Let’s discuss facts about stall-spin
07-23-2009, 02:00 AM
#26
RE: Let’s discuss facts about stall-spin
All AMA model builders should serve at least a 2 year apprenticeship designing, building and competing in AMA Fast Combat.
That will set some sort of a foundation.
Life is too short to put up with models prone to stall spins, I don't care which way the wind is blowing or what your "critical AoA" is..
The truly great models are the ones that you can fly about any way you please and they come in all shapes and sizes.
They all have light wing loadings.
That will set some sort of a foundation.
Life is too short to put up with models prone to stall spins, I don't care which way the wind is blowing or what your "critical AoA" is..
The truly great models are the ones that you can fly about any way you please and they come in all shapes and sizes.
They all have light wing loadings.
07-23-2009, 08:18 PM
#27
Thread Starter
RE: Let’s discuss facts about stall-spin
ORIGINAL: dick Hanson
I never thot a GWS Slow Stick was beyond anybody- but if it is not a known type model to some-I guess it is beyond the realm-
For those who spent their modelling years building flying heavy models - I really suggest (with enthusiasm) that you blow a few bucks on one of these very basic trainers and flatten out the wing and add ailerons
The resultant model is great for showing others how to fly - it is simple to repair and all the laws of flying can be demonstrated the good part is that the accidents are far fewer because the mistakes simply do not result in sudden ''departures'' so common on with many older types which were really never good trainers.
The larger models I added here -are all fully aerobatic and a couple are very faithful to scale
Scale models do not need to be heavy
the usual problem is that the builders /designers of the models simply have never learned good building skills
these skills are of more value (unfortunately) than an extensive background in aeronautics and aerodynamics.
One of my earlier postulates was that
''if the model is too heavy , none of the rules of flying apply''.
I never thot a GWS Slow Stick was beyond anybody- but if it is not a known type model to some-I guess it is beyond the realm-
For those who spent their modelling years building flying heavy models - I really suggest (with enthusiasm) that you blow a few bucks on one of these very basic trainers and flatten out the wing and add ailerons
The resultant model is great for showing others how to fly - it is simple to repair and all the laws of flying can be demonstrated the good part is that the accidents are far fewer because the mistakes simply do not result in sudden ''departures'' so common on with many older types which were really never good trainers.
The larger models I added here -are all fully aerobatic and a couple are very faithful to scale
Scale models do not need to be heavy
the usual problem is that the builders /designers of the models simply have never learned good building skills
these skills are of more value (unfortunately) than an extensive background in aeronautics and aerodynamics.
One of my earlier postulates was that
''if the model is too heavy , none of the rules of flying apply''.
I believe, however, that the interaction between air and wings remains the same; hence, the same physical laws apply for light and for heavy models.
The reaction and performance of these models look different to our eyes, but they all still need some kind of control on pitch, roll and yaw, if they are going to fly successfully and stably.
The lightest model of regular configuration still needs balance, wings, rudder, stab and thrust (energy) to fly.
Please gentlemen, allow me to deviate from the stall-spin main subject by pointing to some facts and videos that clearly show what can be achieved by light and careful construction.
As I stated earlier, light and low drag machines need less energy and material to fly; hence, any manufacturer and operator that wants to make a profit out of the full scale flight business, is building and operating as light and sleek machines as possible.
Available materials, production costs and practical uses are the limit to that goal.
Much is also possible by reducing weight (wing loading) and friction (drag) of model airplanes, among these I can mention:
• Lower level flight speed.
• Lower AOA (and hence, lower total drag) for level flight.
• Lower landing speed.
• Lower inertia (better acceleration and braking).
• Less destructive impacts and crashes.
• Bigger available AOA range between level flight (angle that depends on wing loading) and stall (angle that depends on airfoil), which makes snaps, spins and stalls harder to achieve in maneuvers.
• Smaller G forces developed in turns and loops (which is good for models with big stability margin, or big distance between CG and lift force).
• Less energy use (same motor or engine can achieve more, i.e. higher power to weight ratio).
• Lower stall speed.
• Lower centrifugal force in maneuvers, requiring less elevator power.
• High Gs impose less stress on structure.
In order to better appreciate these possibilities of low weight, I would like to use as example an extreme light type of model: Free flight indoors endurance FAI F1D.
Copied from http://en.wikipedia.org/wiki/Free_flight_(model_aircraft):
“The FAI is the international organizing body for all air sports including aeromodeling. The FAI sanctions World and European Championships for the ultimate indoor duration class designated F1D. F1D models must have a minimum weight of 1.2 grams and a maximum wing span of 55 cm. These models are constructed from very light balsawood sheet and strip, boron filament, carbon fiber, and a transparent covering of plastic film less than 0.5 microns thick. The models are powered by 0.6 grams of rubber in a single loop about 9.0 inches long that can be wound to take around 1500 turns. The average propeller RPM during a flight is less than 50 and these models fly at less than walking pace. F1D models require a large space, such as a sports hall, aircraft or dirigible hangar….. Single flight times approach forty minutes.”
Some recorded times in Europe’s contests:
Duration (ceiling less than 8 m) : 31 min 13 sec
Duration (ceiling 8m - 15m) : 33 min 42 sec
Duration (ceiling 15m - 30m) : 36 min 23 sec
Duration (ceiling over 30m) : 41mn 42s
And all those flying times achieved with just the energy contained in a twisted rubber band!!!
Some example-videos:
1) In the last two minutes of this video, it can be seen that the model hits a balloon in mid flight, wonders “what the heck!?!?!”, stalls and spins just the little amount it needs to recover normal flying speed and stability:
http://www.youtube.com/watch?v=MAmVFfnEdBY
2) In this video, the energy given to the model by an arm throw makes it glide for a whole minute!!:
http://www.youtube.com/watch?v=v2U7T...eature=related
3) Yes, light models can spin and do crazy things with enough power to weight ratio:
http://www.youtube.com/watch?v=RqRLnjydvag
07-24-2009, 01:10 AM
#29
My Feedback: (1)
RE: Let’s discuss facts about stall-spin
“The FAI is the international organizing body for all air sports including aeromodeling. The FAI sanctions World and European Championships for the ultimate indoor duration class designated F1D. F1D models must have a minimum weight of 1.2 grams and a maximum wing span of 55 cm. These models are constructed from very light balsawood sheet and strip, boron filament, carbon fiber, and a transparent covering of plastic film less than 0.5 microns thick. The models are powered by 0.6 grams of rubber in a single loop about 9.0 inches long that can be wound to take around 1500 turns. The average propeller RPM during a flight is less than 50 and these models fly at less than walking pace. F1D models require a large space, such as a sports hall, aircraft or dirigible hangar….. Single flight times approach forty minutes.”
07-24-2009, 01:19 AM
#31
My Feedback: (1)
RE: Let’s discuss facts about stall-spin
Smaller G forces developed in turns and loops
In full size airplanes there is a speed known as "manouvering speed" which the airframe must be kept under to avoid structural failure in extreme turbulance. That speed must be lower for a lighter loaded airplane than a heavier loaded one of the same make and model.
07-24-2009, 02:35 AM
#32
RE: Let’s discuss facts about stall-spin
Highplains, I'm hurt, it's no myth at all that a light version of the same airplane can fly faster than a heavy version. If you need less AOA to maintain flight due to less weight, then the drag must also be less, and given the same thrust, then a lighter model can fly faster as it has a bit of thrust 'left over' as it were. If any turning is required, then the effect is magnified. No myth at all. In fact, the effect has the airlines installing driers in the airframes to dry out the cabin insulation, the 200 odd kg difference saves, over time, much fuel as the airplane can cruise at either slightly less thrust (fuel) or a slightly higher airspeed (Less flight time, less fuel). So even the big guys don't think it's a myth.
Evan.
Evan.
07-24-2009, 09:48 AM
#33
RE: Let’s discuss facts about stall-spin
ORIGINAL: pimmnz
Highplains, I'm hurt, it's no myth at all that a light version of the same airplane can fly faster than a heavy version. If you need less AOA to maintain flight due to less weight, then the drag must also be less, and given the same thrust, then a lighter model can fly faster as it has a bit of thrust 'left over' as it were. If any turning is required, then the effect is magnified. No myth at all. In fact, the effect has the airlines installing driers in the airframes to dry out the cabin insulation, the 200 odd kg difference saves, over time, much fuel as the airplane can cruise at either slightly less thrust (fuel) or a slightly higher airspeed (Less flight time, less fuel). So even the big guys don't think it's a myth.
Evan.
Highplains, I'm hurt, it's no myth at all that a light version of the same airplane can fly faster than a heavy version. If you need less AOA to maintain flight due to less weight, then the drag must also be less, and given the same thrust, then a lighter model can fly faster as it has a bit of thrust 'left over' as it were. If any turning is required, then the effect is magnified. No myth at all. In fact, the effect has the airlines installing driers in the airframes to dry out the cabin insulation, the 200 odd kg difference saves, over time, much fuel as the airplane can cruise at either slightly less thrust (fuel) or a slightly higher airspeed (Less flight time, less fuel). So even the big guys don't think it's a myth.
Evan.
It is simple logic.
The only reason there is an engine on a aircraft is that it is too heavy to move or fly without power to get it aloft.
Models which ar too heavy ae often explained away as flying mor scale like
This old saw simply is an excuse for
" I could not built it lighter".
07-24-2009, 12:34 PM
#34
RE: Let’s discuss facts about stall-spin
Is it just me, or do these conversations (arguments actually) parallel conversations of politics and religious debates? Usually - not alaways- but usually both sides don't have a clue.
I hate getting sucked into these things.
And it happens sooo easily because I have an educated opinion (through experience) people disagree with. I don't think most of these conversations would end up like this if people talk face to face.
Are we really better off with this technology?
(Not off topic. This is the direction the topic took.)
I hate getting sucked into these things.
And it happens sooo easily because I have an educated opinion (through experience) people disagree with. I don't think most of these conversations would end up like this if people talk face to face.
Are we really better off with this technology?
(Not off topic. This is the direction the topic took.)
07-24-2009, 01:03 PM
#35
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RE: Let’s discuss facts about stall-spin
Dude, discussions about stalls have nothing to do with politics. It's a proven fact that Dick Cheney is the source of all stall behavior. Case closed.
07-24-2009, 01:26 PM
#36
Thread Starter
RE: Let’s discuss facts about stall-spin
ORIGINAL: HighPlains
G force is due to the size and speed. Has nothing to do with the weight of the plane.
In full size airplanes there is a speed known as ''manouvering speed'' which the airframe must be kept under to avoid structural failure in extreme turbulance. That speed must be lower for a lighter loaded airplane than a heavier loaded one of the same make and model.
Smaller G forces developed in turns and loops
In full size airplanes there is a speed known as ''manouvering speed'' which the airframe must be kept under to avoid structural failure in extreme turbulance. That speed must be lower for a lighter loaded airplane than a heavier loaded one of the same make and model.
I tried to say that the forces produced by centrifugal effect in sharp turns are smaller for lighter structural elements.
Let's say, a longeron that weights 0.1 ounces, will weight 0.6 ounces during a turn that generates an acceleration of 6 g; those 0.6 ounces will be applied to the glued joints.
A heavier longeron of similar dimensions, that weights 0.3 ounces, during the same turn, will weight 1.8 ounces, imposing a force three times bigger to the same joints.
Check this values I have just founded:
07-24-2009, 07:25 PM
#37
My Feedback: (1)
RE: Let’s discuss facts about stall-spin
it's no myth at all that a light version of the same airplane can fly faster than a heavy version.
It seems reasonable to suppose that the lighter an airplane is the faster it will fly. This is not strictly true. For every attitude of an airplane a definite amount of power is required to drive it through the air at any given speed. Conversely, with a given amount of power the maximum speed can be obtained only when the airplane is in the attitude which permits it to slip through the air easiest. The attitude at which an airplane flies is a function of it's weight The greater the weight the greater the angle of attack required to maintain level flight at any given speed. For a Clark Y wing section for example, zero lift occurs at an angle of attack of about minus six degrees. Minimum drag occurs at minus three degrees, and at this point the wing is exerting considerable lift. We would expect then that an airplane using this wing section would be fastest when loaded so it flew level at an angle of attack of minus three degrees. If lighter it would fly at a smaller angle of attack and if heavier at a larger angle. In either case it would be slower....
07-24-2009, 09:56 PM
#38
RE: Let’s discuss facts about stall-spin
ORIGINAL: HighPlains
I'm not an aeronautical engineer, I studied electrical engineering, but I will quote an article by a man that had both a Masters degree and and Ph.D in aeronautical engineering from MIT.
it's no myth at all that a light version of the same airplane can fly faster than a heavy version.
It seems reasonable to suppose that the lighter an airplane is the faster it will fly. This is not strictly true. For every attitude of an airplane a definite amount of power is required to drive it through the air at any given speed. Conversely, with a given amount of power the maximum speed can be obtained only when the airplane is in the attitude which permits it to slip through the air easiest. The attitude at which an airplane flies is a function of it's weight The greater the weight the greater the angle of attack required to maintain level flight at any given speed. For a Clark Y wing section for example, zero lift occurs at an angle of attack of about minus six degrees. Minimum drag occurs at minus three degrees, and at this point the wing is exerting considerable lift. We would expect then that an airplane using this wing section would be fastest when loaded so it flew level at an angle of attack of minus three degrees. If lighter it would fly at a smaller angle of attack and if heavier at a larger angle. In either case it would be slower....
allof that mumbo jumbo of correct AOA is meaningless because:
A craft which weighs less requires less energy/force/ to stay aloft or move forward.
whatever
IF the power is a constant and the weight diminishes - either the craft will climb or go forward more easily
Ya can't fool Mother Nature
Or me
Idon't care if the wing is a Clark Y or a Clark Kent.
07-25-2009, 03:15 AM
#39
RE: Let’s discuss facts about stall-spin
It would be easy enough to prove or disprove the light VS heavy speed myth. Pick a plane that is both pretty light and over powered, like a control line racer [with a hollow fuselage to store the lead and retain the same CG]. Fly the plane at eye level only. The results would be pretty interesting after about 10-20 runs are made with incremental amounts of lead added. Doing the experiment with RC craft would be too variable with keeping gravity assistance out of the equation. The power system would need to be electric for the most consistency.
07-25-2009, 09:40 AM
#41
RE: Let’s discuss facts about stall-spin
The man from MIT is still just speaking hypothetically. What cases in the full scale are there of powered planes that need ballast to get into the lowest drag sweet spot for best speed [think fuel economy over the long haul].
07-25-2009, 04:35 PM
#42
My Feedback: (1)
RE: Let’s discuss facts about stall-spin
The guy with the Ph.D. from MIT knew a bit about speed. He won the Tompson Trophy in 1932.
An interesting read on fuel efficiency is:
http://www.eaa1000.av.org/technicl/p...s/perfspds.htm
Especially Carson Speed.
An interesting read on fuel efficiency is:
http://www.eaa1000.av.org/technicl/p...s/perfspds.htm
Especially Carson Speed.
07-25-2009, 10:10 PM
#43
RE: Let’s discuss facts about stall-spin
HP, I'll need to read that a few times to fully absorb it.
So he was a leading aerodynamicist back when the scientific community agreed that:
1. curveballs don't really curve, it's just an illusion.
2. man will never be able to break the grip of Earth's gravity with any kind of projectile or vehicle.
3. no dragster will ever be able to break 150 mph in the quarter mile, even on 99% nitro fed through a blown V-8.
I've got some fast combat planes RTF at about 18 ozs. All I should have to do is outfit the top side with a big bubble canopy, cut up some lead sheet and bring a stopwatch to the field. I think underpropping with a 9x4 will give ample thrust to accomodate an extra pound of lead or 2.
So he was a leading aerodynamicist back when the scientific community agreed that:
1. curveballs don't really curve, it's just an illusion.
2. man will never be able to break the grip of Earth's gravity with any kind of projectile or vehicle.
3. no dragster will ever be able to break 150 mph in the quarter mile, even on 99% nitro fed through a blown V-8.
I've got some fast combat planes RTF at about 18 ozs. All I should have to do is outfit the top side with a big bubble canopy, cut up some lead sheet and bring a stopwatch to the field. I think underpropping with a 9x4 will give ample thrust to accomodate an extra pound of lead or 2.
07-25-2009, 11:01 PM
#44
My Feedback: (1)
RE: Let’s discuss facts about stall-spin
man will never be able to break the grip of Earth's gravity with any kind of projectile or vehicle.
What is it about a lift drag polar you don't comprehend? For an airplane to go it's fastest, it needs to operate with the wing's angle of attack where the drag is the lowest. The implicit assumption is of course that this only works with a wing that has camber, but most full size aircraft do have that type of airfoil.
07-26-2009, 07:06 AM
#45
RE: Let’s discuss facts about stall-spin
ORIGINAL: HighPlains
To date, man has never left the grip of Earth's gravity.
What is it about a lift drag polar you don't comprehend? For an airplane to go it's fastest, it needs to operate with the wing's angle of attack where the drag is the lowest. The implicit assumption is of course that this only works with a wing that has camber, but most full size aircraft do have that type of airfoil.
man will never be able to break the grip of Earth's gravity with any kind of projectile or vehicle.
What is it about a lift drag polar you don't comprehend? For an airplane to go it's fastest, it needs to operate with the wing's angle of attack where the drag is the lowest. The implicit assumption is of course that this only works with a wing that has camber, but most full size aircraft do have that type of airfoil.
BUT
clear the field and look at basic laws of physics.
the airplane takes MORE power to stay aloft if it weighs more
It takes MORE power to go faster.
IF it weighs less, the power which was helping it fight gravity, can be used to propel it more rapidly.
Net result:
weigh less=go faster.
07-26-2009, 11:34 AM
#46
RE: Let’s discuss facts about stall-spin
In theory a dragster can't lower it's ET or improve it's MPH by adding weight, but the competition rules have drawings that show how to construct a proper ballast box. In the real world, weight added to a dragster can improve it's performance.
I don't have any problem seeing how a plane designed with an over abundance of lift could have a speed efficient sweet spot with respect to loading. It's a wastefull way of getting there, though. I doubt if a modern purpose built speed plane is ballasted to enhance performance.
Any bets on whether or not my control liner slows down packing an extra pound? It will be flown on 60 foot lines and timed for 7 laps.
I don't have any problem seeing how a plane designed with an over abundance of lift could have a speed efficient sweet spot with respect to loading. It's a wastefull way of getting there, though. I doubt if a modern purpose built speed plane is ballasted to enhance performance.
Any bets on whether or not my control liner slows down packing an extra pound? It will be flown on 60 foot lines and timed for 7 laps.
07-26-2009, 12:14 PM
#47
RE: Let’s discuss facts about stall-spin
You could follow up with a quikee type pylon racer timed over a few laps, then with an extra pound strapped to it. Might even demonstrate the dreaded accelerated stall/spin.
Evan, WB #12.
Evan, WB #12.
07-26-2009, 01:49 PM
#48
Thread Starter
RE: Let’s discuss facts about stall-spin
ORIGINAL: pimmnz
Might even demonstrate the dreaded accelerated stall/spin.
Might even demonstrate the dreaded accelerated stall/spin.
You have just brought the discussion back to the origin of this thread: spin-stall during sharp turns, which I have been waiting for! Thank you.
The thread has deviated to the advantages of light models over heavy ones, which has been good learning, but my target by starting this thread was learning from more experienced modelers about how to avoid spin-stalls in turns and loops (other than flying lighter models).
An earlier thread from the Beginners forum, where several members stated they had lost a model in this type of accident, moved me to start this one:
“I got my plane into a spin and never came out”
http://www.rcuniverse.com/forum/m_89...tm.htm#8947371
Regular Joe’s and beginners like me, who don’t know better or have so good advice before starting, build or buy and fly trainers and other first models that are far from being light.
Then, while we are in the process of learning to fly and to build properly, we may crash some of those models because our inexperience places them in the edge of stall and spin, generally at unrecoverable height.
In the future we may be able to build light models and get rid of the heavy ones; however, we would like to hear from expert pilots some tips and techniques about how to avoid stall-spin when landing and banking and turning our current heavy models.
07-26-2009, 02:17 PM
#49
RE: Let’s discuss facts about stall-spin
To delay the stall spin tendency, use the least amount of elevator travel it takes to have a flyable model. Reduce the throw mechanically by using the inner hole at the servo arm and use the top hole on a tall control horn. Most any plane with a properly located CG will fly with no more than 1/4" of elevator travel from neutral, many will fly just fine with less. Don't go overboard with idea or you might run out of pitch control on your glide in, so it's nice to have 2 rates programmed.
Most models I have ever seen at the field have way too much travel and are balanced too far forward. A nose heavy plane effectively makes the plane fly heavier.
Most models I have ever seen at the field have way too much travel and are balanced too far forward. A nose heavy plane effectively makes the plane fly heavier.
07-26-2009, 02:26 PM
#50
RE: Let’s discuss facts about stall-spin
ORIGINAL: combatpigg
In theory a dragster can't lower it's ET or improve it's MPH by adding weight, but the competition rules have drawings that show how to construct a proper ballast box. In the real world, weight added to a dragster can improve it's performance.
I don't have any problem seeing how a plane designed with an over abundance of lift could have a speed efficient sweet spot with respect to loading. It's a wastefull way of getting there, though. I doubt if a modern purpose built speed plane is ballasted to enhance performance.
Any bets on whether or not my control liner slows down packing an extra pound? It will be flown on 60 foot lines and timed for 7 laps.
In theory a dragster can't lower it's ET or improve it's MPH by adding weight, but the competition rules have drawings that show how to construct a proper ballast box. In the real world, weight added to a dragster can improve it's performance.
I don't have any problem seeing how a plane designed with an over abundance of lift could have a speed efficient sweet spot with respect to loading. It's a wastefull way of getting there, though. I doubt if a modern purpose built speed plane is ballasted to enhance performance.
Any bets on whether or not my control liner slows down packing an extra pound? It will be flown on 60 foot lines and timed for 7 laps.
It is used to setup best traction n control
IF the dragster could weigh less and get same traction -it would accelerate even faster .
