Cosworth Wrote:
-------------------------------------------------------
> With the amount of front end lift, there's no way
> thats the antilag. With no trotle the car would
> nose dive. Common guys, we all know this.


I didnt. But now I do. I knew that worked for bikes and monster trucks. I thought the tire size vs vehicle has something to do with it.

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Welcome to the cult of JVL drink the koolaid or be banned.

With the CG low and in the middle of those cars the momentum reaction of the front and rear wheels changing speed should damn near cancel each other...at the very least it's small.

Tim Taylor Wrote:
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> > With the CG low and in the middle of those cars
> the momentum reaction of the front and rear wheels
> changing speed should damn near cancel each
> other...at the very least it's small.

No dude, its exactly because of the lower CG that the gyroscopic effect from the rotation of the wheels has more of an effect on the pitching line of the car therefore angling it upwards than if it had a higher CG.

Cosworth Wrote:
-------------------------------------------------------
> Tim Taylor Wrote:
> --------------------------------------------------
> -----
> > > With the CG low and in the middle of
> those cars
> > the momentum reaction of the front and rear
> wheels
> > changing speed should damn near cancel each
> > other...at the very least it's small.
>
> No dude, its exactly because of the lower CG that
> the gyroscopic effect from the rotation of the
> wheels has more of an effect on the pitching line
> of the car therefore angling it upwards than if it
> had a higher CG.
>

Theory or testing?

I chatted with someone who has done a fair bit of jump testing and was told that when all 4 wheels are in motion they tend to cancel each other out. Pastrana's NYE jump he used a handbrake (that disengaged the centre diff as well) to stop the rear wheels only, causing the car to pitch down.

---

First Rally: 2001
Driver (7), Co-Driver (44)
Drivers (16)
Clerk (10), Official (7), Volunteer (4)
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Last Updated, January 4, 2015

Quote
john vanlandingham
Blame is for idiots. losers.

Maybe my dynamics are fuzzy...it's been a while. I'll have to go find my dynamics text.

Morison Wrote:
-------------------------------------------------------
> Cosworth Wrote:
> --------------------------------------------------
> -----
> > Tim Taylor Wrote:
> >
> --------------------------------------------------
>
> > -----
> > > > With the CG low and in the middle
> of
> > those cars
> > > the momentum reaction of the front and
> rear
> > wheels
> > > changing speed should damn near cancel
> each
> > > other...at the very least it's small.
> >
> > No dude, its exactly because of the lower CG
> that
> > the gyroscopic effect from the rotation of
> the
> > wheels has more of an effect on the pitching
> line
> > of the car therefore angling it upwards than
> if it
> > had a higher CG.
> >
>
> Theory or testing?
>
> I chatted with someone who has done a fair bit of
> jump testing and was told that when all 4 wheels
> are in motion they tend to cancel each other out.
> Pastrana's NYE jump he used a handbrake (that
> disengaged the centre diff as well) to stop the
> rear wheels only, causing the car to pitch down.

I had been in talks with VSC since PRI regarding product for the jump car and from speaking directly with the guys there (no names on public boards) the point of grabbing a handfull of handbrake WHILE still on the gas was to have the rear squat down while keeping the front as high as possible.

But dont let me be the one to explain how it works, McRae did some vids on certain techniques. Here's one on how to take a jump and why/why nots.




Regards.

We had some of the Lemons team here last night so there were way to many advanced degrees in the room...we still called one guys brother who does theoretical physics for the definitive answer. The wheel angular momentum changes (front and rear) add not cancel and the CG height of the car is actually irrelevant to the reaction. It's the overall mass moment of inertia about the pitch axis that matters. I still need to find my dynamics text and prove it to myself though.

Tim Taylor Wrote:
-------------------------------------------------------
> We had some of the Lemons team here last night so
> there were way to many advanced degrees in the
> room...we still called one guys brother who does
> theoretical physics for the definitive answer.
> The wheel angular momentum changes (front and
> rear) add not cancel and the CG height of the car
> is actually irrelevant to the reaction. It's the
> overall mass moment of inertia about the pitch
> axis that matters. I still need to find my
> dynamics text and prove it to myself though.

The closer the CG is to the pitch axis the less force will be required.

Cosworth Wrote:
-------------------------------------------------------
> The closer the CG is to the pitch axis the less
> force will be required.

How are you defining the pitch axis? Once the car is in the air we're talking aircraft control theory and the pitch axis is through the GC of the car.

Tim Taylor Wrote:
-------------------------------------------------------
> How are you defining the pitch axis? Once the car
> is in the air we're talking aircraft control
> theory and the pitch axis is through the GC of the
> car.
Very true on that one, but remember its the wheels that are the acting force on the pitch, so the closer the weight is to the wheels the easier it is for it to pitch upon its axis wherever that might be.

Sorta like the Archimedes leveral principle.

I'm going to have to get back to you on that one after checking with another source. I'm going strait to the satellite engineer this time and at the very least he can walk down the hall and ask the guy who designs reaction motors.

Last night it was explained to us that the location of the rotating mass on the rigid body is irrelevant and it's only the magnitude of the torque reaction as the result of a momentum change that matters. In practical terms a lower CG may result in a smaller mass moment of inertia in the pitch axis and give the same effect you are describing...or he could have been full of shit and I really need to find my dynamics book.

Just confirmed that the CG-to-wheel location has no effect at all on the rotation of the car. It's entirely the interaction of the pitch mass moment of inertia and the momentum change in the wheels.

Wot the fawk are you guys yapping about Travvies silly JUMP on a thread about a F1 guy who realised what a lame sterile anal place F1 is and made the switch to the better sport, and who seems capable of going surprisingly fast considering maybe 2 events on loose surface.

---

John Vanlandingham
Sleezattle, WA, USA

Vive le Prole-le-ralliat

www.rallyrace.net/jvab
CALL +1 206 431-9696
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is 3 hours behind Eastern Standard Time.

Well to bring the relevance back to John -

Didn't dirt bike guys figure this out years ago. Go off the jump wrong, correct with throttle or brake. Let me see if I get this right.

More gas = back falls (rear tire spinning faster than front), More rear brake = front falls (front tire spins faster than back)?

---

-Jason

Actually, you are transferring the energy in the wheel to the bike, if the wheel is spinning and you tap the rear brake, the energy is transfered from the wheel, through the brake system, causing the bike to rotate in the same direction, which lowers the front of the bike. By trying to spin up the mass of the wheel, the bike tries to spin around the wheel. The heavier the wheel, the more energy it can impart, or needs to spin faster.