11 replies to this topic

[slipstream]

How much influence does the Recpirocating mass of the engine and clutch have on Acceleration ? I am doing a paper for school about the performance of modern F1 cars so I would apperciate any help from the Atlas F1 experts.

[swoopp]

Not exactly sure what influence reciprocating mass has on the performance of cars. But I know it does have a big influence on motorcycles.

[perfectelise]

I would have thought the gyroscopic effect from the spinning crankshaft has a greater effect on handling than reciprocating mass.
I think certain aircraft will turn more easily to one side rather than the other because of gyroscopic effect from the engines.
It's another reason to go for a superlite crankshaft.

perfectelise

[marion5drsn]

Have been considering your question about the reciprocating mass on the acceleration of a car for some time. I believe you have miss worded your question. Firstly the clutch has no reciprocating parts being a rotating part only. The only part of the engine that is considered to be purely reciprocating is the upper part of the con rod and the piston including the rings, piston pin and some other miscellaneous pieces. Such as spiral locks and so forth. Also are you asking about Motion of Translation or Rotary Motion? One must always consider the lower part of the con rod as a purely rotating mass. If this were not so then one could not balance the crankshaft of the Primary Shake. I suggest that you find a copy of Charles Fayette Taylors book,” The Internal Combustion Engine in Theory and Practice”. Also are you asking about the cars acceleration or the engines acceleration? They are not quite the same. Yours, M.L. Anderson

[Ross Stonefeld]

I may have misunderstood the question but...


I know in Formula Ford (depending on rules) some teams machine their fly wheels so its denser in the middle so they meet weight rules for the flywheel, but its spins more easily. I dont know what it does to acceleration, but it sure revs up faster

[tak]

In the simplest form, any recipricating mass has to be accellerated and decelerated. This energy has to come from the engine. The easy way to calculate this is to assume the pistion is 2x oversquare (bore is 2 times stroke). Figure out the maximum piston speed. Calculate the kinetic energy of the piston (KE=.5MVV) (one half Mass x velocity squared). Similarly, calculate the maximum valve speed. Multiply by the number of valves, the number of pistons, number of connecting rods, etc. Add up the energy. That is the energy lost in one engine rotation. Multiply by RPM's. It is quite significant! However, because kinetic energy is .5MVV, and all you're talking about is mass...the relationship is linear.


In the case of pistons, the energy to decelerate and accelerate the piston as it goes through bottom dead center is totally lost. Some of the energy through top dead center on the compression stroke is stored in the compressed air charge. Take a Scientific Wild Ass Guess (SWAG) and write a justification for the efficiency you choose! The energy through Top dead center on the exhaust stroke is totally lost.
Since F1 cars run pneumatic springs, they only lose energy during closing to opening. The opening to closing stroke is recovered through the spring.
For the connecting rods, some of their mass rotates, some recipricates. Again, SWAG the percent and write a justification....

Lot's of simple math here. Great application for a spreadsheet...

Good Luck.

[tak]

Whoops, one last thing--the clutch does not recipricate (move up and down). I guess I should have asked, are you concerned about recipricating mass or rotational inertia? They are very different!!

[XHawkeye]

An example of how rotational mass costs hp.

http://www.turbomaga...09_wheels.shtml

Turbo magazine tested a two-bit Civic with stock vs big wheels which weighed 9.5 lbs more then the stock wheels. The extra 19 lbs of rotational mass reduced drive wheel hp by 3.8

[slipstream]

I am sorry I should have put my question differently. I am looking for the effects of the reduced inertia of a F1 Engine and Clutch on Acceleration ? I know that F1 Engines have a very light Crankshaft and Clutch and that helps the F1 Engine to spin to a High RPM,but how Does the reduced intertia help with Acceleration ?

[david_martin]

Perhaps it might be useful to think about the fundamental definition of intertia for a moment, because I suspect therein lies the answer to your question. Inertia is defined as resistance to acceleration. By definition, low inertia implies low resistance to acceleration, high inertia high resistance to acceleration.

For the case of rotational acceleration, which is at the core of your engine question, acceleration is related to inertia by:

angular acceleration = torque / rotational inertia

ie angular acceleration is inversely proportional to rotational inertia for a given torque. I think that with this relationship, and the other information posted, you have the necessary tools to answer your question

[marion5drsn]

The six laws of motion are at work here I believe; Motion of Translation
(1) Every body continues in its state of rest, or of uniform motion in a straight line, except in so far as it is compelled, by external impressed forces, to alter that state.
(2) The acceleration produced by force acting on a body is directly proportional to the magnitude of the force, inversely proportional to the mass of the body and takes place in the direction of the line of action of the force.
(3) To every action there is an equal and opposite reaction.

The laws of Rotational Motion are as follows
(4) Every body continues in its state of rest or of uniform rotation about an axis fixed in direction, except in so far as it is compelled by external impressed couples, or by a force whose line of action does not pass thru the mass center of the body, to alter that state.
(5) The angular acceleration produced by a couple acting on a body is directly proportional to the magnitude of the couple, inversely proportional to “the moment of inertia of the body about the axis about which the acceleration occurs,” and takes place in the plane of the couple.
(6) To every couple there is an equal and opposite reactionary couple.
If you study Item # 5 I believe you will find that it agrees with David’s statement. Yours M.L. Anderson

[palmas]

And so, enertia will not waiste energy, it will only accumulate it. As for reciprocal movement - if you consider pistons, their velocity can be described as a synosoid (versus time). If you integrate it to time, you will have also a synosoid acceleration. from there you can calculate the energy it uses