When I set my canopy frame on the fuse with the tracks centered where I think they should go (or at least close), the center of the canopy frame doesn't line up with the center of the roll bar - it's off by about 3/16" (the C/L of the frame is about 3/16" to the right of the C/L of the roll bar, when standing at the firewall looking aft). Is this fairly common with slider canopies? If it is, I think it means my canopy tracks will be need to be located more to one side than the other on the fuse (if that makes sense), and they won't be centered as I'd like. Has anyone else had this problem? And if so, what did you do about it. Do I just need to live with it and move on?
Van's Air Force
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Quick slider frame question
- Thread starter ge9a
- Start date
This is the fun part...
My frame was not the right shape at all when I started. Lots of bending, pulling and sweat required to make it fit at all points. So far that has been my least favorite (read: "most hated") part of the project. Even worse than fiberglass!! I'd not suggest shifting the tracks to one side because that just introduces problems aligning the side bows and skirts with the fuselage skin. You really need to center the slider frame on the roll bar and then bend the front bow of the frame to line up with the roll bar and the roller tracks.
It really is a pain but you want to get started with everything as square, straight, centered and lined up as possible because 3 steps down the line any errors have a way of becoming magnified.
My frame was not the right shape at all when I started. Lots of bending, pulling and sweat required to make it fit at all points. So far that has been my least favorite (read: "most hated") part of the project. Even worse than fiberglass!! I'd not suggest shifting the tracks to one side because that just introduces problems aligning the side bows and skirts with the fuselage skin. You really need to center the slider frame on the roll bar and then bend the front bow of the frame to line up with the roll bar and the roller tracks.
It really is a pain but you want to get started with everything as square, straight, centered and lined up as possible because 3 steps down the line any errors have a way of becoming magnified.
Jerry Cochran
Well Known Member
Since you live so close to Van's, do what other locals like me have done, which is to take it back and swap for another. Keep doing this until you find one that lines up more or less. Much easier than cutting, welding, etc. This problem has been common for years. Makes ya wonder about the jig the fabricator is using.
HTH,
Jerry in Sherwood
I agree with rvtach
I just finished main canopy installation and can tell you what I learned.
1) Center of fore frame bow should be aligned with center of roll-bar NOT taking aside one of rails (you will have problems later fitting side skins and/or gap on corresponding aft bow joint where it clears aft top fuse skin), but bending more the longer bow (i.e.: if center of frame is towards copilot seat, you will have to bend more the pilot bow, thus shortening it and pulling the center of the frame in that direction);
2) don't cut forward bows (bottom part...where plastic wheels go) unless it is necessary for compensating for different heights of forward bows; otherwise, you will have to add temporary spacers when fitting windscreen;
3) try to achieve the distance from external part of side bows to fuselage skin projection (this distance is approx. 3/32'') only in the first part of the fuselage (from fore bows towards aft); if distance will be the same along the whole frame sides, you will have problems in sliding the frame/canopy, since aft bows will bump aft fuselage skin (I lost few labour hours for compensating this problem); when you go aft, distance will reduce until it becomes 0 approx. when aft bows join side bows;
AFT BOWS MADNESS:
4) don't jump hard on aft bows to bend them: they are fragile and you will obtain an acute angle, which will be difficult to recover (I lost a whole day for having met this problem);
5) vertical distance between side bows and fuse longerons (which should not vary for more than 4/32'' from fore to aft, according to manual) is obtained mainly playing with aft bows curve and shortening fore bows (the latter only after fitting windscreen with canopy); the more you bend one of the aft bows, the more distance will be achieved vertically from aft part of corresponding side bow and fuselage;
6) if you bend one of the aft bows, it will become shorter thus pulling the whole aft frame part in its direction, misaligning the aft center frame in respect with slide rail laying on the upper aft skin;
7) so, if you need to bend one of the aft bows (in order to let it rest at the same level or just above aft skeen profile: this is important for aft skirt fitting), you have to consider that the bigger section aft side of side bow bending will be prevailing in the fight against smaller section aft bow bending; this mean that bending aft bow will not spread side bow, but only adding bend in a single portion of aft bow and subtracting from another part; so, the best procedure for bending aft bow without misalignind the other parts is the following:
a) bend aft bow;
b) as a result, aft side bow distance will decrease AND center of the frame, at the aft part, will probably get misaligned;
c) so, to recover for this, you will have to elongate again the bow; since it will be useless to act on aft bow again (you will return to situation before stage a), you will have to enlarge SIDE bow (aft part of side bow): I managed to do this placing the frame on the selected side on a table, the fore bow (the big section one, less prone to get misaligned) on a chair [and my left foot on them] and right foot on aft bow, placing force on it in order to elongate it (i.e.: to let it go outside).
I lost approx. 20 labour hours for not having understood point #7. Manual only says that you have to think in three dimensions. Above is an explanation of what worked in my case.
Hope this helps.
Camillo
I just finished main canopy installation and can tell you what I learned.
1) Center of fore frame bow should be aligned with center of roll-bar NOT taking aside one of rails (you will have problems later fitting side skins and/or gap on corresponding aft bow joint where it clears aft top fuse skin), but bending more the longer bow (i.e.: if center of frame is towards copilot seat, you will have to bend more the pilot bow, thus shortening it and pulling the center of the frame in that direction);
2) don't cut forward bows (bottom part...where plastic wheels go) unless it is necessary for compensating for different heights of forward bows; otherwise, you will have to add temporary spacers when fitting windscreen;
3) try to achieve the distance from external part of side bows to fuselage skin projection (this distance is approx. 3/32'') only in the first part of the fuselage (from fore bows towards aft); if distance will be the same along the whole frame sides, you will have problems in sliding the frame/canopy, since aft bows will bump aft fuselage skin (I lost few labour hours for compensating this problem); when you go aft, distance will reduce until it becomes 0 approx. when aft bows join side bows;
AFT BOWS MADNESS:
4) don't jump hard on aft bows to bend them: they are fragile and you will obtain an acute angle, which will be difficult to recover (I lost a whole day for having met this problem);
5) vertical distance between side bows and fuse longerons (which should not vary for more than 4/32'' from fore to aft, according to manual) is obtained mainly playing with aft bows curve and shortening fore bows (the latter only after fitting windscreen with canopy); the more you bend one of the aft bows, the more distance will be achieved vertically from aft part of corresponding side bow and fuselage;
6) if you bend one of the aft bows, it will become shorter thus pulling the whole aft frame part in its direction, misaligning the aft center frame in respect with slide rail laying on the upper aft skin;
7) so, if you need to bend one of the aft bows (in order to let it rest at the same level or just above aft skeen profile: this is important for aft skirt fitting), you have to consider that the bigger section aft side of side bow bending will be prevailing in the fight against smaller section aft bow bending; this mean that bending aft bow will not spread side bow, but only adding bend in a single portion of aft bow and subtracting from another part; so, the best procedure for bending aft bow without misalignind the other parts is the following:
a) bend aft bow;
b) as a result, aft side bow distance will decrease AND center of the frame, at the aft part, will probably get misaligned;
c) so, to recover for this, you will have to elongate again the bow; since it will be useless to act on aft bow again (you will return to situation before stage a), you will have to enlarge SIDE bow (aft part of side bow): I managed to do this placing the frame on the selected side on a table, the fore bow (the big section one, less prone to get misaligned) on a chair [and my left foot on them] and right foot on aft bow, placing force on it in order to elongate it (i.e.: to let it go outside).
I lost approx. 20 labour hours for not having understood point #7. Manual only says that you have to think in three dimensions. Above is an explanation of what worked in my case.
Hope this helps.
Camillo
Last edited:
Thanks for the information Camillo! I wasted over 50 hrs fighting my canopy frame and now have a new one to try again...worst part of the whole build in my opinion and the most frustrating.
I'll apply your "lessons learned" with some other techniques and hopefully have a better result this time!
Doug
90116
vlittle
Well Known Member
I'll chime in here.
Sometimes, it's not the canopy frame that's the problem. There is a critical dimension on the fuselage width at the roll bar position that is not well controlled during construction.
Van's does not publish this dimension directly, although the canopy instructions have dimensions that may not make sense if your fuselage is wider or narrower than normal.
I highly recommend talking to Vans about what this dimension was designed to be, then finding a way (jacks or long pipe clamps) to adjust it before fitting the roll bar, which may also need adjusting.
In my survey of several aircraft, I've found up to a 1 inch variation in fuselage width at this point, which can really mess up the shape and fit of the canopy frame. In general, if the fuse is wider here than nominal, the frame will be difficult to fit at the aft bows without cutting and welding. Somewhat narrower fuselages seem to have an easier time.
My QB 9A fuselage had this problem, and as a result the fuselage sides had a greater curve to them in order to narrow down to the correct width at the seatback brace position. This shape meant a lot of bending of the side bows, cutting of the aft bows and large fish-mouths on the aft part of the slider tracks.
In the end, I got everything to fit well, but it was very frustrating until the light bulb went on.
Thanks, Vern
Sometimes, it's not the canopy frame that's the problem. There is a critical dimension on the fuselage width at the roll bar position that is not well controlled during construction.
Van's does not publish this dimension directly, although the canopy instructions have dimensions that may not make sense if your fuselage is wider or narrower than normal.
I highly recommend talking to Vans about what this dimension was designed to be, then finding a way (jacks or long pipe clamps) to adjust it before fitting the roll bar, which may also need adjusting.
In my survey of several aircraft, I've found up to a 1 inch variation in fuselage width at this point, which can really mess up the shape and fit of the canopy frame. In general, if the fuse is wider here than nominal, the frame will be difficult to fit at the aft bows without cutting and welding. Somewhat narrower fuselages seem to have an easier time.
My QB 9A fuselage had this problem, and as a result the fuselage sides had a greater curve to them in order to narrow down to the correct width at the seatback brace position. This shape meant a lot of bending of the side bows, cutting of the aft bows and large fish-mouths on the aft part of the slider tracks.
In the end, I got everything to fit well, but it was very frustrating until the light bulb went on.
Thanks, Vern
