Announcement

Collapse
No announcement yet.

Prop clocking

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • astjp2
    replied
    Re: Prop clocking

    Originally posted by SpecialT View Post
    Ok, you know it's been a while when you forget your password and need to request a reset...

    So I've been flying the prop clocked at every available angle and the 11'oclock is the best. The 9-3 made it buzz (slight roughness) at most rpms over 2k, the current position with the prop at 11'oclock but with the #1 blade pointing down (180 deg out) seems to be the best for my current set up. I know these Lyc's are not sewing machines, and certainly not paint shakers, but if I ever rebuild one I'm going to balance everything. I thought for sure the 9-3 position was it, but I guess the precession forces have better ideas and Lycoming was right.
    Yep, what I said earlier...11:00

    Leave a comment:


  • SpecialT
    replied
    Re: Prop clocking

    Ok, you know it's been a while when you forget your password and need to request a reset...

    So I've been flying the prop clocked at every available angle and the 11'oclock is the best. The 9-3 made it buzz (slight roughness) at most rpms over 2k, the current position with the prop at 11'oclock but with the #1 blade pointing down (180 deg out) seems to be the best for my current set up. I know these Lyc's are not sewing machines, and certainly not paint shakers, but if I ever rebuild one I'm going to balance everything. I thought for sure the 9-3 position was it, but I guess the precession forces have better ideas and Lycoming was right.

    Leave a comment:


  • astjp2
    replied
    Re: Prop clocking

    I have propped a Comanche set at 9/3 and it sucked, put it at 11 and he done with it, you may have to prop and it's the safest position to start from. Tim

    Leave a comment:


  • PA1195
    replied
    Re: Prop clocking

    Review these. If there's access to a prop balancer that generates a plot of vibes vs rpm then it would be interesting to note any real measured changes or benefits by re-indexing. The rough start-up mentioned will be worth looking for:

    https://groups.google.com/forum/#!to...lt/5vp2oGDiEKE
    https://www.lycoming.com/sites/defau...20Location.pdf

    Gary

    Leave a comment:


  • SpecialT
    replied
    Re: Prop clocking

    We've been fogged in this whole time and not able to fly. I might rent a car and drive the kids to Oshkosh before I get a chance to turn the prop and test it out. But I found some more interesting discussions about prop clocking at the 9/3 o'clock position, which is not an advantageous position for hand propping but seems to reduce 1/2 order vibrations.

    http://mstewart.net/super8/propclock/index.htm

    I guess the 9/3 position (#1 TDC and #1 blade in line with the #1 cylinder) is the one advocated in the Sacramento Sky Ranch manual for smoothness because it's in line with the plane of the front crankthrows. Since I have a starter on the engine this might be a viable option. When I get a chance I'm going to try it and report back.

    Leave a comment:


  • PA1195
    replied
    Re: Prop clocking

    Hi Dave. The weight scheme was and is an experiment in longevity and effectiveness. The Repair Station first tried washers under that bolt head with a longer bolt to maintain full thread penetration in the crankshaft's flange. The added weight of the longer bolt and washers (they need to be small diameter to fit inside the dome) was insufficient to fully balance the engine. They next tried fastening the weight to the dome bracket support leg that's attached to that bolt. Centrifugal force soon partially wear cracked the leg of the bracket the weights were attached to but the dome didn't depart the aircraft.

    This is the latest iteration. A piece of 4130 chromoly strap heat bent to stay as close to the bolt head and required balance weight location. The thickness, width, and length protruding forward determines the balance weight. No other shapes or material thickness were tried.

    Once installed the dome was attached and a balance run done. The weight was made longer and heavier to begin with. The balancer machine calls out the clock position and weight it predicts will balance the assembly. By trimming the forward angle (see shiny cut) the final weight versus indicated balance via sensor movement in inches per second was established (the sensor is installed vertically on top of the upper crankcase split).

    It's now about 50 grams - more than if it had been just washers because a portion is closer to the prop center and has less effective rotating mass. The closer to the hub's center the more weight is required to achieve balance.

    We inspect it periodically and no problems have been noted. It's now a smoother engine than without it installed.

    Gary
    Last edited by PA1195; 07-16-2018, 12:34.

    Leave a comment:


  • drude
    replied
    Re: Prop clocking

    very cool weight scheme!

    before going vertical? or horizontal? I don't follow

    Leave a comment:


  • PA1195
    replied
    Re: Prop clocking

    Here's an example of a balanced prop - Field Approved M76AK-2-40 on my Taylorcraft. This was done by a local prop repair station using an electronic balancing system at about 2400 static/typical cruise rpm. Vibes went from a bit over 0.2 IPS to well below that value. The weight is just under 50 grams, but as I note above would be less providing all the weight could have been placed and centered under a bolt head with room for prop dome installation. Extending the 4130 tab allowed dome clearance and met the balance requirements called for at that clock location by the test instrument.

    In the left pic the prop is at the 11 o'clock position that allows for magneto impulse release before going vertical.

    http://www.propellerman.com/dynamic-balancing.html

    Gary
    Attached Files
    Last edited by PA1195; 07-16-2018, 00:15.

    Leave a comment:


  • N96337
    replied
    Re: Prop clocking

    Originally posted by drude View Post
    It is possible that the manufacturer is specifying a prop position based on the prop's location relative to the crankshaft throws for the purpose of managing engine power pulses and dynamic balance considerations.

    It is also possible that the manufacturer is considering the above and hand propping at the same time and he is giving the best compromise.

    I would just follow the manual.

    I am not sure what you gain with a 180 degree swap, it is a 2 blade, correct?
    I totally agree with this and with what Gary says.
    John

    Leave a comment:


  • drude
    replied
    Re: Prop clocking

    ahhh

    Thanks Gary, I had not realized that tracking was a problem to be solved and what you said makes perfect sense for that.

    Dave R

    Leave a comment:


  • PA1195
    replied
    Re: Prop clocking

    Sometimes and somehow the prop's track between blades can be improved by 180* swapping. Probably a combination of the crankshaft being slightly out of round but within manufacturer's tolerance (https://www.cubclub.org/samples/web_con_maintenance.pdf) in combination with a propeller that isn't perfect either...one blade is slightly deformed relative the other. Swapping "may" both increase (make it worse) or decrease stacking tolerances (make it better) and improve blade tracking (http://okigihan.blogspot.com/p/propeller-vibration.html).

    Prop balancing link: http://okigihan.blogspot.com/p/prope...unbalance.html

    Gary
    Last edited by PA1195; 07-15-2018, 14:24.

    Leave a comment:


  • drude
    replied
    Re: Prop clocking

    It is possible that the manufacturer is specifying a prop position based on the prop's location relative to the crankshaft throws for the purpose of managing engine power pulses and dynamic balance considerations.

    It is also possible that the manufacturer is considering the above and hand propping at the same time and he is giving the best compromise.

    I would just follow the manual.

    I am not sure what you gain with a 180 degree swap, it is a 2 blade, correct?

    Leave a comment:


  • mikerice
    replied
    Re: Prop clocking

    All of my descriptions are based on standing at the prop looking aft. Gary said the same thing - that the mags fire as you pull the prop through 9 o'clock or so. The prop has 6 bolts evenly spaced, so 360/6 is 60 degrees as you move the prop one bolt hole at a time. That means you only have 3 holes to index to, as the other 3 would be the #2 blade in the same relative positions. You will find one position allows the mags to click (fire) on the downward swing. Then you can rotate the prop 180 degrees, and that would put the opposite blade in the correct firing position, if you wanted to see if the balance is affected.

    Leave a comment:


  • PA1195
    replied
    Re: Prop clocking

    Originally posted by SpecialT View Post
    is 11 o'clock the position when looking at the prop from the front when mounting
    In my experience yes. Designed to fire before the prop goes vertical on the down swing.

    Gary

    Leave a comment:


  • SpecialT
    replied
    Re: Prop clocking

    Thanks for the input. Well I was thinking I moved the prop to the "right" position, but is 11 o'clock the position when looking at the prop from the front when mounting, or is is when sitting in the cockpit looking out the front window? Maybe I moved it from 11 o'clock to 1 o'clock. I think I'll try the 180 deg. swap next to see what I get.

    Leave a comment:

Working...
X