PPE for a Sandbag Test

[AeroSD]

My employer at a small startup is looking to sandbag test the composite wing of an aircraft in the size range of a Cessna 152. They have a test fixture that constrains the wing root, and in the past had simply loaded sandbags onto the wing by hand to the target load, without experienced a wing failure.

Now, the layup schedule has been modified, and I have been asked to design a loading schedule to repeat the test on the new wings. I am concerned that, if the wings did fail, there are a couple thousand pounds of force stored in a carbon beam that could be released quite violently. My employer feels that safety glasses are acceptable PPE for this operation. I disagree, but don't have the experience to know exactly what is appropriate.

Where can I find information on the correct type protection for workers in an operation like this? Is some sort of remote loading of the beam absolutely necessary?

 

[rb1957]

make sure no-one's in an area (like under the wing) to be hurt.

maybe erect a barricade around the specimen to capture any pieces.

maybe rig the wing close to the ground (enough clearance so it can deflect as it wants).

maybe drape a sheet over the wing to prevent pieces flying out ?

maybe follow the boss's direction; he'll be signing/approving your test set up (or make sure he does), maybe he has sufficient experience to defend his position in the face of your fears/inexperience (no slight intended, it's ok to worry about things because you don't have the experience but also listen to people who have the experience ... worry if they have responsibility but not experience).

maybe worry about the pile of sandbags becoming unstable if there is a failure ?

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

 

[AeroSD]

Thanks for the suggestions, I will look into the possibility of erecting a barrier and will definitely ask my boss to sign off on everything.

I'm all for leaning on the experience of others. My concern is that since the company has never experienced a failure during similar tests that no one on the team has the experience to know what happens in the case of a failure happening.

 

[rb1957]

yes, but maybe they then have the confidence that no failure will happen ? (that changes are minor)

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

 

[AeroSD]

That begs the question, if there is complete confidence in no failure, why is a test being done? If there isn't complete confidence in no failure, it seems it would be prudent to prepare for the possibility of what may happen if that failure occurs.

 

[rb1957]

it could be "just" to show/prove compliance. You don't test things with an expectation of failure. The test is the proof that the initial opinion is correct.

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

 

[Sparweb]

Having attended many structural load tests, I think your caution is justified.
It's likely that the modification to the wing was done without detailed analysis because the load test was planned from the start. This is often a sound basis for approving modifications, especially when test data is available for the original wing structure.

A few things that I've done to reduce the mess from a potential structural test failure:
[ul][li]Wrap all bags of sand in loose plastic bags. If the canvas bag ruptures there's another layer to break through.[/li]
[li]Cover the wing with rubber mat to prevent the bags from sliding on the slippery surface.[/li]
[li]Apply bags in layers, and apply a mat between the layers, to avoid "towers" of bags that can fall over.[/li]
[li]If there are any questions about getting all of the bags to fit, mark an outline on the floor with tape and stack all the bags in it to check.[/li]
[li]If government officials or customers will be present during the test, make sure to have done the test once BEFORE they arrive.[/li][/ul]

Plan for the best, prepare for the worst...

When combined loads are necessary (I do hope you have not ignored DRAG as you test LIFT, otherwise your tests are not valid) make sure there isn't a lot of strain energy stored in the pulling system you use. The worst thing to use are ropes or steel cables. Chains are much better. Hydraulic actuators are the best, of course, because they allow precise control of force with virtually no recoil if the structure fails.


STF

 

[berkshire]

Aerosd ,
The biggest problem with sandbag tests is that there is very little chance of stopping it when things go bad . If you can, see if you can arrange for hydraulic jacks to carry the load under the wing prior to test, so that you can pre load without fear of failure . You then release the jacks with people away from the wing . The other way of course is whiffle trees , but this involves more cash outlay for the test stand.
B.E.

You are judged not by what you know, but by what you can do.

 

[MikeHalloran]

For composite wings, I'd worry about a fracture liberating a few of those tiny arrows fibers, so I'd support wearing eye protection, including unperforated sideshields. Or maybe the sort of faceshield you're supposed to use with a grinder.

And maybe a floor to ceiling, wall to wall, transparent wall of heavy plastic to protect the visiting firemen in their bleachers from the same hazard without personally inconveniencing them individually.






Mike Halloran
Pembroke Pines, FL, USA

 

[berkshire]

This may help ,
This is an article and video of testing Composite wings in Germany. A few salient points are covered including temperature of the test to cover loss of strength on hot days. You will also see the shield window behind which all employees stand when the test is actually running.
B.E.

https://www.dg-flugzeugbau.de/en/library/testing-destruction-dg

The actual video is here :

https://www.youtube.com/watch?time_continue=119&v=WlqSha2Ve7I

You are judged not by what you know, but by what you can do.

 

[berkshire]

One thing that may be of use in a sandbag test as done by other manufacturers, is the use of a couple of forklift trucks to support the wing instead of hydraulic jacks, they are easier to position . A plexiglass shield taped to the column will protect the operator/s from flying particles.
B.E.

You are judged not by what you know, but by what you can do.

 

[TimMcK_Aero]

The "basic glider criteria handbook" has some good illustrations of sand bag tests. They don't talk about PPE, but do show wooden uprights. An internet search with the above search term should yield some good leads.