basic aerodynamics
03-16-2006, 10:32 AM
#276
RE: basic aerodynamics
Hey fella's, will one (or more) of you please look at the ARF forum and look at the thread titled: Knife edge 4 Star .60? We are getting in way over our heads in there. I am sure that some of you will have the correct answers.
Thank you,
Bill
Thank you,
Bill
03-21-2006, 12:15 AM
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RE: Suggestion for moderators
I am relitively new to RCU and have been mostly reading topics that others have posted.How do I go about posting my own topic? any help will be appreciated.
Old Bob
Old Bob
04-17-2006, 12:03 PM
#279
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RE: Suggestion for moderators
ORIGINAL: antter
This thread is going for years and still not getting anywhere.
What about flat aerofoils on propellers of foamies? If profile of the wing doesnt matter, so should profile of propeller blade.
And if weight is zero, why one need wings? Helicopters have no wings and I bet they have greater than 1 thrust to weight ratio. They fly. Althogh CG placement probably matters for helis.
And hot air baloon fly too! No thrust and very lite indeed.
This thread is going for years and still not getting anywhere.
What about flat aerofoils on propellers of foamies? If profile of the wing doesnt matter, so should profile of propeller blade.
And if weight is zero, why one need wings? Helicopters have no wings and I bet they have greater than 1 thrust to weight ratio. They fly. Althogh CG placement probably matters for helis.
And hot air baloon fly too! No thrust and very lite indeed.
"Flying", meaning controlled manuvering in many directions, including upwind and crosswind, takes more participation on the part of the device being used.
07-08-2006, 04:34 PM
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RE: Suggestion for moderators
I promise this is my last post on this topic, its like discussion about if size does matter, after someone invents extreme argument of zero size, in which case it indeed doesn't matter.
I know well why balloon flies, but doesn't position of center of gravity matters for balloon? Or indeed even for parashute?
I know well why balloon flies, but doesn't position of center of gravity matters for balloon? Or indeed even for parashute?
07-20-2006, 08:05 PM
#282
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RE: basic aerodynamics
ORIGINAL: antter
This thread is going for years and still not getting anywhere.
What about flat aerofoils on propellers of foamies? If profile of the wing doesnt matter, so should profile of propeller blade.
And if weight is zero, why one need wings? Helicopters have no wings and I bet they have greater than 1 thrust to weight ratio. They fly. Althogh CG placement probably matters for helis.
And hot air baloon fly too! No thrust and very lite indeed.
This thread is going for years and still not getting anywhere.
What about flat aerofoils on propellers of foamies? If profile of the wing doesnt matter, so should profile of propeller blade.
And if weight is zero, why one need wings? Helicopters have no wings and I bet they have greater than 1 thrust to weight ratio. They fly. Althogh CG placement probably matters for helis.
And hot air baloon fly too! No thrust and very lite indeed.
When I posted the following site, it was intended for beginners to go there to pick up a few tips on 'basic aerodynamics', and hopefully it's worked. That it has diversified from basic aerodynamics is of no real consequnece.
http://www.grc.nasa.gov/WWW/K-12/airplane/bga.html
Somebody made the point a few posts back that model design doesn't relate to full scale, and that's probably right, but one thing you can be sure of is that ALL obey the laws of aerodynamics even though that may be difficult to understand at times.
I enjoy dropping in fromtime to time and seeing how this has and is developing.
08-22-2006, 02:32 PM
#283
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RE: Suggestion for moderators
ORIGINAL: dick Hanson
of course - the size,weight and airspeed are far greater -and the inertia is in a completely different world.
My point was - the attitudes the craft can operate in are the same -
If you do fly foamies -just for fun - you will find that the CG can be stuck just about anywhere on a really good aerobatic setup and --YOU --acting as the computer (what better computer is there?) , can do all kinds of nutty things with it - take a look on the German modelling sites for the guys who have developed push/pull propeller driven models to a fine art . The models actually back up -
The unusual antics shown in the SU30 were not simply done to amuse someone - they were part of a program to work out the possibilities of going outside the usual limits .
On my precision aerobaic -contest models - I get cg to within 1/2" (on a 25 lb model ) for best use of the design
On my 6 ounce foamies -I fly em with bout the same allowable varience .
Different ballgame .
of course - the size,weight and airspeed are far greater -and the inertia is in a completely different world.
My point was - the attitudes the craft can operate in are the same -
If you do fly foamies -just for fun - you will find that the CG can be stuck just about anywhere on a really good aerobatic setup and --YOU --acting as the computer (what better computer is there?) , can do all kinds of nutty things with it - take a look on the German modelling sites for the guys who have developed push/pull propeller driven models to a fine art . The models actually back up -
The unusual antics shown in the SU30 were not simply done to amuse someone - they were part of a program to work out the possibilities of going outside the usual limits .
On my precision aerobaic -contest models - I get cg to within 1/2" (on a 25 lb model ) for best use of the design
On my 6 ounce foamies -I fly em with bout the same allowable varience .
Different ballgame .
Could you read in 3D Flying Forum my thread MY IDEA: WINGS TAPERED IN THE OPPOSITE WAY?
What do you think about?
Thank you
Littlebrain
09-24-2006, 01:04 PM
#284
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RE: Suggestion for moderators
ORIGINAL: dick Hanson
OK- you tell me why it works -using wind tunnel data .
Believe it ot not you don't need tunnel data to make something work.
Lots of stuff that was designed by wind tunnel research turned out to be a flop.
NOT because of the tunnel - simply because real world use shows up flaws that paper work and controlled enviroments don't/ can't / never will.
Tunnels beat guesswork - I am not a fool.
I never alluded to any explanation of why the stuff works - simply that it does work-
You have to do actual hands on stuff , eventually .
Where are you going to get a tunnel which runs at 10 mph airflow ?
I guess they exist - I don't kno who uses em tho -
You really don't think light weight broadens usable CG range?
Lower loadings = lower angles of attack needed to provide same amount of lift.
So the craft can maneuver at lower angles of attack and will recover to lower angles of attack that is, recover from departure conditions (stalled ) much more readily.
This is not a true statement?
Take any powered plane - fly it - now add weight - keeping speed the same - and see if you can't find the same effect.
eventually it will stall and never take off.
How does lower loading increase CG range ?
It simply reduces the critical nature of the cg --control can become pretty ham fisted in fact .
Attempts at exceeding stall angle have to be really intentional -as opposed to the typical full scale design which must be carefully kept with in the "envelope".
stability can be traded for maneuverability .
OK- you tell me why it works -using wind tunnel data .
Believe it ot not you don't need tunnel data to make something work.
Lots of stuff that was designed by wind tunnel research turned out to be a flop.
NOT because of the tunnel - simply because real world use shows up flaws that paper work and controlled enviroments don't/ can't / never will.
Tunnels beat guesswork - I am not a fool.
I never alluded to any explanation of why the stuff works - simply that it does work-
You have to do actual hands on stuff , eventually .
Where are you going to get a tunnel which runs at 10 mph airflow ?
I guess they exist - I don't kno who uses em tho -
You really don't think light weight broadens usable CG range?
Lower loadings = lower angles of attack needed to provide same amount of lift.
So the craft can maneuver at lower angles of attack and will recover to lower angles of attack that is, recover from departure conditions (stalled ) much more readily.
This is not a true statement?
Take any powered plane - fly it - now add weight - keeping speed the same - and see if you can't find the same effect.
eventually it will stall and never take off.
How does lower loading increase CG range ?
It simply reduces the critical nature of the cg --control can become pretty ham fisted in fact .
Attempts at exceeding stall angle have to be really intentional -as opposed to the typical full scale design which must be carefully kept with in the "envelope".
stability can be traded for maneuverability .
09-25-2006, 12:18 PM
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RE: Suggestion for moderators
I really wish I would have gotten in on this thread a long long long time ago. I am in the Air Force and have been for 14 years one of my primary jobs is that of a load planner. The window in which a center of gravity can be in order for an aircraft to be flyable becomes smaller the heavier the aircraft is and larger the lighter the load is. Pictures are so much easier than trying to explain in terms everyone will understand. Suffice to say the lighter it is the easier to balance.
09-25-2006, 05:58 PM
#286
RE: Suggestion for moderators
yes -that's a fact - I once noted that if a plane was light enough - the CG simply did not matter - you should of heard the learned replies on that one!
I bet you also found that if the load was too heavy --the CG meant nothing (It couldn't fly -so why bother .)
I bet you also found that if the load was too heavy --the CG meant nothing (It couldn't fly -so why bother .)
09-25-2006, 06:22 PM
#287
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RE: Suggestion for moderators
But we're only concerned with real world practical applications. Who cares about the fantasy and the absurd? Of course, if a plane could be so light that air would be like molasses, it virtually wouldn't fall due to gravity, not mention it could hardly move in any direction, thus c.g. doesn't matter (the fantasy) and why would we want to build a plane so heavy that it couldn't fly? (the absurd) I understand what you're saying. It just seems pointless.
09-25-2006, 07:33 PM
#288
Senior Member
RE: basic aerodynamics
Actually, to put the "light enough and the CG doesn't matter" into "real world, practical" context.
I've been messing almost exclusively with 46size airplanes for the last year. And have been instructing. And every student has brought a 46size highwing. And some of them have been HEAVY. And I've built a couple of highwingers. And enough of them have had about the same areas and moments that I'd suggest they were all basically "the same airplane".
And part of the "school sessions" were spent adding nose weight when it was needed. So I've seen the same planes with different CGs.
And when the heavy ones had CGs toward the edges of the envelope, they flew like it. And when the CG moved, you could see it for sure.
And I've got a scratch built of the same size and areas and moments. And have messed with it's CG as a way to teach myself what CG location does. But this scratch one is what anyone would call light. It's better than a pound lighter than the lightest of the student's airplanes. And I'd decided, after the experiments with it, that CG location was overrated. And then this last year, messing with heavy models of this class, I came to the startling conclusion that what Hanson just said is what it is....
In our real world, if the model is light enough (and my old trainer is) the CG don't do as much as you'd think.
I've been messing almost exclusively with 46size airplanes for the last year. And have been instructing. And every student has brought a 46size highwing. And some of them have been HEAVY. And I've built a couple of highwingers. And enough of them have had about the same areas and moments that I'd suggest they were all basically "the same airplane".
And part of the "school sessions" were spent adding nose weight when it was needed. So I've seen the same planes with different CGs.
And when the heavy ones had CGs toward the edges of the envelope, they flew like it. And when the CG moved, you could see it for sure.
And I've got a scratch built of the same size and areas and moments. And have messed with it's CG as a way to teach myself what CG location does. But this scratch one is what anyone would call light. It's better than a pound lighter than the lightest of the student's airplanes. And I'd decided, after the experiments with it, that CG location was overrated. And then this last year, messing with heavy models of this class, I came to the startling conclusion that what Hanson just said is what it is....
In our real world, if the model is light enough (and my old trainer is) the CG don't do as much as you'd think.
09-25-2006, 08:15 PM
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RE: basic aerodynamics
That makes sense. It probably has more to do with wing loading though, than actual weight. But there is still a limit. I bet if you take your light plane and move the c.g. totally off the wing, I'm pretty sure you're going to have a difficult time flying it.
09-25-2006, 10:19 PM
#290
RE: Suggestion for moderators
unless one looks at effects along boundries of parameters -- you can never have full understanding of the parameters .
It is not silly or pointless, rather ,it increases knowledge .
It is not silly or pointless, rather ,it increases knowledge .
09-25-2006, 10:38 PM
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RE: Suggestion for moderators
When you put it that way, I agree that expanding one's knowledge horizons is good. So, understanding the extreme brings the practical into better focus. I like that. I've often thought up extreme scenarios in physics, space and time and try to figure out the "what if" of it. In that respect, I see that it's not as pointless as I said earlier. [sm=thumbs_up.gif]
09-26-2006, 04:11 AM
#292
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RE: basic aerodynamics
But we're only concerned with real world practical applications. Who cares about the fantasy and the absurd?
I bet if you take your light plane and move the c.g. totally off the wing, ................................................
Hey, didn't the same guy post these two ideas almost back to back???????
09-26-2006, 10:37 AM
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RE: basic aerodynamics
I'm sorry, but I'm missing your point.
EDIT: I see. You're taking it out of context. I'm not sure why though. The sentence finishes with, "...I'm pretty sure you're going to have a difficult time flying it." The 2 posts are not in conflict with each other, if that's what you're getting at. They are in support of each other.
EDIT: I see. You're taking it out of context. I'm not sure why though. The sentence finishes with, "...I'm pretty sure you're going to have a difficult time flying it." The 2 posts are not in conflict with each other, if that's what you're getting at. They are in support of each other.
11-24-2006, 07:14 AM
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RE: Suggestion for moderators
Hey guys
Dick Hanson is right from the start of the thread if you check exactly what he says and of course if you have a sense of humour. As a matter of fact he is talking like a modeller and not like a full scale aviator. In full scale it is very difficult to heave the powerplants with extreme power that in modelling we have. So lets say that in full scale the airplanes are limited to less power. Also they are limited with more weight. So the CG makes a lot of sense. Also the dynamic balance makes even more sense.(It is aft the CG).
Now in modelling nowdays we have the choice to overpower our planes and maybe make them also a lot lighter than in the past; so we somehow change the clasic way of aerodynamics. eg. A full scale tail heavy airplane stalls (because of many reasons) in modelling can make 3D aerobatics....
You see our point?
Now if you want to get back to the Classic Aerodynamic theories man I would suggest you check some 3D flying. No pilots inside and full G specifications make a lot of difference in flying.
Cheers
Johnnie
Dick Hanson is right from the start of the thread if you check exactly what he says and of course if you have a sense of humour. As a matter of fact he is talking like a modeller and not like a full scale aviator. In full scale it is very difficult to heave the powerplants with extreme power that in modelling we have. So lets say that in full scale the airplanes are limited to less power. Also they are limited with more weight. So the CG makes a lot of sense. Also the dynamic balance makes even more sense.(It is aft the CG).
Now in modelling nowdays we have the choice to overpower our planes and maybe make them also a lot lighter than in the past; so we somehow change the clasic way of aerodynamics. eg. A full scale tail heavy airplane stalls (because of many reasons) in modelling can make 3D aerobatics....
You see our point?
Now if you want to get back to the Classic Aerodynamic theories man I would suggest you check some 3D flying. No pilots inside and full G specifications make a lot of difference in flying.
Cheers
Johnnie
02-22-2007, 04:42 AM
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RE: basic aerodynamics
ORIGINAL: Rotaryphile
I used to build engine powered freeflight models that balanced on the trailing edge of the wing, but they had stabs with roughly 50% of the wing area. The important thing is to keep the CG slightly ahead of the center of pressure of the entire airplane, and those old freeflights had their center of pressure behind the wing trailing edge.
A hypothetical model with zero mass would probably be unstable, since the air influenced by the airplane has mass, and moves with the airplane. I have built models with wing loadings of well under one ounce per square foot, and their CG location is just as important as with far heavier wing loadings, and seems to like to be a little further forward than that of the heavier jobs. The mass of air influenced by a wing has a significant influence on flutter calculations. Flutter analysts frequently consider the mass of air influenced by a wing or stab to be roughly equal to that of a cylinder of air with radius equal to the wing chord.
I used to build engine powered freeflight models that balanced on the trailing edge of the wing, but they had stabs with roughly 50% of the wing area. The important thing is to keep the CG slightly ahead of the center of pressure of the entire airplane, and those old freeflights had their center of pressure behind the wing trailing edge.
A hypothetical model with zero mass would probably be unstable, since the air influenced by the airplane has mass, and moves with the airplane. I have built models with wing loadings of well under one ounce per square foot, and their CG location is just as important as with far heavier wing loadings, and seems to like to be a little further forward than that of the heavier jobs. The mass of air influenced by a wing has a significant influence on flutter calculations. Flutter analysts frequently consider the mass of air influenced by a wing or stab to be roughly equal to that of a cylinder of air with radius equal to the wing chord.
A heavy aircraft must fly at a greater angle of attack, and this moves the CP forward. This tends to pitch the nose up, and slow the plane down further, leading to a stall. With under cambered wings, a stall will be vicious, as the CP retreats rapidly from the forward position, aft. Even with a lifting tail-plane, one needs longitudinal dihedral to cope with shifting CP.
04-07-2007, 01:22 PM
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RE: Suggestion for moderators
Not to be a stick in the mud, but the Cp concept is a little outmoded. While what you are saying is true (the Cp moves), mathematically, it is much easier to evaluate a wing with a Cm (a moment arm acting around the Cg). That way, you don't have to do the calculation as though you are chasing Cp vs. Cg, you just have to know what the magnitude of Cm is.
What you really want to say is that the idea wing section for a heavy model is one in which the pitching moment is reasonably small through the desired flight envelope, and has the right shape near the stall.
Matt
What you really want to say is that the idea wing section for a heavy model is one in which the pitching moment is reasonably small through the desired flight envelope, and has the right shape near the stall.
Matt
06-01-2007, 03:20 AM
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RE: Suggestion for moderators
i think whats his name dick hansen
is right on the nail here
if u put a big enough engine on just about enthing
u can make it fly
take the original stealth bomber for example
its wings/wing was probably the least aerodynamic of its time
is right on the nail here
if u put a big enough engine on just about enthing
u can make it fly
take the original stealth bomber for example
its wings/wing was probably the least aerodynamic of its time
10-18-2007, 12:28 PM
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RE: basic aerodynamics
Wow - I read a lot of this thread, skipping the 12 pages prior to this one and the only thing that I learned is that once someone makes a statement that is seemingly absurd, a lot of other people chime in, some with good advise, and facts, others with twisted views and mis-information.
CG matters in ALL aircraft, heavier than air, lighter than air too.
Try having the CG of a zeplin 1/2 way from nose to tail, but place it above the centerline. Yeah, it would fly, but upside-down...
Take the ultra low wing loading on some of the indoor free flight models. The CG can be swung around a lot, but it DOES matter.
Try placing the CG behind the front wing, (I say front wing because a lot of the indoor FF models have a tail surface almost 80% of the main wing). If the tail surface were large enough, as many of them are, it would fly more on the principals of a canaard rafther than conventional aircraft.
If you do that on a well proportioned 33% Extra, make sure that there is nobody at the field, 'cause it will be disasterous, and an embarrasing waste of money.
What a lot of modelers may realize through experience, but may not have had it explained to them is, aerodynamics is not proportionate to scale. The size of the air molecules do not change with the size of the model.
When you get really small, the rules change a little bit.
When you get really light wingloading, the widely accepted limits on design are blown open, but they still do matter.
I think that this thread is absurd, and not suprized that the last post was 4 months ago...
It should be wiped clean and restarted without the extremes.
I think this should be for beginners, and there is nothing in here that a beginner can pickup and take to his/her workbench without shaking his/her head wondering what to believe as true fact.
Bob
CG matters in ALL aircraft, heavier than air, lighter than air too.
Try having the CG of a zeplin 1/2 way from nose to tail, but place it above the centerline. Yeah, it would fly, but upside-down...
Take the ultra low wing loading on some of the indoor free flight models. The CG can be swung around a lot, but it DOES matter.
Try placing the CG behind the front wing, (I say front wing because a lot of the indoor FF models have a tail surface almost 80% of the main wing). If the tail surface were large enough, as many of them are, it would fly more on the principals of a canaard rafther than conventional aircraft.
If you do that on a well proportioned 33% Extra, make sure that there is nobody at the field, 'cause it will be disasterous, and an embarrasing waste of money.
What a lot of modelers may realize through experience, but may not have had it explained to them is, aerodynamics is not proportionate to scale. The size of the air molecules do not change with the size of the model.
When you get really small, the rules change a little bit.
When you get really light wingloading, the widely accepted limits on design are blown open, but they still do matter.
I think that this thread is absurd, and not suprized that the last post was 4 months ago...
It should be wiped clean and restarted without the extremes.
I think this should be for beginners, and there is nothing in here that a beginner can pickup and take to his/her workbench without shaking his/her head wondering what to believe as true fact.
Bob
10-19-2007, 10:17 AM
#299
RE: basic aerodynamics
Not having visited this site for a while - -it is interesting to see various interpretations of "rules" .
If all info should be beginners -- beginners in what?
I have worked with beginners trying to fly models - who are accomplished full scale pilots and they simply don't "get it".
They try to follow the rules which worked for them in flying full scale , large machines.
They learned and followed the rules for that task.
That the very small models did not respond in the same time frames etc., simply upset their ability to respond to controls as required .
Are these guys "beginners?"
If you don't care to examine the boundries and the absurd - --you will never see the practical limitions of any theory
That is my take on it .
For example -I would have never developed any patents if I had simply " gone by the rules ". But I do appreciate your input-
without inputs -it is impossible to see if the "output" is relevant to the subject.
If all info should be beginners -- beginners in what?
I have worked with beginners trying to fly models - who are accomplished full scale pilots and they simply don't "get it".
They try to follow the rules which worked for them in flying full scale , large machines.
They learned and followed the rules for that task.
That the very small models did not respond in the same time frames etc., simply upset their ability to respond to controls as required .
Are these guys "beginners?"
If you don't care to examine the boundries and the absurd - --you will never see the practical limitions of any theory
That is my take on it .
For example -I would have never developed any patents if I had simply " gone by the rules ". But I do appreciate your input-
without inputs -it is impossible to see if the "output" is relevant to the subject.
10-19-2007, 01:45 PM
#300
RE: basic aerodynamics
ORIGINAL: bobmac010
Wow - I read a lot of this thread, skipping the 12 pages prior to this one and the only thing that I learned is that once someone makes a statement that is seemingly absurd, a lot of other people chime in, some with good advise, and facts, others with twisted views and mis-information.
CG matters in ALL aircraft, heavier than air, lighter than air too.
Try having the CG of a zeplin 1/2 way from nose to tail, but place it above the centerline. Yeah, it would fly, but upside-down...
Take the ultra low wing loading on some of the indoor free flight models. The CG can be swung around a lot, but it DOES matter.
Try placing the CG behind the front wing, (I say front wing because a lot of the indoor FF models have a tail surface almost 80% of the main wing). If the tail surface were large enough, as many of them are, it would fly more on the principals of a canaard rafther than conventional aircraft.
If you do that on a well proportioned 33% Extra, make sure that there is nobody at the field, 'cause it will be disasterous, and an embarrasing waste of money.
What a lot of modelers may realize through experience, but may not have had it explained to them is, aerodynamics is not proportionate to scale. The size of the air molecules do not change with the size of the model.
When you get really small, the rules change a little bit.
When you get really light wingloading, the widely accepted limits on design are blown open, but they still do matter.
I think that this thread is absurd, and not suprized that the last post was 4 months ago...
It should be wiped clean and restarted without the extremes.
I think this should be for beginners, and there is nothing in here that a beginner can pickup and take to his/her workbench without shaking his/her head wondering what to believe as true fact.
Bob
Wow - I read a lot of this thread, skipping the 12 pages prior to this one and the only thing that I learned is that once someone makes a statement that is seemingly absurd, a lot of other people chime in, some with good advise, and facts, others with twisted views and mis-information.
CG matters in ALL aircraft, heavier than air, lighter than air too.
Try having the CG of a zeplin 1/2 way from nose to tail, but place it above the centerline. Yeah, it would fly, but upside-down...
Take the ultra low wing loading on some of the indoor free flight models. The CG can be swung around a lot, but it DOES matter.
Try placing the CG behind the front wing, (I say front wing because a lot of the indoor FF models have a tail surface almost 80% of the main wing). If the tail surface were large enough, as many of them are, it would fly more on the principals of a canaard rafther than conventional aircraft.
If you do that on a well proportioned 33% Extra, make sure that there is nobody at the field, 'cause it will be disasterous, and an embarrasing waste of money.
What a lot of modelers may realize through experience, but may not have had it explained to them is, aerodynamics is not proportionate to scale. The size of the air molecules do not change with the size of the model.
When you get really small, the rules change a little bit.
When you get really light wingloading, the widely accepted limits on design are blown open, but they still do matter.
I think that this thread is absurd, and not suprized that the last post was 4 months ago...
It should be wiped clean and restarted without the extremes.
I think this should be for beginners, and there is nothing in here that a beginner can pickup and take to his/her workbench without shaking his/her head wondering what to believe as true fact.
Bob
Lots hyperbole and bloviating. aka blah blah blah blah
