AvGas vs. Regular gas for Pawnee?

the 250HP STC for the O-540 engine does not change RPM limits or approved
propellers from the original Type Certificate Data Sheet. It does allow the
use of a different piston resulting in higher compression.

We run "straight pipes" and have noticed no difference in sound.
We also changed to the lighter weight propeller that is approved on the TCDS
And a change to the SkyTec starter.

We have noticed a difference in climb power and resulting rate of climb. It
is an E-Ticket Ride for the 1-26 pilot.. his 10knt vario is pegged all the
way. We've noticed about a 150-200ft rate of climb increase for Grob 103s
and SGS 2-33s with two on board.

BT

"Bob Korves" bkorves@winfirstDECIMALcom wrote in message
. 44...
"Frank Whiteley" wrote in
ups.com:

I should mention that since we had no autogas option on the Pawnee D
model, we went with the 250HP STC also on our spring rebuild and a new
prop. Result appears close to 100fpm better climb on same fuel burn,
or about one more tow per tach hour.

Frank


Frank,
Is the 250HP conversion louder? Higher RPM? Or, maybe just more
compression and a bigger prop?
-Bob Korves

Synopsis from our chief tow pilot

"Per Howard Kron's current STC (which I bought and is our basis):
Higher compression pistons (but not actually THAT high; 90/96 or
100LL required); RPM max still 2575, same as 235; prop replaced due to
hub damage ..... which was not previously
picked up, and Factory New prop pitched to the original factory 84-52
(had been whacked back to ~49 pitch).

Net effect, much stronger, climbs like a raped ape. The AirCare
twicepipes (i.e., dual exhaust, NO!! mufflers) STC probably helps
significantly, too. In our operation, 65-68kts TAS is right at redline.
If anyone wants faster, they'll climb slower, owing to
too-flat AOT, and probably have to throttle back to stay legal."

I recall some discussion that the 250 STC is probably a better option
than the 260 (we couldn't find a core), as the 260 has a jump in fuel
burn for the extra 10hp. Apparently a lot of the 260hp cores are on
those air boats we all saw in Louisiana and Mississippi after Katrina,
with no maintenance records and a lot of swamp water exposure.

Frank Whiteley

Very subjective to say it's noticeably louder though it sounds
healthier and a little different than it did before. Some is prop,
some is exhaust.

Frank

Very subjective to say it's noticeably louder though it sounds
healthier and a little different than it did before. Some is prop,
some is exhaust.

Frank

We burned auto gas in 235 Pawnees 150 Super cub and 230 hp C-182e for
20 years and an estimated 15,000+ hours .

Up side:
We never had an engine that did not make it to TBO. ( At least 8
engines that I can recall)
We had 4 mid life cylinder changes do to cylinder head cracks. (4
cylinders total!)
We saw no difference in performance over 100ll.
No- lead fouling and build up in spark plugs.
As a conservative estimate, we burned over 240,000 gallons with an
average savings of 1.50 per gallon ( when I figure the off road gas tax
refund) is roughly $360,000.00 over
20 years. This is about what my fleet of 8 aircraft is worth today.

Down side:
Mo gas stinks.
Burns dirty. Leaves black soot on belly instead of gray.
Some times it is difficult to get a fuel company to agree to sell it
for the use in aircraft.

I had to switch back to AV gas last year because in California MTBE
fuels are outlawed
and Alcohol based fuels are not approved for airplanes ( alcohol
suspends water).

It was a nice run while it lasted.

I should mention that we operate from a near sea level, 2000 ft runway
and find that 235 HP is quite adequate.

Rex Mayes
Williams Soaring Center, Williams Ca
(formerly Lagoon Valley Soaring, Vacaville Ca)

Nevada still has real auto gas, at least in Douglas County (Minden).

Has anyone tried using water to remove the alcohol in California gas? To do
that, you'd need to agitate the fuel water mixture, the alcohol has a higher
affinity to water than to gasoline, so comes out of suspension in the gas
and joins the water.

Drain water/alcohol from bottom of tank and what remains should be usable
gasoline.

bumper
"Rex" wrote in message
ups.com...
We burned auto gas in 235 Pawnees 150 Super cub and 230 hp C-182e for
20 years and an estimated 15,000+ hours .

Up side:
We never had an engine that did not make it to TBO. ( At least 8
engines that I can recall)
We had 4 mid life cylinder changes do to cylinder head cracks. (4
cylinders total!)
We saw no difference in performance over 100ll.
No- lead fouling and build up in spark plugs.
As a conservative estimate, we burned over 240,000 gallons with an
average savings of 1.50 per gallon ( when I figure the off road gas tax
refund) is roughly $360,000.00 over
20 years. This is about what my fleet of 8 aircraft is worth today.

Down side:
Mo gas stinks.
Burns dirty. Leaves black soot on belly instead of gray.
Some times it is difficult to get a fuel company to agree to sell it
for the use in aircraft.

I had to switch back to AV gas last year because in California MTBE
fuels are outlawed
and Alcohol based fuels are not approved for airplanes ( alcohol
suspends water).

It was a nice run while it lasted.

I should mention that we operate from a near sea level, 2000 ft runway
and find that 235 HP is quite adequate.

Rex Mayes
Williams Soaring Center, Williams Ca
(formerly Lagoon Valley Soaring, Vacaville Ca)

I think we may be on the wrong track here. If water is suspected in a cars
fuel system, you add ethanol to get rid of it. The alcohol combines with
the water and then with the gasoline. With enough ethanol present, the
water/ethanol mixes with gasoline and is burned away.

It used to be when there was no ethanol in gasoline, water would condense in
the tanks and freeze in cold weather blocking the fuel system. You could
buy cans of "fuel anti-freeze" (ethanol) at auto parts stores to get rid of
the water. Now all auto fuel contains some ethanol anyway so no need to use
the stuff.

As I understand it, the reason ethanol in airplane fuel is bad is that it
dissolves aluminum and makes elastomer seals in the fuel system swell until
leaks appear. A couple of tries to burn straight ethanol back in the 1970's
resulted in badly damaged airplanes.

Bill Daniels


"bumper" wrote in message ...
Nevada still has real auto gas, at least in Douglas County (Minden).

Has anyone tried using water to remove the alcohol in California gas? To
do
that, you'd need to agitate the fuel water mixture, the alcohol has a
higher
affinity to water than to gasoline, so comes out of suspension in the gas
and joins the water.

Drain water/alcohol from bottom of tank and what remains should be usable
gasoline.

bumper
"Rex" wrote in message
ups.com...
We burned auto gas in 235 Pawnees 150 Super cub and 230 hp C-182e for
20 years and an estimated 15,000+ hours .

Up side:
We never had an engine that did not make it to TBO. ( At least 8
engines that I can recall)
We had 4 mid life cylinder changes do to cylinder head cracks. (4
cylinders total!)
We saw no difference in performance over 100ll.
No- lead fouling and build up in spark plugs.
As a conservative estimate, we burned over 240,000 gallons with an
average savings of 1.50 per gallon ( when I figure the off road gas tax
refund) is roughly $360,000.00 over
20 years. This is about what my fleet of 8 aircraft is worth today.

Down side:
Mo gas stinks.
Burns dirty. Leaves black soot on belly instead of gray.
Some times it is difficult to get a fuel company to agree to sell it
for the use in aircraft.

I had to switch back to AV gas last year because in California MTBE
fuels are outlawed
and Alcohol based fuels are not approved for airplanes ( alcohol
suspends water).

It was a nice run while it lasted.

I should mention that we operate from a near sea level, 2000 ft runway
and find that 235 HP is quite adequate.

Rex Mayes
Williams Soaring Center, Williams Ca
(formerly Lagoon Valley Soaring, Vacaville Ca)

"Bill Daniels" wrote in message
...
I think we may be on the wrong track here. If water is suspected in a cars
fuel system, you add ethanol to get rid of it. The alcohol combines with
the water and then with the gasoline. With enough ethanol present, the
water/ethanol mixes with gasoline and is burned away.


A common method to test gasoline for presence of alcohol is to put a small
amount of water, about 10% by volume, in a test tube or similar container.
Add suspect gasoline and shake. If the water level appears to rise, it's due
to alcohol coming out of solution with the gasoline and joining with the
water. If there's no alcohol, the water level remains the same.

bumper

That's what we are running also Frank.. but we changed from the 1A200
propeller to the 1P235 propeller, both listed on the TCDS for the PA-25 with
the O-540 engine. The 1P235 is lighter in weight and also provides an
additional 60fpm climb rate at max GW. We are running about 1250 lbs below
Max GW in our tow configuration. The old propeller was totaled in the prop
strike which drove us to a rebuild on the engine. BT

"Frank Whiteley" wrote in message
oups.com...
Synopsis from our chief tow pilot

"Per Howard Kron's current STC (which I bought and is our basis):
Higher compression pistons (but not actually THAT high; 90/96 or
100LL required); RPM max still 2575, same as 235; prop replaced due to
hub damage ..... which was not previously
picked up, and Factory New prop pitched to the original factory 84-52
(had been whacked back to ~49 pitch).

Net effect, much stronger, climbs like a raped ape. The AirCare
twicepipes (i.e., dual exhaust, NO!! mufflers) STC probably helps
significantly, too. In our operation, 65-68kts TAS is right at redline.
If anyone wants faster, they'll climb slower, owing to
too-flat AOT, and probably have to throttle back to stay legal."

I recall some discussion that the 250 STC is probably a better option
than the 260 (we couldn't find a core), as the 260 has a jump in fuel
burn for the extra 10hp. Apparently a lot of the 260hp cores are on
those air boats we all saw in Louisiana and Mississippi after Katrina,
with no maintenance records and a lot of swamp water exposure.

Frank Whiteley