C172 aileron design
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C172 aileron design
Hi everyone
In brushing up on general knowledge of the C172, I've seen written many times that the ailerons, whilst described by the AFM as conventional are in fact of both differential and Frise type.
Having found a maintenance manual I had a look for information with respect to how they're rigged, but couldn't find anything pertaining to whether or not they're differential. Does anyone know of any approved documentation in which this is mentioned (I may well have just overlooked it in the AMM, I only gave it a quick scan)?
As for whether or not they're of Frise type, I'm not sure. At least by my understanding of what constitutes a Frise aileron, they're not though. The axis of the hinge is forward of the upper leading edge, however the lower leading edge does protrude slightly forward of this. It would seem to me, having had a look at an aircraft today, that the extent to which the leading edge travels down when the trailing edge moves up is so small as to almost be negligible.
Having had a look for a clear definition of a Frise aileron, the best I could find was a section from a textbook (Airplane Stability and Control, Second edition), which starts as follows [https://books.google.co.nz/books?id=...ge&q&f=false]:
"The hinge line of the Frise aileron, invented by Leslie George Frise, is always at or below the wing’s lower surface. If one sees aileron hinge brackets below the wing, chances are that one is looking at a Frise aileron."
My own principles of flight textbook, PadPilot, says:
"Frise ailerons. The leading edge of the aileron is asymmetrically shaped and set in front of the hinge. The edge is so designed that when the aileron is deflected upwards its leading edge protrudes into the airstream to increase form drag..."
By my interpretation of the former, the Skyhawk does not have Frise ailerons, but the latter would seem to suggest it does. Is there perhaps an 'official' definition of a Frise aileron published by NACA or even Leslie Frise himself? Perhaps most likely of all, am I missing something fundamental here and is my interpretation is just plain wrong?
In brushing up on general knowledge of the C172, I've seen written many times that the ailerons, whilst described by the AFM as conventional are in fact of both differential and Frise type.
Having found a maintenance manual I had a look for information with respect to how they're rigged, but couldn't find anything pertaining to whether or not they're differential. Does anyone know of any approved documentation in which this is mentioned (I may well have just overlooked it in the AMM, I only gave it a quick scan)?
As for whether or not they're of Frise type, I'm not sure. At least by my understanding of what constitutes a Frise aileron, they're not though. The axis of the hinge is forward of the upper leading edge, however the lower leading edge does protrude slightly forward of this. It would seem to me, having had a look at an aircraft today, that the extent to which the leading edge travels down when the trailing edge moves up is so small as to almost be negligible.
Having had a look for a clear definition of a Frise aileron, the best I could find was a section from a textbook (Airplane Stability and Control, Second edition), which starts as follows [https://books.google.co.nz/books?id=...ge&q&f=false]:
"The hinge line of the Frise aileron, invented by Leslie George Frise, is always at or below the wing’s lower surface. If one sees aileron hinge brackets below the wing, chances are that one is looking at a Frise aileron."
My own principles of flight textbook, PadPilot, says:
"Frise ailerons. The leading edge of the aileron is asymmetrically shaped and set in front of the hinge. The edge is so designed that when the aileron is deflected upwards its leading edge protrudes into the airstream to increase form drag..."
By my interpretation of the former, the Skyhawk does not have Frise ailerons, but the latter would seem to suggest it does. Is there perhaps an 'official' definition of a Frise aileron published by NACA or even Leslie Frise himself? Perhaps most likely of all, am I missing something fundamental here and is my interpretation is just plain wrong?
As to Frise aileron - Frise's design is a very specific geometry to achieve a protrusion of the aileron's lower edge below the wing to add drag when the airleron is up, and minimize adverse yaw.
This would be Frise's classic design, with pivot point well back (~25% chord), and near the lower wing surface:
http://accrodavion.be/Accrodavions/i...on%20frise.gif
However, there are other geometries that can achieve the same thing (leading edge dropping below the wing for drag with up aileron) - even with the hinge near the top. This geometry looks - schematically - a bit more like what the 172 actually has:
http://aeronotes.weebly.com/uploads/...457099.jpg?243
It gets to be a matter of semantics as to whether "Frise aileron" and "Frise-type aileron" mean the same thing or different things that achieve similar ends. I'd say the 172's ailerons are clearly not authentic "Frise ailerons", but may impart some (non-zero, even if negligible) drag when up, to balance the induced drag from lift on the other side.
Technically - this is a C-150 aileron:
http://www.cessna150.net/Assets/Phot...on_weights.JPG
As to differential, again it is a question of naming techniques - or outcomes.
The sloped leading edge of the Cessna aileron:
http://hangarswap.com/image/data/Han...8/IMG_0384.JPG
means that the top chord is an inch or two shorter than the bottom chord. So even if the deflection in degrees is the same up or down (about which I know not), the "up" aileron will present a slighty smaller surface area (chord x span) than when "down". Thus achieving differential aerodynamic effect without differential deflection.
Been a while since I flew a 172 - can't remember how much adverse yaw it demonstrated.
This would be Frise's classic design, with pivot point well back (~25% chord), and near the lower wing surface:
http://accrodavion.be/Accrodavions/i...on%20frise.gif
However, there are other geometries that can achieve the same thing (leading edge dropping below the wing for drag with up aileron) - even with the hinge near the top. This geometry looks - schematically - a bit more like what the 172 actually has:
http://aeronotes.weebly.com/uploads/...457099.jpg?243
It gets to be a matter of semantics as to whether "Frise aileron" and "Frise-type aileron" mean the same thing or different things that achieve similar ends. I'd say the 172's ailerons are clearly not authentic "Frise ailerons", but may impart some (non-zero, even if negligible) drag when up, to balance the induced drag from lift on the other side.
Technically - this is a C-150 aileron:
http://www.cessna150.net/Assets/Phot...on_weights.JPG
As to differential, again it is a question of naming techniques - or outcomes.
The sloped leading edge of the Cessna aileron:
http://hangarswap.com/image/data/Han...8/IMG_0384.JPG
means that the top chord is an inch or two shorter than the bottom chord. So even if the deflection in degrees is the same up or down (about which I know not), the "up" aileron will present a slighty smaller surface area (chord x span) than when "down". Thus achieving differential aerodynamic effect without differential deflection.
Been a while since I flew a 172 - can't remember how much adverse yaw it demonstrated.
Does it matter at all that the Cessna172 is an entry level single? Putting the hinge in the center of the wing's chord would be expensive. That there is a gap on the bottom between wing and aileron is unavoidable, else the aileron would not articulate "down". As I recall, the aileron is affixed with "butt" surface mounted hinges with a pin that is retained by crimping the hinge barrel. A cheaper manufacture can not be envisaged, are we over thinking this?
Weight and money, the enemy of every Aero design?
Weight and money, the enemy of every Aero design?
The Frise discussion is interesting, but doesn't appear applicable to the C-172. The 172 ailerons are of the "differential" type. See the rigging specs for the ailerons in the service manual or TCDS.
See TCDS 3A12. (C-172) For a C-172M (early '70s) model, the specified aileron displacement is 20 degrees up and 15 degrees down. It's bit difficult to explain in words how the amount of differential is controlled, but suffice it to say that when the bellcrank that connects the aileron control rod to the direct and and crossover cables is positioned correctly, the amount of differential travel will be correct if the rigging instructions are adhered to.
As is the case with Frise type ailerons, the differential travel is intended to reduce the amount of adverse yaw induced by aileron deflection. At higher AOA there is just enough adverse yaw to remind one of the need for rudder for proper coordination. I personally find either of these designs preferable to an aileron/rudder interconnect bungee. Especially when landing in a crosswind!
And yes, the "piano-hinge" at the upper surface is a relatively simple and inexpensive method of attachment which seems to work good and last a long time, even if they do require some mx attention. They used it on the elevator trim tabs too. The angled forward surface of the aileron is what allows downward deflection of the surface. Interesting that Cessna decided to go with an elegant single slotted Fowler flap on the 172 rather than a simpler and cheaper plain flap design isn't it?
Anyone ever hit their forehead in the trailing edge of the aileron and imprint themselves with a bloody diamond? If so, you are automatically eligible to be a member of the Cessna-head dummkopf club. I've been a member for over 30 years...
Long live the mighty Skyhawk!
See TCDS 3A12. (C-172) For a C-172M (early '70s) model, the specified aileron displacement is 20 degrees up and 15 degrees down. It's bit difficult to explain in words how the amount of differential is controlled, but suffice it to say that when the bellcrank that connects the aileron control rod to the direct and and crossover cables is positioned correctly, the amount of differential travel will be correct if the rigging instructions are adhered to.
As is the case with Frise type ailerons, the differential travel is intended to reduce the amount of adverse yaw induced by aileron deflection. At higher AOA there is just enough adverse yaw to remind one of the need for rudder for proper coordination. I personally find either of these designs preferable to an aileron/rudder interconnect bungee. Especially when landing in a crosswind!
And yes, the "piano-hinge" at the upper surface is a relatively simple and inexpensive method of attachment which seems to work good and last a long time, even if they do require some mx attention. They used it on the elevator trim tabs too. The angled forward surface of the aileron is what allows downward deflection of the surface. Interesting that Cessna decided to go with an elegant single slotted Fowler flap on the 172 rather than a simpler and cheaper plain flap design isn't it?
Anyone ever hit their forehead in the trailing edge of the aileron and imprint themselves with a bloody diamond? If so, you are automatically eligible to be a member of the Cessna-head dummkopf club. I've been a member for over 30 years...
Long live the mighty Skyhawk!
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With the various definitions floating around It's a bit difficult to put a finger on what exactly constitutes a Frise aileron. My understanding has always been that one element of a Frise aileron is that when the aileron is deflected down (on the rising wing) that some airflow is directed from the underside of the wing to the top surface of the aileron, much like when a slotted trailing edge flap is extended. I don't think that happens on a 172 aileron, so it wouldn't be a Frise aileron in that regard. The ailerons on the 206, however are. they are more of an airfoil cross-section, and they are hinged at pivot points well back of the aileron chord vs the piano hinge of the 100 series Cessna ailerons.
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The sloped lower leading edge aileron spar is forward of the hinge line and gets around the need for a horn on the end of the aileron, as the weight is riveted to the lower edge to balance the aileron and hence forward of the hinge line.
The hinge pin isn't crimped, the early ones had a small split pin in at the end that caused cracking, later hinge pins extend out one end, come back around and have a loop in them and is secured by one of the hinge mounting screws and nut.
The hinge pin isn't crimped, the early ones had a small split pin in at the end that caused cracking, later hinge pins extend out one end, come back around and have a loop in them and is secured by one of the hinge mounting screws and nut.
My understanding has always been that one element of a Frise aileron is that when the aileron is deflected down (on the rising wing) that some airflow is directed from the underside of the wing to the top surface of the aileron, much like when a slotted trailing edge flap is extended.
In addition, the hinge point placement well aft of the aileron leading edge means that the Frise type aileron L/E will deflect downward into the relative wind when the trailing edge is deflected upward. Conversely, the leading edge is hidden in the wing T/E recess when the aileron T/E is deflected downward.
With a "normal" (non-Frise type) aileron, the wing with the upward deflecting aileron produces less total drag than the downward deflected aileron on the opposite wing. Both the Frise and differential deflection aileron arrangement are solutions intended to "recover" some of this lost drag in order to reduce the difference in the amount of drag being produced by each wing. (adverse yaw) In that way, less rudder displacement will be required in order to maintain a neutral slip/skid condition when the ailerons are deflected. Additionally, the control force required will be reduced in roll. The airplane is "easier" to fly if it produces less adverse yaw. While airplanes so equipped can't make a chump fly like a champ, they can help the passengers to maintain control over the disposition of their lunch! Every little bit helps I suppose.
If it's just for fun I'd rather fly a Cub.
With the various definitions floating around It's a bit difficult to put a finger on what exactly constitutes a Frise aileron. My understanding has always been that one element of a Frise aileron is that when the aileron is deflected down (on the rising wing) that some airflow is directed from the underside of the wing to the top surface of the aileron, much like when a slotted trailing edge flap is extended. I don't think that happens on a 172 aileron, so it wouldn't be a Frise aileron in that regard. The ailerons on the 206, however are. they are more of an airfoil cross-section, and they are hinged at pivot points well back of the aileron chord vs the piano hinge of the 100 series Cessna ailerons.
Put even more simply, if an aileron has a piano-type hinge like the Cessna 172's, then by definition it can't be a Frise type as there's no path for the airflow around the leading edge.
There is no requirement in a Frise (or Frise-type) aileron for a slot at the aileron leading edge. The only essential feature is that the upward deflecting aileron leading edge projects downward into the lower wing surface airflow, countering the induced drag from the wing with the downward deflected aileron (and thus opposing adverse yaw). Frise described one geometry that achieved this simply.
The precise shape of the leading edge is important since it is easy to achieve negative aileron force (aileron snatching) particularly at high alpha (low speed), although this effect can also be used to give low aileron operating loads.
All Elliots sailplanes had Frise ailerons, and the chief engineer (one Jim Cramp) used to adjust a section of the aileron leading edge wooden fairing until the test pilot was satisfied with the handling. No doubt in the 21st Century this would be achieved by CFD before the first test flight.
The precise shape of the leading edge is important since it is easy to achieve negative aileron force (aileron snatching) particularly at high alpha (low speed), although this effect can also be used to give low aileron operating loads.
All Elliots sailplanes had Frise ailerons, and the chief engineer (one Jim Cramp) used to adjust a section of the aileron leading edge wooden fairing until the test pilot was satisfied with the handling. No doubt in the 21st Century this would be achieved by CFD before the first test flight.
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You can clearly see that the leading edge of the upward-moving aileron is sharp and deflects down into the airflow, creating drag when applied. It works as a Frise aileron would work, and I would accept the definition "Frise Type" if it was not a true Frise design.
Hi.. " ...piano-type hinge like the Cessna 172's, then by definition it can't be a Frise type as there's no path for the airflow around the leading edge." From Dave Reid
The drag is created "passively". No "drag" when the aileron deflects down....
Whether or not a design feature, the "Frise type" action mimics a full length "spade".
So, a rose by another name? The fundamental foundation in design is the "consideration".
The Wrights used wing warping, not entirely a primitive design? There is a program at Edwards which flies an FA18 with warping wings to establish roll. Really.
The drag is created "passively". No "drag" when the aileron deflects down....
Whether or not a design feature, the "Frise type" action mimics a full length "spade".
So, a rose by another name? The fundamental foundation in design is the "consideration".
The Wrights used wing warping, not entirely a primitive design? There is a program at Edwards which flies an FA18 with warping wings to establish roll. Really.
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A Cessna 152 aileron forward lower leading edge ( that is the same design style as a 172 ) does indeed drop down about half an inch into the airflow when the aileron is deflected fully up.
But not when moved down.....
The geometry moves the lower leading edge into the opening between aileron and wing when the aileron moves downward. The lower leading edge is forward of the hinge axis, any movement of the aileron "down" moves it "upward" following the arc of the described radius?
The geometry moves the lower leading edge into the opening between aileron and wing when the aileron moves downward. The lower leading edge is forward of the hinge axis, any movement of the aileron "down" moves it "upward" following the arc of the described radius?
