Cover: Commercial prototype of a swathe-felling mobile chipper operating in red alder nearSeattle, Washington. The machine fells standing trees and picks up logging debris and downtrees.

Reprinted ft-om the JOURNAL OF FOREsrRYJanuary 1980Nolume 7&INumber 1

Peter Koch and Thomas E. Savage

ABSTRACT -A harvesting machineand allxiliary equipment are being de-~'elopeJ to reco~'er logging residues aschips fiJr filel and fiber, and to deli~'erthese chip.l' to mills at about $18 pergreen ton including 30 percent pre-taxprofit on the equipment investment.The harvester, a 575-horsepo~'ertracked mobile chipper equipped with afront-mounted felling bar, was field-tested on red alder stands (Alnus rubraBong.) north of Seattle, Wa.l'hington,during July and August 1979. On thebasi.l' of these preliminary test,\', the in-stitutions and companies cooperatingin the de~'elopment have scheduled ex-tensive southern field trials for 1980. 1fthe machine meets its performancegoals, it could harvest 30,000 tons ofgreen cull wood from about 1,500 acresannually.

Figure I. Concept of mobile machine»,ith a felling bar arranged to feed adrum chipper. (Top) Approaching tree.(Center) Butt of severed stem thro»'nrear~'ard to rest on liI'e bed. (Bottom)Felled tree moving into dr/1m chipperthrough feeding action o,f felling barand liI'e bed, self-feeding action ofdrum chipper. and forward motion ofthe machine.

.Changes the capital in-vestment for site preparationto a harvesting expense..Should improve publicreaction to harvesting be-cause it eliminates wastewood and unsightly slash..Eliminates the smoke thatoccurs in windrow-and-burnoperations..Compared with the wind-row-and-burn system, in-creases (by perhaps 10 per-cent) the plantable area-because not all windrows arecompletely burnt..Protects land productivity,because scalping inherent inpile-and-burn operations iseliminated..Hastens replanting by sev-eral months, because harvest-ing accomplishes site prepara-tion..Because no wood is skid-ded over the ground, wooddelivered via mobile chipperand chip forwarding binsshould be essentially free ofdirt.The first step in making the pro-

posed system practical was to de-velop a commercial mobile harves-ter. After considering many de-signs, we decided on one in which aground-level cylindrical felling barfeeds a drum chipper (fig. 1). Mate-rial from a drum chipper is easier tohandle in conveyors than chunksfrom a hammer-type hogging head.Also, chips have more potentialthan chunks for use in fiber prod-ucts, which are more valuable thanfuel

To develop a prototype commer-cial machine, the Southern ForestExperiment Station of the ForestService, five timber companieswith southern operations, andNicholson Manufacturing Com-pany signed a cooperative agree-ment.. in March 1977. The U.S.Energy Research and DevelopmentAdministration (now the De part-

Conversion of unmanage.d south-ern forests to pine plan1ations andcultivation of ensuing rotationsnecessitate brush control-, thinning,and disposal of logging s~sh. In theSouth, brush is usually controlledby periodic prescribed burning orby injecting or spraying with her-bicides. Trees are thinned by manymechanical methods, all of whichwaste tons of wood. After croptrees are felled, the tops, branches,stumps, and noncommercial treesare usually windrowed and burnedto facilitate planting of the newstand.

This paper describes a way toaccomplish these operations with amobile machine that. chips residualwood and delivers the chips intomobile bins that carry them toroadside piles. Such chips canserve as fuel or fiber for nearbymills. The system is an adaptationof that suggested by .Koch andMcKenzie (1976). !.(

Besides providing a degree ofenergy self-sufficiency for timbercompanies operating mills, the sys-tem proposed has several otherbenefit~:

ment of Energy) contributed sub-stantially to the cooperativelyfunded effort.

Performance goals were that themachine should:

.Operate primarily on ter-rain that is stone-free, has aslope of 30 percent or less,and supports 8 psi in wheel ortrack pressure..Harvest one acre per hourat I mile per hour on land av-eraging 25 tons (green weight)of logging residue and stand-ing culls per acre..Fell and chip southernhardwood and softwoodstems up to 12 inches in

January I980/JOURNAL OF FORESTRy/I?

diameter (measured 6 inchesabove ground level) whilemoving at I mile per hour..Mill off the top of 12-inchdiameter stumps to 6-inchheight while traveling at Imile per hour (larger stumpsat slower speeds)..Pick up and feed into thedrum chipper the tops,branches, and cull stem sec-tions left by loggers..Chip felled stem sectionsup to 19 inches in diameter ifproperly oriented to the in-feeding hopper and if largelimbs are notched by chainsaw for improved feeding.

Testing the Concept

Koch and Nicholson (1978) re-ported early trials of the felling-barconcept. Tests during summer andautumn of 1977 measured horse-power, feed thrust needed parallelto the ground, and down thrust onthe bar. In January 1978, a fellingbar was coupled with a drum chip-per (as shown infigure 1 but with-out the live bed between felling barand chipper) and power require-ments were monitored while themachine felled and chipped stemsof several hardwood and softwoodspecies.

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Figure 3. Felling an II-inch red alder. .s'ee co~'er photo for sequence.

Nominal feed speed 136 ft./min.Felling bar characteristics

Cutting-circle diameter 16.5 in.Length 93.5 in.Number of knives 4Rake angle of knives 38.5 0

Rotational speed 0-600 rpmClearance above ground 2 to 7 in.

Diameter of side feed rolls 24 in.Machine ground speed Creeping to

3 mph.

Gross vehicle weight 72,000 Ibs.Approx. ground contact

area with 2-inchpenetration of tracks 6,740 sq. in.

Approx. ground pressure 10.7 psiDrum chipper characteristics

Cutting-circle diameter 48.0' in.Spout width 47.5 in.Number of knives 3Rake angle of knives 52.5 0

Drum speed 544 rpm

Commercial Prototype

After these tests, a commercialprototype was designed for assem-bly on the lower hull, undercar-riage, and lengthened tracks of anFMC skidder(cover photo andf;gs.2, 3, and 4). The machine has a575-horsepower Cummins dieselengine, which powers all functions(fig. 5). To better feed brush andlogs into the drum chipper, themachine has two semi- verticalside-feed rollers; their direction ofrotation can be reversed so thatstems 'lying crosswise to machinetra vel can be moved for easierpickup. The cab is positioned togive the operator a view of the fel-ling bar. Placed above the bar is apivoted crowder hydraulically ac-tuated to push brush into the drumchipper (figs. 2 and 3) and to breakstems that lie transversely acrossthe front of the machine.

The chipper is 9 feet and 2 inchesin width and 26 feet long. With thechip spout lowered for travel, themachine's height is 11111. feef. Otherspecifications are:

IS/JOURNAL OF FORESTRY/January 1980

This commercial prototype wasfirst tested in the field during thesummer and early fall of 1979 instands of red alder north of Seattle,Washington. The trees wereclosely spaced, and the machinefunctioned best when operated in arace-course pattern on the standperiphery. When it penetrated di-rectly into a dense stand, severedstems could not fall forward (treecrowns became entangled) and so

Figure 4. Mobile chipper and compan-ion 'forwarders retrieve loggingslash as chips and deposit them inroadside inventory piles. The threemachines in combination should bemechanically functional (al-'ailable) atleast 62 percent of the time, and theyshould all operate at least 75 percent ofthe time they are available: non-operating time should thereflJre be 46.5percent afscheduled time (i.e., 0.75 x0.62 ;= 0.465). If the machine i.\"scheduled 7 days per week, 9.6 hoursper day, 48 weeks per year, actualoperating time should total about /,500hours during II'hich time it should har-vest about /,500 acres. If20 tons (greenbasis) are delivered to the mill fuel pilefrom each acre, annual harvest shouldbe about 30,000 tons of fuel chip~.

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575 HPDIESELENGINE

Figure 5. Drive train from diesel engine to felling bar, drum chipper, and tracks. The hydraulic motor is powered primarily bythe diesel engine, but its short-term peak load capacity is increased by the flywheel effect of the chipper drum.

January 1980/JOURNAL OF FORESTRY/19

Fig/lre 6. Site ajier harl'e.l't. Perjormanc'e gval.l' c'all for pick/lp, in chip ,form. vi 85percent vi the c/lllll'vvd present on each acre harl'ested.

Figllre 7. Red alder chips from drllm chipper. Pen in center of photo is 5 _5 inche.l-long.machine to help in directing the begin during early 1980 nearforward fall of severed trees (fig. Auburn, Alabama. The manufac-3). It also became evident that a .turer will then modify the design tolive bed is needed to form the lower improve performance and Forestsurface of the chipper throat be- Service engineers at Auburn willtween felling bar and drum chipper again test the machine. After these(fig. 1); such a bed would help shakedown trials, performance willthrust the butt of a severed tree to- be studied during the spring, sum-ward the drum chipper. Addition- mer, and fall of 1980 on theally, knife geometry on the drum cooperators' lands in the Carolinas,chipper must be designed to pro- Louisiana, and Arkansas. Also, itsmote aggressive self-feeding. effectiveness in site preparation

The cooperators now plan ex- will be evaluated by Forest Servicetended fie.ld trials in the South. silviculturists at Auburn, who willThese southern trials, which will study -nutrient leaching losses,include extensive eva1,uation by woody and herbaceous vegetationForest Service engineers, s~ould control, and forage growth.

failed to get oriented for self-feeding into the chipping drum.

The felling bar, revolved at lowspeed, effectively picked up woodydebris from the ground and deliv-ered it to the chipping drum (jig. 2).When picking up logging slash anddown trees, the machine workedbest if stems were aligned parallelwith machine travel. Pickup wasleast successful when stems laytransverse to machine travel. Thecrowder bar proved able to break6-inch alder stems that lodgedacross the feed rolls, but its effec-tiveness will be enhanced by in-creasing its stroke speed. Thecrowder bar successfully thrustclumps of wood and brush towardthe drum chipper.

Horsepower and speed wereadequate for alder; when harvest-ing southern oaks and hickory thespeed will be slower. Large-diameter stumps not visible to theoperator may cause unplannedoverloads. If the operator sees suchstumps in time, he can slow for-ward travel or raise the felling bar afew inches (7 inches is themaximum) to clear some of them.Turning radius is large (about 40feet) and steering control needssome improvements through morepositive braking action, [earrange-ment of the steering-brake shoes,or addition of a system to lock theinside track during turns.

.The cooperators were well im-pressed by chipper power, by theappearance of the site after harvest-ing (fig. 6), and by chip quality (jig.7). Stump height-l to 7 inches-was generally considered accept-able, although several observersfelt that these stumps would re-quire use of dibble-type plantersrather than the simple and inexpen-sive coulter-type planters morecommon in the South. This is a crit-ical issue, as a credit for site prepa-ration of about $75 per acre seemsneeded to economically justify useof the machine. Stumps, even whencut flush with the ground, interferewith coulter-type planters. Ifstumps' are not over 6 or 7 incheshigh and not too numerous, acoulter-type planter with shortturning radius can circumventthem. Resulting tree rows will notbe ~traight, and spacing will vary,depending on number and size ofstumps.

During the Seattle trials, frameswere added to the front of the

20/JOURNAL OF FORESTRY/Januarv 1980

of available cull wood recovered aschips. machine operating time as apercentage of scheduled time. andacreage harvested per operatinghour. .

Literature CitedKOCH, P. 1977. Harvesting southern pines with

taproots is economic way to boost tonnage peracre 20 percent. South. Pulp and Paper Manuf.40(5):17,18,20,22.

KOCH. P.. and D. W. McKENZIE. 1976. Machineto harvest slash. brush. and thinnings for fueland tiber-a concept. J. For. 74:809-8]2.

KOCH. P.,'and T. W. NICHOl.SON. ]978. Harvest-ing residual biomass and swathe-felling with amobile chipper. P. ]48-154 in Complete-TreeUtilization of Southern Pine. Proc. Symp..New Orleans, La. April 1978. ed. C. W.McMillin. For. Prod. Res. Soc.. Madison.Wis.

THE AUTHORs-Peter Koch is chiefwood scientist, Southern Forest Exper-iment Station, USDA Forest Service,Pineville, Louisiana. Thomas E. Savageis project engineer, Nicholson Manufac-turing Company, Seattle, Washington.

The machine described was developedunder Cooperative Agreement 19-239 be-tween the Forest Service (with financialassistance from the Energy Research andDevelopment Administration-now De-partment of Energy), five timber com-panies (Boise Southern Company, Geor-gia Pacific Corporation, InternationalPaper Company, Olinkraft, Inc., andWeyerhaeuser Company), and Nichol-son Manufacturing Company. The au-thors acknowledge the technical adviceof Conor W. Boyd, Aaron R. Chesnut,Gordon R. Condit, Ben M. Davis, NelloDel Gobbo, and John E. Wishart.

time. oil costs have increasedgreatly. Though the price of $18may appear high. a ton of thesechips is worth about $36 if theirheat content (taking into accountboiler efficiency) is priced compar-ably with the heat content of No.2fuel oil costing $0.70 per gallon.And fuel oil prices may well reach.or exceed. $1 per gallon.

Perhaps certain classes of cullwood can be harvested more eco-nomically by existing methods thanby the swathe-felling mobile chip-per. For example. the centralstump-root portions of southernpines 5 to 12 inches in d.b.h. can beharvested with treepuller-bunchersand grapple skidders at about $10per green ton (Koch 1977). Also,throughout the South, tree-shearfeller-bunchers teamed with grap-ple skidders can economically har-vest cull trees 6 to 12 inches ind.b.h. at about $10 per green ton.But neither the tree puller-bunchernor the tree-shear feller-bunchercan operate economically on asteady diet of logging slash orstanding culls 5 inches and smallerin d.b.h. Such small material seemsto invite use of the swathe-fellingmobile chipper.

The southern field trials during1980 should provide information onwhich to base more precise eco-nomic assessments. Data will beobtained on terrain for which themachine is best suited, percentage

Overall weight of the machine-72,000 pounds-is cause for con-cern, for resulting ground pressureof 10.7 psi is too great for winteroperation on many southern soils.Some redesign and material sub-stitutions on later production mod-els should reduce ground pressureto an acceptable 8 psi.

Economics

Trials conducted through Sep-tember 1979 have not determinedwhether performance goals can bemet under southern conditions, butwith incorporation of revisionsplanned for early 1980, the outlookseems promising.

The earlier article (Koch andNicholson 1978) projected that theharvested wood could be deliveredto the mill for $13.57 per ton(green-weight basis), including a3D-percent pre-tax profit on anequipment investment of $470,000per machine team (one mobilechipper, two self-powered chipforwarders, and support equip-ment). This cost is for harvestinglogging slash and cull wood from1,500 acres annually and simulta-neously preparing the site. Recov-ery from these acres should beabout 30,000 tons (green weightbasis) of chips.

Inflation has increased thesecosts, which include \ profit, toabout $18 per ton delivered to themill (green basis). At the same

.Reprinted by the Forest Service. U.S. Department of Agriculture, for official use.

January 1980/JOURNAL OF FORESTRY/21()1980 SOCIETY OF AMERICAN FORESTERS