Tag: flight

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Simplify Flying: it’s attitude plus power equals performance

I’ve had the pleasure of flying with a retired airline pilot who really made me think about flying in an entirely different way. His view demystifies flying into it’s basic, component parts to understand a complex task and achieve a certain goal. Attitude plus power equals performance.

He maintains that after over 20 years of airline flying, he found there are two very important concepts in flying airplanes. Once these concepts are understood, will help you understand aviation and flying at it’s core. The most important concepts in aviation are ones we have all heard before, and it’s impossible not to overstate their importance. They are:

  1. Aviate, Navigate Communicate; and
  2. Attitude plus Power equals Performance.

Think about what flight training is trying to achieve. Yes, you are trying to pass your flight test, at a minimum, but you can certainly do better than that. You can be a great pilot. Why practice stalls and spins? To avoid entry, to recognize if one should occour, and how to recover. 

Let’s relate it to a few examples. 

Once our wheels are off the ground, we are in a ‘risky environment’ where it’s important to keep vigilant.  When we are airborne, our one and only task is no minimize the risk, using all of our knowledge and resources. So break it down into what you have to achieve once you’re wheels up.

Remember clearing turns? We do them so we can be safe and check for conflicting traffic, and not just because they are a flight test item. Risk mitigation is also why we have standardized procedures for uncontrolled aerodromes.

On takeoff, after rotation, the airplane is just passing through a very slow speed at a low altitude. On the 172 we rotate at 55 knots, so after we rotate it’s close enough to stall speed to warrant extreme attention, particularly given our proximity to the ground. When you rotate, will you pull the nose up excessively? No, of course not, you can easily enter a stall that way, a departure stall, and you won’t have the leisure of altitude to recover.

So when we depart, we use the combination of attitude and power to produce the desired performance that we want: a climb. When we recover from a stall is it necessary to push the nose down excessively? Not really, and if you think about what stall practice is meant to achieve, we really should avoid pushing the nose down too much.  If it works on a take-off, it should work on stall recovery. If we push the nose down too much, we’ll loose altitude, and if we stall close to the ground that can be dangerous.

The purpose of stall practice

Stalls are a great case in point. Stall recovery has no practical application in everyday flight like short field, soft field landings, navigation, circuits and so on. We only learn them so we can avoid them, learn to recognize when we are in one, and know how to get out of them. Licensed pilots who don’t fly professionally will find stall recovery skills atrophy after awhile, because unless flight training, stalls are something we want to avoid. 

What produces a stall? A high nose attitude where the angle of attack of our airplane can no longer sustain flight. Your attitude is nose high, the airplane will automatically drop the nose because it wants to fly.  A nose down attitude will break the stall, and the application of power will allow you to return to a normal flight attitude. Attitude plus power equals performance. Aviate: break the stall, return to normal flight, navigate: establish where you are; communicate: this includes communicate with your airplane. Why did it stall?  

How about the forced approach?

The forced approach is a good example. With an engine failure, we’ve got to: (1) aviate: establish the best glide speed, establish a controlled approach and landing; (2) navigate by deciding which is the best field to land our airplane at; and (3) communicate, make a mayday call on 121.5 and give our passengers, if any, a full off-airport emergency safety landing briefing.  For the forced approach, we use best glide speed, a combination of attitude and power (in this case, lack of power), that produces a level of performance: the descending glide.

cessna 172 lake view
cessna 172 lake view

A heap of metal

Remember the airplane is just a “thing.”

The airplane is not alive. Many things on the flight test and flying itself can cause confusion, and above all, anxiety, which can take the fun out of flying. When learning to calm anxieties, it’s helpful to think about the airplane having no feelings or malicious intent. It’s just a heap of metal that you control and has no goal or agenda of it’s own. It’s simply a tool, a tool that you, the pilot, control.  You are flying the airplane and the airplane is not flying you.

A blend of two important factors, attitude and power, will produce the environment that we can control. Like a car, the airplane is a predictable thing. When given certain parameters it will always do the same thing. Nose up? Airspeed will decrease. Nose down? Airspeed will increase. No power? It will enter a descent. Full power? It will climb. Winds will push the airplane in known directions, crosswinds will have a known effect on approach paths, and so on. 

It’s all well within our control.

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How to master the power-on stall

The departure stall

Throughout my training, I have done a lot of stalls, and eventually got the point where I was quite comfortable with them. Power off, power on, including the more advanced high power stalls.  I was rather surprised when doing my full review of everything before my flight test, when my instructor asked me to demonstrate high power stalls I became rather nervous and was unable to perform one without throwing in the aileron on recovery.

I had let my training lapse and it had been quite awhile since I’ve done these more advanced stalls.  A few power-off stalls allowed me to feel comfortable with them again but I continued to struggle with stalls using higher power settings, which cause sometimes a very pronounced wing drop due to asymmetric thrust, slipstream and other factors.

Why do we learn power-on stalls?

The power-on stall is basically a departure stall. We practice this stall to simulate a stall on departure, when we have a nose high attitude and high power settings (full power for take off).  How could we stall on departure? If we fly into IMC on climb-out, hence loose the horizon and become disoriented, possibly succumb to an illusion that we are level and not nose-high enough (not reference or trust our instruments which tell us that we are in fact in a climb) and we pull back too much.

The airspeed bleeds off, and without knowing it we are nose high. As the aircraft reaches stall speed one of the wing drops off and when uncorrected, can enter a spin. At low altitudes, we have  no time to recover. Before long we can be nose down in a spin with no altitude to spare.

Cessna 172 about to stall. Image from airfactsjournal.com
Cessna 172 about to stall. Image from airfactsjournal.com

Stall/spin accidents

There are a number of these stall-spin accidents every year, and most of them occour at low altitudes.  According to an AOPA study, from 1993 to 2001 stall-spin accidents accounted for 10% of all accidents and 13% of all fatal accidents for fixed wing aircraft weighing less than 12,500 pounds.   An earlier study by the FAA Small Aircraft Directorate analyzed a sample of 1700 stall-spin accidents as far back as 1973 and found that 93% of them began at or below pattern altitude, which was 800 feet back in the 1970’s.

So the reason we learn a high power stall is to avoid a dreaded departure stall and to recover quickly, with minimal loss of altitude, and in coordinated flight (avoid a wing drop).

More rudder coordination is required

The reason why a power-on stall can be more challenging and more scary, is because it will require more use of rudder than a power-off stall.  We must remember not to use aileron, ONLY rudder, because not is only aileron ineffective in a stall – the wing is stalled – it can also exacerbate or aggravate the  wing drop in a stall, making it even more banked.

Anticipate a wing drop

Generally with a power-on stall, we will get a wing drop. Because of asymmetric thrust and slipstream, we generally see the left wing drop. Recall the left turning tendency of the aircraft at high power settings, for example while on the takeoff roll. On the takeoff roll with full power we always apply plenty of right rudder to keep the aircraft on centreline.

However we will not always get a left wing drop, it can, in fact be the right wing that drops, requiring the use of left rudder instead of right to correct.   There are many reasons for this: one wing could have more fuel than the other and be heavier, it can also vary with the prevailing winds. So it is important not to anticipate one wing dropping but to watch which one does and react appropriately.

So one wing drops, so there is a tendency for us to use aileron to correct.  This is very natural. In a stall, we have to fight the urge to use aileron and instead, “step on the rising wing.” (thanks to my instructor Steve for the tip – it works!)  This means to use rudder instead of aileron, in the same direction if the rising wing:

Left wing drops (right wing rises): instinct will tell you to use right aileron – use right rudder instead

Right wing drops (left wing rises): instinct will tell you to use left aileron – use left rudder instead.

Check out this video as a power on stall develops into a spin. Looks like the student puts it into a spin (on purpose, note how he uses aileron) and the person in the right seat, likely the instructor, recovers.

How can I become more comfortable with these types of stalls?

In a word, practice will make them easier, as you do them over and over again and you are able to control them, you will regain confidence. Another great tip is to visualize the manoeuvre and talk yourself through it, when you are not flying. I used visualization and imagined one of the wings dropping, and what I would do. Eventually lost my fear as I learned I could control the airplane with rudder.  It is important to use rudder opposite to the turn to correct the wing dip as fast as possible, and to leave the aileron in neutral position.

Like anything with flying, repetition will help you learn and feel more comfortable over time. Practice means everything!

 

 

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Aviation and climate change

C-141 Starlifter contrail. Image Courtesy of Wikipedia.org

We live in a world where there are growing concerns regarding human induced climate change. It is very high on the policy agenda of most governments, issues I have experienced first hand working as an environmental economist.   Not surprisingly, in the community it is generally accepted that we are without question experiencing climate change, and there is a consensus that a lot of it is human-induced due to increased carbon emissions.  It is not a debate, but a generally accepted consensus in the scientific community.

Global GHG Emissions By Source (2004). Image from US EPA website.
Global GHG Emissions By Source (2004). Image from US EPA website.

So like you, I love to fly and also love to travel by commercial air service.  How does commercial aviation contribute to climate change?  How do airplanes contribute negatively when it comes to greenhouse gas (GHG) emissions?

Let’s examine what the main contributors are to GHG emissions. Globally, the sources of GHG are primarily from energy supply (26%) and industry (19%). Transportation is close at 13%,  where fossil fuels are burned to power transportation activities such as rail, road, air and marine transport (IPCC 2007) and aviation represents about 12% of the transport figure.  The contribution of civil global aviation is about 2%  of total GHG emissions (CleanSky website). Flights produce about 628 million tonnes of Co2 annually.  A typical car emits about 5 tonnes per year and there are about a billion cars (Huffington Post 2013)  out there in the world (of course, this is a very rough figure) meaning about 5 billion tonnes are produced by cars, making it a greater net contributor. In Europe, road vehicles contribute about 1/5th of carbon dioxide emissions (European Commission 2012b).   In Canada, transportation accounts for over 28% of total GHG emissions (Conference Board of Canada 2010).  But what about per passenger kilometer?

The current rating for car is about 140 g / kilometer (European Commission 2012a). For air travel, this figure is higher, (2000 data) at about 170 g / kilometer (BBC news).   But the figures from aircraft vary extensively, depending on the type of flight, type of airplane used and distance flown.  Domestic short distance are as high as 260 g/km, domestic long distance 178 g/ km and long distance the lowest at 114 g / km (wikipedia.org). British Airways has estimated their per passenger rate at 100 g / km.  Flying trips cover far longer distances than could be undertaken by car, so total emissions would be higher because of the ability to travel longer distances.

The effects of flights at high altitudes may be greater than those at low altitudes. An important effect appears to be from contrail emissions.

Cirrus clouds caused by jet contrails. Image from CO2 offset research.org
Cirrus clouds caused by jet contrails. Image from CO2 offset research.org

Remember from weather theory that jet engines produce contrails, which are mostly water vapor. One of the effects is that jet contrails cause cirrus clouds to form in the higher atmosphere where commercial jets fly (10-12 km above ground, at temperatures of -40). There still appears to be debate about what this contribution is to global warming, and most calculations are done from contributions of fuel burn.  However, a NASA study has found the warming effect caused by increased cirrus cloud formation from aircraft in the US (NASA 2004). Because of this, aircraft cause more than just CO2 emissions but also contribute to radiative forcing, which has to do with contrail production and nitrous oxide emissions.

These contrails are rare for low altitude aircraft or propeller driven aircraft, meaning the contribution of commercial aviation could potentially be more significant than other types of flights.

Another chief concern is the increasing use of air travel.  Since planes continue to run on fossil fuels, the increase in CO2 emissions from aviation will likely grow. In fact, between 1990-2004, number of airport users in the UK rose 120%. On average, global airline growth amounts to approximately 5% per year (MIT 2006).

Winglets on a Boeing aircraft. Image from Boeing.com
Winglets on a Boeing aircraft. Image from Boeing.com

The industry is making changes to be more efficient. Experimenting with cleaner fuels (biofuels), aircraft made of composite materials that are lighter, and addition of aircraft modifications such as winglets or sharklets which block wing tip vortices (and reduce drag) are all being considered.  Wing tip devices, such as winglets or sharklets have been found to reduce fuel burn by as much as 3.5% (wikipedia.org).  Westjet’s 737 airplanes configured with winglets record a decrease of 2.7% fuel burn (Westjet website). The use of biofuels has it’s own issues – we see that with vehicles, where mandatory levels of ethanol (grain alcohol) in gasoline for vehicles has stressed grain markets -so these are being researched and considered. There are little things that can be done to reduce the impact.

It is an interesting issue.  A bit of food for thought!I am no expert in this field and your comments are welcome and appreciated.

Further reading and Sources can be found below.

BBC News (2000) “Pollution Warning on Holiday flights.”

Clean Sky cleansky.eu webpage, “Aviation & Environment”

Conference Board of Canada (2010) “Greenhouse Gas Emissions”

European Commission (2012a). “Co2 emissions from new cars down by 3% in 2011.”

European Commission (2012b) Climate Action. “Road Transport. Reducing CO2 emissions from vehicles.”

Huffington Post.ca. (2013) “Number of cars worldwide surpasses 1 Billion. Can the world handle this many wheels?”

IPCC (2007) Intergovernmental Panel on Climate Change, Climate Change 2007: Synthesis Report.

NASA (2004) “Clouds Caused by aircraft exhaust may warm US climate.”

MIT (2006) “Global Airline Industry Program: Airline industry overview.”

US Environmental Protection Agency, EPA (2010) “Global Greenhouse Emissions Data.”

Westjet.com (2013) “Environmental commitment”

Wikipedia.org (2013) “Fuel economy in aircraft.”

Wikipedia.org “Environmental Impact of Aviation“

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The ‘six-pack’ flight instruments: gyroscopes

Continuing on our review of the ‘six pack’ of flight instruments from the instruments that are powered by the pitot-static system, below we review those that are gyroscopes.

A gyroscope is a rotor or spinning wheel rotating and high speed,  and exhibits two fundamental characteristics upon which all practical applications are based.  These are:

  1. Gyroscopic intertia –  or rigidity in space. This is the tendency of the rotating body to maintain it’s plane of rotation if undisturbed.
  2. Precession: This is the tendency of the rotating body, when a force is applied to it at a point perpendicular to the plane of rotation to react as if the force had been applied 90 degrees in the direction of rotation

The three gryroscopic instruments are:

  1. The heading indicator. The main instrument we use to detect heading of the aircraft.  Only operates when the engine is running.  It runs off a vacuum system so we have to adjust it to the magnetic compass every time we fly. Frictional forces in the gyro bearings cause it to precess, resulting in a creep or drift in reading approximately 3 degrees every 15 minutes.
  2. Turn and bank coordinator, sometimes called the needle and ball.  The needle shows the direction and approximate rate of turn. The ball shows the amount of bank in the turn and whether there is any slipping or skidding. The ball is controlled by gravity and centrifugal force.  In a coordinated turn, the ball will be in the center as the centrifugal force offsets the pull of gravity. The instrument reacts to yaw but can be used for roll control since the aircraft yaws when banked.  It can show a rate one turn which gives us 3 degrees per second or a two-minute turn.
  3. The attitude indicator. Modern attitude indicators have virtually no limits of pitch and roll and will be accurate indicate pitch up to 85 degrees, and will not ‘tumble’ in 360 degree rolls.

The instruments are typically powered by the vacuum system and an electrical system for redundancy in case one of the power sources fails.  Often the heading indicator and attitude indicator operate on the vacuum system while the turn and bank coordinator is electrically operated.

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The “six pack” flight instruments: pitot-static

Flight instruments on a Cessna 172

Let’s do a review of the six main flight instruments: 

Detail is provided, of course, there is so much more we can add here!  The most important and basic flight instruments have remained the same for a long period of time, and are called the ‘six pack’.  Three of them are connected to the static port system which measures outside barometric pressure and the pitot tube which measures ram pressure.   The other three are gyroscopic.

The Pitot Tube on a Cessna 172
The Pitot Tube on a Cessna 172

The pitot tube, located on the leading edge of the wing, and the atmospheric pressure in the tube is increased by the dynamic pressure due to the forward motion of the aircraft while in flight.  The static pressure port is not affected by turbulence or ram air pressures.

The three instruments connected to the pitot-static system are:

(1) Airspeed Indicator (ASI) – pitot and static source; it measures the difference between the pressure in the pitot tube and the pressure in the static system. When the aircraft is on the ground the two pressures become equal, in motion the pressure difference causes the aneroid capsule inside the indicator to expand, moving the needle on the instrument.

The ASI shows indicated airspeed.  Indicated airspeed can be erroneous because of air density, which depends on pressure and temperature, and position error, which is caused by eddies that are formed when air passes over the wings and struts. This is the uncorrected reading from the dial and calibrated airspeed is the indicated airspeed corrected for position error (and installation error). Equivalent airspeed is the calibrated airspeed corrected for compressibility – this applies mainly to high speed airplanes.  Next we have true airspeed which is calibrated airspeed corrected for pressure and temperature. Roughly, to correct calibrated airspeed we add 2% to the indicated airspeed for every 1000 feet of pressure altitude.  We can gain more accurate readings using our flight computer – the E6B.

(2) Vertical Speed Indicator, static source. Operates on the principle that there is a change of barometric pressure with a change in altitude.  Atmospheric pressure is led into the capsule but slowed by a calibrated leak from entry into the case holding the capsule,  and this pressure differential causes the capsule to expand or compress.  There is a 6-9 second lag before it will indicate the correct rate of climb or descent.

(3) Altimeter, static source. Since pressure varies from place to place and the altimeter set to indicate height above sea level at the departure point may give a false reading after the aircraft has flown some distance.  To correct for this, the altimeter is equipped with a barometric scale (inches of mercury) which allows to set the current altimeter setting. We get this each time we depart our airport and can get it enroute.  If we fly to an airport that has a lower pressure than the one we departed from and we don’t change our altimeter setting, we will read higher than the actual height of the airplane. Temperature differences will also cause erroneous readings since the pressure altimeter is calibrated to indicate true altitude in standard atmospheric conditions.  When the temperature of the air beneath the airplane is colder than standard, the aircraft is lower than indicated, and vice versa for warmer than standard temperatures (higher than altimeter reading) .

Here are what we can expect from a compromised static-port system.

Instrument Pitot Tube Blocked Partially Blocked Static Port Fully Blocked Static Port
Altimeter Not connected Under-read in climb, over-read in descent Freezes
Vertical Speed Indicator Not connected Under-read in climb, less than true rate of descent Freezes at 0
Airspeed Indicator Acts like altimeter. Over-reads in climbs and under-reads in descents Under-read in climb, over-read in descent Under reads in climbs and over reads in descents.

Read about the other 3  instruments that are gyroscopes: the heading indicator, attitude indicator and turn and bank coordinator.

Do you have any other specialty instruments in your aircraft?

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New Aviation Movie Review – Flight – Alaska Airlines Flight 261

Alaska Airlines Flight 261

Flight is based on a real life incident involving Alaska Airlines Flight 261

I recently watched the new aviation – themed movie, Flight starring Denzel Washington.   In it, a troubled airline pilot experiences an in-flight emergency where the horizontal stabilizer jams in the down position, sending the jet into a deep nose dive. Because the captain is a maverick pilot, he is able to miraculously save 102 people through a daring maneuver.  However the accident also forces him to deal with some of his other demons with alcoholism and drug abuse.

I really enjoyed the movie and the rest of the weekend I spent thinking if the flight maneuver was aerodynamically possible.  Basically, he inverted the plane while it was in the steep dive, which managed to arrest the dive and allow him some semblance of control of the aircraft.   Given the stress that is associated with in-flight emergencies, it is doubtful that it could be done.  But is it completely impossible?

Forcing the aircraft into an inverted position when the elevator was down would theoretically cause the aircraft to want to pitch up instead of down. Though because the horizontal stabilizer is now inverted as well the effect would be much lessened. The control of the aircraft from the ailerons would be backwards, and lessened given the fact that the airflow is supposed to be on the top side of the wing and not bottom.  I’m not sure if it’s possible, but probably very aircraft specific.  It’s probably not impossible…but the fact that the airplane doesn’t immediately reassume the nose down position when rolled the right side up after flying upside down? Definitely not realistic. 

It is interesting to note that the accident in this movie is based on a real life incident involving Alaska Airlines in January 2000.

What happened on Alaska Airlines Flight 261.
What happened on Alaska Airlines Flight 261. Photo courtesy of iasa.com.au.

In this incident, the horizontal stabilizer jammed and the pilots attempted to fly the aircraft inverted – but they didn’t have enough altitude to recover.

In any case, it is a great movie – and I highly recommend it to anyone, particularly aviation enthusiasts like myself.  The figure below shows what happened on Alaska Airlines flight 261.

Looking to buy Flight DVD?

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