ssbn608
I love flying!
I was flying my homebuilt aircraft with a Rotax 912 iS engine on 2nd flight ever. Took off, turned downwind in pattern. Suddenly:
[list bull-redball][*]at time 00:14:17 Fuel Flow began sharp exponential decay to from 7 gpm to steady at 2.2 gpm by 00:14:30
[*] at time 00:14:18 Fuel pressure dropped from 46 psi to 34.1 (step change) (this concerned me most; thought I might have broken fuel line)
[*] at time 00:14:18 Indicated pressure altitude (PALT) jumped from 2,700 ft to 50,472 ft (step change)
[*} Density altitude has curve that is identical in shape to that of PALT
[*] at time 00:14:18 indicated air speed dropped from 71.3 kts to zero (step change)
[*] EGT's rapidly rise to peak about 3-7 seconds later at about 50-80 degrees hotter (EGT1, 2, 3, 4 at 00:14:18 were 1301, 1285,1351, and 1314 degrees, respectively; they peaked at 1379, 1355, 1400, and 1375 degrees, respectively, at 7, 6, 2, and 4 seconds later, respectively. From the peaks, they pretty linearly decline (to 1343, 1333, 1355, and 1345 degrees, respectively) until 00:14:47, which is when I think I physically cut the throttle back.
[*] both A Volts and B Volts (CAN bus) made a jump from 13. 7 to 13.9 at 00:14:18. I note I was at 13.9V at idle prior to takeoff. But I'm not sure this is significant... CAN bus A&B voltage stayed in a fairly tight range of 13.7 to 14.0 volts the whole flight
[*] RPM began to drop from take-off RPM of 5600 to cruise 4000 rpm right at 00:14:17
[/list]
It appears to me that I was finishing a shallow turn to downwind off of Runway 17, snuck a peek at the altimeter, and saw I was above pattern altitude already, and throttled back to 4000 rpm. Looked outside, then back at panel and I noticed fuel pressure was low (perhaps the audio alarm told me to look - I don't remember)...as opposed to high pressure I normally see with two fuel pumps running. That caught my attention, thinking I had sprung a leak. But... no fuel smell, no burning smell. Took stock of where I was. Knew I could easily glide in (it's a motorglider); wanted to get on ground quickly, but I was on only my second flight, didn't want to do extreme maneuvering that would be required to maybe land down wind on 35, so concentrated on setting up for a landing on 17. Plus, I noted that I had lost airspeed indication, AND altitude was over 55,000 ft indicated. Engine was still running...had it about 1-2 cm open, which is about 200-2500 rpm on the ground, to help me keep airspeed up, whatever it was, and maintain altitude until I was ready to turn to land, because I was expecting to have to cut the engine any second. Runway is very much longer than my landing distance (more than 10 times as long), so didn't fly as far downwind as usual. Visually, I was a little high, but that's what gliders have airbrakes/spoilers for. I made a normal idle throttle descending turn to final (nice to have a yaw string to help coordinate that turn), noted I easily had the runway made, extended the airbrake and kept a good sight picure. Fortunately, had flown just the previous day in similar conditions (very light wind right down the same runway), and a few landings in a similar motoglider on Dec. 30, so was able to judge (I think) airspeed pretty well by sound. Concentrated on keeping speed up...I had plenty of runway to float down. Made a beautiful landing. Could see shadow of aircraft on runway after I had slowed to taxi speed. Noted I could NOT see any shadow indicating fuel was flowing out. Also noted that fuel level hadn't noticibly changed (wing root sight glass on my high wing aircraft are not dependent on electronics to read - in the daytime). So I taxied back to the hangar, took a screen shot of my 10 Dynon (still showed 50,000 + ft altitude and low fuel pressure) and shut down. Then re-started my Dynons... and saw altitude indication at normal.
So what the heck happened? I have no real idea. I THINK that the reduction in Fuel Pressure is related to the change in indicated altitude (difference in air pressure between traffic pattern altitude and 50,500 ft is about the amount (within 1 psi?) that the fuel pressure dropped. But they may be unrelated.
I looked at the static lines, and don't see a problem. We have cross-connected static ports on either side of baggage compartment, feeding a single ADAHRS unit in the top of the baggage compartment.
One thing I regret is that I didn't think to look at the backup analog instruments... but they are small and on far side of panel of the panel. I just reverted to training, and kept my head out of the cockpit and concentrated on flying safely to the ground. Anther thing I regret s that I got frustrated with the little Go Pro camera we tried to set up to monitor things - it has stopped reading the only SD card we have that is 32 GB....So I didn't have it running on this flight
.
I'm uploading the data log. Any thoughts on what might have caused this, or potential troubleshooting steps would be GREATLY appreciated.
[list bull-redball][*]at time 00:14:17 Fuel Flow began sharp exponential decay to from 7 gpm to steady at 2.2 gpm by 00:14:30
[*] at time 00:14:18 Fuel pressure dropped from 46 psi to 34.1 (step change) (this concerned me most; thought I might have broken fuel line)
[*] at time 00:14:18 Indicated pressure altitude (PALT) jumped from 2,700 ft to 50,472 ft (step change)
[*} Density altitude has curve that is identical in shape to that of PALT
[*] at time 00:14:18 indicated air speed dropped from 71.3 kts to zero (step change)
[*] EGT's rapidly rise to peak about 3-7 seconds later at about 50-80 degrees hotter (EGT1, 2, 3, 4 at 00:14:18 were 1301, 1285,1351, and 1314 degrees, respectively; they peaked at 1379, 1355, 1400, and 1375 degrees, respectively, at 7, 6, 2, and 4 seconds later, respectively. From the peaks, they pretty linearly decline (to 1343, 1333, 1355, and 1345 degrees, respectively) until 00:14:47, which is when I think I physically cut the throttle back.
[*] both A Volts and B Volts (CAN bus) made a jump from 13. 7 to 13.9 at 00:14:18. I note I was at 13.9V at idle prior to takeoff. But I'm not sure this is significant... CAN bus A&B voltage stayed in a fairly tight range of 13.7 to 14.0 volts the whole flight
[*] RPM began to drop from take-off RPM of 5600 to cruise 4000 rpm right at 00:14:17
[/list]
It appears to me that I was finishing a shallow turn to downwind off of Runway 17, snuck a peek at the altimeter, and saw I was above pattern altitude already, and throttled back to 4000 rpm. Looked outside, then back at panel and I noticed fuel pressure was low (perhaps the audio alarm told me to look - I don't remember)...as opposed to high pressure I normally see with two fuel pumps running. That caught my attention, thinking I had sprung a leak. But... no fuel smell, no burning smell. Took stock of where I was. Knew I could easily glide in (it's a motorglider); wanted to get on ground quickly, but I was on only my second flight, didn't want to do extreme maneuvering that would be required to maybe land down wind on 35, so concentrated on setting up for a landing on 17. Plus, I noted that I had lost airspeed indication, AND altitude was over 55,000 ft indicated. Engine was still running...had it about 1-2 cm open, which is about 200-2500 rpm on the ground, to help me keep airspeed up, whatever it was, and maintain altitude until I was ready to turn to land, because I was expecting to have to cut the engine any second. Runway is very much longer than my landing distance (more than 10 times as long), so didn't fly as far downwind as usual. Visually, I was a little high, but that's what gliders have airbrakes/spoilers for. I made a normal idle throttle descending turn to final (nice to have a yaw string to help coordinate that turn), noted I easily had the runway made, extended the airbrake and kept a good sight picure. Fortunately, had flown just the previous day in similar conditions (very light wind right down the same runway), and a few landings in a similar motoglider on Dec. 30, so was able to judge (I think) airspeed pretty well by sound. Concentrated on keeping speed up...I had plenty of runway to float down. Made a beautiful landing. Could see shadow of aircraft on runway after I had slowed to taxi speed. Noted I could NOT see any shadow indicating fuel was flowing out. Also noted that fuel level hadn't noticibly changed (wing root sight glass on my high wing aircraft are not dependent on electronics to read - in the daytime). So I taxied back to the hangar, took a screen shot of my 10 Dynon (still showed 50,000 + ft altitude and low fuel pressure) and shut down. Then re-started my Dynons... and saw altitude indication at normal.
So what the heck happened? I have no real idea. I THINK that the reduction in Fuel Pressure is related to the change in indicated altitude (difference in air pressure between traffic pattern altitude and 50,500 ft is about the amount (within 1 psi?) that the fuel pressure dropped. But they may be unrelated.
I looked at the static lines, and don't see a problem. We have cross-connected static ports on either side of baggage compartment, feeding a single ADAHRS unit in the top of the baggage compartment.
One thing I regret is that I didn't think to look at the backup analog instruments... but they are small and on far side of panel of the panel. I just reverted to training, and kept my head out of the cockpit and concentrated on flying safely to the ground. Anther thing I regret s that I got frustrated with the little Go Pro camera we tried to set up to monitor things - it has stopped reading the only SD card we have that is 32 GB....So I didn't have it running on this flight
.I'm uploading the data log. Any thoughts on what might have caused this, or potential troubleshooting steps would be GREATLY appreciated.
