I needed to calibrate the fuel capacitance plates in the fuel tanks. These aluminum plates measure electrical resistance through them. As fuel is added the resistance increases and the Dynon system and convert that to gallons after calibration. The process is pretty simple and the Dynon screen wakes you through it. You start with empty tanks and select start on the screen which takes a snapshot on the exact resistance in millivolts that it is seeing. Then you add two gallons of fuel and push the “add” button. The system takes a look at the resistance and locks it in. You then add two more gallons and repeat the process. You do this until you fill the tank completely. Now the system has 12 snap shots from empty to 21 gallons and their associated resistance. It then can make a curve connecting the dots to give you a very accurate reading of the fuel in the tanks. I didn’t take any photos of this process…that would’ve been boring.
An item that needs to be tested and verified is the electric fuel boost pump had enough power or flow to supply the engine with enough fuel in the case the engine driven mechanical pump were to fail. There is a lot of guidance from the EAA and FAA on how to determine this through a process of steps. In the steps you use a formula to determine how much pounds per hour fuel you would need for your specific engines maximum horsepower. You then can convert this to various numbers such as gallons per hour and gallons per minute.
When I built my IO-375-M1S engine at Aerosport power they were re-building their Dino machine so we didn’t get to determine the exact horsepower of my engine, however we think it’s somewhere between 195 and 200 hp. show for my calculations I went with worst case scenario of 200 hp. BSFC(Brake Specific Fuel Consumption) is a factor that some engine manufacturers and it’s a factor that is used to multiply horse power to enter into the formula. If your Engine manufacturer doesn’t provide one you can use .55 as a conservative number.
So my math is 200HP x .55 = 110lbs/hour. That’s how many pounds of fuel my engine needs at its maximum horse power. The FAA says you need to factor in a margin of error, in my case with a fuel injected engine it’s 25%. So I take the 110 lbs/hour x 1.25 = 137.5 lbs/hour. Now 100LL fuel that my engine burns weighs 6 lbs per gal. I can divid the 137.5lbs/hour by 6 to get gals/hour. 137.5 lbs/hr / 6 lbs per gal = 22.92 or round up to 23 gal/hour. We can convert that number to gal/minute by dividing by 60 minutes. 23 gal/hour / 60 minutes = .383 gal/min. So my plan was to use 4 gal of fuel pumped to determine my fuel flows. That way I have a gallon of space in my 5 gallon gas can for spillage and such. So I needed to know how long I have to fill 4 gallons of fuel into the gas can using my boost pump. So I need to pump .383 gal/min, so I took 4 gal / .383 gal/min = 10.44 min. Therefore that’s the bingo number I need, if my pump transfers 4 gal in 10.44 min it is providing just enough fuel, with the 25% factor, to supply my engine at its maximum horse power.
Now that I know what minimum time I have to fill 4 gallons in the fuel can I can test my boost pump to see if it’s up to the challenge. The RV-8 draws fuel from either the right fuel tank or the left fuel tank based on the fuel selection valves position. So I will need to test each tank separately for flow rates. I also need to test the flow in three different aircraft positions, level, 25° pitch up and 10° pitch down. The process is pretty simple, I disconnected the fuel supply line that connects to the engines fuel servo. I added a AN fitting to the end of the line. Attached to the other end was a short piece of aluminum tube that I could slip a clear plastic hose to. This will allow the fuel to flow into a gas can on the ground. So I just needed to put more than four gallons of fuel in a tank, turn the boost pump on and time the fuel as it fills to four gallons. I would repeat this step for the left and right wing in the three different flight positions.
One cool thing about the Vertical Power system I use for virtual circuit breakers is that you can test and control everything on a laptop via an ethernet cable. So I could turn the boost pump on and off at the laptop while standing next to the gas can rather than running around the wing to flip the pump switch in and off.
One other test I did during all of this was to determine my unusable fuel in each tank. The fuel line in the tanks can only pick up so much fuel based on their positions. So the fuel that it can’t pick for the engine is called the unusable fuel. To know this helps in flight planning so that if you put in ten gallons you know that a certain amount of the can’t be used and not figured into the fuel you want to use. To do this test I emptied the tank completely using the fuel drain on the bottom of the wing. Then I added exactly two gallons of fuel to empty wing followed by turning the boost pump on. When the boost pump stopped or almost stopped pumping I turned it off and documented how much came out which told me how much stayed in.
The pump put out double what I needed in all three positions. The results are listed here along with the unusable fuel data. The results are below:
Pitch down = Left wing 47gal/hr
Pitch down = Right wing 37 gal/hr
Level = Left wing 51 gal/hr
Level = Right wing 50 gal/hr
Pitch up = Left wing 50 gal/hr
Pitch up = Right wing 51 gal/hr
Unusable fuel was a little over .25 gal in both tanks. I think I will use 1 gallon as a conservative number for flight planning.
Finally after getting the dual fuel setup at the workshop, I worked a little in the shop today after being gone for a week for my six month recurrent training in the Lear 45. I finished up the wheel pants where I had filled in some holes and reprimed them. I’m calling those done and removed them for storage until flying time. I helped my buddy Glenn remove his wings now that he has all gear leg Fairings done. After rearranging the shop plus a little sweeping we move my RV into position so I could put the wings on. I’m doing this for two reasons, first to be able to do the fairings from the top of the gear legs to the fuselage/wing and the second is one last fuel leak test. Glenn had 20 gallons of 100LL that he used for his test and he let me have it for mine.
So the fuel went into the left wing and will sit for a week while I’m at the NBAA convention in Las Vegas. If there is no blue stains on the bottom or the paper I laid out I’ll call the a passing test and transfer the fuel to the right wing for its test. I’m slowly getting tasks done ahead of my engine build school, 34 days and counting down.
Once the wings are removed you have access to the fuel tank attach bracket that is part of the wing structure. If you remember I drilled this bracket while it was mated to the bracket that is part of the fuselage. Now that the hole has been drilled in the wing side bracket you need to extend the hole to a slot. The theory for this is in the event of an emergency landing or accident you want the wings to shear away from the fuselage as they absorb some of the energy that you have during an accident. The wings are meant to break away aft or towards the tail so you want the forward part of the wing to be easily separated in this event. This slot allows the bolt to support the inboard end of the fuel tank up and down but will shear away as the wings are bent back in an accident. So I started with a mark 1/4″ wide and cut the slot just inside of those lines. I then used a file to clean up the edges and open until a 1/4″ bolt would easily slide through the slot. Filing this thick bracket is what took the most time but I wanted to make sure I didn’t take too much. All in all I’m real happy with how they turned out.
Today’s task was to complete the left wing leading edge so that I can move on to the top skins. I started by putting the inboard rib in (this is the one that I had to replace) along with the spacer I made yesterday. I wasn’t sure if I would need it on this wing but figured it might be easier to put in before the other ribs were riveted as I had done yesterday. Well it was a little easier but not much. I put the leading edge on the spar with a few clecko’s and added the tank. I was happy to see that the alignment was pretty good so I’m glad I put the spacer in ahead of time. We will see how it all lines up after riveting as things tighten up with rivets compared to the clecko’s.
Unlike the right wing leading the left leading edge had holes punched in it on the forward edge for Van’s stall warning system. I decided to use an AOA (Angle of Attack) to determine an approaching stall. So these holes needed to be filled with rivets.
Next task was to grab the bucking bar and rivet gun and hit the skin to rib holes. I finished the top in about 45min before breaking for lunch.
After a short break for some lunch I got back at riveting. It took me about the same time to finish the bottom of the skin. I then put the leading edge on the spar and checked the fit. I repeated the process of yesterday by riveting the outboard and inboard rib with solid rivets while using the blind rivets LP4-3 & LP4-4 on the 3 middle ribs. The second outboard rib will also get solid rivets on both wings but I need help bucking those so they will wait for now. Next was to squeeze all the rivets along the aft edge on the top and bottom.
With the leading edge riveted on I grabbed the fuel tank and checked the seam alignment. I’m happy to say that it turned out really nice, a little better than the right wing.
The plans call for you to now put about half of the bolts in that hold the tank to the spar.
I wanted to complete one more task today before calling it a day. The next big step in the plans is to rivet the 3 pieces of the tops skins – the outboard, inboard and the doubler for the wing walk area. So I started with getting the doubler prepped for priming. I treated the edges and deburred all the holes before dimpling them with the DRDT tool. I wanted to get these pieces done since I decided that I was going to prime one side of them. I’m sticking to my plan of priming at least one surface where two bare surfaces come together. So one side of the the doubler will mate up to the inside of the skin, both of those would be bare hence my need for priming at least one of those surfaces. I got a couple of coats of primer on the side that needed it and will have a few days for them to cure.
I cleaned up the Hangar and headed inside to listen to a webcast presentation by aerobatic pilot Patty Wagstaff on an introduction to aerobatics.
