Date: Mon, 01 Feb 1999 11:56:53 -0800
From: Paul <rotaryeng@earthlink.net>
To: z <rotaryeng@earthlink.net>
Subject: Strange low frequency vibration.

Tracy Crook wrote:

Paul Yaw wrote:

 Unfortunately the 6-port is here to stay.

Paul Yaw

I think that is a good idea Paul. IMHO the six port has the potential
to be better than the four port because there is more iron in the
end housings to be ground away to make the end ports flow more air.

I am working on a design for a slide throttle that might mitigate
the idle problems of the bridge port. If we can get it to idle
OK at 2000 RPM that should be all the aircraft people need as
most are running a 2.17:1 PSRU so the prop RPM would
only be 920 RPM. Not a lot faster than your average direct
drive aircraft engine. What does it cost to do a bridge port?

As I recall Tracy is already idling at 1500 RPM or so for
one reason or another.

Paul Lamar

According to the guys at Mazdatrix, they always use the six port 

housing

when trying to go for the max HP on a side port engine for the reasons 

you

stated.   2000 rpm idle is fine for land planes but the amphib flyers 

are

complaining that this makes on-water operations dicey at times (no 

brakes

:-).   

Let them eat cake. (Put a variable pitch prop on there:-))

 I use 1500 RPM because at speeds a bit lower than this the resonant
frequency of the drive system (due to the gear lash, not really the 

freq of

the metal parts) causes the system to rattle around a bit.

On the subject of the "props out of sync type vibration", I have this 

as

does everyone else using the Ross.  Very interesting that it went away 

with

the three blade prop.  I am guessing it is due to the prop shaft being 

able

to wobble about in the very loose needle bearings Ross uses.

Tracy Crook   rws@altavista.net

Thanks for that insight Tracy. Sounds plausible. 

Paul Lamar
 
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