Kharkov R-10 – (Free) Flight Report

My wife and I travelled to Geneseo today so that I could meet up with members of the Western New York Free Flight Society at their Spring Opener meet. My hopes were to have some of the experts there help me with the flight trimming and maiden flights of the Kharkov R-10 that I had built over the late fall and early winter.

My build of the Kharkov received high marks from the guys who examined it and no modifications were recommended prior to test glides. A half dozen small test glides with low power (less than 200 motor winds) showed a decided left bank while under power. Engine torque and a little too much washout in one wingtip were thought to be contributors to this issue. The left bank was corrected by first adding in a slight amount of right engine offset and then was finally fully corrected with the addition a 1/16″ strip under the outboard half of the left wing along the trailing edge. This strip acted as a small flap and worked wonderful. After these trim adjustments, the Kharkov flew straight and level under power.

But the Kharkov was under powered and had trouble gaining altitude. Removing some balancing weight from the nose cowl helped but only so much weight could be removed and still maintain a proper center of gravity so it was decided to replace the original motor (rubber band) with a more powerful one. The second motor offered more thrust which made for better flight performance but it was still not enough even when 800 turns were cranked into it. It was also discovered that the rubber was cracking after only 3 flights so it was decided to replace the motor yet again.

The third motor proved to be much stronger. The initial flight on 500 winds was the longest and best of the day with the Kharkov maintaining great flight attitude throughout. It was decided to make a second attempt on this motor with 800 winds. I cranked in the 800 and as I was putting the propeller back into the cowl, the motor blew up (i.e. it broke!) and it blew out part of the fuselage with it! The damage was surveyed and found to be repairable with the replacement of 4 stringer sections and some tissue recovering in various places along the fuselage where the rubber band had punctured holes during its blowout. While repairable, this was not a field repair, so the flight testing of the Kharkov was over with for the day.

All in all, I was very pleased with the days flight results. The Kharkov got high marks for its construction, initial flight trimming proved to be easy and straightforward, and all indications are that the plane will be a good flyer once a proper motor is installed.

My thanks go out to Jim deTar and Dave Pishnery for the warm welcome that they extended to my wife and I. Also, thanks to my wife for her flight photography today! And extra special thanks are directed to Dave for all the great help and mentoring that he gave me throughout the day. It was much appreciated!

The Kharkov will be flying the skies of Geneseo again this summer at the FAC Nats. I’m looking forward to it!

Here are photos from todays activities at Geneseo:
(Click on the photos to get a larger image with higher resolution)

Initial flight preparations, flight instructions from Dave, and low-powered test glides.