CAD design for landing gear

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WARPilot

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I have been in contact with the owner of WAR, and several WAR plane owners that fly them regularly.
Ease of Maintenance is an issue. An update to the design will address this. The gear are already designed but need refreshing and some areas of your comments apply. The trunnion area is one primary area of focus for me. Then there is the motion of the side brace thru gear retraction.
 

WARPilot

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So how does one go about finding an engineer to analyze a landing gear system? Are there small firms that can do this?
 
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wsimpso1

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Paz's book is where you define the loads. After that, this is Machine Design which is a subset of Mechanical Engineering. Start your search for a Professional Engineer with background in hydraulics and machine design. Once you have a few candidates, you can start sorting that list down. If you are really lucky, you might get someone who already understands landing gear for little airplanes, but do not count on that.

Going back to Paz:
  • You do need to define loads per chapter 9. This means max gross weight and range of CG must be estimated, as must positions of main and tail wheels.
  • Pages 108-127 is the regulations that we do not have to meet, but is a really good idea to do so;
  • Figure 9-4 covers ground loads for towing pretty well;
  • Pages 127-135 goes into calculating loads from landings and does a bunch of examples.
Define your package space and geometry. If it already exists in a CAD package, they should get it. If not, you will have to define the coordinate system and coordinates for the various hardpoints in the airplane. If they are not yet fixed, but you will allow the engineer to set them, put a range on each dimension or coordinate that you can live with.

Make sure that your engineer understands that metal and wood parts need a FOS of 1.5 and composites need FOS of 2.0, that weight is enemy number 1, and that if it is not made out of stuff you can buy off the shelf, it is no good.

Get an annual production volume estimate for both you and your engineer, as that will weigh heavily on how much tooling is acceptable. Think aluminum weldments or maybe sand castings, and remember that aluminum alloys that are welded and/or cast usually need to be heat treated afterwards. Steel weldments might be acceptable substitutes... Usually weight is the deciding factor.

Just one more adventure in airplane design.

Billski
 

gtae07

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As someone who designs transport category landing gear repairs for a living (among many other things) I also strongly recommend using bushings at all pivot and attachment points, and leaving a little bit of rework margin at bushing locations and other places. You maybe don't need the margins we target (because our airplanes get flown in crap weather and might see a decade between deep gear inspections/overhauls) but I'd make sure to leave something there for construction errors and corrosion. On the repair/service side there are few things that drive the structures folks nuts more than zero-margin designs.

Balancing margins vs. weight is a hard choice. Our homebuilts typically get babied compared to airliners and business jets, but they're also built by amateurs without the benefits of fancy tooling and inspection equipment.
 

WARPilot

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I’m just a lay person, airline pilot, and stopped short engineer. Any design I decide on will have to have maintenance, reliability, and simplicity in mind. Cost is a factor so that is why I am here to get all the ideas and help I can. This is a great forum.
 
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