+Fireamx - That is the type of reply that makes this forum... informative!
I am curious why Chrysler put the manual switch on the limited and not the SRT. There must be a reason... As Respdoc stated...why not put the more expensive wing on the SRT?
I wonder if the switch could be wired so that one could deploy or not at speed instead of pulling fuse.

 

No one around have the time to model the XF aerodynamics? No I don't either. I agree that time to deploy must be considered, I would like to see some clever logic taken into consideration, ie current speed and rate of acceleration so the wing only opens at 60 if you are still accelerating with menace, that would stop the activation on UK 'A' roads, some of which are peppered with roundabouts or sub 40 mph corners bridges etc that mean I have to put the thing up or have a yoyo spoiler...you US guys don't want to see the fuel bill for that kind of drive at $3.785 a US gallon (first time I have seen £1 a liter in the UK so the conversion is easy).

40 lbs doesn't sound much and it would have to have more effect than that to be important. Imagine putting you arm out of a car window at 60 mph (as a passenger on a quite road etc) tilt you hand at 45 degrees, what's the opposing force feel like? Multiply that by five? Then remember that at 120 mph the effect is four times that at 60 mph. Lets say 40 lbs at 60 mph that's 160 lbs at 120 mph and 250 lbs at 150 mph.

...but it is all about balance, what does the back end weigh? Curb is 3200 lbs so perhaps 1400 lbs rear with 1800 lbs up front. All sorts of things happen, but say at 120 mph lift means you loose 200 lbs at the back, that leaves 1200 lbs. Now remember the XF has big fat tires (fatter than the SLK and TT), contact pressure is what important in determining grip and as the area increases the pressure reduces. Our 1200 lbs is split in two, now only 600 lbs downforce over an area 10% bigger than say a TT. An extra 80 lbs downward pressure per wheel would make me happier, but what if the lift is more than 200 lbs.

I think the danger area is the motorway starting at 90 to 120mph (depending on conditions and road) for the following reasons. Even shallow curves have reasonable G force at 120 mph, I have seen drivers belting down the motorway at over 100 mph in RAIN (must think the aqua tread tires are magic or something), and effects like overtaking a large trailer mean large negative pressures are available to further mess up aerodynamics.

Personally, I would never disable a safety system (that I paid for), just in case it came into my mind (or my wife's) to do 120 mph. (if Ian or others so want to disable a safety system perhaps they should put a blown fuse in the circuit for the accident investigators to ponder over).

I know my guess on lift might be way out but the spoiler effect must be considerable at 120 mph.

 

While we are on the subject of spoilers, I thought I'd throw this in just to show they can be profitable.

nice toy...

http://cgi.ebay.com/ws/eBayISAPI.dll...RK%3AMEWA%3AIT

 

Malcb brings up the "yoyo spoiler" terminology which is appropriate. Anyway, the increased down force in inclement weather or on curves is worth having an extra 40 lbs. at lower speeds. good point!


nice toy...I had no idea, why so much? I am digging thru my sons old toys as we speak!

 

paragraph form an article online from road and track. So obviously it does serve a function.

"Another prominent exterior feature that's more about function than style is the rear spoiler that automatically deploys at speeds over 60 mph. The car looks much better with the spoiler stowed, although when up, it doesn't really affect the view out the rear window all that much. The sound of the spoiler going up and down does take some getting used to." paragraph form an article online from road and track. So obviously it does serve a function.

In regards to the srt not having a switch for manual deployment? ummm. cause its a fixed spoiler. also i think because of the increased power, torque, and speed, imo the fixed spoiler is there to provide down force right away, and it is larger, so i imagine provides more downforce. here is a paragraph in regards to the srt front spoiler.

"Visual changes to make a Crossfire an SRT-6 include adding a more aggressive chin spoiler that reduces lift and funnels extra air in the nose".

so imo the spoiler on both does provide function and is more than just for looks. exactly how much downforce? or at what speeds, still has to be determined.

 

Well not to be too **** about it (HA) but it deploys at 100K and retracts at 60k.

 

Road & Track may provide more in depth on this issue but this excerpt does nothing to shed light other than to say it functions better than it looks.
With the fixed spoiler they give a generic text book definition ... boiler plate "a spoiler provides reduced lift". really?

I believe we all concur that a spoiler serves a purpose. Yet, is it more a statement until one reaches autobahn speeds of 150 mph. ummm.

As far as a switch for the SRT... i believe the issue is why it does not come with the more $$ version. The increased power, torque, and speed does not in itself justify a fixed wing as stated earlier.

I guess it is possible to draw a conclusion that the spoilers are for looks for 90% of the US market similar to the SUVs having 4X4 capability.

 

I haven't had my car now for almost two years, but I seem to recall from the manual that it says to not operate the car about 65 mph if the spoiler is malfunctioning.

The Crossfire is a striking design. But it is NOT aerodynamic and as you approach 100 mph, or even less, that Kam tail design is not aerodynamically sound and the car is designed to get a bit squirrelly in its handling, unless the spoiler is out.

I wouldn't consider driving this car north of 100 mph unless that spoiler was working. Simply not a good body design.

 

Been thinking about why the deployment speed is so low relative to the speed where its "required" to keep the car stable. Most aerodynamic forces are a function of the velocity cubed, so a 40 lb force at 60 mph would be near 320 lb at 120 mph. Looking at the size of the motor that raises the spoiler, I don't think it could move the unit with a 300+ downforce acting on it. The speed appears to be set to allow the spoiler motor to raise and lock the unit while the forces are still low enough to allow it to operate. Once in the upper locked position, the motor is no longer required.

 

I think this will clear something's up for you guys.

 

hey that's not fair ...your pic belongs with my quote!!!

 

ok everybody remember to breathe.

 

rick,
quite possibly you have provided the explanation to solve the real reason for the deployment setting! It also may shed light as to the fixed srt version...it is not worth putting a activated wing as the speeds are potentially greater. (of course for the SRT price tag they could of put a stronger motor) That is assuming your aerodynamic calculation is correct.

 

not a bad theory.

however, the drag force is a function of the square (not the cube) of the velocity so theoretically the force would be 160 lbs. at 120 mph. but that force may actually be less at speed if there is aerodynamic separation from the vehicle before reaching the spoiler.

i think we need to find one of the more credulous crossfire owners to conduct a couple experiments to get some better data. first, i recommend parking a crossfire facing downhill on a very steep grade so that the stowed spoiler is horizontal with the horizon. have a 160 lb. buddy stand on top of the spoiler while you attempt to deploy it. if it goes up easily, the above theory is flawed. if it doesn't go up, rick is really smart, but you will be left to get the spoiler motor or other destroyed parts replaced. the 2nd experiment is to strap a bathroom scale to your spoiler and drive at various speeds to see how much force is being applied (make sure you have an observer do this so you can keep your eyes on the road). you should be able to calculate the actual down force on the spoiler by knowing the surface area of the scale.

 

Anyone can sit on a spoiler while it is stationary -

3rd experiment would be to strap a human on the back and drive at excessive speeds to check for aerodynamic separation around curves to fully determine the scope of the motor capacity.

Maybe we should just get the specs on the motor. nah that's too easy!

 

Hey finally a topic I can put some actual input into!!! IMO, from playing with the Crossfires handling vs speeds before and after chipping I have found this... After chipping, during hard acceleration on the same curve, as before the rear of the car breaks loose as the Wing comes up. My only explanation is that the car accelerates much faster now, and the wing does not rise overly fast. Now other things start to happen like the computer traction control cuts in... but the point is that this wing is functional and not just cosmetic... efficiency etc are not clear however.

Rog

 

I don't have anything informative to add into this which I found already very informative Thread. The Topic being discussed in a nice light headed (with knowledge and some dashes of humor) and by nice light hearted people. Made it interesting.
If there is an open poll for one of the best Thread, this will be the best.

I have read somewhere, the spoiler is chrysler's. A kind of identity or trademark.
My not worth a dime.

 

I got out my old textbooks, and I guess my memory isn't what it used to be. Yes, the drag is a function of the velocity squared.

 

Just how functional it really is, is questionable but its so cool when you are going down the road, your already getting looks. Because there just aren't a lot of us on the road and then that spoiler pops up.
I had a guy pull up beside me a while back and give me a thumbs up. Truly a unique car.
Pat

 

Thanks Pat ...as I said, before it is "cool" looking.