Birdstrike Analysis 1

[feadyna]

I am working on birdstrike analysis on aircraft structures, using Gelatin bird. Could any one describe the method of ALE apporach to carry out the birdstrike analysis using ls-dyna.

 

[radomir]

Well I am neither aware what "ALE approach" is nor what “IS-dyna analysis” is but in engine world bird-strike (ingestion) testing is part of type approval tests.

Once upon a time no "jello birds" but real ones, although already deceased, were launched into a running engine:

- multiple (small) bird ingestion requirement: 3 sparrow size per square feet of intake area, in 1 s time interval between each, an engine has to swallow and to keep on running with reduced thrust or power (if I remember correctly power reduction must not be more than 40% but don’t remember bird impact speed).

- single (large) bird ingestion requirement: 2 lb bird, bird speed = max take-off speed, engine speed = take off speed (rating); no engine particle (minced blades) should be able to pierce any engine casing, all debris must stay within engine envelope, they may leave engine only through exhaust.

So approach was rather direct and analysis was quite forensic.

 

[FredGarvin]

Radomir...it's not once upon a time. Still no jello birds, only real ones. Feathers everywhere.

 

[IRstuff]

It's LS-DYNA, from ANSYS, specifically geared for collision analysis:

http://www.ansys.com/ansys/lsdyna.htm

TTFN

 

[ewh]

While using real birds is the most common and usually prefered method, tests have been done using jello birds on composite turbine blades, and the USAF's AEDC has shot them out of it's "chicken gun" in birdstrike tests.

 

[TheGreatWaldoPepper]

Having done birdstrike tests long ago, I have one correction: the chicken is not dead but asleep, otherwise it will become rigid. I did the test on windshield and canopy, and it was most impressive.
conclusion: a fast chick is a real bullet

 

[gstark]

I have a recollection of a windshield/canopy birdstrike test for a Canadian A/C which continually resulted in failure. After much research, they determined that the frozen birds were the culprit. Once they shot thawed birds, the tests were successful.

 

[FredGarvin]

That story has reached folklore status. I doubt that it ever happened.

We snuff the birds out right before we shoot them.

 

[Sparweb]

That's one of those legends that people use to "insert nationality here" when they want to insult somebody. The story is equally funny if you stick in "american", "french", or whoever, (depending on the audience). It definitely didn't EVER happen.

STF

 

[Miper]

I remember the chief engineer bringing chickens in from his farm for the bird tests. Originally, they were shot live to get a real result, but the ASPCA raised a ruckus; so we started wringing their necks, which gave us the opportunity to weigh them, trim as necessary to the appropriate weight, and then shoot.

Eventually, the ASPCA stopped that, too; so we got FAA permission to use dressed chickens from the local grocery store. We did freeze them and we do suspect that one early test went badly because of insufficient thawing. But I agree that it is highly unlikely that anyone anywhere actually shot a fully frozen chicken.

The dressed chicken made a lot less of a mess, but the real secret to having a clean shot on a windshield is to turn the whole assembly upside down, so the chicken spray goes mostly down instead of up and all over everywhere. Finally, by doing the shots in a local field, we found that the local critters cleaned up almost all of it by the next day.

It is amazing what damage an 8 lb bird can do at 300 kt. High speed cameras show it becoming ssentially "hydraulic", sometimes forcing an opening between fasteners and squirting through like a water jet to cut through internal airframe pieces, which then go flying about the cockpit.

My initial thought on using a dynamic fea method is that it will take a good deal of testing to reliably calibrate the simulation for each structural arrangement.

 

[TheGreatWaldoPepper]

Is it possible to send pictures to this forum? If it is, i might send you some interesting "before" and "after" pictures of a brave chicken

"there are fast chicken and there are living chicken, but there is no living and fast chicken"

 

[GrahamBig]

Used to work for a large aircraft manufacturer. Used a Royal Aircraft Establishment paper to do birdstrike analysis on wing/h. stab leading edges. Also remember a Cranfield method which was essentially the same, but updated.

Both these methods were based upon test and were pretty accurate, as we sized the design based on the analysis and later did certification tests, all of which passed.

Can't remember the name/number of the 2 analyses mentioned, but maybe an internet searh will reveal.

 

[birdstruck]

feadyna,

you wrote:
'I am working on birdstrike analysis on aircraft structures, using Gelatin bird. Could any one describe the method of ALE apporach to carry out the birdstrike analysis using ls-dyna.'

ALE Approach:
I am also not familiar with this terminology. I am familiar with the use of 'Eulerian' and 'Lagrangian' computer techniques for conducting birdstrike analyses. My experience lies with DYTRAN(MSC software). The exercises of performing these analyses have been extremely interesting, however the value added to the development of typical aircraft structure (leading edges, transparencies, radomes, etc)is questionable and depends upon the nature and scope of your project.

Our typical design process involves the use of proprietary software which is based in part on the RAE paper mentioned by Graham and which is supplemented by internal 'curved and flat panel' test data. The energy dissipation curves extracted from this method are applied to a non-linear finite element model typically is used for internal load development.
We have certified structure by analysis alone(supported by historical data and by new product testing alone (last full-scale test conducted in Aug of 2001). While several DYTRAN models have been developed internally: As yet we have not made use of this technique for purpose of certification.

The RAE referenced above is:
"The design of leading-edge and intake wall structure to resist impact." Royal Aircraft Establishment, Technical Report 72056, Farnborough, Hants, March 3, 1972.

A good reference for your question about the gelatin bird would be:
"Validation of a bird susbstitute for development and qualification of aircraft transparencies.", Chalita, A., Flight Dynamics Laboratory, Write-Patterson Air Force Base, Ohio, AFFDL-TR-77-60, Oct. 1980.

 

[KnifeKnut]

Turkey

http://wildlife.pr.erau.edu/Pictures3.htm

Hawk?

http://www.americanaeroservices.com/images/BomberBill/bird strike.jpg

Pigeon

http://www.americanaeroservices.com/images/BomberBill/bird strike.jpg

 

[jammin941]

I have used RAE equations to do preliminary sizing of windshield thickness for bird impact. The equation was developed by Mott of Hawker-Siddeley and it gives very good results. There is also an equation developed by Poullain and Clamigraund of Dassault that is also good. If anyone has a copy of these equations I really need them. I lost my copy of the old reports.

 

[AeroE]

The best approach to this problem is to scrap the analysis and go directly to the lab - you will never accurately predict structural response and failure to real bird strikes. There are more variables in the joint design, backup structure stiffness, and so on to ever hope to model.
You will get in the ball park, occasionally, but will never calculate the precise outcome. After development testing and incorporation of the results into the vehicle design, a physical test is required to validate your method and prove that you met the specs.

By the way, summer is a bad time of year to conduct this work. Hosing the inside of the bunker down barely improves the smell.

The birds are dead for a long time; frozen and then thawed before the shot. Adjust the weight by clipping off parts or injecting water.

If you're working on a thesis, then never mind; no one in industry cares about your results.