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  #21  
Old 08-15-2015, 09:02 PM
jrich jrich is offline
 
Join Date: Apr 2012
Location: Arnaudville, LA
Posts: 57
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Quote:
Originally Posted by RFSchaller View Post
John,

You seem to have extensively tested autogas. What are your thoughts on the variability of results?

Rich
If you are asking what I noted about the vapor pressure when I tested every load of 87 octane:

Every load that I sampled was a pass or safe load. I did not log the vapor pressure numerical results. But, I'd say that most times the readings were right around 8 psi. vacuum which is in the green color "safe region" range of 5.5 to 12.8 psi vac. on the gauge. The 8 psi. reading is, of course, in the pass or "safe region" range. And, this is all I was looking for. Keep in mind that this was for non-ethanol fuel for my Cherokee 235. I also tested a sampling of fuel before I purchase a load of fuel for the presence of ethanol. And, we never found a trace of ethanol in every advertised non-ethanol load we purchased. The issue about ethanol for the Cherokee was that its carb. was susceptible to icing if there was water in the fuel. We never experienced this problem ourselves. In fact, in the 8 yrs. that we had that plane, the engine never missed a beat. Now, back to the ethanol and water connection: Water will not readily mix with pure gasoline. However, water is readily is mixed with ethanol and if water gets in fuel containing ethanol, the ethanol absorbs the water and the water can then be in solution with gasoline and go undetected. That is unless you do the water volume test that I previously mentioned.

Regarding freshness of fuel: In the past two days, I asked RaceTrac and Raceway fuel stations how often the get deliveries of 93 octane, 10% ethanol (what I use in my RV-12 and sometimes from these stations but usually from Walmart). Each of them said that they get deliveries every 2 days. That's pretty fresh. Just FYI: They get a load of 87 octane, 10% ethanol at least every day. A while back, I asked a local tanker re-fueler how often a particular Walmart station got a load of 87 octane, 10% ethanol. He told me at least once a day and often times, twice a day.
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  #22  
Old 08-15-2015, 10:22 PM
RFSchaller RFSchaller is offline
 
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Location: Phoenix, AZ
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Thanks for the detail, John!
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  #23  
Old 08-16-2015, 10:48 AM
Jetguy's Avatar
Jetguy Jetguy is offline
 
Join Date: Aug 2008
Location: Texas, Fort Worth
Posts: 1,190
Default Thinking out of the box when operating inflight in high OAT temp conditions

If operating in severe heat then maybe we could come up with a hot weather checklist if you incur loss of power problems.
Leave electric fuel pump on at all times.
Consider maintaining the carbs within the suggested maintenance schedule.
After shut down leave your oil door open to help evacuate ambient heat.
Try flooding the engine at 3/4 throttle with the choke after landing to increase fuel flow through the system.
Consider a canopy cover with you canopy cracked in the open position when parked for long period of time in high heat.
Land and add 5 or 10 gallons of 100LL to see if this eliminates the problem.
Store your extra fuel out of direct sun light in sealed containers.
Consider leaving your Master Switch on and Aux fuel pump running between flights when participating in Young Eagle Intro Flights when only shut down for 5 or 10 mins.

Others feel free to add to this list!

These suggestions in no way are posted here to reflect negatively toward the author of this thread but are compiled from previously posted suggestions and some added from my own observations for future pilots that may have this problem. And there is a some history on the forum of this problem occurring.
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  #24  
Old 08-16-2015, 05:11 PM
jrich jrich is offline
 
Join Date: Apr 2012
Location: Arnaudville, LA
Posts: 57
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Quote:
Originally Posted by Jetguy View Post
If operating in severe heat then maybe we could come up with a hot weather checklist if you incur loss of power problems.
1. Leave electric fuel pump on at all times.
2. Consider maintaining the carbs within the suggested maintenance schedule.
3. After shut down leave your oil door open to help evacuate ambient heat.
4. Try flooding the engine at 3/4 throttle with the choke after landing to increase fuel flow through the system.
5. Consider a canopy cover with you canopy cracked in the open position when parked for long period of time in high heat.
6. Land and add 5 or 10 gallons of 100LL to see if this eliminates the problem.
7. Store your extra fuel out of direct sun light in sealed containers.
8. Consider leaving your Master Switch on and Aux fuel pump running between flights when participating in Young Eagle Intro Flights when only shut down for 5 or 10 mins.

Others feel free to add to this list!

These suggestions in no way are posted here to reflect negatively toward the author of this thread but are compiled from previously posted suggestions and some added from my own observations for future pilots that may have this problem. And there is a some history on the forum of this problem occurring.
Thanks for your input. Great suggestions except I'm not sure about 4. & 8. above. As I indicated in a previous post, I made sure there was an air gap between fuel hoses and other hotter hoses. I wrapped my exhaust pipes with heat wrap to minimize the heat gain to the engine compartment.
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  #25  
Old 08-16-2015, 05:58 PM
jrich jrich is offline
 
Join Date: Apr 2012
Location: Arnaudville, LA
Posts: 57
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More details on fuel vapor pressure:

I tested some 93 octane, 10% ethanol gas from Walmart today at various temperatures and came up with an average Reid Vapor Pressure of 8.4 psi. for this fuel that I tested. Therefore, according to the chart that I have, when the fuel I tested reaches 98 degrees, this fuel is more volatile than avgas for the FAR part 23.961 hot fuel certification test. What exactly that means, I'm not sure. It is interesting that the chart that I have does not extend beyond approx. 105 degrees.

For reference purposes for FAA certificated aircraft:

FAR part 23.961:

"§23.961 Fuel system hot weather operation.

Each fuel system must be free from vapor lock when using fuel at its critical temperature, with respect to vapor formation, when operating the airplane in all critical operating and environmental conditions for which approval is requested. For turbine fuel, the initial temperature must be 110 °F, −0°, +5 °F or the maximum outside air temperature for which approval is requested, whichever is more critical.

[Doc. No. 26344, 58 FR 18972, Apr. 9, 1993; 58 FR 27060, May 6, 1993]
"

Also for reference purposes for FAA certificated aircraft:

From AC No: 23.1521-2:

"(3) A hot weather operation test (§ 23.961) should be
conducted. The airplane should be tested with the fuel to the
maximum altitude for which approval is requested (see paragraph 7t
and u)."


I did no further research beyond this point. Since the RV-12 is not a certificated aircraft, it does not have to comply with any of these requirements. But, I would like to know if a similar test was performed on the RV-12 and how high a fuel temp. and altitude it was tested to.
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  #26  
Old 08-16-2015, 07:06 PM
rvbuilder2002 rvbuilder2002 is offline
 
Join Date: Jul 2005
Location: Hubbard Oregon
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Quote:
Originally Posted by jrich View Post
But, I would like to know if a similar test was performed on the RV-12 and how high a fuel temp. and altitude it was tested to.
If by similar you mean a test that followed all of the guidance of AC No: 23.1521-2, the answer would be no.

Though there has been a lot of testing and a huge amount of operational experience gained while operating RV-12's with premium auto fuel. The factory prototype/demonstrator has been operated almost exclusively on premium auto fuel (currently at 1500 + hours) with never any vapor lock type symptoms. Before you assume that here in the Pacific North West it never gets hot, we have recently had temps of 102-103 F and the forecast is for more this next week.

But, none of this means anything when relating the info to an RV-12 that is not configured nor operated in a way the matches the certified design configuration. Yes, it is certified. Not as in type certificated....but as an S-LSA. It is certified under an FAA adopted Consensus Standard of ASTM standards. The plans supplied with the kit match the certified S-LSA version because it is technically the factory build manual, and is what allows kit builders to certify as an E-LSA (home assembled clone copy of the S-LSA)

So, if an owner has modified (such as not operating the electric fuel pump full time) their RV-12 (this would only be possible with an E-LSA or E-AB aircraft) they have crossed over into the experimental portion of their certification. In this situation, the testing burden is now technically on the person that did the modification.
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RV-6A (aka "Junkyard Special ")
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  #27  
Old 08-17-2015, 03:13 PM
Mauritz Mauritz is offline
 
Join Date: Sep 2010
Location: South Africa
Posts: 11
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Hi on the 01-05-2015 I have placed a thread “Losing power during extreme heat conditions” http://www.vansairforce.com/communit...1326&highlight

I thought that I have solved the problems through many trail and tests and had experts in to try and solve the problem, to no avail. I had a close shave with fate when I lost total power after a takeoff. I promised myself not to put me and my family through such a horrible experience again.

Then I came across the following explanation: with extreme heat conditions the fuel density decrease resulting in your floats not to float anymore and causes your carburetors to flood. That is why if you are fast enough and you come back on the power the engine will start running normal again all be it not at full power.

With the above explanation it was recommended that I change over to avgas.

Since I have changed to avgas I did not have any incidents again.
I fly from very high altitudes at extreme heat conditions and it is my believe that autogas or mogas is very susceptible to heat and altitude and will not give the performance we require from it at these conditions.
I am now a happy avgas flier.
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  #28  
Old 03-27-2017, 03:56 PM
jrich jrich is offline
 
Join Date: Apr 2012
Location: Arnaudville, LA
Posts: 57
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More about using mogas:

The gasoline providers are allowed by the EPA to dispense "winter blend" gasolines generally from October through April. Winter blend gasolines have a higher [u]R[u]eid Vapor Pressure (RVP) than "summer blend" gasolines. The concern for us, especially RV-12 fliers, is that the winter blend is more volitale than the summer blend. That means that the winter blend gasoline will vaporize or flash to a vapor more easily than a summer blend. As the temperature increases in warmer weather, the winter blend is more likely to vaporize than the summer blend. I mention this because if you have winter blend gas in your tank and you use it in summer you are more susceptible to "vapor lock" (vapor instead of liquid in fuel lines and carb. bowls) and thus loss of power. This becomes even more likely at higher altitude. The higher altitude means less atmospheric pressure on the top surface of the fuel in the fuel tank and thus less pressure in the fuel system, which makes it easier for the suction side of the mechanical fuel pump to vaporize the fuel.

There is a table published by the EPA that shows the maximum allowable RVP during the warmer months generally (there are exceptions) the period from May 1 through Sept. 15 by state and in many cases further broken down by county. This table is online at: https://www.epa.gov/gasoline-standar...vapor-pressure

Be cautious and consider the following conditions in what I consider the order of importance for creating vapor lock:

1. Electric fuel pump not running. This pump should always be on and the fuel pressure checked prior to each engine start up so that you know that it is working and that the pressure looks about right (approx. 2 psi).
2. Hot fuel in the fuel tank &/or hot fuel lines in a hot cabin due to high temp. ambient conditions &/or the sun baking the cabin interior, etc.
3. Hot engine compartment due to heat soaking after flight &/or high temp. ambient conditions. This can be reduced after shutdown and before next fight by opening the oil/coolant inspection door on top of the cowling to allow cooler air from below to be drawn upward around the engine by the warmer engine compartment air convecting and rising out of the open cowl door.
4. High altitude &/or high density altitude due to high temp.
5. Low fuel level in fuel tank. This will affect the pressure at the suction side of the mechanical fuel pump. The lower the level in the fuel tank the less pressure on the suction side of the mech. fuel pump.
6. Steep climbs will cause the fuel level and thus the pressure at the fuel tank outlet to be reduced slightly with the nose up pitch of the airplane and thus also the fuel tank. Remember, you never want to take off with less than 4 gals. of fuel because a high nose attitude may cause the fuel outlet to become un-ported (no fuel draining into the fuel suction side connection on the front of the fuel tank because it is higher than the fuel level).
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  #29  
Old 03-29-2017, 07:06 AM
AJSWA AJSWA is offline
 
Join Date: Sep 2011
Location: Paraburdoo Western Australia
Posts: 40
Default Partial loss of power - higher ambient temps.

In this discussion in some cases i suggest what is being missed /overlooked is the fuel is boiling as it enters the fuel bowl. The fuel stays in a liquid state whilst in the fuel lines due to the raised boiling point which is a result of the pressure increase from the fuel pumps. (the same principle as the engine cooling system uses a pressure cap to raise the boiling point of the engine coolant to keep it in a liquid state) when the under under cowl temps are high and low fuel volatility conditions occur the engine runs rich, not lean and looses power. This is due the rapid expansion of the fuel entering the fuel bowl and some of the fuel boiling / vaporising. The air pressure (normally atmospheric pressure) inside the fuel bowl increases, as the small bowl vent cannot equalise the fuel bowl pressure to the atmospheric pressure outside of the fuel bowl quickly enough. This additional pressure inside the fuel bowl forces additional fuel through the main jet enriching the air fuel mixture usually causing (in my experience), a fuel smell quickly followed by partial loss of power. Fuel pumps on or off makes no difference to this situation occurring if the fuel volatility is low and the fuel bowl temperatures are quite high.
In my case i found turning the electric fuel pump off and on as the engine response changed and lowering the nose then slowly reducing the power i was able to increase airspeed/ airflow cooling to the engine compartment and stabilise the engine operation to get myself better options in case the situation worsened or the engine stopped. It was an extremely uncomfortable few seconds (Felt like minutes) when it happened!

Scott's comments about "changing to 100LL and the problem would have most likely disappeared" in my case and experience was 100% correct. I drained all the ULP and added 100LL Avgas and fuel pressure fluctuations and partial power loss all immediately disappeared, even at ambient temps at 40DegC plus. I also trialed with the electric pump off (after reaching a safe height) in climb power attitude and settings with no power loss issues or fuel pressure fluctuations.
My limiting factor now is coolant and oil temps when operating in high ambient temps.

The fix, In my case,

With the fuel quality we had available last summer (We only have one fuel station in town) was to either run a minimum of 30% Avgas with the unleaded fuel if ambient temperature is likely to be above 35 degC or stop start operation was to occur, i.e. taking friends for a ride with short engine shut downs between flights. This year the fuel quality has been much better, I've still been adding Avgas prior to purchasing a Ray Hodges (Pederson Aviation) voltility tester to check fuel vapour point is safe, as well as minimal flying due to other commitments.
Why not 100% Avgas? Reason - Fuel cost and lack of availability.
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RV 120573
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  #30  
Old 03-30-2017, 02:47 PM
WingedFrog's Avatar
WingedFrog WingedFrog is offline
 
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This thread has brought to our attention a number of important issues regarding this dreaded loss of power on takeoff and in flight due to vapor lock. A big thanks to all contributors!

An aspect of this issue that is specific to the RV-12 is the possibility to unknowingly takeoff with fuel at elevated temperature due to the greenhouse effect created by a closed canopy while the airplane is parked for several hours in the sun. One may think that opening the canopy for a few minutes before takeoff will solve the problem, not realizing that it would take a much longer time to cool down 10 or 15 gallons inside the fuel tank. Someone earlier in this thread mentioned the importance of covering the canopy in this situation and I could not agree more. One year ago it happened to me during a quite moderate temperature (70 F) but sunny Spring day. I mistakenly attributed the loss of fuel pressure on takeoff to the mechanical fuel pump, I now know better! I have to admit that I had two aggravating factors: I was using a 91 Octane Mogas of dubious origin and I did not have the electric fuel pump on. I was lucky enough to get the "low fuel pressure" alarm just before rotation.

I will never ever again:
- Park in the sun without my canopy cover and the canopy crack open
- Switch the fuel pump off from engine start to shut down
- Use Mogas from a non brand station
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