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Rennlist Hoonigan which cost no drachmas Lifetime Rennlist Member
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Joined: Dec 2001
Posts: 13,007
Likes: 1,196
From: Manchester, NH
Driving in the Draft
I thought people would find this interesting. I made up an airspeed sensor for my 914 - a pitot tube - and mounted it near the cowl. You can see it center out the windshield.
It's been really interesting to see how the airflow changes when you are behind people. You can see the airspeed change - being in the draft. The first photo shows being behind 3 cars down the back straight at Watkins Glen. You can see it shows an airspeed about 7 mph slower than the GPS speed.
The other shots are the start of picking up a draft and when you lose it coming out from behind a car. Sometimes it's surprising how clean or dirty the air is behind some cars. I can look up some data from behind an old racing truck and it creates a giant hole in the air! I guess I should get my son (10 years old) working on the aerodynamics degree he wants....
The draft behind 3 cars at Watkins Glen. The start of the draft behind the Miata. When you are out of it. The start of the draft behind a 911. Moved out of the draft.
We are all so happy you have way too much time on your hands!! lol. (and you know I'm only kidding...I know you're wide open all the time).
Very cool and useful stuff you've come up with lately.
I hope my question is not a thread drift. When bump drafting on rovals like autoclub speedway sometimes the hit from the rear is unintentionally hard. I know we are steering straight but there is sort of a down to the left bias from the banking. Why doesn't this hit from the rear destabilize the lead car more or cause crashes? Did we not hit hard enough or is there something about the aerodynamics that sort of suck everyone into a nice line?
It's the top of the hood right in front of the cowl.
This is very cool! It looks big enough, and your data looks good, but I'd be worried about siting it in that area near the bottom of the windscreen. I'm no aero guy but I believe their is a stall in that transition area. As say looks like the tube is above that area.
So I guess the question is now what will you do with it? You could work out your cars drag which would be an interesting challenge. Let us know
Rennlist Hoonigan which cost no drachmas Lifetime Rennlist Member
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Joined: Dec 2001
Posts: 13,007
Likes: 1,196
From: Manchester, NH
Originally Posted by NaroEscape
We are all so happy you have way too much time on your hands!! lol. (and you know I'm only kidding...I know you're wide open all the time).
Very cool and useful stuff you've come up with lately.
Serious. Someday when I'm retired, I will be so busy! I have about a million projects, ideas, and things I want to try out. I've always wanted a pitot tube on a 914 (can you say only one in the world!) and figured it was a cool exercise. Now I just have to figure out the question I answered!
Rennlist Hoonigan which cost no drachmas Lifetime Rennlist Member
Rennlist Site Sponsor
Joined: Dec 2001
Posts: 13,007
Likes: 1,196
From: Manchester, NH
Originally Posted by 924RACR
Now you need to tie that to a dash message that comes up when the delta is high enough: "Slingshot Engaged - Puttin' the hammer down!!!"
This would probably be pretty easy. It would basically be slip percentage based on air speed and GPS speed. The only thing you would not know is if it's a tailwind or draft. Though the better answer is "always hammer down."
Serious. Someday when I'm retired, I will be so busy! I have about a million projects, ideas, and things I want to try out. I've always wanted a pitot tube on a 914 (can you say only one in the world!) and figured it was a cool exercise. Now I just have to figure out the question I answered!
Now that I have this, adding a lidar system......
No half measures: go for a full acoustic Doppler set-up...
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Driving in the Draft
