JK's Track Tool

[JK]

Dalton, The winglets (or to use their correct name dive plates) while creating a small amount of downforce in the case of the GT40 I think are likely to have a major secondary effect. While I'm only guessing I would have thought they would improve the airflow around the front wheel area and may setup a vortex down the side of the car which would reduce air loss from underneath, down side of that theory is that the underside of the original GT40 is terrible for airflow.

JK, I think you are focusing far too much on how aeroplanes work and not how cars work, a major part of the aerodynamics of a car is the ground effect that doesn't affect a plane (Ekranoplan excepted). You dismiss ~30 years of F1 and sports car aerodynamics, why do you think F1 teams go to the expense of creating rolling road wind tunnels?

I found "Competition Car Aerodynamics - A Practical Handbook" by Simon McBeath a very good primer on the subject. You may also want to read "Race Car Aerodynamics: Designing for Speed (Technical including tuning & modifying)" by Joseph Katz

Winglets at the nose and under the diffuser plate are a very interesting option. Actually, I am thinking about this, what holds me off in the moment is simply time. I have none and we have only a few weeks testing left this year.

Just to show, in which direction the next steps will be, a picture of the underbody of a Lola race car

I suppose, this is what you meant with reducing the air loss under the car. I'm afraid this will only work with a specifically formed underbody. But I am definitely interested go in that direction.

But I would like to dicuss about this a bit later, after we have first test results of the actual setup (ok, future setup, still not ready ).

Btw., my emphasis on airfoil aerodynamics was only due to the basic discussion about Bernoulli vs. Newton to describe the function of a car rear diffuser. And the ground effect is not excluded in the basic theory.

I did not read the books, you mentioned, I was reading mainly german books about that topic. So thanks for the hint, I just ordered them. I would like to collect any potentially useful bit of information .

 

[JK]

Now I have to shut down my computer because I have to catch a plane tomorrow morning (it is 3 AM now here in Germany)

I could not even read through all the posts, but it gets very interesting here.

So thanks for your replies for now, I will be back in about two days.

 

[David]

Tunnels are something else entirely, I wouldn't have thought there is significant room to really do them justice on the GT40 without major modifications. I'd be interested to see an attempt though.

It does seem somewhat counter to what you'd instinctively expect but you *want* significant airflow under the car and don't want to lose it.

 

[DARREN]

The venturi effect and how wings work is mathematically the same.

For a wing you apply Bernoulli to the top and bottom surface with the difference equating to the lift or downforce generated. For a diffuser then you are applying Bernoulli to the venturi and the pressure decrease applied to the surface area of the diffsuer equates to your downforce.

Ground effect can be explained with Bernoulli too as you basically get a more effective venturi as the ground approaches the underside of the wing which increases the effectiveness of the underside and increases the downforce.

Bernoulli is the pressure equivalent to the conservation of energy principle, ie the energy in the air at one point must equal the energy of the air at another point, so long as you don't go and add energy into it from an external source. So if you speed up air the airflow the pressure normal to the direction of flow must decrease.

That is the classic theory taught to all engineers however there is a group that claim that lift on a wing is caused by what they term the Coander effect. I think there is a website and an Australian engineer who has tried to invent various products to make use of this effect at the same time as explaining the theory. Personally when i looked at it i still thought that Bernoulli would hold up and still apply.

As far as i can remember the Coander effect is described in a similar way that you feel when you put your hand out the window of a car and angle it to the wind, you feel the force of the air pushing your hand in the direction of the air flow. I think it's explained by the conservation of momentum principle, in that you have millions of air particles hitting your hand at some elevated velocity and the resulting force pushes your hand up/back proportional to the cross section of your hand/angle that you present to the air.

With diffusers you must ake sure they aren't so steep as to stall the air flow. I measured an F1 car diffuser that i was working around once and it seemed to be approx. 17 degrees.

 

[Brett James-McCall]

imho, the main problem with the front is all the high pressure air that gets under the front hood.

We are putting a good solid splitter under the nose and sealing all the entrances for air at the nose.

I am quite sure this will solve the problem with front end lift.

Where are you planning to put the radiator then?

 

[Cliff Beer]

The venturi effect and how wings work is mathematically the same.

For a wing you apply Bernoulli to the top and bottom surface with the difference equating to the lift or downforce generated. For a diffuser then you are applying Bernoulli to the venturi and the pressure decrease applied to the surface area of the diffsuer equates to your downforce.

Ground effect can be explained with Bernoulli too as you basically get a more effective venturi as the ground approaches the underside of the wing which increases the effectiveness of the underside and increases the downforce.

Bernoulli is the pressure equivalent to the conservation of energy principle, ie the energy in the air at one point must equal the energy of the air at another point, so long as you don't go and add energy into it from an external source. So if you speed up air the airflow the pressure normal to the direction of flow must decrease.

That is the classic theory taught to all engineers however there is a group that claim that lift on a wing is caused by what they term the Coander effect. I think there is a website and an Australian engineer who has tried to invent various products to make use of this effect at the same time as explaining the theory. Personally when i looked at it i still thought that Bernoulli would hold up and still apply.

As far as i can remember the Coander effect is described in a similar way that you feel when you put your hand out the window of a car and angle it to the wind, you feel the force of the air pushing your hand in the direction of the air flow. I think it's explained by the conservation of momentum principle, in that you have millions of air particles hitting your hand at some elevated velocity and the resulting force pushes your hand up/back proportional to the cross section of your hand/angle that you present to the air.

With diffusers you must ake sure they aren't so steep as to stall the air flow. I measured an F1 car diffuser that i was working around once and it seemed to be approx. 17 degrees.

Good point. After all, even a piece of flat 4' X 8' plywood can create lift with a decent angle of attack on the wind. In other words, Bernoulli can get stuffed if the suggestion is that low pressure on the top of an airfoil is the only element providing lift.....it's a lot more than that and the angle of attack of the bottom of the airfoil is important and key to maximizing lift for any given wind speed. In the case of GT40s, managing the angle of attach is important for lessening the lift.....

Related, obviously, different airfoils work better for different wind speeds (people seem to forget this....) and at the speeds which our GT40s travel, a big fat airfoil generates the most lift. Trouble is, the underbody of a car doesn't lend itself well to a big fat airfoil.....

Also related, there's some good wind tunnel data floating around from Ford testing back in the day. And, as people have suggested here, the real problem with the GT40 profile is front end lift. As I recall, at 120mph the front end lift is something like 300lbs. Imagine what the lift is like at 160 or 170. Scary. Hence the front winglets on many LeMans cars in an attempt to keep the front wheels on the ground.....

 

[Dalton Veitch]

The Coanda effect is commonly used in air conditioning. If you have, for example, a typical air conditioning diffuser set in a ceiling, the supply air from the diffuser tends to spread out some distance clinging to the ceiling surface. This is the Coanda effect.

 

[JK]

Tunnels are something else entirely, I wouldn't have thought there is significant room to really do them justice on the GT40 without major modifications. I'd be interested to see an attempt though.

It does seem somewhat counter to what you'd instinctively expect but you *want* significant airflow under the car and don't want to lose it.

In this case, I didn't mean the tunnels but the vortex generators at the front. Pepole claim that they will seal the sides of the underbody to prevent air coming in from the sides and reduce the underpressure under the car.

 

[JK]

Where are you planning to put the radiator then?

I do not plan to modify the radiator. The air that goes through the radiator and then over the car is O.K..

I just want to prevent air going to the left and right from the radiator into the car, for example.

 

[JK]

Just a short update:

The car is nearly ready, the engine is running (great sound), only some little fixes here and there are still to be done.

When the temperatures rise again and the salt is washed away from the streets, it will make its first steps outside the garage

Picture below.

 

[JK]

The car is out and running.

Trying to sort out the last problems and drive as many km as possible to have the engine and everything ready for the first track day end of April.

gt40 second test drive - YouTube

 

[JK]

I've had the opportunity to spend two hours in the afternoon at a drivers training facility in preparation for my first track visit with the car.
And I am surprised that the car is easier to drive than I expected and I gained much confidence in it.
Also on the highway it didn't make much of a difference whether I was driving 120 or 190 kmh. I am still a little bit careful with the engine so I didn't go faster.

The aerodynamic measures are still open, most important in the moment is to get a better seat and a different steering gearbox.

Some impressions from the afternoon at the training area:

Drift Training im GT40 - YouTube

 

[EGLITOM]

well done

TOM

 

[JK]

Actually, I originally wanted to post another video.
This is the one, I was writing about in my last post:

Playing around with a GT40 - YouTube

 

[JK]

I was out one day with the Sportscar Drivers Club Hamburg. After driving my first 1000 km without going over 4000 rpm, I thought it was time to floor the throttle once in a while.

Here are a few impressions, mainly from the highway.

Ausflug mit dem Sportscar Drivers Club Hamburg am 29.4.2011 -Teil 1 - YouTube

Ausflug mit dem Sportscar Drivers Club Hamburg am 29.4.2011 -Teil 2 - YouTube

During this trip, I gained some experience with the car.

First, there is coming in way too much air under the front hood. We fixed the front hood in front of the windscreen already, with the result, that the insert in the hood nearly pops out when going faster than 240 km/h.

Second, an oil cooler is necessary for the car. The oil heats up too much, after a few minutes going fast. So we have to install one and it will get a gearbox oil cooler, too.

Nevertheless it was great fun

 

[René]

nice video, and big fun on the speed-limit free parts on the German Autobahn.
indeed when going over 200km/h a lot air goes in, let alone going over 300km/h as I know with my Hartge Z3 more comes in then can go as easy out so it wants to press at things.

for the GT40 I guess a lot can be solved when making the nostril longer so its in one flow whit the radiator, so air comes in and can only come out by the nostril which then also gives some more down-force and no heat air that goes in the car like you can read in this thread>>

http://www.gt40s.com/forum/gt40s-wanted-parts-services-needed/37031-dual-nostril-2.html

 

[JK]

Yes, that's more or less what we want to do. Not really making the nostril longer, because it is quite long already.
But to add a few plates here and there, to not allow the air to get around the radiator or to "míss" the nostril after having passed the radiator.

 

[JK]

After some changes to the car, we finally made it to a race track.
We have been at a track day on the Oschersleben race track in Germany.

After starting with huge respect for the car, I could get faster and faster after a while, only limited at the end, by an alarmingly drop of the oil pressure in long corners

So, another modification is pending, we will doubtlessly need a dry sump, no one of us expected the car to go that quick around the corners

Here is a video of some of the first laps, still with little confidence and much fear

https://www.youtube.com/watch?v=m0WlKWeh2Kc

 

Very nice....

 

[JK]

And another lap, a little bit later

https://www.youtube.com/watch?v=RkkTeytp-bM

It was such a great fun driving the car, only the oil pressure issue made me sick :furious:

The car could have been much faster without taking care not to go too quick around the corners

So we will have look for a nice dry sump kit