RPM -- F1 vs Road Car

[gabe]

Hi,

I was wondering if anyone knew how f1 cars are able to reach such high revs? What would happen if a road car had this many revs? Is it the difference in revs due to the complexities of f1 cars?

thanks

Gabe

[Monstrobolaxa]

Humm....well if you put a F1 engine in a road car one of the first things that would happen probably would be the engine would start overheating fairly fast.

There are a few diferences between a road engine and a F1 engine...the first of all is the weight of diferent components...for example a crank-shaft of a road car is around 3 times the weight of a F1 crank and the piston of a F1 car weighs around 250-300 grams (edited the post to correct this number) compared to the 1,5 kg of a road car (these are general numbers given on a Discovery Channel documentary....they vary from engine to engine). This means that for a road engine to rev at the same speed of a F1 engine the g's forces applied on the pistons, conrods and cranks would be much higher then in a F1 engine....cause the g load on these parts is related to their mass, and in this case I am not counting the speed because we're assuming the F1 and road engine are at the same revs! The very high g load on these parts is important cause it would cause excessive material fatigue ond this parts and on the smaller parts that keep everything connected.

Another important aspect is the type of fuel used in a F1 car....which suposedly is close to road fuel....but not quite...the combustion is much faster then in a road car...and there are other diferences.

Another thing is an financial factor...a Formula 1 engine is built to last a very small distance when compared to a road vehicle! So the component weight and longivity can be reduced to a minimum in a F1 engine. Another thing is the high compression reached in a F1 engine....in a road car the engine wouldn't last too much without major mantenance. Besides this an engine at revs over 16000 needs pneumatic valve actuation (due to valve vibration and resonance)...which is fairly expensive for road vehicle standards.

So basicly were talking of engines build for 2 diferent purposes....one of them is to go as fast as it can and last 600 km and another is an engine that has to last 100's of thousands of km!

Well....this is all I can recall but I'm studying for a test tomorrow....so it was a quick replay....if anyone has anything to add....or correct me if anything isn't totally right!

[Reca]

I was wondering if anyone knew how f1 cars are able to reach such high revs?

Short stroke.

BTW : welcome Gabe.

[pyry]

what are the g loads aplied on the pistons of an f1 compared to a road car?

[Guest]

Thanks everyone

[Monstrobolaxa]

what are the g loads aplied on the pistons of an f1 compared to a road car?

Well in a F1 engine the maximum g load on the pistons are between 7000 and 8000 g's .....well...those damn pistons are much better then me....I'll just pass out at 3 or 4 g's

[Monstrobolaxa]

Humm...just found out something interesting.....it seems quite strange so if someone doesn't agree with me just say so I might have made some mistakes in the calculations....

But lets imagine an engine at 19000 rpm

19000rpm = 19000/60 = 315 rps(econd)

Which means that 1second/ 315 means that it takes 0,00317465 seconds to rotate once!

So with a displacement of 84 mm (cause 1 revolution is 2*displacement)....at 19000 rpm....we can say that the distance the piston travels in a minute is

19000*84*10^-6= 1,596 km/min= 95,76 Km/h

Using the motion equation: X=X0+V0T+0.5A*T^2

X-42mm
X0 - incial position which is considered 0
V0= incial speed of the piston...considered zero because we're considering the crank at the bottom! and we're only analysing the Y-axis!...imagining the piston travells vertically!
T= 0,00317465/2 seconds....time it takes to travel the 42mm, while going up or down
A = the average aceleration

So it comes down to: X=0.5*A * T^2

so we can calculate A

A=(2*X)/t^2

A=33338,62

A/g= 3400 g's (aproximatly) = average aceleration on the piston

Well now that I have had the time to correct everything the average g of a the piston reaches a number that sounds more realistic! Though the average speed still seems to be a little low....if someone detects a mistake let me know....making mistakes is part of life! hehehe....I just hope I don't make them when I graduate!!!

[Guest]

sorry but isnt there 19000*42*10^-6?? 1Km=1000000mm

[Monstrobolaxa]

Yes guest you are completly right.....I have edited my post in order to correct it! thank you
I could have just said the mistake was on purpose and was checking if anyone was really paying attention to the post

[Different Guest]

just wondering....
You are talking of a displacement of 42 mm, gettimg me confused - do you mean that the stroke is 42mm?

cos if you do mean stroke, then shouldnt the distance travelled in 1 rev be 84mm?

also with the accel calc, did you not forget to square the time of 0.003174.. You took the root of accel?

But this is anyhow such a gross simplification... i suppose it does give some sort of insight.

Another thing that may sound silly but, if you think of a say a triple story house ( or a block of flats or whatever ) think about how many g's those poor little bottom bricks are pulling. Sure the load is not cyclic but its just clay for Petes sake...

[Monstrobolaxa]

You are talking of a displacement of 42 mm, gettimg me confused - do you mean that the stroke is 42mm?

Yup I understand your confusion and now thinking about it there is something wrong with my calculations...I'm going to re-edit them...and correct them! I did the calculations only analysing the piston going up or down, not a complete revolution! This means that I forgot to calculate the time for half a revolution.....which is half the time of a complete revolution! Sorry to all about the mistake!

A=sqrt((0,042*2)/0,00317465)

This formula is also incorrect!!!! hehehe...sorry people long day with a flight mechanics test....2 labs...and a long night of studying! I'm very sorry...I'm going to crrect everything at one!

[Reca]

what are the g loads aplied on the pistons of an f1 compared to a road car?

The peak acceleration of the piston in a F1 engine is a bit more than 90k, maybe up to 95k m/s2, for a road engine it varies a lot (obviously). Taking for example two excellent units, the one on the BMW M3 (6 inline, 3246 cc, b/s 87/91 mm, power 252 kW @ 7900 rpm) and the Ferrari 360 Modena engine (V8 3586 cc b/s 85/79 mm, power 294 kW @ 8500 rpm), for both the maximum piston acceleration is in the order of 38-40k m/s2.

Monstro : I can’t write what I think about your calculations, use your imagination.

[Monstrobolaxa]

Monstro : I can’t write what I think about your calculations, use your imagination.

I know what you would write and I know you're right....there are a whole lot more variables in between and I can't do exactly what I did...with all the assumptions.....but using simple day-to-day physics it's a relatively interesting number

(I also talked to a Peugeot engineer for the road division who is studying the fuel flow turbulence inside the combustion chamber...and he said that to a certain extent I can do what I did....though it isn't a acurate number I made too many assumptions and didn't count with any variables)....so no one can really use that number...it's just a kind of curiosity!

[Reca]

So you see nothing wrong in calculating the average acceleration of the piston travelling between two points where piston speed is zero, and obtaining 3400 g ?

[Monstrobolaxa]

Well...to tell you the truth no!

And I'll explain why....I made the following considerations:

- a vertical cylinder (and one cylinder only);
- there is no friction so that the angular speed of the crank is constant (constant rpm at 19000);
- no ignition (and explosion in the fuel chamber...which will speed up the downward movement);
- no compression;

I'm just considering a rotating crank at 19000 with a piston with a 42 mm stroke.......(with the crank being rotated by an outside source of energy)...just a hipthetical crank rotating with a 42 mm stroke piston/conrod combination....and non of the stuff I said I didn't consider.

A starting point (and time) where the piston has just finished it's downward movement and is going to start its upward movement (this point is the lowest point on my Y-axis and the speed is considered 0....same whing when you through a ball upward vertically..there is an instant where it stops going up and starts coming down...that is a V=0 instant) and I'm considering the top of the movement as the point where the cylinder changes its upward movement to downward (this instant is considered as the end of experiment, and also has V=0 acording to the Y-axis).

I know it isn't correct to not consider all the variables but if you don't count with all of them the calculations can be valid.