2006 Pack Pinewood Derby

[FatAlbert'sRacing]

This is year my son raced the "wing" style car with the extended wheel base. We put the weights in the car and got it to 5.00 oz. We used some speed axels and wheels this year just to try them out. The night before the race I went down and helped set up the track. We run a 60ft Beta Craft track.
I had my son run his car from last year against the new car and the car from last year ran better. So we truned the new car around and it ran faster.
My son came in third place in the Bear rank and didn't do so good overall. I couldn't figure how the short wheel base cars was out running his car. The wheel spacing was right and we did everything that we could do. It seems to me that we just flat out got out ran this year.

[MaxV]

If the "Wing" was rear-weighted, then likely the weight was too far back for the long track.

With long tracks, the weight needs to be more center weighted, so that the load is more evenly balanced on the wheels. Otherwise, the car is fast down the slope, but dies early due to the extra weight on the rear wheels.

[FatAlbert'sRacing]

Randy,

That is what I kinda figured out half way throught the race. I watched the other cars and seeing the weight placement for them I had pretty much guessed what happened.
But I was happy with the car that we got from you. I wish I had did the wieghts a little different. Well back to the drawing board for next year.

[Smell of pine]

What constitutes a long or short track? In other words, is there a sliding scale for cg in regards to track length? As an example, for a 30' aluminum Best Track the cg should be 3/4" in front of rear wheels? For a 45' length for the same style track, the cg should be 1" in front of the rear wheels. Then how should the ratio between front-rear weight set?

[Teeeman]

Unless the coefficient of friction is more on the rear wheels (or you are gauling material) I don't see why friction has any bearing on a car's peformance when the weight is in the back... i.e. raising a wheel buys you nothing for sliding friction (between the nail and wheel bore) but buys you a LOT for angular momentum reduction (not spinning up the 4th wheel)...


I thought the issue with a strongly rear-weighted car was with stability...


I am running a daddy car this year that is very rear-weight oriented.

My theory is if the alignment is dead straight for the rear wheels, and the alignment for the touching front wheel is in "rail rider" configuration (1" / 4' steer)...

it might have a chance to being stable and running equally fast on the straights?

-Terry

[WarpSpeedINC]

Sounds to me like an alignment issue more than weight placement. Rear weighting is for potential energy, and how long this weight will fall.
Typicaly, if a car goes faster turned araound, it has alignment issues, and backward was the lesser of 2 evils.

Warp Speed

[gpraceman]

Typicaly, if a car goes faster turned araound, it has alignment issues, and backward was the lesser of 2 evils.

A couple of years ago my older son lost out on the pack championship to a car that started out running forwards, but then the scout started racing it backwards. While running forward, my son's car was beating it, but as soon as it started running backwards it beat my son's car every time. If my son hadn't decided to try his car backwards also (the car's worst run), then he likely would have squeeked by with the win. I tried to warn him, but it was his car to race.

Unfortunately, only the top racer from each pack could go to the council race (no district race), so my son missed out on that experience.

I do agree with you that there was some issue with the alignment going forward that had much less of an impact when it was running backwards.

[FatAlbert'sRacing]

The car went down the track straight. It didn't walk at all. We used axel holes not the slots.
As soon as I figure out how to post the pictures I'll put them up

[WarpSpeedINC]

Even if the car tracks straight, it can still have major alignment problems, more than likely in the rear.
Typicaly, if a car goes faster backwards, it is due to the rear wheels being toe'd in. When the car rolls forward, the wheels migrate heavily against the body. When ran backward, the rear wheels migrate out to the axle heads. The axle head is harder and smoother than the car body, so less energy is required to overcome this type of braking action. The car speeds up.
This is usualy the case, especialy when the car seems to track fairly true.
Because of the set-up we use, our fastest cars are turned to junk when run backwards!


Warp Speed

[Teeeman]

Because of the set-up we use, our fastest cars are turned to junk when run backwards!


Warp Speed

Is your setup a "rail rider" dominant front wheel slight toe-in?

Sounds like something more elaborate... care to elaborate for us?



(or is it a "if I tell ya, I gotta kill ya" type of thing?)



Would be cool if you don't mind telling us more... we are doing our first alignment in 3 days...

-Terry

[WarpSpeedINC]

Nothing different, the same thing we have been discussing here.
You have that car properly aligned to ride the rail, and it is blazing fast. But if you turn it around, this type of alignment will drive the lifted wheel, and the opposite rear wheel into the rail hard.
We have built some fairly fast cars over the last couple of years, but if you try to run them backwards, they will barely make it to the finish.
Our Stock class WIRL cars are pretty aggresivly rear weighted, and they seem to really shine on the flat portion of the track.
I beleive that any performance gains from moving the weight forward, on any lenghth of track with a typical slope, is due to problems elsewhere.
(ie.. alignment, weight placement due to less than optimal car design, or severe track conditions)
Our theory anyway

Warp Speed

[Teeeman]

Man, I am now getting butteflies thinking about the "daddy" car for this year...

for the last 3-4 weeks I had finally come to accept it was doomed due to heavy rear weight placement...

then I got a glimmer of hope reading about "rail riding"...

and you confirm from experience what my thoughts have been leaning towards...


man, race is in 1-1/2 weeks... I can't wait!

One "what if" that still remains on my daddy car is if the front airfoil will lift the wheels up or not... I think it won't be enough (if at all, remember we're talking 11MPH here) lift to raise them off the track, thus the "rail ride" won't be compromised...

if this car works for me this year, I know my son is already talking of copying it for himself next year

For the first time, I see it might be possible for us to win a District race if we can figure out alignment...

-Terry

[Derby Dad]

Warp, can you explain what you mean by your cars are turned to junk when run backwards? Are you saying that the car becomes damaged after being run backwards such that it doesn't perform as well as it formerly did when it's run forward again?

If so, can you suggest a reason for this? My motivation is in regards to my son's car at his race just last weekend. In his first 3 races, his car turned in times that were significantly faster than any other cars throughout the race. But, he accidentally raced it backwards in his next two races. (His car was an neutral airfoil cross section so with the rear very thin rear and the front much thicker and rounded, it looked kind of backwards to him.) The car never did well again and ended up being 11th in the Pack (of around 75 cars).

So, I'm wondering if running the car backwards somehow damaged it.

[Derby Dad]

Teeman, we've done neutral (symmetric) airfoils for two years now. There should be no lift generated if your airfoil is symmetric and if the angle of attack is 0. So, to achieve a zero angle of attack, we've put the rear axle holes as close to the bottom car surface and put the front axle holes a little higher so that the airfoil centerline remains parallel to the surface the car is sitting on.

Good luck.

[WarpSpeedINC]

Warp, can you explain what you mean by your cars are turned to junk when run backwards? Are you saying that the car becomes damaged after being run backwards such that it doesn't perform as well as it formerly did when it's run forward again?

If so, can you suggest a reason for this? My motivation is in regards to my son's car at his race just last weekend. In his first 3 races, his car turned in times that were significantly faster than any other cars throughout the race. But, he accidentally raced it backwards in his next two races. (His car was an neutral airfoil cross section so with the rear very thin rear and the front much thicker and rounded, it looked kind of backwards to him.) The car never did well again and ended up being 11th in the Pack (of around 75 cars).

So, I'm wondering if running the car backwards somehow damaged it.

It usualy doesn't hurt the car (I say usualy, not that it can't) but what I meant was when we run our cars backwards, they have a tough time making it to the end of the track.
The times turn to junk!

Warp Speed