RC Helicopters
Eric Hawkinson 319 Yellowstone Ave., Billings MT 59101 E-mail: [email protected]
Introduction
It's another great month to enjoy RC (Radio Control) helicopters!
You'll read this during the dog days of summer, but I'm hunting and pecking this column out in early May in Montana, which means that every week brings another test flight of someone's new helicopter and another first attempt from a novice pilot. It's a great and interesting time.
The August 2001 column was aimed at pilots new to—or contemplating getting involved in—RC helicopters. I know from experience this means that the non-novice pilots will write asking for more advanced information. That's what I'll discuss this time. It also means that the mailbox will fill with requests for more "beginner" information. See how that works?
As you may recall from the prior issue, I wrote that in the normal mode setup, "midstick gives you approximately half throttle, and traditionally moves the collective pitch to approximately 5° for hovering. Full stick is full throttle and maximum pitch in the main blades; this is usually 9° but is dependent upon blade selection and power available."
Sharp-eyed helicopter pilots will perhaps wonder why I qualified the midstick settings. To understand this, we need to look at the current state of helicopter flying compared to the flying styles that were common 10 years ago.
The evolution of flying style
When I started flying helicopters, the emphasis was mostly on hovering. Almost everyone hovered with the stick at the 50% position, and many pilots still do.
But with the passage of time and the quantum leaps in the performance of our mechanics, radios, gyros, and engines, more emphasis has been placed on aerobatics and "3-D" (three-dimensional) flying.
There are many opinions about proper setups for forward-flight aerobatics (loops, rolls, stall turns, etc.). Almost everyone agrees that midstick should be at zero pitch in the main blades in the idle-up (or "stunt") flight mode.
For the more aggressive 3-D flying, including flips, tumbles, death spirals, and numerous other radical maneuvers, there is no debate at all; everyone agrees that the pitch curve is "V-shaped" and the midstick position is at zero pitch. That means you cannot hover at midstick when this flight mode is engaged.
Unlike forward-flight aerobatics, many of the 3-D maneuvers are performed from a hover (upright or inverted) or slow-speed flight. That is why the "traditional" setup for normal flight mode is no longer the only one being used.
My entire focus within fixed-wing RC was aerobatics, so it will not surprise you that my interest in RC helicopters has been directed toward the aerobatic segments from the start. There's quite a bit of information the advancing novice and intermediate pilot will want to mull over.
Personal setup experience
I was almost immediately uncomfortable with the fact that in normal mode I hovered at midstick, and in my idle-up modes I hovered at 3/4 stick. This meant that switching into idle-up from the normal mode while in a hover was never as smooth and precise as I would have preferred.
I either watched the helicopter drop as the pitch changed from hover pitch to zero pitch or I overcorrected, and the helicopter shot up as I advanced the stick to 3/4 when I activated the idle-up.
I read everything I could about this subject and didn't see many people addressing this annoyance. I decided that I would change my setup to allow more consistency in hovering between the various flight modes and between upright and inverted hovering.
The typical V-shaped 3-D curve was unarguably the only way to go for the idle-up flight mode, so I simply changed my setup in normal mode to have zero pitch at midstick and hover pitch at 3/4 stick. I also changed my throttle-hold pitch curve to have zero pitch at midstick, leaving the top and bottom points alone.
That was many years ago, and I still feel most comfortable with this type of setup. No matter what flight mode is active, I know that midstick is at zero pitch in the main blades and hover will be at close to 3/4 stick. Whether I'm hovering or in forward flight, I can change flight modes transparently with no dropping or jumping of the helicopter.
I'm sure I was not the first to adopt this style of setup, and many other pilots now use the "all-modes, zero pitch at midstick" setup.
For those helicopter pilots who are not interested in aerobatics, there is no advantage to my style of setup. It compresses the throttle/collective response to stick travel from hover to full stick, which makes the throttle/collective more sensitive in that region. So if you are mainly interested in precision hovering, it's probably best to stay with the traditional "hover at midstick" setup.
Pitch and throttle curves
Although I've only been discussing pitch curves so far, you will need to adjust the throttle curves to match. If you are used to hovering at midstick and you change to zero pitch at midstick, obviously the throttle setting at midstick will be lower.
Another advantage of the setup I use is that since all modes are zero pitch at midstick, the correct throttle setting for all flight modes is the same for midstick through full stick.
This brings me to the other part of this month's column: setting the throttle curves. I get many calls each day at the shop from pilots who are not sure how to go about getting their throttle curves set up. Fairly often—especially with novice pilots or pilots who are just moving into aerobatics—there is some confusion about whether to adjust the pitch curve or the throttle curve to fix a problem.
The point to remember is that you can measure the pitch and you cannot measure the power. You should always set the pitch curves first, using a pitch gauge to ensure that you have the settings you want for hover and zero-pitch positions. Then leave those pitch positions alone.
Since you can't measure power output with a ruler or gauge, you have to reach the proper throttle-curve settings through flight testing. The full stick position is simple; you want the throttle barrel at the wide-open position.
Idle is almost as easy; you want the carburetor open just far enough to idle and have enough servo travel to kill the engine with your throttle trim or kill switch.
For hover throttle position, you can usually start at 50% throttle and tune from there. That means that if the head speed is too high, you reduce the throttle opening at hover; if head speed is low, you increase throttle.
The same adjustment is made for any other point(s) between the extreme stick positions; if the head speed is wrong, fix it with throttle-curve adjustments.
The rules change when you are at full stick because you are at maximum throttle, and that's where you want to be. So at full stick you adjust the pitch setting to be compatible with the maximum power output of your engine. If the head speed slows at full stick, you decrease the pitch until the head speed stays consistent. If the rotor speeds up at full pitch, you increase pitch.
Additional throttle setup tips
- Position the throttle arm so that at mid-throttle it is parallel to your throttle servo's output arm. This helps keep your throttle response more linear.
- Set the throttle-channel endpoints (ATV [Adjust Travel Volume]) to maximum so full stick is at 100% on your throttle curves. You will likely use a cyclic-to-throttle mix for aerobatics to add power during maneuvers. With most radios, this mix can overdrive the throttle servo if you haven't already maxed out the travel adjustment on the top end. (The Futaba 9ZH and Airtronics Stylus with helicopter cards are noted exceptions.)
Closing
I've used up my allotment of space again, so I'm going to end here. There's quite a bit of information in this column that the advancing novice and intermediate pilot will want to mull over.
Until next month, fly safe and happy rotoring! MA
Transcribed from original scans by AI. Minor OCR errors may remain.
