RC Jets
Jim Hiller
THIS HAS BEEN a good year of jet modeling and I thought I would share the experiences at some great events I have attended. Let's start with the Bluegrass Jet Jam in Bowling Green, Kentucky.
The SKYMAC club is a great group of modelers. They really know how to make you feel welcome, which makes it easy to enjoy the club's wonderful model field. Mike Kirby is the man who gets everyone together to host a couple days of pure jet modeling.
We take over the field from dusk to dawn, and then the club members bring out their night fliers and get some stick time themselves. The modelers enjoy themselves, and the field is definitely the place to camp because activities just keep happening.
The runway approaches 1,000 feet in length. The overfly area is vast and the view from the flightline is scenic.
One of my favorite events of the year continues to be the annual Jets Over the Heartland gathering in Winamac, Indiana. Tracey and Tim Redelman are the instigators, and then the jet modelers themselves jump in to make this happen.
People such as Francis Pritschner, Ron Ballard, and a cast of hardworking volunteers keep the grills going. You can't help but gain weight flying—or should that read "eating"?—at Winamac.
The flying site is very good, thanks to the support and dreams of Ralph Braun. He is a wonderful host. There is entertainment every night. Something is always happening, and it's hard to get out of there by midnight.
On Saturday evening, let the fireworks begin. Ralph sponsors a wonderful fireworks display that goes on for a long time. It seems that the entire town of Winamac comes out to enjoy the show with us. Thanks, Ralph.
Great food, great friends, and a great flying site—thanks to all who make Jets Over the Heartland a fun time at Winamac.
The quality of jet modelers attending this event is among the best in the country, and perhaps in the world. The flightline boasts some of the best sport and scale models in this country, and they are flown hard.
This year, Francis's new Bandit was in the hangar receiving final assembly following a fresh paint job by the Kramer family. This became the focal point of conversation.
Also included in this column:
- The spectacular Jets Over the Heartland
- Jet trimming: thrust and CG
- Come see us at Spiderman
The closer you look at this aircraft, the more obvious the incredible paintwork becomes. The combination of Larry and Vern Kramer is unreal. The masking to taper paint lines to a fine point, symmetrical on both sides—I thought it couldn't be done.
The colors are not overlapped, but masked and sprayed separately. As you run your finger from one color to the next, it's smooth. No bumps in the clear coat can be detected.
Vern and Larry are glad to share their paint techniques. I learned much talking to them, and it motivated me to go home and start finishing my next project just so I can paint it.
Let's discuss trimming out your model. I find that the most important part of enjoying flying any aircraft is dialing it in to suit your flying style. I'll review how I set up my Bob Violett Models (BVM) BobCat to suit my flying techniques. Pitch trim, CG, downthrust, speed, and maximum thrust are interrelated; change one, and it affects the other.
My first flights with the BobCat were with a 14-pound-thrust Wren 54; a great engine that has good power and is a joy to fly. The original setup was based on the downthrust settings that BVM recommended, and the CG was close to what was recommended.
But you know jet modelers. I wanted more power, so out with the little Wren and in with a Jet Central Falcon. With 22 pounds of thrust for 21 pounds of airplane, it was time for some powerful fun.
The BobCat's first flights with Falcon power followed the tradition of increasing the downthrust to compensate for the additional power. This is done to keep the model from climbing as the speed increases, and it has proven to work well, but I'm never satisfied.
I want to be able to pull up into a slow vertical climb at low speeds—maybe 30 mph—then nail the power and climb straight up, letting the turbine's brute power push the BobCat out of sight while maintaining that slow speed.
The downthrust overpowered the elevator in these slow vertical climbs and pushed the nose down, which is not good. Now what? I removed the downthrust until a straight, low-speed vertical line could be maintained. It almost returned to the original angle of the Wren installation, and I no longer needed to hold up-elevator in the slow vertical push.
Now the old nemesis, pitch-trim changes with climbing at full power, was back. This time I used a throttle-to-elevator mix, eventually ending up with 4% down-elevator trim with full throttle to keep a good pitch trim throughout the full speed range.
Now I can make low passes from 80 mph to maximum speed, whatever that is, without the need to change elevator trim. The BobCat pitch trim is level throughout the complete speed range.
But nothing comes for free. The vertical lines in aerobatic flying have been lost. The BobCat now pulls slightly to the canopy during high-speed, high-power vertical lines. This is hardly noticeable except when nailing a vertical four-point roll. We old RC Aerobatics fliers can see the lack of a well-defined line.
Curiously, with a zoom from high-speed flight, going vertical, and throttling back, there is no pull to the canopy. For now, this is the compromised setup I am flying until I can figure out a way to keep the slow-speed vertical climb and nail the high-speed vertical line.
The next item to set up is the CG. With the Falcon installation, the BobCat required approximately 8 ounces of nose weight. I employ small, flat, flexible sheets of lead in a plastic bag stuffed up in the nose cone of the jet. This allows me to easily adjust the amount of weight I use. I can pull out the plastic bag of lead, add or subtract some pieces, reinstall it, and fly.
As with any jet I fly, I adjusted the CG by concentrating on the BobCat's landing characteristics. It is critical to perform landings well at our jets' high approach speeds. I put much emphasis on setting up my models to make landings as predictable and repeatable as possible. I don't want my jets to surprise me during the flare for landing. The CG and elevator throw are the two important settings that make this happen.
Start trimming for landing by setting up the elevator control throw you want for flying. I set up my elevator throw so the model is slightly short of stalling, with full up-elevator while flying at moderate speeds.
You do not want to pull full up-elevator at high speeds because it can fold up the wings; do this test at 60-80 mph. Full travel should not result in a high-speed stall.
When the elevator travel is set, move on to landing approaches to set the CG. I will land at the same elevator rate as I fly my jets when I have the CG right.
The CG is a balance between two issues when landing your jet. A nose-heavy condition will result in the elevator's not having enough power to raise the nose for a full flared landing. If you run out of elevator and are not fully slowed, your aircraft is nose-heavy. One can land with the elevator high rates on to overcome a nose-heavy condition, but we are discussing trimming our models properly.
As I move the CG back, another issue is the tendency of the model to balloon as I pull back on the elevator initiating the final flare for landing. You might have seen a pilot overcontrol the elevator during landing—usually somewhere between 6 and 3 feet from the ground—and the airplane goes level or climbs and then continues down for the landing.
The sensitivity to the elevator input at this point in the landing approach is a balance between two items: approach speed and CG. Too high of an approach speed and/or aft CG will make the elevator sensitive to the initial round out from approach descent to the final landing flare.
I'm referring to finesse. It isn't only the person on the stick; it's also the time spent setting up the model properly.
I have spent quite a bit of time on my BobCat getting this trim right, by adding or subtracting 1 or 2 ounces of weight each time until I have it where I feel comfortable. A critical pilot can tell the difference.
You have to have repeatable approach-speed control to know the difference, but it is worth the time to work on this with every landing until you are at ease with the model. It's my BobCat, and getting it to fly the way I want is almost as much fun as flying it.
The Spiderman Jet event is September 25-28. If you're in the Midwest area, jump over to Winamac, Indiana, and see us. MA
Sources:
Spiderman Jet event http://winamacaeromodelers.com/
Transcribed from original scans by AI. Minor OCR errors may remain.
