Wing is the Thing

7/27/2019 Wing is the Thing

1/13

1

ME 380The Wings the Thing

Basic Aerodynamic Forces

We need to balance the aircraft weight and

aerodynamic drag with aerodynamic lift and

propulsive thrust - aerodynamics deals with two of

these forces

LIFT

THRUST

WEIGHT

DRAG


2/13

2

Basic Aerodynamic Forces

For steady, level flight, there is no acceleration, so:

Therefore, lift and drag also scale thrust and weight.

Since what dominates the aerodynamics is the wing,

getting the wings right is critical to plane design.

WLFTDF zx ==== 0,0

Design Methodology

There are two tried and tested ways to design an aircraft -

1. Ground up approach

Learn all of the basics, then design your vehicle around your

mission requirements

Aerodynamics propulsion structureperformance etc.

2. Empirical approach

Use essential data from previously designed aircraft in your

aircraft category to determine the baseline, then worry about the

details

Weightwing size engine size etc.


3/13

3

Example: V/STOL

If you can think of it, it has been looked at

Kohlman

Where to start?

Observation - (just like the Wrights did it)both nature and manmade

Results in the Great Flight Diagram


4/13

4

Wing Loading

From observation, it appears that W/S is an importantparameter - thus we will give it a name; wing loading

In ME330, you may have learned:

In level and steady flight, lift must equal weight

222

3.026.02 V

VV

CS

W

L

===

222 38.025.13.03.0 VVVS

W===

2

2VSCL L

= - lift coefficientLC

2

2VSCD D

= - drag coefficientDC

2

2

VSCW L =

L =W

2

2VC

S

WL

=

S: wing area

Horses Go Splat

Drop a mouse, cat, and horse from a 5 story building:

The mouse bounces, gets up, and walks away

The cat hits the ground and dies

The horse splashes

Why?

Square-cube law: surface area is proportional to size2 while

volume (thus, density and weight) is proportional to size3, this also

explains why there is an upper limit to natural flyers

As size increases, so does wing loading: this begs the questions, is

there an upper limit for wing loading?

S l2 WV l

3

W/S l


5/13

5

W, S, & W/S v. l

W/S

SW

l

Velocity, Wing Loading & Size

Using the lift coefficient

Thus, for geometrically similar models, the speed at a

given lift coefficient increases as the square root of

the wing loading or size (thus span)

lS

WV

WSCVL L

==2

21

Basic scaling dictates that larger aircraft

must fly faster.


6/13

6

Power & Wing Loading

Start w/ thrust requirements in level and steady flight

This by itself is very useful - if you know your weight

requirements and your aerodynamic efficiency, you

can determine your necessary minimum thrust. For

power

TR =D =D

WW =

D

LW

TR =W

L/D

=

==

UCC

W

UDL

WUTP

DL

RR

/

/

Power & Wing Loading

Using the lift eqn again

Combining with the power eqn

PBHP =PR

=

W

CD

CL

2W

SCL

L =W= 12U

2SCL

U=

2W

SCL

PR = TU =

W

CL /CD

2W

SCL=

2W3CD2

SCL3


7/13

7

Minimizing Power

Re-arranging

P =1

W

CD

CL

3 / 2

2

W

S

Maximize prop.

efficiency

Minimize weight

Maximize density

(minimize altitude)

Minimize

Wing loading

Maximize enduranceparameter

Power & Size

Back to scaling arguments

Thus, with a reduction in weight (size3), power

requirements decrease faster than the weight

Likewise, as size increases, power requirements

increase faster than the weight, leading to an upper

limit based on current propulsion technology (which is

why so much effort is put into engine design!)

P W3

S

l9

l2

l3.5


8/13

8

Weight vs. Power

From the point of view of flapping fliers, this partlyexplains why insects can fly - they dont need a lot of

power and can be very inefficient; also, larger birds

require a lot of power to generate lift, which is why they

spend most of their time soaring on thermals rather than

flapping their wings

For larger vehicles,

this explains why

their appears to be

an upper limit for aircraft size - the larger they are, themore power they need, which feeds into the design cycle

(more power, more weight, more more more!)

SPRUCE GOOSE

www.sprucegoose.org

Bending Moment & Moment of Inertia

Next, consider wing bending moment

The moment increases the 4th power of the size,

which is the bending moment at the root (plane) or

load on the muscles (birds)

Finally, consider the moment of inertia about the

rolling axis (energy required to flap a wing or roll the

aircraft)

Both the moment and angular acceleration are

important; this helps to explain why insects can beat

their wings so fast while birds must flap more slowly

M= FdWl l4

Ix Mx /Wy2 l

5


9/13

9

Bending Moment Too High

Bending moments higher than the design structuralload are bad, very bad - fatigue can cause this!

C-130 US Forest Service air tanker crash, 2002

Limit to Flapping Size

But it doesnt stop people from trying

Human carrying ornithopter project, headed by Prof.

Emeritus James DeLaurier, Univ. of Toronto


10/13

10

W, S, W/S, P, M, & I v. l

W/S

SW

l

I M PM

Sizing Based on Wing Loading

First, what is it and why use it to size?

Amount of lift each section of wing must generate; greater wing

loading means greater lifting requirements and more stress on

structural elements - comes into play in MANY performance

measures

For example, drag (as will learn later) can be found using

D = qSCDo +

W

S

21

eAR

S

q


11/13

11

Wing Sizing

W/SW/S

586120Jet transport

34279Jet fighter

24450Jet trainer

19540Twin turboprop

12726GA - twin

8317GA - single

5411Homebuilt

306Sailplane

kg/m2lb/ft2Category

Wing loading appears to be mission dependent, notsize dependent

Raymer

UAVs

Do these relations continue to UAVs?


12/13

12

Pioneer UAV

W/S v. V: Selected UAVs

!"

#$%

&'()

#*

*$

W= 0.38V2


13/13

13

Worldwide Operational UAVs

0.1

1

10

100

0.1 1 10 100 1000 10000 100000

Mass (kg)

Preditor

Global Hawk A

Global Hawk B

Shadow 200

Dragon Eye

Wasp

Raven

Deimos*

FASM*

AIRCAT*

MIAV*

Simpson, PhD 2008

Wingspan(m)

Wing is the Thing

Documents

Transcript of Wing is the Thing