Two questions

[Mark Huber]

For all of the racers out there (and anyone else who cares to weigh in):

With these relatively small open wheel cars--I'm referring to F1 cars with wheelbases ranging from say 70mm to 77mm and widths across the rear wheels ranging from say 50mm to 59mm:

Further let's assume that the car weighs 55-65 grams (I chose a range somewhat on the light side since most of my builds are the smaller cars.)

Everything else being equal:

1) How much of performance difference might a 'rattle pan' make?, and

2) How much improvement could result from moving the slot guide forward 5mm? (that's about the maximum I could move a guide forward in most of my cars without it being visible from the top view) Would that extra 5mm length improve a lap time from say 4.5 seconds to 4.0 seconds or would the change be more subtle?

I know the quick response to both of those questions might be... Well just experiment Mark and find out for yourself.

But I have neither a timing system nor a long enough track to assess these sort of changes. To be frank, except in the relatively rare instances such as tire spin, power loss or the car just sliding off the track, I can't discern performance issues on my little oval Ninco track.

[Andrew Rowland]

Lovely questions there Mark, without straight answers....

As I understand it rattle pans are designed to 'unsettle' the car enough to ensure it slides in the corners rather ghan going straight on or overturning. Have I got that right? It enables the car to be on the lkmits of adhesion without deslotting?

If so i'd say a rattle pan on a car with skinny tyres and weighing so little might be less useful than one on a heavy, wide tyred 'thingy' style F1 from the '60's.....

Just my logic anyway. Please tell me i'm wrong as i love to learn!

Similarly the length of the car must have a relationship to its width. If you made it 300mm longer clearly it wouldn't be better so there myst be a balance to be had. Just lengthening randomly by 5mm can't be always good. Can it?

Again those thingy style cars were hugely wide so received wisdom is to set the guide forward. But with the cars you build surely its far more subtle....

By the way it will also deprnd on driver and track of course!!

Just my thoughts.....

[slo]

I know some have their preferences for aspect ratio between guide lead length, ie pivot of guide to rear axle center and width, whether track or overall needs to be clearly defined in calculating this. I know the car is slower to kick out the longer the lead guide length is. I have heard that it also allows the car to drive faster into a corner.
Our Brabham chassis' for the VRAA/Tasman uses a a guide lead length 84-85mm. overall is 50mm ,(1.7 aspect ratio) or, track is about 43mm (1.97 aspect ratio) Significantly different. Pretty sure the common calculation is based on track.
I always try to get the guide as close to the nose as possible, which center is 12-12.7mm in front of the front axle center line, based on the Atlas Brabham body.
Dont know about the rattle pan, but if that weight is not fixed perhaps energy and vibration would not be transferred as readily thoughout the car, also, lower COG.

[David Lawson]

Mark

The three point principle is part of what you are talking about with your two sizes of cars.

This link covers a lot of general principles about chassis design and dynamics that you might find interesting.

www.professormotor.com/category-s/203.htm

David

[ramcatlarry]

I have been building 1/24 IRRA retro cars for over ten years and have incorporated rattle pans in various frames. Most of this type of build use two main rails as torsion bars from the front axle to the motor/axle carrier. Each 'main rail' can be made of single or multiple rails, but the need and goal is to create and vary the amount of flex in the frame. The frame can be bound up or limited (in flex) by sliding or rattle/captive pans while still adding low mass to the center of gravity. Too much 'float' in the pans can alter traction reactions to left/right turns. One theory is to have the pans slide forward/backward to enhance either braking or acceleration traction. This is more wishful thinking and I try to limit this type of movement to less than a millimeter.

Back in the 1960's, I raced Monogram 1/32 F-1 Kits as a 'production' class in our Chicago area club. We could change tires and ratio and HAD to use all of the kit parts and hardware. I glued the bolts to the nuts and allowed the chassis parts to flex freely...My cars still work. I have several Classic resin shells to build that I never had good motors for. Now the FF050 looks real good.