It amazes me what people will put up with to burn kerosene.   .82
lb/(hp-hr) and they talk like its the greatest thing since sliced
bread. 19 gph!  compared to 11.5 running lean with the IO-540. The
world really really needs a heavy-fuel-burning rotary! And this
article - is Amy smart enough to realize that if the CG difference
makes the plane feel so much different than her IO-540 RV-10, it
might mean there could be an aft CG issue with 4 people and bags?
Might that be something to discuss in a flight review article?

David Bonorden

I would never buy one. Diesel fumes stink and they are
carcinogenic. Packard figured that out in 1930"s. The power to
weight ratio sucks.

Diesel should only be used in trucks and ships. The only reason it
is popular in European cars is the tax is a dollar a gallon less.
If they taxed it as high as gasoline ($7 or$ 8 gallon) it would
seriously affect the European economy.


----------------------------------------------------------------------------





C172 gasoline verses C172 diesel data from the Cessna web site.

Diesel fuel is a pound heavier than gasoline. Gas is six pounds per
gallon and diesel is 7 pounds per gallon.

44.6 gallons of diesel weighs 312 pounds of fuel.

Max useful load on a Diesel C172 is 742 pounds. Subtract the full
fuel weight and you get 430 pounds. Range is 588 nm. 85% power is
132 HP. Cruise speed  at 85% power is 118 kts or 5 hours.


8.9 gallons an hour or 62.5 pounds per hour. BSFC is therefore .47.
Not a lot different than a fully leaned Mazda rotary. And typical
for a diesel engine running near full power.

How can this be? Everybody knows that diesel cars get much better
mileage than gasoline powered cars. The fact is diesel engines
running near full power are not much better than gasoline engines
based on a HP per pound of fuel burned. See the attached chart.

A leaned Mazda rotary at 132 HP would be about the same BSFC but
the gallons per hour would be higher at 62.5/6 or 10.4 gallons per
hour.

A turbo compound rotary on the other hand would be down in the
below .4 range or about the same as a truck diesel running at 50%
power.

------------------------------------------------------ The numbers
for a stock Lycoming powered C172 are:

56 gallons of gasoline weighs 336 pounds of fuel. Max useful load
is 758 pounds. Subtract the full fuel weight and you get 422
pounds. Range is 580 nm. 80% power is 128 HP. Cruise speed at 80%
power is 122 Kts or 4.8 hours.

Four kts faster than the diesel.

11.8 gallons an hour or 69.6 pounds per hour. BSFC is therefore .54
which is a typical for a Lycoming rich of peak.

It would take a long time to pay for the extra $15,000 you will pay
for a diesel powered Cessna 172.

Not to mention you are required to throw the diesel away at 1200
hours if it does not pass detailed inspection. No overhaul
allowed. If it does pass 1200 hour detailed inspection you are
required to throw it away at 2400 hours. No exceptions.

At 100 hours a year that is 24 years. At that point the Mercedes A
class diesel engine will probably no longer be available so the air
plane, in theory, will be worthless. One would have to replace the
engine now certified in the Mercedes A class diesel powered Cessna
172 with some other engine and obtain an FAA one time STC.

I don't see it.

Do you want to tow or do you want to go?

Paul Lamar A hobbyist doubt: if the density of Diesel fuel, the
weight per volume, is higher: would this mean that in a liter of
Diesel fuel there are more Carbon and Hydrogen molecules to be
burnt, and thus, the power density of fuel is better, a liter of
Diesel yields more heat when burnt, this adding to explain the
better SFC of Diesels in terms of gr/kW/hr, besides the better
thermal efficiency from the much higher Compression Ratio, or this
was taken into account in Diesel vs Gasoline SFC figures?

I've learned from this e-mail about the meaning of 'Thermal load'
inside an Internal Combustion Engine, HP per surface of combustion
chamber, and MEP, I remembered having read about the worries of
the early Air-Cooled Wankel Engine designers about increasing CR
and Power, because of the dangers of thermal load (on bearings and
shafts?), and on the lubricating oil film, but the chart you added
indicates an extremely low thermal load for the only RCE on it, a
Mistral. Is this because of the poor MEP of Wankel, or for other
reasons?

The high surface to volume ratio of Wankel RCE combustion chamber
was blamed for the improvable fuel economy, but the surface/volume
ratio in the time of top compression may not be the same during
the process of expansion, where the working chamber volume
increases, both in the irregular shaped Wankel and in the classical
cylinder. How does the plot of surface/volume ratio changes from
'TDC' to 'BDC' compare in a Wankel versus a reciprocating engine?
Somebody to forward here a chart about this? Is there a safe way,
safe for the lubricating oil film, the bearings, and the shaft, for
increasing the housing and/or Rotor working surface temperatures, a
condition that was shown improving fuel economy and cleanliness  of
exhaust gases? Some tested an Iron housing, with improved results
in SFC and exhaust gases over Aluminum, but I've read nothing about
differences in thermal dilatation between housing and rotor when
both are made of iron, and if this makes possible having the engine
seized when overheated. Thanks have a nice season. Best regards.
Salut † Jose Gros-Aymerich  Madrid, Spain

PS: the Napier was a Single Sleeve-Valve. 2-Stroke, compression
ignition engine, Harry Ricardo solved the problems met during
development of top power S S-V engines by making the Sleeve Open,
something like an annular piston, 10% of the piston surface, that
contributed with 3% of the total engine output via the
Sleeve-Valve operating mechanism and the crankshaft, this also
eliminated the very complex 'Junk head', of former S S-V engines.
The clean air acts had an influence on the SFC of car engines, as a
clean exhaust required a bit of fuel consumption increase, but I
was told about an experience around 1975 with a Seat/Fiat 4
cylinder,  OHV, camshaft in the block side, 1438 cc car engine
being measured an SFC of 178 gr/HP/hr, pretty good.

=================================================

Jose,

You had asked about the motion of the Wankel Rotor from DTC to BDC vs
the piston in the RPE, The movement of the Wankel Rotor is purely
sinusoidal where s= r*(1-cos(ang)), r= 'E' Wankel shaft eccentricity,
and 'ang' is the crank angle from 0 to 180 degrees in the RPE. In the
Wankel it is 270 degrees which must be divided by 1.5 to have 0 to
180 degrees. It is like having an infinitely long connecting rod,
which is easily explained as the Wankel does not have a connecting
rod and the piston sits (rotates) directly on the eccentric of the
output shaft.

At the RPE, s= r(1-cos(ang)) + L(1- sqrt(1-lmd^2 sin^2 (ang))), where
lmd is r/L, L= length of connecting rod. An approximate formulae is
s= (1- cos(ang) + lmd/2 sin^2 (ang)).

Rolf Pfeiffer

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