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BackcountryAeropup

Bolly

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I'm after a bolly pitch gauge if any one has one the factory are out of them at the moment. Or if you are in S.E QLD and are willing to loan one out I will be appreciative with the guarantee you will get it back.

 

 

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A straight stick or good straight edge (eg aluminium angle) and a tape measure is just as accurate, maybe even more so. Use your phones calculator to check your numbers.

 

Just level the thrust line, get the prop blade horizontal, measure the distance from trailing edge of the blade to the ground at 75% of blade radius. Use a set square to draw a line on the back of the blade with a texter or use a bit of masking tape. Mark the stick so all blades will be consistent, mark the ground vertically below the TE, Divide the distance by 60. Multiply the result by the blade angle you want & mark the ground that distance rearward.

 

Example. Distance to ground = 1200mm divided by 60 = 20. Blade angle required = 20 degrees. 20 x 20 =400, so the distance from the mark below the TE rearward is 400mm.

 

Then loosen the blade & with the stick on the flat back of the blade at 75% radius adjust the angle till the bottom of the stick is on the rear mark. Nip up the blade clamp nuts & repeat for all blades. Easy. I set mine at 75% of blade radius. Bolly say to be sure check at 50%, 75% & 90% but it doesn't matter so long as all blades are exactly the same as you will decide by flying whether to increase or decrease pitch.

 

 

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Or download the inclinometer app to your phone. Measure from prop tip  to mid flat part and draw line at 90 degrees. Level blade and measure blade angle to point one of a degree with the phone.

 

 

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I would check the phone inclinometer carefully before doing that: I had a microwave dish installed a while ago, the tech waved his phone at the little hokeystick mast, then when it came out ridiculously out of plumb, I passed him up a spirit level................

 

 

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I used the inclinometer (part of Smarttools app) on my phone to set the angle of my prop when I levelled it on the bench before installation, calibrated the inclinometer when I got the hub perfectly level with my spirit level & set both blades. The next day I came back to the hangar & before installing the prop checked the details and got different results. I don't know why, maybe it was the temperature, humidity, barometric pressure or something else but that was when I decided to go with a method that uses measurements that can't be changed by electronics.

 

 

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Yep, that...and gravity...are wonderfully reliable things.....)

 

 

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You do need to calibrate the inclinometer before use. Also turn it around and read both ways to ensure they are the same reading.

 

 

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I'm about to pitch a prop for the first time.

 

The Bolly manual details several methods. They describe the stick and measure method in some detail, with the comment 'this method is so simple, no-one thinks it is good enough'. On the Sav, the floor measure per degree will be in excess of 20mm. So if I can set the blades to get the stick within 1mm on the floor, they will be within 0.05 degree of each other.

 

I just spent some time online trying to locate the specs on smartphone inclinometers.

 

I was looking for resolution of plus and minus x degrees; drift due to temperature and other factors; and repeatability, which is with what accuracy the instrument will keep giving the same result when returned to the same angle.

 

I had no success at all: these numbers are certainly not advertised up front.

 

What they do seem to do is fudge round the question by stating the phone/instrument reads to within 0.1 degree. This is essentially meaningless: an instrument with a readout to one decimal place will always give a readout to one decimel place regardless of how accurate it actually is.

 

 

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PS Fallowdeer here suggested using a laser pointer mounted to the blade, intead of a stick. Assuming the mounting was a neat fit on the blade, it sounds like a good idea to me..........

 

 

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I was once checking my prop when this elderly visitor to my hangar  pointed out that the relative airflow into your prop is seldom if ever right on the prop axis. 

 

A degree or so of slip or skid is hardly noticed on the skid ball, and angle-of attack variation will generally be more than one degree.

 

Don't let this knowledge stop you from getting the prop as good as you can, but bear in mind that there are some big other factors involved in the final result of getting smooth running. 

 

 

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PS Fallowdeer here suggested using a laser pointer mounted to the blade, intead of a stick. Assuming the mounting was a neat fit on the blade, it sounds like a good idea to me..........

 

That would work. You will just have to deduct how many mm above the back of the blade the pointer is & that it is dead parallel. By the time you have done everything you could have done it twice with just the straight edge. It doesn't matter if you are 0.1 degrees out, just so long as all blades are the same. Try a fine pitch fly & then record climb, cruise & full power S&L, record the findings including Ts & Ps, set a coarse pitch then & do the same in as close as possible to the same conditions especially temperature & pressure. You can then adjust to what you prefer. I wanted good cruise speed at 70-75% power. The Jab 3.3 has plenty of power in the climb as I am getting around 1200 fpm at 80 knots at about 22deg OAT. When I had the pitch fine I could over rev the engine S&L & climb was over 1500 fpm. Now I can fly S&L at a smidgen under full continuous power. It took me 4 adjustments to get it as good as I want.

 

 

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This is something you can make and the laser pen is a great addition. Gets very accurate adjustment.  Cheers

 

 

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All good ways to adjust pitch. The bolly stick method though needs no specially made tools or lasers so costs nothing so long as you have a straight edge, a tape measure and a spirit level and is as accurate as the best of the others. 

 

 

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I got the Bolly stick instructions with my prop as one of the options for setting the pitch but I was concerned with how accurate it will be with the hanger floor being dirt with a camping mat over it.

 

 

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Nope unfortunately.... Grass strip. Dirt floor hanger. And Beer and Cheese....

 

Place a concrete 450 x 450 mm square for areo-bunnings on the floor where your measuring to, that will maintain your positions.   Images show the laser pen point on the ground and its behind the protractor.  It is good for altering the pitch to get the desired rpm at WOT etc.

 

20180626_182011.thumb.jpg.c4830ea9e5bac3afc4b59d9891181fbc.jpg

 

20180626_182037.thumb.jpg.043c1e1c6ce2c2f8fd9141e067b881f1.jpg

 

168843649_PenLaserdot20180626_174635.thumb.jpg.70dbd31e01600aba196f5da3e9e7978d.jpg

 

 

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Nope unfortunately.... Grass strip. Dirt floor hanger. And Beer and Cheese....

 

As Bluey advised, don't worry about the dirt floor, just make sure the thrust line is level by lifting or lowering the tail. Anything that is flat and big enough, 300 x 300 will usually be enough but a bit bigger may be easier. A flat tile or a bit of gyprock, ply etc will suffice. Just get it level & you are good to go. Even if you have a different height next time, so long as you follow the instructions the result will not change. It is just the 1 in 60 rule.

 

 

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I think you will find that the 1 in 60 rule is nowhere near accurate enough. Using KGWilsons method I calculate the actual angle would be 18.43 degrees.

 

Worked out trigonometricly. 400mm along horizontally and divide by 1200 vert. distance is 0.333. Arctan of .333 is 18.4349.

 

 

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For sure the maths needs to be a bit fancier than 1 in 60 if trying to set an exact known angle using stick and floor measurements.

 

But it should be fine for 'a bit more/less' type adjustments, and for checking that all blades are pitched the same.

 

 

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Who cares about 0.005 degrees or 0.1 degrees. Set it, go flying and then determine whether your pitch is too fine or coarse for the type of flying you do. After the final adjustment I can't even remember what my pitch is. I now have the performance that gives me a good rate of climb with a good cruise speed, max continuous rpm at S&L WOT and fuel consumption that suits my style of flying. My EGTs & CHT are on the low side so I couldn't give a flying fig about what the numbers are.

 

Continuously changing the prop pitch defines you as a fiddler IMHO (more than 6 changes to get it right). We had a couple of those at our airfield. They kept changing the pitch on an almost daily basis and failing to recognise that barometric pressure, temperature and humidity were having an effect as well. These can be dramatic, check the density altitude difference between standard ISO conditions and a 35 degree day at 990 hpa.

 

 

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Negative to the last question. The Bolly pitch tool is graduated to 1/2 degree and very difficult to read. It also suffers from friction and is unstable when holding on the prop blade (needs to be kept accurate and still in 2 axis). I spent a long time adjusting my blades when I installed my new Bolly.

 

Now I have made a precision tool that gives me repeatable results in a few seconds flat and found over 1/2 degree of variations. Preparation work is to have accurate station markings on your blades (I use 500mm from the hub, serves also as the pull-point for the engine friction test).

 

Then set the trailing edge of the blade level through the spirit level (bubble), record the reading on the clinometer and go to the next blade. Pull the prop very slowly and from the top blade to minimise aircraft movement (this set-up is not sensitive to aircraft movement, unlike the stick/laser method).

 

There is a bit more work involved if you are installing a new prop as you need to calibrate the 0 line first. For checking the pitch on each prop or to change the pitch from a known position, real quick and easy.

 

20190314_153748.thumb.jpg.6f77fd489feaa0d82c72499bb771dd67.jpg

 

 

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