Tyre Use - Wheels & Tyres - Airframes & Aircraft Systems #21
Summary
TLDRThis lesson delves into tire-related aviation issues, focusing on aquaplaning, a phenomenon where water builds up under the tire, causing loss of contact with the ground. It teaches how to calculate aquaplaning speed based on tire pressure and emphasizes the importance of monitoring tread depth to prevent it. The lesson also addresses tire wear, damage assessment, and the significance of tire creep, which is the movement of a tire on its rim. It introduces methods to detect creep and the process of tire retreading, highlighting the economic and safety benefits of repairing and retreading tires over replacing them.
Takeaways
- 💧 Aquaplaning occurs when a wedge of water builds up under the tire, causing a loss of contact with the ground.
- 📏 The aquaplaning speed can be calculated using the formula: aquaplaning speed = 9 * √P (psi) or 34 * √P (bar or kgf/cm²).
- 📉 The risk of aquaplaning increases as tire tread depth decreases, emphasizing the importance of tread assessment.
- 🔥 Applying brakes during aquaplaning can generate enough heat to potentially melt the tire tread.
- ⚠️ Pre-flight tire inspections should include checks for cuts, bulges, embedded foreign objects, wear, creep, and local sponginess.
- 🚫 Tires with cuts penetrating to the cords are unserviceable and must be replaced if the fabric is fractured.
- 🛑 Flat spots on tire treads, especially from skidding or aquaplaning, should be carefully examined for fabric weakening.
- 🔄 Tire creep is the movement of a tire on the rim after fitting, which can be monitored using painted marks on the wheel and tire.
- 🔧 Damaged aircraft tires can often be repaired or retreaded, saving costs compared to purchasing new tires.
- 🏗️ Retreading and repairing aircraft tires must be done at certified stations by qualified technicians to ensure safety regulations are met.
Q & A
What is aquaplaning or hydroplaning?
-Aquaplaning or hydroplaning is a phenomenon where a wedge of water builds up under the tread of the tire, causing it to lose contact with the ground.
How is the aquaplaning speed calculated?
-The aquaplaning speed can be calculated using the formula: aquaplaning speed equals nine times the square root of P (in psi) or 34 times the square root of P (in kgf/cm² or bar), where P is the tire pressure.
What factors increase the possibility of aquaplaning?
-The possibility of aquaplaning increases as the depth of the tread is reduced, so it's important to accurately assess the amount of tread remaining.
What happens when a tire aquaplanes?
-When a tire aquaplanes, the coefficient of dynamic friction between the tire and the ground reduces to very low values, typically near zero, making nosewheel steering and braking ineffective.
What can the heat generated during aquaplaning do to a tire?
-The heat generated between the tire and the water, especially if the brakes are applied during aquaplaning, may be sufficient to melt the tread of the tire.
What should be checked during a pre-flight tire inspection?
-During a pre-flight tire inspection, one must examine tires for cuts, bulges, embedded stones, metal or glass, signs of wear, creep, and local sponginess.
What is considered normal tire wear?
-Normal tire wear includes the presence of wear bars or red markers worn to the base of the marker grooves or to the casing cords, indicating it's time for replacement.
What is tire creep and why is it a problem?
-Tire creep is the movement of a tire slightly around the rim after it's first fitted to a wheel. Excessive creep can lead to damage, such as tearing out the inflation valve and causing a tire burst.
How is tire creep monitored?
-Tire creep is monitored by painting white lines, known as creep marks, one on the wheel and a matching one on the tire. Misalignment of these marks indicates creep.
Can damaged aircraft tires be repaired or retreaded?
-Yes, many aircraft tires that become damaged in service can be successfully repaired, and those with worn-out treads but an intact carcass can be retreaded.
What is the benefit of retreading aircraft tires?
-Retreading aircraft tires can save aircraft operators considerable sums of money as it is much cheaper than replacing with new tires and is a common practice.
Outlines
🚗 Tire Safety and Aquaplaning
This paragraph discusses the issues related to tire wear, damage, and the phenomenon of aquaplaning or hydroplaning. It explains how aquaplaning occurs when a wedge of water builds up under the tire, causing a loss of contact with the ground. The aquaplaning speed can be calculated using a specific formula based on tire pressure. The paragraph also highlights the importance of accurately assessing tire tread depth and the risks associated with reduced tread, such as increased likelihood of aquaplaning and reduced effectiveness of steering and braking. It also addresses the need for pre-flight inspections to check for tire damage and the criteria for determining if a tire can be repaired or must be replaced.
🛫 Tire Wear, Creep, and Retreading
The second paragraph focuses on the increased tire wear due to larger taxi distances at airports and recommends maintaining a speed limit to minimize wear. It defines 'creep' as the movement of a tire on the rim after fitting, which is normal initially but can lead to problems if it persists. The paragraph explains how to monitor creep using painted lines and the consequences of misalignment. It also touches on the possibility of repairing and retreading aircraft tires, which can save money for operators. The importance of certified technicians for retreading and repairing tires is emphasized, and the paragraph concludes with a reminder of the importance of understanding tire wear limits and the monitoring of creep.
Mindmap
Keywords
💡Aquaplaning
💡Tire Wear and Damage
💡Tire Creep
💡Tire Pressure
💡Tread Depth
💡Dynamic Friction
💡Retreading Tires
💡Pre-Flight Inspection
💡Tire Bead
💡Tire Cord
Highlights
Discussing the problems of creep and aquaplaning or hydroplaning.
Aquaplaning is caused by a wedge of water building up under the tire tread.
Aquaplaning speed can be calculated using a specific formula.
The possibility of aquaplaning increases as tire tread depth reduces.
Tire tread depth must be accurately assessed to prevent aquaplaning.
Aquaplaning results in a very low coefficient of dynamic friction.
Nosewheel steering and braking are ineffective during aquaplaning.
Heat generated during aquaplaning can potentially melt the tire tread.
Tires must be examined for various damages during pre-flight inspection.
Cuts in the tire that penetrate to the cords render the tire unserviceable.
Bulges in tires may indicate a partial failure of the casing.
Flat spots on tire tread caused by skidding or aquaplaning must be carefully examined.
Foreign bodies embedded in tires must be removed and assessed for damage.
Tire wear limits are indicated by marker grooves or cords.
Tires with visible fabric layers in the tread can continue in service.
Tire wear is increased by the larger taxi distances at modern airports.
Tire creep is a normal phenomenon when a tire is first fitted to a wheel.
Excessive creep can lead to tire damage and the need for replacement.
Creep marks are used to detect and monitor tire creep.
Aircraft tires can be successfully repaired or retreaded if the carcass is intact.
Retreading and repairing aircraft tires can save significant costs compared to new tires.
Retreading and repairing must be performed by certified technicians.
Transcripts
in this lesson we will discuss the
problems of creep
and if aquaplaning or hydroplaning we
will look at tire wear and damage we
will examine the problem of tire creep
and see how it is monitored
to end the lesson we will take a quick
look at the process of retreading tires
aquaplaning or hydroplaning is a
phenomenon caused by a wedge of water
building up under the tread of the tire
and breaking its contact with the ground
aquaplaning speed measured in nautical
miles per hour or knots is the speed at
which the tire loses contact with the
ground it can be found by applying the
formula
aquaplaning speed equals nine times the
square root of P where P is the tire
pressure in pounds per square inch
or aquaplaning speed equals 34 times the
square root of P where P is the tire
pressure in kilograms per square
centimeter or bar
the possibility of aquaplaning increases
as the depth of the tread is reduced it
is therefore important that the amount
of tread remaining is accurately assess
the coefficient of dynamic friction
between the tire and the ground will
reduce the very low values typically 0
when aquaplaning
neither nosewheel steering nor braking
will be effective when the wheels
aquaplaning
the heat generated between the tire and
the water if the brakes are applied
during aquaplaning may be sufficient to
melt the tread of the tire
here you may try an aqua planing
calculation enter a tire pressure
between 50 and 300 psi calculate the
aquaplaning speed and enter it in the
box
press go to check your calculation
you
during your pre-flight inspection tires
must be examined for cuts bulges
embedded stones metal or glass signs of
wear creep and local sponginess
cuts in the tire penetrating to the
chords render the tire and serviceable
the cords will be recognizable as pieces
of white fibrous material embedded in
the rubber of the tire
whether the tie can be repaired or must
be renewed is governed by the depth of
the cut
bulges may indicate a partial failure of
the casing if the casing has failed that
is to say the fabric is fractured and
the tire must be replaced any flat spots
on the tire tread especially those
caused by skidding or aquaplaning must
be examined with great care to determine
if the fabric of the tire has been
weakened unduly
foreign bodies such as pieces of metal
or glass or stones embedded in the tire
must be removed and the cuts probed with
a blunt tool by a technician to
ascertain their dabs
or renewal of the tire is governed by
the extent of the damage
if you are in any doubt about the
serviceability of a tire have it checked
before flight by a suitably qualified
technician
the amount of wear that a tire can be
subject to there is with different tire
types
some tires have market Aybar's in the
center groove on others the center
groove or the two grooves either side of
Center are used as wear indicators
generally patent red covers worn to the
base of the marker grooves or to the
marker tie bars for 25% of the tire
circumference or plain tread covers worn
to the casing cords must not be used
the special high-speed applications some
tires have a layer of fabric woven into
the tread these tires will have
reinforced red printed on the sidewall
this fabric may become visible during
normal wear this is perfectly normal and
the tire can continue in service with
this layer visible
with the increased size of modern
airports taxi distances have also
increased thus increasing the amount of
tire wear and risk of damage
to minimize tire wear it is recommended
that a speed of no more than 25 miles or
40 km/h should be reached during the
taxi run
when a tire is first fitted to a wheel
it tends to move slightly around the rim
this phenomenon is called creep and at
this stage it is considered normal
to the tire settles down however this
movement should cease
in service the timeI tend to continue to
creep around the wheel if this creep is
excessive on a tire fitted with an inner
tube it would tear out the inflation
valve and cause the tire to burst
creep is less of a problem with tubeless
tires as long as the tire bead is
undamaged and any pressure drop is
within limits creep is less likely to
occur if the tire gas pressure is
correctly maintained
in order to detect creep to white lines
known as creep marks are painted one on
the wheel and a matching one on the tire
if the lines become misaligned then the
tire is suffering from creep provided
the marks overlap each other the tire
can remain in service if however the
marks become completely misaligned then
the tire must be changed
many aircraft tires that become damaged
in service can be successfully repaired
tires of which the treads are worn out
flat spotted or otherwise damaged but of
which the core body or carcass is intact
can be retreaded
repairing aircraft tires has been a
common practice for many years and can
save aircraft operators considerable
sums of money
tires can be retreaded or repaired for
continued service at a cost much lower
than that of a new tire
Yaser regulations require retreading
and/or repairing of aircraft tires to be
performed in certified retread and
repair stations by or under the
responsibility of qualified and
certified technicians
you should now have a good understanding
of how much tire wear and damage is
acceptable
the aquaplaning formula is quite
important but probably more important is
the fact that if the tire is aquaplaning
then its coefficient of friction is at
or near zero
you should understand the problems
associated with creep and how it can be
monitored
finally remember that an aircraft tire
whose tread is worn beyond limits could
normally be repaired or retreaded many
times
you
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