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Static load testing of giant models over 25kg

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rossco
Posts: 60
Joined: 30 Mar 2015, 18:56

Static load testing of giant models over 25kg

Post by rossco »

Hi guys wondering if someone can help out here.. I've noticed over the years the Europeans doing static sandbag stress checks on wings and tails of giant models.

Does anyone have a copy of the spreadsheet that they use to calculate how much weight to apply for a given G loading/flying weight and the proximity of the sandbags and how they dimish in weight moving out as the to simulate the flight loads reducing?

Thanks in advance. Rossco.

Barry Atkinson
Posts: 22
Joined: 20 Mar 2015, 22:33
Location: Darkest Gloucestershire

Re: Static load testing of giant models over 25kg

Post by Barry Atkinson »

The best person to speak to is John Greenfield. As the LMA carry out these checks he'll likely know the drill.

I think they normally only test like this if the build hasn't been monitored through the construction phase, as it normally would. I only say that from having watched it happen in the case of a large jet built in Germany, but needing to qualify here under LMA rules. There may be other criteria too....?

Barry A

john greenfield
Posts: 544
Joined: 18 Mar 2015, 07:52
Contact:

Re: Static load testing of giant models over 25kg

Post by john greenfield »

Rossco

I have been trying to get specific detailed info on the process the Germans use for a long time but no one seems to have a definitive answer and it seems to be up to the inspector as to how exactly the process is carried out and how the weight is distributed along the wing. I have seen they also load test tailplanes and even the fin but have no idea how the loads are calculated. During the build of my Wien I even asked the original designer / builder for info on the load test carried out on his model but he could not give me much info !
I do know however the criteria is to test to 3G for non aerobatic and 8G for aerobatic Types BUT they only calculate the G loading EXCLUDING the weight of the wing !!!!
Hopefully some of our European readers will be able to enlighten us further.

AEB
AEB = Aeronautical Energiser Bunny (with thanks to CW)

spike spencer
Posts: 102
Joined: 17 Mar 2015, 22:23
Location: Salisbury UK

Re: Static load testing of giant models over 25kg

Post by spike spencer »

"BUT they only calculate the G loading EXCLUDING the weight of the wing !!!!" Probably because the wing is self-supporting ?

If you get into all the Mathematical flute music, this topic can get very involved. However, the procedure is basically quite simple.
Sandbag weights (or Force Nodes) are adjusted and distributed to equate to the area (lift-product) of any part of the wing. The 'Payload' will be the weight (Mass) of everything other than the wing. e.g. If the payload is 6kg, the weights applied for a 3g test would add up to 18kg.

Depending on the cg location, the Tailplane will be lifting 'downwards' so some adjustment for this should be added to the payload sum. Further complication will be added by non-lifting parts of the wing due to washout etc. A good dose of over-engineering should cope with such variables.

For a fullsize aircraft to achieve Certification for operation at 3g, testing would have to prove structural integrity at some considerably higher load. [edit: UK Civil requirements seem to ask for a factor of 1.5 without showing permanent deformation.]
Giant 'model' aircraft above 25kg are treated in much the same way as 'real' aircraft.

"airworthiness static wing load testing" search gets lots of Google hits. Lots of guff on Wikipedia but UK (BCAR) Requirements can be found here:
https://www.caa.co.uk/Commercial-indust ... -aircraft/
That link also contains the one UK address for an organisation approved under BCAR A8-22
Then, digging a bit deeper:
http://www.eurousc.com/media/1058/luass ... e-web1.pdf

JG:
PM sent
Last edited by spike spencer on 23 Mar 2016, 20:22, edited 2 times in total.
Spike S.

rossco
Posts: 60
Joined: 30 Mar 2015, 18:56

Re: Static load testing of giant models over 25kg

Post by rossco »

Thanks guys this is off to a good start. I'd like to have a calculated method .... just to be sure
.thanks again. Rossco.

Phill Tadman
Posts: 398
Joined: 18 Aug 2015, 20:38
Location: South Cambs

Re: Static load testing of giant models over 25kg

Post by Phill Tadman »

I had a chat with an aerodynamicist today about calculating static load test values. In summary he said it depends on how accurate you want your test to be.

He described 5 levels of accuracy with rough estimates of the effort for creating a program to calculate the values:

1. A simple model for a rectangular wing where weights are calculated as a function of AUW and applied to the wing tips. 0.5 day.

2. An enhanced model using a distributed weight function for a tapered wing chord. 2 days.

3. An aerodynamic model including the wing aerofoil. 2 weeks.

4. An aerodynamic model including aerofoil, dihedral and twist (wash out/in). 2 months.

5. An advanced aerodynamic model incorporating structure deformation and elasticity. 6 months +

Option 2 onwards involves scary maths and would probably need formal proving of the mathematical model.

Phill

rossco
Posts: 60
Joined: 30 Mar 2015, 18:56

Re: Static load testing of giant models over 25kg

Post by rossco »

I found this from the states,

http://www.modelaircraft.org/files/520-a.pdf

Phill Tadman
Posts: 398
Joined: 18 Aug 2015, 20:38
Location: South Cambs

Re: Static load testing of giant models over 25kg

Post by Phill Tadman »

Here's a video of a full size Antares 20e destructive test.

Gets interesting at about 3:30

https://youtu.be/Y5lgTPepN-M

Phill

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