{ "cells": [ { "cell_type": "markdown", "id": "breathing-stress", "metadata": { "slideshow": { "slide_type": "slide" } }, "source": [ "# Hover" ] }, { "cell_type": "markdown", "id": "hundred-humanitarian", "metadata": { "slideshow": { "slide_type": "-" } }, "source": [ "```{epigraph}\n", "An isolated rotor is difficult to simulate... the rotor community requires many more elements of the hovering rotorcraft to be reliably and swiftly simulated.\n", " \n", "```\n", "
AIAA Rotorcraft Hover Prediction Workshop
" ] }, { "cell_type": "markdown", "id": "boolean-property", "metadata": { "slideshow": { "slide_type": "skip" } }, "source": [ "We used the momentum theory to analyse the thrust, power and induced velocity relationships for a rotor in hover and in climb. A ton of assumptions were introduced in order to be able to form nice closed-form analytical expressions that can be used to do quick back-of-the-envelope calculations easily. Even though the induced power factor $\\kappa$ was introduced for a more accurate estimate of induce power, by accounting for some of the effects not accounted for in momentum theory, the reality is far more complex and some of it is further discussed below. Suffice it to say that some of the brightest minds in the field of rotor aerodynamics get together on a regular basis holding conferences and workshops to share advancements that they've made towards accurately predicting every aspect of a hovering rotor using CFD from first principles. These include rotor power consumption, thrust generated, trim angles, tip vortex motion in wake etc. " ] }, { "cell_type": "markdown", "id": "manual-nylon", "metadata": { "slideshow": { "slide_type": "skip" } }, "source": [ "```{admonition} Ideal hover scenario\n", "The blade aerodynamics is steady in hover since no variation occurs over one rotor revolution. A specific amount of rotor collective is applied and the rotor cyclics are zero. The result is a net thrust vector that is along the rotor shaft. Consequently, zero pitch and roll moments are generated. \n", "```" ] }, { "cell_type": "markdown", "id": "generous-capitol", "metadata": { "slideshow": { "slide_type": "skip" } }, "source": [ "```{admonition} Real hover scenario\n", "Helicopter center of gravity (CG) does not lie exactly below the rotor shaft. Fuel consumption, ingress/egress of equipment or passengers, payload drop etc. are some of the mechanisms via which CG might move about during hover. Even pilots shifting in their seats will affect the CG. Clearly CG directly below the rotor shaft is an unrealistic expectation. So symmetric lift distribution over the rotor disk in hover is not viable. Uneven blockage effects from the fuselage, disturbance from the air, minor differences in blade construction (manufacturing defects) etc. exacerbate this situation. Additionally, the rotor shaft angle is tilted forward with respect to the fuselage in order to maintain a favorable fuselage attitude during high speed forward flight. During hover, the rotor disk needs to be tilted 'backwards', to account for the shaft tilt, and sidewards to account for the lateral force due to tail rotor thrust, so non-zero rotor cyclic angles become necessary in hover. More on the what is rotor cyclic control, and why it is necessary, later.\n", "``` " ] }, { "cell_type": "markdown", "id": "straight-premiere", "metadata": { "slideshow": { "slide_type": "slide" } }, "source": [ "## Definition" ] }, { "cell_type": "markdown", "id": "studied-shoulder", "metadata": { "slideshow": { "slide_type": "skip" } }, "source": [ "How do you define the hover state? Does the helicopter in the video below hover at any time during the shown manuever?" ] }, { "cell_type": "code", "execution_count": 13, "id": "activated-placement", "metadata": { "hide_input": false, "scrolled": true, "slideshow": { "slide_type": "-" } }, "outputs": [ { "data": { "image/jpeg": 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\n", "text/html": [ "\n", " \n", " " ], "text/plain": [ "Helicopter rotor blade pitch control via swashplate [source]
\n", "Bo 105 rotor wake visualized using Schlieren method [source]
\n", "Right cylindrical rotor wake model using vortex theory (taken from Rotor Aeromechanics by Wayne Johnson)
\n", "Free-wake simulation of a 4 bladed rotor in hover flight
\n", "\n", "Bell patent: Split-winglet on rotor blades [source]
\n", "\n", "Schematic of blade-vortex interaction and the induce loading [source]
\n", "\n", "A schematic representation of the Rankine model of a finite vortex [source]
\n", "\n", "Effect of tip vortex core radius on circumferential velocity [source]
\n", "\n", "" ] }, { "cell_type": "markdown", "id": "electric-juvenile", "metadata": { "slideshow": { "slide_type": "slide" } }, "source": [ "## \"Steady\" aerodynamics hover" ] }, { "cell_type": "markdown", "id": "written-alexandria", "metadata": { "slideshow": { "slide_type": "skip" } }, "source": [ "It might appear that the hover, given the symmetry of flow conditions and their steady state nature, would be computationally the easiest flight state to model. However, the simple fact remains that the trailing tip vortices do not quickly convect away from the rotor (how would they? small $v_i$ is desirable, remember), unlike in fixed-wing flight. Consequently accounting for the influence of tip vortices on rotor blades is of paramount importance and small deficiencies in the modelling strategies can lead to inaccurate vortex strengths and/or trajectories. This in turn has an influence on the blade loads and vice versa - local blade aerodynamics affects the wake and the wake influences the blade aerodynamics. \n", "\n", "The following show results from a rotor hover test carried out on a calm night on a whirl tower. The variations registered in the measurements suggest that slight unsteadiness associated with evolution of the tip vortices can have a non-negligible influence on the rotor aerodynamics. Fluctuations of ~1% are not negligible and a difference of 0.015 in FM distinguishes a better rotor from a good one. " ] }, { "cell_type": "markdown", "id": "naughty-format", "metadata": { "slideshow": { "slide_type": "-" } }, "source": [ "Variability in rotor performance in hover [taken from Helicopter Aerodynamics I by RW Prouty]
\n", "Sikorsky X2 [source]
\n", "Sikorsky S-97 Raider [source]
\n", "Sikorsky Boeing SB-1 Defiant [source]
\n", "Sikorsky X2-like rotor in hover [source]\n", "
\n", "