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WHEN to mount ELT antenna?
I’ve seen lots of discussion posts on where to mount the ELT box itself, but really haven’t seen anything about the location of the ELT antenna , or when to mount it. I don’t want to mount the antenna before I paint the aft fuselage but by the same token, if I don’t mount it before I rivet everything together then that messes things up as well.
Has as anyone prepped the mount area including running the cable, but didn’t mount the antenna itself until much later? How did you accomplish this? I’m wrapping up the aft fuselage soon so need to line up the ducks.
Thanks for any suggestions. Really don’t want to cut an access hole.
Replies to This Discussion
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Permalink Reply by John Austin on
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I read "somewhere" that in stall-spin/loss of control accidents, there's about a 50-50 chance the plane will wind up belly-up or with the tailcone up. In our high-drag/low speed planes like the STOL 750 and your Cruzer, there's also a good chance in engine-out situations that you will land intact and nose-over if forced into a too short, too soft, too rough, or otherwise less-than-optimal landing site - the nose gear is definitely more fragile than the main gear and if it fails, a nose-over can easily result if much momentum is still there. Great testament to the design, though - usually the pilot/passenger walks away with minimal injuries!
All that is to preface why I mounted my ELT on the belly of my STOL 750. I placed it as far aft as I could comfortably reach from inside the belly hatch, riveting a reinforcing mounting plate to a transverse L stiffener. (My ELT is mounted alongside the belly hatch for easy access, so it made for a short antenna cable run.) I actually mounted mine prior to painting, ran and secured the antenna cable, and then removed the antenna and applied masking tape on the inside of the mounting hole for the trip to the paint shop. It's perfectly fine to paint the exterior where the mount goes - you just need the bare skin on the inside for good contact with the mounting hardware to ensure a good ground plane. Took about 5 minutes to reinstall the antenna after painting.
(In these pictures, the rudder cables are very close to the antenna cable and other structures, but these pictures were taken prior to attaching and tensioning the cables and when that was done, the clearances were OK!)
John
N750A
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Permalink Reply by Carl Orton on
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I thought about that, but I keep reading admonitions that it HAS to be top-mounted. I understand their and your logic though.
Can you really get up there a bit in that belly hatch, even post-construction? Again, the folks that have commented have said it's almost impossible.
Thanks for the idea and pics, though!
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I think that "top mount" vs "bottom mount" ranks right up there with "high wing" vs "low wing" and "Chevy" vs "Ford" !! LOL!
However, for the reasons outlined previously, I do think the "bottom mount" antenna will fare very well in most survivable crashes of 750 airframes. The up-sweep of the rear fuselage and substantial main gear legs are probably just as protective of the antenna, if not more so, than the argument the vertical tail protects the top-mounted antenna in a complete 180 degree nose-over. Of course, in a nose-over, the bottom mounted antenna comes to rest above the airframe.
As far as working through the hatch, I have an Ed.1 with Ed.2 upgrades and before the elevator cables are attached and tensioned, I could actually get my upper body inside the hatch and work inside the fuselage (5'9"/155 lbs). However, seems I recall seeing a picture of a transverse brace across the hatch opening in later Editions that mine doesn't have? Also, if true, I don't know if that's in both STOL and Cruzer, but I see it would be impossible to get up inside with the upper body with that brace in place. If I'm correct, is the brace removable or if not, could it be bolted rather than riveted?
John
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I'm building a Cruzer, relatively new edition (picked up Nov '17). There is no cross bar across the bottom hatch; there's just the back of the baggage compartment that extends down quite a bit, but not all the way to the floor (? about 12"?). I'm more of the large economy size guy, so it would be tight even if just sitting on a workbench!
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I'm more of the large economy size guy, so it would be tight even if just sitting on a workbench!
A smart builder keeps a couple of scrawny kids or grand-kids around for times like that! ;>)
John
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Permalink Reply by Don Morrisey on
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Carl, that cross member was added to the Cruzer along with an anchoring spot for the torque tube. Check out Plan # C75-CA-2 dated 12/15. Pic of the plan section attached below. See pics of mine here and I did attach it with bolts so it's removable:
http://www.mykitlog.com/users/display_log.php?user=n2charlie&pr...
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*sigh* once again a note or something on the "F" pages noting that you need to check CA-2 (in this case) would have been helpful.
That seems like a real PITA, Don. Having to literally remove it if you need access seems to defeat the role of the hatch!
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Permalink Reply by Jim and Amelia Isaacs on
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Thought I’d add a note regarding the new ELTs. They are advertised as 406/121.5 units and they are, but consider the risk before you buy one that without a dedicated GPS feed to the ELT, the search area is much larger than if you crashed with a dedicated GPS feed to the ELT. The SAR teams still use their 121.5 detection equipment to pinpoint your location but the newer 406/121.5 ELTs transmit the 121.5 signal at significantly reduced power as compared to the legacy 121.5 only ELT and the SAR team has to be within a few hundred yards or less to detect the 121.5 signal of a modern ELT.
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Permalink Reply by Bob Jones on
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First ol all its ok to mount the ELT even on the belly if you are only landing on airports , but then why build a STOL airplane , Most brush would tear it off , also you need to be able to remove the ELT from the airplane, and manually place it on a ground plane no matter what position the plane is in and fasten the external antenna to it , good luck getting the belly plate off after a crash , put it where you can get it and stop trying to reinvent the wheel ...BOB
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Well, I came up with a solution.
Since most of my next several tasks will be involving the front portion of the aft fuselage, I decided to delay riveting the aft portion of the upper aft fuselage skin. I've done mine slightly different. After I joined the side panels to the bottom skin panel, I left the longerons in place (reminder: this is a new-model cruzer such that just about everything is pre-drilled, cut, shaped, etc.).
During fitment of the upper skin, I riveted all L-angle diagonal and vertical pieces to the top skin, but left the last rivet holes on each end un-riveted as suggested in the HBH videos. I was able to "coax" the longeron & side skin out enough to slip the vertical angles under the longerons. Quite easily. Since there's a lot of riveting involved on the aft end in conjunction with mounting the tail etc., I figured I'll mount the ELT antenna just in front of the dorsal/vertical. I can easily flex the sides outward and prop up the skin with enough room to get my hand in there to attach the BNC coax connection once I'm near the end of the endeavor.
I just didn't want to buy a 406 ELT and have the warranty run out before I even flew just to mount an antenna early.
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Permalink Reply by David Banahan on
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I read a whole lot of where and how - not so much on when to mount and ELT. What is the requirement of when to mount it? I thought it wasn't required until after Phase 1 testing, is this correct?
Thanks
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Well, I was mostly interested in "when" during construction, since the traditional spot for the antenna is on top of the aft fuselage where the tail should protect it in the case of an inverted stop. When because the aft fuselage must be riveted at some point in order to accommodate mating the fuse halves. I didn't want to buy an antenna now ($$$), then buy an ELT later that had it's own antenna (waste). Didn't want to buy the ELT now, cuz it would be out of warranty by the time of first flight.
The way I understand it, an ELT is only required for airplanes that carry passengers - so a single seater wouldn't need one. I've never heard the Phase 1 limitation, but I'd think that a DAR would have an issue since there are two seats present. Additionally, with the new leeway granted by the FAA for having a "required" crewmember present for first flight, and I intend to have mine installed for first flight.
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