This is a message for Paul Lamar, please return if this address is
incorrect.
Paul,
I worked on the Steve Fossett LSR team that bought and rebuilt Craig
Breedlove's Sonic Arrow. We have been looking for the inventor of the
focusing link and have a lead that it was you. If so, I would like to ask
you several questions regarding the theory of the design and its application
in the Sonic Arrow.
Eric Ahlstrom
President, Star Aerospace LLC
Guilty as charged. How is Craig? I have not heard from him in years.
The links form a virtual pivot ahead of the tire contact patch so it forms a
caster effect.
Here is an example of such a system on my flying motor cycle design.
The two vertical links control the camber of the wheel and the lateral link
mounted at the back of the wheel controls the steer angle. Craig said it
worked very well up to 400 MPH.
http://www.rotaryeng.net/roadable.html
Paul Lamar in Australia back in two weeks.
Paul,
I am very pleased to finally find the designer of this part.
Everyone who looked at the link found it ingenious. Craig and his 2000-2006
crew chief, David Schmidt, were very, very proud of the design. The first
day I saw the car in 2006, David did two things that I had an issue with:
First, he claimed credit for the link even though I knew he was not on the
original build crew. Second, he tried to dazzle me; saying that I could
never figure out how it worked. I'm a flight test ME/AE, and have built
vehicles in 4 different motorsports. David was out of his league with me
and everyone I brought in. So I started questioning Craig about the
original build and the people involved. I never got a straight answer on
anything.
The fact is, I recognized immediately that the lower links pointed at the
steering center. The problem was, Craig had set it up with zero trail. I
had never heard of any steering setup working with zero trail and this made
me question the steering stability. The upper links were harder for me to
understand, since they were parallel. I understood right away that this
created camber with the steering angle, much like a fork front suspension.
Since the whole assembly compressed the shocks when steered, there was a
significant centering force with the car in the air, but not with weight on
the wheels.
Something bothered me about this, and it took a month for me to figure it
out. If we have a single, round profile tire the camber change with
steering angle would be correct. If, on the other hand, we have multiple
front wheels then the positive steering axle camber would lead to negative
roll.
The lack of trail I knew was neutral in stability, the adverse roll was
unstable. I did some research and found that wobble/weave stability was
best at ~5% trail vs. total wheelbase. Less would lead to steering wobble,
more would couple into the chassis and lead to weave. The 1996 accident was
a yaw-roll-yaw-roll-yaw-roll oscillation that looked surprisingly like a
motorcycle weave.
Looking at the car, we designed new lower-aft link brackets that would put
the steering center 18" forward of the axle. This respected 5% of the
wheelbase of 360". I also wanted to flatten out the roll, or even make it
proverse instead of adverse. So we extended the lower vertical link mounts
so that we had a vertical center near the ground plane.
We needed to test this before we got any further. We took the car out in
the parking lot (~100 yds of flat pavement) and pushed it to less than 5
mph.
1. With the 1996-97 setup, the car spontaneously diverged to one side
or the other and full-lock steering would not correct it. The tire tracks
clearly showed only the tire opposite the steering command was on the
ground.
2. With the roll taken out, the car would go straight until we turned
the wheel. Then it would turn in that direction and not come back even with
a full-lock reversal.
3. Once we put the trail in, it steered straight, turned when we
turned the wheel, and straightened itself out hands off.
4. We then repeated the test as fast as we could push. It worked the
same up to 7-8 mph.
Every amateur aerodynamicist (and many professionals who should know better)
believed that the roll was cause by "SHOCK WAVES!!!" under the car. This
never stood up to even the simplest analysis. First, at M.89 it wasn't
going fast enough for shocks of any significant strength to bounce off of
the porous-plastic surface of the playa. Shock waves do reflect, but they
lose energy when doing so and typically don't come back up one half of the
significant length of the object that created them until we get above M1.2
to 1.3 at the point of the reflection. Second, the leading edges of the
struts were swept at 75 degrees which means they would not create a shock
until M3.8! Yes, there were probably local shocks from the intersections
at the leading edge vs. the fuselage and wheel fairing. These would be
pretty weak at M.89 on the high fineness ratios of the strut, fuselage, and
wheel fairing.
Craig was convinced that gyroscopic forces from turning the wheels rolled
the car. I did some quick math and this just didn't add up. The car did
roll in the direction of the engine torque, but it rolled back almost to
level against that torque. The oscillation was also clearly discrete in
roll vs. yaw: first yaw without roll, then roll without yaw, reverse,
repeat.
One last thing about the focusing link: on Sonic Arrow the vertical links
angled slightly aft at the top. This loads them in compression and puts
high shear stress on the pivots. I thought it would be better, if
mechanically less convenient, to move the upper vertical mounts forward and
unload the vertical links. When I visited the Chicago Museum of Industry, I
persuaded the management to let me crawl up in the front wheel well of the
original Spirit of America. The vertical links were installed the way I
would have expected. I think Sonic Arrow was done the way it was for the
mechanical convenience of mounting the links to a common plane, in this
case, the front of the fuel tank structure. SOA had the steering forward of
the driver.
I'd like to hear about everything you did on all of Craig's cars. We've had
to do a lot of forensic engineering and need to know about all of the theory
that went into each area of the design.
Eric Ahlstrom
President, Star Aerospace LLC
I only worked on the American Motors V8 powered version around around the early
70's. Margie Smith, a mechanical engineer from a mining school in Colorado did
all the drawings. That car was intended to achieve the
wheel driven land speed record. Little is known about this car as it never
set any records.
On November 12th 1965 the Goldenrod held the wheel driven land speed
record at an average speed of 409.277 mph (658.526 kph).
I did a manual analysis using a Friden mechanical calculator of the speed verses
time/distance and told Craig I did not think we had enough room at Bonneville
to achieve 400 MPH with the intended power and tire traction available.
I used inverted wings between the fuselage and rear wheel pants to apply down
force to improve the traction. Craig said not to worry and showed
me some Jato bottles. He intended to fire at the start. I said the best
place to fire them was around 375 MPH when the real estate was being used
up much more rapidly.
The following is hearsay. Craig told his ex wife about the Jato
bottles and she told her boy friend who happened to know Joe Petrilli(S?)
of the ACCUS (I think) sanctioning body. Joe called Craig and said three words.
"No Jato bottles." AMC cut the funds and I was laid off. As I understand it The
V8 was removed and a spare lunar landing rocket motor was installed. Craig did
a demo run at a drag strip and achieved 400 MPH in the quarter mile.
The car was banned as too dangerous on drag strips. Craig later told me
he took it to Bonneville and could not get it much above 400 MPH due to
not enough fuel storage. It was stable for a few runs but he decided to take the wheel
pants and wings off to save weight. I was not there. The wings were essential
for wheel driven use as all stabilizing lateral tractions is lost when they
are on the verge of slipping. Not needed for the rocket configuration however
the rocket had a slight down trust angle. A run was made and the car became
unstable as soon as the rocket shut off and crashed at over 400 MPH. Craig
survived of course because the round cockpit was double wall .065 alloy with
two inch high .065 hat section stringers about 10 or 12 degrees apart.
The rear sub frame was separated as was the front suspension in question.
I don't know what happened to the remains.
Margie Smith went on to form her own company building racing car trailers called
IRD designs as I recall.
Paul Lamar
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