M20J circa 79. left tank 93octane no ethanol

[I have this friend..]

Fyi

I have this "friend.." 

Runs about 20% 100ll and 80%  93octane no ethanol  automotive fuel in left tank. Take off and landings on right tank with pure 100LL.

He has a simple ethanol tester uses to prove no ethanol.

Cruise at 65 percent power 50 deg rich of peak.  Runs great..  no issues.

(I would never do this of course) but my friend...

Anyone else have a friend with similar experience?  IO360 A36BD?

[Deb]

Do you know if your friend is doing this to avoid putting lead in his engine (or the environment – very commendable), or just trying to save some hard earned money (equally commendable.) If for financial reasons, could he not achieve the same goals flying LOP?

[aaronk25]

Fyi

I have this "friend.." 

Runs about 20% 100ll and 80%  93octane no ethanol  automotive fuel in left tank. Take off and landings on right tank with pure 100LL.

He has a simple ethanol tester uses to prove no ethanol.

Cruise at 65 percent power 50 deg rich of peak.  Runs great..  no issues.

(I would never do this of course) but my friend...

Anyone else have a friend with similar experience?  IO360 A36BD?

The experimental guys do this all the time in that same engine timed at 25 degrees. They find straight 91 (research scale)

octane runs absolutely fine given chts are under 360, preferably 350. The problem comes if the cooling isn't set up right to keep the chts down and they get above 360 they continue to go up until a piston gets melted.

With modern multipoint cht sensors operating, at least for the "cruise" portion of flight is very possible, however the FAA thinks they no best so they don't allow it.

Others also fly LOP, on auto fuel all day long. Just like 100ll is actually way cooler chts to run at peak or LOP.

If timing was reduced to 20d, I'd wage a bet that staying out of the "redbox" alone would most likely eliminate a destructive condition all together.

[Shadrach]

I don't think anyone's ever claimed that an IO360 won't run fine on auto gas most of the time. One of the problems is that unlike 100LL avgas, the formulation of 93oct car gas changes from state to state and season to season.  In a Mooney, I don't think any of it will perform to FAA STC standards. That does not mean it won't run ok (some blends may run great), it means it will not pass the series of tests required to be granted an FAA STC.  Volatility is a big issue, pound for pound, no mogas is never going to match the ability of Avgas to perform under a wide spectrum of conditions that can chang rapidly. Plus, mogas stinks to high heaven...

Running from Maine to the Carolinas in the spring might make for a surprise at altitude if the plane has winter fuel in the tanks.

Edited September 21, 2015 by Shadrach

[N201MKTurbo]

FWIW

back in about '86 they filled up the airport's 100LL tank with premium unleaded car gas. Oddly, after three days I was the first to discover the fuel was the wrong color. The airport owner called the fuel supplier and they confirmed they delivered the wrong product.

I was pretty empty and topped off, so I had about 90% mogas in my tanks. I drained all but 10 gallons back into the underground tank and flew 10 mi to the next airport to get some real AVGAS.

The engine worked normally.

That was with my '67 M20F

[Shadrach]

I am surprised that no one could smell the difference.

[Parker_Woodruff]

The length of time, effort, and FAA risk your friend went to save about $0.30/gallon.

(These numbers assuming 20% mogas / 80% 100LL.  $2.50/gallon 93 octane with no ethanol and $4.00 avgas.)

*Totally not worth $15 saved on a 50 gallon, 800nm trip*.

EDIT: oh wait, there's only 32 gallons in the one tank.  So he's saving all of $9.60 on the 500nm he will be able to travel if he were LOP on that left tank.

Edited September 21, 2015 by Parker_Woodruff

[I have this friend..]

Interesting responses. Happy to hear my friend is not the only one. 

Yes 50 L.O.P.

Where can we get 100 LL for $4.00?

In upstate ny it is $5.30ish.. carolinas it is $4.65-6.69

Miami $8 or $9?

Last flight was closer to a $55 savings.

Plugs seem to fowl less? Could be imagination.

Correct me if wrong but isnt "mogas" technically aviation sanctioned fuel similar in spec to automotive and sold at airports? I thought it was slightly different from gas purchased at pump on street. Not sure as It gas been years since I have seen any non 100ll sold at airport..

 

 

[aaronk25]

I'm not sure anyone here out right said that they have chosen to run a illegal fuel so I think its incorrect to state that someone else here is doing such.  Shadrach brought up some good points.  The problem is how do you know you won't have a problem.  Today's gas hasn't been thought tested and the stuff of the past failed in almost any airplane that didn't have a high wing positive pressure set up back when peterson was actively researching candidate planes such as Mooney.

There is 3 main issues and the 3rd is the least of my concern.

1. Vapor lock-All fuel will boil.  Altitude and heat both promote boiling and at a high enough altitude and/or temp they will boil.  And yes 100ll will boil to but it takes alot of temperature to do it.  Picture this.  Your plane has been sitting on the ramp in the sun and the fuel in the tanks is 100 degrees and you take off loaded with guests to gross weight so the angle of attack is greater and the nose of the plane is high.  Lets take a break and see if you know how your fuel gets to the motor.  In your car it gets pushed out of the fuel tank to the motor via a pump so the fuel has pressure applied to it which lowers its boiling point.  Did you ever find your fuel pump in your airplane wing?  Thats right you haven't cause it aint there.  So back to climbing out with nose up and a hot load of auto fuel.  The only way to get fuel to the nose of the plane, which now is a couple or several feet higher than the fuel level in the tanks is to suck it out.  When fuel is sucked out do you think the pressure on the fuel increase which lessens the chance of boiling or do you think it decreases pressure and increases the chance?  Thats right the way the fuel delivery system in these planes actually increases the chance of fuel boiling in the lines which is what vapor lock is.  How cool would it be if the engine quit at 500 agl........I get it this is for cruse only so don't ever get the tanks mixed up....ya ...right....  100ll is some pretty awesome stuff and so awesome that the cold start issues folks have in the winter is directly related to the 100ll cause it is difficult to get it to turn into vapor when the temperature is low but the trade off is that it shouldn't vapor lock when hot.

2. Octane-  The auto ignition temp of premium motor fuel is somewhere between 360-420ish....if memory serves me correctly and 100ll is like 600 or 700 degress. Anyway there is a hell of a difference between the two and unless your adjusting cowl flaps AND have a accurate every-cylinder-cht monitor and can catch it quickly with in 20 seconds if the fuel does start to pre-ignite, if any of these factors are missing there is a good chance you may turn your engine into a glob of molten metal which most likely won't aid you in landing safely.  

 

3.  There is different standards in auto fuel compared to 100ll.----This is true but I think this is the least of your worries as how many times has your car shut off driving down the road because the fuel was poor or water saturated?  None-most likely.

 

Do I think that Mogas can be operated on safely?  Yes,  but what if something is wrong with the plane and you make a off field landing and a passenger gets hurt?  The negligence will be off the scale.  

 

I also have my doubts that someones first post on this forum, apparently looking for others to endorse their activity as "OK to do" cause others do it hardly has the capability or knowledge of fuel volatility/octane, test for ethanol ect to be experimenting.  Stick with 100ll.  And yes your insurance will still cover you even if you do run the wrong fuel cause insurance also cover stupidity......

 

 

 

Interesting responses. Happy to hear my friend is not the only one. 

Yes 50 L.O.P.

Where can we get 100 LL for $4.00?

In upstate ny it is $5.30ish.. carolinas it is $4.65-6.69

Miami $8 or $9?

Last flight was closer to a $55 savings.

Plugs seem to fowl less? Could be imagination.

Correct me if wrong but isnt "mogas" technically aviation sanctioned fuel similar in spec to automotive and sold at airports? I thought it was slightly different from gas purchased at pump on street. Not sure as It gas been years since I have seen any non 100ll sold at airport..

 

 

[kortopates]

Great post Aaronk25. Even with 100ll we see a number of vapor lock issues. Just as Aaronk25 described, takeoff with a heat soaked engine is a common way to experience it. Another is in climb in the upper teens and above. Some airframes are just more susceptible than others.

The most harrowing I case I've seen was a takeoff from a very short field. The pilot barely cleared the trees by his own account. It was awhile before the the pilot engaged the electric boost, his first reaction was to change tanks without effect. But by the time the boost came on the engine was surging pretty wildly and it actually went into an overly rich condition nearly killing the engine. The only thing that saved him was pulling the power back which immediately reduced his fuel requirements and everything stabilized.

Given the risk of vapor lock even with the proper fuel, I just don't get why someone would want to give up the added protection of the required 100ll fuel to just save a few bucks. We always say aviation is so unforgiving but in this case even if the pilot has an off field landing for unrelated reasons you can bet the FAA's proctoscopic exam will find the unapproved fuel and yank all pilot certificates. And as aaronk25 said I can't imagine plaintiff attorney's not having a field day. Even a minor incident could end up having astronomical exposure.

What I find most interesting from these threads is the wide ranging risk tolerance and perceptions of what apparently constitutes risk in the pilot community. Luckily 2 sigma deviation from the norm like this are pretty rare!.

Sent from my iPhone using Tapatalk

[Guest]

Imagine the conversation the FAA inspector, NTSB investigator and the insurance claims adjuster could have at the crash site.

Clarence

[garytex]

Currently not an issue, but the conversation is interesting as a prelude to a possible true unavailability of 100LL.  Sorting out some of the possibilities, and considering the possible consequences is a good mental exercise. 

[carusoam]

If you had a friend that decided to put unapproved fuel in his certified plane...

You would not be a friend by finding Internet advice and delivering it to him as fact.

You might run out of friends this way, no?

According to one of the posts above, the total saved was $10.

The number of new risks was a few. Vapor issues, sealant issues, piston melting issues were just some.

For proven modifications look for STCs.

There probably isn't a Mooney STC for a reason.  

Messing around with fuel is too easy to make a mistake unless you are a chemist with laboratory equipment.

Flying safely costs some money.  Increasing your risk to save $10 doesn't make enough Cents.

If there was a way to make sense out of this, I suggest we start a crowd funding campaign and persue an MS STC.

Read through the posts, count the number of mechanics that are saying 'Hey, this is a great idea, you should tell your friend it is OK...'  Or 'I do that all the time in my xx:1 compression Lycoming engine'

Melting a piston is an expensive error.  It could lead to an off field landing.

I'm not a mechanic.  I'm a stodgy old pilot of a factory built airplane.

Best regards,

-a-

 

 

[chrisk]

As I recall, lots of planes have an auto gas STC.  From Peterson 

Auto Fuel STCs are approved on 48 different engine types and 100+ airframes including nearly all 80/87 octane engines and the majority of airplanes in which these engines were

installed. Several high compression engines are also approved for the use of 91AKI auto fuel including the 180 horsepower 0- 60 and the 115hp (or less) 0-235-L2C.

So,  I don't buy that you will instantaneously melt your engine.  And specifically the O-360 used in the M20C/G has a mogas STC for other air frames.  

And also from Peterson

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 carburetor. 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

 

And since I have a turbo Mooney, I would be very reluctant to run Mogas in it.  Having said that, it is a low compression engine when operated below 30 inches and at low altitude (5000 feet).  If I thought my life depended on getting some where, I'd give it a try.   Short of experiencing a coup d'e tat on a small Caribbean island, I can't imagine a case where I would give it a try.  

[Shadrach]

It really has very little to do with "engine damage"  High compression is a relative term.  My IO360 is high compression for an aircraft engine at 8.7 to 1 and would run fine on 93 pump gas with 10% ethanol (until the booze destroyed all of o-rings, hoses and gaskets).  It's mostly about volatility.  However, detonation does become an issue with the more high strung engines like the GTSIO520 that's putting out nearly 20% more HP per cubic inch.

[aaronk25]

As I recall, lots of planes have an auto gas STC.  From Peterson So,  I don't buy that you will instantaneously melt your engine.  And specifically the O-360 used in the M20C/G has a mogas STC for other air frames.  

And also from Peterson

 

And since I have a turbo Mooney, I would be very reluctant to run Mogas in it.  Having said that, it is a low compression engine when operated below 30 inches and at low altitude (5000 feet).  If I thought my life depended on getting some where, I'd give it a try.   Short of experiencing a coup d'e tat on a small Caribbean island, I can't imagine a case where I would give it a try.  

You will melt a piston if you let temps get over 360d in a io360 with 8.7 to one compression Pistons if you don't know what your doing. I've rode in a experimental that has the same 200hp lycoming as a J model. It's amazing how sensitive the engine is to small mixture adjustments.

Absolutely positively you will 100% melt a piston if it is flown with even a little disregard to the "Red box" whe operating on mogas.

Remember mogas is on a octane research scal not motor scale. If 91 octane (reasearch)mogas was compared to 100ll it would be around 86 octane.

Basically what happens when at 70% power is 100ll might have chts around let say 330 and mogas will be at 350. The problem is and I've witnessed it, mogas is already starting to pre-ignite ahead of the spark but only very lightly which is why the chts are slightly elevated compared to 100ll. This is harmless and most modern auto engines run in the exact same mode trying to extract maximum mileage from the fuel. Let say your running at 350cht (auto fuel) 9.6gph 70% power right at peak egt and the mixture richens up to 10gph and it put the engine at 15rop. In a minuet the chts will be at 360 another min they will be at 390 another minuet they at 425 and I'm guessing from this point, but you get the picture.

If the same enriching was done with 100ll chts might climb 20d the stay put.

The problem is the harder the engine is run the more residual heat left over in the cylinder from the last power stroke. Auto fuel just can withstand partially igniting before the spark. Ones it starts prematurely igniting a tremendous amount of heat is generated which leaves the piston and cylinder hotter for the next batch of fuel to ignite even sooner. At this point it's not a run away where it will "diesel" or completely ignite without a spark but you a couple mins away from that.

Now if the cht rise is recognized quickly going 50lop or 150 or more rop stops it immediately. But even with a jpi 830 that flashes there are many distractions and quite frankly more important pilot duties to be monitoring than starting at you engine monitor.

The other 180hp engines that are stcd are fine as they just don't create as much heat soak in regards to internal components so auto fuel is ok per stc.

The reason I believe we don't have auto fuel is the FAA making it cost prohibitive. All we need is liquid cooled cylinder heads and dis redundant in tank fuel pumps and then we could use 87 octane and knock sensors.

Oh well.....

[aviatoreb]

 If I thought my life depended on getting some where, I'd give it a try.   Short of experiencing a coup d'e tat on a small Caribbean island, I can't imagine a case where I would give it a try.  

Not me!  If I were on a Caribbean island in a coup with my turbo Mooney, I would use my tow-bar to fend off the government troops before I would run mogas in my beautiful engine.

[Shadrach]

Basically what happens when at 70% power is 100ll might have chts around let say 330 and mogas will be at 350. The problem is and I've witnessed it, mogas is already starting to pre-ignite ahead of the spark but only very lightly which is why the chts are slightly elevated compared to 100ll. This is harmless and most modern auto engines run in the exact same mode trying to extract maximum mileage from the fuel. Let say your running at 350cht (auto fuel) 9.6gph 70% power right at peak egt and the mixture richens up to 10gph and it put the engine at 15rop. In a minuet the chts will be at 360 another min they will be at 390 another minuet they at 425 and I'm guessing from this point, but you get the picture.

I do not believe that preignition is likely in an IO360 at the CHTs you are talking about.  93 oct car gas has an auto ignition temp of around 400 Celsius, avgas is around 500 Celsius. Avgas gives a higher margins against preignition, but both are well within what is needed to operate normally at the CHTs you mentioned. the elevated CHTs you're seeing are likely due to an increase in peak internal cylinder pressure caused by a more rapidly moving flame front, not preignition. 

I'd be curious to see the differences mpg with the 2 fuels. I have a feeling that mogas does not make as much power per gallon as 100LL.

 

 

I have a vehicle that came stock with 11.5 CR and it does not suffer from pre-ignition on pump gas.

Edited September 22, 2015 by Shadrach

[carusoam]

the technical hurdles...

1) fuel chemistry leading to challenges with polymeric pieces like seals, floats or sealants.

2) Lacking resistance to evaporation prior to getting into the engine.  Bubbles in place of liquid fuel is a big challenge.

3) resistance to preignition leading to piston melting.  Aluminum pistons just aren't very durable. Under the wrong conditions they go away quickly.

4) keeping the 100LL fuel flowing has been proven challenging for some Mooney pilots.  Adding to the challenge is harder to sell.  Additional training and placards are normal for this.

5) If you are seeing your engine being used in a different plane with an STC, a good portion of the work has been done for you.  Focus on getting an STC for your plane.  It's like a marathon, you have to go the whole distance for it to count.

A magnet on the back of the car that says 13.1 doesn't get readily confused with one that says 'I ran the Boston marathon'.

6) good news... Most of our engines have been proven to not need the LL part of the 100LL.  The POH of the IO550 lists this clearly under fuel requirements.  Unfortunately the 100 octane is as expensive as 100LL and not as readily available...

7) Making assumptions like...It is done in this plane, under this STC, it should be good in my Mooney because...

8) simple potential error.  Draining a small amount from both tanks using the fuel selector as standard practice during preflight. Forgetting to put the selector to the 100LL tank prior to T/O.  High power...

9) the potential costs have been outlined from...

-simple fuel disruption from vapor.  Summer at high altitudes could be problematic.

-melted pistons from preignition

-less power per gallon

-lack of valuable savings

-ease of making a potential error

To the OP.  Want to pursue an STC?  There are a couple of people here that have the skill for the documentation writing and submittal side... You may have to come out from behind the curtain to do it...

Just trying to help out.  I would love to be proven able to fuel my IO550 with 2-buck gas...

best regards,

-a-

Edited September 22, 2015 by carusoam

[aaronk25]

Mpg is exactly the same but once over approx 70% power it take more mogas to make the same speed, but this is only a 30 second sample as chts rise quickly.

You know this but others may not; autos run at a cht temp of 190-210f. Airplanes at 280-4xx.

I can tell you that auto fuel runs good at lean power settings ex (peak egt or lop or even 20rop,) all day long at 55%, but when approaching 65% power it needs to be peak to lean of peak to not, let say experience rapid cht rise. If running at 75%-80% better be at 40-50lop. At those numbers chts will remain level and consistent.

If outside of those perimeters temps exponentially increase.

I doubted the pilot and he actually put the mixture in the red box and I could hear a faint yet detectable da..da.da at the rate of a machine gun, but quieter at the same time egt dropped and cht rose rapidly. Egt drops because the fuel started burning sooner so the exhaust sensor picked up less heat.

I'm sure the internal surfaces inside the cylinder wall and piston, spark plug assembly are a lot hotter than the cht probe is picking up even at the start of the following intake stroke.

All I can tell you is you can do anything you want with the mixture even run in the middle of the redbox and the temps will rise relevativly slowly like they would with 100ll but as soon as you get to 355-360cht the rate in which the chts rise is a lot faster and triples in rate by the time it gets to 400 and at that point, inside the cockpit you can here it pinging.

[dmc]

For what it's worth I run mogas frequently in my 225hp Debonair.  But I do have a STC for it, all it amounted to was adding some stickers next to my fuel tanks.  I have not noticed any smell, or any other difference, except cost.  I can buy Rec 90 fuel here in Florida that is ethonal free, and buy mogas at airports when available.  It usually saves me about a dollar a gallon.

 

[carusoam]

Great data point DMC.

Any idea what the STC cost for your plane?

Any altitude or other restrictions?

Best regards,

-a-

[dmc]

It was around $400 for the STC and the IA to send in the paperwork. There are no restrictions.  

[aaronk25]

I'd love to have a mogas STC. I wish we had the option of going upto that motor in a J. It all come down to how much HP can be squeezed out of a cylinder. The J puts out 50hp per cylinder compared to 37.5hp. There is a slight difference in cubic inch size but it's a good representation.

[dmc]

The IO 470J in my debonair has a compression ratio of 7-7.5, not sure the exact number.  It was designed to use the old 80 octain aviation fuel.  I can burn 87 ethanol free gas, but 90-91 is generally all that is available.  I burn around 11.5 to 12 gph to get 150 knots.  160 knots is all I can get around 4500' and ROP.  When I was looking at planes to buy the F & J money's were defiantly on my list.  I just found a nice Debonair first, and being able to burn mogas helped get the fuel cost down some.  

And as I said, I can tell no difference in what fuel I'm using.  I have been told that mogas is not good to let sit in the tank for long periods of time.  But I try to fly regularly.  And there is always some 100LL in there due to availability.