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Friday, September 24, 2021

I contacted the factory about the 108% TCU setting at the 100% throttle position and this was their response (I added some notes):

  1. Set the throttle lever on the quadrant to the 100% stop, then adjust the throttle cable on the left carb from 108% down to 100% (as read from the TCU software in Monitor mode).
  2. Next, you will have to balance the right-hand carb the same at the left (using the usual Rotax carb balancing procedure).
  3. With the throttle set up correctly, the TPS will provide the correct reading to the TCU. If there is slack in the TCU cable it can be adjusted but avoid excessive tension.

I asked them if I can defer fixing this as long as I keep the MAP below Rotax specified max values and they said yes (as expected).  So, I'll keep it below 40" for the takeoff sequence (5-minute max) and below 35" continuous otherwise.

It's clear that this is yet another thing that was not done in Oklahoma...

Wednesday, September 22, 2021

I contacted the factory about the 115% = 41.5" and they said I just needed to do a TCU calibration.

So, I got and installed the TLR4.6a software and the right cable (as all described on Jim's blog) to connect to the TCU and went to the hangar tonight after watching this video on

My setup...

The TLR software is ancient 32b DOS software, so it's a little bit of work to get it all working on a modern 64b laptop running Win10.  The DOS window doesn't scale, so bring a magnifying glass...

Powered up all the electronics and started the software.  The first thing I did was the monitor function to see what the current settings are (Press M).  This is at Idle throttle.  3.7% is out of spec.  Should be no more than 3%. 

This is Throttle @ 100%.  Out of spec.

Throttle @ 115%.  IN spec...  Though this is my problem area....

This is after I ran the calibration (Press T).  Throttle @ Idle = 0%.  Good.

Throttle @ 100%...  The same as before.. Out of spec.  Hmm..

Throttle @ 115%...  The same as before.

Another pic of the 100% position.  Should be within +/-3 of 100.  Nope...

Now what?

Sunday, September 19, 2021

Great flight yesterday!  Both the fuel pressure and flow sensors are working perfectly and no leaks at all.  Yay!...

But, of course, I saw a discussion on Facebook (Sling Airplane Enthusiasts group) yesterday about maximum MAP on takeoff (over the gate) and came to find that what I'm reading in my plane on takeoff is over the Rotax spec'ed maximum...  Why does it always seem that there's something that I need to look into...

The spec'ed maximum is 39.9 inches and I read 41.5.  When I was picking up the plane in Oklahoma nobody expressed any concern about the fact that it was flashing red - the implication being that it was normal when over the gate.  No it's not.  It shouldn't be much over 39.9, if at all.

I'm using the correct sensor, the G3X has the right sensor selected and it reads the correct atmospheric pressure when the engine is off.  So, I think it's a correct reading.

There are no TCU lights illuminated and apparently the TCU has it's own pressure sensor, so it doesn't seem to think there's an issue.  So, what's, what?

Was my TCU never set up properly down in Oklahoma?  That wouldn't be shocking...

Kind of disheartening....

Anyway, here's a video of one of my circuits around the pattern yesterday (you can actually see it flashing red during the takeoff and climbout).

Friday, September 17, 2021

Got the new fuel flow sensor assembly from Torrance and it's now fully installed along with the new fuel pressure sensor.  I'll be testing it tomorrow morning and will hopefully fly if all is well: No leaks and proper readings.

New assembly with new FT-60.  Looks good!  I just had to slide on the firesleeve and clamp them.

Assembling the banjo connections with the crush washers is a bit tricky so I put some paper towel under them so if any washers fell I wouldn't lose them (a royal pain..).

No dropped washers!

Solder butt connectors in place and some heat shield under it to keep the heat away from components that may have some fuel in them.  There's a green wire that comes out of the sensor, but that is not used.

All in and tightened down.  Excited to try it tomorrow.

Sunday, September 5, 2021

I installed the new fuel pressure sensor and did voltage and continuity checks on all the wiring for the fuel pressure and flow sensors.  All checked out.

Installed the new version of the pressure sensor.  This version has a higher burst rating (doesn't really matter at these pressures) and supposedly is more accurate (also doesn't really matter).  I got this version because I was able to get a new one on eBay for much less than either version would otherwise cost.  I'll install this assembly once I have the fuel flow assembly.

Used this on the NPT threads of the sensor.

Wednesday, September 1, 2021

Just so it doesn't all seem negative, here's a picture of me practicing take-offs and landings at my home airport, 6B6, Minute Man Air Field, in Stow, MA.  I LOVE flying my Sling 4!

I don't know that I mentioned this, but on my last flight I noticed the fuel pressure spiking and going offline (the engine sounded perfectly fine), so I ordered a new fuel pressure sensor and it's coming this Friday, and hopefully it was a sensor problem and not anything else.

I also removed the entire fuel flow sensor assembly and re-doing it correctly (with a new sensor).

The only hard part to remove was the fuel line from the sensor to the right carb as it was basically impossible to get the wrenches in there to turn the outer nut.

Grinding down the wrenches though made it super easy.