Aerodynamic vs. vehicle stabilty

[jl222]

Sparky...glad to meet you.

Our bluff wide track roadster...AA/GMR car #920 set the record at 284 MPH...we went out and re qualified at 287 with a 13 MPH head wind...sure wish it was calm ..or better yet a tail wind....Ro Yale said the car handled fine...the wind blew him around a bit but he could drive it back to the middle just fine!

Akk

  Unblown and on parts wash great accomplishment

                JL222

[SPARKY]

Akk,  what constitute the meeting      Slow witted senior minds with CRS ned to know-- lol

[F104A]

The question about Stringfellow and Kirks crash with the Cavelier: I spoke to Jim Kirk and he told me his run was going well but he got a little loose and the car started coming around. He said that once it started getting sideways he know it would spin (we all pretty well know what that feeling is like). As soon as it got backwards, the air got under the car and up it went. My son Cam got it all on a sequence of photo's and donated them to Stringfellow and Kirk.

[saltfever]

Doesn't the car have a wing or flat plate on the back?

[akk]

I have a friend here in Houston with a beautiful Studie...it has a front air dam, low sides and a spoiler on the back.... he took it to a wind tunnel and found significant down force going forward....and that backward it would fly at 200.

Akk

[Cajun Kid]

I have a friend here in Houston with a beautiful Studie...it has a front air dam, low sides and a spoiler on the back.... he took it to a wind tunnel and found significant down force going forward....and that backward it would fly at 200.

Akk

I would agree, backwards is not good on that configuration, I have the same setup, frontwards is stable, like on rails (at least on pavement and concrete).

tunnel test show roof flaps can help,  a tunnel with yaw capabilities  is REAL expensive to use.  You can load the car in the tunnel backwards as well.. we are working on other ways to spoil lift should the car go backwards. (those rear deck spoilers and spill plates work great straight, we are looking into options back there as well (folding, venting etc..)

Charles

[The wonderful One]

It could be worth a trip to Art Chrisman's shop in Santa Ana, CA. His son, Mike, is doing what should be a 300 mph car that incorporates both flaps and a spoiler that opens inward should the car go backwards. TWO

[saltfever]

I have a friend here in Houston with a beautiful Studie...it has a front air dam, low sides and a spoiler on the back.... he took it to a wind tunnel and found significant down force going forward....and that backward it would fly at 200.Akk

Precisely my point!   

[saltfever]

tunnel test show roof flaps can help,   a tunnel with yaw capabilities  is REAL expensive to use.  You can load the car in the tunnel backwards as well.. we are working on other ways to spoil lift should the car go backwards. (those rear deck spoilers and spill plates work great straight, we are looking into options back there as well (folding, venting etc..) Charles

Charles I agree the roof flaps spoil lift caused by the shape of the roof but they are there to primarily reduce roof lift. There "may" be some turbulence spillover from the roof flaps to the wing and this may or may not help reduce wing lift for a couple of reasons. (1) If the car is going directly backwards the "wash" from the roof flaps "may" be across the wing and help a little. But to make it to the 180 position the car had to yaw through those 180 degrees. At some point the relative wind (from the flaps) was not flowing over the wing. So at some point, before you are completely lined up going backwards, the wing will already have produced substantial lift, most likely flying the car and also rendering the roof flaps useless in your new flight attitude.

(2) Most people think the airfoil shape of the wing (which produces lift) is the only issue. The wing produces down force when you are going the right direction and produces the equivalent lift when going the wrong way. Only half right Wind by itself has force. Think of a barn door (certainly not an airfoil). Wind applies pressure/sq.ft. per velocity. What that means is; hold any flat plate area (or spill plate if you will) into a head wind and you will get a force. When the cars is going backward that area under the wing and the new blunt front end become a high pressure area. The high pressure, working on the area of the wing, is enough to raise the attitude of the car. Now many bad things start to happen. The wing can simply be “flat-plate area” and lift due to dynamic air hitting it. Lift increases the angle of incidence and the lift becomes even more aggressive. And, of course, air is now building under the car leading to more bad things.

[krusty]

Having been to the A2 tunnel with a Stude this year, I can confirm that at 180* to the original direction, the lift developed is HUGE! You have to determine how much yaw the vehicle can accept before you are going around; the "big" Aerodyn tunnel can yaw a car up to 3* and identify a "trend". If you can get (and afford) time at Lockheed in Marietta, you can yaw the car on their turntable and identify  the "point of no return".  Then you can develop a sequence to deploy anti-lift strategies (flaps, etc) and their activation.      vic

[jl222]

   
  It will be interesting how Chrisman constructs the spoiler, a piano type hinge with non locking supports?

     JL222

 

[Cajun Kid]

Vic, the Big Tunnel next door to the smaller A2  tunnel is if I remember double or triple the cost per hour.. well above my ability to afford.... I do agree with you about finding out "the point of no return"   but it would be costly to find that out (but less costly than an backwards car going airborn at 200 mph).  

I would think rather than spending research dollars to find that point, when in reality when a car gets to that point, the driver is not going to be able to react quick enough to employ any defensive counter measures to correct.

If my thinking above is close to correct, my plan would be to put the car in the small A2 tunnel and see what we can do to keep the car from flying in the backwards position.

My thoughts are a pivoting rear spoiler that folds up or has a few flaps that release when backwards or when Yaw exceeds  X degrees?  also maybe a rear valance plate the has no front wards aer advantage, but deploys at X yaw, thereby acting like a front air dam but on the rear ?

Just my thoughts and I did not stay in a Holiday Inn Express last night,  and am not even qualified to properly spell Aerodynamic !!!

Charles

[interested bystander]

Anybody notice that WAY too many posters on this topic are like the guy that went to the knife fight with a RUBBER KNIFE?

A2 and Blue - keep posting, WE @ LANDSPEED NEED YOU - (and keep TUFTING, everyone!)

[Cajun Kid]

   
  It will be interesting how Chrisman constructs the spoiler, a piano type hinge with non locking supports?

     JL222

 

I already designed that, have just not tested it yet,,, may go to tunnel late Sept before Maxton or shortly after, depends on time and money.

Charles

[Cajun Kid]

all cool,

Charles