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Sunday, December 13, 2015

Skyline Sukhoi SU-26 70 Sized 10cc Gasser Successful Maiden!



Today was a dreary cold, albeit ill-temperate December day in New Hampshire. Cloudy skies, winds ~0-6 mph with steady gusts to 10 mph consistently and predictably from the north. The field runs north to south, so this worked nicely. 50 degrees (norm is in the 30's with snow by now) but after a while your hands get frosty. Its mostly tall clumpy grass torn up by the kids who play soccer and lacrosse on it (its laid out I think as 4 fields side by side), with parts at the north launch end more mud and less grass, so I launch there. A good day to maiden. I was quite anxious to do and not do this maiden. I spent a lot of time on her.

This was a longer ARF build than most. I worked for over a month and a half just to get the RCGF 10cc engine running, only to find out a quick manual choke of the carb was all she wanted to get started. Now she starts and runs like a champ. I learned a lot about this engine in that process, and learned a lot about how good the service was from RCGF-USA. Today we would see how the engine flies.

This Skyline Sukhoi SU-26 70 from General Hobby came in heavy for the airframe. Its an electric/glow 70 sized that I built with a 10cc gas engine on a 14x8 prop. Its technically a bit more engine for this plane. Performance wise, despite coming in at around 9-10 lbs dry (I need to re-weigh her, but that's what she weighed this morning), she flies fine and fast. The only thing I lose is unlimited vertical: she will climb but loses her grip and can't sustain unlimited vertical. I had been using a 13x8 in setup. I think I would lose thrust if I went back to the 13x7 because the max RPM didn't change much. Maybe I should track down the recommended 14x7? What do you think? With the 14x8 I get an idle around 2000-2300 rpm, and max around 7200 rpm.  In flight she behaved a lot like she did on the ground tests. She idles nicely, no 4-cycling. She goes from Idle to Max throttle clean, comes back quick from 7200 to 3500 rpm, then slowly to 2300 rpm with visits to 1900-2000 rpm. On quick increase from idle to 50%, which comes out around 6300 rpm, pretty close to max, she will jump but then slowly increase rpm. This did not affect my sport flying today (I don't 3D...). I am considering a throttle curve with 50% around 4000 rpm, but this won't change her max performance of course.  The right side of the fuse got a lot less oil, but the landing strut was still coated. Minor annoyance.

Here's the vid from today's flight. I had to clip the phone camera to my jacket, so what you get is what I got. I do run on a bit with the filming, but I love the clean sound this engine makes. The first part is the maiden. I had run her for a few minutes to warm her up, topped off the fuel, and restarted. As you know I had starting issues, but now she starts right away.




This plane flies sweet, as did her sister before her whom I flew as an electric. That was the red Honda one. On higher rates she is wicked responsive and quick. I had to dial down the low DR on the elevator to 25% and increase the expo to 45% on all the rates. Now I have found her sweet spot and she is a pleasure to fly. I need more landings to get her feel, and after this flight I put bigger wheels on her to see if I can keep the prop spinning on rollouts.



The difference from 2.5" to 3" may not look like much, but it usually makes a big difference in the tall grass, and lifts the prop nicely out of the cabbage. I had thought about going with the larger wheel when I first installed them, but was too lazy to remove them from the large axles they were stuck on. Today I unstuck those bigger wheels (subtitled: Vice Grip Always Wins).

Wanted to keep flying, but I was starting to get cold. Looking forward to my next flights!

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