Composite Aircraft: How to Make Airplanes Out of Cloth Aircraft: How to Make Airplanes Out of Cloth Tim Nuhfer Aerostructures Design . ... Images from “Composite Airframe Structures”,

Aurora Flight Sciences Aurora Flight Sciences

Composite Aircraft: How to Make Airplanes Out of Cloth

Tim Nuhfer

Aerostructures Design

Aurora Flight Sciences 2 10/8/2014

How I got to where I am today

• Grew up in Florida

• B.S. Aerospace Engineering

• Lockheed Martin, Marietta, GA F-22 Raptor, Liaison Engineering

• Gulfstream Aerospace, Savannah, GA Material Review Board and

Composites Shop

• Northrop Grumman, Melbourne, FL Vehicle Structures / Crew and

Equipment

Images from Lockheed Martin, Gulfstream Aerospace, Northrop Grumman


• In-house UAV products Orion

Centaur

Skate

• Aircraft structures Sikorsky, Boeing, Northrop Grumman,

Lockheed Martin, and others

Yes, we compete and team together

• Internship opportunities, even to high schoolers!

• Manassas, VA

• Cambridge MA

• Columbus, MS

• Bridgeport, WV


How do we design an airplane?

• Requirements Customer tells us what they would like an

airplane to do

• Concept Design Small teams from several different

companies comes up with designs that meet those requirements. One or more hopefully gets a contract.

• Preliminary Design A larger team brings a dose of reality to the

concept.

Aerodynamics, propulsion, computers, software, electrical, payload, structure, mechanical systems.

• Detailed Design Create drawings, tooling, manufacturing

planning, lots of coding

• Build, Test, Assemble, Test, Integrate, Test, Fly, Test, Modifications and Upgrades, Test……


What are “Composites”?

• Any structure made of multiple types of materials

laminated to form “composite” structure stronger than the

basic materials

Wood, the original composite

Aluminum sheets laminated with other sheets

Carbon fiber, fiberglass, Kevlar, boron fiber


How does carbon compare to other

materials?

Material Tensile

Strength

Modulus

of

Elasticity

Density Cost

Aluminum 65-75 ksi 10 Msi 0.1 lb/in3 Medium

Steel 180-280 ksi 25-30 Msi 0.3 lb/in3 Low

Carbon

Fiber

75-300 ksi 10-33 Msi 0.05 lb/in3 High

Images from “Composite Airframe Structures”, Michael C.Y. Nui, 1992


Carbon Fiber Basics

• Wet Lay-up Dry fabric is layed into a mold

Epoxy resin is mixed then worked into the fabric either by hand or using pressure or vacuum assisted resin transfer techniques

Typical working time with resin is about 1 to 2 hrs

• Pre-impregnated uni and fabrics (pre-preg) Epoxy is pressed into fabric and tape using

high pressure rollers

Material is sandwiched between layers of carrier film and put onto rolls

Bagged and stored frozen until needed Thawed when ready to work, typical outlife is 7 to 25 days

Images from ministryofwood.com and carbonfiberguru.com


Sandwiches, mmmmm…

• What makes a composite sandwich panel better than a solid panel?

• Think of it like a beam

Load Applied

Replace the middle with core.

Make the outer fibers work to

their full capability



Practical uses

• Skin panels

Thin aluminum requires

stiffening to prevent buckling

Composite sandwich panels

can achieve the same or

better buckling strength for

the same or less weight

• Wing spars

• Wing Ribs



How to make a part

• Start with a mold or “tool”

“Female” tools will have the part laid up inside of it

“Male” tools will have the part laid up on the outside

• Variety of tool materials

Aluminum, steel, MDF, foam boards…

Must size the tool for thermal growth

• Clean and seal the tool before beginning the lay-up.


Lay-up

• Thaw carbon

• Cut carbon from

the roll

• Perform lay-up


Bagging and cooking

• Perforated release film

• Breather cloth

• Vacuum bag

• Cook in oven Resin will flow throughout the laminate and take a

set

Some systems require an autoclave


Oven vs Autoclave cure cycles

• Oven cure

Entire cure cycle under

vacuum pressure

Max pressure limited to

atmospheric pressure (1 atm)

• Autoclave cure

Autoclave is a large pressure

vessel

Higher pressure allows for

greater compaction

Tooling may be more

expensive to withstand higher

pressure forces

Images from wisoven.com and autoclavesgroup.com


De-mold and trim

• After cure is done

Cut open bag

Pull part from the mold

Trim part to size

Sand and de-burr


Parts are ready, let’s build an airplane

• Parts are held together in assembly jigs and bonded or

bolted together

Image sources: Lockheed Martin and Aurora Flight Sciences

Aurora’s Orion

Wing Assembly

Lockheed Martin’s

Advanced Composites

Cargo Aircraft Fuselage

Assembly


What I use from school

• Math Algebra, Geometry, Trigonometry on a weekly or daily basis

Calculus somewhat more rarely

• Knowing what the calculus means allows me to make simplifications

• English Need to be able to write reports and make presentations

• Chemistry / Materials science Understanding how materials interact with each other is critical

Understanding crystal structure of metals and how it relates to stresses

• Physics F=Ma ∑F=0 ∑M=0

Knowing how to draw a freebody diagram

• Programming Basic understanding of programming logic is critical to being able to

use most engineering software to its fullest

• Art The most brilliant ideas are useless if you can’t present the idea

clearly enough for someone else to make it

• Crafts With composites, being able to use a ruler to draw and cut a straight

line is critical


Questions?

Documents

Composite Aircraft: How to Make Airplanes Out of Cloth Aircraft: How to Make Airplanes Out of Cloth Tim Nuhfer Aerostructures Design . ... Images from “Composite Airframe Structures”,