Some notes from the Twister's trimming.

I spent the evening indoors tonight working on the decal for Wayne's Cavalier. It came out pretty nice, and at 6.25" tall and 5" wide it should look nice on the inboard wing Tomorrow I'll work on my own wing art for Taz.


Before the first flight, we all know there are checks and adjustments confirm the plane is stable in flight and not going to fly straight into a grocery bag. The pre-maiden trimming of my Twister last week went as follows:
First is to hang the plane by an allen key or small rod from the leadouts and make sure we see 1-2 degrees of nose down attitude, the vertical CG. I had to slide the leadouts significantly aft(from the plan's position) to see any change at all. After I finally got 1 degree of nose-down, I left it like that. Had I not, loose lines would have plagued the first flight. This is the one part of the yaw we are adjusting, and in flight, especially the first, you can and should check this by looking at the wheels as it flies level laps. The outboard wheel should be partially visible peeking out from behind the inboard wheel. This indicates the plane is yawed slightly to the outside of the circle and helping maintain line tension.

For Horizontal CG, balancing the plane in the same position, wings held vertical and supporting it by holding the plane at the nose and tail, revealed no tendency to roll in either direction. When they do roll, it's usually toward the belly-down position. No adjustment was needed on this one. If necessary, lighter wheels may be helpful. I'm not 100% sure what the symptoms would be, except possibly hinging at certain attitudes in maneuvers as if tip weight was lacking. Don't mistake one problem for the other... I'm still learning.

In my maiden trimming report, I mentioned something I learned about tip weight. On my first flight, I ran an MA 10x4 prop. The plane flew with the outboard tip low both upright and inverted. It was so anemic I changed the prop to an APC 10.5x4.5 and it really woke up. The added inertia and resulting gyroscopic precession of the bigger and heavier prop caused the plane to torque roll in the opposite direction of rotation. The plane now flew wings-level both upright and inverted, so no tip weight adjustment was needed. The prop corrected the wing dip. Something to keep in mind while trimming. If you change props, recheck for level wings.

On a side note, there was some concern that the bigger APC prop was too much for the FP.35. But after fixing a plumbing problem from Thursday(I'd forgotten to plug the OF vent while running on pressure... Duh), I got a perfect stunt run all day Sunday, and as I mentioned earlier never had to touch the needle from beginning to end. I got 12 laps after the clover with a full tank. That was on a 98 degree day, and I'll leave it alone for now. Also she's flying at 5 seconds on 61' lines, eyelet to eyelet.

You need an outside observer to get the best read on level flight. A skilled observer can follow the lines and imagine them as an extension passing through the plane and out the other side. About 5 low flat laps, both inverted and upright are necessary for a good read. If you have no observer, from the pilot's position, look and see if the bottom or top of the outboard wing is visible. It should stay hidden by the fuselage. Also see if the outboard wing presents itself in some snap turns and lazy 8s, which would indicate hinging. This happens if one wing is too heavy or light.

Other than the excessive flap throw, which was corrected for Sunday's flights, I believe the trimming I describe here, with Wayne's help, made a huge difference in the confidence I had in this plane after its first day in the sun. Particularly the vertical CG, which was so far off before we checked it, gave me stronger line tension and even a good tight pull when it was straight overhead. I know lots of the stunt pilots will tell you to move the leadouts forward to help overhead tension, but I'm no longer blindly following this line of thought. In fact, when I try to imagine what happens, it seems wrong. For whatever reason, I'm glad I took the time rather than just tossing it into the air and hoping for the best. There are some great articles by paul Walker and others on Flyinglines.org which are worth studying before launching your next build.

Just a few interesting notes to keep in mind for making a better flying plane.
Rusty