How Jim Hall started racing’s aero revolution
Last week I enjoyed a long chat with Jim Hall, the creator of the legendary Chaparral Can-Am (below with Jim driving) and long-distance sports cars from the sixties. Those cars were at the vanguard of the aerodynamic revolution as Hall pioneered the use of high-mounted, driver-controlled wings and rolled out the world’s first, skirted ground-effect car, the Chaparral 2H, in 1970. Hall and his cars won many American sports car races in the mid-sixties and also scored a handful of world championship sports car victories at Sebring, the Nürburgring and Brands Hatch.
I wanted to talk to Hall for a book project I’m working on and also for an upcoming column in Motor Sport. The tall Texan has many tales to tell and plenty of strong opinions, too. We covered a lot of ground but I was amazed when he told me that none of the Chaparrals ever saw the inside of a wind tunnel. Back in those days most race teams had nothing like the sponsorship and technical resources we’re familiar with today, nor were there any wind tunnels with rolling roads or ground planes designed specifically for ground-effect aero development. Hall explained the very basic method he used to calibrate the downforce generated by his Chaparrals.
“We started rudimentarily measuring downforce back in ‘64 when I figured out that I needed to fix the nose on the first mid-engined Chaparral,” Hall recounted. “We measured downforce with a cable and a chart measured off the suspension so that we knew what the lift or downforce was on the car. We just measured it with a pencil that ran across a piece of paper. We did that for a long time and it was easy to set that up and run it, even on the 2K Indy car we ran in 1979-’81. We did that a little in Texas before we took it anywhere so we had a pretty good idea of what the downforce was.
“We calibrated the suspension by just rolling the car out and putting weights on it so we knew what load it took to move the car up and down. We had a cable drive that drove a pencil and a roll of paper that was run by a little motor so you could set your zero point. You would go out and make a run and push a button and make a mark across the paper so we knew what the front and rear downforce was. You could run a couple of different speeds and then you could put it on a graph. You knew that it was increasing as the square of the speed so you knew what the curve looked like and you pretty much had the downforce over a speed range. That was pretty simple to do.”
Hall’s method of measuring the air pressure or downforce on the surface of his car’s wings or bodywork was equally simple in concept. “The other thing we did was when we needed to change the surface we had a manometer that was just a bunch of u-tubes made out of tigon tubing and full of coloured water,” Hall related. “If you were in a sports car you put it in the seat beside you and then went out and tapped a bunch of holes in the. You ran these to one side of the tubes and ran the other one to a pitot tube so you could get the dynamic air pressure on the surface.
“I originally did it with a Polaroid camera. I had a Polaroid camera mounted on the dash and the manometer mounted on the seat back beside me. I didn’t even have a pitot tube for a static pressure source. I read in a book somewhere that a guy in WWI thought about doing this. The way he thought about doing it was you took a thermos bottle and put a piece of tubing in it and right before you made the test you opened it up then closed it so you had static air pressure in it. Then you went out to make your run and compared it to the pressures you got, then opened it and made sure it didn’t change.
“In a matter of about twenty minutes that thermos bottle would maintain an even enough temperature that the pressure wouldn’t change much. So you had some static pressure while you were sitting in the pit and you also had static pressure when you were going down the straightaway. It’s simple-minded, but pretty tricky! And that’s the way we started.
“Then we bought a light airplane pitot tube and mounted it out front of the car. We found a static pressure place where we could run that pitot tube that matched the thermos. Then we had a static pressure source all the time.”
Thus began the serious science of racing car aerodynamics. Of course, Hall had no idea about the depth of the pandora’s box he was opening but he is without doubt the father of the modern aerodynamically-driven racing car. (Above – Honda’s latest wind tunnel).
Filed under: Blogs, IRL, Miscellaneous, Sportscars
He’s been there and seen it all, but GK’s finger is still very much on the pulse of modern US racing. After over 30 years as the American editor of Autosport, he remains one of the most outspoken and authoritative voices on the US scene. Gordon is now Motor Sport’s US editor and monthly columnist, shedding light on everything that is happening on the other side of the Atlantic.
Jon Waterhouse:
November 25th, 2008 4:30pm
Gordon- You might want to talk to Bill Milliken to get some “color” for your upcoming story. I believe he and Jim Hall spoke often.
Brian Brown:
November 25th, 2008 7:39pm
Mr.Kirby - Thank you for directing me to your blog. Certainly a different era of innovation. Mr. Hall must shake his head in wonderment in looking at the current technology available. The gentleman, whose name I couldn’t recall, being discussed on the Nostalgia Forum on autosport.com is Gary Knutson. Jerry Entin supplies some unreal photos & stories on many of the unsung heroes of the past. Great stuff! I thank you again for your continuing help & kindness that you always extend to me & my family. I am honored & humbled. All the best, sincerely, Brian Brown
Steve:
November 26th, 2008 2:02pm
This quote is confusing to me…
“The other thing we did was when we needed to change the surface we had a manometer that was just a bunch of u-tubes made out of tigon tubing and full of coloured water,” Hall related. “If you were in a sports car you put it in the seat beside you and then went out and tapped a bunch of holes in the. You ran these to one side of the tubes and ran the other one to a pitot tube so you could get the dynamic air pressure on the surface.
Tapped a bunch of holes in what? Or am I completely mis-reading this?
Stephen G:
November 26th, 2008 8:57pm
Steve, re confusing quote; there is clearly something missing after “the.”, my guess is that its something like ” body, or aerofoil, surface you are interested in” or words to that effect. The holes are static pressure tappings which are each connected to one side of a U tube, with the other side connected to the common pitot reference pressure. I used a similar technique at university in the 70s, right down to the camera to record the pressures. Nowadays it would be electronic transducers and a datalogger of course.
To digress, I dont think Mr Kirby is using te term ground effect in the conventional way if he is referring to the fan car pictured. Doesn’t it usually refer to cars with inverted aerofoil underbodies as developed by Lotus and others? This is not to take anything away from Jim Hall, one of the outstanding innovators who I was pleased to meet when he brought the Chaparrals to the Festival of Speed some years back. (And didnt he invent that fan car before Brabham did it in F1?)
Gordon Kirby:
November 28th, 2008 7:11pm
Sorry, I’ve been away for a few days for our Thanksgiving holiday. Stephen G is exactly right in what he says. Jim Hall was referring to either the bodywork or the surface he was measuring and I did a poor job of editing it. And yes, I refer to all those cars as ground-effect car because they are part of that particular genre or motor racing revolution. And yes too, Hall (with GM’s engineering help) did invent the fan car before Gordon Murray at Brabham.
Robin Richardson:
December 2nd, 2008 3:30pm
Gordon,
They say there’s nothing new under the sun and that’s certainly the case with the use of wings and oher ground effects devices in motor sport. The RAK1 and RAK2 rocket cars from the 20’s used side mounted wings as did the unraced Mercedes T80 land speed record car. I believe Lee Pendleton also used much larger wings on his Allison engined dragster in the 50’s. And in his book High Performance, Robert C Post quotes a Car Craft article by Terry Cook which talks about ground effects devices used by Peter Robinson on his top fuel cars from 1968 onwards. It seems he had the idea of inducting air from a chamber under the engine to “make the tires think the car weighs about a thousand pounds more than it does, thus providing more traction.” He experimented with a number of devices, one of which is said to have worked too well bogging the engine (a nitro burning top fuel engine!)off the line. I wonder how this could happen so early in a run with anything other than some sort of fan driven device? Whatever, by 1971 he was using a rubber skirted device which also seems to have worked too well, an excess of downforce seemingly pulling both front tyres off their rims at high speed. Sadly, Robinson died in the crash. This is by no means an attempt to upstage Jim Hall’s achievements which are imo every bit as significant as you say.
Robin
Christopher:
December 16th, 2008 6:18pm
Being a native Texan I cannot tell you how proud I am when we get recognition from you guys across the pond. Y’all have Colin Chapman we have Jim Hall. Sadly here in Texas Nascar (booo!!) is king as far as motor racing goes. I was disgusted when Kevin Schwantz, a native Texan, won the GP crown and it was not even mentioned in the paper here. Cheers to you on an article well done!!!