Cirrus LSA Wing Design

Team Lead: David GustafsonTyler Hawkins

Nick BrownBryce Holmgren

Project Goals

• Utilize Edge Bonding

• Try New Light Weight Materials

• Incorporate Spin Resistance

• Total Weight Constraint

–< 170 lbs for entire wing

Obstacles

• Edge Bonding vs. Required Strength and Existing Practice

• New Materials– Cost

– Performance

• Spin Resistance vs. Manufacturing Simplicity

• All of These vs. Weight and Performance

Areas of Design and Analysis

• Loads Analysis

• Aerodynamic Design

• Materials Research and Testing

• Structural Design

Cirrus Wing

Aerodynamics and ControlBryce Holmgren

AerodynamicsDesign Constraints

Light Sport Aircraft Requirements• Maximum Gross Weight: 1,320lbs• Maximum Stall Speed: 45 knots• Required Lift Coefficient to Meet Requirements:

>1.60

Other Considerations• Spin Resistant Design• Enhanced Stall Performance

Aerodynamics

Analysis Tools – XFLR5• Developed by MIT• Contains Airfoil Generation Tool Called Xfoil• Recommended by Cirrus for Preliminary

Design Analysis

Aerodynamics

Initial Wing Design Parameters • Wing Span: 30 ft• Wing Area: 125 square ft

Airfoil Database – University of Illinois at Urbana-Champaign

Aerodynamics

Final Airfoil - NASA/Langley LS(1)-0417mod (also known as the GA(W)-1 airfoil)

Aerodynamics

Drooped Leading Edge• Enhanced Spin Resistance

AerodynamicsDrooped Leading Edge vs Standard Airfoil

AerodynamicsWing Model in XFLR

Plane weight of 1500 lbs and at 44 knotsLift Coefficient of 1.64 at 17˚ angle of attack

AerodynamicsDesign Summary

Parameter Dimension

Wing Area 123.07 ft^2

Wing Span 30 ft

Root Chord 4.5 ft

Tip Chord 3.7 ft

Mean Aerodynamic Chord 4.11 ft

Wing Loading 12.2 lbs/ft^2

Aspect Ratio 7.3

Taper Ratio 1.2

Dihedral Angle 5 Degrees

Max Lift Coefficient 1.86 @ 19 Degrees Angle of Attack

Aerodynamics

Improvements• Less Aggressive Camber• Different Tip Airfoil

Controls

Flaps• Fowler Flaps • Area: 24.4 ft^2

Ailerons• Differential Ailerons• Area: 12 ft^2

Cirrus Wing

MaterialsNick Brown

LSA FAA definition

• Max gross takeoff weight = 1320 lbs

• Max stall speed = 45 knots

• Maximum speed in level flight = 120 knots

ASTM F 2245-07 guidelines

• Limit load factors

• Ultimate load factor of safety = 1.5

• Special ultimate S.F.s for hinges, bearings, pins, control components

• Flight conditions

• Design speeds

Design speeds

• 45 knots = Stall speed (LSA)

• 99.6 knots= Minimum maneuvering Speed

• 108 knots = Minimum cruise

• 120 knots = Maximum cruise (LSA)

• 160 knots = Dive speed

Flight envelope

Flight Envelope

12099.6 159.27

45

-3

-2

-1

0

1

2

3

4

5

0 50 100 150 200

Speed (in knots)

Lo

ad F

acto

r n

Vs

VA VC,max VD

Total Loads

• Level flight 1320 lbs

• Design Limit load = 5280 lbs

• Ultimate load = 7920 lbs (for 3 seconds)

XFLR5

• Simulations– Various A.O.A. and Reynolds numbers

–Wing panels

• Data (spreadsheet)– Aerodynamic coefficients

– Lift, drag, and moment forces

XFLR5

XFLR5

XFLR5

DistributionS ec tional L ift D is tribution

y = -0.6938x 2 + 11.615x + 9.1203

y = -3.255x 2 + 54.497x + 42.791

0

50

100

150

200

250

300

350

0 2 4 6 8 10 12 14 16spa n position (ft)

L' (

lbs/

ft)

real load

real load(drooped L E )

ultimate load

ultimae load (droopedL E )

Shear and bending

• Integrate ultimate load equations– From 0(root) to 8ft (airfoil switch)• F = -5.2139x + 318.37

– From 8ft to tip (15ft)• F = -3.255x2 +54.497x + 42.791

Torsion/control loads

• 75% positive maneuvering load, plus torsion from max aileron displacement

• Gust loads at VF with flaps extended (7.5 m/s)

Gusts

• Symmetric vertical gusts (up and down)– 15 m/s at VC

– 7.5 m/s at VD

Cirrus Wing

Composite Panels & Adhesives

David Gustafson

Composite Panels

• Panels are fiberglass on both sides with a core in the middle consisting of either foam or a honeycomb structure

Fiberglass Core: Foam or Aramid

Core Options

Material DensityCompresive

StrengthTensile

strengthShear

SengthShear

ModulusCost

units (lb/ft^3) psi psi psi psi ($/ft^3)

Cirrus - HT 61 4.1 145 261 131 2900 4.96

Evonik 51 A - PMI Foam 3.248 131 276 116 2760 -

Ultracor UCF-83-1/4-3.0 3 246 27 223 61000

Aramid Core .25 In. Thick 1.8 109 - 52/62 (L/W)1579/2882

(L/W)7.95

Aramid Core .125 In. Thick 1.8 109 - 52/62 (L/W)1579/2882

(L/W)4.95

Final Core Material

• HT Diab 61- Wing Skins

• Ability to lay up curves of Airfoils

• Cheapest that met criteria of foams

• Aramid Core- Spar, Aft Spar, Rib

• Light Weight

• Cheapest per Pound

Adhesive Options• DP 420– 3M, Two Part Epoxy

» From 3M Epoxy Comparison

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

Adhesive Options (Cont.)

• PTM & W: – ES6292 Lightweight Tough Epoxy Adhesive• Two Part Epoxy

• Designed for use in the structural assemblies involving composites

• Already used by Cirrus Design Center

Adhesive Testing

• Objectives:– Test Max Adhesive Loads• Need to make sure adhesives aren’t effected by surfaces

– Test surface preparation techniques

Adhesive Testing (Cont.)

• Materials Tested:– Adhesives:• PTM & W ES6292

• 3M DP 420

– Composites:• Aramid Core with Fiberglass Skin

• HT Diab Foam Core with Tencate Fiberglass

Adhesive Testing (Cont.)

• Tensile Test:– Load Bonds in Tension–Measure Load at Fracture– Calculate Lbs/In. Bond Strength

• Test Equipment:– Constant Strain Load Cell–Measures Load and displacement

Adhesive Testing (Cont.)

Adhesive Testing (Cont.)

• Tensile Load Justification:– Jaws:• 2° freedom on both directions

– Top & Bottom

• All samples were applied within 1 degree of perpendicular

• Therefore: Tension loads were perpendicular to bond

Adhesive Testing (Cont.)

• Surface Preparation:– All surfaces were lightly sanded to rough up

surface

– All surfaces were cleaned with to remove

Adhesive Testing (Cont.)

• Results:– Bond Strength per Inch of Bond (Lbs/In)

• PTM & W ES6292= 81.7 ± 4.1 Lbs/In

• 3M DP 420=87.1 ± 4.4 Lbs/In

» Uncertainty Estimated at 5%

Adhesive Testing (Cont.)

• Conclusions:– Adhesives were comparable in

Strength per Inch

– Both Adhesives meet strength requirements for wing

– PTM & W ES6292 Adhesive is better because of lower cost

Adhesive Testing (Cont.)

• Errors:– Improper preparation:• Issue: Samples broke at surface

• Resolution: Better Surface Preparation– Sanding (possibly Sand Blasting)

– Better Removal of oils from surface

• Effect:– Bonds Broke Prematurely– With Better Preparation Bonds could hold more Weight

Adhesive Testing (Cont.)

– Test Equipment:• Issue: Jaws Slipping• Resolution: Better Transition from Material to Jaw

– Adhere Aluminum Tab into Composite– External Clamp System with Aluminum Tab for Jaw

» Allow Material to be secured by clamp and Jaw to attach to Aluminum Tab

• Effect:– Load might be underestimated. – Result: Bond Strength could be higher than reported

Adhesive Testing (Cont.)

• Further Testing:– Shear Test Side View:

Composite A

Composite B

Adhesive Testing (Cont.)

– Shear Test Top View:(Load Pulling out from picture)

Composite A

Composite B

Bond

Adhesive Testing (Cont.)

• Shear Test:

Cirrus Wing

StructuresTyler Hawkins

Structure

• Goals– Light Weight• < 170 lbs. in total

–Handle All Loads with Extra Safety Factor–Maintain Aerodynamic Shape–Attach to Fuselage Structure

Component Break Down

• Wing Skin• Main Spar• Aft Spar• Ribs• Leading Edge Braces

Wing Skin

• NEEDS–Light Weight–Easily formed into complex

surfaces–Durable –Puncture and Tear Resistant

Solutions

• Use 2-Core-2 construction for the wing• Fiberglass–45o angles

• Core–.25 inch–Density = .00145 lb/in3

Wing Skin Lay Up

Reasoning

• Process is known and used at Cirrus• Creates a Very puncture resistant material• Fiberglass performs well in multiple directions– ±45 degree orientation

• Light Weight material• Possible Improvements– Cut away sections of Foam where not needed– Use Honeycomb Aramid Core to cut weight

Main Spar

• NEEDS–Light Weight–Handle Compression, Tension, and

Shear–Provide Bond Surface for Ribs and Skin–Serve as Attachment to Fuselage

Spar Designs Considered

• C-Channel– Provides Good Bonding Surface– Would be made Entirely of Carbon– Similar to Existing Cirrus Designs

• Why Not– Looking for Two Piece Main Spar Assembly– Incorporating Aramid Core Can Lighten Structure

Rectangle Spars

• 4 – Core – 4– Simple Design– 1 Piece Core– One Width Carbon Cap

• Why not?– Too thick adds core weight– Too thin makes carbon lay up with many thin

strips

Examples of Rectangle Spars

I-Beam Spar

• Provides Similar Shear, Tension, Compression coverage to Rectangle

• Thinner Shear Web • Very Light Weight• Provides Large Bonding Surface to Wing Skin• Potential Drawbacks– Upfront Tooling– Layup Complexity

Caps

• Carbon– Laid Up as T-shape–Carbon Strips– Tensile Strength: 2.62*105 Psi–Compressive Strength: 1.42*105 Psi–Absorbs Forces on Top and Bottom of Spar

at Low Weight Cost

Spar Web

• Core– .3 inch Aramid Core• Very Light Weight• Bonds Well To Cirrus’s Fiberglass

– 4 ply fiberglass quilt on both Sides of Core• Provides the Shear support• Alternate Ply orientations (±45 degrees)• Performs very well in Shear (23800 Psi Shear strength)• Low Cost and Ease of Use

General Lay Up Scheme

*All units in Inches

Specific Modifications

• Taper Layers Until 4 Layers Left• Run 4 Layers to End Plus Alpha Section– Allows for Wide Bond Area– Need to only cut two strip Widths (α and cap)

• Taper These Quickly at the end of the Spar to Avoid Large Stress Concentration

Connection To Fuselage

• Fuselage Width: 48 in.• Extend Both Spars Through Fuselage• Attachments– 2 Hard Points for Bolts Between Spars– Bracket for Spars to Transfer Load to Fuselage– 1 Hard Point each Rear Spar 6 Inches into Fuselage

Attachment Point

Hard Points

• Options– Fiberglass Laid In Through Entire Spar– Aluminum Plug Laid Into Spar– Aluminum Plug Glued Into Spar

• Chose Aluminum Plug Laid Into Spar– 6061-T6• Light Weight• High Bearing Strength

Hard Point Dimensions

• Use .75 inch bolt/plug to attach structure• 0.3 inches thick• 3.75 inches in diameter• Spacing of 46 inches on center, 23 on either

side of WS0.

Aft Spar

• Simple Design• 2-Core-2• Aramid Core• 2 layers of Glass on Each Side• No Caps-Only Shear Felt Here

Ribs and Leading Edge Supports

• 2-Core-2 Construction• Aramid Core• Can Make Sheets of This and Water Jet Cut

Specific Panels– Also Aft Spar

• Provide Bond Length to Hold Skin and Structure Together

Rib Spacing

Airplane Design by Jan Roskam suggest 36” spacing for Light aircraft.

Rib to Skin Bonding

3-D view of Interior Structure

Structure with Skin Attached

Weight Estimate

Cirrus Wing

Build/TestNick Brown

Cirrus Wing

Manufacturing and AssemblyBryce Holmgren

ManufacturingPart Fabrication

Spars made using semi-automated system

ManufacturingPart Fabrication

Ribs and shear web water jet cut from single sheet of Nomex/glass composite

• Ventilation required when machining produces dust, mist or vapor

• Light Hand Cotton gloves for General Protection

ManufacturingPart Fabrication

Wing skins assembled in custom tooled forms

ManufacturingFinal Wing Assembly

ManufacturingFinal Assembly

ManufacturingEpoxy Health Concerns

Effects of Overexposure:– Eyes: Causes severe conjunctive irritation, Corneal injury

and Iritis– Skin: May cause irritation, burns, ulceration, or skin

sensitization– Inhalation: Vapors are irritating and cause tears, burning of

nose and throat, coughing, wheezing nausea and vomiting– Ingestion: Moderately toxic, may cause mouth and throat

burns, abdominal pain, weakness, thirst and coma.– Chronic: Amine vapors may cause liver and kidney injury.

Eye, skin or lung may develop or be irritated by Amine vapors.

[From MSDS of ES6292B with Beads]

ManufacturingSafety Precautions

• Respiratory: Not required unless process is creating dust, mist or vapor.

• Ventilation: Breathing of vapor must be avoided.• Hand Protection: Impervious gloves, neoprene or

rubber, must be worn• Eye Protection: Splash proof Goggles or safety

glasses• Other: Clean body covering clothing and shoes

[From MSDS of ES6292B with Beads]

Business Case

David Gustafson

Project Goals

• Design a Composite Wing– Comoposite Panels– Edge Bonding Technique

• Meet Design Criteria:– 170 Lbs or less– No Spin Criteria in Airfoil

Financial Summary

• Upfront Costs:– Wing Lay up Structure– Final Assembley– Safety Equipment

• Gloves• Goggles• Respirators

– Water Jet Cutting Equipment• Alternate Option:

– Contract for pieces to be Water Jet Cut

Financial Summary

• Material Cost of Wing:– Carbon: $123– Aramid Core: ~$840– Foam: ~$300– Fiberglass: ~$400– Adhesive: ~$100

Total: ~$1700

Justification

• Structure Meets Design Loads– Bonds Safety Factor >5

• Manufacturing Process – Streamlined– Cost Effective

• No Spin– Drooped Leading edge in Airfoil

Justification

• Edge Bonding– Allowed for a low weight design– Less Complex Manufacturing System– Meets strength Criteria

Thank You For Your Time and Consideration