-TLg?

NATIONAL BUREAU OF STANDARDS REPORT

NBS PROJECT October 1, 1954 to December 31,3 .9*NBS REPORT

PROGRESS REPORT OB DP GIBE AXE

CLEAKITG

BY

Car1 T, Coblents

Heating and Air Conditioning Section

Building Technology i vision

to

Office of the Chief of Transportation

Department of the Army

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

The publication, repr Approved for public release by the

1 pa,t| ls prohlblted

unless permission iso C

"dards, Washington

1003-20-4^3 ^ 3$?2

unless permission iso

25. D. C. Such perm

cal ly prepared If t hf

Director of the National Institute of

Standards and Technology (NIST)

on October 9, 2015.

ort has been speclfilort for Its own use.

paoorjtjs u.‘Pq::t of iraxo a ir clears

(Inspection of Two Helicopter Engines)

A 200 H.P. air cooled Franklin en :;ine, j-odel #-335-6,

Serial t/'B 600422, with six opposed cylinders was shipped

here from Port Sill, Oklahoma, According to information,

the engine had been exchanged after 2&1 hour© of service because of high oil consumption.

The cylinders and pistons of the engine were disassembled

me cleaned with varsol. Ho marks of extensive wear wore

noticed on any part and the extent of wear appeared similar

on all cylinders and pistons. Figure 1 shows a photograph

of two pistons with connecting rods. The right hand piston

was only washed and appears as it was removed frost the cylinder whereas on the left hand piston the rings were taken off

and the walls scraped free of carbon so that the score marks

above the first compression ring are clearly visible. These

score marks indicate that dust particles of considerable site

had reached the cylinders through the air induction system.

The piston skirts appeared smooth and showed no score marks.

To determine the extent as well as the similarity of the

wear five micrometer caliper measurements were made on each

piston. 'Hie first three measurements were made at right angles

to the piston pins;
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a. Above the first ring,

b« Just below the oil ring and

c. At the bottom of the skirt.

The two other me .surements were mad© in the axis of

the oins:

d. Above the first ring and

e. Just below the oil ring*

The following table shows the results of these measuremeats;

Piston #3 #2

TABLE 1

... #3 „ Ik. ll. - #6 .

a. 4.4715 4.4741 4.4730 4.4730 4.4710 4.4725

b. 4.4955 4.4950 4.4955 4.4962 4 * 494

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4.4961

c • 4.4971 4.4972 4.4950 4.4930 4.4975 4.4935

d. 4.4713 4.4732 4.4732 4.4732 4.4715 4.4730

0. 4.4525 4.4355 4 . 4*541 4.4541

... a' " • :

4.4335 4.4330

This table indicates that all pistons are worn off more

at the top then on the lower end* The difference between the

measurements at the top and across the skirt varies .from 0.023?

inch on piston 2 to 0.0265 inch on piston 5, the average

difference was 0.0253 inch in the plane vertical to the piston

pins. The difference of measurements in the axis of the piston

pins was much smaller, as was to be expected, since there was

no tilting force in this plane. As the engine had been operating in a vertical position the piston pin covers were worn
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smooth and shiny on the lower side and corroded with carbon

on the upper side* However, no difference in the piston

wear was noticed between these two sides* All upper compression rings had "worn loose in the grooves, whereas the second

rings had become stuck, in the grooves with soot and had to be

tapped to be removed*

Figure 2 shows a photograph of two pairs of valves, the

left pair as it was removed from the cylinder and the right

hand pair with the carbon brushed off* The valve lip of the

cleaned exhaust valve was badly pitted but there was no wear

noticeable on the valve stems*

All valve springs apt eared to be in good condition*

The cylinder diameters were determined twice along a

line drawn between the valves and twice at a. right angle to

that line* One pair of readings was taken near the top dead

center of the piston travel and the other near the bottom of

the cylinder* At T

7 -C the maximum diameter measured was 4*5071

inch in cylinder 4 and the minimum was 4*5020 inch in cylinder

3, the average valve was 4*5041 inch. In all cases, the cylinders were snaller at the base, the diameters ranged from 4.5049

inch to 4.0503 inch, the average 4.5022 inch.

All cylinders appeared in a good condition as ir dl Gated

in the photograph of cylinder i-2 in figure 3. There were no
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visible score marks as on the pistons. The seats of the intake valves showed very little or no pitting at all, whereas

all the exhaust valve seats were more or less pitted.

An oily film noticed in the intake manifold was washed

out with gasoline to determine whether dust particles from

the induction air could be found there. The gasoline was

allowed to settle and a few drops were put on a siicroscopic

slide which was then placed on the bottom of a beaker with

clean gasoline to remove the green dye that was used to identify the gasoline and had deposited on the manifold walls. After

drying, the slides ware inspected on a micro-projector and

dust particles up to 100 micron sis® were found, A high percentage of the larger particles could clearly be identified

as sand,

Sesults of the Inspection of An 0-470 Engine

A 213 l.P* air cooled Continental engine with opposed

cylind rs, . .odd 0-470-11 , Serial ? 100600, arrived at this

Bureau from Fort Bragg* H, 0* , just after the inspection of

the Franklin engine was completed. Information on a form

b'D 535 stated that this engine had operated 255-3/4 hours and

bad been exchanged because of low compression and excessive

oil consumption (4 quarts per hour)..

The inspection of this engine was made in the same manner

as that of the Franklin engine, and the general condition was
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found to be about the same. Figure 4 shows the second piston

with connecting rod, wrist pin and fc e first compression ring*

This ring was found broken in the middle when the piston was

removed from the cylinder* The outside of this ring was shiny

and smooth only about 1/2 inch from either of the four ends,

whereas the rest of the outside was black and covered with

carbon* This showed that only the ends had been b aring

against the cylinder walls and. the break of the ring must

have occurred while the engine was still in operation. There

are score marks on the lower part of the piston but these are

much finer than those on the upper part.

Figure 5 shows the first compression ring of cylinder 3

inserted in the lower part of that cylinder, leaving a gap

of 0.31 inch. This gap indicates .an out side wear of that ring

of nearly 0*05 inch.

The following table shows the piston measurements taken

from this engine in the same order as indicated in Tble I.

TtHtB II

Piston 11 f

2 #3 . 4 . If #6

a* 4.9652 4.9630 4.9650 4.9650 4.9650 4.9645

be 4.9858 4.9844 4.9843 4.9848 4.9840 4.9343

c. 4.9910 4.9910 4.992O 4.9923 4.9920 4.9919

d. 4.9673 4.9675 4.9670 4.9675 4.9672 4.9671

e. 4.9861 4.9375 4.9354 4.9370 4. 9%0 4.9^63
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Measurements of the various inside diameters of the

cylinders were made in the same manner as in the 0-335. At

top dead center, the maximum diameter was 5*0035” in cylinder

'3, the minimum measured was 5*0000” in cylinders f$ and G6 # and the average was 5*0015”* At the bottom of the piston

travel the maximum diameter was 5*0050” in cylinder 2, the

minimum 5 * 0005"in cylinder |5» the average was 5*0029”*

k microscopic examination of the deposits from the intake manifold, conducted in the same manner as previously described, revealed the presence of dust particles of up to

approximately 250-mieron size, also some fibrous particles

were noticed.

examination of he C-rankcase Oil

Approximately two gallons of used engine oil were received

wit; each of the two engines and It was assumed that t

: is oil

had been drained before packing the engines. Gars i £ov B were

packed with the Franklin engine and can Q was packed with the

Continental engine.

To obtain information as to the content of foreign matter

all three cans were turned over to the Fur© Substances Section

of this Bureau for a spectographic examination* A copy of

this report is attached and shows that metallic impurities and

silicon ware found present only as minor constituents of between 0.01 to 0.10.3 by weight*
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It was considered possible that due to the long standing

of the cans the heavy metallic and silicon particles had

settled out and adhered to the bottom in such a manner that,

they could not be removed by suction as in d been the spectroscopic examined samples** special spoon was made and

sludge scraped off the bottom of each can. These samples

were microscopically examined in a way similar to that found

in the intake manifolds. The solid particles observed were

below 20 micron siae and small in number# This leads to the

conclusion that either no appreciable amount of dust penetrated into the crankcase breather system or the sample oil

was drawn off the top of the oil sump and the heavy material

left there and wiped before the engines were packed. The

oil sumps of both engines did not contain noticeable traces

of sludge.

Test Results Gn A ftotat'i nz Filter

A series of 64 tests was conducted with a regular 7-1/2

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•. j inch, squirrel cage blower running in reverse. The only

ffiodif: : -n made on this blower consisted in a 1/2 in. wide

slot cut into the scroll close to a point where it is nearest

to the blower wheel* This point where the concentration of

the dust was high was selected for the blow-down. Figure 6

shows the arrangement made. Air is drawn through the rotating filter by a blower, not shown on this photograph. A
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3 irch duct visible in the upper center has an orifice flow

meter installed and draws the air from the inside of the

squirrel case* The blow-down is flown through a rubber hose

into a rectangular canister underneath the filter* This

canister contains a flannel hag which retained most of the

dust rejected by the rotating filter* The air flow rate

through this bag was also measured with an orifice flow meter

and was adjusted to .maintain the desired ratio between total

air flown through the filter and the blow-down air. . variable speed motor permitted adjustment of the filter speed •

in a wide range*

The dust is introduced 1* to a square duct attached to

the blower by means of an aspirator operated with cor- pressed

air. The aspirator picks up the dust out. of either of two

concentric .grooves on a turntable attached to a Graham variable

speed transmission drive* A hopper feeds the dust into the

grooves of the turntable to an adjustable height so that the

feed rate is constant to a very close degree* The hopper has

a vibrator attached to avoid clogging of the feeder tube*

Four feet from the filter the air sampling device is installed as shown in Fi gure ?• Exchangeable nozzles from

3/4 inch to 13/32 inch diameter permit the drawing of sampling

air isokinetically over a wide range of air velocities in the

duct at a flow rate of between 1 efra and 2 cfm* The maximum
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flow rate of the sampling air is determined by the limited

tensile stren -tb of the absolute filter a 0.3 micron glass

fibre paper which is clamped in a 3 inch holder and will

retain 100$ of all dust particles above 0.3 micron alee.

The sampling paper holder is clamped between two pipe bell

cap© and air is drawn through it by special vacuus pumps.

The samplers are weighted before and after each test to the

nearest 0.1 milligram.

Figure & is a photograph of the test panel showing in

the center a manifold which permits the calibrated gas meter

to be put in series with either of the two constant velocity

flew meters and -to control the air flow rate through the

sampler or cascade Impacter , as is desired. The flow meters

are used to adjust to a certain flow rate and to maintain it

constant ' during the test period whereas the gas meter is used

to determine the actual airflow volume, fids volume divided

by the test duration, determined with a stop watch, was found

to furnish a more precise value for the sampler airflow rate

than could be obtained with the flow meters. The inclined

gage at the top of the board is parallel-connected with the

first U-tube manometer to show the pressure drop across the

orifice in the 3 inch duct. The orifice flow meter was designed. and the flow rates calculated in accordance with the

A.l.h.h. handbook ’ Fluid haters, Their Theory and application-' •
• test #**•• '• a sasa. ;•?. te ^ tt s : -.4 r •'.->* a?: tfo •/•:

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The other three manometers show the pressure at the orifice

plate, the pressure drop across the sampler, and the vacuum

at the sampler flow meter*

The filtering efficiency of the rotating filter was

determined in two independent ways: {1} by using the dust

collected from the blow’ down in the flannel bag

P ~ ci B x 100#

D

where » efficiency determined from the blow- down,

D * total dust introduced i: to the filter, g

dp « weight increase of the flannel bag, g

{ 2) by using the glass fibre sampler

S - x 1Q0$

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where S

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* efficiency determined from the sampler method, f>

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g * weight increase of the sampler, g

H * ratio of total airflow rate to airflow rate

through the sampler.

A series of preliminary tests was conducted during which

the dust was introduced into the duct directly and the efficiency

determined at isokinetic flow at various flow rates was aero

within a satisfactory margin. In subsequent test the E

s values
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were always higher than the Eg values and the conclusion

was drawn that the flannel bag pass d a certain amount of

dust* All tests were made with k* C. Spark Plug dust coarse.

file airflow rate through the filter was tested between

50 efm and 250 efm at speeds ranging free 300 EPF to 1940 Ti- ,

The percentage of blow-down air was changed between l *1> to

24- whereas the dust doaceatratl -n was maintained at close

to 35 null 3 i. grams per cubic foot, the minimum concentration

u-ed was 24*0 ag/eit* ft* and the maximum was 40*9 mg/cu.ft.

The efficiencies observed with the sampler method

av: waged '7*2 and those observed with the blow-down bag

averaged 79* 3P>. Ho distinguished pattern as to a marked influence of any one of the variable indicated above and in

the range tested could be established to a degree of certainty.

Test Cf Air Mag© Aircraft Filters

4 group of seven Air Pass aircraft filters was furnished

this laboratory for the purpose of determining their operational characteristics* ^hese filters had an outside dimension

of T x 6-1/2* x 1* and an effective filter area of 6-1/2* x 6*,

they had a flock cover screen type filter medium and according

to an Air Masse catalogue had a design face velocity of 1050 ft/min

corresponding to 305 cfm for this size filter.*

There were two new filters and five used ones,. Three of

the used filters carried Information of their time of service,
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the other two did not have any identification, The two new

filters appeared to have been oiled in the factory, most of

the oil, however, seeias to have disappeared in storage. The

holding clips and gaskets were removed from the filters for

the purpose of installation in the test apparatus. The follow

ing table summarises the condition of the filters as received,

their weights, stripped of gasket and holding clips and the

pressure drop observed across the filters at 305 cfm airflow

rate.

TABLE III

! c. Condition feight, Pressure Crop, in G

1 used 234.9 1.3ft

2 used 9

;t 7 hrs. 239.7 1.14

3 used 331 hrs. 248.4 1.12

4 used 222.9 0.75

5 used 1226 hrs. 237. 6. O.83

6 new 21$.

1.97

7 new 220.6 1.93

A test apparatus similar to that described for the rotat1 up filter was built. however, a dust sampler was also drawn

upstream the filter for determining the dust content In the

air stream at the same relative position as downstream. Besides two sampling stations were provided to investigate the

•practicability of applying the discoloration tost method for
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engine air ©letters; the discoloration method has been

found the outstanding method for determining the operational

efficiency for dust filters arc has been well developed in

this Bureau* The number of tests conducted at this time do

not permit a decision on the merits of this method*

The efficiency of the filters was determined as

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where E » effiency, %

U « dust collected on the upstream sampler, g

B *» dust collected ©a the downstream sampler, g

The efficiency was also determined as the ratio of the

actual weight increase of th® test filter and the amount of

dust introduced into the apparatus. The efficiency values

obtained by the latter means agreed with those determined

with weighing the sampler, but were always a little lower

because of the unavoidable loss of some dust, when removing

the test specimen from the apparatus*

Figure 9 shows a photograph of the entire test duct with

the test panel in the background* The adapter for holding

the filters is in the middle of the duct and below it on the

floor is shown an inverted funnel used for oiling. and draining four filters at one time. Figure 10 shows a close-up view

of the test panel.
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To determine the effect of oiling on these kinds of

filters the two new filters were loaded up to capacity with

. . C. Spark Plug dust fine and the efficiency determined byweighing the filter after 2Gg dust had been introduced into

the air stream with a dust concentration of approximately

20 ag/cu.ft. The airflow rate was maintained at 305 cfm,

except that at the end of the test with the oiled filter the

pressure drop across the filter increased to such a value that

the exhaust capacity was reduced to 150 cfm. The results of

these tests are plotted in figure 11 which shows that the

efficiency of the oiled filter remains well above 90$ as the

filter clogged up for all practical purposes. The pressure

drop across the filter measured as 23.2 in • ,G. at 150 cfm

would have been very much higher if the airflow rate of 305 cfm

could have been maintained by the exhaust blower. The not

oiled showed an efficiency of $4.7$ at the beginning of the

test which dropped down to 39.2$ the pressure drop at that

efficiency had increased to 20.$ in. .G. and the test was

broken off because the efficiency was below any useful value and

also the limit of the blower capacity was reached.

In another test with a new oiled filter it was determined

that the introduction of 40g of dust i creased the pressure drop

from 3.2 in. 7.G. to 15.6 in. 7.0. and the efficiency computed

with the sampling method was 96.1$. It was noticed that the
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specification XL-P-7194 would require the pres .'.sure droi

of this filter not to exceed 3 In. . .0. after if producing

approximately 5% of dust into the air stream ; the required

filtering efficiency of 90^, however, is well exceeded.

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EFFECT of OILING of AIRMAZE AIRCRAFT FILTERS at 1050 Ft/Min F. V c

DUST LOAD _ GRAMS

FIG. 11

EFFICIENCY

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