Super Rebel - Elevator Construction thoughts!
Posted: Fri Feb 17, 2012 9:59 pm
Been waiting almost a month now for my forward float fittings (and some
other parts for other projects) so I can complete the gear box mods, so in
the mean time I have been working on the 3500 upgrades to the Stab and
Elevator to keep me going. Boy I'll tell you a 90* angle drill and a
threaded bit about 1/2" long is the cats meow to back drill the "strap" area
instead of doing the plastic transfer system!
Just finishing up the upgrades on the Elevator and then today I was working
on straightening out the balance tips, that were constructed previously a
little twisted, and also the trim tab "upgrade" (from the old -4A and
internal linkage to the -8A servo and external linkage and horns) and have a
few thoughts to offer to those that are (or will be) doing the same. Like I
say I'm offering the "thoughts"! MAM has last authority on everything and if
you chose to follow my suggestions you do so at your own risk!
When it comes time to do the elevator tips do yourself an favour and build a
simple jig to hold things straight. DO NOT proceed as spelled out in the
manual as this is how Rob got them built twisted. I found I had to uncleco
the outboard rib on one side and the inboard on the other side so I could
twist the assembly back straight and then was able to drill these now offset
holes to 5/32 to clean up and hold straight. The next thing was that using
the skin holes as punched (that overlap onto the elevator spar and skin)
made the tips locate other than straight and in fact had the tips drooping
about 3/8" from what should have been straight. Therefore I had to adjust
the overlaps location a bit to get thinks straight and ended up with 5/32 on
one side and 3/16 on the other in the outer 4 holes that had already been
drilled. Luckily the other 6 holes per side hadn't been drilled yet.
What I suggest to do when building new is to make a simple jig with a length
of board or aluminum angle to pick up the 4 tooling holes on the end ribs.
That is the two tooling holes in the outboard elevator rib face and the 2
holes in the outboard tip rib face. Measure for there locations and then
drill the 4 holes in a straight line on your jig "fixture". Then put a 3/16
bolt in each of the holes and peg the ribs in a straight line with each
other. Then drill your tip skin to the ribs and then the overlap splice.
If you have an older kit and also have to upgrade from the internal to the
external trim servo hook up I offer the following. First make sure you get
your new -8A servo from MAM and return the -4A! The upgrade instructions
show to put the two attach horns, that go on the elevator, simply on the
skin of the finished trim tab. I can tell you right now that won't last much
past the first nose up trim application, from experience with the Rebel's
smaller trim tab cracking the spar and skin with the same style horn
attached to it in a similar manner. Can't imagine it holding at all on the
SR tab, that is at least 4 times the area as the Rebels. The newer
instructions for building, although not really mentioned in the
instructions, show a drawing of two ribs under the horns. I opened up the
finished trim tab, removed the eyebolt from the internal linkage setup and
added the two ribs (used the ribs removed from the inboard edges of the
elevator during the 3500 upgrade). I also added a .025" gusset plate that
covers from the outboard ribs first 3 rivets across the new double rib to
pick up the horns and then about 2 rivets past the double rib onto the hinge
spar. I also added a corner gusset on the other ends rib to hinge spar
junction (in a triangle 3 rivets each way), as well as the center rib with
a triangular gusset while I had it opened. Thought it could use the strength
as the ribs were only tied in with the skin and a single rivet at the spar,
as no angle brackets spelled out in OLD instructions. I see they are in the
new instructions with a quick line to make some 90* tabs. All three of these
gussets are installed on top of the ribs, under the skin and slipped under
the spar flange for a smooth skin.
ALSO FOR ALL SR's! The Mac-8A servo has the threaded actuator screw
protruding out the opposite end of the unit from the clevis attachment end.
Not mentioned in the manual but, you will need to drill a clearance hole
through the spar so this can extend out to allow ANY nose up travel of the
unit. The threaded screw extends about an inch from the unit with full up
elevator travel, and the servo itself only sits about 3/8" from the spar! If
you don't drill the hole in the spar you will get full nose down trim, but a
jammed (trying to run) servo rod chewing into the spar for nose up. Not a
good thing :>( !!
I also found, on my previously finished elevator, that the "hinge" spar at
the trim tab cutout is basically held in place by the top/bottom skins and
that there is no call out in the manual for brackets to hold it to the full
length elevator rib at either end of the cut out area (probably assumed to
be done, but obviously that doesn't work!). In this configuration you can
flex the trim cutout area up and down in relation to the full length areas
and as such sooner or later the skin is going to crack at the corners of the
trim tab cut out. If you haven't closed it up yet get some angles at the
junctions to tie it all together. If closed already just put the angles
externally (as I did) to stiffen this area up and tie it all together.
Regards,
Wayne G. O'Shea
www.irishfield.on.ca
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other parts for other projects) so I can complete the gear box mods, so in
the mean time I have been working on the 3500 upgrades to the Stab and
Elevator to keep me going. Boy I'll tell you a 90* angle drill and a
threaded bit about 1/2" long is the cats meow to back drill the "strap" area
instead of doing the plastic transfer system!
Just finishing up the upgrades on the Elevator and then today I was working
on straightening out the balance tips, that were constructed previously a
little twisted, and also the trim tab "upgrade" (from the old -4A and
internal linkage to the -8A servo and external linkage and horns) and have a
few thoughts to offer to those that are (or will be) doing the same. Like I
say I'm offering the "thoughts"! MAM has last authority on everything and if
you chose to follow my suggestions you do so at your own risk!
When it comes time to do the elevator tips do yourself an favour and build a
simple jig to hold things straight. DO NOT proceed as spelled out in the
manual as this is how Rob got them built twisted. I found I had to uncleco
the outboard rib on one side and the inboard on the other side so I could
twist the assembly back straight and then was able to drill these now offset
holes to 5/32 to clean up and hold straight. The next thing was that using
the skin holes as punched (that overlap onto the elevator spar and skin)
made the tips locate other than straight and in fact had the tips drooping
about 3/8" from what should have been straight. Therefore I had to adjust
the overlaps location a bit to get thinks straight and ended up with 5/32 on
one side and 3/16 on the other in the outer 4 holes that had already been
drilled. Luckily the other 6 holes per side hadn't been drilled yet.
What I suggest to do when building new is to make a simple jig with a length
of board or aluminum angle to pick up the 4 tooling holes on the end ribs.
That is the two tooling holes in the outboard elevator rib face and the 2
holes in the outboard tip rib face. Measure for there locations and then
drill the 4 holes in a straight line on your jig "fixture". Then put a 3/16
bolt in each of the holes and peg the ribs in a straight line with each
other. Then drill your tip skin to the ribs and then the overlap splice.
If you have an older kit and also have to upgrade from the internal to the
external trim servo hook up I offer the following. First make sure you get
your new -8A servo from MAM and return the -4A! The upgrade instructions
show to put the two attach horns, that go on the elevator, simply on the
skin of the finished trim tab. I can tell you right now that won't last much
past the first nose up trim application, from experience with the Rebel's
smaller trim tab cracking the spar and skin with the same style horn
attached to it in a similar manner. Can't imagine it holding at all on the
SR tab, that is at least 4 times the area as the Rebels. The newer
instructions for building, although not really mentioned in the
instructions, show a drawing of two ribs under the horns. I opened up the
finished trim tab, removed the eyebolt from the internal linkage setup and
added the two ribs (used the ribs removed from the inboard edges of the
elevator during the 3500 upgrade). I also added a .025" gusset plate that
covers from the outboard ribs first 3 rivets across the new double rib to
pick up the horns and then about 2 rivets past the double rib onto the hinge
spar. I also added a corner gusset on the other ends rib to hinge spar
junction (in a triangle 3 rivets each way), as well as the center rib with
a triangular gusset while I had it opened. Thought it could use the strength
as the ribs were only tied in with the skin and a single rivet at the spar,
as no angle brackets spelled out in OLD instructions. I see they are in the
new instructions with a quick line to make some 90* tabs. All three of these
gussets are installed on top of the ribs, under the skin and slipped under
the spar flange for a smooth skin.
ALSO FOR ALL SR's! The Mac-8A servo has the threaded actuator screw
protruding out the opposite end of the unit from the clevis attachment end.
Not mentioned in the manual but, you will need to drill a clearance hole
through the spar so this can extend out to allow ANY nose up travel of the
unit. The threaded screw extends about an inch from the unit with full up
elevator travel, and the servo itself only sits about 3/8" from the spar! If
you don't drill the hole in the spar you will get full nose down trim, but a
jammed (trying to run) servo rod chewing into the spar for nose up. Not a
good thing :>( !!
I also found, on my previously finished elevator, that the "hinge" spar at
the trim tab cutout is basically held in place by the top/bottom skins and
that there is no call out in the manual for brackets to hold it to the full
length elevator rib at either end of the cut out area (probably assumed to
be done, but obviously that doesn't work!). In this configuration you can
flex the trim cutout area up and down in relation to the full length areas
and as such sooner or later the skin is going to crack at the corners of the
trim tab cut out. If you haven't closed it up yet get some angles at the
junctions to tie it all together. If closed already just put the angles
externally (as I did) to stiffen this area up and tie it all together.
Regards,
Wayne G. O'Shea
www.irishfield.on.ca
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