54170b wrote:Easy do it yourself mod. I installed mine via 337 and had to figure it out. Even so it wasn't too bad.
HOLEY-MOLEY! LOOK OUT! THIS changes EVERYTHING!!
A
RED door on a
GREEN airplane! Does it tend to TURN RIGHT?
Aren't you
glad you could find that
RED door to
strengthen that shade-tree'd installation!
(So... what did you do with finish when you completed the project?....or is it still in-progress?)
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minton wrote:Gee, You, (Cessna) engineers a reinforcement so as not to fail and wala no failures! Am I missing something? ....
Perhaps. There have also been no failures without that doubler. It has yet to be established the doubler was specifically to reinforce a door installation as opposed to an assembly-operation for fuselages with doors.
minton wrote:...Did'nt get to finish my thoughts.
I think aircraft are engineered to a 150% design failure or deformation rate somewhere around there maybe more so many design approaches can attain the same result. I wold think the STC'd ones have that engineered in somehow.
.
As would the one in Anacortes just illustrated if it incorporated the door-frame. Think of it as an inspection hole with a convenient cover. The hole is reinforced by the door-frame, which commutes all the torsion/tension/compression loads to the surrounding structure. No weakening of the fuselage occurs with a hole in the side which is surrounded by that frame because the load pathways are still there....in fact it is strengthened. A tubular steel fuselage is constructed entirely of trusses....little or no strength is derived from the fabric covering. But it's heavy, and that's the beauty of monocoque.
A monocoque fuselage is strong because its skin is the outer pathway for all stresses. But dent or damage that skin and with no underlying structure, the monocoque has lost it's strength. With the doorframe, the fuselage has underlying structure to pass-along any stresses the skin where that hole is would have. (At least, that's how Cleo put it.)
The hole created when a bag door is installed is not in the belly (where that doubler is) but is in the side.
It seems to me that if we cut a hole in the belly (like for a camera hole) the doubler of sta 90 would make perfect sense (or if the fwd portion of the fuselage known as the cabin area were constructed seperately to be later mated on an assembly-line with a tailcone unit...that sta 90 bulkhead would be subject to damage until mated...and might need a doubler.
The problem with communications with Cessna these days is the "old, experience" up there is retired and gone. The 1986 shutdown period created a loss-of-continuity in the single-engine line, and the line was started back up in Independence with all new help. They went thru all sorts fo teething troubles making the same airplanes as previously...as if they'd never done it before. (Remember when they couldn't figure out why new C-206 flaps were cracking? They solved it when they reinvented the same solution they did back in 1964. But they'd lost the notes.)
Perfect examples are:
1- When I called for a guest-speaker for the Opening Dinner of the 2007 TIC170A convention, the lady at Cessna listened to my desire for one of the old-timers who might have stories about the factory while they constructed our 170s, then she transferred me to the manager of the single-engine assembly line over in Independence. HE transferred me to production manager, and HE suggested that if I wanted a knowlegeable speaker for a 170 group I should call a guy down in Texas named George Horn and offered to find his contact info for me.
2- When I rec'ed a call from an
engineer at Cessna who claimed to be THE fuel-systems engineer for the single-engine line, and was working on the new Columbia, ...he was calling me to ask for an explanation as to WHY the straight-170 (with a fuel pump) needed a check-valve in what appeared to bypass the pump....and WHERE could he obtain such.
(He admitted that much documentation of earlier production airplanes, including the 170 line, had been deliberately destroyed under instructions from the legal department, in an effort to rid themselves of any liability of ongoing support. The point I'm making is, that common sense and reviews by locally obtained engineering surveys are more likely than Cessna in coming up with answers on matters such as we've been discussing in this thread. )
3-When a three-way partnership in a straight-170 called to get information on where they could get the "STC" for removing the pump in their ragwing. They'd been flying it without a pump for 3 years and realized they had no documentation for no pump. When I suggested they were lucky to be based in OKC and not have been caught in a knowlegeable ramp-check...it came to be revealed the 3 partners WERE FAA.
When we met Mort Brown (Cessna Chief Production Test Pilot, Ret'd) at Branson, MO and spent considerable time with him asking questions about this airplane, he can be forgiven for memory-lapses, as he was 98 years old. But he told me personally that all the old experience was gone up there and it was likely much detail is lost to history about these airplanes.
I'm only sayin'.... even when airplanes are undergoing original design, engineers may differ in opinons as to the necessity of some solutions. It's likely that a contemporary review of structures is just as valid as anything they did back in the 1950's, maybe more so, and an STC'd modification such as the bag door installation is not less-engineered or less safe simply because Cessna didn't do it.
(I realize that bluEldr just nodded-off so I'll stop now.)
even the properly installed ones (factory) have had costly damage done due to hard landings, tail strikes, etc. so play that theme foward to a logical conclusion and It becomes clear to me anyway that a weakened area has a better chance of a failure. 
