Unhappy Ferrari Owner

[WayneB]

Wayne, how odd I have a 1992 Buick Roadmaster... not the LT1 version, but Buick roadmaster non the less... Great long distance driving car as well...

<{POST_SNAPBACK}>

I can honestly say its been one of the best cars Ive ever owned

I have a friend who has a taxi company, and he had one that had over a Million miles on it!

Mine has all Chev Caprice Police suspension , shocks , brakes, ecm( un governed )

and some other stuff (Courtesy a company I do work for that develops and builds the police spec(9C1) vehicles for General Motors).

[molemot]

Wayne, that is one impressive rig! I don't doubt that adding an Esprit on a trailer will slow you down a bit - but it'll be aerodynamic drag and not weight that's doing it. Your motor is unable to deliver enough power to overcome the additional resistance presented by the drag of the car/trailer/car combination. You could try towing the trailer with a flat plate of the same cross sectional area of the car fastened to it; hardly any weight, but I bet you'd be even slower because of the increased coefficient of drag of a flat plate over the shape of the Esprit. Drag depends on the cross sectional area, the drag coefficient, the density of the medium you're moving through and the square of the velocity - so a bit more speed increases the drag a lot, which is why there is such a difference in the power required to do 200 as opposed to 180!

Edited March 25, 2006 by molemot

[WayneB]

My old boat pushes a lot of air

But surely the Car on the trailer is in the low pressere wake or the draft as they call it here?

Racing drivers use this effect to slingshot past cars they are behind.

Like when you come up on a Large truck on the highway and your car starts to gather speed (with no extra throttle imput) when you enter the draft.

[molemot]

Exactly right! And the effect is not just to speed up the following car, but to slow down the car in front - the energy has to come from somewhere, and it's the lead car's engine. It's not called "getting a tow" for nothing! Without wind tunnel tests I can't be definitive, but I'd bet the turbulent flow resulting from the interface between your tow car, the trailer, and the Esprit on top is giving you greatly increased drag. Trucks use curvy things on the cab roof to smooth the transition from cab to trailer, thus lowering the drag of the combination.

[USAndretti42]

Exactly right! And the effect is not just to speed up the following car, but to slow down the car in front - the energy has to come from somewhere, and it's the lead car's engine.  It's not called "getting a tow" for nothing! Without wind tunnel tests I can't be definitive, but I'd bet the turbulent flow resulting from the interface between your tow car, the trailer, and the Esprit on top is giving you greatly increased drag.

<{POST_SNAPBACK}>

I'm not sure that having a car close behind slows the car in front. I think it can speed up the front car by helping to fill in the low-pressure region with the second car's bow-wave. The front car is already doing the work to move the air whether it's being followed or not. The second car is just taking advantage of this. I think that when you are towing with your buick, Wayne, 2 things reduce its top speed. First the extra weight reduces your acceleration a lot so any slight uphill will slow you down and take time and distance to recover. You don't make up this on the downhill bits as the gravitational force you gain is independent of speed but the drag force goes up with the square of your speed. The second effect, and probably the main one, is that the drag of the Buick and the Lotus is greater than that of the Buick only, but, unlike the case of 2 cars on a race track with one in the tow, you have only the Buick's engine to move both of them through the air.

[WayneB]

I used to know all the aerodynamic principles back to front (30 years ago)

Trev (who works in the Indy Car Biz) confirmed my belief that the close following car actually contributes to the forwards motion of the lead car with its "bow wave of air"

I have a bigger engine to install in the Buick(406 cu.in.)

That should do the trick!