Whether
designing aircraft tires or simply talking about them, standardization
of terms is vitally important to ensure a common understanding between
user, supplier and manufacturer.
What
follows, then, is a glossary and explanation of terms, and facts
and figures about aircraft tires in general. You can quickly tour
through them by clicking on these hot-linked list of topics:
Main
Wheel Tires
Nose
Wheel Tires
Inflation Under Load
Tire Measuring Procedure
Operating Tire Temperatures
Load Ratings for Helicopters
Radius of Gyration
.
Main Wheel Tires
In the selection of tires for newly designed aircraft, allowances
should be made to provide an increase in loading capability.
Aircraft
growth is generally experienced during the complete life of the
aircraft starting from the prototype to the first production units
and progressing to heavier weight versions to meet the requirements
dictated by the operators of the aircraft. The selection of a tire
that permits an increased load rating capability will avoid the
costly necessity of a change in tire size or wheel details required
to support the heavier version aircraft.
The main
wheel tire requirements should be based upon the most aft center
of gravity location and the ground operational load-speed-time history
considered to be the most severe during normal service operations.
Consideration should be given to operations at high elevation airports
and also high ambient temperatures.
.
Nose Wheel Tires
It is important that the selection of a nose wheel tire be reviewed
from both a static load requirement and also a dynamic braking condition.
Again, care should be taken during initial selection of the tire
to program allowances for loading growth to avoid possible retrofitting
in the future.
In the
case of the nose wheel tire, the load should be based upon the most
forward center of gravity location.
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.
Inflation Under Load
The inflation pressures shown are for unloaded tires. When tires
are inflated under load, the applicable pressures should be increased
four percent. For example:
| Rated
static load and inflation |
|
38,300
lb at 185 psi |
| Operating
static load |
--
Case 1 |
38,300
lb |
|
--
Case 2 |
37,000
lb |
|
|
|
| For
Case 1, inflate tire |
--
If unloaded |
185
psi |
|
--
If loaded |
185
x 1.04 = 192 psi |
|
|
|
| For
Case 2, inflate tire |
--
If unloaded |
37,000
38,300 x 185 = 179 psi |
|
|
|
|
--
If loaded |
37,000
38,000 x 185 x 1.04 = 186 psi |
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.
Tire Measuring Procedure
Before a tire can be measured, it must be mounted on its proper
rim, inflated to the pressure given in the applicable table of the
Tire Data section, allowed to stand at least 12 hours at ambient
room temperature, and the pressure checked. The outside diameter
of the tire should be determined by measuring circumferentially:
OD = Circumference
-------------
3.1416
.
Operating Tire Temperatures
Aircraft tires shown in this website are not recommended for usage
where tire surface temperatures exceed 225 degrees F (107 degrees
C), or where brake and heat results in temperatures that exceed
300 degrees F (149 degrees C) at wheel surfaces adjacent to the
tire and tube. Consult Goodyear for operation outside these limits.
.
Load Ratings Used for Helicopters
Special load ratings have been set up for tires used on helicopters.
When
used on helicopters, standard aircraft tires may be rated up to
a factor of 1.50 for both load and inflation.
Maximum
permissible inflation is 1.8 times normal aircraft inflation.Maximum
allowance dimensions for new tires used on helicopters are four
percent larger than maximum aircraft tire dimensions. (In calculating
maximum outside and shoulder diameters, rim diameters are deducted
before applying the four percent.)
Radius of Gyration
Tire
Assemblies
The approximate values for the radius of gyration of tire assemblies
are calculated by using the following formula:
Radius of gyration = Max. O.D. + Min. O.D.
---------------------
5.12
Wheel
Assemblies
(Including rotating brake parts)
Approximate values for radii of gyration of wheel assemblies are
calculated by using the following formula:
Radius
of gyration = 0.40 x "D" ("D" = rim ledge diameter).
(The
above formula is accurate to +/- 20 percent.)
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Courtesy
of The Goodyear Tire & Rubber Company
|
