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Old 05-29-2020, 10:17 AM   #31 (permalink)
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reference

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Originally Posted by JulianEdgar View Post
Happy to quote my references. What are yours?

But honestly, to believe that the McLaren F1 had 'intentional lift designed into it' is absolutely absurd. As soon as I saw that had been said, I knew it was wrong - and it took less than 5 minutes in my library to prove it.
My aero library is about 60- linear feet, so it may take awhile. I distinctly recall that the F-1 porpoised, and was a hand full to drive. It was reported that only the 'long-tail' had any significant downforce, which would be handy on the Mulsanne Straight at Le Mans, especially in a rain event.

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Old 08-14-2020, 09:06 PM   #32 (permalink)
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UPDATE

As of July 2020, the underbelly of the car had been modded as such:

1. Plastic undertray from front bumper lip to just after front axle subframe, at the front end of the catalytic converter. It can't be flat, due to engine oil sump and gearbox, what matters is that it's quite smooth, no bits and bobs dangling in the airflow;

2. Aluminum sheet rear edge on the undertray, where it approaches the hot exhaust and catalytic converter;

3. Full undertray from rear bumper forwards to the well of the rear axle;

4. Flat plating as tightly as possible around axle well, leaving the exact space for the axle to move up and down;

5. Aerodynamic exhaust muffler (part of the Milltek exhaust. Milltek muffler is oval in section and with a smooth surface, unlike suitcase-like and ribbed factory muffler);

6. Aluminum sheet flat plates around the exhaust bend, below rear seat. Around the pipe, not over it. Exhaust needs to radiate heat away. There is half-inch of free play between plates and the pipe;

7. Aero (boat prow like) deflectors before front wheels, as the above said SLR McLaren "boat prows";

8. Boat tails behind rear wheels;

9. Front control arms plated over, to achieve smoother lower surface. Golf Mk4 / Leon Mk 1 sheet steel control arms are pretty good for this, since they are smooth from factory. Audi TT Mk1 / Golf R32 cast steel control arms are not smooth, and they are also heavier, with bigger and softer bushings, and they shouldn't be used;

10. Factory flat plates over rear control arms have to be left in place. They are officially called "stone guards", but they are too flexible to claim to protect anything from stones. They had been designed to flatten the surface of the rear axle around the fuel tank and keep the airflow straight.

Materials


All trays have been made from 2mm Coroplast, only the parts near exhaust from 0.8mm aluminum. They were assembled by screws or small bolts wherever possible, glued with strong Mamut Glue where there was no way to screw. Glue hardens itself like RTV silicone, holds even better than small sheetmetal screws and dampens vibration better than silicone. Obviously it has to be used on those parts which are hardly probable to ever be removed for mechanical repairs, throughout the car's life.

Exhaust tunnel has to be left alone. Milltek runs much cooler than factory exhaust, but still it needs air to cool itself. Factory muffler surface may heat itself to 140-145C (284-293F), as measured with a multimeter and a probe. Milltek may be touched unpleasantly by hand after a highway run, may burn hand after city run, but it's nowhere near factory.

Ground effect

Car is pretty low to the ground, minimum ground clearance is in the 80 mm (3.15 inches) range, in front, higher in the rear, with deep side sills. This means, if the highway is very smooth, there is some stability gain once the entire belly had been smoothened as quoted above. Since the highways are often not too smooth, this is not very important.

Cooling

Engine coolant temps in the 85-88C (185-190F) highway in cool weather, 90-93C (194-199F) hot weather, 93-96C (199-205F) city driving, occasional jumps in the ranges where fans go into full speed (over 102C/216F) in stop and go traffic. Intake air temps as read at the manifold 13-15C over atmospheric temps.

Comparisons

As Audi had found out by experiment on an A4, smoothening the underbelly as much as possible may give a delta Cd around 0.024. I've left alone the effect from flat plates front to rear when adding up, on the sides of the exhaust tunnel, since the floor had been already smooth there from factory. Also, their A4 car had already small plates before front wheels. Leon didn't have them from factory, when a Cd of 0.32 had been calculated and published. SAE paper 2004-01-1307 says no deflector before front wheels contributes 13.1% to total car drag, this is why all post-2004 cars have them. Also, there was no quote on how much delta Cd we can gain by closing all useless bumper and body gaps. By useless I mean "which obviously do not feed into various radiators of the car".

This means I might have been lucky enough to achieve a delta Cd of more than 0.025, and therefore cross the barrier of "very aerodynamic cars" set at Cd 0.30.

Road testing


Stability at highway speeds has proven itself pretty good until now. By moving all unnecessary parts rearwards, the front/rear weight ratio has improved by 55kg (121.4lbs), which contributes to superb turning ability, besides suspension and tracking mods.

Milltek exhaust produces less vibration and noise than factory exhaust. Engine airflow measured by mechanical pressure gauge and Torque 7% better than before, which should give a peak hp over 250. Not bad for a factory turbo.

Fuel economy may be in the 24-28 mpg in fast driving, mixed city-highway with moderate traffic, 29-30 mpg in highway driving at constant speed.

(If doing everything possible to hypermile, it may be 36-37 mpg, but this defeats any reason to buy a turbocharged gasoline engine in the first place.)

PS Mr. Julian Edgar gave me the idea to make the aero mods, when I started to test the aerodynamics back in 2011. Nowadays, compared to 2011, I'm 20hp higher, 16lb/ft higher, but also on the second fuel pump, second alternator and third clutch in the car's life

Last edited by Nautilus; 08-14-2020 at 09:32 PM..
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Old 08-15-2020, 04:54 PM   #33 (permalink)
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On topic: how does all those posted above have anything to do with skirts?

Three problems when dealing with skirts:

1. Are they effective at all?
2. How to fit them properly to stay still at 60 mph?
3. How to remove them easily when wheel needs to be changed?

Answers:

1. Yes

2. Use the strength and flexibility of rubber polymer glues.

That is: pick some 2 to 3 mm thick aluminum strips. Bend the strip with pliers into shape. Drill and make a thread into one of the ends of the strip.

Glue the non-drilled end with polymer rubber glue (Mamut from Den Braven, in Continental Europe) to the inner lip of the metal fender. Not into the plastic fender liner. If the wheel well was a clock face, use strips at 12 o'clock, 10, 2, 9 and 3.

Bolt the plastic fender skirt to the drilled end of the strips.

From that point on, a fender skirt has little vibration (polymer rubber glues are about the consistency of tyre rubber when fully cured) and rather good resistance to shock. Which is much better than drilling into the metal fender and/or fit some weird contraptions as struts and springs.
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Old 08-15-2020, 07:36 PM   #34 (permalink)
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Quote:
On topic: how does all those posted above have anything to do with skirts?
Made me look. There was a feud spilling through various threads during 2020-05. The antagonists still post, just not in the same thread.
Quote:
3. How to remove them easily when wheel needs to be changed?
Not familiar with [polymer rubber glue (Mamut from Den Braven, in Continental Europe)]. What I like currently is foaming Gorilla Glue. It's a good gap filler and you can remove it with rubbing alcohol, making it a temporary fastener.
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Old 08-19-2020, 10:44 AM   #35 (permalink)
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effective, stay still, remove

Quote:
Originally Posted by Nautilus View Post
On topic: how does all those posted above have anything to do with skirts?

Three problems when dealing with skirts:

1. Are they effective at all?
2. How to fit them properly to stay still at 60 mph?
3. How to remove them easily when wheel needs to be changed?

Answers:

1. Yes

2. Use the strength and flexibility of rubber polymer glues.

That is: pick some 2 to 3 mm thick aluminum strips. Bend the strip with pliers into shape. Drill and make a thread into one of the ends of the strip.

Glue the non-drilled end with polymer rubber glue (Mamut from Den Braven, in Continental Europe) to the inner lip of the metal fender. Not into the plastic fender liner. If the wheel well was a clock face, use strips at 12 o'clock, 10, 2, 9 and 3.

Bolt the plastic fender skirt to the drilled end of the strips.

From that point on, a fender skirt has little vibration (polymer rubber glues are about the consistency of tyre rubber when fully cured) and rather good resistance to shock. Which is much better than drilling into the metal fender and/or fit some weird contraptions as struts and springs.
I have only one source with a dedicated skirt investigation which dates to 1936. An Adler-Jaray was improved from Cd 0.38, to Cd 0.33 with the addition of skirts on all four wheel openings.
The front skirts were responsible for most of the benefit, 0.04.
Hucho mentioned in the past that, rear skirt performance could be compromised if the flow coming from the front of the car wasn't already cleaned up just as with a diffuser.
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Keep an eye on the skirt panel at speed. Flat stock, used as a reinforcement could deform under aerodynamic forces. Some have bonded carbon-fiber arrow shafts to the inside surface of skirts to mitigate aeroelastic deformation.
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The first-gen Honda Insight uses registration pins to engage slots for the top of their rear skirts, and a type of 1/4-turn Dzus fastener to secure the bottoms against the body. Very easy on and off. If you cant find Dzus fasteners locally, they're available through racing catalogs. I got mine from SUMMIT Racing.
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Old 09-14-2020, 04:14 AM   #36 (permalink)
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Quote:
Originally Posted by freebeard View Post
Not familiar with [polymer rubber glue (Mamut from Den Braven, in Continental Europe)]. What I like currently is foaming Gorilla Glue. It's a good gap filler and you can remove it with rubbing alcohol, making it a temporary fastener.
Mamut High Tack Glue:



Patented by Den Braven, rebranded as Bostik after Bostik took over the original company.

It's not a temporary fastener, after the first 3 hours in summer temps it holds pretty well. Almost fully cured after 1 day. Has the consistency of tyre rubber, does barely flex by hand, unlike RTV silicone. Almost impervious to weather or solvents, it can only be removed by cutting with Stanley knife blade.

Most likely in the US or other continents than Europe there are other glues with similar ability.

The logic of polymer rubber glues: bolt holes should not be drilled at all, if possible, in places where aero plating is done. Underfloor, wheel arches, axle subframes, under the rear well for the spare wheel. Rust which starts there devours the steel in a few months. So we bond ("weld by glue") a frame of drilled aluminum or hard plastic bars and bolt the sheet to them. Sheets of ABS or aluminum are usually of negligible weight, but glues hold as well as 20-22kgs pe square cm (which translates to >300lbs/sq inch), so they wont break and fall, regardless of speed.

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