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Setting the rudder deflection

bruceh

Well Known Member
I'm using the plastic internal rudder stop, so I need to check that I have the correct swing in the rudder. The plans here are confusing.
They call out that the proper deflection angle is 35 degrees, which is attained when the outboard trailing edge of the the elevator skin and rudder skin trailing edge is 46 1/8". I checked the deflection angle with a protractor and it is right on at 35 degrees, but measuring with the tape as they describe is more like 48.5". Since the trailing edge of the rudder is angled, it is hard to really get an accurate measurement. As you can see in this photo, there is an even 2" of space all along the rudder to the inboard edges of the elevators.

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Can someone out there with a 9 confirm that this inboard distance looks OK?
 
If the skin of the rudder is actually parallel to the inner edge of the rudder (or within 1/16" or so), then you can measure the deflection a bit more accuratly.

First you measure the angle of the inner trailing edge of the rudder. It'll be a number above 90, so subtract 90 from it. Now you want the angle between the two rudder skins. Divide this by two and add it to the first number. This is your rudder deflection.
 
simple solution

get a ladder and measure the angle with a protractor or miter guide at the top of the fin and rudder! It's what I am doing right now! simple spot to do it and its accurate.

Dave
 
I too remember that Van's didn't really say where to measure off the rudder, at least not very clearly.

Drop a plumb line from the hinge line to the floor and mark it. With rudder neutral, drop a plumb line from the trailing edge to the floor and mark it. Do the same from trailing edge when rudder is at full deflection. Then, just connect the dots on the floor and use your protractor to measure the angles. Plane should be level side to side when doing this.

Van's provides the acceptable range as 30-35 each side. I would aim for the lower end of that range because you want to leave yourself some wiggle room if you later need to shorten or lengthen the rod end bearings when you go to permanently fit the bottom rudder tip--it will likely rub against the aft. fuselage skin when first fit, requiring either modifying the tip, the fuselage, and/or adjusting the rod end bearings. Moving the rod end bearings in or out will increase or decrease your travel. You can always file off material from your stops to get greater travel, but it's pretty tough to add it back after you've taken off too much!

Hope this helps.
 
RV-9A rudder deflection

Can someone please point me to where Van's says what the rudder deflection is supposed to be? I know I've seen it, but now that I need it, I can't find it! Always in the last place you look, but I haven't looked in the last place

Thanks for the help.
 
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I guess everybody does it differently according to the tools they have and are comfortable using.

I clamped my rudder straight (at the counterweight) and then clamped a straight edge such that it touched the rudder skin.

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Then I unclamped the counterweight and used an adjustable drafting triangle to check the travel against the rudder stops I was making at the time.

5254024934c969cdadfb20.jpg



Funny... There's that piece of DIY store aluminum angle that I used for fabricating the rudder trailing edge. It was a constant companion tool for the whole build.
 
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