Auto conversions & gear boxes

I believe our (Zuehl) spring fly-in will be in May this year.
Drop in and see for yourself...

Richard

Oscar the grouch! That's funny. I could tell you stories about some
of the old men who built the RV-6A I flew. Man, the list of grouches
was long and deep. It was a project where retired men could go each
day and be insulted, embarrased, confronted and ridiculed. It didn't
matter what your background was, everybody hated you until you proved
you had some value. Once you were in, it was okay, but God help you
if you made a mistake on something. I goofed a couple times. That
was 8 years ago and I still remember how I felt as if it were
yesterday.


BWB

Badwater Bill wrote:

I believe our (Zuehl) spring fly-in will be in May this year.
Drop in and see for yourself...

Richard

Oscar the grouch! That's funny. I could tell you stories about some
of the old men who built the RV-6A I flew. Man, the list of grouches
was long and deep. It was a project where retired men could go each
day and be insulted, embarrased, confronted and ridiculed. It didn't
matter what your background was, everybody hated you until you proved
you had some value. Once you were in, it was okay, but God help you
if you made a mistake on something. I goofed a couple times. That
was 8 years ago and I still remember how I felt as if it were
yesterday.

BWB

Big grin!

Kinda like here?


Richard

In article ,
Badwater Bill wrote:

When I was the test pilot on the OMABP RV-6A project, we used the
Chevy Vortec V-6 engine, the PSRU was specifically designed to turn
the prop at tip speed below 80% the speed of sound. Jess Meyers also
used a reduction ratio number that was about equal to the square root
of 2 to eliminate harmonics that could have resulted in reversed
torque pulses reflecting back into the engine. By using a reduction
ratio of 1.41 (or close to it) he eliminated many sympathetic
harmonics that may have occured.

What, in order to have the ratio between the two be an irrational number?
That's not actually going to help eliminate resonances, unless you get
lucky -- and you are about equally likely to get lucky with any number of
about the same size, irrational or not.



--
Norman Yarvin http://yarchive.net

"Norman Yarvin" wrote in message
...
In article ,
Badwater Bill wrote:

When I was the test pilot on the OMABP RV-6A project, we used the
Chevy Vortec V-6 engine, the PSRU was specifically designed to turn
the prop at tip speed below 80% the speed of sound. Jess Meyers also
used a reduction ratio number that was about equal to the square root
of 2 to eliminate harmonics that could have resulted in reversed
torque pulses reflecting back into the engine. By using a reduction
ratio of 1.41 (or close to it) he eliminated many sympathetic
harmonics that may have occured.

What, in order to have the ratio between the two be an irrational number?
That's not actually going to help eliminate resonances, unless you get
lucky -- and you are about equally likely to get lucky with any number of
about the same size, irrational or not.



--
Norman Yarvin http://yarchive.net

Just out of curiosity, how would you get any ratio to be an irrational
number?

Tim Ward

"Tim Ward" wrote in message
...

"Norman Yarvin" wrote in message
...
In article ,
Badwater Bill wrote:

When I was the test pilot on the OMABP RV-6A project, we used the
Chevy Vortec V-6 engine, the PSRU was specifically designed to turn
the prop at tip speed below 80% the speed of sound. Jess Meyers also
used a reduction ratio number that was about equal to the square root
of 2 to eliminate harmonics that could have resulted in reversed
torque pulses reflecting back into the engine. By using a reduction
ratio of 1.41 (or close to it) he eliminated many sympathetic
harmonics that may have occured.

What, in order to have the ratio between the two be an irrational
number?
That's not actually going to help eliminate resonances, unless you get
lucky -- and you are about equally likely to get lucky with any number
of
about the same size, irrational or not.


--
Norman Yarvin http://yarchive.net

Just out of curiosity, how would you get any ratio to be an irrational
number?

Tim Ward

By definition a rational number is any number that can be expressed as a
fraction of two whole numbers.

"Cy Galley" wrote in message
news:ehd_b.377778$xy6.1992385@attbi_s02...

"Tim Ward" wrote in message
...

"Norman Yarvin" wrote in message
...
In article ,
Badwater Bill wrote:

When I was the test pilot on the OMABP RV-6A project, we used the
Chevy Vortec V-6 engine, the PSRU was specifically designed to turn
the prop at tip speed below 80% the speed of sound. Jess Meyers also
used a reduction ratio number that was about equal to the square root
of 2 to eliminate harmonics that could have resulted in reversed
torque pulses reflecting back into the engine. By using a reduction
ratio of 1.41 (or close to it) he eliminated many sympathetic
harmonics that may have occured.

What, in order to have the ratio between the two be an irrational
number?
That's not actually going to help eliminate resonances, unless you get
lucky -- and you are about equally likely to get lucky with any number
of
about the same size, irrational or not.


--
Norman Yarvin http://yarchive.net

Just out of curiosity, how would you get any ratio to be an irrational
number?

Tim Ward

By definition a rational number is any number that can be expressed as a
fraction of two whole numbers.

Yes, I know. Since we're talking about a reduction ratio, it didn't make
any sense. An irrational ratio?
It's... irrational.

Tim Ward

Easy. Just use one gear with 1.4264 teeth in it.

"Tim Ward" wrote in message
...
Just out of curiosity, how would you get any ratio to be an irrational
number?

On 20 Feb 2004 14:19:16 -0600, Barry S. wrote:

On Fri, 20 Feb 2004 18:08:35 GMT,
(Corky Scott) wrote:


Auto engines are tiny when compared to direct drive airplane engines.
Take a 180 hp Lycoming. It's cubic inch displacement is 360. They
turn the prop at around 2600 to 2700. The Ford V-6 in airplane trim,
puts out 180 hp also. It displaces 232 inches and makes it's power at
4800 rpm. No prop will work at that rpm. To harness the power, it
needs to be turned slower. Enter the prop speed reduction unit.

Speaking of Fords! How's your project coming?

__________________
Note: To reply, replace the word 'spam' embedded in return address with 'mail'.
N38.6 W121.4

Slowly. I have the engine assembled and is currently mounted in the
airframe. But there's everything else to do. The airframe has yet to
be blasted and painted. I think that can happen this summer. On the
other hand, we are planning some major kitchen redo's and trust me,
ALL of my attention had better be on that.

I've built an engine test stand that will allow me to wheel the engine
outside and run it, with the prop installed. I'd like to get some 30
or so hours on the engine before it gets it's final installation onto
the airframe. I decided this after listening to a crusty old DAR
speak at a local EAA meeting. It sounded to me like he'd be REALLY
unhappy with such an engine unless I could show him that it had been
thoroughly tested.

At this point, I'm being educated about headers. I was going to just
bend up a bunch of tubes, weld them to be what I need, get them jet
coated and call it good. Then I started doing some research.

It turns out that the diameter of header tubing is critical to the
performance of the engine. Larger diameter is not necessarily better.
In fact in almost all aircraft type applications, bigger is virtually
for sure not better. The exhaust header flange has openings that are
1.75" in diameter. This matches the exhaust port opening in the head.
But the tubing diameter should be 1.5", or possibly even 1 3/8" in
diameter. Also, the length of the runners should be at least over 30
inches, and 36 would be better. In addition, each tube should be as
close in length to each other as possible. Finally, the collector
needs to be about 1 78" diameter and it should be 18" long.

Reality is rearing it's ugly head. The lengths I mentioned literally
won't fit without welding the headers into loops. Not going to
happen.

I think the best I can do is get the runners as long as I can make
them and make sure they are of equal length, and get the proper
collector as that also has a huge affect on engine operation.

Why is it so important to have the runners be the same length?
Because different length runners cause different scavenging effects
within the combustion chamber. You will end up with an engine that
does not respond to ignition adjustments nor mixture adjustments as
some combustion chambers will run rich and some lean. "A series of
single cylinder engines flying loosely in formation." Quote from John
Deakin.

Many builders of the Ford V6 have complained that their engine ran
rough at maximum power. Huge effort was made to modify the intake
manifold to correct the problem. But I have not seen a single picture
of an exhaust manifold where the effort was made to create equal
length exhaust headers of the proper diameter.

I talked with a header manufacturer who told me he had heard of Dave
Blanton because a bunch of builders had asked him about headers. He
told me they all wanted to ignor his advice about tubing diameter.
They all wanted to use bigger tubing than was dictated, because they
all thought bigger was better. It's not.

Why is it so important to have the proper diameter tubing? Because
the bigger the diameter the slower the velocity of the gasses inside
it, and visa versa, up to a point. Eventually you can have exhaust
tubing in a diameter too small such that exhaust flow is restricted.
Large diameter tubing tends to cause the engine's power to peak at
extreme rpms. The smaller the diameter of the tubing, the more low to
midrange power you have.

But everyone wanted to use 1.75" tubing because that's what the
exhaust port was. 1.75" tubing would be what you would use if you
wanted flash horsepower from the engine at 8,000 rpm, like at the
dragstrip.

The header manufacturer also had a lot to say about "Zoomie" type
headers. These are headers without collectors, basically straight
pipes. Not only are these tubes also usually too large a diameter,
they leave off the collector which is crucial to the proper design of
the header system.

So with all this information, I'm taking my time with the header
design. Obviously something so important to the proper running of the
engine is not something I'm going to throw together without using
proper design criteria.

Corky Scott

In article ,
Tim Ward wrote:

"Norman Yarvin" wrote in message
...
In article ,
Badwater Bill wrote:

When I was the test pilot on the OMABP RV-6A project, we used the
Chevy Vortec V-6 engine, the PSRU was specifically designed to turn
the prop at tip speed below 80% the speed of sound. Jess Meyers also
used a reduction ratio number that was about equal to the square root
of 2 to eliminate harmonics that could have resulted in reversed
torque pulses reflecting back into the engine. By using a reduction
ratio of 1.41 (or close to it) he eliminated many sympathetic
harmonics that may have occured.

What, in order to have the ratio between the two be an irrational number?
That's not actually going to help eliminate resonances, unless you get
lucky -- and you are about equally likely to get lucky with any number of
about the same size, irrational or not.

Just out of curiosity, how would you get any ratio to be an irrational
number?

Not with gears! But a belt can provide any ratio. Of course any
irrational number can be approximated arbitrarily well by a rational
number... but the idea is just to choose a number that can't be
approximated well by a ratio of small numbers, not one that's genuinely
mathematically irrational. (Indeed, the latter concept is almost
meaningless in engineering, which is why I felt free to use "irrational"
as shorthand for the former concept.)

The idea isn't complete nonsense. If you had two identical assemblies,
linked by a belt drive, it'd be exactly the thing to do. You wouldn't
pick a 2:3 ratio, for instance, since that would mean the second harmonic
of one would resonate with the third harmonic of the other. But a
propeller and an engine are nowhere close to identical; their resonant
frequencies don't have anything to do with each other in the first place,
so there's no point in trying to do anything to throw them out of match
with each other. (Unless you get unlucky; if resonance problems show up
in testing, then you can try re-machining one of the belt pulleys to a
different diameter, or ordering new gears for a slightly different gear
ratio.)


--
Norman Yarvin http://yarchive.net

For props, bigger is better for static thrust (look at a helecopter)
but what about for top speed, a more desireable figure of merit for
fixed wing aircraft? I seem to remember hearing somewhere that for
top speed there is an optimal prop length that is not infinite. You
need to generate a stream of air that is going faster than the speed
that you want to fly.

I think it relates to why you see high bypass jet engines on sub sonic
airliners but no-bypass engines on supersonic jet fighters.