7

United States

#@A*f Department of

‘&$J$ Agriculture

Forest Service

Southern Forest

Experiment Station

--- ---

so-315

August 1985

Flail-Delimbing of Loblolly Pine-A Case Study

Bryce J. Stokes

SUMMARY OPERATION

Flail-delimbing was tested in small-diameter loblolly pine. Most of the limbs left on the stems were

less than 6 inches long. Over 75 percent of the

delimbed stems had three or fewer remaining limbs.

The cost was determined by comparing skiddingflailing with skidding only. The cost difference was

approximately $6.00 per cunit.

Additional keywords: Skidding, production rates,

costs.

INTRODUCTION

The machine was part of a shortwood operation

in a dense, 20-year-old pine stand that was being

clear cut. The harvesting system was comprised of

a Drott 40 feller buncher, a Hydro-Ax 511 feller

buncher, the skidder flail, and a Barko Loader with

a slasher. The skidder either skidded bunches and

flailed at the deck or flailed bunches in the woods

and then skidded. Trees delimbed at the deck were

placed onto the slasher with the loader and bucked

into shortwood. Trees delimbed in the woods were

skidded to the deck and processed with the slasher.

The shortwood was loaded onto set-out trailers.

Delimbing is a major operational concern of the

Southern pulpwood industry. Because of the costs

and dangers of chainsaw delimbing, at the deck or

in the woods, other methods are needed to efficiently

and safely delimb trees on the site with the comparable quality of the chainsaw. A possible alternative to manual chainsaw-delimbing is flail-delimbing.

In this study, the operation of a Hydro-Ax LL641 portable chain flail delimber was studied and evaluated

in south Alabama during 1982 (fig. 1). The unit consisted of a 7.75ft-wide flail drum with eight sections

of alloy steel chains spaced along the length of the

drum. The drum was powered by a %-horsepower

auxiliary diesel engine. The chain flail was mounted

on a Clark 667 grapple skidder, which was utilized

to perform both skidding and flail-delimbing.

When the full (undelimbed) trees were skidded to

the deck, the skidder picked up bunches made by

the feller buncher. If the bunches had only a few

trees, several bunches were consolidated into one

large bundle of trees for skidding. The bundle was

dropped in front of the slasher at the deck. On the

ground, the bundle maintained its skidded configuration, with the tree butts clumped and stacked

together. The crowns and tops of the trees in the

bundle were slightly spread out, depending on the

number of stems in the bundle. No attempt was

made to spread the stems to facilitate the flailing

process.

‘The use of trade, firm, or corporation names is for the information and convenience of the reader. Such use does not

constitute an official endorsement or approval by the U.S. Department of Agriculture of any product or service to the

exclusion of others which may be suitable.

After dropping the bundle at the deck, the operator secured the empty grapple of the skidder and

drove the skidder backward, straddling the bundle,

to the base of the crowns. If the bundle had many

stems and created an obstacle too large to straddle,

the operator drove the skidder around to the tops

of the trees in the bundle and then drove down the

bundle with the flail held high and prepared for

delimbing.

Southern Forest Experiment StationIl-10210 U.S. Postal Services Bldg., 701 Loyola Avenue, New Orleans, La. 70113

Forest Service, U.S. Department of Agriculture.

Serving Alabama, Arkansas, Louisiana, Mississippi, E. Oklahoma, Tennessee, E. Texas, Puerto Rico, U.S. Virgin Islands

1
Figure l.--The Hydro-Ax LL64 Flail Delimber and Clark 667 Skidder.

Flail delimbing was always done from the base

of the crown to the top of the tree. The flail engine

ran continuously with the flail drum disengaged. To

delimb, the operator engaged the drum, positioned

and lowered the flail head, and drove backwards.

In the woods, the skidder operator always approached the bunches made by the feller buncher

from the tops of the trees and drove down the limbs

and tops to the bases of the crowns. There the operator engaged the drum, lowered the flail head, and

drove backwards to delimb the trees in the bunch.

After delimbing a bunch in the woods, the skidder

operator grappled the bunch and skidded it to the

deck. If the bunch was small, with too few trees for

a full grapple load, the operator would flail-delimb

other bunches. Then the skidder was used to accumulate these bunches into a bundle for skidding.

At the deck, the bundle of delimbed stems was

dropped in front of the slasher to be processed into

shortwood.

During the flail delimbing process, the flail drum

width did not always adequately cover all the crowns

of the trees in the bunches in the woods or the

bundles at the deck. In that case, the operator would

reposition the skidder and make another pass. In

doing this, he raised the flail head and then maneuvered the skidder over to cover the unprocessed

stems. Then he drove the skidder down to the bases

of the crowns and made another delimbing pass on

the bunch or bundle. Sometimes, several passes

were made on the same trees without repositioning

the skidder. This was done to improve the delimbing

quality.

DATA COLLECTION

When a bundle was flailed at the deck, each treebutt diameter was measured. Total heights, clearbole lengths, merchantable heights, and d.b.h. were

measured for two trees per bundle. These data were

used to determine the number of stems, average

d.b.h., average total height, average merchantable

height, average clear-bole length, bundle volume,

and bundle basal area for production analyses. The

same information was collected for the individual

bunches that were flailed in the stand.

Time study data of the operation were recorded

on video tape. Elements were timed from the video

Bryce J. Stokes is a Research Engineer, Southern Forest Experiment Station, Forest Service--USDA, Auburn, Alabama.

2
tapes and analyzed: no skidding time data were

collected. After the skidder had pulled full-tree

bundles to the deck, the following time elements

were recorded after dropping the load: (1) travel

and positioning to flail, and (2) flailing. In the woods,

the same time elements were recorded after the

skidder had traveled empty to the first bunch to be

delimbed.

At the deck, the travel and positioning time included the time to secure the empty grapple, travel

to the crown tops, position the flail, and engage the

flail drum. In the woods, this element began upon

arrival at the first bunch to be delimbed, when the

operator stopped to engage the drum. It also included travel between bunches in the woods during

the delimbing process. The flailing element included

the actual flail time while traveling up and down

the trees for delimbing. It included travel from the

crown top to the lowest limb at the bottom of the

crown, with the flail head positioned above the trees.

Then the head was lowered, and the machine was

driven backwards for delimbing. When delimbing

at the deck, travel and pos,ition time was either the

time to back-up the bundle or to drive around the

bundle and position and engage the flail drum.

A pass consisted of travel with the head down

over the bunch or bundle while the trees were delimbed. The number of passes required varied because of the number of stems and the quality of

delimbing. Bunches and bundles with many trees

had crowns that covered such a large area that it

took more than one positioning of the flail. The flail

element was the time to make the passes and also

included the repositioning of the skidder and flail

head when multiple passes were required. The

number of passes and repositioning occurrences

were recorded for each bunch or bundle.

The quality of delimbing was measured by determining the number and length of limbs remaining

after flailing. Remaining limb lengths were categorized as (1) 2 inches or greater, but less than

6 inches; (2) 6 inches or greater, but less than 12

inches; and (3) 12 inches or greater.

DATA ANALYSES

Preliminary analyses of data on bunches and

bundle characteristics, travel and positioning times,

and flail times are shown in table 1. For simplification, characteristics and time were on a bundle

basis. A bundle is defined as accumulated bunches

of trees skidded to the deck and delimbed or as one

bunch of trees that was delimbed in the woods. The

average bundle consisted of about 38 trees. The

average total time for delimbing a bundle was 1.80

minutes. The operator made an average of 3.57

passes per bundle and had to reeosition 2.71 times

per bundle on the average. Thus, the average number of flail passes per position was 1.32.

Passes per position approximates the number of

passes over a stem. From the data, it was impossible to determine exactly how many times the flail

was operated over each individual stem. The configuration of the bundle dictated how many positions and passes were needed to adequately cover

all the crowns in the bundle. However, the number

of passes over a stem directly controls the quality of

Table l.-Summary of the bundle characteristics and time data

Variable No.

Observ.

Statistics

Mean Std. Dev. Range

Flail time (min/bundle) 2 1 1.10

Secure grapple’ time (min/bundle) 1 7 0.26

Travel & position time (min/bundle) 1 7 0.39

Total delimbing time (min/bundle) 1 7 1.60

Average d.b.h. per bundle (in) 2 1 4.33

Average total height (ft) 2 1 46.32

Passes per bundle 2 1 3.57

Flail repositions per bundle 2 1 2.71

Passes per position’ 2 1 1.32

Stems per bundle 2 1 36.43

0.34 0.67-l .61

0.04 0.22-O-37

0.06 0.30-0.46

0.43 1.32-2.55

0.29 3.5-5.3

1.26 44.249.9

1.21 2-7

0.72 1 4

0.51 l-3

12.29 7-54

‘Secure grapple was inherent to the type of grapple used and not necessarily a portion of

cycle for all skidders.

?Passes per position = (passes per bundle/positions per bundle) = approximate passes over

a stem.

3
the delimbing. Overlapping of the flail results in a

portion of the stems having multiple passes. For an

indication of the average number of passes over all

the stems in a bundle, the total number of passes

per bundle is divided by the number of positions per

bundle, As an example, if the operator makes two

passes before changing positions and one pass at

a new position, there would be three passes and

two positions for the bundle, an average of 1.5

passes over all the stems in the bundle.

Multiple regression analysis was used to model

the time elements as a function of the bundle characteristics, whether delimbing was done at the deck

or in the woods. An equation for the travel and positioning element could not be developed from the

limited data; therefore, the mean was used for this

production element. An attempt was made to predict

flail time as a function of stems per bundle, average

d.b.h., total height, merchantable height, clear-bole

length, crown ratios per bundle, bundle volume and

basal areas, passes and positions per bundle, and

average passes per position.

Correlation coefficients and graphs were used to

determine the influence of the variables in the

model. The only significant variable in the final

model was the average number of passes per position. The equation was: Bunch flail time (productive

minutes) = 0.1867 + 0.7066 X NPT, [FQ = 0.511

where NPT = Number of passes per position

(i.e., passes per stem).

Limb removal quality was analyzed using two

methods. First, the average number of limbs left on

each stem wascalculated for each limb-length category. Most of the limbs left were those of less than

6 inches in length, with a mean of 1.21 limbs per

stem (table 2). Also, the percentage of stems with

limbs left was computed; this was based on the

total number of stems tallied and the number of

limbs left per stem (table 3). This analysis showed

that 75.4 percent of the stems had three or fewer

Table 2.-Overall delimbing quality’

Limb length Limbs-per-tree statistics

(in) Mean Std. Dev. Range

2-<6 1.21 1.25 O-5

6-<12 0.68 1.13 O-5

212 0.70 1.14 O-5

‘During the case study, no attempt was made to determine factors affecting delimbing quality. Logically, delimbing quality is

a function of the number of passes over the stems (passes per

position). In the study, the average was 1.32. Any major deviation would probably result in a different quality.

Table 3.-Remaining limbs per tree

No. limbs No. trees Percentage

0 1 1

1 6

2 1 3

3 1 0

4 4

5 2

8 2

7 3

8 2

Total

20.6

11.3

24.5

18.8

7.5

3.8

3.8

5.7

3.8

100.0

limbs left on the stems after flailing. Also, 20.8 percent of the stems had no limbs greater than 2 inches

in length left on the boles (see figs. 2 and 3).

As an observation, delimbing quality tended to

decrease as the number. of stems in a bundle increased. Also, the longer limbs remaining after delimbing were confined to the tops of the stems,

above the merchantable limit; these limbs were

discarded after slashing.

PRODUCTION AND COSTS

Fixed costs (1984) were calculated and operating

costs were estimated for the machines used in the

study. Because of the short length of the study,

availab,ility and utilization of the machines were not

determined. The skidder with flail was estimated to

have a utilization rate of 70 percent for 2,000 scheduled machine hours per year. Flail production machine hours (PMH) was estimated to be 33 percent

of the skidder productive hours. This was based on

the field study and is assumed to be conservative.

Table 4 summarizes the skidder and flail-delimbing

costs.

Production analysis for the machine was based

on the skidding and flailing operations under the

average study conditions. The skid time per turn

was based on a production equation for a 112-hp

grapple skidder used in clear cutting (Tufts and

Stokes 1983). Table 5 shows that for an average skid

of 600 feet, the production for skidding only was

4.0 cunits (CCF) per PMH (100 ft3 of solid wood per

productive machine hour). At the same distance,

skidding and flailing production was 3.0 CCF per

PMH. Over the range of the skidding distance, the

average difference in production would be 0.58 CCF

per PMH.

Costs per CCF for skidding and skidding-flailing

over a range of distances are shown in table 6. In

determining these costs, the skidder was charged

for the entire productive hour, whether it was used

4
Figure P.-Flaifed trees.

Figure 3.-Flailing quality.

Table 4.-Cost analysis for the skidder-flail combination

Item

Skidder Flail’

Per year Per PMH Per year Per PMH

Fixed cost

Depreciation2

Taxes, int., & ins.

Total

Operating costs

Repair & maint.

Fuel

Lube & oil

Total

Total fixed and

operating

Skidder and flail

Labor3

Total fixed and

operating

$19,000 $13.54 $ 3,905 $ 8.45

13,000 9.29 3,212 8.95

$32,000 $22.83 $ 7,117 $15.40

$17,100 $12.21 $ 3,124 $ 6.76

3,892 2.78 887 1.92

1,168 .83 266 0.58

$22,160 $15.82 $ 4,277 $ 9.26

$54,160 $38.65 $11,394 $24.66

$14,300 $10.21

$65,554 $63.31

Total with labor $79,854 $73.52

‘Based on one-third of skidder production hours. Repair and maintenance costs were 80%

of annual depreciation. Fuel was 1.6 gallons per hour, with lube 30% of fuel cost. These

were considered conservative estimates.

?.kidder and flail life were 4 years; annual productive machine hours were 1,400 and 462,

respectively.

3Base wage was $5.50 per scheduled hour and 30 percent fringe benefits.
Table S-Production for skidding and skidding-flailing l

Skidding Skidding and flailing

Skid Time’ No. No. CCF* Flail time5 Total time No. No. CCF*

distance per turn turns trees per PMH per turn per turn turns trees per PMH

per PMH per PMH per PMH per PMH

ft m/n

300 3.07

400 3.61

500 4.16

600 4.71

700 5.25

600 5.60

900 6.35

1,000 6.69

1,100 7.44

1,200 7.99

1,300 6.53

19.5 351

16.6 299

14.4 259

12.7 229

11.4 205

10.3 165

9.4 169

6.7 157

6.1 146

7.5 135

7.0 126

6.1

5.2

4.5

4.0

3.6

3.2

3.0

2.7

2.6

2.4

2.2

I--m---e-. -m/n ----- -_--

1.56 4.63 13.0

1.56 5.17 11.6

1.56 5.72 10.5

1.56 6.27 9.6

1.56 6.81 8.8

1.56 7.36 8.2

1.56 7.91 7.6

1.56 8.45 7.1

1.56 9.00 6.7

1.56 9.55 6.3

1.56 10.09 5.9

189

173

158

148

137

128

121

113

106

4.1

3.7

3.3

3.0

2.8

2.6

2.4

2.2

2.1

2.0

1.9

‘Productivity is based on turn size of 18 trees as sized in footnote 2. A turn is a complete skidding cycle.

*CCF (cunit) is 100 cubic feet of wood. Tree volume based on study average of 4.5in d.b.h. and 46-ft total height. Volumes were to

3-m (o.b.) merchantable top.

Total flail time per turn is the time required to flail-delimb a bundle, based on 1.0 passes per stem using the equation and adding

travel and position average time, and average time to secure grapple.

Table 6.-Costs for skidding and skidding-flailing1

Skld

distance

Skidding Production machine hour Skidding and flailing $/CCF

Skidder Labor Total Skid Flail Skidder’ Flails Labor Total difference3

ft ------dollars per CCF------ .---percent---

300 6.34 1.67 8.01 6 7 3 3

400 7.43 1.96 9.39 7 0 3 0

500 8.59 2.27 10.86 7 3 2 7

600 9.66 2.55 12.21 7 6 2 4

700 10.74 2.84 13.58 7 8 2 2

800 12.08 3.19 15.27 7 9 2 1

900 12.88 3.46 16.28 8 1 1 9

1,000 14.31 3.78 18.09 8 2 1 8

1,100 14.87 3.93 18.80 8 3 1 7

1,200 16.10 4.25 20.35 8 4 1 6

1,300 17.57 4.64 22.21 8 5 1 5

------dollars per CCf ------

9.43 1.98 2.49

10.45 2.00 2.76

11.71 2.02 3.09

12.88 1.97 3.40

13.80 1.94 3.65

14.87 1.99 3.93

16.10 1.95 4.25

17.57 2.02 4.64

18.40 2.00 4.86

19.33 1.97 5.11

20.34 1.95 5.37

Avg. 1.98

13.90

15.21

18.82

18.25

19.39

20.79

22.30

24.23

25.26

26.44

27.66

5.89

5.82

5.96

6.04

5.81

5.52

6.02

6.14

6.46

6.09

5.45

Avg. 5.92

‘For 1 hour of production, costs are based on the actual time for skidding and the actual time for flail-delimbing at these distances.

The skidder was charged for the entire hour because it is the carrier for the flail. The flail was only charged for that portion of the

hour that it was actually delimbing.

‘Differences are due to rounding errors; with all factors constant for flailing portion of cycle, the flail costs should be constant.
for skidding or flailing. Flail-delimbing costs are

based on the actual flailing time. At the 600-foot

distance, the cost per CCF for skidding only was

$12.21. Skidding-failing cost at 600 feet was $18.25

per CCF, a difference of $6.04 per CCF. This represents the actual cost for flail-delimbing at that distance. The average cost for flailing was $5.92 per

CCF.

SUMMARY AND CONCLUSIONS

The machine in this study worked well on small

pines in the range of 3 to 5 inches d.b.h. The average time to completely flail-delimb a bundle was

1.8 minutes of productive time. An average bundle

consisted of 38 stems. Most of the limbs left on the

stem after delimbing were less than 6 inches long.

Over 75 percent of the stems had three or fewer

limbs remaining after delimbing. No trees in this test

had limbs large enough to determine the upper limb

diameter that could be removed by the flail.

Flail cost was determined by the difference between skidding and skidding-flailing because of the

productivity loss of the skidder when flailing. The

average cost difference for the stand type in the

study was $5.92 per CCF. More field studies of the

flail method of delimbing should be obtained under

various stand conditions to better evaluate the

potential of such a system.

LITERATURE CITED

Tufts, Robert; Stokes, Bryce J. Productivity of

rubber-tired grapple skidders. New Orleans, LA:

U.S. Department of Agriculture, Forest Service,

Southern Forest Experiment Station, in cooperation with Department of Forestry, Auburn, AL;

1983; 34 p,