Presented by Nine Lives Racing
sleepyhead the buffalo
sleepyhead the buffalo Mod Squad
9/11/20 6:19 a.m.

so, there's been some discussion of miata aerodynamics... where to place holes, and vents and stuff.

Scott Robertson has gone 'fully wooly'... and tufted some parts of his car...

 

NOT A TA
NOT A TA SuperDork
9/11/20 10:08 a.m.

The testing shown leads to questions. Did he begin the driving testing with the long yarn strands already hanging out of the louvers or were they tucked inside prior to the road testing? When cutting the fenders and inner fenders was the hole in the inner fender sealed to the vents in the outer fender or was the open gap left as shown in the video allowing air from the upper part of the inner fender to mingle with the air behind the outer fender? How much is drag increased (or not) by having the louver extending out from the fender as opposed to being flush?

apexanimal
apexanimal New Reader
9/19/20 8:21 a.m.
NOT A TA said:

The testing shown leads to questions. Did he begin the driving testing with the long yarn strands already hanging out of the louvers or were they tucked inside prior to the road testing? When cutting the fenders and inner fenders was the hole in the inner fender sealed to the vents in the outer fender or was the open gap left as shown in the video allowing air from the upper part of the inner fender to mingle with the air behind the outer fender? How much is drag increased (or not) by having the louver extending out from the fender as opposed to being flush?

i'll take this one...

the green louvers, which were inside the fenders and hood vents, were inside when we began...

i haven't had inner fenders in well over a year...

"How much is drag increased (or not) by having the louver extending out from the fender as opposed to being flush?" - that's not a question i can answer... i would guess, very minimal, but SleepyHead or the guys at Professional Awesome would be able to answer that better.

sleepyhead the buffalo
sleepyhead the buffalo Mod Squad
9/19/20 12:29 p.m.
apexanimal said:
NOT A TA said:

 How much is drag increased (or not) by having the louver extending out from the fender as opposed to being flush?

"How much is drag increased (or not) by having the louver extending out from the fender as opposed to being flush?" - that's not a question i can answer... i would guess, very minimal, but SleepyHead or the guys at Professional Awesome would be able to answer that better.

I did some digging in Hoerner: Fluid Dynamic Drag... and found an answer.  It's not quite as simple as "this or that"... there's a tradeoff between deltaCd and deltaCp (i.e. you have to factor drag increase and how strong a pressure you need to force at the exit) to make in choosing your exit geometry.  Also, GLTC requires that you not be able to see the wheel when looking down over a fender vent.

I'm going to work on making a drawing of different exits to show the data from Hoerner, and work around upload a picture of the Hoerner diagrams.

Our Preferred Partners
qiJ7ouWr9K2UCFeY5ctETIqEtrCB9kuE9QuknoR1RxOaU0dNCpAm8CdAZHIY3MfW