Yes! Those are just the renderings. Pick out what you want and I
will send the IGES.
Paul Lamar
Hi Paul, I think those AL housings appeared while I was away.
Could you send me some detail of the wear plates and the Al
housings; an AL center hsg would sure cut some weight out of the
total engine weight. I have a friend who has just retired from his
engineering business and has kept a lot of his machine tools so I
have access to CNC mills, wire cutters and lathes. Rs, Dave McC in
Perth
Do you have access to Rhino 3D drawing program? There is no such
thing as a 3 view drawings with dimensions these days. Everything
is done with IGES files. The dimensions are hidden.
The wear plates can be made in at least two ways. A stock cast
iron end housing can be cut down or a new one made of of hard 4130
sheet laser cut and then chrome plated like the stock rotor
housing.
Too bad Australia is so big. Neal Unger in Parkes NSW is doing a
lot of the same things. Neal has a p-ported-13B powered Glastar
flying. Neal is also president of the Sport Aircraft Ass. of
Australia. SAAA.COM You guys should work together. Oz is in real
need of a one rotor all aluminium LSA engine as the Jabiru is
struggling.
http://www.aviationsafetymagazine.com/airplane/LSA-Engine-Safety.html
I'll send you Neal's email address by private email.
Paul Lamar
Paul et al,
I have what is probably a basic question.
I have often read that a propeller induces adverse vibrations into
a drive train and that a belt driven PSRU is the way to isolate
those vibrations from the rest of the components and engine in
general while allowing the propeller and engine to each operate in
their most effective rpm range. Yet I also see a lot of planetary
(and other?) gear drive units, especially in the information shared
here, that would seem likely to transmit those propeller
vibrations. So in the applications being discussed here how is a
direct drive permissible? Is it because the aircraft (e.g. the time
to climb) are limited purpose and limited life and thus not likely
to be adversely affected in the time they are operational?
Just curious and hoping to understand better. Thanks for any
responses!
Brad Chubb
The planetary was universally used in aircraft engines for years.
Only in WW II was a spur gear used in the water cooled V12's. All
the radials had planetary gear box's including the largest
aircraft engine ever made in quantity. That was the P&W R 4360 Wasp
Major. It had 18 planet gears. The latests in large P&W turbo fan
engines for airliners is a planetary gear box that is 98%
efficient.
Direct drive requires a lot of displacement for a limited amount
of HP. The 2 rotor rotary engine is small displacement as aircraft
engine go at 160 cubic inches. However the time to climb engine is
a record amount of HP (650) for it's weight of under 250 pounds
with gear box.
BTW The rotary is also a record amount of HP per cubic inch of
displacement at 4 HP per cubic inch. The former record holder was
the Offenhouser race engine at 3 HP per cubic inch.
The TTC record holder Grumman Bearcat had 2 pounds per HP to lift
while our TTC aircraft (Vans RV4 basically) only has 1.5 pounds
per HP to lift. Weight per HP is the name of the game in high
climb performance. Ask any truck driver :-)
We are about done with the installation and we are waiting until
Dan Gray gets back from vacation to test run the engine on the
aircraft.
Paul Lamar
Paul, The interesting thing I see with the P&W planetary, (besides
the hyper-expensive herringbone cut gears), is the fact that that
planetary must be fully assembled before any other components can
be added. You cannot slide in the sun gear or put on the planet
carrier with herringbone gears. The planet shaft must be removable.
They are even better than straight cut, (stronger for their
diameter), but you need to be a government funded project to
afford them!
Bill Jepson.
One never knows. New methods of making things are invented all the
time.
I just found out fender dies are now EDM'd. A big block of carbon
is 3D NC milled and then it is sunk into a big block of steel with
EDM. Cheaper than 3D milling the female steel dies directly. Also a
better finishing with no hand polishing of the female steel die.
Paul Lamar
Paul, just so that this thread doesn't stay without comment on
Brad's question, there is a lot of misinformation on the net about
propeller gearboxes, much of it wrong.
The propeller does not induce vibrations. Once spinning, it
represents a nearly constant inertial moment. The problem is that
combustion events in the engine deliver pulses of power to that
inertial load through a spring. The spring is made up of all the
parts between the combustion and the air that the prop is pushing.
The combination of the spring and the inertial load define a
resonant frequency just like a clock pendulum has. If you excite
the spring near that frequency, the energy will stay in the spring
rather than coupling out to the air, and each combustion event adds
to the energy stored. (If you put pulses of energy into a clock
pendulum at other than its resonant frequency, it doesn't move
much, but if you do it at the right frequency it will keep swinging
with very little energy input.) The excursion of the spring will
increase for each power pulse until something breaks. You can use a
planetary, or plain gears, or belts, or chains, each one can be
designed so this doesn't happen. Belts in fact are nearly as stiff
as gears, and usually stiffer than any kind of shaft driving the
pulleys. The whole system has to be designed together so you know
where the resonances are, and if they are in the operating range of
the engine you incorporate means to detune them if things get too
excited. Every successful propeller gearbox addresses these issues
in a systematic way, there's no shortcut.
For Brad, Paul's TTC engine has a very stiff and robust planetary
gear set between the engine and the prop. I don't know for sure
but would expect that the resonant frequency of that system is far
below the normal operating range, somewhere in the high idle range.
They will go through that range quickly on startup. During the
brief time when the engine is operating at that range, the rubber
will deform and break the resonance for at least a few cycles. It
does not damp (attenuate) or absorb much power; if it did, it would
burn up in an instant. Above that frequency the rubber will not be
compressed and will behave like a solid block.
David Josephson
Every one we ever tried so far, not including the TTC, resonates
about 1800 engine RPM. This includes all of Ross's, Tracy's and,
of all things, the Rotomax. The Rotomax had a spur gear. I don't
know why. Even my direct drive C 182 O-470 shutters when it is shut
down between propeller 500 RPM and zero. We idle the rotary at 2000
RPM to avoid this. Even on landing as the prop is only turning 650
RPM or so.
We are not sure what the TTC is going to do but my money is on
1800 RPM :-)
Paul Lamar
It has nothing to do with the gear type. Without doing the
measurements I would bet that the prop inertia (divided by the
gear ratio) and the spring constant of the eccentric shaft are the
defining moments. This is a really simple problem; to read about
this magnified to nightmare proportions, find a paper on the web
"Development of the R-2800 Crankshaft." Your O-470 has a resonance
below 500 rpm that's probably set by the crankshaft compliance and
the prop inertia. The bigger 520 engines have pendulum absorbers
to reduce it. Corvairs are at around 1100, Rotaxes around 1600.
There are some weird ways around the problem; the MW Fly engine
from Italy kills the compression by changing valve timing so the
engine can't produce any power in its resonance range.
David Josephson
My first O-470 had one pendulum damper. The one I have now has
two. The input shaft on the Ross and Tracy was only one inch in
diameter. Chris Hoskins input shaft is 1.5 inches in diameter.
Since the torsional stiffness is proportional to the fourth power
of the diameter that is five times stiffer. However Chris's rubber
coupling is going to be adjustable and far more effective than
Tracy's. Ross used a stock spring clutch plate.
Paul Lamar
I have read here and there that the mathematics needed to design a
pendulum damper can be found online, but I have never been able to
find it. I have the Kerr-Wilson book and others on torsional
vibrations, but they are almost unusable to me. I have considered
getting tutoring from a local university prof or working engineer
when the time is right. Anybody know of a SIMPLE mathematical
treatment for pendulum dampers?
Gene Kahn
The first thing you need to know is the resonant frequency of the
shaft you are trying to damp. That info is hard to find for most
aircraft engines and it depends on prop inertia.
Then know that a point on the shaft some distance from the center
is oscillating back and fourth as the point rotates around the
center of the shaft.
Here is a scan from the Sky Ranch Engineering manual.
Paul Lamar
Paul, Thanks again for the info. And to think I even OWN that book,
based on your recommendation!
Gene Kahn
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