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Old 12-03-2017, 13:08   #241
ejabrod
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It was also shown, that to balance the car that the front aerodynamic of the car on the GTA is 100% different to that of the other Evo 7.

So your point is moot
As stated, the car is indeed a fully standard GT-A which, again, was quite obvious from my profile.

So, no, my point is not moot, but this is typical of this forum.
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Old 12-03-2017, 13:36   #242
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Old 12-03-2017, 13:54   #243
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Dynamic weight transfer.

1500kg Evo VII.
Static load on front axle is around 61% which equates to 915kg. Static rear axle load is 585kg.
Assume a CofG height of 60cm. (conservative estimate because couldn't find actual figure in any resources known to me including SAE and technical papers searches.)

Assume a starting speed of 80mph. Perform an emergency braking maneouve with a 0.8g deceleration (conservative for an Evo I think).

Instantaneous dynamic weight transfer would transfer around 240kg of weight to the front axle. Plus any downforce at 80mph. Evo VII *with* bonnet vent has some front downforce to add to make the overall apparent weight acting on the front axle.

Weight transfer away from rear axle gives basic figure of now only 345kg pressing rear tyres down. Plus or minus any downforce or lift.

Assume spoiler less lift is 15kg at 80mph. With spoiler a downforce of 5kg is assumed. Not much. But check out the results below.

The front to rear apparent dynamic weight would swing more to the front without spoiler by around 1.5%.

I did the calculations at 0.9g braking as well and the resultant figures were consistent.

Balance has been altered by a small, but *significant* amount. Here's why...

1.5% doesn't sound very much. However, consider the actual apparent weights on rear tyres with and without spoiler. The apparent weight without the spoiler reduces to 91/92% of what it would be with the spoiler. That means rear tyre lateral grip is reduced by 8% or more without the spoiler. An already skittish rear end during a hard braking manoeuvre has been exacerbated.

If your emergency stop requires you to now steer to avoid a hazard you are clearly not as well placed without a spoiler as you would be with a spoiler. That's without even taking account of any Ackerman angles, yaw effects and tyre slip angles which will have a contributory effect where tyre load is being reduced.

No-one is disputing that a modest acting spoiler is of little value for "maximising corner speed" on public roads. But there are more factors to consider than simply maximising corner speed close to the limit if grip when driving on the public highway.

These figures are repeatable by anyone who wishes to do some basic internet searching and working out the maths. I'm open to scrutinisation on that.

Ramp up the speed a little bit more to 90mph and the weight transfer results are even more dramatic and are exacerbated even more by that little bit extra aero action.

Increase the CofG height in the equations and the results diverge even more.

I just wished you had all trusted what I was trying to say without having to justify the concepts and physical properties that i mentioned before that most people don't even consider.

There are other effects such as spoiler drag that will reduce stopping distance and more. But I can't be bothered to do the calculations today.

Cheerz

Mark H
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Old 12-03-2017, 14:22   #244
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Originally Posted by ejabrod View Post
As stated, the car is indeed a fully standard GT-A which, again, was quite obvious from my profile.

So, no, my point is not moot, but this is typical of this forum.
It is moot, the GTA is too slow to need downforce
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Old 12-03-2017, 14:45   #245
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In my two previous stints on here, I paid for 2 and 3 years of membership fees. Maybe, just maybe I had a different username each time -- Just sayin'
What has that got to do with now? That's like saying I used to be a member of the AA, and now that I've broken down, can I have assistance. The AA would say, yes, join up and we'll help you!

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Originally Posted by ejabrod View Post
As stated, the car is indeed a fully standard GT-A which, again, was quite obvious from my profile.

So, no, my point is not moot, but this is typical of this forum.
You keep criticising this forum and it's paying members, so why are you on here asking questions?

Last edited by Clivew; 12-03-2017 at 14:51..
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Old 12-03-2017, 16:08   #246
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I smell the stench of a troll.
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Old 12-03-2017, 19:28   #247
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What has that got to do with now?
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Originally Posted by Clivew View Post
And let's also ask the OP, what has he contributed to the MLR? Nothing financially, as he isn't a member

So, as normal, it's take, take, take, then to top it off, bite the hand that feeds you.
As you asked what have I contributed to the MLR - 5 years of subscriptions is what I contributed to the MLR financially.

If the paying members feel so strongly about this why not make the forum a subscription only forum? probably because the members wouldn't be able to make disparaging remarks like that above.

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You keep criticising this forum and it's paying members, so why are you on here asking questions?
I'm not critising. I have accepted the various answers presented by various members. I expressed appreciation to both yourself and Rampant for your input, however the tone of disdain towards me for asking the question is actually quite sad.

The question was asked and was scoffed at by people as well as personal attacks due to my consideration of removing the rear spoiler.

IMO many of the members on here are zealots when it comes to discussions about evo's and this has been shown on a regular basis in many different threads.

On the subject of the GT-A and it not being a 'real' evo - the same argument erupts every now and then about the 260. Derogatory remarks about GT-A's not being fast or real evo's is quite disgusting as the GT-A is the only way that some people can experience evo's due to various reasons but that is just an insight to the mentality of some of the members on here.

In response to the 'troll' comments - yes, the post last night and subsequent posts were indeed intended as troll comments in response the the utter obnoxiousness of some of the members.
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Old 12-03-2017, 21:13   #248
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In my two previous stints on here, I paid for 2 and 3 years of membership fees. Maybe, just maybe I had a different username each time -- Just sayin'
Say no more.
Ban the man not the profile I say.
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Old 12-03-2017, 21:52   #249
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Originally Posted by lawsy View Post
It is moot, the GTA is too slow to need downforce
But least its a silverish one

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Originally Posted by macrosszero View Post
I smell the stench of a troll.
Methinks it was the curry you had last night

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Originally Posted by EVO VI View Post
Say no more.
Ban the man not the profile I say.
Ah , but what if "he" is female
Thank fl˙ck i dont drink these days
Many of the supposed ****s on here are actually really good chaps ...and the reverse scenario holds water too .....strange innit
Better go and fit that spare spoiler blade i didnt carbon wrap
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Old 12-03-2017, 22:06   #250
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Originally Posted by ejabrod View Post
As you asked what have I contributed to the MLR - 5 years of subscriptions is what I contributed to the MLR financially.
I was a member, and contributed financially to the AA for 15 years, but when I ring up for help now, they tell me, no thanks, unless I join again.

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Originally Posted by ejabrod View Post
If the paying members feel so strongly about this why not make the forum a subscription only forum? probably because the members wouldn't be able to make disparaging remarks like that above.
The forum isn't run by members, it's run by Darin Frow.

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I'm not critising
You're not criticising?;

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Originally Posted by ejabrod View Post
the tone of disdain towards me for asking the question is actually quite sad.
Quote:
Originally Posted by ejabrod View Post
The question was asked and was scoffed at by people as well as personal attacks due to my consideration of removing the rear spoiler.
Quote:
Originally Posted by ejabrod View Post
IMO many of the members on here are zealots when it comes to discussions about evo's and this has been shown on a regular basis in many different threads.
Quote:
Originally Posted by ejabrod View Post
Derogatory remarks about GT-A's not being fast or real evo's is quite disgusting that is just an insight to the mentality of some of the members on here.
Really?

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Originally Posted by ejabrod View Post
In response to the 'troll' comments - yes, the post last night and subsequent posts were indeed intended as troll comments in response the the utter obnoxiousness of some of the members.
So, you again criticise others for their disparaging comments, then post this;

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Originally Posted by ejabrod View Post
So take all your egos, dick and self righteousness stick them where the sun don't shine and try to become a better person than you already are.
Rather hypocritical don't you think?

Last edited by Clivew; 12-03-2017 at 22:12..
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Old 14-03-2017, 10:15   #251
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<<<stunned silence>>>


*picks up the mic*


All gone a bit quiet in here... So does anyone have any feedback or acknowledgement on the weight transfer issue I described above?

There are a few more things I can elaborate on if anyone is interested. I'd like to assume that this thread wasn't a wind-up from the start, and that actual science and figures would be of useful interest...

Yours Aye

Mark H
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Old 14-03-2017, 13:48   #252
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For me, what you have written here, and previously wrote, is spot on Mark. As we discussed previously, the centre of pressure is the important factor here, for stability and safety.

No one is going to gain anything from the marginal increase in max possible cornering speeds unless you are competing against the clock, and anyone who is using that as an arguement, is either trolling, or very naive.

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Old 14-03-2017, 17:27   #253
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Quote:
Originally Posted by Clivew View Post
For me, what you have written here, and previously wrote, is spot on Mark. As we discussed previously, the centre of pressure is the important factor here, for stability and safety.

No one is going to gain anything from the marginal increase in max possible cornering speeds unless you are competing against the clock, and anyone who is using that as an arguement, is either trolling, or very naive.
Thanks Clive.

I was wondering whether I'd get any response or acknowledgement at all. I didn't know whether to expect at least one of the following:

1. An acknowledgment that maybe I had some valuable material to offer after all;
2. A negative come-back based on semantics; or,
3. Keep silent and hope no-one notices.


Anyway, those Dynamic Weight transfer (static) equilibrium equations are really key to the discussion. I tried to be conservative with the weight transfer result because the height of the CofG was an educated estimate.


Another key impact is the fact that with around 9% more weight acting on the rear axle in the case of a WING compared to having no WING in situ, in a straight line, this gains another 9% of rear axle braking force across the rear axle for the same brake pedal pressure.

Effects?:

If we assume that the front brake is "tuned" to lock up first, (Understeer front brake-lock is almost always more desirable to a design engineer than rear brake-lock turn-oversteer where the back tyres lose traction going from static coefficient of friction to dynamic coefficient of friction and the rear axle tries to spin around to overtake the front axle)
... This means that primarily the overall *maximum* braking force achievable without locking any wheels is increased initially by around (9% of the rear brake force) available compared to having no WING attached, before the front wheels lock up. (Not an overall gain of 9% of the total braking force, mind, I don't want to over-state the effect, just 9% of the rear brake force, which is already smaller than the front brake force by a good margin, but still a useful gain.) (Understand also that the extra of 9% of rear is only available at the beginning of the deceleration from 80mph. As the speed decays, so does the aerodynamic lever, and the percentage advantage decreases quickly with speed. This WING advantage doesn't "drop to zero" at a slower speed - the wing still cancels any lift plus a bit more at all speeds. But at 40mph during the deceleration, for instance, the added benefit of braking is 2% of rear brake force.) This summation/integration, because it changes with speed, is very complex to model and difficult to calculate with pen/paper/excel. Having said that my initial number came in at around 3 metres. So a 3 metre reduction in stopping distance could be the beneficial impact to having a WING during an emergency stop. Almost a car's length, given all other factors remain constant.

Additionally, although the extra drag that a rear WING and wing support struts create is an unwanted consequence, when you consider a braking maneouvre, the impact of the WING is to shorten the stopping distance not only by adding extra rear braking (or extra rear lateral control by adding lateral grip during braking), it also contributes through aerodynamic braking. The wing blade itself contributes nearly no drag at all. The WING coefficient of drag is around one half to one third of the WING coefficient of lift. The frontal area is approximately one tenth of the plan area of the WING. The WING induced drag is therefore only around one twentieth to one thirtieth of the downforce being produced. Agruably negligible. However, the drag of the WING support struts is quite large, particularly the "interference" drag where the supports join the boot and the form drag from the trailing edge of the bottom of the supports is a net drag contribution.

I couldn't find the actual Cd for ANY of the Evo cars on any online resource or from Mitsubishi documentation. However, an educated estimate would be in the region of 0.34 Cd for an Evo VII. (Equivalent to similar Imprezza generation with similar form and aero.) For a spoiler-less car this should see a reduction to the Cd of, conservatively, at least 0.1 to 0.33 or maybe slightly less. Again, the modelling for that Cd reduction in the case of braking from 80mph is a bit to labour intensive for my spare time, so if you would indulge me and accept that the Cd from a WINGed Evo contributes to another net reduction to stopping distance. In the realms of the small, but useful. Added onto the gain from braking considered above... Well, it is a personal call as to whether you would remove the WING given this knowledge, but my advice would be to leave it alone.


Another important aspect on "handling" when considering a hard braking maneouvre is the effect the WING, and the WING support struts in particular, add to the yaw stability of the car. The struts are at the very back of the car, as far from an already <forward> CofG as it can be, meaning that the lever arm of sideways stability is maximised over a WING-less Evo. The WING has the impact of resisting any yaw motion that can develop during hard braking whether that be from a small steering wheel input or from a car that already has a small amount of tyre slip angle due to cross-wind. Added to the increased lateral grip available from the tyres in a dynamic weight transfer situation, this is another incremental benefit. True that you could leave the struts on and remove the WING section and still retain this benefit. Or at least most of the benefit, because by removing the WING blade reduces the effect of the struts by themselves...

If you read this far, well done for staying with it and congratulations for your better than average attention span in the face of a long wall of text.

Finally, the aerodynamic appendage that is fitted to the rear of Evos IV to X can be called either a spoiler or a WING. No-one really cares if you use these terms inter-changeably. Even Mitsubishi do that in their Technical Papers. However, if one were to make a definitive distinction between the 2, then the Evo has a WING, rather than a spoiler.

First of all, the cross section is an aerofoil section. The top surface is almost flat. The leading edge is round. The bottom surface is curved with greatest curvature towards the front. The greatest depth between upper and lower surfaces can be found at aroun one-quarter of the distance from the leading edge to the trailing. The lower surface curvature reduces markedly aft of the quarter distance (to control the adverse pressure gradient and prevent separation occuring). And the trailing edge terminates at as well a defined sharp edge as is possible with production materials and methods. The downforce is being produced *mainly* by the lower surface.

A spoiler, on the other hand, would produce downforce by brute force methods of disturbing the air by an upper surface. Spoilers produce an order of magnitude more drag for a unit amount of downforce. A normal Porsche 911 has an active "spoiler". No-one cares if you call it a wing, though. Or a spoiler. They are interchangeable after all.

Except when you make a distinction, and that distinction isn't the correct one.

Yours Aye

Mark H
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