Teaching Aerodynamics
06-15-2007, 02:11 PM
#1
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Thread Starter
Teaching Aerodynamics
I've recently been helping out at our clubs training night and have noticed a few issues that come up frequently. Each major mistake most beginners make can easily be explained by a basic understanding of aerodynamics. I don't believe it is enough to know that ailerons move the airplane on the longitudinal axis; It is necessary to know why. Learning to fly a model airplane is not like learning to drive an R/C car. Due to our life experiences, our minds are stuck on movement with reference to the ground. This line of thought is of no help and can in fact be a great inhibitor to learning to become a competent model pilot. We have a great training program and I'm not trying to criticize it, but I think these concepts need to have a greater emphasis in a comprehensive training program. What do you think?
How many times have you seen a beginner lower their throttle to idle when flying the downwind leg to minimize ground speed only to have their ailerons become "mushy" and ineffective, causing a loss of control?
How many times have you seen a beginner stall an airplane while diving and not realize they could possibly stall in that position? What about a pilot telling you that their airplane has so much extra lift it climbs really fast?
How many times have you seen a beginner lower their throttle to idle when flying the downwind leg to minimize ground speed only to have their ailerons become "mushy" and ineffective, causing a loss of control?
How many times have you seen a beginner stall an airplane while diving and not realize they could possibly stall in that position? What about a pilot telling you that their airplane has so much extra lift it climbs really fast?
06-15-2007, 02:59 PM
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RE: Teaching Aerodynamics
Definetly.... tip stalls and snap rolls on landing or during premature takeoffs from sudden and severe applications of ailerons while flying slowly is another source of demonic mystery for those that don't understand that they caused their own problem.
06-15-2007, 05:42 PM
#3
RE: Teaching Aerodynamics
G'day Nathan,
I totally agree, & how many students will tell you that there engine stalled on take off, & caused the crash, when it was the wing that stalled, after the engine STOPPED, & the wing didn't stall because the engine stopped, but because the first thing they did after it stopped, was to apply UP elevator, because in a plane, engines don't stall, but wings DO, engines STOP.
It takes a lot more to teach a student to fly, than just how to take off, fly around & land.
I totally agree, & how many students will tell you that there engine stalled on take off, & caused the crash, when it was the wing that stalled, after the engine STOPPED, & the wing didn't stall because the engine stopped, but because the first thing they did after it stopped, was to apply UP elevator, because in a plane, engines don't stall, but wings DO, engines STOP.
It takes a lot more to teach a student to fly, than just how to take off, fly around & land.
06-18-2007, 06:40 PM
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RE: Teaching Aerodynamics
I believe that knowing why something happens and when to anticipate something in an airplane is important although no need to go far in depth
For a given airplane, a stall will always occur at the same angle ( a.k.a. the critical angle of attack), regardless of airspeed, flight attitude or weight.
The three axes of flight, longitudinal, lateral and vertical axes.
Balancing an aircraft both along the lateral and longitudinal axes.
Understanding torque and where to expect it most. Low airspeeds, high power setting, and high angles of attack. When sitting inside a plane you can picture the propeller spinning clockwise. The clockwise action of a spinning propeller causes a torque reaction, which tends to rotate the airplane counterclockwise about its longitudinal axis. To better understand, when flying a propeller driven plane at high angles of attack the descending blade of the propeller takes a greater so called bite of air than the ascending blade on the other side. This creates P-factor making your plane yaw among the vertical axis. In terms of tricycle landing gear you should apply right rudder during take off because of this asymmetrical thrust.
When turning an airplane you should always apply rudder because of adverse yaw. Adverse yaw is caused by higher induced drag on the outside wing which is producing more lift.
For a given airplane, a stall will always occur at the same angle ( a.k.a. the critical angle of attack), regardless of airspeed, flight attitude or weight.
The three axes of flight, longitudinal, lateral and vertical axes.
Balancing an aircraft both along the lateral and longitudinal axes.
Understanding torque and where to expect it most. Low airspeeds, high power setting, and high angles of attack. When sitting inside a plane you can picture the propeller spinning clockwise. The clockwise action of a spinning propeller causes a torque reaction, which tends to rotate the airplane counterclockwise about its longitudinal axis. To better understand, when flying a propeller driven plane at high angles of attack the descending blade of the propeller takes a greater so called bite of air than the ascending blade on the other side. This creates P-factor making your plane yaw among the vertical axis. In terms of tricycle landing gear you should apply right rudder during take off because of this asymmetrical thrust.
When turning an airplane you should always apply rudder because of adverse yaw. Adverse yaw is caused by higher induced drag on the outside wing which is producing more lift.
06-18-2007, 08:51 PM
#5
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RE: Teaching Aerodynamics
Yes, the reactive force rotates the aircraft about the longitudinal axis (counterclockwise), but there's more to this picture. The spiraling slipstream causes the airplane to rotate around the vertical axis (yaw) to the left as well (not to mention effects of gyroscopic precession, asymmetric prop loading). That's why most people can't smoothly take off a piper cub. The short coupled nature of the aircraft combined with these forces mandates precise inputs along with anticipation.
Your stall scenario is slightly simplified since stall speeds also need to be considered. In a 60 degree bank the model will stall at a speed roughly 1.5 times faster than normal, and in a 75 degree turn the aircraft will stall at an airspeed twice as fast as normal. [X(] These bank angles seem excessive and they are in the real world, but most modelers turn this sharply on a regular basis.
That's great. You have more aerodynamic knowledge than 90% of all model pilots that I've seen, and I'd bet your flying along with an ability to anticipate the performance of your aircraft shows it. I agree, there is no need to delve deeper than necessary, but most model fliers don't seem to be jumping to this important subject at all. Or worse, they jump in with misleading and incorrect information; however, I really didn't intend for this post to be an aerodynamics primer.
Your stall scenario is slightly simplified since stall speeds also need to be considered. In a 60 degree bank the model will stall at a speed roughly 1.5 times faster than normal, and in a 75 degree turn the aircraft will stall at an airspeed twice as fast as normal. [X(] These bank angles seem excessive and they are in the real world, but most modelers turn this sharply on a regular basis.
That's great. You have more aerodynamic knowledge than 90% of all model pilots that I've seen, and I'd bet your flying along with an ability to anticipate the performance of your aircraft shows it. I agree, there is no need to delve deeper than necessary, but most model fliers don't seem to be jumping to this important subject at all. Or worse, they jump in with misleading and incorrect information; however, I really didn't intend for this post to be an aerodynamics primer.
06-18-2007, 10:09 PM
#6
RE: Teaching Aerodynamics
Someone said the magic word, "airspeed." This is what, in my opinion, makes RC flying more difficult that full scale.
Since I have taught RC for several years and was also an Air Force instructor pilot in T-37s teaching the basic stuff, well, now that I think about it, I taught everything in the Tweet. I gave those T-38 guys a pilot. I got a rookie coming in. The only thing I can thing of that the student learned in T-38s that I didn't teach was 4 ship formation. We only did 2 ship in the 37. But I digress.
We don't know the airspeed for an RC plane. We see the ground speed and mentally guess the wind speed and subtract it from the aparent ground speed to get a safe airspeed. That's hard. Couple this with a wind that may be a third to a half out landing speed, something no full scale pilot would attempt, and you can easily have a sporty landing.
Angle-of-attack! Don't you wish we had an AOA indicator? That made landing so easy you could sleep walk through one. I flew the F-4 and the FB-111, both had AOA readouts and indicators. Landing was a no brainer. You dropped the gear & flaps and held on speed AOA with the stick and used the throttle to put the plane where you wanted it. The 111 came down final at 120-125 knots. This is walking speed. I digressed again-I must be getting over the hill.
I think you need to explain basic aero to a student, how the plane flies, how it turns, airspeed vs. ground speed, stalls ("no, it's not the engine quitting," I have answered many times). If you don't do this, I think you are cheating the student.
Since I have taught RC for several years and was also an Air Force instructor pilot in T-37s teaching the basic stuff, well, now that I think about it, I taught everything in the Tweet. I gave those T-38 guys a pilot. I got a rookie coming in. The only thing I can thing of that the student learned in T-38s that I didn't teach was 4 ship formation. We only did 2 ship in the 37. But I digress.
We don't know the airspeed for an RC plane. We see the ground speed and mentally guess the wind speed and subtract it from the aparent ground speed to get a safe airspeed. That's hard. Couple this with a wind that may be a third to a half out landing speed, something no full scale pilot would attempt, and you can easily have a sporty landing.
Angle-of-attack! Don't you wish we had an AOA indicator? That made landing so easy you could sleep walk through one. I flew the F-4 and the FB-111, both had AOA readouts and indicators. Landing was a no brainer. You dropped the gear & flaps and held on speed AOA with the stick and used the throttle to put the plane where you wanted it. The 111 came down final at 120-125 knots. This is walking speed. I digressed again-I must be getting over the hill.
I think you need to explain basic aero to a student, how the plane flies, how it turns, airspeed vs. ground speed, stalls ("no, it's not the engine quitting," I have answered many times). If you don't do this, I think you are cheating the student.
06-19-2007, 05:33 AM
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RE: Teaching Aerodynamics
Most modellers have no real interest in understanding the principles of flight. In exasperation, after hearing so many myths assumed to be true, I put the following up on the field notice board:
A Dozen Aeronautical Myths
One often overhears comments about the behaviour of model aircraft at the field, and while the remarks are about models, they would also apply to full size machines.
Some of these expressed ideas reflect common myths, so I dug into my memory from 40 plus years ago for the explanations of why they are wrong, and present them for discussion.
Myth 1:
A model will tend to weather cock into wind during flight.
Assuming a steady (non gust) wind, the aircraft can do no such thing, short of being anchored to the ground in some way. A fuller explanation follows below at myth 4.
Myth 2:
A model will stall if it flies too slow.
This one can be correct, but not necessarily so. It is not speed that causes a stall, but separation of the airflow from the wing. This means an aircraft can stall at high speed, e.g. a snap roll, or not stall at zero speed, e.g. the top of a hammer head (sometimes called a stall turn despite no separation burble). Think of stalling as an angle of attack (around 16 degrees), rather than speed.
It is the higher angle of attack in a turn that can cause a stall, leading into a low speed snap roll (By the way, a 60 degree level turn increases your stall speed by 41%)
If you lose power, you are unlikely to stall if you get the nose down below level flight. Warning signs to get the nose lower come from having a lot of up elevator applied. It means you are approaching 16 degrees.
Myth 3:
The more stable an aircraft, the better it is at aerobatics.
Quite the opposite. A stable aircraft wants to keep doing what it is designed to do, normally regain level flight if disturbed from it. You don't need this stability fighting you if you are trying to make the aircraft follow your commands. A good trainer should be stable, but few are these days.
Neutral stability best serves the aerobatic pilot since the machine keeps doing what was last commanded to, with no deviation.
Unstable aircraft are usually beyond human control, as they increase any deviation input given to them. Too far back a C.G. can make a simple up command turn into an unwanted loop for example. Modern fighter jets are unstable in order to attain rapid response, but need a computer to fly them.
Myth 4:
Turns down wind are more dangerous than turns upwind.
In some ways this is true, but not for the usually given reasons. In a turn downwind, a gust will tend to roll you on your back since the high wing usually presents more under wing area to the gust, than the low wing. Secondly, your ground speed downwind makes a prang take place at higher ground speed than turning up wind. That said, the aircraft has no way of keeping track of what the earth is doing below it. This is an important point to remember and this enlarges on the explanation on Myth 1. Assuming a non changing wind, once the machine is airborne, the ground relationships cease. It is in a river of air, and the motion of the river over the earth, doesn't affect it's flight characteristics. One way to get this clear, is to imagine you are in a free floating balloon watching the model. The balloon may be doing 100 kph over ground, but you won't fell a breath of wind. Only when a machine reemerges from the "river" and touches the shore do we need to worry about the earthly relationship.
Thus a 180 degree turn involves reversing ground speed from say + 100 to - 100, (no wind) a total of 200 change within the time of turn. Whether one goes from + 0 to - 200 (100 head wind), or as above, the aircraft undergoes the same accelerations within the time of the turn.
The high downwind ground speed is often to blame for the pilot assuming the airspeed is also high, and slowing to the stall airspeed.
Myth 5:
The model can make a tighter turn if it slows down.
Look at our pylon champ for an answer to that one. It again comes down to angle of attack and it is the stalling angle of your machine that determines it's minimum radius turn. You can turn at the minimum radius at more than one speed, but the faster the speed, the more bank is required which in turn means you increase angle of attack. If one stalls at these speeds, a snap roll usually results. The increased angle of attack required in a level turn will slow you down if you don't add power.
Myth 6:
A high wing gives pendulum stability.
This is misleading, because a pendulum is fixed to a support, whereas the aircraft is not fixed in any way. What happens is that as the aircraft banks, It side slips towards the low wing, and it is the retarding effect of this relative airflow on the top wing that rights the plane (see myth 7).
Myth 7:
Dihedral works because the horizontal lift component of the lower wing is greater than the other.
Partly. Imagine you can slide the model along a wire through it's C.G., and it's not hard to see that while the above effect will slow a rotation, it won't stop it, and certainly won't bring the model upright. Once again, it is the side slip that increases the lift on the lower wing and levels it.
Myth 8:
"Dual servo rate should be low for strong winds and high for light winds". (I assume the thinking is that strong winds give more airflow and less control deflection is thus required.)
If one realizes that an airplanes "wind" is due to it's motion, and not the wind speed (remember it is in a river of air), then different rates of throw are not involved with wind speed although they are with airplane speed through the air (relative wind).
Myth 9:
Big vertical stabilizer (fin) means directional stability.
If we remember that an aircraft will side slip towards the lower wing in a bank, the relative air stream creates side forces either side of the C.G. These can either yaw the model into the slip or out of it. Too large fin acts like a weather cock during the slip, and tightens the turn. The end result is the nose dropping and a spiral dive. The perfect size fin will balance the area ahead of the C.G., so that the yaw is appropriate for the side slip involved. Too small a fin will yaw a machine out of the turn.
It is the rudder effect that turns (yaws) the airplane (else it would crab in a straight line but wouldn't turn), despite the fact you may only use aileron input. The bank causes the machine to side slip, which brings in the rudder yaw effect.
Myth 10:
A model will glide farther if it is light.
Assuming no wind, the angle of glide relates to the lift and drag of the machine. Without drag you would glide horizontal indefinitely and without lift, you have a vertical descent (don't we know). The actual glide angle is thus a ratio of these two (Lift to Drag), and not related to weight. Wind has an effect on the angle over the ground, but not through the "river of" air. The heavy model will reach the ground sooner, since it glides at a higher speed, but both will glide the same distance in still air.
The minimum sink speed of a model is flown slower, near the maximum angle of attack (not the faster best distance speed), since one is more concerned with lift than speed. Here a light model will glide a longer period than a heavy one.
Myth 11:
A model will gain the most height in a given time, if we climb it at the best angle of climb.
There is a difference between angle and rate of climb. The first compares altitude to forward distance and is affected by wind, the second compares altitude to time and is not influenced by wind. Best rate of climb is done faster than best angle of climb.
Myth 12:
A headwind will slow a model more than an airliner.
If we go back to out "river of air" concept, one will find it easier to grasp the picture that everything in the "river" is carried along at the same speed. Hence a ten knot headwind will take 10 knots off the model and airliner speed, equally.
Now let the arguments begin. Arnold
A Dozen Aeronautical Myths
One often overhears comments about the behaviour of model aircraft at the field, and while the remarks are about models, they would also apply to full size machines.
Some of these expressed ideas reflect common myths, so I dug into my memory from 40 plus years ago for the explanations of why they are wrong, and present them for discussion.
Myth 1:
A model will tend to weather cock into wind during flight.
Assuming a steady (non gust) wind, the aircraft can do no such thing, short of being anchored to the ground in some way. A fuller explanation follows below at myth 4.
Myth 2:
A model will stall if it flies too slow.
This one can be correct, but not necessarily so. It is not speed that causes a stall, but separation of the airflow from the wing. This means an aircraft can stall at high speed, e.g. a snap roll, or not stall at zero speed, e.g. the top of a hammer head (sometimes called a stall turn despite no separation burble). Think of stalling as an angle of attack (around 16 degrees), rather than speed.
It is the higher angle of attack in a turn that can cause a stall, leading into a low speed snap roll (By the way, a 60 degree level turn increases your stall speed by 41%)
If you lose power, you are unlikely to stall if you get the nose down below level flight. Warning signs to get the nose lower come from having a lot of up elevator applied. It means you are approaching 16 degrees.
Myth 3:
The more stable an aircraft, the better it is at aerobatics.
Quite the opposite. A stable aircraft wants to keep doing what it is designed to do, normally regain level flight if disturbed from it. You don't need this stability fighting you if you are trying to make the aircraft follow your commands. A good trainer should be stable, but few are these days.
Neutral stability best serves the aerobatic pilot since the machine keeps doing what was last commanded to, with no deviation.
Unstable aircraft are usually beyond human control, as they increase any deviation input given to them. Too far back a C.G. can make a simple up command turn into an unwanted loop for example. Modern fighter jets are unstable in order to attain rapid response, but need a computer to fly them.
Myth 4:
Turns down wind are more dangerous than turns upwind.
In some ways this is true, but not for the usually given reasons. In a turn downwind, a gust will tend to roll you on your back since the high wing usually presents more under wing area to the gust, than the low wing. Secondly, your ground speed downwind makes a prang take place at higher ground speed than turning up wind. That said, the aircraft has no way of keeping track of what the earth is doing below it. This is an important point to remember and this enlarges on the explanation on Myth 1. Assuming a non changing wind, once the machine is airborne, the ground relationships cease. It is in a river of air, and the motion of the river over the earth, doesn't affect it's flight characteristics. One way to get this clear, is to imagine you are in a free floating balloon watching the model. The balloon may be doing 100 kph over ground, but you won't fell a breath of wind. Only when a machine reemerges from the "river" and touches the shore do we need to worry about the earthly relationship.
Thus a 180 degree turn involves reversing ground speed from say + 100 to - 100, (no wind) a total of 200 change within the time of turn. Whether one goes from + 0 to - 200 (100 head wind), or as above, the aircraft undergoes the same accelerations within the time of the turn.
The high downwind ground speed is often to blame for the pilot assuming the airspeed is also high, and slowing to the stall airspeed.
Myth 5:
The model can make a tighter turn if it slows down.
Look at our pylon champ for an answer to that one. It again comes down to angle of attack and it is the stalling angle of your machine that determines it's minimum radius turn. You can turn at the minimum radius at more than one speed, but the faster the speed, the more bank is required which in turn means you increase angle of attack. If one stalls at these speeds, a snap roll usually results. The increased angle of attack required in a level turn will slow you down if you don't add power.
Myth 6:
A high wing gives pendulum stability.
This is misleading, because a pendulum is fixed to a support, whereas the aircraft is not fixed in any way. What happens is that as the aircraft banks, It side slips towards the low wing, and it is the retarding effect of this relative airflow on the top wing that rights the plane (see myth 7).
Myth 7:
Dihedral works because the horizontal lift component of the lower wing is greater than the other.
Partly. Imagine you can slide the model along a wire through it's C.G., and it's not hard to see that while the above effect will slow a rotation, it won't stop it, and certainly won't bring the model upright. Once again, it is the side slip that increases the lift on the lower wing and levels it.
Myth 8:
"Dual servo rate should be low for strong winds and high for light winds". (I assume the thinking is that strong winds give more airflow and less control deflection is thus required.)
If one realizes that an airplanes "wind" is due to it's motion, and not the wind speed (remember it is in a river of air), then different rates of throw are not involved with wind speed although they are with airplane speed through the air (relative wind).
Myth 9:
Big vertical stabilizer (fin) means directional stability.
If we remember that an aircraft will side slip towards the lower wing in a bank, the relative air stream creates side forces either side of the C.G. These can either yaw the model into the slip or out of it. Too large fin acts like a weather cock during the slip, and tightens the turn. The end result is the nose dropping and a spiral dive. The perfect size fin will balance the area ahead of the C.G., so that the yaw is appropriate for the side slip involved. Too small a fin will yaw a machine out of the turn.
It is the rudder effect that turns (yaws) the airplane (else it would crab in a straight line but wouldn't turn), despite the fact you may only use aileron input. The bank causes the machine to side slip, which brings in the rudder yaw effect.
Myth 10:
A model will glide farther if it is light.
Assuming no wind, the angle of glide relates to the lift and drag of the machine. Without drag you would glide horizontal indefinitely and without lift, you have a vertical descent (don't we know). The actual glide angle is thus a ratio of these two (Lift to Drag), and not related to weight. Wind has an effect on the angle over the ground, but not through the "river of" air. The heavy model will reach the ground sooner, since it glides at a higher speed, but both will glide the same distance in still air.
The minimum sink speed of a model is flown slower, near the maximum angle of attack (not the faster best distance speed), since one is more concerned with lift than speed. Here a light model will glide a longer period than a heavy one.
Myth 11:
A model will gain the most height in a given time, if we climb it at the best angle of climb.
There is a difference between angle and rate of climb. The first compares altitude to forward distance and is affected by wind, the second compares altitude to time and is not influenced by wind. Best rate of climb is done faster than best angle of climb.
Myth 12:
A headwind will slow a model more than an airliner.
If we go back to out "river of air" concept, one will find it easier to grasp the picture that everything in the "river" is carried along at the same speed. Hence a ten knot headwind will take 10 knots off the model and airliner speed, equally.
Now let the arguments begin. Arnold
06-19-2007, 07:06 AM
#8
Senior Member
RE: Teaching Aerodynamics
Not only are almost none of us capable of reading our models airspeed worth spit, but we most certainly can't come close to judging the difference between the couple of mph difference on a landing approach that gives a slow landing or gives a stall.
And stalls are nothing more than the aiplane's AOA pushing the wing into too much AOA. And not a one of us can see the difference between the AOA just before stall and just safely under the AOA of stall.
So forget about teaching your newbies too much detailed aerodynamics, and emphasize that they don't try to land at idle setting and that they don't try to keep the airplane in the air with the elevator.
Newbies almost always try to slow to a stop on landing approaches. If it slows some, they want to slow it more. If it's still flying after slowing more, they try to slow even more. Teach 'em all the aerodynamics they can stand, but don't let 'em out of class until they learn to land with some speed on. Throttle to idle if they must, but as soon as they got that position for reference, put that stick back up a couple of clicks.
Newbies almost always try to "elevator" the airplane into the landing. They also try to keep a deadstick in the air by pulling UP. A bunch of people think they can hold an airplane up with the UP stick. Teach 'em whatever it is about aerodynamics you want, but make some time to get across a simple idea. If they can't see the top of their model's nose on landing, they've got the airplane at too high an AOA.
And newbies and a lot of somewhat experienced guys think the safe way to take off is firewall and pray. Get it over with as quickly as possible and maybe they won't ball the sucker up like they did the last one. Teach 'em whatever aero they're still awake to learn, but make sure they understand that the propeller works far sooner than the rest of the airplane. And the propeller will pull a marginally flying airframe wherever the prop wants to go and the airframe hasn't built up enough aero strength to do spit. And the airplane is going to arc up and over.
And stalls are nothing more than the aiplane's AOA pushing the wing into too much AOA. And not a one of us can see the difference between the AOA just before stall and just safely under the AOA of stall.
So forget about teaching your newbies too much detailed aerodynamics, and emphasize that they don't try to land at idle setting and that they don't try to keep the airplane in the air with the elevator.
Newbies almost always try to slow to a stop on landing approaches. If it slows some, they want to slow it more. If it's still flying after slowing more, they try to slow even more. Teach 'em all the aerodynamics they can stand, but don't let 'em out of class until they learn to land with some speed on. Throttle to idle if they must, but as soon as they got that position for reference, put that stick back up a couple of clicks.
Newbies almost always try to "elevator" the airplane into the landing. They also try to keep a deadstick in the air by pulling UP. A bunch of people think they can hold an airplane up with the UP stick. Teach 'em whatever it is about aerodynamics you want, but make some time to get across a simple idea. If they can't see the top of their model's nose on landing, they've got the airplane at too high an AOA.
And newbies and a lot of somewhat experienced guys think the safe way to take off is firewall and pray. Get it over with as quickly as possible and maybe they won't ball the sucker up like they did the last one. Teach 'em whatever aero they're still awake to learn, but make sure they understand that the propeller works far sooner than the rest of the airplane. And the propeller will pull a marginally flying airframe wherever the prop wants to go and the airframe hasn't built up enough aero strength to do spit. And the airplane is going to arc up and over.
06-19-2007, 09:11 AM
#9
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RE: Teaching Aerodynamics
Basic aerodynamics serves the newbie as well as anyone else regardless of whether you can judge airspeed of a model.
It gives the reason for responses rather than the more arbitrary "because I said so or that's the way it is" type of instruction.
Also if you can't learn to land throttle off it won't be too long before a dead stick forces one into that position ready or not. Trainers can leave a person soloing with some bad habits but learning to land power off as well as power on is not one of them.
I fly and instruct in everything from basic training to heavy Iron warbirds and giant scale so I am not saying this just to further an arguement.
Going back to my days as a full scale instructor I believe that one should never talk down to students. Give them a segement of information and then show them how it is applied followed by making sure the student understands what was presented.
It gives the reason for responses rather than the more arbitrary "because I said so or that's the way it is" type of instruction.
Also if you can't learn to land throttle off it won't be too long before a dead stick forces one into that position ready or not. Trainers can leave a person soloing with some bad habits but learning to land power off as well as power on is not one of them.
I fly and instruct in everything from basic training to heavy Iron warbirds and giant scale so I am not saying this just to further an arguement.
Going back to my days as a full scale instructor I believe that one should never talk down to students. Give them a segement of information and then show them how it is applied followed by making sure the student understands what was presented.
06-19-2007, 12:34 PM
#10
RE: Teaching Aerodynamics
This is one of those`It depends' type of questions. If you are teaching aerodynamics, then one of the usual texts, even Kermode's `Mechanics of Flight' will have enough math and fact for your students. If you are teaching someone to fly, then you can do worse than to go to your local (full size) airfield and get get a copy of their training curriculum and adapt that (short bit of ground theory, then a practical flight to demonstrate the theory) for you training programme. This works best if you have the `Buddy box' set up, the same thing as a dual cockpit, so to speak.
Evan, WB#12.
Evan, WB#12.
06-19-2007, 06:37 PM
#11
Senior Member
RE: Teaching Aerodynamics
Since Nathan's stated purpose for teaching aeronautics to his class was to help them avoid crashing their models, it's reasonable to also throw in a few helpful hints covering 90% of the reasons newbies crash.
05-07-2009, 10:08 AM
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RE: Teaching Aerodynamics
True we don't have an airspeed indicator, but we do have some clues. If the model is trimmed for level flight, a reduction in power will lower the nose to give a fast glide. I tell my students to keep the nose just a little below the horizon with the elevator, and the machine will usually settle on a safe airspeed. The second clue, other other than the visual, is the amount of elevator being used. If one finds he is holding a lot of 'up', it is time to lower the nose for more airspeed. The sink rate is controlled by power, not elevator. Elevator controls the speed. Having said that, and having full size experience, I realize the two aspects are related and integrated.
05-07-2009, 10:12 AM
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RE: Teaching Aerodynamics
ORIGINAL: da Rock
And the propeller will pull a marginally flying airframe wherever the prop wants to go and the airframe hasn't built up enough aero strength to do spit. And the airplane is going to arc up and over.
And the propeller will pull a marginally flying airframe wherever the prop wants to go and the airframe hasn't built up enough aero strength to do spit. And the airplane is going to arc up and over.
http://www.youtube.com/watch?v=o4JSpF7Gzdc
05-07-2009, 01:23 PM
#14
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RE: Teaching Aerodynamics
OK, that playboy took off straight up, why? Is it an example of what happens when a newbie closes his eyes, firewalls his Kadet Senior with the .40 on it, and prays............????
Yeah, the playboy took off straight up, but we're not talking about special built, obscure classes of models and how they perform. The topic of this thread is the value of teaching aerodynamics to people just starting off in the hobby.
That video has a good probability of doing more damage than good for most of those beginners UNLESS a concerned teacher takes the time and effort to explain why it's NOT pertinent to their immediate problems and goals.
Bottom line on that playboy is that it's power to weight allows the airframe to be flying almost instantly thanks to the awesome acceleration capability. And of course, the specialized launch. Seldom do we launch our trainers from restraint at wide open throttle, and their gear is seldom designed to point the nose that far up.
Yeah, the playboy took off straight up, but we're not talking about special built, obscure classes of models and how they perform. The topic of this thread is the value of teaching aerodynamics to people just starting off in the hobby.
That video has a good probability of doing more damage than good for most of those beginners UNLESS a concerned teacher takes the time and effort to explain why it's NOT pertinent to their immediate problems and goals.
Bottom line on that playboy is that it's power to weight allows the airframe to be flying almost instantly thanks to the awesome acceleration capability. And of course, the specialized launch. Seldom do we launch our trainers from restraint at wide open throttle, and their gear is seldom designed to point the nose that far up.
05-07-2009, 03:59 PM
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RE: Teaching Aerodynamics
The multiplex M-link, 2.4 system, has the provision for up to 16 "downlinks", so it should soon be possible to have reliable A of A information on your model.
05-07-2009, 06:57 PM
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RE: Teaching Aerodynamics
I realize the Playboy launch is not beginner related, and I do see your point. The odd thing though, is that I see the opposite to 'full power' happening. Students timidly adding power while using up lots of runway that they try to steer straight on. The aircraft sits a long time in the transition zone too slow to fly, and too fast to steer easily, getting father and father away. I like to see the power come on smoothly, to full power once the early roll confirms the aircraft is under control. A tail dragger benefits from the airflow over the control surfaces.
Here is an example of the power coming on quickly, and I find it a lot easier than the alternative. I'm not necessarily disagreeing with you, because every situation is different, and every student is a variable. I am only suggesting that sometimes there are cases where it is good to get the power on and the aircraft into the air quickly.
http://www.youtube.com/watch?v=BfUdls5K_7k
Here is an example of the power coming on quickly, and I find it a lot easier than the alternative. I'm not necessarily disagreeing with you, because every situation is different, and every student is a variable. I am only suggesting that sometimes there are cases where it is good to get the power on and the aircraft into the air quickly.
http://www.youtube.com/watch?v=BfUdls5K_7k
05-07-2009, 07:01 PM
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RE: Teaching Aerodynamics
ORIGINAL: bogbeagle
The multiplex M-link, 2.4 system, has the provision for up to 16 "downlinks", so it should soon be possible to have reliable A of A information on your model.
The multiplex M-link, 2.4 system, has the provision for up to 16 "downlinks", so it should soon be possible to have reliable A of A information on your model.
05-07-2009, 08:33 PM
#18
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RE: Teaching Aerodynamics
ORIGINAL: aeomaster32
I realize the Playboy launch is not beginner related, and I do see your point. The odd thing though, is that I see the opposite to 'full power' happening. Students timidly adding power while using up lots of runway that they try to steer straight on. The aircraft sits a long time in the transition zone too slow to fly, and too fast to steer easily, getting father and father away. I like to see the power come on smoothly, to full power once the early roll confirms the aircraft is under control. A tail dragger benefits from the airflow over the control surfaces.
Here is an example of the power coming on quickly, and I find it a lot easier than the alternative. I'm not necessarily disagreeing with you, because every situation is different, and every student is a variable. I am only suggesting that sometimes there are cases where it is good to get the power on and the aircraft into the air quickly.
http://www.youtube.com/watch?v=BfUdls5K_7k
I realize the Playboy launch is not beginner related, and I do see your point. The odd thing though, is that I see the opposite to 'full power' happening. Students timidly adding power while using up lots of runway that they try to steer straight on. The aircraft sits a long time in the transition zone too slow to fly, and too fast to steer easily, getting father and father away. I like to see the power come on smoothly, to full power once the early roll confirms the aircraft is under control. A tail dragger benefits from the airflow over the control surfaces.
Here is an example of the power coming on quickly, and I find it a lot easier than the alternative. I'm not necessarily disagreeing with you, because every situation is different, and every student is a variable. I am only suggesting that sometimes there are cases where it is good to get the power on and the aircraft into the air quickly.
http://www.youtube.com/watch?v=BfUdls5K_7k
Now, we're cookin..................
We've both noticed that takeoffs require the right amount of power fed in at an appropriate rate. Teaching them the appropriate rate has a lot to do with what trainer they have. But all of them are trainers.
It's not easy getting across the controlled throttle deal. There really isn't a one liner, sound bite, single sentence description that work for all our models. So this threads message about teaching aerodynamics might pay the most dividends for this one aspect of model flying, the takeoffs. For example, tail draggers usually take different throttling to get off without the sudden snap they are so good at when their pilot closes his eyes and slams the throttle. For example, knowing that the wing on most taildraggers starts it's roll with it's AOA already past stall can go a long way...... (is that a pun?)........ toward teaching our beginners things that'll help 'em beyond their graduation.
We're both after the same thing maybe..........
05-08-2009, 02:14 AM
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RE: Teaching Aerodynamics
WRT airspeed indication...I don't know how the readout will be presented. I would imagine that it would be aural, but I suppose that a display could be incorporated in a pair of glasses. I mean, you don't need to know the actual speed or A of A, you just need to know when the A of A is approaching its optimum...a bit like the display in Moorman's F-4.
Of course, you the operator, will still need to have programmed in the "set points" for your system.
I understand that the M-link already has the facility to provide a readout/warning of the RX' battery' condition. Airspeed, alt and fuel conditions would be useful information for most flyers. There's a deaf chap, at my flying site, who would benefit from an indication of his engine's RPM.
Of course, you the operator, will still need to have programmed in the "set points" for your system.
I understand that the M-link already has the facility to provide a readout/warning of the RX' battery' condition. Airspeed, alt and fuel conditions would be useful information for most flyers. There's a deaf chap, at my flying site, who would benefit from an indication of his engine's RPM.
