Mounting Position OF The Prop In Relation To TDC

Once watched a couple of helicopter mechanics doing the tracking of the blades on an S-55. Three blades, each with red, blue or green chalk on each rotor tip. A long stick with a strip of fabric stretched tight between two blocks on one end, sorta like one of those little dental floss tools, was held against the rotor tips once they were at working RPM, with just a bit of collective applied. The high and low blades were easy to identify from the colored stripes on the fabric.

Best done in the daylight:)

Dan
 
Dan Thomas said:
Once watched a couple of helicopter mechanics doing the tracking of the blades on an S-55. Three blades, each with red, blue or green chalk on each rotor tip. A long stick with a strip of fabric stretched tight between two blocks on one end, sorta like one of those little dental floss tools, was held against the rotor tips once they were at working RPM, with just a bit of collective applied. The high and low blades were easy to identify from the colored stripes on the fabric.

Best done in the daylight:)

Dan
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I've done it that way, and also used the stick method with a piece of chalk on the tip. Get the helicopter flat pitch at power and stand underneath the rotor disk and raise the stick till it just touches the chalk.

Fun times.
 
Dave Krall CFII said:
Yes that would be easy enough. I was envisioning checking the track while under full power to check for balanced prop flex. I guess for that super slow motion video might show it.
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You can also watch it from the edge using a strobe light and you'll be able to see it.
 
Henning said:
You can also watch it from the edge using a strobe light and you'll be able to see it.
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you don't need a strobe, just a flash light, you will see the 3 lines of different colored light reflecting off the tape.

Problem is, when you do see three lines of light what do you do about it?

McCauley says send it back.
Hertzeljerk says nothing.

EXP Ground adjustable? well maybe you can adjust it maybe not.

Wooden, Oh Well your just SOL.
 
NC19143 said:
Wooden, Oh Well your just SOL.
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You can shim the prop under the flange to get it to tract correctly. Seems like a piece of paper under the flange is about 1/32" - 1/16" by the time the increase gets to the end of the prop. The tract and torque should be monitored several times a year due to temperature / humidity changes.
 
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Geico266 said:
You can shim the prop under the flange to get it to tract correctly. Seems like a piece of paper under the flange is about 1/32" - 1/16" by the time the increase gets to the end of the prop. The tract and torque should be monitored several times a year due to temperature / humidity changes.
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You can shim as required to get static tracking correct, but as soon as you add power no two pieces of wood flex the same.

the blade that has the most mosture will flex more, So we fly for an hours and try it again, and always leave the wooden prop in the horizontal position when parked.

Unless a wooden prop has been over torqued it will not need shimming. If it has been over torqued you have compression wood near the bolt hole, and the prop should be thrown away.
 
NC19143 said:
If it was cut wrong, it will be wrong for ever.
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Maybe yes, maybe no. If it was cut out of dimension, then yes, it's f-ed up. If it is just out of shape, then there are ways to pull it into shape.
 
NC19143 said:
Unless a wooden prop has been over torqued it will not need shimming. If it has been over torqued you have compression wood near the bolt hole, and the prop should be thrown away.
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I see your point, but would not the crush plate prevent this? I mean, yes, if you over torqued by alot, but within reason I can't imagine distorting it to the point where it would track wrong. Depending on the humidity level in the prop you can adjust the track by shimming it. We do it often, however, most owners never check.
 
NC19143 said:
You can shim as required to get static tracking correct, but as soon as you add power no two pieces of wood flex the same.

the blade that has the most mosture will flex more, So we fly for an hours and try it again, and always leave the wooden prop in the horizontal position when parked.

Unless a wooden prop has been over torqued it will not need shimming. If it has been over torqued you have compression wood near the bolt hole, and the prop should be thrown away.
Click to expand...

If a blade was power flexing out of symetry and the shimming wasn't enough to correct it, couldn't a common balancing weight be drilled in and embedded in one blade to get it to flex right? Personally, I think I'd just put such a prop up on the wall with a clock in the hub...
 
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