Measuring aerodynamic lift and downforce through trailing vortex rotation

If you have a fastback or modern-shaped sedan, you can see whether the car is developing lift or downforce by looking at the rotation of trailing vortices. Sounds complex? It isn't! Buy my book at www.amazon.com/dp/B0C87VYVL8 or Amazon in your country.

[@marlinmack2570]

The legend is back! glad to see you're back making videos

[@shlomilevi1457]

Would have loved to see the actual test video as well 😊

[@indopleaser]

So cool your back on the Aerodynamic KZbin. Came up in my suggestions

[@O-cDxA]

Welcome back !

[@stuartstevens472]

Thank you Julian , this great practical stuff to show the results and adjust what im visualizing to do to my hardtop v8 mg for road and track days. Will have to buy your book.

[@TheObserver567]

I wished you had footage of the system in action when the wing was deployed.

[@stigastondogg730]

Another timely video. Had noticed the pattern on the rear window of my falcon sedan during rain - showed clearly air was flowing up from doors / quarter panels onto the glass and boot lid. Now I know why!

[@jasonrivers7518]

I know why you didn't use a Chrysler Crossfire, mate. Good job, great video. ❤

[@alastairchestnutt6416]

Great presentation thanks

[@JulianEdgar]

Glad you liked it!

[@stickman-1]

I experienced this by using 6' long tuffs on the rear window. They kept "tangling" and at the time I did not understand why. Now I know. Thank you. I'll see if I can find the videos I shot and put them up if I can.

[@JulianEdgar]

I'd be interested to see the video.

[@MrDahl-kj5qm]

on your measuring device the twist on the metal lengths will have an effect on the rotation of each arm. I would suggest using aluminum tubes to negate any unwanted outside aerodynamic affects to your measuring device.

[@JulianEdgar]

It's an interesting point but the twist in the arms is inconsequentially small compared with the area of the flat plates.

[@beyondpistache8413]

Hi, just finished your book, fascinating and well put together piece of litterature. Please could you go into more details about how to create a surface pressure measurement patch

[@JulianEdgar]

First, if you enjoyed the book, please leave a review on Amazon. Second, I suggest you buy the Scanivalve pressure measuring patch - you'll not be able to make one as good at home and so it's well worth the cost. The pic on Page 77 shows a home-built one - basically just a piece of alloy bar cut off with two holes drilled in it at right angles, meeting in the middle.

[@robertoriveros3053]

i own a Citroen C4 Vts coupe...i always wonder how airflow works behind it and if rear wing works properly. (i think it works but theres no info about it)

[@temporalmadness3756]

Pardon my ingenuity but, wouldn't a long string with a ping pong ball or similar attached to its end, be sufficient to detect the airflow rotation and calculate its rotation speed?

[@JulianEdgar]

In my book I also use a ribbon. The vortex flow isn't a regular, nice-looking flow pattern, so the ribbon (or ping pong ball) doesn't give you a lot of measurable behaviour.

[@MrFturner]

I was just wondering if you could explain what happens if you take a modern mid-size SUV (jeep grand cherokee in this case) and attach a camper to it. The camper's forward face is slanted back from approximately 1/3 up to the top at around an angle of 20 degree's from the vertical. The lower 1/3 is slanted back approximately 20. The camper is is wider than the jeep quite significantly... probably around 10" either side. I know the camper is totally destroying the aerodynamics of the jeep as I believe the Jeep on its own is trying to bring the air flow back together behind it, and that is slamming into the camper. I have been thinking of ways to deflect the air flow out wards from the back of the jeep and adding something on the front of the camper to bring the air flow back in, maybe vortex generators at the front instead of the back. Just curious what ideas you would have in this case.

[@JulianEdgar]

Caravan / camper / trailer design and testing is covered in my new book. No point in my trying to summarise thousands of words and dozens of pics in a post here!

[@j7...]

Is your book available in German language? Would like it as a present for my dad, but although he can understand and speak some English he is not profitient enough to read a book. Thanks

[@JulianEdgar]

The book is not available in the German language. However, it does have a lot of pictures (over 800) and many of those are self explanatory - eg tuft testing, pressure testing, aerodynamic features. Using Google translate on the captions and looking at the pics would convey most of the ideas in the book.

[@j7...]

@@JulianEdgar thank you for the insight. Sounds great!

[@matteoricci9129]

Could it be possible to create aerodynamic features with an air compressor? If I put a reservoir in the car and blow out in the wake of the car in a sort of curtain? And stop this happening?

[@JulianEdgar]

Yes, blown wakes have been tried in the past. The issue is the energy required to provide the compressed air is greater than the energy saved by lower drag. In terms of lift / downforce, active blown aero has always been good - but banned in racing.

[@arrindaley3714]

Could the Cayman's rear wing or any other also be moving the location of the rear vortices and therefore effect the indicated strength?

[@JulianEdgar]

I don't understand.

[@arrindaley3714]

@@JulianEdgar couldn't aero elements like that on the Cayman effect where the vortices are located as well as thier strength and direction? F1 I think direct thier vortices to create different effects so it seems feasible. If so then if you site the paddles at the centre of the vortices (presumably by experimenting) to get the best indication of thier strength you may no longer be sited at the centre of the vortices after an aero change, even if it is an active aero element. For example I find the vortices and get 100rpm, I trial a lip and the rpm drops to 70rpm but I might have only moved the vortices upwards and the paddles are no longer at the centre and not as effected by the vortices, I've not effected lift as much as I think. In your Cayman example I don't think it could've moved enough to change the direction but rpm / strength is certainly a possibility? It may be spinning faster than thought in the opposite direction. Obviously your not readjusting the paddles whilst driving at 110km on the freeway, although your back to back or more formal testing might.

[@JulianEdgar]

A formula car and a fastback road car body develop vortices in completely different ways. When up, the wing of the Cayman (really, a spoiler) increases pressures on the top of the spoiler. Refer to Pages 240-243 of my book.

[@beyondpistache8413]

This is really interesting and should be looked at, maybe trying different position of the measuring tool

[@jidofole]

So?

[@JulianEdgar]

Relevant if you want to reduce lift or drag on a fastback shaped car.