Electrical System ULP V06

After several comments/mail and reading books about this stuff, I think I'm finally converging to something usable.

The primary system is taken straight out of the ULPower manual. I have added the fuel pump 2 and manual switches for fuel pump 1 and 2. The isolation switch is a manual one installed with the battery (this may change, not sure yet).

The Mascot 8660 is removed. The reason is it will be impossible to isolate all the components from the common ground. The RDAC needed for EGT, CHT and MAP must be grounded to the engine, or it wont be able to read anything, and so on. Ideally all the RDACs should be in the primary system, and communications should be optical (fiber), maybe in 100 years. With a common ground, all isolation is gone. The 8660 would really only function as a current limiting device. Another reason is the 8660, when taking into account the efficiency (81%) will be too small. This could be fixed by dividing the system and install another ECB, but then things gets too complex for this little aircraft.

Pondering on fuel system

I think I found a good fuel surge tank. It's a "universal" version with 6 AN8 connections. There are several manufacturers of similar devices, and they can be had for 1 to 4 L sizes. A 2L tank seems to be suitable for me. It's simply an aluminium box with 6 holes in it.

Looking a bit closer at these tanks, it should be very easy to make an inverted system, with no moving parts, no flop tube. I may do that later on, it shouldn't be more to it than installing two tanks in series, like the sketch below.

Normal flying would cause no change. Gravity fills up both surge tanks.

When inverted, the inlet line will eventually be evacuated, while the vent line will close due to the gravity valve (also off the shelf racing part). The first tank will then gradually empty, while the second tank remains full.

When applying positive G again, the second tank will gradually empty while the first tank gets filled up. When the first tank is filled up, fuel starts flowing into the second than and they both eventually gets filled up. It should work I think, but should probably be tested in the shop first :-)

There are a few snags here, like what will happen if the aircraft goes inverted again, before the second tank is filled up completely? but nothing that can't be fixed by positioning the outlet to the EFI pumps vertically down towards the middle, and sizing the tanks correctly. The first tank should be smaller than the second. It would probably be better to build them as one single invertible surge tank.

Fuel system ULPower

A thing I haven't thought about is the fuel system. The AeroVee use max about 20 L/h of fuel. The fuel lines are dimensioned for this. The UL350 draw at max more than 120 L/h, where 100 of those are fed back to the tank. The gascolator also house the draining. The old system looks like this:

This will not work on the UL350. I have finished the tank, plugged and secured all holes, oops fitting etc. I will not take all that apart again due to the risk of leakage (except oops fittings). The simplest way to fix this, I think, is a header tank.

Reading a bit about fuel systems for high pressure fuel injected engines, this is a common thing in the auto/racing industry. In racing they don't call it header tank, but swirl tank or surge tank, sometimes also catch tank. From what I gather, it is pretty much a necessity for fuel injected engines doing racing. There are tons of these surge tanks available, several different shapes and sizes. ULPower has a header tank, and this tank looks exactly like a surge tank. The basic principles for the surge tank can be found here.

So for the new fuel system, I need a header tank and a new shut off valve. The existing shut off valve will simply be a service valve for future changes.

The surge tank can also be fitted with a flop tube for negative G, but that will be for later, if ever. The surge tank is actually a very clever device. Normally it is completely filled with fuel. If negative G is encountered, it will therefore still deliver clean fuel to the pumps. The reason is that for a pocket of air to occur, the air has to first get in there. That has to be through the vent line or main inlet line, and they are full of fuel. It will take more than a few seconds of negative G before the pumps start sucking air. If air comes into the surge tank while maneuvering, that air will be vented through the main inlet and vent line. In a way, it is kind of a big gascolator with a vent line more than it is a header tank.

For better negative G handling, I think the next drawing probably is a bit better. But, if it is a good idea to have a fuel system that is capable of longer runs (minutes) with negative G when the engine itself cannot handle it, is another question. Maybe I will install an oil accumulator later, if possible on the UL350.

Electrical system ULP v02-03

Studied the manuals a bit more yesterday. I have been mistaken about a few things. The new diagram:

FP1 and FP2 are just manual switches. FP1A is the ECU governed relay switch. This makes much more sense. Normal operation: FP1 = ON, and the ECU runs the thing. FP2 is backup and can be run in addition or instead of FP1.

If I draw the diagram "as recommended" by UL, it will look like this:

I don't understand the use of that 30A fuse. All engine systems are connected to the ECU. Also, the starter button is always "hot", even though it won't start without FP and ECU switches "ON". The 60A fuse seems way over-sized. Both the 8660 and the Mascot charger have fuses.

IMO the philosophy must be that the primary system runs the engine, and it should contain no protective devices for the secondary system. The engine should run even though the master switch is "OFF", similar to the AeroVee. The ECU, FP1 and FP2 switches should be more than enough. The revised diagram will look like this (I think):

The master switch isn't really a master switch, it's a switch for the secondary system. The ECU switch is the "master" sort of.

Electrical system ULP

The installation manual for the ULPower engine has several diagrams for how the electrical system is recommended to be set up. It is different than the Aerovee in several aspects.

• The starter and regulator shall always be directly connected to the battery (no switches or fuses).
• The battery is in parallel with a huge 65k micro F capacitor.
• The battery is recommended to have an isolation switch.

The ECU have a separate on/off switch and ignition switches. The fuel pumps have an option to have relays that are governed by the ECU. In addition each one has a manual switch. The idea of ECU governed switches is that they will be "on" whenever the engine is running, and will shut of the fuel when the engine is stopped. In an accident they will shut off automatically. If only one pump is used, the whole system runs automatically. I'm not sure that option is a good idea, it also means each pump relies on two relays to work.

Further, the ECU has a CAN bus where most data are sent. I believed this would enable direct link to the CAN bus on the MGL EFIS, but that is apparently not the case. An additional MGL ULP DAC has to be installed. This box talks to the ECU, but transform the data to some pseaudo analog data before it sends them to the EFIS/EMS on the CAN/RS232 bus. Seems a bit odd to me.

EGT, CHT and MAP are not send by CAN bus. A normal XDAC is needed for those. Seems that I need yet another "box". Where to put them all?

 

Engine arrived

The engine has arrived. Simply beautiful :-)

Kaolin is making the mount, and propeller is ordered from Prince. I feel really good about this and I'm looking forward to flying this plane instead of worrying about if the engine will run or not, or if it will be powerful enough in the mountains here.

Painted some stuff and made the rudder wire holes etc to correct dimension, lots of small details here and there-

I need to reiterate the electrical scheme. The UL350i requires two fuel pumps drawing lots of amps in addition to lots of new wires and switches. The main data is all through CAN bus, so that should be simple. I also want to make it all a bit simpler if possible.