Pendulum dampers were invented for use on the big radials. read a first person account of that here:
Piston Engines
The hockey puck type has been completely eclipsed by the the roller-weight type. Hockey puck type was actually available as The Rattler for Detroit V-8's, it replaced the front pulley/ harmonic damper. Story was it worked at higher rpm, had rollers tuned to 4th and 8th order of rotation (the biggies in V-8's), but is no longer available.
Roller-weight type have been applied to airplane piston engines since the late 1930's, and are currently in use in some cars, mostly diesels, supplied by ZF-Sachs and LuK. LuK holds the patents, so ZF-Sachs sells under license. There are even multiples of them hung on some large helicopter rotor sets. These gadgets must be designed and developed to rather precisely match the vibe orders you are after, one swing radius per order attacked. Where they are designed/developed to work, they work extremely well, sucking off firing pulses very nicely on diesel engines. I have seen data indicating 95% reduction of tuned order. But if you need 2x engine order and yours absorbs 2.25x engine order, it is doing just about zero for you. So the design has to be adjusted to be very close to what you need. And once you suck off the biggest order, what used to be the second biggest vibe order now becomes the biggest vibration. It is like the light under the door... LOL.
On the crankshaft, they have small radius and so these tuned counterweights have to be pretty big to be effective. For vehicles with transmissions, these gadgets can go on at larger radius on a flywheel or inside a torque converter and so can be lighter. In automatic transmission vehicles, they actually work better on the wheel downstream of the spring element. Tuning to run in air (manual trans flywheel mounted) is different from tuning in oil (mounted inside torque converter), so be careful to run in the intended fluid or it simply won't work. Also, know that cars and trucks make their big firing pulses during accel, so the manufacturers actually tune the tracks to be ever so slightly above the intended firing order - you get better isolation during accels that way. Buying car systems to attach to your airplane may not be an effective strategy.
Now how would this apply to our problem? Order Tuned Torsional Pendulums will reduce the order attacked. but not eliminate it. In cars and trucks, they are used to reduce firing order vibration through the drivetrain because the customers can feel that vibe. Turbocharged diesels are particularly bad, so more effort is applied there. They are not being used to suck off driveline resonance in cars and trucks. Resonance is handled by driving resonant frequencies low with arrangement of inertia and springs, adding soft elements, then applying frequency tuned absorbers where needed.
To have value in Engine-PSRU-Prop arrangement, the pendulum could be applied to reduce engine firing pulses, but they are still there and so damaging amplification can still occur. The other engine orders are also still there with all their damaging potential should they line up with system vibe modes. Even fire four cylinder engines have 2x (compression-firing), 4x (pistons accelerating back and forth in the bores), and a bunch of others due to all sorts of issues that no one has been able to control. So maybe you put the gadget between engine and prop and tune it to absorb the natural frequency between engine and prop. That absorber might have to be big indeed. Maybe you tune the order of the gadget coincide with the vibe on frequency and rpm. OK, that gets one. Ross and his buddies have already experienced more than one rpm range - these vibes may be the same mode but with a different order coming from engine or the same order from the engine but a different mode. We do not know without more involved modeling and/or instrumentation.
Instead of an order tuned absorber, would not a frequency tuned absorber work better on beating something that happens at a particular frequency? They too exist and are way simpler. Steel sleeve on a rubber sleeve pressed over a shaft, used on front crankshaft pulleys (called harmonic dampener) and driveshafts/halfshafts on some vehicles. But you only get one frequency per gadget, and with a poor scheme, you might have more than one mode you need to beat. Be careful which ones you beat, and which ones you leave.
The really big trick in managing vibration is not in knowing the gadgets that can handle any one mode and forcing function combination, but in having a strategy of knowing all of the vibe modes and exciters of each layout so that you can pick a layout that can then have gadgets added to handle the modes. In road vehicles, we put the clutch or torque converter at the engine with a soft element there to isolate the engine firing order from everything else, then add the gearbox. Layouts with the clutch elsewhere, gearbox remote, etc have way more troublesome situations than what is common in cars and trucks. AWD racecars have been built using unusual configurations and had problems no one ever solved.
Much more complicated schemes exist. A standard helo is one with a piston engine, transmission, flexible shafting to one big rotor, even more flexible shafting to another gearbox and rotor. Turbines appear to have made part of it simpler - no firing pulses - but there are still a bunch of other vibe forcing functions out of the engine, accessories, gearboxes, shafts, and rotor sets). Then there are multiple engine sets, double main rotor helos, and then tilt-rotors - an engine and gearbox on each wing, a rotor on each wing, a shaft system with clutches between the engines for cross driving in an engine-out situation, and tilting the whole thing so it can fly as an airplane and as a helo. And all of these have ground resonance as significant modes too. Ugh.
By comparison we have it easy - put the firing frequency well below idle but safely above cranking speed with a soft element, make everything else stiff enough so the remaining modes are off range high, then see if anything else is hiding, and handle them. Keep your torsional vibe analyst and instrumentation geek in the loop, as you will still need their help at any stage of the process.
Billski
Piston Engines
The hockey puck type has been completely eclipsed by the the roller-weight type. Hockey puck type was actually available as The Rattler for Detroit V-8's, it replaced the front pulley/ harmonic damper. Story was it worked at higher rpm, had rollers tuned to 4th and 8th order of rotation (the biggies in V-8's), but is no longer available.
Roller-weight type have been applied to airplane piston engines since the late 1930's, and are currently in use in some cars, mostly diesels, supplied by ZF-Sachs and LuK. LuK holds the patents, so ZF-Sachs sells under license. There are even multiples of them hung on some large helicopter rotor sets. These gadgets must be designed and developed to rather precisely match the vibe orders you are after, one swing radius per order attacked. Where they are designed/developed to work, they work extremely well, sucking off firing pulses very nicely on diesel engines. I have seen data indicating 95% reduction of tuned order. But if you need 2x engine order and yours absorbs 2.25x engine order, it is doing just about zero for you. So the design has to be adjusted to be very close to what you need. And once you suck off the biggest order, what used to be the second biggest vibe order now becomes the biggest vibration. It is like the light under the door... LOL.
On the crankshaft, they have small radius and so these tuned counterweights have to be pretty big to be effective. For vehicles with transmissions, these gadgets can go on at larger radius on a flywheel or inside a torque converter and so can be lighter. In automatic transmission vehicles, they actually work better on the wheel downstream of the spring element. Tuning to run in air (manual trans flywheel mounted) is different from tuning in oil (mounted inside torque converter), so be careful to run in the intended fluid or it simply won't work. Also, know that cars and trucks make their big firing pulses during accel, so the manufacturers actually tune the tracks to be ever so slightly above the intended firing order - you get better isolation during accels that way. Buying car systems to attach to your airplane may not be an effective strategy.
Now how would this apply to our problem? Order Tuned Torsional Pendulums will reduce the order attacked. but not eliminate it. In cars and trucks, they are used to reduce firing order vibration through the drivetrain because the customers can feel that vibe. Turbocharged diesels are particularly bad, so more effort is applied there. They are not being used to suck off driveline resonance in cars and trucks. Resonance is handled by driving resonant frequencies low with arrangement of inertia and springs, adding soft elements, then applying frequency tuned absorbers where needed.
To have value in Engine-PSRU-Prop arrangement, the pendulum could be applied to reduce engine firing pulses, but they are still there and so damaging amplification can still occur. The other engine orders are also still there with all their damaging potential should they line up with system vibe modes. Even fire four cylinder engines have 2x (compression-firing), 4x (pistons accelerating back and forth in the bores), and a bunch of others due to all sorts of issues that no one has been able to control. So maybe you put the gadget between engine and prop and tune it to absorb the natural frequency between engine and prop. That absorber might have to be big indeed. Maybe you tune the order of the gadget coincide with the vibe on frequency and rpm. OK, that gets one. Ross and his buddies have already experienced more than one rpm range - these vibes may be the same mode but with a different order coming from engine or the same order from the engine but a different mode. We do not know without more involved modeling and/or instrumentation.
Instead of an order tuned absorber, would not a frequency tuned absorber work better on beating something that happens at a particular frequency? They too exist and are way simpler. Steel sleeve on a rubber sleeve pressed over a shaft, used on front crankshaft pulleys (called harmonic dampener) and driveshafts/halfshafts on some vehicles. But you only get one frequency per gadget, and with a poor scheme, you might have more than one mode you need to beat. Be careful which ones you beat, and which ones you leave.
The really big trick in managing vibration is not in knowing the gadgets that can handle any one mode and forcing function combination, but in having a strategy of knowing all of the vibe modes and exciters of each layout so that you can pick a layout that can then have gadgets added to handle the modes. In road vehicles, we put the clutch or torque converter at the engine with a soft element there to isolate the engine firing order from everything else, then add the gearbox. Layouts with the clutch elsewhere, gearbox remote, etc have way more troublesome situations than what is common in cars and trucks. AWD racecars have been built using unusual configurations and had problems no one ever solved.
Much more complicated schemes exist. A standard helo is one with a piston engine, transmission, flexible shafting to one big rotor, even more flexible shafting to another gearbox and rotor. Turbines appear to have made part of it simpler - no firing pulses - but there are still a bunch of other vibe forcing functions out of the engine, accessories, gearboxes, shafts, and rotor sets). Then there are multiple engine sets, double main rotor helos, and then tilt-rotors - an engine and gearbox on each wing, a rotor on each wing, a shaft system with clutches between the engines for cross driving in an engine-out situation, and tilting the whole thing so it can fly as an airplane and as a helo. And all of these have ground resonance as significant modes too. Ugh.
By comparison we have it easy - put the firing frequency well below idle but safely above cranking speed with a soft element, make everything else stiff enough so the remaining modes are off range high, then see if anything else is hiding, and handle them. Keep your torsional vibe analyst and instrumentation geek in the loop, as you will still need their help at any stage of the process.
Billski
