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The TRUTH about MOGAS (very long)

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jmsears(at)adelphia.net
Guest

Posted: Sat Jul 08, 2006 4:13 am Post subject: The TRUTH about MOGAS (very long)

 	  Quote: 	
		  > I am not ANTI Mogas or anyone who uses it, but 

I would like present some of the FACTS, negatives 
	


or CON's, in addition to all the PRO drinking the 

cool-aid comments for MOGAS. <<



George and I have had some discussion on this subject 

off line; and, I thought the topic was over with.  I guess

he doesn't feel that way.  Actually, George has thought

seriously about using mogas in an airplane.  However,

George is like many on this list who have a nice sum of

cash to work with.  With that, he doesn't have the 

need, or desire, to try alternative things to help keep

his aviation expenses down.  George also has an 

engineering background; so, he's not dumber than a

box of rocks, like some of us out here.    



 	  Quote: 	
		  > I appreciate the passion and support some have 

for MOgas. Hey 5,10 and 15 years of successfully 
	


operation is not bad. I appreciate the sense of 

humor as well.<<



Where we lack in education, those of us who've used

auto gas with FAA's blessings do have a background

of experience.  Mine has lasted for about 20 years and

about 2000 hours of flying time with auto gas.  Some

of the others have been flying with auto gas for just as

long, if not longer.  I don't consider my good fortune 

with auto gas to be an exception.  It's most likely more

the rule.     



 	  Quote: 	
		   Now for facts.


	


Now, this is where George, in his good meaning way, 

has messed up a little.  He's got most things right; but,

he's just like us in that some of his information is not

correct.  I don't know all the facts, either.  I'm no

engineer and am no expert.  I do read a lot and have

the experience with mogas. 



 	  Quote: 	
		  > besides the OCTANE molecule (distilled petroleum).

Gas has 200 of chemicals in it, some are good 
	


for aviation some not, <<



This can be true.  In the past, we've been alerted about

some of those chemicals.  However, I think it was found

that some of those chemicals were harmful to the 

environment and were disallowed.  MTBE seems to be

one of the chemicals that is mentioned often.  However, 

it is approved for our usage.  What works in a car should

be OK for the airplane, in most cases.  Of course, that's 

just speculation on my part; but, I don't think the fuel 

manufacturers want autos to fail any more than we want

our aircraft engines to fail.  I certainly don't want my fuel

delivery system to melt down, my engine to detonate, 

and my engine to melt down, whether it be my auto or

my airplane.  



 	  Quote: 	
		   Auto gas has lower vapor pressure, which means it 

 is more susceptible to vapor lock.


	


Sorry, Goerge; but, you still have that one backwards,

which helps to debunk the rest of what you say.  Don't 

worry, I have had a hard time keeping this one straight, 

myself.   



 	  Quote: 	
		   Auto gas, even premium does NOT have the same 

 octane as 100LL Avgas by quite a bit.


	


I've got to admit he's right.  However, most engines 

we use today, and certainly most engines we use for

our RVs don't require the use of 100LL.  At least, 

that's what I've read several times on this list and

in publications.    



 	  Quote: 	
		   Low octane can cause detonation, and uncontrolled 

 burning of fuel which can lead to severe engine 

 damage.


	


If it's too low for the engine.



 	  Quote: 	
		  > In the past Av gas came in grades of 80-87; 91-98, 

100-130 and 115-145. That has given way to the 
	


ubiquitous 100/100LL<<



One can still sometimes find the 80/87 fuel; but, it's 

pretty rare.  However, what happened to those engines

that ran on 115/145 fuel?  Did those go away; or, did

they get derated to run on 100LL?  Surely the FAA

didn't say it's OK to run them on 100LL without some

sort of investigation into it.  Can anyone answer that?

Isn't that sort of what we're doing?  We're going to

a lower antiknock fuel that can be used instead of

one that is forced on us because nobody makes the

other, anymore?    



 	  Quote: 	
		   Why two numbers? The low number is the lean octane 

 rating and the higher number is rich octane rating. 



 There are four ways to measure fuel for octane: 

 Automotive Research, Automotive Motor, 

 Aviation Lean and Aviation Rich.


	


There is more information in the archives about this.

It's interesting reading material for those who are 

interested.  

 

 	  Quote: 	
		   Auto gas has one rating and is average of lean and 

 rich rating and there are two methods as listed 

 above. 


	


Yes.  Check the archives for more info.



 	  Quote: 	
		  > Aviation gas lean is about equal to automotive motor 

octane.100LL avgas if sold at the car pump would be 
	


105. Premium 91 octane MOgas sold as Avgas 

would be about equiv to 86UL. <<



I won't dispute this because I'd have to look it up; 

but, I do remember that the octane rating is lower

for avgas, as he suggests.  I think 87 antiknack is

translated to 82UL avgas.



 	  Quote: 	
		   STC for Mogas was when 80/86 went a way and 

 the low compression engines ran terrible on the 

 default gas grade 100/100LL. 


	


And can be damaged by the lead content.



 	  Quote: 	
		   Despite the LL  (Low Lead) designation, 

 there's a lot of lead in 100LL. 


	


About ten times as much as leaded mogas

and four times as much as 80 avgas, per

Petersen's STC information.



 	  Quote: 	
		  > Therefor low compression engines 

designed to run on low octane fuel did not 
	


need or work well on leaded fuel. Lead boost 

octane.  That was the beginning of STC's for 

automotive unleaded (UL) fuels for aircraft as 

a substitute for low lead/UL 80 octane.<<



This may be a true statement.  Many were 

already using the mogas illegally, anyway.  The

STC just made it legal.



 	  Quote: 	
		   Just because the FAA approves STC's is not mean 

 much in a high compression homebuilt.


	


Yep; but, I think many of us already realize that there

is a limit as to what engines can use it.  However, the

FAA, which George doesn't trust to have the sense

to know what the experts know, thinks that over 90%

of the GA fleet can run on a lower octane fuel, if we

were to lose 100LL.  I'm hoping that the FAA has

its own set of experts to work with.  I'm betting 

they're working with the fuel and engine manufacturers

on this.  Surely, they have the right experts.   



 	  Quote: 	
		  > Lycomings come in to flavors, which are certified 

for 80 octane and have a compression ratio about 
	


7.2:1CR or have about 8:50:1CR and are certified 

for 100/100LL gas, or the old  91/96 Avgas grade. <<



According to my engine list, the engines are 7.5:1 and

8.5:1.  I'm no expert on the subject, though.  



 	  Quote: 	
		  > If you buy the Super gas at the mini-mart and it 

said 92 octane it is only worth about 87 octane. 
	


We assume you test it for ethanol and alcohol 

every time of course. <<



I think it has to maintain what's stated on the pump

for a period of time.  That means it's most likely

the octane that's stated, or very close to it.  It 

certainly won't be that much below what's stated

on the pump unless George really means the 87

is the avgas equivalent.    



 	  Quote: 	
		  > Can you run your 91/96 octane Lyc on it? Well that 

is subject to debate, but it does not fly in my plane. 
	


I guess you can reduce the timing advance a little 

as a precaution?<<



And this is where we differ.  George won't use it in 

his airplane; but, I might.  It depends on what engine

I have.    



 	  Quote: 	
		   Lycoming strongly recommends NOT using MOGAS.


	


As I told George off line, Lycoming is not going to stick

its neck out because its lawyers are dead against it.  To

cover their asses, they'll stick with certified fuels in their

certified engines.  Of  course, the same company is 

being left behind by companies like Superior and ECI

who aren't as afraid as Lycoming.  Superior and ECI

tend to cater more to us and are willing to try new 

things.  Lycoming may end up finding itself without a 

customer base, if it continues listening to lawyers

instead of the fastest growing segment of GA.  



 	  Quote: 	
		  > Lycoming does know about auto gas and in fact 

makes a very low compression O360 for flying in 
	


third world countries to run on low grade fuel. <<



I'm betting that's the 167hp version with the 7.5:1

compression ratio.  I've thought about building one

of those up for myself.  With that, I'd have a lot

more hp than my current 150 hp engine and could

still run my engine on 87 antiknock fuel.  



 	  Quote: 	
		   Unfortunately most 320's and 360's have 8:50:1CR 

 and need the 91/96 (100LL) gas.


	


I have a new car that requires 91, or better, antiknock

fuel.  However, I read the fine print and found that it

will run on 87 antiknock fuel.  There would be some

power reduction, though.  I may be wrong; but, I'm 

betting Lycoming has done the same thing.  They've

given themselves a nice margin for error in their 

fuel requirements.  That's why it's been found that

we can actually run them on lower octane fuels with

no adverse effects.  Of course, this is speculation on

my part.  



 	  Quote: 	
		  > If you are willing to test, haul and store your 

own auto gas and run your engine on less than the 
	


recommended octane, than OK, do that. If you have 

a low compression engine than auto gas makes more 

sense. <<



Which many of us are doing.



 	  Quote: 	
		   You may want to look into reducing your timing and 

 all the other things 


	


For those with very high compression ratios, and some

who have the lower compression ratios and want to 

do it that way, having automatic retardation is the cat's

meow and may be the way of the future for us to get

away from 100LL, altogether.  



 	  Quote: 	
		  >.I mentioned about keeping the 

fuel cool, that where somewhat ridiculed by the 
	


MOgas experts. I would do everything I could to 

assure no loss of power due to vapor lock.<<



I don't know who ridiculed George; but, it was not I

I've flown three airplanes extensively on auto gas.  Not

one of them had a fuel return system.  Since I don't

consider firesleeve a good insulator in normal operation,

I don't have my fuel system insulated.  I do have a couple

of blast tubes for the RV; but, my prior two aircraft did

not have them.  All three have worked well with auto gas. 



If I were going to use a FI engine, I'd most likely install

a fuel return system to make me more comfortable with 

it.  However, I've not had that much trouble with vapor

locking and would opt to stay with the KISS method

on my carb engines.  That works for me.  You guys may

want to go with fuel returns.  That's what makes this

whole thing so neat.  We can do what is right for each

of us.   



 	  Quote: 	
		  >If you have a 7:1CR engine than it is safer from an 

octane stand point, as long as it does not have the 
	


alcohol and ethanol. (However ethanol does increase  

the octane rating, see below).<<



I believe ethanol is a form of alcohol; but, I might be

wrong on that.  I do think the 7.5: 1 engines have the

advantage, though.  When one does the formula to

convert the 87 antiknock to avgas, it's the 82UL

we've seen in the past, if memory serves me.  Since

7.5:1 engines are designed for 80, I don't worry

about the octane, as much.



 	  Quote: 	
		  > If you get a load of ethanol gas you run the risk 

of water contamination since it absorbs water. Once 
	


airborne it cools the water comes out of the fuel 

and water contamination result in loss of power. <<



This could be a real problem in cold weather.  Here

is one little rub in that, though.  What about all the 

cars that run on it?  Why don't they have frozen fuel

lines, stopped up tanks, and stopped up fuel filters

from using it?  Anyone ever given that one a thought?

It may not be that much of a problem, in that sense.

I wonder how cold it would have to be for the

separation to happen.  I'm more concerned about

what it can do to components in the system.  As

others have stated, that may not be as much of a

problem, anymore.        



 	  Quote: 	
		   Carb ice is more likely with ethanol (alcohol). 


	


I won't dispute that because I don't know.  I do

know that my Lycoming engines have rarely, if 

ever, showed symptoms of icing up.  The C172

I owned had a Continental in it.  Boy, that thing

would ice up, in a heart beat.  I'm not saying it

won't happen; but, I'm betting it would be a

minor issue.  I'd be more concerned about the

power output from alcohol.  From what I'm 

reading, it takes a lot more alcohol to produce

what gas produces.      



 	  Quote: 	
		  >That is why it is important to test your auto gas.

Also ethanol is not compatible with the rubber 
	


and gaskets used in aircraft and they will swell, 

which has caused aircraft engines to stop in the 

past. <<



I must admit I haven't been real good about testing

my fuels.  I have tested it, in the past; but, I'm not

one to do it with every fuel purchase.  Some will

critisize me for my lack of action; but, I tend to 

buy gas where alcohol is not in the fuel.  If I lived

near a large city, I'd test it regularly.  



 	  Quote: 	
		  > These are facts. If you do go auto fuel please please 

ask lots of questions of those who are experts in the 
	


topic. I think we have a few on this list (seriously <<



I don't claim to have all the answers; but, I do try to

help.  Our archives are full of good information on 

the use of auto gas.    



 	  Quote: 	
		  > I am not an expert but than I don't have to jump of a 

bridge to know it might hurt when I hit the water. I 
	


know if your engine stops while flying in a plane it 

can be a bad thing. MOgas is NOT as good as 

AVgas. The debate is it good enough. May be.  <<



Actually, I think mogas is better than avgas.  I have

less problems with mogas than I do with avgas.  I've

had cylinders off my engines for problems not relating

to mogas usage and have yet to find symptoms of 

detonation,etc.  On the contrary, I've found the engine

to be clean on the inside.  No lead.  Every time I fill

my plane up with 100LL, I get the fouled plugs and

lead related bad run ups.  



 	  Quote: 	
		   What I know about auto gas is enough to discourage 

 me.  


	


George is lucky in that he has a job that pays very well.  

Making his decision was easy for him.  However, there

are those of us who are grass roots enthusiasts who do

not have large incomes.  We have to think differently

and search out alternatives that work for us.  Either is

just fine.  As best I know, I'm probably the only one

at our airport who regularly uses autogas for fuel.  I'm

probably one of the few who is retired, as well.  The

rest are well paid folks, with most having businesses 

of their own.  They complain about the cost of 100LL;

but, they continue to use avgas because they can 

afford it.  I can't.  Mogas works for me. 



 	  Quote: 	
		  > Ethanol does help octane so if you can get some 

"sub grade" fuel before the distribution puts in 
	


the additives, like ethanol you can expect a 5% hit 

on octane. So basic fuel planned for 91 octane 

with ethanol is really 89 octane without the ethanol.  

This is like 84 aviation.  To get "sub grade" you need 

to get it at the distribution terminal before they add 

the ethanol.<<



Let me try to remember.  If octane increases, that

slows the burn more to make it more uniform.  That

translates to more power.  Why is it that ethanol is

apt to give less power and require more fuel to do

the same thing as ethanol free fuels?  Just curious.

I would think ethanol is more of an environmental

issue additive than for octane boosting.  That's why 

one will find it more around big cities where smog

is a problem.  What say you experts? 



 	  Quote: 	
		  > 84 octane is not enough for higher compression 91/96 

engines. If you have a 80 octane O320 140/150HP Lyc, 
	


than by all means go for it. <<



I'm sorry, George, I'm getting lost in your octane ratings.

They're jumping all over the map.  However, if one is 

using a 140/150/167/235 hp Lyc, one is safe to use

87 antiknock fuel.  As for the 8.5:1, Superior stands

behind their engines using 91-92 antiknock mogas.  I

suggest that they would not do that unless their engines

can be run safely on it.  If I were to buy a new engine

for my RV, I'd look very seriously at buying a new 

engine from an engine manufacturer that supports our 

needs.  It appears that Superior, and maybe ECI, 

does. Lycoming would be my last choice, even 

though their engine will most likely do as well as

the Superior engine on the same fuels.   



 	  Quote: 	
		  > Some debate about reducing timing for the high 

compression engines.<<
	




At some point, this will probably have to be done.



 	  Quote: 	
		  > Lycoming is testing UL blends and the gas companies 

are working on the 95UL as a 100/100LL replacement. <<
	




Most of our engines can run on it.



 	  Quote: 	
		  >Remember there are more high compression than low 

compression engines. Also the real fire breathing high 
	


end piston engines, turbo charged and so on NEED 

the high end gas, only make up 30% of the fleet but 

use 70% of the gas. So all you C65 & C85 engine 

Piper Cubs are stuck using the 95 octane but with 

the UL it should be OK.<<



I'm betting a lot of cub drivers are pouring in auto gas.

Those engines will run nicely on it.  They aren't stuck

with avgas.  The ones in trouble are the ones with the

super hot engines.  



 	  Quote: 	
		  > IF I HAD an 80 octane engine AND the gas prices 

kept going up I would consider auto gas it. (THERE I 
	


SAID IT, ARE YOU HAPPY....)<<



Not really.  Gas is always going to go up.  One has to

get to where the cost is prohibitive.  It hasn't gotten 

there for most of us.  When it does, many of us will 

just get out of aviation.  Look at the other countries

where gas is way more than we pay.  There is very

little general aviation.  We'll see the same thing, here.

It won't have to go up much more to leave this 

retiree behind.  There is already talk around our 

airport by some who think it's about time to get out.

The fuel is still cheap enough that we can sell our

airplanes at reasonable prices.  If it goes up much 

more, and aviation declines, we won't be able to 

give them away.  Oh, yeah.  Aviation is declining, 

it seems.  That's why AOPA is asking us to help

out.  The average Joe can't afford start in aviation, 

anymore.  Some of us may fall by the wayside, as

well.  It will trully become a rich man's hobby.  The

use of auto gas may not matter, then.            



 	  Quote: 	
		  > As I said for the real world guy $400-$800 is about 

what you can expect to save per year. Some of the 
	


guys who live where fuel is cheap and ethanol is not 

forced down their throat, good for them. If you have a 

High compression engine and ethanol free fuel is hard 

to find at the pump than not so good.<<



This is a fact of life.  Not everyone can partake in its

use; but, many of us can and do. 



 	  Quote: 	
		  > For the convenience of pulling up to the airport pump, 

filling with very high octane fuel, with very high vapor 
	


pressure and knowing there's no bad chemicals in it 

with out having to test it, is worth it to me.<<



Yep.  Isn't it nice you can have it your way?  The key

is doing what makes you feel comfortable.  Many of

us feel very comfortable pouring auto gas into our 

tanks.  It works for us.   



 	  Quote: 	
		  >To each his own, I'll never say never but at some 

point I just will not fly as much or at all, sadly. <<
	




That is a fate that all of us face.  I see my end in 

aviation coming too fast.  



Sorry for the long response; but, I feel it's necessary

to defend what I believe in.  Use of mogas in airplanes

isn't for everyone; but, giving false information isn't 

going to help, either.  George means well; but, he's

like the rest of us.  He's learning.  However, one 

must realize that the old tales about how mogas will

cause us to crash have been disproved.  Now, some

engine manufacturers are backing its use.  That's 

good enough for me!



Jim Sears in KY

do not archive

ebundy(at)speedyquick.net
Guest

Posted: Sat Jul 08, 2006 7:08 am Post subject: The TRUTH about MOGAS (very long)

As someone who long ago made up my mind not to use Mogas (for a variety of

reasons) I still found this discussion interesting.



I personally don't think the *potential* risks outweigh the monetary

savings.  I don't know if I fit into the "nice sum of cash" camp, but I know

that I DO give up other things that I would like (such as an automobile

built after 1988) in order to fly an RV.



One thing I haven't seen mentioned (although I confess I have skipped a lot

of this topic) is that a few years ago Avgas was twice as expensive as Mogas

($2 vs. $1).  Now the same $1 differential exists, but at $4 vs. $3 Mogas is

"only" 25% cheaper.



Sorry, but with all the expenses of airplane ownership, a 25% savings on

fuel is not worth ANY possibility of Mogas problems.  Not to mention the

hassle factor of lugging your own airplane fuel around.  Yuck.



Ed Bundy

 	  Quote: 	
		  > I am not ANTI Mogas or anyone who uses it, but

 I would like present some of the FACTS, negatives

 or CON's, in addition to all the PRO drinking the

 cool-aid comments for MOGAS. <<


	


 	  Quote: 	
		   George is like many on this list who have a nice sum of

 cash to work with.  With that, he doesn't have the

 need, or desire, to try alternative things to help keep

 his aviation expenses down.  George also has an

 engineering background; so, he's not dumber than a

 box of rocks, like some of us out here.  


	


--

rocketbob(at)gmail.com
Guest

Posted: Sat Jul 08, 2006 8:44 am Post subject: The TRUTH about MOGAS (very long)

I don't think anyone can claim to be an expert on whether or not mogas is suitable for their airplanes unless they try it and see if it works in their airplane.  Forget the numbers (compression ratio, octane, vapor pressure, etc.)  For me 25% 100LL and 75% 87 octane sans alcohol mix works for me and I can't tell a bit of difference when I'm fueled up with 100% 100LL.  My lines are firesleeved, no problem in the summer temperatures.  It works for me and as far as I care those are the facts, everything else is conjecture.  I've borescoped the cylinders to look for any signs of detonation, and there are none.  My oil analysis reports always come back good. 



I have 9:1 pistons in the rocket, will likely go 50/50 on the fuel mixture, but have to see what works best thru some trial and error.



Regards,

Bob Japundza

RV-6 flying 700+hours, F1 under const.

ronlee(at)pcisys.net
Guest

Posted: Sat Jul 08, 2006 9:14 am Post subject: The TRUTH about MOGAS (very long)

 	  Quote: 	
		  Actually, I think mogas is better than avgas.  I have

less problems with mogas than I do with avgas.  I've

had cylinders off my engines for problems not relating

to mogas usage and have yet to find symptoms of detonation,etc.  On the 

contrary, I've found the engine

to be clean on the inside.  No lead.  Every time I fill

my plane up with 100LL, I get the fouled plugs and

lead related bad run ups.


	


Don't take this the wrong way but that may be operating

technique.   I use 100LL and fly more than most folks and

I don't have fouled plug issues on every fillup.  I think that

I have had three cases in 900 hours and most were probably

because I failed to lean the engine after startup.  I would

prefer a fuel with little or no lead because it does require

periodic maintenance to clean the plugs.



Ron Lee

jmsears(at)adelphia.net
Guest

Posted: Sat Jul 08, 2006 9:24 am Post subject: The TRUTH about MOGAS (very long)

 	  Quote: 	
		   As someone who long ago made up my mind not to use 

 Mogas (for a variety of > reasons) I still found this 

 discussion interesting.

 


	


These discussions can be very interesting, especially if there

is a distinct polarity between those who use auto gas and 

those who don't.  



 	  Quote: 	
		   I personally don't think the *potential* risks outweigh the 

 monetary savings.  I don't know if I fit into the "nice sum 

 of cash" camp, but I know that I DO give up other things 

 that I would like (such as an automobile built after 1988) 

 in order to fly an RV.

 


	


Each of us less fortunate folks has to give up something to 

get to fly.  I had to give the idea of having a big fancy house

and the mortgage payments that go with it.     As for the

potential risks, I've found very few.  In fact, I feel good

enough about using auto gas that I've taken up over 300

kids in the Young Eagles program with auto gas in the 

tanks.  I've not lost one, yet.  I've had more problems with

100LL and its fouling tendencies.  



We all get so hooked on the risks involved that we forget

the risk we take by just driving to the airport.  I'm not going

to belittle anyone for not wanting to try mogas; but, I would

not tell you that it's safe knowing it's not.  I'm not the most

brave/macho pilot in the world; so, I'm not fond of taking 

risks, either.  I trusted in those who did the testing to be

right and gave it a try.  I've not regretted it, yet.  



 	  Quote: 	
		   One thing I haven't seen mentioned (although I confess 

 I have skipped a lot > of this topic) is that a few years 

 ago Avgas was twice as expensive as Mogas ($2 vs. $1).  

 Now the same $1 differential exists, but at $4 vs. $3 Mogas 

 is "only" 25% cheaper.

 


	


That's a neat way to look at it; but, it's more than that.  There

is still that $1+ price differential that keeps that savings  way

up there.   Also keep in mind that our incomes haven't been

inflated at the same rate as gas; so, that savings that we were

talking about a couple of years ago is still substantial to us, 

today.  As a note of interest, my retirement income will never

increase; so, a dollar saved is a dollar earned.    



 	  Quote: 	
		   Sorry, but with all the expenses of airplane ownership, 

 a 25% savings on fuel is not worth ANY possibility of 

 Mogas problems.  Not to mention the hassle factor of 

 lugging your own airplane fuel around.  Yuck.

 


	


Ed is comfortable with his decision and has his reasons; 

but, there aren't that many risks.  I've had engine problems

with my aircraft, just as any aricraft owner does.  I've had

to replace cylinders because the tubes in the sump loosened

up.  I've had to overhaul an engine because it had sat for

a while before I bought it.  The cam gave it up.  I had to

replace a cylinder because the oil ring stuck.  Have you 

noticed I've said nothing about detonation, yet?  There 

hasn't been any that we've found.  In each case, the

problem was something totally unrelated to the type of 

fuel I was using.  That's in about 2000 hours of flying on 

auto gas.  



Gang, I'm not here to recruit anyone from joining me 

unless you want to.  If you want to, there are those of 

us who have chosen to try auto gas and have been 

very successful at it.  To me, it's worth the hassle.  When

it no longer is, I'm sure I'll be priced out of aviation.  At

that point, it will be moot.  



Jim in KY

do not archive.

jmsears(at)adelphia.net
Guest

Posted: Sat Jul 08, 2006 9:33 am Post subject: The TRUTH about MOGAS (very long)

 	  Quote: 	
		   I don't think anyone can claim to be an expert on 

 whether or not mogas is suitable for their airplanes 

 unless they try it and see if it works in their airplane.  


	


That's kinda how I see it.  Those who haven't tried it,

and are listening to others who are dead set against it,

may be missing out on something that not only saves

money from fuel purchase.  It could reduce costs in 

operation from lead deposit problems, as well.   



 	  Quote: 	
		   Forget the numbers (compression ratio, octane, 

 vapor pressure, etc.)  For me 25% 100LL and 75% 

 87 octane sans alcohol mix works for me and I can't 

 tell a bit of difference when I'm fueled up with 100% 

 100LL.  


	


Bob is using a little more conservative mix than I do; 

but, I've found that having a 25% mix of 100LL all

but eliminates vapor lock problems on those days 

when I'm doing quick turnarounds for Yound Eagles.

Like Bob, I can't tell the difference between the 

performance of 100LL and the 87 antiknock from 

around the corner.  In fact, my little RV's engine ran

just fine on it, this morning.         



 	  Quote: 	
		   My lines are firesleeved, no problem in the summer 

 temperatures.  It works for me and as far as I care 

 those are the facts, everything else is conjecture.  


	


I like this man's attitude.  



 	  Quote: 	
		   I've borescoped the cylinders to look for any signs 

 of detonation, and there are none.  My oil analysis 

 reports always come back good. 


	


Same here on both counts.  In fact, I get better oil 

analysis reports on auto gas.  



 	  Quote: 	
		   I have 9:1 pistons in the rocket, will likely go 50/50 

 on the fuel mixture, but have to see what works best 

 thru some trial and error.


	


That kind of testing should be report to us, Bob.  I'd 

like to know how well the higher compression ratio

engines do with it.  I'm confident with the 8.5:1 engines

because Superior has stepped up to back it.   



So, you see, here is another happy RVer who is using

auto gas with no problems.  We aren't alone, fellas.  



Jim in KY

do not archive

rocketbob(at)gmail.com
Guest

Posted: Sun Jul 09, 2006 4:54 pm Post subject: The TRUTH about MOGAS (very long)

Here's one for the "you're gonna die because you use autogas" folks:



Today's OAT: 87 deg F.  



This morning filled up with three six-gallon jugs of 87 octane gas (not 93, not 91, but 87 octane), pulled the airplane up to the gas pump on our airpark and added 6 gallons of 100LL.  75/25 mix.  Flew to a flyin, ate lunch then did a balloon pop contest and a spot landing contest.  Had a passenger with me.  Flew around the flyin for about an hour, in the pattern mixed in with several spam cans, super cubs, a T-6, PT-19, all in the pattern at 100-120mph (didn't win the spot landing contest but got two out of three balloons for a tie for first place).  After we did that climbed out to 6500 and headed home, and had some fun with some cumulus.  Hottest CHT hit 400 on the climb to 6500.  After leveling off it settled back down to 365.  Oil temp was 202.  In other words, some ideal conditions for vapor lock. 



I'm here to tell you that I survived yet another hot but fun day using autogas, with not even a hint vapor lock and no signs of overheating.



Regards,

Bob Japundza

RV-6 flying, F1 under const.

do not archive

Hopperdhh(at)aol.com
Guest

Posted: Wed Jul 12, 2006 5:56 am Post subject: The TRUTH about MOGAS (very long)

 

  

 Here is something I didn't know until recently.  When the engine's  bore is increased from 4" to 5", the octane required increases by 10  units.  That's from "The Internal Combustion Engine in Theory and Practice  -- Volume II." by Charles Taylor.  (Thanks Jim Baker for recommending this  book.)  Most car engine's bores are well under 4" and the Lyc 360 is 5  1/8".  From the same reference, our 8.7:1 compression ratio looks like more  than 10:1 if the bore were the size of a car engine's.

  

 Those using auto gas should keep this in mind when thinking that the low  compression ratios of aircraft engines should allow us to use low octane  gas.  Your engine may be closer to detonation than you  realize.

  

 Dan Hopper

 RV-7A

chaztuna(at)adelphia.net
Guest

Posted: Wed Jul 12, 2006 6:39 am Post subject: The TRUTH about MOGAS (very long)

Dan

  Thanks for the info. I'm curious however. What is the date of publication of this tome? Also, where might one find a copy?

 Charlie Kuss



 

  	  Quote: 	
		   

  

 Here is something I didn't know until recently.  When the engine's bore is increased from 4" to 5", the octane required increases by 10 units.  That's from "The Internal Combustion Engine in Theory and Practice -- Volume II." by Charles Taylor.  (Thanks Jim Baker for recommending this book.)  Most car engine's bores are well under 4" and the Lyc 360 is 5 1/8".  From the same reference, our 8.7:1 compression ratio looks like more than 10:1 if the bore were the size of a car engine's.

  

 Those using auto gas should keep this in mind when thinking that the low compression ratios of aircraft engines should allow us to use low octane gas.  Your engine may be closer to detonation than you realize.

  

 Dan Hopper

 RV-7A

Hopperdhh(at)aol.com
Guest

Posted: Wed Jul 12, 2006 8:22 am Post subject: The TRUTH about MOGAS (very long)

 

 Charlie,

  

 "The Internal Combustion Engine in Theory and Practice -- Volume II." by  Charles Taylor was published in 1968 by the Massachusetts Institute of  Technology.  I found a copy on Ebay.

  

 Dan

  

  

 In a message dated 7/12/2006 10:41:24 A.M. Eastern Daylight Time,  chaztuna(at)adelphia.net writes:

  	  Quote: 	
		  Dan

 Thanks for the info. I'm curious however. What is the date    of publication of this tome? Also, where might one find a copy?

Charlie    Kuss

    	  Quote: 	
		  

 

Here      is something I didn't know until recently.  When the engine's bore is      increased from 4" to 5", the octane required increases by 10 units.       That's from "The Internal Combustion Engine in Theory and Practice -- Volume      II." by Charles Taylor.  (Thanks Jim Baker for recommending this      book.)  Most car engine's bores are well under 4" and the Lyc 360 is 5      1/8".  From the same reference, our 8.7:1 compression ratio looks like      more than 10:1 if the bore were the size of a car      engine's.

 

Those using auto gas should keep this in mind when      thinking that the low compression ratios of aircraft engines should allow us      to use low octane gas.  Your engine may be closer to detonation than      you realize.

 

Dan      Hopper

RV-7A

tedd(at)vansairforce.org
Guest

Posted: Wed Jul 12, 2006 8:56 am Post subject: The TRUTH about MOGAS (very long)

 	  Quote: 	
		   Here is something I didn't know until recently.  When the engine's  bore is

 increased from 4" to 5", the octane required increases by 10  units.


	


Dan:



This is a rule of thumb that is meant to compare similarly designed engines of

different displacements, such as the O-320 and O-360.  It would be a mistake to

apply it to significantly different engine designs without taking into

consideration other factors.  For example, combustion chamber shape is equally

significant, so that a smaller-bore combustion chamber can require higher

octane than a larger-bore chamber, at the same CR, if its shape is more

conducive to detonation.  One can't simply conclude that one engine requires

higher octane than another simply because its bore is larger.



Tedd McHenry

Surrey, BC

dsvs(at)comcast.net
Guest

Posted: Wed Jul 12, 2006 8:58 am Post subject: The TRUTH about MOGAS (very long)

Also available from amazon.com

 -------------- Original message ----------------------

 	  Quote: 	
		    

 

 Charlie,

  

 "The Internal Combustion Engine in Theory and Practice -- Volume II." by  

 Charles Taylor was published in 1968 by the Massachusetts Institute of  

 Technology.  I found a copy on Ebay.

  

 Dan

  

  

 In a message dated 7/12/2006 10:41:24 A.M. Eastern Daylight Time,  

 chaztuna(at)adelphia.net writes:

 

 Dan

 Thanks for the info. I'm curious however. What is the date  of publication of 

 this tome? Also, where might one find a copy?

 Charlie  Kuss



 

 

 

 

 Here  is something I didn't know until recently.  When the engine's bore is  

 increased from 4" to 5", the octane required increases by 10 units.   That's 

 from "The Internal Combustion Engine in Theory and Practice -- Volume  II." by 

 Charles Taylor.  (Thanks Jim Baker for recommending this  book.)  Most car 

 engine's bores are well under 4" and the Lyc 360 is 5  1/8".  From the same 

 reference, our 8.7:1 compression ratio looks like  more than 10:1 if the bore 

 were 

 the size of a car  engine's.

 

 Those using auto gas should keep this in mind when  thinking that the low 

 compression ratios of aircraft engines should allow us  to use low octane gas.  

 Your engine may be closer to detonation than  you realize.

 

 Dan  Hopper

 RV-7A

Hopperdhh(at)aol.com
Guest

Posted: Wed Jul 12, 2006 3:10 pm Post subject: The TRUTH about MOGAS (very long)

 

 Ted,

  

 Yes, lots of things determine the octane required.  Combustion chamber  shape is certainly one which is very significant.  In fact the open chamber  like our Lycomings, in general, are the least resistant to detonation according  to this book.

  

 All other things being equal, it IS fair to say that a larger bore  engine requires higher octane fuel.  This is not a rule of thumb, but was  determined by a lot of testing.  There are many graphs in this book which  show the data from these tests.  The book admits that there was (is?)  still much to learn about the causes and cures of detonation.  I'm not sure  how much we've learned since then, but I think anything written in  1968 still applies to Lycomings! 

  

 Dan Hopper

 RV-7A

  

  

 In a message dated 7/12/2006 12:58:46 P.M. Eastern Daylight Time,  tedd(at)vansairforce.org writes:

  	  Quote: 	
		  -->    RV-List message posted by: Tedd McHenry    <tedd(at)vansairforce.org>



 	  Quote: 	
		   Here is something I didn't know    until recently.  When the engine's  bore is

 increased from    4" to 5", the octane required increases by 10     units.


	


Dan:



This is a rule of thumb that is meant to compare    similarly designed engines of

different displacements, such as the O-320    and O-360.  It would be a mistake to

apply it to significantly    different engine designs without taking into

consideration other    factors.  For example, combustion chamber shape is    equally

significant, so that a smaller-bore combustion chamber can require    higher

octane than a larger-bore chamber, at the same CR, if its shape is    more

conducive to detonation.  One can't simply conclude that one    engine requires

higher octane than another simply because its bore is    larger.



Tedd McHenry

Surrey,  =========================es  Day                                                     

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flyrv6(at)bryantechnology
Guest

Posted: Thu Jul 13, 2006 8:10 am Post subject: The TRUTH about MOGAS (very long)

  "This is a rule of thumb that is meant to compare similarly designed engines of

 different displacements,"

  

 Ted, you hit the nail more on the head with the term "displacements".  Dan actually said bore size and I am thinking either he meant different or the book was a little skewed based on it's age.  Of course bore size, chamber shape, stroke, piston composition, piston shape, and squish all play an active role in this.  I don't know much about the lycomings, but even with a relatively high compression ratio, you can achieve pretty good dynamics by optimizing the squish and picking the right piston for the application.  Lycomings may not apply since the availability of products is more limited than typical auto engines.

  

 Tim

 ex Auto Machine Shop Owner but did not stay in a Holiday Inn Express last night

 RV-6



  

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