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Adding extra rib to rudder

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reinkings(at)comcast.net
Guest

Posted: Fri Jan 04, 2008 5:09 pm Post subject: Adding extra rib to rudder

I'm considering fabricating an "end" rib to close the open area at the 

bottom of the leading edge of the rudder?   Would this create any problems?

dredmoody(at)cox.net
Guest

Posted: Fri Jan 04, 2008 6:21 pm Post subject: Adding extra rib to rudder

Wait until you have mounted the rudder and trimmed  the bottom of the rudder nose skin to clear the fiberglass rudder  fairing. Once you have done that, go for it if you want to. I think other  builders have mentioned closing that open bottom area and have not had any  trouble caused by the mod.

  

 Dred

 [quote]   ---

Martin Pohl

Joined: 30 Jan 2006
Posts: 118
Location: CH-8645 Jona SG, Switzerland

Posted: Sat Jan 05, 2008 5:37 am Post subject: Re: Adding extra rib to rudder

I will also fabricate an end rib for the rudder leading edge bottom. As Dred said, do that only when you have installed both rudder and "plastic"-fairing to the horizontal tail. In my case there is a 1/2 inch gap between fairing and rudder which I will adjust with this additional rib.



Cheers Martin

_________________
Martin Pohl
Zodiac XL QBK
8645 Jona, Switzerland
http://www.pohltec.ch/ZodiacXL/Main.html

ashontz

Joined: 27 Dec 2006
Posts: 723

Posted: Sun Jan 06, 2008 3:09 pm Post subject: Re: Adding extra rib to rudder

A couple of drain holes wouldn't be a bad idea either.



 	  reinkings(at)comcast.net wrote: 	
		  I'm considering fabricating an "end" rib to close the open area at the 

bottom of the leading edge of the rudder?   Would this create any problems?

tjs22t(at)verizon.net
Guest

Posted: Mon Jan 07, 2008 4:27 pm Post subject: Adding extra rib to rudder

 	  Quote: 	
		   I'm considering fabricating an "end" rib to close the open area at the 

 bottom of the leading edge of the rudder?   Would this create any 

 problems?


	


John,



It should not cause any problems but take the advice to wait until final 

fitting of saddle piece over stab.



You can make a rib out of .016 aluminum or take a look at this method and 

see what you think - it's only one other way to tackle the problem.  Works 

for me but everyone has their preferences:



Even builders of metal a/c need to cultivate a skill with working in 

fiberglass.



Take a piece of builders foam (often scraps are thrown away at new home 

sites); usually this stuff is blue, green or pink, and is available in 

various thicknesses from 1/2 inch up to 3 inches.  You need a piece of one 

inch for this.



Press foam against rudder spar and then into the open bottom end of leading 

edge - this will leave an impression of the opening.



Cut out this piece on the bandsaw and sand (the stuff sands easily) until it 

is a somewhat loose fit into the area to be filled.  If you ended up putting 

a gentle curve into the bottom of the leading edge to fit the saddle it 

won't matter as you can easily sand the side profile to match.



Cover the top surface of the piece (draping some cloth over the sides) with 

a layer of 5 to 8 ounce fiberglass.  One layer will do for this piece.  Use 

finishing resin which you can get in larger qualities from ACS or go to 

local hobby store (Tower Hobbies for mail or on-line orders) and see what 

they have.  It's normally one-to-one in ratio from the hobby store venue. 

Apply with the cheap acid brushes you get at hardware store for $.49 so they 

can be tossed - though acetone will clean 'em if you want to reuse.



Allow resin to set and scuff a bit with 50 to 80 grit paper, then apply 

another coat of finishing resin.



This should be sufficient thickness to allow sanding to a smooth surface; if 

not, apply more resin.  Start with 80 grit and move to 220.



Sand edges carefully checking often for fit into the rudder opening.



Attach into opening with RTV (the RV crowd uses this all the time).  Mine 

has held through 310+ hours.



The "rudder plug" is shown installed in one attachment and sitting atop the 

stab tips in the other (providing the attachments come through).



The stabilizer tips are another easy fiberglass project that clean up an 

area in the tail surfaces.  I did not care for the look of a row of rivets 

running to the aft end of the tips and the creases formed by the rib running 

the rear length.



Take the same process as above: trace around the aft of the stab tip, cut a 

piece of builders foam, epoxy in place, sand with a big block, cover ONLY 

the foam being careful to keep the piece of cloth just large enough to 

extend past the edge.  When the resin is almost cured you can take a 

single-edge razor blade and trim the fiberglass "whiskers" off.  The reason 

for this is to minimize the amount of sanding needed on the gel coat of the 

tips.



The ribs that would have been used can now go into the elevator where the 

rudder cutout is (mine is an HDS; the XL kits may come with extra ribs for 

this purpose?).



In the second attachment the tips are shown, the plug for rudder is atop, 

and the cutout ribs are the ones with rivet holes.  The primer is Randolph's 

two-part epoxy, Epibond.



Presently I'm working on new wheel pants for the S83 Michelin smaller 

diameter tires using much the same techniques as above with one and two inch 

foam in contrasting colors to aid in symmetrical contouring.



If anyone is interested a tutorial of making a fiberglass fairing for atop 

the rudder utilizing the position light in that location, it can be 

forwarded to you.  Please contact off-list at tjs22t(at)verizon.net.



cheers  jeff  HDS/3300

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PatrickW

Joined: 27 Oct 2006
Posts: 380
Location: Fort Worth, Texas

Posted: Mon Jan 07, 2008 5:45 pm Post subject: Re: Adding extra rib to rudder

Just make sure it's attached well so it doesn't come partially out and interfere with rudder travel.



Patrick

XL/Covair

daveaustin2(at)primus.ca
Guest

Posted: Mon Jan 07, 2008 6:39 pm Post subject: Adding extra rib to rudder

Just my thoughts on this..  Why add extra weight when not needed?  I cut off 

the corners of every "L" piece to keep weight down.  Rounded ends of 

longerons and u/c slides etc..  I'm not smart enough to do the math to 

decide if the drag reduction is more valuable than the extra weight. 

Anybody out there..?

Dave Austin  601HDS - 912, Spitfire Mk VIII

psm(at)ATT.NET
Guest

Posted: Mon Jan 07, 2008 8:21 pm Post subject: Adding extra rib to rudder

Hi Dave,



Engineering is always about trade-offs.  Airplane engineering is 

about trade-offs that are often difficult to make.



One important concept in engineering is the concept of 

"Metrics".  This is not centimeters vs. inches.  It is about 

measuring stuff to determine what is better and what is not.  For 

this question the metrics to use are probably airspeed and weight.



It might be best to leave the extra rib (fairing) off until you have 

completed your initial testing.  Then you could add it - perhaps in a 

temporary fashion (like duct tape?) - and measure the difference in 

airspeed.  If you can't measure any difference then you don't need 

the extra weight.  If you can measure a speed difference (and it is 

in the right direction) then you can scratch your head and decide 

whether you want faster speed (with a known speed gain) or less weight.



You could use a different set of metrics and get a different answer 

to your question.  Maybe you are concerned about the noise level 

while flying your plane.  You could perform the same experiment but 

instead of measuring airspeed you might measure sound level.  The 

fairing might reduce the sound level or it might not.  Again, you can 

make a good, informed, decision once you have made the measurements.



Good luck,



Paul

XL fuselage



At 05:03 PM 1/7/2008, you wrote:



 	  Quote: 	
		  Just my thoughts on this..  Why add extra weight when not needed?  I 

cut off the corners of every "L" piece to keep weight down.  Rounded 

ends of longerons and u/c slides etc..  I'm not smart enough to do 

the math to decide if the drag reduction is more valuable than the 

extra weight. Anybody out there..?

Dave Austin  601HDS - 912, Spitfire Mk VIII

tjs22t(at)verizon.net
Guest

Posted: Tue Jan 08, 2008 2:56 am Post subject: Adding extra rib to rudder

do not archive    

 

 	  Quote: 	
		   Engineering is always about trade-offs.  


	


On the Zenith Matronics list "engineering" is usually about b___s___.

planecrazydld(at)yahoo.co
Guest

Posted: Tue Jan 08, 2008 3:24 am Post subject: Adding extra rib to rudder

Corvair

        Be a better friend, newshound, and  [quote][b]

john.marzulli(at)gmail.co
Guest

Posted: Tue Jan 08, 2008 3:36 pm Post subject: Adding extra rib to rudder

I think another way to look at this is safety -



If you plan on taking this plane to fly ins, then closing large gaps where children may stick their hands is a great idea.



Ron Wanttaja wrote a great article about this a few months ago. Have you looked at sealing the area with tape or fabric instead? 



DO NOT ARCHIVE



On Jan 7, 2008 7:21 PM, Paul Mulwitz <psm(at)att.net (psm(at)att.net)> wrote:

[quote] --> Zenith-List message posted by: Paul Mulwitz <psm(at)att.net (psm(at)att.net)>



Hi Dave,



Engineering is always about trade-offs.  Airplane engineering is

about trade-offs that are often difficult to make. 



One important concept in engineering is the concept of

"Metrics".  This is not centimeters vs. inches.  It is about

measuring stuff to determine what is better and what is not.  For

this question the metrics to use are probably airspeed and weight. 



It might be best to leave the extra rib (fairing) off until you have

completed your initial testing.  Then you could add it - perhaps in a

temporary fashion (like duct tape?) - and measure the difference in

 airspeed.  If you can't measure any difference then you don't need

the extra weight.  If you can measure a speed difference (and it is

in the right direction) then you can scratch your head and decide

whether you want faster speed (with a known speed gain) or less weight. 



You could use a different set of metrics and get a different answer

to your question.  Maybe you are concerned about the noise level

while flying your plane.  You could perform the same experiment but

instead of measuring airspeed you might measure sound level.  The 

fairing might reduce the sound level or it might not.  Again, you can

make a good, informed, decision once you have made the measurements.



Good luck,



Paul

XL fuselage



 

At 05:03 PM 1/7/2008, you wrote:



 	  Quote: 	
		  Just my thoughts on this..  Why add extra weight when not needed?  I

cut off the corners of every "L" piece to keep weight down.  Rounded

ends of longerons and u/c slides etc..  I'm not smart enough to do http://701Builder.blogspot.com/


	


"Flying a plane is no different than riding a bicycle... it's just a lot harder to put baseball cards in the spokes.

-Airplane The Movie  [quote][b]

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