Chapter 11 - Elevators

Templates and hot wire

To be sure I didnt loose the remaining little scraps of paper from M17 I cut my contour checkers and elevator templates while doing those for the canard. Before cutting the last canard core we practiced by cutting a couple of elevator cores. Both cores came out perfect. Haven't made a bad cut since upping the voltage on the regulator. Thinking about the voltage regulator, I can't see how you can get a consistant hotwire cut using a 12v battery. I'm set on 15v. You'd need two in series. As the battery charge dissipated the power would reduce. I'm glad I bought the regulator from Wicks.

I left the elevator cores on the shelf under my bench and the dogs chewed one of them, so I'll have to cut another.

Head's Up

I spoke to Jeff Russell of Aerocad Inc. about the elevators. He's made hundreds of cozy elevators and told me to watch out for a couple of issues. First thing is to be sure and sand a 1" * 1/16" depression for the mass balance, otherwise I'll have a bump there. Secondly, before glassing the top of the elevator, Jeff says make a hard template and press it down into the top foam till it meets the glass at the trailing edge, then sand until the creases made by the template go away. he says you have to sand the top of the elevators looking out for the "ski ramp".

Installing the torque tubes

First problem was that my cores were 3 inches too long on each side. Ah! the extra 3 inches on the canard raises its ugly head once again. Cores need to be 52 inches, not 55. I trimmed the cores to match the torque tubes. The archives say its easier to slide the tubes in, then add the jigs. I quickly figured out that there was no way to "rotate" the tubes into the hole in the foam like the plans say. The "mouth" of the hole is way too small for that. I microed the tubes and tried to slide them in. You have to be really careful to ensure that the angle of the tube is correct as it goes in. There's a tendency for it to start angling out of the hole and ripping the foam. Destroyed two out of the four cores, but got one elevator set up correctly with the jigs. No big deal. These cores are real small and easy to cut, and you can only make one at a time anyway unless you have 4 jigs.

Skinning the elevator

Wayne Hicks suggests skinning the top first, then the bottom. I stuck to the plans and filled the groove on the top with dry micro. I had a bit of trouble wrapping the top skin around the torque tube to overlap the bottom skin. Because of the way I had the elevators proped I couldn't get under the elevator to ensure a good layup in that area or to peel ply. I decided to carry on and deal with this after cure. I pushed a brush into the gap and did my best to get a good overlap. After cure it was no problem to sand the joint and get a nice smooth leading edge. The dry micro trough and the 1 ply of BID for the ends went on easily. After cure I sanded the elevators and weighed them with my postal scale. Plans say that they need to be as light as possible, but dont tell us what that weight should be. My elevators, without the counterbalance weights added, weighed in at 24.5 and 25 ounces. I'm told that the Long EZ plans state a maximum weight of 3.5 lb for each elevators without counterbalance weights.

Fitting the hardware

I found what I think is a minor discrepancy in the plans. According to Step 4 page 6 the distance between the inner hinge points is supposed to be 31.2 and the spool piece is supposed to be 30.2. This allows 1/2 inch either side for the CZNC-12A flange. On page 3 the dimentions of the 12A flange are shown as .265 plus half of the .220 gap which totals .375, not 1/2. When I fitted the spool piece I found that I had to slide the 12A out about 1/8 on each side to get the correct gap between the hinges. I had plent of tubing spare, so I made another one 30.45 long. This one fitted snuggly on the 12As with the correct hinge gap. I advised Nat of this and received the following reply:

 Your arithmetic is correct. I am not sure now why I called out the 30.2
 dimension on the spool piece. I may have been to allow for the welding bead
 on the CZNC-12A offsets. It isn't critical, however, because there is
 plenty of length where it passes through the fuselage side, and the high
 density inserts are 1 inch wide so the location of the hinges can be plus
 or minus 1/4 inch. 

Installing the hinges

I made the L jigs and bondoed them to the canard. When I came to slide the elevator assembly in from underneath it wouldnt go in. The trailing edge of the canard was in the way. I removed the jigs, inserted the elevator, then re bondoed the jigs. The gap between the trailing edge of the canard and the elevator was not 0.2 as shown in Fig 18, but zero. After a lot of jockying around, sanding the canard, rereading and experimenting I think found the problem. The L jigs shown in figs 17 and 18 page 7 set the elevator at 0 degrees. In fact step 5 uses an L jig to ensure 0 degrees. But, the L jigs on M18 set the elevators at 12.5 degress, so the gap you need with this setting is very small. Eventually I used mixing sticks as spacers and went on to flox the hinges. Again, I advised Nat of the problem. His reply was:
 On the first edition plans, the L jig on M-18 was shaped as shown in Fig.
 18, but some builders were having a problem obtaining the .2" minimum gap,
 and as a consequence, they couldn't get the required 15 degree trailing
 edge up elevator travel, so I changed the jig on M-18 in the 2nd edition
 plans to make sure that builders would have the 15 deg trailing edge up
 elevator travel. 

Floxing the hinges in was interesting to say the least. I dug the holes [without drilling through the canard top skin]. My hinges wouldnt rotate into the holes. Rather than make the holes any longer I decided to remove the hinge pins, flox, lower the hinges into the holes, then reinsert the pins. Real bad idea! The hinge pins tend to sag downwards away from the holes and are almost impossible to insert with the canard upside down. I proceeded to fill the three holes on one side with flox, then started to reinsert the pins. After a few minutes of messing with the pins I noticed that the flox in my first hole was "boiling" out of the hole. You guessed it! I had exotherms going on inside all three of my hinge pin holes! I grabbed a 1/4 wood chisle and dug out the boiling flox as best I could. The flox that had already hardened had to be drilled out. Uggh! Once I had the holes redug I extended the holes to allow the hinges to rotate in, reinstalled the hinge pins, mixed more flox and did one hole at a time. This worked much better.

After cure I removed the mixing stick spacers and found that I have a full 15 degrees down travel and the gap with zero degrees travel is exactly 0.2. Like Wayne, I had some interference with the arms of the 12As hitting the bottom of the canard at 27.5 degrees up travel. Slight modification to the arms gave me a full 30 degrees.

Fancy canard tips

I cut the blue foam blocks with my hot wire saw and microed them to the canard. It took me a little while to figure out how the foam should be carved, but then I dived in, marked the M template curve and started sanding the top with a 2 inch pipe wrapped in 33 grit. Plans say to make a glass to glass bond on the trailing edge and half way up the leading edge. I had a little trouble working out how to get a smooth transition from overlapped glass at the leading edge to a glass to glass bond along the side. In the end I made flox corners along the leading part of the sides. After sanding my canard tips look good [to me].

Mass balance

Adding the mass balances was no problem, except that I had a feeling they were much too heavy. These counterweights cause the elevators to balance nose down. My elevators are quite light (25oz each) so, in theory, the counterwieghts dont have to be as heavy. I'd like to save 1lb in unnecessary lead if I can. I asked the mail group and got some fairly obtuse answers. The answer which made most sense was to attach the mass balances as they are. I can adjust the weight later by drilling them once I know how the finishing and painting affects the weight. I cut and glasses recesses in the canard for the weights to fit in and then reassembled the elevators on the canard. The hinge pins are quite stiff and I needed to use a drill to spin the pin as it went in. The elevators will have to come off again for painting, so I left out the hinge washers for now. Plans say to bolt the inboard weights on. They don't say what with. I need to order 4 AN3-10 bolts.

Final Fitting

I had a bit of trouble with the hinge pins and damaged some of the little brass inserts. Did I say damaged. I should have said destroyed. My own clutsy fault. My hinge pins are fairly tight. One way I've found to get them in and out is to use a drill to rotate them. I thought the hinge pin was aligned and tapped it with a hammer. At least two of them broke. I'll get a new set of inserts and will replace them during finishing.
[Later note: Done. I also had to redo the hinge pin support at one end. The reason I had trouble inserting the hinge pins was that the support was not aligned properly with the hinge holes. I dug out the hole in the end of the canard, covered the pin with grease, then pushed it in place without the elevators. Next I put flox in the enlarged hole and repaired the glass with 2 ply BID.]
When the mass balances and canard tips had cured I reassembled everything and found that I as a couple of degrees out with the amount of travel at each end. I think the tips are slightly off. A little sanding on the top of one and the bottom of the other got everything level. The only other issue is that I now have only 27 degress of nose up. The mass balance is impacting on the one ply BID in the cut out. I'll have to sand this. Finally, I couldn't find the threaded holes for the set screws. I found out where they SHOULD be and dug through the epoxy. Once I'd drilled out the micro and retapped the threads the set screws went in just fine. Only took me about half the day.

[Another note: A year later, when it came time to do final finish on the elevators I found that all the steel parts had accumulated a fair amount of surface rust. I cleaned the rust off with a wire brush and used some of my engine enamel primer, then gold, to paint the parts. I wish I'd done this a year ago. If you live in a humid climate, paint all you're steel parts when you get them.]

Mass balance fairings

About a year later, while preparing the canard for painting, I made the fairings suggested in the plans. Some say they just generate drag, but I'd rather have a little drag than an iced up elevator. My first attempt was to make two plugs and use them to make small 2 bid glass fairings. My plan was to stick these in place with flox. When they cured I didnt like them and decided it would be better to make the fairings in place with a glass to glass bond. First I had to adjust the maximum deflection which was being restricted by the trailing edge of the canard and the hinge inserts. A little work with a sanding block and a dremel and I got full deflection. Next I held the elevator in full nose up position with weights, put duct tape over the weights and made a dam all around with duct tape. A little pour foam filled the hole and expanded to cover the weights. I carved the foam into shape and glassed this with 2 ply bid. Once this cured and I, eventually, got the elevators off, I trimmed the glass and covered it with micro. Putting micro on a small curved shape isnt something you can do accurately. I used a mixing stick and shovelled it on like icing on a [british] Chrismas cake. When this cured I cleaned it up with a 30 grit board, then carved with a dremel. Finally a little hand sanding and I had two matching fillets over the glass fairings. Hey. I like them. Somehow having two chunky weights hanging out in the breeze seems wrong.

Making a fairing in stages

the original rejected 'stick-on' fairing blocking the hole with duct tape building the damn dam filled with pour foam Carved foam Glassed foam - note the elevator angle check template in place Christmas cake icing with micro The final product before paint

<<< Back | Index | Next >>>