- Jul 29, 2005
- Orange County, California
Do understand that I didn't mean any kind of offense. Of course you're learning. I'm an amateur designer just like you, and good lord knows that I'm still a raw newbie in many areas, particularly structures. I'm sure that Orion, experienced professional that he is, would say that he's learning new things every day. This is a simply huge endeavor, designing an airplane and doing it in such a way that there's some assurance that it will fly safe and well, and will hold together when flown as it's expected to be flown. I don't speak for anyone else here (although I know that they probably feel the same) that if we're expressing concerns is simply because you're one of our little family here, and we want to see you succeed and be safe. I suppose my comments do fall under the heading of criticism, but they're intended to be constructive criticism - I really like your design and I very much hope to see it in the air!Hello Topaz...
...Chances are good that you may be right. With my limited knowlege and experience it may be 57 steps missed, but, I'm doing the best that I can with what I have and, I'm not designing the new and improved shuttle. I do however understand that either one can kill you if done incorrectly so I am proceeding with intended speed and caution....
I've been around here for about three years now, off and on, and in my own case and in many others that I've seen, questions and design issues usually follow a fairly 'common' progression when a new person comes along wanting (seriously) to design their own airplane. It's also pretty common, as Orion has alluded, to see someone get frustrated with the volume and pace (and iterative nature) of the work, and start to convince themselves that they don't need to really do this or that part of the process, so that they can just "get it done!" In the course of the posts that I've seen you make here, there were some holes in the 'usual process'. And based upon some of the questions you've asked here and privately, it suggests that you're at (or should be at) a certain point in the overall design process. To then hear you talk about a step much farther along in the process raises a little red flag - "Why is he talking about that already? It doesn't seem like he's done 'X' yet." It's not that you're deficient in some way, it's just that it seems from the information at hand like you should be "here", but you're already talking about being "there" in the process of designing your airplane. Part of that information at hand is simply some of the questions you've been asking - about things that should already be 'nailed down' before you can do a real loads analysis, for example.
The process is long and it's sometimes frustrating, especially for people new to it. As you said, sometimes a change at Step 3 means you do have to go all the way back to Step 1 and start parts of the work over. Part of that is a function of the relative inexperience of guys like you or me. Orion or some other professional engineer has already done that sort of thing so many times that they've developed the experience to know how to "get it largely right" earlier in the process and not have to "go back" so many times - and yet I'd be willing to bet that some level of iteration like this is simply a part of the design process at any level of experience. Good, flexible design tools are probably critical for making the iteration process as pain-free as possible. And it also explains why "conventional" designs are so prevalent in the world - there are a lot more "rule of thumb" guidelines to at least get the design in the ballpark, so that the real analysis proceeds more smoothly.
Don't be discouraged! One of the most difficult things about learning to design an airplane, from my own experience, is that there are few learning tools that can show you simply the steps in the process - "Where do I start, and how do I get from Point A to Point B?" Raymer comes the closest yet that I've seen, and even he is hindered by the broad nature of the process. I fervently wish, since I'm studying it now, that someone would do something similar for structural work. Bruhn, thorough as it is, is a classic college text - long on theory and very, very short on process. That may be more appropriate for structures. I don't know enough to make a judgement on the subject yet.
You're doing a great job, and just need to go back and fill in some of the details before you move on to the more advanced stuff. My personal suggestion is that you go back to either of Raymer's books (and especially the larger one, if you're willing), and do for your airplane the type of conceptual work that you see for the 'homebuilt' (aerobatic) example at the back of Aircraft Design, A Conceptual Approach. To my mind, that sort of basic work on stability and control, performance, and weights has to be completed in its entirety before you move on to loads work. Otherwise, there will be so many iterative 'loops' as you finally do fill in the 'early' numbers, that it will become incredibly frustrating.