Pitch theory
A pitch gauge is a measuring device for setting the pitch angle of the rotor blades of a model helicopter .
Structure and application
A pitch gauge is used in model helicopters that can be flown with adjustable rotor blade pitch (pitch-controlled models). With these models, the rotor blades are brought into a certain angle of attack by means of a radio remote control while the rotor speed remains constant in order to give the helicopter more or less lift : The RC pilot needs it
- for hovering or climbing flight approx. ≥ 5 ° angle of attack
- for a descent <5 °
- for an autorotation maneuver approx. -4 ° in the descent and approx. + 10 ° in the interception / landing phase,
to move the model accordingly.
Furthermore, negative angles of attack (-5 ° to approx. -15 °) may also be required, namely when the model is suitable for aerobatics or 3D. A pitch gauge is necessary to ensure that the entire rotor system is coherent and that each rotor blade hits the same angle of attack when it rotates around the rotor axis as the other rotor blades mounted on the same rotor head.
A pitch theory consists of two basic elements:
On the one hand, it consists of a fastening unit that is pushed over the tip of the rotor blade to be adjusted. There is usually a spring-loaded clamp on this unit so that the fastening unit cannot slip and the user has both hands free for further adjustment measures. The second unit has a measuring scale . Both units are axially connected to one another so that a starting point, usually identified by a small tongue on the fastening unit, can be brought into relation to the scale.
Since the 0 ° position of the rotor blade angle is based on a 90 ° angle to the action of gravity , the 0 ° position of the rotor blade is always identical to a plane that is at a 90 ° angle to gravity. This 0 ° position thus serves as a reference plane; a table or floor without inclination can represent such a reference plane. The helicopter model is also to be aligned parallel to this reference plane in relation to its transverse axis and longitudinal axis . The 0 ° value of the scale unit of the pitch gauge must therefore be aligned parallel to the reference plane in order to be able to initiate the measuring process. Depending on the alignment of the fastening unit of the pitch gauge with the clamped rotor blade, the pitch angle can now be read, which is indicated by the position of the aforementioned tongue.
The scale on the pitch gauge ranges from + 10 ° to –10 ° on some models and from + 15 ° to –15 ° on more recent models.
In addition to the analog measuring process described above, digital pitch gauges are now also available that can digitally display the angle of attack of the rotor blades up to one place after the decimal point.
Since there are different rotor blade sizes on which a pitch gauge has to be pushed, there are also different sizes of the pitch gauges for the different blade depths.
The pitch gauge can not only be used for the main rotor blades, but can also be used for the tail rotor blades . The tail boom of the model on which the 0 ° position of the pitch gauge is to be aligned in parallel is then used as the reference plane.
Similar measuring devices
Some applications for mobile phones can serve the same purpose as a pitch gauge. The long edge of the mobile phone is placed on top of the angled rotor blade. The difference to the reference plane is measured using position sensors contained in the mobile phone and read digitally on the display so that the rotor blade angle can be read off. However, since rotor blades for model helicopters usually have a curved cross-section, the mobile phone can usually not be placed flush on the rotor blade, so that the measurement results with the mobile phone application are quite inaccurate and thus only give a rough guide to the correct rotor blade angle. However, some model builders fix the mobile phone to the rotor blade with adhesive tape so that the measurement results can be made more precise with this procedure.
Remarks
- ↑ There are also models with a non-adjustable pitch. Here, a climb or a descent is achieved via the speed of the entire rotor head: high speeds mean climb, low speeds mean descent, medium speeds hover. A pitch gauge is not used with these models.
- ↑ after Day.
- ↑ The information can vary depending on the model and is dependent on the engine, take-off weight, rotor blade properties, wind and possibly other factors.
- ↑ 3D flight is a kind of aerobatics in which the model can be flown in all directions over all axes.
- ↑ Models suitable for aerobatics or 3D can also fly overhead. Without negative rotor blade adjustment, these models would e.g. B. no longer develop lift when hovering overhead, but follow gravity and crash, unless an escape maneuver can be flown at a sufficient altitude.
- ↑ Model helicopters can now be flown with pitch values of + 15 ° to -15 °, depending on the agility of the system, the motorization, the rotor blade properties and the take-off weight. However, with increasing pitch in certain flight maneuvers, the risk of a so-called "boom strike" increases. , i.e. an impact of the rotor blades in the tail boom, which leads to the model crashing.
- ↑ Semi-symmetrical, fully symmetrical or S-shaped profile.
Sources / literature
- Georg rods: DMFV helicopter primer . DMFV publishing house.
- Georg rods: DMFV Heli Primer II . DMFV publishing house.
- Dave Day: RC helicopters fly properly tuned . Verlag für Technik und Handwerk, Baden-Baden 2005, ISBN 3-88180-404-8 .
- Dieter Schlueter: remote-controlled helicopter . 11th edition. Neckar-Verlag, Villingen-Schwenningen 1999, ISBN 3-7883-3126-7 .