FF2017 Int. Racers: Folkerts Speed King SK-3 "Jupiter"
- Thread starter Mid7night
- Start date
Zero. Straight-straight.
Bigger problem; after reviewing the hat-cam video (which I'm not sure I'll post), it looks like it was still a bit tail-heavy, even though I put the CG basically right on the 1/4-chord. Then again, my previous FT-scratchbuilds have been tail-heavy in my initial estimations. I should've gone a bit more forward.
The nose is easy enough to cut off and repair, and the wingtip shouldn't be too bad either. I don't know if I have another pitot tube though, so I might have to ditch that sensor.
But I definitely want to at least put some fall-away gear on it for the next flight, and add a functional rudder. Those tip ailerons are all but non-existent at low speed. A rudder in the propwash will be much more effective, and landing gear will allow me to get a better feel for it as it gains speed on takeoff.
Alright, she's back together and ready for another go tomorrow. I didn't add a rudder, but I did throw together some fall-away gear so I won't have to throw it this time. I don't think I got any different thrust-angle in it, but I plan on looking at that for the future.
I just did the minimum for now, just to get back in the air. At first I had thought I'd chop the whole nose off and splice on a new one (also allowing me to adjust the thrust angle), but the more I looked at it the more I saw that I could just cut away the lower half of the cowl and reinforce it, leaving the motor alone. This made the repair a lot quicker.
I also had to replace one of the aileron servos - the wingtip hit pretty hard along with the nose. I did lose the pitot tube for now, but I'll probably throw it back in at some point. I've still got altitude and power sensors on board, so I'll at least be able to tell how hard I'm pushing the motor/battery/ESC.
Stay tuned!
I just did the minimum for now, just to get back in the air. At first I had thought I'd chop the whole nose off and splice on a new one (also allowing me to adjust the thrust angle), but the more I looked at it the more I saw that I could just cut away the lower half of the cowl and reinforce it, leaving the motor alone. This made the repair a lot quicker.
I also had to replace one of the aileron servos - the wingtip hit pretty hard along with the nose. I did lose the pitot tube for now, but I'll probably throw it back in at some point. I've still got altitude and power sensors on board, so I'll at least be able to tell how hard I'm pushing the motor/battery/ESC.
Stay tuned!
Looks good.
For v2 you are definitely going to want that thrust angle tweaked. For small high speed planes like this the torque effects are really noticeable. If you don't want to build in the right thrust just put a washer or two under the X mount on the left side. Nic is probably right about 3* being a good figure, but anything will help.
For ROG with no rudder be prepared that she will pull hard to the left as you add power. Make sure you plan for that before you go to take off as you won't be able to counter it.
Good luck!
For v2 you are definitely going to want that thrust angle tweaked. For small high speed planes like this the torque effects are really noticeable. If you don't want to build in the right thrust just put a washer or two under the X mount on the left side. Nic is probably right about 3* being a good figure, but anything will help.
For ROG with no rudder be prepared that she will pull hard to the left as you add power. Make sure you plan for that before you go to take off as you won't be able to counter it.
Good luck!
Thanks wilm...I like the simplicity of a washer under the mount, but for today I'll just have to be extra careful on the sticks.
Would you recommend some right-aileron trim dialed in before? I remember from my FT-Mustang that I ended up with quite a bit of right-Ail trim to level it out at full throttle.
Would you recommend some right-aileron trim dialed in before? I remember from my FT-Mustang that I ended up with quite a bit of right-Ail trim to level it out at full throttle.
Thanks wilm...I like the simplicity of a washer under the mount, but for today I'll just have to be extra careful on the sticks.
Would you recommend some right-aileron trim dialed in before? I remember from my FT-Mustang that I ended up with quite a bit of right-Ail trim to level it out at full throttle.
A few clicks before maiden may help a bit, but obviously trim effectiveness is tied directly to speed. It would probably be worth it on this maiden.
Good luck!
Well I wish I had better news....but this model is dead. I need to build another, and make some tweaks before I do.
Second "maiden" went marginally better, only insofar as it actually got going forward, and I made a few turns, but it was still way off. It still had a CG problem, but I started noticing some other weird behaviors as it picked up speed.
The CG for this flight was forward of where it was last time, so I had better control in pitch. However, it was ALL over the sky laterally. I think it is a combination of the giant nose (right behind the prop no less), and the tiny tail. These two things together are incredibly destabilizing in yaw.
Secondly, the high-mounted prop (high on the fuse, that is) has a bit of a ramp as it transitions to under to the belly. I suspect that this ramp is getting pressurized by the powerful prop, generating lift forward of the wing - THIS is the primary reason why I think the "normally safe" CG location is not working out as expected.
The real SK3 is a lot more rounded and streamlined, especially on the nose, so I need to come up with some solutions to either 1) Round the nose more, or 2) Move the CG even further forward.
Either way, the tails need to be upsized a tad, especially the vertical to combat the giant schnoz. Also, it really does need a rudder. This airplane just doesn't work as a bank-n-yank.
I'm learning a lot, which I take as a win.... I just wish I hadn't broken the stuff I can't fix (namely the motor, this last crash bent the shaft)
Second "maiden" went marginally better, only insofar as it actually got going forward, and I made a few turns, but it was still way off. It still had a CG problem, but I started noticing some other weird behaviors as it picked up speed.
The CG for this flight was forward of where it was last time, so I had better control in pitch. However, it was ALL over the sky laterally. I think it is a combination of the giant nose (right behind the prop no less), and the tiny tail. These two things together are incredibly destabilizing in yaw.
Secondly, the high-mounted prop (high on the fuse, that is) has a bit of a ramp as it transitions to under to the belly. I suspect that this ramp is getting pressurized by the powerful prop, generating lift forward of the wing - THIS is the primary reason why I think the "normally safe" CG location is not working out as expected.
The real SK3 is a lot more rounded and streamlined, especially on the nose, so I need to come up with some solutions to either 1) Round the nose more, or 2) Move the CG even further forward.
Either way, the tails need to be upsized a tad, especially the vertical to combat the giant schnoz. Also, it really does need a rudder. This airplane just doesn't work as a bank-n-yank.
I'm learning a lot, which I take as a win.... I just wish I hadn't broken the stuff I can't fix (namely the motor, this last crash bent the shaft)
Congrats on the learning event! http://headsuphobby.com has a bunch of motors on sale at the moment - maybe that will help getting back into the air with the next prototype a little less painful
I DID get video, but it's not something I think I want to share widely...I may upload it and send you a private link though, if you like.
You mentioned full-span ailerons on your thread; this was another change I was thinking about today. On the takeoff throw I had about 40% of full-flaps down, but it didn't feel like it needed it, so I think I can ditch the inboard flaps. With all that power I think it'll pull out just fine.
I may still forego the rudder as well, but I forgot to consider the thrust-angle Nic (and others) mentioned...and looking at the video again it's clear that plays into the problem. The plane kept inexplicably pulling left, to the point where near the end I literally could not get it to turn right (which was also back into the wind... that didn't help).
So I can confirm: A few degrees of right-thrust angle is important!!
(as if that needed confirmation) I don't think any of these are a showstopper for us, but some mods are definitely in order. Chiefly: Larger tails, ~3° Right-thrust on the motor mount, Forward CG.
Tench745
Master member
Sorry to hear about the crash/loss. But hooray for learning things! Any chance for a video would be informative for the rest of us.
Racers of this era, particularly the inline engine planes, ala Caudron c.560, Goon, SK, etc had a big problem with yaw-stability. Because there is so much surface area forward of the wings when you yaw too far that forward area can overpower the rudder and get what I believe is called "rudder lock." For example, if you yaw left, then apply right rudder to straighten out, even full rudder won't be able to overcome the side forces on the fuselage. So you might think, just yaw it left and turn around. No can do. Even at full left deflection the rudder is blanketed by the fuselage and is entirely ineffective.
THIS is why all these scale racers really need bigger rudders/ v-stabs.
I'm really jazzed about all these racers popping up.
(If anyone has information or corrections to add, I appreciate the input.)
Racers of this era, particularly the inline engine planes, ala Caudron c.560, Goon, SK, etc had a big problem with yaw-stability. Because there is so much surface area forward of the wings when you yaw too far that forward area can overpower the rudder and get what I believe is called "rudder lock." For example, if you yaw left, then apply right rudder to straighten out, even full rudder won't be able to overcome the side forces on the fuselage. So you might think, just yaw it left and turn around. No can do. Even at full left deflection the rudder is blanketed by the fuselage and is entirely ineffective.
THIS is why all these scale racers really need bigger rudders/ v-stabs.
I'm really jazzed about all these racers popping up.
(If anyone has information or corrections to add, I appreciate the input.)
That's really interesting about 'rudder lock'....even though I didn't have a controllable rudder on mine, I think I experienced a form of "yaw lock", because no matter what I did I couldn't get it to turn where I wanted.
P.S. Video of both flights is exporting/uploading now. Stay tuned. I want people to learn from my, er..."experience".
P.S. Video of both flights is exporting/uploading now. Stay tuned. I want people to learn from my, er..."experience".
Alright, here are my two 'maiden' flight fails. The first one is literally seconds; partly because it was SO out of control, and partly because I intentionally grounded it as quickly as possible to keep it from going into the walking path.
The second flight was longer, but I was fighting it the entire time; I was basically flying a right-hand knife edge the whole time because as soon as I leveled the wings out it pulled HARD to the left. I basically was trying to fight massive P-factor and torque-roll with undersized controls. >_<
I hope y'all can learn from this and not have to crash for the same reasons - crash for a different reason, and share it, so I can learn from you too!
The second flight was longer, but I was fighting it the entire time; I was basically flying a right-hand knife edge the whole time because as soon as I leveled the wings out it pulled HARD to the left. I basically was trying to fight massive P-factor and torque-roll with undersized controls. >_<
I hope y'all can learn from this and not have to crash for the same reasons - crash for a different reason, and share it, so I can learn from you too!
Ok, I'm going to honestly give my assessment, given that I've built a racer of this size in the past a learned a lot from it.
Flight #1: Yeah, tail heavy.
Flight #2: control surface deflections seem high. Judging from quick up on launch and other corrections. Tone that way back. With how it wanted to track on its side I have two notes. #1 you are getting a lot of back-torque into the airplane from the motor. #2 You need yaw authority.
Please note how my Goon flew in the first video:
Then in the second:
The MAJOR change I made was increasing the V-stab and rudder area. I enlarged it to 140% of the scale area. This DRAMATICALLY changed the overall stability of the airplane and I was able to manage the back torque with rudder use. Eventually I could never fully eliminate the back torque with thrust angle entirely so I programmed a throttle-rudder mix. More throttle gave more right rudder.
I think you are finding that this is the more challenging stage of the design-off. Keep up the great work, brother!
Flight #1: Yeah, tail heavy.
Flight #2: control surface deflections seem high. Judging from quick up on launch and other corrections. Tone that way back. With how it wanted to track on its side I have two notes. #1 you are getting a lot of back-torque into the airplane from the motor. #2 You need yaw authority.
Please note how my Goon flew in the first video:
Then in the second:
The MAJOR change I made was increasing the V-stab and rudder area. I enlarged it to 140% of the scale area. This DRAMATICALLY changed the overall stability of the airplane and I was able to manage the back torque with rudder use. Eventually I could never fully eliminate the back torque with thrust angle entirely so I programmed a throttle-rudder mix. More throttle gave more right rudder.
I think you are finding that this is the more challenging stage of the design-off. Keep up the great work, brother!
Awesome. Thank you willsonman for your honest assessment, it really helps to hear someone else confirm my own suspicions.
Yeah, tail heavy was obvious, and I'm kicking myself for not pushing the CG further forward based on previous experience. The next iteration will DEFINITELY have upsized-tails and a functional rudder.
Thank you for sharing your videos too! I feel like maybe we need a "lessons learned" thread for this Design-Off, if only for the safety aspect of it, where we can post our fails & fixes. I know designers generally don't like sharing their 'secrets', but with so many of us (likely) new at this kind of design, I think it would be irresponsible of us to NOT share the things we did 'wrong' and how we corrected them to make a safe flying aircraft (not that I'm there yet ).
Yeah, tail heavy was obvious, and I'm kicking myself for not pushing the CG further forward based on previous experience. The next iteration will DEFINITELY have upsized-tails and a functional rudder.
Thank you for sharing your videos too! I feel like maybe we need a "lessons learned" thread for this Design-Off, if only for the safety aspect of it, where we can post our fails & fixes. I know designers generally don't like sharing their 'secrets', but with so many of us (likely) new at this kind of design, I think it would be irresponsible of us to NOT share the things we did 'wrong' and how we corrected them to make a safe flying aircraft (not that I'm there yet
).
SlingShot
Maneuvering With Purpose
I think you did well with the second flight. I know nothing about aircraft design but I believe that you've been done in by the dreaded Reynolds Number. If you want to keep your wing length you might try fattening up you wing core. Perhaps making it symmetrical. Otherwise, lengthen the wing some along with the tail surfaces and I think you'll get some better tracking.
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