Today's Message Index:
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1. 03:37 PM - Re: DYNAMIC BALANCE (jetboy)
2. 04:07 PM - Re: Re: DYNAMIC BALANCE (Peter Harris)
3. 04:26 PM - Re: Prop speed reduction unit (PSRU) (Gilles Thesee)
4. 04:44 PM - Re: DYNAMIC BALANCE (promod69camaro)
5. 06:03 PM - Re: Re: DYNAMIC BALANCE (Peter Harris)
6. 10:12 PM - Re: Prop speed reduction unit (PSRU) (jetboy)
Message 1
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| Subject: | Re: DYNAMIC BALANCE |
Peter,
Having had dynamic balancing and similar weights applied to a C150 I understand
your concern about the engine balance.
I do wonder though, if the prop is still the problem? Can you be sure that the
weight distribution within the prop is the same for each blade? If not, then
the solution for static balance will be different to that of dynamic balance,
and the reaction to yaw will also be different.
Ralph
--------
Ralph - CH701 / 2200a
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=131004#131004
Message 2
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| Subject: | Re: DYNAMIC BALANCE |
Ralph,
I cannot be sure if the weight distribution in the prop is uniform. I can
only say that it is a wooden prop made by Ed Sterba (US) and he has a good
reputation for high performance wooden props. It would be fair to say that
the prop is an average wooden prop with average density characteristics.
Do you have any information about variability in wooden props?
In my case the correction was very large ie a 1/4"X 3/4 bolt nut and washer
at about 4" from centre. Seems like a lot of imbalance to attribute to the
light weight prop. It would be a good thing to get some more data and I
would recommend dynamic balance to all J3300 users. Provided the job is done
starting with a static balanced prop then we could see if there are any
others. It took 3/4HR and cost me AU$120.
Peter
-----Original Message-----
From: owner-jabiruengine-list-server@matronics.com
[mailto:owner-jabiruengine-list-server@matronics.com] On Behalf Of jetboy
Sent: Sunday, 26 August 2007 8:37 AM
Subject: JabiruEngine-List: Re: DYNAMIC BALANCE
Peter,
Having had dynamic balancing and similar weights applied to a C150 I
understand your concern about the engine balance.
I do wonder though, if the prop is still the problem? Can you be sure that
the weight distribution within the prop is the same for each blade? If not,
then the solution for static balance will be different to that of dynamic
balance, and the reaction to yaw will also be different.
Ralph
--------
Ralph - CH701 / 2200a
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=131004#131004
Message 3
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| Subject: | Re: Prop speed reduction unit (PSRU) |
promod69camaro a crit :
> Propellers seem to operate much better around 2200 to 2500 RPM. And at lower
RPM, there is less prop noise to deal with. Lets say a person put a 1.5:1 reduction
PSRU on the motor, and had a new cam ground for operation to 4000 rpm
if necessary, which it probably would be. That would allow the engine to make
about 25% more power, and the prop speed would slow into the more efficient speeds.
There would be cooling issues, and it would not necessarily have to run
at the higher RPM all the time.
> I am sure there are all kinds of reasons not to do it. For one, its a direct
drive aircraft engine and why mess with it. But the fighter planes in WWII all
had PSRU's on them, even the radial power plants.
Shawn,
Your observations on PSRUs and WWII engines are correct.
Actually, some propellers can an do perform well at high RPM.
Nevertheless, with a fast turning prop, the diameter must be limited,
and the overall propulsion efficiency goes down. There is an optimal
prop disk area for each output.
For a high power engine, you need a large disk area, hence a slow
turning prop, because the tip speed limit is the same.
Bottom line, 2700 rpm is just about right for a 100 hp direct drive engine.
Concerning your projected modification, you may end with a completely
new engine, but why not ?
Best regards,
--
Gilles
http://contrails.free.fr
Message 4
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| Subject: | Re: DYNAMIC BALANCE |
Peter,
I know that what you have already done is working, but if you put weight further
out on the propeller, it won't require as much to be dynamically balanced.
And the lighter weight further out will not affect the static balance as much
either. Or you could just cut of several inches of prop on the heavy side and
call it fixed. [Laughing]
--------
Sport Pilot (almost) - Waiting for good weather to take flight exam.
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=131012#131012
Message 5
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| Subject: | Re: DYNAMIC BALANCE |
Ha Ha
But the application of weight is off axis with the prop in my case, I would
have to mount an outrigger (LOL)
Peter
-----Original Message-----
From: owner-jabiruengine-list-server@matronics.com
[mailto:owner-jabiruengine-list-server@matronics.com] On Behalf Of
promod69camaro
Sent: Sunday, 26 August 2007 9:44 AM
Subject: JabiruEngine-List: Re: DYNAMIC BALANCE
<shawn-bishop@verizon.net>
Peter,
I know that what you have already done is working, but if you put weight
further out on the propeller, it won't require as much to be dynamically
balanced. And the lighter weight further out will not affect the static
balance as much either. Or you could just cut of several inches of prop on
the heavy side and call it fixed. [Laughing]
--------
Sport Pilot (almost) - Waiting for good weather to take flight exam.
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=131012#131012
Message 6
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| Subject: | Re: Prop speed reduction unit (PSRU) |
Shawn,
you have more or less answered your question, I would like to add that
the 3300 or 2200 for that matter is unlikely to last with a prsu because you
wont be able to cool it sufficiently. I understand a helicopter company was
using the 3300 but gave up after burning up 2 or 3.
The torsional vibrations to the crank will need addressing. Rotax dont just bolt
any old set of gears on the 912 and even their current setup doesn't do that
well. For a study on torsional vibration do a search using that term and BD5
might yield a very good paper on the difficulties.
If it were me trying to do more with the unit I would be looking at mild supercharging
first.
Ralph
--------
Ralph - CH701 / 2200a
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=131030#131030
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