VAF Forums

VAF Forums (https://vansairforce.net/community/index.php)
-   RV General Discussion/News (https://vansairforce.net/community/forumdisplay.php?f=2)
-   -   Mogas vs. 100LL? (https://vansairforce.net/community/showthread.php?t=174063)

TXFlyGuy 08-10-2019 05:51 PM

Quote:

Originally Posted by Pilot135pd (Post 1365594)
The previous owner/builder flew my plane for 400+ hours with 100LL in the right tank for takeoff and landings and 82 non-ethanol in the left tank for when he’s in cruise.

I’ve been doing the same but using 91 non-ethanol. I’ve done touch and goes on 91 with no issues except twice already if I land on 91 and shut down when I go to start it has a crazy misfire until I suppose the fuel lines get full of fuel (about 15 seconds) then it settles down to a smooth idle as normal.

Lately prices for 100LL are about the same as 91 non-ethanol so I don’t mess with it just to save $4 or $5 per tank load.

After the state tax rebate, 93UL is $2.39/gallon. Avgas here is $4.25-$4.50/gallon.

Burned 89 Octane pump gas in my C-172 for hundreds and hundreds of hours. Not only did the engine run so much better, but we saved $$$ on the gas!

We are not concerned about Ethanol, as our fuel line and tank sealant is chemical/alcohol tolerant.

Pilot135pd 08-10-2019 06:07 PM

100LL in East Texas is just $3.60 and the airport is just 15 minutes away while 91 Non-Ethanol is $3.48 and is 45 minutes away, so not worth the hassle. I do have for my convenience a 55 gallon barrel at home so I can fill up at the airport then empty at my house so I?m not flying around heavy with full tanks. https://www.facebook.com/49032794805...695494&sfns=mo

Capt 08-10-2019 06:11 PM

We can only dream of fuel being that cheap!
Avgas can be around $12 gallon in the more remote places outback!
I run a 25% 98 'shandy' in the cooler months, engines runs just fine:)

TXFlyGuy 08-10-2019 07:22 PM

It's not just a cost issue, but the big factor for us is the engine was designed to burn 93UL fuel.
Much cleaner, longer life oil and plugs too.

TXFlyGuy 08-13-2019 11:10 AM

Just found 93UL Ethanol free gasoline, about 3/4 mile from my house! The price? $7.00/gallon.

gmcjetpilot 08-13-2019 11:11 AM

Quote:

Originally Posted by TXFlyGuy (Post 1364815)
The benefits of burning 93 Octane pump gas:

1. $2.80/gallon vs. $5.00/gallon for 100LL. [False Econ when your engine flames out due to vapor lock]
2. No lead, so your engine burns much cleaner. [Lead increases Octane and Lubrication]
3. Longer spark plug life. [No, Lead can be cleaned from plugs with pick, blast good to go]
4. Longer engine oil life. [Doubt that (without data) especially if flame out due to vapor lock and forced landing is less than successful]
5. No ugly exhaust smudge down the side of your cowling.[You will not eliminate streaks from oil or exhaust]

We found a good means of transporting fuel here:

Avgas has a lower and more uniform vapor pressure than automotive gasoline so it remains in the liquid state despite the reduced atmospheric pressure at high altitude, thus preventing vapor lock

Only for LOW compression engines and need to have excellent cooling to avoid vapor lock. STC for Motor-Gas still results in vapor lock issue. When I say vapor lock I mean engine stops running. RV cowls are compact and hot.

Ethanol and Alcohol can cause swelling of seals in fuel system and loss of power.

TXFlyGuy 08-13-2019 11:24 AM

Well...trying to remember the last time we had vapor lock with a fuel injected engine...never is the answer.

We run Reformulated Gasoline here year round. The RVP is maxed at 7.8. For 100LL, the max allowed is 7.0, although the numbers I see more often are in the 5.0 to 6.0 range.

My engine was designed for lead free gas. It will burn cleaner, so longer life oil and plugs is just a fringe benefit.

If there is oil streaking down my fuselage, it will be due to an oil leak. If there is an exhaust smudge on the cowling, the mixture is overly rich.

My C-172 ran for 100's and 100's of hours, all the way up to the low teens on 89 Octane pump (auto) gas. Vapor lock? Never.

I guess I have just been lucky? Maybe all those who burn mogas in their RV's are just lucky too? I honestly don't know.

edit: I do have a friend who likes burning the dreaded-leaded, simply because that is the only way he gets that "50 Mission" exhaust stain, just like a real P-51.

airguy 08-13-2019 02:01 PM

Quote:

Originally Posted by gmcjetpilot (Post 1366292)
Avgas has a lower and more uniform vapor pressure than automotive gasoline so it remains in the liquid state despite the reduced atmospheric pressure at high altitude, thus preventing vapor lock

Only for LOW compression engines and need to have excellent cooling to avoid vapor lock. STC for Motor-Gas still results in vapor lock issue. When I say vapor lock I mean engine stops running. RV cowls are compact and hot.

Ethanol and Alcohol can cause swelling of seals in fuel system and loss of power.

It can be done, it's not impossible and it's not even as difficult as you make it out to be.

Those who say something is impossible should not mess with those that are doing it.

skylor 08-13-2019 02:06 PM

High Wing
 
Quote:

Originally Posted by TXFlyGuy (Post 1366296)
Well...trying to remember the last time we had vapor lock with a fuel injected engine...never is the answer.

We run Reformulated Gasoline here year round. The RVP is maxed at 7.8. For 100LL, the max allowed is 7.0, although the numbers I see more often are in the 5.0 to 6.0 range.

My engine was designed for lead free gas. It will burn cleaner, so longer life oil and plugs is just a fringe benefit.

If there is oil streaking down my fuselage, it will be due to an oil leak. If there is an exhaust smudge on the cowling, the mixture is overly rich.

My C-172 ran for 100's and 100's of hours, all the way up to the low teens on 89 Octane pump (auto) gas. Vapor lock? Never.

I guess I have just been lucky? Maybe all those who burn mogas in their RV's are just lucky too? I honestly don't know.

edit: I do have a friend who likes burning the dreaded-leaded, simply because that is the only way he gets that "50 Mission" exhaust stain, just like a real P-51.

One minor word of caution: Cessna 172's are not very prone to vapor lock because the high wing fuel tank provides good head pressure to the fuel pump or carburetor. Low wing aircraft and steep climb angles, on the other hand, can more readily develop vapor lock issues . Some folks running auto fuel in their RV's have installed electric fuel pumps at or near each wing root to help ensure positive pressure and low vapor enter the pumps under conditions conducive to vapor lock.

Skylor

Mark33 08-13-2019 04:47 PM

Quote:

Originally Posted by gmcjetpilot (Post 1366292)
Avgas has a lower and more uniform vapor pressure than automotive gasoline so it remains in the liquid state despite the reduced atmospheric pressure at high altitude, thus preventing vapor lock

Only for LOW compression engines and need to have excellent cooling to avoid vapor lock. STC for Motor-Gas still results in vapor lock issue. When I say vapor lock I mean engine stops running. RV cowls are compact and hot.

Ethanol and Alcohol can cause swelling of seals in fuel system and loss of power.

Adding just a small amount of AvGas to MoGas will change the specific-gravity of the mixture which will lower the vapor pressures quite a bit. As an example, a 90/10 (MoGas/AvGas) blend will bring the total vapor pressure down very close to the vapor pressure as pure AvGas.

TXFlyGuy 08-13-2019 04:50 PM

Quote:

Originally Posted by skylor (Post 1366342)
One minor word of caution: Cessna 172's are not very prone to vapor lock because the high wing fuel tank provides good head pressure to the fuel pump or carburetor. Low wing aircraft and steep climb angles, on the other hand, can more readily develop vapor lock issues . Some folks running auto fuel in their RV's have installed electric fuel pumps at or near each wing root to help ensure positive pressure and low vapor enter the pumps under conditions conducive to vapor lock.

Skylor

I agree. Our low wing configuration is all gravity feed to the center tank. The dual pumps are located at or near the lowest part in the fuel line plumbing, right at the center tank. There should always be positive pressure to the pump (s).

TXFlyGuy 08-23-2019 05:39 PM

Question for you engine tuners...as we plan to burn both 93U E10 and 100LL, with the ECU being programmed only for 93U, what will the default program do when burning 100LL? Will it burn richer than the Mogas?

cdeerinck 08-23-2019 05:55 PM

Just a data point
 
Just a data point here. I was in Davis, CA two days ago.
At the airport (EDU) the price of 100LL was $4.07 ($4.02 if pre-paid), and the price for 87 at the pump was $3.87.

I was suprised at only a 20 cent spread between the two.


TXFlyGuy 08-23-2019 05:58 PM

Quote:

Originally Posted by cdeerinck (Post 1368827)
Just a data point here. I was in Davis, CA two days ago.
At the airport (EDU) the price of 100LL was $4.07 ($4.02 if pre-paid), and the price for 87 at the pump was $3.87.

I was suprised at only a 20 cent spread between the two.


Wow...100LL is $4.50/gallon here in North Texas.

Pilot135pd 08-23-2019 07:34 PM

Quote:

Originally Posted by TXFlyGuy (Post 1368831)
Wow...100LL is $4.50/gallon here in North Texas.

Fly 15 minutes east and its just $3.69 in Greenville.


All times are GMT -6. The time now is 04:56 AM.