Chapter 21: Strakes                                                                Next  Previous  Home
                         
The last glass chapter!
Well I'm onto the last glass chapter and I gotta say I'm really glad.
Although I really enjoy the glass work what I really hate is all the head scratching that goes on before you can build something, chapter 21 will be no exception to that, the EZ gods will have at least one more crack at my poor tired head before I can move on to stuff I can understand, like quantum mechanics. I spent an entire day trying to make sense of all the angles, dangles,bevels, FS's , BL's, WL's etc. At the end of the day I had almost no work done and a R33 rib that was now too short to use after wrongly trimming it to try to meet the F.S.60 line. But I did have it all figured out finally and all the parts coming together nicely.   What I found is  the forward bulkheads meet at the F.S. 60 mark, the leading edge goes on ahead of that. Now with a new rib in hand it all finally came together for me, I hope. I will also mention that I'm going with a central sump, simple fuel on/off valve. I'll include pics of those components  here as well.



One of the first things I did was attach the RH wing so I can make sure things line up well. I already knew this wings leading edge was off the 17.4 water line by an 1/8" so I wanted to make it all line up. I got tired of "Duck Walking" under the wing real quick so after initial assembly & checking I made this template and removed the wing.



Here I took a tip from Wayne Hicks & used the dental floss. This worked well, I'm accustomed  to using string lines or "Alturas Lazer Beams"  but the floss is strong, light and doesn't stretch much. I also used the tapered board but mainly to hold the leading edge of the skin up during cure. You will likely need to make some foam wedges to  hold the skin up to the ribs aft of the L.E/ tapered board. Also shown here but not really discussed in the plans is the bevel that needs to be put on the ribs. If you note the outboard edge of the rib bevel..... This is wrong! Don't bevel the ribs.  Once again I read something that wasn't in the plans. You don't bevel the rib, if you do it won't match the strake contour. No matter for me as I cut mine off anyway to make it easier to glass the outside skins. I 'm going to hot wire some cores for my leading edges.



Assembling the parts. One thing that threw me, I was trying to line the L.E. up with FS 60 and it wasn't working out. In fact I trimmed a rib trying to make things fit. I eventually studied the drawings again and discovered the L.E. goes ahead of FS 60. The BLE/TLE bulkhead goes on the FS 60 line. I think! Also note the Jorgensen clamps holding the ribs in place. This worked out real nice, one of the challenges at least for me, was getting a few parts "anchored" or floxed into position so other parts could be added. Until then your are defiantly herding cats. I don't recommend the plans way of assembling these parts, (although I didn't even try it) I positioned  & floxed the bottom skin and both ribs one night and added parts in the following work sessions. I don't want to even think about holding all these parts (cats) in position while  applying flox and keeping everything straight. I also don't really understand why the plans have you raise the skin up to the ribs & bulkheads. This seemed much more complicated than what I did, which was to flox the lower skin to the spar & tub, then assemble parts onto it. You get much greater control of each part and can control the flox joint on each part as it goes in. I will concede  that this way will likely take a little longer, but I think most builders in this chapter have a greater concern over leaks than getting the Strakes done in a couple of weeks.  A few builders have suggested cutting off the rib ends and making the BLE & TLE bulkhead into one part. If starting over I would defiantly do this. I did cut off my rib ends, and will either flox them back on after the outer skin is done or  hot wire some leading edge cores, make a plug and then make my leading edges from the plug. You probably don't want the  wing foam that close to a possible fuel leak.

Two things I would pass on regarding the Cozy girls "strake kit". I know most of us feel like one ply on these parts is a little flimsy.  I had decided to follow the plans though as you cant argue with success. Meanwhile I liked the Cozy girls method of cutting the parts out of 2 sheets of foam all glassed at once and followed their instructions.  But there are 2 pitfalls you need to be aware of before doing this: 1; their instructions have you use 1 ply on one side and 2 on the other. This I discovered later after reading the plans is NOT the glass schedule the plans call for, which is 1 ply each side.  I had already glassed my foam so I was too late to learn this. One thing though, I believe  you should have 2 plys on the parts that face into the baggage areas to prevent damage from somebody getting too aggressive with the ski poles, So I would have put this second ply on some of these parts anyway. The second issue, and they tell you, is using the "strake kit" method will make you run short of foam. I did not catch this and will now need to order another sheet of foam.


Here are all the ribs & bulkheads taped into position. The plans leave a little to be desired as far as some of the parts true location. For example, I could find no dimension  listed for placement of  the inboard aft bulkhead or the outboard rear bulkhead. One edge is to be found at the forward end of B33 but the inboard edge is kind of left to chance. I just made sure it was clear of the fuel sight gage location. Same thing for the rear bulkhead. These both can have a significant effect of fuel capacity and the only way to get the dimension is to scale it from the drawings which doesn't seem like a good way to impart this info, to me anyway.  Someone will call now and tell me chapter & verse where it's spelled right out for everyone to read but I couldn't find it. Well mea culpa! Some of them are shown on the M drawings of the R33 & R57 ribs, but it still only shows one end.
         
   

So you can see from the pic above I have gone with the cap strip method. This was an easy decision for me, I was NOT comfortable with the plans method for several reasons, and I know there are many flying that were built according to plans. But for one thing if you look at the bond you would have between the ribs, bulkheads & the lid there is NO glass to glass bond there, just a foam to glass bond and not a lot of surface area. The other thing is I wanted a better sealing surface than what you get from the plans method, especially along the rear of the tank and along the side of the tub, To me the seal method along the tub is just asking for problems.
     I used the traditional cap strip method along the baffles & ribs, cutting  the cap strip flush with the ribs anywhere I can get to later to use conventional taping, like along  inside the baggage compartment and outboard of R57. Then I made some "glass angle". This is 1 BID layed up over Peel Ply inside an aluminum angle, then another layer of Peel Ply. After cure I trimmed these to fit along the front of the spar and along the tub to the rear baggage compartment bulkhead. These were then taped with 1 BID. 

           

    Her you can  the vent line and fuel strainer (LH pic) and the RH Strake complete except for the outer layups. The strainer was bought at ACE hardware and is perfect for this purpose.   I debated the various vent philosophies and in the end I went with the plans method. The hole in the line at the rear of the tank method is flawed in my opinion.  Here's why; assuming a full tank and flight condition, the hole in the line at the back is going to allow fuel to flood the line. Now as the plane climbs and atmospheric pressure decreases, air in the tank must force that slug of fuel out in order to escape. In practice the air may percolate through the fuel and escape but it seems like  a poor way to do this . My thoughts are that it's not likely you will ever top off and then park it in the sun, a full tank of fuel is probably going to be a rare occasion.  Doug Pitzer told me that in order to get enough fuel into his plane to have a problem with this he must raise the nose to a certain position to get the last 3 gallons in there. 
The way the vent line leaves the tank leaves something to be desired in my opinion. I did not want to complicate that by adding another line (another probably better way than the hole in the tube).  You can see in the pics above I made a little glass bracket along the tub where the vent leaves the tanks. This allowed me to seal the tube before the lid was put down and maintain a nice seal surface for the lid. The vent line was drilled along the top near the tip to prevent a stray piece of debris from plugging the line.  
    I had no problem at all with the dreaded skin sag on the  top skin. I kept watching for it during trial fits and it always just sat flat.  Don't know what I did right, I just hope I can do it again on the LH strake! Update: The LH skin did end up with a slight depression just aft of the leading edge and right between the 2 ribs, only about 3/32" at the worst. I was able to spline sand most of it out and will take care of the rest with Micro at finishing.

                                                                                                                                                        

Above you can see a repair to the top skin I hade to make, I had a slight bubble right there I missed when I left it for the night. I warmed it up, pressed it down until cool then inject epoxy. You can see the wet area under the repair where the epoxy flowed, also under the skin is visible if it was a high rez pic. Above Right getting ready for the big flip. I ended up not using the "rockers". I just didn't trust them. For one thing they are slanted inward because of the sweep in the spar, but they also did not seem rigid enough. I ended up using my saw horses. Thet are  very strurdy and the flip went off without a hitch. Presently I'm trimming out the openings into the baggage compartment and getting ready to do all the taping in there. Should be a real blast!  Another one of those tape jobs you do by brail.

       

Here you can see the fuel sump ready to install. The inside has been seal coated like the tanks as well as the tub side. These things turned out much bigger than I thought they should but they are according to plan except I put a taper to them to allow the fairing to be smaller.
I built a manometer from clear tubing and charged the  central sump, then each strake separetly with 14" of water and then tested all the fuel lines etc all connected to the firewall and rechecked. NO- LEAKS!  It held the air pressure for over a week with no  significant loss. By that I mean it did lose about 1" after that time but it's difficult to be sure as the temperature is constantly changing and the temp in the tanks will lag behind ambient by a great deal. The plans say 24 hours so I feel pretty good about 1" after a week. It more than likley was internal tank temp different than the original temp and I was only measuring outside temp. Also barometric pressure will have changed over that much time.

Since I cut my rib nose tips off I had to make leading edges. These would have been nice to hot wire from PVC but it's not fuel resistant. This should never be a problem but for safety sake I used urethane and sanded it to shape using templates. You can also see the outline of the sump fairing here.

Here's a shot of the the central sump inside the RH rear seat, the fuel shut off valve and primary fuel filter. The valve will be cable operated from just aft of the throttle quadrant.  I will mount the fuel injection boost pump on the forward  side of the firewall and  a gascolator will be in the plans location.  I would have liked to mount the boost pump directly at the sump but Airflow Performance wants the filter upstream of the boost pump and I could not make it all fit alongside the sump.  As it stands the pump should flood just fine with fuel in the tanks even though  it will be 2" higher than the sump tank. This because of  head pressure from the tanks on the sump  and pump being below the tank level.  

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