Happy New Year!
I have been in Europe since Thanksgiving now. Working mostly on the Merlin, Merlin Lite, and Merlin II, with a visit to Spain to work on the TrueLite. Kinda looking forward to getting back to Florida for a bit of warmer weather. But I bought a one-way ticket here and am not leaving until my work plan is complete. That work includes refining the designs and making the build specifications perfect. Plus, getting a bunch of parts completed to get builders back on track to complete their aircraft. Then a return trip to Spain to fly the new TrueLite longer wing with flaps that I commissioned to fit Part 103. Here is a sample of some of the work-in-progress:
We have been flying the Merlin with the Vtwin for some time now with the dual fuel pump system mounted on the firewall. It is a serviceable system. And quite similar to the system Rotax and others use for EFI. But it never felt perfect. To me, it seemed convoluted. Fuel hoses from twin tanks to a duplex electronic fuel selector valve, then to two fuel pumps, then to a pressure regulator and fuel filter then splitting again to the EFI rail, plus, 2 lines back to the fuel selector then back to the fuel tanks. We built a circuit board to control the valve and pumps and programmed to automatically switch fuel tanks based on user-selected time or fuel consumption.
This was a lot of work. We should be satisfied with it. But I am not. There had to be a better way. Builder and colleague Ben took a hard look at the way ATVs manage their fuel and found a way to make it work for the Merlin.
This one pump system has everything integrated. High-pressure fuel pump, fuel pressure regulator, fuel filter, and fuel level sensor. It is built to be installed inside the fuel tank. This means that the pump can be much lighter as the fuel to cool the pump is already circulating around the pump. It also means that a fuel return line is not required. Excess fuel from the pressure regulator stays in the tank. No separate fuel filter is required. Same for fuel level sender. This is fantastic! And when we install one in each wing fuel tank, we have redundancy. Plus, all we have to do is turn on or off a fuel pump to switch tanks.
So, how do we make it work for the Merlin tanks?
Here you have it. We dismantle the fuel pump to allow it to fit inside our fuel tank. Then design a mounting bracket to hold it to the fuel tank bottom. Then attach to a side plate for installation, and removal for service, and for the fuel line, power lines, and for sender lines to egress. Then a quick disconnect for easy wing removal.
Currently, Builder Don is redesigning the fuel control circuit board. It will now have a big electronic rotary switch with 5 positions: Off, Left, Right, Both, and Auto positions. And we will make new instrument panels to accommodate this new circuit board with laser-etched labels. Next step will be to design and fabricate a fuel system upgrade kit.
Fuel system side mount prepared in wing tank.
Some of the Merlin changes include a repositioning of the instrument panel so it is slightly smaller. And the avionics tray has a reinforcement stringer, so the avionics are now repositioned. The control circuit board and EFIS are shifted a bit to the right to create room for the headset jacks on the panel. And the circuit board will now include a USB C post for phone charging.
We have the avionics tray and panel in the design office now to CAD up the exact positions so the tray will be pre-punched, and we can install rivenuts for quick and easy component installation. And the wiring harness lengths will then be adjusted to fit perfectly.
Moving on now to the battery. For weight and balance considerations we have moved the battery to the rear baggage bulkhead. For safety, and space, we designed a battery box that hinges on the bulkhead.
In this series of photos, you can see the battery box with built-in hinge and panel cover. The bulkhead has rivenuts to secure this box. The fuselage has plastic tubing routed all the way to the engine and solenoid for the battery cable. The rear fuselage now has two access panels for easy cable connection to the battery.
The cowl has been a big issue for us. You may have seen some of the modifications we have made along the way to get aircraft flying. Not all have been good. But now we are doing it right. We have made a new engine mount, radiator mount, exhaust mount, and component mount for the Vtwin. Now we know exactly how to make a new cowl to fit. Here is how we are calculating the size of the fuel injector bubbles to have adequate clearance. We have to be careful not to have any interference with the injector wires.
We also plan to design an access door for the oil dip stick access. But first we have to redesign the dip stick a bit to clear the engine bracket.
Oil dip stick in progress. Plus, new mounting of engine ECU and voltage regulator.
Next step is the cabin heat cuff and system.
Here you can see the new cuff which will have an air feed from the front cowl below the radiator. Then scat tube connect to a butterfly valve on the firewall center to warm your junk.
Now the cooling system hoses are being 3D modelled so we can send the send out for fabrication for a quick and perfect hose installation.
The cabin air and defrost system will be a separate system from a NACA vent on the fuselage side to the defrost eyeball vent.
A Prague Christmas. Carp for sale on every corner! I pass. And a few days skiing with Davi.
Now back to work, and for Davi, school.