HALE UAV: AeroVironment Pathfinder

HALE UAV:

HALE UAV:

AeroVironment

AeroVironment

Pathfinder

Pathfinder

Desta Alemayehu Elizabeth Eaton Imraan Faruque

Aerodynamic and Stability

Analysis

Case Study: Planform

Optimization

2

Pathfinder History

Pathfinder History

•

•

Designed and fabricated by

Designed and fabricated by

AeroVironment

AeroVironment

in 1981

in 1981

•

•

Determined technology insufficient to support

Determined technology insufficient to support

mutli

mutli

-

-

day

day

duration flights under solar power and Pathfinder was put into

duration flights under solar power and Pathfinder was put into

storage

storage

•

•

In 1993, brought back to flight by Ballistic Missile Defense

In 1993, brought back to flight by Ballistic Missile Defense

Organization

Organization

•

•

Transferred to NASA in 1994 to support Environmental

Transferred to NASA in 1994 to support Environmental

Research Aircraft and Sensor Technology (ERAST) program

Research Aircraft and Sensor Technology (ERAST) program

•

•

ERAST program demonstrated that a high AR, solar

ERAST program demonstrated that a high AR, solar

-

-

powered

powered

lightweight craft could take off and land at an airport and fly

lightweight craft could take off and land at an airport and fly

at extremely high altitudes (50

at extremely high altitudes (50

-

-

80K ft)

80K ft)

•

•

ERAST also determines feasibility of such

ERAST also determines feasibility of such

UAVs

UAVs

for carrying

for carrying

instruments used in scientific studies

instruments used in scientific studies

ERAST Milestones

ERAST Milestones

•

• Sept. 11, 1995: Sets first altitude record for solarSept. 11, 1995: Sets first altitude record for solar--powered aircraft at powered aircraft at 50,000 ft during 12

50,000 ft during 12--hour flighthour flight •

• October 21, 1995: Damaged in hangar mishapOctober 21, 1995: Damaged in hangar mishap •

• July 7, 1997: Sets new altitude record for solarJuly 7, 1997: Sets new altitude record for solar--powered and powered and propeller

propeller--driven aircraft at 71,530 ftdriven aircraft at 71,530 ft •

• Modified into the longerModified into the longer--winged Pathfinder Plus, still used for tests at winged Pathfinder Plus, still used for tests at NASA DFRC

NASA DFRC

•

• Aug. 6, 1998: Pathfinder Plus breaks old record with flight at aAug. 6, 1998: Pathfinder Plus breaks old record with flight at altitude ltitude of 80,201 ft

of 80,201 ft

•

• Aug. 13, 2001: Helios sets record at 96,863 ft in near 17Aug. 13, 2001: Helios sets record at 96,863 ft in near 17--hour flighthour flight •

4

Pathfinder Configuration

Pathfinder Configuration

Center Panel: 22.1 ft span and 0° dihedral

Mid Panel: 18.9 ft span (each) and 3° dihedral

Tip Panel: 18.8 ft span (each) and 6.5° dihedral

Specs and Performance

Specs and Performance

•

•

W=550 lbs (includes 50 lbs payload)

W=550 lbs (includes 50 lbs payload)

•

•

-

-

W/S=0.694

W/S=0.694

psf

psf

•

•

Solar array covers 75% of upper surface and can

Solar array covers 75% of upper surface and can

generate near 8000 W at solar noon

generate near 8000 W at solar noon

•

•

Six gearless 1.5 hp electric motors consisting of

Six gearless 1.5 hp electric motors consisting of

fixed

fixed

-

-

pitched, 2

pitched, 2

-

-

bladed 79

bladed 79

-

-

inch diameter props,

inch diameter props,

brushless DC motor, nacelle, cooling fins, and

brushless DC motor, nacelle, cooling fins, and

composite mounting strut

composite mounting strut

•

•

-

-

T/W=0.10 at 60,000 ft, P/W = 13.6 W/lb

T/W=0.10 at 60,000 ft, P/W = 13.6 W/lb

•

•

Composed of carbon composite spar, lightweight

Composed of carbon composite spar, lightweight

composite ribs and transparent plastic wing skin

composite ribs and transparent plastic wing skin

•

•

-

-

Can withstand 3.2g

Can withstand 3.2g

•

6

Airfoil: LA2573A

Airfoil: LA2573A

• Modified Liebeck Airfoil

• Max t/c = 0.137 • x/c of max t = 0.288 • Max camber/c = 0.032 • x/c of max camber = 0.261 x/c -0.30 -0.25 -0.20 -0.15 -0.10 -0.05 0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90 1.00 y/c

-2.5 -2 -1.5 -1 -0.5 0 0.5 1 1.5 0 0.2 0.4 0.6 0.8 1

Pressure Distribution

Pressure Distribution

8 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 -4 -2 0 2 4 6 8 10 12 14 16 18

Lift Curve

Lift Curve

• Zero lift angle α = -0.82 ° α, degrees

-0.04 -0.02 0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 -4 -2 0 2 4 6 8 10 12 14 16 18

Moment Curve

Moment Curve

• Requires positive C to trim so must not exceed α = 18° α, degrees

10

Drag Polar

Drag Polar

• C_D0 = 0.014

• (L/D)_max = 25 •_{does not exceed 1.2 (}Best performance of airfoil when CL_{α = 10°)}

C_D C L -0.40 -0.20 0.00 0.20 0.40 0.60 0.80 1.00 1.20 1.40 0.00 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09

Wind Tunnel Data

Wind Tunnel Data

12

Analysis in AVL

Analysis in AVL

• Mach = 0.097

Span Loading at

14

Derivatives

Derivatives

0

0

--

.008

.008

--

.002

.002

--

.064

.064

--

.001

.001

0.002

0.002

C

C

--

.015

.015

--

.005

.005

--

2.72

2.72

.016

.016

.002

.002

--

1.34

1.34

C

C

0

0

.22

.22

.036

.036

--

.61

.61

--

.13

.13

0.026

0.026

C

C

0

0

.044

.044

.009

.009

--

.066

.066

--

.022

.022

0.006

0.006

C

C

.030

.030

.017

.017

7.47

7.47

--

.050

.050

--

.005

.005

4.94

4.94

C

C

δ

δ

r

r

q

q

p

p

β

β

α

α

Derivatives,

Derivatives,

¾

¾

chord elevator

chord elevator

0

0

--

.008

.008

--

.002

.002

--

.064

.064

--

.001

.001

0.002

0.002

C

C

--

.022

.022

--

.005

.005

--

2.72

2.72

.016

.016

.002

.002

--

1.34

1.34

C

C

0

0

.22

.22

.036

.036

--

.61

.61

--

.13

.13

0.026

0.026

C

C

0

0

.044

.044

.009

.009

--

.066

.066

--

.022

.022

0.006

0.006

C

C

.048

.048

.017

.017

7.47

7.47

--

.050

.050

--

.005

.005

4.94

4.94

C

C

δ

δ

r

r

q

q

p

p

β

β

α

α

16

Results

Results

•

•

e = 0.92

e = 0.92

•

•

Neutral Point = 26% of chord

Neutral Point = 26% of chord

•

•

(

(

C

C

C

C

)/(C

)/(C

C

C

) =

) =

-

-

3.82

3.82

--

This must be greater than 1 to be

This must be greater than 1 to be

spirally stable

spirally stable

Optimization of Planform

Optimization of Planform

•

Objectives:

- Maximize Power

- Minimize Weight

- Minimize Drag

•

Design Variables:

- Spans of center, mid, and tip panels

- Chord

•

Create model in Model Center using MATLAB modules

for weight, drag and power

•

Use the Darwin genetic algorithm to perform

18

Modules

Modules

•

Weight: Assumed evenly distributed

•

Drag: Assumed a drag polar, C

= C

+ C

_/(πARe)

•

C

: Used equations from ‘friction’ to obtain C

, assuming a high

laminar to turbulent ratio

•

Power: Solar panels cover 75% of the upper surface

Constants for Optimization: - e = 0.92 (from AVL) - ρ = 0.0002256 sl/ft3 _{(60,000 ft)} - µ = 0.297·10-6 _sl/ft-s - M = 0.097 (V=94 ft/s at 60K ft) - FF = 2.12 - Q = 1.0 - W/S = 0.694 psf - P/S = 13.5 W/ft2

Optimization Results

Optimization Results

Pareto designs are those that have a better value for at least one objective function than similar designs.

Nearly linear relationship between objective functions for the non-dominated

frontier.

Ideally look for designs with comparatively higher power than those with similar

weight and drag. These designs are referred to as “knees in the curve.”

20

Best Design for W=550 Pounds

Best Design for W=550 Pounds

550 lbs

550 lbs

542 lbs

542 lbs

Weight

Weight

21.8 lbs

21.8 lbs

19.3 lbs

19.3 lbs

Drag

Drag

8002.5 W

8002.5 W

7879 W

7879 W

Power

Power

8.96 ft

8.96 ft

8 ft

8 ft

Chord

Chord

16 ft

16 ft

18.8 ft

18.8 ft

Tip b

Tip b

14.9 ft

14.9 ft

18.9 ft

18.9 ft

Mid b

Mid b

13.3 ft

13.3 ft

11 ft

11 ft

Center b

Center b

Optimized

Optimized

Pathfinder

Pathfinder

21

References

References

• Curtin, Bob and Kirk Curtin, Bob and Kirk FlittieFlittie. . ““Pathfinder SolarPathfinder Solar--Powered Aircraft Flight Performance.Powered Aircraft Flight Performance.”” AIAA, AIAA, 1998.

1998. •

• Noll, Thomas E, et al. Noll, Thomas E, et al. ““Investigation of the Helios Prototype Aircraft Mishap.Investigation of the Helios Prototype Aircraft Mishap.”” NASA, 2004.NASA, 2004. •

• LiebeckLiebeck, R. H. , R. H. ““Laminar Separation Bubbles And Airfoil Design at Low Reynolds NuLaminar Separation Bubbles And Airfoil Design at Low Reynolds Numbers.mbers.”” AIAA, 1992.

AIAA, 1992. •

• SolarSolar--Powered Research and Dryden Fact Sheet, avail. at NASA DFRC websPowered Research and Dryden Fact Sheet, avail. at NASA DFRC website:ite: http://www.nasa.gov/centers/dryden/news/FactSheets/FS

http://www.nasa.gov/centers/dryden/news/FactSheets/FS--054054--DFRC.htmlDFRC.html •

• NASA Dryden Photo Gallery, avail at NASA DFRC website:NASA Dryden Photo Gallery, avail at NASA DFRC website: http://www.dfrc.nasa.gov/gallery/index.html

http://www.dfrc.nasa.gov/gallery/index.html •

• UIUC Airfoil Coordinates Database, avail. at UIUC website:UIUC Airfoil Coordinates Database, avail. at UIUC website: http://www.ae.uiuc.edu/m

http://www.ae.uiuc.edu/m--selig/ads/coord_database.htmlselig/ads/coord_database.html •

• The Incomplete Guide to Airfoil Usage, avail. at UIUC website:The Incomplete Guide to Airfoil Usage, avail. at UIUC website: http://www.ae.uiuc.edu/m

http://www.ae.uiuc.edu/m--selig/ads/aircraft.htmlselig/ads/aircraft.html •

• XfoilXfoil Source and Materials:Source and Materials: http://raphael.mit.edu/xfoil/ http://raphael.mit.edu/xfoil/ •

• AVL Source and Materials:AVL Source and Materials:

http://web.mit.edu/drela/Public/web/avl/ http://web.mit.edu/drela/Public/web/avl/ •

• MATLAB, courtesy MATLAB, courtesy MathWorksMathWorks •

22

T/W and P/W

T/W and P/W

supporting calculations

supporting calculations

P

= (6)(1.5hp) = 9hp

∗

= 4950f tlb/s

T

=

P/V

=

= 52.66lb

T /W

=

= 0.096

P/W

= (9hp)(832W/hp)/550lb

= 13.6 Watts/lb