More chasing

Please take a look at these two sorrowful pages of sketches of today's oscilloscope output.

The engine always starts easily and idles very smoothly. Roughness starts around 1,800 RPM. Misfiring is very pronounced, really shakes the engine, and the exhaust is momentarily black.

Page 1.

First wave is pretty much what it looks like with both the 6" and 7 1/2" wheel, at idle. With the 7 1/2" wheel there is a little more of a hump in the middle of the trigger wave. The peak-to-peak amplitude is pretty even and is about 4 volts p-p.

2nd wave. This is what it looks around 2,000 RPM. Notice that the amplitude varies greatly, from about 3 V to 7.5 V p-p. We tried adjusting the air gap from .015 to .060 and didn't see a change here. We thought maybe the variations in amplitude might be from the prop bolts and flange lugs. Just speculation.
3rd wave. Another sketch at high throttle. Here, I tried to include the trigger wave. The trigger wave, at higher RPMs, always had a greater p-p voltage than any other part of the wave, while at idle, the trigger wave was the same.


Page 2.

There always is a consistent phase shift (skipping a tooth?) at any speed. In the sketch, I am attempting to show how it would bounce back and forth. We feel this is a key issue, but have no idea why it is occurring.

We also saw that the amplitude of the wave is pretty even at low RPMs, but at higher revs the amplitude varies a lot. Click on the sketches to better read the voltage ranges.


Other things we tried and noticed:

Changed from 1 1/2" to 6" wheel. no change seen on scope.
Removed the prop bolt closest to the trigger gap. - no change
Tried a smaller diameter sensor. - a little smoother.
Degaussed the crankshaft flange. - no change.
Ran on the single magneto only. - a little smoother.
An automotive timing light flashes consistently at low RPMs, but becomes intermittent, in sync with misfiring, at higher speeds.
Installed the 6" wheel and used the 7-1/2" sensor mount bracket. This caused the sensor to kind of be extended way out from the aluminum bracket. No effect.

I sent these sketches to Tracy Crook, at RWS and he thinks that the change in amplitude is the source of the problem and what I perceived as a "phase shift" is not an issue. Given that, I will be concentrating on eliminating all vibration in the sensor mount bracket.

Sam

All Things Electrical

I've been trying to concentrate on all of the electrical items from the firewall aft. This is cool, since I am actually bolting parts on the airframe, and the piles of parts in boxes are getting smaller.

With the exception of the wiring, I have the instrument panel largely complete. The Biggies are; handheld GPS dock for my old Garmin GPSMap196, Dynon D180, ICOM A210 Com., Transponder, and RWS ECU programming panel. You will also notice about 20 pounds of switches, used to control the ignition/injection/fuel pumps. As always, click on the photo for more detail.
On the backside of the panel, you can see two fuse blocks, a couple of diode sets and a couple of switching relays.

Throughout the airframe, I've also installed the engine and battery busses and contactors, the voltage regulator and filter capacitor and the big ammeter shunt device.

Soon, I'll get some preliminary wiring done on the panel, then get it permanently installed.

The biggest challenge, right now, is sizing the batteries. My load analysis shows that I'll need about 13 amps to keep this thing in the air. To make my system redundant, I'll need a backup battery capable of delivering 13 amps for a half hour. Yeauch!

I figured out how and where they should go, I just hate adding all that weight.

Sandy said I should just eat less and get some exercise and not worry about the battery.

Now - Where was I?

Time to get back to the fun stuff. While I was waiting for the paint to dry I did get some other work in on the aft side of the firewall. Specifically, I'm working on the instrument panel, location of the batteries, and getting the fuel system in.

Because I'm using fuel injection, I will need a fuel pump to boost the fuel to about 45 psi. It is a closed loop system, meaning, the fuel is in constant circulation as it's filtered, boosted and regulated. The pump and filter package is mounted to the fuselage wall, just aft of the pilot.

I chose Walbro pumps and I have a second as a backup. Fuel leaves the header tank via the black fuel line and goes to an aft mounted 70 micron gascolator. Then through the fuel pump, through a 10 micron filter, then through the aluminium tubing to the firewall. After making the circuit around the engine, it returns back through the firewall and is delivered to the fuel pressure regulator. After the regulator, the excess fuel is dumped back into the header tank.

One of the biggest challenges was bending the aluminum tubing, especially the 1/2" stuff. It was tough even finding the right bender. Fortunately, I was again able to tap into SIU AvTech and got hold of Professor Billy Cheek. Billy used to bend tin for the Air Force and pulled me out of the deep hole I'd gotten myself into.

The photos are showing the work in progress. Click on 'em to see 'em bigger. Please excuse the dust.










Today I actually applied power to the fuel pumps and pressurized the system. For testing purposes I took it to 80 psi, but I think I will normally run it at 45 psi. The test was a great morale boost!