Cessna Anticipates AvGas Demise

M wrote:
Another factor, which only has to do
with economy, is that we pay for fuel in volume (gallons), not
pounds. If Jet A and 100LL are both $4 per gallon, you get more
pounds of jet A with that $4. These two factor combined, diesel
powered Cessna would burn about 30% less $ worth of fuel per hour at
the same power output, assuming JetA and 100LL cost the same per
gallon. That's quite significant. These days it seems that Jet A is
consistently less per gallon than 100LL.


Its also true that the federal taxes on JETA is significantly higher
than AVGAS, thus the price you actually pay is not a lot less than
AVGAS.

On Sat, 06 Oct 2007 01:41:50 GMT, "Vaughn Simon"
wrote in
:


"Larry Dighera" wrote in message
news

I like the idea that there is more energy per pound in Jet A fuel than
AvGas,

Whoa! There is more energy in Jet A per GALLON. Depending on which weight
and BTU averages you are using, Jet A and Avgas come out pretty close on BTUs
per pound. Remember, Jet fuel is heavier than gasoline.

Vaughn


Okay. The point is, that there should be a commensurate increase in
range.

Larry Dighera wrote:
On Sat, 06 Oct 2007 01:41:50 GMT, "Vaughn Simon"
wrote in
:

"Larry Dighera" wrote in message
news
I like the idea that there is more energy per pound in Jet A fuel than
AvGas,
Whoa! There is more energy in Jet A per GALLON. Depending on which weight
and BTU averages you are using, Jet A and Avgas come out pretty close on BTUs
per pound. Remember, Jet fuel is heavier than gasoline.

Vaughn


Okay. The point is, that there should be a commensurate increase in
range.


That depends. Most diesel engines weigh more than similar power gas
engines. So, you may well have less fuel capacity to stay within weight
limits.

Matt

..

I like the idea that there is more energy per pound in Jet A fuel than
AvGas, but I have no idea of the failure modes nor expected TBO and
other performance, operational, and maintenance issues. What should a
pilot expect to find has changed in the Thielert engine equipped C-172
other than higher power available at altitude, increased range, and
fewer refueling options?

The lower fuel burn comes not from the higher energy of Jet-A, but
rather from the higher compression ratio which converts a higher
percentage of the energy to useful work. Diesel comes closer to an
ideal Carnot cycle than gasoline.

wrote:

The lower fuel burn comes not from the higher energy of Jet-A, but
rather from the higher compression ratio which converts a higher
percentage of the energy to useful work. Diesel comes closer to an
ideal Carnot cycle than gasoline.


How much better fuel economy and efficiency would result
if modern internal combustion designs were made easily
available to the GA fleet (versus diesel engines) ?

These new diesel engines employ the latest of modern technology
in terms of materials and design, where our old Lycomings and
Continentals are basically 75 year old technology. Not a
fair (or even logical) comparison IMHO.

On Oct 6, 7:26 am, kontiki wrote:
wrote:

The lower fuel burn comes not from the higher energy of Jet-A, but
rather from the higher compression ratio which converts a higher
percentage of the energy to useful work. Diesel comes closer to an
ideal Carnot cycle than gasoline.

How much better fuel economy and efficiency would result
if modern internal combustion designs were made easily
available to the GA fleet (versus diesel engines) ?

These new diesel engines employ the latest of modern technology
in terms of materials and design, where our old Lycomings and
Continentals are basically 75 year old technology. Not a
fair (or even logical) comparison IMHO.

Turbo diesel auto engines get around 50mpg compared to equivalent
gasoline engines that get around 30mpg. That's apples to apples for
you. Diesel is more efficient. Higher compression buns more of the
fuel and captures more of the thermal expansion in the form of
mechanical piston energy. Basic physics.

On Oct 6, 6:26 am, kontiki wrote:


How much better fuel economy and efficiency would result
if modern internal combustion designs were made easily
available to the GA fleet (versus diesel engines) ?

These new diesel engines employ the latest of modern technology
in terms of materials and design, where our old Lycomings and
Continentals are basically 75 year old technology. Not a
fair (or even logical) comparison IMHO.


If you have seen the BSFC numbers of the latest and greatest
automobile gasoline engines, they're really not better than a
IO-520. Why? because it's a lot easier to optimize a gasoline
engine for fuel efficiency when it's operated at a narrow RPM range
with little power variation. Automobile engines achieve good fuel
efficiency through electronic engine control only because it's much
harder to gain good efficiency across a much wider RPM range and
throttle setting. From a thermo efficiency point of view, the
gasoline aircraft engines designed in the 50s are very good, if
they're leaned properly (which can be easily done with good fuel
injection and EGT instrumentation), I doubt they can get much better
in fuel efficiency regardless of what electronic you put on them.

Diesel engine has better BSFC because they have fundamentally better
thermo efficiency, not because they have fancy electronics.

"Larry Dighera" wrote in message ...

CESSNA TO OFFER DIESEL SKYHAWK
(http://www.avweb.com/eletter/archive...ll.html#196294)
Cessna will offer the 172S Skyhawk with a Thielert turbo diesel engine
with deliveries to start in mid-2008. In an announcement at AOPA Expo
in Hartford, Conn., Cessna officials said the decision to offer the
diesel came after extensive market surveys and flight testing. "The
Skyhawk is already the best-selling, most-flown airplane ever with
more than 43,000 delivered and this option further expands the market
due to the worldwide availability of Jet A fuel," said John Doman,
Cessna vice president of propeller aircraft sales. Cessna will install
the engines at its Independence, Kan., factory under the supplementary
type certificate already held by Thielert.


Yup, gotta pay for the new improved NAS.
JetA power GA aircraft are going to pay more taxes per gallon than the 100LL drivers, so UnkaSam wants more JetA
sales...

On Sat, 06 Oct 2007 20:03:28 +0000, Blueskies wrote:

Yup, gotta pay for the new improved NAS. JetA power GA aircraft are
going to pay more taxes per gallon than the 100LL drivers, so UnkaSam
wants more JetA sales...

The salespeople at AOPA were really cagey WRT the Diesel 172. As best
several of us can figure, this is for the overseas market.

The salesperson did mention, for example, that 100LL was not to be found
in South Africa. I've no idea whether or not this is true, but it seems
to indicate the target market at which this is aimed.

- Andrew

In the short-term, my Cessna 172E has an AutoGas STC and runs just fine
on the stuff. In the long term, I will turn into a dinosaur, fail my
medical, be unable to afford a $100k LSA, and just rock in my chair all day.

;^)

Al
1964 Skyhawk