Pitch gage (was Re: YS Engines)

[David Lockhart]

Dave,

I know in an effort to simplify some of the old pylon events, there was a
rule stating only one blade of the propeller could be modified (presumably
to balance the prop).  I knew pylon racers that would go through entire
boxes of props looking for the ones with the greatest imbalance - and then
they would customize the heck out of the heavy blade until the prop
balanced - they figured 1 bad blade and 1 good blade was better than 2
matched bad blades.

Dave


----- Original Message -----
From: "David Harmon" <K6XYZ at comcast.net>
To: <discussion at nsrca.org>
Sent: Tuesday, March 30, 2004 3:38 PM
Subject: RE: Pitch gage (was Re: YS Engines)


> You are right Dave....that has been my experience as well.
>
> This thread reminded me that Rich Verano used to live close by...one
> time he heard me test running an engine so he came over and we got to
> talking about these props and I mentioned the slight difference in the
> pitch of each blade on the occasional prop and that I had a couple of
> 'favorite' props that just seemed to work better than another prop the
> same size from the same mfg.
> Then he said that a pylon prop technique for more airspeed was to use
> the gauge to pitch each blade differently.
> Hard to believe....but he da' man!
>
> Regards
>
> Dave Harmon
> NSRCA 586
> K6XYZ[at]comcast[dot]net
> Torrance, Ca.
>
> -----Original Message-----
> From: discussion-request at nsrca.org [mailto:discussion-request at nsrca.org]
> On Behalf Of David Lockhart
> Sent: Tuesday, March 30, 2004 12:18 PM
> To: discussion at nsrca.org
> Subject: Pitch gage (was Re: YS Engines)
>
> A little more detail - the Prather Pitch gage has been around as long as
> I
> can remember, and the guys I originally knew to use it were RC pylon
> (and a
> couple pattern guys) and CL speed and stunt guys that were modifying
> existing props or carving their own from scratch - the biggest props
> commonly used at the time were 12" diameter.  The Prather gage would
> (and
> could) accommodate up to 14" diameter (more than enough at the time).
>
> You can measure pitch on a given prop blade as far as 7" from the hub
> with
> the Prather.  My experience (I've measured hundreds) with stock APCs
> tells
> me that if the pitch of the blades are equal to a distance of 4 or 5"
> from
> the hub, they will also be equal at the tips.  With the larger props
> (over
> 14"), you do have to either assume the pitch at the tips is equal, or,
> go
> through a fair bit of fuss to check symmetry by other means (surface
> gage
> works well enough, but doesn't tell you the pitch).
>
> As most of the thrust generated by the prop is centered somewhere around
> a
> point about 75% of the way from the hub to the tip, and the Prather will
> allow readings out to about 83% on a 17" prop, you can effectively
> measure
> 17" props.
>
> For the props I've repitched, the majority of the repitching occurs
> within
> 3" of the hub, and outside of about 5", the blades are not subjected to
> any
> stress.  I have come across props where the blades did not track in the
> same
> plane - and it was due to a difference in pitch of the blades.  I have
> not
> had this problem with any stock APCs I've run or any APCs I have
> repitched.
>
> The gage itself is a pretty simple device - a jig that holds the prop,
> and
> the jig is placed in various positions on a machined aluminum tray, and
> then
> a hinged arm is matched to the backside of the prop blade.  What the
> gage
> actually does is measure the angle of the bottom of the prop blade.  The
> arm
> lines up on a graph where the pitch is labeled.  Note that this pitch
> reading is really only a reference.  IF the angle of the bottom of the
> prop
> blade represented zero angle of attack for the prop blade, the pitch
> reading
> would be accurate.  However, most props do not use a flat airfoil, so
> the
> true pitch reading could only be determined if the zero angle of attack
> of
> the prop blade were known.
>
> Getting consistent readings with the gage does take a bit of practice -
> and
> I would say the gage is really only accurate to within an 1/8" of pitch.
> Having gauged and fixed many a wood prop, I can tell you that the APCs
> were/are the first truly mass produced prop that are consistent - blade
> to
> blade, and prop to prop.  The largest pitch imbalance I ever found on an
> APC
> was 1/2" - and that prop ran without blade tracking problems or
> vibrations.
> I have found some props (not APCs) where the blades were rarely within
> 1/2"
> of each other and the average pitch on a given sized varied by as much
> as
> 1.5" of pitch.
>
> I  know a number of guys have been bugging Terry for at least a year now
> -
> and more gages have "been in the works".  Hopefully they will arrive
> this
> spring/summer, and a larger size would be a definite bonus!!!!!!!!!!!!!
>
> Regards,
>
> Dave Lockhart
> DaveL322 at comcast.net
>
>
> ----- Original Message -----
> From: "David Harmon" <K6XYZ at comcast.net>
> To: <discussion at nsrca.org>
> Sent: Tuesday, March 30, 2004 2:46 PM
> Subject: RE: YS Engines
>
>
> > Dean...I just had a nice conversation with Terry Prather and he said
> the
> > next run of pitch gauges will be next month.
> > I also mentioned the current need for a larger size gauge for today's
> > props and he said that he had been thinking about it and would develop
> a
> > new model this summer capable of handling props up to 24".
> >
> > Personally, I have had no problem using the original gauge to repitch
> > APC props up to 16".
> > I use it quite a bit to determine if the prop in question is what the
> > mfg says it really is.
> > Usually, the blades are not equal in pitch and neither blade is the
> > pitch as marked.
> >
> > Regards
> >
> > Dave Harmon
> > NSRCA 586
> > K6XYZ[at]comcast[dot]net
> > Torrance, Ca.
> >
> > -----Original Message-----
> > From: discussion-request at nsrca.org
> [mailto:discussion-request at nsrca.org]
> > On Behalf Of Dean Pappas
> > Sent: Tuesday, March 30, 2004 10:34 AM
> > To: discussion at nsrca.org
> > Subject: RE: YS Engines
> >
> > Prather make them up in batches fairly rarely, they are too small for
> > 15, 16, and 17 inch props let alone the IMAC stuff, and it is
> otherwise
> > a fine high-quality product. I've had mine since the great quiet
> > struggle of '82/'83.
> > Dean
> >
> > -----Original Message-----
> > From: David Harmon [mailto:K6XYZ at comcast.net]
> > Sent: Tuesday, March 30, 2004 1:33 PM
> > To: discussion at nsrca.org
> > Subject: RE: YS Engines
> >
> >
> > Hey Dean....does Prather still make that pitch gauge?
> > I have one and it works well.
> >
> > Regards
> >
> > Dave Harmon
> > NSRCA 586
> > K6XYZ[at]comcast[dot]net
> > Torrance, Ca.
> >
> > -----Original Message-----
> > From: discussion-request at nsrca.org
> [mailto:discussion-request at nsrca.org]
> > On Behalf Of Dean Pappas
> > Sent: Tuesday, March 30, 2004 10:11 AM
> > To: discussion at nsrca.org
> > Subject: RE: YS Engines
> >
> > Hi Anthony,
> > The economics are not there, we have spoken to Fred at APC about this
> > already. The propellor pitch gauge construction article will appear in
> > FM. Now, all I have to do is write it ...
> > Dean P.
> >
> >
> >
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