Does the HP Spoiler with Gurney Flap Actually Generate Downforce?

[gbadger]

That makes complete sense

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[glenng6]

These types of discussions I find superfluous. The spoilers may produce downforce, but be honest, we have them mostly for styling. In the examples given, you have to be driving 124 mph or 180 mph to get those results. I'm not saying I haven't done that, but if I do, I'm not really thinking about downforce. You are not going to do that commuting to work, going grocery shopping, or even cruising on a weekend. I would rather have someone drool over the looks of my car than say, ”Where’s that idiot going?” If you are racing on a road course, then you can reap the benefit; otherwise, a spoiler is just another passenger. IMHO Glenn

 

[Junkyard Dog]

These types of discussions I find superfluous. The spoilers may produce downforce, but be honest, we have them mostly for styling. In the examples given, you have to be driving 124 mph or 180 mph to get those results. I'm not saying I haven't done that, but if I do, I'm not really thinking about downforce. You are not going to do that commuting to work, going grocery shopping, or even cruising on a weekend. I would rather have someone drool over the looks of my car than say, ”Where’s that idiot going?” If you are racing on a road course, then you can reap the benefit; otherwise, a spoiler is just another passenger. IMHO Glenn

Sorry to post a superfluous discussion, but I have tracked the car, and I intend to do so again, and given the aggressive nature of the gurney flap, I was genuinely curious whether it did anything at all, especially since it is bolted to a spoiler which is bolted down to a trunk lid.

gbadger appears to have provided some information to indicate it is doing something at higher speeds, but those speeds are mainly above what my car is doing in turns, so probably something but not much.

 

[Junkyard Dog]

indeed (it was tongue in cheek), but those figures for the spoiler at speeds of 200kph+ (120mph) are marginal at best. What you would gain in a corner from an extra 60kg of rear downforce (very fast corners at that) you would almost certainly lose down the straight from the drag. Never mind that the additional rear downforce may actually increase understeer in those corners!

Downforce per se is no use unless it is efficient downforce and a huge gurney is NOT efficient!

Without a wind tunnel it is all just finger in the air stuff, but underfloor downforce from the strakes that Ford designed using a wind tunnel will almost certainly do more.

So the answer to the thread title is YES it will generate downforce but also a lot of drag and may make the car slower over a lap!

FYI, the flap in that link generated downforce not of 60kg but 110kg, or 242 pounds, almost twice what you posted.

Your points are otherwise clearly understood, though, and it makes me wonder whether a really good driver could post better, same, or worse times on a high speed road course with v. without the gurney flap installed.

 

[Junkyard Dog]

Never mind that the additional rear downforce may actually increase understeer in those corners!

Understeer was the very first discovery upon the Gurney Flap's initial use in racing by Gurney:

"The first application of the flap was in 1971, after Gurney retired from driving and began managing his own racing team full-time. His driver Bobby Unser had been testing a new Len Terry early CAD/CAM designed car at Phoenix International Raceway and was unhappy with the car's performance on the track. Gurney needed to do something to restore his driver's confidence before the race and recalled experiments conducted in the 1950s by certain racing teams with spoilers affixed to the rear of the bodywork to cancel lift (at that level of development, the spoilers were not thought of as potential performance enhancers, merely devices to cancel out destabilizing and potentially deadly aerodynamic lift). Gurney decided to try adding a "spoiler" to the top trailing edge of the rear wing.[11] The device was fabricated and fitted in under an hour, but Unser's test laps with the modified wing turned in equally poor times. When Unser was able to speak to Gurney in confidence, he disclosed that the lap times with the new wing were slowed because it was now producing so much downforce that the car was understeering. All that was needed was to balance this by adding downforce in front.[12]

Unser realized the value of this breakthrough immediately and wanted to conceal it from the competition . . . "

https://en.wikipedia.org/wiki/Gurney_flap


And of course it creates drag. Certain airplanes use a gurney flap to create additional lift at low speed, such as those banner towing planes you see at the beach (they are under the wing instead of on top). They go slower but the flap creates increased lift so that the stall speed is lower, but the throttle application must be higher at the same speed as without the flap. Same thing applies to a Mustang Dark Horse handling package with the gurney flap installed, drag, less maximum speed, and higher fuel consumption. Ford says to install it for the track and take it off for the street. Everybody seems to leave them on for the street because of the way that they look.

 

[gbadger]

Sorry to post a superfluous discussion, but I have tracked the car, and I intend to do so again, and given the aggressive nature of the gurney flap, I was genuinely curious whether it did anything at all, especially since it is bolted to a spoiler which is bolted down to a trunk lid.

gbadger appears to have provided some information to indicate it is doing something at higher speeds, but those speeds are mainly above what my car is doing in turns, so probably something but not much.

You didn’t. It is a good discussion. I didn’t link the aero wind tunnel diagrams for gt3 style wings because it was part of the discussion. 9 lives and APR as well as others have some great wind tunnel results from S650 with wings both with and without a gurney flap.

It starts to come online around 60-80mph and really kicks in the faster you go.

It’s going to be very track dependent. If your track has higher speed turns but not intense long straightaways the drag may be worth it for the added rear grip (without carrying dead weight at lower speeds).

It’s easy enough to remove that you can runs one laps with or without it and see.

It really will come down to your style, the track, and your car but to your first question - it does add significant downforce at the cost of drag.

Keep the discussion questions coming! Love talking about road racing and these cars.

 

[gbadger]

Understeer was the very first discovery upon the Gurney Flap's initial use in racing by Gurney:

"The first application of the flap was in 1971, after Gurney retired from driving and began managing his own racing team full-time. His driver Bobby Unser had been testing a new Len Terry early CAD/CAM designed car at Phoenix International Raceway and was unhappy with the car's performance on the track. Gurney needed to do something to restore his driver's confidence before the race and recalled experiments conducted in the 1950s by certain racing teams with spoilers affixed to the rear of the bodywork to cancel lift (at that level of development, the spoilers were not thought of as potential performance enhancers, merely devices to cancel out destabilizing and potentially deadly aerodynamic lift). Gurney decided to try adding a "spoiler" to the top trailing edge of the rear wing.[11] The device was fabricated and fitted in under an hour, but Unser's test laps with the modified wing turned in equally poor times. When Unser was able to speak to Gurney in confidence, he disclosed that the lap times with the new wing were slowed because it was now producing so much downforce that the car was understeering. All that was needed was to balance this by adding downforce in front.[12]

Unser realized the value of this breakthrough immediately and wanted to conceal it from the competition . . . "

https://en.wikipedia.org/wiki/Gurney_flap


And of course it creates drag. Certain airplanes use a gurney flap to create additional lift at low speed, such as those banner towing planes you see at the beach (they are under the wing instead of on top). They go slower but the flap creates increased lift so that the stall speed is lower, but the throttle application must be higher at the same speed as without the flap. Same thing applies to a Mustang Dark Horse handling package with the gurney flap installed, drag, less maximum speed, and higher fuel consumption. Ford says to install it for the track and take it off for the street. Everybody seems to leave them on for the street because of the way that they look.

Ok. I am home now. All the data I have seen in wind tunnels is on wings so the spoiler will have a reduced affect but the principle is the same. I legit could not find any studies (other than the college kid I linked below) on mustang spoilers and gurney flaps with hard numbers.

Let's see if I do this right. This is data from Nine Lives on the big wang -

Here is APR with their 71" GTC-250 wing -

Here is a really cool article from HotRod on the design of the spoiler / gurney but not a lot of specifics - Ford claims it comes online at 30mph but even says drivers need to experiment.

https://www.hotrod.com/features/ford-mustang-dark-horse-200-mph-wind-tunnel

I am also attaching (if it will let me) some research a college student did on a model of a mustang that is pretty cool. Take it for what it is worth but its a fun read.

 

[Gregs24]

FYI, the flap in that link generated downforce not of 60kg but 110kg, or 242 pounds, almost twice what you posted.

Your points are otherwise clearly understood, though, and it makes me wonder whether a really good driver could post better, same, or worse times on a high speed road course with v. without the gurney flap installed.

Did it not say the standard wing was 60kg hence the 120kg with the gurney is an additional 60kg as I said?

 

[Danee]

Here is some data of other spoilers with and without flaps. The flap is pretty significant. Similar car, different spoiler, should be ballpark.

https://www.herrodperformance.com.au/2020-mustang-r-spec-gurney-flap/?utm_source=chatgpt.com

Thanks for sharing the link.

 

[glenng6]

Sorry to post a superfluous discussion, but I have tracked the car, and I intend to do so again, and given the aggressive nature of the gurney flap, I was genuinely curious whether it did anything at all, especially since it is bolted to a spoiler which is bolted down to a trunk lid.

gbadger appears to have provided some information to indicate it is doing something at higher speeds, but those speeds are mainly above what my car is doing in turns, so probably something but not much.

As I said. If you are road racing, figure out the most efficient spoiler/wing that works for your setup/track. However, for most applications the effect is more visceral than it is functional. Glenn

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