Frond end design questions

[fnord1138]

Hey all! This is my first post. I have 2 questions regarding front end design.
My 6 yr. old son is going to compete in his first Tiger Cub derby in January. I recently saw a "Starting Line Hint" on another derby page that we was going to try out. It calls for the front of the car to be 'cut in' about 3/8ths of an inch. Then, you mount a front spoiler that rises above the car. This allows the spoiler to be the only point of contact with the starting post. The hint was that when the post drops, the spoiler-car gets a 3/8ths inch 'jump-start' over the other cars.

The first Question. The rules state:

E: THE UNDERSIDE OF THE FRONT OF THE CAR CANNOT BE UNDERCUT SO AS TO ALLOW THE CARS NOSE TO HANG OUT THE TOP OF THE STARTING GATE. IF THE NOSE PROTUDES OVER THE STARTING GATE AND THE OFFICIAL STARTER IS NOT ABLE TO ADJUST FOR A FAIR START, THE CAR WILL NOT BE ALLOWED TO RACE.

If we go with the spoiler design, does anyone reading this feel it will violate this rule? Our plans have the height from the track to the spoiler exactly 1". The Derby will be using a BEST TRACK. I don't know the specs of their starting posts. I don't want my son's car disqualified due to a dimentional mistake of mine!!!

The 2nd Question: Front wheel spacing [width]

I was considering narrowing the front of the cars' wheel base by 1/16th of an inch on each side, to a max width of 1 & 3/4". The BEST TRACK center rail is 1 5/8th" wide X 1/4" tall. I was thinking that with less 'wiggle-room' up front, his car might suffer less drag from the wider side-to-side motion. Am I totally off the mark with the second modification?

Thanks in advance for ANY imput that you all may give us!!!
Steve Craven & son [Joel]

[wheeler]

Steve, pin rotates forward faster than car accelerates so there would be no advantage. Body width between wheels is minimum 1 3/4.

[Mr. Slick]

At the Cub Scout level this would be viewed as trying to cheat the starting pin.

The rules we use state that the front end can not be more than 1/4 inch above the axle height. It just makes the expectations clear.

It used to be an advantage with a starting gate that was lowered by hand and not spring/solenoid driven.

[fnord1138]

Hey Wheeler and Mr. Slick---

Thanks to you both for the info. I certainly don't want to start off my son's 1st Derby by "trying to cheat the starting pin"! Regarding the whole front spoiler design, I just thought it looked really cool! And, [so I understand], the whole narrower front end doesn't help matters, so keep it simple, right?...the K.I.S.S. principal applies, that is to say?

Again, thanks guys!

[Mr. Slick]

You would have a hard time beating the physics in order to "beat the pin" and would most likely just irritate other parents.

I would encourage you to work with your son to get a cool design. I undercut most all of my cars cause I like the looks. ;D

I even show the undercut car on the diagrams at the bottom of the the rules for our district.

www.pwdracing.com/cbd_rules_2007.html


The second mod would be better followed up with investigation into "rail hugger" design and alignment methods. I have narrowed fronts and widened rears on cars to make the most/least out of the center guides.

[fnord1138]

Hello again, Mr. Slick!

As you say, that Mod might just serve to irritate other parents...not a good way to start off his Tiger Scout experience..

He did pick out the design...kind of a blend of top-fuel dragster, ZZ Top chopped-top '34 3-window Coupe and Back To The Future DeLorien...I know, hard to picture..

Um...where might I look for "rail-Hugger" design/alignment methods, if you don't mind my asking?
Later!

[Mr. Slick]

This is where you want the true car builder pros, not me. . . I specialize in running races and putting on workshops.

OK everyone, he's primed and wanting to learn.

BTW, you could try the search feature at the top of the board.

[docb]

fnord1138 said:

The 2nd Question: Front wheel spacing [width]

I was considering narrowing the front of the cars' wheel base by 1/16th of an inch on each side, to a max width of 1 & 3/4". The BEST TRACK center rail is 1 5/8th" wide X 1/4" tall. I was thinking that with less 'wiggle-room' up front, his car might suffer less drag from the wider side-to-side motion. Am I totally off the mark with the second modification?

Thanks in advance for ANY imput that you all may give us!!!
Steve Craven & son [Joel]

I would say that narrowing the width between the front wheels can have some positive effect on reducing the energy lost when the car migrates side to side as is moves down the track. Make sure you polish the inside edge of the wheel where it will rub up against the center rail.

As always, to build a fast car you have to do alot of little things right. I think using this technique is one of the things you can do.

Good luck

[fnord1138]

Thanks docb...

We are goin' to Grandma's and Grandpa's for Turkey Day, and taking the 'kit' with us. Grandpa has all the nice tools, so we will have grandfather/father/grandson bonding time while we work on the car together...looking forward to that!!!

I read somewhere about 'EZ-Slide' graphite paint...would that work as a paint behind the wheels? That is, where the wheel hubs would contact the car body? I was planning on doing a few coats of clear nail polish, and buff the heck out of it.

I planned on polishing the axles, as well as the interior wheel rims, and the inside of the wheel hubs...and I will rough cut the bloct to son's chosen car shape, but he will do all of the rest: sanding/priming/painting/polishing, as well as some drilling and adding weights...just planning on having a GREAT TIME watching him get into "Derby-Madness"!!!

Everybody have a Happy Thanksgiving!
Go Chiefs!

[warthog]

fnord1138 said:

I read somewhere about 'EZ-Slide' graphite paint...would that work as a paint behind the wheels? That is, where the wheel hubs would contact the car body? I was planning on doing a few coats of clear nail polish, and buff the heck out of it.

Yes. There are a couple of ways to apply it either tape the car with painters tape except for the areas where the hub will contact and spray. Or the way my kids and I do it it is a little quicker - we use a piece of cardboard from the back of a notepad with a small hole cut in the middle of it (the size that we want painted at each wheel hub rubbing spot on the body) - hold it up by each axle hole and spray one at a time (we put a tooth pick in each axle hole to keep the paint from getting in there)- keeps the rest of the car clean.

[fnord1138]

Hey...one more question before we go to Gma/Gmpas...

I have noted that many cars that finish well in races have a great amount of wood removed [the Wedge design]...My son pointed out another design that he wanted to incorporate...based on the WWII P-38 Lightning. I have seen cars that have the entire center carved out [like the forked tail of the P-38]..but how do you maintain front end control, as well as find the CoG with so much car cut away? Is the frame stable? Is it inherently or overly fragile?

OK, so that was more than one question...just wanted to get them in b-4 we leave, and have all the good advice in our 'Derby File", so he can build a good car, and most of all, HAVE FUN!
Thanx again

[docb]

fnord1138,

the idea behind removing a "great amount of wood" or cutting out a portion of the middle of the car (like the P-38) is so that you can move as much weight as you can to the back of the car. If you are planning to cut out a hole in the middle you just need to keep enough wood on the sides to maintain stability. I think a quarter inch should be fine. If you are going to have a very light car you need to use dense weight like tungsten to get your center of mass in the right place. If done right you shouldn't have any stability problems.

Good luck, sounds like you are going to have a fun time at Gram and Gramps! ;D