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All you home builders out there. Is there a good aircraft design software program that you can use to design and. Hold an aircraft before actually. Holding it. Looking for something that will enable me to con up with some basic plans and be able to do some checking on the structural load limits on the airframe.
Thanks
Keith
What you're describing is several different programs. CAD to design/model/draw your airplane, FEA for structural analysis, and an aerodynamics program to analyze its performance. CAD is approachable for the amateur, ranging from simple drafting programs to professional (and expensive) solid modeling systems. However, FEA is not something that an amateur will be able to get good results with (you need a thorough ground in structural analysis to set it up and interpret the results), and the available aero packages like AirplanePDQ, while useful for preliminary work, make many simplifying assumptions and thus are no substitute for a proper aerodynamic analysis.
The way one of my professors put it to me: "If someone can't do the basic stress calculations by hand and needs a program to do it for them, they have no business even trying to read, let alone run a finite element analysis."Quote:
However, FEA is not something that an amateur will be able to get good results with (you need a thorough ground in structural analysis to set it up and interpret the results),
Likewise for structural analysis. This is one reason I try to keep an aerodynamicist and structures guy owing me a favor at all times. LOLQuote:
thus are no substitute for a proper aerodynamic analysis
To answer part of the question, I use the low end Autocad to make basic parts drawings, and I use Google Sketchup to do 3-D assembly drawings. Both have a learning curve, but since Sketchup is free, you can give it a try and see if you have an aptitude for that part of the design process. I have to say that since I started drawing assemblies in 3D, I really am hooked on being able to rotate and view all sides of an assembly.
If you are new to thinking about stress and strain for aircraft structures, I suggests starting simple. Martin Hollman has some books that will introduce you to that sort of stuff. Try Modern Aircraft Design for starters. If you get serious, will will need to find a college level statics text. Perhaps one of the other posters here can reccomend one.
Best of luck,
Wes
N78PS
I agree. Since mine is a tube frame I am using MathCad to run the calculations, but you still need to be able to run the calculations on paper to be able to do this. The advantage to MathCad is it gives me the ability to change input variables & quickly get results.Quote:
Originally Posted by steveinindy
I have done basic FEA in the past, but I don't know that I would want to attempt it now even with good software. There is a reason most of the guys getting paid to do it at major companies all have masters degrees in mechanical engineering.
You mean besides the fact that one has to be a bit masochistic to either enjoy FEA or to get a masters in ME? ;)Quote:
There is a reason most of the guys getting paid to do it at major companies all have masters degrees in mechanical engineering.
Gentlemen,
You are missing the point that homebuilding is educational. There is more to the educational component than learning to buck rivets and heat shrink fabric.
I will confess that sitting next to a fresh-out-of-college Mechanical Engineer at work was a great help in remembering the math when I needed it.
I will suggest that the math is not hard, just tedious. If I can do it and convince the FAA that I produce the right answers, anyone can do it.
And taking a swing at figuring this stuff out helps you appreciate guys like Burt Rutan who are up to their eye balls in it.
Best of luck,
Wes
N78PS
Agreed. The point we are trying to make is not that we shouldn't learn this stuff (if one is so inclined....personally, I'm more inclined to learn FEA than how to work with fabric because I have zero interest in rag aircraft) but just that one has to be damn sure they have done it correctly so looking for shortcuts or software to do it for you isn't a great idea if you don't understand the underpinnings. Even as reasonably knowledgeable about some things as I am, I still double check and sometimes triple or quadruple check my work and then run it by three or four other people who know more about the technique and/or subject matter than I do before finalizing it. My life and the lives of my passengers may well depend upon it.Quote:
You are missing the point that homebuilding is educational. There is more to the educational component than learning to buck rivets and heat shrink fabric.
Rutan freely admits that he hands (handed?) the really specialized stuff over to experts in those fields. That's why any of us have heard of John Roncz. ;)Quote:
And taking a swing at figuring this stuff out helps you appreciate guys like Burt Rutan who are up to their eye balls in it.
The math isn't hard, but if one doesn't have a good understanding of trig, vector mechanics, statics, mechanics of materials, etc it is pretty hard to know which formula to use. You need to know when to use Euler, when to use Johnson, or when to use something really obscure from Roark's book.
Guys thanks for all the great replies. I would love to build a replica of the Piper Skycycle but as piper drawings were never drafted I am
On my own to come up with the structure underneath the skin.
I'm thinking tube construction for the fuselage and tail feathers and aluminum for the wings.
Al I have to go on are some 3 view drawings. I'll get a copy of that book and start reading. After I get something drawn up maybe someone could take a look at them for me. We are talking a pretty light and slow aircraft. Less than 700-800 pounds and less than 100 mph cruise.
Thanks again
Keith.
....or when to break down and buy lunch for (or give a good bottle of wine to) someone from the local engineering department. LOLQuote:
Originally Posted by Mike Switzer
Yep. That combined with the equally masochistic tendency to enjoy higher math.Quote:
Originally Posted by steveinindy
I should introduce you to my soon-to-be father-in-law. He's a huge math geek. I've never seen someone so excited about his daughter having a boyfriend that can use "coefficient" in a debate.Quote:
Originally Posted by Mike Switzer
Steal liberally from other designs!
Fuselage design from a Champ, wing from a Cub, gear from a Husky (or whatever). Deviate slightly from them, but use them as templates.
You'll learn plenty about design and structural loads as it is - but the materials and design work heavy lifting will have been done for you.
The problem with "slight" deviations is that they can cause major shifts in load paths if the more or less ignorant would-be builder changes the wrong thing 'slightly'. You have to still do at very least a basic stress analysis make sure you're not going to pull the wings off your bird in a sharp turn or wind up with me helping to pick pieces of your skull out of the cowling after the plane folds up in a relatively low speed forced landing (I'm not being dramatic....I've had to help do this before). Similarly, I point you to the case of a guy who literally used an Aeronca for most of his build (how he got it approved as a "homebuilt" still baffles me). He failed to figure in the forces acting on a restraint attachment (it's not clear whether he installed it or if it was part of the original frame) which led to it failing and his smashing his face into the instrument panel. The aircraft was largely intact with only some relatively superficial damage but the pilot ended up dying.Quote:
Originally Posted by Frank Giger
Contrary to popular belief, it's not the major oversights that kill most often when it comes to structural design. Usually, it's someone taking the "Eh, close enough" approach to things like seat attachments, harness tiedowns, etc. They may not be as dramatic as a wing separating in flight but they can turn a survivable crash into a fatal event. This happens very, very frequently especially with regards to seat attachment failures in GA aircraft.
I was thinking more in terms of rudder size and shape or using a push-pull control system versus a pull-pull type tinkering, or installing a rudder bar versus pedals.
I've heard restraint harness horror stories, like the fellow who put in automobile seat belts!
OTOH, I know of one homebuilt that was a "plane of many colors" where the guy pretty much borrowed the layout of the major components from other aircraft for his own. Naturally he had a LOT of knowlegeable people critique both the design and build, and made adjustments in the direction of safety.
Well if you look at the stuff in Aircraft Spruce that is rated for like 1500 lbs etc, those pretty much are automobile safety belts. That's probably the most common easily correctable single mistake homebuilders make when it comes to safety (besides exercising questionable ADM): underestimating the needed strength in restraint harnesses and seat attachments.Quote:
I've heard restraint harness horror stories, like the fellow who put in automobile seat belts!
If you really want to be able to successfully use the types of programs you'll need to do this, you may want to consider taking some classes, that is unless you have the time to try to figure out all of the different functions and programs on your own. A class would at least teach you the basics, and you may even be interested enough to make a career out of it later on. Some of the best designers start out with an interest in a hobby like this one. If you need help finding a place to take these classes, check out my website to find the right school for you.
You might want to contact Carlson Aircraft. They designed a replica of the PA-8 Sky Cycle for the homebuilt market in the mid 1990's. The company still exists, making aircraft components - spar extrusions, strut extrusions, wing ribs, etc. The replica was "appearance only", not an exact structural replica. Used fiberglass-covered steel tube fuselage, 2024 for the tail cone. I'm guessing fabric covering where appropriate (wing, tail, control surfaces) because the parts they make now are for fabric-covered designs.Quote:
Originally Posted by KDoersom
http://www.carlsonaircraft.com
Let us know if they have any interest in providing parts and/or plans...
With due respect, Piper didnt need flash Computer software to design it in the first place, so why do you need something now? Something at that end of the scale is quite suitable for "TLAR" methodology (That looks about right) and common sense - face it as far as structural loads go, on something that light, anything you build will be stronger than required. Aircraft design isnt a black art - I managed to do it and have a Beautifully performing aircraft. You will get bogged down in numbers, which at the end of the spectrum you are talking, are going to be exceeded by the margin of error anyway.... Just do it :)Quote:
Originally Posted by KDoersom