Graupner Cirrus Aileron Modifications

I decided to make a new set of wings from the plans. These were to have ailerons (as rudder authority is poor) and spoilers. This page describes the aileron modification as I built the new wings. The plans give some hints, but some of it I did differently.

If you make ailerons, you should reduce the dihedral from 6deg (3deg per wing) to 3deg to avoid adverse yaw.

• Do not glue ribs 83 to 92 in place

• Remove trailing edge from rib 82 on (or better don’t build it in the first place).

• At rib 82, cut the trailing edge in line with the rib (so the aileron will be angled). I also doubled rib 82 (On the wing tip side) with a 1mm ply rib for strength and added a corner brace on the root side.

• Fabricate a new rib 92 with an extension out to the rear of the TE line and glue in place. Block up the TE point per the plans with a 5mm piece of scrap to accommodate the washout.

• From 32x9.5mm TE stock cut the aileron longitudinally so that it tapers from 32mm (rib 82) to 25mm (rib 92). Make the cut from the thick end. Use a matching TE section underneath so that the cut can be made vertically through the aileron. Cut the aileron to the correct length, and sand in the angle at rib 82, and of course leave surrounding gaps for surface motion and covering.

• Pin the aileron in place, making sure to block it up along its length to accommodate the wing washout (which begins roughly around rib 82).

Fig 1 - Aileron blocked up for washout (this view was after completion but just to show block)

• Now cut a 10mm x 3mm trailing auxiliary spar. Cut to the correct length so that you can pin it in place just in front of the pinned aileron, leaving an appropriate gap for the hinge mechanism. I used centre mounted CA hinges so my gap was about 1.5 - 2mm. Pin the auxiliary spar in place, ensuring it is vertical. Also block the spar up to accomodate the wing washout. You will find that the because the spar is angled forwards (from rib 82 to rib 92), it will intersect the ribs at a location where their height is 10mm (or there about). Very nice engineering from Graupner. So the aileron and spar will both be blocked up. This is not precisely how Graupner seem to suggest to do it, but I couldn’t exactly fathom their more complex method.

• You are ready now to trim the ribs to the correct length buy marking/measuring. Make sure you understand the shaping of the washout in the ribs so that when you trim them, the rear end is now parallel with the auxiliary spar (it’s easy to get that angle wrong, so I tend to make them too big and sand down).

• Now glue the ribs in, but only glue the location at the main lower spar (don’t attach to trailing auxiliary spar yet). Make sure the ribs are pressed down onto the front sheeting so that the washout shaping leaves the rear of the ribs elevated.

Fig 2 - Ribs glued to main spar and all other components pinned - you can see the aileron taper from 32 to 25mm (L to R)

• Now remove the pinned TE and auxiliary spar.

• We are going to make centre CA hinges. Mark the hinge slot locations on the TE and auxiliary spar. I made (4 so that they were symmetric): between 82&83, 85&86, 88&89 and 91&92. Cut the hinge slots to the appropriate depth (all the way through the auxiliary spar). Because the aux. spar is only 3mm, cut some additional 3mm sections (slightly longer than the hinge slots) and glue on to the LE side of the spar so that the hinges will have 6mm to hang on to. Then cut the hinge slots through these additional pieces as well. Put some hinges in temporarily to make sure it’s all aligned and workable.

Fid 3 - Additional hinge block

• Now glue the auxiliary spar to the ribs. Take great care that its straight (if your ribs are the right length) and that it is blocked up for the washout. You should find the 10mm height pretty much exactly matches the rib height. Add some corner braces to the auxiliary spar to strengthen the butt joint (unless you did something cleverer and slotted the ribs in to it).

• Now you can round the LE of the aileron by hand sanding. This will allow sufficient throw on the aileron (30 deg is plenty).

• Then you can press the aileron onto the CA hinges and convince yourself everything is aligned and functional. Later, you will cover the aileron before the final glueing in of the hinges.