Airplanes Don't Stall, Pilots Stall Them

Image via Wikipedia

By Doug Daniel

When smooth airflow separates from your wings they stall, losing most of their lift. If you are lucky the airplane drops like a brick, pitches down, accelerates and starts to fly normally again. If you are not so lucky, one wing stalls, rolling your airplane toward the stalled wing as it progresses to a spin before you can recover. It is probably a good idea to keep the airflow attached to the wing and the tail and every other surface needed for controlled flight.

An aerodynamicist would tell you that stalls can only occur when an airfoil reaches or exceeds its critical angle of attack. I would say that a stall occurs only when you try to make the wind turn too sharp a corner.

You see, air is sticky. Not very sticky but it is a little sticky. An aerodynamicist would clear his throat; raise his eyebrows and say, "Viscous." So let's ignore the aerodynamicist. It's sticky. When air blows past a gently curved surface, like a wing, it tends to stick to the surface even though the surface curves away from the wind.

If the wing is symmetric top and bottom and the wind is coming straight on, the wind impacts the front of the wing and builds a high pressure area there. Then as it starts to follow the contour of the wing, like anything following a curved path, it gets pulled out. But its stickiness holds it next to the surface. The result is low pressure over most of the surface, top and bottom.

Now if you pitch the wing up a bit by pulling back on the stick a bit, the air on top must change direction a bit more than the air on the bottom. The result is more low pressure on the top and less on the bottom. Perhaps the high pressure area on the bottom of the wing is bigger than before. The wing is sucked up by the top and pushed up by the bottom. We call this lift.

Suppose you pitch the wing up a lot by pulling the stick a long way back. The air on the top has to change direction a lot and the pressure on the top drops a lot. If you pull the stick far enough, the low pressure area on the top of the wing sucks air from the back of the wing forward, separating the airflow from the top of the wing. This is bad. The low pressure area on the top of the wing disappears as it is filled by the forward flowing air. The wing loses lift. This is a stall.

The airflow separates from the wing of a properly designed airplane before it separates from the tail. If the tail has lift and the wing doesn't the airplane's wing drops and the tail doesn't. This is a good thing because the wing comes down and faces a lower pitch attitude. The results are that the wind re-attaches to the upper surface, lift is restored and the airplane returns to normal.

Now suppose the pilot continues pulling back on the stick. As soon as the wing develops lift, it goes up too far again and stalls again. We call this bobbing action 'buffeting.'

Buffeting is good because it warns the pilot that he or she is pulling too hard on the stick and the wing is ready to enter a serious stall - one that could lead to a potentially fatal spin.

So now we know that the real warning of an impending serious stall is buffeting. We also know that buffeting is caused by pulling the stick too far. So we know that the way to avoid a stall is to pull less when we feel buffeting. We also know that if we pull less on the elevator, that the airplane will go down. That could be a really bad thing. Increasing the engine's power simultaneously with easing up on the elevator can mitigate that sinking feeling

Notice that no where in this discussion of what causes stalls and what to do about them was the concept of airspeed needed. Stalls are only caused by pitching the wings up too far - nothing else. Even though stalling speed is a useful term, there really is no unique stalling speed for an airplane. You have to read the fine print. What 'stall speed' usually means is the speed at which an airplane's wing exceeds its maximum pitch attitude if the airplane is loaded to maximum landing weight, is in the landing configuration and flying straight ahead

Doug Daniel is a long time pilot, flight instructor, software engineering manager and author. His department developed the software for the out-the-window-displays for the space shuttle, F-117, RS-71 and numerous other exotic aircraft simulators. His writing focuses on flying techniques designed to make flying easier and safer. If this was interesting, visit his website at http://www.FlyingSecretsRevealed.com/flying_questions/

Article Source: http://EzineArticles.com/?expert=Doug_Daniel
http://EzineArticles.com/?Airplanes-Dont-Stall,-Pilots-Stall-Them&id=2010448

How do Ryanair make money?

Image via Wikipedia

I read an interesting article from Wired magazine recently which basically stated that on a typical London to Barcelona flight it costs Ryanair $70 per seat. (This is the cost to the airline NOT the price of the ticket).

So I got to thinking about this and wondered about the economics.

The plane used on that flight will probably be the B737-800 which has 180 seats. At $70 per seat the cost of the flight is $12600. The flight lasts somewhere in the region of 2 hours therefore the cost per hour to Ryanair is $6300.

Within that $6300 the following has to be included:

• Fuel for 1 hours flight on a medium sized 2 engine commercial airliner
• Half the landing fee for the destination airport
• 1 hours salary for a pilot and co-pilot
• 1 hours salary for 4 cabin staff
• Maintenance costs for 1 hours flight
• Aircraft leasing costs for 1 hours flight
• 50% of the handling fees for the baggage at the destination.
• Salary of the check-in staff at the departure airport
• A proportion of head-office overhead fees
• Profit.

Let's take the head office overhead and the profit out of there so as not to confuse matters too much.

Now let's look at some figures we know: A Gulfstream IV aircraft carries up to 13 passengers over 4500 miles at a time. It has two small engines and can be leased for around $5200 per hour

Commercial aircraft leasors will lease an Airbus A320 (similar to a Boeing 737) on an
ACMI (Aircraft, Crew, Maintenance & Insurance model) (i.e without fuel and other costs) for $2750 per hour On top of that the airline will have to pay for items such as:

• fuel and oil;
• aircraft landing, handling, navigation and terminal charges;
• passenger and cargo handling;
• airport taxes, all passenger related taxes and security taxes;
• aircraft parking and ground security;
• ramp services including towing, push-back, de-icing, nitrogen and oxygen services;
• all dry goods, including but not limited to head rest covers, airsickness bags, blankets and pillows;
• ATC fees and all international route charges;
• cabin cleaning and water services;
• aircraft interior deep cleaning and exterior cleaning;
• airport security passes and permits, if required;
• over-flight permits;
• custom taxes, immigration and inspection fees, import and export duty's;
• landing and traffic permit and slots;
• office space including telephone, fax, email;
• spare parts facilities (storage) including air conditioning;
• one van for transportation of mechanics and parts;
• insurance - passengers, baggage, mail, cargo and war risk insurance;
• any additional cost reference to insurance coverage will be on Lessee's account;
• any and all other reasonable direct operating costs, incurred in the performance of the flights whether or not listed above.

Aviation fuel is currently charged at around $830 per metric tonne (assuming a 45% reduction of the price of $1280 at the height of the fuel issues). Fuel to Barcelona is about 6.65 metric tonnes which gives a cost per hour (assuming the two hour flight) of $2400

So we know so far that we are looking at approx ($2400 + $2750 = $5150) just for the aircraft and fuel The landing charge at Barcelona is approx €6 per tonne which would equate to approx €250 for the plane or €125 per hour. This doesn't include any of the salaries for the crew, nor any of the additional costs listed above. Flight crew earn less than $72 per hour (which equates to $145 per hour for the two flight crew) Cabin crew are on considerably less than that (say $20 per hour * 4 = $80.

While these figures are only approximate (and the result of some investigative digging on the internet), it does prove a couple of things

1) Ryanair are not good staff payers
2) The margins are very thin
3) Somewhere cuts must be being made to ensure the costs are kept down. Remember in the remaining $100 per hour Ryanair must pay for ALL the maintenance costs, and insurance as well as those costs detailed in the list above

How do they do it? Are my figures inaccurate? Can anyone with inside information let me know please?

Related articles by Zemanta

• Boeing 737800: safety record (telegraph.co.uk)
• General Aviation Sounds Mayday as Fat Cats Ditch Their Jets (wired.com)

Cost free flying? Worth considering...

Image via Wikipedia

What if I told you there was a way to fly as often as you like, in all weathers, in whichever aircraft you want, from wherever you want, with live ATC and it won't cost you anything. You'd like that wouldn't you? Of course you would. But you would also want to know what the catch was wouldn't you?

Well, I have one word for you: Simulation.

Flight simulation is a growing industry. Since the early days of the Microsoft Flight Simulator the state of the art has moved on in leaps and bounds. Whole industries have sprung up to manage the ancilliary markets with thing such as new planes, scenery and adventures. A whole host of forums, web-sites and communities have appeared dedicated to the art and science of flight simulation. I even heard about a guy who is building his own 747 flight simulator - with full motion control - in his garage!

The problem with a lot of this was always twofold:


1) Even if you get all the latest add-on's, up-to-date software and patches, it was still a case of sitting in your room staring at a screen and playing with a keyboard.
2) It didn't fully replicate the flying experience because it was missing one vital ingredient - proper Air traffic control.

Well unfortunately the problem of 1) is not going to go away soon. Even the guy building his own 747 simulator is still a guy sat at home - albeit with some sophisticated machinery. But the problem of 2) is more easily solved.

Flight sim manufacturers have included some pretty good ATC functionality in their packages. Each release brings more and more advanced settings and realistic situations. But at the end of the day it is all preprogrammed and cannot take the place of 'real' controllers. Back in the early days of flight simulator software there began a parallel movement to create and run a community of Air Traffic Controllers using ATC simulation software. The software was fairly rudimentary to start with, but as with the flight simulators it has increased in sophistication to the point where it can be very lifelike indeed.

Except that it is not, actually real life. It's computer controlled planes in a computer created environment.

So on the one hand you have the pilots wishing they could have ATC that was 'real' and on the other controllers wishing they could have 'real' pilots to control. It didn't take long for someone to make the logical connection and pretty soon VATSIM was born.

VATSIM is the Virtual Air Traffic Simulation Network which uses some sophisticated software to link pilots, planes and air traffic controllers together across the internet.

It works very simply:

With your flight simulator program you download a small piece of software which acts as a "squawkbox" to provide a transponder type functionality to your machine. This channels all your typical transponder type information from your flight sim to the web.

On the web are servers which monitor this data and pass it to other simmers who are running the same squawbox software as well as ATC's simmers who are running controller software.

The net result of this is that you fly your own simulation on your own machine, but - with the aid of the squawbox and a headset/microphone - you are connected to controllers who can both see your plane AND interact with you as a pilot, along with all the other pilots who are currently using the squawbox.

The beauty of this is twofold:
a) You get to fly your own planes in your own environment whenever you want, thereby increasing your flight time and experience (albeit simulated).
b) You get fully managed ATC cover - with ALL the appropriate terminology - which thereby increases your comfort level and experience when interacting with real ATC and flying real planes.

The whole process is very well thought through and it works like this:

• Once connected you file a flight plan. This can be VFR or IFR. You can fly long distance in a 747 or just do circuits in your Cessna, or any combination in between.
• You tune your flight simulator radio to the correct frequency and a real live voice greets you and issues instructions. (These folks, by the way have gone through some fairly extensive training and mentoring and are every bit as good as the real thing)
• When you fly you can both see other (non AI) planes in your sim AND hear their transmissions on the radio.
• Air traffic control will act in the expected manner providing directions, asking questions, giving clearances and providing flight following. It's pretty much as close to the real thing as you can get it. The system is even designed to download the real weather from the nearest airport to your current location and update your simulator.

In recent days I have flown my Cessna around the outer edges of the London CTR and been directed away from controlled airspace. I have taken a Dash-7 from Farnborough to Amsterdam, an Airbus A320 from Amsterdam to Gatwick and even flown circuits in a Cessna around Gatwick (It's not recommended in real life as the landing fees are so high and dodging the 747's can be tricky, but it is possible). This weekend I will be flying an A320 from Frankfurt to Hamburg as part of a 'Real Ops' exercise to simulate the real life movements around a major airport. There will be upwards of 400 flights arriving and departing. Should be fun.

Now before you look at this and say "It's not the same as flying the real thing because you would never be able to fly an Airbus without years of training" let me just clarify one thing. I fly all sorts of planes in the simulator, including the ones I was originally trained on - single engine propeller planes - and every time I fly one in the simulator it improves the way I fly them in real life. I can use this as an exercise to do all those things I would never want to do in reality - such as simulate an engine failure or something equally as nasty. It also allows me to practice my instrument flying (Which you will all have done some of in your PPL training) without worrying about really getting lost. Now imagine being able to do all this AND have some friendly controller watching over you - all for free!

I thoroughly recommend having a look at flight simulation and VATSIM. It can surely only improve your flying can't it? Even if it makes you more comfortable talking with controllers this is a great benefit to it.

Here are some links to help you get started:

VATSIM - The central hub for this. Create a free acount and log in
Squawkbox - The connection software (again free)
FSInn - An alternate connection software (A lot more functional but a bit too complex for my liking)