Chapter 21 – Fuel Strakes
In my last update back in March, I mentioned I had permanently installed the main spar and the plane had become too big for the garage. I had posted some pictures and a brief story on the move at the end of Chapter 14 if you are interested.
Here are the new digs. The hanger is located at Lincoln Airport (KLHM) about 10 miles from the house. There is about a year long waiting list for a full hanger but an end unit was vacant so I moved in immediately. It is half of a “T” or in my case a backwards “L”. Plenty of room for what I need and I will be able to complete the plane at this location. The hanger won’t hold a fully assembled plane, but it is big enough for attachment of one wing at a time. Here are a couple shots of the new building area……
This chapter deals with the fabrication of the strakes that will hold the fuel and some small baggage areas. I opted to purchase
the Featherlite leading edge kits. I don’t think they cut down on build time, but they do add about 5 gallons of fuel per side.
(about an hour more endurance) The leading edge is a highly visible part of the plane and these will guarantee a nice straight
You first start by making a series of bulkheads that also double as dividers between the fuel tank and the storage area. They
also have small notches in them to act as baffles so the fuel doesn’t slosh around as much. These bulkheads are flat pieces of
foam that are cut out and glassed on both sides. Nothing magical here. Next, I started mounting the leading edges. They
come oversized by about a foot and they need to be cut down. Here is a picture of me cutting the leading edge to size.
Before permanently mounting the leading edge, I painted on 3 coats of pure epoxy as a sealer so I won’t (hopefully) have any
fuel leaks. This is what I am doing here….
Once this is done, the leading edge is put in place and a small table jig is constructed so the bottom skin and bulkheads can be
placed in the proper location. The picture below shows the leading edge and jig table in place. The yellow foam is the leading
edge. Just to the right of it is the main wing. I mounted the wing to ensure a perfect alignment between the wing and the strake.
This area is what separates the craftsmen from the backyard builders….I have seen some pretty ugly work as some of the
fly-ins…….I want to avoid this if at all possible.
Next, the top and bottom skins are measured and cut out of the same foam as the bulkheads. This was different for me since I
was using the prefab leading edges. The plans call for larger skins because they must extend further forward without the leading
edges. To get the correct size, I taped together some poster board and cut it to size. I then just traced the poster board onto
the foam and cut the foam to size.
Here you can see the bulkheads in place. The lumpy foam towards the back of the strake is pour foam that is mixed up from
two liquids. They quickly cause a chemical reaction and the foam expands. Great for irregular areas that would be tough to
shape regular foam to fit. This area is closed off because we don’t want fuel getting this far back in the airframe and causing a
rear CG problem. I later sanded the foam to match the tops of the surrounding bulkheads.
Once everything is in place it is taped with 2” wide bid tap and coated with 3 layers of pure epoxy to stop leaks. Lastly, before
closing out the strake, vent lines and fuel strainers are installed as you can see from the pictures below.
For the strainer on the right, I used a tea strainer from Walmart that cost $.97 cents for two. I cut the small handle off and floxed
it in place. The picture on the left shows a ¼” aluminum vent line that exits out the back of the tank area and goes up and around
Before closing out the strake, my EAA tech inspector said he wanted to see my work. Once the strake is closed out, there is no
way to tell if everything was done correctly. My tech inspector is Milt Ciarlariello. He is a retired United Airlines captain and I
he spent some time working at Boeing as well. He flew over from nearby
owned for over 35 years. He had a good look at everything, asked some questions, and reviewed the plans. After about an
hour, he wrote up the report that is mailed in and kept on file with EAA. In his comments he said….”Inspected left main fuel
tank prior to closure. No faults found. Workmanship remains excellent. Plans being followed carefully.” Here are a couple of
pics of Milt doing the inspection and the paper work.
Finally the strake is closed out by floxing the top skin in place. The milk jugs filled with water have never failed me yet, so I
used them here again.
I went on and built the right side up to this stage as well. Milt inspected it and found no irregularities. Once both sides have been
closed out, the outside foam needs to be glassed. Many other builders have pointed out how Nat (the designer) sometimes has
a wonderful economy with words….at this point in the plans, there are 4 little words that say “flip the fuselage over”……..the
problem is the weight is now up over 400 lbs. and the fuselage is rather bulky. Needless to say…..easier said than done.
Some people have come up with 5 to 10 people to manhandle the airframe on its back. Others have come up with big
clamshell wooden wheels attached to the spar to flip it over. I used my own version of the clam shell. I remember during the
move to the hanger, the airframe was very easy to lift the nose and set the airframe on its butt. I figured if I built two small
clamshells, that’s all I would need to roll it over on its back. I just made them big enough so the turtleback would not contact
the ground while I was flipping it over. This worked beautifully. The clamshells are very lightweight and are easy to mount to the
spar by one person. I can flip the plane over by myself in about 2 minutes. Works great. Here are a few shots…..
I cut the top (bottom?) of the clamshell so when the plane was inverted, it wouldn’t want to roll anywhere. This provides
a solid working platform. Now, on to skinning the outside of the strakes.
When we last left our intrepid builder, he had finished closing out both fuel strakes. All that remained was to skin the outsides of the strakes and then do the all important leak test. The outcome of this test would be the difference of happily moving on to Chapter 13 and installing the front retractable gear, or…..weeks if not months chasing down hard to find leaks. I have heard horror stories of people trying to track down leaks. One builder took 30 hours trying to find a leak that turned out to be a small leak through the wood grain of the upper longeron. Others have come up with ideas of using A/C refrigerant and a sniffer with varying degrees of success. Needless to say, I did everything I could to make sure I had a good seal on the tanks when I closed them out.
Let’s see what happened……..
The plans call for hooking an altimeter up to a vent line and blowing pressure into the tank through the other vent line until you attain 1500’ of pressure. I didn’t have an altimeter and I don’t plan on using steam gauges in the panel, so I built a manometer. It’s simply a tube that is made in the shape of a “U” and is partially filled with water. With no pressure applied the water seeks an equal level and is equal in height on both legs of the “U”. To use it as a measuring device, you blow air into onside of the “U” and this forces the water up the other leg. 13.6” up the other leg equals 1,000’ in altitude so I measured up the board 20.4” and made a mark for 1500’. Here is my home made manometer…
Next, I made sure that all the other fuel lines, vents, and fittings were completely plugged. You blow into the line with your mouth because if you used compressed air, you could blow the skins right off the plane, yes, it’s been done…. Sounds easy, but the amount of effort required to pressurize an area that holds 30 gals of liquid is rather substantial. Once the head rush subsided, there was nothing else to do but wait for 24 hours. It is surprising how much the water recedes and rises with the difference in temperature. It will easily move up or down a couple of inches for every 10 degree change. This fluctuation is unimportant. What you are looking for is the tanks to retain that pressure over 24 hours. Try to check them when it is the same temp as when you started the test.
And the verdict is………………..NO LEAKS!!!! Yea!!! Through almost 4 years of building, this was my biggest fear. It almost feels like the first flight. I didn’t sleep that great that night and as I was unlocking the hanger, the anticipation was unbearable. Well, it all worked out. Lastly, I installed the end ribs. These are put in place to give the leading edge a little more strength in case of a bird strike.This ends chapter 21 and now we can move on………but first a note on
The dangers of Aircraft building….(at least in
I’ve always considered myself a pretty safe worker around the various power tools and chemicals used in building anything. The airplane has been no exception. I always wear my safety goggles when I use the drill press or the dremel. I make certain to watch my fingers around the bandsaw. I wear my respirator when I’m sanding, etc. I even make sure to drink plenty of water while I’m working, especially when the thermometer looks like this:
But there was one thing I ran into this Summer that I never bargained for, It was this little guy………
Now, don’t get me wrong, I’m not afraid
of spiders and this guy (girl) is barely an inch big. I had heard about them but I haven’t seen any
in the 5 years that I have been living in
Now, take a look on the other side………..
The picture’s a little blurry, but yeah, that is the unmistakable red “hourglass” marking of the black widow spider. I found this description on the web (no pun intended) about the black widow bite…..
Black Widow spiders - - painful rigidity of the abdominal wall muscles, tremors, nausea, vomiting, leg cramps, “tightness’” of chest, and rise of blood pressure. Severe cases are hallmarked by difficulty in breathing and unconsciousness, which may lead to death due to asphyxia preceded by convulsions.
Not exactly my idea of a fun time. I have found a total of 6 of them, one even in my toolbox. Fortunately, they are not aggressive and are not particularly quick. You just have to be careful where you put your hands. I don’t blindly put my hand in to a box or under a shelf anymore, that’s for sure!
Well, on to the nose gear………………