Below is an explanation of the power losses we experienced and our thought process in solving it. I?m posting it here to accomplish the following objectives:
1. If the problem we?ve experienced is truly ?vapor lock?, then RV-12 owners and pilots need to be made aware of what conditions might trigger vapor lock and to consider operating the RV-12 as it was designed: Run the electric fuel pump at all times.
2. Solicit thoughts on how confident we can be that the problem we experienced is ?vapor lock? and if not, what might be the root cause of the loss of fuel pressure as the apparent cause of power loss.
Lost power and fuel pressure on (4) occasions with conditions noted:
1. 6/6/15, 9:20 a.m. began flight of approx. 2 hrs. without issue. Plane sat in sun for approx. 5 hrs. without canopy cover; note that 5 gals. of extra fuel in a jerry can was inside cabin;
6/6/15, 3:15 p.m. poured warm (> 100 deg. F) fuel from jerry can into fuel tank; 3:30 pm, 99 deg. F, 200? MSL airport elev., fuel press. during initial climb out approx. 4.1 psi., 18 mins. after eng. start and during climb out ? engine sputtered with power loss; during approx. time of power loss, Dynon data shows a relatively sharp (30 secs. ) drop in fuel press. from 3.75 to 1 psi during climb from 700? MSL to 1000? MSL and fuel press. remained abnormally low for the next 4 mins. of ?flight? back to airport with only approx. 30 secs. of normal press. (3.4 psi.) part way during that 4 min. time period and then it dropped somewhat again.
2. 6/7/15, 10:45 a.m., 92 deg. F, 200? MSL airport elev., fuel press. during initial climb out approx. 4.25 psi., 13 mins. after eng. start and during climb out, Dynon shows continual but gradual fuel press. decrease from 4.2 psi to 1 psi as altitude increased from 900? MSL to 4,300? MSL; then, an avg. fuel press. of 1.125 is maintained for approx. 2 mins. of continual climb to 5,100 MSL where engine sputtered with power loss, then, Dynon data showed continual, gradual (4 mins.) rise in fuel press. to approx. 5.4 psi and held an avg. of 5.4 psi during remainder (2.5 mins.) descent to airport.
3. 7/11/15, 8:30 a.m. began flight of 2 hrs. without issue. Plane sat in sun for approx. 5 hrs. without canopy cover; note that 5 gals. of extra fuel in a jerry can was inside cabin;
7/11/15, 2:00 p.m. poured warm (> 100 deg. F) fuel from jerry can into fuel tank; 2:30 pm, 98 deg. F, 200? MSL airport elev., fuel press. during initial climb ran 4.1 to 3.75 psi.; 18 mins. after eng. start and during climb out ? engine sputtered with power loss; during approx. time of power loss, Dynon data shows a sharp drop in fuel press. from 3.75 to 1 psi; during descent from 1800? MSL to 1480? MSL, fuel press. made a relatively sharp (40 secs.) increase from 1 psi to 4.5 psi. and remained normal (4.375 psi) for the next 4 mins. of ?flight? back to airport.
4. 7/25/15, ground testing with intent to replicate conditions (except altitude change) as in flights 1. & 3. above: 3:00 p.m., 97 deg. F, ran engine to normal oper. temp., shut down, and left plane to heat in sun with jerry can in cabin, no canopy cover;
7/25/15, 5:00 p.m., added warm (> 100 deg. F) fuel from jerry can into fuel tank; ran engine to oper. temp.; performed run-up check; ran at W.O.T. for a short period, then, 5,000 rpm for a few minutes, shut off electric fuel pump and within a minute or so, fuel flow went to zero and fuel press. went down to 1.2 psi. and shortly thereafter, engine sputtered; put electric fuel pump back on and conditions returned to normal.
We downloaded data from the Dynon for recent flights inclusive of the ones we experienced power loss. The first flight (1. above) with the significant power loss showed after approx. 13 mins. of flight time, a sharp drop in fuel pressure and loss to about zero of fuel rate. The third flight (3. above) with power loss showed less than 18 mins. of flight time, a sharp drop in fuel pressure and loss to about zero fuel rate. We know for sure that during the third flight we had shut off the electric fuel pump just prior (approx. 30 seconds) to loss of power. We probably shut off the electric fuel pump for the first and second power loss flights because that has been our normal procedure since we've been flying the RV-12 (about 3 yrs.). Both the first and third power loss flights had nearly exact conditions: 2 hr. flight, landed, shut down with about 10 gals. of fuel in the fuel tank, a 5 gal. plastic "jerry" can of fuel in the cabin, canopy closed and entire airplane exposed to full sun in 96 degree environment for at least 2 hours. Then, added the fuel from the 5 gal. jerry can to the fuel tank. Started engine, idled between 2000 and 2500 rpm until oil temp. reached 122 degrees. Then, runup at 4000 rpm with usual checks including ignition drop check. All normal. Take off, climb, shut off electric fuel pump (absolutely sure on third flight) and then onset of significant power loss. The differences on the second flight was that there was not an already warm engine, ambient temp. was 90 degrees or less because takeoff occurred mid to late morning, fuel pressure and flow loss as recorded was gradual over a long period of time 20 - 30 mins. and power loss was not as pronounced or as severe. Again, we are not absolutely sure about whether the electric fuel pump was turned off after takeoff for flights 1. & 2. above. But, the turning off of the electric fuel pump after takeoff had been our standard operating procedure.
See next post for continuation of this.
1. If the problem we?ve experienced is truly ?vapor lock?, then RV-12 owners and pilots need to be made aware of what conditions might trigger vapor lock and to consider operating the RV-12 as it was designed: Run the electric fuel pump at all times.
2. Solicit thoughts on how confident we can be that the problem we experienced is ?vapor lock? and if not, what might be the root cause of the loss of fuel pressure as the apparent cause of power loss.
Lost power and fuel pressure on (4) occasions with conditions noted:
1. 6/6/15, 9:20 a.m. began flight of approx. 2 hrs. without issue. Plane sat in sun for approx. 5 hrs. without canopy cover; note that 5 gals. of extra fuel in a jerry can was inside cabin;
6/6/15, 3:15 p.m. poured warm (> 100 deg. F) fuel from jerry can into fuel tank; 3:30 pm, 99 deg. F, 200? MSL airport elev., fuel press. during initial climb out approx. 4.1 psi., 18 mins. after eng. start and during climb out ? engine sputtered with power loss; during approx. time of power loss, Dynon data shows a relatively sharp (30 secs. ) drop in fuel press. from 3.75 to 1 psi during climb from 700? MSL to 1000? MSL and fuel press. remained abnormally low for the next 4 mins. of ?flight? back to airport with only approx. 30 secs. of normal press. (3.4 psi.) part way during that 4 min. time period and then it dropped somewhat again.
2. 6/7/15, 10:45 a.m., 92 deg. F, 200? MSL airport elev., fuel press. during initial climb out approx. 4.25 psi., 13 mins. after eng. start and during climb out, Dynon shows continual but gradual fuel press. decrease from 4.2 psi to 1 psi as altitude increased from 900? MSL to 4,300? MSL; then, an avg. fuel press. of 1.125 is maintained for approx. 2 mins. of continual climb to 5,100 MSL where engine sputtered with power loss, then, Dynon data showed continual, gradual (4 mins.) rise in fuel press. to approx. 5.4 psi and held an avg. of 5.4 psi during remainder (2.5 mins.) descent to airport.
3. 7/11/15, 8:30 a.m. began flight of 2 hrs. without issue. Plane sat in sun for approx. 5 hrs. without canopy cover; note that 5 gals. of extra fuel in a jerry can was inside cabin;
7/11/15, 2:00 p.m. poured warm (> 100 deg. F) fuel from jerry can into fuel tank; 2:30 pm, 98 deg. F, 200? MSL airport elev., fuel press. during initial climb ran 4.1 to 3.75 psi.; 18 mins. after eng. start and during climb out ? engine sputtered with power loss; during approx. time of power loss, Dynon data shows a sharp drop in fuel press. from 3.75 to 1 psi; during descent from 1800? MSL to 1480? MSL, fuel press. made a relatively sharp (40 secs.) increase from 1 psi to 4.5 psi. and remained normal (4.375 psi) for the next 4 mins. of ?flight? back to airport.
4. 7/25/15, ground testing with intent to replicate conditions (except altitude change) as in flights 1. & 3. above: 3:00 p.m., 97 deg. F, ran engine to normal oper. temp., shut down, and left plane to heat in sun with jerry can in cabin, no canopy cover;
7/25/15, 5:00 p.m., added warm (> 100 deg. F) fuel from jerry can into fuel tank; ran engine to oper. temp.; performed run-up check; ran at W.O.T. for a short period, then, 5,000 rpm for a few minutes, shut off electric fuel pump and within a minute or so, fuel flow went to zero and fuel press. went down to 1.2 psi. and shortly thereafter, engine sputtered; put electric fuel pump back on and conditions returned to normal.
We downloaded data from the Dynon for recent flights inclusive of the ones we experienced power loss. The first flight (1. above) with the significant power loss showed after approx. 13 mins. of flight time, a sharp drop in fuel pressure and loss to about zero of fuel rate. The third flight (3. above) with power loss showed less than 18 mins. of flight time, a sharp drop in fuel pressure and loss to about zero fuel rate. We know for sure that during the third flight we had shut off the electric fuel pump just prior (approx. 30 seconds) to loss of power. We probably shut off the electric fuel pump for the first and second power loss flights because that has been our normal procedure since we've been flying the RV-12 (about 3 yrs.). Both the first and third power loss flights had nearly exact conditions: 2 hr. flight, landed, shut down with about 10 gals. of fuel in the fuel tank, a 5 gal. plastic "jerry" can of fuel in the cabin, canopy closed and entire airplane exposed to full sun in 96 degree environment for at least 2 hours. Then, added the fuel from the 5 gal. jerry can to the fuel tank. Started engine, idled between 2000 and 2500 rpm until oil temp. reached 122 degrees. Then, runup at 4000 rpm with usual checks including ignition drop check. All normal. Take off, climb, shut off electric fuel pump (absolutely sure on third flight) and then onset of significant power loss. The differences on the second flight was that there was not an already warm engine, ambient temp. was 90 degrees or less because takeoff occurred mid to late morning, fuel pressure and flow loss as recorded was gradual over a long period of time 20 - 30 mins. and power loss was not as pronounced or as severe. Again, we are not absolutely sure about whether the electric fuel pump was turned off after takeoff for flights 1. & 2. above. But, the turning off of the electric fuel pump after takeoff had been our standard operating procedure.
See next post for continuation of this.