1.Search and list out the total weight of various types of aircrafts.

MTOW = Maximum take-off weight, MLW = Maximum landing weight, TOR = Take-off run

Type	MTOW [kg]	MLW [tonnes]	TOR [m]	LR [m]
Antonov An-225	640,000	591.7	3500
Scaled Composites Model 351 Stratolaunch	589,670		3660
Airbus A380-800[1][2][3]	575,000	394	3100	1930
Boeing 747-8F	447,700	346.091	3100	1800
Boeing 747-8	443,613	306.175	3100
Boeing 747-400ER	412,770	295.742	3090
Antonov An-124-100M	405,060	330	2520	900
Boeing 747-400	396,900	295.742	3018	2179
Lockheed C-5 Galaxy[4][5][6]	381,000	288.417	2530	1494
Boeing 747-200[7]	377,840	285.700	3338	2109
Boeing 747-300[7]	377,840	260.320	3222	1905
Airbus A340-500[8]	371,950	240	3050	2010
Airbus A340-600[8]	367,400	256	3100	2100
Boeing 777F	347,800	260.816	2830
Boeing 777-300ER	351,800	251.29	3100
Boeing 777-200LR	347,450	223.168	3000
Boeing 747-100[7]	340,200	265.300
Airbus A350-1000	308,000	233.5
Boeing 777-300	299,370	237.683	3380
Boeing 777-200ER	297,550	213.00	3380	1550
Airbus A340-300[8][9]	276,700	190	3000	1926
McDonnell Douglas MD-11	273,300	185	2990	1890
Airbus A350-900	270,000	175	2670	1860
Ilyushin Il-96M	270,000	195.04	3115	2118
McDonnell Douglas DC-10	256,280	183	2990	1890
Boeing 787-9[10]	254,000	192.777	2900
Boeing 787-10[10]	254,000	201.849
Airbus A340-200[8][11]	253,500	181	2990
Airbus A330-900	251,000	191	3100
Ilyushin IL-96-300	250,000	175	2600	1980
Airbus A330-300[12][13]	242,000	185	2500	1750
Airbus A330-200[12][13]	242,000	180	2220	1750
Lockheed L-1011-500	231,300	166.92	2636
Boeing 787-8[10]	228,000	172.365	3300	1695
Lockheed L-1011-200	211,400
Ilyushin IL-86	208,000	175
Boeing 767-400ER	204,000	158.758	3414
Airbus A300-600R[14]	192,000	140	2385	1555
Boeing 767-300ER	187,000	136.08	2713	1676
Concorde	185,000	111.1	3440	2220
Airbus A300-600[14]	163,000	138	2324	1536
Boeing 767-300	159,000	136.078	2713	1676
Airbus A310-300[14]	157,000	124	2290	1490
Vickers VC10	152,000	151.9
Boeing 707-320B[15]	151,000	97.5
Boeing 707-320C[15]	151,000	112.1
Douglas DC-8-61	147,000
Airbus A310-200[14]	142,000	123	1860	1480
Airbus A400M	141,000	122	980	770
Douglas DC-8-32	140,000
Douglas DC-8-51	125,000
Boeing 757-300	124,000	101.6	2550	1750
Boeing 707-120B[15]	117,000	86.3
Boeing 757-200	116,000	89.9	2347	1555
Boeing 720B[16]	106,000	79.5
Boeing 720[16]	104,000	79.5
Tupolev Tu-154M	104,000	80
Tupolev Tu-204SM	104,000	87.5	2250
Convair 880	87,500
Boeing 737-900	85,000	66.36	2500	1704
Boeing 737-900ER	85,000	71.35	2804	1829
Boeing 727-200 Advanced[17]	84,000	70.1
Airbus A321-100[18]	83,000	77.8	2200	1540
Boeing 737-800	79,000	65.32	2308	1634
Boeing 727-200[17]	78,000	68.1
McDonnell-Douglas MD-83	73,000	63.28
Boeing 727-100[17]	72,500	62.4
Boeing 727-100C[17]	72,500	62.4
McDonnell-Douglas MD-90-30	71,000	64.41	2165	1520
de Havilland Comet 4	70,700
Boeing 737-700	70,000	58.06	1921	1415
Airbus A320-100[18]	68,000	66	1955	1490
Boeing 737-400	68,000	54.9	2540	1540
de Havilland Comet 3	68,000
Boeing 377	67,000
Boeing 737-600	66,000	54.66	1796	1340
Airbus A220-300	65,000	57.61	1890	1494
Hawker Siddeley Trident 2E	65,000
Airbus A319[18]	64,000	62.5	1850	1470
Boeing 737-300	63,000	51.7	1939	1396
Boeing 737-500	60,000	49.9	1832	1360
Airbus A220-100	59,000	50.80	1463	1356
Airbus A318[18]	59,000	57.5	1375	1340
Boeing 717-200HGW	55,000	47.174	1950
Douglas DC-7	55,000
de Havilland Comet 2	54,000
Boeing 717-200BGW	50,000	46.265	1950
de Havilland Comet 1	50,000
Douglas DC-6A	48,600
Douglas DC-6B	48,500
Embraer 190[19]	48,000	43	2056	1323
Caravelle III	46,000
Fokker 100	46,000	39.95	1621	1350
Douglas DC-6	44,000
Avro RJ-85	42,000	36.74
Handley Page Hermes	39,000
Embraer 175[20]	37,500	32.8	2244	1304
Bombardier CRJ900[21]	36,500	33.345	1778	1596
Embraer 170[22]	36,000	32.8	1644	1274
Bombardier CRJ700	33,000	30.39	1564	1478
Douglas DC-4	33,000
Vickers Viscount 800	30,400
Bombardier Q400	28,000	28.01	1219	1295
Bombardier CRJ200	23,000	21.319	1918	1479
ATR 72-600	22,800	22.35	1333	914
Saab 2000	22,800	21.5	1300
Embraer ERJ 145	22,000	19.3	2270	1380
ATR 42-500	18,600	18.3	1165	1126
Saab 340	13,150	12.930	1300	1030
Embraer 120 Brasilia	11,500	11.25	1560	1380
BAe Jetstream 41	10,890	10.570	1493	826
Learjet 75[23]	9,752	8.709	1353	811
Pilatus PC-24[24]	8,300	7.665	893	724
Embraer Phenom 300[25]	8,150	7.65	956	677
Beechcraft 1900D	7,765	7.605	1036	853
Cessna Citation CJ4[26]	7,761	7.103	1039	896
de Havilland Hercules	7,000
Embraer Phenom 100	4,800	4.43	975	741

2.Is there any difference between ground speed and air speed?

Airspeed vs. Ground Speed

As mentioned above, true airspeed is simply the speed at which an aircraft is moving relative to the air it is flying in. As such, it’s also the speed at which the air is flowing around the aircraft’s wings.

Ground speed, on the other hand, is the aircraft’s speed relative to the ground. One thing that should be noted here is that it’s its horizontal rather than vertical speed – an aircraft climbing completely vertically would have a ground speed of zero.

In other words, while airspeed is what determines whether there is enough airflow around an aircraft to make it fly, ground speed is what determines how fast an aircraft will get to its destination.

DIFFERENCE BETWEEN GROUND SPEED AND AIR SPEED

GROUND SPEED AIR SPEED

Ground speed is the airplanes speed relative to the surface of the earth Air speed is the speed relative to the air it is flying in

Ground speed is what determines how fast an aircraft will get to it destination Airspeed is what determines whether there is enough airflow around an aircraft to make it fly

3.Why is it not recommended to use aircraft engine power to move it on the ground at Airport

Large international airports can be massive places. Denver, Colorado’s main airport, for example, takes up an area of 53 square miles. By comparison, the area of Manhattan is 34 square miles, San Francisco is 47 square miles and Miami is 36 square miles. At some airports like Amsterdam, once you’ve landed you can still have several miles left to taxi until you reach the terminal building. Conversely, some busy airports are so restricted for space that it poses real issues for aircraft getting around on the ground. New York’s JFK is a prime example of this.

he area on which aircraft move on the airfield can broadly be separated into three separate categories. The ramp, or apron, is where the stands are located for aircraft to park. The runways are what the aircraft use to takeoff and land. And the taxiways, which they use to get between the two.

Stands, Taxiways and Runways

At most international airports, the runways are either 45 meters or 60 meters wide and can vary in length. London Heathrow has one of the longest runways in the UK at just under 4 kilometers, or around 2.5 miles. At around 380 tons on landing, runways have to be able to withstand repeated impact from aircraft such as the Airbus A380. They also need to ensure that water drains off quickly when it rains so that it doesn’t become too slippery.

Taxiways, too, can vary in width and load-bearing strength depending on the airfield. Depending on these factors, they are categorized so that pilots know which taxiways they are able to use for their aircraft type. The taxiways at some airports can be particularly tight, especially for bigger aircraft. With a wingspan of more than 60 meters, pilots on the 787 Dreamliner always have to be mindful of their wingtips.

Parking stands can also vary in width and length, depending on the aircraft type they are to accommodate. It is on these stands where aircraft park and are unloaded and loaded between flights. They have to provide electrical power for the aircraft whilst the engines are shut down and also enough area around the aircraft to give the multitude of servicing vehicles space to access the aircraft. At some big airports, when not in use by a bigger aircraft, one stand can be used by two smaller aircraft.

Most Aircraft Can’t Reverse

When you arrive at the gate for your flight, more often than not you’ll get a great view of the nose of the aircraft through the terminal window. If you look closely, you’ll be able to see us pilots preparing the aircraft for departure. Funny enough, we can see you peering out at us too, so if we wave, don’t be embarrassed to wave back.

However, the obvious problem with parking facing the terminal is that in order to get to the runway, we need to move backward off the stand first. If this was on your drive at home, you’d just pop your car into reverse, back out onto the street and off you go. Unfortunately, aircraft are unable to do this as they don’t have a reverse gear. In order to get round this problem, we use the assistance of a pushback tug.

ushback Tugs: The Little Engines That Could

For smaller aircraft, the pushback tug doesn’t require a massive amount of power. They utilize the weight of the tug, sometimes up to 60 tons, to ensure that the wheels don’t just spin on the tarmac. “The small ones have enough power to push and tow an aircraft up to a 757,” says Airside MUC, a pushback driver at Munich International Airport. “The functionality is pretty simple. We connect a tow-bar at the aircraft first, then at the tug.”

It takes skill to push an aircraft back using these types of tug. “You have two steering axis here at the nose gear and at the tug where the tow-bar is connected,” he said. “So when you steer right, the nose of the aircraft goes opposite.”

However, with bigger aircraft, tug designers ran into a problem. Even with a 60-ton tug, there isn’t enough weight to stop the tug wheels spinning. To get round this problem, they needed something to weigh the tug down. Something like the weight of a 560-ton A380.

Tow-barless tugs clamp around the nose wheel of the aircraft and lift it up, thus utilizing the weight of the aircraft to provide the traction for its wheels. “We need between 40 and 90 seconds to connect the tug with the aircraft and lift it up,” he added. “The Goldhofer AST-1X is the Godfather of all tugs because at 32 tons, its 16-liter 700 HP engine is enough to push all heavies easily. We use that tug for 767 up to A380.”

Engines Provide the Thrust

Once the tug has disconnected and the engines are running, the pilots call ATC for their clearance to taxi to the departure runway. They will then be issued with a series of taxiways, which will eventually take them to the departure point. At smaller airports, this may just be one taxiway. At larger airfields it could be a number of taxiways, broken up into segments to give way to other aircraft. It’s worth noting that aircraft don’t ‘taxi down the runway’. They taxi on taxiways, hence the name, taxiway. (Sometimes aircraft do have to taxi on the runway, but this is relatively infrequent. So, for the case of this article, I decided to keep it simple.)

If this was your car, you’d put the gear into drive or first gear and press the accelerator. This would inject fuel into the engine and provide power to turn the wheels and off you’d go. However, aircraft wheels aren’t connected to the engines in any way. When the pilots squeeze the thrust levers forwards, the thrust generated from the engines pushes the aircraft forwards. The wheels merely turn under this forward power allowing the aircraft to move.

Steering System

Once moving, pilots need to be able to steer the aircraft around corners. With a wingspan of 60.1 meters, the 787-8 is wider than it is long. The pilot’s eye level is 5.5 meters above the ground, and this creates a 14-meter blind spot ahead of the aircraft. So, accurate taxiing is essential.

This is done through two different sets of controls. Limited steering is possible using the rudder pedals, which sit underneath the pilot’s feet. Unlike in your car, the pedals under our feet have very little to do with acceleration and a lot to do with braking and steering. These primarily control the rudder on the tail (mainly used in crosswind landings) and also control the brakes. However, the main source of steering comes from the nosewheel steering tiller, which can turn the nose wheel up to 70 degrees.

4.How an aircraft is pushed to runway when its ready to take off?

Ready for take-off in ten steps…

The pilot parks the aircraft in exactly the right place. Usually with the help of an automatic system, but occasionally guided by a marshaller waving two paddles or wands. Dozens of handling personnel are already standing by to perform a whole range of tasks simultaneously.

As soon as the aircraft is stationary and the engines are switched off, the first priority is to disembark the passengers as quickly as possible. The apron handler places chocks in front of the wheels and connects the ground power. Meanwhile, the passenger bridge manoeuvres up to the door and a belt loader rolls up to the cargo hold. Luggage is unloaded and transferred to the terminal on baggage carts.

Refuelling begins, usually from a hydrant at the stand. A hose is attached to this from a special vehicle called a dispenser, with the other side connected to the fuel tank in the wing. Read more about refuelling here.

Now it is time to service the aircraft. The caterer loads new meals and takes away the food waste and used cutlery and crockery. Other activities include draining the lavatories, replacing the headrest covers, removing rubbish and distributing fresh blankets and in-flight magazine.

A specialist team – or sometimes the crew themselves – cleans the cabin so that the new passengers board a pristine aircraft.

Meanwhile, specialists from the airline conduct a technical check to make sure that the engines, wings, control surfaces, landing gear, instruments, doors and other equipment are in full working order.

The aircraft is now ready for baggage to be loaded for the next flight. This is a quick process, on average taking only 10-15 minutes. A little later the passengers start boarding. As soon as they are all in their seats, the door is closed and the pilot informs air-traffic control that the flight is ready for departure.

The apron handler removes the chocks. A so-called pushback truck reverses the aircraft into taxiing position, pushing it with a towbar attached to the nose-wheel strut. Or, in the most modern versions, by actually lifting the wheel. That speeds up coupling and decoupling.

The aircraft taxis to the runway to depart at the agreed time.

The pilot waits for permission to take off from air-traffic control. This is possible once the departure route is clear. As soon as the go-ahead is received, the plane takes to the air at full power.

5.Learn about take off power, tyre design, rolling resistance, tyre pressure, brake forces when landing

Why are tyres important in Aircraft?

When it comes to safety, tyres are one of the most important components of aircraft. They help to absorb the shock of landing and provide cushioning. It also provides the necessary traction for braking and stopping of an aircraft.

An aircraft tyre is designed to withstand extremely heavy loads while landing, take off, taxing, and parking. The number of wheels required for aircraft increases with the weight of the aircraft, as the weight of the aeroplane needs to be distributed more evenly.

A Boeing 737NG & 737MAX uses 6 wheels, Boeing 787 uses 10 wheels, Boeing 777 uses 14 wheels and Airbus A380 uses 22 wheels. Aircraft tyres work under extreme conditions, carrying up to 340 tons and accelerating at over 250 km/hour at takeoff, in addition to enduring varied environmental stress when in flight and taxiing.

Design and Construction of Aircraft tyre

Carcass plies are used to form the tire. They are sometimes called casing plies. An aircraft tyre is constructed for the purpose it serves.

1. They support the weight of an aircraft while it is on the ground.
2. It also provides the necessary traction for braking and stopping of an aeroplane.
3. Tyre also helps to absorb the shock of landing and provide cushioning the roughness of takeoff, roll-out, and taxi operations.

Unlike an automobile or truck tyre, it does not have to carry a load for a long period of continuous operation. However, an aircraft tyre absorbs the high impact loads of landing, and also it’s operating at high speeds for a short time when required.

Retreading – Retreading is methods of restoring a worn tyre by renewing the tread area or by renewing the tread area plus one or both sidewalls. Repairs are included in the tyre retreading process.

Load Rating – Load rating is the maximum permissible load at a specified inflation pressure.

Ply Rating – Ply Rating is used to identify the maximum recommended load rating and inflation pressure for a specified tyre. It is an index of tyre strength.

Speed Rating – The speed rating is the maximum takeoff speed to which the tyre has been tested.

Skid Depth – Skid depth is the distance between the tread surface and the deepest groove as measured in the mould.

Aircraft tyres must have an approved speed and load rating and have sufficient clearance when retracted through landing gear to allow for tyre growth. Tyre growth is the increase in the size of the tyre due to centrifugal forces at high speed.

Aircraft tyres may be Tube-type or Tubeless

Tubeless tyres are more advantageous over tube-type. There is no longer the use of tube-type tyre in recent aviation. Nowadays all airliners are using tubeless tyres. Tubeless that are meant to be used without a tube has the word TUBELESS on the sidewall of the tyre.

Aircraft tyres may be Radial or Bias

Almost all airliners are using Radial tyre. Bias is an older design, and it’s mainly used for road vehicles. Radial tyres have the word RADIAL on the sidewall. Radial tires are more expensive than bias-ply tyres. Radial tires are in demand because of their lower life cycle cost and long term value.

Further Read: Aircraft Radial vs Bias Tyre

Are aviation tyres are conductive?

Yes, Today’s tyres are conductive. Aircraft tyres are manufactured with tread rubber with conducting compounds to permit earthing of static charges.

What is the purpose of Chines in aviation tyre

Chines are also called deflectors. Chine tyre used on the nose wheel of aircraft, specially fuselage-mounted jet engines. It diverts runway water away from the engine inlets.

Chines are circumferential protrusions that are moulded into the sidewall of nose tyres that deflect water sideways to help reduce excess water ingestion into the engines. Tyres may have chines on one or both sides, depending on the number of nose tyres on the aircraft

Aircraft Tyre Standards

Each tyre manufacturer produces their own designs of the tyre with different tread patterns, wear patterns, wear limits etc, and in some cases, different names for the same part of the tyre. But all tyres must meet the approved standards before being accepted by the FAA or CAA.

All commercial aircraft tyres approved under FAA Requirement Technical Standard Order (TSO) C62. A TSO is a minimum performance standard for specified materials, parts, and appliances used on civil aircraft.

Rolling resistance

When a loaded wheel and tyre is compelled to roll in a given direction, the tyre carcass at the ground interface will be deflected due to a combination of the vertical load and the forward rolling effect on the tyre carcass (Fig. 8.10). The vertical load tends to flatten the tyre's circular profile at ground level, whereas the forward rolling movement of the wheel will compress and spread the leading contact edge and wall in the region of the tread. At the same time, the trailing edge will tend to reduce its contact pressure and expand as it is progressively freed from the ground reaction. The consequences of the continuous distortion and recovery of the tyre carcass at ground level means that energy is being used in rolling the tyre over the ground and it is not all returned as strain energy as the tyre takes up its original shape. (Note that this has nothing to do with a tractive force being applied to the wheel to propel it forward.) Unfortunately when the carcass is stressed, the strain produced is a function of the stress. On releasing the stress, because the tyre material is not perfectly elastic, the strain lags behind so that the strain for a given value of stress is greater when the stress is decreasing than when it is increasing. Therefore, on removing the stress completely, a residual strain remains. This is known as hysteresis and it is the primary cause of the rolling resistance of the tyre.

The secondary causes of rolling resistance are air circulation inside the tyre, fan effect of the rotating tyre by the air on the outside and the friction between the tyre and road caused by tread slippage. A typical analysis of tyre rolling resistance losses at high speed can be taken as 90–95% due to internal hysteresis, 2–10% due to friction between the tread and ground, and 1.5–3.5% due to air resistance

Rolling resistance

Rolling resistance is the opposing force a rolling body in motion experiences when it comes in contact with a surface. The energy required for the motion is not fully recoverable and some of it is lost when the pressure is removed [47]. The rolling friction opposes the motion of the car, increasing the energy consumption of the EV. A rubber tire will thereby experience higher rolling resistance on an unpaved road than on a smoother road. Also, sand provides more resistance than a concrete floor. The rolling resistance of a vehicle has a significant impact on its motion and thereby its energy consumption [48]. The coefficient of rolling friction can be expressed as

(4)F=CrrN

where F is the rolling resistance force,C_rr is the coefficient of rolling resistance, and N is the normal force perpendicular to the surface on which the tire is rolling. Rolling resistance losses are associated with the force necessary to overcome the friction of EV tires.

(5)Proll=MGr.vehgR0+vR1+v2R2+v3R3v

where M_Gr.Veh is the gross vehicle mass in kg, G is acceleration due to gravity in m/s² and R₀, R_1, R_2, R₃ are the coefficients of rolling

Tire Pressure Maintenance Impact Aircraft Safety

Making sure that the aircraft tires are properly inflated is a crucial part of preflight and routine service checks which can go a long way to maximizing tire utilization and minimizing risks to safe operations.

With good reason, aircraft safety concerns are paramount in maintenance operations. No one wants to see loss of life, injuries, or serious property damage as a result of poor aircraft maintenance. Aircraft maintenance manuals have very detailed, step-by-step procedures, tool, and parts lists. Certified inspectors must sign off on work cards, validating that the mechanic completed the job and completed it correctly. These procedures and checks and balances are all designed to insure the aircraft remains safe to operate. Making sure that the aircraft tires are properly inflated is a crucial part of preflight and routine service checks which can go a long way to maximizing tire utilization and minimizing risks to safe operations. At Michelin, we are committed to aircraft safety and we are proud to share our expertise with pilots, A&P mechanics, and the FAA.

Aircraft tires are not the same as passenger car or truck tires. As a result, their care and service requirements differ. Figure 1 below compares key parameters between a passenger car tire and two aircraft tires of about the same dimensions:

Car Tire Aircraft Tire Aircraft Tire

(Typical) (737 NLG) (F-16 Blk 40 MLG)

Size P205/75 R15 27x7.75 R15 27.75x8.75R14.5

Outside Diameter 27.2 inch 27 inch 27.75 inch

Selection Width 8.1 inch 7.75 inch 8.75 inch

Max Inflation 35 psi 200 psi 320 psi

Max Load 1,598 lbs. 9,650 lbs. 21,500 lbs.

Speed Rating 106 mph 225 mph 259 mph

Operation Continuous Intermittent Intermittent

Temperature Equilibrium No Equilibrium No Equilibrium

Note that although the tires are dimensionally similar, they differ significantly in rated inflation pressure, load, and speed. Additionally, the passenger car and truck tires are able to operate continuously because they reach thermal equilibrium while aircraft tires do not. An aircraft tire which taxis continuously at rated load and 40 mph will continue to heat up until the tire fails. The failure to reach thermal equilibrium is a consequence of the high deflections (the difference between the unloaded and loaded tire section height) at which aircraft tires operate. High inflation pressure and high deflection rates – 2.5 times greater than a car tire – allow relatively small tires to support the high loads of an aircraft.

Because aircraft tires operate at such high extremes of pressure, load, and speed, their care and service is critically important. The most important action an operator can take to prevent tire-related events is to maintain proper tire inflation pressure. Failure to keep aircraft tires properly inflated can lead to very serious consequences. The most serious of these is the structural failure of the tire. If the tire operates underinflated or overdeflected/overloaded, the nylon cords which form the structure of the tire go in and out of compression as the tire rotates. This weakens the cords – much like a paperclip which is bent back and forth – until eventually the cords break. If enough cords break, the entire structure will eventually fail. Figure 2 shows what a compressive break in an interior ply looks like. This particular break damaged the inner liner, allowing air to migrate through the tire to the atmosphere.

Another serious consequence of under-inflation is the thrown tread. Overdeflection increases shear between components in the tire as it rolls in and out of contact and deforms. This results in a more rapid build‐up of heat within the tire than would be evident if the tire were properly inflated. At some point the excessive heat will cause the rubber to revert, or reverse cure. This reverted rubber is like grease with no strength or adhesion to contain the structure. This can allow the tire to decompose, throwing the entire tread or pieces of it. In addition to destroying the tire, thrown treads often result in expensive aircraft damage. Figure 3 is an example of reversion.

How can an operator know what the proper pressure is for their tires? Aircraft tires are designed and tested to “rated” conditions. These rated conditions are specified by industry standard’s bodies like The Tire and Rim Association (T&RA) and The European Tyre and Rim Technical Organisation (ETRTO). However, most aircraft are not operated at the rated limits. This means that an operator must consult the aircraft’s Aircraft Maintenance Manual (AMM) or Pilot Operating Handbook (POH) to find out the recommended operating pressure range.

In order to ensure that an aircraft’s tires are properly inflated, Michelin recommends checking the inflation pressure, with a calibrated gauge, before the first flight of the day or before each flight if not flown daily.

Why is it important to check the pressure every day? Because of the high pressures and extreme temperatures at which aircraft tires operate, they do not hold air perfectly. In fact, an aircraft tire can lose up to 5 percent of its pressure in 24 hours and still be perfectly serviceable.

Why check the tires before a flight rather than after? It’s important to check tire pressures when they are cold if at all possible. Michelin recommends checking a tire’s pressure no sooner than three hours after it has last rolled. Tires that have rolled under load recently heat up, making it very difficult to determine what the proper pressure should

Take off power brake forces when landing

This paper describes airfield measurement of forces and moments that act on a landing gear wheel. For the measurement, a wheel force sensor was used. The sensor was designed and built based on strain gage technology and was embedded in the left landing gear wheel of a test aircraft. The sensor is capable of measuring simultaneously three perpendicular forces and three moments and sends data to a handheld device wirelessly. For the airfield tests, the sensor was installed on a PZL 104 Wilga 35A multipurpose aircraft. The aircraft was towed at a “marching man” speed and the measurements were performed at three driving modes: Free rolling, braking, and turning. The paper contains results obtained in the field measurements performed on a grassy runway of the Rzeszów Jasionka Aerodrome, Poland. Rolling resistance of aircraft tire, braking friction, as well as aligning moment were analyzed and discussed with respect to surface conditions.

Keywords: airfield performance, landing gear, wheel, force and moment measurement, strain gage, wheel force sensor, wireless data transfer, grassy airfield, GARFIELD System

Airfield performance of an airplane plays an important role in the analysis of takeoff and landing and determines, among others, ground roll distances. Forces and moments that act on aircraft landing gear wheels are effects of gravitational acceleration, as well as surface reactions. These reactions are easily obtainable on paved runways, but difficulties arise when an airplane operates on unpaved, grassy, or gravel surfaces. One method is to monitor surface mechanical data, related to weather conditions. The GARFIELD information system [1] is based on a wheel–grass model that includes analysis of wheel–soil (wheel–grassy surface) interactions considering soil modeling with a special caution to loads by aircraft tires [2]. The model will respect non-linear, dynamic effects such as hyper-elastic tire deflection, rheological soil response to high rate deformation, and effects of grass and roots. The wheel–grass model also employs the analysis of weather impact upon mechanical characterization of runway surface, which can be identified and verified by means of wheel–force measurements in full-scale tests [3].

Researchers dealing with flight tests of aircraft, piloted or unmanned, pay significant attention to the importance of ground tests, including measurements for the validation and verification of landing gear systems [4,5,6].

Significant emphasis is placed on the development and research of new measuring technologies and, as an example, a new solution in the field of strain gauge sensors can be cited. Pecora et al. have presented an innovative strain gauge for monitoring of inflatable structures, suitable for an use in aerospace [7]. Another interesting example is given by Petritoli et al. (2019-1), who investigated uncertainty and measured errors of an inertial navigation systems for UAV (Unmanned Aerial Vehicle) [8]. Petritoli et al. (2018) and Petritoli et al. (2019-2) targeted the problem of collocation of the sensors to be installed in a UAV with a reduced space, together with the allocation of the payload [9,10]. This problem is vital for full size aircrafts, not only typically smaller UAVs, especially if a sensor has to be embedded in an existing part of an aircraft. Eling et al. (2015) presented an innovative georeferencing system for the guidance, navigation, and control of UAVs [11]. This is an example of an inertial measurement unit (IMU)-based system, the method of a wide spectrum of applications in aerospace.

Measurement of forces and moments that act on a road wheel is a well known practice in automotive research and development. It is usually done either on laboratory test stands or on a test vehicle. Either way, a device that provides wheel forces and moments is a wheel dynamometer. A wheel dynamometer is a measuring device that enables to measure forces and moments acting on a wheel in real time on a moving vehicle. The majority of wheel dynamometer solutions comes from the automotive industry or research, and a typical solution has a form of a 6-element sensor that measures three orthogonal forces, F_X, F_Y, and F_Z, together with corresponding moments, M_X, M_Y, and M_Z [12,13,14,15]. The measurement principle is based either on the strain gage or piezoelectric sensor technology. Some selected works that describe the use of such dynamometer systems for measurement of wheel forces and moments in various applications are included in the reference list [16,17,18,19].

The horizontal force, F_X, measured by a wheel dynamometer can be correlated with bending or shearing the grass plants, as well as soil deformation. The braking friction force can be correlated with sliding over the grass. The vertical force, Fz, depends the grass compression and can be used for coefficient calculations (braking friction, μ, and rolling resistance, k_RR, coefficients, as well as aligning moment, M_Z). This approach is alternative to commonly used laboratory drop tests of landing gear [20,21,22]. The aim of this study was to apply a wheel force and moment sensor for measurement of aircraft landing gear on grassy surface. The primary paper, entitled Measurement of Forces and Moments Acting on Aircraft Landing Gear Wheel, was presented during the 2019 IEEE International Workshop Metrology for Aerospace in Torino, Italy [23].

Wheel Dynamometer System

The wheel dynamometer system used in the experiment consisted of a sensor, modified wheel and tire, wireless data transfer unit, and software. The sensor core was made of steel, and strain gages were used as sensing elements. The instrumentation amplifiers, which prepare the outgoing signals for data acquisition, were placed outside the sensor in a small box, together with a board of the microprocessor data analysis and transfer system. Figure 1 shows a schematic of the sensor, but without the electronics. This schematic also includes the orientation of forces and moments.