Rudder vertical alignment

[Meyertheflyer]

After attaching the rudder to the vertical stab, I noticed a very slight left alignment near the upper 20% of the rudder trailing edge. I bent the top frame to try and make it perfect but still has a little left of center line. It this so critical? The lower remaining 80% is perfect. I'm thinking this a 100 kt airplane and I won't notice, but I wonder what other builders thoughts are.

[Meyertheflyer]

I took a picture looking at the rudder from behind.

[Dave S]

Robert,

The rudder on my series 7 is about the same. I didn't do anything with it, assembled/covered it that way and have been flying it for 4 years with absolutely no noticeable effect.

Sincerely,

Dave S
KF7 Trigear - Flying
912ULS, Warp Drive

[Esser]

My gut feeling is that is there from the factory to counter act torque in flight.

[jtpitkin06]

Yes, you need to do a little straightening. It's not uncommon for welded frames to warp and twist a bit as they cool from the welding process.

Fortunately, it is not difficult to align the rudder. Simply note where you need to bend and mark it with a piece of tape. I see in the photo you have a long level which you can use as a straight edge to check your progress. To straighten the rudder and control how much you bend for correction, place it on the floor and put wood blocks or shims under the tubing then using gentle foot pressure make the corrections. 4130 tubing can be a bit springy so don't be surprised if it takes a lot of opposite bend to get things straight. Just start small and use more only if necessary.

Sometimes you will only need a single block or shim under one corner. Other times you may need four. When you think you have it straight place it on the flat floor to check for any rocking motion. Then flip it over and check it again.

To answer the question of whether you need to fix it for a 100 knot airplane... just hold a clipboard out the car window at 55 mph and see how much lift it gets. Now double that for 100 knots. You might look at some of the pictures posted on rudder trim tabs to see how small they are. They are very powerful; so yes, the rudder needs to be straight.

You're on the right track... just spend a little more time on the details.

John

[n85ae]

My vertical stab was worse, it's just the normal 4130 cooling and moving
after welding. Nothing a 2x4 and some muscle couldn't fix. Don't be afraid
to bend it. It's a lot tougher than you realize and you won't hurt it.

Regards,
Jeff

[Meyertheflyer]

I bent the rudder and made it straight. Not too hard. Then today I looked at 3 other foxes to compare tails and none is perfectly straight , but now mine is (or at least as straight as I could get it). I tend to think a little bend is necessary to compensate for the P-factor but ill find out when the flight day finally arrives. Thanks!

[ken nougaret]

mine was off too. i ended up welding material to the tabs and filing new holes to properly align the rudder.
ken

[jtpitkin06]

I tend to think a little bend is necessary to compensate for the P-factor but ill find out when the flight day finally arrives. Thanks!

Just wondering... how do you plan to correct the bend after the airplane is completed if it is too much compensation? Would it be better to build the airplane straight and simply angle the engine mount as needed with shim washers during the testing phase?

John

[Meyertheflyer]

Yes, that would be the better plan. I'm bonding the rudder fiberglass leading edge today. Gotta love this weather