Description
Construction of Tubular Steel Fuselages is written to assist the average mechanic or aircraft builder to produce a tubular steel airframe that is as good as one from the factory.
The assembly methods in this manual are intended to produce a highly accurate fuselage in such a way that expansion and contraction occur symmetrically with no distortion.
The techniques given including those on jigging and alignment methods will also help in rapid prototyping where a high degree of accuracy is necessary without elaborate welding jigs.
This pdf ebook details the entire fuselage design and construction process in a practical way for the builder (not the engineer) including consideration for loads, evaluation and placement of fittings and joints, jigging, welding and other metal working techniques, tool use, and the actual step by step construction of top and bottom halves of a steel fuselage as well as the many sub assemblies common to every tubular aircraft fuselage type from J3 replicas to high performance aerobatic aircraft.
INTRODUCTION
The intent of this book is to help the average motorhead produce a tubular steel airframe that is about as good as one from a factory.
Most people can’t afford to buy an Extra, Pitts Special, or a winning Formula 1 mount.
Effort in construction (and some good materials) are about the only difference between a Ferrari and a mass produced sports car.
The assembly methods given in this manual are intended to produce a highly accurate and symmetrical fuselage by jigging in such a way that expansion and contraction occur symmetrically with no distortion. The techniques given in this book may also help in rapid prototyping where a high degree of accuracy is necessary without elaborate welding jigs.
There is much information here for the casual builder, as the jigging and alignment methods given in this manual may be taken to degrees to fit the situation. I’ve found that some bit of information from a book that saves a days work or even less, was worth the cost of the book.
This book is directed at anyone who would consider building a fuselage like this and so provides some information that experienced builders are already familiar with, like aircraft drawings. It may be found though that there are bits of useful information embedded in paragraphs on old subjects. It is suggested that the manual be skimmed over in its entirety before beginning, and a plan formulated for the construction of a particular type of fuselage.
Why a tubular steel fuselage? They are easy to build and all the performance aircraft are built like that. You’re probably building an aircraft this way because you want to pull G’s and go really fast with a minimum amount of cash (or it’s a historic reproduction). Have you seen any heavy duty aluminum sheet metal aerobatic mounts? Try attaching all the little sub-assemblies that an airplane needs to an aluminum or wood airframe, in such a way that it is not going to bend or break at 8 G’s. With a tubular steel fuselage, you just weld it on and it won’t come off with a hammer. It does mean you’ll have to learn to weld if you can’t already, but it’s not difficult and practice makes perfect.
Not to put down other forms of construction, they each have their advantages. Wood is used for a lot of wings on aerobatic and racing aircraft and it’s easy to work with. There are some popular factory-built aerobatic airplanes with wood wings. High performance wings are easily done in wood because there is very little attached to them. Wood is so good in some regards that there are helicopters with wooden main rotor blades that do not have a life limit, compared to aluminum and composite blades which must be discarded after a certain number of flight hours.
There are a couple of books that are important if you plan to fabricate an aircraft. They don’t need to be read, just pull them out when you need some bit of information. The titles don’t do justice to the information they contain. They provide almost all the information you’ll need on aircraft materials, processes, and standards, and they are dirt cheap. They are published by the FAA and can be had from nearly any aviation book store:
– AC 65-9A, A & P Mechanics General Handbook,
– AC 65-12A, A & P Mechanics Powerplant Handbook,
– AC 65-15A, A & P Mechanics Airframe Handbook,
– AC 43.13-1B, Acceptable Methods, Techniques and Practices – Aircraft Inspection and Repair,
– AC 43.13-2A, Acceptable Methods, Techniques and Practices – Aircraft Alterations.
The last two books on the list are usually sold bound together as one. This manual occasionally will refer to one of those books. In addition, a series of books written by Tony Bingelis on homebuilt aircraft construction will provide many ideas and answers to constructiondetails. A list of other excellent books is given in the back of this manual. The manufacturers of welding equipment also provide some excellent information as many of the materials and processes used in aviation are the same used in other motor sports.
So having said all that, to be more precise, the intent of this manual is to aid the builder of tubular steel aircraft fuselages with:
– alternative methods of jigging and assembling that can result in a high degree of precision in the finished fuselage,
– techniques in welding to improve accuracy, productivity, and quality,
– methods of cutting the various members so as to minimize waste and frustration, as well as produce a higher quality product,
– the use of tools that will be helpful to the builder,
– the construction of inexpensive and fast-to-fabricate jigs,
– ideas for creating and/or modifying structures to accommodate aircraft systems and sub-assemblies.
The information provided throughout this book should make the building process more enjoyable for anyone by providing advance information on some of the subtleties and difficulties that are expected to be encountered.
A significant part of this book is dedicated to achieving a high degree of precision in the finished product. For the average builder who flies 150 KTS or less without much yanking and rolling, perfect symmetry in the airframe isn’t going to be a priority. Why is it a priority for the rest of us? Trim drag. Not the deflection of elevator trim. For every slight deviation from airframe symmetry, some control or surface has to be deflected some amount to allow the pilot to maintain the aircraft in a state of equilibrium for a given maneuver (trimmed). Anytime a surface is producing some lift it is producing drag. If the lift isn’t contributing directly to the maneuver at hand, it is taking away potential energy. This imperfect state also detracts from handling and response because some amount of control authority is being used to maintain equilibrium.
Table of Contents:
Chapter 1
Welded Fuselage Construction and Design – 1
Terminology for Tubular Steel Fuselages – 1
Longerons – 2
Member – 2
Crossmembers – 2
Cluster – 2
Tail Post – 2
Attach-Point or Boss – 2
Gusset – 2
Bay – 2
Axes – 2
Fuselage Geometry and Construction – 4
Intersections – 4
Flat Pattern Layout – 4
Order of Construction – 4
Upsweep – 5
Drawing Conventions – 6
Airframe Coordinates – 6
Drawing Scale – 8
Features – 9
Lines – 9
Cutting Planes – 9
Symbols – 9
Weld Symbols – 10
Dimensioning – 10
Weld Design – 12
Strength of Welded Joints – 12
Weldments under Stress – 13
Materials – 15
4130 Steel – 16
Surface Finish and Fatigue Strength – 20
Properties of Tubing – 20
Designing Parts – 21
Aircraft Loads – 21
Factors in Sizing a Piece – 22
Structural Lugs – 23
Chapter 2
Methods and Processes – 27
Working with Steel – 27
Working with Sheet Steel – 27
Working with Tubing – 27
Clamping Tubing – 33
Abrasives – 33
Welding – 34
Processes for Aircraft – 34
Welding 4130 Steel Structures – 35
Common Welded Joints on Aircraft Structures – 44
Repairing Misplaced, Elongated, or Worn Bolt Holes – 49
Non-Structural Attach Points – 50
Corrosion and Corrosion Removal – 52
Corrosion Prevention during Construction – 53
Internal Rust Prevention – 54
Cleaning and Painting – 54
Sandblasting/Beadblasting – 54
Cleaning – 55
Painting – 55
Metrology for Jigging – 56
Symmetric Distribution of Error – 56
Accumulation of Error or Tolerance Stack-Up – 56
Accuracy, Resolution, and Repeatability – 57
Chapter 3
Tools – 59
Levels – 59
Common Levels – 59
Machinist Level – 59
Checking a Level – 60
Blocks – 60
1-2-3 Blocks – 60
V Blocks – 60
Squares – 61
Combination Square – 61
Rulers – 62
Dial Caliper – 62
Protractors – 62
Trammel Bar – 63
Plum Bob – 63
Calipers – 63
Compass Set – 64
Angle Finder – 64
Layout Fluid – 64
Scribe – 65
Mechanical Pencil – 65
Permanent Markers – 65
Clamps – 65
90 Clamp – 66
Welding Vise – 66
Drill Rod – 66
Air Compressor – 66
Drill Press – 66
Drill Press Vise – 66
Parallels – 67
Center Drills – 67
Unibits – 68
Band Saw and Blades – 68
Die Grinder – 69
Cut-Off Wheel – 69
Rotary Burrs – 70
Dremel Tool – 70
Sand Blaster – 70
Tubing Notchers – 70
Milling Cutters – 71
Welding Table – 71
Pipe Strap – 71
Shim Stock – 72
Deburring Tools – 72
Reamers – 73
Bench Sander – 73
Bench Grinder – 73
Abrasive Cut-Off Saw – 74
Oxyacetylene Torch – 74
GTAW Equipment – 74
GTAW Torch – 75
GTAW Torch Nozzles – 75
Collets/Collet Bodies – 76
Tungsten Sharpener – 76
Amperage Control – 76
Auto-Darkening Helmet – 76
Welding Fingers – 76
Magnets – 77
Brushes – 77
Fuselage ‘Rotisserie’ – 77
Dehumidifier – 77
Chapter 4
Jig Tables – 79
Flat and Level – 79
Solid – 79
Size – 79
Materials – 79
Order of Construction – 80
Skirt – 80
Legs – 81
Top – 83
Finishing Up – 85
Chapter 5
Layout – 87
Drawing a Centerline – 87
Drawing the Top and Bottom – 87
Chapter 6
Constructing the Top and Bottom – 91
Blocking – 91
Shims – 91
Making the Longerons – 92
Constructing the Top – 93
Setting the Longerons – 93
Preparing for the Rudder Post – 94
Securing the Longerons – 95
Bilateral Symmetry of the Longerons – 96
Installing the Crossmembers – 97
Constructing the Bottom – 99
Chapter 7
Fitting the Top to the Bottom – 101
Hangers – 101
Preparing To Set the Bottom Side – 102
Preparing the Curved Bottom – 103
Preparing the Straight/Flat Bottom – 104
Establishing the Curved Bottom – 104
Establishing the Straight/Flat Bottom – 104
Installing the Hangers – 106
Firewall-Reference-Plate – 107
Setting the Top – 108
Establishing Centerlines – 108
Straightening and Aligning the Top Side Precisely – 110
Cutting and Fitting the Upright Crossmembers – 111
Cutting and Plugging the Longerons on the Firewall – 113
Finishing Up – 114
Chapter 8
Welding the Fuselage – 115
General Order of Welding the Joints – 115
Specific Order of Welding the Joints – 115
Longeron Straightening Caused by Welding – 116
Starting Welding – 117
Rejigging for Welding – 117
Fabricating and Installing the Engine Mount Pads – 118
Locating the Pads – 119
Finishing Welding – 120
The Rudder Post – 121
Chapter 9
Horizontal/Vertical Stabilizer and Control Surfaces – 123
Vertical Stabilizer – 123
Constructing the Vertical Stabilizer – 123
Attaching the Vertical Stabilizer – 124
Horizontal Stabilizer and Control Surfaces – 125
Chapter 10
Seats, Rollover Structures, and Harness Installations – 127
Seats – 127
Design Considerations – 127
Fuselage Attach Points – 128
Seat Designs – 129
Rollover Structures – 130
Design Considerations – 130
Planning a Rollover Structure – 131
Harness Installations – 133
Design Considerations – 133
Harness Geometry – 134
Fuselage Attach Points and Connections – 139
Appendix A
Attach-Points and Bosses – 145
Distortion – 145
Figuring Out In What Order to Do It – 145
When to Weld on Hinges – 146
Examples – 146
Appendix B
Useful Reference Material and Material Suppliers – 149
Useful Reference Material – 149
Material Suppliers – 150
Appendix C
Geometry – 151
Layout Tools – 151
To Find the Middle of Line AB and Draw a Line Perpendicular to It – 151
To Erect at Point A, a Line Perpendicular to Line AB – 151
To Find the Center of A Given Circle – 151
To Find the Exact Point of Tangency To An Arc or Circle From a Given Point A – 152
To Find the Center of Arc AB and Draw a Line through the Middle of It – 152
To Bisect any Angle, ABC – 152
To Draw an Angle Equal to another Angle ABC – 153
To Draw a Line Perpendicular to a Given Line, From a Given Point A – 153
Trigonometric Functions – 154
Definitions – 154
Solving Right Triangles – 155
Solving Oblique Triangles – 156
Appendix D
Recommendations for Welding of 4130 Steel – 157
GTAW – 157
Oxyacetylene – 158
