Thread: Point of mechanical engineering "balance"

Amen

(And don't forget the use of unusual fasteners to fit into tiny spaces and their expensive/rare special tools to undo them...)

Originally Posted by Lionelgee

Hello All,

What is the point of balance called when something round and dynamic - such as a car tyre, is put into a "balancing machine" and weights are added to it until it is "balanced". Or in the case of a flywheel metal is removed until the fly wheel is balanced or runs "true". Other than "balanced" or "True" what is the term used in mechanical engineering parlance?

Is it the point of equilibrium? Or is it known by another name? For instance, in the example of a balance beam with two uneven weights located at opposing ends - a pivot can be repositioned under the beam until a point of equilibrium is reached and the beam is horizontal.

What is the term used when a disk is revolving from a central point and the disk is adjusted until it reaches a point of being in balance?

Thanks

Kind Regards
Lionel

You're not thinking centre of gravity?

What sometimes leads to confusion with balance is "resonance" or the mechanical resonant frequency of a moving mass.

A small example is the balance wheel in a clock, where it is used to advantage to regulate the movement to maintain the time as we known it.

Your Land Rover has an harmonic balancer, which if not working is likely to shake a lot of money out of your pocket!

Big ship marine diesel engines ALWAYS have a certain critical RPM, which if allowed to run at critical speed will rapidly destroy the engine. I am talking about slow speed diesels of around 100 to 120 RPM.

An extreme example of resonance is shown with the video of the Chinook helicopter. The type of rotor system used is prone to "ground resonance", no matter how well balanced the rotor system may be.

Originally Posted by Old Farang

What sometimes leads to confusion with balance is "resonance" or the mechanical resonant frequency of a moving mass.

A small example is the balance wheel in a clock, where it is used to advantage to regulate the movement to maintain the time as we known it.

Your Land Rover has an harmonic balancer, which if not working is likely to shake a lot of money out of your pocket!

Big ship marine diesel engines ALWAYS have a certain critical RPM, which if allowed to run at critical speed will rapidly destroy the engine. I am talking about slow speed diesels of around 100 to 120 RPM.

An extreme example of resonance is shown with the video of the Chinook helicopter. The type of rotor system used is prone to "ground resonance", no matter how well balanced the rotor system may be.

High speed turbines also have critical speeds that need to be pushed past quickly during startup. They will often have 2 or 3 critical speeds on the way up to opertating speed. A good example of a critical speed is a bench grinder when its running down - starts to reduce speed nice and smoothly, then gets a point where is shakes itself around a fair bit and then smooth off again. Thats a critical speed and occurs when the rotating speed lines up with a resonate frequency - which then amplifies the machines vibration

One of the aircraft types I used to fly (can't remember which one) had the usual band of green ending in a red line on the tacho - with an orange band about 100rpm wide a few hundred rpm below the red line, and a placard warning you not to operate in that band.

Same thing.

John

Originally Posted by JDNSW

One of the aircraft types I used to fly (can't remember which one) had the usual band of green ending in a red line on the tacho - with an orange band about 100rpm wide a few hundred rpm below the red line, and a placard warning you not to operate in that band.

Same thing.

John

Was it an arrow?

Yes, I think that would be right - an Arrow 180.

John

Originally Posted by JDNSW

Yes, I think that would be right - an Arrow 180.

John

G'day John & BBD,

One of these ... Accessed February 7, 2016 from,
Piper PA 28R Arrow aircraft history performance and specifications

Kind Regards
Lionel