Other Requirements, Specifications, and Restrictions Handling Qualities I am a low-time pilot. As such, I want to make sure that the airplane isn't more than I can handle. I've already made sure the stall speed is low. When I need values for things like tail volumes, etc., and other specifications that define stability and handling qualities, I'll use values from trainers and basic aircraft such as the C-152, PA-38, and C-172. In any event, measurable handling characteristics should always meet or exceed CS-22 minimums. Trailerability This has been a tough question to answer in any kind of rational way. Hangars are insanely expensive to rent in southern California. You could rent an apartment for less in many cases. Tie-down rentals are very high and their price constantly fluctuates with demand, making any analysis obsolete almost as soon as it's completed. I'd certainly like to save the monthly expense of a hangar or tie-down. On the other hand, making the aircraft trailerable adds weight and cost to a design where weight and cost are already going to be at a premium. After vacillating back and forth over this for a couple of days, and re-reading the various related threads on HBA, I've decided to simply punt the final decision down the road into the design phase. I'll set trailerability as a goal, but it's not a threshold requirement. If everything else about the airplane meets my requirements but making it trailerable pushes it out of the cost threshold, I'll allow that requirement to fail and do the airplane without the ability to regularly trailer it. I'll just have to figure out where and how to store it affordably at that time. This means "trailerability" becomes another trade-study for the program. The storage space for the airplane would be my garage, shown in Figure 1 below. Requirements related to Trailerability If the aircraft ends up being trailerable, it imposes a few requirements on the project: . Maximum Legal Road Width - California 8 feetMaximum Legal Road Length - California 40 feetTrailer Required - California The aircraft may not be trailered on its own landing gear.Garage Door Opening Width (Physical Limitation) 8 feetMaximum one-person assembly or disassembly time Fifteen Minutes. Build Space Restrictions My baseline build-space is my one-car garage. The rules of my condominium association require that the garage be used to park a car at all times, and are enforced by a parking permit system. Temporary parking passes can be obtained for short-term outside storage or for visitors. So my build will need to share the garage with one vehicle most of the time. The smaller of my two vehicles is my '73 Porsche 914, which I want to store indoors anyway (they tend to rust). The layout of the garage is shown in Figure 1 below. There is a non-removable shelf at the back of the garage, and a structural beam crossing the ceiling. The automatic garage door opener has been removed since I prepared this drawing several years ago. Figure 1 - My Garage The green area denotes wing storage, blue for fuselage. These can be reversed if need be. My preference is to store the fuselage high in the blue volume, allowing space for my work table below. If the wing chord is short enough, it may be better to store the wings over the work table instead. Pulling out my tape measure, I get the following workspace dimensions: . Maximum Part Length (These values include clearances - actual garage maximum dimensions are approximately 1' longer) 19 feet maximum (object extends under or over the back shelf) 17 feet easy and practical work and storage (front edge of the shelf to the door). Regular Work Table Size The work table will run along the left wall of the garage, looking in. The garage door spring occupies about the first foot of the available length. Length: 16 feet long Width: 3 feet wide. Tool Noise I have an unusual restriction for my build. My garage is underneath an occupied condominium unit - and it's not my own. The ceiling of my garage is the floor of their unit. Also, there are other units directly across the garage access road from my garage, approximately 25 feet away. My complex has specific rules against the use of power tools in the garage spaces, not to mention that I like my neighbors and don't want to annoy them with a lot of noise. Unhappy neighbors leads to complaints to the Association, which ultimately leads to my build effectively being shut down. Yes, the Association has the power to do that. There are no rental shops available in the area, and driving any significant distance means I won't be out building as often. All that said, I have no intention of strictly adhering to the rules on this subject. You can't build an airplane effectively without any power tools at all. You could do it, but going all 18th century would needlessly extend the build. Fortunately, I have some options: . I work for myself, so I have some flexibility to adjust my work hours when my workload permits. Unless I need to work with freelancers, have a particularly large project on tight deadline, a client meeting, or need to devote time to date-driven marketing, sales, or admin tasks for my own business, I can often go in to work early and then close the shop early, giving me a couple of hours a day for the build before my neighbors come home from work. On hot summer days, I can sometimes take those couple of hours in the morning after they've gone to work. Depending upon the materials I choose for the build, I can also work in the evenings. I just need to control the noise I produce, mostly as a consequence of the tools the material requires. There will be some pieces that are just going to be noisy to build but, to an extent, I can also schedule "noisy" work for the daytime work sessions, and "quiet" work for evening or weekend sessions. I'm making the acquaintance of my neighbors,and especially the ones that will be most affected by my build noise. I've done some small projects in my garage using the same time patterns I intend to use for the airplane, and asked those neighbors if I was making too much noise. So far, everyone has been very gracious and said that it hasn't been a problem. They've noted the noise occasionally, but so long as it's not more frequent or louder, they've said they have no complaint. Mostly they just seemed happy that I asked. I've stressed that if my shop work ever does become annoying, to please let me know directly as soon as possible and that I'd do what I could to make it right for them. Much better to have them complain to me than the Association! I think it's really important to be kind to your neighbors in a project like this. . To a certain extent then, choosing a construction material that requires less use of power tools, and designing the airplane to minimize the need, gives me more opportunities to work on the airplane on evenings or weekends. This gives me more available working hours during a given week without risking a complaint to the association about noise. That's a big plus. So I'm going to add this subjective goal for the project: The airplane should require a minimum of noisy power tools for its construction. Technology Availability In Aircraft Design: A Conceptual Approach, Dan Raymer talks quite a bit about looking at the level of technology that will be introduced into the aircraft design, particularly where it concerns technologies that will need to be developed for the design. While this usually isn’t much of a concern for homebuilt designs, it does come up sometimes. When Rutan decided to adapt the German akaflieg’s foam-and-glass technology to then-modern American homebuilding, that was a technological risk in terms of having to develop that technology for the purpose he had in mind. For this airplane, I want to minimize the amount of technology development I’ll need to perform. There are four areas where I am willing to explore adapting or developing new technology for this aircraft. In all other ways, I’ll use existing technologies that have already been demonstrated in other aircraft. . Engines: If it should prove possible to develop this airplane for the crop of industrial motors with which people have been tinkering for airplane application, I’m willing to explore that provided it can be shown to result in a significant cost savings for this one-off aircraft. Using a dedicated aircraft engine (certified or experimental) may result in savings compared to adapting an industrial motor, or the reverse may be true. This will be a design study for the project. . Throttle and Air Brake Controls: I would very much like to try out my combined throttle/drag-brake “quadrant” control system on this airplane. . Landing Gear Retraction: I have an idea for a low-cost and simple landing gear retraction system that may be applicable here. I’d like to try that out if possible. . Commercial tablet-based flight display: This may end up being a commercial system that I purchase outright, if one can be found for a reasonable price. Otherwise, I would like to experiment with a low-cost primary flight display hosted on a commercial Android OS tablet. This does not have to be installed in the airplane for first flight, but rather can be a developmental item for after the aircraft is done with its flight-test period. . Safety and Crashworthiness Airplanes crash. That’s reality. People are injured and sometimes die as a result. To ignore that fact is foolish. I’ve lost two friends to airplane crashes. To become obsessed with it results in an airplane that’s very likely to be heavily compromised in every other area. I’m going to say two things about safety: . I’m also not up to re-inventing the wheel when it comes to developing safety standards that are a reasonable balance between safety and inflicting too much of a performance penalty on the aircraft. Wherever practical, the airplane will try to satisfy the safety requirements in CS-22 for single-seat powered sailplanes. SVSUSteve, wherever you are, you had an effect on me. And watching my friend Bill crash in front of me and sustain injuries that killed him later that day had an effect on me. Losing Woody just a few weeks later to another crash had an effect on me. Regardless of the overall method of construction, I would like this aircraft to have a welded steel-tube safety cage, unless I can be sure of meeting the CS-22 standards without one. The cage can be part of the primary structure, if need be to save weight. Total Project Cost I've made the choice that this will be an "inexpensive" airplane. What does that mean? I've pointed out before that it's impossible to state what "inexpensive" means without saying what kind of airplane will be built. In this case, I'm defining the airplane very tightly with this set of specifications and requirements. What's "inexpensive" in this context? And what's "inexpensive" to me in this context, given that this is a one-off airplane for my own use? It's really easy to overthink this. I could run all sorts of financial analyses, but I already know how much money I'd be willing to spend upon this airplane before it just makes more sense to shelve this project and focus upon the two-seater. I know, roughly, how much that latter airplane will cost and if this one costs more than a substantially large fraction of one that can carry two people, there's little point to me in "settling" for just one seat and substantially less cross-country capability. I'm also not taking market considerations into account here at all, since this airplane is just for me. If I develop a "production" version later, I'll worry about the business plan and economic viability of the airplane as a product at that time. What does deserve some consideration is what's included in the prices I'm about to set. Do I only include the airplane itself; just everything that leaves the ground? The airplane plus the trailer, since a trailerable aircraft isn't much good without a trailer? All of this plus the tools needed to build the airplane? Here's my thinking: Pretty much every tool I might buy to build this airplane is good for other purposes, be it building another airplane or another project of some kind. The tools aren't single use. I also already own quite a few of them. That money is already spent. So I'm not going to include them in the total. Same goes for work tables and suchlike. I am going to include the cost of the trailer, however. Since I've decided that this will be a trailerable airplane, a trailer is necessary to its use. It'll be important for me to make sure the trailer is as inexpensive as possible while being adequate to the task, since every dollar is taken from what's available to build the airplane itself. Another issue is that of new versus "scrounged" parts. Scrounging or buying "used" can result in very significant savings, of course. But it's not reliable. You can't depend upon the parts being available when you need them with any reasonable level of assurance. So my price estimates resulting from this study will reflect all parts and materials being purchased from regular retailers. Things like remanufactured instruments, such as those sold by Aircraft Spruce, are fine, since they're coming through a national retailer who stocks them as regular inventory. If I do decide to build this airplane, of course I'll try to find deals on some parts, but for planning purposes I'm going to assume that I have to buy everything retail. So after a little soul-searching and without further to-do, here are my threshold and goal project costs for the airplane and trailer together. Costs of tools is not included. Goal: $5,000 Threshold: $8,500 Yes, those are challenging numbers, and cost of building an airplane is one of the most controversial subjects ever discussed on HBA. Before anyone jumps in on how "realistic" these values might be, I'll remind you that determining whether or not the airplane I've defined in these specifications can be built for these kind of prices is the entire point of this design study. I'm not much interested in opinions about whether or not it can be done - I'm going to find out. If you think that building this airplane and a trailer for it is impossible for these prices, you may well be right! Or you're not. We'll find out at the end, and I personally think it's entirely worth my own time to go through this study to find the answer. So, now, after all of these posts above, I think I'm done defining the specifications and requirements for this design. I'm going to spend a couple of days reviewing my work and making sure that there's nothing else I need to pin down. I'm open to suggestions if someone can see that I've missed something important. Once I think I'm done here, I'll post a final requirements and specifications document. And then the actual design process begins.