Penetration
10-19-2009, 06:31 PM
#26
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RE: Penetration
BMatthews
"Does that sort of describe your findings? "
Yes, BUT ........
Close to the ground (landing) the lightly loaded Eratix feels completely under control. Matter of fact you can even play with it and put the tail wheel down first.
It feels as if you have COMPLETE control, even in a substantial crosswind.
Typical of a Pattern type design, the Diamante feels as if she's on rails ....... until that last bit of pitch correction. Then it feels as if she's on the ragged edge!!!
It really felt as if the reaction of the two aircraft was 180 degrees out of phase. Certainly the opposite of what I had expected.
Unfortunately rounds two, three etc. got no better with the Diamante.
The last bit of pitch correction felt like an over center spring.
Dick's comments about thin vs. thick airfoils seems "right on" as the Diamante does have a thin Selig airfoil. It is either all lift or slow settling in a flat attitude.
With a relatively fast airplane this eats up runway at an alarming rate..
In defense of the airfoil it is simply not possible to have a stall result in anything other than a straight ahead drop and then immediate recovery.
However, do not expect anything other than a flat landing attitude!
'Cause if you do you are in for a surprise.
Keep it flat and let the speed bleed off. There isn't another way, at least in winds/cross winds of a
substantial nature.
I realize that my last comments are far afield from the 'penetration' question. But that was the order of the thought processes involved. And the trigger for the question.
"Does that sort of describe your findings? "
Yes, BUT ........
Close to the ground (landing) the lightly loaded Eratix feels completely under control. Matter of fact you can even play with it and put the tail wheel down first.
It feels as if you have COMPLETE control, even in a substantial crosswind.
Typical of a Pattern type design, the Diamante feels as if she's on rails ....... until that last bit of pitch correction. Then it feels as if she's on the ragged edge!!!
It really felt as if the reaction of the two aircraft was 180 degrees out of phase. Certainly the opposite of what I had expected.
Unfortunately rounds two, three etc. got no better with the Diamante.
The last bit of pitch correction felt like an over center spring.
Dick's comments about thin vs. thick airfoils seems "right on" as the Diamante does have a thin Selig airfoil. It is either all lift or slow settling in a flat attitude.
With a relatively fast airplane this eats up runway at an alarming rate..
In defense of the airfoil it is simply not possible to have a stall result in anything other than a straight ahead drop and then immediate recovery.
However, do not expect anything other than a flat landing attitude!
'Cause if you do you are in for a surprise.
Keep it flat and let the speed bleed off. There isn't another way, at least in winds/cross winds of a
substantial nature.
I realize that my last comments are far afield from the 'penetration' question. But that was the order of the thought processes involved. And the trigger for the question.
10-19-2009, 07:39 PM
#27
RE: Penetration
Does this have to do with decreasing gradient of the wind speed as it approaches to the ground level?
It seems like at landing, the penetration property of each model doesn't matter as much as at high altitude.
It seems like at landing, the penetration property of each model doesn't matter as much as at high altitude.
10-19-2009, 08:27 PM
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RE: Penetration
Onewasp, without seeing the model fly all I can suggest from this end of my keyboard is that you may be working so hard at keeping it in the high drag glide slope that when it drops into the ground shear layer it suddenly move much closer to the stall point and as a result becomes super sensitive on the elevator. In a strong wind you really want to be holding a touch of reserve speed as you enter the ground shear. In effect make sure that when you're at the 10 foot high mark that you have what you know is the correct ground speed for a light headwind. Because by the time you drop through the shear that's what you need. You may even want to hit this altitude from a shallow dive or with power on to get to that ground speed and then as you drop through the last 10 feet reduce power to hold that amount of ground speed and only be hitting idle with about a foot or two to go. I'll bet is you work it that way it'll be solid, or as solid as the conditions allow, right to touchdown.
This is actually a good example of exactly what I was talking about. The super lightly loaded 3D model has such a wide speed range that you can get away with murder in this ground shear layer. Meanwhile the Diamante does not enjoy this same ability so you need to ensure that you keep it over the stall point.
The proof in the pudding would be if the Diamante acts the same way up high if you slow it down and try to hang it near the stall point. If it acts the same way as it does during the landing approaches then you can bet it's due to the same flying speed.
This is actually a good example of exactly what I was talking about. The super lightly loaded 3D model has such a wide speed range that you can get away with murder in this ground shear layer. Meanwhile the Diamante does not enjoy this same ability so you need to ensure that you keep it over the stall point.
The proof in the pudding would be if the Diamante acts the same way up high if you slow it down and try to hang it near the stall point. If it acts the same way as it does during the landing approaches then you can bet it's due to the same flying speed.
10-19-2009, 08:28 PM
#29
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RE: Penetration
lnewqban
I think this:
Imagine being in a car being driven at a constant 50mph.
Stick a baseball bat out the window, steady for the obvious force of drag and rotate the bat.
You'll feel no change.
Now, stick a 1/4 inch thick piece of aircraft ply cut to the outline of the bat out of the same car window and car speed. Steady it so that the narrow edge (1/4") is dead into the airstream.
Rotate the 1/4' thick outline of the bat. I doubt that you can hang on to it.
I don't really care whether you do this in Denver or at Daytona Beach. The force difference will be beyond extreme!
Dick Hanson has stated that he has experienced exactly the same phenomena on exactly the same model set ups.
He is located at 4300 feet ASL. I am at 1500 feet ASL.
Air density is not even a major factor.
This somewhat homely example illustrates the difference (two extremes) between thick and thin airfoils.
This, as I noted earlier, is rather far afield from my original question on penetration.
I think this:
Imagine being in a car being driven at a constant 50mph.
Stick a baseball bat out the window, steady for the obvious force of drag and rotate the bat.
You'll feel no change.
Now, stick a 1/4 inch thick piece of aircraft ply cut to the outline of the bat out of the same car window and car speed. Steady it so that the narrow edge (1/4") is dead into the airstream.
Rotate the 1/4' thick outline of the bat. I doubt that you can hang on to it.
I don't really care whether you do this in Denver or at Daytona Beach. The force difference will be beyond extreme!
Dick Hanson has stated that he has experienced exactly the same phenomena on exactly the same model set ups.
He is located at 4300 feet ASL. I am at 1500 feet ASL.
Air density is not even a major factor.
This somewhat homely example illustrates the difference (two extremes) between thick and thin airfoils.
This, as I noted earlier, is rather far afield from my original question on penetration.
10-19-2009, 08:57 PM
#30
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RE: Penetration
BMatthews
Our last posts were almost simultaneous.
The landing speed for the Diamante is rather high. Witness the wing loading.
It is actually higher than most Pattern style ships I've flown (a big bunch in 49 years).
I have always enjoyed landing corrections down very low (two to three inches off the ground). I even fly the DX7se/AR7600 combo (11ms frame rate) to enhance this aspect. I have an X9303 also but the 'se' is quicker. At least that is how I see it,
The reaction is taking place at about six inches or lower as I try to put it down in a conventional manner.
This airplane (even without the wind) does NOT like that !
You simply have to fly it on to the ground or if conditions are calm enough drop about 20 degrees of flaperon AFTER getting into ground effect. If you are nimble enough you can actually get a nose high 'induced' flare.
You've got one shot at that and one only and it must be under calm conditions.
Under those conditions (calm) I can nail that about 90% of the time.
Under windy and/or variable crosswind conditions ( today it was gusting into the low teens) you fly it on to the ground period, paragraph.
In all other attitudes and altitudes it has a typical Pattern plane response. It flies cleanly through all the maneuvers.
BUT its says LAND ME FLAT.
P.S. After returning home today and thinking it through, I'll bet I could add spoilerons at the same time
that I put in the final pitch correction and carry it off.
Then again, at this point in the season I do not need to splash any more airframes,
Our last posts were almost simultaneous.
The landing speed for the Diamante is rather high. Witness the wing loading.
It is actually higher than most Pattern style ships I've flown (a big bunch in 49 years).
I have always enjoyed landing corrections down very low (two to three inches off the ground). I even fly the DX7se/AR7600 combo (11ms frame rate) to enhance this aspect. I have an X9303 also but the 'se' is quicker. At least that is how I see it,
The reaction is taking place at about six inches or lower as I try to put it down in a conventional manner.
This airplane (even without the wind) does NOT like that !
You simply have to fly it on to the ground or if conditions are calm enough drop about 20 degrees of flaperon AFTER getting into ground effect. If you are nimble enough you can actually get a nose high 'induced' flare.
You've got one shot at that and one only and it must be under calm conditions.
Under those conditions (calm) I can nail that about 90% of the time.
Under windy and/or variable crosswind conditions ( today it was gusting into the low teens) you fly it on to the ground period, paragraph.
In all other attitudes and altitudes it has a typical Pattern plane response. It flies cleanly through all the maneuvers.
BUT its says LAND ME FLAT.
P.S. After returning home today and thinking it through, I'll bet I could add spoilerons at the same time
that I put in the final pitch correction and carry it off.
Then again, at this point in the season I do not need to splash any more airframes,
10-20-2009, 09:52 AM
#31
RE: Penetration
The setup which makes for a good precision aerobatic setup ,has it's quirks.
One of em is this tendency to "drop" when airspeed hits a certain low point
Without this, the stall entry for spins gets tricky.
The Diamante- is like my old designs for pattern
-You can setup a spin entry using a little power and holding a slightly nose high attitude without gaining altitude.
When you arrive at th desired position in th judging frame, just reduce power and add rudder for desired spin direction
It looks good and does not look forced.
Ideally, the model drops its nose and falls off to one side -all at the same time
No rudder and you get a sinking result (along with sinking score).
The Diamante will drop smartly and also does a nice crossover spin-as the nose can drop beyond vertical and adding down elevator will make the transition appear seamless.
Here , faster penetration is again demonstrated as the model appears to momentarily drop like a stone ,not simply mush along.
I swapped the landing gear on my Diamante for a wire setup which trails slightly
If I land too hard, the gear just rotates slightly back n out.
The stock setup can easily be dislodged as it has no shock absorbing ability - It just looks Kool.
One of em is this tendency to "drop" when airspeed hits a certain low point
Without this, the stall entry for spins gets tricky.
The Diamante- is like my old designs for pattern
-You can setup a spin entry using a little power and holding a slightly nose high attitude without gaining altitude.
When you arrive at th desired position in th judging frame, just reduce power and add rudder for desired spin direction
It looks good and does not look forced.
Ideally, the model drops its nose and falls off to one side -all at the same time
No rudder and you get a sinking result (along with sinking score).
The Diamante will drop smartly and also does a nice crossover spin-as the nose can drop beyond vertical and adding down elevator will make the transition appear seamless.
Here , faster penetration is again demonstrated as the model appears to momentarily drop like a stone ,not simply mush along.
I swapped the landing gear on my Diamante for a wire setup which trails slightly
If I land too hard, the gear just rotates slightly back n out.
The stock setup can easily be dislodged as it has no shock absorbing ability - It just looks Kool.
11-02-2009, 11:27 AM
#32
RE: Penetration
Onewasp,
After reading this discussion I can't seem to find a direct answer to your question regarding penetration.
Penetration is in my understanding, the ability to make forward progress (ground speed) in extreme wind while remaining pitch stable.
A good example of penetration is in slope soaring. These unpowered planes can accelerate to very high ground speeds because of their ability to "penetrate" using added ballast weight. At the top of a ridge the airstream is flowing with a vertical component. If we assume a 45 degree slope that means for every foot the wind travels horizontally it must also flow one foot straight up and "0" AOA is a 45 deg nose down pitch relative to ground! In a light wind a glider with no ballast will move slowly forward horizontal (relative to the ground) by assuming a tail up attitude as viewed by the pilot. However, the plane really has a high positive angle of attack relative to the airstream and that generates lift to maintain altitude. The plane can even fly backwards. However, as wind speed increases the plane will quickly gain altitude because of excess lift and the pilot must dive the plane but pitch ultimately becomes uncontrollable.
Adding ballast allows the plane to generate more aerodynamic force (sum of lift and drag) without gaining altitude. As the pilot adds more down elevator to a properly ballasted plane the tail lifts higher and the aerodynamic force tilts further and further forward until there is a forward component accelerating the plane to a higher ground speed.
If the wind speed dies the plane becomes a rock.
Flying powered planes on level ground is basically the same. A lightweight electric in a high wind must dive to prevent the generation of excessive lift and becomes uncontrollable. Adding ballast allows the plane to "penetrate" into a headwind because the added ballast counters the higher lift force. (Recall that a plane at "0" AOA still has drag that must be overcome.) The plane MUST fly faster (airspeed, not ground speed) so it needs more power too.
After reading this discussion I can't seem to find a direct answer to your question regarding penetration.
Penetration is in my understanding, the ability to make forward progress (ground speed) in extreme wind while remaining pitch stable.
A good example of penetration is in slope soaring. These unpowered planes can accelerate to very high ground speeds because of their ability to "penetrate" using added ballast weight. At the top of a ridge the airstream is flowing with a vertical component. If we assume a 45 degree slope that means for every foot the wind travels horizontally it must also flow one foot straight up and "0" AOA is a 45 deg nose down pitch relative to ground! In a light wind a glider with no ballast will move slowly forward horizontal (relative to the ground) by assuming a tail up attitude as viewed by the pilot. However, the plane really has a high positive angle of attack relative to the airstream and that generates lift to maintain altitude. The plane can even fly backwards. However, as wind speed increases the plane will quickly gain altitude because of excess lift and the pilot must dive the plane but pitch ultimately becomes uncontrollable.
Adding ballast allows the plane to generate more aerodynamic force (sum of lift and drag) without gaining altitude. As the pilot adds more down elevator to a properly ballasted plane the tail lifts higher and the aerodynamic force tilts further and further forward until there is a forward component accelerating the plane to a higher ground speed.
If the wind speed dies the plane becomes a rock.
Flying powered planes on level ground is basically the same. A lightweight electric in a high wind must dive to prevent the generation of excessive lift and becomes uncontrollable. Adding ballast allows the plane to "penetrate" into a headwind because the added ballast counters the higher lift force. (Recall that a plane at "0" AOA still has drag that must be overcome.) The plane MUST fly faster (airspeed, not ground speed) so it needs more power too.
11-03-2009, 06:55 AM
#35
RE: Penetration
[sm=thumbs_up.gif]..........and I will add:
Flying faster is a privilege of low drag and/or overpowered models.
Profile drag depends exponentially of the air stream velocity; just as the needed thrust does.
That is one of the reasons that airliners have to fly at 30 000 feet high, since high altitude equals low air density and viscosity.
Flying faster is a privilege of low drag and/or overpowered models.
Profile drag depends exponentially of the air stream velocity; just as the needed thrust does.
That is one of the reasons that airliners have to fly at 30 000 feet high, since high altitude equals low air density and viscosity.
11-03-2009, 10:03 AM
#36
RE: Penetration
ORIGINAL: Bozarth
How is ''wind penetration'' any different from simply flying faster?
Kurt
How is ''wind penetration'' any different from simply flying faster?
Kurt
Kurt, simply adding power to the plane will not cure the problem of pitch stability. As airspeed goes up so does lift sensitivity. The gusty, unpredictable behavior of extreme wind conditions near the ground makes the problem more acute. The pilot get's into an uncontrollable pitch oscillation without additional ballast. The pilot must add the ballast to reduce the pitch sensitivity back to a manageable level.
11-03-2009, 11:51 AM
#37
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RE: Penetration
ORIGINAL: CrateCruncher
''Penetration is in my understanding, the ability to make forward progress (ground speed) in extreme wind while remaining pitch stable.''
Kurt, simply adding power to the plane will not cure the problem of pitch stability. As airspeed goes up so does lift sensitivity. The gusty, unpredictable behavior of extreme wind conditions near the ground makes the problem more acute. The pilot get's into an uncontrollable pitch oscillation without additional ballast. The pilot must add the ballast to reduce the pitch sensitivity back to a manageable level.
ORIGINAL: Bozarth
How is ''wind penetration'' any different from simply flying faster?
Kurt
How is ''wind penetration'' any different from simply flying faster?
Kurt
Kurt, simply adding power to the plane will not cure the problem of pitch stability. As airspeed goes up so does lift sensitivity. The gusty, unpredictable behavior of extreme wind conditions near the ground makes the problem more acute. The pilot get's into an uncontrollable pitch oscillation without additional ballast. The pilot must add the ballast to reduce the pitch sensitivity back to a manageable level.
Kurt
11-03-2009, 11:54 AM
#38
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RE: Penetration
I think, to answer your question, Bozarth.
How is ''wind penetration'' any different from simply flying faster?
The answer is "flying faster at the same L/D.
How is ''wind penetration'' any different from simply flying faster?
The answer is "flying faster at the same L/D.
11-03-2009, 12:35 PM
#39
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RE: Penetration
Kurt, at the basis of it you're entirely right. And in the world of the sailplane or slope flyer penetration is merely the ability to make ground in a headwind which translates entirely to flying faster at an acceptable L/D.
But in the powered model world it has taken on a slightly different meaning. Good ol' sematics and misunderstanding that becomes generally accepted. For power models it's just a case of advancing the throttle to make ground as long as the model isn't trying to fly in a wind that is faster than it's top forward speed. But the only time I can see that being an issue would be scale biplanes or slow parkflyers that do not have a high top speed.
Instead the accepted meaning of penetration for sport power flyers seems to be one that indicates a model that rides through turbulent air in a stable manner. If all of you stop and think about how folks have used the term penetration and read into their statements what they are implying at the time I think you'll find that this is most often the case. I think it was "stolen" from the glider guiders and twisted to mean "stable in wind" instead of able to cover ground. It's a misinterpretation that's not hard to see. A fast glider coming back upwind will often look like it's on rails as it punches through any and everything turbulent in it's path. Only when it slows down again will it seem to bobble about in any turbulence. A power flyer seeing that and hearing folks say "WOW! LOOK AT THAT BABY PENETRATE!" could easily take away the wrong meaning.
This thread has pretty much covered all the meanings but some of you seem to think that it should only have ONE meaning. But it just ain't the case. Rightly or wrongly it's been transffered and made to mean different things to different groups within the modeling community.
But in the powered model world it has taken on a slightly different meaning. Good ol' sematics and misunderstanding that becomes generally accepted. For power models it's just a case of advancing the throttle to make ground as long as the model isn't trying to fly in a wind that is faster than it's top forward speed. But the only time I can see that being an issue would be scale biplanes or slow parkflyers that do not have a high top speed.
Instead the accepted meaning of penetration for sport power flyers seems to be one that indicates a model that rides through turbulent air in a stable manner. If all of you stop and think about how folks have used the term penetration and read into their statements what they are implying at the time I think you'll find that this is most often the case. I think it was "stolen" from the glider guiders and twisted to mean "stable in wind" instead of able to cover ground. It's a misinterpretation that's not hard to see. A fast glider coming back upwind will often look like it's on rails as it punches through any and everything turbulent in it's path. Only when it slows down again will it seem to bobble about in any turbulence. A power flyer seeing that and hearing folks say "WOW! LOOK AT THAT BABY PENETRATE!" could easily take away the wrong meaning.
This thread has pretty much covered all the meanings but some of you seem to think that it should only have ONE meaning. But it just ain't the case. Rightly or wrongly it's been transffered and made to mean different things to different groups within the modeling community.
11-03-2009, 01:27 PM
#40
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RE: Penetration
ORIGINAL: BMatthews
Instead the accepted meaning of penetration for sport power flyers seems to be one that indicates a model that rides through turbulent air in a stable manner. If all of you stop and think about how folks have used the term penetration and read into their statements what they are implying at the time I think you'll find that this is most often the case. I think it was ''stolen'' from the glider guiders and twisted to mean ''stable in wind'' instead of able to cover ground. It's a misinterpretation that's not hard to see. A fast glider coming back upwind will often look like it's on rails as it punches through any and everything turbulent in it's path. Only when it slows down again will it seem to bobble about in any turbulence. A power flyer seeing that and hearing folks say ''WOW! LOOK AT THAT BABY PENETRATE!'' could easily take away the wrong meaning.....
Instead the accepted meaning of penetration for sport power flyers seems to be one that indicates a model that rides through turbulent air in a stable manner. If all of you stop and think about how folks have used the term penetration and read into their statements what they are implying at the time I think you'll find that this is most often the case. I think it was ''stolen'' from the glider guiders and twisted to mean ''stable in wind'' instead of able to cover ground. It's a misinterpretation that's not hard to see. A fast glider coming back upwind will often look like it's on rails as it punches through any and everything turbulent in it's path. Only when it slows down again will it seem to bobble about in any turbulence. A power flyer seeing that and hearing folks say ''WOW! LOOK AT THAT BABY PENETRATE!'' could easily take away the wrong meaning.....
Kurt
11-03-2009, 04:56 PM
#41
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RE: Penetration
ORIGINAL: Bozarth
But let's not attribute this ability to some magical aerodynamic feature called wind penetration. Increased mass flying at a higher speed has higher inertia and momentum, which will reduce the effects of gusts.......
But let's not attribute this ability to some magical aerodynamic feature called wind penetration. Increased mass flying at a higher speed has higher inertia and momentum, which will reduce the effects of gusts.......
Quite right, quite right. There's nothing magical about it. Mind you to SOME extent model trim comes into play. For examble a trainer that is set up for a higher degree of pitch stability may tend to balloon when it runs into a localized gust that momentarily raises the flying speed until the model is slowed enough to restore the original trimmed airspeed. Fighting this along with the tendency to drop the nose when encountering a sudden lull or back wind due to strong turbulence would make such a model more demanding to fly well in turbulent conditions compared to a model that is much more pitch neutral to changes in airspeed. Examples of such would be racers, pattern or 3D models and serious speed gliders that are set up for only a small or even no pitch stability margin. I wonder if such things are part of what the penetration myth is all about?
As you say though, all this can be fully explained in regular terms once we know what version of "penetration" the person subscribes to.
11-03-2009, 05:41 PM
#42
RE: Penetration
penetrating a myth is quite a task-
The old answers about "how airfoils lift and how one airfoil is a higher lift type than another persist -as does the business about how a particular airfoil penetrates better
etc., etc..
ANY flight requires the ability to confront (or use) gravity
weight/aerodynamics and or speed, EACH are involved
There is no single factor which improves penetration.
So far -for me- the lightest model with the most power wins on all fronts.
The old answers about "how airfoils lift and how one airfoil is a higher lift type than another persist -as does the business about how a particular airfoil penetrates better
etc., etc..
ANY flight requires the ability to confront (or use) gravity
weight/aerodynamics and or speed, EACH are involved
There is no single factor which improves penetration.
So far -for me- the lightest model with the most power wins on all fronts.
11-03-2009, 07:20 PM
#43
RE: Penetration
For most glow powered planes talking about penetration is admittedly kinda silly but considering all the tiny electrics I've seen lately and the windy conditions here in Central Texas it is becoming relevant.
The added ballast does more than just damp turbulence with it's inertia. It moves the airfoil angle required for level flight to a more reasonable positive aoa and makes pilot inputs to that angle less important. With additional ballast the plane's weight is better matched to the lift and drag forces acting on the airframe.
I used the term while slope soaring. Launching into a constant 70 mph gale at the top of a ridge, proper ballast is critical for good "penetration".
The added ballast does more than just damp turbulence with it's inertia. It moves the airfoil angle required for level flight to a more reasonable positive aoa and makes pilot inputs to that angle less important. With additional ballast the plane's weight is better matched to the lift and drag forces acting on the airframe.
I used the term while slope soaring. Launching into a constant 70 mph gale at the top of a ridge, proper ballast is critical for good "penetration".
11-03-2009, 08:58 PM
#44
RE: Penetration
It seems that high wing loading is good for wind penetration.
But I don’t believe so, or at least I don’t understand the physical reason.
I insist on that low drag is the key for good penetration.
Some birds have to glide thermals and penetrate wing, according to the circumstances.
How do they do it without adding ballast?
Modifying the area of their wings by extending o retracting them.
However, increasing the wing loading is a sub-product of reducing lift capacity and both types of drags.
A diving hawk has a tremendous penetration and diving speed, and it can also slow to zero in a few feet.
But I don’t believe so, or at least I don’t understand the physical reason.
I insist on that low drag is the key for good penetration.
Some birds have to glide thermals and penetrate wing, according to the circumstances.
How do they do it without adding ballast?
Modifying the area of their wings by extending o retracting them.
However, increasing the wing loading is a sub-product of reducing lift capacity and both types of drags.
A diving hawk has a tremendous penetration and diving speed, and it can also slow to zero in a few feet.
11-03-2009, 09:42 PM
#45
My Feedback: (15)
RE: Penetration
ORIGINAL: CrateCruncher
The added ballast does more than just damp turbulence with it's inertia. It moves the airfoil angle required for level flight to a more reasonable positive aoa and makes pilot inputs to that angle less important. With additional ballast the plane's weight is better matched to the lift and drag forces acting on the airframe.
The added ballast does more than just damp turbulence with it's inertia. It moves the airfoil angle required for level flight to a more reasonable positive aoa and makes pilot inputs to that angle less important. With additional ballast the plane's weight is better matched to the lift and drag forces acting on the airframe.
What is a "more reasonable positive aoa" and if it were more reasonable, why wouldn't you fly at that aoa all of the time? What do you mean by "and makes pilot inputs to that angle less important?" And "the plane's weight is better matched to the lift and drag forces acting on the airframe?" What are the physics and aerodynamic fundamentals behind your conclusions? I guess I have a very hard time discussing aerodynamics when someone uses such subjectives terms ("more reasonable," "less important," and "better matched"). Thanks!
Kurt
11-03-2009, 10:33 PM
#46
RE: Penetration
ORIGINAL: lnewqban
It seems that high wing loading is good for wind penetration.
But I don’t believe so, or at least I don’t understand the physical reason.
I insist on that low drag is the key for good penetration.
Some birds have to glide thermals and penetrate wing, according to the circumstances.
How do they do it without adding ballast?
Modifying the area of their wings by extending o retracting them.
However, increasing the wing loading is a sub-product of reducing lift capacity and both types of drags.
A diving hawk has a tremendous penetration and diving speed, and it can also slow to zero in a few feet.
It seems that high wing loading is good for wind penetration.
But I don’t believe so, or at least I don’t understand the physical reason.
I insist on that low drag is the key for good penetration.
Some birds have to glide thermals and penetrate wing, according to the circumstances.
How do they do it without adding ballast?
Modifying the area of their wings by extending o retracting them.
However, increasing the wing loading is a sub-product of reducing lift capacity and both types of drags.
A diving hawk has a tremendous penetration and diving speed, and it can also slow to zero in a few feet.
One of the things I remember living near the ocean was feeding seagulls from my outstretched hand. In a stiff breeze they could effortlessly hover by changing pitch and wing area. I assume they have much better piloting skills than the average biped but I remember that to "penetrate" or gain ground in wind they flapped their wings. When raptors tuck in a dive its to maximize speed so drag reduction is everything. Big scavengers split their air miles between soaring in uplifts and gliding to the next one. It's during the gliding part that they need good penetration. But they also have another trick planes can't pull off. Again, they can flap! Bird physiology and planes are so different that I have trouble comparing them on specifics like this.
11-03-2009, 10:55 PM
#47
RE: Penetration
ORIGINAL: Bozarth
What is a ''more reasonable positive aoa'' and if it were more reasonable, why wouldn't you fly at that aoa all of the time? What do you mean by ''and makes pilot inputs to that angle less important?'' And ''the plane's weight is better matched to the lift and drag forces acting on the airframe?'' What are the physics and aerodynamic fundamentals behind your conclusions? I guess I have a very hard time discussing aerodynamics when someone uses such subjectives terms (''more reasonable,'' ''less important,'' and ''better matched''). Thanks!
Kurt
ORIGINAL: CrateCruncher
The added ballast does more than just damp turbulence with it's inertia. It moves the airfoil angle required for level flight to a more reasonable positive aoa and makes pilot inputs to that angle less important. With additional ballast the plane's weight is better matched to the lift and drag forces acting on the airframe.
The added ballast does more than just damp turbulence with it's inertia. It moves the airfoil angle required for level flight to a more reasonable positive aoa and makes pilot inputs to that angle less important. With additional ballast the plane's weight is better matched to the lift and drag forces acting on the airframe.
What is a ''more reasonable positive aoa'' and if it were more reasonable, why wouldn't you fly at that aoa all of the time? What do you mean by ''and makes pilot inputs to that angle less important?'' And ''the plane's weight is better matched to the lift and drag forces acting on the airframe?'' What are the physics and aerodynamic fundamentals behind your conclusions? I guess I have a very hard time discussing aerodynamics when someone uses such subjectives terms (''more reasonable,'' ''less important,'' and ''better matched''). Thanks!
Kurt
Either you get it with what I said or you never will. Showing pitch sensitivity in the lift equation is going to put everyone to sleep and probably confuse things more.
11-03-2009, 11:05 PM
#48
My Feedback: (15)
RE: Penetration
[/quote]
Bozarth,
Either you get it with what I said or you never will. Showing pitch sensitivity in the lift equation is going to put everyone to sleep and probably confuse things more.
[/quote]
It's "Kurt." I get the lift equation, and always have. I don't get your use of the phrase "pitch sensitivity" in regards to it. I would think those reading this forum would enjoy the explaination/discussion.
Kurt
Bozarth,
Either you get it with what I said or you never will. Showing pitch sensitivity in the lift equation is going to put everyone to sleep and probably confuse things more.
[/quote]
It's "Kurt." I get the lift equation, and always have. I don't get your use of the phrase "pitch sensitivity" in regards to it. I would think those reading this forum would enjoy the explaination/discussion.
Kurt
11-04-2009, 01:35 PM
#49
RE: Penetration
A pilot of a very light (1/2 pound) electric plane is flying in calm conditions at 40 mph
ground speed. A front rolls in changing the conditions to a headwind of 20 mph and a 60 mph
airspeed required to maintain the same ground speed. (1) What is the effect on AOA due to change
in speed AND an added ballast of 3/4 pound? (2) How is control sensitivity effected by the
change in weight at the higher airspeed?
weight(mg)= 0.5 lbm (slugsft/s^2) weird units huh?
wing area= 1.29 ft^2
V1 = 40 mph(58.7 ft/s)
V2 = 60 mph(88.0 ft/s)
airfoil: naca 0006 (cl/AOA data from Abbott, pg.452)
air density (R) = .002378 slug/ft^3
1) Starting with the equilibrium between weight and lift we have:
weight = 0.5*(air density)*(velocity squared)*(wing area)*(lift coefficient)
or
mg = .5R(V^2)S(Cl)
Rearranging terms to get Cl:
Cl = (2mg)/[R(V^2)S]
Airspeed w/o ballast(.5) w/ballast(1.25)
Cl AOA(deg) Cl AOA(deg)
40mph 0.10 1.0 0.24 2.5
60mph 0.04 0.2 0.11 1.0
Notice the AOA of the plane without ballast is very close to zero at the higher airspeed while
the ballasted plane restores the AOA for level flight back to one degree.
2) Sensitivity of +/- 0.5 degree change in AOA at 60mph:
Weight AOA Cl Net Force(Fr) Fr/W*100(%)
0.5lbm +.7/-.3 +.1/-.05 +.7/-1.1 +140/-220
1.25lbm +1.5/+.05 +.2/+.05 +2.4/+.6 +92/-52
Pitching the plane half a degree has a dramatic effect on the plane without ballast. In the last
column the unbalanced reaction force is divided by the total weight of the plane. The
unballasted plane is virtually uncontrollable.
ground speed. A front rolls in changing the conditions to a headwind of 20 mph and a 60 mph
airspeed required to maintain the same ground speed. (1) What is the effect on AOA due to change
in speed AND an added ballast of 3/4 pound? (2) How is control sensitivity effected by the
change in weight at the higher airspeed?
weight(mg)= 0.5 lbm (slugsft/s^2) weird units huh?
wing area= 1.29 ft^2
V1 = 40 mph(58.7 ft/s)
V2 = 60 mph(88.0 ft/s)
airfoil: naca 0006 (cl/AOA data from Abbott, pg.452)
air density (R) = .002378 slug/ft^3
1) Starting with the equilibrium between weight and lift we have:
weight = 0.5*(air density)*(velocity squared)*(wing area)*(lift coefficient)
or
mg = .5R(V^2)S(Cl)
Rearranging terms to get Cl:
Cl = (2mg)/[R(V^2)S]
Airspeed w/o ballast(.5) w/ballast(1.25)
Cl AOA(deg) Cl AOA(deg)
40mph 0.10 1.0 0.24 2.5
60mph 0.04 0.2 0.11 1.0
Notice the AOA of the plane without ballast is very close to zero at the higher airspeed while
the ballasted plane restores the AOA for level flight back to one degree.
2) Sensitivity of +/- 0.5 degree change in AOA at 60mph:
Weight AOA Cl Net Force(Fr) Fr/W*100(%)
0.5lbm +.7/-.3 +.1/-.05 +.7/-1.1 +140/-220
1.25lbm +1.5/+.05 +.2/+.05 +2.4/+.6 +92/-52
Pitching the plane half a degree has a dramatic effect on the plane without ballast. In the last
column the unbalanced reaction force is divided by the total weight of the plane. The
unballasted plane is virtually uncontrollable.
11-04-2009, 02:00 PM
#50
RE: Penetration
Not to blow a hole in all the nice math How much actual flying have you done with small light models
To put a fine point on it
-here is what really happens-
the lighter model is stil lthe best
Why?
because you can more easily accelerate it and retain positioning .
I went thru all this on pattern models many years back- the light stuff wit throttle control again the best
the sensitivity /uncontrollability -I just can't buy- done too much flying of these types
-If the power is correct you simply add power when needed to overcome a upset
IF-you are trying to fly a 20 mph plane in a 20 mph gusty winds - you are sunk -for openers -Nothing works
Heavy models suck- unless you are flying slope and using wind/gravity for power.
To put a fine point on it
-here is what really happens-
the lighter model is stil lthe best
Why?
because you can more easily accelerate it and retain positioning .
I went thru all this on pattern models many years back- the light stuff wit throttle control again the best
the sensitivity /uncontrollability -I just can't buy- done too much flying of these types
-If the power is correct you simply add power when needed to overcome a upset
IF-you are trying to fly a 20 mph plane in a 20 mph gusty winds - you are sunk -for openers -Nothing works
Heavy models suck- unless you are flying slope and using wind/gravity for power.
