ENGINE ROTATIONAL INERTIA

[Engelbert]

I dont spose anyone out ther has the inertias or similar of rotating engine components, or just weights even (so I can get a closer approximation) ?

I've done an approximate calc and come up with about 30KJ of energy at 10000rpm for the crank/flywheel/clutch basket, and about 5KJ for the rest of the engine/driveline (in 1st gear, crank at 10000rpm, 1:4 final ratio, equals about 15m/s road speed).

So thats 25KJ of energy available in engine inertia alone...released over 1 second is 25KW...

Sound right ? I figure it must be in the ballpark. Heavy things spinning real fast can hold a heap of energy !

I'm starting to think a high speed clutched flywheel might be good for those running single cylinder engines....use stored energy to launch off the line in acceleration events etc....is a clutched flywheel against the rules ? I remember something about not being able to store energy or something ?

Any comments, or DATA!, calculated, measured, assumed, made-up, bullsh!t, etc, would be appreciated!

I can send my spreadsheet with calcs if anyone's interested.

Sam.
2001 UQ FSAE.

[Lyn Labahn UW-Madison]

No you can't use a flywheel like that, its somewhere in the rules where all mass must be at rest at the start of an event, or something along those lines anyway.

2002/2003 Team Leader
Best overall average finish of the new millenium http://fsae.com/groupee_common/emoticons/icon_smile.gif

[gug]

are you sure about that rule? ive been searching for bloody ages and i cant find it, even though it does ring a bell. could someone post up where it is in the rules? thanks!

- if it isnt coming, you need a bigger tool.

[Mark100]

Engelbert, what engine are you running? Are you looking to reduce your rotational inertia or add to it?

[Engelbert]

Hi Mark,

I'm not currently competing in FSAE. When I was, the engine was an F3. Did its job well too.

I wasn't looking to specifically increase or decrease inertia of the engine, just find an approximate value, and discuss ways of using the extra energy.

I think it's an aspect of fsae cars that gets overlooked, but could be used advantagously.

I'll have another look in the rules tonight.

Sam.
2001 UQ FSAE

[Richard Lewis]

There are other ways to store energy other than a flywheel... lots of ways around that rule if it exists. (I don't recall it)

-------------------------
UVIC Formula SAE Team
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http://uvic.fsae.ca

[BA]

In reply to the rotational inertia stuff, we're also running an F3. While knowing the numbers on your rotational energy is neat, the real question is whether you should increase or decrease it to get more power or better response out of the engine.

I've been under the impression that a lower rotating mass would be better for performance. We run these cars in short bursts of high acceleration and deceleration. Wouldn't a lower rotating mass allow for a quicker transfer of power to the wheels? It's just like putting lighter wheels on your car.

I just rebuilt our engine - completely. We managed to remove 2.7lb from rotating components in the block. I think I'll let everybody wait until competition to find out how.

If anybody else has info on raising or lowering rotating masses, let's hear it.

Brian Auer
University of Idaho
Vandals Racing (http://www.uidaho.edu/~racing)
FSAE 2003/2004

[This message was edited by BA on August 01, 2003 at 03:25 PM.]

[gug]

having a look at the con-rods, camshafts and crankshaft out of an f4, there seems to be a lot of flashing. cleaning them up could save you a bit.

anyone know how much weight can be lost by going to aftermarket pistons (keeping cost in mind, this aint no F1 team!)? incase you havent looked in the gallery yet, our team is now looking for some new ones. http://fsae.com/groupee_common/emoticons/icon_frown.gif

- if it isnt coming, you need a bigger tool.

[Frank]

Sam,

remember Larry got that data.. I did another SE model of the internals, and I'm fairly sure what he got was correct


Inertia for CBR about output shaft, 6th gear selected

Value includes gearbox, crank, and reciprocating masses.
Does not include valve train.

The Value is 0.076 kg.m^2 at crank

Stiffness is 4000 Nm.rad^-1 in 6th gear ( as measured experimentally at output shaft )

Frank

ps if you're not sure... try and get a junk 600 engine (any model would do).. SE model it, shaft by shaft and add the inertias... (gear ratio squared etc etc blah blah)

[Charlie]

<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by gug:
anyone know how much weight can be lost by going to aftermarket pistons (keeping cost in mind, this aint no F1 team!)? incase you havent looked in the gallery yet, our team is now looking for some new ones. http://fsae.com/groupee_common/emoticons/icon_frown.gif

<HR></BLOCKQUOTE>

Little to none, we ran Wisecos in 2002.

-Charlie Ping
Auburn University FSAE (http://eng.auburn.edu/organizations/SAE/AUFSAE)
5th Overall Detroit 2003
? Overall Aussie 2003. http://fsae.com/groupee_common/emoticons/icon_smile.gif

[Mark100]

Were those higher compression pistons, too?

Crank assembly and clutch assembly are the places to really shave off the weight, we found.

[BA]

The crank has to be a fairly balanced shaft because of it's rotation speed. How do you ensure that it stays that way if you remove weight from it? We were worried about our clutch being out of balance after modification, I'd be sweatin' bullets over a crankshaft. 12,000 RPM and a shaft wobbling on journal bearings...

Brian Auer
University of Idaho
Vandals Racing (http://www.uidaho.edu/~racing)
FSAE 2003/2004

[MikeWaggoner at UW]

Getting rid of the stock charging system and going to an external, lightweight alternator can reduce rotating inertia by bringing the mass to a smaller radius (5" bike alternator to 3" alternator). It's only worth it if you're doing other pulley driven systems though.