Denny Dart Mk II H First Flights

Last night I completed the Denny Dart Mk II  H variant I proposed on September 9.  The most obvious difference is the use of trapezoidal tips rather than sharp triangular points.

I was going to use a 1/8″ x 1/4″ fuselage stick with a 1/8″ square x 1/2″ long nose block for the prop hanger, but I forgot and cut a 7/32″ in 2 3/16″ tailplane taper in a 1/8″ x 3/8″ x 12″ stick.  The 6″ span tailplane has a 2″ root chord and a 1 1/4″ tip chord.  There is no center rib, but I did put a 1/2″ long gusset in the vertex.  The 2″ span fin has a 1 3/4″ root chord and a 1 1/4″ tip chord.  There is no root rib, the fuselage stick forms the base of the fin, just as on the AMA Cub.

The right handed pigtail motor hook is bent up from a pin with the head cut off and the end filed round.  A short straight piece goes 45 degrees from the loop to a straight piece that runs along the stick where there is a reverse 45 degree bend to a piece that sticks into the stick.  It is held on with a couple layers of glue.

The wing is layed out inside a 3 1/8″ x 15″ rectangle.  There is 1/4″ sweep back on the top edge and 3/4″ of sweep forward on the bottom edge in the picture.  The wing can go on the plane either way.  The center started as an 8″ in span rectangle, but the trailing edge points of the dihedral break are moved 1/8″ left and the leading edge points are moved 1/8″ right.  They are reversed in the picture because this is a bottom view.  Canting the dihedral breaks produces washin on the left tip and washout on the right tip that counters motor torque produced roll.  I have not cranked in full torque yet, but preliminary tests suggest that this may be more than necessary.  I suggest reducing the offsets to 3/32″.  The hard 1/16″ x 1/8″ wing mounting stick must be carefully centered and exactly perpendicular.  It takes the place of the center rib.  There are no intermediate ribs.

The wing is held on with two 3/4″ rubber bands that are triple looped around the stick. I put on a 1/2″ x 1 1/2″ paper rudder tab. I grabbed a 10 1/2″ loop of 3/32″ rubber for some quick hand wind tests for trim and circle at the park just before sunset. There was very slight drift, excellent flying conditions. It is 9 1/2″ between the hooks.

Weights are:

7″ NP Prop 3.35 gm
Wing 1.45
Fuselage 1.95
Sub Total 6.75
Motor 1.25
Total 8.00 gm

First flights with 200-250 turns went down pretty much straight. Getting up to 500-600 turns, it wanted to go right until I bent in some left rudder and left thrust. Even then, it straightens when the motor runs down. Less wing twist may be advisable. At 800-900 turns, flights were about 40 seconds. Slow steady climb, nice cruise, somewhat steep descent. See the attached video. CG is at 0.6″ behind the wing LE, 19.2% of the chord. Maybe less tailplane incidence could be used. The wing LE is 2 5/8″ behind the nose. This is with low turns on a less than optimum motor. A few more tests and I will be able to resize the motor. Then I will go to Burnett Field where there is enough room to wind the motor to near capacity for a long, high flight.

Gary Hinze

2 thoughts on “Denny Dart Mk II H First Flights

  1. Great demonstration, thank you. We have been inspired to follow your directions and will soon be test flying.

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