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Bud's Philosophy
1 Preface
2
Don't be tempted to build a hot rod engine
3
Torque and Horsepower Charts
4
Auto engines VS. certified aircraft engines
5 Belts, chains, and planetary gears
6
Use the auto engine as it was intended to be used
7
Resolve torsional vibrations by using a centrifugal clutch
8
Engines require different lubrication than the PSRU
9
Be sensible, honor
others, and have integrity
1 Preface:
The following is a synopsis of Bud’s personal
opinions about the auto engine conversion industry, and some of the concepts
that are in use regarding automotive conversion technologies. As you hear about
his philosophy, please remember that he is not trying to offend anyone.
His many years of personal experience with auto
engines, experiences with certified engines in aircraft as an A & P, and his
knowledge and experience as a job machine shop owner and operator for thirty
years has given him a unique perspective based on actual knowledge. Bud feels
that has respected basis upon which he can offer an opinion based on real
experience, not just theory.
He may have what you might consider to be some rather
strong opinions regarding some issues and designs that you might differ with.
Bud does not wish to alienate anyone or make any enemies.
It is very important to him that you know that he will
not advocate for what he knows is dangerous, based on his own personal experiences.
Doing so goes against his values and concern for fellow man. So, be advised that
Bud will speak honestly and without reserve regarding his philosophy.
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2
Don’t be tempted to build a hot rod engine
Race car engines are not the best for aircraft use
so don’t make the mistake of building a race car engine for your airplane. Use a
mild engine at a conservative power setting. For instance, a stock Chevrolet
LS1 crate engine has a nice flat torque curve in relationship to HP.
Ideal auto conversion engines will have a low lift and
low duration cam in combination with heads that had very small air chambers.
This combination allows for a stronger power stroke and increased torque, much
like one would want for use in a truck or a tractor.
For example, the torque curve of this engine shows
maximum torque between 3000 and 4000 RPM. Now, add a prop reduction drive
utilizing straight cut spur gears with a mild reduction ratio of 1.562:1.00 and
the result is a conservatively built engine, operating at a conservative engine
RPM, using less fuel, creating less engine heat, and at the same time amplifying
torque to the prop.
Performance being one of the goals, our automotive
conversion aircraft will fly circles around the same airplane with a certified
aircraft engine, due to amplification of torque to the propeller through our
Geared Drives PSRU.
For instance, 350 ft lbs of torque to the crankshaft at
takeoff results in 546 ft lbs of torque to propeller. With a constant speed prop
and the Geared Drives PSRU, you will not believe the climb rates that you will
have at your disposal. Believe me, when you need it one day, you will be glad
you have it.
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3
Torque and
Horsepower Charts-click on the links below to view the graphs.
Once you open the graph, move your mouse to the lower right of the image and
click on the small box with four arrows on it to expand each graph to full size
for easier viewing. Click your browser's back button to return to the previous
page.
LS1 Horsepower vs.
Torque at crankshaft
Prop RPM vs. Engine RPM
Through the Geared Drives PSRU, Comparing Reduction Ratios 1.562 : 1 and 1.72 :
1
Torque to Prop as
multiplied through the Geared Drives PSRU, comparing Reduction Ratios of 1.562 :
1 and 1.72 : 1
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4
Auto engines VS.
certified aircraft engines
Automotive engine technology is the best it
has ever been, however, as an A & P, Bud has seen the inner workings of
certified engines on a consistent basis. He says that it seems that the FAA has
made it so costly and difficult to have any new advancements for certified
engines approved for use that he believes that the industry has found it more
realistic to just stick to the status quo when it comes to engines.
After all, he says, they are still selling new
aircraft, and there is no real reason to change anything up in the area of the
engine technology. Advances such as a spiffy new paint scheme, leather interior
and a new flat panel instrument set are about all it takes to make a sale.
Certified aircraft engines utilize virtually the same technology that they have
for the last fifty years or more.
Today’s automotive engines have technological advances
that in many cases render them virtually ideal for use in our experimental
aircraft, due to their compact size, fuel injection systems that automatically
adjust for altitude and a variety of horsepower ranges available.
With the advancement of superior aluminum casting
techniques within the automotive industry and the availability of even lighter
complete engine packages, auto engines now can compete with, and in many cases,
are even lighter weight than the certified engines that they would replace,
offering a superior horsepower to weight ratio.
Bud has observed that a lot of resistance to
auto engines in aircraft is a direct result of the lack of a dependable way to
convert horsepower and torque to the propeller. Belt and chain drives have
achieved marginal success, but marginal success was not what Bud was willing to
settle for. No offense to anyone, he says, because he could have developed a
belt or chain drive as well, but his plan was to set out to build a better
mousetrap.
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5 Belts, chains and planetary drives
From Bud’s perspective, the inherent danger with a
belt drive is the belt itself. He has been behind the wheel of many race cars
and personally experienced the sudden loss of power due to a belt catapulting
off into the atmosphere.
This might be an accepted risk in a race car since you
have a chance to come back next round and start over, but in aircraft there
might not be another opportunity. He was not willing to stake his life or
anyone else’s on any belt of any kind.
He has personal experience with chain drives as well,
and says he doesn’t like the idea that chains are only as strong as their
weakest link. Chains fail too, and Bud has had too many horror stories relayed
to him regarding slack in the chain of a PSRU, whose builder had dismissed as
“normal”.
These chains can crawl off the sprockets at an
inopportune time, leaving the pilot with no choice but to put the aircraft down
wherever he happens to be and pray for the best. Bud is not resistant to taking
a calculated risk, as there is always risk, but this kind of risk is not
acceptable to him when there are more safe and dependable options that he had
the experience and knowledge to develop.
Being a former drag racer of many years, Bud has
hands-on experience with planetary gears, which do well in situations that
require high RPM for a very brief period, but are not designed to operate under
consistent and continuous use. They were designed to simply transition from one
gear to another.
This ultra high RPM due to the gears being so small is
not conducive to long life of a PSRU. Bud is strongly opposed to using
planetary gears in something as vital to safety as a PSRU, especially when the
straight cut spur gear is the superior option and has been incorporated into a
superior redrive, such as the Geared Drives PSRU.
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6
Use the auto engine as it was intended to be used
Bud’s challenge was to engineer a PSRU that would
allow an aviator to use an auto engine in an airplane in exactly the same way
that it was designed to be used in a car. Therefore, his design transfers power
to the prop from a series of spur gears driven off the crankshaft on the
transmission end of the engine, and through an input shaft just like an
automotive transmission.
In doing this, there are no side or thrust loads on the
crankshaft from the propeller, so you can expect long engine life,
dependability, and similar service as you would obtain from your family car. In
addition, by reducing RPM’s from the engine to the prop through sturdy spur
gears, torque is multiplied to the prop.
Actually, the Geared Drives PSRU is probably more
accurately described as a single speed transmission in its design and function.
Another important consideration of the design of the
Bud's PSRU is that it must maintain the propeller thrust line while allowing the
engine to be placed in a lower position within the cowl.
Driving the prop directly off the crankshaft of an auto
engine, in Bud’s opinion, is simply a major failure waiting to happen. Some are
doing it and appear to be doing it successfully, but he says that he personally
knows too much about automotive engines to advocate for direct drive.
Bud says that you can do just about anything for some
period of time before suffering a catastrophic failure. Direct drive off an auto
crankshaft is not wise because crank bearings on auto engines are narrow and
comparatively offer perhaps 20% the bearing surface for support of the
crankshaft than that of a certified aircraft engine.
Auto engines were not designed to take the side and
thrust loads that the propeller will apply to the engine if directly driven off
the crank. With this in mind , he developed a PSRU that would allow the engine
to drive the prop the same way it would drive a transmission.
Bud’s PSRU does not apply any loads to the engine that
it was not designed to accommodate. Therefore, longer engine life, a higher
safety factor, and greater dependability is the result.
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7
Resolve torsional vibrations by using a centrifugal
clutch
The Geared Drives PSRU incorporates a rather
ingenious custom design in an automatic centrifugal clutch and flywheel. The
centrifugal clutch assembly keeps the starter from pulling the inertia of the
prop just long enough for the engine to start, which will contribute to longer
starter life. It also acts as a damper, eliminating harmful harmonic vibrations
and offers smooth operation.
Once the engine is started, the prop will begin to spin
due to inertia. At around 900-1000 engine RPM, the counter weights engage,
capturing the clutch disc between the flywheel and pressure place, fully
engaging the propeller.
The harder the engine runs, the harder the clutch is
engaged; therefore the more firmly the prop is engaged. The prop will remain
engaged as long as the engine is spinning. As a result, when the engine is
turned off, the propeller spins down to a stop-similar to a turbine engine
aircraft.
Bud has been developing his PSRU since the early
1990’s. He had many exciting victories, and moments of pure let down when he
realized that the theory did not result in success. The result was the PSRU
being redesigned multiple times, each time resulting in a better unit with fewer
issues. It had to be smaller, lighter, stronger, more dependable, and simplify
the installation of an automotive engine within the cowling. After years of
development, Bud is happy with the performance and longevity and is pleased to
offer it to other aviators.
He says that all of the experiences in his life have
lead to the development of this PSRU. Without these experiences, the development
of this unit would not have been possible.
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8
Engines require different lubrication than the PSRU
Gears require different lubricant than does the
engine. Bud says that the kiss of death for a set of gears is in not
using the proper lubrication. Separate lubrication systems are required
for safety and for proper engine and gear function. Sharing engine oil with the
PSRU is asking for engine and/or PSRU failure in advance.
The Geared Drives PSRU has its own reservoir, forced
and filtered lubrication by means of a dedicated oil pump, and utilizes the
proper weight and type of gear lubricant that ensures long life of the unit.
Synthetic lubricants certainly sound great, but they do not perform well in a
gear box.
Bud says that he has tested multiple synthetic
lubricants and each failed to provide adequate cooling and eliminate noise. Bud
recommends the use of all mineral 85-140 Gear Lube, of a type containing anti
foaming properties, which is indicated for fill up, not just top off.
Bud says that use of any lubricant other than what is
recommended could void the Geared Drives warranty.
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9
Be sensible, honor others, and have integrity
Bud says that he has developed his PSRU from the
sweat of his brow and from his own personal earnings. Though he says he has had
many offers, he has been resistant to taking on any investors or partners. “I
have a huge personal commitment to this project” says Bud, just as each and
every kit or scratch builder has. Bud flew his PSRU in his test aircraft for
nearly 400 hours before he was prepared to offer it to other aircraft owners at
Oshkosh in 2006. “We flew our Geared Drives PSRU on a 383 Chevrolet engine in
our Wheeler Express with great success” Bud comments, “I do not know of any
other PSRU builder that has actually owned and flown his own invention in an
aircraft for any period of time. Until we lost our Wheeler in October 2008 due
to a failed fuel line and resulting fire, we had flown just under 700 hours in
approximately three years, including trips to Oshkosh and Sun N Fun.”
Bud has a lot of empathy for those that he has met that
have expressed to him that they have been taken to the cleaners by someone who
came before. “I feel strongly that no designer or builder should finance the
research and development of his design concept from the funds of fellow aircraft
owners.
I have met some of the victims of this kind of
activity, and I find it deplorable. Doing business like that creates bad will in
the aviation community and the end result is just downright dishonest.
If you are going to do that, just go ahead and collect
money from folks and call then investors, not customers, so at least they will
know that there is a chance that they will lose their money in advance, and that
they never receive the product that they have ordered and paid for. At least
that would be honest.
"My opinion is that nothing should be offered for sale
until it is tried and true and the designer can ship it out with confidence that
the customer will enjoy a good flying experience with the product.” Bud
acknowledges that experimental aviation is a risky endeavor, and he is
constantly striving to implement new changes and modifications to make his units
even more stable. Insurance is never a bad thing.
Safety being his first consideration, Bud does not
advocate the use of belts, chains or planetary gears in something as important
as a propeller drive. His experienced opinion is that belts break, chains
stretch, and planetary gears are simply not designed to operate at high RPM and
under such a great and constant load as they are under while in use in an
airplane.
Planetary gears do well in situations that only require
high RPM for a very brief period of time, but are not designed to operate under
consistent and continuous use at high RPM, as they were designed to simply
transition from one gear to another.
Use of planetary gears in a PSRU, in our experienced
opinion, is a recipe for disaster. Straight cut spur gears, as we use in our
PSRU on the other hand, are designed to safely operate at a high RPM and under
continuous use. Noisy? No. Many will argue with that statement. Using fine
quality gears (these are not farm tractor gears) setting the unit up with the
correct lash and clearances, and keeping the gears cool and well lubricated is
the key.
We chose to use what we know to be the best technology
for this application because our objective was to do what makes sense in terms
of safety, reliability, and ease of maintenance.
Thank you for taking the time to read about my opinions.
Bud Warren
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