Chpt 11 - Elevators


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updated: 01/01/2020

 

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19/01/2009 - In this chapter the elevator cores are hot wire cut, fixed to the torque tubes, fibreglassed and then mounted onto the canard.

Step 1 Cutting Foam Cores & Bonding to Torque Tubes

I started off by cutting out the elevator templates from the M17 drawing and spray glued them onto 3mm Masonite board.  They were then cut out using the band saw.  The two foam blocks let over from Chapter 10 were then trimmed to 55" and then cut in half to make 4 x 27.5" long pieces.  Bernardine then gave me a hand with operating the Wire cutter and in about an hour we had 4 nice looking elevator sections.

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I then proceeded to fish out the Torque tubes and prefabricated metal parts purchased from CG Products and checked how it is all supposed to come together.  I did not order the manual Pitch Trim Bellhorn assembly - NC-5A, as I will be fitting the Alex Strong Electric pitch trim unit, which connects to the control stick and not directly onto the elevator torque tube.  I found that the plans again are very unclear on the orientation of the 4 x NC-2's and I had to re-read this section about a dozen times, before I understood how they were supposed to be fitted I.E. with the Hinge Pin Hole on the top or bottom. The hole goes to the bottom and don't forget that you have to make a left and right torque tube, so make sure you have the tubes positioned correctly before fitting the NC-2's. The "CG"  supplied NC-2's fitted perfectly into the torque tube cut-outs and were easily riveted into place using the plans specified BSPQ-43 Pop rivets. The "CG" supplied Torque tubes are supplied cut and finished to the required length and DO NOT require any further cutting as specified in the plans. With the NC-2's fitted I then proceeded to file the slots in the left & right torque tubes, to match the slots in the 4 x NC-2's.

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 Next I test fitted each core onto the torque tubes and found that they were all too tight and required additional sanding to get then to slide on. I used sandpaper wrapped around a wood dowel to do this. I then prepared to micro the cores in place by first wiping the torque tubes down with acetone (no sanding required as the "CG" supplied tubes are anodized). I then laid down some plastic, made some micro, and smeared a thin layer into the core cut-out. I then slid the two cores into place. I made sure the cores were even with the outboard end of the torque tube. I then slid the hinge pin in place along with the two NC-7 templates and got the cores and the tube aligned correctly. Finally I placed some weights on the cores to make sure that they cured flat.

Step 2 - Installation of the Bottom Skin

Using Templates H and I the foam core on the leading edge was sanded to conform to the Torque tube.  I then setup the elevators on the work bench, flat side up, using the foam off cuts left over from the elevator hot wire cutting.  The off-cuts were trimmed front and back to allow the elevator leading and trailing edges to over hang the foam jig.  The foam jig was then glued to the table using 5 minute epoxy and then using small amounts of 5 minute epoxy, the elevator was then glued to the jig.  Before proceeding with applying the 2 pieces of UNI, cut at 30, I carefully made sure all the holes for the hinge pin in the NC-2's were again filled with Vaseline.

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Step 3 - Installation of the Top Skin

After cure the elevators were trimmed and sanded and then jigged on the worktable flat bottom down, with tape under the trailing edge and the leading edge overhanging the table.  Using a dremel the foam along the trailing edge was removed as per plans and the 2 pieces of UNI, cut at 30 was applied.  Dry micro was trowelled into the depression along the trailing edge before the complete elevator was peel plied.  After cure the elevators were again trimmed and sanded.  The trailing edge was also checked and sanded to suit templates H and I.

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Step 4 - Installing the NC-6 Inserts and the NC-3 Hinges into the Canard

The glass covering the slots on the NC-2's was removed and the out board ends squared before applying a single layer of BID over the exposed foam, using small flox corners.  I up ended the elevators and placed a flat board and a weight on the wet glass and flox, to ensure the ends dried nice and flat.  After trimming the BID on the end I prepared to install the NC-6 inserts.  I measured about 3 millimeters in from the edge, and marked where to drill #30 hole for the the BSPQ-44 rivet. I also marked and drilled the #10 holes for the grub screws, before riveting the NC-6 inserts into place, as I thought it would be easy to do this now and less risk of damage doing it later.  At first the BSPQ-44 rivets seemed to be too long to fit, but if you push them in whilst slowly crimping the rivet, it will pull up fine.  Final weights at this stage were 789g (27oz) for the right elevator and 810g (28oz) for the left one.

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The Spool was then assembled and bolted on the bench as per plans and then fitted to the torque tubes and CZNC-12A offsets. Another lesson I learned the hard way was I drilled through torque tube and CZNC-12A offset, then bolted in place without disassembling and clearing out the swarf accumulated from the drilling of the holes. The hinge pins got stuck half way through and would not slide easily, and I later realized how much debris settled in the hinge pin holes that needed to be cleared out.

Next step was to align the CZNC-12A's with the NC-2's and NC-6's. so that the hinge pin ends up straight and, more importantly, the offset weights that are bolted onto the CZNC-12A's later on end up at the right position. The plans just say to use the pins to force alignment, which I thought was a bit under-specified given you can easily rotate the CZNC-12A's, 20 degrees with the pin in place. So I traced a template with the angle shown on the large M18 drawing between the canard and elevator and used this template to setup the CZNC-12A's.

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The 4 "L" Templates were made from 1/4" masonite board, cut out on the band saw and finished with a rotory sander. Took some work to get the depth and clearance for NC3s. I glued the L templates onto the elevators first using 5-minute, which is not as per plans, and then temporaly fitted the elevator to the canard.  It was at this point that I run into a fitment issue, which seems to be the same as everyone else has apparently encountered. While jigging the elevators into position with the canard, I am getting a bit of interference at the trailing edge of the canard / leading edge of the elevator. To fix the problem I removed the elevators and sanded the inside of the canard trailing edge and also removed about 1mm off the trailing edge.  After resolving the interference issue, the elevators were then ready to have the hinges floxed into the canard.  I was a little nervous cutting into the canard bottom skin, as a mistake at this point would be difficult to fix.  After cutting the slots with the Fein, I filled the slots for the hinges about half way up with wet flox, using a plastic bag with the corner removed, lowered the hinges vertically into place with the elevators, and then proceeded to re-jig the elevators to the canard using the L jigs. After checking that everything lined up OK, the hinge slots were then filled to the top with flox and left overnight to cure.

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With the elevators now firmly attached to the canard by the NC6 hinges, I removed the L jigs hold the elevators in position. Made the elevator travel checking template and verified that I had a full -15 degrees to +30 degrees of elevator travel.  Next Step was to now make the canard tip fairings.

Step 5 - Checking the Elevator Travel and Installing the Tip Fairings

After the flox cured and I knocked off the L jigs, flipped the canard right side up to install the tip fairings. The plans indicate to reattach the L jigs to hold the elevators at 0 degrees in trail. However the newest L templates (which are included with our plans) hold the elevators at -15 degrees. Being we needed the elevators at 0 degrees for forming the proper contour of the tips, I made a couple of new L jigs that would hold the elevators appropriately. This is easily achieved with the existing L jig template, and a protractor.  Here's a couple photos of the blocks being attached. I used a couple 4" long steel nails, pushed through the foam and into the canard end, to hold them in place whilst the micro cured.  I also fitted a plastic straw over the steel hinge pin at this point    

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With the elevators positioned correctly, I started carving and sanding the foam down to the bottom radius working my way forward.  I worked on both tips at the same time.  I would complete one section on the right and immediately do the same on the left.  This seemed to work for me and I obtained two canard tips, which looked pretty much the same.  Once I had obtained a shape on the top that I was happy with, I then proceeded to glass the top with 2 layers of UNI. Before glassing I protected the top of the elevator with box tape just in case epoxy dripped onto the elevator.  After glassing the top of the tips, the canard was flipped over and the bottom of the tips were carved to shape.  The plastic straw fitted earlier made removal of the elevator hinge pins quite easy. The bottom of the tips were then glassed, as are the inboard faces alongside the elevators.

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Step 6 - Installing the Pitch Trim Belcrank & the Elevator Mass Balance Weights.

As I am using the Alex Strong Electric Pitch Trim, I did not fit the CS5A pitch trim belcrank, and moved straight onto fitting the inboard and outboard elevator mass balance weights. The outboard CS10 mass balance weights are installed by carving foam spacers (Wicks Part No. F400-090) to hold them out in front of the leading edge of the elevators. I used a piece of sandpaper on the leading ledge of the elevator to obtain the correct radius for the spacers.  They are first installed with 5 minute epoxy and positioned using the 2 "J" jigs, and then glassed onto the elevator with 2 plies of UNI. The bottom of the canard must have a notch cut into it to allow the CS10 weights to swing freely through the elevator range of motion. The CS11 inboard weights are simply bolted to the elevator control arms, CZNC-12A.

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Slots were cut into the Canard bottom skin to accommodate the balance weights and then glassed with a single ply of BID.

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The plans state that at this point you should now contour finish the canard, I was going to leave this until later, but reading ahead to Chpt 12 the canard top and bottom contour checking jigs, E & F are used to set the correct angle of incidence and if your canard is not finished and contoured it is going to be very difficult to obtain the correct angle of incidence.  I had already decided not to use MGS with the micro to finish the aircraft, as it sets like concrete and is too difficult to sand.  It is generally recommended by other builders to use the West system 105 resin with the 206 hardener.  Talking to my SAAA Technical adviser, who has built a couple fiberglass aircraft and is still currently flying a LongEze he built, mentioned that the West system was OK for finishing, but it has a tendency to exotherm and the pot life is very short.  He pointed me towards the Araldite LC3600 Epoxy product he uses and which I believe Jabiru Aircraft also use.  It is mixed to a 3:1 ratio and has a pot life of 70 minutes at 25c.  A 3kg Resin & 1kg Hardener kit from Kirkside Products in Perth cost me $130.90.

After reading up on the method Wayne Hicks used to contour finish his canard :- http://www.maddyhome.com/canardpages/pages/waynehicks/chapter_25_canard.htm, I decided to make myself a sanding block out of left over Blue foam, glassed all over with 2 layers of BID. The work table was leveled and the canard fixed to the table using a small amount of 5-minute epoxy.  The centre section of the canard was marked to ensure that no micro was spread onto the surface where the canard alignment brackets will be glassed.

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I applied an excessive amount of dry micro to both sides of the canard with the intension to try and minimize the possibility of having low spots and having to refill and start sanding again.  After the canard was sanded to suit the testing template, the leading edge was still a little undersize, so a 2nd coat of micro was applied and the canard was then sanded all over again.  It took me an extra 23 hours of filling and sanding, before I was happy with the final finish.

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Before moving onto chapter 12, I decided to weigh the left and right elevators before re-assembling them onto the torque tube, as well as the complete Canard with elevators fitted.

Canard with Elevators = 14.3kgs (31.5lb)

Right Elevator = 1092grams (38.5oz)

Left Elevator = 1063grams (37.5oz)

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