Sebart Mythos 2M
08-19-2014, 12:43 PM
#55
Sfg
I decided to add an SFG to the stab to improve yaw stability and reduce the rudder authority that comes from the Contra Drive.
Once again the anhedral stab makes this a little more difficult than it needs to be.
I used the little jig that I made to check each half of the stab alignment to each other. Glued down to a piece of foam board marked with reference lines for the position of the SFG it supports the stab. Some scrap material is used to prop up each side of the stab equally. Now I can transfer my reference lines to a piece of tape on the stab. This marks the position of the SFG that is parallel to the center line of the plane.
I made the SFG's from firm balsa that was left rectangular as it was opened up to fit the line drawn. Tabs were added with new pieces of balsa with the grain vertical to make them stronger. Matching cutouts were made in the stab skin top and bottom. After first cutting slots in the top of the stab, the SFG blanks were taped in place perpendicular to the table using a square. Then the lower tab openings were marked and cut. This way the SFG's should be parallel to the vertical fin and not angled.
Only then did I cut the SFG to shape and after making sure that they fit covered them in Ultracoat.
Not sure if a second SFG will be needed or not.
Once again the anhedral stab makes this a little more difficult than it needs to be.
I used the little jig that I made to check each half of the stab alignment to each other. Glued down to a piece of foam board marked with reference lines for the position of the SFG it supports the stab. Some scrap material is used to prop up each side of the stab equally. Now I can transfer my reference lines to a piece of tape on the stab. This marks the position of the SFG that is parallel to the center line of the plane.
I made the SFG's from firm balsa that was left rectangular as it was opened up to fit the line drawn. Tabs were added with new pieces of balsa with the grain vertical to make them stronger. Matching cutouts were made in the stab skin top and bottom. After first cutting slots in the top of the stab, the SFG blanks were taped in place perpendicular to the table using a square. Then the lower tab openings were marked and cut. This way the SFG's should be parallel to the vertical fin and not angled.
Only then did I cut the SFG to shape and after making sure that they fit covered them in Ultracoat.
Not sure if a second SFG will be needed or not.
08-20-2014, 11:18 AM
#56
I decided to add a second SFG to each stab half. From my limited experience with Contra's I didn't think I could overdo the yaw stability and even with 2 SFG's per stab the rudder is still very sensitive. For the outside SFG I was able to use the Episode SFG as a template and just shorten it a bit. It matches the airfoil very accurately.
I flew the plane again today with the SFG's and I think they are an improvement although the rudder is still very sensitive and I ended up reducing the throw for regular flight otherwise all of the rolling elements end up in a climb. I may need to put stall turns on a switch to increase the throw for them. I will have to fly it more to see.
I did move the CG back even further and I think I have hit a sweet spot as the pull to the canopy in verticals and knife edge seems to have diminished or vanished. Only flew 3 flights today and there was a decent cross wind, so this will need further confirmation. I think I am well back of the recommended CG. I will report further once I measure it again.
Stuart C.
I flew the plane again today with the SFG's and I think they are an improvement although the rudder is still very sensitive and I ended up reducing the throw for regular flight otherwise all of the rolling elements end up in a climb. I may need to put stall turns on a switch to increase the throw for them. I will have to fly it more to see.
I did move the CG back even further and I think I have hit a sweet spot as the pull to the canopy in verticals and knife edge seems to have diminished or vanished. Only flew 3 flights today and there was a decent cross wind, so this will need further confirmation. I think I am well back of the recommended CG. I will report further once I measure it again.
Stuart C.
08-21-2014, 10:19 AM
#57
Mythos CG 215 mm back
The Mythos 2M manual calls for a CG range of 190 to 210 mm back from the leading edge of the wing at the fuse. First flights were made in the 190 to 200 range and following information in Bryan H's triangulation trimming the plane was likely nose heavy or needed the wing incidence increased. The plane went to the canopy in both verticals and knife edge, both sides. The manual would suggest that properly trimmed the plane should pull to the belly on knife edge as an up elevator mix of 1% with rudder is suggested.
It also felt a bit nose heavy when inverted although throws and expo can affect the feel quite a bit.
As the plane does not have incidence adjusters for the wing I kept moving the CG back. The last two flights felt pretty good both in verticals and knife edge. I figured I would just keep going until something felt wrong. Limited flights but nothing else felt "broke".
I put the plane together and measured the actual CG today and I was little surprised it was only at 215 mm behind the leading edge. Still outside the recommended range but I thought it might be further back.
While the plane was on the balance jig I also was curious as to how far I would have to shift the battery when switching from the APC Contra props to the CF APC clone props. Answer was about 44 mm using TP G8 5000 nah packs.
I did some rough measurements and plugged the info into an online MAC calculator http://www.nasascale.org/howtos/mac-calculator.htm
These are rough measurements as the front of the wing is elliptical and I did not include the portion through the fuse but I got numbers between 24 and 28% of MAC for a CG at 215 mm back. Certainly seems to be in a normal ball park range and makes me wonder if the manual is off. I can't imagine anyone being happy at 190 mm unless a single prop is much different than the Contra in CG requirements.
Stuart C.
It also felt a bit nose heavy when inverted although throws and expo can affect the feel quite a bit.
As the plane does not have incidence adjusters for the wing I kept moving the CG back. The last two flights felt pretty good both in verticals and knife edge. I figured I would just keep going until something felt wrong. Limited flights but nothing else felt "broke".
I put the plane together and measured the actual CG today and I was little surprised it was only at 215 mm behind the leading edge. Still outside the recommended range but I thought it might be further back.
While the plane was on the balance jig I also was curious as to how far I would have to shift the battery when switching from the APC Contra props to the CF APC clone props. Answer was about 44 mm using TP G8 5000 nah packs.
I did some rough measurements and plugged the info into an online MAC calculator http://www.nasascale.org/howtos/mac-calculator.htm
These are rough measurements as the front of the wing is elliptical and I did not include the portion through the fuse but I got numbers between 24 and 28% of MAC for a CG at 215 mm back. Certainly seems to be in a normal ball park range and makes me wonder if the manual is off. I can't imagine anyone being happy at 190 mm unless a single prop is much different than the Contra in CG requirements.
Stuart C.
08-22-2014, 09:18 AM
#59
If everything else feels OK, check how the plane behaves in spin. The spin entry where there should be a clearly visible stall may be difficult to do perform if the plane is too tail heavy.
08-22-2014, 10:09 AM
#60
10-05-2014, 05:02 AM
#61
My Feedback: (41)
Guys I'm determined to sell out of what was a too large of an inventory of this plane even at a loss.
http://www.f3aunlimited.com/sebart-mytho-s-pro-2m-arf
Anyone who has seen this plane or flown it knows what a beautiful airframe and how well made it is.
40% off till we are out is as good as it can get for these. It's below our costs by a large margin and $1000 less than originally listed.
Thanks, Mike
http://www.f3aunlimited.com/sebart-mytho-s-pro-2m-arf
Anyone who has seen this plane or flown it knows what a beautiful airframe and how well made it is.
40% off till we are out is as good as it can get for these. It's below our costs by a large margin and $1000 less than originally listed.
Thanks, Mike
10-05-2014, 05:03 AM
#62
My Feedback: (41)
40% off inventory blowout
Guys I'm determined to sell out of what was a too large of an inventory of this plane even at a loss.
http://www.f3aunlimited.com/sebart-mytho-s-pro-2m-arf
Anyone who has seen this plane or flown it knows what a beautiful airframe and how well made it is.
40% off till we are out is as good as it can get for these. It's below our costs by a large margin and $1000 less than originally listed.
Thanks, Mike
http://www.f3aunlimited.com/sebart-mytho-s-pro-2m-arf
Anyone who has seen this plane or flown it knows what a beautiful airframe and how well made it is.
40% off till we are out is as good as it can get for these. It's below our costs by a large margin and $1000 less than originally listed.
Thanks, Mike
01-03-2015, 11:17 AM
#63
I'm curious how everyone set the incidences on the stab with the anhedral? I don't trust the incidence meter but what I ended up with is setting the stab almost all the way to the end of travel in one direction of the allen screws. I took the stabs off and then reassembled them with them together off the plane and ensured the stabs had identical allen screw settings. Back on the plane they measured within a tenth of a degree with each other (horizon digital incidence meter). The wings and engine thrust are essentially identical. I'm not using wing adjusters, just the stock holes. The engine originally sat so the spinner identically matched the front of the fuse perfectly but that gave it about a degree of POSITIVE incidence relative to the stock wing settings so I modded the engine mount to give it a slight down thrust which now matches the wings settings. Right now I have the stabs set to be the same as the wing and engine lines. Going to just start off flying at 210mm back from the wing leading edge as that seems to be where everyone else ends up settling at.
01-03-2015, 11:38 AM
#64
Lucky, having seen quite a few maidens and having maidened my own Monday, I can tell you that unless you want to fly a homesick angel you need to get all the positive incidence you can on the stab. I backed out the bottom screws fully, turned the top screws down until they touched the incidence pin and then fully tightened the bottom screws. My elevators ended up just about at neutral for level flight and cruise power.
I'm running my CG much further forward than 210 initially as again from previous experience this design is much more directionally stable with it forward but it does lead to other trim issues. Mine is at 3.25" forward of the wing tube centre with the wings and canopy off.
Malcolm
I'm running my CG much further forward than 210 initially as again from previous experience this design is much more directionally stable with it forward but it does lead to other trim issues. Mine is at 3.25" forward of the wing tube centre with the wings and canopy off.
Malcolm
01-03-2015, 11:43 AM
#65
Lucky, having seen quite a few maidens and having maidened my own Monday, I can tell you that unless you want to fly a homesick angel you need to get all the positive incidence you can on the stab. I backed out the bottom screws fully, turned the top screws down until they touched the incidence pin and then fully tightened the bottom screws. My elevators ended up just about at neutral for level flight and cruise power.
I'm running my CG much further forward than 210 initially as again from previous experience this design is much more directionally stable with it forward but it does lead to other trim issues. Mine is at 3.25" forward of the wing tube centre with the wings and canopy off.
Malcolm
I'm running my CG much further forward than 210 initially as again from previous experience this design is much more directionally stable with it forward but it does lead to other trim issues. Mine is at 3.25" forward of the wing tube centre with the wings and canopy off.
Malcolm
01-04-2015, 09:04 AM
#66
Hi Lucky,
I'm afraid I have no clue as to the relative incidences as I don't measure them just adjust as necessary. The only measuring I do is to ensure both tail halves have the same incidence to start with. What I can tell you is that out of the box the motor is at considerable down thrust relative to the wing.
We are in the middle of winter here so flying is very weather dependent. I will let you know how my CG ends up as trimming progresses.
Malcolm
I'm afraid I have no clue as to the relative incidences as I don't measure them just adjust as necessary. The only measuring I do is to ensure both tail halves have the same incidence to start with. What I can tell you is that out of the box the motor is at considerable down thrust relative to the wing.
We are in the middle of winter here so flying is very weather dependent. I will let you know how my CG ends up as trimming progresses.
Malcolm
06-20-2016, 12:42 PM
#67
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Rudder servo in the tail or in the middle of the fuse
Hi,
I'm building the Mythos pro, and I've a doubt about the installation of the rudder servo. The manual give us two options: to install the servo in the tail, or to install it in the middle of the fuse with a push-pull cable.
I'm going to install Hacker Q80 14xs, and I'm using light power batteries (Exton 5s+5s 4500mAh, 970grams aproximately),... I'd prefer to install it in the middle of the fuse using cable, but I'm not sure that the center of gravity was too nose heavy.
Any suggestion?
Sergi.
I'm building the Mythos pro, and I've a doubt about the installation of the rudder servo. The manual give us two options: to install the servo in the tail, or to install it in the middle of the fuse with a push-pull cable.
I'm going to install Hacker Q80 14xs, and I'm using light power batteries (Exton 5s+5s 4500mAh, 970grams aproximately),... I'd prefer to install it in the middle of the fuse using cable, but I'm not sure that the center of gravity was too nose heavy.
Any suggestion?
Sergi.
06-20-2016, 01:54 PM
#68
Finish everything but the rudder servo and battery tray. Mock it up with the rudder servo where you want it and see if the batteries can be positioned properly to balance the plane. As long as you can move the main batteries forward or back from where the CG is set in the middle of its range, you should be fine.
06-21-2016, 04:47 AM
#69
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Thanks sc204,
I'm going to mount all other components, and then I'm going to play with the battery tray to decide the proper position of the rudder servo.
I've been looking photos, and the most part of them people mount the servo in the tail. In some cases they use 5000mAh batteries that are heavier than the 4500mAh I’m using.
Thank you for your attention.
Sergi.
I'm going to mount all other components, and then I'm going to play with the battery tray to decide the proper position of the rudder servo.
I've been looking photos, and the most part of them people mount the servo in the tail. In some cases they use 5000mAh batteries that are heavier than the 4500mAh I’m using.
Thank you for your attention.
Sergi.
08-02-2016, 10:00 AM
#70
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Hi sc204,
I’ve checked the COG of my Mythos with the rudder servo installed more or less in the same position than you.
I can balance the plane at 210mm from the leading edge, with the battery 110mm back of the motor (Q80 14XS). I’m using very light battery packs (Exton 5s+5s 4500mAh, 970grams approx.). It indicates that to mount the rudder servo in the tail would have been a bad choice in my case.
Finally, I glued the support of the rudder servo in this position,…
I’m really happy with the final weight of the plane: 3650g (complete without motor battery). I’ve used Futaba SBUS servos, and I’ve used the bus connection to save some wiring weight, and I connected both elevator servos to SBUS2, and both aileron servos to SBUS. On the other hand I’ve installed a double battery regulator to power the receiver (with two 2S 500mAh batteries), but I’ve tried to use short cables to connect all components.
I’ve checked the incidences and I have a doubt. I’ve found that the motor incidence is 0.7º up with respect to the wings. I’ve the plane of the spinner perfectly aligned with the fuse. And it’s the first time I find a setup like this. It’s more usual to set the engine incidence with a little downthrust. I think that Sebart made this setup for some reason, so I have the idea to start with a wing incidence of +0.25º and the stab incidence at 0º.
In any case, I’d like you give my some information about your incidences setup.
Thank you for your attention.
Sergi.
I’ve checked the COG of my Mythos with the rudder servo installed more or less in the same position than you.
I can balance the plane at 210mm from the leading edge, with the battery 110mm back of the motor (Q80 14XS). I’m using very light battery packs (Exton 5s+5s 4500mAh, 970grams approx.). It indicates that to mount the rudder servo in the tail would have been a bad choice in my case.
Finally, I glued the support of the rudder servo in this position,…
I’m really happy with the final weight of the plane: 3650g (complete without motor battery). I’ve used Futaba SBUS servos, and I’ve used the bus connection to save some wiring weight, and I connected both elevator servos to SBUS2, and both aileron servos to SBUS. On the other hand I’ve installed a double battery regulator to power the receiver (with two 2S 500mAh batteries), but I’ve tried to use short cables to connect all components.
I’ve checked the incidences and I have a doubt. I’ve found that the motor incidence is 0.7º up with respect to the wings. I’ve the plane of the spinner perfectly aligned with the fuse. And it’s the first time I find a setup like this. It’s more usual to set the engine incidence with a little downthrust. I think that Sebart made this setup for some reason, so I have the idea to start with a wing incidence of +0.25º and the stab incidence at 0º.
In any case, I’d like you give my some information about your incidences setup.
Thank you for your attention.
Sergi.
08-02-2016, 11:42 AM
#71
Sergi,
I found the same upthrust with 3 different Wind S Pro's (Same Fuz moulding as Mythos). Tail at 0° reference, wing at +0.5° relative to tail & Motor +1.4° (upthrust) relative to tail - so your +0.7° relative to the wing is close to what I found.
I emailed Seba & he said the upthrust was required for straight vertical uplines.
Steve
I found the same upthrust with 3 different Wind S Pro's (Same Fuz moulding as Mythos). Tail at 0° reference, wing at +0.5° relative to tail & Motor +1.4° (upthrust) relative to tail - so your +0.7° relative to the wing is close to what I found.
I emailed Seba & he said the upthrust was required for straight vertical uplines.
Steve
08-03-2016, 12:12 AM
#72
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Hi Steve,
Thank you for your advice.
The relative incidence between the motor and the wings (+0.7º) is approximated, because there is some measuring error. So, it would be more or less the same you have in your Wind S Pro.
I’m going to set the incidences like you recommend me (stabs – 0º/wings – 0.5º/motor – spinner plate parallel to fuse), and I’ll fly it to start the trimming process.
I’m really happy with this plane, it is reasonable good quality kit, easy to mount, and good final weight. I’m going to upload some photos when I test it.
Thanks.
Sergi
Thank you for your advice.
The relative incidence between the motor and the wings (+0.7º) is approximated, because there is some measuring error. So, it would be more or less the same you have in your Wind S Pro.
I’m going to set the incidences like you recommend me (stabs – 0º/wings – 0.5º/motor – spinner plate parallel to fuse), and I’ll fly it to start the trimming process.
I’m really happy with this plane, it is reasonable good quality kit, easy to mount, and good final weight. I’m going to upload some photos when I test it.
Thanks.
Sergi
