This is a really good video and I think it's going to save a lot of people headache and heartache, if not lives. Something I think needs mentioning is that vapor lock is *impossible* inside of the pressurized fuel system, and this can be proven mathematically. A fuel injection system runs at 50 PSI, the RVP of even the worst fuels is only 15 PSI. Even pure butane with a boiling point of 32 F, has its boiling point rise to 123 F when you subject it to 50 PSI (+ 14.7 PSI atmospheric). What about altitude? Even if you somehow flew to 30,000 ft and atmospheric pressure was down to 4 PSI, pure butane under 50 + 4 PSI still needs to be 111 F to boil. The entire problem is the stretch of hose between the tank and the fuel pump (and technically speaking, the low pressure side of the fuel pump itself). In that stretch of hose, the pressure is slightly less than ambient (because it's being sucked on by the fuel pump), At 10,500 ft altitude your air pressure is only about 10 PSI, which is below the 15 PSI vapor pressure of winter mogas - so if that gas is 100 F, it's going to boil. When designing a fuel system, the goals are to make that line as short as possible, and as cold as possible. Auto-makers had vapor lock until they went to fuel injection and their engineers started relocating the fuel pump inside of the fuel tank. This shortens the suction line to a couple inches also uses the fuel in the tank as a means to keep it cool (heat coming from the fuel pump motor is a major risk here). Submersible pumps may not be realistic in existing wing tank designs, but I do think engineers and experimental builders should be looking at ways to shorten and cool the before-pump fuel system. But there is one thing that I think everyone running mogas should have, and that's a flow meter. A healthy fuel injection system is flowing a LOT of fuel and returning almost all of it back to the tank via the fuel pressure regulator. Even if the system is severely compromised, you won't know from the pressure because the regulator will hold shut until it gets to 50 PSI. Pressure will only drop when the situation becomes so dire that it can't keep up with the needs of the engine, and at this point it goes off a cliff. When you heard the pumps laboring, it's almost certain that they were not producing the normal fuel flow because of the cavitation. If you had had a flow meter, you probably would have aborted the mission before even taking off. P.S. Based on what you have presented, I would never fly mogas in anything carbureted.
This is an exceptional video on Mogas/Avgas... I'm building a plane with a 915 in it and was going to use exclusively Mogas to help with costs/oil changes... That plan has gotten a lot less rigid now. I'm also sharing it with our flying organization in Colorado.
Thank you Ron for building such an informative presentation. It is really well thought out and backed by solid data. Thank you also for taking the time to swing by EAA 105 to deliver this in person, and for adding the awesome video with Rian Johnson. It is all very much appreciated and I look forward to catching up with you at 7S5, or back at KOSH when you hopefully give this presentation again.
Thanks for the compliment Chad! Rian and I are thinking about presenting this at Airventure this summer. Email me (ronsingh75@gmail.com) for my other contact info if you fly in to 7S5 - it would be fun to catch up.
You are welcome! We have been flying our RV-12iS for almost 2 years now and truly enjoy it. Tomorrow makes the one year anniversary of our near-engine-out experience, and we plan to make that same flight again... this time with a lot more knowledge of fuel.
Would be nice if this hour and a half long video was prefaced with a note saying, "Only applicable to frozen hellholes", rather than waiting a hour for Rian to tell us it doesn't happen in Brazil.
Hi Ron. That was an excellent presentation. Technical, but presented in an easy to understand format. I fly 2 RV12iS airplanes and would love to see more videos on flying the RV12iS if you have the opportunity. Also loved the presentation from Rian and how they test fly over the Alvord desert. We are currently running our 2 RV's on 100LL and before that on 91UL this is both winter and summer mostly below 6000ft AMSL. As they are used for training the oil is changed every 25hrs.
Thanks for the compliment! The videos that I produce are just for fun, but this was to share some serious information. If I do other presentations relating to the RV-12iS, I'll post it to CZcams again. I don't monetize my videos.
General aviation needs to have alternatives to leaded fuel. The production, transportation, sale and use of leaded fuel needs to be totally banned NOW!
I noticed that too, but (while editing) neglected to place some text on the screen to correct that. What he meant to say was "if you're running AVGAS you're fine, but if you're running MOGAS, you have to do this test".
Thanks Ron and Rian for this very well researched and presented info, and sharing your experience. The info is particularly timely for myself, as I'll be flying an RV12 in that area over and around the mountains soon. This is clearly a significant safety contribution for many people, beyond just RV12 operators. I look forward to learning more as this testing plays out further. Does the requirement of retailers to only sell summer blend apply to FBOs as well as retail auto gas stations? I've heard that the sales of many FBOs has fuel in their tanks for several months in some cases.
The Environmental Protection Agency requires "all regulated parties including retailers and wholesale purchaser-consumers" to comply with the RVP standards. I have not seen an exemption for FBOs or anything relating to aviation. I believe that anyone selling mogas (especially an FBO) would need to track their usage in the winter months and somehow use up as much of their high RVP fuel before early May. I hope that FBOs do not stock up with cheaper winter fuel before the May 1st deadline. I say May 1st because the fuel terminals are required to only sell summer blend (low RVP) fuel after that date... in other words, an FBO ordering fuel after May 1st will get summer blend, Thanks for your comments - fly safe!
Can anyone explain the warning at 1:19:25 a bit more about the risks of vapour lock when switching between one tank with mogas and another with UL91 (or similar)? I’ve been doing this when uncertain for a while, keeping the UL91 for low level, landing and take off only, but am keen to understand why I shouldn’t!
Daniel the warning was to move the mixture to full rich when switching tanks. This warning was given in the AC. The warning is saying that you want to maximize the fuel flow to the engine if switching from 100LL for example to MOGAS. Flying on 100LL you would be able to lean the engine much further. If you switched to the MOGAS which needs to be richer then the engine may quit. What you are really asking is why is this the case. The answer is the MOGAS may be partially vaporized. If you install a translucent tube just before the fuel pump you would see fuel and every so often a bubble of vapor passing through the lines. The pump compresses this vapor back into a liquid but since vapor is less dense, overall past the pump there is less flow rate (See the NOTE below). As altitude increases the atmospheric pressure on top of the fuel in the tank pushing the fuel to the tank decreases and the vaporization of the fuel increases. More vapor results in less fuel flow until you reach a point that there is insufficient fuel flow to keep the engine running. This results in power loss and eventually power failure. MOGAS therefore will require a richer mixture to keep the engine running (if you have a mixture, Rotax does not, Lycoming does). NOTE: On Lycoming or Rotax carbureted engines that only pressurize to a few PSI or even in the case of Lycoming fuel injected models that may pressurize to 1 to 1.5 atmospheres (bar) the pump may not turn all the vapor back into a liquid. Rotax fuel injected engines pressurize to 3 bar (atmospheres ... most cars use 3 bar) and therefore have better resistance to vapor lock. Fuel injected engines use much higher pressure pumps and therefore are better at turning the vapor into liquid. This is why fuel injected engines are much less prone to vapor lock.
Really enjoyed this. I have a Cherokee 140 with a mogas STC and I use mogas whenever I can. This was incredibly informative. I learned a ton about gas that I didn't know. The good news for me is that my gas never stays in the airplane long enough to end up with winter blend in the summer. In reviewing some of the other information on vapor lock, it seems like it's a much bigger problem in fuel injected engines than carbureted engines. Did you find anything confirming or refuting that?
I don't think it would be reasonable to make a blanket statement that vapor lock is more prevalent in a fuel injected engine Vs a carbureted engine (or visa versa). I believe that its also very dependent on the design of the fuel system and other features of a particular aircraft. As an example, in the case of a Van's RV-12, Rian Johnson has stated that the carbureted version is much more susceptible to vapor lock then the fuel injected one. This may be due to the location of the oil tank (that retains a lot of heat after shutdown) being close to the right side carburetor. RV-12 owners can expect to see more stringent limitations for the carbureted version expected in the upcoming POH and other documents. In the case of a typical installation of a Rotax 912 carbureted engine, there is no circulation of fuel (fuel return) beyond the fuel mixing block. This leaves the fuel static in the line leading from the mixing block to each carburetor. If you have a heat soaked engine and you take vapor lock preventative measures by running the fuel pump prior to engine start, that section of fuel line doesn't get flushed which makes that area susceptible to vapor lock. In my opinion, the vapor lock I experienced was occurring nowhere near the hot engine compartment, which is where most people believe it occurs. My vapor lock (better described as "cavitation") occurred at the dual fuel pump location in the tailcone area. This was caused by the low pressure of the pumps sucking fuel from the tank at . I say all this because at this point in the fuel system, it wouldn't matter what type of engine (injected or carbureted) was installed firewall forward. I'm glad you enjoyed and got something out of the video. Thanks for your comments!
I just noticed that one of the sentences in my response was messed up by CZcams. Every word that I had underlined got removed. It should say: "This was caused by the low pressure of the pumps sucking hot volatile fuel from the tank at low atmospheric pressure."
@@1dullgeek No, I'm actually still comfortable flying with Mogas. I just assume that I have the worst case fuel and behave accordingly. In cool conditions (OAT, fuel temp, non heat soaked engine) I use 100% mogas. In warm/hot conditions when I expect to fly above 6,000 ft, I fly with a mixture of mogas and avgas. Several people after my presentation told me that they will just switch to avgas and do the added maintenance... which is reasonable.
This is a really good video and I think it's going to save a lot of people headache and heartache, if not lives. Something I think needs mentioning is that vapor lock is *impossible* inside of the pressurized fuel system, and this can be proven mathematically.
A fuel injection system runs at 50 PSI, the RVP of even the worst fuels is only 15 PSI.
Even pure butane with a boiling point of 32 F, has its boiling point rise to 123 F when you subject it to 50 PSI (+ 14.7 PSI atmospheric). What about altitude? Even if you somehow flew to 30,000 ft and atmospheric pressure was down to 4 PSI, pure butane under 50 + 4 PSI still needs to be 111 F to boil.
The entire problem is the stretch of hose between the tank and the fuel pump (and technically speaking, the low pressure side of the fuel pump itself). In that stretch of hose, the pressure is slightly less than ambient (because it's being sucked on by the fuel pump), At 10,500 ft altitude your air pressure is only about 10 PSI, which is below the 15 PSI vapor pressure of winter mogas - so if that gas is 100 F, it's going to boil.
When designing a fuel system, the goals are to make that line as short as possible, and as cold as possible. Auto-makers had vapor lock until they went to fuel injection and their engineers started relocating the fuel pump inside of the fuel tank. This shortens the suction line to a couple inches also uses the fuel in the tank as a means to keep it cool (heat coming from the fuel pump motor is a major risk here).
Submersible pumps may not be realistic in existing wing tank designs, but I do think engineers and experimental builders should be looking at ways to shorten and cool the before-pump fuel system.
But there is one thing that I think everyone running mogas should have, and that's a flow meter. A healthy fuel injection system is flowing a LOT of fuel and returning almost all of it back to the tank via the fuel pressure regulator. Even if the system is severely compromised, you won't know from the pressure because the regulator will hold shut until it gets to 50 PSI. Pressure will only drop when the situation becomes so dire that it can't keep up with the needs of the engine, and at this point it goes off a cliff.
When you heard the pumps laboring, it's almost certain that they were not producing the normal fuel flow because of the cavitation. If you had had a flow meter, you probably would have aborted the mission before even taking off.
P.S. Based on what you have presented, I would never fly mogas in anything carbureted.
Very thoughtful of you. Thanks Ron for sharing your knowledge and talking about your own incidents. Amazing presentation.
I'm glad it was helpful. Fly safe!
This is an exceptional video on Mogas/Avgas... I'm building a plane with a 915 in it and was going to use exclusively Mogas to help with costs/oil changes... That plan has gotten a lot less rigid now. I'm also sharing it with our flying organization in Colorado.
I'm glad you got some value from the video... experimental aviation is all about learning and sharing! Good luck on your build.
Thank you Ron for building such an informative presentation. It is really well thought out and backed by solid data. Thank you also for taking the time to swing by EAA 105 to deliver this in person, and for adding the awesome video with Rian Johnson. It is all very much appreciated and I look forward to catching up with you at 7S5, or back at KOSH when you hopefully give this presentation again.
Thanks for the compliment Chad! Rian and I are thinking about presenting this at Airventure this summer. Email me (ronsingh75@gmail.com) for my other contact info if you fly in to 7S5 - it would be fun to catch up.
Thank you Ron - well done and should be seen by anyone who flies with Mogas. I am a new RV12is owner and very thankful for the information.
You are welcome! We have been flying our RV-12iS for almost 2 years now and truly enjoy it. Tomorrow makes the one year anniversary of our near-engine-out experience, and we plan to make that same flight again... this time with a lot more knowledge of fuel.
Would be nice if this hour and a half long video was prefaced with a note saying, "Only applicable to frozen hellholes", rather than waiting a hour for Rian to tell us it doesn't happen in Brazil.
thank you , you've helped me solve mogas problems
You are welcome!
Hi Ron. That was an excellent presentation. Technical, but presented in an easy to understand format. I fly 2 RV12iS airplanes and would love to see more videos on flying the RV12iS if you have the opportunity. Also loved the presentation from Rian and how they test fly over the Alvord desert. We are currently running our 2 RV's on 100LL and before that on 91UL this is both winter and summer mostly below 6000ft AMSL. As they are used for training the oil is changed every 25hrs.
Thanks for the compliment! The videos that I produce are just for fun, but this was to share some serious information. If I do other presentations relating to the RV-12iS, I'll post it to CZcams again. I don't monetize my videos.
@@rsingh75 Look forward to it Ron. Many thanks.
General aviation needs to have alternatives to leaded fuel. The production, transportation, sale and use of leaded fuel needs to be totally banned NOW!
When Rian said, “if your running auto gas your fine but if your running MOGAS you have to do this test”, did he mean to say AVGAS instead of auto gas?
I noticed that too, but (while editing) neglected to place some text on the screen to correct that. What he meant to say was "if you're running AVGAS you're fine, but if you're running MOGAS, you have to do this test".
are you familiar with solubilized oxygen and dissolved air in refined fuels?
Thanks Ron and Rian for this very well researched and presented info, and sharing your experience. The info is particularly timely for myself, as I'll be flying an RV12 in that area over and around the mountains soon. This is clearly a significant safety contribution for many people, beyond just RV12 operators. I look forward to learning more as this testing plays out further.
Does the requirement of retailers to only sell summer blend apply to FBOs as well as retail auto gas stations? I've heard that the sales of many FBOs has fuel in their tanks for several months in some cases.
The Environmental Protection Agency requires "all regulated parties including retailers and wholesale purchaser-consumers" to comply with the RVP standards. I have not seen an exemption for FBOs or anything relating to aviation. I believe that anyone selling mogas (especially an FBO) would need to track their usage in the winter months and somehow use up as much of their high RVP fuel before early May. I hope that FBOs do not stock up with cheaper winter fuel before the May 1st deadline. I say May 1st because the fuel terminals are required to only sell summer blend (low RVP) fuel after that date... in other words, an FBO ordering fuel after May 1st will get summer blend,
Thanks for your comments - fly safe!
Can anyone explain the warning at 1:19:25 a bit more about the risks of vapour lock when switching between one tank with mogas and another with UL91 (or similar)? I’ve been doing this when uncertain for a while, keeping the UL91 for low level, landing and take off only, but am keen to understand why I shouldn’t!
Daniel the warning was to move the mixture to full rich when switching tanks. This warning was given in the AC. The warning is saying that you want to maximize the fuel flow to the engine if switching from 100LL for example to MOGAS. Flying on 100LL you would be able to lean the engine much further. If you switched to the MOGAS which needs to be richer then the engine may quit. What you are really asking is why is this the case.
The answer is the MOGAS may be partially vaporized. If you install a translucent tube just before the fuel pump you would see fuel and every so often a bubble of vapor passing through the lines. The pump compresses this vapor back into a liquid but since vapor is less dense, overall past the pump there is less flow rate (See the NOTE below). As altitude increases the atmospheric pressure on top of the fuel in the tank pushing the fuel to the tank decreases and the vaporization of the fuel increases. More vapor results in less fuel flow until you reach a point that there is insufficient fuel flow to keep the engine running. This results in power loss and eventually power failure. MOGAS therefore will require a richer mixture to keep the engine running (if you have a mixture, Rotax does not, Lycoming does).
NOTE: On Lycoming or Rotax carbureted engines that only pressurize to a few PSI or even in the case of Lycoming fuel injected models that may pressurize to 1 to 1.5 atmospheres (bar) the pump may not turn all the vapor back into a liquid. Rotax fuel injected engines pressurize to 3 bar (atmospheres ... most cars use 3 bar) and therefore have better resistance to vapor lock. Fuel injected engines use much higher pressure pumps and therefore are better at turning the vapor into liquid. This is why fuel injected engines are much less prone to vapor lock.
Really enjoyed this. I have a Cherokee 140 with a mogas STC and I use mogas whenever I can. This was incredibly informative. I learned a ton about gas that I didn't know. The good news for me is that my gas never stays in the airplane long enough to end up with winter blend in the summer.
In reviewing some of the other information on vapor lock, it seems like it's a much bigger problem in fuel injected engines than carbureted engines. Did you find anything confirming or refuting that?
I don't think it would be reasonable to make a blanket statement that vapor lock is more prevalent in a fuel injected engine Vs a carbureted engine (or visa versa). I believe that its also very dependent on the design of the fuel system and other features of a particular aircraft. As an example, in the case of a Van's RV-12, Rian Johnson has stated that the carbureted version is much more susceptible to vapor lock then the fuel injected one. This may be due to the location of the oil tank (that retains a lot of heat after shutdown) being close to the right side carburetor. RV-12 owners can expect to see more stringent limitations for the carbureted version expected in the upcoming POH and other documents.
In the case of a typical installation of a Rotax 912 carbureted engine, there is no circulation of fuel (fuel return) beyond the fuel mixing block. This leaves the fuel static in the line leading from the mixing block to each carburetor. If you have a heat soaked engine and you take vapor lock preventative measures by running the fuel pump prior to engine start, that section of fuel line doesn't get flushed which makes that area susceptible to vapor lock.
In my opinion, the vapor lock I experienced was occurring nowhere near the hot engine compartment, which is where most people believe it occurs. My vapor lock (better described as "cavitation") occurred at the dual fuel pump location in the tailcone area. This was caused by the low pressure of the pumps sucking fuel from the tank at . I say all this because at this point in the fuel system, it wouldn't matter what type of engine (injected or carbureted) was installed firewall forward.
I'm glad you enjoyed and got something out of the video. Thanks for your comments!
@@rsingh75 Does this experience make you want to stay away from mogas in your rv12?
I just noticed that one of the sentences in my response was messed up by CZcams. Every word that I had underlined got removed. It should say:
"This was caused by the low pressure of the pumps sucking hot volatile fuel from the tank at low atmospheric pressure."
@@1dullgeek No, I'm actually still comfortable flying with Mogas. I just assume that I have the worst case fuel and behave accordingly. In cool conditions (OAT, fuel temp, non heat soaked engine) I use 100% mogas. In warm/hot conditions when I expect to fly above 6,000 ft, I fly with a mixture of mogas and avgas. Several people after my presentation told me that they will just switch to avgas and do the added maintenance... which is reasonable.
@@rsingh75 That seems reasonable to me.
I watched this on 1.75 speed and it was still too slow
Omg blah blah blah
My story about flying
Blah blah blah
Make your point