WTB pitch gauge

[ZUL8TR]

Prop pitch

David; -I have a guage similar to the one closest to the drill press,
not exactly like that one, but close. I have some questions;

-at what diameter do you measure the pitch?
The scale on mine has 12" scribed in at 45deg, which is only true at a diameter of 1.92". Maybe close for a 7" prop, but what is the accepted protocol ?

-my scale in linear, from 6" to 18",
ie; 6" at 22.5 deg
12" at 45deg
18" at 67.5deg.
High school trig tells me that pitch, ie; rise over run,
is a function of the tangent of the angle,
so the scale should not be linear.
Are your scales linear, and at what diameter does it indicate true pitch?

You are correct pitch at a point on the blade is related to the tangent of the angle between a 90 degree pointer and the centerline of the prop bore hole that fits on the prop shaft of the motor.

Here is a pic of the scale on Ron Hill gage and it is nonlinear. The different scales are for different radai from the centerline of the prop bore hole.

http://www.boatracingfacts.com/forum...ght=pitch+gage

The pitch scale is calculated by:

Pitch = 2 x Pi x R x Tan(Angle)

Pi = 3.141.....
R = radius from the prop centerline
Angle = measured as stated above and shown in the picture.

Based on above formula the pitch numbers on your scale calculate to be 3 different radai: 2.31", 1.19" and 1.19". It appears the gage scale is not correct unless you select the correct radius. I suggest to read the angle directly since that would be a linear scale at a selected radius and calculate the pitch from formula. The tangent function is on most hand held calculators.
I know it is not conveinent but then only one scale is needed the angle scale.

The radius to measure at is variable but it is usually taken at 70% of the radius. For simple consistency I measure at the widest chord length of the blade and start at the lead edge (LE) and go to the trail edge (TE) (not including any cup) in 1/2" increments then average the calculated pitch measurements to get an approximate value of pitch at that radaius. True pitch would be how far the prop would advance in one revolution without slip like if it was advanced into a solid medium just like a woodscrew. However measureing with these type gages does offer a relative way to compare props as long as the same gage is used with the same selected location to measure the angles.

This incremental measurement is needed for progressive pitch props that have increasing pitch fron LE to TE as Ron notes on the prop blade in the pictures.

Note that pitch is different at different radai so you can measure at different radai and see what results. That causes much confusion when pitch is reported without how measured and by what device.

[david bryan]

very articulate but the numbers that mater the most are the ones on your GPS

[bh/]

[QUOTE=ZUL8TR;190497]You are correct pitch at a point on the blade is related to the tangent of the angle between a 90 degree pointer and the centerline of the prop bore hole ...."

Thanks for confirming that. This gauge, although well made, is only accurate at one point, ie; 12" pitch at about a 2" radius. Like the clock that is only right twice a day. As it circulates among a bunch of us, it is the cause of much argument. Probably best if I just overlay it with a protractor degree scale,
and go from there.
bh/

[blueskyracer]

very articulate but the numbers that mater the most are the ones on your GPS

So true plus you need a driver that can use those high numbers

[ZUL8TR]

Gps

very articulate but the numbers that mater the most are the ones on your GPS

Well of course testing is the last word but he asked about pitch.

[david bryan]

you can covert degree to pitch quite easily that is how the gauge i have Ben using for 50 years works i have won national championships and set world records by pitching my own props it is not rocket science

[david bryan]

Well of course testing is the last word but he asked about pitch.

you can covert degree to pitch quite easily that is how the gauge i have Ben using for 50 years works i have won national championships and set world records by pitching my own props it is not rocket science

degree to pich

[ZUL8TR]

prop pitch or ------?

degree to pich

Cool you jets David there was no challange to your prop bending ability or your past history of racing which I know nothing about either, so why bring that up here?

And yes prop pitch is not rocket science just simple math and understanding what you are doing. You have to explain to us how a roof pitch to angle conversion table gives you prop pitch which I noted is related to not only the angle of the blade and the radius where it was measured.

A point to note: if one creates a measuring gage with any arbitrary scale just to be used as a reference and that gage is always used to measure whatever and then the result is tested a correlation of the test result can always be made directly back to that gage scale for future use because that gage measurement produced this specific result. This process is used all the time in various fields of work.

[David_L6]

....i have won national championships and set world records by pitching my own props it is not rocket science

Seems more like MAGIC to me!

[bh/]

degree to pich

David is simply referring back to the science of the 'framing square' ,
a device which preceded trig tables, slide rules, and calculators.
It is said that a man that 'knew the square',
could do his taxes on it, build barns, and calculate when the best day of the month to put the bull in with the cows.

Note that in Davids table, when the rise over run is 12/12, ie; 1/1,
it equates to 45deg, the tangent of which is 1.
As I said, the only time my prop scale is correct, is at 12",
ie; 45deg, when the trammel bar is set at 1.92".
At that radius the run of the prop is 12".

We do not seem to have helped the 1st poster in his quest to buy one.

[david bryan]

pich gage

David is simply referring back to the science of the 'framing square' ,
a device which preceded trig tables, slide rules, and calculators.
It is said that a man that 'knew his the square',
could do his taxes on it, build barns, and calculate when the best day of the month to put the bull in with the cows.

Note that in Davids table, when the rise over run is 12/12, ie; 1/1,
it equates to 45deg, the tangent of which is 1.
As I said, the only time my prop scale is correct, is at 12",
ie; 45deg, when the trammel bar is set at 1.92".
At that radius the run of the prop is 12".

We do not seem to have helped the 1st poster in his quest to buy one.

i do not know how you figered that out but i did lay out my my first prop gauge whith a framing square i made one for ron hill showed it to dewald and to bob davidson who went on to set 13 kilo records one day at parker az and i think i sill have one Craig Dewald made

[bh/]

[QUOTE=david bryan;190576]i do not know how you figered that out../QUOTE]

It has much to do with when we were born....
bh/