Club 80-90 Forums

Now I know a t25 is about as aerodynamic as a brick but I flew in a beeckcraft twin engined thing today and noticed that as it taxied faster so the damping of bumps in the runway go much better as the aerodynamics reduced the apparent weight of the plane. As my t25 has a slight 'nose up' stance is it possible it is acting as a 'thick' wing thus making the steering increasingly vauge as speed increases? Or at least the air pressure under the van is reducing the apparent weight on the front wheels? Apparently a front skirt will counter this 'lift'? Ive never driven anything without pas that felt this light at 50.

As my t25 has a slight 'nose up' stance is it possible it is acting as a 'thick' wing

Not at any speeds your engine is going to push a T25 to. The steering feels light thanks to rear engine and rear wheel drive I guess.

All vehicles generate slight lift at speed, caused by the air beneath the vehicle essentially being dragged along by all the lumpy bits beneath, slowing the airflow down beneath relative to the air travel travelling over the top, which increases the pressure differential - higher beneath, lower above.

In order to reduce this effect, you need to either reduce the amount of air allowed to enter beneath the vehicle (by fitting a splitter) or by reducing the drag beneath the vehicle (by fitting a flat floor).

Hope this helps

Dave

Doesn't the airflow under the van actually generate a ground effect as it's forced into the smaller space between the van & the road? Isn't the net effect downforce not lift?

If you fit a floorpan and skirts you can create ground effect but not with a standard van setup

Do you think Mclaren would let us borrow their wind tunnel to prove it one way or the other?

Steering starts to get weird at about 80.
Fitting a front spoiler reduces it.
Hang on, I remember seeing a picture on the Internet somewhere, I'll see if I can find it..

80! Ha! Still, need to buy a splitter I think.

They must be aerodynamic because the enlightened amongst us call them wedges!

Is a Dehler Profi lower than a pop top Westy?

Is the lesson here" don't drive below 80 mph if you have a spoiler fitted?"

Ive had mine off the clock at 100 befor (dont know how true the speedo is) without a chin spoiler and it felt very light. But after fitting a spoiler thinking about it there is a difference!

BOXY wrote:Doesn't the airflow under the van actually generate a ground effect as it's forced into the smaller space between the van & the road? Isn't the net effect downforce not lift?

As said, a flat floor will help, but all the exposed cross members etc drag the air along under the van, increasing the pressure beneath the van. If you want a graphic demonstration, look at early Audi TT's, they took off at speed, necessitating the fitment of the spoiler at the back to make them more stable at speed. The spoiler works by disrupting the air flow off the rear of the vehicle, slowing it down and therefore increasing its pressure on the rear of the car.
Very, very few cars actually generate downforce, usually those adorned with huge wings and complex aerodynamics, such as Lotus Exiges, Mc MP4-12, Bug Veyron etc

Fitting a splitter works in two ways:
1 - it creates a barrier across the front of the vehicle preventing as much air from entering the underside of the vehicle, so less air equals less drag equals lower pressure under vehicle

2 - the front of the vehicle is a high pressure area, caused by the vehicle compressing the air as it tries to push it out of the way, so this high pressire actually pushes down on the angled splitter surface, pushing the front of the van down onto the road surface.


Dave

Those pics prove that pop tops are not aerodynamic.
But take a look at the high top... I think thats a respectable air flow