NATIONAL BUREAU OF STANDARDS REPORT

4086

RESULTS OP STATIC LOADING TESTS OP

ELPACA GRATINGS BY AIRCRAFT TIRES

by

L* K* Irwin

Report to

Equipment Laboratory

Wright Air Development Center

Department of the Air Force

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
U. S. DEPARTMENT OF COMMERCE

Sinclair Weeks, Secretary

NATIONAL BUREAU OF STANDARDS

A. V. Astin, Director

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NATIONAL BUREAU OF STANDARDS REPORT

NBS PROJECT NBS REPORT

0201-20-2331 May 1955 i;086

RESULTS OP STATIC LOADING TESTS OF

ELFACA GRATINGS BY AIRCRAFT TIRES

by

L 0 K 0 Irwin

Engineering Mechanics Section

Mechanics Division

Equipment Laboratory

Wright Air Development Center

Department of the Air Force

NBS Lab. No. 6. 4/2-85-

2

<^NBS>

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

The publication, reprii

unless permission Is ob

25, D.C, Such permis

cal ly prepared If that

Approved for public release by the

director of the National Institute of

Standards and Technology (NIST) on October 9, 2015

tart, is prohibited

ards, Washington

t has been specifit for its own use,
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RESULTS OP STATIC LOADING TESTS OP

ELFACA GRATINGS BY AIRCRAFT TIRES

by

L® Ko Irwin

1® INTRODUCTION

The need for illumination without obstructions on or

very near to runways and deceleration areas of airports led

to the design of a system of recessed lights with steel

grids or gratings to protect the lights from aircraft tires»

Limited use has been made of gratings with the trade name

"Elfaca" at overseas installations® The performance of these

gratings has not been determined and evaluated for the large

variety of tire sizes and landing and deceleration loads

that can be expected in civil and military aircraft

At the request of the Equipment Laboratory* Wright Air

Development Center* tests with static loads were undertaken

to ; study the effects of Elfaca gratings upon two sizes of

aircraft tires<>

2® TEST SAMPLES AND APPARATUS

The aircraft tires were sizes 20xl4.®l^* 10-ply rating and

26x6®6* 12-ply rating® Two Elfaca gratings* designated types

0200-SB and 3130-E* were used® Compressive loads were applied to the tires and gratings with a testing machine of

10,000,000-lb capacity® An auxiliary load measuring system

was placed in series with the reaction head and the loading

fixture to indicate the loads applied by the machine with increased sensitivity® The test fixture* a 20xi^o4 tire* a

type 0200-SB grating and the load sensing devices are shown

in figure 1® The load was applied by means of a test fixture

of rolled steel sections and 1 l/l^-inch steel plate to a

steel shaft through the wheel® Precautions were taken to

prevent motion of the test fixture parallel to the axis of

the wheel® Deflection measurements were made during these

tests with dial gages®
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NBS Lab. No. 6.4/2-85-2 page 2

3 . TEST PROCEDURES

The tires and gratings were set up in a compression

testing machine so that the tires could be loaded by the gratings with various orientations of the bars relative to the

tires® Also each tire was loaded on a flat steel plate to

provide a base for comparing the load-deflection relations

of the tire on the gratingSo The test positions of each tire

and grating combination are given in table 1©

Continuously increasing compressive loads were applied

and values of load and deflection were determined simultaneously,, The vertical deflections of the axis of the wheel

relative to the top of the grating or flat plat were measured

for all tests© Also the deflections of the tops of the bars

parallel to the axis of the wheel were measured during tests

!j. and 5 of the 26x6® 6 tire©

The position of no load and zero deflection was taken

to be that position in which the tire and one or more bars

of the grating had made sufficient contact to prevent easy

rotation of the wheel by hand© The air pressure in the tires

with no load was measured periodically to be 155 Ib/in? in

the 20xi;o 4 and 165 lb/in? in the 26x6 ©6 tire©

4© RESULTS

4.1 Size 20x4ol|. Tire

The tire was photographed for each test position while

sustaining the rated static load* 3750 lb* and the maximum

load applied© These load conditions are shown in figures 2

to 11* inclusive© Load-deflection curves for the 20xij.ol4.

tire in the various test positions are shown in figure 12©

The deflections for opposite sides of the tire were averaged

for each load© The tests were stopped when it appeared that

the wheel flange was bearing directly on double thicknesses

of the casing and tube* or the deflections were large enough

to cause the lower edge of the flange to be below the tops

of the bars* see figure 11©

The deflections at the rated static load* 3750 lb* and

the loads required to cause 2- inch deflection for the various

test positions are listed in table 2©
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NBS Lab. No. 6.U/2-85-2 page 3

lj..2 Size 26x6o6 Tire

Photographs of the 26x6.6 tire in each test position

while sustaining the rated static load, 8,000 lb, and the

maximum load applied are shown in figures 13 to 22, inclusive. Load-deflection curves for this tire in each test

position are given in figure 23® The deflection values are

the average of measurements made on opposite sides of the

tire. The tests were stopped at 20,000-lb load with the

tire on a flat plate and at 18, 000-lb load in the other

test positions to avoid possible damage to the tire which

might influence the results of subsequent tests.

The deflections measured at the rated static load,

8,000 lb, and the loads required to cause 3”in. deflection

are given in table 2. The lateral deflections of the top

of the bars as measured during tests Ij. and 5> of the 26x6.6

tire, figures 19 through 22, ranged from 0.02 to 0.07 in. at

the maximum test loads. Visual examination of the bars and

gratings after the tests did not reveal any damage.

5. DISCUSSION

The load-deflection curves for the tests of the 2OXI4.J4.

tire on two Elfaca gratings indicate that when the tire is

supported by one bar of the gratings and the load sustained

by the tire and grating exceeds the rated static load, the

deflections of the tire are sufficiently large that the flange

of the wheel lies below the top of the grating as shown in

figure 11. It seems likely that relatively large forces

might result from operating conditions under which the wheel

is required to climb out of the grating while sustaining

maximum service loads. The magnitude and effects of these

forces on the tire and aircraft should be determined analytically or experimentally.

The tests of the 26x6.6 tire on two Elfaca gratings

Indicate that the tire probably would traverse the two types

of gratings considered without serious damage to either tire

or grating.

Several factors which cannot be evaluated adequately

from the static tests reported include

(a) the tendency of rolling wheels to "track", that

is, to travel parallel to the axes of bars while

the main body of the aircraft travels skew to

the axes of the bars.
,-T «< -
NBS Lab Noo 6«l|./2-95-2 page I4.

(b) the cutting action of the bars on the tread of

skidding tires*

(c) the forces developed in the undercarriage when

tire is required to climb out of the grating*

(d) the structural strength and stability of the

bars which make up the grating when loads are

applied skew to the axis of the maximum principal moment of inertia of the bars*

The effects of these factors should be determined analyt

ically or experimentally*

For the Director,

7$

B* L® Wilson, Chief,

Engineering Mechanics Section,

Division of Mechanics*

Washington, D* C*
.

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NBS Lab. No. 6.lj./2-85=2 page 5

Table 1. Test Positions of 20 and 26x6.6 Tires On

Elfaca Gratings

Test

Type of

grating

No® of bars

supporting tire

Average distancebetween bars

under of wheel

Figure

Nos©

1 (a)

20x14.. 4- Tire

(a)

in*

2 , 3

2 0200-SB 2 2.51 b» 5

3 0200-SB 3 1.22 6, 7

b 3130-E (b) 3.18 8, 9

5 3130-E 1 2.30 10, 11

1 (a)

26x6.6 Tire

(a) O as 13, 11+

2 3130-E 2 2.30 15, 16

3 3130-E (b) 3.18 17, 18

b 3130-E 3 2.30 19, 20

5 0200-SB 5 1©22 21 p 22

(a) Tire supported on flat plate

(b) Axis of tire at l\.5 e to long dimension of bars
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NBS Lab. No. 6.4/2-85-2 page 6

Table 2» Results of Static Load Tests of 20x4*4 and

26x6o6 Tires on Elfaca Gratings

Test

Deflection

at rated

static load

Load at

2 inche s deflection

Load at

3 inches

deflection

Maximum

test

load

in« lb lb lb

20x4*4 Tire

1 0.98 10,900 — 11,500

2 0 o 97 10, 900(a) -- 10,000

3 1*12 8,100 OK> HO 11,000

4 1*29 6,600 — 9,000

5 1*93 3,900 — 5,800

26x6 0 6 Tire

1 1.58 ob e=> 18,100 20,000

2 1*70 e=» eo 13,950 18,000

3 1.74 a so 16,600 18,000

4 1*70 — 17,400 18,000

5 1.68 flees 16,400 18,000

(a) Load=»deflection curve extrapolated to obtain

this value

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Figure 1. Test set-up of a 20x4.4 aircraft tire and a

type "Elfaca" grating.

ozoo~ 5*B

m

Figure 2.

A 20x4.4 aircraft tire on a flat steel plate.

Load = 3,750 lb.

i

El

M

II

Figure 3. A 20x4.4- aircraft tire on a flat steel plate,

• Load = 11,500 lb.

<$BS>
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Figure 4. A 20x4.4 aircraft tire on two bare of a type

0200- SB ’‘Elfaca 11 grating. Load = 3 , 75° lb.

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Figure 5. A 20x4; 4 aircraft tire on two bars of a type

0200-S3 11 Elfaca'1 grating. Load = 10,000 lb.

Figure 6. A 20x4.4 aircraft tire on three bars of a

type 0200- SB "Elfaca" grating.

Load = 3,750 lb.

I ' si/ t #

Figure 7. A 20x4.4 aircraft tire on three bars of a

type 0200- SB "Elfaca" grating.

Load = 11,000 lb.

Figure g. A 20x4.4 aircraft tire at 45° to the bars of

a type 3 ^- 3^-E n Elfaca H grating.

Load = 3,750 lb.

Figure 9. A 20x4.4 aircraft tire at 4^° to the bars of

a type Jl'yQ-E "Elfaca" grating.

Load = 9,000 lb.

\

Figure 10. A 20x4.4 aircraft tire on one bar of a type

3130-S "Elfaca 11 grating. Load = 3,750 lb.
#
Figure 11. A 20x4.4 aircraft tire on one* bar of a type

3130“S M ElfacaM grating. Load = 5 ,300 lb.

Load,

lb

Symbol Test Grating

2,000 -

0200-SB

0200-SB

31 30 -E

3130-E

Fig. 12 Load-deflection relations for c 20 x 4.4 aircraft

tire on "E/faca"grating.

I

Figure 13. A 26x6.6 aircraft tire on a 'flat steel plate

Load = g,000 lb.

Figure 1U-. A 26x6.6 aircraft tire on a flat steel plate

Load = 20,000 lb.

f

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Figure 15. A 26x6.6 aircraft tire on two bars of a type

3130-2 n Elfaca H grating. Load = 3,000 lb.

<NBS>

Figure 16. A 26x6.6 aircraft tire on two bars of a type

313O-E "Elfaca” grating. Load = 12,000 lb.

#)

A 26x6.6 aircraft tire at ^5° to the bars of

a type 3 1 3°“E

H Elfaca M grating.

Load = 13,000 lb.

• A 26x6.6 aircraft tire on three bars of a

type 3130-E "Elfaca” grating.

Load = g,000 lb.

Figure 19

Figure 20. A 26x6.6 aircraft tire on three bars of a

type 3130-E "Elfaca" grating.

Load = IS, 000 lb.

I

type 0200-SB "Elfaca" grating.

Load = 8,000 lb.

I

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Figure 22. A 26x6.6 aircraft- tire on five bars of a

type 0200-SB "Elfaca" grating.

Load = 18,000 lb.

Fig. 23 Load -deflection relations for a 26 x 6.6 aircraft tire on

"E/faca "gratings.

THE NATIONAL BUREAU OF STANDARDS

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3, 1901, as amended by Congress in Public Law 619, 1950. These include the development and

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