Denny Dart Mk II Build, Proposed Modifications

I recieved the two DennyDart II kits which Ding traded to me for two Squirrel kits.

This differs from the standard DennyDart in that the prop bearing is the old bent metal strip with a hole drilled in it style. This puts the prop shaft parallel with the stick. Since the wing is flat on the stick, it also puts the prop shaft parallel with the wing chord. With the paper on top, the wing has maybe a bit less than one degree of effective incidence. I was wondering how that would work. The tailplane incidence is 2.86 degrees and the paper is on the bottom, giving it maybe another degree of effective down incidence. This could force the wing incidence up a bit, but not near the 7 degrees the AMA Cub prop shaft makes with the wing chord. It would also put the prop up at an angle to the airflow. I expect that would make it turn right. Ever notice how a ROG takes a sharp right once the tail comes down and the prop is pointing up? DD II has about 35 square inches of area compared with about 36 for the AMA Cub. McCombs prop formula specifies an 8.8″ diameter for this size wing. The AMA Cub uses a 5.5″ prop, Ding’s kit has a 6″ Peck prop and the DD II instructions call for a 7″ prop. The wing hold down stick is the hardest piece of 1/16″ x 1/8″ in the set. Ding provided two 17 1/8″ lengths of 3/32″ rubber for each plane. This comes a bit snug between the hooks, which is good for hand winding.

I spent a pleasant afternoon building the plane. I left out the center wing rib because the hold down stick does that job. I left out the center rib on the tailplane and glued the fin sticks on the stick as base, as on the AMA Cub, because the stick does those jobs. That saves a tiny bit of weight. I put the wing on, weighed the prop and put 1.9 grams of clay on the prop bearing, slid the wing till it looked about right and took it outside for some glides. It was a bit windy, but the plane was making good, slow, soaring glides. Definitely better than the AMA Cub. CG was 1.15″ behind wing leading edge. I came back in, took the clay off, put on a prop and motor, reset the wing, took it outside and put 200 turns into the motor. It climbed steeply to the right and went into the Fir tree. I got it down with the Jackite pole unharmed. If it climbs steeply on 200 out of 990 turns, full winds will be wild. I expect this plane will fly with a much thinner motor that will take many more turns for a much longer flight.

Just a dimensional check, is the center panel 8″ span? Is the wing chord 3 1/8″? The instructions say the left wing is longer than the right, but that was not the case on mine.

I am looking to build another with the following modifications from plan:
1. No center rib in tailplane.
2. No center rib in wing.
3. No root rib on fin, build to fuselage stick.
4. 7″ Dandiflyer prop with plastic bearing. The bearing angle creates wing incidence. It also permits ROG.
5. 1/8″ x 1/4″ stick with 1/8″ square nose block for prop hanger.
6. Trapezoidal wing tips.
7. Slant dihedral breaks to give washout on the right wing tip and washin on the left wing tip for torque roll control.
8. 1/16″ x 1/8″ hard balsa wing mount stick.
9. No intermediate wing ribs.
10. Right handed pigtail motor hook.
11. Put tailplane parallel with prop shaft.
12. Trapezoidal tailplane.
13. Trapezoidal fin.
14. Motor twice the hook distance and thinner for more turns.

I’d better be careful. I might lose this one. I could lose the stock DennyDart II.

Gary Hinze

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