Composite Reinforcement, beyond 43.13
Composite Reinforcement, beyond 43.13
(OP)
Hi All,
This is not a repair but an access hole to be put in belly shell of a vintage Bell 206 helo. Say 4" x 6" for discussion purposes with radiused corners in flat honey comb floor and say 1" thick with .025 al facings on H'comb panel.
Current thoughts are to reinforce around opening with 1.75 wide,.040 2024-T3 top and bottom, apply doubler with CherryLocks and fill voids with Hysol/Loctite EA 934 epoxy. We will also use Delron plug/sleeve inserts to get 10-32 thds around hole for closure plate. Any thoughts on doubler thickness and analysis methods if required? Gut feel says this scheme is OK but the Feds may require more detail. 43.13 no help since this is not a repair of damaged h'comb.
Thanks for your comments. John Cragin
This is not a repair but an access hole to be put in belly shell of a vintage Bell 206 helo. Say 4" x 6" for discussion purposes with radiused corners in flat honey comb floor and say 1" thick with .025 al facings on H'comb panel.
Current thoughts are to reinforce around opening with 1.75 wide,.040 2024-T3 top and bottom, apply doubler with CherryLocks and fill voids with Hysol/Loctite EA 934 epoxy. We will also use Delron plug/sleeve inserts to get 10-32 thds around hole for closure plate. Any thoughts on doubler thickness and analysis methods if required? Gut feel says this scheme is OK but the Feds may require more detail. 43.13 no help since this is not a repair of damaged h'comb.
Thanks for your comments. John Cragin





RE: Composite Reinforcement, beyond 43.13
Just about Everything in that helicopter is attached to the belly panel, so you have to provide a stress analysis (or test) that shows that your mod doesn't affect hard landing and crash conditions.
Where's the hole? I hope for your sake you've picked the passenger foot-well, because anywhere else is "busy" doing something else. Not too close to the cargo hook, though, I hope. Most attachments to the panel apply loads out-of-plane, causing local bending loads and core shear or compression. Other cases, like hard landings, imply bending of the entire fuselage. The way the 206's are designed, that may not be as bad as it sounds - I haven't done the math, but there's a lot of "straight-line-of-action" members between the engine and the landing gear.
Again, you really need a DER familiar with 206's to look over the project to tell you what should be done, by figuring out where the critical stress cases are. Hard to do over the 'net.
"Restricted Category" may also be an option to bear in mind, but that's a hit against the value of the helicopter for the rest of its life.
Good luck.
Steven Fahey, CET
RE: Composite Reinforcement, beyond 43.13
This access hole is enlarging a 10 year old existing 3" dia access hole fwd and outbd of R/H aft cargo hook and is clear of the prohibited repair areas in the SRM. It is in the rh flat floor well. I have for ref a Bell dwg showing a 8"x 12" oval camera port in the same area.
BTW I am a structural DER but do not pretend to know it all. Never ran into this situation before. Any analysis suggestions without resorting to FEA? Thanks JQC
RE: Composite Reinforcement, beyond 43.13
Stache
RE: Composite Reinforcement, beyond 43.13
regards, Steve
RE: Composite Reinforcement, beyond 43.13
I assume that this is unpressurised (i'm not that familiar with the 206).
a 0.04" doubler riveted onto the skin really doesn't provide much reinforcement; and btw, why reinforce only one side of the original panel ?
i'd like to see an edge frame, which is probably a complicated piece to machine or assemble, with a fairly robust connection in the corners.
good luck
RE: Composite Reinforcement, beyond 43.13
"How do I restore equivalent strength and stiffness of this material"? I doubt that a loads analysis will lead anywhere (now that I've had some time to think about it). So you're probably going with #2.
"Any analysis suggestions without resorting to FEA"
Try hand analysis techniques first to get a feel for what the materials can withstand.
Sandwich panel analysis methods can be found in a variety of published data from honeycomb panel manufacturers, like Teklam and Gill. The panel you're working on is almost certianly a honeycomb cell core (don't know the density), bonded to the facings with (probably) Hysol. There's nothing fancy about it, although in some of their helis Bell has multiple facing laminations that build up at high stress areas (hence reducing core depth), plus inserts, plates, and cavities potted in at various locations to pick up on the attached structures.
Steven Fahey, CET
RE: Composite Reinforcement, beyond 43.13
RE: Composite Reinforcement, beyond 43.13
That just means you're crazy!
Steven Fahey, CET
RE: Composite Reinforcement, beyond 43.13
RE: Composite Reinforcement, beyond 43.13
It's a Canadian accreditation - there's no equivalent in the US, as far as I know.
Steven Fahey, CET
RE: Composite Reinforcement, beyond 43.13
Thanks JQC
RE: Composite Reinforcement, beyond 43.13
Canadian engineers use "PE", when they qualify and have been given accreditiation by the local engineering professional organization. This is roughly equivalent to the american system, and most companies in Canada hiring PE's don't care if you got in the US or Canada.
It's when you try to run your own engineering business that "us vs. them" applies. To practice in Alberta, you must be registered with Alberta's PE organization.
Steven Fahey, CET
RE: Composite Reinforcement, beyond 43.13