Vertical Lift Research Center of ExcellenceDepartment of Aerospace Engineering

Penn StatePAX Streamline

Tushar Prabhakar

•From New Delhi, India.•Easy going, can work alone/team.•Student Envoy for the Dept. of Aerospace.•Penn State football fan, love to tailgate.•Love to run, use to play Tennis and Badminton for my high school. •Military (WWII/Modern) History buff.•Avid reader (Fiction).•Favorite TV show – Anthony Bourdain, no reservations.and I am proud to be a nerd……

Personal Background

MSc in Aerospace Eng. (Dec 07)

BSc in Aerospace Eng. (May 05)

Courses taken: -Aeronautics, Astronautics, Smart structures, Aircraft and space-craft design, Advanced Experimental methods, Experimental modal analysis, structural optimization, Aerodynamics of V/STOL Aircraft, Fluid Mechanics…

Computer Languages: -AutoCAD (2000, 2006-07 – Lite), Solidworks, MathLab and Ansys. Familiar with C++, Pro-E 4, AcuSolve/Console

Microsoft Office Suite (Word, Power Point, Excel and Access.

Educational Background

Educational Background (cont…)

Familiarity with labs: -Know my way around labs, and machines. Familiar with the workings of lathes, mills and hand tools. Worked with instruments like oscillopscopes, HP Signal analyzers, High-low pass filters etc.

Teaching Experiences: -TA for Aerospace Aerodynamics and Structures lab.

•Duties included setting up of labs exercises ranging from wind tunnel and water channel testing to beam vibration and bending experiments.

• Supervised students (Juniors and Seniors) for these exercises.

• Responsibilities also included teaching students about technical report writing formats.

Educational Background (cont…)

TA for Advanced Experimental Methods.

•An experimental course utilizing various lab instruments used above.

•Worked with Sine/Square waves and white noise. Taught students basic use of lab instruments in conjunction with LabView and MatLab.

•Performed FFT analysis to show frequency response functions, time decay etc.

TA for Aerospace projects course where I had to aid different groups of students working on different projects. Part of my responsibilities included giving advice to students regarding their projects (hands on or design), editing reports, and presentations.

Master’s Thesis and other Projects

Design and Model Testing of Rotor Blades using “fluid elastic embedded chordwise inertial lag Dampers”

•Bench top/static tests only•Investigated natural frequencies of the blade with and without dampers•Conducted Cantilevered testing of the blade to show change in frequencies with dampers

Experimental testing for a new de-icing system for rotor-craft/aircraft•De-icing system utilized shear and ultrasonic waves to remove the ice•Main part for us was modeling the bending and twisting behavior of the plate with and without ice.

Masters Thesis Topic – Centrifugal Force Actuated Variable Span Morphing Rotor.Presented at the 63rd Annual Forum of the American Helicopter Society,Virginia Beach, Virginia, May 1 – 3, 2007.

Why Variable Span

• Compact span rotors for Naval operations and operation in confined spaces. Expanded rotors better for efficiency/ performance when space is not a constraint

• Tiltrotors – Ideally, larger span rotor for hover, smaller span for propeller

• Slowed-Rotor Compound Helicopters or Co-axial rotors – large rotor span for hover and low speed operations, smaller span ideal for high-speed flight

Previous Work… and New Ideas

Previous Work on Variable Span Rotors

• Sikorsky’s Variable Diameter TiltRotor – VDTR – concept

• Bell’s Variable Span Rotor (under the Army Variable Geometry Advanced Rotor Technology – VGART – Program)

• Both need complex mechanical actuation system

Our Idea – Centrifugally Actuated Variable Span

• Achieve change in blade span without any mechanical actuation

• Exploit change in centrifugal force with change in RPM

• Possible implementation – Blade could have a fixed inner section and a telescoping outer section that is spring-restrained

Fixed inner section of

blade

Sliding outer section

Restraining SpringHigh Ω

Low CF Force Little extension

High CF Force Large extension

Retracted or short configuration

Extended or long configuration

Low Ω L - Position of center of mass of sliding section + end cap u - Deformation

Schematic Representation of a CF actuated Variable Span Rotor

Uses of CF actuated Variable Span

• Tiltrotors – Desired larger span for hover, smaller span for propeller. Hover mode RPM typically larger than propeller mode RPM. With the current concept, the Proprotor would naturally expand when the RPM is increased in hover mode (and vice-versa)

• Slowed-Rotor Compound Helicopters or Co-axial rotors – In high speed forward flight, wing and auxiliary propulsion provide lift and thrust. Slowed main rotor is a source of drag, and has potentially poor gust response and stability characteristics. With current concept, reduction in span as the rotor RPM decreases alleviates these problems

Uses of CF actuated Variable Span (contd).

• For shipboard operations and operations in confined spaces, operate at lower RPM, smaller span and very high pitch. When space is not a constraint, slight increase in RPM can result in an increase in span and potentially improved efficiency.

• Ability to morph to a smaller helicopter when operating off smaller Navy ships (Arleigh-Burke class) and transform to heavy lifters when operating off larger Navy ships (Wasp-class or Nimitz-class). Reduces the need for the Navy to keep different classes of helicopters in its inventory.

Outline

• Design and Fabrication -CF actuated Variable Span Rotor

• Test and Validation-Extension vs. increase in RPM

• Simulation Studies-System parametric variations-Operational Analysis

•Concluding Remarks

Inner fixed portion of blade(connects to hub)

Outer telescoping portion

Spring-Restrained,(extends as RPM

increases)

Main Objectives

Variable Span Rotor , Designed and Fabricated (disassembled)

Inner fixed section of blade (11” span)

Guide-rail groove / Safety slot

End Cap

Outer sliding (telescoping) section of blade (11” span)Connection to Hub

Screw connecting end cap to outer sliding section of blade

3”

Variable Span Rotor , Designed and Fabricated (assembled)

Extension (Span Change) of such a System

• Extension depends on equilibrium between CF force on the outer sliding section and the spring restoring force. • Extension over a given RPM range determined by the initial position and mass of the outer telescoping section of the blade, and the restraining spring characteristics and max strain capability

2

2

MK

LMu

Rotor Test(s)

• Measure span change with change in RPM

• Carried out at 0, 5, and 10 deg collective

Extension Measurements with increase in rotational speed

Extension Measured using Linear Potentiometers

• Linear potentiometers (a 10 kohm slide with a 100 mm travel), affixed to rotor hub

• Signal generated controlled by a voltage regulator and Microcontroller.

• Transmitted via a LINX 433 MHz Transmitter.

• Receiving unit consisted of another voltage regulator, a receiver and a level shifter connected to a PC

Extension Measurements with increase in rotational speed

Extension measured using a video camera

• Set-up consisted of a infra-red triggered strobe light allowing the blade to appear stationary over the camera

• Using a frame grabbing procedure, a frame at any rotational speed could be obtained and extension of the blade measured

Sony Video Digital Camera

Infra-red Triggered Strobe Light

5 HP Motor

Infra Red / Trigger Mechanism

VSR Video

Inner fixed section of blade

Guide rail groove / Safety slot

Outer sliding section of blade starting position.35” Extension

3.7” Extension

Outer sliding (telescoping) section of blade

Test VideoSingle Frame at 100 RPM

Test VideoSingle Frame at 240 RPM

• Blade extension not reduced at higher collective• Predicted extension compares well with test data

Test results showing span increase with increasing rotational speed

The use of non-linear springs

Results show a more-or-less continuous variation in span with increase in RPM

It might be desirable to obtain a relatively large change in span over a relatively small change in rotor RPM

•RPM is being used as the “actuation” mechanism•Span change is the desired result•Should not require large changes in RPM for modest changes in span. Ideally you would like the reverse.

An initially stiff spring that softens could achieve the characteristics described above

Simulations with non-linear softening springs

Buspring eAufF 1)(

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 50

5

10

15

20

25

30

35

Extension (in)

Forc

e,

(Lbs.)

Linear Spring Force

Exponential Fn. Case IExponential Fn. Case II

Extension (in)

For

ce (

lbs)

)(2 ufFuLM spring

0 50 100 150 200 2500

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

Rotational Speed (RPM)

Ext

ensi

on (

in)

Closed Loop solution for Linear Springs

Nonlinear Spring, case INonlinear Spring, case II

Rotational Speed (RPM)

Ext

ensi

on (

in)

The use of non-linear piecewise-continuous springs

Extremely stiff to a critical force, then displays soft linear behavior

Virtually no extension up to a certain RPM, followed by a large extension over a very small increase in RPM

BO – 105 Properties

• Built by EUROCOPTER

• Number of blade = 4

• Maximum gross weight = 5,512 lbs

• Maximum speed = 131 kts

• Radius, R = 16.2 ft

• Rotor angular velocity = 40.12 rad/sec

• Linear twist (assumed) = 0 deg

• Solidity σ = .1

• Chord, c = 1.3 ft

• Tip-Mach # = .58

• Engine = 2x 420-shp Allison 250-C20B turbo-

shaft

Analytical simulations for short/long span configurations (modeled on the BO-105)

Rotor WITHOUT a locking mechanism

For CF actuated span change, shorter span corresponds to lower Ω and vice-versa

Can the short-span, low-Ω rotor (with high collective pitch) generate required thrust?

If span is increased along with increase in Ω and simultaneous reduction in collective, does that yield power reductions?

Mission Analysis/Con-OPS, without locking mechanism

Collective (deg)

Th

rust

(lb

s)

Shorter span with decrease in rotational speed, higher collective provides enough lift for the BO-105

Larger span with increase in rotational speed, increased payload capability within the power requirements BO-105 Rotor Thrust (lbs)

Rot

or P

ower

(H

P)

Analytical simulations for short/long span configurations (modeled on the BO-105)

Rotor WITH a locking mechanism

Previous Figure showed that a large span rotor with a simultaneously large RPM did not yield power reductions because of a much higher tip mach number relative to the baseline.

If the radius was decreased, with increase in Ω such that the tip mach number is the same as the baseline/nominal configuration, how much collective would be needed to provide lift?

What if the RPM was increased to achieve the span increase, but then locked in place, and the RPM then reduced to produce the same tip mach number as the baseline/nominal configuration

Mission Analysis/Con-OPS, with locking mechanism

Shorter span, increased ΩM = .58 in all cases, marginal increase in collective

Collective (deg)

Rot

or T

hru

st (

lbs)

Larger span, decreased ΩM = .58 in all cases, leading to reduction in power reqd. + increase in payload capability Rotor Thrust (lbs)

Rot

or P

ower

(H

P)

PAX Streamline (Design Engineer)

• Contracted Design Engineer for PAX Streamline,

• Wind Turbines– CFD Analysis/Experimental Testing for multiple Small Scale Wind Turbines

– Turbine Blade design study (make it cheaper/lighter/easier manufacturing techniques)

– Environmental impact study for turbines (cause of bird deaths/noise pollution)

– Research on Dragonfly wings/airfoils

– Airfoil research/experimental testing on PAX Airfoils

– CFD Analysis of Winglets on Turbines

• Water Turbines– Equipment testing/calibration (“Water Channel”)

– CFD Analysis/Experimental Testing of multiple Small Scale Water Turbines

PAX Streamline (Design Engineer)

Wind Turbines• CAD/Mechanical Design for small scale wind tunnel test apparatus for turbines

• CFD Analysis and comparison with experimental testing of turbines

• Blade study/prototype for a– Blade that is cheaper

– Blade that can be used on 100KW to 700KW turbines (so would need to be easily scalable)

– Ease of Manufacturability of the blade

– Strong blade, should be able to withstand blade bending/twist

• Environmental Impact studies – Study involving bird/bat deaths because of turbines (Problems with Altamont Pass)

– Noise Issues relating to Turbines

– Legal issues involving Turbine development/location/placing

• Bio-mimicry/Airfoil Research– Designed airfoils modeled on Dragonflies and based of a NACA 0012 profile

– Experimental testing of Airfoils and comparison with NACA 0012

• Winglet CFD Analysis– CFD Analysis of PAX Winglets on Wind Turbines

Circulation Control Wing Concept

The Idea behind this was to actively reduce drag on cars/suvs. Studies by Georgia Tech (Dr. Robert Englar), have shown that this concept can reduce drag on Semis. Using the Coanda Effect, is it possible to manipulate the actual shape of cars at different speeds?

Active Reduction of Drag (Using Coanda Effect)

CCA SUV Project 1. Started with GTRI, Volvo and Novatek

2. Wind tunnel modeling/real time testing showed an increase in mileage by 8-9%, Drag by about 25%

3. Infrastructure for further truck testing already in place at GTRI

4. Each modification in its current state expected to approximately add $8K for a tractor trailer

5. Stable yawing effects

1. Basic wind tunnel tests for the SUV conducted at GTRI2. Basic/quick modifications were made to the SUV (see

picture)3. Able to reduce drag by around 10%4. No fuel efficiency tests conducted5. Suburban with GTRI is a hybrid

Trucks – Previous research

Suburban – Previous research

Circulation Control Aerodynamics for SUVs

Circulation Control Aerodynamic Device

Inlet – 30.5 m/s

Wind Tunnel CAD, I/2 of the model. (Back of the tunnel identified as a Symmetrical Side)

CFD Analysis of a SUV (Modeled on the Suburban at 67 MPH (30.05m/s).

Parameters/Assumptions

• To show reduction of Aerodynamic Drag with the use of Coanda Effect

• Modeled on the Suburban, same dimensions.

• Inlet velocity in the “Tunnel” = 30.05 m/s or 67 MPH

• Wind Tunnel walls (identified as a slip condition)

• 16-18Million Element Mesh, not fine, not coarse

• Chevy Suburban Coefficient of Drag – .36*

• *Note – Not aware of the conditions/parameters used to calculate Cd.• Average Millage based on this Cd @ 67 MPH is around 19 MPG

Results for Coefficient of Drag for model

Case # CCW Inlet Velocity m/s Coefficient of Drag

1 0 .70

2 15 .68

3 30 .62

4 40 .57

5 50 .70

6 80 .80

•Cd twice that of the suburban however, the model used, is very basic, does not incorporate any aerodynamic improvements the suburban has.

Notes1.Cannot prove the validity of the CFD model2.Based on a steady state modeling

16.8% Decrease in Drag

Questions ?

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