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mogas/ethanol
- Thread starter gp456
- Start date
Ethanol in mogas
The main issue with having ethanol in fuel is the effect it might have on any rubber and plastic within the fuel system. Ethanol can cause a lot of rubber gaskets, o-rings, and hose to swell and disintegrate if they are not rated to work with ethanol/alcohol.
To ensure your fuel system can handle ethanol, you'll need to check with the manufacturer of all the components from your fuel cap to your intake system if they have been tested to be compatible with ethanol. Fuel pumps, hoses, gaskets in the carburator, and o-rings are the main possible problem areas. Your RV fuel tanks probabably do not have a rubber bladder, but a previous owner may have sloshed with something that is not happy with alcohol.
This all assumes of course that your engine is rated for mogas.
Since your aircraft is experimental, the FAA has delegated responsibility to you to designate an appropriate fuel for your aircraft. If your POH/AFM does not include mogas as an approved fuel, I'm not sure if it is required to add this, or if Phase 1 testing is required. Those would be good questions for people that know what they are talking about, unlike me.
The main issue with having ethanol in fuel is the effect it might have on any rubber and plastic within the fuel system. Ethanol can cause a lot of rubber gaskets, o-rings, and hose to swell and disintegrate if they are not rated to work with ethanol/alcohol.
To ensure your fuel system can handle ethanol, you'll need to check with the manufacturer of all the components from your fuel cap to your intake system if they have been tested to be compatible with ethanol. Fuel pumps, hoses, gaskets in the carburator, and o-rings are the main possible problem areas. Your RV fuel tanks probabably do not have a rubber bladder, but a previous owner may have sloshed with something that is not happy with alcohol.
This all assumes of course that your engine is rated for mogas.
Since your aircraft is experimental, the FAA has delegated responsibility to you to designate an appropriate fuel for your aircraft. If your POH/AFM does not include mogas as an approved fuel, I'm not sure if it is required to add this, or if Phase 1 testing is required. Those would be good questions for people that know what they are talking about, unlike me.
JordanGrant
Well Known Member
I don't really intend to run mogas, but I'm very curious about the concern over ethanol in aviation fuel. Can anyone point me to some more reading on the subject? (preferably internet, of course)
gmcjetpilot
Well Known Member
KiloWhiskey
Member
BTU per gallon
Just a reminder for those that snoozed during chemistry class, alcohol has less energy per gallon than gas (122,000 BTU/gallon for gas, 84,000 BTU/gallon for ethanol).
While this may not be an issue at 10% blends, fuels like the currently hyped E-85 with significant proportions of alcohol will reduce your range enough to notice, about 27 percent. Unless the carburator jets or fuel injectors are modified, takeoff power will also be noticeably reduced, but the power produced without mods may be OK for cruise flight.
I'm sure most of the serious mogas junkies already know this.
Just a reminder for those that snoozed during chemistry class, alcohol has less energy per gallon than gas (122,000 BTU/gallon for gas, 84,000 BTU/gallon for ethanol).
While this may not be an issue at 10% blends, fuels like the currently hyped E-85 with significant proportions of alcohol will reduce your range enough to notice, about 27 percent. Unless the carburator jets or fuel injectors are modified, takeoff power will also be noticeably reduced, but the power produced without mods may be OK for cruise flight.
I'm sure most of the serious mogas junkies already know this.
SmittysRV
Well Known Member
Has anyone noticed any kind of disclaimer or documentation on the gas pumps that the mogas contains 10% alcohol? Or are we going to have to do the test recommended by Petersen STC?
http://autofuelstc.com/autofuelstc/pa/ethanoltest.html
http://autofuelstc.com/autofuelstc/pa/ethanoltest.html
RVbySDI
Well Known Member
Here is another thread with some comments on this issue. Hecilopter has some interesting links on ethanol use.
http://www.vansairforce.com/community/showthread.php?t=8229
http://www.vansairforce.com/community/showthread.php?t=8229
mlw450802
Well Known Member
Smitty,SmittysRV said:
All pumps (at automobile service stations) are required to have a sticker stating that they have ethanol added if that is the case.
I am unclear whether supplies at airports have the same requirement although I believe they would more than likely be free of ethanol since the STC's generally forbid the use of auto fuel with added ethanol.
But, caveat emptor; test to be sure.
-mike
gp456 said:I fly rv6 with a 0320 e2d in the NE .I believe most of the NE states now blend 10% ethanol ,can I run the fuel or do I have to modify fuel system. What does FAA say about experimental and fuels ?? Any help would be appreciated.
FYI, if you use Airflow Performance's fuel injection system, you won't have any seal or gasket issues with their equipment.
Charlie Kuss
RVbySDI
Well Known Member
I am not an expert so don't quote me on any posts on this topic. It is my understanding that the 10% ethanol mixture does not negatively affect any of the gasket or rubber materials used. In this mixture the ethanol is serving primarily as an octane booster for the gasoline. However, the 85% "Gasahol" or whatever they are calling it these days that has 85% ethanol and 15% gasoline can damage gaskets, seals, rubber, etc. if these parts are not rated for use with ethanol.gp456 said:I fly rv6 with a 0320 e2d in the NE .I believe most of the NE states now blend 10% ethanol ,can I run the fuel or do I have to modify fuel system. What does FAA say about experimental and fuels ?? Any help would be appreciated.
IMHO, I would not be concerned about running 10% ethanol but would do much research to make sure my system can support the 85% mixture before I would ever consider using it.
gmcjetpilot
Well Known Member
Vapor Lock
I did a search of "vapor lock" and also "automotive fuel" in the NTSB. I got about 250 hits, about 50 with experimental. Some hits where unexplained loss of power with out mention of vapor lock, but the signs where there, erratic fuel pressure, power surge and high ambient temperatures. IN many cases the FAA just came out and said vapor lock, which is hard to prove, since the evidence is not there later when things cool down. It's like carb ice, the ice melts there is no evidence.
You'll hear stories of someone's buddy who has flown 20 years in a 150 HP Piper Cherokee on auto fuel. No doubt true and he is happy, but this is low compression engine, large cowl, may be flown in temperate climates and not at high altitude. All effect vapor lock. A high compression, tight cowled RV flown at high altitudes and hot temperatures may not do as well.
Yes the EAA has done great work on the subject, and lead the development of STC's for autofuel, but I have my doubts RV's with the tight cowls, wrap around cross over exhaust pipes would pass a formal STC approval out of the box or at all, even after fuel system modification. I don't know that is a guess and don't think anyone has done formal flight test with fuel temp monitoring.
Before any one tells me we don't need a STC, I know. However lets be realistic. Consider this from Petersen:
Q. Why isn't the Mooney M-20-C (or Piper Comanche) approved?
A. The Mooney and Comanche both experienced vapor lock problems when they were tested. We solved the vapor lock problem, but could not overcome pneumatic lock. Pneumatic lock takes place when the fuel boils as it enters the carb. The engine then dies due to an over rich mixture. This is just the opposite of a vapor lock where the engine quits or runs poorly due to a lean mixture. The better an airplane performs, the more difficult it is to get it through the flight test program.
The above is from experts in the field. They did have vapor lock but needed to modify the fuel system. They could not solve the other issue. I'm not anti-autofuel just be careful. The Mooney with a 180HP carb engine and constant speed prop is a pretty close match to the RV. In fact my RV-7 engine and prop are identical to a Mooney-C model. So why would I not suffer the same issues if I used auto fuel.
On a related topic, Octane. The Octane on auto pump gas is about 5 points less than if it was sold as AVgas. Low compress in engines (in the low/mid 7.0:1CR range) where certified for 80/87 octane. Higher compression engines in the mid 8.0:1CR range are certified for 91/96 octane. The two numbers are for lean / rich octane respectively. This is unique to AVgas ratings. Car gas has a combined single rating. Bottom line if you buy premium auto gas rated at 92 octane it is really like 89 octane AVgas. Will your 160/180 Lyc engine certified for 91/96 octane run on 87. May be? I don't know. You might be able to retard the timing a degree or two. I know the combo of retarded timing and lower octane means less power. At worst it could produce detonation and engine damage.
I try to be straightforward with the facts and not prejudicial. I am a little immune to testimonials. I did fly a C182 over 10 years ago. We (a group owner ship) decided to stop using autogas, despite having a for it STC. Carb ice was worse with autofuel. Also the engine ran fine on 100/100LL and was easy to buy. The price difference at the time was less than 0.50?, sometimes less. To use auto fuel for some where MOgas is not pumped at the field, you have to haul it in cans to your plane. This opens a whole can of whoop a** and possible ways to contaminate your fuel, not to mention the hazard of handling fuel. It can be done safely but look at the NTSB reports, they are full of fuel contamination accidents related to autogas and poor handling and transfer.
Last is my pet peeve is cost savings. Yes it is true it MIGHT BE cheaper. However if you look up the Min/Max of 100/100LL AVgas, MOgas (sold at airports) and premium auto gas sold at your local corner gas station you will find AVgas can be cheaper than MOgas. Also the price differntial between AVgas and premium auto gas can be a $1 or a few dimes. So the average savings my be in the $4.00/hr range? Is it worth the risk and hassle?
There are folks that live in a part of the country that can get ethanol / alcohol free cheep premium autogas and have low compression engines in certified planes with an auto gas STC. I understand why they use auto gas. I would also use auto gas in that situation. However, I have a high compression experimental with a tight cowl, exhaust pipes that go next to the carb, fuel pump, gascolator and all the fuel lines. Yes I could shield, insulate and air blast tube everything, but I would rather use AVgas. I also like to fly high cross country. Not all airports carry MOgas. Besides low octane MOgas is not suited for high compression engines (160/180HP Lycs).
Clearly the work the EAA has done is great. The fact is those 80 octane engines don't run well on 100/100LL. They NEED auto fuel. 100/100LL has a lot of lead in it, so you hear stories of how much better an engine runs on auto gas, it's true. Low compression engines that used 80 octane AVgas where made for basiclly unleaded gas. This is not the case with high compression engines, However unleaded fuel (UL) is coming for EPA reasons. Lead is a way to get the octane up, but it is not needed as an ingreadent in its self. The future of AVfuel is likely an unleaded version of 100/100LL for a UL95, like they have in Europe. They need to do more tests and figure out ways to keep the octane up. Also UL95 will (may?) not work for the highest compression engines, but it will work for our little 320/360's.
As far as autogas please be careful. Here is a source for new fuel pump cooling shroud (select products, scroll to bottom): http://www.showplanes.com/index_1024.htm
Vapor lock can even happen with AVgas, but have gas has a Vapor pressure 3 times lower and tightly controlled. Auto gas especially in the winter when they blend it for higher vapor pressure for easy starting in cold weather can be a real pain. Just keep that in mind.
Thanks for mentioning it. MOgas discussions can get into heated debates. Autogas proponents defend the use vigirously, but tend to not mention the down side. There are both good and bad.61DX said:
I did a search of "vapor lock" and also "automotive fuel" in the NTSB. I got about 250 hits, about 50 with experimental. Some hits where unexplained loss of power with out mention of vapor lock, but the signs where there, erratic fuel pressure, power surge and high ambient temperatures. IN many cases the FAA just came out and said vapor lock, which is hard to prove, since the evidence is not there later when things cool down. It's like carb ice, the ice melts there is no evidence.
You'll hear stories of someone's buddy who has flown 20 years in a 150 HP Piper Cherokee on auto fuel. No doubt true and he is happy, but this is low compression engine, large cowl, may be flown in temperate climates and not at high altitude. All effect vapor lock. A high compression, tight cowled RV flown at high altitudes and hot temperatures may not do as well.
Yes the EAA has done great work on the subject, and lead the development of STC's for autofuel, but I have my doubts RV's with the tight cowls, wrap around cross over exhaust pipes would pass a formal STC approval out of the box or at all, even after fuel system modification. I don't know that is a guess and don't think anyone has done formal flight test with fuel temp monitoring.
Before any one tells me we don't need a STC, I know. However lets be realistic. Consider this from Petersen:
Q. Why isn't the Mooney M-20-C (or Piper Comanche) approved?
A. The Mooney and Comanche both experienced vapor lock problems when they were tested. We solved the vapor lock problem, but could not overcome pneumatic lock. Pneumatic lock takes place when the fuel boils as it enters the carb. The engine then dies due to an over rich mixture. This is just the opposite of a vapor lock where the engine quits or runs poorly due to a lean mixture. The better an airplane performs, the more difficult it is to get it through the flight test program.
The above is from experts in the field. They did have vapor lock but needed to modify the fuel system. They could not solve the other issue. I'm not anti-autofuel just be careful. The Mooney with a 180HP carb engine and constant speed prop is a pretty close match to the RV. In fact my RV-7 engine and prop are identical to a Mooney-C model. So why would I not suffer the same issues if I used auto fuel.
On a related topic, Octane. The Octane on auto pump gas is about 5 points less than if it was sold as AVgas. Low compress in engines (in the low/mid 7.0:1CR range) where certified for 80/87 octane. Higher compression engines in the mid 8.0:1CR range are certified for 91/96 octane. The two numbers are for lean / rich octane respectively. This is unique to AVgas ratings. Car gas has a combined single rating. Bottom line if you buy premium auto gas rated at 92 octane it is really like 89 octane AVgas. Will your 160/180 Lyc engine certified for 91/96 octane run on 87. May be? I don't know. You might be able to retard the timing a degree or two. I know the combo of retarded timing and lower octane means less power. At worst it could produce detonation and engine damage.
I try to be straightforward with the facts and not prejudicial. I am a little immune to testimonials. I did fly a C182 over 10 years ago. We (a group owner ship) decided to stop using autogas, despite having a for it STC. Carb ice was worse with autofuel. Also the engine ran fine on 100/100LL and was easy to buy. The price difference at the time was less than 0.50?, sometimes less. To use auto fuel for some where MOgas is not pumped at the field, you have to haul it in cans to your plane. This opens a whole can of whoop a** and possible ways to contaminate your fuel, not to mention the hazard of handling fuel. It can be done safely but look at the NTSB reports, they are full of fuel contamination accidents related to autogas and poor handling and transfer.
Last is my pet peeve is cost savings. Yes it is true it MIGHT BE cheaper. However if you look up the Min/Max of 100/100LL AVgas, MOgas (sold at airports) and premium auto gas sold at your local corner gas station you will find AVgas can be cheaper than MOgas. Also the price differntial between AVgas and premium auto gas can be a $1 or a few dimes. So the average savings my be in the $4.00/hr range? Is it worth the risk and hassle?
There are folks that live in a part of the country that can get ethanol / alcohol free cheep premium autogas and have low compression engines in certified planes with an auto gas STC. I understand why they use auto gas. I would also use auto gas in that situation. However, I have a high compression experimental with a tight cowl, exhaust pipes that go next to the carb, fuel pump, gascolator and all the fuel lines. Yes I could shield, insulate and air blast tube everything, but I would rather use AVgas. I also like to fly high cross country. Not all airports carry MOgas. Besides low octane MOgas is not suited for high compression engines (160/180HP Lycs).
Clearly the work the EAA has done is great. The fact is those 80 octane engines don't run well on 100/100LL. They NEED auto fuel. 100/100LL has a lot of lead in it, so you hear stories of how much better an engine runs on auto gas, it's true. Low compression engines that used 80 octane AVgas where made for basiclly unleaded gas. This is not the case with high compression engines, However unleaded fuel (UL) is coming for EPA reasons. Lead is a way to get the octane up, but it is not needed as an ingreadent in its self. The future of AVfuel is likely an unleaded version of 100/100LL for a UL95, like they have in Europe. They need to do more tests and figure out ways to keep the octane up. Also UL95 will (may?) not work for the highest compression engines, but it will work for our little 320/360's.
As far as autogas please be careful. Here is a source for new fuel pump cooling shroud (select products, scroll to bottom): http://www.showplanes.com/index_1024.htm
Vapor lock can even happen with AVgas, but have gas has a Vapor pressure 3 times lower and tightly controlled. Auto gas especially in the winter when they blend it for higher vapor pressure for easy starting in cold weather can be a real pain. Just keep that in mind.
Last edited:
N162RV
Active Member
Engine CERTIFICATION for STC
Below is how Peterson tested engines and airframes for the STC. My biggest concern was detonation and looks like that was thoroughly tested. Also the test for the airframes for vapor lock was absolute worst case scenario with pre-heated winter mix fuel.
CERTIFICATION
All of our engine STC approvals are based on 150 hour ground endurance runs. A total of 105 hours is conducted at rated sea level power, (full throttle - 100% power) with the remaining 45 hours conducted at various throttle settings from 60 to 85 % power.
Extensive detonation testing is conducted prior to the endurance testing to establish the engine's ability to function without damage and to develop rated power.
Airframes are tested against vapor lock by conducting flight tests to a minimum of 12,500 feet. The first series of tests is conducted on high volatility winter blend fuel which is heated in the wing to 85 degrees before takeoff and climb. The second is conducted on winter blend fuel heated to 110 degrees prior to takeoff and climb. Any loss of power or excessive fuel pressure loss during these tests results in a failure of the test. Extensive fuel flow tests are also conducted on airframe fuel systems to insure adequate fuel flow.
Below is how Peterson tested engines and airframes for the STC. My biggest concern was detonation and looks like that was thoroughly tested. Also the test for the airframes for vapor lock was absolute worst case scenario with pre-heated winter mix fuel.
CERTIFICATION
All of our engine STC approvals are based on 150 hour ground endurance runs. A total of 105 hours is conducted at rated sea level power, (full throttle - 100% power) with the remaining 45 hours conducted at various throttle settings from 60 to 85 % power.
Extensive detonation testing is conducted prior to the endurance testing to establish the engine's ability to function without damage and to develop rated power.
Airframes are tested against vapor lock by conducting flight tests to a minimum of 12,500 feet. The first series of tests is conducted on high volatility winter blend fuel which is heated in the wing to 85 degrees before takeoff and climb. The second is conducted on winter blend fuel heated to 110 degrees prior to takeoff and climb. Any loss of power or excessive fuel pressure loss during these tests results in a failure of the test. Extensive fuel flow tests are also conducted on airframe fuel systems to insure adequate fuel flow.
Stopping Vapor Lock
The best way to prevent vapor lock is to have the fuel pumps in the fuel tanks. This keeps the fuel under pressure, greatly reducing the chance of vapor lock.
This is what Diamond has done on at least one of their aircraft, perhaps all of them. This is also what all the car manufacturers have done. It's clearly not too useful an idea as a retrofit, but something new builders or entrepreneurs may want to think about.
The best way to prevent vapor lock is to have the fuel pumps in the fuel tanks. This keeps the fuel under pressure, greatly reducing the chance of vapor lock.
This is what Diamond has done on at least one of their aircraft, perhaps all of them. This is also what all the car manufacturers have done. It's clearly not too useful an idea as a retrofit, but something new builders or entrepreneurs may want to think about.
Pump in tank
At least in some other cool place. I had the opportunity to handle the mechanical pump, equipped with shroud and blast tube, soon after the engine was run. Heat is transfered through the engine case and through the oil bath on the backside of the diaphram. It was for all practical purposes at the oil temp. I'm guessing that fuel leaves the pump at close to 200 degrees at least some of the time! It is under pressure (less likely to boil) from there to the carb or injector body where it may have a chance to cool down again (or boil!).
Given the low rate of fuel flow through the pump and the agitation that goes on in the pump, I believe that any robust alcohol enabled conversion will have to eliminate this huge heat source. I'm with George that for now it is hard to realize any real benifit. encouraged to know thogh that our Lycomings, with some reengineering, can be made to run on other fuels.
At least in some other cool place. I had the opportunity to handle the mechanical pump, equipped with shroud and blast tube, soon after the engine was run. Heat is transfered through the engine case and through the oil bath on the backside of the diaphram. It was for all practical purposes at the oil temp. I'm guessing that fuel leaves the pump at close to 200 degrees at least some of the time! It is under pressure (less likely to boil) from there to the carb or injector body where it may have a chance to cool down again (or boil!).
Given the low rate of fuel flow through the pump and the agitation that goes on in the pump, I believe that any robust alcohol enabled conversion will have to eliminate this huge heat source. I'm with George that for now it is hard to realize any real benifit. encouraged to know thogh that our Lycomings, with some reengineering, can be made to run on other fuels.
They're doing it in Brazil
I read this a few months ago. Apparently Embraer is retrofitting some certified planes (crop dusters running Lycoming IO-540s) to run on the Brazilian version of ethonal (made from sugar cane instead of corn). Brazil has recently become energy independent as a result of a 30 year program to convert to cane based gasoline.
http://www.avweb.com/avwebflash/11_18a/briefs/189678-1.html
I read this a few months ago. Apparently Embraer is retrofitting some certified planes (crop dusters running Lycoming IO-540s) to run on the Brazilian version of ethonal (made from sugar cane instead of corn). Brazil has recently become energy independent as a result of a 30 year program to convert to cane based gasoline.
http://www.avweb.com/avwebflash/11_18a/briefs/189678-1.html
