Month: May 2016

Flight #20

Preflight: Removed elevator bell crank inspection ports on both sides to inspect the elevator push/pull tube, jam nut, and bolt holding the elevator horns together. All was nominal. Added torque seal to the jam nut and elevator horn bolt so I can see if it ever moves. Reinstalled two inspection ports (7 #6 screws each).

Fuel starting was 20L/20R. Totalizer remaining: 40.

Oil was above 6.0.

Preflight: Engine: 29.9, Total: 32.4

I installed the passenger seatback which had been removed for many flights. I filled a 5 gallon gas jug with water (40 lbs), and strapped it to the passenger seat. Slowly beginning to increase the weight to explore the CG envelope. I did some stalls at 0, 1/3, 2/3, and Full flap settings near the beginning of the flight while the tanks were still relatively full. The stall behavior is slightly sharper, but still very benign. The AoA audio tone warning beeps are now active since I calibrated the AoA gauge last flight and it is a very nice feature.

I also spent a bunch of time leaning the engine and watching EGT readings…see the flight data link below and plot EGT, RPM, FF, and MAP.

Post flight: Engine: 31.6, Total: 34.2

Time: Engine: 1.7, Flight: 1.8

Fuel ending was: Gauge: 15L/13R. Dip 12L/10R. Fill: 7L/9.9R (16.9 total)

Fuel totalizer used: 16.9

Remaining: 23.1

Flight Data

Flight Map

The totalizer seems to agree well with the fuel truck. The gauges seem to read 2-3 gallons too high in the mid range.

Oil Pressure Sensor Fix

Worked on the oil pressure sensor trouble shooting today, and think I have found and fixed it. I found a bundle of wires entering the G3X EIS that when tugged caused the oil pressure gauge to fluctuate. Strangely with Mom and Rachel helping, we discovered that it also caused the fuel pressure and manifold pressures to wiggle also. Here is the text from my writeup on VAF:

VAF Post

I may be closing in on it
Ok. Far too many hours in the hangar tonight but finally may have found the culprit: enlisted help from my family to watch the gauges while I hunted for wiring problems. Finally found that tugging/bending the large bundle of wires going into the 78 pin connector on the eis caused the oil pressure gauge to do is jumpy thing

Surprisingly it also disturbed the gauges for the manifold pressure and the fuel pressure. Checked my wiring diagram and found the following wires in common among those three gauges:
Three grounds spliced together and three 5v lines spliced together and also sharing the 5v pin with the two capacitive fuel level senders.

The 5v and ground splices used those heat shrink solder bands and both looked only partially melted solder. I heated both and got much better solder flow. Put it all back together and gauges now steady when flexing and tugging same connector wire bundle. Will fly tomorrow and test. But I’m hopeful it is found.

Thanks Walt for the offer but I will wait and test for a bit more. I had tried swapping gauges without recal just to see but didn’t carry it to far or fly that way.

VAF Oil Pressure Post

VAF Post:

Ok this is driving me nuts. My new RV7A has 20 hours on it, and everything is just lovely…except this darn oil pressure intermittent problem where the oil pressure gauge suddenly pegs off-scale high (data download shows 155 psi, in abrupt change from minutes of nominal readings)

Here is a description, and what I have tried:

First cropped up after ~12 hours on new engine:

Kavlico 150 PSI 3 wire sensor (GND, 5V, signal)
0.5V = 0 PSI
4.5V = 150 PSI
Mounted on transducer block on firewall. Plumbed to the engine with a restrictor valve on the engine side of the hose.

Gauge will read fine: 50-60 PSI during taxi, 70-80 PSI during runup.
It will react normally and then just suddenly jump to 150PSI+. When it jumps there, it usually stays there while I terminate the flight. After engine shutdown, it stays reading pegged 150 PSI+. After avionics power cycle withe engine off, it will sometimes show 150+ and sometimes clear the error and show 0 PSI. If it crops up, it likely crops up in the first 10 minutes after engine start. If it doesn’t crop up, I can fly for 2 hours (2 times) and not have a problem.

The 2nd and 3rd time it happened, I landed, quickly removed the cowl and wiggled wires near the oil pressure sender…no change. I separated the connector near the oil pressure sensor (3 lines) and measured 0V GND, 5.01V, and 4.5 V on the sensor return line (this is with sensor disconnected)…Also, seem to have measured 0V GND, 5.01V and 0V on the sensor return line sometimes when I disconnect it (each time i disconnect, I do see a change from off-scale high to red X on display)…this made me suspect the sensor return line was somehow shorting to the 5V supply, or that it has a pull-up resistor in the G3X GSU73 that is pulling high when the gauge is disconnected.

So I spent 2 hours, digging under the panel and disassembled the connector shell at the GSU73 and checked all wiring…the only wiring i haven’t check is if there is chafing where it goes thru the firewall pass thru since that is covered in fire seal. With the GSU73 connector removed, none of the 3 wires seems shorted to each other.

This leaves me thinking I should try replacing the $90 gauge. but this is weird failure mode right? Could this be a firmware glitch that is solved by G3X firmware update. Could this be an intermittent GND line? When the ground goes away the pull-up brings the line high and thus the off-scale reading?

I also plumbed a mechanical gauge in parallel with the G3X Kavlico sensor, and the readings during a full runup are within 1-2 PSI from 0 to 50 to 80. But, since it seems i need to fly to get the glitch, I haven’t had the mechanical gauge plumbed during any of the actual glitch events. But I’m convinced it is not a real pressure event and it gauge or wiring…

Why would sometimes an avionics power cycle clear the error and return it to 0PSI if it was a wiring problem?

Any ideas would be much appreciated.

Flight #14

5/24/16

Returned to the airport to investigate the oil pressure gauge problem. The goal was to get the sensor to do its off-scale high in the pattern, land, and investigate by probing the wires, switching the gauge plugged in, and cycling power.

Preflight: Measured 5.9 quarts on the dipstick. Added 0.5 quarts oil.

Fuel totalizer not reset from yesterdays 2nd short flight.

Time before: Engine 16.8, Total: 19.4

Time after: Engine 19.0, Total: 21.6

Flight time: 2.2

Flight Data

Flight Map

Well, I filed a flight plan to depart, on the off chance the gauge behaved. It did, and so I departed Manassas and did a climb to the moderately high altitude of 13,500 feet.

I spent a hour or so flying straight and level doing the first leaning of the mixture. Till now, I have almost entirely been flying full rich. This is pretty costly as I’m burning 14+ gallons per hour. This is done to help keep the engine cool during this break-in period. During the leaning, I was able to see the EGT’s rise from ~1200 to ~1550 before peaking and going lean of peak. I continued to lean and saw 7.2 GPH before I noticed any engine roughness; the engine was really beginning to threaten to quit at 6.9 GPH. I didn’t want to push it further, and returned to running full rich. I’ll need to check with VAF to see when I can stop burning 14+ GPH.

Spend the remainder of the flight doing 2600 RPM climbs and 2650 (Full) RPM climbs. These performed better than the 2400 and 2500 RPM climbs from flight #11. I will need to download the data and add it to that flight’s data table.

Oil pressure was entirely nominal throughout the flight. Weirdness.

After landing:

Fuel totalizer: Remaining: 19.1, used: 22.9 (includes flight #13 & 14)

Gauges: L Remaining: 11, R Remaining: 13

Dipstick: L Remaining: 8, R Remaining: 10

Fill: L: 11.4, R: 10.4 (T:21.8)

Flight #13

5/23/16

Fuel totalizer reset prior to flight. Flash data card installed before flight.

Attempted to do a second flight today. Filed flight plan to depart Manassas, but immediately after takeoff, the oil pressure gauge did it’s off-scale high anomaly again…Dammit…thought it was fixed. Aborted flight plan and immediately landed. This leaves only a few things left to try: Plug the oil pressure sensor wires into the manifold pressure gauge to see if that changes things or helps isolate, buy a new oil pressure gauge, and update the computer firmware. I’ve checked wiring at each connector end.

Time before: Engine 16.6, Total: 19.0

Time after: Engine 16.8, Total: 19.4

Flight time: 0.4

Good news is my takeoff and aborted departure saved me from having to wait out the rain cell on the ground in Warrenton while Manassas got drenched for an hour.

Flight Data

Flight Map