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Wing Strut Fairings

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7suds(at)Chartermi.net
Guest

Posted: Fri Mar 27, 2009 11:49 am Post subject: Wing Strut Fairings

All,

The wing struts for my Model 5 have the PVC fairings, the end that attaches

to the fuselage has the aft fairing squared off and covered with fabric and

then the gap between them covered with sheet aluminum. I decided I wanted to

block out all the extrusion lines in the PVC fairings so I removed the

fabric and the aluminum and found all the gaps in that area filled with

bondo, which I have removed. Is the bondo thing normal? I do not have the

instructions for the install of the struts so I was wondering what others

have done and what others have seen for a finished weight for a strut with

the PVC fairings?  What have other used for fairings besides the PVC?



Lloyd C

UP Mi.

Mod 5 912ul

IVO IFA



Checked by AVG. 

8:05 PM

Lynn Matteson

Joined: 10 Jan 2006
Posts: 2778
Location: Grass Lake, Michigan

Posted: Fri Mar 27, 2009 1:06 pm Post subject: Wing Strut Fairings

I have a Model IV, with the same fairings that you describe, but I  

left the "extrusion lines" as is, covered them, and the sheet  

aluminum at the lower end, with fabric and let it go at that.



Lynn Matteson

Kitfox IV Speedster, taildragger

Jabiru 2200, #2062, 618.4 hrs

Sensenich 62x46

Electroair direct-fire ignition system

Status: flying





On Mar 27, 2009, at 3:44 PM, Cudnohufsky's wrote:



 	  Quote: 	
		   

 <7suds(at)chartermi.net>



  All,

 The wing struts for my Model 5 have the PVC fairings, the end that  

 attaches

 to the fuselage has the aft fairing squared off and covered with  

 fabric and

 then the gap between them covered with sheet aluminum. I decided I  

 wanted to

 block out all the extrusion lines in the PVC fairings so I removed the

 fabric and the aluminum and found all the gaps in that area filled  

 with

 bondo, which I have removed. Is the bondo thing normal? I do not  

 have the

 instructions for the install of the struts so I was wondering what  

 others

 have done and what others have seen for a finished weight for a  

 strut with

 the PVC fairings?  What have other used for fairings besides the PVC?



 Lloyd C

 UP Mi.

 Mod 5 912ul

 IVO IFA



 Checked by AVG.

 8:05 PM

_________________
Lynn
Kitfox IV-Jabiru 2200
N369LM

skyflyte(at)comcast.net
Guest

Posted: Fri Mar 27, 2009 1:38 pm Post subject: Wing Strut Fairings

Those "extrusion lines" are actually vortex generators which were  part of the design to reduce drag.  Eliminating them increases DRAG!! 

   Mike 

   490MC  

   M II   582

---

Tom Jones

Joined: 12 Mar 2006
Posts: 752
Location: Ellensburg, WA

Posted: Fri Mar 27, 2009 2:40 pm Post subject: Re: Wing Strut Fairings

 	  7suds(at)Chartermi.net wrote: 	
		  All,

The wing struts for my Model 5 have the PVC fairings, the end that attaches

to the fuselage has the aft fairing squared off and covered with fabric and

then the gap between them covered with sheet aluminum. I decided I wanted to

block out all the extrusion lines in the PVC fairings so I removed the

fabric and the aluminum and found all the gaps in that area filled with

bondo, which I have removed. Is the bondo thing normal? I do not have the

instructions for the install of the struts so I was wondering what others

have done and what others have seen for a finished weight for a strut with

the PVC fairings?  What have other used for fairings besides the PVC?



Lloyd C

UP Mi.

Mod 5 912ul

IVO IFA



Checked by AVG. 

8:05 PM 	




LLoyd, I talked with The Kitfox folks at the Arlington Wash. fly in last summer before I bought my PVC strut fairing.  They suggested using hysol (structrual epoxy) to fill the gaps and finish the trailing edges on the fuselage end of the fairing where they are cut.  The aluminum cuff is the option they sell to cover the fuselage end.  The hysol provides a sturdy base to rivet into along the trailing edge of the aluminum cuff.



The demonstrator kitfox there had the extrusion lines smoothed out.  I think Debra said she had installed those and had sanded the lines off before painting the fairing.



Wood fairing covered with fabric is used also.  It is a little lighter but a lot more work than the PVC.



I installed the PVC fairing according to their suggestions.  I mixed cotton flox with the hysol so it is very hard when set up.  I weighed before and after.  Gained 12.5 pounds.  I can't tell any difference in climb rate and gained about 8 MPH cruise speed with my little 52 horse engine.  84 mph true airspeed at 5800 RPM now.

_________________
Tom Jones
Classic IV
503 Rotax, 72 inch Two blade Warp
Ellensburg, WA

7suds(at)Chartermi.net
Guest

Posted: Sat Mar 28, 2009 5:23 am Post subject: Wing Strut Fairings

Mike,  

Thanks for the reply, you are probably correct that they are in by design since extrusion processes have evolved to the point where the outcome will be exact to the design. I guess in my thinking I have never seen vortex generators as continual lines on a surface especially strut fairings, all the strut fairings I have seen on aircraft are smooth. I suppose if I was building a Lancair I would kick myself but since I am building a Kitfox Iâ€™m not too alarmed over my decision. Offhand do you know what the difference in drag coefficient is with and without the vortex generators on the struts? I would imagine the manufacturer would have developed some numbers before investing in the dies.  

   

Lloyd  

       

From: owner-kitfox-list-server(at)matronics.com [mailto:owner-kitfox-list-server(at)matronics.com] On Behalf Of skyflyte(at)comcast.net

 Sent: Friday, March 27, 2009 4:37 PM

 To: kitfox-list(at)matronics.com

 Subject: Re: Wing Strut Fairings  

  

  

     

Those "extrusion lines" are actually vortex generators which were  part of the design to reduce drag.  Eliminating them increases DRAG!!  

   Mike  

   490MC   

   M II   582

 ---

Lynn Matteson

Joined: 10 Jan 2006
Posts: 2778
Location: Grass Lake, Michigan

Posted: Sat Mar 28, 2009 8:50 am Post subject: Wing Strut Fairings

Perhaps John McBean can shed some light on these "vortex generating"  

ridges? Why don't we see this same design on wings, wheelpants, etc?



Lynn Matteson

Kitfox IV Speedster, taildragger

Jabiru 2200, #2062, 618.4 hrs

Sensenich 62x46

Electroair direct-fire ignition system

Status: flying

do not archive



On Mar 28, 2009, at 9:23 AM, Cudnohufsky's wrote:



[quote] Mike,



 Thanks for the reply, you are probably correct that they are in by  

 design since extrusion processes have evolved to the point where  

 the outcome will be exact to the design. I guess in my thinking I  

 have never seen vortex generators as continual lines on a surface  

 especially strut fairings, all the strut fairings I have seen on  

 aircraft are smooth. I suppose if I was building a Lancair I would  

 kick myself but since I am building a Kitfox I’m not too alarmed  

 over my decision. Offhand do you know what the difference in drag  

 coefficient is with and without the vortex generators on the  

 struts? I would imagine the manufacturer would have developed some  

 numbers before investing in the dies.



 Lloyd



 From: owner-kitfox-list-server(at)matronics.com [mailto:owner-kitfox- 

 list-server(at)matronics.com] On Behalf Of skyflyte(at)comcast.net

 Sent: Friday, March 27, 2009 4:37 PM

 To: kitfox-list(at)matronics.com

 Subject: Re: Wing Strut Fairings



 Those "extrusion lines" are actually vortex generators which were   

 part of the design to reduce drag.  Eliminating them increases DRAG!!



    Mike



    490MC



    M II   582

 ---

_________________
Lynn
Kitfox IV-Jabiru 2200
N369LM

propellerdesign(at)tele2.
Guest

Posted: Sat Mar 28, 2009 9:20 am Post subject: Wing Strut Fairings

because wings ... are not under critical on Re Nr. as short chord wingstruts 

are.



Jan

---

7suds(at)Chartermi.net
Guest

Posted: Sat Mar 28, 2009 11:00 am Post subject: Wing Strut Fairings

Jan,

Excuse my ignorance but what does "critical on Re Nr. " mean?



Lloyd



--

propellerdesign(at)tele2.
Guest

Posted: Sat Mar 28, 2009 12:10 pm Post subject: Wing Strut Fairings

it is the critical number of Reynolds number, sorry.



if it is under the critical number the drag increase, it can be helped with 

some sort of VG's, look at the golf ball, the "dimples" make the air to 

become turbulent near the surface, (laminar layer/turbulent layer) the 

turbulent layer hold more energy that can follow the curved surface better 

to the back side, making the "wake" smaller, same on wing struts, if it is 

poorly shaped or to short/to fat it will help if laminar layer is tripped to 

turbulent.



Jan

---

Lynn Matteson

Joined: 10 Jan 2006
Posts: 2778
Location: Grass Lake, Michigan

Posted: Sat Mar 28, 2009 2:25 pm Post subject: Wing Strut Fairings

So I did good to leave the ridges as is, then, on mine? Sounds like  

it, and thanks for the explanation, Jan.



Lynn Matteson

Kitfox IV Speedster, taildragger

Jabiru 2200, #2062, 618.4 hrs

Sensenich 62x46

Electroair direct-fire ignition system

Status: flying

do not archive



On Mar 28, 2009, at 4:08 PM, JC Propeller Design wrote:



[quote] 

 <propellerdesign(at)tele2.se>



 it is the critical number of Reynolds number, sorry.



 if it is under the critical number the drag increase, it can be  

 helped with some sort of VG's, look at the golf ball, the "dimples"  

 make the air to become turbulent near the surface, (laminar layer/ 

 turbulent layer) the turbulent layer hold more energy that can  

 follow the curved surface better to the back side, making the  

 "wake" smaller, same on wing struts, if it is poorly shaped or to  

 short/to fat it will help if laminar layer is tripped to turbulent.



 Jan

 ---

_________________
Lynn
Kitfox IV-Jabiru 2200
N369LM

lcfitt(at)sbcglobal.net
Guest

Posted: Tue Mar 31, 2009 4:41 pm Post subject: Wing Strut Fairings

Lloyd,



I sanded them off with a belt sander then finer sand paper, then used a 

sanding primer (maybe a bit of spot putty first) and painted right over 

them - no lines.



Lowell



---

lcfitt(at)sbcglobal.net
Guest

Posted: Tue Mar 31, 2009 4:52 pm Post subject: Wing Strut Fairings

I respectfully disagree that these are vortex generators.  If you look at 

the ridges, they exactly line up with the internal beads designed to grip 

the lift strut.  With a thicker mass of hot plastic in these areas, a 

disproportunate amount of shrinkage will occur on the surface opposite the 

beads - presto a slight depression.



Lowell

---

7suds(at)Chartermi.net
Guest

Posted: Wed Apr 01, 2009 6:38 pm Post subject: Wing Strut Fairings

Lowell, 

Thanks for the feedback, that is pretty much the process I am using other

than beginning with an automotive DA Sander. 



Lloyd



--

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