Once a month SZP opens the airport for visitors. Those of us with
unusual air planes open our hangar doors and people stroll by and ask
questions. Many are questions I have heard over and over again.
The rotary powered RV4 with the cowl off is prominent and draws a lot
of people,
I am scheduled to give a talk about rotaries at AusFly in Narrowmine NSW
Aus next week. To speed the process I am getting a large poster printed
with some of those questions.
Here is a preliminary version. Comments are welcome.
Paul Lamar
Paul,
You know far more about rotary engine durability than I do, but you
continue to bury your head in the sand when it comes to the fuel
efficiency of rotary engines--at least when it comes to cars. The fact
of the matter is that rotaries use 20-30 percent more fuel than
comparable, modern piston engines. That's why even Mazda has given up on
them. The proof of this is incontrovertible and as a rational engineer,
you should accept this fact. That shortcoming doesn't disqualify the
rotary as an aircraft engine, where its other virtues--light weight,
compact size, smoothness, and durability--might be more important.
Csaba Csere
The BSFC is now within 5% of a piston engine
The car problem has more to do with the gear box chosen by Mazda than
the BSFC of the rotary.
My RX8 is doing 3000 rpm at 80 while my 250 HP Honda Odysseys is doing
1800 RPM. This the same reason the 400 HP Corvette gets 25 MPG on the
free way. My 1994 Mercury Cougar was doing 1900 at 80 MPH.
At a steady 70 MPH the RX8 is getting 25 MPG. The same as my old RX2 and
the two RX7s I have owned. All had the wrong gearing.
All you need do is look at the OBD data attached.
Another factor is when the Mazda computer leans the engine and when it
does not. Leaning improves the BSFC. Honda circumvents the NOX
emissions laws by not leaning the engine during the smog test. The rest
of the time they lean it frequently. Nox is a big problem for diesels as
nox increases when running lean. Mazda never leans the RX8 engine no
matter what.
I have developed and patented a high speed MSD ignition system that I
hope will knock a few points off of the BSFC.
The exhaust valve, in a 4 stroke, waste 20% of the of the recoverable
energy in turbo compound use. The exhaust normally waste 50% of a gallon
of gas. Harvesting in F1 speak. A turbo compound rotary would therefore
become the most efficient IC in the world maybe short of some diesels.
The F1 hybrid scheme is not the most efficient for free way use,
http://www.rotaryeng.net/Oxford-TC-talk.mp4
If Mazda does not build a turbo compound rotary they are not informed.
Mercedes, Renault , Ferrari and Honda will.
We now have a RB 650 HP 2 rotor that weighs less than 200 pounds in a
time to climb project air plane. It has a controlled leak in the exhaust
manifold because there is too much energy in the exhaust. In other words
it would over boost the engine. This is in addition to the waste gate.
Mazda ought to hire me as a consultant. I would straighten them out damn
quick :-)
Paul Lamar
Paul,
The rotary has relatively short gearing because it has little low-rpm
torque and if the gearing were any taller, it would have no acceleration
in top gear--at least with a manual. Most of the other cars you quote
are non -porting and have automatics, so they kick down when you floor
the accelerator.
Also, there are other cars with similar gearing to the Mazda, such as a
BMW 335i. But that car gets better mileage--over 30 mpg at 70 mph--while
delivering far more performance--in a much heavier car.
As to the Honda leaning out during off-cycle driving, I don't know what
your car does, but such a calibration would be highly illegal and I
doubt that Honda, or anyone else, uses it.
Your turbo-compound rotary idea has merit, but it says nothing about the
efficiency of real-world rotaries.
Csaba
Of course. It does need an automatic manual. (Computer controlled hyd
shiifting}.
30 MPG verses 25 MPG is 20% not 30%.
My neighbour has an M3 and I will ask about the 80 MPH RPM.
The piston engine has millions of more hours of R & D.
Due to new apex seal materials the leaning angle can be increased
allowing a higher compression ratio or a better combustion chamber
shape.
I had the OBD II on the Honda and I saw a lot of situations where it went
way lean. The gov only cares about the arbitrary driving cycle and
they don't peer over the shoulders of the company EFI programmers.
From a software point of view it is easy to detect the silly driving
cycle.
The nox v BSFC situation was discussed in Bruce Briggs book War against
the Automobile.
Paul Lamar
What is not real world about turbo compound. CW made thousands
of R3350 TCs. A Super Connie could stay aloft for 24 hours.
Actually the exhaust valve was the Achilles heel. The head would
come off and take out the turbine. Rotary no problem no exhaust
valves.
Paul Lamar
Paul,
Here are the relevant numbers for a 2007 Mazda RX-8 versus a 2007 BMW
335i coupe, both with 6-speed manuals (Car and Driver tests):
RX-8 335i
Weight 3060 3557 lbs
rpm@80 mph 4020 2974rpm
claimed power 232 300 hp
claimed torque 159 300 lb-ft
0-60 mph 6.5 4.9 sec
0-100 mph 18.0 12.1 sec
1/4-mile 15.0/93 13.6 sec @ 105 mph
50-70 mph top gear 10.9 6.0 sec
EPA city mpg 18 19 mpg
EPA highway mpg 24 28 mpg
Observed mpg at 70 25 32 mpg
In what world is the efficiency of the RX-8 engine the same as the BMW
engine, which is moving a substantially heavier car, and delivering much
greater performance, while using less fuel?
You can say that the Mazda gearing is too short for optimal fuel
economy, but if you made it any taller, it would exacerbate the car's
already poor flexibility. Yes, an automated manual with 7 or 8 gears
would help address the fuel economy/performance trade-off, but such a
gearbox would help the BMW's performance and efficiency as well. And
keep in mind that modern piston engines are more efficient than this
8-year-old BMW.
No car manufacturer that examines the above performance/efficiency
comparison would chose a rotary for a modern car in a world where the
mandated fuel economy is increasing every year (2010-2025).
As I said earlier, this doesn't mean that a rotary has no merit for an
airplane, but it explains why rotaries are extinct in automobiles.
Csaba Csere
Quote Csaba;
"Observed mpg at 70 25 32 mpg" How was this done?
Quote Csaba;
"No car manufacturer that examines the above performance/efficiency
comparison would chose a rotary for a modern car in a world where the
mandated fuel economy is increasing every year (2010-2025).
As I said earlier, this doesn't mean that a rotary has no merit for an
airplane, but it explains why rotaries are extinct in automobiles."
All this is biased opinion on your part. Very clever of you to mix
opinion with facts :)
I am on to you :) You get an F for this :-) (Csaba is a former student
of mine.)
http://www.zeroto60times.com/vehicle-make/mazda-0-60-mph-times/
Zero to 60 2004 RX8 5.7 seconds. Not C&D 6.5.
Perhaps Car and Driver had/has defective data taking :)
The EPA MPG numbers tell a different story.
................................RX8.....Bmw
EPA city mpg ........... 18....... 19 mpg
5% better for the BMW which is what I stated for the rotary.
................................RX8.....Bmw
EPA highway mpg .... 24....... 28 mpg
16% better for the BMW a long way from "20 to 30% better"
This is where the better gear box would help the most.
You are also ignoring the turbo compound situation which makes the rotary
uniquely qualified for application of such. All F1 engines are turbo
compound
and will be for the next few years. The piston engines will have exhaust
valve
problems.
BTW thousands of turbo compound DD15 engines have been sold and are
selling like hot cakes to the trucking industry. If that is not real
world I don't
know what is.
Paul Lamar
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