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1. 09:00 AM - How to tame the Lycomisaur (LesDrag@aol.com)
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| Subject: | How to tame the Lycomisaur |
--> Rocket-List message posted by: LesDrag@aol.com
Lycoming - tractor engine or turbine smooth?
This is the real question that needs to be asked when you are considering
which propeller to buy. (Based on multiple cruise performance tests using
several different propellers on the same aircraft with the same pilot.)
I had an opportunity to test four different constant speed propellers on one
aircraft. There were three different 2 blade propellers and one 3 blade
propeller. This aircraft was owned by a friend who flew the aircraft. I just
went along as the observer and data recorder.
The original 2 blade CS propeller on the aircraft had been dynamically
balanced on the engine. Since the plan was to leave the original propeller on
the
aircraft when we were finished with the testing, we did not removed the
dynamic balance weights from the engine ring gear.
All three of the 2 blade propellers had about the same vibration level
during their flights.
Then we flew the 3 blade propeller. On the takeoff roll and initial climb,
I noticed the pilot was highly stressed about something. About mid field, as
we were climbing out, he finally said that something must be wrong with the
engine. That the engine wasn't producing power.
We laughed about this later.
We seem to expect a certain vibration level which can be directly related to
the engine power. We don't even think about this. And it's not something
that any instructor I have had has ever talked about. It's just there.
I've been told that a 2 blade propeller has a 2nd order harmonic on the
Lycoming engine.
And the 3 blade propeller does not have the 2nd order harmonic on the
Lycoming engine.
What does this really mean?
On another test sequence, I had an opportunity to again ride in a friends
aircraft. On this friends Harmon Rocket 2 with a stock Lycoming IO-540-C4B5,
we removed a 2 blade propeller and installed a 3 blade propeller.
The 3 blade propeller made the Lycoming run like it was an electric motor,
it was so vibration free.
When we installed a second 2 blade propeller, the same old vibration came
right back. At the same level as the first 2 blade propeller.
So the question goes back to you, the builder/flyers. Do you want "turbine
smooth" or "tractor engine"?
Regards,
Jim Ayers
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