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#1 jacko

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Posted 25 June 2020 - 14:44

I have had a keen interest for some time in the 3 litre ford prototypes built by Alan Mann in 1968/69. I have seen photos of both machines at the 1968 1000kms at the Nurburgring and noticed that only the car that started the race, race No.7, had the protruding lower "lip" modification. Was this done before or after the practice accident to Chris Irwin and could it have been a factor in the loss of control at the "flying place"?



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#2 Tim Murray

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Posted 25 June 2020 - 15:25

Here’s an earlier thread on the cars which may be of interest, although it doesn’t address your specific question:

Ford P68 and P69

My understanding has always been that the Irwin crash was caused by hitting a hare.

#3 cpbell

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Posted 25 June 2020 - 17:40

Here’s an earlier thread on the cars which may be of interest, although it doesn’t address your specific question:

Ford P68 and P69

My understanding has always been that the Irwin crash was caused by hitting a hare.

I'd never heard the animal hypothesis, but I did enquire something along these lines on the "Mulsanne's Corner" Facebook group:

https://www.facebook...&epa=SEARCH_BOX



#4 1969BOAC500

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Posted 25 June 2020 - 19:07

Alan Mann's memoir contains some interesting information about the P.68 - including the 'hare' theory. Apparently the decomposing remains of the animal were found in the wreck of the car which had been covered by a tarpaulin and pushed into a corner of the workshop/



#5 cpbell

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Posted 25 June 2020 - 19:30

Alan Mann's memoir contains some interesting information about the P.68 - including the 'hare' theory. Apparently the decomposing remains of the animal were found in the wreck of the car which had been covered by a tarpaulin and pushed into a corner of the workshop/

Interesting - it does seem plausible that it might have been enough to lift the front of the car enough to cause it to take off.



#6 Doug Nye

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Posted 25 June 2020 - 21:01

Still something of a mere sticking plaster theory which may well have caused a violent swerve but the notably short-wheelbase P68 was conceived as a nimble, swerveable low-polar-moment-of-inertia platform - and any 'hare' incident could well have triggered a 'tank-slapper' type gyration which ended up with the car leaving the road and somersaulting.  I was told that Chris Irwin had commented on it feeling "a bit nervous" before the incident.  

 

He was certainly a talented driver. Barely four weeks earlier he had won the F2 EifelRennen on the Nurburgring Sudschleife in a Lola T100.

 

DCN



#7 cpbell

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Posted 25 June 2020 - 21:47

Still something of a mere sticking plaster theory which may well have caused a violent swerve but the notably short-wheelbase P68 was conceived as a nimble, swerveable low-polar-moment-of-inertia platform - and any 'hare' incident could well have triggered a 'tank-slapper' type gyration which ended up with the car leaving the road and somersaulting.  I was told that Chris Irwin had commented on it feeling "a bit nervous" before the incident.  

 

He was certainly a talented driver. Barely four weeks earlier he had won the F2 EifelRennen on the Nurburgring Sudschleife in a Lola T100.

 

DCN

I see - I was under the impression that the car just took off as the Mercedes CLRs did at Le Mans in 1999.



#8 Stephen W

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Posted 26 June 2020 - 07:09

I was always under the impression that the "remains of the hare" were found mangled around one of the front disk brakes.



#9 jacko

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Posted 26 June 2020 - 10:19

Cheers folks, but still no explanations or theories as to why the nose mod was applied to only one entry at the Nurburgring?



#10 blueprint2002

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Posted 27 June 2020 - 06:28

I have had a keen interest for some time in the 3 litre ford prototypes built by Alan Mann in 1968/69. I have seen photos of both machines at the 1968 1000kms at the Nurburgring and noticed that only the car that started the race, race No.7, had the protruding lower "lip" modification. Was this done before or after the practice accident to Chris Irwin and could it have been a factor in the loss of control at the "flying place"?

 

 

Still something of a mere sticking plaster theory which may well have caused a violent swerve but the notably short-wheelbase P68 was conceived as a nimble, swerveable low-polar-moment-of-inertia platform - and any 'hare' incident could well have triggered a 'tank-slapper' type gyration which ended up with the car leaving the road and somersaulting.  I was told that Chris Irwin had commented on it feeling "a bit nervous" before the incident.  

 

DCN

 

 

With a somewhat shorter than usual wheelbase, and not many fittings located beyond that wheelbase, the P68 would probably have achieved a lower than usual polar moment of inertia, about the yaw axis. This should make it more than usually responsive to steering inputs, or to other yawing moments, such as a nudge from another car at either end. With that long tail, however, which should result in a Centre of Pressure well behind the CoG, a destabilising aerodynamic yawing moment is rather less likely.

On the other hand, the polar moment of inertia about the pitch axis would also probably be lower than usual, this being the result of some of the same changes which reduced the PMoI about the yaw axis. The car would then also be more responsive to pitching moments, and from its appearance, with long overhangs at both ends, such a moment could be caused by aerodynamic forces. Thus, coming over a brow at high speed, at first there could be an abrupt rise in the lift force acting under that jutting “chin”, particularly in a headwind which happened to be following the hillside at that point. This would add to the inertia which anyway would tend to cause the nose and the front wheels to leave the ground. The result could be loss of steering control, and even a “back flip” under the right conditions. And if at the same time the car were following a bend in the road, the response would be still more complex.

You will recall that there was much aerodynamic experimentation at that time, a number of cars appearing with chin spoilers (A.J. Foyt’s 1967 Indy winner comes to mind) or with steeply downsloped fins on either side of the nose (Chaparral 2C, Ferrari 312-68), which evolved into inverted aerofoils by 1969, on the single-seaters. The “lip” you have mentioned seems to have been one of these experiments, and its absence might have contributed to Irwin’s accident, provided it was effective.

In the days of front axles, pre-IFS, under the right conditions, cars could exhibit severe “shimmy” along with axle-tramp, causing the front wheels to oscillate violently from lock to lock as the result of one wheel going over a bump. The consequent sharp tilt of the axle set up a gyroscopic moment that would swing both wheels over to left or right. This could initiate the oscillation under the right conditions, but independent front suspension has cured this tendency, and the phenomenon is unknown in modern cars, so far as I am aware.



#11 cpbell

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Posted 28 June 2020 - 12:17

With a somewhat shorter than usual wheelbase, and not many fittings located beyond that wheelbase, the P68 would probably have achieved a lower than usual polar moment of inertia, about the yaw axis. This should make it more than usually responsive to steering inputs, or to other yawing moments, such as a nudge from another car at either end. With that long tail, however, which should result in a Centre of Pressure well behind the CoG, a destabilising aerodynamic yawing moment is rather less likely.

On the other hand, the polar moment of inertia about the pitch axis would also probably be lower than usual, this being the result of some of the same changes which reduced the PMoI about the yaw axis. The car would then also be more responsive to pitching moments, and from its appearance, with long overhangs at both ends, such a moment could be caused by aerodynamic forces. Thus, coming over a brow at high speed, at first there could be an abrupt rise in the lift force acting under that jutting “chin”, particularly in a headwind which happened to be following the hillside at that point. This would add to the inertia which anyway would tend to cause the nose and the front wheels to leave the ground. The result could be loss of steering control, and even a “back flip” under the right conditions. And if at the same time the car were following a bend in the road, the response would be still more complex.

You will recall that there was much aerodynamic experimentation at that time, a number of cars appearing with chin spoilers (A.J. Foyt’s 1967 Indy winner comes to mind) or with steeply downsloped fins on either side of the nose (Chaparral 2C, Ferrari 312-68), which evolved into inverted aerofoils by 1969, on the single-seaters. The “lip” you have mentioned seems to have been one of these experiments, and its absence might have contributed to Irwin’s accident, provided it was effective.

In the days of front axles, pre-IFS, under the right conditions, cars could exhibit severe “shimmy” along with axle-tramp, causing the front wheels to oscillate violently from lock to lock as the result of one wheel going over a bump. The consequent sharp tilt of the axle set up a gyroscopic moment that would swing both wheels over to left or right. This could initiate the oscillation under the right conditions, but independent front suspension has cured this tendency, and the phenomenon is unknown in modern cars, so far as I am aware.

Thanks for a detailed and iluminating post!  Do you think the lip spoiler would have actuaaly had any effect in reducing lift, and can you shed any light on the downforce-generating tail that was supposed to achieve this by inducing a vortex?



#12 blueprint2002

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Posted 30 June 2020 - 01:36

Thanks for a detailed and iluminating post!  Do you think the lip spoiler would have actuaaly had any effect in reducing lift, and can you shed any light on the downforce-generating tail that was supposed to achieve this by inducing a vortex?

Appreciate your kind words. I'm no expert on the subject, just applying logic and a few engineering principles.

Hard to say about that lip spoiler. it seems rather similar to what the BRM P160 and the Brabham BT33 had, though both had front wings as well. By itself, I'd guess it could even create a small upward force, depending on the angle of attack. (So can an inverted aerofoil, but only at quite extreme negative angles).

I am under the impression that the vortex-generating tail was to reduce drag, but accessible contemporary literature is not very helpful. There was apparently a technical paper on the subject of the car's aerodynamics, but I have been unable to find it. Some useful information in DSJ's report in "Motor Sport" of April 1970, though not of a very technical nature. Still, pole position at Spa must mean something, I'm not sure what exactly!    



#13 Glengavel

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Posted 30 June 2020 - 07:22

Appreciate your kind words. I'm no expert on the subject, just applying logic and a few engineering principles.

Hard to say about that lip spoiler. it seems rather similar to what the BRM P160 and the Brabham BT33 had, though both had front wings as well. By itself, I'd guess it could even create a small upward force, depending on the angle of attack. (So can an inverted aerofoil, but only at quite extreme negative angles).

I am under the impression that the vortex-generating tail was to reduce drag, but accessible contemporary literature is not very helpful. There was apparently a technical paper on the subject of the car's aerodynamics, but I have been unable to find it. Some useful information in DSJ's report in "Motor Sport" of April 1970, though not of a very technical nature. Still, pole position at Spa must mean something, I'm not sure what exactly!    

 

It means Frank Garner must have an enormous set of...anecdotes.

 

Did Frank have any comments about the P68? It sounds like the sort of car that would have interfered with his "aim to be not the fastest driver in the world, only the oldest".



#14 10kDA

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Posted 30 June 2020 - 11:19

One of the reports of Irwin's practice crash mentioned something about the front bodywork being significantly distorted by the impact with the hare, causing a drastic change to the aerodynamics at a place on the circuit where it resulted in the worst problem. Post-crash pictures show the front body section completely separate from the rest of the car, though that could have happened at any time during the incident.

 

One more factor re: front lip - these cars seemed to have problems with cooling. Could the lip have been an attempt to direct more airflow into the radiator duct?

 

I was very interested in this car as well, from the first time I saw pics of it in 1968, and I've tried to find as much info as I could ever since. A couple of things that have surfaced over the years are:

 

1 Alan Mann reportedly hated the car even though it had come out of his shop and he was relieved when Ford told him there was no budget to continue with it. Some of the mechanics and crew reportedly felt Irwin's #8 Nurburgring car was somehow jinxed. Whether this had anything to do with Alan Mann's feelings toward the car(s) is not clear.

2. Mike Spence insisted on either adding a rear spoiler or modding the existing one when he did the initial test sessions, upsetting Len Bailey, the designer. Once the spoiler was tweaked, Spence was able to beat the lap record for prototypes by a significant amount - but I don't remember which track this was.

3. Richard Attwood thought the car was very good, and has stated that at every race they were entered in 1968, the P68s had led, was on the pole, or set fastest lap.

 

I don't have sources for this info at hand but if I find them I'll post.



#15 cpbell

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Posted Yesterday, 21:45

Appreciate your kind words. I'm no expert on the subject, just applying logic and a few engineering principles.

Hard to say about that lip spoiler. it seems rather similar to what the BRM P160 and the Brabham BT33 had, though both had front wings as well. By itself, I'd guess it could even create a small upward force, depending on the angle of attack. (So can an inverted aerofoil, but only at quite extreme negative angles).

I am under the impression that the vortex-generating tail was to reduce drag, but accessible contemporary literature is not very helpful. There was apparently a technical paper on the subject of the car's aerodynamics, but I have been unable to find it. Some useful information in DSJ's report in "Motor Sport" of April 1970, though not of a very technical nature. Still, pole position at Spa must mean something, I'm not sure what exactly!    

Cheers - were you able to find the Facebook discussion from the link I included?



#16 blueprint2002

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Posted Today, 11:01

Cheers - were you able to find the Facebook discussion from the link I included?

 

Sorry, I seem to have missed that. Could you please repeat?

Thanks