Thiokol Design Report

A&AE451 Aircraft Design Class

Fall 2000

Team DR2

Purdue University

School of Aeronautics and Astronautics

1282 Grissom Hall

West Lafayette, Indiana 47907-1282

Thiokol Design Report

A&AE451 Aircraft Design Class

Fall 2000

Team DR2

December 7, 2000

Code of Ethics

Taken from the Purdue University Handbook, Section II: Student Code of Honor:

“The purpose of the Purdue University academic community is to search for the truth and to endeavor to communicate with our fellowman. Self-discipline and a sense of social obligation within each individual are necessary for the fulfillment of these goals. It is the responsibility of all Purdue students to live by this code, not out of gear of the consequences of its violation, but out of self-respect.

As human beings we are obligated to conduct ourselves in accordance with moral law. As members of the civil community we have to conduct ourselves as responsible citizens in accordance with the rules and regulations governing all residents of the state of Indiana and of the local community. As members of the Purdue University community, we have the responsibly to observe all University regulations. As members of the academic community, our foremost interest should be toward our education and our foremost responsibility is to maintain academic honesty. A student who assists in any form of dishonesty is equally as guilty as the student who accepts such assistance.”

The members of Team DR2 subscribe to the above Code of Ethics and maintain that the information contained within this report is original unless otherwise referenced.

Team DR2

Mark Blanton Team Historian, Propulsion and Cost

Chris Curtis Construction Method and Structures

Loren GarrisonAerodynamics, Stability&Control, and Performance

Chris PetersTeam Leader, Aerodynamics, Stability&Control, and Performance

Jeff RodrianTeam Co-Leader, Construction Method, and Structures

Table of Contents

Section Page

Executive Summary...... 1
Request For Proposal...... 2
Design Objectives...... 2
Design Requirements...... 2
Concept Evaluation and Selection...... 4
Aircraft Description...... 5
Aerodynamics...... 7
Introduction...... 7
Two-Dimensional Aerodynamics...... 7
Three-Dimensional Aerodynamics...... 8
The Warner Three-Dimensional Lift Calculations for Biplanes...... 8
Computational Fluid Dynamics Analysis...... 9
Parameter Selection...... 10
Stability and Control and Dynamic Modeling...... 11
Introduction...... 11
Dynamic Model...... 11
The Dynamic Modeling Design Approach...... 12
Stability and Control...... 14
Static Margin, Neutral Point, and Center of Gravity...... 14
Horizontal Tail Sizing...... 14
Control Surface Sizing...... 14
Trimibility...... 15
Structure Design and Construction Method...... 16
Introduction...... 16
Weight, Center of Gravity Location, and Inertias...... 16
Design...... 16
Composite Wing Manufacturing...... 17
Propulsion and Power System...... 20
Introduction...... 20
Design Methodology...... 20
Component Selection...... 21
Economic Plan...... 23
Conclusion...... 24
References...... 25

Appendix

Contact Information
Concept Selection
Aerodynamics
Dynamic Modeling
Stability and Control
Structure Design and Construction Method
Propulsion and Power System
Economic Plan
Flight Test Results

List of Tables

Section Page

Executive Summary
Request For Proposal
Concept Evaluation and Selection
Weighted Objectives Criteria Selection and Design Aircraft Selection.....4
Aircraft Description
Brief Aircraft Description...... 5
Aerodynamics
Stability and Control and Dynamic Modeling
Stability Derivatives for Dutch Roll Approximation...... 13
Structure Design and Construction Method
Propulsion and Power System
Astroflight 640G Motor Characteristics...... 21
Master Airscrew Propeller Characteristics...... 21
Astroflight 204D Speed Controller Characteristics...... 22
Sanyo 3000SCR Battery Characteristics...... 22
Aircraft Endurance Time Calculation...... 22
Economic Plan
Total Cost of DR2...... 23
Conclusion
References

List of Figures

Section Page

Executive Summary
Request For Proposal
Sketch of Mission Profile...... 2
Concept Evaluation and Selection
Initial Design Concept...... 4
Aircraft Description
Aircraft 3-View...... 5
Initial Constraint Diagram...... 6
Aerodynamics
Stability and Control and Dynamic Modeling
Overall Aircraft Model...... 12
Structure Design and Construction Method
Fuselage Structure...... 16
Checking Upper Surface of Finished Mold...... 17
Checking Lower Surface of Finished Mold...... 17
Vacuum Bag Setup...... 18
Lower Skin, Outer Layer of Fiberglass As Foam Is Placed Into Mold.....18
Breather and Bleeder Cloth Applied to Lower Skin Mold...... 19
Final Vacuum Bag Setup for Wing Skins...... 20
Propulsion and Power System
Economic Plan
Conclusion
References

List of Symbols

AOCAngle of Climb

ARAspect Ratio

T/WThrust-to-Weight Ratio

buSpan of the Upper Wing Surface

blSpan of the Lower Wing Surface

CDCoefficient of Drag

CDoZero-lift Drag Coefficient

CLCoefficient of Lift

CGCenter of Gravity

DDrag

FSFlight Station

gAcceleration due to Gravity

G/bGap-to-Span Ratio

G/cGap-to-Chord Ratio

LLift

NPNeutral Point

qDynamic Pressure

rmaxMaximum Turning Radius

SrefReference Area

STOTakeoff Distance

SMStatic Margin

t/cThickness-to-Chord Ratio

VloiterLoiter Velocity

VstallStall Velocity

W/PPower Loading

Angle of Attack

Warner Biplane Parameter

Flight path angle

Dihedral

pPropulsion Efficiency

Taper Ratio

Sweep Angle

Induced Drag Factor

Viscosity

Air Density

Warner Biplane Parameter

Executive Summary

The objective for the Fall 2000 A&AE451 Aircraft Design Project was to design a small remotely piloted variable stability aircraft using feedback control. Feedback control is often employed to modify, or improve, the dynamic response of the aircraft in flight. Using a feedback sensor, in the yaw axis, an analytical prediction of the dynamic motion of the aircraft was made.

Several constraints, defined in the Request for Proposal, name the challenges that must be overcome. The design must be flown inside the Mollenkopf Athletic Center at the Purdue University campus. The aircraft’s propulsion system must be an electric motor for indoor use. The aircraft’s dimensions must also not be excessive as to be able to fly indoors. The aircraft must be robust to crash yet stable in all flight regimes, exemplifying exceptional flying qualities. The aircraft must also display a conventional takeoff and maintain powered flight for twelve minutes.

The design selected by Team DR2 is a bi-wing, tail-dragger aircraft design. The design incorporates and electric propulsion and power design, a small sized aircraft, as well as the use of advanced composites for the aircraft wing structures. The feedback control of the yaw axis is controlled by a rate gyro and servo. The system is easily transportable in a compact car and has an appealing design for both engineers and pilots. The versatility of this design allows for easy internal modifications as well as displaying advanced composite construction, which will appeal to the customer.

This variable stability aircraft will be marketed to existing companies who sell and manufacture model aircraft. The aircraft will also be made available, as a teaching aid, to courses at the university level, especially Purdue University.

Completion of flight tests revealed that the remote controlled aircraft flew for nine minutes and eight seconds and demonstrated exceptional flying qualities. The aircraft demonstrated these qualities, both with and without the feedback gain implemented, indoors and outdoors. The robust aircraft design met the strength and crash test, withstanding heavy loads and rough landings. The overall evaluation of the aircraft design by Team DR2 and the pilots was an outstanding design.

2.Request For Proposal

2.1.Design Objectives

The reusable design vehicle must loiter for at least 12 minutes within the Mollenkopf Athletic Facility. It must carry an easily accessible payload consisting of a gyroscope, gain control box, Tattletale 8 data logger in a shielded box, and an interface module. Feedback control will modify the dynamic response of the yaw axis during flight and have two feedback gains (off and nominal) that are selectable by the pilot during flight. The data logger must record in-flight the yaw rate and rudder deflection as well as the airspeed. This data will be compared to the analytical predictions made for the vehicle.

The vehicle will be propelled by a single electric motor running off a battery and must exhibit exceptional handling qualities because of the requirements for confined, indoor flight. It will, therefore, have a minimum of two axes flight control system.

2.2.Design Requirements

No disassembled aircraft component will exceed 6.0 feet in length so that the aircraft can be transported in a compact car. For safe indoor flight operations, a margin of 30 feet from each wall will be maintained throughout the airborne part of the mission. Two missions must be achievable within the Mollenkopf Athletic Facility. The first is an abort mission in which the aircraft must land if an altitude of 6.0 feet is not attained by the time the aircraft is 212.0 feet from the take-off wall as shown in Figure 2.1. The abort mission consists of a take-off, short climb to ‘abort-height’, landing and full stop safely using less than the length of Mollenkopf.

Figure 2.1: Sketch of Mission Profile

The second, primary mission’s goal is to loiter for 12.0 minutes after a rolling take-off and climb. The aircraft maximum stall speed was chosen at 20.0 feet per second based on previous A&AE 451 and UAV designs, which had stall speeds ranging from 9.0 to 22.0 feet per second. A low stall speed will be needed for good aircraft handling qualities inside Mollenkopf.

The minimum climb angle of the design vehicle was set at AOC = 5.5. The climb angle must be met to prevent the need for an aborted take-off due to insufficient altitude before the first turn. Vehicle altitude must remain between 6.0 feet and 30.0 feet during loiter. The minimum altitude was set at 6.0 feet to allow approximately 1.0 wingspan margin between the aircraft and the ground. The maximum loitering height was set at 30.0 feet to allow 12.0 feet separation from the lowest obstacle within Mollenkopf.

The turn rate was calculated based on making a 180+ degree continuous turn with a radius of 50 feet (66% of the maximum turn radius) and a loiter speed of 22 feet per second.

Figure 2.1 details the primary mission flight profile. The aircraft launches 30.0 feet from the south wall and must lift off in less than 120 feet. The aircraft will then climb at an angle greater than 5.5 until it at least reaches the minimum cruise altitude of 6.0 feet. It will then turn and begin a loitering circuit around Mollenkopf. During this 12-minute loiter, the pilot will be required to remotely switch the feedback control gain to increase the stability of the vehicle. The loiter speed must be greater than 1.2Vstall and provide 10 seconds of straight and level flight. After the 12 minute loiter phase, the aircraft will safely descend, land, and come to a complete stop within the length of Mollenkopf.

Structural considerations set the limit load factor at 2.5 and net safety factor at 1.5, subsequently the ultimate load factor for the aircraft is 3.75 (safety factor  limit load factor). Impact loads during a crash should not result in catastrophic failure of any portion of the vehicle.

3.Concept Evaluation and Selection

3.1.Concept Criteria and Weighted Objectives Selection

The weighted objectives method was used to determine which of three aircraft concepts shown in Figure 3.1 will be best suited to meet the mission requirements. These concepts from left to right are a traditional hi-wing aircraft, a biplane, and twin-boom design.

Figure 3.1: Initial Design Concepts

Concept evaluation began by team members brainstorming criteria that should be used to choose a design. These criteria listed below in Table 3.1 were then ranked using weighted values and the three lowest ranked criteria were dropped and the remaining criteria were re-ranked.

The next step was evaluating each of the three design concepts based on these aspects. Each group member voted on each concept rating the excellent to bad. A corresponding number was assigned to the quality and the numbers totaled for the concept. This vote was a group evaluation; hence the group vote was discussed if the values for the individual votes differed. These numbers were then multiplied by the whole number percentage to determine the number of votes that each concept earned. These votes can be seen in Table 3.1. Since the votes for the biplane and high wing concepts were close, a group discussion resolved the design concept using sound engineering judgment and desirability. The biplane concept was chosen based on these characteristics.

Criteria Evaluation / Concept Evaluation
Re-evaluated
Rank / Criteria / Votes / Percentage / Percentage / Biplane / High Wing / Twin Boom
1 / Turn rate / 71 / 14.2 / 16.7 / 5 / 0 / 0
2 / Ease of Analysis / 55 / 11.0 / 12.9 / -3 / 5 / 3
3 / Ease of Construction / 53 / 10.6 / 12.8 / 0 / 3 / -3
4 / Stability / 48 / 9.6 / 11.3 / 3 / 5 / 3
t-5 / Wing Length / 45 / 9.0 / 10.6 / 5 / 0 / 0
t-5 / Takeoff / 45 / 9.0 / 10.6 / 5 / 3 / 0
6 / Accessibility / 39 / 7.9 / 9.2 / 3 / 3 / 3
7 / Fuselage, Internal / 34 / 6.8 / 8.0 / 3 / 3 / 0
8 / Drag / 32 / 6.4 / 7.5 / 0 / 3 / 3
- / Ease of Assembly / 29 / 5.8 / Total Votes / 236.3 / 264.4 / 85.2
- / Simplicity / 24 / 4.8
- / Propulsion / 22 / 4.4

Table 3.1: Weighted Objectives Criteria Selection and Design Aircraft Selection

4.Aircraft Description

4.1.The System Configuration

The biplane concept, as shown in Figure 4.1 is a puller prop, tail-dragger, conventional tail, bi-wing design. Table 4.1 gives major attributes of the design aircraft. The fuselage is designed to hold all the required payload and flight instruments listed in the design mission specification. The aircraft fuselage and wings will be built using fiberglass and foam construction techniques. Selig S 1210 airfoils will be used on both untapered, unswept wings.

A three-axis flight control will be used in the biplane, hence four servos located in the wings, with two additional servos responsible for rudder and elevator control. For radio control, a single six channel receiver and receiver battery are needed. For this mission, a Tattletale 8 data recorder and one gyro, intended for yaw rate measurements, will be installed. An Astro 640G electric motor, powered by a 14-cell Nickel-Metal-Hydride (NiMH) battery, will be used to propel the biplane during the 12 minute flight. The propeller is a Master Airscrew 14-inch diameter and 10-degree pitch propeller.

Figure 4.1 Aircraft Three-View

Aerodynamics / Weight / Propulsion
Fuselage Length [ft] / 5.10 / Payload [oz] / 18.5 / Propeller / 14x10
Wing Span [ft] / 7.84 / Fixed [oz] / 59.57 / Motor Type / Astro 640G
Wing Chord [ft] / 0.97 / Fuselage [oz] / 37.08 / Cell Type / NiMH
Wing Area [ft^2] / 15.20 / Wing [oz] / 93.12 / Number Cells / 14
Aspect Ratio / 8.1 / Horizontal Tail [oz] / 4.00 / Horsepower / 0.94
Gap [in] / 8 / Vertical Tail [oz] / 3.50
Span Ratio / 1 / Misc. [oz] / 5.49 / Dynamics and Control
Stagger [in] / 0 / Total [lb] / 221.2488 / # Axes of Control / 3
Declage [in] / 0 / Feedback Axis / Yaw
Gear Type / Tail-dragger
Table 4.1: Brief Aircraft Description

4.2.Constraint Diagram

The wing loading (W/S) and power loading (W/P) for the aircraft design were chosen from the constraint diagram shown below in Figure 4.2. The initial weight estimate was made using historical data gathered from past AAE 451 designs (specifically the tow plane) and fixed weights such as the servos, the speed controller, the payload and the receiver. The initial weight estimate was 10.2 lbs gross takeoff weight. Below Equations 4.1 through 4.5 are the constraints used to determine the appropriate wing loading and power loading. Derivations of these constraints can be found in Appendix F.

Equation 4.1: Loiter VelocityEquation 4.2: Climb Angle Constraint

Equation 4.3: Sustained Turn Rate Constraint

Equation 4.4: Ground Roll ConstraintEquation 4.5: Stall Speed Constraint

Figure 4.2: Initial Constraint Diagram

The best design point from the constraint diagram will have both large W/P and W/S values. Large power loading will allow lighter, less powerful engines to be used and large wing loading will decrease the overall wing area and wing span of the aircraft. A conservative value of CLmax=1.1 was set for the stall speed constraint, thus the design point at W/S = 0.52 and W/P =0.173 was chosen. An insignificantly larger power loading value could have been attained, but it would have required a lesser wing loading.

Aerodynamics

5.1.Introduction

The objective of the aerodynamic analysis is to obtain an adequate lift and drag model for the DR2. Mission specific considerations are the main driver in the selection process of the airfoil, wing and empennage parameters, lift analysis and drag model. The results of the aerodynamic analysis are a crucial part in the analysis of stability and control, structures, and the dynamic modeling of the aircraft. The unique characteristics of the indoor mission calls for a rather unconventional approach to the aerodynamic analysis. The low Reynolds number flight regime, mission airspace, payload considerations, and exceptional flying qualities resulted in the selection of the biplane concept. Consequently a couple of biplane analytical methods are described and compared to determine an appropriate model for the DR2.

5.2.Two-Dimensional Aerodynamics

The first step in the aerodynamic analysis was to determine the Reynolds number range in which the aircraft would most likely fly. To determine this, the flight altitude, the range of cruise velocities and the approximate range of wing chords were determined. From these parameters, it was determined that the Reynolds number would range from 100,000 to 150,000. These values would later be used in determining an airfoil section for the main wing.

The two-dimensional analysis began by compiling a database of airfoils. The airfoils in this database were selected from the NASG website (Reference 12). The data from this website was primarly compiled from experimental data collected by Michael Selig at the University of Illinois at Urbana-Champaign. Since the NASG website contained over a thousand airfoils, only airfoils with a Clmax of more than 1.35 at the predicted takeoff Reynolds number (approximately 100,000) were chosen. This process yielded a database of about 30 airfoils; the lift curves and drag polars of these airfoils were then plotted for comparison, Appendix C Figures C-1.1, C-1.2. Two key characteristics of the airfoils were evaluated in this comparison process. First, a high Clmax was desired so that the aircraft could obtain stall speed requirement with a minimum wing area. Second, the airfoil should have a wide drag bucket with low overall drag to minimize the number of batteries required to meet the endurance requirement.