Couple questions about the GM lakester and lakesters in

[Bob Drury]

Don't believe it?  Look at a picture of a Top Fuel tire at speed.  The back of the tire is flat and perpendicular to the ground...........

[JackD]

The 600 mph you mention is surface air speed, nothing more. The top of the tire in relation to the air tends to cool it and reduce the failure rate. The power thru the contact pateh generates the heat and contributes to ahe failure.
 All tires at speed have a stending wave shape that is more exagerated in a low preassure top fuel rear.

[Bob Drury]

Jack, I am not arguing with you, but the cylical speed up the back side, and slowing down the front side has got to stress a tire more the faster it goes.  I bring this up only because you and I both know that a lot of people are running unrated (for the record in their class) tires out there, and I sometimes wonder if they even think about the stresses on a tire.

[RichFox]

Maybe I'm just to dumb to see it, but I would think the only speed working on a tire would be rotational speed. Granted the faster it runs the more often any point hits the ground and is flexed but I don't believe the accelaration from the ground to over the top affects the tire.

[JackD]

At a steady speed, the tire does not change speed except as it encounters surface speed in relation to the air. The portion of the air around the tire at any place tends to remove the heat generated by a combination of HP transmission, surface temp,and flex.
 Remove the airflow around a tire and you have reduced it's ability to shed heat.
 The centrifical force changes with the rotational speed and the distance to the centerline.
 HI speed shots of Top Fuel tires are the best study to see the forces that act on all tires.
 
  <small>[ February 16, 2005, 11:39 PM: Message edited by: JackD ]</small>

[Bob Drury]

Anyone who thinks centrifugal force doesn't enter the picture, should talk to Gene Burkland, who in testing LSR tires for M/T has sent many tire shards into orbit.  Look up and you may see a few just now coming down.  My concern is that we don't know with any amount of accuracy at what point a given tire comes appart.  At least the Goodyear LSR (not to be confused with Goodyear Front Runners) and the M/T LSR tires are load tested at speed.

[John Burk]

Was looking at the picture of the Hammond lakester shown earlier in this topic and got wondering if the big scoop could have contributed to the lift that may have doomed the car . I went to interactive airfoil analysis (first item on yahoo under that title) and tried to simulate the shape . It showed a big spike in negative pressure in that area . If only the air inlet had been in the center of the nose the lakester might still be setting records .

[ddahlgren]

You gotta be kidding.. Yahoo solves this.. Next they will have the solution about Micheal Jackson and all his little friends.. LOL.. have you ever been to the place we are talking about or doing a Google search for it? Things are way more complicated than  I think you might imagine.. Math is good I use it every day to solve many problems but I doubt that Yahoo has the definative answer..... Or even has the question at best...

[John Burk]

Dave
    If you prefer google , interactive airfoil analysis is the first item there also . I used this interactive site because it lets you experiment with non-standard shapes .

[ddahlgren]

How would it simulate the air going into the scoop? The engine is consuming the frontal area if the soop is sized correctly.
 Dave

[John Burk]

Dave
 At 300 mph unless the scoop was supplying 75 or 100 cubic feet per second to somthing there would have been a lot of spill over . The engine would have used less than half that volume .

[Bob Drury]

Ever notice how small the air inlet is on the Nish streamliner?  I think John may have a valid point.  I spent 33 years in the HVAC field, and over the years discovered that more is not allways better when it comes to moving air.  One mistake people tend to make with scoops is to have them end at the back of the inlet to the manifold.  A plenum needs to have a buffer rearward from the inlet or a turbulance will occur right over the inlet and create a "back pressure" of sorts, which sort of defeats the whole "ram air " principle.

[Sumner]

One mistake people tend to make with scoops is to have them end at the back of the inlet to the manifold. A plenum needs to have a buffer rearward from the inlet or a turbulance will occur right over the inlet and create a "back pressure" of sorts, which sort of defeats the whole "ram air " principle.  

Bob could you elaborate on all of that a little.  I'm a little slow and don't quite know what you are saying, but I'm interested.
 
 Thanks,  
 
 Sum

[Bob Drury]

Sum, air does't like to make tight turns.  If you radius your scoop into say a carburator or injector like a current NHRA injected nitro dragster, the air has a chance to make the turn.  If, however, you run a scoop that doesn/t allow for a radius to the injector, the air has a tendency to "swirll" or tumble, when it hits the back.  If you are stuck with this type of plenum or scoop you can alleviate this problem by running the plenum past the rear of the carb or injector by a foot if possible.  This lets the air swirl behind the opening into the manifold rather than spining over the top.  This is a lot easier to explain with a blackboard and chalk, so I hope you can kind of picture it.  The bottom line is you need a cushion at the rear of the scoop to negate the swirll and create the possitive pressure into the intake.  In a common ductwork design using a rectangular plenum, a engineer will never draw a perpendicular takeoff in the last two feet for this very reason, and even though a internal combustion engine has the advantage of pulling air from the scoop, You still are dealing with air.  This would not be nearly as important on a blown engine, but for those of us normally aspirated cars, I think this would be valid.  My thoughts only.

[Sumner]

Thanks Bob, I have a better picture now and that all makes sense.
 
 Have a good weekend,
 
 Sum