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tonyrenshaw268(at)gmail.c
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 Posted: Thu Sep 15, 2011 11:06 pm Post subject: Baggage Bay Upper Fuselage Attachment |
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I'm trying to minimise the amount of redux and work needed to get a good job gluing on this top. It aint for some time yet, but I'd like to bond in my extended baggage bay floor, and bulkhead. I can do this but then it sticks up in the breeze acting as a nuisance. I've already layed up flanges on the arched section to mate with the roof, but what I'd really like to do is cut it off, and bond it on later, once the top is on. It will be easy as I'll just redux it in as one piece, and then I only need to do strapping patches both front and back of the cut areas. Does anyone see anything wrong with doing this?
Reg
Tony Renshaw
Sydney Aussie
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budyerly(at)msn.com
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| Posted: Sun Sep 18, 2011 7:18 am Post subject: Baggage Bay Upper Fuselage Attachment |
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<?xml:namespace prefix="v" /><?xml:namespace prefix="o" /><![endif]--> Tony,
Yes it is possible, but take your time and make yet another flange to be able to glue the all too important back bulkhead to the top. The short answer is the baggage bay bulkhead sticks up only a little higher than the rear bulkhead so it is worth it in my opinion to leave it alone and glass it in later...
Now the reasons (read as the long and boring answer):
I am getting less maneuverable with age so anything I can do to finish the lower canoe and make my time in the aft fuselage more comfortable, I try to do. It is no secret that I glass in my baggage bay floor prior to putting the top on. Much fitting and adjusting is necessary adding a number of hours of trimming, measuring, and fitting. However all the tasks of installing trigears, and fitting rear mounted batteries, flap drives, antenna planning, fuel pump installation, wiring, guiding rudder cables, fuel and brake lines, and the tedious upside down work glassing of those baggage bay supports, becomes a snap. If time is taken to properly prep the bulkhead and make a flange on the inside of the top, it makes the task of crawling in the rear of the aircraft a final inspection and hookup exercise rather than a construction exercise. This is important, and very welcome, when working alone where time is not a factor.
A minor but important technical point is that the rear bulkhead has a foam core, and I see many folks just cut the bulkhead to shape without considering the edge of the bulkhead closeout. Technically the foam core, if cut and exposed, needs to have the skins attached together by cutting out the foam core material back 1/4 to half inch and filling with flox (done when the part is attached to a flange forming an L bond), or leave the foam exposed and glass the front and back (inner and outer) skins to each side of the top forming a TEE FLANGE. Hard to use words to explain, but the strength of composites in bending and buckling is the foam core to fiberglass bond. We know the foam is supposed to be hollowed out at the exposed edge and filled or tapered to make a glass to glass bond, but that is forgotten many times with the bulkhead and access panels. Note that in a perfect world, if we make a flange joint in the aircraft, it is assumed to be a glass to glass bond. My technique is, if I expose the foam core on the bulkhead, I glass both sides so I don’t have to cut back the foam and refill the void, or taper the end, to get the important glass to glass bond. Refer to Chapter 23 or 33T on the techniques for a glass to glass bond.
I spend a lot of time making bulkhead flanges and mass balance tower flanges fit perfectly so I can put the top on in one shot, and I rely on my clecos and screws to hold the tabs and flanges in position, all while keeping the top, tail and stab perfectly aligned until the glue dries. The long pole in the tent is that the top has to be final fitted (many times) and clecoed on as if it were just glued in so all your flanges have the right shape and position...
On a personal note, if you leave your bulkhead alone, sticking up, and spend the time in the hole later, glassing the flange in position, it is actually faster and stronger to just leave your bulkhead loose and crawl in and glass it in place on both sides after the top is on. All it takes to keep the bulkhead where you want it for glassing, is to tack in a small block of foam or wood to keep the bulkhead fixed and steady.
In my opinion, if you you can't get into the hole, get a smallish helper, and train him, it is faster and cheaper. The baggage bay bulkhead sticks up only a little higher than the rear bulkhead and allows any wire tabs or attachments to be fitted and clearanced also, so it is worth it in my opinion to leave it alone and glass it in later...
Regards,
Bud
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tonyrenshaw268(at)gmail.c
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| Posted: Mon Sep 19, 2011 5:44 am Post subject: Baggage Bay Upper Fuselage Attachment |
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Whoa Bud,
I didn't realise this response even existed when I rattled off my request for a picture. Thanks heaps. I am going to digest it tomorrow, but I don't know how you manage to get any work done with the amount of good gen you spread on the list. Thank you once again Bud.
R
TR
On 19/09/2011, at 1:16 AM, Bud Yerly wrote:
[quote] Tony,
Yes it is possible, but take your time and make yet another flange to be able to glue the all too important back bulkhead to the top. The short answer is the baggage bay bulkhead sticks up only a little higher than the rear bulkhead so it is worth it in my opinion to leave it alone and glass it in later...
Now the reasons (read as the long and boring answer):
I am getting less maneuverable with age so anything I can do to finish the lower canoe and make my time in the aft fuselage more comfortable, I try to do. It is no secret that I glass in my baggage bay floor prior to putting the top on. Much fitting and adjusting is necessary adding a number of hours of trimming, measuring, and fitting. However all the tasks of installing trigears, and fitting rear mounted batteries, flap drives, antenna planning, fuel pump installation, wiring, guiding rudder cables, fuel and brake lines, and the tedious upside down work glassing of those baggage bay supports, becomes a snap. If time is taken to properly prep the bulkhead and make a flange on the inside of the top, it makes the task of crawling in the rear of the aircraft a final inspection and hookup exercise rather than a construction exercise. This is important, and very welcome, when working alone where time is not a factor.
A minor but important technical point is that the rear bulkhead has a foam core, and I see many folks just cut the bulkhead to shape without considering the edge of the bulkhead closeout. Technically the foam core, if cut and exposed, needs to have the skins attached together by cutting out the foam core material back 1/4 to half inch and filling with flox (done when the part is attached to a flange forming an L bond), or leave the foam exposed and glass the front and back (inner and outer) skins to each side of the top forming a TEE FLANGE. Hard to use words to explain, but the strength of composites in bending and buckling is the foam core to fiberglass bond. We know the foam is supposed to be hollowed out at the exposed edge and filled or tapered to make a glass to glass bond, but that is forgotten many times with the bulkhead and access panels. Note that in a perfect world, if we make a flange joint in the aircraft, it is assumed to be a glass to glass bond. My technique is, if I expose the foam core on the bulkhead, I glass both sides so I don't have to cut back the foam and refill the void, or taper the end, to get the important glass to glass bond. Refer to Chapter 23 or 33T on the techniques for a glass to glass bond.
I spend a lot of time making bulkhead flanges and mass balance tower flanges fit perfectly so I can put the top on in one shot, and I rely on my clecos and screws to hold the tabs and flanges in position, all while keeping the top, tail and stab perfectly aligned until the glue dries. The long pole in the tent is that the top has to be final fitted (many times) and clecoed on as if it were just glued in so all your flanges have the right shape and position...
On a personal note, if you leave your bulkhead alone, sticking up, and spend the time in the hole later, glassing the flange in position, it is actually faster and stronger to just leave your bulkhead loose and crawl in and glass it in place on both sides after the top is on. All it takes to keep the bulkhead where you want it for glassing, is to tack in a small block of foam or wood to keep the bulkhead fixed and steady.
In my opinion, if you you can't get into the hole, get a smallish helper, and train him, it is faster and cheaper. The baggage bay bulkhead sticks up only a little higher than the rear bulkhead and allows any wire tabs or attachments to be fitted and clearanced also, so it is worth it in my opinion to leave it alone and glass it in later...
Regards,
Bud
---
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