## Propeller Thrust

This post is about how a propeller Works, from a Principles of Flight point of view.

## What is a propeller?

A propeller is a device that transforms rotational power into linear thrust by acting upon a working fluid.

In principles of flight the propeller is considered an aerofoil, so we can apply all definitions of the wing to the propeller plus:

• Plane of rotation:

The Plane of Rotation is an imaginary plane perpendicular to the propeller shaft.

is an imaginary straight line joining the centre of curvature of the leading edge of the propeller blade to the blade’s trailing edge.

The Blade Angle or Blade Pitch is the angle between the blade chord line and the plane of rotation.

The Blade Angle of Attack is the angle between the chord line of any given blade element and the relative airflow.

• Geometric Pitch

The Geometric Pitch is the distance the propeller would travel forward in one complete revolution.

• Effective pitch

The distance that the propeller actually moves forward with one revolution

• Propeller Slip

The difference between Geometric Pitch and Effective Pitch is called Propeller Slip.

• Helix Angle

is the angle between the Plane of Rotation of the propeller and the path of the Effective Pitch.

## What is thrust and how is created ?

Thrust is force in the direction of the movement created by the engine in concrete by the propeller.

We must consider the propeller as an aerofoil, so the lift and drag are actuation to it.

The concept of how the lift force is created, we can apply it in this case.

Notice that the incoming air to the propeller is slower that the outcome air resulting in creating a force backwards. Due to the third Newton´s law it results in a forwards movement.

This movement forwards is called Thrust. Depends on the quantity of air we are able to accelerate, and the acceleration of the air.

T= G (Ve- Vo)

• T: Thrust
• G: Air mass flow  ( mass/time)
• Ve: Exit velocity of air
• Vo: Entry velocity of air

As we have created the “lift”, also appears the “Drag”. This “lift” we have called it Thrust, and this “Drag” we will call it Torque. Which is always opposite to the movement direction.

## How does it work ?

While the propeller is working we can encounter a velocity triangle, where the TAS is true air speed, RPM it is a circular speed.

Depending of the angle of attack, the Torque (Drag) will be modified so the efficiency of the propeller will change, as the thrust will change.

The efficiency it is measured with this formula:

Propeller Efficiency= Thrust Power/Shaft Power

## Types of propeller:

We have two types of propeller, depending on the blade angle. Fix pitch propeller and variable pitch propeller.

Fix pitch propeller Consideration:

If  the True Air Speed increases, with constant RPM. The angle of attack is reduced, so the torque is reducing as well. It can happen in a descend with a constant RPM

If we increase the RPM maintaining constant the TAS the angle of attack increases so the Torque increases. This situation can happen in a constant TAS climbing.

This problematic it is solved with the variable pitch propeller, it can adjust the angle of attack in each phase of the flight.

## Why The Propeller is twisted ?

Every propeller best efficiency is only at one combination of aircraft forward speed, and propeller rotational speed. The RPM of the root of the propeller is higher than the tip of the propeller, that´s why we have to modify the angle of attack for having the best efficiency.

## Things to keep in mind before diverting to the alternate aerodrome

Things to keep in mind before diverting to the

# alternate aerodrome

There are many things to take in account before selecting an alternate aerodrome to divert.

First of all we have to select an adequate aerodrome. But …  what is an adequate aerodrome ?

Adequate aerodrome  is the aerodrome on which and aircraft can be operated, taking account of the applicable performance requirements and runway characteristics, and of course the fuel requirements we need to reach it.

• ## Runway characteristics:

First of all we must check the landing distance available and landing distance required.

• Landing distance available
• Landing distance required

Secondly: we must check  in which condition is the runway :

• Contaminated runway:

A runway is considered contaminated when more than 25% of the surface area is covered  by the following:

• Water more than 3 mm deep, or by slush, loose snow.
• Snow which has been compressed into a solid mass which resists further compression and holds together or break into lumps if picked up.
• Ice, including wet ice.

Thirdly: we must check the operative restrictions . Written in the NOTAMS , status of the plane.

## PLANNING CONSIDERATIONS WHEN WE CHOOSE AN ALTERNATE AERODROME

### Take off alternate:

When do we have to select a take off alternate aerodrome different from which we have taken off ?

When it is not possible to return to the aerodrome which we have taken off due to weather conditions or performance ( for example we have enough runway distance for take off but not for landing).

Which aerodrome is suitable as a take off alternate ?

By law it must:

• The weather forecast  must be appropriate during a period that starts 1 hour before and 1 h after our estimated time of arrival. Which means that must be at or above our approach minimuns taking in account the capability of our plane.
• In case of the twin engines , the aerodrome must be within 1 hour flight time at cruise speed (wind calm)  with 1 engine inoperative ( if it is ETOPS 2 hours with an engine inoperative).
• In case of three or more engines : the aerodrome must be within 2 hour flight time at cruise speed (wind calm)  with 1 engine inoperative.

### Route Alternate :

In the event of the failure of the critical engine at any point along the route, the airplane must be able to continue the flight to an aerodrome, which the landing can be performed safety.

Minimum en route altitude ( MEA) :  Segment length up to 100 NM = +/- 10 NM of track, with radio navigational aids reception and minimum of :

• 1500 ft OC elevation below 5000 ft, and between 5000 and 10000 ft. We must have 2000 ft avoidance. And above 10000 ft , we must have 10% + 1000 ft.

Minimum sector altitude (MSA): 1000 ft above above terrain and obstructions within the sector distance ( 25 NM) rounded up to 100 ft.

Minimum off-Route altitude (MORA)

Is calculated for an area bounded by every or every second LAT/LONG square on the route facility chart, and is based on a terrain clearance as follows:

• Terrain up to 6000 ft, 1000 ft above the highest
• Terrain above 6000 ft, 2000 ft above the highest

### Destination Alternate:

It must be an adequate aerodrome ( check above the definition of adequate aerodrome)

For planning reasons at least one destination alternate must be selected in case our destination does not accomplish with this requirements:

• The duration of the planned flight from take off to landing does not exceed 6 hours.
• 2 Separate runways (both usable)
• The weather 1 hour before and after from our ETA ( estimated time of arrival) must be at or above:
• The ceiling will be at least 2000ft or circling height + 500 ft ( whichever is grater)
• The visibility not must be less than 5 KM.

Summarizing:   by law if our destination does not accomplish with this requirements or you can not have weather information you must select two alternate aerodrome.

When selecting an alternate aerodrome it must be above the minima shown in the table below:

• Which means if our alternate aerodrome has CATII or CAT III approach we take the minima of CATI as it is said in the table below.

(For checking what a CATII or CAT III mean check our article : low visibility definitions ).

# How to fill up a flight plan part B

## Gap 13:  Departure aerodrome and time (8 characters)

• Departure aerodrome must be in the OACI code, but if we are departing from an aerodrome without OACI code, we must write ZZZZ in the gap 18 ( DEP/ZZZZ).

If the flight plan has been send by a already flying plane, it is written AFIL in gap 18.

## Gap 15: Route

1. ### Crusing speed ( maximum 5 characters):

N, Knots

K, Kilometers hour

M, Match number

### 2. Flight Level ( 5 characters):

F, Flight level following by 3 characters (F100)

A, Altitude  following by 3 characters

### 3. Route

Imagine we want to fly from LEPA to LEBL . After checking the SID , STAR and the different airways. We finish up in this route :

```N0403F180 ESPOR1A ESPOR W2 NEPAL NEPA1W

```

## Gap 16: Arriving aerodrome, alternate aerodrome, endurance of the flight.

• Destination aerodrome must be in the OACI code, but if we are departing from an aerodrome without OACI code, we must write ZZZZ in the gap 18 ( DEST/ZZZZ).
• Alternate aerodrome must be in the OACI code, but if we are departing from an aerodrome without OACI code, we must write ZZZZ in the gap 18 ( ALTN/ZZZZ).

## Gap 18: Other details

REG/ registration of the airplane

SEL/  selcall code

OPR/ name of the operator

STS/  special things as medical plane…

COM/ if they have UHF

RMK/ remarks

## Gap 19: Supplementary information

• Autonomy : E/ ( 4 characters of hous and minutes)
• Number of people on board : P/ ( number of passengers and crew)
• Emergency/survival equipment: R/ we have to cross what we do not have. U (UHF), V (VHF) ,E  (ELT beacon).
• S/Survival equipment, we have to cross what we do not have. P, polar equipment, D, desert equipment. M, Sea survival equipment. J, jungle equipment.
• J/Life jacket cross what we do not have. L, life jacket with lights. F, fluorescent. U or V, depending the radio equipment that the life jacket has.
• D/ pneumatic boats
• A/ color and marks of the airplane
• N/ any other survival equipment
• C/ name of the pilot

## How to fill up a flight plan part A

What is a flight plan?

A flight plan ( FPL) is information provided to air traffic service unit, relative to an intended flight or portion of a flight.

Things to consider about the flight plan:

• It is a must to do a new flight plan in the case that there is a delay of 30 min or more.
• It must be sent at least 30 minutes before the departure of the flight, but 60 minutes before crossing the international boundary.

Definitions:

• Estimated off-block time (EOBT): Estimated time at which the aircraft will commence movement associated with departure.
• Estimated time of arrival (ETA): The time at which is atimated that the aircraft will arrive over that designated point, aerodrome…

## How to fill a flight plan:

The  four numbers of the hours or time etc, must be written and always in UTC for example 04:00 UTC.

### Gap 7 Aircraft identification:

• It can be either the registration of the plane or the callsign of the company is flying to. ECMJV or if it was IBERIA would be IBE401.

### Gap 8 flight rules ( 1 or 2 characters):

Flight rules we are going to follow:

• I if it is IFR ( instrumental flight rules).
• V if it is VFR ( visual flight rules).
• Y If it starts as an IFR and finish VFR
• Z If it starts as an VFR and finish IFR
• Note : If we are performing an V or Z flight , we must to write down at the gap 15 of our flight time the point where we start the VFR/IFR flight.

Type of flight :

• S if it is a regular air service
• N If it is a regular transport
• G General aviation
• M army flight
• X other kind of flights

### Gap 9: Number and type of airplanes and wake turbulence

Number of airplanes ( 1 or 1 characters)

Type of airplane ( 2 or 4 characters) for example :Cessna 172 (C172), Airbus 320 (A320).

Wake turbulence ( 1 character)

• H, Heavy if the maximum take off mass is 136.000 Kg or more.
• M, Medium if the maximum take off mass is less than 136.000 Kg, and more than 7000 Kg
• L, Light if the maximum take off mass is 7000 Kg or less.

### Gap 10: Equipment:

• N if we are not carrying COM/NAV radio aids
• S If we are carrying normal COM/NAV radio aids:

C: Loran C, D: DME, F: ADF, G: GNSS, H: HF RTF, M: Omega, O: Vor, R:Rnp,T: TACAN, U: UHF RTF,I: Inercial navigation,K: MLS, L: ILS.

Survillance system (SSR)

• N, nil
• A, Transponder mode A.
• C, Transponder mode C.
• X, Transponder mode S without transmitting the identification of the airplane, and not the pressure altitude.
• P, Transponder mode S without transmitting the identification of the airplane, but transmitting the pressure altitude.
• I, Transponder mode S transmitting the identification of the airplane, but not transmitting the pressure altitude.
• S, Transponder mode S transmiting the identification of the airplane, and the pressure altitude.

• D

## How to know if a plane is suitable to fly

How to know if a plane is suitable to fly

The operator must ensure that the commercial air transport is airworthy, and the PIC must check the necessary forms and documentation to ensure the airworthiness of the airplane.

What do we have to check ?

## 1-. Status of the airplane :

For this we have the technical logbook. Where it says if the airplane is suitable to dispatch safely.

At the technical logbook the pilot must ensure that the maintenance have checked the airplane and signed the maintenance release ( also called daily check). The maintenance release must contained :

• The basic details of the maintenance carried out.
• The data where it was performed
• The identity of the approved maintenance organization
• The identity of the person who has performed the job.

Also at the technical logbook is written all the malfunctions that the plane has. That´s why it is mandatory to check the MEL in order to see if the airplane can be dispatched.

#### What is the minimum equipment list (MEL)?

For explaining what is the MEL, I am going to explain first what the master minimum equipment list is (MMEL).

The MMEL is a book made by the manufacturer which says the minimum equipment that must be operative to perform a safe flight. Imagine we are going to a plane with one inoperative PACK. In this case if we check the MMEL, it says the conditions under we are allowed to fly, in this case probably fly lower as if it had the both PACKS operative.

The MEL it is almost the same as the MMEL, but the MEL is made by the operator and it is equal or more restrictive than the MMEL.

The MEL has 3 parts, How to use, MEL items, MEL operations.

• How to use is the part of the MEL dedicated to the instructions.

• In the MEL items part  are written all the errors and in which part of the MEL are.

• In the MEL operations are the procedures to follow against a failure.

#### When is valid the MEL?

It is valid until the plane is able to move by itself. That means that if we are taxiing and suddenly we have a failure it is not applicable. However I strongly recommend to have a look on it before taking off.

The different failures have different repairs intervals:

• Repair interval A: No standard interval is specified, depends on the manufacturer.
• Repair interval B: 3 consecutive days.
• Repair interval C: 10 consecutive days.
• Repair interval D: between 100-120 days.

It starts at 00:00 UTC on the calendar day following the day of discovery, and it finish 23:59 UTC .

For example we record a MEL item class B the 5th of February at 15:00 UTC. It must be repair within the 6th at 00 UTC and 23:59 of the 7th of february.

## 2-. Documents that we must  carry in the plane:

• The certificate of registration
• The certificate of airwothiness
• The Noise certificate
• Air operator certificate
• Insurance

Manuals to be carried :

• Operation manual
• Aeroplane flight manual
• Minimum equipment list

## Non Precision Approach

NON PRECISION APPROACH

A non precision approach is a kind of approach that doesn´t provide vertical guidance, the most common are VOR/DME.

The operator must ensure that the minimuns of the approach are higher than the minimuns of the facility which are :

Also the operator must ensure that the RVR  minimuns are over certain range, it depends on the category of the aircraft. The aircrafts are classified by the speed they have at threshold, which is Vat=1.3 x Vso.

The RVR minima is :

HOW TO FLY A NON PRECISION APPROACH

Here you will find an amazing course of how to do a non precision approach:

# LOW VISIBILITY OPERATIONS

## – Weather minima:

It is the limits of usability of an aerodrome for take or landing in terms of  visibility or runway visual range. It consider to be at low visibility conditions ( LVO) when the RVR is less than 400m

There are different types of weather minima:

• Airfiel operating minima : established in accordance with the airport authority and publish on the approach charts.
• Operator´s minima: Lowest minima that an operator is allowed to use at a specific airfield.
• Crew minima : Lowest minima that an crew is allowed to use at a specific airfield.
• Aircraft minima : Certification of the aircraft.

## – Runway visual Range ( RVR):

Is the range over which a pilot of an aircraft on the centreline of the runway can see the runway surface markings or the lights delineating the runway or identifying  its centreline. It is measured by the transmissometers located at

• The touch-down zone ( TDZ).
• The mid runway portion ( MID).
• The roll-out portion or stop-end.

note: ICAO recomends that RVR reports are given with 50m increments when the RVR is less than 800m, and 25m when the RVR is less than 150m. Any change of                                                                      RVR value must be kwonn by the ATC in less than 15 seconds.

## – Precision approach:

An approach and landing using instruments for navigation guidance based on an instrument approach procedure. It gives accurate track guidance (azimuth) during the final approach segment and information concerning height above the threshold. (ILS)

## – Non precisión approach:

An instrument approach procedure designed for 2D instrument approach . Where there is no ground equipment that can provide height ( elevation) data to the aircraft

## – Minimun Decision heigh (MDA):

The Minimum Descent Altitude (MDA) or Minimum Descent Height (MDH) is a specified altitude or height in a Non-Precision Approach or Circling Approach below which descent must not be made without the required visual reference.

## – Decision height (DH):

is the height at which the pilots should have runway visuals to continue the landing in a instrumental approach. If runway is not visible, we must perform a  Missed Approach.

## OEB 48 abnormal v alpha prot

The OEB 48 abnormal v alpha prot  was made due to an incident of Lufthansa near Bilbao.

According with Aviation herald , the Lufthansa A321 had a conflict between what was happening and what the aircraft detected it was happening.

For explaining what happened we are going to start talking about the angle of attack probe (AoA). The AoA is mounted on the fuselage , by measuring the pressure  differential then it creates an electrical signal.

The airbus has different laws, with any failure the aircraft flyes in normal law which means it has some protections, such as :

• Normal law : load factor protection, pitch attitude protection, high angle of attack protection and high speed protection.
• Alternate law : the same protections mentioned before, less the pitch attitude protection , and the high angle of attack protection is replaced by stall warning.

What happened to the Lufthansa flight was that the AoA got frozen sending a high angle of attack signal to the aircraft, which means that the aircraft thought that it was on stall , so it applied for what it was programmed to. Which is to pitch down to recover the stall, but in fact it wasn´t.

How to know if we have had our probes frozen?

The red strip completely hides the black and ambar in a wings level flight path , with no load factor

If the black and amber strip moves by more that 30knt during flight maneuvers

How to react against it ?

To stop the uncontrolled descend due to frozen AoA is to apply a procedure which the pilot could take control of the situation, I want to remark that during that descend the aircraft don´t respond to the pilot orders because it things that the pilot wants it to be in a greater stall.
So under those circumstances there must be something that the pilot could do , which is forcing it to the alternate law.

How to force it to the alternate law ?

Now you can watch  all I have explained above

## Introduction of jet aircraft

In this set of posts I will write about the performances of an jet engine JAR/FAR-25. The most important of the performance subject, is the relation between a manoeuvre such as, cruise, climb …. And the engine of the plane. For this reason I am going to start explaining the basics of an jet engine.

## How does a jet engine works?

Jet engines are based on the second and third Newton´s law. Basically it increases the air backwards for moving forwards

We define thrust as follows: the amount of mass of air per second by the variation of gas velocity.

## How to know the jet engine power?

In the cockpit there are some instruments related to the measurement of the engine power.
This instruments give us the revolutions oh the hight pressure turbine (N2) and low pressure turbine (N1).

Engine pressure ratio (EPR), is the ratio between of the total output pressure and engine input pressure, therefore the EPR is proportional to the thrust and is always greater than one.

## How do we know that the engine is working properly?

The manufacturer of any jet engine establishes operating margins based on the temperature of the exhaust gas temperature  (EGT)

The motor settings are time-limited:

– Take off thrust (TO): It is the maximum power that a jet engine can reached, its limitation depends on the engine, and it varies between 5 min-10 min

– Go-around thrust (GA): matches with the time and temperature with the take off thrust.

– Maximum continuous thrust (MCT): Maximum thrust adjustment for maximum power with no time limitation. It is mainly used in an engine failure

### Jet Engine power considerations

The thrust is function of the quantity of the air that enter to the engine, as well as the speed increment between the inlet air and outlet air.

T= G(Vs-Ve)

T: Thrust, force in the sense of the movement.

G : the waste of air. It is the quantity of air per unit of time (air mass/ time).

Vs: velocity of the outflow air.

Ve : velocity of the inlet flow.

All that affects the waste of air, velocity of the outflow air, and velocity of the inlet flow, will result in a change in the thrust.

For example:

Density altitude (DA): If the density altitude is high, the density drops down, the mass of air drops down, the Waste drops down so, the thrust drops down.  DA ↑: ρ ↓ G ↓ T↓.

There are other factors, which are controllable from cockpit:

Water Injection: It makes that the exhaust gas temperature drops down, so the temperature limitation is higher, leading in an increased Thrust.

Engine Bleed: The plane uses some air from the engines to feed the air conditioning among other systems, that makes that the air used to create the thrust is reduced, So the Thrust is lower.

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