Back to the New World

They let me back into USA. Shocking, I know. Back in Florida now after nearly 2 months in Europe. No idea where my luggage went. Same luggage was lost 5 days on the way to Spain. Now pushing 5 days back in USA and still not delivered. My plan was to go to Alabama right away to ship out parts. But those parts are in my luggage!

I expect the luggage to arrive today, then I will get over to M-Squared and get to work. Some of the work done or in progress:

  • A lot of design details on both the Merlin & Merlin Lite were discussed and sorted so it is now clear exactly what the production aircraft will be.
  • Merlin Lite production is now finally starting. One aircraft will be built to flying for the flight test program in CZ along with documentation and additional structural testing.
  • The next 4 Merlins ship the end of February. Painting has already begun.
  • The balance of the parts needed for the early customers and the build center are under construction.

Here is the mold for the top cowl modification. We needed bigger bubbles to provide fuel injector and cowling hose clearance.

This new brake plumbing simplifies installation. The reservoir is now in the cockpit and the parking brake in line with the brake tubing.

Here are the details of the new fuel panel from builder Don:

Fuel control is now a rotating knob. The CPU retains the auto fuel balance. Select time or fuel level and the CPU will switch tanks based on pre-programmed settings. Here is the description from Dr. Don:

The holes for the LEDs, Fuses, and the Rotary Switch are on mechanical layer #2.  The mounting holes are on the “multi-layer” layer…

There are:

  1. Four mounting holes for #6 screws.
  1. Six holes for the LEDs that are .200″ diameter.
  1. One hole for the rotary switch that is .250″ diameter.
  1. Two rectangular holes for the two fuses (remain unchanged).
  1. No toggle switches — all replaced by the single rotary switch.
  1. One USB connector and related components that are only going to be populated on a couple of these boards for testing and for use later if needed.  I’m assuming a sudo-linear slope from the fuel sending units. The customer units won’t have the USB connection components populated on the PCB unless absolutely necessary.

The adjustment/calibration of the fuel level is like this — It needs to be done in the following order:

  1. Set the “FULL” calibration by completely filling the respective fuel tank then adjusting the corresponding trim pot until the “FULL” LED illuminates.  The “FULL” LED must only illuminate when the tank is “full” or very-nearly “full”.
  1. Set the “EMPTY” calibration by completely draining the respective tank and then momentarily shorting the corresponding “EMPTY SET” pad to ground.  The “EMPTY” LED should then only illuminate when the tank is “empty” or very-nearly “empty”.

I’ve included several fuel sampling “Test Points” on the circuit board to facilitate troubleshooting (if necessary).

The overall board size is smaller than before — now 3.525″ wide by 3.650″ tall.

The rotary switch is 60 degree indexed, and the corresponding functions are shown on the top layer silkscreen.  Here is how it functions:

Whenever the “MASTER” switch is “ON”, the microprocessor is powered and the “POWER” and “HEARTBEAT” LEDs will operate.  The rotary switch operates like this:

“OFF” is precisely that — Both tanks (pumps) are “OFF”

“LEFT” — Left tank (pump) is manually commanded “ON”.  The Left pump is powered and LED (DS2) illuminates, and the “MANUAL” LED (DS6) illuminates.

“BOTH” — Left AND Right manually commended “ON”.  The Left and Right pumps are powered and LEDs DS2, DS4, and “MANUAL LED (DS6) illuminate.

“RIGHT” — RIGHT is manually commanded “ON”.  The Right pump is powered and LED (DS5) illuminates, and the “MANUAL” LED (DS6) illuminates.

“TIMER” — “AUTO” LED (DS5) illuminates and the microprocessor toggles between the Left and Right tanks at whatever interval we want (presently set to 10 minutes).  The corresponding tank’s LED illuminates.

“BALANCE” — “AUTO” LED (DS5) illuminates and the microprocessor toggles between the Left and Right tanks, selecting to feed from the “most full” tank.  The tanks will toggle when the feeding tank is about half gallon below the non-feeding tank.

In either of the “AUTO” modes (“TIMER” or “BALANCE”), if both tanks are below a specific (yet to be determined appropriate) fuel quantity, the microprocessor will feed from “BOTH” tanks, in order to maximize the amount of usable fuel / prevent fuel starvation.

In all instances (except “OFF”), there will be about a 2-Second delay before switching “OFF” either tank (pump).  This should ensure that either pump coming on-line will have developed sufficient fuel pressure before switching off the previously-feeding tank.

When selecting “OFF”, the microprocessor will immediately kill power to the fuel pumps.

When switching from “OFF” to either “LEFT”, “BOTH”, or “RIGHT”, those respective pumps will power “ON” immediately (no 2-Second delay).

The rotary switch has a hard mechanical stop.  “OFF” is always at the Counter-Clockwise limit of rotation.  One can’t rotate the switch Clockwise to go from “BALANCE” to “OFF”, etc.



That is a pretty sophisticated fuel control for anything smaller than a business jet.

There are three more chapters to the fuel story.

The avionics tray is now installed into the Merlin. The avionics components have new positions centered behind the instrument panel. The components are connected to the wiring harness with circuit boards, The components are bolted onto the avionics tray with pre-installed rivenuts. The left-side main circuit board and the EFIS are shifted to the right about 3/4 inch. This provides space for headset jacks on the panel’s left side.

The instrument panel itself is slightly smaller due to its relocation for greater leg room.

Now we have a new fuel circuit board, and that CAD data has been sent to TPA to cut new panels.

We have ordered 50 fuel tank pump assemblies. These pumps will be mounted to the new fuel tank side access panel. We are working on the protocol for the retrofit of this new fuel pump system. When finished, TPA will ship 16 sets to USA for distribution to those who would like to upgrade.


And here we have the new long wing with slotted flaps installed on the TrueLite in Spain!!! And a look at the improved wing tip. Now just waiting on good flying weather for the test flights.


The TrueLite has electric flaps operating twin telefex cables. The control and flap indicator will be on the instrument panel. Come see this cool ultralight at Sun N Fun this April!!!

And yes, of course the wings still fold in under 2 minutes!

Been two months since I cut the grass. Back to work.