Wing-Wheel Attachment for Rumpf Dolly

With very little expense or work, the popular Udo Rumpf one-person assembly dolly can be converted into a very effective wing wheel. Many wing-tip wheels are poorly constructed, allowing the wheel to turn out of alignment and scuff along the ground. This is encouraged by the flexibility of the wing at the tip and, if the attachment is in the area of the aileron, undesirable stresses can be put on the aileron.

The Pictures on the left show my wing-wheel conversion. Click an image for a full size view.

A front-wheel yoke assembly from a small bicycle (Fig. 1) slips nicely into the support tube descending from the Rumpf wing saddle. The yoke is secured by means of a lock-pin (Fig. 2) through a hole drilled across the support tube and wheel yoke. The lock pin can also be used to secure the saddle to the Rumpf dolly undercarriage. In that case, the screw lock is not needed and you will always know where the lock-pin is.

A bracket is needed to keep the wheel-yoke and support tube from pivoting. I made a simple one (Fig. 2) of aluminum bar stock. It is only necessary to cut it to length, drill a hole at each end, and make two bends. One end is permanently attached to the wheel yoke with a nut and bolt. The other end is secured by the hand screw used to secure the trailing edge wing pad assembly. The bracket fits loosely at the hand screw since the screw shaft is slightly too long. I take up most of the play with a washer. The hand screw is not designed to take a pulling load, since it has a plastic handle. However, close examination revealed a shoulder of metal where the plastic handle begins. I think the shoulder will bear the load of the bracket well enough. A better design is needed, however, one that attaches the bracket to the saddle with a lock pin. This would also be less tedious than removing and reinstalling the hand screw (and washer) when attaching and removing the wheel. Some modification of the saddle will be needed to achieve this.

The wheel swivels a limited amount because of end-play in the horizontal pivot bar at the saddle end of the support tube and looseness in the lock-pin hole. Also, the support tube leans and the wheel-axle trails toward the leading edge of the wing. These factors work together to align the wheel with the ground path, like a coaster.

The wheel seems to run true, but even if it should drift out of line and scrub the ground, as many wing wheels do, it won't matter since the saddle attaches to the wing at mid-span where the wing is stronger and where there are no ailerons to foul. The attachment of the Rumpf wing saddle is very secure.

There is an advantage to attaching the wheel at mid-span. When you push the glider around (e.g., when shoving it into the fuselage cradle for disassembly) there is much less of a turning moment than with a wing-tip wheel. Although the wheel itself is light weight, the whole assembly weighs enough to hold the wing down nicely, even at mid-span. It gives a very secure feeling when towing the glider.