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 Post subject: interesting aero
PostPosted: February 18, 2018, 12:30 pm 
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This turned up while smurfing for 7 pictures:

http://www.racedandrallied.com/performa ... ally-built

The builder added a number of aero tweaks that mostly seem intended to reduce cockpit turbulence. The windshield sits back close to the seat, the sides of the frame are high, and there's a horizontal deflector at the top of the side. There's a boxlike deflector behind the front wheel, and one just ahead of the A-arms, tied into the winglets.

I also note the windshield has a bit more rake than normal, and it's formed from two round tubing hoops instead of the usual C channel. I expected to see triangular Lexan windows there, but it looks like he didn't bother. It looks like the windshield is held in a 360 degree hoop with mounting legs. I can't see a good reason for that, unless the windshield is removable for track events. The back of the cowl seems to be pulled into a more or less rectangular shape, which let him use a straight bottom on the glass.

Thread with Locost CFD streamlines: https://www.locostusa.com/forums/viewto ... 23&t=13379


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 Post subject: Re: interesting aero
PostPosted: February 19, 2018, 1:29 am 
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It does kill some of the 'traditional' looks, but seems like it should be functional. If nothing else, they're definitely interesting solutions. I kind of like it.

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 Post subject: Re: interesting aero
PostPosted: February 19, 2018, 8:14 am 
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Should be functional if the intent is to reduce the max top speed!
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 Post subject: Re: interesting aero
PostPosted: February 19, 2018, 12:56 pm 
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It's hard to guess at the builders intent, but the nearly flat pieces on the cockpit sides would make nice arm rests if they were padded. Also,they could be to prevent heat radiating up from the exhaust system, or to deflect stones away from the driver. I'm sure there are other possibilities too.

On an intuitive level, the only thing that looks like it would cause real trouble are those vertical pieces from the winglets. I'm seeing nothing but turbulence, hence drag, from those. You've got to test this stuff to know, however. Obviously, I could be wrong.

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Damn! That front slip angle is way too large and the Ackerman is just a muddle.

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 Post subject: Re: interesting aero
PostPosted: February 19, 2018, 2:01 pm 
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It looks like part of what's going on is he is trying to vent the engine compartment and make his radiator and cooling more efficient. it's putting low pressure areas where there are side opening form the engine compartment....

It looks like he lives in a warm/desert area.

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 Post subject: Re: interesting aero
PostPosted: February 19, 2018, 2:21 pm 
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davew wrote:
Should be functional if the intent is to reduce the max top speed!
I wouldn't be too sure about that.

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 Post subject: Re: interesting aero
PostPosted: February 19, 2018, 3:26 pm 
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[quote="TRX"]This turned up while smurfing for 7 pictures:

http://www.racedandrallied.com/performa ... ally-built

An attractive rig. Some of the work I don't fully understand, like the front winglets. It looks that the aluminum "elbow guards" (my words) are designed to protect the driver from gravel stones and other debris thrown by the front wheels. The deflectors behind the wheels? I assume that the idea is to improve air flow on each sides of the vehicle. I guess many people would think all this was a good idea. I am not sure that (if I build a third seven) I will do any of that. On the issue of better protection for the driver and passenger for instance I would consider clam shell fenders or even better fabricate my own fixed front fender system that would take into consideration all the issues that this builder was attempting to address. I am thinking of fuller bodied sevens à la Donkervoort.


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 Post subject: Re: interesting aero
PostPosted: February 20, 2018, 3:12 pm 
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Wossname's CFD plot of 7 airflow around the cockpit shows some of the streamlines curling up and over the sides of the cockpit. The "armrests" (not a bad idea...) would move the air stream a bit further away from the driver's head.

Likewise, the box structures behind the wheels look like they're intended to deflect air away from the sides.

The winglets and vertical pieces at the nose do look more like cooling aids, though.


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 Post subject: Re: interesting aero
PostPosted: February 20, 2018, 3:44 pm 
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Also note the grill screen on the scuttle in front of the windshield. Possible air inlet (engine intake?) that takes advantage of the higher pressure in front of the windshield.

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 Post subject: Re: interesting aero
PostPosted: February 20, 2018, 4:03 pm 
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seattletom wrote:
Also note the grill screen on the scuttle in front of the windshield. Possible air inlet (engine intake?) that takes advantage of the higher pressure in front of the windshield.
Good eye.

Image

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 Post subject: Re: interesting aero
PostPosted: February 21, 2018, 9:25 am 
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"Wossname's CFD plot of 7 airflow around the cockpit shows some of the streamlines curling up and over the sides of the cockpit. The "armrests" (not a bad idea...) would move the air stream a bit further away from the driver's head."
The trouble is that the arm rest would increase the air flow outboard around the rear fender, making the outboard fender appear wider to the air stream which would add to the drag vs over and inboard flow. Also there is a substantial net affect of increasing frontal area around the fender including the other additional structures.
It there is an over heating issue a small vertical lip in front of the side panel opening, would cause a low pressure area behind opening, Vs all the induce drag of the pod added to the sides of the vehicle.
None of these changes are simple form radius or bevel changes. when you start hanging stuff out in the air stream, it is going to increase the drag.
Dave W


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 Post subject: Re: interesting aero
PostPosted: February 21, 2018, 12:40 pm 
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davew wrote:
when you start hanging stuff out in the air stream, it is going to increase the drag.
Often, but not always.

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 Post subject: Re: interesting aero
PostPosted: February 21, 2018, 2:16 pm 
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It shouldn't be too hard to mock up those arm rests in cardboard and duct tape. Then go for a ride to see if there is any benefit. My gut feel is, maybe as much as a 50% reduction in dis-comfort level. Not gone, but an improvement.

That might be why half-doors are such a thing in the UK.

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 Post subject: Re: interesting aero
PostPosted: February 22, 2018, 8:06 am 
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Chuck
You are right about the half doors. It is surprising how much air is re-directed rearward over the fender, Vs into the cockpit area. My half doors are on 90% of the time. Only when it is extremely hot do they get removed. The nice part about half doors, is if you leave early in the morning and later it gets hot out on the road, you can remove them, because the half door will actually fit in the trunk area.
Dave W


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 Post subject: Re: interesting aero
PostPosted: February 22, 2018, 9:50 am 
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Dave, you guys with trunks make me laugh :lol:

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