Alabama (hauck's holler)

Posted: Sat May 29, 2010 1:26 pm Post subject: drag conundrum

jack,



  Also, if you are used to using a yaw string and always

 	  Quote: 	
		   fly with the string centered, why would you expect for it to change

 indication?




	




i don't know.  why?

 	  Quote: 	
		   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

_________________
John Hauck
MKIII/912ULS
hauck's holler
Titus, Alabama

jbhart(at)onlyinternet.ne
Guest

Posted: Sat May 29, 2010 2:23 pm Post subject: drag conundrum

At 04:25 PM 5/29/10 -0500, you wrote:

 	  Quote: 	

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.

 	  Quote: 	

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.

 	  Quote: 	

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.

 	  Quote: 	
		  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

John Hauck

Joined: 09 Jan 2006
Posts: 4639
Location: Titus, Alabama (hauck's holler)

Posted: Sat May 29, 2010 3:10 pm Post subject: drag conundrum

 	  Quote: 	
		   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

_________________
John Hauck
MKIII/912ULS
hauck's holler
Titus, Alabama

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