Should wide,flat trailing edge be included in Chord?
08-28-2004, 10:33 AM
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Should wide,flat trailing edge be included in Chord?
I know most of you guys on this section aren't into SPADs but you could probably answer my question.
When a typical SPAD- FLAT BOTTOMED wing is built using 2mm corrugated plastic board, the trailing edge is formed by gluing the top layer to the bottom layer. This produces a flat spot about 2" wide and 4mm thick onto which the aileron is glued to the last 1" of this wide Trailing Edge. The aileron is say 1 1/2" wide. Therefore, the whole trailing edge width is now about 1" plus 1 1/2" = 2" wide and is flat.
On a typical Balsa FLAT BOTTOM wing, the aileron is actually an integral part of the airfoil shape as it is wedge shaped and built into the wing, not an added on piece to the TE.
Question: Would such a wide flat TE have little lift of it's own?
If it does not , then could I deduct at least part of the TE width from the Chord width?
It seems to me that the reason for including Ailerons in the Chord width is since they usually form part of the airfoil shape and hence produce part of the overall lift of the wing. Including the Aileron dimensions then is necessary to calculate wing loading.
In my SPAD wing scenario, if the aileron and part of the TE are really not producing much lift, why should I include them in the Chord to determine Wing Loading? They may not be really lifting much, if any, weight to begin with.
Matt Bourdeau
When a typical SPAD- FLAT BOTTOMED wing is built using 2mm corrugated plastic board, the trailing edge is formed by gluing the top layer to the bottom layer. This produces a flat spot about 2" wide and 4mm thick onto which the aileron is glued to the last 1" of this wide Trailing Edge. The aileron is say 1 1/2" wide. Therefore, the whole trailing edge width is now about 1" plus 1 1/2" = 2" wide and is flat.
On a typical Balsa FLAT BOTTOM wing, the aileron is actually an integral part of the airfoil shape as it is wedge shaped and built into the wing, not an added on piece to the TE.
Question: Would such a wide flat TE have little lift of it's own?
If it does not , then could I deduct at least part of the TE width from the Chord width?
It seems to me that the reason for including Ailerons in the Chord width is since they usually form part of the airfoil shape and hence produce part of the overall lift of the wing. Including the Aileron dimensions then is necessary to calculate wing loading.
In my SPAD wing scenario, if the aileron and part of the TE are really not producing much lift, why should I include them in the Chord to determine Wing Loading? They may not be really lifting much, if any, weight to begin with.
Matt Bourdeau
08-28-2004, 11:29 AM
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RE: Should wide,flat trailing edge be included in Chord?
Interesting question..
Considering that all-wing planes are less efficient relative to the same sized "normal" plane, not using some of the area to compute loading might make sense, IF we knew the percentage difference in effectiveness between an all-wing and the normal type.
We don't, so the wing loading is computed using all the planform area.
When the numbers are crunched, it's understood an all-wing will be less efficient.
Considering that all-wing planes are less efficient relative to the same sized "normal" plane, not using some of the area to compute loading might make sense, IF we knew the percentage difference in effectiveness between an all-wing and the normal type.
We don't, so the wing loading is computed using all the planform area.
When the numbers are crunched, it's understood an all-wing will be less efficient.
08-28-2004, 12:49 PM
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RE: Should wide,flat trailing edge be included in Chord?
Tall Paul, when you say"all wing" plane are you referring to a Flying Wing? The plane I am discussing is a Balsa Trainer fuselage with a Spad, Dihedral flat bottomed wing. Length 65" with chord of 14" including 2" ailerons.
08-28-2004, 01:05 PM
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RE: Should wide,flat trailing edge be included in Chord?
If it's there then it's included. You may not think it's part of the EFFECTIVE wing but it is. It still contributes and enhances the airflow over the forward part of the wing. If you can look down on the model and see the surface area then it counts... all of it.
The efficiency of the airfoil is another whole issue. THIS is where you take all the oddities into consideration, not the area. The odd shape will probably affect the lift coefficient the airfoil is capable of attaining depending on the overall shape. The typical SPAD type flat bottomed shape with flat trailing edge and aileron is much like a reflexed type airfoil. The reflex portion helps you fly the model inverted easier but it will limit the maximum lift you get from the airfoil. But at the same time it helps the model to fly faster. Now if you reversed the trend and glued the lower surface to the upper surface such that the trailing edge and aileron drooped downwards in line with the upper surface then the camber % would be increased, the maximum lift coefficient attainable would rise greatly and you could fly a LOT slower before stalling. However the max flying speed would go down due to the extra drag.
But you would still say you had the same wing area.
That help?
The efficiency of the airfoil is another whole issue. THIS is where you take all the oddities into consideration, not the area. The odd shape will probably affect the lift coefficient the airfoil is capable of attaining depending on the overall shape. The typical SPAD type flat bottomed shape with flat trailing edge and aileron is much like a reflexed type airfoil. The reflex portion helps you fly the model inverted easier but it will limit the maximum lift you get from the airfoil. But at the same time it helps the model to fly faster. Now if you reversed the trend and glued the lower surface to the upper surface such that the trailing edge and aileron drooped downwards in line with the upper surface then the camber % would be increased, the maximum lift coefficient attainable would rise greatly and you could fly a LOT slower before stalling. However the max flying speed would go down due to the extra drag.
But you would still say you had the same wing area.
That help?
08-28-2004, 01:12 PM
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RE: Should wide,flat trailing edge be included in Chord?
"all-wing" is no horizontal tail.
It can have a fuselage, either rudimentary, or like the lower image, the fuselage is per kit, the horizontal sawed off at the roots.
It can have a fuselage, either rudimentary, or like the lower image, the fuselage is per kit, the horizontal sawed off at the roots.
08-28-2004, 01:27 PM
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RE: Should wide,flat trailing edge be included in Chord?
BMatthews, that sounds interesting to me to glue the lower panel to the top one. Would I keep the ailerons drooping in line with the downward angle of the top panel?
Would you think this would be a better performing wing for a Trainer as opposed to the one with the top panel glued to bottom?
Also, that reflexed undercambered section causes more drag than a flat bottom right"
Matt
Would you think this would be a better performing wing for a Trainer as opposed to the one with the top panel glued to bottom?
Also, that reflexed undercambered section causes more drag than a flat bottom right"
Matt
08-28-2004, 01:55 PM
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RE: Should wide,flat trailing edge be included in Chord?
Yep, that's right. It'll be the first ever slowfly SPAD... 
If you look at it this way it's sort of like having flaps deployed all the time. Or using one of the "old timer" undercambered wing sections. In fact it'll look a lot like this Jedelsky section from Profili2. These were used on a lot of the all balsa designs from a couple of decades ago before corrugated plastic was invented. The model will fly slower, will require a slightly larger horizontal stabilizer and if you use ailerons then be sure to use extreme differential so the one side moves up a lot more and quicker than the other side moves down to avoid the often nasty adverse yaw effect that comes with highly cambered airfoils. Or you can mix in some rudder so the ailerons and rudder are coupled to move together.
Low, slow and super close in would be the name of the game with one like this. Perhaps even a powered glider SPAD? Cropdusting? Nap of the earth flying?
If you look at it this way it's sort of like having flaps deployed all the time. Or using one of the "old timer" undercambered wing sections. In fact it'll look a lot like this Jedelsky section from Profili2. These were used on a lot of the all balsa designs from a couple of decades ago before corrugated plastic was invented. The model will fly slower, will require a slightly larger horizontal stabilizer and if you use ailerons then be sure to use extreme differential so the one side moves up a lot more and quicker than the other side moves down to avoid the often nasty adverse yaw effect that comes with highly cambered airfoils. Or you can mix in some rudder so the ailerons and rudder are coupled to move together.
Low, slow and super close in would be the name of the game with one like this. Perhaps even a powered glider SPAD? Cropdusting? Nap of the earth flying?
08-29-2004, 02:00 AM
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RE: Should wide,flat trailing edge be included in Chord?
mattbeme,
I think you might get in to real problems with the dropping rons...once the plane has any speed up they tend to dart and tuck wildly (that's been my experince anyway....I don't have a real good handle on dynamic stability but I do know that I've had some real control issue with very cambered foils).....If you fly very slow then it might work....or like BMatthew said increase the tail size...or if you limit it to a small section inboard on the wing(inboard flaps). I think a slightly undercamber foil with reflexed rons is going to give you the slowest flying plane and the best all round proformance for a trainer. I don't remember the article but I have seen some data that suggest that slightly undercambered reflex foils generate more lift and less drag than the same foil not reflexed....I have build a few spad undercambered wings that actually flew slower with reflexed rons. I think the thickest point on the wing was at about 20 percent rather than 25 percent. But all that being said, the Nice thing about SPAD is you can try it out pretty easy and cheaply and see if it works.
Some other things you might look at to reduce speed are, reducing wingloading, or increasing span but each change may create other problems.
Happy Flying!!!!
Steve
I think you might get in to real problems with the dropping rons...once the plane has any speed up they tend to dart and tuck wildly (that's been my experince anyway....I don't have a real good handle on dynamic stability but I do know that I've had some real control issue with very cambered foils).....If you fly very slow then it might work....or like BMatthew said increase the tail size...or if you limit it to a small section inboard on the wing(inboard flaps). I think a slightly undercamber foil with reflexed rons is going to give you the slowest flying plane and the best all round proformance for a trainer. I don't remember the article but I have seen some data that suggest that slightly undercambered reflex foils generate more lift and less drag than the same foil not reflexed....I have build a few spad undercambered wings that actually flew slower with reflexed rons. I think the thickest point on the wing was at about 20 percent rather than 25 percent. But all that being said, the Nice thing about SPAD is you can try it out pretty easy and cheaply and see if it works.
Some other things you might look at to reduce speed are, reducing wingloading, or increasing span but each change may create other problems.
Happy Flying!!!!
Steve
