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  #1  
Old 04-12-2012, 10:35 AM
newtech's Avatar
newtech newtech is offline
 
Join Date: Mar 2006
Location: Evansville, Indiana
Posts: 663
Default Tip: Getting rid of the rudder trim tab

Last Fall I hosted one of our EAA meetings at my hangar and demonstrated how to make a fiberglass nose gear fairing for an "A" model. The program started out with applying the clay, shaping it, and took it up to the point where a coat of epoxy gel-coat was applied. To be able to finish the clay modeling and get the gel-coat applied I didn't have much time for quality control issues; I actually was planning on redoing it after the meeting and making a finished fairing from the second clay model. Well, the first attempt didn't look too bad so I went ahead and made a mold and subsequently a fiberglass fairing.

After pulling the part from the mold it was pretty obvious that I didn't get the trailing edge of the fairing straight. If I aligned the leading edge and trailing edge of the fairing at the top of the fairing the gear leg would be offset to the airflow causing a rudder effect on the nose gear leg. Bummer, I was going to have to make a new mold. After looking at it for a while it dawned on me that it was offset in the direction that would push the nose to the right. I went ahead and finished up the part so it would make a stator vane out of the nose gear and test flew it.

The test flights were very interesting, ball centered with feet on the floor through out my usual cruise speed range. Pretty cool, my mistake turned out to be a pretty good solution to the right rudder usually needed on RVs. I haven't convinced myself if this solution is causing more or less drag than the usual rudder trim tab. Doesn't matter, my RV-7A is ball centered without a trim tab



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Steve Eberhart, W9JUQ
3EV - Evansville, IN
Where is Steve and the Sky Terrier?
RV-7A Slider, O-360 A1A, Catto 3 blade, 2 screen Garmin G3X Classic, GTN 650, Bionics APRS. FLYING since June 24, 2009
EAA Chapter 21
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  #2  
Old 04-12-2012, 10:55 AM
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Toobuilder Toobuilder is offline
 
Join Date: Jul 2009
Location: Mojave
Posts: 4,841
Default

It's nice when mistakes turn out for the better!

One question though: Your new fairing looks to be tight against the front leg. This leg is fixed a significant amount of distance from this contact point. Since this leg is highly flexible in all axis, do you see a bunch of wear? It also seems like the first hard landing is going to shatter the fairing. How many hours do you have on this configuration?
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WARNING! Incorrect design and/or fabrication of aircraft and/or components may result in injury or death. Information presented in this post is based on my own experience - Reader has sole responsibility for determining accuracy or suitability for use.

Michael Robinson
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Harmon Rocket II -SDS EFI
RV-8 - SDS CPI
1940 Taylorcraft BL-65
1984 L39C
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  #3  
Old 04-12-2012, 11:24 AM
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newtech newtech is offline
 
Join Date: Mar 2006
Location: Evansville, Indiana
Posts: 663
Default

Quote:
Originally Posted by Toobuilder View Post
It's nice when mistakes turn out for the better!

One question though: Your new fairing looks to be tight against the front leg. This leg is fixed a significant amount of distance from this contact point. Since this leg is highly flexible in all axis, do you see a bunch of wear? It also seems like the first hard landing is going to shatter the fairing. How many hours do you have on this configuration?
It has about 50 hours on it. My plane is based at 3EV, a nice little grass strip, so it hasn't been babied. You will notice from the rear view pictures that the lower portion of the fairing is open at the back allowing the gear to flex back without causing any problems. In the front it has about a 1/4" extra clearance. I switched to the Grove nose wheel as soon as they were available so the gear doesn't flex anywhere near as much as the stock configuration does. The inside of the fairing, that rubs on the gear leg cover, has anti wear tape on the inside wear surface. It is hard to insure no wear on the landing gear fairings so they just get a periodic touch-up coat of white. That is why the wing leading edge and landing gear components were all painted white. Much easier to touch up.
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Steve Eberhart, W9JUQ
3EV - Evansville, IN
Where is Steve and the Sky Terrier?
RV-7A Slider, O-360 A1A, Catto 3 blade, 2 screen Garmin G3X Classic, GTN 650, Bionics APRS. FLYING since June 24, 2009
EAA Chapter 21
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  #4  
Old 04-13-2012, 02:04 PM
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rvbuilder2002 rvbuilder2002 is offline
 
Join Date: Jul 2005
Location: Hubbard Oregon
Posts: 9,656
Default It may also cause other unknown issues...

Since the nose leg fairing is now inducing a yaw moment ahead of the C.G. this could actually have a negative affect on yaw stability and possibly even spin recovery.

Anything that induces a yaw moment on the front of the airplane has the same effect as removing some yaw authority of the tail (such as making the tail slightly smaller). The effect will also be variable based on airspeed.

The major difference compared to a trim tab on the rudder is that with pressure from your foot, you can for the most part remove the trimming force any time you desire. With the trimming force being caused on the nose leg, it is always there.

I don't mean to imply that you have degraded your spin recovery and yaw stability, but without testing there is no way to know for sure (I used the word could)


The primary reason for my post is to emphasize that people need to use care when deviating from standard configurations... Sometimes the smallest changes can have an effect that would never have been considered.

Last edited by rvbuilder2002 : 04-13-2012 at 09:35 PM. Reason: added negative emphases
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  #5  
Old 04-13-2012, 02:49 PM
RV8R999 RV8R999 is offline
 
Join Date: Dec 2008
Location: na
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Quote:
Originally Posted by rvbuilder2002 View Post
Since the nose leg fairing is now inducing a yaw moment ahead of the C.G. this could actually have an affect on yaw stability and possibly even spin recovery.

Anything that induces a yaw moment on the front of the airplane has the same effect as removing some yaw authority of the tail (such as making the tail slightly smaller). The effect will also be variable based on airspeed.

The major difference compared to a trim tab on the rudder is that with pressure from your foot, you can for the most part remove the trimming force any time you desire. With the trimming force being caused on the nose leg, it is always there.

I don't mean to imply that you have degraded your spin recovery and yaw stability, but without testing there is no way to know for sure (I used the word could)


The primary reason for my post is to emphasize that people need to use care when deviating from standard configurations... Sometimes the smallest changes can have an effect that would never have been considered.

you beat me to it... +1
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  #6  
Old 04-13-2012, 09:30 PM
don.olandese don.olandese is offline
 
Join Date: Aug 2007
Location: San Antonio, TX
Posts: 200
Default how do we adapt this...

to benefit airplanes that don't HAVE a nose gear? hmmm, maybe a mod to the tailwheel "strut?"
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  #7  
Old 04-15-2012, 09:54 PM
newtech's Avatar
newtech newtech is offline
 
Join Date: Mar 2006
Location: Evansville, Indiana
Posts: 663
Default

Quote:
Originally Posted by rvbuilder2002 View Post
Since the nose leg fairing is now inducing a yaw moment ahead of the C.G. this could actually have a negative affect on yaw stability and possibly even spin recovery.

Anything that induces a yaw moment on the front of the airplane has the same effect as removing some yaw authority of the tail (such as making the tail slightly smaller). The effect will also be variable based on airspeed.

The major difference compared to a trim tab on the rudder is that with pressure from your foot, you can for the most part remove the trimming force any time you desire. With the trimming force being caused on the nose leg, it is always there.

I don't mean to imply that you have degraded your spin recovery and yaw stability, but without testing there is no way to know for sure (I used the word could)


The primary reason for my post is to emphasize that people need to use care when deviating from standard configurations... Sometimes the smallest changes can have an effect that would never have been considered.
Thanks for the input. Please, anyone that that ever sees anything about me, my airplane or my flying, that causes any question or concern, let me know. In this case, it is going to make for a really fun Summer. I will be getting with my friends at the University of Illinois and will be putting together a complete test flying program to characterize the effects of using the nose gear fairing as an offset stator.
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Steve Eberhart, W9JUQ
3EV - Evansville, IN
Where is Steve and the Sky Terrier?
RV-7A Slider, O-360 A1A, Catto 3 blade, 2 screen Garmin G3X Classic, GTN 650, Bionics APRS. FLYING since June 24, 2009
EAA Chapter 21
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