Edge 540 and precision
10-20-2004, 12:39 PM
#1
Edge 540 and precision
George,
Congrats and thanks for doing this forum. Your help is great for us mortals.
I am just curious as to why model versions of the Edge get such a bad rap for precision. Do you think it is something that doesn't scale down well, i.e. the straight leading edge or is it the current available designs? As you know, I am a little partial to the Edge.
I know you have flown a number of different Edge design and am curious as to which one you feel is best at precision. Are there mods you have in mind that might help?
Obviously with Kirby Chambliss winning his 3rd straight national title, the full scale Edge does well with the precision stuff.
Thanks,
Dan Bierly
Congrats and thanks for doing this forum. Your help is great for us mortals.
I am just curious as to why model versions of the Edge get such a bad rap for precision. Do you think it is something that doesn't scale down well, i.e. the straight leading edge or is it the current available designs? As you know, I am a little partial to the Edge.
I know you have flown a number of different Edge design and am curious as to which one you feel is best at precision. Are there mods you have in mind that might help? Obviously with Kirby Chambliss winning his 3rd straight national title, the full scale Edge does well with the precision stuff.
Thanks,
Dan Bierly
10-20-2004, 02:39 PM
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RE: Edge 540 and precision
Hi Dan,
Great to hear from you...I was glad to see you flying in the SC Regional Championships.
My intention here is certainly not to open up a can of worms about the Edge 540 but rather to explain what myself and other R/C pilots have discovered by competing with the airplane. Obviously the airplane is well liked amongst the lower classes in IMAC (Basic-Intermediate and some Advanced pilots too) and especially liked by the giant scale 3-D pilots. My feeling after flying both the Aeroworks and Carden 40% Edge 540's (I actually owned a Carden and got 65 flights on it before it crashed due to an severe interference lockout...but that's another story) is that the Carden is the better airplane for reasons we'll get into a little later.
As you well know very few, if any, top-level Unlimited class precision pilots fly this design because of the rolling characteristics. Having said that I don't think the airplane's problems stem from the way it rolls but rather the rudders ability to direct the nose of the aircraft at various angles of attack and angles of sideslip. I believe that if one were to measure the side-force and yawing moment as a function of sideslip, alpha, and rudder deflection one would find some very non-linear characteristics. I think that these traits make it more difficult to perform precision rolling maneuvers with the Edge. I know that when I had my Carden Edge that I had to relearn how to roll the airplane. My pitch and roll mix curves were totally different than setups that I'd used on other designs, which in itself is not a bad thing. The reality of it was that while rolling the Edge 540 it seemed almost like a very steep cliff that you would fall off of any time if you had too much rudder or sideslip on the airplane...the non-linearity with the Aeroworks that I'd flown seemed much more severe than with the Carden. The rapid changes in characteristics are what cause pilots trouble. How Bill Hempel was able to fly his Edge as well as he did is beyond me...he is obviously a fantastic pilot and great pilots can almost always make up for design deficiencies. Nevertheless I still believe that there is a directional control/side-force problem inherent to that design which I do not fully understand nor have I taken the time to explore. I personally found 4-point rolls to be difficult to replicate with the Edge...it was a hit or miss situation for me. I remember cringing if the unknown had two consecutive 4-point rolls in a sequence. Any other time this would be a maneuver that was a piece of cake. Certain parts of 8-point rolls were difficult too...while passing from inverted to the first 45 degree point I'd often have to hold a touch of up elevator to keep the airplane on line...this was very strange to me.
Having said all these things I'd like to point out that the Edge was always rock solid in pitch...it drew lines as good or better than any design I've flown and that's what makes it a favorite amongst the lower classes. It's easy to fly in that respect. The forward swept 1/4 chord really makes the stall characteristics forgiving and the newer pilots love this. The Edge design certainly has it's place in model aviation.
I hope this helps,
George
Great to hear from you...I was glad to see you flying in the SC Regional Championships.
My intention here is certainly not to open up a can of worms about the Edge 540 but rather to explain what myself and other R/C pilots have discovered by competing with the airplane. Obviously the airplane is well liked amongst the lower classes in IMAC (Basic-Intermediate and some Advanced pilots too) and especially liked by the giant scale 3-D pilots. My feeling after flying both the Aeroworks and Carden 40% Edge 540's (I actually owned a Carden and got 65 flights on it before it crashed due to an severe interference lockout...but that's another story) is that the Carden is the better airplane for reasons we'll get into a little later.
As you well know very few, if any, top-level Unlimited class precision pilots fly this design because of the rolling characteristics. Having said that I don't think the airplane's problems stem from the way it rolls but rather the rudders ability to direct the nose of the aircraft at various angles of attack and angles of sideslip. I believe that if one were to measure the side-force and yawing moment as a function of sideslip, alpha, and rudder deflection one would find some very non-linear characteristics. I think that these traits make it more difficult to perform precision rolling maneuvers with the Edge. I know that when I had my Carden Edge that I had to relearn how to roll the airplane. My pitch and roll mix curves were totally different than setups that I'd used on other designs, which in itself is not a bad thing. The reality of it was that while rolling the Edge 540 it seemed almost like a very steep cliff that you would fall off of any time if you had too much rudder or sideslip on the airplane...the non-linearity with the Aeroworks that I'd flown seemed much more severe than with the Carden. The rapid changes in characteristics are what cause pilots trouble. How Bill Hempel was able to fly his Edge as well as he did is beyond me...he is obviously a fantastic pilot and great pilots can almost always make up for design deficiencies. Nevertheless I still believe that there is a directional control/side-force problem inherent to that design which I do not fully understand nor have I taken the time to explore. I personally found 4-point rolls to be difficult to replicate with the Edge...it was a hit or miss situation for me. I remember cringing if the unknown had two consecutive 4-point rolls in a sequence. Any other time this would be a maneuver that was a piece of cake. Certain parts of 8-point rolls were difficult too...while passing from inverted to the first 45 degree point I'd often have to hold a touch of up elevator to keep the airplane on line...this was very strange to me.
Having said all these things I'd like to point out that the Edge was always rock solid in pitch...it drew lines as good or better than any design I've flown and that's what makes it a favorite amongst the lower classes. It's easy to fly in that respect. The forward swept 1/4 chord really makes the stall characteristics forgiving and the newer pilots love this. The Edge design certainly has it's place in model aviation.
I hope this helps,
George
10-20-2004, 04:06 PM
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RE: Edge 540 and precision
ORIGINAL: GRH
Having said all these things I'd like to point out that the Edge was always rock solid in pitch...it drew lines as good or better than any design I've flown and that's what makes it a favorite amongst the lower classes.
Having said all these things I'd like to point out that the Edge was always rock solid in pitch...it drew lines as good or better than any design I've flown and that's what makes it a favorite amongst the lower classes.
Could you comment on how the tail volume coefficient plays into that? I remember when I calculated the horizontal tail volume coefficient (Vht) for the Carden Edge and Extra, the Extra had a significantly higher Vht. I don't remember the numbers exactly, but I seem to remember around .54 vs .64 or so... And the vonExtra 260 had an even higher Vht at around .69 or so...
I look forward to your response
Baron
10-20-2004, 04:52 PM
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RE: Edge 540 and precision
Hi Baron...it's great to hear from you.
For those who don't know the term VHt that Baron's referring too, it is simply a number that gives the designer or engineer an idea of how big the horizontal tail is and how far away from the wing the tail is.
VH= (St/S) * (Lt/C)
where:
St = horizontal tail planform area
S=wing planform area
Lt=distance between the aerodynamic centers of the wing and horizontal tail
C=mean aerodynamic chord of the wing.
St/S is typically 25% saying that the tail is 25% of the wing area in size and a good number for Lt/C is 2 saying that the horizontal tail's aerodynamic center is roughly 2 mean aerodynamic chords away from the wing's aerodynamic center.
The tail volume coefficient is useful because it simplifies the equations used in stability and control analysis by consolidating 4 individual terms into one term that has some physical meaning. This term is a big driver in determining how strong the tail surface is...tails with high VH values can run the CG further aft and will have a wider allowable CG range. This isn't the whole picture because you must include the way downwash changes with angle of attack and the aspect ratio of the tail itself.
I think that the aspect ratio of the Edge tail is a bit less than the Extra which moves the neutral point of the wing-tail combination even further forward. I'm stepping out on a limb here but I theorize that the Edge locks in so well in pitch because of the relaxed stability that most are flown at. The very nature of the forward swept wing and the small horizontal tail volume means that it takes significant effort to make this design super stable statically because you can't get the CG far enough forward. I think an airplane with reasonably relaxed static stability will lock into lines with ease. I also think that the Edge is very linear in pitch which is in sharp contrast to its non-linear lateral-directional characteristics.
So far we've only talked about horizontal tail volume but there is an equivalent tail volume coefficient for the vertical tail. All of this talk is really only good for determining static or steady-state stability. I think the roll problems with the Edge arise from a nonlinearity which is probably viscous related (i.e. caused by separated flow). What do you think Baron...you've put a lot of time on the Carden Edge. The Carden is clearly the best of the Edge designs in my opinion.
George
For those who don't know the term VHt that Baron's referring too, it is simply a number that gives the designer or engineer an idea of how big the horizontal tail is and how far away from the wing the tail is.
VH= (St/S) * (Lt/C)
where:
St = horizontal tail planform area
S=wing planform area
Lt=distance between the aerodynamic centers of the wing and horizontal tail
C=mean aerodynamic chord of the wing.
St/S is typically 25% saying that the tail is 25% of the wing area in size and a good number for Lt/C is 2 saying that the horizontal tail's aerodynamic center is roughly 2 mean aerodynamic chords away from the wing's aerodynamic center.
The tail volume coefficient is useful because it simplifies the equations used in stability and control analysis by consolidating 4 individual terms into one term that has some physical meaning. This term is a big driver in determining how strong the tail surface is...tails with high VH values can run the CG further aft and will have a wider allowable CG range. This isn't the whole picture because you must include the way downwash changes with angle of attack and the aspect ratio of the tail itself.
I think that the aspect ratio of the Edge tail is a bit less than the Extra which moves the neutral point of the wing-tail combination even further forward. I'm stepping out on a limb here but I theorize that the Edge locks in so well in pitch because of the relaxed stability that most are flown at. The very nature of the forward swept wing and the small horizontal tail volume means that it takes significant effort to make this design super stable statically because you can't get the CG far enough forward. I think an airplane with reasonably relaxed static stability will lock into lines with ease. I also think that the Edge is very linear in pitch which is in sharp contrast to its non-linear lateral-directional characteristics.
So far we've only talked about horizontal tail volume but there is an equivalent tail volume coefficient for the vertical tail. All of this talk is really only good for determining static or steady-state stability. I think the roll problems with the Edge arise from a nonlinearity which is probably viscous related (i.e. caused by separated flow). What do you think Baron...you've put a lot of time on the Carden Edge. The Carden is clearly the best of the Edge designs in my opinion.
George
10-20-2004, 05:42 PM
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RE: Edge 540 and precision
Good Stuff George [8D]
Honestly, all the time I have on the Carden 35% Edge has been primarily freestyle. I agree completely with your roll assessment... I found it most affecting me in rollers. Similar to the 8 point roll scenario you described, I just couldn't get comfortable pulling up elevator during inverted portions of rollers.
I haven't really played around with spin entries with my Edge, but that is a complaint I hear often. I think it can be attributed to your assessment that Edges are generally flown more tailheavy than other designs, plus the more forgiving stall characteristics. It seems to become easy to simply transition to a harrier/elevator without ever showing the pitch break as described in the judging guide.
Baron
Honestly, all the time I have on the Carden 35% Edge has been primarily freestyle. I agree completely with your roll assessment... I found it most affecting me in rollers. Similar to the 8 point roll scenario you described, I just couldn't get comfortable pulling up elevator during inverted portions of rollers.
I haven't really played around with spin entries with my Edge, but that is a complaint I hear often. I think it can be attributed to your assessment that Edges are generally flown more tailheavy than other designs, plus the more forgiving stall characteristics. It seems to become easy to simply transition to a harrier/elevator without ever showing the pitch break as described in the judging guide.
Baron
10-20-2004, 08:58 PM
#6
RE: Edge 540 and precision
George,
What you say makes sense. What I am curious about is if you have any theories on why the nonlinearity of the rudder occurs. What seems to cause the seperation issues. One thing I was considering was trying a smaller, more scale counter balance on the rudder and then maybe using an anti-servotab for boost. Do you think this would help? I am just really curious being that on models there really isn't that much difference between an Extra 260 and Edge other than horizontal size and wing leading edge. One thing I was also thinking about is that it seems that the side of an Edge cowl is flatter than some Extras. I will pick Todd's brain a little as well.
I know that the full-size Edge point rolls well. When I ask pilots about rollers they say they really don't care and don't practice them because if you do one well you get an 8 and if you do one poorly, you get a 6.5 so with the low K it doesn't really matter.
Thank you for feeding my curiousity.
Dan
What you say makes sense. What I am curious about is if you have any theories on why the nonlinearity of the rudder occurs. What seems to cause the seperation issues. One thing I was considering was trying a smaller, more scale counter balance on the rudder and then maybe using an anti-servotab for boost. Do you think this would help? I am just really curious being that on models there really isn't that much difference between an Extra 260 and Edge other than horizontal size and wing leading edge. One thing I was also thinking about is that it seems that the side of an Edge cowl is flatter than some Extras. I will pick Todd's brain a little as well.
I know that the full-size Edge point rolls well. When I ask pilots about rollers they say they really don't care and don't practice them because if you do one well you get an 8 and if you do one poorly, you get a 6.5 so with the low K it doesn't really matter.
Thank you for feeding my curiousity.
Dan
10-21-2004, 08:11 AM
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RE: Edge 540 and precision
Dan,
I did have a plan to mount some video cameras on a 40% Aeroworks Edge 540 and put tufts on the side of the fuselage and fin/rudder area. I think watching these areas during a divergent maneuver would at least point us to the mechanism that's causing this. I don't like to offer theories about such things because people often mix it up with reality and then you have a myth with your name attached to it.
The truth is I don't know what causes this problem.
The rudder horn balance can cause trouble...I'd certainly look there. The "anti-servo tab" would make the hinge moment greater not lighter...I think you mean a "servo-tab" or "balance-tab". I don't think the issue is with rudder hinge moment so I doubt a balance tab would help much.
Most people think that the culprit is the straight leading edge because it's the one obvious difference that the Edge has when compared to other aerobatic designs...I'm not convinced of this but it's worth mentioning. I've always wanted to put an Extra wing on the Edge and see what happens. Honestly the main thing that the Edge and 260 have in common is the wing placement...from an S&C point of view I feel the two airplanes are quite different. Do you guys have any lateral-directional wind tunnel data on the Edge? Todd would know and you might want to look there. Let me know what Todd says...I've been interested in this one ever since we went through Guthrie at the 1999 IMAC Nats...BTW, thanks for the tour.
George
I did have a plan to mount some video cameras on a 40% Aeroworks Edge 540 and put tufts on the side of the fuselage and fin/rudder area. I think watching these areas during a divergent maneuver would at least point us to the mechanism that's causing this. I don't like to offer theories about such things because people often mix it up with reality and then you have a myth with your name attached to it.
The truth is I don't know what causes this problem.The rudder horn balance can cause trouble...I'd certainly look there. The "anti-servo tab" would make the hinge moment greater not lighter...I think you mean a "servo-tab" or "balance-tab". I don't think the issue is with rudder hinge moment so I doubt a balance tab would help much.
Most people think that the culprit is the straight leading edge because it's the one obvious difference that the Edge has when compared to other aerobatic designs...I'm not convinced of this but it's worth mentioning. I've always wanted to put an Extra wing on the Edge and see what happens. Honestly the main thing that the Edge and 260 have in common is the wing placement...from an S&C point of view I feel the two airplanes are quite different. Do you guys have any lateral-directional wind tunnel data on the Edge? Todd would know and you might want to look there. Let me know what Todd says...I've been interested in this one ever since we went through Guthrie at the 1999 IMAC Nats...BTW, thanks for the tour.
George
