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Old Dec 29, 2009, 04:56 PM
Meditative flight
ibcellist's Avatar
Virginia
Joined Jun 2009
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Give me some ideas for a big fast flying wing!

ANOTHER BUILD!!! I'm feeling rather crazy since this will be the fourth plane I've built in the last month or so XP I have a relatively large brushless outrunner that I got for Christmas and want to put to use. It's a 35-30B 1400Kv Turnigy. Based on some reviews it looks like with the 9x5 props I have it can get upwards of 26oz of thrust...

So here's what I'm wanting suggestions on. I want to build a large but fast flying wing using said motor and a 2200mAh 25c lipo pack. I'm looking for material suggestion, span, root cord, airfoil, building techniques, and whatever else you want to throw at me. I have plenty of extra servos and a 35-40amp ESC to use and enough spare change to invest in some good material. If you help significantly I'm planning on doing somewhat of a paintjob on it (as I'm somewhat of an artist) and I'll toss your name on there somewhere and post a dedication page with pictures galore if all goes well
Let me know what you people are thinking!
-Evan
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Old Dec 29, 2009, 09:03 PM
The 6 P principle works for me
elecfryer's Avatar
Ventura CA
Joined Aug 2007
980 Posts
Well........Turnigy 35-30B is ONLY around a 120 watt motor. So my question to you is if that is a large motor, what is the wing span of the LARGE wing that you want to put it into? Also the KV for that motor is more like 1400, not 4000 and a 15amp ESC is all you need to run it! Any wing that has say 100 watts per pound of weight (RTF) should be fun to fly! So with this motor you would want to keep your weight to around 1.25 pound RTF.

I build wings based upon the Diamond Dust deign by Jeff Gilbert. Wing spans from 18" up to 34.5". They are a lot of fun!
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Old Dec 29, 2009, 10:50 PM
24 yrs. of Aircraft flying
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United States, GA, Rockmart
Joined Oct 2004
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Originally Posted by elecfryer View Post
Well........Turnigy 35-30B is ONLY around a 120 watt motor. So my question to you is if that is a large motor, what is the wing span of the LARGE wing that you want to put it into? Also the KV for that motor is more like 1400, not 4000 and a 15amp ESC is all you need to run it! Any wing that has say 100 watts per pound of weight (RTF) should be fun to fly! So with this motor you would want to keep your weight to around 1.25 pound RTF.

I build wings based upon the Diamond Dust deign by Jeff Gilbert. Wing spans from 18" up to 34.5". They are a lot of fun!
those look great, I am guesisng there built up balsa ones. I have always wanted a diamond dust but never got one.
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Old Dec 29, 2009, 10:50 PM
Meditative flight
ibcellist's Avatar
Virginia
Joined Jun 2009
133 Posts
AH! I'm sorry that was a terrible typo! You were right the motor is a 1400 and I meant to type that... Either way, it seems to be a pretty strong motor and with that amount of thrust should be able to fly a pretty big wing pretty fast. As for the ESC, I might just use a 25-30A as the max rating for the motor is 29A or so. Sorry for the mistake.
-Evan
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Old Dec 30, 2009, 01:41 AM
The 6 P principle works for me
elecfryer's Avatar
Ventura CA
Joined Aug 2007
980 Posts
The 35-30B is a nice motor, they rate it as being equivelent to the AXI 2808 of course there are at least 3 different AXI 2808's! Are you using Motocalc at all? It is a great way to simulate how your setup will work. You are able to list specific motor, prop, battery, esc combinations and it will give you the general performance results that you can expect. It will list things like Amp draw, Pitch speed, stall speed and more, it is a great tool! If you do not have it but want to try it out, it is free to download and use for 30 days (or at least is was when I started using it a few years ago!). I think that they are now up to Motocalc8.

There is also a ton of info in various areas here in RCGroups as I am sure that you are finding out!

My Diamond Dusts (5 different sizes) are all scratch, balsa - ply - CF tubes and Ultracoat. I am using inrunners and outrunners. My smallest is 18" w.s. and with the Little Jet Screamer motor and a 1600 2S LiPo weighs in @ 12 oz RTF. Top speed is just over 100mph and the roll rate is crazy, like 6 rolls per second at least! And yes, you bet I need dual rates and I do! However with a wing loading of just 10.6 oz per square foot it can still slow way down for landing. What can I say, I build em cause I love em!

Michael (if your not fryin, your not tryin!)
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Old Dec 30, 2009, 02:59 AM
Meditative flight
ibcellist's Avatar
Virginia
Joined Jun 2009
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Motocalc... I'll be looking up that one! Sounds like a hugely helpful tool. And as for your diamond dusts, they sound pretty awesome. I just built a quick foam board flying wing with a 30" wingspan and it must go 50-60mph with a little bell motor I put on it. Either way, thanks for the tips and if you have any suggestions on a wing to build for this motor let me know!
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Old Dec 31, 2009, 12:09 AM
Meditative flight
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Virginia
Joined Jun 2009
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So what kind of speed could I get with this motor on 30-35" wing using a 2200mAh pack and 9x6 apc prop? Also, is it better for speed to make it as a flat board style or symmetrical airfoil?
-Evan
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Old Dec 31, 2009, 01:59 AM
The 6 P principle works for me
elecfryer's Avatar
Ventura CA
Joined Aug 2007
980 Posts
Edit: I typed this up thinking that you were interested in wings like the Diamond Dust and that you like a sharper sweep angle, If I am wrong on this I apologize!

Good question however, only indirect answers along with more questions! I luv this hobby! One caveat, there is no free lunch when it comes to aerodynamics! That being said, here we go!

You seem to like a lot of sweep on your wings so I will assume (guess?) that you would not be against a 60 degree sweep.

30" wing span (ws) and 60 degree sweep = 450 square inches (with a sharp nose of course!) With a flying weight of 2 pounds the wing loading would be 450/144 = 3.125 square feet and 2/3.125= 10.24 ounces per square foot. For a wing of this size, that is a very light wing loading (in my opinion). This wing should handle very well and be capable of very slow forward flight.

Ansering your last question, a symetrical airfoil will be "less dragy" than a flat bottom or flat sheet airfoil.

Moving on, in general you will need something around 300 watts per pound to get up to 100 mph. Looking above, at 2 pounds you would want around 600 watts in to get to 100mph. I am just bringing up the speed of 100 as it is a commonly used yard stick. With a proper setup, a motor (with a prop) will unload in the air and what ever your pitch speed is on the ground you should get up to at least 90% of it in the air (with a lower drag airplane). Pitch speed is the pitch of the prop X rpm X .000946 (.000946 is a constant) this is the theoretical speed that the prop is moving the air thru the prop. (by the prop?)

Next......lets asume your 2200 (LiPo?) is a 3 cell LiPo and has a 25C rating, 2.2 X 25 = 55Amps. Lets further assume that under load your LiPo can sustain 3.5 Volts per cell, 3.5 X 3 X 55 = 577 watts (Volts X Amps = Watts). Hey!, thats pretty close to the 600 watts listed above! Looking good so far!

A 6 inch pitch prop (9 X 6) spinning at 18,000 rpm will have a pitch speed of around 102 mph. An 8X6 and a 7X6 and a 6X6 all spinning at 18,000 rpm would also have the same pitch speed! You need to balance the Pitch Speed + Thrust + Power in (watts in) to get the best out of your airframe. This exercise becomes VERY motor/esc dependant!

In an earlier post you said the you have a 35-40 Amp ESC. Amps X Volts = watts, 40 Amps X 3.5 Volts X 3 cells (3 cell lipo) = 420 watts in. This is only about 2/3 of the suggested 600 watts however it still gives us good direction regarding motor selection! AND your plane may come out lighter and have very little drag so.......

You may want to consider a Turnigy TR35-36A. Good for 15-25 Amps continuous and 35Amps for 30 seconds, so 40 Amps for 10-20 seconds should be OK! (yes it's pushing it a bit, hence - Electric Fryer!) Recommended prop for this motor is 9 X 6. However I think that your plane will have low drag meaning you may not need that much thrust so an 8 X6 or even a 7 X 7 prop may work as well! Hoping for 85% effeciency, 3.5 V X 3 cells X 1450 (Kv) X .85 = 12941 rpm and 12941 X 6 (6" pitch) X .000946 = 73 mph pitch speed. Now to make you work, do the math for a 7" pitch prop! Getting closer to 100 mph

Yup, this is what we go thru every time we get out a fresh sheet of paper and I did not even use motocalc! Motocalc will give you a better idea of performance however I am missing some of the parameters for the Turnigy motors so no motocalc this time!

Michael (if your not fryin, your not tryin)
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Last edited by elecfryer; Dec 31, 2009 at 02:13 AM. Reason: Clarification
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Old Dec 31, 2009, 02:34 AM
Wake up, feel pulse, be happy!
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United States, AK, Fairbanks
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Alright, well, Michael just blew through about every major, important formula pertinent to electric flight, and wings in general . Now I present myself as Exhibit B.

Reading the last post I was shocked at how close it is to me. 300W/lb for 100mph? Guess what.... I've got a flying wing that runs right at 300W/lb and it goes just over 100mph. It weighs 13.9oz at last weigh-in and totals about 275W.

Further, it's swinging a 7x6 prop (another parallel with Michael's example). I even used to fly it on a 7x7. I honestly don't know the kV of my motor; it used to be a 1500kV outrunner but it's been through the wringer a few times and when you heat up these magents they lose strength, so the motor spins faster (less magnetic resistance) but with less torque (and more amp draw on a given prop). This is how I went from 250W to 275W on the same motor

Mostly, I present this information here to prove that all the math and crazy formulas above are true, and that they work. Yes, my plane is real, by the way. If you want I can post a link to this plane's thread with PDF plans. It's a 30" foam jet (yeah, it's got a fuselage but you could "edit it out" if you want-- the wing will fly great by itself).
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Old Dec 31, 2009, 02:52 AM
The 6 P principle works for me
elecfryer's Avatar
Ventura CA
Joined Aug 2007
980 Posts
Thanx TP-14

Thank you for your kind words.

Numbers, can't live with them and can't live without them! In general, the less drag your airframe has the less power you need to get to speed. I took my smallest wing, went with a smaller motor and tried to streamline it a bit and its going just over 100 with about 230 watts in static and maybe less watts in a speed.....maybe! All up RTF at 12.0 ounces and lets see 230 watts divided by .75 pounds = 306.67 watts per pound! There's that pesky 300 number again! I am sure that there are people with planes going 100 mph on less than 300 watts per pound, I'm just not one of them!
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Old Dec 31, 2009, 08:20 AM
24 yrs. of Aircraft flying
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United States, GA, Rockmart
Joined Oct 2004
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Quote:
Originally Posted by elecfryer View Post
Thank you for your kind words.

Numbers, can't live with them and can't live without them! In general, the less drag your airframe has the less power you need to get to speed. I took my smallest wing, went with a smaller motor and tried to streamline it a bit and its going just over 100 with about 230 watts in static and maybe less watts in a speed.....maybe! All up RTF at 12.0 ounces and lets see 230 watts divided by .75 pounds = 306.67 watts per pound! There's that pesky 300 number again! I am sure that there are people with planes going 100 mph on less than 300 watts per pound, I'm just not one of them!
Thanks for the write up above I need to print that off for myself. my father has try to just explain it but explaning and writting it down two driffrent things.

I love your wings and looking at those pics they have to be balsa? they just something you came up with or a kit?
that one on the right. and i seeing it right the esc sits on top of the battery? it doesn't heat up like that!
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Old Dec 31, 2009, 09:53 AM
Meditative flight
ibcellist's Avatar
Virginia
Joined Jun 2009
133 Posts
Thanks!

WOW! I was hoping for a simple answer, and I got so much more than I hoped for XP Thank you so much! I'll be saving that little tidbit and using it on a regular basis. And as for my wing, 60 degree sweep isn't too much at all I love lots of sweep on my wings.

So with a 30" wingspan, 60 degree sweep, I was thinking a 3" tip cord and a 28" root cord. According to the CG calculator that's actually 480 square inches. So 480/144=3.33 square feet. Lets say I can keep the weight down to say 20oz, thats a pound and a quarter. 20/3.33=6.006 oz/square foot THAT is light wing loading right there XP I know all of my gear weights in a 333 grams exactly, so all that's left after that is airframe, and I'm thinking that 20 oz total isn't an unreasonable number here I will use a symmetrical airfoil shape, Now I just need to figure out what material to make it out of... Also, pusher or puller??

As for motor, I'm stuck on using 35-30 1400kv motor I have right now, so performance may suffer slightly, but we can at least see what kind of power this plane could have! I posted a picture of the wing CG calculator to give you an idea of what it might look like
Thanks again so much to elecfryer! SO HELPFUL! Your name will be on this one for sure.
Let me know what you're thinking and ideas for the actual build!
-Evan
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Old Dec 31, 2009, 12:33 PM
The 6 P principle works for me
elecfryer's Avatar
Ventura CA
Joined Aug 2007
980 Posts
Evan, Thanx

You are welcome Evan! Bottom line is, YOU ARE Modeling/Creating and I salute you! You are already using the CG calculator (nice tool yes?, nice to post a thanx to Z-80 ). I think your design is looking great. Once you build it and fly it, you can always make modifications such as, move the CG around, try different props and even different motors then you will be the one with experience!

Michael (if your not frying, your not tryin!)
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Old Dec 31, 2009, 12:53 PM
Meditative flight
ibcellist's Avatar
Virginia
Joined Jun 2009
133 Posts
Starting

Yeah, I just fried an EDF unit on another quick scratch build this morning so I'm looking forward to building a new plane XP Apparently snow and EDFs don't mix.... OH WELL! Everything else is fine. And I've started making a full size plan to lay things out on. I'm debating making it out of a combination of balsa and foam board... Thin out the board at the front and back and half the top half balsa ribs to create a symmetrical ish airfoil. That way the foam is there to help with strength but the balsa creates a better airfoil and keeps weight down. Ideas?
-Evan
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Old Dec 31, 2009, 12:58 PM
The 6 P principle works for me
elecfryer's Avatar
Ventura CA
Joined Aug 2007
980 Posts
re: Dust

This one is for you epwr. Construction is balsa, ply, Carbon fibre tubes, basswood for motor mounts, and some Kevlar thread in the high stress areas. The original Diamond Dust was designed by Mr. Jeff Gilbert and the sizes ranged from 34.5" ws to 28.5" w/s. My first electric version flew in 1994 and it was a bit of a dog! If I recall right, 34.5" w/s, 60 oz RTF and maybe 60mph! Of course we are talking Brushed motor and NiCads for power however, it did fly!

Michael (if your not frying, your not tryin!)
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