Local Strengthening of Skin : Doubler Design

[zainulabidin]

I have been trying to install a knife blade antenna subjected to a significant load on composite skin of an aircraft. I am trying to sandwich the skin with two doublers for strengthening of skin. I cant find any method to size the doublers ( thickness, and diameter). I have consulted flabel chap 9 and C Niu Chap 6 but could not proceed.

 

[rb1957]

you'll probably need more than doublers, depending o the significance of the load. Typically the critical load is out-of-plane (of the antenna) putting torque into the skin. We find that a U-channel typically kills this problem "dead".

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

 

[SWComposites]

Ah, re "composite skin of an aircraft" - what exact aircraft? where on the aircraft? solid laminate or sandwich panel?

Flabel and Niu don't cover composite structure stress analysis. You are going to need a composites expert to help with this.

 

[zainulabidin]

the skin is composite laminate. There are no stiffener or bulkhead in vicinity of installation area.
are there any references?

 

[SWComposites]

I doubt you will find a reference, except if this is for some sort of kit airplane. Its not a simple design. Would help if you provided a drawing and loads.
Please answer all of the previous questions. Plus,
Is this for a pressurized fuselage?
Is this a one off or serial production?
Who is the certifying agency?

 

[Stress_Eng]

Just food for thought. Are you able to determine equivalent axial and bending moduli, in the two perpendicular axes of the skin? Would you then be able to investigate plate displacement behaviour under the combination of existing and new load conditions, taking into account load transfer between the skin and the doublers?

 

[rb1957]

along with SWC's questions ... how big is this antenna ? (large VHF, small L-band ?)
What is causing these "significant" loads ?
Is the composite it is mounted on laminate or sandwich ?
It sounds like you're introducing a moment into a "plate" and this is going to be harder to reinforce and substantiate.

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

 

[WKTaylor]

In addition to everyone else's questions...

Be explicit... which 'Niu' textbook are You referring-to?

What is the size of the antenna and the 'foot print' [mounting/bolting pattern]?

High radius of curvature? Compound curvature? Is this install on the upper, side or lower surfaces of the fuselage[?] or ????.

How is the 'antenna backplane' and bonding been defined? Have moisture sealing and grounding... for static/corona and lightning... design issues been considered?

Is the composite structure hand-laid-up... or mandrel-wound.... directional fiber/tape, woven cloth, etc?





Regards, Wil Taylor
o Trust - But Verify!
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", HBA forum]
o Only fools and charlatans know everything and understand everything." -Anton Chekhov

 

[WKTaylor]

zainulabidin appears to be taking some time to think about our responses... before replying?

Regards, Wil Taylor
o Trust - But Verify!
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", HBA forum]
o Only fools and charlatans know everything and understand everything." -Anton Chekhov