Click here to upgrade to a newer version of Internet Explorer or Microsoft Edge.
Building a Tube and Fabric Airplane Part 1
By Ron Alexander (originally published in EAA Sport Aviation, July 1997)
Building an airplane is a challenging task. The decision should be made only after you have determined what is required financially, emotionally, and physically. It is impossible to completely understand what lies ahead but you can acquire enough information to have a good concept. Thousands of people have successfully built an airplane and any one of them can provide you with the facts pertaining to the building process. Many people want to acquire and fly an airplane as quickly as possible. If you are in that group you may want to consider buying an airplane thus eliminating the time involved in building your own. However, if you want a rewarding and satisfying experience, I recommend you choose the airplane you want and begin the building process. You will find a large fraternity of builders ready to assist you in any way possible. It is noteworthy that there is a growing number of individuals who simply want to build an aircraft solely for the experience. You may be in that category. Regardless, make sure you become involved with your local EAA chapter. Chapter members will assist you in deciding what type of airplane to build and they will provide necessary encouragement and support.
Once the decision to build has been made, the next step is to determine what type of airplane you desire. There are over 500 choices available. You can build an aircraft from a set of plans or you can purchase a kit to assemble. You can build anything from an ultralight to a high performance cross-country airplane. The choices are unlimited. First of all, I will discuss a few of the general factors involved in this decision and then I will explain the specifics concerning building a tube and fabric airplane. Other types of construction will follow in subsequent articles.
Many elements are involved in deciding what type of airplane to build. Some of these include the purpose for which you will use the airplane, your flying skills, building skills, history of the airplane, type of construction, finances needed, time required, ease of construction, technical support, etc.. I will discuss them individually recognizing there are many more that could be listed. First of all, what are you going to do with the airplane? Specifically, decide whether you want to fly cross-country, do acrobatics, or simply do pleasure flying. Will it be used to fly out of sod strips or a paved runway? Will the airplane serve your purposes when it has been completed? Consider your flying skills. Are you selecting an aircraft design that requires more flying experience than you currently have logged? Be careful not to choose an airplane that you will not be comfortable flying. To do so will certainly sentence your airplane to be a hangar queen because you will be afraid to fly it. Next, assess your own building skills. If you have experience with welding you might want to choose a tube and fabric airplane. If you have no building skills to assess you will need to be willing to acquire the ones that are necessary.
One of the most important considerations is the history of the airplane. Individuals who have successfully built an aircraft are the people to question. They can tell you how much builder support they received from the manufacturer, the completeness of the manual and/or plans, how the aircraft handles, how much money was spent, how much time it took, etc. In short, the information received from the successful builder is invaluable in assisting you with your decision. The next element is the type of construction. Basically, the following types are available: (1) tube and fabric, (2) composite, (3) sheet metal, and (4) wood. Usually a combination of these is found in the majority of airplanes. Most amateur-built aircraft contain tubing, aluminum, and wood. When choosing the type of construction think about what you enjoy doing along with the finished product you desire.
Estimating the total cost of the airplane prior to beginning is very important. Remember, if you purchase a kit the kit price does not include the cost of shipping the kit, cost of tools, workshop, engine, propeller, etc.. Time is also a major factor. The actual time listed by the kit manufacturer or designer is often optimistic. It usually does not include preparation to begin work, correcting mistakes, travel time to a workshop, etc.. As a rule of thumb, an airplane will take between 1,000 and 4,000 hours to complete. Obviously, a kit aircraft will not take as much time as a plans built aircraft.
With this general information in mind, lets get down to the basics involved in building a tube and fabric airplane. When you have decided to build a tube and fabric airplane, there are 6 primary steps involved in the building process. These steps are as follows:
• Decision and Planning
• Basic building
• Preliminary assembly, rigging, and systems installation
• Disassembly, covering and painting
• Reassembly, final rigging and final systems installation
• Inspection, certification, and final pre-flight
Most building tasks that you will perform will be in one of these categories. If you will spend a large block of time in step number 1 (Decision and Planning), the entire project will move very smoothly.
Decision and Planning
Of course you first must decide the model of airplane you will build. There are many factors involved in this decision several of which are listed above. I will not spend time comparing tube and fabric airplane choices. After choosing the airplane of your dreams, you must prepare yourself for the beginning stages of construction. First of all, prepare a workshop space. Ideally, you should have a space at least the size of a two-car garage. I recommend a workshop at home rather than at another location. The reason - you will spend more time working on the project if it is convenient plus you can more easily involve your family. If you locate away from your home try to make the workshop space as comfortable as possible. You will spend a lot of time there and you also want it to be comfortable for your family. If you have purchased a kit aircraft, one of your first problems will be transporting the kit and then removing it from the trailer into your workshop. Think about this step before the kit arrives.
Your workshop should contain a worktable where component parts can be assembled in addition to a workbench. Keep in mind ventilation needs, electrical requirements, lighting, heating, etc. Fumes will more than likely be a problem when the fabric covering process begins. Consider this problem before you begin. You should also plan where you will store tubing, fabric, and the flammable materials for fabric covering. Tool storage must be considered along with storage of completed component parts.
The tools necessary for a tube and fabric airplane will depend upon whether you are building a plans-built airplane or a kit airplane. If you are building from a set of plans you will need welding equipment. I recommend gas welding. The equipment you will need will cost about $300-$400 to get started. You can rent the oxygen and acetylene bottles from a local vendor. If possible, try the torch you would like before purchasing. Evaluate the different designs based on cost, weight, warranty, performance, and flame patterns. You will need a good set of welding goggles. Do not try to save money on safety, get a quality set. Gloves and a leather apron are also recommended. You will want an air compressor capable of at least 125 psi. The size of the air tank is as important as the size of the motor. Concerning the basic tools needed, those found in most home workshops will usually be sufficient with a few additions. A drill press and a bench grinder are helpful. I will discuss spraying equipment and fabric covering tools in the fabric covering section. Several other tools are nice to have with the bottom line being "you can never have too many tools." Keep in mind you can often rent expensive tools from a local source.
Do not forget to prepare yourself for the beginning day. You can do this by thoroughly studying your plans or assembly manual. Kit manufacturers tell me that if builders would simply review their manual before beginning construction, a large number of problems would be avoided. You should also purchase a AC43-13 to use as a reference along with a number of other manuals and books you will find useful. If you do not know how to weld you must learn the skill. The EAA/SportAir workshops are an excellent source for learning and practicing this skill. Fabric covering workshops are also presented. It is important that you gain the technical knowledge necessary to build an airplane as early as possible in the building process. Failure to do so will surely result in a lack of confidence that will translate into a work stoppage on the project. You will be astonished at how easy several of these skills are if you have received the proper training. Of course, there are many good books and videos available to assist. The two major skills involved in a tube and fabric airplane are welding and fabric covering. Even if you purchase a <kit aircraft> you will want to have enough welding knowledge to be able to check the existing welds on your airplane.
Now that we have prepared our workspace and ourselves for the task at hand we are ready to begin the actual building of component parts. Remember to establish a relationship with a DAR (Designated Airworthiness Representative) or an FAA inspector at this point. Also find an EAA Technical Counselor who will assist you throughout the entire project. Remember to follow the certification checklist presented in the May issue of Sport Aviation.
Prior to beginning our project we should be aware of the safety aspects involved in building a tube and fabric airplane. First of all, I will begin with welding. Of course one of the most important safety factors involved with welding is eye protection. Looking at a welding flame can permanently damage your eyes. Good quality goggles are an absolute necessity. With goggles, go to the darkest shade possible. Eye protection under the goggles is a good idea as added assurance sparks will not reach your eyes. Wear proper clothing. Synthetic fabrics will often burn from a stray spark. Wear blue jeans and invest in a good leather apron. Be sure to keep safety caps on all tanks. A broken valve on a high-pressure tank will make the tank into a rocket. The tanks should be secured before removing the safety caps. Have a fire extinguisher readily available and DO NOT weld near flammable materials. The chemicals used in fabric covering are flammable. Keep them away from your welding area.
Other safety factors include safety glasses for eye protection when you are drilling, etc. Ear plugs may be necessary for some tasks. Generally, common sense prevails concerning safety items within your workshop. When discussing fabric covering however, there are very definite safety problems. The first problem is with skin contact from the chemicals. Protect your skin from these chemicals by wearing long sleeve shirts and long pants. A Tyvek spraying suit is recommended when you begin spraying. Protect your hands using one of the barrier hand creams. In addition to the hand cream, you should use disposable latex surgical gloves. They are cheap and you can don new ones whenever the solvents begin attacking the ones you are wearing. Of utmost importance with fabric covering is to protect your lungs. A quality charcoal filtered respirator is a must. Do not rely on dust masks. They are ineffective in protecting your lungs. If you are using a polyurethane paint or covering system, it is imperative that you purchase a forced air system that presents a fresh air source. Polyurethane paints contain polyisocyanides as in CYANIDE. Breathing the spray mist from these paints can result in severe sickness or even death. Do not take a chance. A charcoal-filtered respirator is not adequate for polyurethanes. One other caution, when you are mixing and pouring chemicals be sure to wear eye protection and do not use an electric drill to mix paints. Don’t forget to have plenty of fire extinguishers in the shop.
Finally, we are ready to start building. Regardless of whether you are building from a set of plans or from a kit, start with a small piece such as a control surface or stabilizer. You will need some practice and if you ruin a part it is much less time consuming and less expensive to redo a control surface. Also, when a small part is complete it can be easily stored until assembly. Storing a completed fuselage consumes too much space. For this reason do the fuselage last. Be sure to have a good assortment of aircraft hardware in your shop. Several of the supply houses offer hardware kits for bolts, nuts, cotter pins, etc.. Try to have the hardware sorted and stored for easy retrieval.
Most tube and fabric airplanes use 4130 steel tubing. This tubing is the standard for aircraft use. It is a chromium-molybdenum tubing that is very strong and weldable. Steel tubing is defined by wall thickness and by the outside diameter (OD). These sizes are typically provided in thousandths of an inch. The length of the tubing is usually 18-22 feet and is cut to even lengths prior to shipping. The largest length that can be shipped via UPS is 8 feet. Anything longer than that will have to be shipped by truck. Store the tubing in a dry area to prevent corrosion. A cut-off saw will be very useful in cutting steel tubing and a tubing notcher is a tool you will want if you are building from a set of plans. The notcher will cut a very precise, measurable joint that will overlap another tube. Many ultralights and several <kit aircraft>s use aluminum tubing instead of steel tubing. Aluminum tubing is difficult to weld so rivets or bolts are used to attach the tubing.
It is essential that you protect the tubing, both internally and externally. On the fuselage I recommend you open the longerons at the forward end with a small hole and pour Tubeseal into the tubing. When welding diagonals, drill a hole in the longeron where the diagonal will be welded. This will allow the Tubeseal to flow into the diagonals. Rotate the fuselage to insure coverage throughout all of the tubes. Tubeseal is an internal tubing corrosion inhibitor. All steel tubing must be protected externally with an epoxy primer. Do not try to save money at this step. Use only an epoxy primer. Any other primer will be susceptible to penetration by the fabric covering chemicals that will ultimately result in corrosion. Remember to use your respirator when spraying. If you are purchasing a kit aircraft, I would advocate a powder coated fuselage. It will cost a little more but be well worth it in the long run.
The basic building phase usually requires a considerable amount of time. Be prepared to need some encouragement along the way. This can be provided by attending airshows, EAA Chapter meetings, and talking to other builders within your area. It is imperative that you involve your family. Failure to do so may pose an insurmountable obstacle to completion of the project. There are many ways to include your family in the basic building stage. As an example, you can have them assist in building the wings, assembling the parts, sorting hardware, etc.. You will find many times when you will need assistance. Your family can be a big help.
Be sure to have "in-process" inspections. These can be conducted by an EAA Technical counselor or by another builder. Do this throughout the entire building process and document each one in your builder’s log. Someone looking over your shoulder will often observe a problem area you have been overlooking for months.
Preliminary Assembly, Rigging, and Systems Installation
Upon completion of the component parts of the airplane, you now will want to assemble the aircraft prior to fabric covering. This should be done to check for all potential problems including incorrect attach points, control cable freedom, improper mating of parts, engine control movement, interference of control movements, etc.. It is important to check all of these areas and to correct them now before the fabric is in place. After the fabric is in place, it will be very difficult to correct problems without creating new issues. Totally assemble the airplane with all controls in place. You should rig the controls for proper travel and freedom. You only need to secure the control surfaces temporarily, as they will be removed for cover. You will want to attach the tail surfaces last so you do not have to walk around them while attaching the wings.
All electrical wiring should be completed. The fuel system should be in place along with any hydraulic lines. Wheels and brakes should be attached and tested. Avionic trays should be installed. Finally, all engine controls should be tested. You do not want to attach the engine at this time, however, you will want to insure all fuel lines, controls, etc. are attached and in place. In short, you will have the skeleton of the entire aircraft together with all controls operating. This phase of construction is very important. Take your time and look for potential areas of concern. It will be much easier to fix a problem now rather than waiting until the final assembly stage. This is an excellent time to have an "in-process" inspection. Try to have more than one experienced person examine the airplane in detail. This is the last chance you will have to correct problems without a major effort.