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Incidence Angles

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Thom Riddle

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

Posted: Sun Oct 11, 2009 5:44 am Post subject: Incidence Angles

While I had my Warp Drive Protractor out measuring the new pitch of my TN prop yesterday, I decided to see what the incidence angles were on my Slingshot out of curiosity. I borrowed Jack Hart's drawing of his FireFly with incidence angles shown and edited the numbers to correspond to what I measured on my Slingshot. Image attached. 



The Slingshot has a rather tall main gear so the root tube is angled up a lot more than the short leg Kolbs when on the ground. 



In my mind, the numbers worth noting are the Horizontal Stabilizer angle is the same as the Root Tube. If at cruise speed the HS is even with the relative wind, then the wing bottoms are at about 7 degrees AOA and the engine centerline is pointing UP about 3 1/2 degrees from relative wind. 



If my assumption is wrong about the HS being level at my normal cruise airspeed then this would be wrong. Since it is supposed to provide a small down force at the tail, it is probably pointing down a little bit during cruise flight. In any case, the difference in incidence between the wing and HS is 7 degrees which seems like a lot to me.



I'd like to hear from others about these angles on their Kolbs. Especially from the few other Slingshot flyers on the list, but others as well.

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Thom Riddle
Buffalo, NY (9G0)

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

mdnanwelch7(at)hotmail.co
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Posted: Sun Oct 11, 2009 6:44 am Post subject: Incidence Angles

> In my mind C the numbers worth noting are the Horizontal Stabilizer angle is the same as the Root Tube. If at cruise speed the HS is even with the relative wind C then the wing bottoms are at about 7 degrees AOA and the engine centerline is pointing UP about 3 1/2 degrees from relative wind. 

 	  Quote: 	
		   

 If my assumption is wrong about the HS being level at my normal cruise airspeed then this would be wrong. Since it is supposed to provide a small down force at the tail C it is probably pointing down a little bit during cruise flight. In any case C the difference in incidence between the wing and HS is 7 degrees which seems like a lot to me.

 

 I'd like to hear from others about these angles on their Kolbs. Especially from the few other Slingshot flyers on the list C but others as well.

 

 --------

 Thom Riddle

 Buffalo C NY

 Kolb Slingshot SS-021

 Jabiru 2200A #1574

 Tennessee Prop 64x31

  
	


  

 Thom C

  

   I have done quite a bit of research on the Kolb MkIII wing's incidence angles C (and have a data table of results) C since I am having to change the incidence from the Classic angle to the Xtra angle (since my MkIII has undergone a rather complete transformation from starting out as a Classic to now being an Xtra).

  

   Yes C believe it or not C 7 degrees incidence  C in level flightseems to be pretty close to what my research has shown.  7 degrees incidence sounds like a lot C and frankly C I think it is C but it must be what Homer had intended.  Evidently C a high incidence wing angle gives the performance that the Kolb are known for.

  

   I do know of at least one individual who is considering lowering the incidence on his MkIIIC.

  

 Mike Welch

 MkIII

 

 

 		 	   		  Hotmail: Free C trusted and rich etarget='_new'>Get it now.  [quote][b]

Thom Riddle

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

Posted: Sun Oct 11, 2009 7:18 am Post subject: Re: Incidence Angles

Mike,



I was not surprised at the approx. 7 degrees AOA (wing vs relative wind) which varies with airspeed. The higher the airspeed the lower the AOA and vice versa.



What I was surprised at is the decalage, i.e., the difference in incidence angles between the wings and the horizontal stabilizer. Attached is Jack Hart's drawing of his FireFly which shows a decalage of only 2 degrees, 11 (wing) minus 9 (HS).



I was also surprised to see the major difference in thrust lines relative to wing incidence. Note that on Jack's FireFly, at least at the time of this drawing, shows his thrust centerline to pointing down relative to the wing bottom with a negative difference of about 5 1/2 degrees. My SS thrust line is pointing up relative to the wing bottom by a positive 3 1/2 degrees.



I know these airplanes are different in many ways but these incidence and thrust-line differences are pretty major, which is what prompted my query about other Kolber's incidence angles. I've not looked at the SS plans to see what they call for but suspect mine is pretty close to plans and it handles very well. But I'm curious if any other Kolbs have this sort of incidence and thrust-line relationship.

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Thom Riddle
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rickofudall

Joined: 19 Sep 2009
Posts: 1392
Location: Udall, KS, USA

Posted: Sun Oct 11, 2009 7:25 am Post subject: Incidence Angles

Guys, Let's get back to basics before people start changing angles of incidence. There's a reason for that 7 degrees. The Kolb flies at about 9 degrees angle of attack. You might remember that number from the factory recommendation for weight and balance measurement.  Do the math for the amount of lift needed at whatever you consider your cruise speed. You know, dynamic pressure X wing area X lift coefficient. What you find is that the lift coefficient that works out is in the 8 to 9 degree AOA range.

 So what you end up with is less trim drag when flying at cruise when the AOI is set at something near the AOA required for cruise. Lower the angle of incidence and now the fuselage flies at a higher angle of attack in cruise flight and produces more drag, Then there's the lift needed by the horizontal stabilizer to hold the wing at that higher AOA (compared to AOI), net result more trim drag.

 Of course this is experimental aviation and you can do whatever experiment you like to validate Homer's calculations, but I think you'll find he was right on the money.

MHO with Beauford's maxim.

Rick Girard

do not archive

On Sun, Oct 11, 2009 at 9:43 AM, Mike Welch <mdnanwelch7(at)hotmail.com (mdnanwelch7(at)hotmail.com)> wrote:

 [quote]     > In my mind, the numbers worth noting are the Horizontal Stabilizer angle is the same as the Root Tube. If at cruise speed the HS is even with the relative wind, then the wing bottoms are at about 7 degrees AOA and the engine centerline is pointing UP about 3 1/2 degrees from relative wind. 

 > 

 	  Quote: 	
		   If my assumption is wrong about the HS being level at my normal cruise airspeed then this would be wrong. Since it is supposed to provide a small down force at the tail, it is probably pointing down a little bit during cruise flight. In any case, the difference in incidence between the wing and HS is 7 degrees which seems like a lot to me.

 > 

 	  Quote: 	
		   I'd like to hear from others about these angles on their Kolbs. Especially from the few other Slingshot flyers on the list, but others as well.

 --------

 Thom Riddle

 Buffalo, NY

 > Kolb Slingshot SS-021

 	  Quote: 	
		   Jabiru 2200A #1574

 Tennessee Prop 64x31

 Thom,

   I have done quite a bit of research on the Kolb MkIII wing's incidence angles, (and have a data table of results), since I am having to change the incidence from the Classic angle to the Xtra angle (since my MkIII has undergone a rather complete transformation from starting out as a Classic to now being an Xtra).

   Yes, believe it or not, 7 degrees incidence , in level flightseems to be pretty close to what my research has shown.  7 degrees incidence sounds like a lot, and frankly, I think it is, but it must be what Homer had intended.  Evidently, a high incidence wing angle gives the performance that the Kolb are known for.

   I do know of at least one individual who is considering lowering the incidence on his MkIIIC.

 Mike Welch

 MkIII

Hotmail: Free, trusted and rich etarget='_new'>Get it now.

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get="_blank">http://www.matronics.com/Navigator?Kolb-List

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Posted: Sun Oct 11, 2009 7:34 am Post subject: Incidence Angles

At 06:44 AM 10/11/09 -0700, you wrote:

 	  Quote: 	
		  



In my mind, the numbers worth noting are the Horizontal Stabilizer angle is 

the same as the Root Tube. If at cruise speed the HS is even with the 
	


relative wind, then the wing bottoms are at about 7 degrees AOA and the 

engine centerline is pointing UP about 3 1/2 degrees from relative wind. 

 	  Quote: 	
		  

If my assumption is wrong about the HS being level at my normal cruise 

airspeed then this would be wrong. Since it is supposed to provide a small 
	


down force at the tail, it is probably pointing down a little bit during 

cruise flight. In any case, the difference in incidence between the wing and 

HS is 7 degrees which seems like a lot to me.

 	  Quote: 	
		  


	


Thom,



What is your slip indicator doing at cruise?  Is the ball centered?



Jack B. Hart FF004

Winchester, IN

Thom Riddle

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

Posted: Sun Oct 11, 2009 7:45 am Post subject: Re: Incidence Angles

Jack,



My slip indicator is a yaw string and it is centered with feet off the rudders at my normal cruise speed. The rudder trim tab is bent only very slightly to the left, giving a little right rudder to accomplish this. 



The ailerons do not have trim tabs but the left aileron actuating rod is extended a lot further than the right one to give wings level flight with no apparent force on the stick. But the ailerons appear to be in alignment with the bottom of the wings with stick neutral.



I have electric elevator trim and it flies with the trim indicator near center at normal cruise. What I have not looked at is the angle of trim tab with respect to the elevator when in neutral indicator position. I'll check then next time I am at the airplane.



I'm not very concerned about the difference in incidence of the HS and wings but am very curious about the thrust line difference. When I go to the airport next time I'll fetch the plans and see what was called for.

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Thom Riddle
Buffalo, NY (9G0)

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

Joined: 19 Sep 2009
Posts: 1392
Location: Udall, KS, USA

Posted: Sun Oct 11, 2009 7:52 am Post subject: Incidence Angles

To carry on the discussion, the engine is set at a different angle to offset that other airfoil characteristic, the pitching moment. The wing wants to tumble AOTK (a** over tea kettle), the engine driving forward through a lesser angle counters this and once again, reduces trim drag. 



Rick Girard

do not archive



On Sun, Oct 11, 2009 at 10:45 AM, Thom Riddle <riddletr(at)gmail.com (riddletr(at)gmail.com)> wrote:

 [quote]--> Kolb-List message posted by: "Thom Riddle" <riddletr(at)gmail.com (riddletr(at)gmail.com)>

  

 

Jack,

 

 My slip indicator is a yaw string and it is centered with feet off the rudders at my normal cruise speed. The rudder trim tab is bent only very slightly to the left, giving a little right rudder to accomplish this.

 

 The ailerons do not have trim tabs but the left aileron actuating rod is extended a lot further than the right one to give wings level flight with no apparent force on the stick. But the ailerons appear to be in alignment with the bottom of the wings with stick neutral.

  

 I have electric elevator trim and it flies with the trim indicator near center at normal cruise. What I have not looked at is the angle of trim tab with respect to the elevator when in neutral indicator position. I'll check then next time I am at the airplane.

  

 I'm not very concerned about the difference in incidence of the HS and wings but am very curious about the thrust line difference. When I go to the airport next time I'll fetch the plans and see what was called for.

  

 --------

 Thom Riddle

 Buffalo, NY

 Kolb Slingshot SS-021

 Jabiru 2200A #1574

 Tennessee Prop 64x31

 

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jbhart(at)onlyinternet.ne
Guest

Posted: Sun Oct 11, 2009 9:52 am Post subject: Incidence Angles

Thom,



Been thinking about this a little more.  I lowered my thrust line by 

rotating the belt reduction unit on the Victor 1+.  By doing so, I believe, 

it moved the thrust line closer to the center of drag.  This in turn reduced 

stabilizer and wing loading for the same cruise speed.



See:



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



We seem to have the same angle difference between the wing and the 

horizontal stabilizer.  But where I am trimmed for cruise at 50-55 mphi, and 

max weight of 500 pounds, you are banging along at greater speed, weight and 

thrust, with a higher thrust line and working the wing much harder than the 

FireFly.  I don't believe a FireFly comparison is valid.  I believe your 

best hope is to find another SlingShot owner.



I tried a string as a slip indicator, and then I tried a ball.  I like the 

ball.  I still use the string, but only as a taxi out and in cross wind 

indicator.



Jack B. Hart FF004

Winchester, IN

pj.ladd(at)btinternet.com
Guest

Posted: Sun Oct 11, 2009 9:56 am Post subject: Incidence Angles

My slip indicator is a yaw string and it is centered with feet off the 

rudders at my normal cruise speed. The rudder trim tab is bent only very 

slightly to the left, giving a little right rudder to accomplish this.



Mine too on my Xtra but the rudder trim is a length of door draught 

excluder.stuck to the trailing edge The sort with a flat section and a small 

tube on one edge.



Pat

Thom Riddle

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

Posted: Sun Oct 11, 2009 10:20 am Post subject: Re: Incidence Angles

Jack,



I agree that the only things our airplanes have similar other than being Kolbs, is that the wings are similar in size so the comparison is probably not a good one. But yours is the only one I have data on to compare too, not to mention your drawing also being available for me to copy .



On the ground my wing bottoms are at 12 degrees and horizontal stabilizer is at 5 degrees which is a difference of 7 degrees. That is a lot of decalage, compared to yours which is 2 degrees (11 minus 9). Yours is similar to most aircraft that I'm familiar with. As you know the more decalage there is the more longitudinal stability if all else is constant. The Slingshot is pretty short coupled, so that relatively short arm that the horizontal stabilizer is working with may require that much extra decalage. I'll know when I check the plans, if that is close to what was intended. I expect it is about right because the builder was something of a perfectionist, much to my benefit.



As you noted, your thrust line is much lower than mine and perhaps the major difference in thrust angle is also required for that high engine centerline, which I'll also measure on next trip to airport.



Thanks for your thoughts on this.

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Buffalo, NY (9G0)

Don't worry about old age... it doesn't last very long.
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John Hauck

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

Posted: Sun Oct 11, 2009 1:54 pm Post subject: Incidence Angles

> The ailerons do not have trim tabs but the left aileron actuating rod is

extended a lot further than the right one to give wings level flight with no

apparent force on the stick. But the ailerons appear to be in alignment with

the bottom of the wings with stick neutral.

 	  Quote: 	
		  

 Thom Riddle


	


Thom R/Gang:



Adjusting length of aileron push/pull tube(s) does a couple things:



a.  Changes the position of the control stick when the ailerons load up and

equalize in flight.



b.  Increases or decreases droop/reflex.



What it doesn't do is change roll trim.



john h

mkIII

Blanding, UT

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

JetPilot

Joined: 10 Jan 2006
Posts: 1246

Posted: Sun Oct 11, 2009 8:27 pm Post subject: Re: Incidence Angles

 	  John Hauck wrote: 	
		   



Thom R/Gang:



Adjusting length of aileron push/pull tube(s) does a couple things:



a.  Changes the position of the control stick when the ailerons load up and

equalize in flight.



b.  Increases or decreases droop/reflex.



What it doesn't do is change roll trim.



john h

mkIII

Blanding, UT 	




John is correct, changing the length of those tubes will have no effect on Roll trim.  It will change where the stick physically centers when flying...



Mike

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Kolb MK-III Xtra, 912-S

russkinne(at)mac.com
Guest

Posted: Mon Oct 12, 2009 5:52 am Post subject: Incidence Angles

ThomInteresting discussion about AOL's of HS & wing. But I wonder if the boom tube of a Kolb  in level flight is absolutely horizontal? Anyone have a good picture of a Kolb  in  flight with the horizon behind it?

Russ

do not archive

On Oct 11, 2009, at 10:43 AM, Mike Welch wrote:

 	  Quote: 	
		  > In my mind, the numbers worth noting are the Horizontal Stabilizer angle is the same as the Root Tube. If at cruise speed the HS is even with the relative wind, then the wing bottoms are at about 7 degrees AOA and the engine centerline is pointing UP about 3 1/2 degrees from relative wind. 

 	  Quote: 	
		   

 If my assumption is wrong about the HS being level at my normal cruise airspeed then this would be wrong. Since it is supposed to provide a small down force at the tail, it is probably pointing down a little bit during cruise flight. In any case, the difference in incidence between the wing and HS is 7 degrees which seems like a lot to me.

 

 I'd like to hear from others about these angles on their Kolbs. Especially from the few other Slingshot flyers on the list, but others as well.

 

 --------

 Thom Riddle

 Buffalo, NY

 Kolb Slingshot SS-021

 Jabiru 2200A #1574

 Tennessee Prop 64x31

 
	


 

Thom,

 

  I have done quite a bit of research on the Kolb MkIII wing's incidence angles, (and have a data table of results), since I am having to change the incidence from the Classic angle to the Xtra angle (since my MkIII has undergone a rather complete transformation from starting out as a Classic to now being an Xtra).

 

  Yes, believe it or not, 7 degrees incidence , in level flightseems to be pretty close to what my research has shown.  7 degrees incidence sounds like a lot, and frankly, I think it is, but it must be what Homer had intended.  Evidently, a high incidence wing angle gives the performance that the Kolb are known for.

 

  I do know of at least one individual who is considering lowering the incidence on his MkIIIC.

 

Mike Welch

MkIII



 



Hotmail: Free, trusted and rich etarget='_new'>Get it now. 	  Quote: 	
		  



href="http://www.matronics.com/Navigator?Kolb-List">http://www.matronics.com/Navigator?Kolb-List

href="http://forums.matronics.com">http://forums.matronics.com

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slyck(at)frontiernet.net
Guest

Posted: Mon Oct 12, 2009 6:24 am Post subject: Incidence Angles

Russ, we've been through that point way in the past.  -including inflight pix.Most Kolbs, especially the MkIII, fly tail high.  A lesser incidence on the wing, like the SS and the Xtra,

will reduce the boom tilt

BB

On 12, Oct 2009, at 9:52 AM, russ kinne wrote:

[quote] ThomInteresting discussion about AOL's of HS & wing. But I wonder if the boom tube of a Kolb  in level flight is absolutely horizontal? Anyone have a good picture of a Kolb  in  flight with the horizon behind it?

Russ

do not archive

On Oct 11, 2009, at 10:43 AM, Mike Welch wrote:

 	  Quote: 	
		  > In my mind, the numbers worth noting are the Horizontal Stabilizer angle is the same as the Root Tube. If at cruise speed the HS is even with the relative wind, then the wing bottoms are at about 7 degrees AOA and the engine centerline is pointing UP about 3 1/2 degrees from relative wind. 

 	  Quote: 	
		   

 If my assumption is wrong about the HS being level at my normal cruise airspeed then this would be wrong. Since it is supposed to provide a small down force at the tail, it is probably pointing down a little bit during cruise flight. In any case, the difference in incidence between the wing and HS is 7 degrees which seems like a lot to me.

 

 I'd like to hear from others about these angles on their Kolbs. Especially from the few other Slingshot flyers on the list, but others as well.

 

 --------

 Thom Riddle

 Buffalo, NY

 Kolb Slingshot SS-021

 Jabiru 2200A #1574

 Tennessee Prop 64x31

 
	


 

Thom,

 

  I have done quite a bit of research on the Kolb MkIII wing's incidence angles, (and have a data table of results), since I am having to change the incidence from the Classic angle to the Xtra angle (since my MkIII has undergone a rather complete transformation from starting out as a Classic to now being an Xtra).

 

  Yes, believe it or not, 7 degrees incidence , in level flightseems to be pretty close to what my research has shown.  7 degrees incidence sounds like a lot, and frankly, I think it is, but it must be what Homer had intended.  Evidently, a high incidence wing angle gives the performance that the Kolb are known for.

 

  I do know of at least one individual who is considering lowering the incidence on his MkIIIC.

 

Mike Welch

MkIII



 



Hotmail: Free, trusted and rich etarget='_new'>Get it now. 	  Quote: 	
		  



href="http://www.matronics.com/Navigator?Kolb-List">http://www.matronics.com/Navigator?Kolb-List

href="http://forums.matronics.com">http://forums.matronics.com

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jbhart(at)onlyinternet.ne
Guest

Posted: Mon Oct 12, 2009 4:20 pm Post subject: Incidence Angles

From: russ kinne <russkinne(at)mac.com>

Date: Mon, 12 Oct 2009 09:52:26 -0400

 	  Quote: 	

Thom

Interesting discussion about AOL's of HS & wing. But I wonder if the boom 

tube of a Kolb  in level flight is absolutely horizontal? Anyone have a good 

picture of a Kolb  in  flight with the horizon behind 

it?

 	  Quote: 	

Russ,

I checked the FireFly out with a AOA meter.  At cruise the tail boom tube 

would be 4.5 degrees up.

I have some photos that help but none with the horizon.  The first is a 

ground effect fly by at:

http://jackbhart.com/firefly/firefly87.html

Then there are several low level flight photos that were taken from the 

ground at:

http://jackbhart.com/firefly/firefly137.html

If you click on the photos they will enlarge.  It is difficult to judge from 

these photos if the tail boom 4.5 degrees up, but it would be difficult to 

say that it is not up 4.5 degrees too.

Jack B. Hart FF004

Winchester, IN

Thom Riddle

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

Posted: Mon Oct 12, 2009 4:38 pm Post subject: Re: Incidence Angles

Jack,



If your tail boom is inclined 4.5 degrees up at the tail end during cruise that means your nose rotates down about 6 degrees from 3-point and gives a cruise wing AOA of 5 degrees, which is pretty close to cruise AOA of lots of airplanes, and the HS AOA of about 3 degrees positive. Useful and interesting information.

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