I am designing a L3 build for this summer, for a BALLS launch or locally if the waiver is approved. The overall concept is a 60" carbon airframe from Wildman with a 2" switch band and a 24" VK nosecone. Redundant Raven4 altimeters and Raptors for the drogue deployment. It is a head-end dual deployment concept with a Sim max altitude of ~85,000 according to RASAero II (rounded fin edge for a conservative estimate) with a max Mach of ~3.6. Planning on 3 or 4 #6 shear pins for each section.
One of the biggest things I am struggling with is the fin attachment method. I am not planning on a tip to tip, mainly due to lack of the equipment to make this happen to be completely honest. The fin design right now is 0.1875" G10 with a 1" bevel (made by PML). The question I would like some help with is will a solid fillet be sufficient using hysol loctite ea e-120hp epoxy? The other option I am looking into is drilling and tapping holes in the fin and using steel screws through the tube wall to help reduce the chance that the peel strength of the tube wall will be the limfac. I am not set on the number of screws but from an engineering point of view I like the concept. I can't help but feel like this would be more common if it was really necessary though...
Any additional BS flags would be greatly appreciated. Thanks!
-Tony
My apologies for being 3 weeks late to the party.
As an aerospace systems engineer who works with system level reliability analysis, we use a tool called Fault Tree Analysis (FTA) which analyzes both the probability and severity of faults. On an airplane with certified software, tested and inspected wiring, and no technician level configuration prior to flight, dual identical systems are usually a good approach. But I will explain below why dual identical altimeters are not a best practice for an amateur rocketry application.
A few months ago at FAR, I watched a 54mm minimum diameter M motor University project lawn dart. They used expensive and identical altimeters. Telemetry showed that neither altimeter commanded chute deployment at apogee. They will never know if it was due to a setup error or a software issue. I would suspect a setup error but can't eliminate a software issue. This anecdote is backed by sound reliability and safety practice however.
Identical altimeters protect against wiring problems (very likely) and hardware failures (very unlikely). They don't protect against user setup errors (very likely) or software issues (somewhat likely, particularly when pushing the flight envelope).
Dissimilar altimeters protect against setup errors (very likely) and software issues (somewhat likely), in addition to the protection that redundant identical altimeters would buy you. Yes, the chance of a single setup error doubles when two different setups are used, but since it only happens on one altimeter, the failure is inconsequential.
But If a setup error occurs on one identical altimeter it will likely be repeated on the other identical altimeter, and thus a single failure leads to catastrophe. This is what we call a common cause failure in the industry and these are designed out of any certified aircraft system. I personally don't believe common cause failures belong in a high performance rocket configuration either.
P.S. Ditto on what others wrote regarding the Fingertech switches. These are robust switches and I used them on my L3. Typical screw switches may vibrate into the closed position in the trunk of a car after a four hour drive (don't ask me how I know).