Preflight Setup

Nov 14, 2012 1 Comment by

Although computer radios make adjusting the helicopter very easy, I prefer to make mechanical adjustments first to get everything as close as possible to the settings I want, and then I use the radio’s features for fine-tuning. As an example, let’s consider the type of flying you would like to do. If you are ready for aerobatics, you’ll need full aileron, elevator, tail rotor and collective pitch throw to make the helicopter maneuverable enough. To do this, you’ll have to connect the pushrods to the outer part of each servo arm. If, however, you’re a novice and learning to hover, such a setup would be much too sensitive for you to practice with; half throw on the aileron, elevator and rudder is more than sufficient. You can set this mechanically by connecting the pushrods to the center of the servo arms. And since you’ll need hardly any collective pitch for hovering, connect the pushrod to the innermost hole on the servo arm. For helicopters with cyclic collective-pitch mixing (CCPM), the aileron, elevator and pitch servos will be connected to the swashplate, and using the servo arm’s middle hole will also provide enough control for hovering.

PITCH CURVES


My Stratus has CCPM to control the swashplate. Note that the two ball links for the elevator and pitch servos are 120 degrees apart from each other and on the outer edge of the swashplate. The third aileron-servo ball link is out of view at 120 degrees from these ball links.

 

One of the features of a helicopter radio that make it unique is that it allows you to adjust the pitch of the rotor blades and to control the throttle differently in various flight modes according to your flying style or for a specific maneuver. We refer to these setups as pitch and throttle curves. Although, at first, they may seem rather complicated, once you understand how they work and have used them a few times, you’ll find them easy to work with.

Although working with the throttle curve does not require additional equipment, you’ll need a pitch gauge to adjust the rotor blades’ pitch. This is a basic piece of equipment for any helicopter flier, so I suggest that you look closely at the pitch gauges on the market and choose one that best suits your helicopter: check that the gauge is large enough (but small enough for a small electric helicopter) for you to easily read its scale, and check that the flybar is easy to see when the gauge is on the rotor blade. As you shop for a pitch gauge, you will also find other products to level the flybar swashplate and tail boom. But I have not needed these added products because: the pitch gauge gets the pitch in the ìballpark,î and you make final adjustments after flying the helicopter; no pitch gauge or related equipment can be guaranteed accurate; and initial setup parameters are ìbest guessesî and based on your flying experience.

It’s very easy and quick to use the pitch gauge if you follow this procedure:

  • Put your helicopter on your workbench so that the tail boom is level (you are looking at one side of it), and then level the swashplate.
  • Extend the rotor blades to their normal flying position, and rotate the head so that the flybar is aligned with the tail boom. This will place the rotor blades at 90 degrees to the helicopter; you can now put the pitch gauge into position and sight along the rotor blade.
  • Now use one hand to level the flybar so that it’s parallel to the tail boom, and with your other hand, adjust the pitch gauge so that it’s aligned with the flybar. Read the blade pitch on the gauge scale.

Note that the tail boom really doesn’t have to be level. The important point is that the swashplate and flybar have to be parallel with the tail boom (whether it’s level or not) for the reading to be accurate.

To practice using the pitch gauge, disconnect the linkage to the pitch servo (or, for CCPM systems, all three linkages to the swashplate), and move the swashplate to its maximum-pitch position. Use the techniques just described, and read the blade’s pitch. Now move the swashplate to its low position and check the blade’s pitch again. The difference in pitch from their maximum position to minimum position is what I refer to as their ìpitch window. Example: if the maximum pitch is 10 degrees and the minimum pitch is minus 3 degrees, the pitch window is 13 degrees. This pitch window is the first thing I check when I set up a new helicopter because it tells me exactly how much pitch I have to work with.

From experience, I know that the following numbers are in the ballpark for setting up a new helicopter with symmetrical rotor blades:

  • 14 degrees–maximum usable pitch just before the blade stalls. Max blade pitch also means max lift, so I use this as my maximum pitch for autorotations to provide maximum lift at touchdown.
  • 10 degrees–maximum sustained pitch without overloading the engine; and, since the rotor blades are symmetrical, minus 10 degrees is the maximum negative pitch. This minus 10 to plus 10 degrees produces a pitch window of 20 degrees for aerobatics.
  • 4 degrees–normal hover pitch.
  • Minus 3 degrees–required for landing and autorotations to maintain rotor speed while descending.
  • Minus 5 degrees–a good setting for low stick pitch for normal, idle-up 1 and throttle hold. Although this is slightly more negative pitch than is needed for normal flight, I like to use this for a low stick position in case I need a faster descent when I overshoot my landing spot, in a tailwind, etc.Use these pitch settings as starting points to achieve the pitch window you want; and depending on your flying skills, here are a few other points to consider:
  • If you are learning to hover, altitude is not your friend. If you can hover at 6 inches, you can hover at 6 feet, but being closer to the ground is obviously safer for your helicopter. Therefore, to avoid climbing too rapidly, I recommend that you limit your maximum pitch to about 5 degreesójust slightly more than that required to hover.
  • To avoid descending too quickly, limit low pitch to about 0 degree. These settings will provide a built-in governor that will prevent you from being too aggressive as you learn and will reduce collective pitch sensitivity. As your skill increases, you can increase this pitch window to give you more control of the helicopter. Intermediate fliers can use minus 5 degrees to 10 degrees for normal and idle-up 1 and 14 degrees for throttle hold/autorotations.

 

Helicopter Flight School

About the author

A regular contributor to Model Airplane News, he is also the columnist for our “Rotor Speed” helicopter column. Paul has been flying RC helicopters since the early ‘80s and now enjoys all types of rotary machines, including scale and aerobatics, and he continues to experiment with modifications to improve performance.

One Response to “Preflight Setup”

  1. michaelpowell says:

    Bravo, too many pitch recommendations at in the range -12 to +12, suggesting that we all need a hyper sensitive helicopter from the start. The biggest problem early on is an untrimmed helicopter, and the second is over control by a beginner trying to correct it.

    Zero to six degrees sound fine. But even 2 to 6 would work because as the blades slow a pitch of 2 degrees will have very little lift, but might hold the blades up, and prevent then hitting the ground or the tail boom in a heavy landing.

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