Nickodell
Donation Time
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moved stuff
- Thread starter Nickodell
- Start date
Nickodell
Donation Time
Good try, but actually no photoshop or other electronic image trickery, or cut-and-paste. There really is a solid Alpine front at each end on the photo. How I did it you'll have to guess.
P. Scofield
Bronze Level Sponsor
I always take a plug out and slip a piece of rope in the #1 cylinder prior to re-torquing.
Not sure why, just something I picked up here on the board.
Paul
Not sure why, just something I picked up here on the board.
Paul
sammaw@bellsout
Silver Level Sponsor
I also shove some rope up the tailpipe, I don't know why
Nickodell
Donation Time
Nope. Then the Twinpine would have the 1725 badge on both ends instead of one (the right-hand-side clip did not come with that badge), I would be appearing in a mirror image at both ends (sorry, you have to pay double for two of me) and the background would be mirrored on both sides instead of being different.
P. Scofield
Bronze Level Sponsor
I've thought that but felt it would be very uncomfortable pulling the rope out!
skywords
Donation Time
In my younger days I rebuilt very large engines with 2800 cubic inch of displacement. Eighteen cylinders. The crankshaft was a three piece affair held together with very large bolts of the internal spline type. To torque these bolts the crankshaft was place into a large horse like fixture with a rack and pinion that hydraulically applied torque to these bolts. The proper torque was achieved when the proper amount of stretch was measured in the bolt. I believe it was around .006". This horse we nicknamed the atom smasher for it loved to snap the splines that were inserted in the bolts making our boss very upset for he had them fabricated specially for this task, not cheap.
This is what the crank looks like (face spline type).
http://www.enginehistory.org/NoShortDays/CrankHX.pdf
This is what the crank looks like (face spline type).
http://www.enginehistory.org/NoShortDays/CrankHX.pdf
Nickodell
Donation Time
Rick: IIRC, Bugatti used built-up crankshafts too, because he preferred ball bearing mains instead of sleeve bearings.
And it's always surprised me that you can balance a radial engine with a master rod design, considering that all the other rods and pistons move slightly less distance than the master rod does, so you have one cylinder firing x cu.in. and six (or eight) firing x-y. One would think it would create some sort of vibration harmonics that would cause trouble. With the millions of similar radials out there, obviously it doesn't.
And it's always surprised me that you can balance a radial engine with a master rod design, considering that all the other rods and pistons move slightly less distance than the master rod does, so you have one cylinder firing x cu.in. and six (or eight) firing x-y. One would think it would create some sort of vibration harmonics that would cause trouble. With the millions of similar radials out there, obviously it doesn't.
Nick,
I assume Rick will reply, but it seems to me that the displacement of each cylinder in a radial engine would be identical. The master rod (and piston) does not move any more or less than the others, but rather its location (distance from the crank center is different). I think all you need to do is simply make the master rod length a little longer than the others.
I am quite unfamilar with radial engines, but my recent experience with designing my Chevy rod engine has taught me a litttle about stroke, displacement, rod length, and cranks. And I drew a diagram to help understand.
Boy, have we highjacked this thread !
Tom
I assume Rick will reply, but it seems to me that the displacement of each cylinder in a radial engine would be identical. The master rod (and piston) does not move any more or less than the others, but rather its location (distance from the crank center is different). I think all you need to do is simply make the master rod length a little longer than the others.
I am quite unfamilar with radial engines, but my recent experience with designing my Chevy rod engine has taught me a litttle about stroke, displacement, rod length, and cranks. And I drew a diagram to help understand.
Boy, have we highjacked this thread !
Tom
skywords
Donation Time
Tom you correct the stroke is identical in every cylinder. The master rod does take more of a beating than the other eight cylinders. The master rod cylinder is always the trickiest to change because if you let the rod lean past center in the crankcase you risk having a bottom ring pop out of the bottom of a skirt on one of the cylinders with a slave rod. Ask me how I know.
Lets take this to chit chat so not offend. sorry guys we are easily side tracked.
I myself would re torque the head but without backing off the bolts. I think backing off and changing to a lower toque setting is asking for trouble with the gasket. Stick with the 48 and use the newer setting next time you change a head.
Lets take this to chit chat so not offend. sorry guys we are easily side tracked.
I myself would re torque the head but without backing off the bolts. I think backing off and changing to a lower toque setting is asking for trouble with the gasket. Stick with the 48 and use the newer setting next time you change a head.
MikeH
Diamond Level Sponsor
Has to be a double exposure. The bottom door lines of both are visible and the windshield heights are different.
Nickodell
Donation Time
Rick: Thanks for the correction. According to the two authorities I use, the great books Allied Aircraft Engines by GrahamWhite, and various books by the great Bill Gunston, e.g. Development of Piston Aero Engines, later radial engine designs had piston travel, and hence swept volume, of the cylinders served by the articulated rods almost identical to that of the master rod.
To achieve this, the attachment points for the knuckle pins of the articulated rods were placed so as to cancel out the different motion paths of these and the master rod big-end bearing itself.
However - and this is what I was dimly remembering but erroneously attributed to different cylinder volumes - only the master rod bearing moves in a circular path. None of the knuckle pins moves in a circle (they move in ellipses), and no single knuckle pin follows exactly the same path as any other. In order to compensate for what would otherwise be different piston strokes, each knuckle pin is at a slightly different distance from the crankpin center. As a result, each piston has a unique motion (not stroke distance, as I erroneously thought).
When one looks at this, and the difference in mass between the huge master rod and the much smaller articulated rods, it amazes me that the whole thing can be dynamically balanced. But obviously it can.
To achieve this, the attachment points for the knuckle pins of the articulated rods were placed so as to cancel out the different motion paths of these and the master rod big-end bearing itself.
However - and this is what I was dimly remembering but erroneously attributed to different cylinder volumes - only the master rod bearing moves in a circular path. None of the knuckle pins moves in a circle (they move in ellipses), and no single knuckle pin follows exactly the same path as any other. In order to compensate for what would otherwise be different piston strokes, each knuckle pin is at a slightly different distance from the crankpin center. As a result, each piston has a unique motion (not stroke distance, as I erroneously thought).
When one looks at this, and the difference in mass between the huge master rod and the much smaller articulated rods, it amazes me that the whole thing can be dynamically balanced. But obviously it can.
Nick,
I appreciate this discussion since I had often wondered about Radial engine cranks and now I understand. ( I think!) BUT. I do not see any need for the articulated rods to be pinned at different distances from the crank center. I see that the motion is eliptical. This results in the "motion" of each articulated piston being slightly different- i.e. the vertical velocity of each piston will be slightly different at mid stroke points. But the end points,TDC and BDC, will be the same assuming the same rod length . No? And thus the stroke length is the same for all. And if you made different locations for each knuckle it would simply require different rod lengths and then you still have the same stroke length for each.
But I see the drawing in your post and that end view drawing seems to show two different stroke lengths - looks like A1 and B1. But I can't make out enough detail. Is this drawing on line somewhere?
Tom
I appreciate this discussion since I had often wondered about Radial engine cranks and now I understand. ( I think!) BUT. I do not see any need for the articulated rods to be pinned at different distances from the crank center. I see that the motion is eliptical. This results in the "motion" of each articulated piston being slightly different- i.e. the vertical velocity of each piston will be slightly different at mid stroke points. But the end points,TDC and BDC, will be the same assuming the same rod length . No? And thus the stroke length is the same for all. And if you made different locations for each knuckle it would simply require different rod lengths and then you still have the same stroke length for each.
But I see the drawing in your post and that end view drawing seems to show two different stroke lengths - looks like A1 and B1. But I can't make out enough detail. Is this drawing on line somewhere?
Tom
Nick, I found the dwg on line:
http://www.enginehistory.org/NoShortDays/Vibration.pdf
And it Does indicate that the stroke lengths are different for the articulated rods. I'm puzzed.
Also see this link:
http://www.howstuffworks.com/framed...ine.htm&url=http://www.5bears.com/curproj.htm
See the master rod and articulated assembly. It says they are NOT 40 deg apart! I think THIS has something to do with the different stroke lengths, because TDC and BDC for the articluated rods do not occur at the peak points of the main crank relative to each cylinder. My brain hurts from trying to visualize these!
Tom
http://www.enginehistory.org/NoShortDays/Vibration.pdf
And it Does indicate that the stroke lengths are different for the articulated rods. I'm puzzed.
Also see this link:
http://www.howstuffworks.com/framed...ine.htm&url=http://www.5bears.com/curproj.htm
See the master rod and articulated assembly. It says they are NOT 40 deg apart! I think THIS has something to do with the different stroke lengths, because TDC and BDC for the articluated rods do not occur at the peak points of the main crank relative to each cylinder. My brain hurts from trying to visualize these!
Tom
Nick, I figured out why the knuckles are not at 40 deg (on a 9 cyl radial). Consider if the "hub" that the articulated rods were connected to was somehow magically constrained to maintain its vertical orientation as it rotated about the crank. Then the knuckles would be located at exactly 40 deg apart, the knuckles would all rotate in perfect circles, and all the stroke lengths would be the same as the crank stroke.
But, in fact, the "hub" for the knuckles is the bottom end of the master rod. This means that the "hub", instead of maintaining its vertical orientation, actually tilts left and right as the crank rotates. Picture a 4 cyl radial (not practical due to 4 cycle timing but easier to visualize the angles). At the 3 oclock piston, this tilt would cause the TDC position to be "retarded" by an angle equal to the angle the master rod is from vertical. To compensate for this the knuckle is positioned not at 90 deg but rather is advanced on the hub by the same angle. Thus it hits TDC at exactly the 90 deg crank angle. And the distance of the knuckle from Crank center is a simple calculation as the crank center, crank offset center, knuckle center and piston center are all in a straight line. This angle offset is most for the pistons at (or near) 3 oclock. But is zero (or near zero)for pistons at (or near) 6 oclock.
But this same offset to get the TDC at the right place in crank rotation causes twice as much "error" and in the opposite direction at the other end of the stroke. Consider the knuckle for the 3 Oclock piston when the crank is fully at the 9 oclock position. The angle offset plus the master piston rod angle causes the knuckle position to be "retarded" by twice this offset.
What I still can't figure out is when BDC occurs ! Somewhere between crank position of 9 O clock and a little past that (I think) . Furthermore, I cannot figure out the distance of the knuckle from crank center at BDC, so I cannot tell what the stroke length is. The drawing you showed and I linked shows the Stroke length of the articulated pistons (B1) to be slighty longer than the master. But I don't think so. For sure the knuckle location for a piston at 6 O'clock would not have any offset and thus the stroke would be identical to the master. I also think the article accompanying the drawing is just trying to simplify things when it says the knuckle pins are at different distances from the crank center.
This is pretty interesting stuff. I think my brain was better at spacial understanding when it was younger! But execises like this may delay Alzheimers - unless it's already here!
Tom
But, in fact, the "hub" for the knuckles is the bottom end of the master rod. This means that the "hub", instead of maintaining its vertical orientation, actually tilts left and right as the crank rotates. Picture a 4 cyl radial (not practical due to 4 cycle timing but easier to visualize the angles). At the 3 oclock piston, this tilt would cause the TDC position to be "retarded" by an angle equal to the angle the master rod is from vertical. To compensate for this the knuckle is positioned not at 90 deg but rather is advanced on the hub by the same angle. Thus it hits TDC at exactly the 90 deg crank angle. And the distance of the knuckle from Crank center is a simple calculation as the crank center, crank offset center, knuckle center and piston center are all in a straight line. This angle offset is most for the pistons at (or near) 3 oclock. But is zero (or near zero)for pistons at (or near) 6 oclock.
But this same offset to get the TDC at the right place in crank rotation causes twice as much "error" and in the opposite direction at the other end of the stroke. Consider the knuckle for the 3 Oclock piston when the crank is fully at the 9 oclock position. The angle offset plus the master piston rod angle causes the knuckle position to be "retarded" by twice this offset.
What I still can't figure out is when BDC occurs ! Somewhere between crank position of 9 O clock and a little past that (I think) . Furthermore, I cannot figure out the distance of the knuckle from crank center at BDC, so I cannot tell what the stroke length is. The drawing you showed and I linked shows the Stroke length of the articulated pistons (B1) to be slighty longer than the master. But I don't think so. For sure the knuckle location for a piston at 6 O'clock would not have any offset and thus the stroke would be identical to the master. I also think the article accompanying the drawing is just trying to simplify things when it says the knuckle pins are at different distances from the crank center.
This is pretty interesting stuff. I think my brain was better at spacial understanding when it was younger! But execises like this may delay Alzheimers - unless it's already here!
Tom