Ch 11.4: Elevator Construction (1 of 2)

Now that I have two elevators, I need to attach them together into a single structure.  This section is all mechanical, no glass work here.


Close-Out the Outboard Ends
The first task was to clean out the outboard ends of each elevator torque tube and install the NC-6 insert end pieces to cap them off.  In doing so, I had to drill two holes, one for a rivet (in front in the picture) that holds the NC-6 in place, and the other on the bottom where a small threaded lock screw will eventually lock in the stainless hinge pin.  The bottom one was a little nerve racking because your drilling blind into an already threaded hole.  Missing the hole would be bad and blowing through the torque tube and into the threads would screw them up.    TIP:  I did this work in a serial manner...install rivet, then figure out the blind hole to drill.  What I should have done was use the rivet to hold the part in place (but not permanently squeezing it in) while I located the blind hold to drill.  Then removed the part, drilled the hole, and then permanently installed the part with the rivet.  That would have eliminated the risk of ruining threads in the part.  Oh well, this is an educational activity after all!  I'll probably be saying that a lot.

I did my best to measure the location of the hole using a digital caliber and transferring the location onto the outside of the torque tube.  I was dead on the first time. On the second I was close enough but I think I ate up a few threads in the insert.  There are clearly some still there so all is good.

Uh Oh...Questioning the Dimensions
Now I laid all the parts out on the bench end-to-end to make sure everything was looking correct before I started drilling holes.  I compared the hinge locations in the hardware to the hard points embedded in the canard and noticed that the first inboard hinge points were not falling quite in the middle of the hard point at B.L. 15.6" per plans.  It was only off by .1" at 15.7" and would work fine, but it shouldn't have been off at all...what was up?

I did multiple measurements of all the parts and hard point locations and what I found was that the
Cozy Girls CZNC-12A offset torque tube dimensions were slightly longer than the plans on the inboard side of the hinge slot which made the overall length of the part .2" longer than the plans indicate.  So it that was the case, why weren't my elevators .2" longer on each side?  Something had to be wrong in the plans.  Additionally, only the first hinge slot is off and by only .1".  It falls at B.L. 15.7" vs the plans 15.6".  The outer two hinge locations were per plans and when I measure the overall length of the elevator assembled on the bench it comes to 140.8" just as it should be.  What's going on here?  The only answer I could come up with was that are multiple places in the plans dimensions for the offset torque tube as well as hinge hard point locations in the canard that must be incorrect.

I spent way to long on this for a .1" difference but I wanted to understand what was going on.  Here is what I found.  I already mentioned the CZNC-12A being .2" longer than plans spec.  Additionally, I believe the B.L 15.6" callout for the location of the center of the first inboard hinge hardpoint and hinge slot in the CZNC-12A is wrong in the plans (Ch 10 pg 7, fig 48, and Ch 11 pg 2).  I know this because if you starting from the center line and add up the length of the center torque tube (15.1") and the length of the plans dimensions for the CZNC-12A up to the center of the inboard hinge slot(.265" +.110"), you find the location of the center of the inboard hinge should be 15.475" or 15.5" rounded up instead of 15.6" per plans.  Now, when you use the Cozy Girls .2" longer CZNC-12A, it places the hinge slot at B.L. 15.7", .1" outside the plans incorrect 15.6" callout but .2" outside the calculated location based on the plans .2" shorter CZNC-12A dimension.  The other two hinge slots in the elevators are correctly called out and work perfectly with the Cozy Girls part.

Ok...what's the bottom line?  My conclusion is that the plans .265" dimension inboard of the hinge slot in the CZNC-12A, Chpt 11 pg 2, is incorrect and should be .465" like the Cozy Girls version of the part.  And, the callouts of the B.L. location of the inboard most hinge hard point and the matching CZNC-12A hinge slot, Ch 10 pg 7, fig 48 and Ch 11 pg 2, are incorrect and should be B.L. 15.7" instead of 15.6".  Fortunately there is enough margin in the location of the 1" wide hinge hard points to account for this slight difference.  So if you built it to plans, and used the Cozy Girl parts, all is still good.  If however you built your own CZNC-12A to the plans dimensions, your elevator length is likely .2" too short on each side and none of the hinge hard point centers will match the torque tube hinge slots correctly.  I remember in Chapter 10, when laying out the hard point locations, it recommended laying out the elevator torque tubes to check the hinge locations.  This would have been smart to do.

I'm guessing that sometime way back the Cozy Girls knew to correct for this in order to make the overall length work out correctly and that the plans somehow didn't get these dimensions updated.  I don't know for sure.  Searching the archives (which BTW I usually do before starting a chapter and didn't) revealed that others found the same anomaly with the offset torque tube but nobody seems to know exactly why.  Reported discussions with the Cozy Girls also showed they apparently don't remember why the dimension was different.  There is no mention of the hard point location possibly being incorrect.  Some builders adjusted the length of the center torque tube to compensate.  Others didn't, but it seems to me that if you do that you'll end up with slightly shorter elevators and will have to sand your canard slightly shorter to obtain the .1" elevator-to-canard tip gap.  I'll go back and put a link to this discussion on my canard build page so future builders will at least be aware of this and can adjust the inboard hardpoint slightly should they so chose.  A bigger issue is that anyone building their own CZNC-12A needs to know the plans dimensions are incorrect.

Puttin it All Together

Offset torque tube, "spool" (center torque tube),
Drill Hog drill bit set, and reamer

Now that I decided everything was ok, it was time to start drilling holes to assembly all torque tube pieces that tie the two elevators together.  This was simple enough...it's just 4 bolt holes that have to be drilled, but you have to do it in a way that ensures everything is aligned properly.

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TIP:  Let me say that you want to be careful drilling holes in any control mechanisms.  You can easily accidentally drill them slightly over-sized and over time they could develop slop...not something you want in your control system.  Some builders use taper pins, which are great, but expensive.  Some experts on the forum suggest that there's really only one place that makes sense for taper pins and that's the rudder torque tube assembly because of the amount of torque involved when applying the brakes.  This is probably what I'll do.  For the rest of the control system I'll stick with the plans bolts and if they give me any problem later I can always switch to taper pins.  I doubt that will be the case.

So, to ensure I didn't over-drill a hole, I started with a pilot hole per plans and then stepped up to the final size a little at a time.  I stepped up 5 numbered drill sizes at a time and stopped with a drill that was 2 numbered drill sizes smaller than the bolt.  Then I used a reamer for the finish size making sure the reamer matched the actual bolt being used.  This resulted in a nice tight fit.

Get yourself a set of numbered drill bits, 1 thru 60.  I got mine from Drill Hog on Ebay and they have a lifetime warranty.  Break one, send it back, get another.
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Elevator assembly jigged on the work bench

The first two bolt holes are the ones that connect the left and right offset torque tubes (CZNC-12A) to the "spool" piece (center torque tube).  You can see that in the pic above.  Using the process in the tip above this was straight forward and when done aligns the two offset torque tubes together.

The next two attach the elevator torque tubes to the other side of the offset torque tube.  This requires aligning the entire elevator assembly,  bondo'ing it to the work bench, and dialing the center spool piece to the same position where the hinge pin will insert properly.

Close up of one side showing the two bolts
on each side of the offset torque tube.
Note:  Not done yet was the last step which
was to auger out foam from the inboard end
of the elevator in order to attach the back
side nut on the elevator torque tube bolt.

There was actually a wide margin where I could rotate the center torque tube assembly and still insert the torque tube so I did my best to match the clocking of the hinge pin hole inside with that of the elevators and marked it on the outside to get it as close as I could.

The only thing left to do is auger out the inboard foam to allow installation of the back side washer and nut on the torque tube bolt.  The augered out foam will get filled in later after the inboard side of the elevators get trimmed to match the fuselage sides.

NOTE:  The plans don't say it but the bolt length assumes you put AN960-10 washers under the head and nut of these bolts.  You should always put the appropriate washer under bolt heads and nuts.

Onward to hinge the elevator to the canard !

Ch 10.6: Canard Top Spar and Skin

The 1st Lifting Surface...for the 2nd Time !...continued


Ok...Canard flipped.

Canard...now right-side up.

After re-jigging the canard and turning it over, it was time to set about prepping it for the top spar and skin.  I removed the fishtail per plans and began to remove the 1" strip of peel ply laid at the trailing edge.  This proved to be extremely difficult and time consuming!  The peel ply did not want to be removed.

If that wasn't bad enough, it was difficult to tell when the peel ply was fully removed and there was only glass remaining.  See a tip on the previous post about a possible way to prevent this.  Perhaps a different peel ply would work better.








Elevator Hinge Hard Points

Hard points in place and curing.  After cure
the excess above contour is cut off.

Next I cut and installed the more dense foam (6 lb / cubic ft) used for the hinge hard points.  I marked the locations and used a Dremel tool to auger out the foam.  The plans were a little vague on the fore/aft location of the hinge hard point foam.  I settled on a position about 1/4" below the spar cap down to about 1.3" from the trailing edge.



Micro Fill the foam gap...

Hinge hard point sanded flush and micro
filling the transition to the trailing edge.
(Note the TE is preserved for glass to glass bond)

When pulling off the peel ply you pretty much destroy the foam just in front of the clean trailing edge.  Since this would have been foam anyway, I went ahead and filled the area with micro and created a smooth transition from the contour to the trailing edge.  I reserved .6" of clean trailing edge glass for the glass-to-glass bond (hash marks).  The FAQs say to leave no less than .5".  After skinning I"m sure this area will need some additional external micro to bring the full contour back to where it's supposed to be.
NOTE:  After assembling the elevators, I believe the B.L. 15.6" dimension for the inboard hard point shown in the plans should be 15.7".  See my post on Ch 11.4 for my explanation.


Top Spar

Ready to roll...or.."un"roll as it were.

Since I laid up the bottom spar, Aircraft Spruce has starting sourcing their spar tape from an Australian company named Colan.  Marc Zeitlin checked it out and gave it a rave review.  I ordered this new tape for the top spar.  I was able to get 13 plys of spar tape into the top spar trough compared to 12 on the 1st canard.  This took me ~9 hrs working alone.  Below are the layer lengths I was able to get.

Layer     Length each side of center
1                        62.5
2                        62.5
3                        62.5     
4                        58.5 
5                        56.5     
6                        50.5           
7                        50.5
8                        46.5
9                        44.5
10                      34.5

11                      30.5
12                      28.5
13                      18.5

A total of 33.7 yards of spar tape was used on the top spar cap.  All total I used 53.3 yards of spar tape for the 2nd canard...about 3.5 more than the 1st canard.  Not a significant difference however my technique was better and I tried do a better job this time of not overfilling the contour too much and having to sand.  Although I still had a few small high spots to sand, it was very minor compared to the 1st canard and thus I'm very happy with canard #2.   I suspect my first canard may have been perfectly fine, but I didn't want that unsure feeling on such a critical part.  I'll call the 1st canard the "practice" canard...although it was an expensive way to practice.

TIP:  The plans call for ordering 42 total yards of spar tape so buy extra spar tape!  You don't want to be in the middle of a spar layup and run out.


Skinning the Top

Placing the 2nd ply (BID) on to the canard.

Skinning the top went according to plans with no issues.  The only added complexity here is that you have to be sure to end each ply in a different spot around the leading edge to properly taper into the bottom and not leave a bump.

When finished, I did find these air bubbles you see in the picture at the right.  These are not in the glass itself but mostly just on top of the glass, between fibers, just under a thin coat of epoxy left by the peel ply.  They are a result of a poor peel ply job done after ~9 hrs of spar cap layup...I was tired.  After confirming this with the experts in the forum, I was happy that this was no issue and has no impact on the finished product.


At long last, this completes Chapter 10.  If you've been noticing the dates on these posts don't interpret those as having anything to do with how long this work took.  1st, sometimes it takes me a while to write a post for something I did a while back.  2nd, I've had numerous breaks in building over the years as normal life and priorities get in the way.  I will say though that I did have some trepidation in getting those spar caps done again which caused me to procrastinate a while.  I now have some momentum and hope to keep that up.

I can finally move on to the ups and downs of the elevators.

Onward.

Ch 11.1-3: Elevators

Building the Elevators...

Like the canard, I built my elevators with foam cores from Eureka CNC.  They are perfectly shaped to contour and makes the job so much easier.

Do You Do Impressions?

Canard Jig impression made
in the bottom of my elevator core

I did have one problem...  Eureka packed my canard jigs in the same box with the elevators and they were so tightly packed against the elevator cores that they ended up causing some impressions in the core foam.  You can see the impression in the pictures at the right.

Normally this wouldn't be a big deal but balancing elevators and ailerons is difficult and I'll have to add micro fill to fix this which means unnecessary extra weight.  You have to use a minimum of micro, resin, etc. when making these control surfaces for them to balance properly.  It becomes that much harder when you have to do any micro contour filling like this.  I did contact Eureka and Steve offered to send me a section of elevator to replace the damaged section if needed.  In this case however, I think it will work out.  You can see that when the end is trimmed to the end of the torque tube, much of the problem is eliminated.  Added to that, since I made sure to place the damaged area on the inboard side, it will be further trimmed to an angle to match the fuselage so about 80% of the damaged area will probably end up being cut off after it's all said and done.



Torque Tube Hinges

Left elevator about to be mounted onto
the torque tube

First up is installing the hinge mechanisms into the torque tubes.  This went pretty much to plans but I would offer a few Tips.

1st, I've probably said this before but I purchase all the hardware I can from the Cozy Girrls.  Their workwomanship is first rate!  I like to build but I don't like it so much that I'm willing to manufacture my own metal parts.

2nd, it wasn't obvious to me in the plans which direction the NC-2 inserts are installed into the torque tubes...hinge pin hole up or down?  I didn't think any of the drawings made it perfectly clear.  The best picture was Figure 4 where you can see that the hinge pin hole is at the bottom of the insert relative to the interior flat portion and with the elevator upright.

3rd, before you secure the inserts with rivets, place the hinge pin through the NC-2 inserts.  This will help ensure they are aligned and help you end up with fewer problems getting the hinge pin in and out later.

And lastly, there have been some questions about which side of the NC-2 inserts do the torque tubes get the notch filed.  The archives have different answers, the most recent being that the drawing on Ch. 11 pg 2 is incorrect in showing dotted (hidden) lines for the notches (indicating the notches are only filed on the bottom side of the torque tubes) and that both sides should be filed.  When you go to mount the elevator with the NC-7 jigs, you realize the top (side furthest from the hinge pin hole) must be filed for that jig to work correctly.  The bottom side, doesn't end up needing to be filed at all to obtain full movement of the elevator.


Skinning the Elevators

Right elevator bottom skin (far) curing
while the left elevator (near) torque tube
mounting is curing.

Glassing the elevators is pretty straight forward however you need to do your best work getting all the excess epoxy out of the layup.  This will help you be able to balance them.  I wet out my glass on a sheet of plastic and leave the plastic on when applying to the part.  Leaving the plastic on makes it easy to eliminate air and squeeze out as much extra resin as possible.  I then remove the plastic and apply peel ply which soaks up more of the excess...more than I would have thought it would.

Glassing the bottom skin

Tip: Leave the trailing edge glass a bit long so you have room to cut and sand it to the correct length before the top skin is applied.






Before glassing the top skin, the plans have you remove some foam at the trailing edge, layup the top skin, trowel micro  in the void left on top of the glass-to-glass trailing edge and then leave to cure.  I did everything in the same order however I let the top skin cure before applying the micro at the trailing edge.  I had a slight twist in the aileron and wanted to weight down the trailing edge nice and flat while it cured.  I couldn't do that if the trailing edge was wet with micro...so I simply performed that step after the top glass cured and I had trimmed the trailing edge to the proper length.









Now that I had a left and right elevator, it was time to assemble them into one piece.

Onward!