DESIGN AND CONSTRUCTION  OF A LAND SPEED RECORD   
 STREAMLINER


STREAMLINER
DESCRIPTION AND CONSTRUCTION

 
Copyright 2012, 2013, 2014, and 2016. All rights reserved.
No part of this website may be copied or distributed without the author’s express written permission except for research, personal use, or brief excerpts for quotation.




Much of the information on this website is applicable to the safety and performance of LSR vehicles of all types. My streamliner has only two wheels, which entails some unique stability issues. The above photo shows a scale model of the streamliner that I am building. It is no longer completely faithful to the latest design iteration, but it gives some idea of what I think it will look like when completed. The nose shape has recently been modified, and the vertical airfoil tail has been shrunk (and I may eliminate it) to avoid a possibly excessive destabilizing roll moment. There will be dorsal, ventral, and side fins for yaw and pitch stability, to help keep the streamliner pointed downrange whether it is upright on its wheels or sliding on its side.

Text and photos on this page describe my streamliner construction. There are seven more pages (buttons are located at the top of the each page) where you can find out detailed information on several subjects - possibly more than you ever wanted to know.

Top reasons why the streamliner will probably be painted orange:
        Home team colors. Go Illini! 
       Dutch heritage. Viva L'Oranje!
        If I get off-course on the salt flats, I want the course workers to be able to find me.   :)
     

WEBSITE MAP

Navigate to pages by clicking on the buttons near the top of each page, between the two orange blocks.

Page 1...... STREAMLINER DESCRIPTION AND CONSTRUCTION. This page. Photos and text that describe design and construction.  <> April  2014. 
Page 2...... GUEST BOOK A place for you to enter comments or questions.
Page 3...... EVENTS. Land speed record sanctioning bodies and venues.  <> February 2016
Page 4...... DESIGN TOPICS. Technical discussions of various streamliner aspects: 
    • Introduction  <> October 2012
    • Safety Equipment  <> October 2012
    • Aerodynamics  <> Now on page 5
    • Friction, Traction, Tire Slip, and Wheelspin  <> April 2012
    • Roll Cage Strength, Stiffness, and Safety  <> Coming soon
    • Rolling Resistance  <> September 2012
    • Wheels and Tires  <> August 2012
    • Chassis  <> Coming soon
    • Cooling and Ventilation  <> Coming soon
    • Weight  <>September 2012, more coming 
Page 5......AERODYNAMICS
    • Introduction  <> 12/12/12 
    • Basic Concepts, Aerodynamic Coefficients, and Reynolds Number  <> 12/12/12
    • Aerodynamic Coefficients Magnitude <> 12/12/12
    • Center of Pressure  <> 12/12/12
    • Drag  <> 12/12/12
    • Choosing My Streamliner Body Shape  <> 12/12/12
    • Effect of Body Surface Characteristics on Drag  <> 12/12/12
    • Drag Calculations  <> 12/12/12 More coming
    • Lift  <> Coming soon 
    • Lateral Forces due to a Crosswind  <> Coming soon
    • Dynamic and Aerodynamic Stability  <> Coming soon
Page 6...... PERFORMANCE. Estimates of potential top speed by two different methods.  <> August 2012
Page 7...... REFERENCES WITH ANNOTATIONS. Where to go for further information.  <>  April 2013 
Page 8...... MY SONG  <> August 2012

This website is a continual work in progress. Some sections will be revised. Check back occasionally for updates.

UPDATE February 2016. 
In early 2013 I had to temporarily abandon my streamliner project. I made some progress in 2014, but was pulled away again in 2015.  Now, in early 2016, I am making progress on the build. I plan to update the website pages to discuss things that I have learned and done.


DISCLAIMER - README:

Notice to everyone who reads and/or makes use of any information on this website. I make no claim, warranty, or assurance that any aspect of the information that you find on this website is correct or complete or useful. If you make any use of it, you do so entirely at your own risk. You agree to this by the act of reading and/or using any information presented on this website. Take all of the information and conclusions presented on this website with a "grain of salt." I accept no liability for any damage or injury that might result from making use of any aspect of this website. If you have any doubt about any aspect, carefully check it out. The responsibility for using it rests entirely with you.

There is a fine line between recklessness and courage.
Paul
McCartney

 

WEBSITE OVERVIEW

This website is a work in progress. I plan to update and augment it as I make progress and find time. My vehicle is a two-wheeled streamliner, but the website describes design, construction, and performance aspects that are applicable to any land speed racing vehicle intended to compete in Land Speed Record (LSR) time trial events. This page presents text and photos that describe construction progress. Another page describes land speed event sanctioning organizations and venues. Other pages are devoted to design topics, where I discuss my conclusions regarding questions and obstacles that arose during the project, and also a list of references.

I take this opportunity to thank those who shared their time, knowledge and experience during the past few years to help guide me to a safer design. I will not name them here, but you know who you are, and I am forever grateful. Perhaps someone will find similar benefit from this website.
 

 



Here is a photo showing the first Bonneville rule book that I purchased (in 1970), a more recent rule book, and a layout drawing of a previous streamliner design version.


PROJECT HISTORY


I became interested in running at Bonneville when I was a twenty-something engineering graduate student and was racing motorcycles as a hobby. I developed an interest in land speed racing (I caught "salt fever") in 1970 when I saw a short Bonneville segment in the movie On Any Sunday. I ordered an AMA Bonneville rule book and began sketching design ideas. For a while I thought I had invented a new type of steering system, which I later learned is called hub-center steering and had been in use long before I was born. Oh well.

After graduation I shelved the idea (but kept my Bonneville folder), devoting my time and resources to my family, my engineering career, and other hobby activities. In 2007 and 2008, while recuperating from surgeries, my Bonneville dream resurfaced, and I began reading, studying, calculating, and drawing. In 2009 I retired from my engineering career. During 2010 I set up a workshop and, after 40 years, got serious about building a land speed record (LSR) vehicle. I did an initial design layout drawing, recognized several problems, and made a second design drawing. I sent that drawing to land speed sanctioning organizations, as they suggest for new vehicles, for review and comment. Boy, did I get comments! I then spent a few more months revising the design, primarily for better safety, and sent it in again. More comments -- all good advice! And more design changes. I also attended four time trial events at the salt flats during 2009-2013, met a lot of people, asked a lot of questions, kept my eyes open, and learned a lot. The current design version continues to evolve.

I don’t know, but I’ve been told,
If you never slow down, you never grow old.
Tom Petty




This drawing showing chassis and body shape in side, top, and bottom views and sections at various longitudinal stations.  The roll cage structure and major items including engine, wheels, and pilot are shown. This drawing is obsolete; I have made several changes (hopefully improvements), particularly the nose shape.
 

STREAMLINER DESIGN SUMMARY

My streamliner is intended to compete in SCTA/BNI/USFRA and AMA/BMST frame classifications “S” (Streamliner) and FIM “Category 1 - Group A1 - Division C”. It is designed to be able to use various engine classifications and sizes. Throughout design and construction, safety considerations were paramount, often trumping budget or performance. Top speed depends on engine power, traction, available acceleration distance, weight, drag, rolling resistance, weather, and pilot skill and judgment. I estimate a potential top speed of about 240 mph (400 kph) is possible using a 600 cc engine (details are on the Performance" page). I designed the vehicle to meet safety and performance requirements for higher speeds to provide an extra safety margin and to accommodate future changes.

The above (now somewhat obsolete) drawing shows chassis details and the body shape in outline. Dimensions are given in terms of inches and feet, which can be converted into the metric system according to 1 inch = 2.54 cm and 1 foot = 30.5 cm (one meter = 39.37 inches = 3.28 feet). The vehicle design layout began with the smallest available front tire I could find that is suitable for the anticipated top speed (there are very few). A smaller diameter tire enables smaller frontal area and smaller aerodynamic drag and facilitates a clear view of the course. Vehicle width, height, and length followed to accommodate dimensions of driver, engine, tires, and parachute tubes, all enclosed in a low-drag body shape. The vehicle will be about 18 feet (5.5 m) long, 23 inches (58 cm) wide, and 32.5 inches (83 cm) high plus 3.5 inches (8.9 cm) ground clearance for a total height of 36 inches (92 cm). The wheelbase is about 11 feet (3.3 m) and the operating weight will be about 1100 pounds (500 kg) ready to run including the pilot. I originally planned to have smaller size and weight, but I ended up with numbers quite similar to other successful designs. The width just accommodates my shoulders in a fire suit and the width of the engine. The height is sufficient to enable the pilot to see over the front tire, plus some extra clearance above the pilot's head to help avoid neck injury if a crash should occur. The larger-than-desired frontal area will compromise potential performance to some degree in favor of increased safety. The body shape was chosen to have small drag, as described in detail on the "Aerodynamics" page.
 
The central portion of the chassis is a steel roll cage composed of longitudinal rails, cross-members, roll hoops, and bracing. The roll cage surrounds the driver entirely and is made of steel as required by sanctioning regulations. I chose to use mild steel tubing, rather than stronger material such as 4130 "chrome-moly" steel, for superior welding properties and higher impact energy. The body shell will consist of an inner skin of either metal sheet (in the roll cage and engine bay) or fiberglass cloth in epoxy resin, and an outer body skin of fiberglass or Kevlar cloth in epoxy resin. The space between the inner and outer layers will be filled with an expanded foam core, a structure developed for composite aircraft that is stiff and strong and also offers some impact cushion and absorption. My design mantra is that the roll cage must protect the pilot, and the rest of the structure is sacrificial for the sake of safety. The body shell, with the exception of the removable canopy and engine bay covers, will be bonded to the steel chassis structural members. The body and chassis are thus integrated into a strong and stiff stressed-skin structure that complies with streamliner regulations. This construction avoids the common streamliner difficulty of sealing the engine bay from the cockpit to avoid ingress of liquids or fire into the cockpit. It also facilitates an exterior surface with fewer flow-disturbing roughness elements such as rivets or screws that increase drag force. The importance of avoiding roughness elements and panel gaps is discussed is some detail on the "Aerodynamics" page of this website. The lower body shell is one piece, which avoids gaps between body panels for both strength and aerodynamic reasons, though it somewhat impedes engine and tire servicing. The bottom of the body is rounded to reduce lift. Necessarily removable canopy and engine covers are composite structures that are strong and durable, can be securely attached to the chassis, and can be quickly and easily opened.
   



I chose a 2008 Yamaha YZF-R6 600 cc (36.6 cubic inches) "crotch rocket" motorcycle, shown in the above photo, as the donor bike for my streamliner. In stock form it produces more than 100 claimed  horsepower (75 kilowatts) at the rear wheel at sea level (about 2.7 HP/cubic inch or 125 kilowatts/liter) at an engine speed of 14,000 rpm, with a 16,000 rpm redline, naturally aspirated burning pump gasoline. This provides a powerful but durable engine, so that I can, at least initially, concentrate on driving. The stock bike is claimed to be capable of speeds over 150 mph (240 kph). I used two methods, computerized modeling and a curve fit of existing records, both described on the Performance page, to estimate a streamliner possible top speed of about 240 mph (386 kph). The speed increase over the stock bike is primarily the result of reduction in aerodynamic drag.
 



CONSTRUCTION

A first step was to build a wooden mockup to check whether I (my height is 70 inches or 178 cm), along with required safety equipment, could fit into the planned cockpit size. Safety equipment visible in this photo includes a helmet, HANS device, SFI-compliant 7-point harness, fire suit, and gloves (A more complete safety equipment list is 0n the "Design Topics" page.). Planned width is 20 inches (51 cm) inside at the shoulder rails, and roll hoops height is 31 inches (76 cm) inside. Some streamliners are smaller. Extra room in the cockpit increases the streamliner frontal area and thus aerodynamic drag, which reduces the potential top speed.
One very successful streamliner builder told me that if he had it to do over again, he would nevertheless make his cockpit one inch wider. I increased the inside height from 29" to 31" at the strong urging of experienced LSR competitors and officials who reviewed my plans, to allow additonal space above the rider's head to reduce the risk of neck injury. The front roll hoop shape shown in this photo was later changed to a stronger shape. 
  



This is a plywood template, hung on the shop wall, of the streamliner top view shape. The contour is derived from a low-drag NACA-66A “laminar” airfoil shape; an extensive discussion is presented on the "Design Topics" page of this website. Because I will use a stressed-skin structure, the chassis side rails must conform to this shape. This was a demanding task, since the curvature is slight and is different at every point along most of the length.



This photo shows the table, 18 feet long and 32 inches wide, that we built for layout and assembly of the chassis. It is supported by stacks of concrete blocks, with a 1.5 inch square x 1/8 inch wall steel tube table top frame, topped with 2 layers of 5/8 inch thick OSB and a top layer of concrete board to protect it during welding. We used shims to get the top surface flat and level within 1/32 inch (less than 1 mm). You also see
Dave and Jeff, friends who have helped greatly in the build. Among many other things, they helped develop a method to bend those curved side rails accurately. We spent several months accomplishing it. Our first try, hot bending them against cement board forms, was a total failure; there was far too much spring back.
 
 



A tube roller can form steel tubing to a gently curved shape. A high quality tube roller such as a Baileigh is far too expensive for my streamliner build budget. Also, control software for such machines does not allow for continuously varying bend radius. We finally managed the job using an inexpensive HF tube roller, much modified and powered by a winch motor. It barely lasted through the job of making the two side rails. We gradually formed the 1.50 inch square 0.12 inch wall side rail tubes to final shape in about 3 inch length increments, by trial and error, using dial indicators to check the curvature. The lady in the photo is Carolyn, my tolerant wife who supports me in this project, but does not like the heat at Bonneville in August and September.
 



We are using the tube roller to bend chassis side rails that are almost as long as the shop. The plastic sheet across the door helps to keep some heat inside the shop on a chilly winter day. Sometimes this project is not as much fun as I thought it might be...

 



The chassis side rails are finished and held in place by blocks on the assembly table - a huge milestone! After an extended effort, we achieved good accuracy. We measured the chassis width at 6 inch (152 mm) longitudinal increments to be within +- 0.010 inch (0.25 mm) of the planned contour, well within the goal we set of +- 1/32 inch (< 1 mm). We did not quite manage to maintain this accuracy after welding the chassis members together, but were able to keep everything true to plan well within less than 1/8 inch (3 mm), with symmetry about the centerline held closer . The tube in the middle is a 4 inch x 1.5 inch x 0.12 inch wall rectangular steel tube that is remarkably straight and accurate. We used it as a reference throughout the roll cage assembly process, and will use it as a reference during chassis and suspension alignment.
 



We formed the chassis roll hoops and curved lower cross members by hot bending (note the short section of orange-red color) 0.12 inch wall mild steel tubing, using a "bushy flame" propane rosebud torch and truck/bus wheels, brake drums, etc., as bending dies. We filled each tube with sand to prevent collapse during bending, with welded caps on the tube ends to keep the sand inside the tube, but with small gaps to allow steam to escape. After initial attempts that resulted in some kinky tube contours, we learned to produce decent heavy-wall steel tubes bent to any required bend radius we needed for the chassis. Hot-bent tubing has less residual stress, and thus can carry greater loading, compared to cold-bent tubing, for mild steel tubing whose strength is not degraded by heating nor improved by cold working.
 



This is the partially assembled skeleton of the lower portion of the chassis, upside down on the assembly table, viewed from the rear quarter. The front bulkhead and the lower portion of the firewall are in place. Both are 11 gauge 0.12 inch thick mild steel sheet, welded to cross members and braces around their entire periphery.

 



Welding the curved lower cross members, keel tube, and side rails together to form the chassis roll cage, upside down on the assembly table. In this photo, not all of the welds have been completed.
  



A foot rest and front bulkhead brace, with an 11 gauge 0.12 inch thick steel sheet web, have been securely welded into the (upside down) chassis skeleton. This reinforces the region on the bulkhead where the front suspension pivots, and the pilot's feet, will be located.

 




The first trial fitting of the rider in the chassis. When the temporary cross-brace (partially hidden by the gloves) located between the 72 inch and 75 inch stations (measured from the nose and labled on the side rail) was later removed, the side rail width at that location increased by 0.1 inch (less than 3 mm), probably due to welding distortion.  This causes an inconsequential small change in the top-view profile shape. Symmetry about the chassis centerline changed by much less, so the chassis profile remains very straight and true, minimizing any sideways aerodynamic lift due to planform camber; such sideways lift could upset high-speed stability.
 



This rear quarter view of the chassis shows metal inner liner panels that have been installed in the cockpit as required by regulations. These metal panels were also installed in the engine bay behind the firewall for added fire safety. The panels, made of 16 ga (0.06 inch) mild steel sheet, were slip-roll formed and continuously welded to the chassis keel, side rails, and cross members around their entire periphery on both the inside and outside. These curved steel panels, required by sanctioning organization rules to contain the pilot's body extremities inside the roll cage if an exterior body panel is lost, also provide very strong bracing for the chassis roll cage. At some time in the future, expanded foam will be deposited on the outer surface of the panels and sanded to the body shape. [Easy to do, right?  Just sand away everything that doesn't look like a streamliner.] Fiberglass cloth in epoxy resin will then be bonded to the foam and to chassis structural members to form the body exterior surface. The result will be a very strong and stiff stressed-skin structure that meets SCTA rulebook requirements and also provides some sideways impact energy absorption. This photo also shows the 11 gauge 0.12 inch thick mild steel sheet firewall welded to the upper firewall hoop and the assembly tack-welded in place. This completes an 11 gauge 0.12 inch thick steel firewall between the cockpit and the engine bay.
 



The firewall roll hoop and upper firewall 0.12 inch steel sheet have been welded in, and the forward roll hoop and four roll hoop braces have been tacked in place. We are checking to ensure that helmet clearances satisfy regulations before welding these roll cage members together.
 



The roll hoops have been welded to the side rails, and four horizontal longitudinal braces have been welded between the roll hoops. Roll hoops are 1.625 inch diameter 0.12 inch wall round tubing, and the side rails and roll hoop braces are 1.50 inch square 0.12 inch wall tubing, all mild steel. Inclined brace tubes connect the keel, a lower cross member, and the firewall cross brace between the side rails, and are reinforced by steel sheet panels. These inclined braces also serve as the seat back. There is a water tank integrated into the structure under the seat back. Longitudinal braces between lower cross members, one located on each side, have four harness lap belt attachment locations.

   

 



The Yamaha YZF-R6 motorcycle frame and engine have been mounted in the streamliner chassis. This provides engine mounting and rear suspension with good mutual alignment.

Regulations require that motorcycle streamliners have a roll hoop cap of at least 0.090 inch steel sheet spanning at least 140 degrees of the roll hoop to contain the pilot's head within the roll cage. My roll cage cap is 0.12 inch steel sheet, the same thickness
as the roll cage tubing walls and the firewall.  The cap is welded to the roll hoops around the entire periphery except for the corners.

 


 


This photo shows an overall view of the partially completed chassis. Sanctioning organization safety regulations require a steel roll cage that completely surrounds the driver/rider. For motorcycle streamliners, regulations require that the steel tubing must be a minimum of 1.25 inch diameter by 0.095 inch wall. On the advice of experienced LSR participants, and to conform to roll cage regulations for cars (Hmmm - maybe this chassis could be used as the basis for a lakester), I opted to make my roll cage stronger for improved safety. I used 1.625 inch diameter round steel tubing with 0.125 inch wall thickness, as is required for cars over 175 mph, and 1.5 inch square x 1.8 wall square tubing that has even stronger and stiffer section properties. The 1.625 inch diameter by 0.125 inch wall thickness tubing dimensions are the largest required by the rules for any LSR vehicle, including highway hauler tractors, some of which weigh 6,000 pounds or more. These tubes are about 70% heavier than the minimum tube size required for motorcycle streamliners. The added weight of the heavier tubing is likely to reduce attainable top speed in the fifth mile by a few miles per hour, according to calculations that I carried out using my performance model. Safety trumps performance.


I later made some engineering calculations that cause me to be unsure that the larger roll cage tubing was a wise decision. The 1.625 inch diameter x .12 inch wall tubing, compared to 1.25 inch x .09 inch tubing, for equal loading and equal length straight sections, and for various loading types (axial, bending, torsion, buckling), is about:

  • twice as strong (stress ratio based on section modulus ranges from 1.72 to 2.22 for various loading types);
  • up to nearly 3 times as stiff (deflection ratio ranges from 1.72 to 2.94; the larger number is for bending and torsion);
  • with section area and weight per length both about 73 percent larger.

 Stiffness and strength are design aspects with different consequences. There is little doubt that a stronger roll cage is better for survival of the vehicle. Survival of the pilot is a different and more important issue. A stiffer structure may increase the g-loads on the pilot during a crash. I did some dynamics calculations that indicated that a threefold stiffness increase, for a given vehicle mass, could increase the impact force and g-load on the driver by a factor of perhaps about 1.7, a 70% increase. This obviously indicates a significant additional potential risk of pilot injury. In actuality, the g-load and impact force on the pilot/driver/rider (2 or 4 wheels) depend on the entire chassis construction, not just the roll cage, and also on characteristics of the track surface and on accident circumstances. The potential consequences of this issue warrant further investigation. Engineering analysis is one tool, but it cannot provide definitive conclusions in such a complex and ill-defined scenario.
 
A criterion for whether a roll cage has adequate strength is analysis of historical accident data. Salient questions, and probable answers, include:

  • In how many accidents have motorcycle streamliner roll cages that are well-constructed and meet current SCTA and AMA/BMST/FIM regulations (1.25-inch diameter 0.09-inch wall) collapsed or sustained significant structural damage? Preliminary anecdotal information indicates "none".
  • How many accidents have resulted in an undamaged roll cage but a damaged pilot? This has happened. 
  • How many accidents have resulted in no serious damage to either the vehicle or the driver? This has also happened.

Definitive answers to these questions, along with data on vehicle design, speed, weight, etc., should be informative regarding assessment of whether a stiffer roll cage is beneficial or hazardous to a streamliner pilot.

At the rear of the vehicle you see a wooden mockup of the parachute tubes. I have provided for three parachutes. My anticipated speed is near the speed (250 mph) at which two parachutes are required by the rules for motorcycle streamliners, and I want a backup in case one fails to open. The wheels are only sitting in place in this photo. The next steps are to complete the front and rear hubs and suspension. Also fabricate and install an exhaust system and a custom gas tank, wire the engine and controls, and install an engine cooling system. The chassis needs to be cleaned and painted. It will then be ready for initial testing.
      



Selecting wheels and tires that can be safely used at the anticipated top speed was a major design hurdle. Very few are available, none intended for motorcycles. I chose Goodyear Eagle Land Speed tires (not to be confused with "Frontrunners"), which are expensive but are acceptable for use at sustained speed of 300 mph (480 kph). These are car tires that must be mounted on rims that have automobile wheel bead shape. The wheels I will use are Centerline racing wheels that will be mounted on custom-built hubs at both the front and rear. Reasons for these choices are discussed in more detail on the “Design Topics” page of this website.
  





The stainless steel exhaust system is completed and installed. The strings approximately provide the eventual location of the body panels, within which all components must fit. The rear wheel is still just set in place; the hub is not yet fabricated. The aluminum gas tank was later replaced by an improved version. 
 



There are no motorcycle tires available that are suitable for use at speeds that I expect to reach, as is discussed in detail on the "Design Topics" page of this website. Motorcycle streamliner builders (of which there are not very many) typically use car tires built for land speed racing. These are made by Goodyear and Mickey Thompson and are generally accepted for use at speeds of up to 300 mph (480 kph). Car tires should not be mounted on motorcycle wheels because the bead shape is different. Thus I will use custom-made wheel hubs to accommodate the Goodyear tires mounted on Centerline  brand racing wheels. The front hub will have hub-center steering, and the rear hub will accept R6 drive sprockets of appropriate tooth count. This photo shows a collection of parts and raw materials that will become the custom hubs.
  



Front and rear wheel hub parts at a later stage of fabrication.
  




This photo shows all of the parts that make up the hub-center steering front hub that I designed and built for my motorcycle streamliner. Hub-center steering (HCS) is a steering arrangement that has the advantage that the top of the wheel can be the tallest part of the front suspension. No conventional motorcycle “triple tree” is needed, because the steering pivot pin (kingpin) is located inside the hub. This reduces the required height of the body, which reduces frontal area and drag. 

Basic parts:
Hub: mounts the wheel and brake rotor, rotates on wheel bearings.
Spindle: wheel bearings ID mounts on the spindle, and the spindle pivots on the kingpin (pivot pin).
Axle: Locates the kingpin, connects to the chassis via control arms, springs, and shock absorbers (not shown). The kingpin pivots in tapered roller bearings with seals to retain lubrication.

HUB: The hub is made of 6061-T6 aluminum, three pieces welded together. This material has an as-received yield stress of about 40,000 psi. The wheel and tire mount on the hub. The wheel lugs are 14 mm (about 9/16”) grade 9 bolts, pressed into the aluminum hub and backed up by 316 SS washers. The lug nuts are rather unique, spherical rather than tapered seat, and are over 1” OD which gives large bearing area. The wheel design I plan to use was original equipment on early (about pre-1968) VW cars. They have a 5 x 205 mm (a bit over 8 inches) bolt circle and a center hole of about 6.25", which is large enough to fit over the HCS assembly. The hub is designed to mount a disk brake rotor. The braking torque is a critical loading on the HCS assembly, since the braking torque is transferred to the suspension arms through the spindle, kingpin, and axle. A front brake is not really needed at the salt flats, but is useful at venues such as the Ohio Mile and for road testing.

Wheel bearings fit inside the hub. The bearings are 85 x 120 x 18 mm ABEC-7 precision 15-degree angular contact bearings with phenolic cages and steel balls (ceramic balls offer less drag but cost several hundred dollars extra). They carry thrust in only one direction, so two bearings are mounted face-to-face to carry thrust in both directions, each one backed up by a substantial retaining ring in a groove in the hub bore. The bearings will be oil lubricated by light mineral oil, which greatly increases the allowable speed and reduces friction compared to grease lubrication. They are rated for over 17,000 RPM and more than 10,000 lbs load, which is more than 3 times the expected speed and more than 25 times the expected steady state loading. The wheel bearings are larger than is normally required in more conventional steering configurations. I used zero offset in the steering geometry to keep the wheel bearings as small as possible. The oil seals are “wave” seals that have a special lip shape for reduced drag and wear.

The spindle is located inside the hub. This part that I am calling the “spindle” does not look very much like a conventional automobile spindle, but it performs the same functions. The wheel bearings mount on the spindle, and the spindle pivots on the kingpin (pivot pin). The spindle is made of 304 stainless steel for good corrosion resistance to salt and salt water, good weldability (the spindle is six pieces welded together before machining), and reasonable strength and ductility. The name “hub-center steering” refers to the fact that the kingpin is located inside of and at the center of the rotating hub.

The axle locates and supports the kingpin, and connects the front wheel and hub assembly to the chassis via control arms, springs, and shock absorbers. The axle and the kingpin are made of 17-4 PH (precipitation hardening) stainless steel, which has excellent corrosion resistance to salt water and high strength to carry the suspension loads and braking torque. Annealed condition yield stress is 110,000 psi which can be increased to 185,000 psi by a relatively simple H900 heat soak. The kingpin is mounted in the spindle by tapered roller bearings and seals on each end. These bearings are lubricated by grease. A seal carrier made of 303 stainless steel carries three x-ring (square O-ring) viton seals: a dust seal seated against the axle, a small diameter seal that seats on the OD of the kingpin, and a larger diameter seal that seats in the spindle cross-bore. A tapered roller bearing fits on the kingpin and in the spindle cross-bore, and is held in place by a steel threaded end cap that is prevented from rotating by a cotter pin. The end cap supports the tapered roller bearing cup to carry suspension loads that act on the axle and are directed along the axis of the kingpin, while the kingpin carries brake torque loads in shear. Steering arms (not shown) will be attached to the ends of the spindle, via the threaded holes, to steer the vehicle. 
  



This is the outer housing of the front wheel hub, which is of HCS (hub-center steering) type. The 120 mm OD wheel bearings fit into the bore of this part. The wheel lugs mount the Centerline racing wheels. 
   
   



This photo shows the hub-center steering front hub fully assembled.

Designing and building a hub-center steering assembly is not a trivial exercise, and also is not inexpensive. I spent many hours working with my non-CNC lathe and mill. A hub-center steering system that is not correctly and carefully designed and built could prove to be dangerous. I used stress analysis, with a generous safety factor, to choose materials and size parts. If you decide to use a HCS hub, be very cautious.


In retrospect, I could have designed a more compact hub that would have smaller rotational inertia and could use smaller wheel bearings that could be expected to have less rolling resistance. A small maximum steering angle helps to minimize the size of the wheel bearings. This hub design allows a turn angle of about 15 degrees in each direction; land sped racers often use much smaller maximum turn angles. The braking torque load dictated the size of some components; a front brake is not really needed at the salt flats. Using plain bushings, rather than tapered roller bearings, to support  the pivot pin is another measure that would allow a smaller front hub. I would do all of these things if I were to do this again.
   


This is a photo of the completed rear hub before final assembly. All fasteners can be safety wired. A description of materials and components will be added soon.
    

  
This is a photo of the rear hub fully assembled, including the axle and centering spacers. The driven sprocket and the brake rotor are mounted on their respective mounting disks. The wheel fits over the sprocket carrier and mounts on the wheel lugs on the central disk. All bolts and nuts, including wheel lugs and lug nuts, are grade 5, 8, or 9 high strength steel and all (except the lug nuts) are either captured or can be safety wired to prevent loosening. An extra set of holes in the wheel mount disk of both the front and rear hubs are provided to secure the wheel in place via captured or safety-wired bolts and nuts. The bolts visible on the hub tube are oil fill ports, three equally spaced around the periphery.  
  
 

Here you see the custom swing arm extenders, including chain tension adjusters, that I designed and built. A custom axle made of 400 series case hardened stainless steel is mounted in the extenders. The swing arm extender is required because the rear tire is about 4 inches (100 mm) larger than the OEM tire. The extenders are a special design that allows the wheel, hub, and part of the extenders to be lifted out vertically as an assembly, since the chassis and body construction will not permit the axle to be extracted horizontally. The extenders are made of 6061 aircraft aluminum in T6 condition. All fasteners in the assembly are grade 5 or grade 8 high-strength steel, and all nuts and bolts are either captured or can be safety wired to prevent them from loosening.
  
 
This photo shows the wheel, tire, and custom rear hub and axle assembly mounted in the swing arm. Another important milestone!
  

This is the custom 5052 aluminum fuel tank, beautifully TIG welded by my friend Paul Cain (I wish I could weld like that!). The fuel tank accommodates the stock R6 fuel pump and fuel lines. It holds about 1.5 gallons of gasoline, which for my small 600 cc stock engine is sufficient for three or four runs including warm-up. Some supercharged LSR vehicles burn as much as 60 gallons of fuel in a single run. 
    
  

Copyright, all rights reserved.
No part of this website may be copied or distributed without the author’s express written permission except for research, personal use, or brief excerpts for quotation.

Website Builder