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dwight(at)openweave.org
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 Posted: Sat Dec 22, 2007 6:44 pm Post subject: Canopy "Big Cut" Question |
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Ok gang ... my canopy trimming is going quite well. And I am getting
close (already there?) to being ready for the "big cut". I'm building
an RV-7 with a tip-up canopy, and I intend to glue with SikaFlex.
At this point I have the rough-trimming done all the way around. The
front of the canopy comes to the spot that the instructions suggest
is the "right place" (though I know this can easily vary a bit from
installation to installation). I have the "do not cut" line drawn
along the back of the canopy matching the curve of the rear fuselage
skin. I've trimmed to within 2 inches of that "do not cut" line. I
have also trimmed away the bits of plexiglas with the molding lines
from the sides, but am clearly not done trimming to an exact fit (nor
should I be, according to the instructions), at least on the sides
and along the back. The only place I'm trying to get the trim _exact_
is along the front. I tell all this to paint a picture of exactly where
I am in the canopy trimming/fitting process.
With the situation as described above, and with the sides of the canopy
being pressed firmly against the side of the fuselage, I am showing
roughly a 1-inch gap between the roll bar and the inside of the canopy.
Gus at Van's suggested that getting it down to a half-inch was ideal,
but I've heard others say they did the "big cut" with a as much as a
whopping 2-inch gap there.
So ... my question is, should I continue to trim to reduce the gap or
should I just DO it? If I want to reduce the gap the only option is to
trim from the front, I believe. I figure taking off a 1/4 inch at a
time would be the way to go. True? That would be tedious ... but ... at
this point I take "tedious" as a given.
Suggestions? Insights? Comments? Any and all are welcome.
-- Dwight
RV-7, Tip-up, XP-360, API fuel injection, Hartzell BA prop
(The slowest builder in the east .... )
do not archive
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webmaster(at)flion.com
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| Posted: Sat Dec 22, 2007 9:35 pm Post subject: Canopy "Big Cut" Question |
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I just did my 6A tip-up with Sika and I'm not a big fan of the "make the big
cut and let the canopy settle" line of thinking. I had made 1/4" spacers
and set them on the bow and glare shield and found that I ended up with
about a 1" gap between the canopy and spacers. Because of the angle of the
front of the canopy, trimming the front 1" up would also move the front edge
back about the same amount. However, when I moved the canopy forward an
inch, I found that the gap had lessened and so I kept cutting the front
until I reduced the gap. Then I trimmed the sides until they fit into the
channels, and finally I marked and trimmed the aft curves after drilling the
canopy to the aft skin and channels and made sure the gaps for gluing were
still appropriate.
Before you cut any more from the aft area, you should still have enough room
to improve your fit. I varied the gluing process because I want that "Big
Cut line to be neat and also the overall canopy line to flow. So I masked
the rollover structure and glued the canopy to the canopy frame with the
frame in place on the fuselage. I crawled in from behind the baggage area
(that top skin is not in place yet, while I do some antenna wiring), and did
the fillets around the glare shield and bow and then crawled back out and
clecoed the aft skin on to position the rear of the canopy and I also did
the outside fillet on the glare shield. After it had set a week, I removed
the aft skin and the whole canopy lifted with the frame just fine.
It's been too cold here to continue, so I've been working on electrical
stuff. I've masked the rollover again, this time to expose where I want the
Sika to adhere. I've also masked the inside of the canopy in the same area.
My next step will be to glue the canopy to the rollover (I can reach in from
the aft to make the fillet on the back side of the bow). I'll cleco the aft
skin on again to set the position of the canopy. After it sets, I'll make
the big cut (I used red electrical tape to mask the inside of the canopy, so
it will be easy to see where to cut). Any Sika that has oozed forward can
be trimmed down to the rollover structure with a razor blade, and the
masking will keep the ooze from sticking to either the canopy or the
rollover.
To the question of the gap you have, I don't see how making the cut and
letting the pieces drop down to the canopy will fail to alter the entire
geometry of the canopy. Try a little more patience and get a better fit to
begin with.
Pat Kelley - RV-6A - routing antenna cables in a freezing hangar...
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davist(at)xsinet.co.za
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| Posted: Sun Dec 23, 2007 6:20 am Post subject: Canopy "Big Cut" Question |
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I glued my entire canopy on without any hole being drilled in the
plexiglass. some points to watch out for are:
1. Get the gap down to 1/8 -1/4 above the roll bar - the cut will then
line up with the roll bar. Any larger gap will cause a "departure" with the
two halves as the canopy "sinks" into position.
2. Remember that as you trim the front you will constantly have to move
the canopy forward which also closes the gap at the roll bar due to the
sloping of the canopy.
3. Leave a 1/4 " gap at the front for the Sikaflex to bond but no gap at
the aft end - you'll see why later
4. You will need to put spacers on top of the roll bar 1/8" min for the
Sika bond. There are a couple of ways to set the cut gap. Butt them up
like Van's says, trimming so as to get a nice even line and then either fix
in this way or, as I did, open the gap to 1/8' and fill with Sika, using
release agents on the tip up part. The Sika that squeezes out can be cut
and sanded down, when set, to make a nice air tight and streamlined seal.
Remember to raise the tip up side by means of spacers as well so that the
halves meet at the same level. To hold in place while setting I used straps
going right around the fuse.
5. Don't try and do all the gluing at once. In fact it is far easier to
do sections at a time and then come back to fill in. The Sika bonds well to
set Sika.
6. Use electrical tape to mask off areas you dont want glue on. Don't use
masking tape as it will stay under the Sika when you try and pull it off.
7. The Sika skins over quite quickly. If you haven't smoothed it by the
second or third pass then leave it, let it dry and cut away and try again
later.
8. Very important to use the correct Sika Primers and to follow the
instructions.
9. If you want to cover the glare shield with Leather/vinal then you need
to think about putting it in place and masking it about 1/4' from the plexi
before laying a bead inside to give it a nice finished look .
10. To glue the front of the canopy, I filled the gap with dollops of Sika
and then built up layers on the outside, shaping as I went to form a sloping
filler ( used an old credit card) I was going to sand and leave the Sika as
the final fairing but decided against as the inevitable someone would as
sure as hell come and stick his fingernail in it just to see how hard it
sets! I fibreglassed over the Sika - easy to do as it is already shaped and
it bonds well to the Sika without any primer
11. Remember to roughen the plexi where you want the Sika to bond (100
grit works well)
For the sides I drilled five of the fairing attach holes (only thro the
frame - fairing will be match drilled later) in order to hold scrap 1/4" bar
stock clecoed to the frame and overlapping the plexi in order to keep the
plexi in place while the Sika set. Remember to mask off the plexi at frame
height as the glue will ooze out. Not necessary to have a gap as your
adhesion for strength will come from the fillet you place in the recess of
the frame and the bottom of the plexi, before closing with the alu fairing
and backdrilling the five holes you drilled previously.
The aft canopy you do by cutting the overlap to +/- 1", roughen up, mask
off, apply Sika and have some broomsticks and foam handy so that you can
wedge the plexi up nice and tight against the rear skin. Let set, reapply
the masking on the inside, so as to have a 1/4" gap from the plexi and then
apply your fillet to give a nice strong and finishing edge. You should get
a nice even and almost flush fit to the aft skin. Use some tank sealant
along the outside to really give it a smooth transition.
I have not covered all the nitty bits as it would take all day to read but
if you would like any further info I'll be glad to pass it on or refer you
to fellow RV-Sika Stickers here in South Africa.
Trevor Davis: RV-7 tip up also building -7 slider with Sika
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rv9jim(at)juno.com
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| Posted: Sun Dec 23, 2007 12:02 pm Post subject: Canopy "Big Cut" Question |
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Dwight,
I did the skia flex on my canopy. Make sure you have the spacers
in place that will keep the canopy up away from the metal structures that
you will glue to. This will require the canopy to be "longer" on the
sides to make up for the raising of the canopy. I did the slider and
"forgot" about the difference. Needless to say, I had to make the side
skins again to make up for the taller canopy. I had cut to fit and then
went oops! I also had to make my rear canopy fairing from glass as the
aluminum would not work as the canopy was taller back there. It worked
out ok and I'm happy with the fit. The same goes for the windscreen in
the front. I used about a 3/8" spacer to let the adhesive work properly.
I did bolt the sides thru the canopy to the frame. Those are the only
holes in my canopy.
Jim Nelson
RV9-A
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dcw(at)mnwing.org
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| Posted: Sun Dec 23, 2007 1:04 pm Post subject: Canopy "Big Cut" Question |
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Hmm.. thus you have more headroom in the airplane. How much did you think
you added? One of our local RV-9A folks used this technique and it never
occurred to me that you would be increasing headroom. I have just started
an RV-7 and may consider the sikaflex method when the time comes.
Doug Weiler
RV-4, 450 hours
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acepilot(at)bloomer.net
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webmaster(at)flion.com
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| Posted: Sun Dec 23, 2007 1:24 pm Post subject: Canopy "Big Cut" Question |
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He added 3/8". That's the recommended spacing. It may make the difference
between wearing a cap or not, but it's not huge.
Pat Kelley - RV-6A - Hoping Santa brings me an engine...
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