Ah yes, the DeltaWing...

[Andres125sx]

For a given mass, more weight on a wheel (or moving the CG) means more grip.

Sure, but we typically think of oversteer/understeer in terms of the moments caused by forces, and not the forces in isolation.

Ok good point here, maybe this is the reason of the misunderstanding. The moment caused will be higher obviously, but then you´re talking about the moment after the slide, when there is a turn (yaw) it will be higher if the mass is higher, agree.

But a tendency to oversteer, or a inherent stability when braking, is about what happens before the slide, not after....



ups, sorry but have to go out, will continue later

[autogyro]

You can convert over steer to under steer using car positioning at corner entry balanced with braking, gear shifting and many other techniques.
The same for under to over steer and right through the corner into corner exit.
Such a pity that in modern F1 the drivers no longer have such fine manual control.

[DaveW]

Then might you explain me the reason 911´s are usually acused of understeer when the engine is so far back?

I guess that the springs & geometry are set to force understeer. I believe the theory (not mine) is that with the engine placed so far aft, the inertia forces accompanying an oversteer event will make it terminal.

I did a quick check & discovered that, in one case, moving the CG forward did move balance towards understeer (according to my measures) but the effect was quite small, and could easily be rectified by damper changes. I suspect that your experience was caused by changes you made to the position of the Neutral Steer Point (by working the tyres differently).

[Jersey Tom]

Then might you explain me the reason 911´s are usually acused of understeer when the engine is so far back?

Springs / bars aka FLLTD aka mechanical balance. Tires as well, drivetrain, etc etc.

while braking, when the CG is moving forward

CG does not move forward during braking (fuel slosh and minor pitch angle effects neglected). Mass distribution is what it is. BIG difference between moving mass and moving dynamic inertial loading.

[gixxer_drew]

Then might you explain me the reason 911´s are usually acused of understeer when the engine is so far back?

Springs / bars aka FLLTD aka mechanical balance. Tires as well, drivetrain, etc etc.

JT,

I think we can agree that a having a "heavy ass" or whatever you want to call it will help you with straight line braking, on that issue we are down to semantics. I think the issue with Bowlby's statement is that he used the word "stability" which is incorrect for what he is trying to say.

As for springs bars/FLLTD... I am inclined to say it is tires, tires and tires. Since all of the rest are just tires and a compensation for tires. They still act like that when there is no suspension and the reaction to loading (and CoG results in a difference in loading between front and rear as well) is still the same when there is no suspension at all. It pops out at me in rig test data but sure as hell doesn't in a coulomb friction model of a tire (or a steady state calc like RCVD either).

I would like to add the 911 is also infamous for snap oversteer. Understeer and oversteer.

[zenji]

Could anybody please tell me in what way this car is a 'delta wing'?
The space shuttle is a delta wing, at high alpha (angle of attack) it generates a strong 'tornado' vacuum of air behind wings upper edge. (gripping the wing)
Did they propose feeding the rear diffuser with the such a vortex of air?

The car should really be called the 'force fed diffuser type' perhaps, the diffuser would provide barely any space for a vortex to develop, it would just be a plain old venturi.

[gixxer_drew]

Could anybody please tell me in what way this car is a 'delta wing'?
The space shuttle is a delta wing, at high alpha (angle of attack) it generates a strong 'tornado' vacuum of air behind wings upper edge. (gripping the wing)
Did they propose feeding the rear diffuser with the such a vortex of air?

The car should really be called the 'force fed diffuser type' perhaps, the diffuser would provide barely any space for a vortex to develop, it would just be a plain old venturi.

Well, sort of

One is a delta wing and the other is DeltaWing....

Both shed a pair of (shockingly simlar shaped) vortices around a similar plan view layout, one is a wing and the other has under-wings.

The main purpose of the design is low drag and you can see it in use everywhere including F1 wishbones where for any given surface area you just have a lot less drag when the surface doesn't need to expand to full width right away like a squared plan view layout does. This is a very very old concept and that is exactly the point. I dont think it is that important to get caught up in how they answered the question but more important that someone said: These cars re totally controlled by aero now, so why are we using the identical layout as 100 years ago when we had no idea about aero? Thats what I like about it. I think everyone should appreciate that and I think the future is there whether you dislike this particular design or not, the regulations are the thing keeping the old concepts rolling.

With that said,the aero side conceptually is not all new. That shape evolved from the early 80s Indy Cars designed at AAR by Hiro Fujimori and later with Yoshi Suzuka. The trick I am sure was making downforce with that shape because it seriously limits the surface area. Really its the combination of this and the vehicle dynamics that is interesting along with the details of how the aero evolved 30 years later.

Attached 1983 Eagle and DeltaWing 2013 photos

[DaveW]

Attached 1983 Eagle and DeltaWing 2013 photos.

i guess that both were designed for oval courses. High L/D, aft C.G., and (I think) transient oversteer to negotiate turns with minimum drag penalty would be the quick way....

[gixxer_drew]

Attached 1983 Eagle and DeltaWing 2013 photos.

i guess that both were designed for oval courses. High L/D, aft C.G., and (I think) transient oversteer to negotiate turns with minimum drag penalty would be the quick way....

I may understand the chronology wrong... but I thought the aero was not developed until it was decided to be taken to road courses. However, I still agree with all of that.

[rjsa]

The main purpose of the design is low drag and you can see it in use everywhere including F1 wishbones where for any given surface area you just have a lot less drag when the surface doesn't need to expand to full width right away like a squared plan view layout does.

Sorry, wrong.

F1 wishbones, also called A-Arms are not delta shaped, they are triangular because triangles provide for better load bearing, since it's members are always under tension/compression, never bending or tortion.


Low drag wings, like those of sail planes and low powered planes, are long and square.

Delta wings primary reson of use is supersonic flight, since said wings will not touch the sonic boom. Same goes for sweepback wings, like the used on modern airliners, which can cruise up to around mach 0.85.

Delta wings in fact produce a lot of induced drag due to their small aspect ratio.

[DaveW]

Sorry, wrong.... Delta wings in fact produce a lot of induced drag due to their small aspect ratio.

You are correct in principle, of course, but perhaps not so much in deep ground effect....

It would be interesting to see your example negotiate Indianapolis. I guess overtaking would be something of an issue (sorry, I couldn't resist)....

[rjsa]

Indycar wings are square. Even on high speed oval setup:


The delta wing shape of the so called DeltaWing car has nothing to do with groud effect. Which is achieved by the underbody ventyry tunnels, not the leading edge of the side pods.

The delta wing resembles a delta winged plane, that's where it got it name from. It has nothing to do with it's aerodynamic characteristics. The delta wing has no wings. Body and sidepods fairing are not wings.

[Andres125sx]

Then might you explain me the reason 911´s are usually acused of understeer when the engine is so far back?

I guess that the springs & geometry are set to force understeer. I believe the theory (not mine) is that with the engine placed so far aft, the inertia forces accompanying an oversteer event will make it terminal.

Thanks, that´s what I was trying to explain... the inertia forces accompanying an oversteer... so you´ve already passed the limit and once you´re sliding the extra weight make it more difficult to control, agree.

But that´s passed the limit, before that the extra weight is more grip for the rear wheels and I think that´s the reason they say it´s more stable for braking. If you go too far and the car slides (oversteer), then you have a problem because of that inertia, but keeping within the limits you can brake harder with more weight back

[Andres125sx]

while braking, when the CG is moving forward

CG does not move forward during braking (fuel slosh and minor pitch angle effects neglected). Mass distribution is what it is. BIG difference between moving mass and moving dynamic inertial loading.

True, thanks for the correction

[Lycoming]

... but keeping within the limits you can brake harder with more weight back

Yes, but that does not equate with stability. You can still lock the rear wheels before you lock the fronts and spin off.