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Land Speed Record
Recently developed alloy steel used for reduction gears of
class-beating wheel-driven car
Team Vesco Racing says its Turbinator III, which this year will be making an assault on both the US national and international land speed records for wheel-driven automobiles, is the most aerodynamic and technically advanced 'streamliner' ever to pursue either the US record of 267 mph or the world record of 409 mph.
The car, looking more like a low-profile wheel-mounted projectile, is 31 ft long and 3 ft wide. It weighs in at 3,400 1b and is powered by a specially adapted Lycoming T-55-L- II helicopter engine that generates 3,750 hp at 16,000 rev/min. This turbine power plant is the product of a five-year project to develop an engine of high reliability; while the four-wheel-drive vehicle already holds one 'gas' record at 310 mph - set during chassis testing while powered by two 900 hp Indy car engines (the car actually reached a top speed of 397 mph) - a broken exhaust valve terminated the run and triggered the search for a more durable engine.
Although the car's driver, Don Vesco, now had a proven vehicle body and a reliable engine, he also needed a 'state of the art' drive system to transfer the awesome power of the Lycoming turbine equally to all four drive wheels. This requirement has been satisfied with a newly designed reduction gearbox. It incorporates Grade 12 gears, because every power transfer component must be able to withstand the incredible torque and stress that will be encountered while accelerating up to and through the 7 second mile. When the Turbinator is building up to speeds in excess of 400 mph, the transmission loading with 2:1 ratio will be a gear tooth-wrenching 9,000 1b.
For maximum strength, Mr Vesco decided to make the gears in the new reduction box from the steel alloy AerMet 100. Developed by the US-based company Carpenter Technology Corporation, of Reading, Pennsylvania (Tel: 1 610 208 2524), this material is said to offer an excellent combination of high tensile and shear strengths, high fracture toughness, and resistance to fatigue and stress corrosion cracking. Intended originally for aerospace applications, it is a nickel-cobalt steel strengthened with carbon, chromium and molybdenum. Its nominal analysis is 13.4% cobalt, 11.1% nickel, 3.1 % chromium, 1.2% molybdenum, 0.23% carbon and the balance, iron.
The gears and gearbox were designed by Vesco's consulting engineer Bob Hodgkinson, and subsequently made by the Gear Works in Seattle. Just three gears are used in the gearbox to transmit drive from the turbine output shaft, running at 16,000 rev/min, to line shafts (7,000 rev/min at 450 mph) that run to the front and rear wheels.
The particular strength of the Carpenter AerMet 100 alloy meant that the Gear Works was able to make spur gears instead of helical gears, which often require costly lead corrections. To date, the company has made five gears from this alloy -- three input gears, one idler gear and one output gear, together with their integral shafts.
The three input gears were designed to be interchangeable, and so allow for fine tuning with gear ratios of 2.00, 1.88 and 1.50 (the idler gear has a concentric positioner that allows the gears to be easily changed). Power is transferred from the reduction box to the output gear and shaft, with all gears and bearings alike being pressure-fed by a dry sump oiling system that utilizes 12 spray nozzles and oil galley ports.
A number of unusual conditions presented to the designers of Turbinator III and its gear system were particularly testing; while the 11-mile race course - known worldwide as the Bonneville Salt Flats - looks very flat, it actually has quite a rough surface, with small potholes of varying size and depth. This surface roughness makes the traction that propels and steers the racer unpredictable from one run to the next. Furthermore, seldom are all four wheels driving against the surface at the same time; at high speed, the wheels are actually dancing randomly on the track, thousands of times per second. In addition to the pulsing torque from erratic traction, the driver must also accommodate varying and gusty side winds.
Mr. Vesco hopes to cope with these situations by not only designing gears that will take the maximum required load, but also designing the drive system so that the four wheels will lose grip and begin spinning before maximum tooth load is reached. Tires are a major consideration: Mr Vesco has run the Turbinator at speeds approaching 4OOmph -- easily enough to break the world speed record for this type of vehicle. If he were to use full power and there was enough length of track, a speed of 6OO mph could theoretically be reached, but no tire is rated for speeds higher than 5OOmph. Don Vesco hopes to use his 3,750hp Turbinator III to establish new US National and world land speed records for wheel-driven cars.
Gear Manufacture
Manufacture of the unique gears started with a 70 in length of stock 8 in-diameter AerMet 100 alloy, supplied by Carpenter in the annealed condition. The material was cut to the required lengths and then rough-machined on a CNC lathe to produce the gear blanks, using carbide inserts and removing the stock patiently (because this is an ultra-high strength steel). The alloy proved to be very stable, and it exhibited minimal distortion as a result of machining. The Gear Works then produced the gears in pitch diameters of 3.50 in, 4.17 in and 4.67 in for the input gears, 7.50 in for the idler gear and 7.00 in for the output gear. Each gear was finished to AGMA Quality 12 standard using a combination of hobbing and Maag grinding. Between roughing and finishing operations, the gears were heat treated. This entailed solution-treating the parts for 1 hr at 1,625° F, deep freezing them for 1 hr at -100° F, and finally aging them at 885° F for 5 hr. Following this heat treatment schedule, the AerMet 100 alloy attains a tensile strength of 2,046 MPa, excellent fracture toughness and better resistance to stress corrosion cracking than that of common low alloy high-strength steels. The Gear Works held all dimensions including gear lead, profile and spacing to very close tolerances and achieved a 32 RMS finish. A tooth thickness of barely ¼ in was held to a tolerance of ±0.0007in (holding this tolerance prevents backlash in the gear box, which was machined from two sections of 4 in. and 6 in. thick 6061 T6 aluminum). The gear maker also noted that the Carpenter alloy was very stable after heat treatment, simplifying the finishing operations.
A Year of Destiny?
This could be a great year for Don Vesco: in addition to gunning for the US automotive national land speed record this summer, and the international record later in the year, he hopes to become the first driver in history to set both automotive and motorcycle speed records in the same year. Mr Vesco held the motorcycle land speed record at 319 mph for 19 years, and currently holds 18 different motorcycle and five automotive records (his brother currently holds two automotive and one motorcycle land speed records). Mr Vesco will try to regain his motorcycle land speed record using a totally new twin-engine, supercharged 3,000cm³ Vincent-powered motorcycle that produces well over 400hp and has a projected speed of 350 mph.
This article reprinted from the May 8 1997 issue of Machinery Market.
To visit Carpenter Technology go to: http://www.cartech.com
To visit Wm. Watts Machinery Market go to: http://www.wmwatts.co.uk
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Last Update:11/29/2004
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