J

Juicegoose

Well Known Member
Aight guys I'm an electrical designer by profession. But on the side i dabble with 3D modeling software. Not the animation kind i'm talking Autodesk Inventor 2009 edition. For those that don't know what it does go to you tube and type in autodesk inventor. Basically its software used to generate 3D models of items for prototypes and such. The cool thing about the software is that you can run stress analyzes on a part you make and tell before the first cut on actual steal is ever made, fix the stress or weak point and then manufacture it from there. Now that the background is out of the way what i was thinking about doing was modeling an RV-8. Mainly because i plan on making mine a fastback and i want a slider but i don't want the frame in my view. So i'm going to design a canopy opening device like this http://www.diamondaircraft.com/aircraft/da20/gallery.php (look at the first picture under exterior). I was wondeing if any of you guys have modeled a part or your whole plane in any type of 3d modeling software. By using the preview plans i've got at the house i should be able to accuratly reproduce a rv to scale and then run the canopy mod through it's range of motion to see where i might be hitting and stressing to much.
 
good idea! I'd like to see 3D models for all the current RV's just for tinkering with... might be a good way to visualize paint jobs? Just being nosy here, but how'd you get into 3D modeling? Its always interested me...
 
your right thats exactly my thoughts. Right now i don't have the space or funds to go all out and start really building so a 3d model will have to do. I have a degree in Computer aided drafting and through it have been introduced to the inventor suite of programs. It's amazng stuff as the program has a huge database built into it with screws and bolt and rivets and materials. All 100% accurate as to their load capabilities orbending radi and such. same thing with sheetmetal. The Autodesk software comes with sheetmetal specific tools. So what i can do(and have done) if have someone ask me to model up a new enclosure for a vent fan out of say 16g alum. I am able to model the shroud using 16g alum and the program will only bend it so far and tell me i need relief cuts where it knows it will crack. Once i'm done it i can flatten the shroud and print out a flat pattern of the shroud including bend lines and radi of bend. Amazing stuff truly. It evn has electircal components like wires and switches and relays all accurate to real life specs.
 
I think I recall someone modelling a 3-D RV-7A for one of the flight simualtor programs, and it was an excellent and very detailed rendition. might also have done an RV-8, but not sure. Not sure if its usable for your purposes or software, but it might be worth getting in touch with the individual. I hope someone reading this has ther eference to him and his website.

Allan
 
http://www.baytower.ca/index.htm is the link you're looking for but his site is down right now. He's still working on the model; it's a CAD designed RV-7/7A tipup/slider for FSX. The model is extremely detailed and pretty much what you are describing. There's been a few mentions of him on this forum and he just replied to one today, so he hasn't fallen off the face of the earth despite his website troubles.

Edit: here is the thread he's replied to today; he's posted a few images of his rendered work.
 
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Nose Gera Failure

I have been working with Mr. Nomad on the failure of the nose strut on his RV9A. You may have seen the recent thread on the incident. The nose strut bent around nearly 180 degrees with a resultant prop strike. We have invested around $10,000 in repairs so far and are nearing completion of the engine rebuild and other repairs.

There are many theories on the cause but nothing conclusive has surfaced. It would be a great help to see if your analysis software could produce some insight on the cause. Let me know your thoughts.

Stabird.
 
Stabird said:
It would be a great help to see if your analysis software could produce some insight on the cause. Let me know your thoughts.

Stabird.
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I'm a Mechanical Engineer and have probably around 10,000 hours of experience modeling aerospace hardware in Pro Engineer. I've toyed with the idea of modeling up the "A" nose gear and running a structural analysis on it, but never could get motivated. I have thought about this a lot, and it would not be a trivial task.

The actual part modeling would be pretty straightforward. The hard part is coming up with the right set of boundary conditions, which accurately represent the forces acting on the nose gear during landing and proper modeling of the bearings. We model bearings as spring systems, but it takes a thorough understanding of the bearing (bearing friction, pre-load, race material, etc) to get the spring constant right. Without all that the analysis is useless.

I'm not saying this can't be done, it just would take a lot of work. Hence, my lack of motivation. In fact if someone could model the bearings and knew the bearing friction I could take a cut at the forces and run a simple model if provided with the drawings.
 
I'm not 100% sure but i do know that Inventor already has bearings in the software. you don't have to draw the bearings at all simply insert bearing and then you can adjust the size and specs of it. Now it might not be the exact bearing used in the RV but it will extremly close. I doubt that if you stuck one RV bearing next to the other and tested them they would fail at the exact same point simply from the manufacturing process. I'll look it up and get back with ya.
 
Juicegoose said:
I'm not 100% sure but i do know that Inventor already has bearings in the software. you don't have to draw the bearings at all simply insert bearing and then you can adjust the size and specs of it. Now it might not be the exact bearing used in the RV but it will extremly close. I doubt that if you stuck one RV bearing next to the other and tested them they would fail at the exact same point simply from the manufacturing process. I'll look it up and get back with ya.
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I'm not sure how the structural analysis package in Inventor works, but I'm guessing it's similar to NASTRAN or Pro Mechanica. The mechanical model (the 3D looking part) and the structural model are very different. Since bearings are flexible elements (vs. rigid elements such as beams or plates) they are structurally modeled as springs. In order for the structural model to give valid results the characteristics of the bearings must be specified, usually we simplify this as a spring in series with the structure it's mounted to.

I've been thinking a lot about this and I'm pretty sure in order to account for all the forces acting on the nose gear during landing the characteristics of the bearing/axle interaction have to be modeled. The bearing drag and any imbalance of the wheel itself can impart an oscillating load into the nose wheel if the friction isn't constant. So that needs to be modeled structurally (again this is very different than the 3D mechanical model).

I'll be thinking more about this and see if I can't come up with a way to model this. If anyone has copies of the nose wheel drawings they can send I can bang out the mechanical model. I'd have to make some drag/balance measurements on an actual nose wheel in order to build a structural model.

Just my 2 cents...four times over! :D
 
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