Category Archives: Wings

Fuel Tank Calibration

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Time: 2 Hours

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.

Fuel Flow Testing

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Time: 4 Hours

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.

Autopilot Roll Servo

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Time: 2 Hours

One of the items delivered today was the second autopilot servo that will function as the role component of the autopilot. To install this is exactly the same as the servo I put in for the pitch. One thing I found was that I made an error in the D sub pin layout way back when I installed the servo wiring harness when I was wiring the fuselage. It was not the same layout as what Dynon called in their installation manual, so I needed to correct this. It was the same in the pitch servo harness and I will correct that one as well shortly. So I needed to remove all the pins from the housing and reinstall them in the correct holes.

After inserting the pins correctly i laced the wires and reinstalled the housing.

I had to add pin and housing to the servo wires as well. The process was the same and ended with lacing and the install of the housing.

The install of the servo into the right wing is pretty easy, just three bolts hold it in place followed by two bolts holding the servo arm connected to the aileron bell crank. After torquing all the bolts and applying torque seal I powered up the Dynon Skyview to configure the network for this new servo. The system worked perfect and now I have expert autopilot controls including a flight director.

Dynon Heated Pitot

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Time: 8 Hours

I finally got back to working on the RV. When I built the wings one of the items I planned for was the Dynon heated pitot, for the non pilots it’s the tube that measures the air pressure to determine airspeed and angle of attack. I had installed the mast that would hold the pitot since it needed to be riveted and the hole cut into the wing so it made sense to install this early on. I had also wired for the pitot which includes the power, ground and indication wire. The wiring is for the heat controller that allows the pitot tube to keep ice from forming as you fly through moisture which could freeze on an I heated pitot and block it’s function. First task was about getting the pitot attachment screws drilled, tapped and countersunk.

This pitot has a special function in that it has one hole on the tip to measure pressure indicating airspeed but also has one in the angled face. This hole compares pressure between the two and as the angled ones pressure increases and the tip decreases it can measure the angle of attack, the angle of the wing relative to the air it’s traveling through. This angle of attack or AOA is used to determine when the wing stalls or no longer produces lift.

First up was to determine where the screws need to go. The pitot has some thicker sections on the wall to allow for the screw holes. I transferred where those would line up on a piece of tape I put around the edge so that I could reference them onto the mast.

I also used some electrical tape to help make the fitting tight. I put the pitot tube in place on the mast and used the reference lines on the blue tape to transfer those marks onto the mast. I then used those marks to drill the initial holes after removing the pitot.

I then returned the pitot tube back to the mast and used the previously drilled holes to mark the pitot tube itself. This way I could remove the pitot tube and drill in a more controlled environment as you need to be careful to not drill too deep and hit Bart if the inner tubes or wires.

With the holes drilled in the pitot I could then use my tap for 6-32 screws. I then countersunk the mast to accommodate the screws to be flush.

Once the pitot was secured into place with its new countersunk screws I marked the ends of the aluminum tubes inside the wing so that I would have good clearance. I need to transition from the aluminum tubes to the plastic SafAir pitot/static hose that I had installed a few years ago. I removed the pitot again so that I could cut the aluminum tubes to the final length. I decided to stager them to help with installing the pitot with the fittings installed. I needed to flare the the aluminum tube to work with a compression fitting that allows to transition to the push-to-connect fitting that allows the plastic hose to connect.

The next step was to mount the heater controller. I searched several websites prior to this and decided that I would mount the controller directly to the access panel. This allows for easy installation and removal as needed. So I took some measurements and decided exactly where to mount it on the panel. I made some reference marks and clamped the controller to the panel so I could drill the four mounting holes.

After I had the holes drilled in the panel I went to work on the attachment hardware on the controller. I decide to use nutplates to make installation of the controller as easy as possible. This included drilling for the nutplate rivers and countersinking for the dimples that would be in the panel. Once all cleaned up I riveted the nutplates and dimpled the panel for the #8 screws. Overall a pretty easy process just time consuming.

Now I needed to figure out exactly how to route the wires to make sure they don’t interfere with the aileron bellcrank or the edge of the rib. Once that was decided I started lacing the wires so that they would lay correctly. I also added a couple of adhesive zip tie attach points to help secure the wires.

I laced up the wires that come off the pitot so they look good as well.

The last task is to cut the two plastic lines inside the wing. I had left these long when I installed them a few years ago since I wasn’t sure how they would be routed in the final install. I made some marks where I thought the should end up and cut them about an inch long to start with. After a few trial fits I removed a little at a time to get a perfect fit. I decide to go with two 90° push connect fittings versus bending the aluminum tubes which will all for easy removal of the pitot should it need replacing.

just need to order and install some edge guard along the rib lightning hole to protect the tubing. I also did a pitot test with a 12cc syringe and some surgical hose following the HomeBuiltHelp technique from this video: Leak Testing. My system stayed pressurized and a constant indicated airspeed help for several minutes which tells me I have no leaks. I will test the static side after I crawl into the tail to add a tee fitting. I then tested the heating function of the pitot by powering up the RV and flipping the Pitot switch on. I watched the VP-X screen to see the AMP draw increase indicating the that controller and pitot are drawing power. The indicator I created on the Dynon screen turned green, that’s how I programmed it, to give an indication that the pitot was turned on and is functioning properly. I also tried to use a laser thermometer to see if the probe was actually heating. I could get a good reading so I quickly touched it with the back of my hand. It was hot but not so hot to burn me so that was good enough for me to say it’s working. One more task done on the RV!

Aileron Boots

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Time: 1 Hour

One complaint with Vans aircraft is sometimes they can be crafty and let cooler air in via some of the holes required in the fuselage. Two of the bigger holes are where the aileron control rods go from the fuselage to the wings. These holes can allow a lot of air to work it’s way into the fuselage. So Abby at Flightline Interiors, who I bought the carpet kit for the RV-8, also make boots that cover this area and allow the control rods to move freely. They are easy to install and have a slot down the side that is secured with Velcro allowing them to be installed after the rods are already in place. They have a plastic disk that has Velcro to attach them to the fuselage side wall. So another little task is complete and hopefully these help keep us warm on our future flights.