Additional holes in Aircraft Frame
Additional holes in Aircraft Frame
(OP)
Our company has a project in which we are installing new avionics in a Aerobatic General Aviation aircraft. In the aircrafte frame, there are existing holes though which wiring harnesses are routed. For the added avionics harnesses, we want to increase the size of some these holes and in certain case add new holes.
What analysis / calculations are required to determine if the frames can be modified?
If the frames required reinforcement after making / enlarging holes, how to design the reinforcement scheme?
What data is required to perform this analysis?
Thanks in advance
What analysis / calculations are required to determine if the frames can be modified?
If the frames required reinforcement after making / enlarging holes, how to design the reinforcement scheme?
What data is required to perform this analysis?
Thanks in advance
RE: Additional holes in Aircraft Frame
Also take a look in ac43.13 for guidance on the design of the repair.
For substantiation - in absence of verifiable internal loads data, you would want to demonstrate equivalent strength to the baseline structure. I.e. analyse the affected details to demonstrate that the doublers and joints that you have added restore the capability ( ultimate strength, and stability) that was removed from the baseline structure. Be conscious of not introducing poor fatigue details in the process.
Is there a senior engineer who can check your work?
RE: Additional holes in Aircraft Frame
There are so many considerations... where to start.
Are you adding any load to these frames? Where are these avionics boxes installed?
You need to substantiate the net area loss in the frame. If you have non-OEM loads, you can't simply compare to adjacent minimum cross sections.
The bottom line is, you need to show the frame material can handle the maximum load it is subject to. So you either need to know the value OEM load + modification induced load, or you need to show the OEM margin is sufficient to cover load increase, or you need to show the amount of reinforcement you install is commensurate with the load increase.
You are talking about harnesses which are normally very low mass, but I'm concerned about what else might be done in this installation.
If you are starting by posing a question in this forum, you are starting in the wrong place to be honest.
"Aerobatic general aviation aircraft"... do you know which CFRs you need to comply with? Is this an STC? Who is approving this?
Keep em' Flying
//Fight Corrosion!
RE: Additional holes in Aircraft Frame
Once upon a time there was a shop in town that installed new antennas in a composite plane GA plane. They had no idea the skin was a fiberglass foam sandwich. torqued the hardware down, crushed the sandwich. I heard a few were totaled after they couldn't decide on a repair.
RE: Additional holes in Aircraft Frame
RE: Additional holes in Aircraft Frame
In any case seek advice and support from someone who knows what they're doing and has the appropriate delegations/authorisations. You won't get an answer on eng tips.
RE: Additional holes in Aircraft Frame
We don't know all the details. You can't necessarily treat it as a repair. It should be treated as a modification. The distinction:
A repair restores the structure to TCDS basis.
A modification may show the structure acceptable for alternate or additional load.
We really should not be giving specifics on how to substantiate it since it is largely speculation.
Keep em' Flying
//Fight Corrosion!
RE: Additional holes in Aircraft Frame
RE: Additional holes in Aircraft Frame
another day in paradise, or is paradise one day closer ?