Yesterday was a beautiful clear day, so we took the opportunity to get my IFR cross country flight done. Its seems rather counter-intuitive, to wait for a clear day to go file IFR, but the Twin Comanche isn't certified for flight into known icing conditions, and in the winter essentially any flight through cloud will be into icing conditions, so even though we file IFR, we still have to make sure the weather is reasonably clear.
In the end it doesn't matter a whole lot however, IFR training is almost all about the procedures. So I got my first ever experience filing and flying under IFR flight rules, which was pretty cool, and not nearly as intimidating as I was expecting. I understand everything that's going on at this point during my training, the mistakes that I do make are usually things I know I have to do, but just forgetting to do them at the proper time.
The flight as far as the training side of things went relatively well, the mistakes I made I thought I could have avoided if I was more deliberate with my procedures, but it all comes with practice I guess. Unfortunately the airplane is once again back in the shop. Landing gear problems this time. Our flight was from London to Hamilton to Kitchener and back to London with missed approaches in Hamilton and Kitchener, and during our climbout on the missed approach in Hamilton we noticed the landing gear lights indicated the gear was stuck in transition. In the mirror it appeared to be retracted all the way up. We checked the circuit breaker, which was still engaged, and then tried to recycle the landing gear. No luck, the gear wouldn't move at all. In between the seats there is a floor panel that can be opened up to provide access to landing gear motor, screw jack, the actuator arm that moves the gear, and the handle for manually extending the gear, so we opened that up to see what we could find. The position of the actuator arm confirmed what I saw in the mirror, the gear was indeed retracted fully.
I figured there wasn't much we could do at this point, so I suggested we continue our flight to Kitchener, do our missed approach, and then continue on back to London as planned.
Coming into London we tried cycling the circuit breaker and then selecting the landing gear down one more time with no luck. So it came down to a manual landing gear extension. I briefed my instructor on the procedure so he could do it while I flew the VOR approach into London. I've done manual gear extensions on the ground before with the airplane up on jacks during maintenance, so I knew exactly what to expect. Its electrically driven gear, so after slowing the airplane down to blue line, you just have to disengage it from the motor, and then insert a lever to push forward and lock the gear down. No pumping necessary, which is generally the procedure for hydraulically operated gear. Gravity usually negates the need for step 2 however. For the post part as soon as you disengage it from the motor the gear just falls down into place due to both gravity and a bungie system. It pays to know your airplane! The procedure went off without issue, I made a smooth touchdown and breathed a sigh of relief with the sound of wheels rolling beneath me. With landing gear problems despite every indication showing the gear is down and locked there's always that little bit of fear (I can't decide if its a rational fear or not, lol) in the back of your mind that the gear could fold back up as soon as you touchdown. Thankfully that wasn't the case though, and we taxied in to end the flight.
Thursday, January 21, 2010
Tuesday, January 19, 2010
Busting Bernoulli's Lift
Today I'm sick with a cold, and the weather's been crap for almost a week now, so no flight training at the moment. Tomorrow is looking up however.
In the meantime I've been lazing around the house, playing computer games and browsing some aviation blogs. I came across one blog by an American flight instructor, which in one post was explaining the theory behind lift - incorrectly. That same incorrect explanation has been a persistant myth among laypeople and pilots alike for a long time now, and every time I hear it repeated it just raises my pet peeveness of it one more notch. So today we'll set the record straight, and I'll do my best to provide proof for any persistent skeptics out there.
The myth is that lift is produced by the curvature, or camber, of the top surface of a wing. The air being divided by the wing at the leading edge must meet up again at the trailing edge, and because the air has further to go over the top (due to the camber), its velocity increases and pressure decreases. The decrease in pressure causes a pressure differential between the top and bottom of the wing, which sucks the wing upwards, thus creating lift. This decrease in pressure is in reference to Bernoulli's Principle, which states that as the velocity of a fluid increases, its pressure decreases.
I am not disputing the validity of Bernoulli's Principle, because that part is true. The error however comes in the assumption that the pressure differential can create enough lift to counteract the weight of the airplane. If this explanation were true, it immediately raises some questions if one thinks about it:
For one, how does an aerobatic airplane fly upside-down? The quick answer is that aerobatic aircraft are equipped with a symetrical wing, which is a wing with an equal camber (curvature) on both the top and bottom. But that explanation creates yet another problem. How does a symetrical wing fly at all?! According to Bernoulli's Principle, it can't, because due to the symetry of both the top and bottom the air wouldn't create a pressure differential. Similarily, in theory, a flat wing, like what you would find on a balsa wood model, or many fabric wings like on hang-gliders and ultralights, would not be able to produce any lift at all either, but we've all seen balsa models fly.
Another problem we come upon is that our current explanation completely ignores what we know about angle of attack. Every pilot knows that term. Angle of attack is the angle that the wing meets the oncoming air. The illustration above would be a wing at an angle of attack of zero degrees. The myth would seem to indicate that a wing could produce lift at an angle of attack of zero. The myth also seems to say that it would be possible to maintain that zero angle of attack through the entire speed range of an aircraft, since lift is created by the Bernoulli Principle, and not angle of attack. This is at odds with any pilot's observations of how an airplane reacts as it is decelerated. It only takes a single demonstration of slow flight to show that as an airplane slows down, the angle of attack increases, which can be observed by the fact that the nose raises higher and higher into the air to the point of an aerodynamic stall. It is this observation of angle of attack that leads us forward to the true explanation of how a wing creates lift.
The majority of lift is in actual fact produced as a result of the angle of attack, which creates both a deflection force underneath the wing (resulting in higher pressure), and a vacuum effect on top of the wing (lower pressure). The vacuum effect above is not however a result of a wing's camber, it is a result of angle of attack. With a wing at a positive angle of attack, the air flows over the top of the wing and is forced to turn a corner down towards the wing. It is at this corner the low pressure zone develops. Note the illustration below of a flat wing moving through the air at a certain positive angle of attack. You'll have to forgive the pathetic visual, I made it in paint, but it gets the point across. I chose to illustrate a flat wing because its easy to visualize the "corner" that the air has to turn as it passes over the top.
So if all a wing needs is angle of attack to fly, why the heck do they give it a camber?! Well the primary reason is for smooth airflow, at a range of attack angles. A flat wing will stall at a very low angle of attack because it creates a very sharp corner over the top of the wing for the air to have to travel. At some point the air won't be able to make that corner, and will seperate from the wing, producing a turbulent airflow. We know this as a stall. When the top surface of a wing is cambered, it allows the air to make that corner over the top of the wing at much higher angles of attack without seperating and causing a stall. The camber makes for a much smoother corner. This, in effect allows the wing to produce lift at slower speeds, which is generally a good thing. This also explains effectively why airplanes designed to fly slow and carry big loads have a wing with a high camber. Its not because the camber itself produces the lift, but because the camber allows the wing to fly at greater angles of attack without stalling, and the greater the angle of attack, the more lift a wing will produce.
This explanation also neatly answers all of the questions that came up with the popular mythical explanation. Aerobatic airplanes can fly either right-side up or upside-down, regardless of whether they have symetrical wings, because they just have to maintaint a positive angle of attack. Flat wings like balsa gliders and hang-gliders are also explainable. Finally it also fits better in with a piot's observations during slow flight, because as the aircraft decelerates, the angle of attack must increase, which is observable in the form of a raised nose.
While the mythical explanation of lift may not be ENTIRELY false (the Bernoulli Principle), it may contribute to the total lift of an airfoil a little bit, but the effect is negligable for practical purposes. One thing in that explanation that is completely false is the idea that air being split at the leading edge must meet back up at the trailing edge. There's no law anywhere that says air particles have a "memory" to them and must return to the particles they began with. They are carried to wherever the forces acting take them. Wind tunnel tests with time-pulsing coloured smoke actually show that the above air accelerates far past where the lower air ends up at the back, and also are forced downwards. The downward flow is known as downwash (which is also an unexplainable phenominon with our mythical understanding of lift).
So, now you know the rest of the story...
In the meantime I've been lazing around the house, playing computer games and browsing some aviation blogs. I came across one blog by an American flight instructor, which in one post was explaining the theory behind lift - incorrectly. That same incorrect explanation has been a persistant myth among laypeople and pilots alike for a long time now, and every time I hear it repeated it just raises my pet peeveness of it one more notch. So today we'll set the record straight, and I'll do my best to provide proof for any persistent skeptics out there.
The myth is that lift is produced by the curvature, or camber, of the top surface of a wing. The air being divided by the wing at the leading edge must meet up again at the trailing edge, and because the air has further to go over the top (due to the camber), its velocity increases and pressure decreases. The decrease in pressure causes a pressure differential between the top and bottom of the wing, which sucks the wing upwards, thus creating lift. This decrease in pressure is in reference to Bernoulli's Principle, which states that as the velocity of a fluid increases, its pressure decreases.
I am not disputing the validity of Bernoulli's Principle, because that part is true. The error however comes in the assumption that the pressure differential can create enough lift to counteract the weight of the airplane. If this explanation were true, it immediately raises some questions if one thinks about it:For one, how does an aerobatic airplane fly upside-down? The quick answer is that aerobatic aircraft are equipped with a symetrical wing, which is a wing with an equal camber (curvature) on both the top and bottom. But that explanation creates yet another problem. How does a symetrical wing fly at all?! According to Bernoulli's Principle, it can't, because due to the symetry of both the top and bottom the air wouldn't create a pressure differential. Similarily, in theory, a flat wing, like what you would find on a balsa wood model, or many fabric wings like on hang-gliders and ultralights, would not be able to produce any lift at all either, but we've all seen balsa models fly.
Another problem we come upon is that our current explanation completely ignores what we know about angle of attack. Every pilot knows that term. Angle of attack is the angle that the wing meets the oncoming air. The illustration above would be a wing at an angle of attack of zero degrees. The myth would seem to indicate that a wing could produce lift at an angle of attack of zero. The myth also seems to say that it would be possible to maintain that zero angle of attack through the entire speed range of an aircraft, since lift is created by the Bernoulli Principle, and not angle of attack. This is at odds with any pilot's observations of how an airplane reacts as it is decelerated. It only takes a single demonstration of slow flight to show that as an airplane slows down, the angle of attack increases, which can be observed by the fact that the nose raises higher and higher into the air to the point of an aerodynamic stall. It is this observation of angle of attack that leads us forward to the true explanation of how a wing creates lift.
The majority of lift is in actual fact produced as a result of the angle of attack, which creates both a deflection force underneath the wing (resulting in higher pressure), and a vacuum effect on top of the wing (lower pressure). The vacuum effect above is not however a result of a wing's camber, it is a result of angle of attack. With a wing at a positive angle of attack, the air flows over the top of the wing and is forced to turn a corner down towards the wing. It is at this corner the low pressure zone develops. Note the illustration below of a flat wing moving through the air at a certain positive angle of attack. You'll have to forgive the pathetic visual, I made it in paint, but it gets the point across. I chose to illustrate a flat wing because its easy to visualize the "corner" that the air has to turn as it passes over the top.
So if all a wing needs is angle of attack to fly, why the heck do they give it a camber?! Well the primary reason is for smooth airflow, at a range of attack angles. A flat wing will stall at a very low angle of attack because it creates a very sharp corner over the top of the wing for the air to have to travel. At some point the air won't be able to make that corner, and will seperate from the wing, producing a turbulent airflow. We know this as a stall. When the top surface of a wing is cambered, it allows the air to make that corner over the top of the wing at much higher angles of attack without seperating and causing a stall. The camber makes for a much smoother corner. This, in effect allows the wing to produce lift at slower speeds, which is generally a good thing. This also explains effectively why airplanes designed to fly slow and carry big loads have a wing with a high camber. Its not because the camber itself produces the lift, but because the camber allows the wing to fly at greater angles of attack without stalling, and the greater the angle of attack, the more lift a wing will produce.
This explanation also neatly answers all of the questions that came up with the popular mythical explanation. Aerobatic airplanes can fly either right-side up or upside-down, regardless of whether they have symetrical wings, because they just have to maintaint a positive angle of attack. Flat wings like balsa gliders and hang-gliders are also explainable. Finally it also fits better in with a piot's observations during slow flight, because as the aircraft decelerates, the angle of attack must increase, which is observable in the form of a raised nose.
While the mythical explanation of lift may not be ENTIRELY false (the Bernoulli Principle), it may contribute to the total lift of an airfoil a little bit, but the effect is negligable for practical purposes. One thing in that explanation that is completely false is the idea that air being split at the leading edge must meet back up at the trailing edge. There's no law anywhere that says air particles have a "memory" to them and must return to the particles they began with. They are carried to wherever the forces acting take them. Wind tunnel tests with time-pulsing coloured smoke actually show that the above air accelerates far past where the lower air ends up at the back, and also are forced downwards. The downward flow is known as downwash (which is also an unexplainable phenominon with our mythical understanding of lift).
So, now you know the rest of the story...
Wednesday, January 13, 2010
Training has Commenced
Airplane is finally fixed, and I had a training flight today, more booked for tomorrow. The crunch time is really on now because I have only six weeks until my INRAT exam expires.
Today we did a quick review of VOR holds, then did some localizer holds, and finished with an ILS approach. To be honest I'm having a pretty tough time. It feels like it takes me a long time to grasp even a little of what we're covering, while the rest of it goes right over my head. Its been a while since I've felt this dumb. I'm both amazed at and thankful for my instructor's patience. He'll calmly walk me through each step over and over again, and never gets upset or impatient that its taking me so long to catch on.
I do feel like I am making progress though, bit by bit, but I was hoping I would catch onto things much quicker than I am. The airplane is still causing frusteration however. The #1 VOR was replaced last year, and its a brand new unit, however it was doing funny things today. For some reason it refused to pick up the Morse code idents for the London VOR. It worked fine for every other VOR however. Finally once we were back on the ground we checked it again and it worked fine. Ghosts in the machine I guess. Those are the worst kinds of problems, where sometimes it works, other times it doesn't. We tried every possible combination of settings on the audio panel and the instrument, but we couldn't manage to figure out why we couldn't hear the Morse code audio. Its especially frusterating because not only does trying to troubleshoot those problems in the air take away from the training experience, its a brand new unit, so in theory it should work perfectly. The best we can do is cross our fingers and hope for the best tomorrow.
A part of me wants to go crawling back into the comfortable world of VFR flying and forget about advancing into the IFR realm. VFR doesn't take any effort for me anymore, its home for me, but I know that it'd be a mistake to limit myself like that. Not only because an IFR rating opens up better jobs with better pay, but because the longer I put off IFR training the more I become entrenched in VFR flying and the harder it would be to learn IFR later on.
That being said, there's been a couple job possibilities coming over the horizon for me this summer in the fire-patrol sector. I've always wanted to do that, either water-bombing or bird-dogging. Those are both VFR jobs, and I could see myself doing something like that for a while. I did some research today just out of curiosity to learn a little more about those jobs, and here's the short explanation of how I understand it for my readers who are also uneducated in the subject. Its all very cool.
Aerial fire-fighting is divided into 3 different "units" we'll call them. There's Fire Detection, Bird-dogs, and the Water Bombers themselves. The first, which is what I would start out doing if I end up getting a job in the fire-fighting field this year, is called Fire Detection. From what I gather its essentially what it sounds like. Small aircraft, like a Cessna 337, patrols a large area of wilderness with forest-fire potential looking for fires. If a forest fire is spotted, it calls in a Bird-dog aircraft. The Bird-dog aircraft essentially takes command of the entire operation. It will fly over the area and a fire-expert on board the aircraft will assess the forest fire and develop the attack plan for the water bombers, such as the best places to drop the water loads based on the winds and conditions for best control of the fire. Since water bombing is done at tree-top altitudes, the Bird-dog aircraft will then fly the low-altitude bombing route that the water bombers will fly, to note any obstacles that could prevent a hazard to the bombers. We're talking flying over fires and past smoke at 200 ft above the ground, cool stuff. After the bombing runs have been safely tested by the bird-dog, the bird-dog will then climb up higher and orbit the area to call in the water bombers. Since the airspace near a forest fire can naturally become very busy due to the boming activity, the bird-dog's next responsibility will be to act as Air Traffic Control for the water bombers conducting their runs, coordinating everything to make sure aircraft are kept safely apart during operations as well as monitoring the progress of the operation. At least thats my understanding of how things go, I'd love to hear the comments of any readers who have real experience doing this. I've always thought its sounded like a pretty fun job. All a very coordinated team excercise. As for me, we'll see how things pan out.
Today we did a quick review of VOR holds, then did some localizer holds, and finished with an ILS approach. To be honest I'm having a pretty tough time. It feels like it takes me a long time to grasp even a little of what we're covering, while the rest of it goes right over my head. Its been a while since I've felt this dumb. I'm both amazed at and thankful for my instructor's patience. He'll calmly walk me through each step over and over again, and never gets upset or impatient that its taking me so long to catch on.
I do feel like I am making progress though, bit by bit, but I was hoping I would catch onto things much quicker than I am. The airplane is still causing frusteration however. The #1 VOR was replaced last year, and its a brand new unit, however it was doing funny things today. For some reason it refused to pick up the Morse code idents for the London VOR. It worked fine for every other VOR however. Finally once we were back on the ground we checked it again and it worked fine. Ghosts in the machine I guess. Those are the worst kinds of problems, where sometimes it works, other times it doesn't. We tried every possible combination of settings on the audio panel and the instrument, but we couldn't manage to figure out why we couldn't hear the Morse code audio. Its especially frusterating because not only does trying to troubleshoot those problems in the air take away from the training experience, its a brand new unit, so in theory it should work perfectly. The best we can do is cross our fingers and hope for the best tomorrow.
A part of me wants to go crawling back into the comfortable world of VFR flying and forget about advancing into the IFR realm. VFR doesn't take any effort for me anymore, its home for me, but I know that it'd be a mistake to limit myself like that. Not only because an IFR rating opens up better jobs with better pay, but because the longer I put off IFR training the more I become entrenched in VFR flying and the harder it would be to learn IFR later on.
That being said, there's been a couple job possibilities coming over the horizon for me this summer in the fire-patrol sector. I've always wanted to do that, either water-bombing or bird-dogging. Those are both VFR jobs, and I could see myself doing something like that for a while. I did some research today just out of curiosity to learn a little more about those jobs, and here's the short explanation of how I understand it for my readers who are also uneducated in the subject. Its all very cool.
Aerial fire-fighting is divided into 3 different "units" we'll call them. There's Fire Detection, Bird-dogs, and the Water Bombers themselves. The first, which is what I would start out doing if I end up getting a job in the fire-fighting field this year, is called Fire Detection. From what I gather its essentially what it sounds like. Small aircraft, like a Cessna 337, patrols a large area of wilderness with forest-fire potential looking for fires. If a forest fire is spotted, it calls in a Bird-dog aircraft. The Bird-dog aircraft essentially takes command of the entire operation. It will fly over the area and a fire-expert on board the aircraft will assess the forest fire and develop the attack plan for the water bombers, such as the best places to drop the water loads based on the winds and conditions for best control of the fire. Since water bombing is done at tree-top altitudes, the Bird-dog aircraft will then fly the low-altitude bombing route that the water bombers will fly, to note any obstacles that could prevent a hazard to the bombers. We're talking flying over fires and past smoke at 200 ft above the ground, cool stuff. After the bombing runs have been safely tested by the bird-dog, the bird-dog will then climb up higher and orbit the area to call in the water bombers. Since the airspace near a forest fire can naturally become very busy due to the boming activity, the bird-dog's next responsibility will be to act as Air Traffic Control for the water bombers conducting their runs, coordinating everything to make sure aircraft are kept safely apart during operations as well as monitoring the progress of the operation. At least thats my understanding of how things go, I'd love to hear the comments of any readers who have real experience doing this. I've always thought its sounded like a pretty fun job. All a very coordinated team excercise. As for me, we'll see how things pan out.
Saturday, January 2, 2010
Quick Update
Just thought I'd write a quick update since its been a month since I've written last now. No IFR training yet, the Twin Comanche's MP gauge decided it would be a good time to kick the bucket, so I had my AME take a look at it, and while looking at the airplane he also found a landing gear downlock spring that was broken as well, so we've been waiting for parts for the last couple weeks. The Christmas season is apparently a bad time to order airplane parts, cause we've been waiting for 3 weeks already.
So that's about all I have to report, as soon as that gets fixed I'll be able to jump headfirst into IFR training and get it all finished up. In the meantime its been snowing rediculous amounts in London. Which means I'm gonna have a lot of fun extricating the airplane from the mounds of snow that I'm sure its buried under. I can't wait.
So that's about all I have to report, as soon as that gets fixed I'll be able to jump headfirst into IFR training and get it all finished up. In the meantime its been snowing rediculous amounts in London. Which means I'm gonna have a lot of fun extricating the airplane from the mounds of snow that I'm sure its buried under. I can't wait.
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