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  #1  
Old 08-13-2015, 10:06 PM
jrich jrich is offline
 
Join Date: Apr 2012
Location: Arnaudville, LA
Posts: 57
Default Loss of Power Experiences - Due to vapor lock?

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.
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  #2  
Old 08-13-2015, 10:07 PM
jrich jrich is offline
 
Join Date: Apr 2012
Location: Arnaudville, LA
Posts: 57
Default Loss of Power Experiences - Due to vapor lock? continued

A person might and should ask: Why or how in the heck would someone put themselves in the position of (2) in-flight power losses after the first in-flight power loss? Here’s how this came about:

The first power loss, occurred two hours after replacing the “bad batch” of carb. floats per the recent Rotax S.B. Immediately after the power loss event, we took the top cowl off and looked for something obvious and found nothing wrong. Since the carbs and floats were the last thing we touched, we dropped the float bowls, inspected for trash, water, etc. in the bowls, properly floating floats, and any abnormality and found none. We re-mounted the bowls, started the engine and found fuel dripping out of the air cleaner on the right carb. and jumped to the conclusion that the needle valve in the right carb. was not shutting off fuel into the bowl. So, we dropped the right carb. float bowl again, turned on the electric fuel pump to “clear” any trash. But, we didn’t think to catch the fuel in this clearing process. We actuated the needle by hand to check that the fuel would shut off and it did. So, we re-mounted the bowl, started the engine and ran it with no leak and no indication of a problem. Thus, we thought the problem was solved and decided that since it was getting late, we’d fly out the next morning. The next morning is when flight 2. above resulted in power loss after we had cautiously circled the airport up to 5000’ and when we were just leaving the area to head for home. So, we landed safely, left the plane, got a car ride home, and retrieved the plane with our trailer the next day and trailered it home. We got some advice on the situation (many thanks to Roger Lee for all his assistance). First, we thoroughly check for debris in the fuel system. So, we did that and started with the right carb., cleaning it with carb cleaner and then air pressure. We noted significant wear on the bottom end of the needle valve. There was so much wear that the retaining clip was going to be lost. Also, the mating face of the float arm bracket tab had a .006” wear depression. The arms of the float arm bracket were obviously not parallel with the carb base as required by the Rotax manual. At this point we found no trash in the carb. fuel line going to the carbs. and the right carb. had no trash. So, we’re thinking that all this wear could be the cause of why we found fuel coming out of the right carb air cleaner. We put a new needle valve and float arm in the right carb. and got the float arms very nearly exactly parallel to the carb. base. Re-assembled the carb., remounted it, turned on the electric fuel pump to check for leaks and there was no leak from the right carb. But, there was fuel dripping out of the overflow tube on the left carb. We were going to clean and inspect the parts on the left carb. anyway, so we did the same for the left carb. and found exactly the same conditions for it as for the right carb.: No trash, but a lot of wear on both the bottom of the needle valve and mating tab of the float arm bracket, and the arms of the bracket were not parallel with the carb. base. Reassembled and remounted the left carb. Turned on the electric fuel pump and no leaks anywhere. Ground ran the plane without a problem and then flew the airplane for 30 mins. circling our home base airport. So, we were thinking that our problem was due to flooding the carbs. As it turned out, this was not the problem. Take advice: If in doubt, check the Dynon data to confirm your theory. However, since we had not checked the Dynon data and had jumped to yet another false conclusion, we flew flight 3. above which is a virtual repeat of flight 1. Got a ride home, and trailered the plane back home once again. After three times, we thought we’d duplicate conditions as best we could, but with staying on the ground. We were able to get the loss of fuel pressure in 4. above when we shut the electric fuel pump off.
Since 4. above, we’ve check/tightened every fuel connection up to the mechanical fuel pump, put an air gap using zip ties between fuel lines and warm/hot coolant hoses and oil lines and wrapped each exhaust pipe with heat wrap from each cylinder head to the muffler. We’ll keep any extra fuel in the shade and try and keep the cabin ventilated or cover it. Most importantly, the plan is to always have the electric fuel pump on and in the future either eliminate the fuel pump switch or place a safety cover on it. Also, we’ll consider adding a second electric fuel pump as a back up.

So, back to my original question:

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?

Has anyone else experienced similar problems? Also, has anyone installed a backup (second) electric fuel pump for their RV-12?
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  #3  
Old 08-13-2015, 10:19 PM
jrich jrich is offline
 
Join Date: Apr 2012
Location: Arnaudville, LA
Posts: 57
Default Loss of Power Experiences - Due to vapor lock? cont.

FYI

RV-12 completed 2010 and had approx. 350 hours at the beginning of these issues.
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  #4  
Old 08-13-2015, 10:57 PM
RFSchaller RFSchaller is offline
 
Join Date: Oct 2010
Location: Phoenix, AZ
Posts: 2,000
Default

I have a switch on my fuel pump, and I turn it off after takeoff and turn it on for landing. Today I took off at 1270 lbs with two people onboard to give a prospective RV-12 pilot a demo. It was 112F and DA 4850 Ft. As we climbed out we started getting CHT and Oil Temp alarms that did not clear (eventually reached 255F oil and 275F CHT). We decided to make a precautionary landing and the engine faltered. Turning the electric pump on we did not experience another falter before landing. I suspect it was vapor lock. I run premium autogas. BTW after a 30 min cool down I flew back to my home field 10 miles away alone and temps were high but below the alarms. I did receive a "Teperature Above Specification" message on my D-180.

I checked the ROTAX Manual, and it appears no maximums were exceeded, but from now on I will place a personal limit of 105F OAT and single occupant only limit on my 12.
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  #5  
Old 08-13-2015, 11:02 PM
sailvi767 sailvi767 is online now
 
Join Date: Sep 2010
Location: Charlotte NC
Posts: 765
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I am assuming you are using auto gas. The problem could be a different formulation in the fuel. Auto gas is like a box of chocolates, you never know what you are going to get!
G
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  #6  
Old 08-14-2015, 06:06 AM
BigJohn BigJohn is offline
 
Join Date: Nov 2008
Location: Gloversville, NY
Posts: 1,422
Default

Also assuming you are using car gas. Seems to me it would be an interesting experiment to try and duplicate the conditions using 100LL.

BTW, you guys who fly in those climates must wear asbestos underwear! I can't even imagine getting in an airplane under those conditions! I guess us northern boys are just wimps!
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RV-12 N37JP 120176 Flying since 2012.
VAF paid through 10/2017. Best bargain in town.

Last edited by BigJohn : 08-14-2015 at 06:09 AM.
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  #7  
Old 08-14-2015, 06:51 AM
Jim T Jim T is offline
 
Join Date: Jan 2005
Location: Independence, OR
Posts: 159
Default

Rich,
When you mention running auto gas are you referring to premium auto gas containing ethanol or non-ethanol super unleaded?

John R,
Would you also elaborate on exactly what fuel you're using?

Thanks, Jim
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  #8  
Old 08-14-2015, 07:05 AM
rgmwa rgmwa is offline
 
Join Date: Feb 2010
Location: Perth, Western Australia
Posts: 1,508
Default

We have those kinds of temperatures in summer too, so I'm very interested in these reports. I installed a switch, but primarily for ground operation so I can isolate the electric fuel pump easily instead of pulling a fuse. However these reports suggest that it's a good idea to leave the pump running continuously as Vans intended, at least in hot conditions and when using mogas, which is a variable product due to winter and summer fuel blends, age of fuel, additives and possible questionable quality control.
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  #9  
Old 08-14-2015, 09:00 AM
rvbuilder2002 rvbuilder2002 is offline
 
Join Date: Jul 2005
Location: Hubbard Oregon
Posts: 6,513
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As already mentioned, auto fuel can be highly variable. One of those variables is the Reid vapor pressure (RVP). This can have a big influence on how easily an aircraft can experience vapor lock issues. A common problem is that refiners vary the formulation depending on the time of year. If you end up with some winter blended fuel in hotter summer temps (not at all uncommon) it can cause a lot of problems. A different RVP is used in the winter to improve vaporization in cold temps to improve cold starting performance, etc. If conditions are extreme, it might not matter what season blend you are using. Another factor can be who the fuel is purchased from. I would recommend that RV-12 owners only purchase fuel from top tier retailers (Chevron, Shell, Texaco, etc) and only ones with a high sales volume. One problem with us using premium fuel is that it is not a high volume seller at most retailers (most people only buy regular grade unless their vehicle specifically requires something else)

The actual vaporization of the fuel is effected by atmospheric pressure and temp. When an aircraft climbs, it is artificially lowering the atmospheric pressure. When any type of pump is pulling fuel through a fuel system, the inherent resistance to flow within that system will also have an influence on lowering the pressure up stream of the pump.

Because the RV-12 was designed expecting auto fuel to be used extensively, the described situation is one of the primary reasons the fuel system was designed with the aux. electric pump as close to the fuel tank outlet as possible, and configured so that it would be operating at all times.

This assures that at least one fuel pump will be operating in the coolest fuel present in the system, and the majority of the system is operating at a positive pressure.

So, based on the info you have provided I would say that all of the data points to vapor lock of some degree.
Chances are, that if at any point in the process you had drained the fuel and put in 100LL, the problem would have been gone.

Side note regarding the wear you discovered in your carb's at 350 hrs.....
This is why there is a prescribed carb inspection to be done every 200 hrs. You didn't mention it ever having been done. You are almost due for a second one.
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  #10  
Old 08-14-2015, 10:32 AM
jrich jrich is offline
 
Join Date: Apr 2012
Location: Arnaudville, LA
Posts: 57
Default fuel used

For the conditions we experienced, we were using Walmart's 93 octane with 10% ethanol. We pretty much have always used Walmart or Ractrac 93 octane fuel.

Thank you, Scott, for your input. We agree with all that you wrote. However, we are somewhat wary because others are telling us that it can't just be explained as vapor lock.
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