Landing gear load calculation

[Bozo_Sam]

Hi there,

I am working on the project regarding the landing gear structural analysis. I have gone through the FAR part 25 for the ground loads. The load cases seem quite reasonable, the only problem is that I am not sure how these should be calculated for a given aircraft. The part I find confusing is that I am not sure which loads can be calculated as static and which have to be considered as dynamic loads.

I am asking that to know, for which load cases "hand calculations" are sufficient and for which, the multibody dynamics analysis should be performed.

thanks,

Sam

 

[WKTaylor]

BS...

Request a refined definition of Acft class/type/size/weight, etc.

Ultralight GA?
Light GA?
Medium/heavy GA?
Sport category or fully certified per part25?
Any potential military application?

Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]

 

[Bozo_Sam]

Hi Wil,

thanks for a quick reply. So the aircraft is short- to medium-range, narrow-body, commercial passenger twin-engine jet airliner. So full certification part 25 probably and no military application.

Best regards,

Sam

 

[IRstuff]

Wouldn't the stressing case be a hard landing, possibly on a single strut?

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[SWComposites]

For that type of aircraft - go hire someone who has done it before.

 

[Bozo_Sam]

I know that the topic is challenging but I am just trying to get my head around the standard and all the info would be appreciated.

BR.

Sam

 

[Sparweb]

Some books that will help you:
[ul]
[li]Roskam, Design of Aircraft (series of 8 volumes)[/li]
[li]Niu, Airframe Stress Analysis And Sizing[/li]
[li]Niu, Airframe Structural Design[/li]
[li]Lomax, Structural Loads Analysis[/li]
[/ul]

I'm tempted to include the book by Dan Raymer, but I haven't read it myself, so I don't actually know how helpful it would be. But other engineers like it.


No one believes the theory except the one who developed it. Everyone believes the experiment except the one who ran it.
STF

 

[verymadmac]

The best landing gear related textbooks would be

For part 25 and the like landing gear the principle textbook is
Aircraft Landing Gear Design: Principles and Practices by Norman S Currey

For small aircraft but also with good worked examples and probably the best place to start
Landing Gear Design for Light Aircraft by Ladislao Pazmany

And for how it was done in the bad old days there is (mostly out of date but really interesting but almost as rare as hens teeth)
Landing Gear Design by Conway H G

Also there is a Mil spec that defines all the landing gear part names which is really annoying to find after you have finished the drawing stack for landing gear.

 

[Bozo_Sam]

Great, thanks to both! I will take a look at all the literature and see which fits my needs the most.

 

[rb1957]

also look into the FAA's AC material on LG loads.

True static and true dynamic loads are really quite difficult to determine for LG. You avoid a lot of these problems if you use a simple gear (a pair of wheels on an axle on a main fitting. An example of what I mean is ultimate load. What deflection do you apply to the "simple" mechanism of a simple gear (a piston stroking inside of the main fitting) for 150% of limit load ? (a load that can never be achieved in practice) The typical assumption is to apply ultimate loads with limit deflections.

Yes, there are true dynamic tests (wheel spinning) that capture some of these effects.

Really a very complicated topic. Some good specialised reading given above.

another day in paradise, or is paradise one day closer ?

 

[Andries]

I have used the books by Currey and Conway for preliminary loads calculations and found them very useful. You may also need tire specs found in the manufacturers' data manuals.

Andries

 

[WKTaylor]

B_S... In addition to the great references mentioned by IR, SWC, SparWeb, VMM, rb...

1. Military insight may/may-not be any help... mostly available free thru ASSIST quick search, EverySpec, DTIC, ARC, etc...

Landing gear design can involve some complicated considerations... take-off and landing are major elements... but taxi, turning, braking, ground tie-down, stability, etc are also important...

MIL-A-8862 AIRPLANE STRENGTH AND RIGIDITY, LANDING AND GROUND HANDLING LOADS

MIL-T-6063 TESTS, IMPACT, SHOCK ABSORBER - LANDING GEAR, AIRCRAFT

AGARD-CP-484 Landing Gear Design Loads

AIAA 1996-4038 Landing Gear Integration in Aircraft Conceptual Design

2. Some SAE documents, if you have access...

AIR1489 Landing Gear Systems Terminology

AIR1594 Plain Bearing Selection for Landing Gear Applications

AIR4894 Landing Gear Stability

AIR5451 A guide to Landing Gear System Integration

AIR5565 Historical Design Information of Aircraft Landing Gear and Control Actuation Systems

AIR5631 Catalog of Landing Gear Systems and Suppliers

ARP1311 Landing Gear Structures and Mechanisms

ARP5556 Landing Gear Alignment

ARP5908 Landing Gear Servicing

Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]

 

[Bozo_Sam]

Great! Thanks to all. I have already visited a local library and the books that you proposed seem very useful. WIll, thanks also to you for the great articles, I will check them out and see if there is something I could use.

 

[Bozo_Sam]

Also, Andrias, if you are interested we can get in contact and see if there is a possibility for some consulting for your side.

 

[Andries]

Hi Bozo Sam,

Thanks for the invite. I am an old, retired guy way down in South Africa, so I don't think that I will be of much value to you at this stage of the game.

Regards,

Andries