Set up End-Point, Idle-Down, and Throt-Curve for nice bottom-end throttle response.

Eric and his 3-Channel Kadet in the dirt at Aux. Field #1.Today, Monday, 3/19/18, was the first day of RC flying at the club’s Aux. Field #1!
… and I was out there at 8-o’clock sharp.

My “Kadet” was the FIRST plane to fly on this field! … and it was ALSO the first time I have flown it with my “new” Futaba 8J 2.4Ghz radio system. Up until now, I had been the only one of us still running an old-style 72 Mhz FM radio.

For me, it was like a Maiden Flight… my old ship with that new receiver dropped into it. In my workshop I had set up everything as far as I could without actually flying the model… including the “new to me” options of Idle-Down and Throttle-Cut.

Throt-Cut is easy to set up… you just determine which transmitter-switch to put it on… and then set it so that, when engaged, the throttle is closed, enough, for a reliable engine stop.

Idle-Down is a great idea! It lets you set your throttle low position (idle) high enough to ensure no flame-out… and then, with a click of your designated switch, the idle drops below that position to a safe “at idle” RPM.

On my workbench, at home, I did it all by eye-ball… setting the idle, low-idle, and throt-cut to what “looked good”.

An important part of the process was the End-Point Adjustment (EPA) for that servo. When I dropped that new S-FHSS receiver into my Kadet, I was too hasty in setting the EPA for my servos. I DID set my elevator for proper deflection, high-rate and low… and I did set my Rudder (aileron stick on my Kadet) for proper deflection, high and low… and I saw that the throttle would open wide at full-throttle and I set the EPA for a nice, slightly high idle… knowing that I would use that idle-down switch for a low RPM idle. I set the Throt-Cut to close the venturi when activated.

The Futaba 8J Owners manual recommended putting those throttle functions all onto a single 3-way switch. “Up” for running, “Mid-Low” for Idle-Down, and Low for Throt-Cut… so, that’s how I set it up.

At the field… I started my engine and found that my eye-ball set-up was actually pretty-close to what I wanted! My running-throttle had a too-high idle, so I adjusted that EPA down to get it right. Doing THAT meant that I had to reset the Idle-Down setting for a nice, low RPM… and I reset the Throt-Cut to be “just right”.

Control surfaces were all moving the proper directions… motor was running nice… up, up, and, away – my Kadet was the first model to lift-off from Aux. Field #1!

It was kind of a Maiden Flight… I had to tweak the trims, here and there, and get used to “the feel” of my new sticks… but the model flew well and it was a successful “first flight”.

The First issue… was that three-position switch! It was super-easy to click from “run”, through “Idle-Down” and into “Throt-Cut” by moving that switch too far. I DID that while the model was still on the ground. I made a mental note to FIX that before the day was out.

The NEXT issue… was that I felt like my engine was at full throttle with my throttle-stick at less than about 70% of its available motion. I noted no difference between about half- and full-throttle.

I went ahead and got in, like, four flights before those of us, out there, decided to break it up and call it a day. I headed out to run some errands and then, on my way home, I decided to drop-in at Aux. Field #1 and work on that throttle issue.

I fiddled with the Throttle-Curve settings to try to put more finesse in the bottom-end of the throttle… with my old Kadet, that’s where I do most of my flying… using the last three or four clicks above idle. What I found was that I could not balance my throttle EPA and set a throttle-curve to a satisfactory level. After some head-scratching, I determined that my throttle linkage was incorrect at the servo, the linkage was too long. After about 60% of stick-motion, the engine’s throttle was wide-open and, beyond 60%, the linkage was flexing to absorb the servo motion. … I loosened the set-screw holding the throttle linkage to the throttle-servo arm, remembered to reset the throt-curve to its default straight-line, centered the throttle-trim, set the Servo 3 EPA at 50 (mid-range)… and then moved the throttle-stick to max throttle, slid the control linkage so as to open the throttle to max, and tightened that set-screw. NOW… stick to full-throttle moved the engine to full throttle with no binding of the linkage. I adjusted the EPA for the bottom-end of throttle for what looked like a nice, slightly-high idle. I, again, set Idle-Down and Throt-Cut … only NOW I assigned them to different switches!

I put the Idle-Down on a two-position switch (on the right side of the radio)… UP for Run, and Down position for Idle-Down. I put the Throt-Cut function onto another two-position switch (on the left-side of the radio)… UP for Run and Down for Throt-Cut. Doing so makes it unlikely that I will kill the motor while trying to Idle-Down. Before flight, I click both switches to the UP (run) position.

Finally… Throttle-Curve… with the throttle-stick at half… my engine’s throttle looked like 80%. I adjusted the various points of the curve until the engine seems to be at about 50% with that throttle-stick at half-throttle. I fine-tuned the curve until I had smooth response at the small end and, above 50% throttle, it climbed rapidly to full throttle. The “default” numbers for that curve were 0-25-50-75-100… by the time I was finished, they read 0, 14.5, 29.5, 52.5, 100.

Wow! … I found that the model had plenty of throttle-control through the full range and especially at the bottom-end of the stick-action… nice finesse on the control of the engine.

I made those changes… and flew another four flights before heading for home… a fun day at Aux. Field #1.

Come out and fly with the Kingman Golden Eagles RC Club!