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drag conundrum
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jbhart(at)onlyinternet.ne
Guest

Posted: Sat May 29, 2010 5:03 pm Post subject: drag conundrum

At 06:09 PM 5/29/10 -0500, you wrote:

 	  Quote: 	
		  

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.

 	  Quote: 	
		  

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.

 	  Quote: 	
		  

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.

 	  Quote: 	
		  

i use the wind sock when taxiing.



Not all fields have wind socks.
	


 	  Quote: 	
		  


	


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 6:13 pm Post subject: drag conundrum

> The yaw string only gives an indication of relative wind over one spot of

 	  Quote: 	
		   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.

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

jbhart(at)onlyinternet.ne
Guest

Posted: Sun May 30, 2010 6:42 am Post subject: drag conundrum

At 09:06 PM 5/29/10 -0500, you wrote:

 	  Quote: 	
		  

p factor at cruise is probably not measureable.




	


Take the trim tab off the rudder and start adding and subtracting washers to 

change the engine angle and see what happens. 



 	  Quote: 	
		  

how do you calibrate your slip/skid indicator?




	


To mount it I hung a plumb bob from the root tube with the bob directly over 

the tail tube.  Then I shimmed under a wheel until the bob point was over 

the middle of the tail tube.  I picked this as wings level.  Then I glued 

and taped the indicator to the panel with the ball centered.  After the glue 

had set up, I drilled and bolted the indicator to the panel.



 	  Quote: 	
		  

what kind of slip/skid indicator do you have?




	


Don't know of the brand, it is just a ball and curved tube type that I 

purchased out of the experimental aircraft supply catalogs.



 	  Quote: 	
		  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.




	


Yes there is, but I believe it is minor compared to the offsetting roll 

induced from the propeller torque reaction.

 	  Quote: 	
		  

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.




	


Due to the low position of the horizontal tail surfaces they do not receive 

much propeller air flow.  That is why it is so important to keep the thrust 

line as slow as possible.  On the FireFly with the 447 mounted only 23% of 

the horizontal stabilizer area was swept by propeller wash.  With the 

elevator full up, received 11% and in the neutral position 1%.  By dropping 

the thrust line with the Victor 1+ those numbers were 29%, 14%, and 2%, 

respectively.  Not a huge improvement, but it was worth doing and lead to 

the addition of VG's on the bottom of the horizontal stabilizer.  This study 

can be seen at:



http://jackbhart.com/firefly/firefly129.html



 	  Quote: 	
		  

23 years ago i experimented with thrust line of my firestar.  up, down, 

left, and right.  no change in performance, yaw, or pitch.




	


I suspect your ability to measure the resulting performance changes was not 

up to the task.  If I hold my hand out in the FireFly slip stream it will 

turn in that direction and I do not see a change on any of the flight 

instruments.  If you are interested, that is why it is so important to make 

changes that should improve the flight performance.  If you make enough of 

them, the accumulative effects will show in increased performance.  The end 

result is an aircraft that can be safer and more fun to fly, and easier on 

your wallet.



Jack B. Hart FF004

Winchester, IN

John Hauck

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

Posted: Sun May 30, 2010 7:09 am Post subject: drag conundrum

> I suspect your ability to measure the resulting performance changes was 

not

 	  Quote: 	
		   up to the task.



 Jack B. Hart FF004

 Winchester, IN


	




jack,



i am going to elect not to comment on the above statement.



however, i am interested in your ability to measure performance changes and 

the precision instrumentation you utilize to come to your conclusions.



john h

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

jbhart(at)onlyinternet.ne
Guest

Posted: Sun May 30, 2010 8:07 am Post subject: drag conundrum

At 10:09 AM 5/30/10 -0500, you wrote:

 	  Quote: 	
		  

however, i am interested in your ability to measure performance changes and 

the precision instrumentation you utilize to come to your conclusions.




	


John,



Most of my ability to detect performance changes comes from record keeping.  

I log and record the infight time, the fuel burned, engine rpm and egt.  I 

am fortune in that I can fly to my local EAA Chapter meetings so that I am 

flying the same path fairly often.   From these data one can determine 

trends that indicate performance changes.  It wasn't until I was able to 

control in flight EGT, that really good things began to happen.  This 

allowed me to fly with predictable/repeatable fuel rate burns even though 

metrological conditions changed over the period of the flight/trip.  This 

ability insures than one is flying at constant and repeatable power 

settings.  This is how I was able to compare the performance of the 447 and 

the Victor 1+.  Also with EGT control, I could investigate the fuel burn 

rates for different throttle settings with out the results being masked by 

changing atmospheric conditions.



These comparison studies where documented in:



http://jackbhart.com/firefly/firefly146.html



As far as changes in stall speed, one can do fairly well with the ASI and 

back it up with a GPS.  The lift increase brought about by VG's is easily 

done by determining the lowest flight speed at which one can maintain 

altitude before and after the addition of VG's.  Also, one can document the 

ability to fly slower in ground effect, and shortened distance for lift 

off.



See: http://jackbhart.com/firefly/firefly18.html



Some things I have tried, I could not see any change or improvement and so I 

have removed them.  Others in the same category, I have retained as in that 

past studies by NACA and NASA indicate they will be helpful.  

Jack B. Hart FF004

Winchester, IN

John Hauck

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

Posted: Sun May 30, 2010 10:41 am Post subject: drag conundrum

jack,



 > As far as changes in stall speed, one can do fairly well with the ASI and

 	  Quote: 	
		   back it up with a GPS.


	


how do you back up the asi with the gps?

The lift increase brought about by VG's is easily

 	  Quote: 	
		   done by determining the lowest flight speed at which one can maintain

 altitude before and after the addition of VG's.  Also, one can document 

 the

 ability to fly slower in ground effect, and shortened distance for lift

 off.


	




how precise is the above?

 	  Quote: 	
		   See: http://jackbhart.com/firefly/firefly18.html

 > Jack B. Hart FF004
	




i took a look at your web site.



"It wasn't until I was able to

control in flight EGT, that really good things began to happen."



how many engines have you seized because of over leaning mixture and 

tinkering with good carbs and engines to save a tea spoon of fuel and lower 

cruise rpm, performance, and reliability?



I experimented with a CPS inflight adjustable main jet on my cuyuna ULII02 

powered Ultrastar in 1984.  Soon discovered that was a bad idea and promptly 

removed it.  too easy to overlean, too easy to forget to reset to landing 

and takeoff settings.  Many of these caused an immediate engine shut down 

with the mikuni carb.



how many fun, reliable flight hours have you amassed in the life of your 

fire fly?



how many years since your first flight in your fire fly?



how did you determine i was not capable to test my three kolb aircraft over 

the past 26 years and 5,000+ kolb flight hours?  Actually, the last aircraft 

i tested was the latest model kolb mkiii extra at the kolb factory a couple 

years ago.  next time they need a test pilot i'll recommend they give you a 

call.  



take care,



john h

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

jbhart(at)onlyinternet.ne
Guest

Posted: Sun May 30, 2010 1:09 pm Post subject: drag conundrum

At 01:41 PM 5/30/10 -0500, you wrote:

 	  Quote: 	

how do you back up the asi with the gps?

In level flight and with out changing the throttle fly different directions 

and record the gps ground speeds.  The average of these speeds should 

approximate your ASI.

 	  Quote: 	

The lift increase brought about by VG's is easily

> done by determining the lowest flight speed at which one can maintain

> altitude before and after the addition of VG's.  Also, one can document 

> the

> ability to fly slower in ground effect, and shortened distance for lift

> off.

how precise is the above?

You have to guessimate the one mile point on the ASI, for slow flight, the 

gps does better but again one must fly in several directions and take and 

average.  Ground effect flying is easier in that you can fly both direction 

of the runway and take the average.

 	  Quote: 	

how many engines have you seized because of over leaning mixture and 

tinkering with good carbs and engines to save a tea spoon of fuel and lower 

cruise rpm, performance, and reliability?

None so far. 

 	  Quote: 	

I experimented with a CPS inflight adjustable main jet on my cuyuna ULII02 

powered Ultrastar in 1984.  Soon discovered that was a bad idea and promptly 

removed it.  too easy to overlean, too easy to forget to reset to landing 

and takeoff settings.  Many of these caused an immediate engine shut down 

with the mikuni carb.

I have no experience with this system.

 	  Quote: 	

how many fun, reliable flight hours have you amassed in the life of your 

fire fly?

Not as many as I would like.

 	  Quote: 	

how many years since your first flight in your fire fly?

eleven

 	  Quote: 	

how did you determine i was not capable to test my three kolb aircraft over 

the past 26 years and 5,000+ kolb flight hours?  

In a previous email, you made the following statement, "23 years ago i 

experimented with thrust line of my firestar.  up, down, left, and right.  

no change in performance, yaw, or pitch."  I assumed you were jesting when 

you made this statement in that the only way it can possibly be true is if 

the firestar is sitting still on the ground.  Newtonian physics will not be 

denied.  This List has had it's share of those who thought they could defy 

Newton's Laws.  Some have died, others banged up, and others have been lucky 

to escape with just a warning.  You, John have been very lucky.

 	  Quote: 	

Actually, the last aircraft 

i tested was the latest model kolb mkiii extra at the kolb factory a couple 

years ago.  next time they need a test pilot i'll recommend they give you a 

call.  

I appreciate the offer, but I have enough fun with my own FireFly.

Jack B. Hart FF004

Winchester, IN

Dennis.Kirby(at)kirtland.
Guest

Posted: Fri Jun 04, 2010 8:02 am Post subject: drag conundrum

"Thom Riddle" wrote:   

<< I recently downsized my Slingshot tires from 800x6 to 600-6 …  

I'm looking for feed back … Results: Zero change in IAS or TAS at same rpm setting. !(at)#$% >>  

   

   

Thom, Kolb Friends –  

   

Your findings mirror my own observations for the same modification on my Mark-3.  

Namely, that switching tire size from big to smaller resulted in zero difference in IAS.  

   

To make the drag conundrum even more frustrating for me, I also installed two other drag-reducing modifications to my Kolb at the same time, thinking that the combination would surely yield an extra mile per hour or two of increased air speed.  But not the case.  

   

In addition to switching from 800x6 to smaller 600x6 tires, I also installed aerodynamic fairings around the landing gear legs – the same plastic fairings that TNK provides to cover the wing struts.  To smooth the air flow around the upper-aft area of the pod, I installed Lexan panels on the sides of the cage (one on each side) to cover the open areas behind the pilots (below the wing, above the gas tanks).  I thought that cleaning up the air flow before it goes into the prop would help.  

   

I’ve flown two flights since these mods and have collected detailed airspeed data.  So far, I’m seeing zero change in indicated air speeds for the same power settings.  The only benefit I’m seeing is that it’s less windy in the cockpit, so I guess I’ll leave the Lexan panels in place.  

   

What this experiment reveals to me is, the Mark-3 is a very draggy airframe, and I’m not gonna squeeze any more blood (airspeed) from this turnip.  But what a wonderful turnip it is!  

   

Dennis Kirby  

Mark-III, 912ul  

Sandia Park, NM  

   

   

      [quote][b]

Thom Riddle

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

Posted: Fri Jun 04, 2010 10:32 am Post subject: Re: drag conundrum

Dennis,



Thanks much for your feedback. The SS is not quite as draggy as a MKIII but it IS a Kolb with the same high lift, high drag wing profile. I am therefore modifying my expectations for drag reduction results, from a several MPH increase to zero change. If I want to go faster I'll just spend the money on gas by moving the throttle forward, but won't expect much return for this expenditure .



Any more mods I do, will have to be justified by other factors. I'm still glad I changed the tires because the 15x600-6 appear to be better tires for pavement than the 800x6 tires. They also make the brakes more effective due to the smaller diameter.

_________________
Thom Riddle
Buffalo, NY (9G0)

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

John Hauck

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

Posted: Fri Jun 04, 2010 3:10 pm Post subject: drag conundrum

Operating primarily on pavement with 800X6 I run 15 psi.



Improved grass 10 psi.



Rough unimproved 4 to 6 psi.



john h

mkIII



---

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

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