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Old Yesterday, 15:07   #151
KNOXVILLE
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Originally Posted by Evosick View Post
The E7-9 boot lid is wider than the E4-6 boot but had no centre support like the E6 does.
More quality postings, and to say you own one...
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Old Yesterday, 15:48   #152
Rampant
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Originally Posted by Evosick View Post
OK well done ..you won your so called Challenge

Are we happy
Happy? Not particularly.

Instead of getting defensive, how about we have a grown up discussion from which you could actually learn something. Which was my only reason for "waffling on". Personally, I'm not interested in "winning". I'm much more interested in passing on knowledge and this is why I find my instructing job so rewarding.

If you'd like to learn something, let's have a serious discussion.

Your call.

Regards

Mark H
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Old Yesterday, 15:57   #153
Rampant
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Originally Posted by Ben_r1 View Post
This don't happen to carbon unless your applying considerable force on it:
Above around 130 mph the IX spoiler blade starts to twist really badly. (IX blade is hollow carbon.) I was a bit concerned about mine doing a 30-130 a few years ago watching it in the rear view mirror distorting in the airflow at 150+mph. At that speed it twists leading edge downwards. The extra aerodynamic drag being generated must be huge.

I've asked a couple of carbon places whether they could manufacture a centre support. To no avail. Although I'm not sure whether the spoiler is supposed to twist like that to increase stability? (That would be called Aero-elastic tailoring if it was a genuine design intent.)

Cheerz

Mark H
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Je cherche l'orgasme d'auto
J'ai trouve l'orgasme d'auto
C'est une evo IX bleu par le Rountree

***Go soothingly on the grease mud, as there lurks the skid demon***
//// Do as you OUGHT, not as you WANT ////
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Old Yesterday, 16:26   #154
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Originally Posted by Rampant View Post
Above around 130 mph the IX spoiler blade starts to twist really badly. (IX blade is hollow carbon.) I was a bit concerned about mine doing a 30-130 a few years ago watching it in the rear view mirror distorting in the airflow at 150+mph. At that speed it twists leading edge downwards. The extra aerodynamic drag being generated must be huge.

Mark H
Interesting comment Mark

When I bought my IX (June 05) Ralliart had a stick on "Gurney" for the rear blade - circa 20mm high with a 3mm radius to the top edge

They also supplied a circa 30mm rubber extension, downwards, for the front splitter
Would these items have minimised your issues at 30-130?

Would vortex generators be the next subject on the curriculum

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Old Yesterday, 19:20   #155
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Quote:
Originally Posted by grants View Post
Interesting comment Mark

When I bought my IX (June 05) Ralliart had a stick on "Gurney" for the rear blade - circa 20mm high with a 3mm radius to the top edge

They also supplied a circa 30mm rubber extension, downwards, for the front splitter
Would these items have minimised your issues at 30-130?

Would vortex generators be the next subject on the curriculum

The rear spoiler gurney wouldn't stop the blade twisting because that is a function of the aerofoil section of the blade itself.

The blade has a cross section that is identical to an aircraft wing cross section, except obviously it is upside-down in order to create downwards "lift".

The centre of pressure of the spoiler is closer yo the front of the blade than the rear: around 1/4 of the distance from the leading edge to the trailing edge. If you imagine putting a large weight on a point half way from left to right and around 1/4 distance from the leading edge - this is the equivalent of the forces that the blade experiences moving quickly through the air.

Since the downwards load is much closer to the leading edge than the trailing edge it will tend to twist the leading edge downwards.

There is then a second order effect - the twist increases the aerodynamic angle of incidence or angle of attack of the blade and it produces even more downforce - which adds a bit more twist force.

Adding a gurney flap (a well designed one) only serves to increase the downforce created by serving two purposes. First the angle of attack between the leading edge and the trailing edge is naturally increased, increasing downforce produced. Second is that the wing-gurney combination has a more pronounced aerodynamic curve, which also increases downforce. The drawback of a gurney is that they are inefficient. They contribute a lot of drag as well as the downforce they create. The same downforce could be created by a more efficient smooth aerofoil section. But rallying is often limited to homologation and a more efficient aerofoil spoiler would probably have a negative effect on the overall balance of a road car over a larger range of speeds...

Another phenomenon I've always wondered about with the hollow blade on the IX is whether aerodynamic forces change the cross section of the blade. They can be squeezed in your fingers and flex quite easily.

The topic of vortex generators has been discussed on here before. Suffice to say that vortex generators create drag. But when placed intelligently they can reduce drag created by structures in their wake. Mitsubishi were clever. By adding a drag generator, they reduced the overall drag coefficient of the Evo VIII by 0.08Cd (figure from memmory, so could be inaccurate.)

Regards

Mark H
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Je cherche l'orgasme d'auto
J'ai trouve l'orgasme d'auto
C'est une evo IX bleu par le Rountree

***Go soothingly on the grease mud, as there lurks the skid demon***
//// Do as you OUGHT, not as you WANT ////
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