ABSTRACTThe Department of Mechanical Engi-

neering at the University of Canter-bury, Christchurch, New Zealand, was

commissioned by the Physical EducationDepartment to build a dynamic calibra-tion rig for an air-braked Repco cycleergometer. The project was part fundedby the Hillary Commission on the rec-ommendation of the New Zealand SportScience and Technology Board. Thispaper describes the conceptual approachand embodiment design of the apparatusand presents calibration test results.

1. INTRODUCTIONAthletes and coaches in most sports

are interested in the measurement of per-formance, and athletes need a reliablequantitative means of assessing theirlevel of fitness or the effectiveness of atraining programme. Methods of assess-ment range from field performance tests,through trials on laboratory exercise ma-chines, to biochemical tests on musclecondition. Quality control is a basicrequirement of any method used, i.e. in-struments must be accurate and experi-mental data reliable.

Air-braked cycle ergometers are ex-tensively used in training and in sports-science research for various athletic dis-ciplines in New Zealand, eg. ice racers,skiers, cricketers and triathletes. At pre-sent it is difficult to compare perform-ance data from one athlete using thesame assessment exercise programme ondifferent ergometers as the various insti-tutions have not had the means to checkthe accuracy of their equipment. It wasseen that a common means of calibratingergometers accurately would facilitatecoordination of sport-science supportservices nationally.

The Physical Education Departmentat the University of Canterbury has anumber of exercise machines, includinga cycle ergometer, which may be usedfor training and for experimental studiesof human physical performance, and tomeasure physiological response tograded exercise. The Repco HP5209Air-Braked Cycle Ergometer contains abuilt-in power meter of limited

accuracy, and it was decided to designand build an accurate calibration systemfor this machine to enable indicated in-stantaneous power readings from the er-gometer to be converted to true readings.

This project aimed to provide a port-

able system that would allowsports-science researchers in various lo-cations to calibrate their air-braked cycleergometers, thus establishing a commonstandard throughout the country. A sec-ondary aim was to provide a rig whichcould be evaluated as a speed-controlledsystem for load application and measur-ing for incorporation into athletic train-ing machines.

The calibration system now commis-sioned is portable and can be used bysports scientists throughout New Zea-land. This will allow comparison of per-formances of the same athlete tested ondifferent ergometers in the future.

The operation of the equipment isbased on precision measurement of thetorque and speed of a geared electricmotor that drives the pedal shaft of theergometer. This paper describes thebackground to the project, details of the

design, and calibration test results forthe Repco ergometer.

2. CONCEPTUAL DESIGN2.1 Cycle ergometry - background

The cycle ergometer is one of themost commonly used devices in exercisetesting and, depending on the level ofinstrumentation, can measure torque ap-plied at the pedals, instantaneous humanpower output, or energy expended over atest programme by integration of poweroutput with time. Cycle ergometers are

available at relatively low cost and insome configurations offer precise andaccurate control of the load (1). Thepresent project focuses on an air-brakedergometer which allows steady speedmeasurement of the rider's power input.The calibration rig developed could,however, be used to calibrate an un-braked inertial flywheel ergometer suchas described by Kyle and Mastropaolo(2)

The quality of the power meters onthese machines is often unsatisfactoryfor laboratory research work. Lack ofrepeatability over time means that fre-quent calibration checks are required(3). Telford (4) claims that authorsshould describe the calibration system oftheir ergometers with the same care theydescribe the calibration procedures ofthe gas-analysis equipment. Cummingand Alexander (5) state that ergometers

p.4 Human Power, spring-summer 1994, vol. 11/2

DESIGN AND PERFORMANCE OF ADYNAMIC CALIBRATION RIG FOR A

BICYCLE ERGOMETERby

J.K. Raine, H.P. Trolove & H. Beveridge

1z, O

1

0.8

0.6

1 0.4

0.2

n10-1 00 101 102

DURATION OF POWER OUTPUT - MINUTES

Fiouro I MHuman nnwpr nutnut for various durations

_

............... .. : :.:...........: .:.. , . , . , .:.:....i

), el- " "~-r-J' " --'J"I - -

the load button of the Bongshinstrain-gauge load cell. An oil-filleddashpot is fitted between the motormounting plate and the underframe toreduce any vibratory influence on thebehaviour of the load cell. The load cellamplifier circuit also includes a low-passfilter to smooth the torque indicationwhich is read at the instrument panel.All fabricated metal components areblack painted or powder coated for cor-rosion protection.

To calibrate the torque-measuringload cell a counterbalanced calibrationarm is attached to the underframe of theelectric drive motor and loaded withdead weights to check span and linearityof the torque reading. This is shown

rigged for calibration in Figure 5. Theweight hanger has a knife-edge supporton the calibration arm.

3.4 Drive shaft and connection toergometer

The geared motor output shaft is con-nected by means of rubber-booted Fen-ner universal joints and an intermediateshaft to the coupling to the centre of thepedal crank shaft. This coupling pro-vides concentric alignment, while atorque bracket which attaches to onepedal crank transmits the drive torque(See Figure 6). The drive-shaft overalllength across the universal couplings isapproximately 400 mm and is run closeto truly aligned to minimise any forces

internal to the drive train caused by off-set of the universal joints.

It was later found that, while the cali-bration drive system experienced mini-mal vibration from misalignment, theergometer itself tended to become un-steady and rock at high pedal cadences.To handle this some deadweights havebeen designed to anchor the back feet ofthe ergometer to the floor.

3.5 UnderframeThe black-powder-coated hol-

low-section-steel framework sits onlockable threaded height adjusters whichare used to align the driveshaft betweencalibration rig and the ergometer. Thefeet of these adjusters have rubber capsto offer quiet and secure standing on thefloor.

3.6 Test procedure and dataprocessing

After a warm-up period of, say 10minutes, a typical test will involve driv-ing the ergometer or exercise machine ata series of constant speeds throughout itsspeed range in each gear, and measuringthe torque at each speed. From themeasured data a calibration curve ofpower versus speed can be plotted forthe given machine in its configuration astested. This curve can be used to correctthe indicated power on the machine'sown power meter. This may be done byeither(i) using polynomial regression to fitcurves through the calibration testpoints, so that the true power may thenbe calculated at each speed for each gearratio; or(ii) creating a look-up table which is

used to read off power at any speedin any gear.

In both cases the calculation ofpower is easily done in a personal com-puter which may also be used for record-ing and processing data from test runs.The PC will also be used to log data ofphysiological importance such as atmos-pheric pressure, ambient temperatureand humidity.

At any instant during a motoring test,power is calculated using the formulaPower (W) = torque (Nm) x speed(rev/min)

9.5493

p.8 Human Power vol. 11/2, spring-summer, 1994

TABLE 1INDICATED AND TRUE POWER vs PEDAL CADENCE

(atmoshperic pressure 757.45 mm Hg; temperature 20 C)

1st Gear Torque Power 4th Gear Torque Power(6.078:1) (7.038:1)Cadence Nm W Cadence Nm Wrev/min rev/min

37.5 7.8 30.6 37.0 8.0 31.061.4 12.7 81.7 69.5 18.4 134.079.5 18.0 150.0 88.4 28.6 265.091.7 22.9 220.0 101.2 36.9 391.0

115.3 32.8 396.0 118.7 49.0 609.0124.4 38.2 498.0 142.2 71.8 1070.0141.4 49.1 727.0 154.0 87.9 1420.0154.7 60.2 975.0168.8 65.0 1150.0 5th Gear Torque Power

(7.866:1)2nd Gear Torque Power Cadence Nm W(6.367:1) rev/minCadence Nm Wrev/min 19.3 5.6 11.3

44.3 12.7 58.935.5 6.6 24.5 68.3 21.0 150.275.2 17.0 134.0 87.9 32.7 301.099.0 26.9 279.0 99.4 42.8 446.0

115.1 34.6 417.0 114.9 57.5 692.0137.3 49.5 712.0 127.8 75.6 1010.0163.2 67.3 1150.0 141.0 94.9 1400.0181.7 87.2 1660.0

6th Gear Torque Power(10.286:1)

3rd Gear Torque Power Cadence Nm W(6.686:1) rev/minCadence Nm Wrev/min 21.7 8.5 19.3

47.8 25.7 129.042.3 8.2 36.3 64.6 44.0 298.077.7 20.6 168.0 80.5 70.2 592.0100.1 33.3 349.0 92.3 92.1 890.0137.6 59.5 857.0 100.3 104.7 1100.0153.4 72.3 1160.0 109.8 131.2 1510.0173.7 93.0 1690.0

__ _ _

4. ERGOMETER CALIBRATIONTEST RESULTS

The system was first calibrated fortorque and speed measurement, then runat various speeds against the Repco cy-cle ergometer in each gear to establishthe corresponding power curves. Re-corded indicated and true power data areshown in table 1, and true power isgraphed against pedal cadence in figure7. The aerodynamic drag of the Repcobrake wheel does not fully load the mo-tor at lower cadences, so there is drivecapacity in hand for an ergometer withmore demanding power characteristics.Polynomial regression analysis was car-ried out on the test data to produce apolynomial expression for the powercurve in each gear. These are shown intable 2. Further tests will be carried outduring working trials to experimentwith the various power and control con-figurations of the electronic elec-tric-motor drive.

The power relates strongly to N3 athigher speeds, while showing some lin-ear proportionality to N at low speeds.This is reasonable to expect, since trans-mission friction will be a significantcomponent of the absorbed power at lowspeed.

Ambient-temperature and atmos-pheric-pressure variation will affect theperformance of the ergometer, the air

density affecting the aerodynamic dragof the machine, and temperature affect-ing transmission efficiency. It would beconvenient to pre-determine a perform-ance map of the type in figure 8 over arange of atmospheric temperatures andpressures, so that by interpolation an ap-propriate look-up table or set of regres-sion formulae can be referred to underany given test conditions.

With the precision of the presentload cell giving a torque read-out accu-racy of +/-0.6%, and pedal-crankshaftspeed being readable to +/-0.1 rev/min,overall system accuracy at a pedallingcadence of 100 rev/min'is estimated tobe +/-0.7%. This would improve to+/-0.4% if a high-resolution load cellwith +/-0.25% accuracy were fitted.Four or five significant figures havebeen retained for the power calculationpolynomial regression formulae in Ta-ble 2, but results of these calculationsshould always be rounded to recognisethe limits on system accuracy. Calcu-lated power figures in Table I have

TABLE 2POLYNOMIAL-REGRESSION FORMULAE FOR

DYNAMIC CALIBRATION CURVES IN THE VARIOUS GEARS

Human Power, spring-summer 1994, vol.11/2, p.9

I

a 9 a A o s 8 ° 8 8 5 F a R §

Atmospheric pressure 757.45 mm Hg; temperature 20 KFigure 7 True power output vs pedal cadence

Calibration Curves for Cycle ErgometerLeast-Squares Regression has been applied

P, (N) =0.1851 x10'NS'-1.1188x10-'N2-0.2013N+4.0798ON<170RPM

First Gear ratio = 6.078

P2(N)=0.3351 x104N'-1.8117x10

~2N 2,

1.2955N-4.0352

0xN180RPM

Second Gear ratio = 6.367

P(N) =0.31 70x1 0-SNS-0.1 427x1 0-2N2

+0.4021 N-0.6745OsN170RPM

Third Gear ratio =6.686

P4(N) =0.5204x10-SN'-3.1762x10-2N2

1.6681 N-3.3902OsNs16ORPM

Fourth Gear ratio = 7.038

P( N) =O.770x10-3N-5.5689x10-2N

22.3626N-6.3383

OsN14ORPM

Fifth Gear ratio = 7.866

P,(N) = 1.2876x10-N-2.6888x 10 -2N2

+ 1.0471 N- 1.2606OiNs110RPM

Sixth Gear ratio= 10.286

I

therefore been rounded to three signifi-cant figures.

5. CONCLUSIONThe ergometer calibration rig which

has been developed should be a usefuladdition to the equipment available forsports-science research at the Universityof Canterbury, and is sufficiently port-able to enable it to be easily transportedto other laboratories in the country.

It is the intention of the PhysicalEducation Department to mount a fur-ther project to develop a computer pro-gram with computation or look-up tableto convert indicated readings to truepower. Once the data-handling systemis fully developed the rig should providea versatile dynamic calibration facility.Ultimately, implementation of a pro-grammed torque-versus-time input to theelectric motor would provide a usefulmeans of evaluating the effect of riderinduced pedal crankshaft speed varia-tions on the mean power consumption ofbicycle ergometers.

The rig design and fully built-up sys-tems are available to other persons, whoshould contact the first author.

6. ACKNOWLEDGEMENTSThe authors gratefully acknowledge

the financial support provided for thisproject through the New Zealand SportsScience and Technology Board and theHillary Commission.

7. REFERENCES1. Smodlaka, V.N. Treadmill vs Bicy-cle Ergometer, in Mellerowicz, H.Smodlaka, V.N. (eds): Ergometry. Ba-sics of Medical Exercise Testing. Balti-more - Munchen. Urban andSchwarzenburg, pp 385-392, 1981.2. Kyle, C.R., and Mastropaolo, J.Predicting racing bicyclist performanceusing the unbraked flywheel method ofbicycle ergometry. Proceedings of thenternational Congress of Physical Ac-

tivity Sciences, Quebec City. Canada,July 1976.3. Wilmore, J.H., Constable, S.H.,Stanforth, P.R., Buono, M.J., Tsae,Y.W., Rody Jr F.B., Lopden, B.J., Rat-liff, R.A. Mechanical and physiologicalcalibration of four cycle ergometers.Medicine and Science in Sports and Ex-ercise 14: 322-325, 1983.4. Telford, R.D. Calibration and com-parison of air-braked and mechanically-braked bicycle ergometers. Australian

Journal of Sports Medicine: 12(2):40-47, 1980.5. Cumming, G.R. & Alexander, W.D.The calibration of bicycle ergometers.Canadian Journal of Physiology andPharmacology. 46: 917-919, 1968.6. Kyle, Chester R. and Caiozzo, Vin-cent J. Experiments in Human Ergome-try. Proceedings of 'the 1st InternationalScientific Symposium on Human-Powered Vehicles, Anaheim, California,USA, 1981.7. Brooks, A.N. Some observations onthe energy consumption of human pow-ered vehicles. Proceedings of the 1stInternational Scientific Symposium onHuman-Powered Vehicles, Anaheim,California, USA, 1981.8. Whitt, F.R. A note on the estimationof energy expenditure of sporting cy-clists. Ergonomics, 14, No.3: 419-424.9. Whitt, F.R. and Wilson, D.G. Bicy-cling Science. The MIT Press, Cam-bridge Massachusetts, 2nd Edition,1982.10. Hull, M.L. and Davis R.R. Meas-urement of pedal loading in bicycling: I.Instrumentation. Journal of Biomechan-ics, 14, No.12, 843-856, 198111. Hull, M.L. and Davis R.R. Meas-urement of pedal loading in bicycling:II. Analysis and Results. Journal ofBionzechanics, 14, No. 12, 857-872, 1981

J. K. Raine, BE (Hons), PhD, CEng.University of Canterbury, Christchurch,New Zealand

John Raine teaches mechanical-engineering design and management atthe University of 'Canterbuly at whatwould be the professor level in the U.S.He worked extensively in the U.K en-gine and vehicle test-plant industry andis active in research into alternative en-ergy resources in transport.

Ilamish Trolove has recently com-pleted an M.E. on solar-poweredStirling engines supervised by JohnRaine and is now employed in industry.Hamish is a keen cyclist and orienteer.

Hugh Beveridge completed his B.E.in 1992 and now works in the NewZealantd public service.

LetterACCUMULATOR DEBATE

This response is to the letter of Wil-liam J. Moriarty (HP, vol. 11/1) com-menting on the human-energyaccumulator debate. Mr. Moriarty isable to convey a great many attitudesand assumptions with a minimum ofwords. His advice for resolving the is-sues, based on his authority as an engi-neer and a rule maker, is to do nothinguntil accumulators are built and havedemonstrated their merit. The IHPVAwould then, he confidently reassures us,revise its rules.

I assume that he would have givensimilar reassurances to Charles Mochet,who in 1932 built an aerodynamicallysuperior recumbent bicycle that provedto be meritorious in the extreme, only tohave it later declared a non-bicycle andplaced indefinitely in its own irrelevantrecord category by the UCI. Mr. Mo-chet is still waiting patiently, beneath aField of Dreams, for a rule revision. Ofcourse, the present circumstances aredifferent. The UCI did not originallyprohibit recumbents, whereas the IH-PVA already prohibits accumulatorsfrom its record categories, thus makingit even more difficult to demonstratemerit in the first place.

Consider how ridiculous it wouldhave been if the IHPVA had bannedstreamlined bodies from record competi-tions until after they proved their merit.The whole point of the IHPVA is to pro-vide a context in which HPV innova-tions can prove their merit. CertainlyMr. Moriarty would not exclude newtypes of transmissions, brakes, or sus-pensions from IHPVA record competi-tions until after they had independentlyproved their merit. That would be ab-surd. But that is exactly what he recom-mends, since accumulators are newtypes of transmissions, brakes, and sus-pensions. So why does he treat accumu-lators differently? And why does hethink his advice is neutral, even gener-ous, when it is so clearly discriminatory?

Apparently, he still believes the"energy-storage myth": that a "real" or"pure" HPV does not store energy, so anaccumulator is inherently less legitimatethan other devices, and it therefore doesnot deserve equality of opportunitywithin the IHPVA. Obviously, I rejectthat myth, and I have explained my posi-tion in detail.

( 'ontinued oil p. 13

p.10 Human Power, spring-summer 1994, vol. 11/2

THE LINK BETWEEN STABILITYAND PERFORMANCE

byAndreas Fuchs

In the HPV-world, the basic law is'power output of rider equals the sum of11l resistive forces multiplied by the;peed and divided by the transmissionefficiency". Since power output is lim-ted and since the transmission efficiencys given by the state of the technical art,from this law one readily concludes thatn order to maximize speed, the coeffi-:ient of drag Cd, the frontal area A of theiehicle, the mass m and the coefficientAf rolling resistance Cr all have to beminimal. However, you may find, afterhaving built your dream machine (forexample with two wheels for minimumrag) while riding the vehicle into theirst comer and while falling over - thathere might be some hidden secrets... Of:ourse there are: the "Power law" wasvritten for zero angle of attack (the angle)etween the main axis of the vehicle andhe relative wind, which in turn is thevector sum of the mirrored vehicle,round speed and the wind speed) andzero angle of slip (the angle between theirection of travel and the wheel mainlane) and therefore does not explainverything.

If it is your main goal to build vehi-cles for maximum-speed attempts, then)f course you do not mind corners and:he power law in its form for in-linenovement applies. But if you want toise a faired vehicle in velodrome racesor for daily commuting, preferably thatvehicle handles well and has good over-ill performance on a course with a lot oforners (even if it might not be the fast-

est on straights).

Cornering stabilityThe ratio of the aerodynamic forces

:o the weight of faired bikes is largerthan that for cars because the bodies ofthe faired and much lighter bikes aremore streamlined than those of cars.Therefore one could believe that it mustLe lift (perpendicular to the lifting sur-Face, which in turn is vertically in the:ase of a symmetrical fairing) that dis-turbs the path of an HPV. But if a steady-state turn is analyzed, it is found that thevertical component of lift is usuallysmall compared with the weight on either

wheel and that thecornering velocityis reduced onlyslightly comparedwith the higher ve-locity that could beachieved without a

fairing (in a lean, a component of theweight counteracts the centrifugal forceas well as a component of the lift. Inpresence of lift, that is, with a fairing, inorder that the forces balance, the leanangle has to be bigger than without lift.But the lean angle is limited due to themaximum adhesive friction of the wheelson the ground, and therefore the corner-ing velocity without a lift-producing fair-ing can be higher). Are there any otherreasons for the sometimes sudden fallingover of faired single-track HPVs? Yes...maybe the faired HPV experiences a stallsimilar to that of a stalling aircraft: thelift vanishes while the drag increases(due to flow separation).

Stalling aircraft have to dive to gainthe speed that is needed to reestablishthe airflow around the wings. Bikes can--- + Ai- train _-]k _+U-4- nrtzie

they fall. Rough calculationsshow that increasing drag due toseparation of the flow consumesa lot of kinetic energy. This thendrops and the leaning vehiclecan not return to the higheststate of potential energy: thevertical position. In more tech-nical words: to have predictablebehaviour of your vehicle (es-sential if you ride it in densetraffic!) at angles of attack dif-ferent from zero degrees, that isif the relative wind is transverseto the longitudinal axis of yourvehicle, drag has to be minimal.Good handling is associated withthe Cd being small over a broadrange of angles of attack (andnot only at zero degrees).

Roughly, from the point ofview of the aerodynamicist, theexisting velomobiles (Europeanexpression for HPVs) can be di-vided into two categories: thefm-like and the airship-like. Themain difference between thesetwo forms lies in the height-to- Figuwidth ratio. This ratio is higher fore

In th,for fin-like designs than forairship-like designs. For this rea- origison transverse airflow is less dis- locitturbed on airship-like forms (the biggo

Cd of a flat plate is much higher thanthat of a cylinder at 90 degrees to the air-flow). If airship shapes are chosen forfairings, the increase of the drag with theangle of attack will be less severe thanfor fin shapes. Therefore, to fair practicalvehicles, you will prefer round, airship-like forms over sharp, fin-like forms. Formere speed-record vehicles, both formsare feasible. If you are optimizing yourminimal-drag-machine (with a givenfrontal area) and if you can decrease theheight - do it.

Stability and performanceThe fastest vehicle will be the one

that suffers from the least accumulateddrag along its path. Therefore it is first ofall essential that the vehicle travels asstraight as possible - to minimize thelength of the path and thus the timeneeded to travel it - and second that thevehicle's wobbling is minimal because ora fairing the drag increases with the an-gle of attack and on wheels the rollingresistance increases with the slip angle.This is now the point where we have to

re I Typical three-wheeler: the laterales acting on the wheels and on the fijiring.e case shown the vehicle will return to itsnal path of movement (direction of the ve-y) because the wheels produce a torqueer than the torque due to lift (T > T2).

Human Power, spring-summer 1994, vol.11/2, p.11l1 -

,

Bill! IV -lJmI 111111 ·- ImlIl~.Wli. r

build a great racing velomobile, the Cut-;ing Edge (Ref. 4). On difficult trackswith a lot of corners Cutting Edge out-)aced Gold Rush, which for sure hasproven to perform well on straights!

Is that all (?), you may ask. No! Theconcept of static stability allows us tocompare vehicles and to find the rela-:ionships among the parameters and thehandling characteristics. Ref. 2 showshow to calculate the parameters that de-:ermine stability or instability. Even ifthe simple means of calculating the posi-tion of the CP presented there are not ab-solutely precise, interesting insight canbe reached when comparing differentvehicles for which the behaviour in sidewinds or wind gusts is known frompractice.

Roll stabilityHere the most interesting question is

whether or not it is possible to constructa faired single-track vehicle that handleswell even in gusty crosswinds. From ex-erience is known that multitrack vehi-

cles are easy to handle over a wide rangeof wind speeds, but that in heavy windfaired bikes can be ridden only by expe-rienced riders or sometimes even not atill. If your vehicle is to be a commuter,:hen you are interested in how much;pace on the street is needed in order toavoid collisions with cars (while oscillat-ing from left to right and vice versa incase of a single-track vehicle). Formulti-track vehicles, the width of thestripe needed is given by the width of thevehicle, because they do not oscillatemuch.For bikes, the maximum width is thelouble of the sum of the amplitude of theFront-wheel path and of the lean at thelimit of adhesive friction and of the halfwidth of the vehicle itself. Therefore itis found that under the worst windy con-litions, a bike needs much more spaceon the street than a tricycle or a quadri-cycle. In a calm a bike requires lessroom, which usually is an advantagewhen overtaking cars in a total trafficstandstill. The roll-oscillation of bikes isdriven by gravity (the contact point ofthe front wheel is moved from one sideof the main plane to the other side andgravity acting on the CG accelerates thebike from left to right and to the leftagain...). One could therefore consider abike as being an inverted pendulum. Itsoscillation-period then is proportional tothe square root of the height of the center

of gravity (Ref. 5 and 6) and this periodis a measure for how long it takes for abike - due to roll-yaw coupling - tochange its direction of travel slightly.In a gusty wind, a bike needs to changethe direction of travel very often in orderto stay on only one lane of the street. It istherefore concluded that the roll-oscillation period and hence the height ofthe CG need to be as small as possiblefor good handling in windy situations.So the construction of a faired bike thathandles well in gusty cross winds (in 99percent of all situations) seems to be pos-sible: its CG-height has to be as low aspossible. Probably such bikes would evenbe quite safe in traffic. But when I askpeople why they have not changed fromnormal bikes to recumbents, they mostoften say "Well, I feel better when I havea good overview about what happens onthe street"...

Final remarksOf course some statements made

above need more proof before they couldbecome accepted truth. For example thehypothesis that flow separation makesfaired bicycles tip over should bechecked in wind-tunnel experiments.Faired vehicles are often similar to formsthat have been studied in wind tunnels,and that is why some statements abovemay be quite correct, but these vehiclesand the tested forms are always not ex-actly identical. For precise statements weneed more specific experimental data.

ReferencesO. Price, Robert. Human-powered vehiclesteering and suspension design. HumanPower Vol. 7 No. 3, 1989.1. Buelk, Eggert. Aerodynamik an HPV-Fahrzeugen. Series of articles starting inPro Velo No. 31, 1992.2. Fuchs, Andreas. Towards the under-standing of (dynamic) stability of velo-mobiles: The forces, their distributionsand associated torques. The Proceedingsof the First European Seminar on Velo-mobile Design, held July 8 1993 at theTechnical University of Denmark. ISBN87-984875-0-7. Publisher: Dansk CyklistForbund, Roemersgade 7, DK-1362 Co-penhagen K, Denmark,Fax +45-33-32-76-83.3. Milliken, Doug. Stability? or Control?.Human Power Vol. 7 No.3, 1989.4. Weaver, Matt. The Cutting Edgestreamlined bicycle. Cycling Science,Sept/Dec 1991.

5. Drela, Mark. Letter to the SonomaHPV Mailing list, January 1993.6. Burrows, Mike. Riding high, ridinglow. Bike Culture No. 1, December1993. Bike Culture Quarterly, OpenRoad Ltd, 4 New Street, York, Y01 2RA,UK.

The author thanks D.G. Wilson for com-menting on and editing the article.

Andreas Fuchs, Neufeldstrasse 129,CH-3012 Bern, Switzerland(Member of the IHPVA and of FutureBike CH).

ANDREAS FUCHS is doing a PhD-studyof the physics of the past climate and istherefore analyzing air trapped in polarice cores. For Future Bike's periodicalINFOBULL he reviews (scientific) arti-cles about HPVs. Additionally he ispromoting the faired tricycle Leitra.

Letter from Peter Sharp

Continuedfrom p. I0

The burden is on Mr. Moriarty to jus-tify why he is opposed to treating accu-mulators equally, within the constraints Ihave recommended.

Mr. Moriarty's advice is also back-wards. Instead of using records as incen-tives for developing accumulators, hewants to use meritorious accumulators asincentives for changing the record rules.To make progress, one holds the carrotahead of the donkey, not the donkeyahead of the carrot. The history of theIHPVA demonstrates that his advice hasalready had 20 years of no progress.

This is not an academic debate. If webelieve that accumulators can improveHPVs, and that advanced HPVs are ur-gently needed as global short-distancealternatives to the automobile, then wemust act. My understanding is that wemay have that opportunity.Peter A. Sharp2786 Bellaire PlaceOakland, CA 94601

Human Power vol. 11/2, spring-summer, 1994, p.13

Ten years ago, when outsiders askedme why I got involved with HPVs, I be-:ame long-winded. Today, I simplyanswer:

"18 kJ for transporting 1 person over1 km bicycle,

2,160 kJ for transporting 1 personover 1 km by car."

As the IHPVA prepares to celebrateits 20th anniversary, it seems fair to takestock of tangible HP-commuting results.The same picture prevails in most indus-trial countries. As soon as we leave theerudite circle of practical HPV adepts,what do we find but the roar of fossil-powered-displacement battles filling ourstreets? Hardly any HPVs are in regularuse. Are they acquiring the same reputa-ion as motorbikes, namely that of pureleisure machines? Is it sane to load ourHPVs on cars before taking them for aspin?

We must not close our eyes to thepossibility that present-day HPVs are notis practical, streetwise, as we would wishthem to be. In most countries, tax lawslip the act of HP-commuting in the bud,;ince while car kilometers are tax de-luctible, muscular kilometers rarely are.Political innovations are long overdue,)ut perhaps our HPVs are unsuited forthe challenges of traffic and climate.rrue, HP-record achievements have beenutstanding. We must give high-speed

)rotagonists credit for their help in)reaking down ideological barriers. But;urely, our daily salvation cannot lie in:

105 km/h = 65 mph human-powered-record vehicles,'

105 km/h = 65 mph wasteful, fossil-powered cars

)ut rather in machines evolving some-vhere in between, capable of bringinghe two into harmony.

How close to petrol - how closeto people?

Why should the IHPVA shun assistedIPVs (AHPVs) of the bridled type? By'bridle" is meant "power-limited," so thatnotors are used solely as adjuncts to hu-nan power. Thus, they will be restrainedfrom evolving into the behemoths on mo-orcycles. Bridling is discussed in moreletail later in this article. In 1987, weaccepted solar energy enough to keep*ecords of genuine solar-car achieve-

Inents. In 1993, board members wereI

asked to debate the addition to our com-petition rules of:· further energy forms derived from the

environment* human-powered energy accumulators

Today, our 200-m speed grapes arehanging so high that wordsmithing soph-istry alone will allow specialists to climbthe speed ladder further. It is time tolook for the speedway exit named "Prac-ticality." Beside huge expendituresneeded for the next speed-recordincrement, 2 ) who can afford lawyers toward off ensuing strife?

This is why I sympathize with themembers who have asked our associationto take AHPVs more seriously. Thereare immense energy savings dormant,provided the assist is somehow keyed toour legwork, for example, if:* assist is geared so low that it can be

used for climbing only (as dem-onstrated convincingly in 1991by John Tetz (3 ))

* assist is spread, but available onlybeyond and in addition to hu-man power input in accordancewith the No Potatoes - No Des-sert principle.

* etc., etc., (the reader's creativity issolicited)

Where could the auxiliary pushcome from?

Cold-pressed plant oils may be devel-oped. Solar-produced hydrogen may bea distant goal. Yet, such substitutes aregenerations away. Since time is runningout, we must make astute use of existingsources now. Electric drive is one op-tion. Apart from liquid fuels, anotherreadily available alternative seems to benatural gas in compressed form (CNH).It is clean and relatively cheap (billionsworth are lost every day into the atmos-phere). Micro-diesels could be renderedclean also, but their mass and bad start-ing habits militate against them. Stirlingengines are too bulky and complex forour niche.

a) Battery-powered electrical assistBased on my 1986 entry in the Swiss

Tour de Sol of a battery-buffered solarHPV, I am inclined to delay giving elec-tricity a serious chance, because of pre-vailing battery problems. Weight anddeep-cycling characteristics in a tough

p.14 Human Power, spring-summer 1994, vol. 11/2

climate are anathema to lightness andreliability.

Contrary to popular belief, hybrid bi-cycles with battery assist are not a newinvention. In Europe, electrically as-sisted tandems appeared as early as 1895in competitions.'4' Since then, dozens ofcommercially available electric bicycleshave been launched, only to disappearagain. Initial owner pride suffered be-cause of tough pushing after battery fail-ure, or the hard search for chargingopportunities, or frequent battery-replacement costs. Interestingly enough,almost a hundred years later, the Japa-nese motorcycle giant Yamaha'5s optedfor batteries to power its 1993 P.A.S. hy-brid bicycle. It possibly did not have asmall enough, de-toxed, 2-stroke engineready for adaptation. Motor manage-ment may also have played a role in fa-vor of electric drive. Anyhow, Yamahaplans to sell 10,000 P.A.S. units in 1994and 100,000 in 1995 to its domestic mar-ket alone. Market feedback will tellwhether the electric option meets com-muter aspirations.

Basically, energy savings are possi-ble, thanks to high-efficiency motors andelectronic controls. However, even formodest operating ranges (say 15 - 30 km= 10 - 20 miles per charge), the cumula-tive mass of motor + control box + bat-tery + charging unit is critical in anultralight design. Once the long-awaitedjump in accumulator technology materi-alizes, electric drive will spread.

b) Hydrocarbons burned in I.C.micro-engines

Here, small 2-stroke engines, as con-ceived for portable implements, may beused. They are of simple design andhave a good power-to-weight ratio.However, they do pollute and small en-gine makers are aware the California AirResources Board (ARB), might extendstiff limits(6 ) on their products. Controlof the most minute fuel injection-quantities and -times will decide whetherthese make the grade.

FMS of Switzerland7 ) has developed2-stroke motor management, typicallyapplicable to spark-ignited micro-enginesbetween 20 - 80 c.c. Their metering de-vice, i.e., injectors plus catalytic convert-ers, represent a logic system with softand hardware, capable of de-toxing mosttwo-strokers. Since metering and fine-dispersing require high pressures, itwould seem advantageous to start withpressurized energy in the first place.Thus, the injection part becomes simpler,lighter, and cheaper.

BRIDLED ASSISTED HPVs,UNBRIDLED CHANCES

byPeter Ernst

L ---------------------

the rocking-piston patent,'8 ) proposes fur-ther savings in weight through reductionof moving parts. As shown in figure 1,the mushroom-shaped piston is of a piecewith the connecting rod. Hence, its cyl-inder liner is waisted in the middle. Theinventor reckons that it should soon bepossible to build high performance, ultra-light 10 c.c. assist engines, weighingLtank inclusive) around 1.5 kg (3.3 lb).

It is instructive to note that world-wide, large sums are invested to lift two-strokers into the league of compact, light,but clean-running engines, also suitableFor hybrid powered cars, using I.C. en-gines for charging batteries.

Assist-source comparisonsIf one cares to look back, a rough

trend emerges. As can be inferred fromtable I and figure 2, assisted two-wheelers seem to converge toward a totalvehicle mass of:

approx. 30 kg (66 lb) for battery-assisted bicycles

possibly 10 kg (22 lb) for fuel-assisted bicycles

The latter would guarantee handiness ineveryday use and ease of parking andstorage. Such solutions imply high-techmaterials, which are acceptable if theoverall energy balance is backed by lon-gevity and recyclability.

Most of the listed examples do notexceed 500-watt nominal assist power,with correspondingly modest speed andinsurance levels: hence, no driver's li-censes are required! The next higherclass are heavy models, mobylettes, andmopeds, whose tiny pedals are never-used adornments, i.e., they are not

0)

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r4-)

crankshaft counterweightFigure 1 The rocking piston, the basisof several Salzmann patents

AHPVs, since constant use of the 900(legal) watt = 1.2 hp limit is made.

I am very concerned about the psy-chological profile of the average mobil-ity consumer, perhaps comparable to thatof a TV-watcher behind a bag of saltedpeanuts. Hard as it may sound, I am forcompulsory bridling devices, especiallyfor the young two-wheel fans in their for-mative years.

Free will, versus tutelageWhen I earlier suggested that leg

power be augmented, I was met with op-position, "Do not patronize mature citi-zens!" Yet, appeals to common sense area dead end. In traffic, man copies elec-tricity and will always follow the path ofleast resistance. Hence, a "bridle orbust" tamperproof link is perhaps not soodd. Have no fear, such links do nothave to be complicated. Fuzzy logicmight, for example, probe the tension onthe drive chain via a spring-loaded idlersprocket, which acts on engine output(throttle control or chopper amplitude).'

Clearly, if our AHPVs grant humanpower its right of way, we shall enjoy:· better health, via cardiovascular

exercise· lower vehicle mass (rider's too,

ultimately)Indeed, hyperlight vehicles are possible,if one limits fairings, etc., as shown infigure 3. Climate control is warrantedvia enforced hp-metabolism. Semi-fairings also meet the exigencies of hotclimates, where ample air exchange anda modicum of roof shelter are a must. Itis unrealistic to think of adding activeair-conditioning devices to closed vehi-cles intended to be moved chiefly by ourown anatomy.

First production of "bridle"control, 1993

Apart from their choice of assist en-ergy, Yamaha must be given due credit

for the world's first production APHV,having a bridled assist control, without a'hand gas' grip. In 1993 a thousand unitswere built to conduct national markettests. Typically, an electronic motormanagement senses the load of the ped-als, plus the vehicle speed. If there is nohuman base load, there is no assist. Ifthere is, the control unit releases auxil-iary push "in proportion to pedal load" upto 15 km/h (4.2 m/s). Beyond that, up to24 km/h (6.7 m/s) the released push willbe decreased gradually.

Figure 4 confirms that the assist isabout equal to the "do-it-yourself' contri-bution. The electric motor is of a DC-brush type and has a nominal output of235 watts. That means that, for climbinghills, combined tractive power is about 2x 235 = 470 watts.

Figure 5 shows that the assist iswisely meted out when most needed,namely during ascents, rides into thewind, or for load-carrying. Beyond 25km/h (16 mph = 7 m/s), the assist quits.The brightest fitness news in Yamaha'sdocumentation reads:

"The bike never runs on motor poweralone..."

What a hope-inspiring acknowledg-ment by one of the world's leading mo-bility providers, in stark contrast tohyper-mobility exhortations made by gi-ant car makers.(9 ) Yamaha reckons witha 20 km (12 m) operating range per bat-tery charge.

The shape of future APHVsKnowledge gained during 20 years of

practical HPV-building might (eco-)logically also recognize meritorious ef-forts such as Yamaha's P.A.S. upright.

Not speed, but user comfort, energyrequirements, and environmental effectswill thereby improve. To stay legallywithin the bicycle category, maximumassist speed might be pegged at 25 - 30km/h (16 -19 mph). National legislation

Human Power vol. 11/2, spring-summer 1994, p.15

Table 1 ONE CENTURY OF HARDWARE DIETING

a) battery assisted cycles kg b) fuel assisted cycles. kg

1895 DUTRIEU stayer tandem (B) 97 1899 WERNER cyclomoteur (F) 511961 GARELLI elettro bici.(I) 39 1947 HONDA 49 cc mobike (J) 321976 HERCULES el. Zweirad (D) 35 1950 LOHMANN Diesel Zweir(D) 291982 SINCLAIR C-5 el.trike(GB) 45 1956 PARILLA Parillino bi(I) 271983 PANDORA el. bicycle (GB) 38 1964 GARELLI Mosquito bic(I) 241984 GEIGER Elfa el.Zweir.(CH) 33 1967 BSA Ariel-3 trike (GB) 321988 BINDER-Matic el.Zweir.(D) 30 1976 MX-3 SUPERBIKE bicyc(K) 191991 VELOCITY-Cann.el.MTB (CH) 28 1984 F+S Saxonette KATzwr(D) 261993 YAMAHA P.A.S.bicycle (J) 31 1991 TETZ Lightning HPV (USA) 15

1995 SALZMANN 10 cc Velo(CH) 12

Such a device was patented by Henri Rosen of Boston for his "Goped" AHPV - editor

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o battery assisted bicycles_ a fuel assisted bicycles

night have to be adapted to allow low-ower assist (on both two- and three-vheelers) to take advantage of cycle)aths.

Since APHVs purport to replace com-nuting cars, they should also make sec-ind (regular) bicycles superfluous. Thessist might come as a removable powerPack to reconvert APHVs quickly to{PVs for flat flings. With an electrichive, this is difficult. This would beLuite possible though with fuel assist, ifhe tank is pack-integrated and smallerhan 500 c.c. ('/2 liter = 1 pint).

Aren't grandmas and grandpas poten-ial AHPV users? They are little inclinedo recharge batteries, nor to clip on/take>ff engines. For them, evolution ispelled:

I I [ I I

ed 17 cyclesilly selectedast 50 years

CD

battery :Q.

VS. m

'90 2000TIME ( YEARS) -

OFTEN = daily/nightly, electricrecharge...

SOMETIMES = weekly/monthly, fillingof tank...

NEVER EVER = yearly replenishing bydealer, during maintenance, se-curity check

Indeed, synergetics occur if the tankis a frame-member, as in fig. 3. Recum-bents can easily take a central tube of 2m(6'6") length by 72mm (2.84") diameter,to hold some 8 liters (about 2 US gal =1-3/4 imp. gallons) lasting for 1 year, i.e.,for about 8000 km, or 5000 miles, basedon conservatively estimated 1000km/liter, or 2350 mpg (US), or 2820 mpg(imp.), thanks to a modest assist portionof 10% only!

If CNG is used, the equivalent energymay be stored under pressure of a few

Figure 3 Partial weather protection - e.g. semi-fairing "45° apron"

dozen bars in a filament-wound tube, re-fillable yearly by bike-shop personnel(AHPV users won't buy via dept.store/mail order). A further CNG spin-off is an appreciable simplification of theinjection metering system (because it ispressure-fed) while emission standardsare more easily reached. Such AHPVswill be energy misers. Displacements of10 - 20 c.c. will suffice to deliver the oc-casional peak approaching 440 watt, or0.6 hp. De-toxing cures by FMS, (7 ) ap-plied to German 2-stroke chainsaw en-gines, confirm that typical consumptionsof 260 - 300 g/kwh are possible with in-novative motor management. The firstfigure would correspond to a high-techmetering system, the latter to a cheaperinjection version, both coping with grow-ing environmental demands.

I visualize the ideal AHPV of theyear 2000 to be a 1+1 seat three-wheelerhaving the banking characteristics of abicycle. Hence, the two independentlysprung rear wheels must provide suspen-sion and roll freedom, i.e., I imagine thefront wheel to be steered and driven. My2000 x 750 mm (6'6" x 2'6") vehiclewould be only scantily faired by an aero-dynamic, close-fitting "45' apron."Shopping loads, up to two beveragecrates, would be accommodated. Thebottom bracket is to be adjustable, whilethe seat will be the part of load-bearingstructure, with a child-seat attachable toits back-face, etc., etc ...

In short, if advanced AHPVs cannotbe bought soon at the friendly cycle shoparound the corner, IHPVA members musheed Mike Burrows' °° ) advice, "Goodmachines need building, not talking." Toget into gear, are we passively waitingfor Far-Eastern mailers to offer cheap,de-toxed, two-strokers, or possibly evendo-it-yourself AHPV-building kits?

We can do better. As a first step, Iinvite those HP-readers with a sharpsense of things to come to write in andsuggest a typical AHPV testing cycle and-circuit, with length, profile, speeds, etc.Indeed, only exact consumption andemission figures will allow us to com-pare energy balances of emergingAHPVs. Hardware suggestions areequally welcome in our discussion. Let'spush-start them!

This does not betray our credo, butwill draw the IHPVA away from pro-tected circuits and will bring it closer toeveryday road users. Without support ofthe latter, we and our eocsphere arebound to back the oars.

p.16, Human Power, spring-summer 1994, vol. 11/2

0

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Figure 2 Trends of decreasing vehicle mass

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as a function of speed _

Figure 5 Power ratio (assisted/human power) as a

Peter ErnstAlex. Moser Str. 15CH-2503 Biel-BienneSwitzerland

References(1)du Pont de Nemours prize of $18,000UIS, won May 11, 1986 by Fred Mark-ham (Easy Racer team of Gardner Mar-tin, USA) at 65.48 mph = 105.36 km/h =29/27 m/s over 200 m(2) At least 5% faster than current world

speed record of 68.73 = 110.59 km/h =30.72 m/s, held by Chris Huber (Chee-tah team, USA), dated Sept. 22, 1992

(3) John Tetz, IHPVA member7B Mark LaneSuccasunna, NJ 07876 USAtel. (201) 584-6481describing his experience with a con-verted Lightning recumbent HPV + 21c.c. McCulloch engine in HPV Newsissue Nr 8/2 1991 and 8/5 1991 (alsosee his paper in the Fourth IHPVAScientific Symposium).

(4) Helena and Eugene Dutrieu of Bel-gium. Successful world-class pacerracers of the last century (soon realiz-ing that it is deadly to perform behind

fuming pacemaking ma-chines). Source: W.Gronen, Geschichte desRad Sportes, Edit. FuchDruck Verlag, Hausham,Germany

(5) Yamaha Motor Co.,Ltd.2500 Shingai, IwataShizuika 438 Japantel. 81-538-32-1145fax 81-538-37-4250

(6) Air-pollution laws bythe State of California,handled by the CalifornianAir Resources Board(ARB)P.O. Box 28151102 Q StreetSacramento, CA 95812USAtel. (916) 445-4383ATSS 8-485-4383in particular, title 13, re-lating to miscellaneousengines(7)Inventor + patentholder: B. Frey, Ing. ETH,partner in:Fuel Management Sys-tems, FMS Fuel Manage-ment Systems, Inc.Eschenhof

529 N. MorrisAve.Mundelein, IL 60060US tel. (708)

566-8820CH-4512 BellachSwitzerlandtel. 65-38-1797, tel. 77-31-6037fax 65-38-3663(8) Rocking piston and further I.C.engine patents by:W.E. SalzmannDipl. Eng. ETH, MSIA, MSAESchoenegg 7, CH-6300 ZugSwitzerland, tel. 42-22-2235

(9) Mercedes-Benz board member Dr.Rudolf H6rnig, in Der Spiegel, weeklymagazine, Hamburg, Nr 25, 1987,"We can hardly be expected to makeour cars artificially slower."(10)Mike Burrows, hon. chairman +press sec., British Human Power ClubBurrows Engineering16 Thunder Lane, Thorpe, Norfolk,England; tels. 0603-72-1357 (wk),0603-3-2142 (hm)British activist, prolific designer,builder, rider of: Windcheetahs/otherHPVs/UCI-approved competitionmachines.

Peter Ernst is a mechanical engineer,a past IHP VA board member, co-bunderand first president of Future-Bike (Swit-zerland); team chief and designer of theworld's only three-wheeled lightweightsolar-powered grand piano competing inthe Tour de Sol, now in the Christchurch,UK, museum for three-wheelers.

Review1993 HPV SYMPOSIUM

Technical University of EindhovenIt is always humbling to realise that

whereas I find the production of HumanPower in my own language an enormoustask, my fellow editors in Europe andmany other places in the world publishdual proceedings, one in the local lan-guage and one in English. Thus I amhappy to be able to review the prelimi-nary proceedings in English of the HPVSymposium held at the Technical Uni-versity of Eindhoven on March 18, 1993(W.S.V. Simon Stevin, Eindhoven, TheNetherlands).

The proceedings consist of someshort introductory pieces, three main pa-pers, and a catalog of HPVs available oron display. One introductory piece de-scribed how three mechanical-engineering students tried out a FWDFlevobike while on vacation and subse-quently campaigned to have the con-struction of Flevobikes as the principalactivity of a new course. Thereby hasenthusiasm for HPVs grown atEindhoven.

The first of the main papers is a re-peat of a 1978 publication by Chet Kyle:"Predicting HPV performance using er-gometry and aerodynamic-drag measure-ments". It has a footnote indicating thatChet would bring it up to date in hispresentation. I presume that the updatedversion will be seen in the final proceed-ings. In any event, it is full of usefuldata and correlations.

"Muscle involvement in cycling: canwe get more efficient?" is the title of thesecond paper, by Gerrit Jan van IngenSchenau, who is on the faculty of theuniversity of Amsterdam. This is a paperthat starts with the fundamentals ofmusle energy supply and action and de-duces that the peak metabolic efficiencycan get to around 30%. Bicycle pedalingproduces 23-24% which is therefore,states the author, close to the theoreticalmaximum. Therefore we camnot expectto do much better.

( Continued on p. 21

Human Power, spring-summer 1994, vol.11/2, p.17

as a function of time

Figure 4 Power ratiofunction of time.

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Supplementary powerdecraases

Manpower I -Supplementarypower up to I

firnction of speed

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( p ( k0

landlebars and swing arm pivot oneedle-roller bearings running on slightly,versize inners. For the steering pulleys I[sed a hard aluminium alloy (obtained inLseful offcuts from a local scrapyard).

iingesThe folding bike's main hinge is in

he middle at the bottom, just ahead ofhe seat, and takes the form of a skewedube with threaded end plugs brazed in.lolts passing into these plugs secure twoPrecisely fitting end caps which are partof the back section of the bike. An ex-Pander bolt can be screwed through aush to spring the back section apart.

qext time I might slant the hinge the)ther way, avoiding the acute angle athe left end of the tube and bringing theront of the bike to the chain side of theack when it is folded.

Two pairs of conical couplings aretsed at the top joint, which is com-)ressed by the rider's weight. The han-Ilebars fold inwards onto the seat, andhe back of the seat folds rearwards usingt hinge which also allows useful adjust-nent of the angle for riding, using a strutvith some carefully placed holes.

Dn the roadI finished the folding two-wheeler in

rune 1993, and clocked just over 1600kma thousand miles) by the autumn (whenhe mileometer failed during heavy rainn France). Much of this distance was:overed while carrying camping gear.[Heavier items like a cooking stove were,towed between the wheels, and itemsneeding easy access behind the seat. A-olled-up tent was carried under one sidef the seat, and a sleeping mat on the

)ther side, projecting backwards to over-lap the rear wheel.)

Overall I am pleased with the ma-chine, and while there are a few things Iwould change, I do not have any plans tomake a substantially different two-wheeler. Personally however I doubtthat any 2-wheeled recumbent can beideal for heavy touring, and with this inmind I have recently started building afolding 3-wheeler.

DimensionsWheelbaseOverall LengthFolded Size

1190 mm 47"1700 mm 67"610x330x860 mm

24"x13"x34", approx.Weight 15 kg 331b.(with rear fairing, dynamo, mudguards)Gears 18 speed; 25" to 101"Wheels 500A rims from

Pashley, Michelin tyresFolding Time about 10 minutes, with

out fairing

Nick Abercrombie AndrewsDepartment of ComputingUniversity of BradfordWest Yorkshire, U.K.Email N.Andrews@bradford.ac.uk

Nick Andrews is at present a PhD studentresearching into parsing methods fornatural languages. Before returning touniversity he manufactured Bikeasypanniers.

Letter

Regarding "Assault on the hour" inHPV News, Dec. 93, Tim Leier threwout the rolling-resistance part of hisequations to obtain a simple closed-formsolution, his rationale being "rolling resistance becomes relatively minor athigher speeds". This is true for un-streamlined bicycles but not at all truefor a super streamliner. Using his figuresfor a streamlined and a regular bike ofCd 0.10 and 0.85, and frontal area of 0.4and 1.0 m2, we get a power consumed at90 km/h of 376W and 8 kW. The rollingresistance is 85 W for each, which is al-most 25% of the streamliner's power butonly about 1% of the huge power re-quired by the regular rider.

The message is that when you loweraero and other drag, the rolling drag isquite important!

Doug Malewicki, 14962 Merced Circle,Irvine CA 92714, USA

Review, cont. from p. 171993 HPV SYMPOSIUM

Technical University of Eindhoven

I am sure that HPV designers wouldregard this range as huge: an increase inmuscle efficiency from 23% to 24%would yield an increase in output of over4%, enough to make a huge difference ina race or speed contest.

There are some interesting graphsshowing the efficiency and oxygen con-sumption for various sports. Cross-country skiing seems to be top in bothcategories. "The more muscles, the morejoy" is how the author recommends weshould design transmission interfaces infuture.

The third major paper was missingthe first page in the preliminary copy Ireceived, but the general topic was gov-ernment bicycle and HPV policies.

The last part of the proceedings con-sists of 27 full-page descriptions and il-lustrations of various HPVs, showing therange of creativity we have come to ex-pect in Europe. They are from TheNetherlands, Germany, Denmark, Britainand Belgium, and about half are tricyclesand half bicycles. Each entry has usefulinformation in a standard format, includ-ing the price. There's no doubt that thebest place to try out HPVs is a sympo-sium or a race-meet; having these stan-dard data made the proceedings all themore useful.

The address given to order the vol-ume isstudieveriging "Simon Stevin"W-Hoog 1.07A, Postbus 5135600 MB Eindhoven, The NetherlandsPh. 31-40-473-313; fax 31-40-437-175

The third major paper was missingthe first page in the preliminary copy Ireceived, but the general topic was gov-ernment bicycle and HPV policies.

The last part of the proceedings con-sists of 27 full-page descriptions and il-lustrations of various HPVs, showing therange of creativity we have come to ex-pect in Europe. They are from TheNetherlands, Germany, Denmark, Britairand Belgium, and about half are tricycle:and half bicycles. Each entry has usefulinformation in a standard format, includ-ing the price. There's no doubt that thebest place to try out HPVs is a sympo-sium or a race-meet; having these stan-dard data made the proceedings all themore useful.

The address given to order the vol-ume isstudieveriging "Simon Stevin"W-Hoog 1.07A, Postbus 5135600 MB Eindhoven, The NetherlandsPh. 31-40-473-313; fax 31-40-437-175

Dave Wilso

Human Power vol. 11/2, spring-summer, 1994, p.21I

l

very fast, and the rider's center of gravityis so close to the front wheel.

The Rotator has the front wheel be-hind the captain's pedals. This short-wheelbase option is a natural choice for arecumbent tandem, because the extralength for he second rider places thecenter of gravity farther toward the back,and slows the steering.

However, the Rotator also has the rearwheel tucked in under the stoker, andthis may be a factor in its most seriousdifficulty, its slow-speed handling.

If you have ever ridden a bicycle witha very large, heavy package on your rearrack, you have some idea of how the Ro-tator feels to the captain. If you haveever ridden on the rear rack of a bicycle(I will assume no responsibility...), youhave some idea how it feels to be thestoker.

The Rotator's wheelbase is only about54 inches, shorter than that of a conven-tional tandem or solo long-wheelbaserecumbent. The stoker's mass is almostdirectly over the rear wheel, and contrib-utes almost nothing to the quick balancecorrections achieved by steering motionsof the front wheel. Larger steering mo-tions are necessary to maintain balance atlow speeds than with any other bicycle Ihave ridden. The Rotator develops apronounced, and fast, weave -- about twocycles per second -- which can be verydisconcerting to the stoker and hard tocontrol for the captain.

The recumbent rider position exacer-bates these handling difficulties for tworeasons I can think of: the riders arelower, making the bike fall over faster(like the difference between trying tobalance a yardstick and a foot ruler onthe end of your finger); and the riderscan not shift their upper bodies sidewaysto adjust balance as on an upright bike.Solo recumbents, however, remain pre-dictable and easy to steer despite thesedifferences.

When I asked Delaire about the Rota-tor's handling, he indicated that a recum-bent tandem handles better with the frontwheel farther forward. The first proto-type of the Rotator tandem has its frontwheel directly under the captain, withdirect steering from under-the-seat han-dlebars. According to Delaire, this pro-totype is even more difficult to steer thenthe current Rotator: "like a unicycle,"

because the captain is right over the frontwheel. He also indicates that he has ex-perimented extensively with steering ge-ometry, and changes in fork rake canmake the Rotator's steering lighter orheavier but that the slow-speed weave ismore-or-less "in the nature of the beast."

The problem is that the front wheelcan not be directly under the crankset; ifmoved far enough forward to clear thecrankset, the tandem has "tiller steering"and a 97-inch wheelbase. Delaire hasactually built a tandem this way andfinds it OK to ride, at least at high speed.

Controlling the Rotator does becomeless difficult with experience. The han-dling might also become more controlla-ble with a rear wheel farther behind thestoker position. With a wheelbase onlyas long as that of a conventional tandem,the stoker's mass would shift farther side-ways with steering motions, and theywould more quickly correct balance.

I rode the' Rotator in both the captain'sand stoker's position, with my friendSheldon Brown and with my wife.

Since a herniated spinal disc made ituncomfortable for her to ride an uprightbicycle, my wife Elisse has put in over30,000 miles on her Tour Easy solo re-cumbent. The recumbent riding positionin and of itself holds no terrors for her.Nor does riding on the back of a tandem.My wife once tried riding on the back ofmy upright tandem. We kept going ahalf-mile, until her back pain stopped us.She did not feel uneasy or nervous.

The Rotator was another story. BothSheldon and my wife felt insecure in thestoker's position, as though we wereabout to fall over. In the captain's posi-tion, I felt that we were not, and thatcontrol would improve if we just gainedsome speed; but that's not how my stok-ers felt.

Elisse also had a problem with theheight of the seat. She is used to theTour Easy, which lets her comfortablyput both feet on the ground when startingand stopping. The Rotator's seats mustbe high for the riders to clear the wheels.It is necessary to slide back into the seatwhen starting and forward out of it whenstopping. I was used to this, from myexperience with a Counterpoint Prestosolo recumbent, but my wife was not.

Delaire indicates that design modifi-cations to compact the front fork as much

as possible have lowered the stoker's sad-dle by two inches in newer versions.

The Rotator reminds me of a goose,very clumsy in takeoffs and landing butgraceful once in flight. However, I knowthat Delaire is confident to ride hillydouble centuries on the Rotator with hiswife -- and the low bottom gears indicatethat they expect to be climbing at lowspeeds. Clearly, experience plays a bigpart in feeling confident on this bike.

The Rotator is equipped with a Ma-gura hydraulic caliper brake on the frontwheel and an unidentified motorcycle-type disk brake on the rear wheel. Brak-ing is powerful and easily controlled.The usual rule that a tandem needs threebrakes can be broken here because therear disk brake is powerful enough toserve also as a stopping brake.

The rear seat is attached with quick-release clamps which allow an almostinstant adjustment for different stoker leglengths. The captain's position is adjust-able by a telescoping boom holding thefront crankset, as on Counterpointrecumbents.

Certain details could use refinement.A kickstand is appropriate, and useful, ason any long recumbent. But with severalfeet of bottom tube, there is no need toposition the kickstand right behind thecrankset, as on a conventional bike.If you roll the bike backwards with thekickstand down, the crank will run into itand probably damage it. The stoker'sthumbshifter levers are inside the seatrails where they are difficult to operate.

The bike uses a hodgepodge of im-ported metric and U.S. inch-size fittings,making it necessary to carry more tools.This is not the builder's fault but ratherthat of our political process which leavesus as one of two nations in the world (theother is Liberia) which has not adoptedthe metric system. One easily-remediedreason that the U.S. has trouble compet-ing in world markets. But I digress.

John Allen, 7 University Park, Waltham,MA 02154, USA; ph. 617-891-9307

John Allen is an MIT graduate, authorof bicycling books, expanded antd revisedGlenn's New Complete Bicycle Manualand co-edited the revised Sutherland'sHtandbookfo/r Bicvcle Mechanics:efjective-cvcling instructor.

Human Power, vol. 11/2, spring-summer, 1994, p. 23l

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