Front end advice PICS

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davet
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Front end advice PICS

Post by davet »

I have 12 cubes behind axle and 6 in front with room for 4 more. I can't get a DFW weight higher than .59 oz and COM of more than .66".

My boy is making an aircraft carrier so we made front hull look. Was this a bad idea? Should I cut it off and bull nose it then taper it down?[imgImage][/img]

[imgImage][/img]
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Re: Front end advice PICS

Post by Stan Pope »

davet wrote:I have 12 cubes behind axle and 6 in front with room for 4 more. I can't get a DFW weight higher than .59 oz and COM of more than .66".
Reducing the CM location is hard; increasing it is easy. Leave the car short of 5 ounces by about 1/4 ounce. Make a "trim weight", a small dome-shaped piece of lead (or other dense material), that, when added to the car brings the total to 5 oz. Use a scale to decide where to glue the trim weight to the car. Placing it over the front axle will increase the DFW weight by the weight of the trim weight. Placing it over the rear axle will leave the DFW weight unchanged. Placing it all the way forward flush against the nose will add more than the trim weight to the DFW!
davet wrote:My boy is making an aircraft carrier so we made front hull look. Was this a bad idea? Should I cut it off and bull nose it then taper it down?
Looks good to me! :) OTOH, I usually "knife edge" the front, but I doubt I'd gain 0.001 sec over your nose by doing so!
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davet
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Re: Front end advice PICS

Post by davet »

Thanks Stan. Last year we were very fast with 12 cubes behind, 5 cubes just ahead then another 4 ahead of that. This yr we went with 6 cubes just ahead of rear axle and that may be causing this difference. I thought that if I added weight further forward with this setup that it would slow me down vs last yrs cube arrangement. What does this COM and DFW weight look to you as it is.

Last year after 4 heats at Districts we took 1st by only .0008 second combined over the 4 races. At Council last year there was a dead tie for 3rd place and they took the time to the .0000 sec. I may need to redo that front.
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Re: Front end advice PICS

Post by LightninBoy »

davet wrote:Thanks Stan. Last year we were very fast with 12 cubes behind, 5 cubes just ahead then another 4 ahead of that. This yr we went with 6 cubes just ahead of rear axle and that may be causing this difference. I thought that if I added weight further forward with this setup that it would slow me down vs last yrs cube arrangement. What does this COM and DFW weight look to you as it is.

Last year after 4 heats at Districts we took 1st by only .0008 second combined over the 4 races. At Council last year there was a dead tie for 3rd place and they took the time to the .0000 sec. I may need to redo that front.
The thing that worries me about that nose is that it looks like it comes to a point in the center. This will make the car difficult to stage straight when it rests on the round starting pin. That can really cost you. But I wouldn't worry about the aero impacts in the slightest.
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Re: Front end advice PICS

Post by Vitamin K »

LightninBoy wrote:The thing that worries me about that nose is that it looks like it comes to a point in the center. This will make the car difficult to stage straight when it rests on the round starting pin. That can really cost you. But I wouldn't worry about the aero impacts in the slightest.
Ooh, good catch LB. Actually, our rules would not permit this, as we require a 1/4" flat space on the front of the car for staging purposes.
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Re: Front end advice PICS

Post by davet »

Thanks guys. The pic is angled such that it looks like a point in front but it's actually straight across flat.
Do you guys think the .59 oz on DFW and .66" COM is OK or should we try to rework weight setup?
I think we can go a little thinner on the body. My boy cut it a little narrow (1/8") on one of the sides which then needed repair so the entire bottom will get 1/64" plywood then the top will get photo paper epoxied over it so it should be pretty stiff. I don't think we'll have to add any cross braces.

I've seen cars with 12 cubes and 12 in front of rear axle. I don't know how they get that much wood out. They must also have to add some tuning weight to the front end.
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Re: Front end advice PICS

Post by Stan Pope »

The numbers you gave (0.59" CM loc, 0.66 oz DFW wt) indicate a wheel base of 4.47" That sounds strange, but is that your wheel base?

If the track is good and you get the right amount of toe-in, those numbers work.

If you can get some track time before you have to glue the trim weight on, you can try taping it on at several locations, adjust toe for best times for each, and decide exactly where that trim weight should go. (In the several iterations I done like that, the trim weight almost always ended up either at the back edge of the car or over the DFW axle! Talk about extremes!)
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Re: Front end advice PICS

Post by LightninBoy »

davet wrote:Thanks guys. The pic is angled such that it looks like a point in front but it's actually straight across flat.
Do you guys think the .59 oz on DFW and .66" COM is OK or should we try to rework weight setup?
I think we can go a little thinner on the body. My boy cut it a little narrow (1/8") on one of the sides which then needed repair so the entire bottom will get 1/64" plywood then the top will get photo paper epoxied over it so it should be pretty stiff. I don't think we'll have to add any cross braces.

I've seen cars with 12 cubes and 12 in front of rear axle. I don't know how they get that much wood out. They must also have to add some tuning weight to the front end.
Ok, glad to read that about the "point" just being an optical illusion in the photograph.

And like VK's rule, our NSC rules also forbid front ends that come to a point. For some reason, I was thinking it was just a suggestion, but it is an actual rule, here's the text:

Front: the front edge of the car must be no more than 1 inch above the wheel lane of the track
and be at least ½ inch wide at the center of the car.


Anyways, glad this isn't an issue.

Overall, I think the aircraft carrier idea is super cool and would design it without regard to aero if that is really what he wants. One thing to keep in mind is that the council race is open to all this year - in other words you don't have to qualify by being one of the fastest cars in the district. So you are free to run what you want in the pack and district races and then build another no compromise car for the uber competitive NSC council race.
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Re: Front end advice PICS

Post by davet »

LightninBoy wrote:
davet wrote:

Overall, I think the aircraft carrier idea is super cool and would design it without regard to aero if that is really what he wants. One thing to keep in mind is that the council race is open to all this year - in other words you don't have to qualify by being one of the fastest cars in the district. So you are free to run what you want in the pack and district races and then build another no compromise car for the uber competitive NSC council race.
I didn't think of doing that but it's a good idea.
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Re: Front end advice PICS

Post by davet »

Stan Pope wrote:The numbers you gave (0.59" CM loc, 0.66 oz DFW wt) indicate a wheel base of 4.47" That sounds strange, but is that your wheel base?

If the track is good and you get the right amount of toe-in, those numbers work.

If you can get some track time before you have to glue the trim weight on, you can try taping it on at several locations, adjust toe for best times for each, and decide exactly where that trim weight should go. (In the several iterations I done like that, the trim weight almost always ended up either at the back edge of the car or over the DFW axle! Talk about extremes!)
.59 oz on DFW and .66" COM.
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Re: Front end advice PICS

Post by Stan Pope »

davet wrote:.59 oz on DFW and .66" COM.
OH!!! :oops:

Wheelbase is 5.59"?

Numbers still work.
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Post by sporty »

:?: I think the front end will be a tad light. Gonna have to tune it good. rail riding.

The air is going to go under the car a bit more. So I would add some tungsten putty in side the hole there. I recommend 2.2 grams of weight. May be 2.5 grams.

Once you got the wood cover on. See what you got.
I would not do less than .77 oz I. Front. That's with the wheels on.
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Re: Front end advice PICS

Post by davet »

No less than .77 oz on DFW because of the front end design or just in general?
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Re: Front end advice PICS

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davet wrote:No less than .77 oz on DFW because of the front end design or just in general?
I've done that design before and the issue I had. Was to light. In the front end. The weight was allot like yours.
but also yes. Both. The nose shape will allow air under it and cause slight lift. It will take more drift to keep it to the rail. More than what you should need.
this will take some speed away.

In the end. It's you and your sons car. I just provided my recommendation.

Your current front end weight. Is pushing the builder skills to a very high level. Even I would have trouble not giving up speed with that weight ratio/ design.

Typically. I try and run 2 3/8 drift at 4 feet with using my kitchen floor.
not sure with a raised board. What that would be. For thats is my own way and not all follow and use it. Some do.

But I'm guessing and pretty good guess. Is that you will need 3 to 3 1/4 drift.
For how I do it. That's scrubbing off some speed.

That might be. Say 42 foot best track.
3.01 as is at best
where my suggestion and what I would do. Would get a 2.99 or 2.98.
with assuming everything was what I would do. Just a time reference of difference in times.
but also is could be even slower. I don't know the builder skills and what level you are at.
it could be a 3.02

Your close. 2.2 grams would be what I would suggest.
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Re: Front end advice PICS

Post by bracketracer »

Davet, if you're going to be adding 1/64" plywood to the bottom I think you'll be fine with your current setup. You're nearly at 17 grams on the DFW already, by the time you add a skin of plywood and a sheet of label paper on top I bet you'll be pushing 19 grams or more.

I didn't see where you mentioned what configuration of track it'll be racing on, but if it's a Best track I would be happy with 19 grams or even a little less if I was confident in the rear axle drill. If it's a continuous arc ramp and it's smooth I'd go even a little lighter in the nose. If it's a homemade "gravel road", I'd be shooting for 22 or 23 g and praying.........

Best of luck!

p.s. Some of the cars you read about that are running 12 x 12 cube packages are running lighter wheels than a cub build and ultralight bodies. Some of the cars aren't even pine (gasp!)!
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