Cleanest Design Produced for the Class

[Hardingfv32]

You are talking about vertical load changes that can happen anywhere on the circuit not just the turns. These changes do cause the grip levels to change and thus the G loads. Other than changing the the G load constant it has no bearing on weight transfer. Weight transfer, as stated in pounds (lb), is measured at a moment in time. There is no time descriptor in the answer, lb/sec for example. As far as the weight transfer calculation is concerned, the track surface condition is not relevant.

A driver inputs can change the amount of weight transfer. He is look for feedback before formulating the next input. With vertical loads caused by the track surface, the driver has provided no input before the vertical load change and thus does not expect feedback. A driver can only react to these vertical load changes.

I have to think about the FV response to rear vertical load changes, zero roll and chassis stiffness. I'ii get back to you on that.

Brian

[Daryl DeArman]

You are talking about vertical load changes that can happen anywhere on the circuit not just the turns.

Exactly.

These changes do cause the grip levels to change and thus the G loads. Other than changing the the G load constant it has no bearing on weight transfer.

It does. The weight is transferred diagonally.

I have to think about the FV response to rear vertical load changes, zero roll and chassis stiffness. I'ii get back to you on that

That's the direction I've been trying to nudge you the entire debate and the main reason the requirements of a zero-roll FV and a typical formula car chassis have very different design requirements.

[Jnovak]

I and another builder built a vee with adjustable rear roll stifness and adjustable rear rc height

[problemchild]

First it is important to understand that the load transfer numbers are generated at a constant lateral G load number. In the spreadsheet I am using it is 1.5G. Tire grip level, suspension type.... even car type are not required to be known. !.5G is the constant that makes for a simplified calculation. The CG height and how the chassis reacts to this height are what is important.

So that said, it is probable that a FV, with its lower CG, has a lateral load transfer numbers at least equal to a FF.... at 1.5G. So from that one could logically imply that if chassis stiffness is important to FF, then it must be important to FV.

FYI. You cannot walk up to a FF and lift a front wheel 6" off the ground (by hand) while leaving the rear tires in contact with the ground and with virtually equal rear corner weights (as you can with a FV or FST car built with zero-roll suspension). On my super soft FFs, if I jack up a front wheel by 2", the other front wheel comes off the ground, and the same side rear will be light. By the time I have jacked that front wheel to 6", the only wheel touching the ground is the diagonal rear.

[problemchild]

I and another builder built a vee with adjustable rear roll stiffness and adjustable rear rc height

Several versions of my Shirley MacLane FV were 4 shock cars. There is no doubt in my mind that a developed 4-shock car that is tuned to a particular track will generate more cornering performance than a zero-roll car. Since low-speed power-on push is the limiting factor on a FV, using the rear to help combat that, is a useful tool. I was not able to develop and tune my car to it's potential enough to make it successful. While I could go through some corners 10mph faster, my net performance was rarely better, and I had my best days with a conventional zero-roll configuration. Zero-roll is a fascinating compromise that provides consistent performance with aero, cost, and simplicity benefits. Once most FV racers find their "sweetspot" with zero-roll they may go decades without changing their settings.

Adjustable rear RC? I have been told that swing axle suspensions have a fixed roll center that can only be moved by changing ride height. Mercedes even introduced a single joint swing axle design to lower the rear roll center.

[Hardingfv32]

FYI. You cannot walk up to a FF and lift a front wheel 6" off the ground ....

The point of this discussion is to emphasize the importance of chassis stiffness in a FV.

So from your last statement I am going to assume you think there is very little weight transfer at the rear suspension of a FV. I think you would agree that there is a lot of weight at the rear, engine,transaxle,etc., that is transferring while in a turn. So if the rear suspension is not processing this weight transfer then it must be the front that gets 100% of the responsibility. That being the case would it not be of benefit to the driver to have a stiff chassis? All that weight at the rear being transferred to the front through a flexing chassis certainly cannot be a good accurate and timely driver feedback.

Brian

[Daryl DeArman]

Adjustable rear RC? I have been told that swing axle suspensions have a fixed roll center that can only be moved by changing ride height.

A wider track would lower the RC w/o changing ride height. I narrower track would raise the RC w/o changing ride height.

I'm not sure if there are more than 1 or 2 tracks in the USA where not taking advantage of the max allowable track width could be a net performance advantage. Don't know. I never experimented with changing rear track. Just ran as little toe as I possibly could get away with.

[Hardingfv32]

FYI. You cannot walk up to a FF and lift a front wheel 6" off the ground...

I know you must find this hard to believe, but the formula for lateral weight transfer at a given point in time has no input for any suspension information. A simple fact that can be verified with a Google search.

So a story about what happens when you raise one corner of a FF provides absolutely no new information about lateral weight transfer.

As an aside, you know karts have no suspension and yet there is weight transfer in the corners. And no, chassis flex is not a suspension!

Brian

[Daryl DeArman]

The point of this discussion is to emphasize the importance of chassis stiffness in a FV.

So a story about what happens when you raise one corner of a FF provides absolutely no new information about lateral weight transfer.

Yep. Yet you still remain hung up on lateral weight transfer.

[Hardingfv32]

Yep. Yet you still remain hung up on lateral weight transfer.

Yes, because it is a simple number that can be used to demonstrate the importance of chassis stiffness in a FV.

Since the formula for weight transfer has no input for suspension type, there is no need to discuss zero roll. If you cannot understand the simple weight transfer formula, there is certainly no need to discuss the much more complex subject zero roll rear suspensions.

Agree on simple things first before moving on to the more complex.

Brian

[problemchild]

So a story about what happens when you raise one corner of a FF provides absolutely no new information about lateral weight transfer.

Perhaps you should make up your mind. You keep referring to FFs then dismissing FF comparisons as not relevant.

You clearly do not understand zero-roll as used on FV and FST cars. Perhaps someone with a FV in your area can invite you over to look at their car. Any lateral weight transfer from one rear wheel does not transfer to the chassis or diagonally to the opposite front wheel, but just back and forth between rear wheels. There is literally no mechanical way to transfer lateral load between each end of the car.

In order for an engineering formula to be applied to an application, one must select the correct formula for that application. It does not get any more simple than that. There certainly is longitudenal weight transfer from end to end, but that would need the correct formula too.

On a kart, as on a FF, there is a mechanical connect between each end of the kart, which does allow lateral weight transfer.

[Hardingfv32]

Any lateral weight transfer from one rear wheel does not transfer to the chassis or diagonally to the opposite front wheel, but just back and forth between rear wheels. There is literally no mechanical way to transfer lateral load between each end of the car.

Excellent statement we can discuss.

1) So where is the exact location of the mass that is being transferred laterally at the rear? At the ring gear located between the rear axles? Does it include the engine & transmission? These components are a solid mass so it is easy to accept, but you have by definition started to include mass that is not directly between the axles. Why wouldn't half the driver& fuel load also be included? They are connected to the rear transfer point through the chassis. Thus my statement about chassis stiffness. The engine & transmission mass cannot be causing lateral load transfer, at the axles, without dragging the mass of the driver and fuel cell with it.

As Jay stated earlier, there is a lateral load transfer at the rear axle level.

2) To repeat, there are two types of lateral sprung weight transfer: Through the CG (rear axles FV) and around the CG, roll couples (front axle/beam FV) In a FV the front 100% around the CG (roll couple) and 0% through the CG. The rear is just the opposite, 100% through CG and 0% around CG. The total weight transfer at either end is the sum of the two.

Brian

[Daryl DeArman]

Last statement on this subject from me towards Brian, as I simply don't have it in me (any teachers out there) to find other ways to explain things other how I already have.

Weight transfer isn't the primary concern in determining desired chassis torsional rigidity of a typical formula car. It's keeping inboard ends of suspension and steering bits as fixed as possible.

[Jnovak]

Several versions of my Shirley MacLane FV were 4 shock cars. There is no doubt in my mind that a developed 4-shock car that is tuned to a particular track will generate more cornering performance than a zero-roll car. Since low-speed power-on push is the limiting factor on a FV, using the rear to help combat that, is a useful tool. I was not able to develop and tune my car to it's potential enough to make it successful. While I could go through some corners 10mph faster, my net performance was rarely better, and I had my best days with a conventional zero-roll configuration. Zero-roll is a fascinating compromise that provides consistent performance with aero, cost, and simplicity benefits. Once most FV racers find their "sweetspot" with zero-roll they may go decades without changing their settings.

Adjustable rear RC? I have been told that swing axle suspensions have a fixed roll center that can only be moved by changing ride height. Mercedes even introduced a single joint swing axle design to lower the rear roll center.

I am not stating that what we built had an advantage. It is my opinion that the rear tire desigñ is simply optimized for the existing rear susp design, so i think that if new tires were developed for the improved geometry that FVs could handle better than they do! In the mean time race what you have, and have fun!

[FVRacer21]

My 2 cents:

Relative to 2 formula fords - 30 series Crossle - if one of the diagonals under the engine breaks (and they did) the handling goes bonkers - from experience.

84 Mondiale - we saw fretting on the plates for the rear suspension - made different types of brackets and braces and fretting went away and handling improved.

84 Citation FV - have run with and without front motor mount - seems to make a difference. (with better)

So far I have not seen any hard figures, and I am sure Steve has tested all his chassis. A stiffer chassis will not hurt a FV, but I have to believe there is a point where a lack of chassis stiffness does hurt.

I am building a Caracal D and while it looks strong, I can't help but think some diagonals from the roll hoop might make things better....

Zero roll hides a multitude of things - but does not excuse bad chassis design.

ChrisZ

[Daryl DeArman]

A stiffer chassis will not hurt a FV

If you can handle the extra 20-40# of tubing, I believe it would be better to use it for driver side impact protection and/or chassis rigidity from main hoop forward.

but I have to believe there is a point where a lack of chassis stiffness does hurt.

Absolutely, and as long as we're speaking about areas aft of your front motor mount that "magic number" is a whole lot lower in a zero-roll FV than a more conventional formula car chassis.

[Campbell Motorsport]

This is an interesting discussion but let's get back to post 1, it is nice clean design. Its design merits can be debated, it may be of a traditional FV design, but you can't argue with success. Lots/ most of the successful FV's have been built using this design. Ed's cars have done well and the drivers love them.

Ed doesn't need me or anyone to defend him, but he builds a good car that incorporates more driver protection than many. The craftsmanship is first rate, and they fit drivers of almost any size. He is available and is often at the track helping those driving his cars, and other designs. He is exactly what FV & FST needs, a guy who puts cars on the track and helps keep them there.

Well done Ed.

FWIW, I've been around FV 40 years and have heard many times about the design that was going to be the DB-1 of FV. I'm still waiting, as the story hasn't died. IMO, a well prepared Lynx B, the right driver, maybe a bolt on Citation 0 roll, and they would have been in the pack fighting for the lead at the Runoffs this year. YMMV.

Back to the discussion.

Larry Campbell
Campbell Motorsport

[problemchild]

84 Citation FV - have run with and without front motor mount - seems to make a difference. (with better)

Z

OMG, I hope you are joking. Lateral weight transfer on the rear is just is going back and forth between the rear wheels. If a FV handles worse without a front mount, which I would believe, it is because of longitudenal weight transfer, or because the rear end is not anchored solidly and is steering the car. Clearly that is a mechanical issue and has nothing to do with lateral weight transfer from one rear wheel into the chassis to the diagonal front wheel.

[problemchild]

Last statement on this subject from me towards Brian, as I simply don't have it in me (any teachers out there) to find other ways to explain things other how I already have.

I don’t understand what game he is playing, but I am not playing any more either. Complete nonsense with no value to anyone trying to tune their FV or FST car.

Glad to see Ed finally got his car together, but I am sure others might conclude the best FST was already built and raced.

[Hardingfv32]

I don’t understand what game he is playing, but I am not playing any more either. Complete nonsense with no value to anyone trying to tune their FV or FST car.

Not a game, just trying to learn something about the importance of chassis stiffness related to cars using zero roll. Never claimed it would have anything to do with tuning a FV/FST. My discussion was never intended interest the average FV competitor. If I bore you then do not engage.

I found a paper that helped me understand the importance of chassis stiffness as it applies to roll stiffness distribution. Obviously a std zero roll FV with no rear sway bar has no roll stiffness distribution.

Brian

[Daryl DeArman]

I found a paper that helped me understand the importance of chassis stiffness as it applies to roll stiffness distribution. Obviously a std zero roll FV with no rear sway bar has no roll stiffness distribution.

Brian

Did you read SAE 2000-01-3554?


A bit too complex for me to easily digest, perhaps you'll find it helpful.

[Diamond Level Motorsports]

I had a gen one Laser back in the mid 80's with a dual shock zero roll system. The frame would flex so much during lateral load transfer that the front pulley would hit the battery which was over a quarter inch away. The car would take a set in the corner and then just break away. Although Brian is turning checkers into chess I do agree with him that chassis stiffness, in a zero roll car, might be a bit under appreciated. Additionally I like to run a rear anti roll bar on my zero roll cars which increases the importance of rear chassis stiffness.

[Daryl DeArman]

Additionally I like to run a rear anti roll bar on my zero roll cars which increases the importance of rear chassis stiffness.

When is a zero-roll car not a zero-roll car?

You put a anti-roll bar on it, and I argue it's not a zero roll car and rear chassis stiffness requirements rise dramatically.

[Diamond Level Motorsports]

When is a zero-roll car not a zero-roll car?

You put a anti-roll bar on it, and I argue it's not a zero roll car and rear chassis stiffness requirements rise dramatically.

True, I will call it a mono shock system then!

I think if you were to put some kind of strain gauge on the frame behind the roll bar I think you would see chassis flex vertically and laterally on most FV's and FST's. I think Brian's point is that the less the flex the better whether it is zero roll or not. I fundamentally agree with this.

[swiftdrivr]

Really nice looking car, and the frame-strength for driver protection looks reassuring. I do wonder why there is no front roll hoop? How do you get by the broomstick test?

And just because I don't know, how do the larger tires affect typical FV "momentum" / drafting-pack style racing? Less slide but same drafting / momentum skills, just faster?

[Diamond Level Motorsports]

The FST top speeds are not much more then the FV top speeds. May even be less on certain tracks like Road America. The FST engine tends to run out of power around 6500 possibly because of the restrictor plate. Additionally many of the FST cars are larger then the FV's and have more frontal area. Then the much wider tires obviously create more drag. My experience has been that it is very difficult to pass in a FST in the draft cause when you pull out the car slows down. The real fun of driving the FST is the torque coming off the corners.

[Daryl DeArman]

I think if you were to put some kind of strain gauge on the frame behind the roll bar I think you would see chassis flex vertically and laterally on most FV's and FST's.

Agreed.

I think Brian's point is that the less the flex the better whether it is zero roll or not. I fundamentally agree with this.

I would agree that less flex the better. But we don't need 1 degree per 5000ft/lbs of twist in the rear of a zero-roll FV. We certainly may in a P1/P2 car.

However, Brian's point was that the torsional rigidity is just as important in a zero-roll car as a FF/FC and I whole-heartedly disagree with that premise. We have a finite amount of material with which to build a chassis. I want the tubes in places where they serve the most good, adding a whole bunch of bracing in the rear of a zero-roll FV isn't the best use of those tubes, IMO.

[problemchild]

Agreed.



I would agree that less flex the better. But we don't need 1 degree per 5000ft/lbs of twist in the rear of a zero-roll FV. We certainly may in a P1/P2 car.

However, Brian's point was that the torsional rigidity is just as important in a zero-roll car as a FF/FC and I whole-heartedly disagree with that premise. We have a finite amount of material with which to build a chassis. I want the tubes in places where they serve the most good, adding a whole bunch of bracing in the rear of a zero-roll FV isn't the best use of those tubes, IMO.

If I understand correctly, although Harding could not initially accept our conclusions, he eventually found some paper that convinced him that. "Obviously a std zero roll FV with no rear sway bar has no roll stiffness distribution."

I too, use rear ARBs on FVs, but they are so slight, that I do not believe chassis stiffness is relevant, certainly to the point of "rear chassis stiffness requirements rise dramatically.". Most of any force is going into the triangle of the transmission mounts which is stiffened in the 3rd dimension by the transmission case.

Finally, while Scotts Laser anecdote is convincing on the surface, zero-roll is zero-roll. There are many reasons that 80s era FVs handled poorly, mostly due to design and tune, but chassis stiffness effects on lateral weight transfer, is no more or less significant on any zero-roll FV, whether in the 1980s or 2020s. Checkers is checkers. Chess is a different game although played on the same board. An excellent analogy, BTW, and probably more applicable than the standard "apples and oranges" analogy.

[Daryl DeArman]

I too, use rear ARBs on FVs, but they are so slight, that I do not believe chassis stiffness is relevant, certainly to the point of "rear chassis stiffness requirements rise dramatically."

Rise dramatically is subjective. If the price of your favorite chocolate ice cream (I can't remember what this month's flavor is ) goes from $2.50/pint to $3.75/pint that's a dramatic rise (50%) even though it's still a whole lot cheaper than Yuengling's at $16/pint.

[Jnovak]

What a very interesting discussion.

I have personally torsionally tested at least 50 different cars and the lowest number i have ever seen was a vee that twisted at 900 ft-lb/deg. I have also tested a single seat tube frame chassis that twisted at 4500 ft-lb/deg. I have no doubt that the range is much much wider as I have twisted many pro type cars at Ford Racing labs, including NASCAR and F1 cars.

[Hardingfv32]

If I understand correctly, although Harding could not initially accept our conclusions, he eventually found some paper that convinced him that. "Obviously a std zero roll FV with no rear sway bar has no roll stiffness distribution."

You do not understand correctly. My statements relate to the relationship of chassis stiffness to lateral load transfer. Roll stiffness distribution was never part of my original statements. The paper mention does make an effort to equate chassis stiffness, lateral load transfer and roll stiffness distribution into ratios that determine how easy a chassis design is to tune.

A zero roll FV has no roll distribution, with a roll resistance distribution of 100% at the front and 0% at the rear. In this regard a FV will be harder to tune than a FF that can use sway bars, etc. to adjust chassis balance. From that one could assume that since chassis stiffness is important for FF's using roll resistance distribution to balance the chassis and FV's, not tuning with roll resistance distribution, would not be concerned with chassis stiffness in regard to the use of this type of chassis tuning. Is this the only requirement for chassis stiffness?

The importance of chassis stiffness in different car types is a little hard to establish without some form of criteria or measurement. Take Lazer example of chassis flex, how can it be good for driver feedback if the front of the engine is rotating 2-3deg in relation to the front suspension (beam) when the chassis is subjected to a lateral loading? Maybe this could be stated as some kind of time delay before engine position achieves a steady state. Maybe it does not reach steady state but instead oscillates.

Jay's FV chassis stiffness number is 70-80% stiffer than the FV front suspension roll stiffness.

Brian

[problemchild]

The importance of chassis stiffness in different car types is a little hard to establish without some form of criteria or measurement. Take Lazer example of chassis flex, how can it be good for driver feedback if the front of the engine is rotating 2-3deg in relation to the front suspension (beam) when the chassis is subjected to a lateral loading?

Which is why I said, in other posts, that the engine and transaxle needs to be secure in the chassis, for longitudenal weight transfer, and so the chassis flexing is not steering the car, but any effect that may be having is not due to lateral weight transfer to the front of the car. Zero-roll is zero-roll. Without a mechanical coupler, the chassis could be made of rubber, and twist like a rotini noodle, and weight and force is not being transferred laterally between the ends of the car.

Even with the ARBs that Scott and I have used on the rear, a 1" OD x .050 ARB with 15" levers to 1/4" diameter links and transferring 2-3 lbs of force is not going to be significantly effected by using on a FV with 2 x 4 x .120 frame rails in a ladder construction with only 200 ft-lb/deg of rigidity. I question how much more effective that little bar would be if you doubled or tripled the chassis rigidity.

[Ed Womer]

You need to go back and look at the picture, there is a front roll hoop. I just attached the bracing from the front to rear outside of the front hoop instead of butting against the tube like I do in the FV chassis.

Although you really have a hard time seeing it, the frame from the rear hoop back to the junction of the engine and tranny, is 2x2" square tubing with a short 1"x2" between them that the tabs that hold the tranny tabs attach to. That triangulation along with the braces to nearer to the top of the rear hoop and a front motor mount makes the rear of the chassis much stiffer than the standard ladder chassis style that is common on a lot of FV that rely on the massive 2"x4" tubing hanging out the back of the chassis that holds the engine tranny and the rear facing trailing arms. That style of design adds well over 20 lbs to the chassis due to its mass.

I did not weight the chassis before I started putting everything together but my FV chassis weighs less than 100 lbs with a weld on 18 gauge steel belly pan. I am guessing this chassis is probably in the 120-130 lb range and it also has a welded stainless steel belly pan.

It is interesting that Bob mentioning my new First car has been the start of this interesting thread.

Ed

[Hardingfv32]

Zero-roll is zero-roll...

Zero-roll is 'zero' roll stiffness distribution. There is still load transfer at the rear from items like the chassis, driver and fuel load.

Take your example of holding the front end up and rotation the beam and chassis. Everything including the engine and transaxle rotate along with the chassis. So is all the rotating mass of the engine and transaxle being controlled by the front suspension? That is a lot of mass that the front end is providing roll resistance for. It is obvious that the engine and transaxle, 400-500lb., are clearly fixed to the front suspension.

Would our single spring package and 3/4" sway bar front suspension be able to control this amount of rotating mass? So what gives?

Brian

[Hardingfv32]

That triangulation along with the braces to nearer to the top of the rear hoop and a front motor mount makes the rear of the chassis much stiffer

Stiffer is a subjective term here. Talking only about chassis twist. I am going to assume the two lower engine bay rails do not come together to form a triangle. If so, there is a lot of lost triangulation strength. No triangle between the top braces. What is the engine mount like? Is it a complex piece bolted to the vw motor mount holes (wide based) and then fastened to the side chassis rails. Using the center engine mounting hole bolted to the center of the chassis is not going to cut it if we are talking about chassis twist.

Brian

[problemchild]

Zero-roll is 'zero' roll stiffness distribution. There is still load transfer at the rear from items like the chassis, driver and fuel load.

Take your example of holding the front end up and rotation the beam and chassis. Everything including the engine and transaxle rotate along with the chassis. So is all the rotating mass of the engine and transaxle being controlled by the front suspension? That is a lot of mass that the front end is providing roll resistance for. It is obvious that the engine and transaxle, 400-500lb., are clearly fixed to the front suspension.

Would our single spring package and 3/4" sway bar front suspension be able to control this amount of rotating mass? So what gives?

Brian

Yes, all that mass is controlled by the front springs, FARB, front dampers, and front droop limiters. That is why I tune with front droop limiters. It is also why I tried to develop a 4 shock car (non-zero-roll) but I abandoned it because I did not have the resources to develop it. Chris said earlier "Zero roll hides a multitude of things" but he had it dead wrong. Zero roll simplifies the process by eliminating a multitude of things. Things that matter on most race cars have absolutely none, or insignificant effect, on zero-roll FVs and FSTs. Conversely, things like rear roll steer, which is so critical on any FV/FST car, tends not to even be in the vocabulary of most other junior open wheel racers.

[Hardingfv32]

Yes, all that mass is controlled by the front springs, FARB, front dampers, and front droop limiters...

From that statement can I infer that it is your opinion that when a FV (zero roll) is cornering, the weight on each rear wheel stays equal side to side? No longitudinal loads from acceleration or braking are involved.

Does that sound reasonable to you?

Brian

[B Farnham]

I'd have to agree with Greg and Daryl.

Two years ago I was graciously given the opportunity to race someone else's FV.

Right from the get go the car handled great but I had a hell of a time shifting. Come to find out that all of the bolts that mount the transmission to the frame had backed out. This car didn't have any bracing from the roll bar to the engine and I was having trouble shifting as everything was flexing so much. The only things holding the engine and transmission in the car was one rear aluminum plate and the trailing arms.

If an FV needed so much bracing and chassis stiffness at the rear then I probably would have had the car split in half with the way things were.

It wasn't a planned experiment but it goes to show how little bracing we really need.

PS. Once we replaced the bolts the car shifted better but it didn't change the handling characteristics.

Brian

[problemchild]

From that statement can I infer that it is your opinion that when a FV (zero roll) is cornering, the weight on each rear wheel stays equal side to side? No longitudinal loads from acceleration or braking are involved.

Does that sound reasonable to you?

Brian

I would not agree with any part of that statement, but perhaps if you were simplifying a model, you could stretch it to that premise ..... like a Morgan 3-wheeler. You have a triangle rather than a square.
The weight on each rear wheel may average out to equal, but I expect is never actually equal.
Managing longitudinal load movement is most of what tuning these cars is all about.
Torsional rigidity of the chassis, beyond a basic level, has no relevance.

[Hardingfv32]

Can you expand on your thought.

Why would the FV, zero roll, rear wheels weights not be equal in a corner? Use a corner like the RA Carousel where there can be a long steady state period, no longitudinal accelerations or decelerations.

Brian