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Old Feb 28, 2013, 01:59 PM
59 years of RC flying
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Canada, ON, Ottawa
Joined Feb 2006
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Originally Posted by flybyjohn View Post
Ok, so lets try and size this model. I was going to use two thicknesses of dollar tree foam laminated together (about 9 mm thick) for the entire bird. I was thinking two carbon fiber arrow shaft spars perpendicular to thrust line, and half round balsa leading edges. I think this will be stiff enough. 4 sheets of dollar tree foam will weigh about 23 oz + glue and carbon fiber. Hopefully I can stay below 27 oz. for airframe for a 150% with 9mm foam. That leaves me right about where Burnzy was with the 150% he was projecting.
You might consider something like 3/16" dowel for the leading edges -- stiffer and tougher than balsa.

Quote:
Well I guess the first thing is to mount the motor up to something and give it a test with a few props and see how hungry it is for amps. That will give me a battery and esc size and weight to work with.
If it's 450 watts and you use a 3s battery, that's about 41A. So a good 60A ESC should do. 50A would definitely be marginal unless you were content to run the motor below say 300 watts.

It's quite high KV so you could start with an 8x6 APC prop. If it doesn't pull say 35A, try 9x5.

EDIT. Thinking about the battery some more. If you are building 150% and not super light, you are probably going to pull 20A or so for cruising flight. Let's say average of 24A for the whole flight. Take a 3000 mAh battery for example. Using the 80% rule, that gives you 2400 mAh of available power. At 24A, that means 1/10 hr duration or 6 min. If you are buying batteries, you should probably consider that the minimum. If you already have 2200 batteries, two in parallel should work well.

As for C-rating, I like to limit my current draw to about 60% of battery rating. This gives long life and avoids battery heating issues. A 3000 20C battery is rated for 60A continuous so meets this requirement, but I'd pick something in the 20-30C continuous range. Note that while the 133% XL works quite nicely on a 2200 20C, your 150% would be pushing such a battery very hard, but two of them in parallel would have an easy time.

I hope all this helps.
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Last edited by Daedalus66; Mar 01, 2013 at 05:12 PM.
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Old Mar 01, 2013, 05:46 PM
chronic in training
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L.A. beautiful san fernando valley
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Originally Posted by Daedalus66 View Post
You could do the Foam Tac hinge and then add tape on just the top surface for peace of mind.

Something else I've seen is smearing a very thin layer of Foam Tac on the Depron to improve the bonding of the Blenderm. The glue is allowed to dry before the tape is applied. I've tried this on a small section where the tape had come loose. So far, so good.
How long does the foam tac take to dry before you put on the blenderm?
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Old Mar 01, 2013, 09:11 PM
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brooklyn,ny
Joined Jul 2007
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finished polaris 42 for browneyefool!!!i know you going to enjoy this plane buddy

my record also, 4 1/2 hours from start to finish,

just air frame, no electronics what so ever.
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Old Mar 01, 2013, 09:43 PM
59 years of RC flying
Daedalus66's Avatar
Canada, ON, Ottawa
Joined Feb 2006
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Originally Posted by grfcon View Post
How long does the foam tac take to dry before you put on the blenderm?
I'm learning the techniques of Foam Tac and am getting comfortable with it. I've just finished building a model from Model Plane Foam using almost exclusively Foam Tac. Things went well generally, though it took a bit of getting used to after all my building with epoxy and CA. I'll report fully when I've done more experimenting.

The way I did the hinges on my latest model (not a Polaris!) was to use the usual 45* bevel on the control surface. Then a narrow bead of Foam Tac along the edge, touch that to the trailing edge and pull away. Let it dry for a few seconds, then push back together. That makes a remarkably tough hinge when dry (an hour or so), but I decided to add Blenderm (1") on the top surface only. I smeared a very thin layer of Foam Tac where the tape would go and waited a couple of minutes before applying the Blenderm.

Thanks to Meanbaby for the video on Foam Tac hinges. I'm probably being too conservative in adding Blenderm!
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Old Mar 01, 2013, 09:48 PM
59 years of RC flying
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Canada, ON, Ottawa
Joined Feb 2006
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Quote:
Originally Posted by meanbaby View Post
finished polaris 42 for browneyefool!!!i know you going to enjoy this plane buddy

my record also, 4 1/2 hours from start to finish,

just air frame, no electronics what so ever.
I once finished a Polaris Mini from receipt of the kit to maiden flight in 24 hours. I estimated that actual build time, including radio installation was about 7 hours. The Mini is probably a little quicker to build than the regular Polaris.
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Old Mar 02, 2013, 07:53 AM
chronic in training
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L.A. beautiful san fernando valley
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Quote:
Originally Posted by Daedalus66 View Post
I'm learning the techniques of Foam Tac and am getting comfortable with it. I've just finished building a model from Model Plane Foam using almost exclusively Foam Tac. Things went well generally, though it took a bit of getting used to after all my building with epoxy and CA. I'll report fully when I've done more experimenting.

The way I did the hinges on my latest model (not a Polaris!) was to use the usual 45* bevel on the control surface. Then a narrow bead of Foam Tac along the edge, touch that to the trailing edge and pull away. Let it dry for a few seconds, then push back together. That makes a remarkably tough hinge when dry (an hour or so), but I decided to add Blenderm (1") on the top surface only. I smeared a very thin layer of Foam Tac where the tape would go and waited a couple of minutes before applying the Blenderm.

Thanks to Meanbaby for the video on Foam Tac hinges. I'm probably being too conservative in adding Blenderm!
thank you I'll give this a shot. I have foam tack and blenderm. finishing up my 2 1/2 year scratchbuild.
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Old Mar 02, 2013, 10:09 AM
chronic in training
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L.A. beautiful san fernando valley
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scratchbuild question.. do you guys taper TE's of control surfaces?

I have heard this increases performance.. or do you just leave em square?

thanks.
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Old Mar 02, 2013, 10:29 AM
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Seattle, WA
Joined Jun 2002
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I doubt the TE shape makes any noticeable difference. I round mine mostly for aesthetics, gives the airplane a more polished look. Tapering the edges would reduce drag a little, but I really doubt you could see or measure the difference.
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Old Mar 02, 2013, 10:38 AM
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Just an uncut video of the day.
100% polaris, AXN motor (12min flight) with 2200mAh, KFM2 airfoils
KFM2 Polaris Seaplane : 2 min uncut (0 min 0 sec)

(few minutes to wait)
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Old Mar 02, 2013, 12:06 PM
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Mounting LEDs

I have a Polaris XL that, with a little experimentation, finally flys well at high altitude using a 3s battery I'm looking for suggestions for mounting LEDs. I have 3 strings, red, green, and while. I'm planning on using the white down the center of the fuse, with red and green on opposite wings. Is the best setup with the lights on top on the wings or on the leading edge facing forward? I plan on flying at dusk, not after dark.
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Old Mar 02, 2013, 01:22 PM
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United States, OR, Portland
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Cobralaris is alive and well! Flew her yesterday and seemed no worse for the wear. Interestingly, I got her to flat spin twice for the first time ever on this flight. Not sure if a slight change in aerodynamics after the repair made it easier to enter, or if I didn't measure the CG the same as normal (It seemed right where it always is). Flew completely as I am accustomed to otherwise, nice and stable, not overly nose heavy in turns, but when simply cutting throttle to idle in a shallow climb and holding full up elevator, I was able to enter a pretty flat spin that went for several revolutions and looked like it would have continued to the ground if I didn't add throttle, then easily flew out of it! Looked really cool!
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Old Mar 02, 2013, 02:47 PM
chronic in training
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L.A. beautiful san fernando valley
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Quote:
Originally Posted by jetset44 View Post
I doubt the TE shape makes any noticeable difference. I round mine mostly for aesthetics, gives the airplane a more polished look. Tapering the edges would reduce drag a little, but I really doubt you could see or measure the difference.
Great..thanks.
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Old Mar 02, 2013, 02:53 PM
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My friend finally uploaded the on board video from my Cobralaris crash Kinda low res, but fun to watch anyway TURN VOLUME DOWN, cam is mounted on nacelle and the prop gets really loud.
http://m285.photobucket.com/albumvie...l?o=0&newest=1
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Old Mar 02, 2013, 05:08 PM
Aus
ʎןɟ inverted ɹǝpunuʍop
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Australia, ACT, Amaroo
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Quote:
Originally Posted by Bledi View Post
Just an uncut video of the day.
100% polaris, AXN motor (12min flight) with 2200mAh, KFM2 airfoils
http://www.youtube.com/watch?v=LdubVRSyLno
(few minutes to wait)
Looks successful. I have an AXN and would have thought the motor would have been a little small for the 100% Polaris - obviously not. What prop are you using and where is your throttle positioned in cruise?
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Old Mar 02, 2013, 05:42 PM
Aus
ʎןɟ inverted ɹǝpunuʍop
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LEDs

Quote:
Originally Posted by bob93447 View Post
I have a Polaris XL that, with a little experimentation, finally flys well at high altitude using a 3s battery I'm looking for suggestions for mounting LEDs. I have 3 strings, red, green, and while. I'm planning on using the white down the center of the fuse, with red and green on opposite wings. Is the best setup with the lights on top on the wings or on the leading edge facing forward? I plan on flying at dusk, not after dark.
Here's mine on a 100%.

http://www.rcgroups.com/forums/showp...ostcount=14256

http://www.rcgroups.com/forums/showp...ostcount=14258

I've been happy with the LEDs on my leading edge as it lights up the ground/water on landings.

Post any further questions here and I'll be happy to respond.
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