Aerodynamic vs. vehicle stabilty

[A2WindTunnel]

Hi Dave. Sorry about my disconnect and thanks for introducing yourself. You bring up a good point that I have always found difficult to resolve. You have customers that are paying, not only for your facility, but for your expertise. Before you built A2 you had a lifetime of experience. However, undoubtedly you have gained more knowledge from former customers and their experiments. As a professional you have to protect that intellectual property gleaned from others. However, as a customer I am paying for as much of your grey matter as possible.   I would want all your knowledge focused on my problems at hand. I would think finding the right balance is quite difficult.

Your postings to this forum are always interesting. I respect your protection of customer’s IP. You have done a good job.  Thanks

It’s no problem at all.  At A2, we do try give our customers the best experience possible in the wind tunnel and get them to start thinking about aerodynamics, and the higher the speeds the more important it will become (landspeed racing).  I don’t want someone to walk in and hand me a car to develop nor do I just want to spout off a bunch of speed secrets to them.  I want to step by step get them involved in the process so they can understand what wind tunnel testing is all about and why teams use them so at the end of the day they know what changes worked, didn’t work, (& why) and to know that their car/motorcycle will perform better then the last time they took it out.  Yes, I have seen a lot throughout the years in both our wind tunnels and there is a fine line I walk every test to not give out information another team learned but give each customer the same attention to detail and tip toe around the “grey matter” as you put it.  I’m used to being around the NASCAR crowd (whether anyone likes it or not) and some might give up their first born before they give out any data about their Daytona cars.  That is just how I was raised (to speak) in the wind tunnel business over the years. So, while some of you think it could make life a whole lot easier for me to just openly talk about testing and numbers, I can’t.  I have said this many times and I’m sure this wont be the last, but I am on here to try and help people understand about a process that there is not a lot of information about. And as Salt said, paying customers get the facility, and although I don’t claim to be an expert I am a racer down inside and love to help people go fast. I need everyone to remember that I am NOT getting paid by anyone to post on this form so as “nonpaying” customers you guys are getting more then most.

 

[4-barrel Mike]

Well -- speaking of motorcycles in the wind tunnel -- Dave Salazar and I have decided that we'll put both of the SSS fast bikes in the tunnel sometime soon -- but probably only after the '10 season is done.  By then he'll (hopefully) have all of his instrumentation in place and we'll be riding in glory from all of the records we got this year.

And so, when we do go to the tunnel, I'll see if it's okay to release lots of the data we gather.  That way ALL can see what happens, what gains, what losses, and all of that stuff.  I'll write a full report on it -- and it'll be available for all to read.

Later --
Jon a/k/a SSS

It's a shame that Amo didn't sell the website to a roadster guy! 

Mike

[sabat]

Thanks Jon & Dave, I look forward to the write up. Once I'm out of power and chassis tweaking, a day in the wind tunnel is on my list. -Dean

[Seldom Seen Slim]

Mike, maybe if a roadster guy had started the website way back when. . .

[1212FBGS]

A2
in your pix of the airfoil overlaying the blue car.... if only the trailing air actually did converge down like the airfoil...you should know that it never happens.... see the trailing from your NASCAR CFD pix... that's more realistic.... why is it that aerodynamicist always want to compare ground plane vehicles to airplane crap
Kent

[k.h.]

http://www.kasravi.com/cmu/tec452/Aerodynamics/WindTunnel.htm. . . . with an index covering other issues.  Course syllabus from a Michigan university.  I tagged it a couple of years ago while looking for information on skin friction for nanotech surface coatings.  Good overview.  We hope to use a college's (restricted size) wind tunnel for skin friction tests on small flat planes.  However, a full scale model in the wind tunnel appears to be the best format for evaluating separation comparisons between different membranes vs commercial paints surrounding the streamlined surface of an aero shape.  If the budget allows, full scale shapes in a wind tunnel allows evaluation of reduction in the slowing forces of the surface frictional component.  

A tip of the hat to JackD for steering me toward the Human Powered Vehicle realm for low drag shapes, back before he went into self-imposed exile.  And another tip of it to Blue for reinforcing the importance of a testing factor available in a wind tunnel and not in Computational Fluid Dynamics computer programs.  

And, if La Fortuna allows, 2011 may be when the friction reducing membrane gets tested for corrosion resistance on that practical factor test facility in Utah.  This has been in the shoulda-coulda-wanta category so long, I might have to hang a prop on it.

http://www.kasravi.com/cmu/tec452/Aerodynamics/VehicleAero.htm

[A2WindTunnel]

Kent, as I said in the previous post. DON'T take it that I am calling those shapes air foils. A production car without a rear spoiler (unlike in NASCAR) will produce lift.  Most of it is off the top of the roof because the air is moving faster over those surfaces and creating a low pressure... In a similar way an air foil will do the same.  IF THAT IS "CRAP" then please tell me what other (my racecar is better than your racecar) shape I can easily explain lift to people on the tread? I’m not into airplanes and am not calling anything on here an airplane!! A bluff body object such as a car is NOT an air foil or airplane and I am just using a simple illustration to show that. Please don’t take so literal. There is only so much I can find on the internet as far as pictures go and I am also trying to run a wind tunnel and only get a minute or two to pop on.  I agree that I could go into more detail or even publish a CFD drawing of exactly what I am talking about, but I simply do not have the time.
 
PS: there are some cars that dont make a big wake.



video of same car you can see on youtube:
http://www.youtube.com/watch?v=2CYUuBiW_lY
.

 

[Cajun Kid]

A2/ Dave,

I for one certainly appreciate your posts and help on these forums.  I know you do so freely and with a passion for informing all of us.  If a few hardcore know it all types get a but sassy to you on here please do not take it personally... the majority of us understand and appreciate your time and information.

Jon/SSS.... I live less than 2 hours from the A2 Tunnel,,, when you set the date please let me know,,, I will be there with bells on to help you in any way possible and my shops are open to you if you need help, tools or just storage.

Charles

[Seldom Seen Slim]

Charles, did you get the emails from me today?

[saltfever]

A2/ Dave,
If a few hardcore know it all types get a but sassy to you on here please do not take it personally...

Missing an extra "t", Charles.   

Ok ok, I know what you really meant but I just couldn't pass up the Freudian slip! 

[Cajun Kid]

A2/ Dave,
If a few hardcore know it all types get a but sassy to you on here please do not take it personally...

Missing an extra "t", Charles.   

Ok ok, I know what you really meant but I just couldn't pass up the Freudian slip! 

was it a slip   LOL

[Cajun Kid]

Charles, did you get the emails from me today?

Yes Jon I did get the file but it was an .ai  (adobe illustrator) file and I can not open it,,,

I sent you two emails asking if you could send it again in another format like a pdf file or even a jpeg,,,, pdf is better.

I am going to print tomorrow (as soon as I can open and download your file)

Thanks

CV

[jl222]

Blue...you talk of your pilots and drivers, who are they and what planes-motorcycles-or cars have you designed?


                        JL222

#2

[1212FBGS]

dave
im not saying you posts are crap im just saying compairing flying aero to ground vehicles is....
kent

[akk]

I tried to take this topic seriously in reply #21...and no response, I then tried to take it funny in reply #51 and got one cheer. I now try to take it seriously again.

Aerodynamic stability to airplane people is about an airplane oscillating or fluttering up/down or side/side ....or even worse being totally uncontrollable. The common sense understanding is that the center of gravity (the balance point of the airplane..a point about which the vehicle may be lifted without rotating or flopping around) should be in front of the center of pressure (the point about which all drag forces may be thought to be applied). I know this to be a gross over simplification. The center of pressure in an airplane is easier to locate than in a car. the center of pressure in a car is affected by ground interference, ground clearance, angle of attack, cross winds...... The center of gravity can move about as fluids slosh in the tanks.

Airplanes, when they are being airplanes, with aerodynamic stability... you know ...flying , do not have front wheels on the ground. If the back end of a flying stable air plane is shifted to the side, the rudder (major contributor to moving the center of pressure back) levers the airplane straight again ...working against the center of gravity which acts as a pivot point and a momentum induced force, pulling the airplane forward.

An "aerodynamically stable" airplane with only the front tire on the ground (this is very hard to do in a tricycle gear airplane as they are designed to land on the rear tires first for reasons soon to be revealed) becomes unstable. The front tire takes control and changes the center of gravity momentum force to a destabilizing force. A tail movement to the right steers the airplane left, the front tire becomes the pivot point, pulls the airplane to the left and the center of gravity pulls the airplane right. If the tail feathers are powerfull enough to overcome the tire force to the left the airplane may recover ...this is usually accomplished with active rudder control.

When the front tires are rolling on a car, aerodynamic stability as in airplanes doesn't, mean much!!!!

On our car we bias the brakes full forward so that the front tires can skid with the rear tires rolling. When the car gets out of control the driver hits the clutch and slams the brakes on. The front tires skid and loose all lateral forces, the back tires roll and the car straightens right up.

Aerodynamic stability of car should be concerned with keeping the tires rolling at all times!

Think about it!

DW what do you think about "Land Speed Chute Pulling"?

Akk