Marty d's CH-701 build log

[Marty_d]

Prop pitch done!  (First attempt anyway!)

 

I made a tool to hold a laser pointer which I bought on Ebay for $17.   I think it might be slightly illegal as the damn thing is very powerful - you can clearly see the beam in low light conditions and even in broad daylight you can see the spot on a tree that's 100m or more away.

Anyway, I was interested in @IBob's method of attaching a piece of wood and aluminium to the prop, but being someone who likes to over-complicate things I 3D printed a holder for the pointer based on measurements of the prop blade at 300mm from the tip (600 from the centre).  It slips on and stops at the same spot on each blade, and features a sliding switch which holds down the spring loaded button.

If anyone has a Bolly 3 bladed prop of the same model and wants to print their own, I'm quite happy to email you the STL file.

 

I ensured the prop is as vertical as possible, found the height where the blade is parallel to the ground and leveled the flat back of the blade vertically.  From this point I turned on the laser and made a cross on the floor where it hit.

Then used a calculator to get the adjacent length of the right angle triangle where I knew the vertical length and a 19 degree angle.  Marked a line at that point forward of the mark on the floor.  (Just to check, I calculated for 18.9 degrees and 19.1 degrees.  Each 1/10th of a degree is around 2.2mm.)

After that it was just a matter of swiveling the blade until the laser line exactly hit the front line, and repeat for the other 2 blades.  I nipped up the bolts just enough to hold the blades from turning - less than 8nm.  When I recheck with the spinner thingy off completely I'll tighten up the bolts to the recommended torque settings in the recommended order.

 

 

[IBob]

Marty......much tidier than the thing I cobbled up!

Apart from very accurate measurements from floor to blade (I use a stick with a clamp on it, bring the each blade down onto the clamp) and very accurate measurement from blade tip to laser position (I use a sliding square and mark the location with masking tape).........there is one other thing to watch for using this method, and that is blade tracking:
One of my blades tracks about 2mm further forward at the tip than the other two, so I factor that in. If I were using a similar method, but with an inclinometer on the blade, I wouldn't have to be concerned with the tracking. The only proviso then would to be sure I was using a good quality inclinometer, as they are not all born equal........
For myself, I will carry on with what I've got: done with care it does get very accurate results.

PS I tighten all bolts fully then check all blades again, as sometimes the tightening does shift the pitch a bit.
 

Edited Friday at 02:19 AM by IBob

[Marty_d]

1 hour ago, IBob said:

Marty......much tidier than the thing I cobbled up!

Apart from very accurate measurements from floor to blade (I use a stick with a clamp on it, bring the each blade down onto the clamp) and very accurate measurement from blade tip to laser position (I use a sliding square and mark the location with masking tape).........there is one other thing to watch for using this method, and that is blade tracking:
One of my blades tracks about 2mm further forward at the tip than the other two, so I factor that in. If I were using a similar method, but with an inclinometer on the blade, I wouldn't have to be concerned with the tracking. The only proviso then would to be sure I was using a good quality inclinometer, as they are not all born equal........
For myself, I will carry on with what I've got: done with care it does get very accurate results.

PS I tighten all bolts fully then check all blades again, as sometimes the tightening does shift the pitch a bit.
 

Thanks Bob!

 

I like the idea of the stick with clamp to get vertical distance.  Especially if the stick is a spirit level so you know it's vertical.  Will double check with that next time I do this.

 

With the blade tracking further forward, do you mean if the prop hub was sitting on a flat surface then that tip is 2mm higher than the other 2?  According to the instructions that came with mine, the flat table test should come after pitch - so now I have to take the prop off and do that test before putting it back on again.

 

[IBob]

Marty, for the stick with clamp, I just hold it vertical to start with and put a masking tape marker on the floor where it lands. I then position the stick on that marker for each blade.
I also use masking tape on the floor where the laser hits, so I can make precise marks with a pen.

As for tracking, I can't remember clearly how I did it. I think I had the aircraft facing a wall, brought each blade round onto the stick then measured to the wall. Or something like that. I certainly didn't go to the bother of removing the prop.

 

I'm not sure if you have measured and marked in from the tips for the laser location on the blade. If not, I would definitely recommend that too.

I guess it all sounds like a lot of mucking around, but I have found it simple and not a long job once you have the tools and method sorted.

An additional check as to how well you've done can be made in flight: at certain sun angles, the sun flashes off the back of the blade and all the flashes will look the same if the pitching is accurate.



 

[IBob]

After that, I think smooth running comes down to carb synchronisation.

 

That starts with the standard Rotax adjustment of the idle throttle stops and idle jets, which is a quick and simple job.

 

I took particular care installing my throttle linkages and routing the cables, then adjusted the cables so that both carbs come off the full throttle stop at the same time when when throttling back. Since much of flying is done at higher engine speeds, this seemed to me to be the most important end of the range. I do check at the other end of the range...that both carbs come off the idle throttle stops simultaneously, and in my case they do that too.
I made minor adjustments to maintain the synchronisation over the first 50hrs. Since then I have checked periodically but no further adjustment has been necessary.

I also fitted a simple idle position stop to the throttle bar that runs across the firewall: without this, if the pilot pulls back hard on the throttle, the load goes onto the carb throttle arms, and once they hit the carb idle stops, the arms will flex or distort.

 

 

Edited Friday at 05:26 AM by IBob

[Blueadventures]

3 hours ago, Marty_d said:

Prop pitch done!  (First attempt anyway!)

 

I made a tool to hold a laser pointer which I bought on Ebay for $17.   I think it might be slightly illegal as the damn thing is very powerful - you can clearly see the beam in low light conditions and even in broad daylight you can see the spot on a tree that's 100m or more away.

Anyway, I was interested in @IBob's method of attaching a piece of wood and aluminium to the prop, but being someone who likes to over-complicate things I 3D printed a holder for the pointer based on measurements of the prop blade at 300mm from the tip (600 from the centre).  It slips on and stops at the same spot on each blade, and features a sliding switch which holds down the spring loaded button.

If anyone has a Bolly 3 bladed prop of the same model and wants to print their own, I'm quite happy to email you the STL file.

 

I ensured the prop is as vertical as possible, found the height where the blade is parallel to the ground and leveled the flat back of the blade vertically.  From this point I turned on the laser and made a cross on the floor where it hit.

Then used a calculator to get the adjacent length of the right angle triangle where I knew the vertical length and a 19 degree angle.  Marked a line at that point forward of the mark on the floor.  (Just to check, I calculated for 18.9 degrees and 19.1 degrees.  Each 1/10th of a degree is around 2.2mm.)

After that it was just a matter of swiveling the blade until the laser line exactly hit the front line, and repeat for the other 2 blades.  I nipped up the bolts just enough to hold the blades from turning - less than 8nm.  When I recheck with the spinner thingy off completely I'll tighten up the bolts to the recommended torque settings in the recommended order.

 

 

Looks good Marty, I’m not sure about the 0.1 degree measurement as I’d expect the distance to be 2 to 3 times the distance (5-6mm)  You may have read my posts where I have been doing laser adjusting for about 5 years and is the way to do it. Keen to hear how you find it and learn the adjusting method to align rack blade on the dot.  What is the distance between the blade and the dot on floor? About 1100mm?

Edited Friday at 05:18 AM by Blueadventures

[Marty_d]

Yep, 1113 I think.

At 19 degrees that gave me 383.23 on the floor, whereas if you stick 19.1 degrees in the calculator it gives 385.41.

[IBob]

Blue, if the blade height is 1100mm, then 1 deg of pitch is about 20mm of laser spot movement. Actually a bit more, but not hugely so:

1100 x 2 x 3.14 = 6908

Divide by 360 = 19.2

[Blueadventures]

39 minutes ago, IBob said:

Blue, if the blade height is 1100mm, then 1 deg of pitch is about 20mm of laser spot movement. Actually a bit more, but not hugely so:

1100 x 2 x 3.14 = 6908

Divide by 360 = 19.2

Yes; just asking measurement from blade (top) to the dot on floor.  To make one side of a triangle, I then calculate as a right angle to get an approximate pitch angle.  (Nynja is about 1220mm)

[IBob]

Gotcha............)

[facthunter]

Got the message or him.?   It's ambiguous.  Nev

[Blueadventures]

8 minutes ago, IBob said:

Gotcha............)

I should have added that it is how I determine the amount of adjustment to get the target rpm S&L Wide open throttle.  So I start with a pitch and then adjust. Usually takes three processes.  I have found the laser is the way to go for this. To get pitch equal each prop is a method of tightening the prop hob bolts in a certain sequence that you learn after a number of torque sessions and with observation to get the dot on the spot for each blade.

[IBob]

Ops....certainly not got him!
Got the message....and added the method he outlined to my quite narrow fund of knowledge.
Thanks, Blue.