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1980-81 Eagle-BLAT


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#1 blueprint2002

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Posted 14 July 2020 - 06:01

The baffling aspect of racing car aerodynamics is, at least partly, due to the fact that the few who do understand it, possibly don’t have the time or the inclination to write about it for the edification of the rest of us.

For example, I have never seen a comprehensive and/or comprehensible description of the application of Boundary Layer Adhesion Technology to the 1980-81 Indianapolis Eagles. While everyone else was busily copying the Lotus 79 and its derivatives so as to generate the indispensable downforce, Dan Gurney and AAR struck off in a completely different direction. Very effective it was, too, on the front row at Indy, and a stunning victory at Milwaukee: only to be banned, and apparently forgotten.

Anyone know where I might find a decent explanation of the principle involved? (Preferably with suitable illustrations). Thanks for your time.

 



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#2 Greg Locock

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Posted 14 July 2020 - 08:05

From what I've just read BLAT seems to be a very misleading name. But I don't understand it. It seems to be a vortex generator towards the rear of the car. This creates high velocities and hence low pressures. i don't know why this is better than venturi style downforce, but since they banned it I suppose it is.



#3 TennisUK

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Posted 14 July 2020 - 10:46

I don't think anyone really understands how it worked to be honest. I've read a few bits and pieces but they seem very vague. And the bodywork evolved a lot from the first run (when it had a huge diffuser and no rear wing) to when it actually raced, which tends to suggest (as it did with the Lotus 80) that something wasn't working as they intended during the design phase:

 

LcFniN2.jpg

 

Given it was the only car in the field with a stock block NA Chevrolet, I wonder how much of the differentiation came from the difficult to understand aero, and how much from the engine?


Edited by TennisUK, 14 July 2020 - 11:09.


#4 Fat Boy

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Posted 14 July 2020 - 15:32

I've sat in that car at Gurney's shop. You'd have to be nuts to drive it at Indy. There's about 5mm of fiberglass protecting you from the wall.

 

I'm friends with Rocky Moran Sr.. As an up & coming rookie, He led the 1981 Watkins Glen race in that car going away. Something happened on the last fuel stop where they couldn't get a full load in the car. The buckeye was damaged so they couldn't stop later & put fuel in the car, either. He ran out of fuel with a couple laps left and Mears won the race. He says after that drive he expected calls from everyone with offers to drive, but it didn't happen. That was his only CART race that year. He said the car was really impressive aerodynamically for the time.



#5 TennisUK

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Posted 14 July 2020 - 15:51

The Longhorn LR03 had a couple of variants, one of which used a similar concept - by raising the side pods and having a delta shaped faring underneath. 

 

0211c0fd214b859f8a01b030b44c7622.jpg

 

I think the standard side pods were used in the race.

 

I guess the Deltawing is another car that used a similar concept.



#6 desmo

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Posted 15 July 2020 - 14:16

What is the concept? All I see in the photo is a big diffuser (and a turbo).



#7 ensign14

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Posted 15 July 2020 - 15:02

John Zimmerman's book suggests the 1980 idea was basically to have a massive wing at the back, instead of the sidepods being the wing. 

 

But I can't make sense of it at all...this is a quote from designer John Ward:

 

The vorticity off of the triangular plan forms along the sides of the tub sort of rolled itself up into an ever-increasing hollow tunnel.

 

Looks more like the title of a track by The Orb.



#8 TennisUK

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Posted 15 July 2020 - 15:45

What is the concept? All I see in the photo is a big diffuser (and a turbo).

The Eagle looked like this:

 

Mosley2.jpg

 

Bear in mind this was the era of ground effect - and all the other cars were Lotus and Williams clones with long side pods with venturi tunnels underneath. This thing had a triangular silhouette with tiny side pods holding radiators at the back - kinda like the 1983 Brabham. It then seems to have had a honking great (and very steep) diffuser out the back.

 

4f2d75396c4eba72aee35300c6e77d34-pepsi-w

 

You can see the little slot under the 'h' of Challenger where the air was channeled in - which then grows wider with the delta shaped body work and then much wider when it hits the diffuser.

 

The Longhorn in my post above has the side pods moved up and the triangular section underneath that. I think broadly the idea was to have a small aperture for the air to come inside, which was then accelerated rapidly by increases in volume of the diffuser/venture vertically and horizontally. Which must have lead to an odd centre of pressure - which presumably only worked effectively at a specific speed - not a problem on an oval compared to a road course.

 

Given the original plan had been for no aerofoil above the 'diffuser' I suspect the effect either wasn't as powerful as they hoped, or perhaps not as predictable.


Edited by TennisUK, 15 July 2020 - 15:57.


#9 ensign14

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Posted 15 July 2020 - 16:17

50115531228_c0946a5f50_b.jpg

 

Better angle of the slot, which is indeed tiny, given that I assume air may be fairly churned up by the time it gets there, I wonder how much ever got in...

 

50115531178_8cd797e53e_b.jpg

 

...and a bit more detail of the diffuser as it was raced.



#10 TennisUK

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Posted 15 July 2020 - 16:37

The lack of fins sealing the ‘diffuser’ to the ground make me think it would have lost a majority of the potential low pressure built up.

Basically I don’t get it!

Edited by TennisUK, 15 July 2020 - 16:38.


#11 desmo

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Posted 16 July 2020 - 02:58

Imagine how far back the center of pressure might be if there were a proper fence around that monster. You could use bicycle tires for the front.



#12 TennisUK

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Posted 16 July 2020 - 08:37

50115531178_8cd797e53e_b.jpg

 

...and a bit more detail of the diffuser as it was raced.

just noticed the the central element (presumably a gearbox cowling) trailing edge has what looks to be a plinth extending rearward about 20cm maybe. I wonder if this was on the car in period - as I would have thought that, in combination with the lack of vertical stabilisers each side of the diffuser it would have ruined the ground effect by creating loads of turbulence.

 

Still, what do I know. Would be interesting to hear what someone more versed in actual aerodynamics, rather than arm-chair aerodynamics has to say about it.



#13 ensign14

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Posted 16 July 2020 - 08:53

They did run the 1980 model with skirts originally but Mike Mosley said that the car ran better when the skirts wore out. 



#14 TennisUK

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Posted 16 July 2020 - 09:59

They did run the 1980 model with skirts originally but Mike Mosley said that the car ran better when the skirts wore out. 

I think these might be the two variants:

 

ef8db97f04442285a16b855dc1231f0d.jpg

 

3514484638a4441bdabb865ee0f0af3f.jpg

 

The first a more conventional ground effect machine - albeit a bit agricultural looking compared to the Penskes and Wildcats, the second the one with the confusing aero. Unsure if these are actually the same chassis type or not, though, but both appear to have been used in 1980 - and both use the same number, so I assume under Indy rules they were the same chassis? 



#15 ensign14

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Posted 16 July 2020 - 10:37

The one with the fuller sidepods is 1982. The bottom one is 1980. 

 

They did have nominal model numbers - 8000, 8100, 8200, and the chassis were e.g. 8001, 8002; the Pepsi Challenger is 8103 - and the 8100 was a slightly revised 8000 after Eagle found a better wind tunnel. 

 

The 8200 was based around the same chassis/suspension.  But they couldn't get the turbo wastegate to work after an engine regulation change, which killed it off after it blew seven engines in a week at Indy.  That was its one and only appearance. 



#16 Sisyphus

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Posted 16 July 2020 - 16:56

It would be great to hear a full description of BLAT. 

 

My interpretation of the BLAT magic is that the side pods are shaped uniquely to create vortices along the outer sides of the sidepods along the bottom which created a relatively low pressure area that helped seal them more effectively without using skirts (which were illegal).  Otherwise, what I see in the tunnels is more or less a venturi which other designs incorporated.

 

But I'm a structures guy and spent most of my career arguing with the aero guys so I may be completely wrong.  Hope someone responds with the correct answer.



#17 PayasYouRace

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Posted 16 July 2020 - 19:30

You're all basically there. It's just a big diffuser, and the sidepods are shaped in a way that helps seal the sides of the car with vortices. Simple principle, you have a big opening at the back which forces a smaller amound of air under the car to go faster through it. If you're a bit clever and can seal the underside, you get better suction. It's remarkably similar to what current F1 cars are doing. The centre of pressure is in the centre of the car because it's the flat floor that is experiencing the lowest pressure, as opposed to the very visible diffuser at the back.

 

For those that haven't come across the word outside of racing cars, a diffuser is simply a passage of increasing cross-sectional area. The opposite is a nozzle.

 

The traditional ground effect side-pods work on a similar principle, but they work by having a more distinct tunnel under the car with a noticeable throat where the centre of pressure resides.

 

Where the name comes from probably originates in the biggest challenge with any diffuser, which is keeping the airflow attached to the surface of the diffuser. If it becomes detached, then the diffuser stalls and becomes less effective. The name is probably in reference to techniques they used to keep the boundary layer (the small region of air next to the solid surface of the car) attached to the diffuser. Ironically this was probably done by making the boundary layer turbulent, which counter intuitively makes it stick better around convex curves. It is entirely possible to have a laminar flow with a turbulent boundary layer, and in a diffuser, that's an ideal situation.



#18 Sisyphus

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Posted 16 July 2020 - 19:38

... The name is probably in reference to techniques they used to keep the boundary layer (the small region of air next to the solid surface of the car) attached to the diffuser. Ironically this was probably done by making the boundary layer turbulent, which counter intuitively makes it stick better around convex curves. It is entirely possible to have a laminar flow with a turbulent boundary layer, and in a diffuser, that's an ideal situation.

 

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.



#19 PayasYouRace

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Posted 16 July 2020 - 19:40

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.

 

Yes exactly. You also see it on the upper surfaces of aircraft wings.

 

vortexgenerators1.jpg



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#20 ensign14

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Posted 16 July 2020 - 19:47

So effectively the swirls of confused air just outside the tunnel were acting as skirts?  Preventing air from rushing in from the side to fill the vacuum?



#21 PayasYouRace

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Posted 16 July 2020 - 20:09

So effectively the swirls of confused air just outside the tunnel were acting as skirts?  Preventing air from rushing in from the side to fill the vacuum?

 

Potentially, yes. F1 are currently doing that with the bargeboard gubbins they're using.

 

just noticed the the central element (presumably a gearbox cowling) trailing edge has what looks to be a plinth extending rearward about 20cm maybe. I wonder if this was on the car in period - as I would have thought that, in combination with the lack of vertical stabilisers each side of the diffuser it would have ruined the ground effect by creating loads of turbulence.

 

Still, what do I know. Would be interesting to hear what someone more versed in actual aerodynamics, rather than arm-chair aerodynamics has to say about it.

 

I think that's just a drip tray on the floor to catch gearbox oil.



#22 TennisUK

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Posted 16 July 2020 - 20:10

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.

Reminds me of the OAK racing LMP1 with the wacky rear wing a few years ago:

 

uppess.jpg

 

More here and here:

 

So effectively the swirls of confused air just outside the tunnel were acting as skirts?  Preventing air from rushing in from the side to fill the vacuum?

I'm interested in why the original concept had the vertical 'skirts' on the diffuser but they were later dispensed with?


Edited by TennisUK, 16 July 2020 - 20:11.


#23 PayasYouRace

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Posted 16 July 2020 - 20:20

So effectively the swirls of confused air just outside the tunnel were acting as skirts?  Preventing air from rushing in from the side to fill the vacuum?

 

Pepsi-vortex.png

 

That sharp edge is going to create a mighty vortex.

 

 

 

I'm interested in why the original concept had the vertical 'skirts' on the diffuser but they were later dispensed with?

 

Possibly because it wasn't adding much to the diffuser. It's likely that they just produced a lot of drag, especially with the wheels right next to them.



#24 Henri Greuter

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Posted 16 July 2020 - 20:42

The lack of fins sealing the ‘diffuser’ to the ground make me think it would have lost a majority of the potential low pressure built up.

Basically I don’t get it!

I once made that comment to a mechanic on such an Eagle in the past and he answered me that the downforce as it was, was so effective that the car didn't need it at all.

 

I was flabberghasted after that.



#25 Henri Greuter

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Posted 16 July 2020 - 20:44

I don't think anyone really understands how it worked to be honest. I've read a few bits and pieces but they seem very vague. And the bodywork evolved a lot from the first run (when it had a huge diffuser and no rear wing) to when it actually raced, which tends to suggest (as it did with the Lotus 80) that something wasn't working as they intended during the design phase:

 

LcFniN2.jpg

 

Given it was the only car in the field with a stock block NA Chevrolet, I wonder how much of the differentiation came from the difficult to understand aero, and how much from the engine?

Interesting to see that this prototype was powered by a DFX instead of a Chevy!!!



#26 TennisUK

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Posted 16 July 2020 - 20:55

Interesting to see that this prototype was powered by a DFX instead of a Chevy!!!

Chip Mead's Eagle was DFX powered - though he failed to qualify... 

 

mead_orig.jpg


Edited by TennisUK, 16 July 2020 - 20:57.


#27 PayasYouRace

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Posted 16 July 2020 - 20:59

I once made that comment to a mechanic on such an Eagle in the past and he answered me that the downforce as it was, was so effective that the car didn't need it at all.

 

I was flabberghasted after that.

 

Probably because it made it worse with the endplates, as I've alluded to.



#28 Henri Greuter

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Posted 16 July 2020 - 21:05

Probably because it made it worse with the endplates, as I've alluded to.

Probably.

 

Anyway, I have seen a few of them in real and I must agree with TennisUK, when you see one you don't understand why the rear end looks so inefficient and way below optimal but the fact remains that they worked very well as they were.



#29 PayasYouRace

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Posted 16 July 2020 - 21:09

Probably.

 

Anyway, I have seen a few of them in real and I must agree with TennisUK, when you see one you don't understand why the rear end looks so inefficient and way below optimal but the fact remains that they worked very well as they were.

 

You mean, why aerodynamics novices don't understand why the rear end looks so inefficient and way below optimal.

 

I've already explained in thread that it's not much of a mystery.



#30 Henri Greuter

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Posted 16 July 2020 - 21:11

Chip Mead's Eagle was DFX powered - though he failed to qualify... 

 

mead_orig.jpg

Chet Philip did qualify an Eagle DFX in 1982 that looked much like this one.

Pete Halsmer qualified one with a turbocharged Chevy V6 stock block that very same year.  That car loked much like it though the intake of the turbocharger was a bit weird standing within the airflow above the left `sidepod`

 

 

and.....

 

Mike Mosley failed to qualify the factory car that year .....


Edited by Henri Greuter, 16 July 2020 - 21:18.


#31 Henri Greuter

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Posted 16 July 2020 - 21:14

You mean, why aerodynamics novices don't understand why the rear end looks so inefficient and way below optimal.

 

I've already explained in thread that it's not much of a mystery.

 

 

Hope you had a field day with the opportunity to point me and TennisUK out as an aerodynamic novice.

 

 

 

About the vortexes, I knew that already,

But there is also the thing of the open sidepods above the diffuser, the exists for the radiators, right behind the rear wheels.

 

And I have to admit that I haven't worked out yet for myself why these were not vented off at the end of the car but at the sides behind the wheels.

On first thought I would thing about the moving rear wheells helping to accelerate the air out of the ducting.

But then, the airstream is released fairy close to the top end of the diffuser, thus with a posibility of ruining the efficiency over there.

 

But oh well, I'm not an aero expert to understand all of that.


Edited by Henri Greuter, 16 July 2020 - 21:27.


#32 TennisUK

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Posted 16 July 2020 - 21:20

I am quite happy to be described as a aerodynamics novice. I do find it interesting - particularly in this era because most of the stuff makes sense with just a bit of observation and thought, even to someone as ignorant as me.

With the exception of BLAT :)

#33 PayasYouRace

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Posted 16 July 2020 - 21:29

Hope you had a field day with the opportunity to point me and TennisUK out as an aerodynamic novice

Yeah, well I went to all the trouble to explain how it works, with all the benefit of the knowledge gained in race car aerodynamics since the car ran, only to seemingly be ignored and for you to pretend it’s still a mystery.

I’d be surprised if either of you were qualified professionals in the subject, and TennisUK is quite happy to accept being called that too by the looks of it. Now I’m happy to explain aerodynamic concepts to anyone here. Maybe I’m just a bit tired tonight, but it would be nice after a well thought out post to get some follow up questions or something if people don’t understand.



#34 TennisUK

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Posted 16 July 2020 - 21:35

Chet Philip did qualify an Eagle DFX in 1982 that looked much like this one.
Pete Halsmer qualified one with a turbocharged Chevy V6 stock block that very same year. That car loked much like it though the intake of the turbocharger was a bit weird standing within the airflow above the left `sidepod`


and.....

Mike Mosley failed to qualify the factory car that year .....


I have seen both those - the Chevy looked like it had an F3-style air intake on the side..

The photo I had was certainly 1981. He also ran at Phoenix and Pocono (which sounds like a weird event - still USAC sanctioned and grid stuffed with front engines champcar machinery to make up the numbers... which just have been interesting. Both races were in a DFX powered Eagle (8102 apparently).

http://www.kmvintage...eagle-8101.html has quite a bit more about the car and the ford engine.

#35 Henri Greuter

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Posted 16 July 2020 - 21:36

I am quite happy to be described as a aerodynamics novice. I do find it interesting - particularly in this era because most of the stuff makes sense with just a bit of observation and thought, even to someone as ignorant as me.

With the exception of BLAT :)

I know about a number of aero effects and matters. I won't call myself a novice anymore though I definitely don't pretend to know a lot about it let alone call myself a specialist.

I think I can say about myself that I understand the general outlines of the BLAT technoly byt definitely not into the details. Like the radiator exits I mentioned  ( An edit I added to my original post. ) being an integral part of the entire design and enhancing it. If not understanding such instantly means that you're qualified as nothing but a aerodynamic novice, well, then I have to accept that I'm such and won't go into debate about that any longer.


Edited by Henri Greuter, 16 July 2020 - 21:37.


#36 TennisUK

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Posted 16 July 2020 - 21:37

Yeah, well I went to all the trouble to explain how it works, with all the benefit of the knowledge gained in race car aerodynamics since the car ran, only to seemingly be ignored and for you to pretend it’s still a mystery.
I’d be surprised if either of you were qualified professionals in the subject, and TennisUK is quite happy to accept being called that too by the looks of it. Now I’m happy to explain aerodynamic concepts to anyone here. Maybe I’m just a bit tired tonight, but it would be nice after a well thought out post to get some follow up questions or something if people don’t understand.

One thing I’d be interested to know.... why did conventional ground effect cars not use much smaller throats so the air would have the potential to lose more pressure as the space expanded? Or is it simply a case if it being a compromise to avoid violent changes in downforce depending on velocity (I guess porpoising)?

And if so, why was it not an issue with BLAT?

Edited by TennisUK, 16 July 2020 - 21:38.


#37 Henri Greuter

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Posted 16 July 2020 - 21:40

Yeah, well I went to all the trouble to explain how it works, with all the benefit of the knowledge gained in race car aerodynamics since the car ran, only to seemingly be ignored and for you to pretend it’s still a mystery.

I’d be surprised if either of you were qualified professionals in the subject, and TennisUK is quite happy to accept being called that too by the looks of it. Now I’m happy to explain aerodynamic concepts to anyone here. Maybe I’m just a bit tired tonight, but it would be nice after a well thought out post to get some follow up questions or something if people don’t understand.

 

In that case, Let's both go to sleep by now and quit being nasty to another, OK? Please?

Tomorrow another day, new chances.



#38 PayasYouRace

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Posted 16 July 2020 - 22:07

One thing I’d be interested to know.... why did conventional ground effect cars not use much smaller throats so the air would have the potential to lose more pressure as the space expanded? Or is it simply a case if it being a compromise to avoid violent changes in downforce depending on velocity (I guess porpoising)?

And if so, why was it not an issue with BLAT?

 

So the trick with any underbody aero, is getting the right amount of air under the car. In a way, it's usually better to get more air under, so that it doesn't starve the tunnel (whatever physical shape it might be). If that happens, you end up with low pressure behind the car, and drag. The idea is to get as much air as you can into those tunnels, which will then accelerate it through faster, and then provide more downforce.

 

So in a conventional ground effect car, the entrances to the sidepods provide the volume of air required, which can then be forced through the tunnel and out the back. The porpoising is caused primarily by pitch sensitivity, as the ground effect car has a very specific centre of pressure. Small changes in velocity, ride height cause the centre of pressure to move about a lot, and the suspension follows, giving the undulating ride. Not inevitable, but common.

 

BLAT was more of a flat bottomed car, so the centre of pressure wasn't so much a point but an average of the entire floor, so you wouldn't have had the pitch sensitivity. To your main point, the air is being drawn in under the entire floor. Had the concept stuck around for a few more years, it might have benefited from an innovation tried in F1.

 

alesi3bz1.jpg

 

By raising the nose, the underside of the car could be fed with much more air, increasing the effectiveness of the diffuser. I suspect the BLAT cars were essentially just "brute forcing" the air under the car by having such a large and evidently well thought out diffuser design, but the air would have been sucked through from around the entire floor at the front. The vortices we suspect were present sealed the low pressure area under the car and forced the air to be drawn in from the front.

 

I hope that makes some sense. I'll probably re-read this in the morning and check it makes sense to me.



#39 ensign14

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Posted 16 July 2020 - 22:36


I'm interested in why the original concept had the vertical 'skirts' on the diffuser but they were later dispensed with?

That's how they did it in F1 to exclude the air from rushing in either side side, so they copied it for the BLAT triangle.  (I do wonder how the March 701 would have gone had they just added "endplates" along the length of the between-wheels sidepods.)

 

It does seem that they did not know quite how it worked and the explanations in the Eagle book are, well, not explanations at all.  (Could be trade secret though.)



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#40 Henri Greuter

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Posted 17 July 2020 - 06:28

I have also been at Santa Ana for a visit.

Speaking briefly with some people over there about their involvement with the recent Nissan Le Mans adventures one person told me that the original Deltawing did not work well at all original but once they introduced features from the BLAT Eagles on the car ("We almost made it like a BLAT Eagle with little front wheels within the monocoque")  the creation came alive and worked at last, aerowise that is.

 

(I refuse to call the Deltawing a `car` )


Edited by Henri Greuter, 17 July 2020 - 06:28.


#41 TennisUK

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Posted 17 July 2020 - 08:01

So the trick with any underbody aero, is getting the right amount of air under the car. In a way, it's usually better to get more air under, so that it doesn't starve the tunnel (whatever physical shape it might be). If that happens, you end up with low pressure behind the car, and drag. The idea is to get as much air as you can into those tunnels, which will then accelerate it through faster, and then provide more downforce.

 

So in a conventional ground effect car, the entrances to the sidepods provide the volume of air required, which can then be forced through the tunnel and out the back. The porpoising is caused primarily by pitch sensitivity, as the ground effect car has a very specific centre of pressure. Small changes in velocity, ride height cause the centre of pressure to move about a lot, and the suspension follows, giving the undulating ride. Not inevitable, but common.

 

BLAT was more of a flat bottomed car, so the centre of pressure wasn't so much a point but an average of the entire floor, so you wouldn't have had the pitch sensitivity. To your main point, the air is being drawn in under the entire floor. Had the concept stuck around for a few more years, it might have benefited from an innovation tried in F1.

 

alesi3bz1.jpg

 

By raising the nose, the underside of the car could be fed with much more air, increasing the effectiveness of the diffuser. I suspect the BLAT cars were essentially just "brute forcing" the air under the car by having such a large and evidently well thought out diffuser design, but the air would have been sucked through from around the entire floor at the front. The vortices we suspect were present sealed the low pressure area under the car and forced the air to be drawn in from the front.

 

I hope that makes some sense. I'll probably re-read this in the morning and check it makes sense to me.

This is pretty much as I had understood it all to work. 

 

My confusion with BLAT is in two areas:

 

1: The lack of vertical edges on the diffuser - though your explanation of additional drag does make sense to me - which is probably more important on an oval than a road course I'm assuming.

2: Why the apertures at the front of the 'delta' that let air in were so small on the Eagle - if stuffing as much air in as possible is desirable why did they not do what everyone else was doing with large inlets at the front of the sidepods? The Tyrell-style high nose is a different way of feeding air to the diffuser but in lieu of that why not use honking-great-sidepods?

 

This subject led me to think a bit more about the Lotus 80, Arrows A2 and the initial version of the Brabham BT48 - all of which had honking great diffusers like the Eagle - and also had extended vertical endplates like the prototype Eagle. They would also all have had comparatively massive aperture at the front of the side pods to feed more air in than the tiny inlets on the Eagle.

 

One thing the Lotus 80, Arrows A2 and the Brabham BT48 all had in common is that they were all failures. The wingless BT48 and Lotus 80 never even raced as intended. As I understand it the common issue was pitch sensitivity causing porpoising. I may be wrong here, but I would have thought that oval racing would be less likely to induce porpoising as generally the car is operating within a much narrower window, so the variation in pressure would be less. Maybe the 80, BT48 and A2 would have been better Indycars than F1 cars?



#42 TennisUK

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Posted 17 July 2020 - 08:02

That's how they did it in F1 to exclude the air from rushing in either side side, so they copied it for the BLAT triangle.  (I do wonder how the March 701 would have gone had they just added "endplates" along the length of the between-wheels sidepods.)

And, as legend would have it, Rudd and Wright's experiments at BRM in 68/69 which never saw the light of day.


Edited by TennisUK, 17 July 2020 - 08:02.


#43 PayasYouRace

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Posted 17 July 2020 - 08:39

 

2: Why the apertures at the front of the 'delta' that let air in were so small on the Eagle - if stuffing as much air in as possible is desirable why did they not do what everyone else was doing with large inlets at the front of the sidepods? The Tyrell-style high nose is a different way of feeding air to the diffuser but in lieu of that why not use honking-great-sidepods?

 

This subject led me to think a bit more about the Lotus 80, Arrows A2 and the initial version of the Brabham BT48 - all of which had honking great diffusers like the Eagle - and also had extended vertical endplates like the prototype Eagle. They would also all have had comparatively massive aperture at the front of the side pods to feed more air in than the tiny inlets on the Eagle.

 

One thing the Lotus 80, Arrows A2 and the Brabham BT48 all had in common is that they were all failures. The wingless BT48 and Lotus 80 never even raced as intended. As I understand it the common issue was pitch sensitivity causing porpoising. I may be wrong here, but I would have thought that oval racing would be less likely to induce porpoising as generally the car is operating within a much narrower window, so the variation in pressure would be less. Maybe the 80, BT48 and A2 would have been better Indycars than F1 cars?

 

So those examples are of the traditional ground effect venturi type (moving on from the Lotus 79) where the airflow is channelled through tunnels.

 

The Eagle is more of the flat bottom variety, and as ensign points out some teams in F1 were using similar skirts in the 70s, like the McLaren M26 or Williams FW06, but they hadn't yet worked out that you can put a diffuser on the back of it. Using that Arrows A2 as an example, the air drawn in through the sidepod inlets is likely to stay in the sidepods, so it requires tunnels. If the Eagle had big sidepods inlets it would have needed "conventional" tunnels too to direct that air. What a big diffuser at the back does is pump air in under the whole car, so the air needs to come from the front to be effective. If it's coming in from the sides, it would need to cross over out of the tunnel entrances which wouldn't work very well.

 

Porpoising is as much a function of overall chassis stiffness and resonance than simply aerodynamics. So it could be likely on a speedway too.



#44 TennisUK

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Posted 17 July 2020 - 09:59

Ferrari seemed to have some idea about diffusers as a means of overcoming the flat 12 compromising the venturi in 1979, although this never raced in this format:

 

1f6204f52bedd92ee85276933e95edbe.jpg

 

 

I'm interested to understand the point of the inlets on the Eagle - if the diffuser was primarily fed air by the flat underbody, what was the purpose of the inlets?


Edited by TennisUK, 17 July 2020 - 10:00.


#45 PayasYouRace

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Posted 17 July 2020 - 13:47

I'm interested to understand the point of the inlets on the Eagle - if the diffuser was primarily fed air by the flat underbody, what was the purpose of the inlets?


Do you mean the bit I circled in red?

I wouldn’t call them inlets. Look more like how they set up the vortices to get that seal.

#46 TennisUK

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Posted 17 July 2020 - 14:34

I wouldn’t call them inlets. Look more like how they set up the vortices to get that seal.

I get ya. It would be interesting to see what the car looked like underneath.



#47 ensign14

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Posted 17 July 2020 - 15:38

Here you go...

 

A911-D810-7-F3-D-4156-9479-24499-D713-E0

 

...not brilliant but I hope you can get the overall idea.



#48 PayasYouRace

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Posted 17 July 2020 - 15:53

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

#49 TennisUK

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Posted 17 July 2020 - 16:04

Here you go...

 

A911-D810-7-F3-D-4156-9479-24499-D713-E0

 

...not brilliant but I hope you can get the overall idea.

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.


Edited by TennisUK, 17 July 2020 - 16:07.


#50 Henri Greuter

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Posted 17 July 2020 - 16:38

Ensign14 beated me to it. I have the exact same picture but then taken in color.

I think we both made the pictuer at the same location, someweher in California????

But since I am unable to post pics, I couldn't post it myself and I wanted to ask TennisUK if he could PM me an email address so I could forward that image to him and then he could post it.

 

Now, if anyone posting here thinks that a color image could be of help to maybe deduct some more details......

 

If you are willing to post it over here too, PM me an email address and I'll send it to you. First one who reacts will receive it.

Sorry that I need help for this all on myself but I can't help that. I hope the offer I put up her is of any help to begin with.