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Human PowerThe technical journal of the
International Human-Powered VehicleAssociation
David Gordon Wilson, editor21 Winthrop Street
Winchester, MA 01890-2851, USAPhones: 617-729-2203 (home)
617-253-5121 (MIT)617-258-6149 (FAX)
Associate editorsToshio Kataoka, Japan
1-7-2-818 Hiranomiya-MachiHirano-ku, Osaka-shi, Japan 547
Theodor Schmidt, EuropeHoheweg 23
CH-3626 HunibachSwitzerland
Philip Thiel, watercraft4720 7th Avenue, NE
Seattle, WA 98105, USAIHPVA
P.O. Box 51255Indianapolis, IN 46251, USA
Phone: 317-876-9478Qfficers
Marti Daily, president andexecutive director
Adam Englund, secretaryBruce Rosenstiel, treasurer
Paul MacCready, int'l presidentDoug Milliken, VP water
Glen Cole, VP landChris Roper, VP air
Matteo Martignoni, VP ATVTheodor Schmidt, VP hybrid power
Board membersAllan AbbottMarti DailyPeter Ernst
Dave KennedyChet Kyle
Gardner MartinGaylord HillDennis Taves
David Gordon Wilson
Human Power is published quarter-ly by the International Human-PoweredVehicle Assoc., Inc., a nonprofit orga-nization devoted to the study and appli-cation of human muscular potential topropel craft through the air, in and onthe water and on land. Membershipinformation is available by sending aself-addressed stamped business-sizedenvelope to the IHPVA address above.
Additional copies of Human Powermay be purchased by members for$3.50 each, and by nonmembers for$5.00 each.
Material in Human Power is copy-righted by the IHPVA. Unless copy-righted also by the author(s), completearticles or representative excerpts maybe published elsewhere if full credit tothe author(s) and the IHPVA is promi-nently given.
We are indebted to the authors, toMarti Daily and to Carolyn Stitson,whose dedicated help made this issuepossible. Dave Wilson
EditorialsAn historic battle
You may be blissfully unaware of it,but a battle that concerns us all is ragingaround us in learned circles. It concernsthe originator(s) of the pedalled bicycle.We usually give a nod towards Kirkpa-trick Macmillan, a Scots blacksmith,who seems to have made the world'sfirst pedalled bicycle in around 1841 -but we have to rely on second- or third-party accounts that are either vague orconflicting or both. It doesn't matter toomuch, because he had virtually no effecton the world. Apparently he didn'twrite, and he shied away from publicity.
The position of the Michaux familyseemed, on the other hand, assured. His-torians have told us that they developedthe front-wheel-pedalled bicycle in1861, and that they were showmen andbusinessmen and started a craze thatlasted for the rest of the century. I seethat I wrote (in American Scientist, July-August 1986) ". . credit for the bicycl-ing revolution belongs indisputably toPierre Michaux and his son Ernest and toa controversial employee-turned-competitor, Pierre Lallement."
Now I am an amateur, not a profes-sional, historian. I rely nowadays on thewritings of a very professional amateur,Derek Roberts, founder of the SouthernVeteran-Cycle Club in the UK. When Istarted adding historical notes to mywritings I was not as careful in mychoice of people to quote. I was gentlytaken to task by Derek Roberts over thehistorical section I wrote for BicyclingScience. He has the reputation of a cur-mudgeon, and at the time I agreed withthat perjorative label. But increasinglyhe has become one of my heroes. His-torical accuracy seems trivial until onetries to understand why an inventor didwhat s/he did, or until one becomes avictim oneself.
I found myself becoming curmud-geonly when, for instance, someonemade a presentation of recent develop-ments in some aspect of human powerand used, without attribution, data andgraphs produced by my students and my-self as if they were his own. I decided toswallow my pride and to keep quiet - butsince then people have used his paper asthe fundamental reference, and my stu-dents have gotten no credit. Once a"history" has been written, it is taken astruth by others, and the falsehoodspropagate like crab grass. Derek Rob-erts calls them "myths", and he has writ-ten a book about them. He also writes a
correction sheet for each new book thatrepeats any bicycling myths
Derek Roberts still believes that theoriginal invention of the so-called"French bicycle" in the 1860s was thework of Pierre and Ernest Michaux. Hehas translated a book from the Frenchabout the family. But another bicyclehistorian I respect, David Herlihy, be-lieves that Pierre Lallement was the in-ventor, and that he was shafted by theMichaux family, who were very good atself-promotion. It turns out again thatthere was nothing written by the Mi-chaux until decades after the supposedinvention, and no patent, whereas Lalle-ment did take out a (US) patent.
You may not be excited to delirium- I am - by this battle of the champions.I mention it, of course, as a sermon.Please make truth and accuracy and ac-knowledgment of the work of othersyour holy grail when you write for anypublication, especially Human Power.So far, you have bestowed an unsulliedreputation on the journal.
Upturn in the economyOrders for recumbents have sharply
increased lately. The reason can betraced to marital love. Vic Sussman, awriter for, among other publications,Newsweek, had given up conventionalbicycling because of the pain he suf-fered. He happened to try out a RyanVanguard, took home Dick Ryan's videoabout it, and "watched it, fantasizing,twice a week ". Eventually his wifebought him a Ryan, and he has beencrazy about recumbents ever since. Hisability to channel his enthusiasm into atwo-page spread in a national newsmagazine has produced a small but verywelcome blip in the economy of several
struggling recumbent-bicycle manufac-turers. His piece could also encouragestirrings in designers of regular bikes.We are grateful for Vic's wife's lovingconcern for her spouse.
HP OlympicsWhen Chet Kyle and Jack Lambie
organized the first International Human-Powered Speed Championships in 1975(they formed the IHPVA a year later)there was one event: the 200-m flying-start speed trial. This year Chet broughtthe IHPSC back to California - to thebeautiful area of Yreka in near Mt. Shas-ta. He and his small band of mainly lo-cal non-IHPVA members put on a tourde force. We now have so many
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(Continued from p. 2)different events that a prodigious effortis demanded of the volunteers. Are thedemands too heavy? Our new president,Marti Daily, and the board of directorsare asking for your views on the futuredirection of the IHPVA. Some (see thenext editorial) believe that the diversityof interests is becoming so great that weare losing our focus. When Ellen and Ireturned to our motel room each eveningwe would watch a little of the Olympics,and we were struck by the similaritieswith the modern IHPSC. There weresports that we had never heard of pre-viously (e.g. rhythmic gymnastics) thatnevertheless attracted enthusiastic audi-ences. The commentators were suffi-ciently skillful and knowledgeable thatwe could find ourselves rooting for someunknowns. Perhaps the IHPSC shoulduse the Olympics as a model. Weshould set a limit to the duration and thenumber of events, and admit and dropevents using a criterion of popularity orof worth.
Vigorous debate bycorrespondence
When Rob Price sent his manuscripton "what is and what is not a HPV, andwhy" I reviewed it and wrote to him thatI would love to publish it in HP, eventhough I did not agree with all his opin-ions. I thought that he would raise thehackles of a few people. I was certainlyright! His article stimulated more corre-spondence than HP has ever had on onesubject. Some of the letters were a littlemore vitriolic than I would have liked.We are publishing all except one some-what incoherent letter, although we havehad to shorten some. Rob Price is a su-perb engineer and author, as we haveseen from his earlier contributions, andhis views are always thought-provokingand insightful. He has sent along a"side-bar" to his response to the corre-spondence that I hope I have room forin this issue. It is on the subject of theIHPVA's diversity. Rob, as usual, is un-orthodox: he believes that the ICU wasright to ban recumbent bicycles fromcompetition so that it could concentrateon athletic contests rather than engineer-ing. The IHPVA must face some limitsto its scope eventually. Read andponder!
Dave Wilson
Letters to the editorCompliments andsuggestions
I am pleased with the consistentquality of the publication Human Power.The authors have written technical yetvery readable articles and the generallayout looks professional. Vol.9 nos.3-4are no exception. I especially enjoyed"Modelling energy consumption on theTricanter HPV" by John Raine and Mau-rice Amor. Their work suggests somemethods to try for testing rolling re-sistance (a problem I have been trying tosolve), and shows the detail of their de-sign process. Great publication!Mark E. Mueller, 1161 I St. #6, Arcata,
CA 95521-5558; 707-822-4771
HP is looking good! Great articles,interesting letters, and I fully agree withthe editorial comments on internationalcooperation. John Allen's article "Insearch of the massless flywheel" wasfascinating and thought-provoking. Itprompts me to recommend anothermethod for minimizing the dreadeddeadspot.
Add a pair of arm cranks. My re-cumbent trike, designed by Gary Hale ofEugene, OR, has substantially smootherpower output with arms cranking. Theweight penalty is about 5 kg, 10 lbm.The two pairs of cranks are offset about90 so that the hands don't hit the knees.I discovered that the standard reciprocat-ing crank arrangement caused noticeablezig-zagging, wasting energy and wearingout tires. This problem was solved byputting the cranks in unison. The actionis somewhat like rowing with a slidingseat. Acceleration is tremendous andsustained speed is 10-15% greater thanwith reciprocating cranks. The tech-nique takes a little practice. .. but theeffort is well repaid. .. While touring,the arms really save my knees on thehills, sharing the load. The arms may bea flywheel to dampen the dead spot andenhance the power stroke.
Larry Warnberg, P.O. B. 43, Nahcotta,WA 98637.
The Flevo FWDPlease allow me to add my further
observations on the Flevo bike as re-ported in Mike Eliasohn's article onFWD recumbents in HP 91/9/2 p. 14.
Unlike other FWD's swivel mounts,the Flevo's steering employs the princi-ple of flap-banking. A dislocated mid-frame joint serves the dual purpose ofproducing lateral sway to the front wheeland at the same time, maintaining therigidity necessary to utilize it as a drivewheel. As can be seen in Johan's dia-gram, the mid-section free swivel is re-strained by a spindle-shaped PVCgrommet producing an ingenious, butcrude. self-centerin, device.
Mastering the Flevo bike requires agreat deal of practice, patience and self-confidence. It took me almost fifteenhours and ten falls over a period of threeweeks before I could counter the rodeo-effects of its steering mechanism andalmost a year before I weaned from handto leg steering. The constant new dis-coveries of slalom turns and leg steersmake this one of the most interestingand challenging recumbents I haveridden.
Li Hock Hung, 9 East Coast Avenue,Singapore 1545, ph.. 4453838
fax. 2205714
What is an HPV?(All the following letters are commentson Rob Price's article in the last issue ofHP)
I find Rob Price's article "What isand What is Not a Human -Powered Ve-hicle and Why" in Human Power 9/3and 9/4 generally thoughtful and well-considered: but in describing canoeing,he gets in a bit over his head in the wa-ter; and in describing Nordic skiing, hegoes into a snowbank.
Price describes canoeing as follows:"The paddler dips one end of the oarthen paddles a few strokes on one side ofthe boat while providing a fulcrum forthe paddle end with the other hand.The paddle then changes hands so theaction is moved to the opposite arm forthe next series of power strokes. In thisway power is balanced on both sides ofthe boat and both arms, and the boat
P.R 4 Human Power, Spring-Summer, Vol. 10/1
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goes in a fairly straight line atop thewater."
This describes a single-ended paddle(not "oar") technique used by rank nov-ices. Experienced canoeists propelthemselves forward primarily bystraightening up into a sitting positionout of a forward crouch while rotatingthe upper body from the waist, bringingthe powerful muscles of the trunk intoplay. The arms are held relatively rigidand nearly fully extended; neither handis used as a fulcrum.
The experienced canoeist does notchange sides to steer when using asingle-ended paddle, as the paddle isused to steer at the end of every stroke.The common technique (the "J stroke")uses the paddle as a rudder, but a moreefficient technique is to pull down on thehandgrip at the upper end of the paddle,using the gunwale at this time as a ful-crum to lever the paddle's blade awayfrom the boat. I learned this techniquefrom my grandfather, who learned itfrom the Algonquins.
The paddle is capable of a wide vari-ety of specialized forward and reversesweep strokes, push-off and pull-instrokes and sculling strokes. Thoughsomewhat less efficient for forwardpropulsion than oars, the paddle is farmore versatile; for this reason, and be-cause the paddler faces forward, paddlesare always used in white water and othersituations requiring tricky maneuvering.
In the light of these facts, I am aston-ished by Mr. Price's disqualification ofthe canoe and kayak as human-poweredvehicles on grounds that they lack animpedance-matching device. If he werecorrect, our language would lack the col-orful saying "up the creek without apaddle;" bare hands would do nearly aswell.
The paddle transforms impedance byincreasing the sweep of the arms, and byimproved connection to the waterthrough its large blade. A wide range ofimpedances may be selected not only bythe choice of a paddle but by varyinghand positions and strokes. One validconceptual difference between paddledand rowed boats is that the paddle lacksa constant fulcrum or point of supporton the vehicle -- but the paddle is none-theless an impedance-transforming de-vice: so, if a rowboat is a hand-crankedhuman-powered vehicle according to
Mr. Price's criteria, then so is a canoe orkayak!
As to skiing: not all Nordic skis havea "fishscale-shaped or stepped bottomsurface construction." Instead, many usespecial waxes which have high stickingfriction against snow, but very low slid-ing friction. Even waxed skis are capa-ble of climbing grades several timessteeper than the 0.5% which Mr. Pricecites. Ski waxes are an interesting topicfor human-power research even if thismay not qualify as human-powered ve-hicle research.
The parallel-ski technique which Mr.Price describes has largely been re-placed, at least in competition on packedsnow, by a faster version of the "herring-bone" or "skating" technique previouslyused only for uphill propulsion. Tosome degree, this development reflectschanges in the Nordic skis themselves,including the adoption of composite ma-terials, steel edges and improvedbindings.
Note that this technique involves animpedance transformation of a slow dropin the skier's center of gravity and slowsideways motion of the leg into fast for-ward motion of the skier. There is alsoan inherent acceleration to couplingspeed, as each stroke propels the bodytoward the opposite leg by action/reac-tion. An important impedance trans-formation also occurs through the skipoles, with a short downthrust becominga longer backthrust.
Therefore I do not agree that Nordicskis disqualify as a human-powered ve-hicle on grounds that they lack an im-pedance transformation. Should theydisqualify on grounds that they attach tothe feet like shoes? The same questionapplies to ice skates, roller skates andin-line skates, whose means of attach-ment and propulsion are similar. Iwould opt for the broadest definition ongrounds of consistency, recalling that theIHPVA was forced into existence sometwenty years ago by the InternationalCycling Union's restrictive definition of"bicycle." While the IHPVA's approachproduces true innovation, the ICU's ruleslead only to evolutionary monsters, up-right bicycles with aerodynamic partswhich pretend not to be in order to beatthe rules.
Price comments about Nordic skibraking that "Basket brake force may beincreased by placing the poles betweenthe legs and using the seat area as a
fulcrum, a favorite of men contemplat-ing castration. As with Alpine skis, thequickest way to stop is to fall over."
Perhaps YOU go into the snowbank,Mr. Price, but these gratuitous com-ments do not contribute to an under-standing of the sport, and do not reflectthe grace of the sport as practiced bytrained athletes. I am sure that the U.S.Consumer Product Safety Commissionwould have devised an equally gratu-itous safety regulation for ski poles, as ithas for bicycles, if a Nordic castrationepidemic had been demonstrated in themedical literature.
The discussion of skiing raises a seri-ous question, however: IHPVA mem-bers' research has led to radical advancesin land and water speed records - and tohuman-powered aircraft, an entirely newcategory of vehicle. Can we expect tosee similar radical developments inhuman-powered travel over snow?
John S. Allen, 7 University Park,Waltham, MA 02154-1523
(617) 891-9307
I have intended for some time tosubscribe to the IHPVA ... I enjoyedyour review of my paper on high-speedAleut kayak design (HP 9/2: 10) and oth-er items passed to me by your memberLarry Warnberg. .. Now I have just re-ceived a copy of Rob Price's piece on (inpart) why kayaks should not be consid-ered human-powered vehicles. Withoutaddressing his argument (you can inferthe details) I am now sending in our $20for membership and a subscription, tolend this little bit more weight to the op-posing view. Lending more weight, Iexpect, will be the current work of...William S. Laughlin on the Aleut hyper-trophic humerus.... The Aleut kayakincorporated impedance-matching tech-nique and technology on several levels,perhaps not as immediately visible to anuntrained eye as the gears on a ten-speedbicycle, but nonetheless effective inmaking the most of human power forlong-distance work.
George Dyson, Baidarka Historical Soc.P.O. Box 5454, Bellingham, WA
98227-5454
In the 1991-2 Fall and Winter issueof Human Power, Rob Price attempts todefine a human-powered vehicle ("WhatIs And What Is Not A Human-PoweredVehicle And Why"). The critical
Human Power, Spring-Summer, Vol. 10/1, P. 5
I found Rob Price's article ... inter-esting and useful. However, it is clearthat Price has a number of misconcep-tions about canoes and kayaks.
Canoes are paddles with single-bladepaddles (not 'oars'), but directional con-trol comes not from switching sides, butthrough the use of strokes such as theJ-stroke, which provides both forwardthrust and steering action. With the ex-ception of marathon racers, anyone whocontrols a canoe by switching needs tolearn to paddle. Any book on canoeingmakes this clear.
The kayak, as suggested by the edito-rial note, was devised for use in the Arc-tic. The various Inuit groups developedboats and paddles to suit their localneeds. Their boats were used on theopen sea, and they, like modern-day sea-kayakers, often travelled considerabledistances, in sometimes stormy condi-tions. Very different from the 'runningwater .. directional control. . fending offobstructions' that Price describes.
As for impedance matching, thechoices are limited, but more than real-ized by Price. Change of hand positionis used by some paddlers, but paddlelength, and to a lesser extent blade area,are used to match boat speed to paddlecadence and paddler's power. To taketwo examples, paddles used in white-water and sea touring differ quite mark-edly. In white-water the speed is rela-tively low, but acceleration andmaneuverability are important, and thepaddle is relatively short. A sea kayak isfaster and travels at more or less con-stant speed (about 1.5 m/s) and the
IREENS.PIEED GSP 2 as
paddle is long, 2350 mm being common.Matching the paddle to the boat and pad-dler is important. Just as too high a gearon a bicycle can lead to knee problems,so can the wrong paddle result in wristinjuries. Again, [these] are well ex-plained in the literature, and familiar tothose involved. (I might point out that Iam an Australian Canoe Federation se-nior instructor and a part-time builder ofsea kayaks).
Canoes and kayaks are definitely ve-hicles and certainly human powered. Isuspect that they are closer to beingHPVs than Price believes.
On another subject, I ride a vehiclethat is definitely an HPV: an Australian-made Greenspeed GTR 20-26. It ismade in Melbourne by Ian Sims (69Mountain Gate Drive, Ferntree Gully,Victoria 3156, Australia). Enclosed is abrochure ('1 send this on to ,S'telve l)es.Jardins fir the new .Soure (;ide - ed)and an illustration I drew for a localcycle-club newsletter.Peter.1. ('arter. 28 Rowe/lts Road. Iock-levs. South Australia 5032. (08)43-4298
Rob Price chooses to define HPVs bythe quality of their "impedance-matching" and denies many vehiclestheir HPV status on this basis. I think heis looking at it too mechanically, as weare never concerned with just a vehicle,but rather with a vehicle-person combi-nation. The human body achieves a fan-tastic range of impedance-matching allby itself, being able to sprint at up to 10m/s, yet also climb vertically. Evenwhen using simple devices like skates,skis, and paddled boats, people canmaintain this degree of adaptability andoften even extend the range. A goodkayaker or canoeist can paddle efficient-ly at low or high speeds at various load-ings imposed, for example, by theweather. Different strokes and grips helpand "impedance-matching" is actuallybetter than with boats using propellerswith fixed pitch and fixed gearing, evenif these have a higher peak propulsiveefficiency. The reason paddling seemslike such hard work to untrained personsis that most people have fairly weakarms which tire quickly just holdingup the paddle whereas most have legsstrong enough to support their bodies forhours each day.
In a similar manner nordic-skiers canachieve fairly high speeds on the level(and of course downhill) yet instantlyadapt to steep gradients or poor snow. Ifail to see an intrinsic difference be-tween this sort of impedance-matchingand that done with pedals and gears.
The other point is that except to peo-ple establishing racing categories or bu-reaucrats looking for things to ban ortax, it makes very little difference whatwe define as an HPV or not. In the IHP-VA we are also concerned with humanpower in a wider context, e.g. for de-vices such as hand-drills, lawnmowers,pumps or generators. Even in this age ofelectric toothbrushes and pencil-sharpeners, good hand-tools are far fromobsolete and well-designed ones are of-ten more useful than many poweredones.
7lheo Schmidt (assoc. editor, Europe.)
I am rather disturbed by Rob Price'sarticle... I am not an engineer or de-signer of any kind, but I am a skier, skat-er and cyclist. As such, many of Mr.Price's statements trike me as wrong.
Some of this "wrongness" seems tocome from a simple lack of research. Itis known, for example, that although theside cut of a ski helps to initiate the ski'sturn, a turn at speed is achieved primari-ly by the ski's flex during the turn. Inthe extreme, one can see this by carvinga turn with a track-style cross-countryski (one with no side cut). Discussionsof how a ski carves a turn is rather com-mon in the popular skiing magazines.Similarly, when Mr. Price talks aboutcross-country technique, he mentionsonly diagonal stride techniques, not skat-ing techniques (very important in thecurrent racing scene), he fails to mentionthe use of wax (rather than steps or fishscales) for ascending, and his working of"gradual slopes" is rather misleading.
During his discussion of wheeledvehicles, he claims that roller blades arenot HPVs as ) they can't be steered, and2) they don't allow for "impedancematching". For 1), what can I say' HasMr. Price ever used a roller blade? Al-though I spend more time on "regular"roller skates, I have used in-line skates,and I know that leaning one's foot rela-tive to the ground causes them to track aturn. ...
Impedance matching seems to be amajor pitfall for me... After all, many"real" machines (such as steam locomo-tives and turbine engines in jet
Human Power, Spring-Summer, Vol. 10/1, P. 9
airplanes) don't use any impedancematching. Second, I quite frankly can'tbelieve that a row boat is not a HPB, andby this criterion neither is the Decavita-tor. .. But to top it off, skating tech-niques in general ... do allow forimpedance matching, simply by varyingthe angle between the axis between thetwo skates or skis.... just like selectingthe "right" gear on a bicycle.
Eric Schweitzer, 166 East 96th StreetNew York, NY 10128
Rob Price replies.John Allen details the more efficient
paddling techniques used by experiencedcanoeists and describes a steering tech-nique handed down from the Algonquinsvia his grandfather. This forces a pointthat I failed to make in the article: howmuch training is necessary to overcomeidiosyncrasies in some drives to get areasonable output? A good impedancematch, or good efficiency, ought to berealizable by "rank novices", to borrowAllen's words.
Allen and George Dyson take me totask for excluding kayaks. Dyson madethe point that the Aleut kayak usedimpedance-matching technique andtechnology on several levels, perhapsnot as visible to the untrained eye as thegears on a ten-speed. In the absence ofmore data I suspect the training issuenoted above would apply. I am pleasedthat I helped the IHPVA obtain anotherdues-paying member.
Allen and Eric Schweitzer wouldinclude Nordic skis, both citing the skat-ing technique used in competition. Onceagain the novice-vs-trained-user argu-ment could be applied.
Allen's comments on braking withski poles between the legs and skep-ticism about my 0.5% ruling grade areentirely appropriate. My lapse into whatI though to be a light-hearted relief fromthe frustration I feel as an eternally ama-teur skier was unfortunate and inap-propriate for Human Power.Incidentally, I have never resorted to thecastration technique, but have read aboutit in a newspaper article.
The reason I excluded Nordic skis,canoes, kayaks and roller-blades is thatthey all share a poor impedance matchbecause they use a power stroke that isintermittent, that is limited to less thanhalf the available time, that requiresconsiderable energy to reset the drivemechanism, and that involves wastedeffort in bringing the drive up to syn-chronous speed. That low efficiency iswhy we on mountain bikes can easily
pedal past well-trained and hardworkingroller-bladers on level concrete paths.
Peter Sharp noted Dave Wilson'sdiscussion of impedance matching andthat forced rowing produced (some 15%)more power than pedaling - for a periodof five minutes. This is possible forshort periods using both arms and legsanaerobically. Wilson was using datafrom a paper by J. Y. Harrison. In thatpaper, Harrison said that hands-and-feetdrive complexities are negated after theswitch to aerobic work, after 4 or 5 min-utes, because legs alone can utilize moreoxygen than can be supplied by thebloodstream. Wilson discussed the ad-vantages of forced rowing on p. 133,which is lacking in the machines I dis-cuss in the previous paragraph. He ex-tols the virtues of derailleur gearing onp. 141 (of the quoted reference). Ishould not have used the word "ulti-mate" in connection with derailleur-gearimpedance matching; "unchallenged"would have been a more-appropriateword. Like many others I seek a betterdrive system.
Schweitzer indicated that many"real" machines do not use impedancematching, and he cited steam locomo-tives and aircraft gas turbines. Thesteam engine produces its greatesttorque at the drive wheels when the ma-chine is starting from rest, the exactpoint where the greatest traction is re-quired to initiate motion in the train.The gas turbine is ideally suited to thecruise altitudes and speeds of modernaircraft. Both these transport devices aredesigned, or impedance matched, tomaximize efficiency at the design pointsyet provide acceptable performance inoff-cruise conditions.
Sharp makes a valid point that im-pedance matching should be expandedto include the usage of a vehicle over aroute and for a given purpose. He goeson to say that multi-gear bicycles mightbe well-suited to a bicycle used on train-ing rollers or as an air plow. I disagreewith the former and agree with the latter.Rollers were originally designed for usewith one-speed fixed-gear (track) bikesand the constancy of the roller-ridingenvironment makes a fixed gear an ex-cellent impedance match in that applica-tion. Conventional upright bicycles areexcellent air plows and the variablegearing allows riders to work at opti-mum muscle speed in varying gradientand wind conditions. Since routes andpurposes vary widely, even by an
individual rider on any single vehicle, itseems plausible to provide a wide rangeof gears to allow driver selection of theoptimum ratio.
Sharp labeled my figure 5 a taxono-my, stating they were inevitably arbi-trary and incomplete, and indicated thata comprehensive list would become ho-pelessly confusing. He compared it un-favorably to Jim Kor's morecomprehensive "open-ended and cross-indexed list" which he found quite usefulfor generating new ideas. My list is sim-ply a subset of Kor's list. Kor stated thathis list was not complete, which I didnot explicitly do, and should have done.
Sharp made a long list of items thatostensibly qualify as HPVs. If he wishesto consider everything that humanstouch to be an HPV he is welcome to doso. His frustration with the IHPVA isevident: he states (twice) that the IHP-VA should sponsor more, not less, com-petitions to promote development. Hehas all but witnessed the barring ofwheelchairs from competition because Ifound their drive system lacking. I sawtwo unique chairs at the Bolder Boulderfoot race this year, one with three con-centric push rings to effect ratio changeswith speed increases, and another with asmall-radius hand crank. These aremuch more efficient.
The intent of the article was to getpeople thinking about efficient drives intheir HPV designs. Contrary to Sharp'snear-racial slurs about proclaiming thepurity of master racing vehicles overother sub-human-powered machinery, Iam interested in the speed champion-ships only for their contribution to effi-cient transport for the general public.
Rob Price. 73 78 S. Zephyr WayLittleton, CO 80123
//
Cartoon draw'n1 a nd donated l)! Ron Sol - thanks!
P. 10 Human Power, Spring-Summer, Vol. 10/1
(( mntiued fi-,l p. 3)the then long-ump record, 7.61 in. Theprize was eventually won nine years lat-er (see next entry).
Poulain-FarmanAn lIPA was built by the Farman
company and was pedalled by GabrielPoulain, a racing bicyclist ad uan experi-enced pilot, over the course in bothdirections on the morning of July 9,192 1, yielding a flight of I 1.98m. Thecraft was a biplane with a spatl of 6. Im(20 ft) and a wing area of 12.3 sq m ( 132sq l). A fiuring enclosed the bicyclistand rider. The plane had no propelleruld, apparently, no aerodynamnic con-trols. 'The all-up weight was 91.2 kg(201 Ibm).
LippischDr. Alexander .ippisch, a prolific
designer of sailplanes and other aircraft,built an ornithopter in 1929. T'is wasalways launched as is a glider. Thewings twisted during the flapping cycle.The pilot, Hans Werner Krause,achieved a flight of 300m after L.ippischset up an attractive bonus as a reward fora successful flight.
Muskelflug Institut.In 1935 the Institute of Muscle-
powered flight (Muskelfilug-Institut) wasset up within the (iesellschaft Polytech-nic, Frankfurt, and a prize was offeredfor the tirst German flight of I km. Thedirector, Oskar Itrsinus, carried out testsof the power developed by humans andmade the data available in 1936.However, before these data were givenout, Helmut Haessler and Franz Villing-er, who both worked at Junkers, madetheir own tests by having one bicyclisttow another. Unfortunately, an error inmeasurement or interpretation resultedin false readings of power levels at leasttwice the actual power that it was possi-ble tfor a human being to develop unlderthe circumstances. Accordingly the air-craft design, although having a neat andvalid configuration, a low frontal area, apylon that did not interfere with thewing, and a short transmission, was in-capable of unassisted take-otf.
Hans SeehaseSeehase built an aircraft for the Mus-
kelflug competition. There is no recordof it taking ot'ff. It had, however, severalinteresting design features. The wingstructure was an aluminum-alloy tubewith widely spaced ribs and fabric cov-ering, similar to that of modern hang-gliders. Htis aim was to reduce weighteven at the expense of increased drag, aprinciple that was ignored by other de-signers for 42 years.
The transmission was also unique.The pedals drove, through a chain, atwo-throw crankshaft. This was coupledthrough light connecting rods to a simi-lar crankshaft on the propeller shaft, atright angles to the first. Compliant rub-ber "big-ends" were used to take up thesmall changes in length and angle set-ting that such an unorthodox arrange-ment theoretically requires.
PedalianteEnea Bossi, an Italian aircraft de-
signer, started his research into HPF bytitting a propeller on to a tricycle in the1930s. It was unstable, and Bossi con-cluded that two wing-mounted counter-rotating propellers would be required foran HPA. Hence his drive train was com-plex and heavy. The Pedaliante was ofconventional glider construction,weighed 99 kg (220 Ibm), and had awing span of 17.7m (58 ft) and area of23.2 sq m (250 sq ft).
Pedaliante made dozens of flightsafter towed launches. There has beenmuch dispute as to whether it ever tookoff under the pedal power of the pilotalone. If it did, it would have been aworld first, preceding SUMPAC (q.v.)by 35 years. Sherwin (1976) reviews thearguments for and against the validity ofBossi's claim that Pedaliante took offunder human power.
Emiel HartmanAn ornithopter roughly sketched by
tlartman, a sculptor, was built in En-gland in 1958 by a glider-repairer. Itused a mechanical linkage to provide thenecessary twisting of the wings duringthe flapping cycle. Only towed flightswere made, but the builder told the au-thor in 1961 that by flapping the wings,forward progress had been made on theground. Springs were used to give a
natural flapping frequency similar to thatof rowing.
Daniel PerkinsPerkins worked tfor the Royal Air-
craft Establishment at Cardington, Brit-ain's largest experimental-airshipfacility. lie decided to build aninflatable-wing (parasol) HPA with apod-and-boom fuselage. All his variedtests came up against a strange speedbarrier of 6.3 m/s ( 14 mph). His laterefforts reached success with the Reluc-tant Phoenix (q.v.).
Alan StewartStewart built HP ornithopters at least
from 1959 - 1979 in and around Green-hill, UK. One succeeded in gliding.
SumpacThree undergraduates at Southamp-
ton University, Alan Lassiere, AnneMarsden and David Williams, decided intheir last term (spring 1960) to attemptto build a man-powered aircraft (henceSUMPA'C). The first Kremer prize com-petition had been announced the pre-vious November Other undergraduatess(oo joined them. Tests of human pow-er output were first carried out by timingpeople running upstairs, but after a re-cumbent position was chosen for thesingle pilot an ergometer rig was builtfor more-relevant power measurements.Other choices were of the planform, theairfoil section, and the method of con-struction. (Lateral control through aile-rons was regarded as the acceptedmethod, not needing any analysis forchoice).
The planform was that of a conven-tional single-seat monoplane. The spanwas chosen to be 24m, 80 ft. Theiranalysis showed that a larger span wouldrequire less power but the aircraft wouldbe more difficult to turn. A NACA air-foil section designated as 65-818 wasselected. The primary structure was aspruce-girder box-spar using spruce 1.6mm (1/8th") thick. The propeller andthe main wheel were driven, with theratio between them chosen to match theprevailing wind speed.
Wind-tunnel tests were made of thewing section, the propeller, and of amodel of the complete aircraft. Themodel showed excessive drag (almost
Human Power, Spring-Summer, Vol. 10/1, P. 11__
30% of the total) at the junction of thewing and the pylon, which had to belarge enough to enclose the pilot's head.A compromise reshaping was adopted,as a complete solution was impractical.
Construction started in January 1961,and the first flight, with Derek Piggott aspilot, was on November 9, 1961. Sum-pac made a total of 40 flights, mostlytotally under human power, so that itwas the first HPA (if Bossi's claims arenot substantiated) to take off in additionto fly. Some later flights were made un-der tow or with the assistance of amodel-airplane engine.
In early 1963 Lassiere, one of theoriginal three in the SUMPAC team,took the plane to Imperial College andrebuilt the fuselage, the pylon (to avoidthe separation problem) and used newmaterials for the transmission (fabricinstead of steel belt) for the fuselage(Melinex polyester) and for the forwardstructure (light-alloy sheet). Thesemodifications took longer to accomplishthan did the building of the originalplane. Unfortunately on its first flight in1965 under the pedalling of a strong bi-cyclist, John Pratt, the plane went steep-ly up to 10m (30 ft), stalled and crashed,breaking the wing and fuselage beyondwhat was considered repairable.
(This is taken from a manuscript ChrisRoper has written covering all knownHPflight; part will appear in theabove-mentioned HP handbook. Hehopes to find a publisherJbr his com-plete manuscript.
Chris Roper (VP-air), 19 Stirling Court,29 Tavistock St., Covent Garden, Lon-don WC2E 7NUJ, UK
AN AERODYNAMIC STABI-LIZER FOR BICYCLES
by Peter A. Sharp
In an article in Human Power (Spring1989), Doug Milliken reported a simple,but elegant, experiment concerning bi-cycle stability. He wanted to determinethe effect of cross winds. So he and hisfriend Max Behensky tied a string to aconventional bicycle and, while it wasbeing ridden, pulled the string to simu-late side forces. The attachment point ofthe string simulated the center of pres-sure of the bicycle-and-rider. Theyfound that if the string were tied behindthe center of gravity, the bicycle wasunstable. But if the string were tiedahead of the center of gravity, the stabil-ity was quite good. The reason was thatthe tug tended to steer the bicycle quick-ly in the direction of the tug, but thatthen caused the bike to quickly leanaway from the tug, thereby balancing theforce of the tug. This finding is counter-intuitive, but it works. And the rider cankeep the bike going pretty much straightahead.
Matt Weaver later used this principleas part of the design for his extraordi-narily fast and stable bicycle, the "Cut-ting Edge". This bike is fully faired andhas a very long nose ahead of the frontwheel. It looks as if it would be quiteunstable in cross winds. But the exactopposite is true. When a cross wind hitsthe bicycle, the nose of the bike isquickly pushed downwind, thus inducinga quick lean into the wind, and therebyenabling the bike to maintain a straightline. In fact, the bike steers slightly up-wind. And Weaver uses the same
technique to initiate a quick lean into aturn - he momentarily steers in the oppo-site direction. This technique is standardwith motorcycle racers. Weaver haswritten a computer program that inte-grates the various forces. (Cycling Sci-ence, Sept. and Dec. 1991).
This basic aerodynamic techniquecould be used by conventional and re-cumbent bicycles to maintain stability ingusting cross winds. One way to do thiswould be to mount a vertical wing aheadof the bicycle. The best size and posi-tion of the wing would need to be deter-mined for each type of bicycle, withadjustments made to compensate for dif-ferent riders. This wing would serve tomove the center of pressure ahead of thecenter of gravity. When bikes wereequipped with partial or full fairings,the wing size and/or placement wouldneed to be modified. However, thewing would need to be incorporated insuch a way that it did not significantlyincrease aerodynamic drag if used forrecord attempts or sprints.
- fixed LWinS adJ'sHable b1beclamps /
igure Aerodynamic stabilizer
For practical vehicles, a stabilizingwing would offer an additional advan-tage. It would produce some degree oflift and thrust when the wind was blow-ing. Chester Kyle has shown that eventhe aerodynamic tubing used for someconventional bicycles can provide mea-surable lift and thrust (Cycling Science,Sept. and Dec. 1991). A more signifi-cant contribution of lift and thrust couldbe made by the wing if it could be main-tained at the most efficient angle of at-tack to its relative wind. A fixed wingwould function like a Darrieus-rotorwind turbine (egg-beater type) thatneeds to spin at high speed to keep therelative wind within the efficient range-of-attack angles. A fixed wing on a bi-cycle would be efficient only at bicyclespeeds that were many times the speedof the wind. But if the wing used a
P. 12 Human Power, Spring-Summer, Vol. 10/1
-. -JAf _ . .
UMPAC, from Southampton University man-powered aircrajift. 1960-63
variable angle, it would be able to func-tion as a true wing sail while maintain-ing its function as a stabilizer. This is acounter-intuitive combination.
Cloth sails have been used a fewtimes in the past on bicycles. They werefast and exciting, but difficult to controland not safe for normal bike riding. TheRans tricycle produced a few years agowas a combination of a pedaled tricycleand a cloth sail. It seems to haveworked well, but the market was limited.It was perhaps too wide for normal bi-cycling, and not wide enough to functionas a competitive landsailer.
A bicyclist has enough to worryabout when riding without having tocontrol a wing sail as well. So a wingsail would need to be automatically con-trolled. The increased lift of the wingsail would require the rider to lean more.The technique of leaning continuouslyinto the wind for balance is common tobicyclists and wind surfers alike. Bi-cycles with full fairings do this as wellbut their placement of the center of pres-sure too far rearward has tended to makethem unstable.
Figure 2 Stabilizer/wing-sail
Achieving automatic control of awing sail would seem to be relativelysimple. First, an orienting vane isplaced behind the wing sail, and pivotedon the same axis as the wing sail. Thena control-cable loop is used to rotate thewing sail a fixed angle (the optimumangle of attack, left or right) relative tothe orienting vane. The rider need onlypull the cable loop forward or backwardto adjust the wing sail for winds comingfrom the right or from the left. Whenthe rider moved the lever/cable-loop to
the middle, or neutral position, the wingsail would, like the orienting vane,merely face into the relative wind andproduce neither stabilization nor thrust.Installing shock cords (bungee cords) onthe cable loop would permit the wingsail to dump excessive wind pressures,and might thereby permit the use of alarger wing sail. This is made possibleby pivoting the wing sail at its center oflift (about 25% of chord), so that it willnaturally try to face the relative windunless restrained. An interesting ques-tion is how large the wing sail can be-come before the increase in stability itprovides becomes a source of decreasingstability. And another option to consideris that of using another wing sailmounted to the rear of the bicycle, butthen moving the forward wing sail far-ther ahead.
A wing sail could also be used fortricycle propulsion. And it might alsobe used for aerodynamic stabilization,but in a quite different manner. Whenroad racing, tricycles could use a wingsail to increase cornering speeds. Thewing sail would be linked to the steeringso that the wing sail turned as the wheelsturned. This would create lift toward theinside of the turn (assuming windlessconditions), and higher possible corner-ing speeds. The wing sail would be usedto counteract the tipping forces. Whenthe wind was blowing, however, thingswould get complicated. But some smartperson who can solve that problem
might end up with a very fast trike. (Apartial solution would be to use the wingsail for propulsion on straight sectionswhen the wind was blowing, and for cor-nering when the wind was not blowing.)This would then be the trike equivalentof down-force wings on racing cars. Iwish the future would hurry up andarrive.
((Author's note: In a personal commu-nication, Doug Milliken noted that,"...vertical surfaces are used by somerace cars (sprint cars) to produce aerody-namic lateral force to aid corneringspeed. We have a picture of a car lean-ing into a turn (rather than rolling out-ward) because of the aero effects of alarge 'sideboard' while the car is at a bigtail-out side-slip angle." This is sort of a"square rigger" (aerodynamic drag) ver-sion of what I am proposing(aerodynamic lift) for tricycles.))
Peter A. Sharp, 2 786 Bellaire PlaceOAKLAND, CA 94601, USA
Peter's success as an inventor allowshim to earn his living as a self-employedcraftsman. He is happily married to hisTour Easy, and they have recently con-ceived a new type of HPV, to be named
"Quicycle".
Human Power, Spring-Summer, Vol. 10/1, R 13
Figure 3 Automatic wing-sail control
l
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Distonce from Outer Tip of the Eor [mm]
[1 Bore Ear + Device "A" o Device "C" A Device "D"
Figure 3 Turbulence vs anemometer position (at freestream velocity of 1.2 m/s, 25 mph)
those in figure 2 but are, of course, lesspronounced.
Also shown in figure 2 are the root-mean-square (RMS) values of the micro-phone readings. We see that, as indi-cated by the RMS values, the noise levelwhen device "A" is in place is only 26percent of that when no device is pres-ent. The other two devices yield lesssignificant reductions.
Turning now to the relation betweennoise and turbulence, turbulent flow istypically described by the equation
u[i] = 5i + u[i]' (1)
where u[i] is the instantaneous fluid ve-locity, the mean velocity, and u[i]' thefluctuating component of the velocity.Since the time average of the fluctuatingcomponent of turbulent flow is zero, it iscommon practice to describe the magni-tude of the fluctuating component, thatis, the magnitude of the turbulence, by aroot-mean-square value [4]:
u[i]'(RMS)= { (u[i] - u) /N} (2)
where N is the number of datum points.Figure 3 shows typical turbulence
values when (2) is applied to the veloc-ity data collected in the vicinity of theear. We see that the magnitude of theturbulence falls dramatically as theanemometer moves into the ear and that,in every case, when a device is in place,the turbulence within the ear is less thanthat when no device is present. Finally,
we note that, as indicated by the outputof the microphone and consistent withLighthill, reduced turbulence within theear corresponds to reduced noise levels[5].
As may be obvious, it is importantfor the entire ear to be in the "dead air"behind the device. This was confirmedby attaching a string to the pinna (theouter cartilage shell of the ear) and pull-ing it into the airstream. The result wasan increase in noise level of up to ninetypercent.
IV. SummaryThe experimental results show that
some very simple passive devices at-tached to the leading chin-strap of a bi-cycle rider's helmet greatly reducewind-induced noise and, therefore, im-prove the bicyclist's ability to hearsounds emanating from his/her environ-ment. The results indicate that, for theconditions tested, noise levels can bereduced by approximately 75 percent.
The early work on this device wasfeatured on Cable Network News (CNN)in August, 1990.
AcknowledgmentsThe author wishes to express his ap-
preciation to the following former un-dergraduate students who contributedsignificantly to the endeavor: Paul Mil-lman, Parker Shectman, Jimmy Whitneyand Karl Zimmermann.
References and footnote1. Lighthill, M.J., On Sound GeneratedAerodynamically, Proceedings of theRoyal Society, 1952, Vol. 21 1, pp.564-587.2. Lighthill, M.J., On Sound GeneratedAerodynamically II: Turbulence as aSource of Sound, Proceedings of theRoyal Society, 1954, Vol. 222, pp. 1-32.
C.H. TreatDepartment of Engineering Science
Trinity UniversitySan Antonio, Texas 78212
Herb Treat has been on the faculty atTrinity University in San Antonio for thepast 25 years. An enthusiastic bike-riderhimself he reports here the results ofone of his senior-engineering-studentdesign projects.
Book review
Velomobileby Vytas Dovydenas
German Edition: Verlag Technik Berlin1990, ISBN 3-341 00790-3
Original Russian: Leningrad 1986127 pages
Reviewed by T7teo SchmidtThis book gives an East-European
view of HPV development, describingmany vehicles which will be unknown towestern IHPVA members. Basic designcriteria for HPVs are also competentlydescribed. An HPV-based transport sys-tem for the 21 st century is presented.Although written in German, the manyexcellent drawings and colored pictures(not photos) make the book interestingfor anyone to look at. This book is diffi-cult to get but may be borrowed fromthe IHPVA library for a deposit pluspostage both ways.
Editor's apology: apologies forbeing late with this issue! Produc-ing a journal seems easy, butaround five hours of my time perpage is needed to get HP to thepoint I can send it to Marti Daily.Now, for the next issue, we needmore input from you. Send pa-pers, letters, reviews, reports!Dave Wilson
Human Power, Spring-Summer, Vol. 10/1, P. 15
I I I I I I I I I�--
_
SUMMARYPhysiological responses associated
with varying crank-arm lengths in arm-ergometry indicate that during submaxi-mal steady-state arm exercise, an opti-mal crank length may exist.Furthermore, when using an arm-ergometry work test to fatigue, a higherpower-output level may be achievedwith a relatively longer crank-arm. Un-fortunately, no significant differenceswere found in efficiency values compar-ing crank lengths to suggest an optimallength for power production.
INTRODUCTIONWith the development of arm pow-
ered vehicles for the lower-body dis-abled (i.e. "Freedom Ryder", NewEngland Handcycle, etc.) as well as de-velopment of arm- and leg-poweredHPVs, the characteristics of arm-crank-drive systems are of technical impor-tance to overall efficiency. Althoughthere is ample research on leg-drive sys-tems and leg ergometry, there is littleknowledge available to guide one whendesigning a HPV with a physiologicallyefficient arm-crank-drive system.
Efficient power production dependson a number of factors such as body-segment lengths, muscle mass, spinningor cranking rate and the length of thecrank-arm. Identifying an optimal crank-arm length for average riders was thefocus of this study.
By keeping power-output constantand maintaining the crank rotational ve-locity at a constant revolutions per min-ute (RPM), one can vary the crank-armlength and determine the body's physio-logical response to such a variation.
A crank handle attached to a longercrank-arm must turn through a largercircumference and at a higher velocityand therefore will put a greater demandon a subject's speed of muscular contrac-tion. However, because of a longer ra-dius arm, there will be an enhancedmechanical advantage due to increasedleverage. The result is less force beingrequired to turn the crank and less de-mand in terms of force of muscular con-traction of active muscles.
A shorter crank-arm, by contrast,would require more force to turn be-cause of reduced leverage; however, thisextra demand is theoretically offset by aphysiological advantage gained as aresult of the point of force applicationturning through a shorter distance and ata slower speed. With this in mind, itseemed unlikely that different crank-armlengths would greatly affect the physio-logical cost of producing work, becausethe power-output in both cases would bethe same. However, with a significantvariation in crank-arm length, this as-sumption may not be true due to possi-ble variation in the underlyingphysiology of muscular contractions pro-ducing the power-output. The purpose ofthis study was to help clarify thisuncertainty.
BACKGROUNDResearch that has addressed crank-
arm length variation has related to legcranking only. In this regard, however,Simpson (1979) has argued:
"A longer crank-arm permits the useof a bigger gear with less fatigue, eventhough the feet are moving in a circleof greater diameter. With a shortercrank, the advantages are reversed: moreforce is required, but the smaller circleof rotation makes for smoother pedal-ling, the quality called 'souplesse'.Where spinning is desirable, a shortercrank is more efficient." (p.29) Simp-son's sentiments are echoed by Hull andGonzalez (1988) in their statement:
"On the one hand, at a constant pow-er and constant crank-arm length, in-creasing the pedalling rate allows acorresponding reduction in the pedalforce and hence joint movements due topedal force. On the other hand, at con-stant power and constant angular veloc-ity, increasing the crank-arm length alsoallows a corresponding reduction in ped-al force. Intuitively, a longer crank-armwould lead to reduced pedal force butincreased dynamic action of the limbwhereas a shorter crank-arm would re-sult in increased pedal force but de-creased dynamic action." (p. 840)
Clearly, the pedal or handle speed isnot the samne as the crank rate. Thepedal-hand speed is faster for the longercrank than for the shorter crank eventhough both travel through the same de-grees of rotation per unit of time. Theforce dynamic of muscular contractionsat varying rates of speed can be illus-trated by the force-velocity curve (figure1), and can help to clarify the nature ofmuscular force production as it relates todifferences in velocity of movement dueto different lever-arm lengths.
Increased handle or pedal speed canbe obtained only by the muscles exercis-ing or contracting at a faster rate. Theincreased velocity of contraction willdecrease maximal force production ca-pable in the muscles and limit the forceapplied to the crank handle or pedal(Kreighbaum and Barthels, 1985; Bo-lourchi and Hull, 1985). When shortercrank-arms are employed and the RPMis held constant, the handle or pedalmust travel at a slower speed than thelonger crank to maintain the same RPM,while at the same time leverage is sacri-ficed. With less leverage the body has toapply a greater force to turn the shortercrank-arms. Slower cranking speeds ne-cessitate the development of greatermuscular tension to perform the samepower-output. Such muscular work maytherefore become more anaerobic athigher power-outputs and mnore ineffi-cient. The reason for this cin be ob-served in the power-velocity curve ofmuscular contraction (figure 2). Here itcan be seen that highest power-outputsare achieved at relatively higher contrac-tion velocities despite the sacrifice ofcontraction forces.
Human Power, Spring-Summer, Vol. 10/1, P. 19
EFFECTS OF CRANK-ARM LENGTH ONPHYSIOLOGICAL RESPONSE IN
ARM ERGOMETRYby Brent L. Gravelle and Richard R. Powell
8
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VELOCITY OF MUSCULAR CONTRACTION
'Figure I Force-velocity relationship
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I II I I
Based on the theoretical power-output being equal under varying crank-arm length conditions, it could be sup-posed that the interplay among theabove variables would render all cranklengths equal in terms of submaximaland maximal muscular-performanceoutcomes. However, it was suspectedthat maximum power-output achieved asmeasured by time to exhaustion wouldfavor a longer crank-arm length becauseof the more dominant influence of aero-bic metabolism (characteristic of a lowertotal muscular force and higher velocity)in a multistage progressive ergometrytest to fatigue.
Accordingly, we proposed the fol-lowing two hypotheses:
1. when performing submaximalarm-ergometry power-outputs at threedifferent crank-arm lengths, physiolog-ical responses would remain unchanged;and
2. when performing a multistagearm-ergometry exercise test to ex-haustion using three different crank-armlengths, a relatively long crank-armwould result in a longer work time priorto exhaustion.
APPROACHAn arm-crank ergometer was used
that was an electrically braked systemenabling a standard power-output re-gardless of ranking speed (Unit PE,Pedal-Mode Ergometer, Warren E. Col-lins, Inc., Braintree, Mass.). Theergometer was mounted on a woodenframe and a seat was positioned in frontof the crank-arms so that the axis ofrotation was at shoulder height. Threesets of interchangeable crank-arms of 4,
5 and 6-1/2 inches (101.6, 127 and 165mm) in length were used.
Twelve physically active male stu-dents were selected as experimental sub-jects with a mean age of 21.8 years, R =18-25. Subjects were selected for simi-lar arm lengths in an attempt to controlfor variations in leverage associated withforce production. An anthropometriccaliper, graduated in centimeters, wasused in conjunction with a method byPlagenhoef (1971) for locating joint cen-ters and determining limb lengths. Theupper and lower right arm of each sub-ject was measured to insure an averageupper-arm length of 31.5 cm + 1.5 cmand an average forearm length of 25.5cm + 1.2 cm. Variance was relativelysmall, measuring 1.01 for the upper armand 0.38 for the forearm. Consequently,subjects were considered similar in thisanatomical feature.
The three different crank-arm lengthsconstituted three test conditions witheach subject randomly exposed to all
1. -
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t17 so1 125 a O
F'igure 3 Oxygen consumption (VO).7ulmonarv ventilation (VE,) and heart-rate (HR) responses during steady-state
nrm exercise at 50- Wpower output usinlthree different crank-arm lengths: 102,127 & 165 mm.
1.0 -
5 05-I8I '
f O-
.0.5 -
conditions. During each exercisesession, physiological determinations ofoxygen consumption (V02), heart rate(HR), and pulmonary ventilation (VE)were made at rest and every fifteen sec-onds until exercise ceased. The workrate of power-output started at 25 wattsand increased 25 watts every two min-utes until the subject reachedexhaustion.
By monitoring V02, HR, and VE at25- and 50 -watt work outputs, steady-state physiological cost was determinedfor each crank length. Time to ex-haustion (TIMEEXHST) was also usedas a measure of maximum power-outputfor each test condition. Collected datawere statistically analyzed to determinesignificant difference.
FINDINGSNo significant differences among the
three crank lengths were found for thephysiological variables at a power out-put of 25 watts. However, at a 50-wattwork output, VE, V02 and HR re-sponses were significantly affected bycrank lengths (figure 3). Results indi-cated significant differences betweencrank lengths of 102 mm and 127 mmand 102 mm and 165 mm on all physio-logical variables. In contrast no signifi-cant differences (p<.05) were foundbetween the 127 mm and 165 mm crank-arms. Had more data points existed overa wider range of crank-arm lengths,these relationships may have been ex-trapolated to more clearly definable cur-vilinear relationship.
Figure 4 represents the maximalpower-output achieved and time to ex-haustion plotted against crank length. Ascrank length increased from 102 mm to127 mm then to 165 mm, TIMEEXHSTsignificantly increased (p<.05) from 6.75min. to 7.85 min., and then to 8.79 min.,respectively. Accompanying the gain inexercise time is a corresponding rise inpower-output with a mean maximumpower-output of 125 watts achieved at amean time of 8.79 minutes using a 165mm crank-arm.
CONCLUSIONSThis investigation explored physio-
logical responses associated with vary-ing crank-arm lengths in arm-ergometry.Physiological responses suggest the fol-lowing. 1) During submaximal arm exer-cise, an optimal crank length foraverage-sized male adults exists 127 mm
P. 20 Human Power, Spring-Summer, Vol. 10/1
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VELOCITY OF MUSCULAR CONTRACTION
Figure 2 Power-velocitv relationship
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HR I - - _"`
VF . .........
I I I
devices are permitted in these eventsprovided no energy is stored before thestart of the race (this means absolutelyno chemical, electrical, kinetic, poten-tial, or other form of energy storage atthe start)." The problem here is that anHPV, itself, is an energy-storage device.A bicycle includes an aggregation ofvarious energy accumulators that storeenergy produced by the rider. The mostobvious one is the whole bicycle/ridercombination which stores kinetic energyas long as it is moving. Another obviousexample is that of the wheels acting asflywheels to store kinetic energy. Inaddition, merely standing up a bicyclerequires storing potential energy - untilit falls down again. The various springsand the steering mechanism also storepotential energy, and usually for morethan one leg stroke. Note carefully thatthe restrictions on energy storage beforeany road race, and before or during anyother race, are "absolute". No excep-tions. Therefore, any flying starts, orany pedaling in excess of one leg stroke(except in a road race, etc.), is strictlyprohibited. Also prohibited are startingany race with a bicycle upright, or withany spring at other than minimum com-pression, or with steered wheels pointingother than straight ahead, or even withinflated tires. Any win or record set inviolation of this absolute rule is there-fore invalid.
It is ironic that an organizationwhose intent was to prohibit as little aspossible should end up prohibiting justabout everything. Of course, the solu-tion to the problems created by theserules - the invalidation of probably allwins and records - is to simply rewritethe rules correctly and then to validateall previous wins and records using agrandfather clause. But I also suggestthat the current prohibition against ener-gy accumulators be eliminated. It iscontrary to the goals of the IHPVA; con-trary to the recommendations of our in-ternational president, Paul MacCready;and contrary to the best interests of bi-cycle development. It is certainly con-trary to my interests, since I and othersin the bicycling community might profitfrom the invention of an improved HPV.And we should be encouraged to do sorather than being handicapped by preju-dicial rules.
To quote the IHPVA rules, "The spir-it of these rules is to avoid inhibiting de-sign innovation by not establishing
unnecessary restrictions." To prohibit anenergy accumulator which stores humanenergy through pregenerative pedalingand/or regenerative braking is in directviolation of the spirit of the rules.
Our international president wrote, inhis recommendations for rules and goals,"In open categories, especially as exem-plified by the IHPVA races, a useful phi-losophy is to have the rules lag technicaldevelopments and so not inhibit the de-velopments. Thus, although the HPVArules prohibit stored energy from sourcesoutside the rider, a rider might be per-mitted to store energy (as in a battery)during one part of the event for use in alater part. Also, the vehicle could bepermitted to exploit real-time wind pow-er via a sail wing or onboard windmill.If energy storage or wind augmentationproduce a race winner, great! If the ad-vantage was so large that the new tech-nique would be essential for futurewinners, then a new 'open' categorycould be set up permitting it, and anoth-er 'semi-open' category could be devisedprohibiting it, or a single dominant cate-gory could be selected. Innovation isserved by this attitude." (HP, Summer'87) The current IHPVA rules directlycontradict this recommendation.
My own argument is that energy ac-cumulators would enable HPVs toachieve much-improved accelerationfrom a standing start using pregenerativepedaling. In combination with goodaerodynamics, that would enable HPVsto accelerate with and run with automo-biles on level city streets, thus enablingHPVs to catch the majority of stop lightsand significantly improve commutetimes on favorable routes. (Hills wouldstill be a problem.) It would also begreat fun for an average rider to be ableto out-accelerate and outrun a profes-sional cyclist on a conventional roadbike. For IHPVA road racing, an energyaccumulator would be charged using pri-marily regenerative braking, since therewould be little time for pregenerativepedaling. The tighter the road course,and the more braking that was required,the greater would be the advantage ofusing an energy accumulator. It wouldbe of little or no advantage in events re-quiring continuous maximum aerobicpedaling, such as timed events or specif-ic distance events. Since an energy ac-cumulator's main advantage is inproviding improved acceleration, itshould definitely not be prohibited from
the sprints. Would it provide an unfairadvantage? Of course it would. That'sthe whole point of using an energy accu-mulator - to gain an advantage by meansof a technical innovation. That's justwhat the IHPVA is supposed toencourage.
The original reasons for banning en-ergy accumulators from the sprints arenot clear. But a knowledgeable membersuggested two possible reasons. First,based on some informal studies by Ches-ter Kyle indicating that energy accumu-lators would not be likely to improvecommuting times, it may have been de-cided to save competitors the time andmoney that developing energy accumu-lators would have required. If this wasone of the original reasons for the ban,then I would contend that the reasoningwas, however well intended, anti-innovation and a self-fulfilling prophesy.A second possible reason may have beenthat energy accumulators present diffi-culties in insuring that competitors donot store energy before the race. But Iwould contend that this is a non-problem. Let the energy be stored!That's what an energy accumulator isfor! All that is required is some reason-able time limit (so as to prevent pedalingall year just to provide the power for onesprint). A one-, five-, or ten-minute lim-it would be practical. My reading of therules suggests a third possible reason:that of simple prejudice, i.e. the assump-tion that an energy accumulator wouldnot be consistent with the "purity" of abicycle.
The critical question is, "Is a bicyclewith an human-energy accumulator stilla real bicycle?" That is precisely thequestion that was answered so infamous-ly in the negative by the UCI when itbanned recumbents and fairings. TheIHPVA is now doing exactly the samething by banning energy accumulatorsfrom the sprints. It's time for a change.
Peter A. Shaip, 2 786 Bellaire PlaceOakland, CA 94601
(see earlier for Peter's bio)
Editorial retraction: in an editorial inthe last issue, I made some snide com-ments about an article in CYCLINGSCIENCE and about its editorial policy.I apologize to Chet Kyle and Peter Steg-mann! Dave Wilson
P. 22 Human Power, Spring-Summer, Vol. 10/1
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