62 replies to this topic

[Henri Greuter]

Interesting. It’s a lot more “hollow” than I expected.

 

PaYR,

 

Because of owning an image like this I rated myself to know at least a little bit about the car. But since things went out of control between the two of us I didn't want to go into it in more details. But on that picture you posted in wich you put the red circle as of the creators of the vortices, that little opening is actually the entry for the `underwing-like` tunnels under the car.

 

As I was told in the past and as I understood it: the main principle for the BLAT cars wasn't so much generating downforce by accellerating the air under the car as fast as possible like on a `conventional` wingcar, instead the downforce was primarily the result of trying to keep the vacuum under the car as high as possible due to small air entries but a big diffuser to create that vacuum. But the success of retaining that vacuums was with the creation of the vortices next to the car.

Still, the underside being as hollow as it is, there are still some simularities with regular wing cars. Because I was aware of that, that caused my comments about the car looks such and inefficient design on first sight, but that is when compared with genuine wingcars. And that was what I did.

 

 

 

That makes it look a lot more like a couple of weirdly shaped venturi tunnels. I can't see any evidence of the two inlets, interestingly...

 

Also congrats Ensign - that is a highly specific image to have magicked up in 64 minutes.

At this picture is is difficult to see but go up to that post #23 by PAYR in which a red circle appears when seeing the car from up front. That tiny square next to the cockpit is the entry to the tunnels you see on Ensign's picture.

 

BTW, I think that the car we see in Ensign14's image is the 1980 version of the car, not the 1981/1982 version

Edited by Henri Greuter, 17 July 2020 - 16:55.

[PayasYouRace]

That makes it look a lot more like a couple of weirdly shaped venturi tunnels. I can't see any evidence of the two inlets, interestingly...

 

Also congrats Ensign - that is a highly specific image to have magicked up in 64 minutes.

 

It's definitely a different spec to the museum one from earlier in the thread.

[PayasYouRace]

PaYR,

 

Because of owning an image like this I rated myself to know at least a little bit about the car. But since things went out of control between the two of us I didn't want to go into it in more details. But on that picture you posted in wich you put the red circle as of the creators of the vortices, that little opening is actually the entry for the `underwing-like` tunnels under the car.

 

-----------------------------------------------------

 

At this picture is is difficult to see but go up to that post #23 by PAYR in which a red circle appears when seeing the car from up front. That tiny square next to the cockpit is the entry to the tunnels you see on Ensign's picture.

 

BTW, I think that the car we see in Ensign14's image is the 1980 version of the car, not the 1981/1982 version

 

 

It's not the opening that creates the vortices, but the edge or corner of that skirt. Now, such a small opening is not big enough to feed the diffuser, or "tunnels" if you prefer. The air has to come from the front like on a flat bottomed, F1-style car. Simply, not enough air will enter that small opening.

 

 

As I was told in the past and as I understood it: the main principle for the BLAT cars wasn't so much generating downforce by accellerating the air under the car as fast as possible like on a `conventional` wingcar, instead the downforce was primarily the result of trying to keep the vacuum under the car as high as possible due to small air entries but a big diffuser to create that vacuum. But the success of retaining that vacuums was with the creation of the vortices next to the car.

Still, the underside being as hollow as it is, there are still some simularities with regular wing cars. Because I was aware of that, that caused my comments about the car looks such and inefficient design on first sight, but that is when compared with genuine wingcars. And that was what I did.

 

 

If that's what you were told, I suspect you were being told something to perhaps throw you off the scent, or perhaps try to make an analogy you could understand. Because while you appear to be describing two different things, it's actually the same thing. You're accelerating the air under the car is the way that you create the low pressure "vacuum" under the car. It's not really a vacuum of course, but a loss of static pressure due to the increased dynamic pressure of the air. The total pressure of the air is the same top and bottom. Dynamic pressure is the pressure due to the velocity of the air.

 

In the photo of the car on a crane (I wonder where it was being shipped to?), what you can see is essentially a very long diffuser, and to bring things back to earlier in the thread, possibly where the name comes from. Because by having a very long and shallow diffuser, the boundary layer is more likely to stay attached. The photo is very revealing, and speaks to the theory behind flat bottomed cars with diffusers, which of course only really started appearing in F1 a few years after the Eagle was raced. So really, it was something new at the time and it's not surprising that few observers understood it back then.

[Henri Greuter]

It's not the opening that creates the vortices, but the edge or corner of that skirt. Now, such a small opening is not big enough to feed the diffuser, or "tunnels" if you prefer. The air has to come from the front like on a flat bottomed, F1-style car. Simply, not enough air will enter that small opening.

 

 

If that's what you were told, I suspect you were being told something to perhaps throw you off the scent, or perhaps try to make an analogy you could understand. Because while you appear to be describing two different things, it's actually the same thing. You're accelerating the air under the car is the way that you create the low pressure "vacuum" under the car. It's not really a vacuum of course, but a loss of static pressure due to the increased dynamic pressure of the air. The total pressure of the air is the same top and bottom. Dynamic pressure is the pressure due to the velocity of the air.

 

In the photo of the car on a crane (I wonder where it was being shipped to?), what you can see is essentially a very long diffuser, and to bring things back to earlier in the thread, possibly where the name comes from. Because by having a very long and shallow diffuser, the boundary layer is more likely to stay attached. The photo is very revealing, and speaks to the theory behind flat bottomed cars with diffusers, which of course only really started appearing in F1 a few years after the Eagle was raced. So really, it was something new at the time and it's not surprising that few observers understood it back then.

Poor english by me again I fear.

Anyway, you are of course right that it isn't the air entry that creates the vortex but the outer part.

But I am sorry to disappoint you, that edge is, at least on the cars that I could inspect the entry into the diffusers/tunnels (whatever)

Perhaps some air was also leaking into the diffuser from aside. I know you are the specialist among us in this but I can't help but describing what I have seen and writing down what I was told.

And the mechanic I spoke back then talked about most of the time about the vacuum that was under the car and that is was essential to prevent too much air under the car. When I asked him then why the venturi behind the rear wheels wasn't sealed off at the sides he then told me that was not necessary to do over there any longer. I didn't dug into it any deeper back then.

Nowadays, thinking it all over, I assume that the conclusion must be that as it was essential to prevent that too much air could enter the tunnels ahead of the rear wheels. Once this was achieved the downforce was generally fine and effective. Apart from assisting in the creation of the vortices, that may also explain the deltashaped bottom ahead of the rear wheels, as you know even better than I do, that's one manner to make it more difficult for air to leak into a diffuser

 

 

As for your question where the car was shipped to, my best guess is that the ship is the Queen Mary at Long Beach and the car being a part of decoration for a party on board.

The color picture I have of the shot makes me believe that the car we see is a 1980 version and that one was sponsored by Theodore Racing = Teddy Yip. A party at the QM sounds as something he would not hesitate to organize if there is a good reason to do so.

[TennisUK]

which of course only really started appearing in F1 a few years after the Eagle was raced.

In fairness - that was only due to regulations. And the Ferrari I posted earlier could make a claim for an earlier 'diffuser' of sorts - as their flat(ish) bottom was mandated by the flat-12 rather than the ban shaped undersides.

Edited by TennisUK, 17 July 2020 - 18:21.

[ensign14]

In the photo of the car on a crane (I wonder where it was being shipped to?), what you can see is essentially a very long diffuser, and to bring things back to earlier in the thread, possibly where the name comes from. Because by having a very long and shallow diffuser, the boundary layer is more likely to stay attached. The photo is very revealing, and speaks to the theory behind flat bottomed cars with diffusers, which of course only really started appearing in F1 a few years after the Eagle was raced. So really, it was something new at the time and it's not surprising that few observers understood it back then.

 

Not being shipped anywhere - being winched up onto the Queen Mary for display purposes before the Long Beach GP, I assume 1980.  Does the pointy bit ahead of the rear wheel have any relevance to anything?   Would that be creating some sort of vortex just as the air passes around the suspension?

 

The original Ligier JS19 concept had skirts all the way behind the rear wheels, and a very boxlike rear end, so it may have had a similar diffuser appearance.  I assume that was not BLAT, but trying to take advantage of the rules governing bodywork and skirts (didn't work, they had to scrap the aero work behind the rear suspension).

 

 

 

 

[TennisUK]

The original Ligier JS19 concept had skirts all the way behind the rear wheels, and a very boxlike rear end, so it may have had a similar diffuser appearance.  I assume that was not BLAT, but trying to take advantage of the rules governing bodywork and skirts (didn't work, they had to scrap the aero work behind the rear suspension).

The Lotus 80 had skirts all the way back too - and all the way to the tip of the nose. Or at least it did sometimes, but as with most things on the car it didn't work.

 

 

Edited by TennisUK, 17 July 2020 - 19:15.

[PayasYouRace]

Poor english by me again I fear.

Anyway, you are of course right that it isn't the air entry that creates the vortex but the outer part.

But I am sorry to disappoint you, that edge is, at least on the cars that I could inspect the entry into the diffusers/tunnels (whatever)

Perhaps some air was also leaking into the diffuser from aside. I know you are the specialist among us in this but I can't help but describing what I have seen and writing down what I was told.

 

No Henri, that is not what that opening (which isn't present on the "Queen Mary spec" car btw) does. The air feeding it would simply be that coming from ahead of the car, like a flat bottomed F1 car pre-1990 (before raised noses became a thing).

 

I can't say that's not what you were told, but I can say that what you're saying is not correct.

 

 

And the mechanic I spoke back then talked about most of the time about the vacuum that was under the car and that is was essential to prevent too much air under the car. When I asked him then why the venturi behind the rear wheels wasn't sealed off at the sides he then told me that was not necessary to do over there any longer. I didn't dug into it any deeper back then.

Nowadays, thinking it all over, I assume that the conclusion must be that as it was essential to prevent that too much air could enter the tunnels ahead of the rear wheels. Once this was achieved the downforce was generally fine and effective. Apart from assisting in the creation of the vortices, that may also explain the deltashaped bottom ahead of the rear wheels, as you know even better than I do, that's one manner to make it more difficult for air to leak into a diffuser

 

You spoke to a mechanic? So not one of the designers, or part of whatever constituted the aero team at Eagle? Because a mechanic probably only had a basic grasp of the aerodynamics involved at best.

 

When you look at flat bottomed cars with diffusers, especially in the early days, they don't have the sealed of sides because that's not where the pressure difference needs to be contained. It's not surprising that it worked better without those side panels, which would also have produced a lot of drag being so close to the rear wheels. This links into why racing cars have the "coke bottle" rear bodywork too, keeping as big a space around the wheels free for the air to pass round them.

 

Whether on this sort of car, or with traditional ground effect, the aim is to have as much air enter from the front (hence raised noses), then seal the sides (hence skirts or vortices), and then a big smooth opening at the rear (hence diffusers).

[Henri Greuter]

No Henri, that is not what that opening (which isn't present on the "Queen Mary spec" car btw) does. The air feeding it would simply be that coming from ahead of the car, like a flat bottomed F1 car pre-1990 (before raised noses became a thing).

 

I can't say that's not what you were told, but I can say that what you're saying is not correct.

 

 

You spoke to a mechanic? So not one of the designers, or part of whatever constituted the aero team at Eagle? Because a mechanic probably only had a basic grasp of the aerodynamics involved at best.

 

When you look at flat bottomed cars with diffusers, especially in the early days, they don't have the sealed of sides because that's not where the pressure difference needs to be contained. It's not surprising that it worked better without those side panels, which would also have produced a lot of drag being so close to the rear wheels. This links into why racing cars have the "coke bottle" rear bodywork too, keeping as big a space around the wheels free for the air to pass round them.

 

Whether on this sort of car, or with traditional ground effect, the aim is to have as much air enter from the front (hence raised noses), then seal the sides (hence skirts or vortices), and then a big smooth opening at the rear (hence diffusers).

OK.

If you tell me that what I have seen with my own eyes is not what is the actual situation, then I rest my case.

 

 

 

My last contribution of information I share in this thread will be the following.

 

Source:  Indianapolis 500 Yearbook 1980. Article "Ground effects: a half hour History of the latest chassis Innovation to invade the Speedway" by Philip LeVrier

Starting at page 179.

 

I quote the following that appears on page 180. It starts with a general description about the 1980 Eagle which I don't reproduce of lazyness. But then there is the following:

 

"But the unique thing about the car's design was John Ward's ground effects solution. He sealed off the air beneath the car rather than have it flow under the car in a venturi effect as in the Chapman-Hall concept with the wide side pods.

In doing this, he created a low pressure area at the rear of the car which creates the down force which exemplefies ground effects. In addition, the rear end was swept upwards like the Chapparal so the ground effects is experienced along the length of the car."

 

And since I am still in a helpful mood....

 

Another quote in the same article, still on page 180.

 

"In a familiar ground effect puzzler, the Eagle was not getting consistant down force because of the chassis lifting in the turns and too much air was disturbing the suction. This problem was overcome by adding thin body structures to the lower outside forward sections of the tub supported by dihedral supports in an attempt to give a greater sealing effect to the chassis and in effect desentisizing the car."

 

 

A call made upon other owners of the 1980 Indy 500 yearbook

 

Since it is suggested that in the past my eyes deceived me, am I permitted to call upon posters within this thread who also own a copy of this book to verify if what I qouted from my particular copy is indeed the same as what is printed on the page of their particular copies, give and take some possible typo's.

And tell me what is different in my copy compared with theirs?

 

To everyone:

Thanks for time and attention.

Enjoy the discussion of this topic from here one.

I have shared what I know and what I've seen.
But if this can't have been the case, time for me to leave the discussion and leave it to better informed more reliable withnesses and/or specialists and quit causing confusion.

[PayasYouRace]

I’m pleased you posted that, Henri, because is backs up my explanations perfectly.

[blueprint2002]

Thanks to all who have contributed their views, knowledge and personal pictures. When I started this thread I never thought it would meet such an enthusiastic response, or such a lively discussion. Much appreciate your time and trouble! 

[werks prototype]

More or less what dimples on golf balls are for--creating a turbulent boundary layer on the surface in order to keep flow attached further around the ball.  They are trying to reduce drag on the golf ball but the physics is similar.

Looks very much like Bugatti are reimplementing this idea, with an 'inflatable' variation.

 

[mariner]

I guess it all pretty much been said but to add one thought - the Concorde used vortex generation to provide its lift as do most delta winged aircraft. Any pics of Concorde landing wil show a very steep nose-up attack angle , hence the droop nose. Often the vortices are very well demonstrated when humidity is high.