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→FGRotor
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**Various NACA Technical Notes and Reports | **Various NACA Technical Notes and Reports | ||
== FGRotor == | == FGRotor == | ||
FGRotor moodels a helicopter rotor. | |||
=== Configuration File Format === | |||
<syntaxhighlight lang="xml"> | |||
<rotor name="{string}"> | |||
<diameter unit="{LENGTH}"> {number} </diameter> | |||
<numblades> {number} </numblades> | |||
<gearratio> {number} </gearratio> | |||
<nominalrpm> {number} </nominalrpm> | |||
<chord unit="{LENGTH}"> {number} </chord> | |||
<liftcurveslope Xunit="1/RAD"> {number} </liftcurveslope> | |||
<twist unit="{ANGLE}"> {number} </twist> | |||
<hingeoffset unit="{LENGTH}"> {number} </hingeoffset> | |||
<flappingmoment unit="{MOMENT}"> {number} </flappingmoment> | |||
<massmoment Xunit="SLUG*FT"> {number} </massmoment> | |||
<polarmoment unit="{MOMENT}"> {number} </polarmoment> | |||
<inflowlag> {number} </inflowlag> | |||
<tiplossfactor> {number} </tiplossfactor> | |||
<maxbrakepower unit="{POWER}"> {number} </maxbrakepower> | |||
<controlmap> {MAIN|TAIL|TANDEM} </controlmap> | |||
<ExternalRPM> {number} </ExternalRPM> | |||
<groundeffectexp> {number} </groundeffectexp> | |||
<groundeffectshift unit="{LENGTH}"> {number} </groundeffectshift> | |||
<freewheelthresh> {number} </freewheelthresh> | |||
</rotor> | |||
</syntaxhighlight> | |||
* LENGTH means any of the supported units, same for ANGLE and MOMENT.X unit-attributes are a hint for currently unsupported units, so values must be provided accordingly. | |||
=== Parameter definitions === | |||
{| class="prettytable" | |||
|- | |||
|diameter | |||
|Rotor disk diameter (2x R). | |||
|- | |||
|numblades | |||
|Number of blades (b). | |||
|- | |||
|gearratio | |||
|Ratio of (engine rpm) / (rotor rpm), usually > 1. | |||
|- | |||
|nominalrpm | |||
|RPM at which the rotor usally operates. | |||
|- | |||
|chord | |||
|Blade chord, (c). | |||
|- | |||
|liftcurveslope | |||
|Slope of curve of section lift against section angle of attack, per rad (a). | |||
|- | |||
|twist | |||
|Blade twist from root to tip, (theta_1). | |||
|- | |||
|hingeoffset | |||
|Rotor flapping-hinge offset (e). | |||
|- | |||
|flappingmoment | |||
|Flapping moment of inertia (I_b). | |||
|- | |||
|massmoment | |||
|Blade mass moment. Mass of a single blade times the blade's cg-distance from the hub, optional. | |||
|- | |||
|polarmoment | |||
|Moment of inertia for the whole rotor disk, optional. | |||
|- | |||
|inflowlag | |||
|Rotor inflow time constant, sec. Smaller values yield to quicker responses (typical values for main rotor: 0.1 - 0.2 s). | |||
|- | |||
|tiplossfactor | |||
|Tip-loss factor. The Blade fraction that produces lift. Value usually ranges between 0.95 - 1.0, optional (B). | |||
|- | |||
|maxbrakepower | |||
|Rotor brake, 20-30 hp should work for a mid size helicopter. | |||
|- | |||
|controlmap | |||
|Defines the control inputs used (see notes). | |||
|- | |||
|ExternalRPM | |||
|Links the rotor to another rotor, or an user controllable property. | |||
Experimental properties | |||
|- | |||
|groundeffectexp | |||
|Exponent for ground effect approximation. Values usually range from 0.04 for large rotors to 0.1 for smaller ones. As a rule of thumb the effect vanishes at a height 2-3 times the rotor diameter. formula used: exp ( - groundeffectexp * (height+groundeffectshift) ) Omitting or setting to 0.0 disables the effect calculation. | |||
|- | |||
|groundeffectshift | |||
|Further adjustment of ground effect, approx. hub height or slightly above. | |||
|- | |||
|freewheelthresh | |||
|Ratio of thruster power to engine power. The FWU will release when above the threshold. The value shouldn't be too close to 1.0, 1.5 seems ok. 0 disables this feature, which is also the default. | |||
|} | |||
=== Notes === | |||
==== Controls ==== | |||
* The behavior of the rotor is controlled/influenced by following inputs. | |||
** The power provided by the engine. This is handled by the regular engine controls. | |||
** The collective control input. This is read from the <tt>fdm</tt> property <tt>propulsion/engine[x]/collective-ctrl-rad</tt>. See below for tail rotor | |||
** The lateral cyclic input. Read from <tt>propulsion/engine[x]/lateral-ctrl-rad</tt>. | |||
** The longitudinal cyclic input. Read from <tt>propulsion/engine[x]/longitudinal-ctrl-rad</tt>. | |||
** The tail collective (aka antitorque, aka pedal) control input. Read from <tt>propulsion/engine[x]/antitorque-ctrl-rad</tt> or <tt>propulsion/engine[x]/tail-collective-ctrl-rad</tt>. | |||
==== Tail/tandem rotor ==== | |||
Providing <tt>\<ExternalRPM\> 0 \</ExternalRPM\></tt> the tail rotor's RPM | |||
is linked to to the main (=first, =0) rotor, and specifing | |||
<tt>\<controlmap\> TAIL \</controlmap\></tt> tells this rotor to read the | |||
collective input from <tt>propulsion/engine[1]/antitorque-ctrl-rad</tt> | |||
(The TAIL-map ignores lateral and longitudinal input). The rotor needs to be | |||
attached to a dummy engine, e.g. an 1HP electrical engine. | |||
A tandem rotor is setup analogous. | |||
==== Sense ==== | |||
The 'sense' parameter from the thruster is interpreted as follows, sense=1 means | |||
counter clockwise rotation of the main rotor, as viewed from above. This is as a far | |||
as I know more popular than clockwise rotation, which is defined by setting sense to | |||
-1. Concerning coaxial designs - by setting 'sense' to zero, a Kamov-style rotor is | |||
modeled (i.e. the rotor produces no torque). | |||
==== Engine issues ==== | |||
In order to keep the rotor speed constant, use of a RPM-Governor system is | |||
encouraged (see examples). | |||
==== Development hints ==== | |||
Setting <tt>\<ExternalRPM> -1 \</ExternalRPM></tt> the rotor's RPM is controlled by | |||
the <tt>propulsion/engine[x]/x-rpm-dict</tt> property. This feature can be useful | |||
when developing a FDM. | |||
=== References:=== | |||
{| class="prettytable" | |||
|- | |||
|SH79 | |||
|Shaugnessy, J. D., Deaux, Thomas N., and Yenni, Kenneth R., "Development and Validation of a Piloted Simulation of a Helicopter and External Sling Load", NASA TP-1285, 1979. | |||
|- | |||
|BA41 | |||
|Bailey,F.J.,Jr., "A Simplified Theoretical Method of Determining the Characteristics of a Lifting Rotor in Forward Flight", NACA Rep.716, 1941 | |||
|- | |||
|AM50 | |||
|Amer, Kenneth B.,"Theory of Helicopter Damping in Pitch or Roll and a Comparison With Flight Measurements", NACA TN-2136, 1950. | |||
|- | |||
|TA77 | |||
|Talbot, Peter D., Corliss, Lloyd D., "A Mathematical Force and Moment Model of a UH-1H Helicopter for Flight Dynamics Simulations", NASA TM-73,254, 1977. | |||
|- | |||
|GE49 | |||
|Gessow, Alfred, Amer, Kenneth B. "An Introduction to the Physical Aspects of Helicopter Stability", NACA TN-1982, 1949. | |||
|} | |||