Evaluating Landing Gears for Crashworthiness

[SwimBikeRun4342]

I am planning to simulate the crashworthiness of various landing gear designs for an aircraft and I have many questions regarding the process to evaluate crashworthiness. In summary, I want to compare the performance of a couple landing gear designs with respect to crashworthiness.

Questions Set 1:
What is the primary measurement that is used to quantify crashworthiness? My initial research shows that it is "energy absorption" but there are many different types of energies that a landing gear can absorb during impact - frictional energy dissipation, plastic dissipation, kinetic energy, strain energy, etc. Is there a specific energy quantity that must be measured in a simulation?

Questions Set 2:
How do you simulate the loss of these energy quantities? I plan on beginning with commercial finite element packages. Do you simulate the actual impact (the entire impact of the structure, which is a very advanced FEA simulation)? Do you just model the forces that act on each component and document the resulting strain energy and plastic energy dissipation? Currently, I have information on the time-varying forces that act on each component, would it be sufficient to model just the energy absorption due to these forces? I feel that this would yield inaccuracies since only measuring the energy absorption due to these forces may neglect the frictional energy dissipation as well as other important energy quantities? Is it best just to simulate the entire impact of the model?

Questions Set 3:
What is the best FEA package for simulation crashworthiness? I am most experiences with ABAQUS. Is there an FEA software specifically focused on crashworthiness or impact simulations?



If anyone can help with ANY of the above questions, I would greatly appreciate it. Thanks!

 

[GregLocock]

LS Dyna

Not very surprisingly there is an enormous indsutry associated with crash testing, for automotive work. I suggest you read up on that. Sorry I have no suggestions in particular, I only get involved at second hand.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[IRstuff]

What type of crashworthiness? In aerospace specifications, there are generally two types of crash-level shocks: hard landings and actual crashes. In the latter case, the g-levels are on the order of 25 to 40, and the only real requirement is that stuff does not break loose from the aircraft and shmush someone. A hard landing is typically specified in the 12g range, and typically requires "survive and perform after," meaning that the system in question must still meet its requirements after such an event.

TTFN
faq731-376

Need help writing a question or understanding a reply? forum1529

 

[GregLocock]

If you just want the hard landing thing, and it is primarily acting as a suspension, then you probably need to look at MBD software rather than FEA

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[rb1957]

student post ?

Quando Omni Flunkus Moritati

 

[WKTaylor]

SBR4342...

http://www.dtic.mil/dtic/

Typical simple search: " uh-60 and landing gear and crash testing " and following appeared.

Helicopter Landing Gear Design and Test Criteria Investigation
Aircraft Crash Survival Design Guide [several volumes]
Army Helicopter Crashworthiness
Advanced Technology Helicopter Landing Gear Preliminary Design Investigation

etc...

There are hundreds of documents on this complex subject...

Regards, Wil Taylor

Trust - But Verify!

We believe to be true what we prefer to be true.

For those who believe, no proof is required; for those who cannot believe, no proof is possible.

 

[Sparweb]

... different types of energies that a landing gear can absorb during impact - frictional energy dissipation, plastic dissipation, kinetic energy, strain energy, etc. Is there a specific energy quantity that must be measured in a simulation?

Isn't that strongly dependent on the nature of the impact, the structure you are interested in, and the path the loads and energies take? The landing gear in question could be tubular skids (helicopters), or wheels with long oleo struts (Boeing), or cantilevered beams with wheels (Cessna 180), or an articulated truss (Super Cub). I would count on different factors in each scenario. A factor such as friction could be a major part of the energy transfer, or it could be a small factor that would simplify the work to ignore and maybe even conservative to do so (though not likely). Again, depending on the situation. If it's isn't stating the obvious: there are a number of design requirements, FAR/military, that tell you what the criteria are in the design of landing gear. You can infer a lot of relevant information from those.


STF

 

[rb1957]

perhaps the best way to gauge crashworthiness of a configuration is to examine statistics of crash fatalities for each config ?

Quando Omni Flunkus Moritati

 

[Aerodesign]

SwimBikeRun4342,

Your question surely relates to a compliance issue with regard to the chosen regulations for the plane? Example: Crashworthiness in CS-23 relates to 23.721 where the gear may be overloaded and will need to break away. This then requires that the tanks are protected: compliance to the following being required:

CS 23.561 – emergency landing conditions
CS 23.721 – landing gear, general requirements
CS 23.967 – fuel tank installation
CS 23.994 – fuel system components

Part 25 equivalent and associated CRI (or FAA AC) may apply.

The aim of the exercise is to prove the airframe can take the loads and the peoapl survive. This is normally done by rationale analysis, including some FEM work. Do not rush into the FEM stage before you have considered the basics, such as defining the decent velocity, understanding the effect any wing lift may give. Essentially it can be a less daunting task than first apprears. Equate PE and KE, obtain an understanding of the equivalent decent or drop height, conduct a global scenario based study of impact locations. Determine what will crush and what will not. Focus any FEM work on the detail design of the crushable parts, in order to show the tanks are protected. This is NOT an automotove style crashworthiness approach - it is generally not required unless your speeds (decent) are very high (>>5fps).

Summary

Basics first
FEM approach later
Show compliance in a rationale way

regards JW