handling problem......

[hitz]

 
  Hotnuts,

  Lots of information so far on handling problems in this thread. Some of it has to be good. I'm a neophyte to LSR so I can't say much that I can prove.

  Front axles:
   
    The wheels should point straight ahead and be straight up and down to start.

    The scrub radius should be as small as you can get it. The smaller it is the less toe in you will need you will need to offset the tire scrub. Bias ply tires will need a little         
  more toe in than radials. Start at zero toe with radials.

    Increasing caster seems to move the tire scrub toward negative scrub. ( I'll probably hear about that statement). It moves the inside of the scrub radius out.

    Increasing caster tends to unload one of the rear wheels more (takes weight off) when turning. That's not good especially with open differentials

    If you need a lot of toe in or toe out something is not right. This means you have a lot of alignment drag somewhere. Drag uses up horsepower!

    Might think about what Burkeland had to say about your car's nose.

    Hope some of this is of help.

    Harvey

     

[Jonny Hotnuts]

Sorting out all the info here and applying it to the known (and yet to be discovered) issues with the suspension geometry is proving somewhat difficult but without the support of the people here I would be up a turd river with only my hands for paddles.

Today for the first time put the car on stands to check the balance point.
I was actually surprised to find it further forward than I had originally thought.
And I did the cut out car to find the COP. Here are the results.....and take into consideration that this is with an empty tank (located in the most rearward section) and at about 7 pounds per gallon my 3 gallon fuel cell would add about 21 pounds rearward. I suspect that with a full tank the COP and COG will be dead even as they are already so close.

Might think about what Burkeland had to say about your car's nose.

I dont mind saying it but ironically I am copying the form of a nose Tom designed for another car. The nose I built was for a large amount of down force with most almost all the air going over the top. The new nose I am shooting for 33X33X33 (equal amounts of air on both sides and over the top) But may have to build one with more air over the top because the car is wider than it is tall.

What ever the outcome is.....it will be vastly different from the current nose. I have almost a year to do it without the pressure of last year. Because the COG is further than I suspected I am now convinced more than ever that the massive amount of frontal down force and ridged suspension in the front did in fact cause the back to get light and while may not been 100% of the problem I am thinking it is somewhere in the 50-75% range!


So how bad is it to have your COP and your COG this close?

-JH

[Unkl Ian]

If the rear toe was off that far,I'd be checking the front as well.

Check them relative to the vehicle center line.

[1212FBGS]

was the cog with driver and fluids?
by the way, haw did ya do? i think i saw the car in impound.. did ya have some rookie luck?
kent

[Sumner]

Might think about what Burkland had to say about your car's nose.

I don't mind saying it but ironically I am copying the form of a nose Tom designed for another car. .....................................................................So how bad is it to have your COP and your COG this close?

-JH

I was talking to JH and Tom and suggested that maybe he should consider a different nose shape.  I suggested looking at Blowfish's nose as I like the way it sends some of the air down the sides of the car.  I asked Tom what he thought about it.  He just started smiling and said "do you know who suggested that shape?"  I said "I guess it must have been you!!".  He said he designed it on a napkin over lunch with I think Troy.

I've also  talked the yellow Stude from Wash. into pursuing a similar nose for next year as they have had way too much down-force on the front of their car at speed.  If we stretch the front of Hooley's stude out we will probably go after a similar shape.  I did do concepts of these a while pack on here and posted pictures, but I'm not sure I could find them.

JH if you moved the front wheels forward and extended the nose that would help to move the CP rearwards and there is nothing wrong with putting weight in the nose.  Look what Mike has done with Ack Attack with the water tank making up the whole nose.

If the CG and CP are in the same place you can have a pretty good "spinning top", just what you don't want.  If the CG is behind the CP then as soon as something upsets the car the back will be wanting to pass the front.  Look at how the Cup cars can be loose at the beginning of a run with the fuel load in the back.  As soon as the car gets loose the weight back there will have a "moment" on the car and try to keep it going in the direction it started when it got loose (back-end into the wall).  When the fuel load burns off the car will start to push and it is easier to chase after the front, especially in our case where there isn't a wall there.  If the front is heavy it will try and stay ahead of the back.

Congrats on your record and I'm sure you will be running much faster next year.  I still didn't get a chance to talk to you about Busa motors 

c ya,

Sum

[Jonny Hotnuts]

I was talking to JH and Tom and suggested that maybe he should consider a different nose shape.  I suggested looking at Blowfish's nose as I like the way it sends some of the air down the sides of the car.  I asked Tom what he thought about it.  He just started smiling and said "do you know who suggested that shape?"  I said "I guess it must have been you!!".  He said he designed it on a napkin over lunch with I think Troy.

Funny thing is once Tom explained the reasoning why frontal aerodynamic down force does not help forward stability it was like getting hit in the head with a brick, at that point I knew he was correct and the nose on the car would have to be changed. It was a mistake on my part.....but I would rather be wrong based on a concept that has validity then correct by accident....
This was a test year for the car and while setting an open record is great the real victory for me is getting the info needed for next year (and getting the rookie, d license stuff out of the way is cool also).
This is why it was so important for me to get the car to the salt this year.....in truth the car was not ready but I would of made the same mistakes because you just dont know what needs to be changed until it becomes a problem.



And yes the Fish is the nose I using as a design model......cats out of the bag!

[Sumner]

And yes the Fish is the nose I using as a design model......cats out of the bag!

I took quite a few pictures of it this year.  Let me know if you need them.

Every year I learn more about what I never though about thinking about and some of the things I did think about and thought I knew about ended up being wrong  ,

Sum

[RidgeRunner]

Every year I learn more about what I never though about thinking about and some of the things I did think about and thought I knew about ended up being wrong  ,

Sum

     A true feast of food for the brain.

[RidgeRunner]

Sum,

     I like your close CG/COP - spinning top analogy. 

     Until reading this thread I had always thought of the CG/COP in the single plane terms of a weathervane with the CG being the pivot point of the vane.  Now I am starting to also think about the effects of the relationship of the height of the CG  to aero downforce front and rear in a second plane.

                                   Ed