The no-stc thing is indeed a deal killer if you want to fly legally. The logistics thing is different for everyone, I guess. My 1st airplane burned about 5.5 gph, second one about 7.5, this one about 8.5. I have always just used 5 gallon (actually 5.5) cans to haul my gas, 4 of them are good for about 2-1/2 hours flying. Doesn't help on trips but for most of my local flying filling up at home works out just fine. I'm lucky in that I have always owned airplanes for which mogas is a viable choice, and had a handy source of good mogas either right near the airport or on my way to the airport. (but who knows how long that'll be true?)
Just got my gas bill from last month-- 92 octane E-zero was $1.50 a gallon cheaper than the 100LL at my airport, so I'm saving about $12.75 an hour. If I fly 100 hours this year (a conservative estimate), that'll be almost $1300. Looking at it another way, saving $12.75 an hour over the 2,000 hour life of the engine will be enough ($25,500) to not only pay for an engine overhaul at TBO, but also a top overhaul halfway through if required.

hotrod180 wrote: Just got my gas bill from last month-- 92 octane E-zero was $1.50 a gallon cheaper than the 100LL at my airport, so I'm saving about $12.75 an hour. If I fly 100 hours this year (a conservative estimate), that'll be almost $1300. Looking at it another way, saving $12.75 an hour over the 2,000 hour life of the engine will be enough ($25,500) to not only pay for an engine overhaul at TBO, but also a top overhaul halfway through if required.

That makes it worth it! I flew my R-22 Mariner for over 1000 hours on straight mogas from the gas station down the road from my house. When it came time for the engine overhaul the person I sold it to said it was very clean with nothing bad to write home about.

hotrod180 wrote:The no-stc thing is indeed a deal killer if you want to fly legally. The logistics thing is different for everyone, I guess. My 1st airplane burned about 5.5 gph, second one about 7.5, this one about 8.5. I have always just used 5 gallon (actually 5.5) cans to haul my gas, 4 of them are good for about 2-1/2 hours flying. Doesn't help on trips but for most of my local flying filling up at home works out just fine. I'm lucky in that I have always owned airplanes for which mogas is a viable choice, and had a handy source of good mogas either right near the airport or on my way to the airport. (but who knows how long that'll be true?)
Just got my gas bill from last month-- 92 octane E-zero was $1.50 a gallon cheaper than the 100LL at my airport, so I'm saving about $12.75 an hour. If I fly 100 hours this year (a conservative estimate), that'll be almost $1300. Looking at it another way, saving $12.75 an hour over the 2,000 hour life of the engine will be enough ($25,500) to not only pay for an engine overhaul at TBO, but also a top overhaul halfway through if required.

What power setting are you using to get 8.5 GPH with your 180? I guess I like the throttle too much!

29singlespeed wrote:

Bugs66 wrote:.....I believe it has to do with the fuel pump that is added on.. Petterson had an issue and discontinued tests and EAA doesnt list it.....

I have a '67 172H with AVCON conversion and 180hp 0-360-A4M. Peterson told me the same thing BUT when I told him the AVCON conversion allows for 2 different installations he got interested. I sent him copies of my installation and the AVCON approved paperwork that lets you install with or WITHOUT a fuel pump. He told me that since my airplane has a gravity flow fuel system ( no pump ) then it's approved by him and he'll sell me the STC.

EastTexasPilot wrote:

29singlespeed wrote:

Bugs66 wrote:.....I believe it has to do with the fuel pump that is added on.. Petterson had an issue and discontinued tests and EAA doesnt list it.....

I have a '67 172H with AVCON conversion and 180hp 0-360-A4M. Peterson told me the same thing BUT when I told him the AVCON conversion allows for 2 different installations he got interested. I sent him copies of my installation and the AVCON approved paperwork that lets you install with or WITHOUT a fuel pump. He told me that since my airplane has a gravity flow fuel system ( no pump ) then it's approved by him and he'll sell me the STC.

Funny how old threads get resurrected.

My Avcon conversion on my P172D has a fuel pump--it was standard equipment on the P172D. Although I don't always remember to turn it on when switching tanks like the manual says I should, I can tell you because I have an EI FP5L fuel computer, the pressure really drops before the other tank starts flowing. I can't think of any time that I haven't taken off with the fuel pump on, also SOP in the manual, which is a reasonable safety issue to keep the fuel flowing in the event of some other failure.

I frankly don't know what having or not having a fuel pump would have to do with a mogas STC, but it seems to me that since mogas is more subject to vapor pressure issues than avgas, it ought to be the other way around--mogas OK with a fuel pump, avgas only without one. Who knows what intelligence or non-intelligence goes into getting an STC approval?

Cary

robw56 wrote:

hotrod180 wrote:....My 1st airplane burned about 5.5 gph, second one about 7.5, this one about 8.5.....

What power setting are you using to get 8.5 GPH with your 180? I guess I like the throttle too much!

I was wondering the same thing myself!
Then I checked the date on my post (2012) and realized that I was referring to the C150/150TD I owned then.

The numbers are different now, but still valid re mogas savings.
Currently I'm paying $2.94 for 87 octane mogas at the local Cenex / Co-op, and $4.80 for 100LL at my airport.
At a conservative 11 gph, 100% mogas use equals $32.34 per hr vs 52.80 for 100LL-- just over 20 bucks an hour savings.

I like to keep a little lead in the mix, so I actually burn 1 can of 100LL for every 4 cans mogas.
That ration works out to $36.41 per hr -- still a savings of over $16 an hour with the thirsty O-470.

I'd be careful running auto fuel in any airplane with bladders.

The restriction on a gas with a pump is a concern for possible cavitation of the pump, I believe.

MTV

Sorry for resurrecting a 5 year old thread. I was searching for something else and found all these interesting topics. When I saw someone asking why no Peterson mogas STC for the 180hp AVCON conversion I figured I could add some light to the subject for future pilots joining and doing the same thing as me.

hotrod180 wrote:

robw56 wrote:

hotrod180 wrote:....My 1st airplane burned about 5.5 gph, second one about 7.5, this one about 8.5.....

What power setting are you using to get 8.5 GPH with your 180? I guess I like the throttle too much!

I was wondering the same thing myself!
Then I checked the date on my post (2012) and realized that I was referring to the C150/150TD I owned then.

Ahhh it all makes sense now.

mtv wrote: I'd be careful running auto fuel in any airplane with bladders.....

I am vigilant in making sure it doesn't have ethanol, otherwise I don't sweat it.
The previous owner ran mogas for the 17 or so years he owned the airplane, I've been doing it for 2-1/2 (so far)--
and no sign yet of any problems.

hotrod180 wrote:

mtv wrote: I'd be careful running auto fuel in any airplane with bladders.....

I am vigilant in making sure it doesn't have ethanol, otherwise I don't sweat it.
The previous owner ran mogas for the 17 or so years he owned the airplane, I've been doing it for 2-1/2 (so far)--
and no sign yet of any problems.

Alcohol isn't the only additive that MAY attack rubber, but it's certainly the primary concern. There are a lot of seasonal additives that may or may not cause problems. And I'm sure you test every can of gas for ethanol?

MTV

Also, a friend got field approvals to remove the fuel pumps on a number of Avcon converted 170 and 172s. He did so by replacing the fuel line between the fuel selector and the gascolator with a larger diameter line. The original line was too small to reliably flow max fuel for an O-360 in all attitudes. Pretty simple way to get rid of two pumps and some weight.

MTV

mtv wrote:Also, a friend got field approvals to remove the fuel pumps on a number of Avcon converted 170 and 172s. He did so by replacing the fuel line between the fuel selector and the gascolator with a larger diameter line. The original line was too small to reliably flow max fuel for an O-360 in all attitudes. Pretty simple way to get rid of two pumps and some weight.

MTV

I wonder why he wouldn't just use AVCON's instructions instead of going through the FA process?

EastTexasPilot wrote:

mtv wrote:Also, a friend got field approvals to remove the fuel pumps on a number of Avcon converted 170 and 172s. He did so by replacing the fuel line between the fuel selector and the gascolator with a larger diameter line. The original line was too small to reliably flow max fuel for an O-360 in all attitudes. Pretty simple way to get rid of two pumps and some weight.

MTV

I wonder why he wouldn't just use AVCON's instructions instead of going through the FA process?

I would think that if the airframe as originally configured was certified with fuel pumps, like my P172D was, a field approval would be necessary, as the STC for Avcon is pretty sparsely written, from my recollection (my IA has my log books). They may say how to do the modifying of the fuel system, but that doesn't necessarily mean that it's authorized in the STC.

Cary

Cary wrote: I would think that if the airframe as originally configured was certified with fuel pumps, like my P172D was, a field approval would be necessary, as the STC for Avcon is pretty sparsely written, from my recollection (my IA has my log books). They may say how to do the modifying of the fuel system, but that doesn't necessarily mean that it's authorized in the STC.

Cary

Probably because of the serial number. This was approved for serial numbers 17249545 and after

The IA I mentioed was modifying early 172 and 170s which are not covered under that portion of the STC. That part of the STC is good for the mod.....it is part of the STC for those planes. I've forgotten why it wasn't approved for other planes.

He also was getting some 172s increase gross weights, based on the engine, and, I think, T-41 data. GW to 2500 or 2550 as I recall.

MTV

mtv wrote:...... And I'm sure you test every can of gas for ethanol? ...MTV

I buy my mogas 4 cans at a time, and yes, I do test for ethanol every time.

I owned a 1969 with a Bush conversion, CSP. Never worried about weight, always burned 100LL and got 9-10 GPH.

First fell in love with backcountry Idaho with her. Can't imagine that the Avcon would be much different. Smooth flier.
Have fun!

One of the reasons for the electrical fuel pump was that the conversion often used an engine off of a low wing plane and ALL parts supporting the engine had to come along for the STC ride. Always liked having the option of the lecrtric backup.
Was allegedly to be used with low fuel qty because climb angel could put the a low fuel condition with not enough "head pressure for Vx departures" Same reason for the RED lines on the old gauges. BUT with 180hp+CS+10-20 flaps the [my] 170B would essentially lift off in a near "flat" attitude.

Spent LONG hours with Harry Delicker back when putting in his long range tanks.
one of the best aviation information sources especially if you bought him lunch at some small run down country corner Mexican store / "restaurant"

Mine was an early BUSH conversion but put Harry's front mount exhaust.

Still recommend the EXTENDED range tanks over the LONG range tanks.
The extended range tanks match the C-175 fuel system.

Hope I got it straight

Chris C N4650C a few years ago.

I agree with Gary or Cary
Spent $24K on prime [blue printed to my specs] engine + new prop.

Flew according to LYC. recommendations.

Every new passenger it seemed had an new way THEY had been told,
or read, on how to operate MY engine. BUT- it was not their wallet.

Wannabe keepin on keepin on.

No complaints from buyer.