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FireFly Propeller Wash Over Horizontal Tail Surfaces

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jbhart(at)onlyinternet.ne
Guest

Posted: Wed Aug 09, 2006 7:28 am Post subject: FireFly Propeller Wash Over Horizontal Tail Surfaces

At 04:43 PM 7/31/06 -0400, you wrote:

 	  Quote: 	
		  



Well, maybe.  I'm not convinced, but I have to admit I don't really know.  

I've never thought it was necessary to "tease the throttle forward".  I 

don't JAM it forward, but that's out of respect for the engine, not concern 

about nosing over.  Empirically, it would be easy enough to determine 

whether the prop wash extends down as far as the elevator or not, just by 

getting down on your hands and knees immediately behind a Kolb with the 

engine running.  I'm going to guess you will get a faceful of wind.  




	




Lee, John H. and FireFlyers,



It has been HOT and so I took some measurements to determine what the true 

case would be for the FireFly.  Then I tufted the horizontal tail surfaces 

to see the direct airflow over the stabilizer and elevator.  I found out 

that John H. was correct in that the propeller wash does contact the 

horizontal tail surfaces on the FireFly.



At maximum up elevator, 14.3% of the elevator area is hit by propeller wash. 

 At the neutral position, 1.8% of the elevator area is hit by the propeller 

wash. I tufted the tail to see if these numbers were reasonable and they 

are.



How it was done can be seen at:



http://www.thirdshift.com/jack/firefly/firefly129.html



If you are interested in checking out your plane, I would recommend using a 

fishing rod with a foam fishing bobber attached.  This way you can readily 

feel the difference between entrained air and direct propeller wash.  It is 

much simpler than tufting.



Jack B. Hart FF004

Winchester, IN

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Richard Pike

Joined: 09 Jan 2006
Posts: 1671
Location: Blountville, Tennessee

Posted: Wed Aug 09, 2006 7:53 am Post subject: FireFly Propeller Wash Over Horizontal Tail Surfaces

Thanks for the info Jack, this makes me even more eager to seal the gap between the horizontal stab and the boom tube.

 

 Richard Pike

 MKIII N420P (420ldPoops)

 do not archive

 

 

 Jack B. Hart wrote:  	  Quote: 	
		      	  Quote: 	
		  --> Kolb-List message posted by: "Jack B. Hart" <jbhart(at)onlyinternet.net> (jbhart(at)onlyinternet.net)



At 04:43 PM 7/31/06 -0400, you wrote:

        	  Quote: 	
		  --> Kolb-List message posted by: "LEE CREECH" <dcreech3(at)hotmail.com> (dcreech3(at)hotmail.com)



Well, maybe.  I'm not convinced, but I have to admit I don't really know.  

I've never thought it was necessary to "tease the throttle forward".  I 

don't JAM it forward, but that's out of respect for the engine, not concern 

about nosing over.  Empirically, it would be easy enough to determine 

whether the prop wash extends down as far as the elevator or not, just by 

getting down on your hands and knees immediately behind a Kolb with the 

engine running.  I'm going to guess you will get a faceful of wind.  



    	
   



Lee, John H. and FireFlyers,



It has been HOT and so I took some measurements to determine what the true 

case would be for the FireFly.  Then I tufted the horizontal tail surfaces 

to see the direct airflow over the stabilizer and elevator.  I found out 

that John H. was correct in that the propeller wash does contact the 

horizontal tail surfaces on the FireFly.



At maximum up elevator, 14.3% of the elevator area is hit by propeller wash. 

 At the neutral position, 1.8% of the elevator area is hit by the propeller 

wash. I tufted the tail to see if these numbers were reasonable and they 

are.



How it was done can be seen at:



http://www.thirdshift.com/jack/firefly/firefly129.html



If you are interested in checking out your plane, I would recommend using a 

fishing rod with a foam fishing bobber attached.  This way you can readily 

feel the difference between entrained air and direct propeller wash.  It is 

much simpler than tufting.



Jack B. Hart FF004

Winchester, IN

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_________________
Richard Pike
Kolb MKIII N420P (420ldPoops)
Kingsport, TN 3TN0

Forgiving is tough, being forgiven is wonderful, and God's grace really is amazing.

George Alexander

Joined: 10 Jan 2006
Posts: 245
Location: SW Florida

Posted: Wed Aug 09, 2006 8:03 am Post subject: FireFly Propeller Wash Over Horizontal Tail Surfaces

Whether you agree or disagree with what he is saying, understand what he is

saying, want to challenge what he is saying, you gotta love this guy.

Can't wait for Ralph of Ohio's response.

Thanks Jack!



Awed George



PS: He did live in the "Show Me" state before he moved to the "Hoosier"

state didn't he?

DO NOT ARCHIVE



--

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_________________
George Alexander
FS II R503
E-LSA N709FS
http://www.oh2fly.net

tkrolfe(at)usadatanet.net
Guest

Posted: Wed Aug 09, 2006 9:34 am Post subject: FireFly Propeller Wash Over Horizontal Tail Surfaces

Jack,



You did it again!!!  Thanks for sharing your information with us.  I 

always look forward to seeing what your doing and the innovative 

solutions you bring to problems or questions.



I noticed that you have raised the horizontal stab above factory specs 

as have I.  I got a cleaner flight by doing so with out doing trim 

tabs.  I have mine 5/8" above standard, what is yours?  I know this is 

dependent on the pilots weight being a factor and the speed at which you 

cruise.  For me, I have found the sweet spot on my FireFly.



For Richard, concerning sealing the gap between the stab and boom, would 

an air dam made out of lexan along the inside edge of the stab work as 

well?  Let us know how you make out with this.



Terry -  FireFly #95

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Eugene Zimmerman

Joined: 10 Jan 2006
Posts: 392

Posted: Wed Aug 09, 2006 1:26 pm Post subject: FireFly Propeller Wash Over Horizontal Tail Surfaces

On Aug 9, 2006, at 1:32 PM, Terry wrote:



 	  Quote: 	
		   For Richard, concerning sealing the gap between the stab and boom,  

 would an air dam made out of lexan along the inside edge of the  

 stab work as well?


	


I thought about gluing a strip of foam rubber to the boom tube.



The up elevator seems plenty effective enough as it is on my  

Firestar, but a Mark III with two up may find some definite advantage  

with the gap sealed.



Perhaps I'll wait till someone finds a noticeable advantage with this  

gap sealed.



Gene

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John Hauck

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

Posted: Fri Aug 11, 2006 11:46 am Post subject: FireFly Propeller Wash Over Horizontal Tail Surfaces

|   I found out

| that John H. was correct in that the propeller wash does contact the

| horizontal tail surfaces on the FireFly.

 |

| Jack B. Hart FF004

Thanks Jack B:



Really had no reason to BS you about prop wash and tails, hehehe.



Just goes to show you I have learned something about the airplanes I 

have been fly for a while now.



john h

Candy Hill RV Park, Winchester, VA (where they have more rules than 

the Army.  Nell said it is because we are so close to Wash, DC.

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

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