Diesel genset torque

[a64pilot]

After sleeping on it, of course it’s torque, for every action you get an equal and opposite reaction.
I was thinking about the source of the torque was all.

But I still believe the thrust centerline is why the front comes up, tie a farm tractor to a stump and it will raise the front end, tie a bulldozer to a stump and it won’t, even one without a blade.

So far as weight shift I guess it depends, in motorcycle drag racing we went fastest getting our bodies as far forward as we could to resist front end lift as opposed to sitting further aft, motorcycles you could control weight shift to a degree not possible in a car.

[a64pilot]

To further beat this dead horse, it should be easy to calculate the torque produced by a generator?
HP formula is torque x RPM/ 5252?
RPM is known, HP should be able to be determined by output in Watts of the generator?
Assumes 100% efficiency, but we are just after a SWAG right?

[Wotname]

Originally Posted by tkeithlu

Enough of basic physics class for one day.

Originally Posted by Captain Bill

I would argue that any time you have rotary motion you have torque. The effects depend on the moments of inertia of the two items in question. In this case the engine and generator head. If neither were attached to anything i.e floating in space the parts would rotate in opposite directions proportionally to the ration of their moments of inertia. Of course since there is no reference plane in space one could decide arbitrarily that one or the other was sitting still and the other was rotating. Here on earth the ground or water gives us a fixed reference plane and since the engine is coupled to it either by the boat or and engine mount to the ground the engine has a a huge moment of inertia and the generator head has a very small moment. Running in a steady state the engine only has to provide enough torque to replace the energy being extracted in the form of electricity and of course bearing and cooling friction. If the engine stopped applying this torque the generator head would come to a halt rather quickly as the energy stored in the rotating mass of the armature would be quickly extracted in the form of electricity. Remembering that for every action there is an equal and opposite reaction for every ft-lb or newton of torque applied the the generator head an equal and opposite force is applied to the engine. Only the large moment of inertia made by coupling (even if only by gravity and a frame of some sort) to the large mass of the earth prevents the engine from spinning. If this coupling is rather flexible such as on a floating boat there may in fact be detectable movement between the boat and the earth. In a monohull not in motion the keel might be heeled until the righting force (which is also a torque) is equal to the torque being applied to the armature by the engine.



In AH64s description of helicopters the torque applied to the rotor blades in a steady state is simply to replace the energy being extracted from the blades to keep the helicopter in the air. The tail rotor is used to counteract this torque and prevent the helicopter from rotating the the opposite direction of the blades. The long tail boom increases the moment arm of the anti-torque rotor allowing it to be much smaller than main rotors. Most helicopters moving forward also are designed to get some of the anti-torque effect from aerodynamic forces. Even in the event of a tail rotor failure at low speed the fuselage of the helicopter will rotate in the opposite direction of the main rotor much slower than the rotors because it has a much higher inertia than the light weight rotors. If a helicopter has to lift a larger load more energy is required to lift the load and more torque must be applied to the main rotors and more counter torque is required from the tail rotor.



On my boat the generator is mounted so that the torque is applied to the boat along the fore-aft axis and since the boat has a huge moment of inertia along that axis any movement is essentially undetectable. If I had a rather narrow monohull and mounter the genset so that the torque was applied along the roll axis I would not be surprised at all if there was a bit of detectable heel, especially if there was not a heavy keel and one needed to depend on buoyancy to counter the torque.

Thanks Capt Bill, you have made a very good analysis of the situation.

It must be right because I agree with it .

More seriously - it seems to me to agree with the basic physics that I was taught long ago although that in itself is not proof. I have learnt over the years not everything taught is factual!

As you state, it is the moments of inertia that is the key to understanding the issue and (unsaid), the conservation of energy. Further, a vector analysis of the forces make for clarity of the relative movements. One also must be able to comprehend the difference between theoretical movement and detectable (i.e. measurable) movement.

I offer only one comment.
Your first sentence is true and add that torque can exist without motion being present.

[admikar]

Helicopter analogy is not applicable, since it is a open system, which means engine is pushing rotors which then spill that energy to outside air. Hence the need for tail rotor to close that system. Tandem/coaxial helicopters are the same, only tail rotor is substituted for another main rotor.
Genset is closed system by itself. Engine is pushing generator and producing torque to one side. There is rotating resistance inside generator that tries to push outer casing to same direction, producing torque opposite to engine's torque. Since the engine and casing are bolted together, torque is mutually cancelled. Only way torque could spill to boat if is only engine or generator are affixed to boat and other part to outside.

[tkeithlu]

admikar, in all due respect, the helicopter analogy is completely appropriate and Captain Bill speaks wisdom. That taail rotor pushes against air the same way your propeller, and in this case the keel, pushes against the water. The torque has to go somewhere.

In case this seems a new issue,

Archimedes quotes: "Give me a lever long enough and a fulcrum on which to place it, and I shall move the world."

[tkeithlu]

Hey, a64pilot, when you lean forward on the accelerating motocycle you have converted the torque to potential energy in the front suspension lifting, and get it back when it slams down and you go over the handlebars. Be careful with the tractor model - you have the length of the moment arm (how high above the axle you attached the rope, when you should have used the draw bar). In that there have been a lot of fatal tractor accidents.

[admikar]

Originally Posted by tkeithlu

admikar, in all due respect, the helicopter analogy is completely appropriate and Captain Bill speaks wisdom. That taail rotor pushes against air the same way your propeller, and in this case the keel, pushes against the water. The torque has to go somewhere.

In case this seems a new issue,
Archimedes quotes: "Give me a lever long enough and a fulcrum on which to place it, and I shall move the world."

I agree with you, but genset is not pushing on water
If you're standing on that world, you can have lever as long as you wish, you're not moving it an inch. Here is the same: engine and generator are bolted to each other, so they are not moving anywhere.
Yes, there is a torque in engine, but there is equal and opposite torque in generator, so they cancel out. Of course, this is in case of constant RPM. If there is slowing down/speeding up, due to different inertia moments of engine and generator, there will be imbalance that can be interpreted as genset torque.

Edited to add: there are gyroscopic moments that can influence boat, but those are not part of this subject.