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Old Feb 02, 2015, 02:16 PM
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New scratchbuild, need drivetrain recomendations :)

Well, I got bored today and have been itching to build something for a while. I want something that can fly fairly stable at higher speeds but with the option to be flown quite slowly. Seems like the washout style delta wings make the most sense for such an application. That being said, I dont think "slow flight capable" means a plane has to "look" slow, ya know? So I just mocked up this F-117ish delta wing thing you see here. At 20" long with a 22" wingpsan, the whole thing is made from one sheet of DTF--whatever that weighs.

So my questions are as follows:

1. Motor/ESC recommendation?
All my current motors are way too big, but I never really got into the finer points of Size, vs, KV, vs, Watts, vs Wire Winds, yada yada yada... I'm just looking for a recomendation or two given the ballpark airframe weight (one sheet of DTF + two 9g servos + Rx) and the plane's delta wing w/dehedral shape.

I dont care about flying fast, but I do want enough power so as not to "wish it had more" or find myself struggling to fly it on a breezy day. Erring on the side of "a tad-more" is certainly fine but I dont need it to fly 3D or anything. I've got 1S 350mAh, 2s 350mAh, and some 3s 750 mAh packs lying around to work with, so I'd like to stick with those.

Any advice or pros/cons to a mid engine pusher vs a tail pusher? Seems like less turbulent air over the elevons with tail pusher, but I see that most "jets" seem to opt for the mid-engine design.


2. EDF options?
IDK @ what point small EDFs become useless. I've seen 1:1.5 as a general weight to EDF thrust ratio, but are 35mm fans really going to do much? It seems by the time the motor sits behind such a small ducted fan, very little air is going to get pulled in. How long can a 35-40mm EDF run on a 2S 350mAh battery pack?

Can I make the EDF chamber any shape I want, or do I have to engineer something round and very particular? Anyone more familiar with small-sized EDF applications, plz chime in here. I think I like the idea of running an EDF on this baby, but I'm not familiar with 'em at all.


3. RE: Geometric Airfoil Design...
I already know it doesnt need it, but call me old fashioned when it comes to airfoils and dehedral. I like them--it gives DTF planes more credibility IMO, not to mention a bit more strength, and in this plane's case, a closer resemblance to the original F-117.

As long as it creates some kind of lift, I'm okay with it. I dont care a whole lot about the drag inefficiency, but having never made a triangulated airfoil like this before, will it work? Or at a bare minimum, are any particularly negative behaviors going to be born of this triangular airfoil?


DISCLAIMER: I'm just a "winging it" kind of guy, so while I know many knowledgable forum members can give me all kinds of formulas and ratios and theory-to-practice information, I just wanna fly a plane. A plan being flyable is more important to me than perfect efficiency... that being said, any mention of obvious red flags is certainly appreciated.
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Last edited by tripn4days; Feb 02, 2015 at 02:27 PM.
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Old Feb 02, 2015, 02:54 PM
Hot glue held together by foam
United States, WA, Vancouver
Joined Aug 2010
3,417 Posts
I'm also a "wing it" guy - build mostly "TLAR" ( That Looks About Right )

That airframe looks good , it will probably work best as a pusher with the battery all the way up front for good CG balance . FYI , the only way it's going to fly slow is high alpha ( nose up ) . For a plane to fly slowly non-high alpha it needs light wing loading .

For that size/weight plane my go-to motors are the Blue Wonder style . You can get them at HobbyKing ( hexTronik 24 gram ) , for some zip get the 1700 kv . You can also get them at Strong RC Motors . HeadsUp RC has HURC brand BW motors with the connectors already soldered on , and they have a 1900 kv that should give you a lot of zip . For that motor , get their 12 amp ESC with the connectors already soldered on .
http://www.headsuphobby.com/HURC-300...otor-B-702.htm
http://www.headsuphobby.com/HURC-12-...-ESC-G-268.htm

Here is my Dollar Tree flying triangle with a 1700kv BW motor .

Simplest simple delta (1 min 20 sec)
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Old Feb 02, 2015, 04:28 PM
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Thanks for the info BoC! That delta you've got there looks like a ton of fun! Talk about "snappy!" huh? Between the triangle shape and the responsiveness, it looks like you've got yourself an RC stunt kite! LOVE IT

I'll checkout the BW motors you recommend. Are you running that delta on a 3s?
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Old Feb 02, 2015, 04:43 PM
Hot glue held together by foam
United States, WA, Vancouver
Joined Aug 2010
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Quote:
Originally Posted by tripn4days View Post
Thanks for the info BoC! That delta you've got there looks like a ton of fun! Talk about "snappy!" huh? Between the triangle shape and the responsiveness, it looks like you've got yourself an RC stunt kite! LOVE IT

I'll checkout the BW motors you recommend. Are you running that delta on a 3s?
Yes , 500 mah 3S battery , 7x4 prop .

That delta is a blast to fly , and RIDICULOUSLY easy to make ! It's not much to look at sitting still on the ground , but in the air ......

Here are the "plans" if you want to make one :
http://www.rcgroups.com/forums/showthread.php?t=2145562

Al
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Old Feb 06, 2015, 10:19 PM
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Ordered a pair of the 24g hextronik motors. Should be plenty of power. Found the perfect gliding CG, so im eager to get this puppy assembled

Anyone have suggestion for fuse attachment ideas? Id like to be able to remove the fuse to access the electronics, but tha may prove difficult with triangluar fuse amd wings that tab into the fuse. If all else fails, i cam keep things pretty clean by burying servos and batteries into foil of wing, but that seems to create a sort of permanen setup.... maybe thats ok? IDK.... my planes traditionally have fuse access due to removeable wing, bu this is kind of a one piece fold up style build

Suggestions?
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Old Feb 06, 2015, 10:46 PM
Hot glue held together by foam
United States, WA, Vancouver
Joined Aug 2010
3,417 Posts
On this plane I could open it up on top - hinged in the front .
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Old Feb 08, 2015, 05:24 PM
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Wow!

So after trying out my new scale and running some numbers, this plane of mine is going to have 5.23oz/sq ft of wingloading! Is there such thing as too little? The 1400kv hobbyking engine I bought is going to have ~12oz of thrust.

Soooooo what am I in for, exactly? That seems like a lot of power, yeah?

Is wingload calculated any differently for delta-wings? If not, seems like this puppy is gonna really scream at WOT, which I dont mind at all, considering how slow and docile she should be at low speeds and such light wingloading. I just wonder what kind of erratic behavior this thing's going to exhibit at the high end of the throttle?
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Old Feb 08, 2015, 05:47 PM
Hot glue held together by foam
United States, WA, Vancouver
Joined Aug 2010
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Quote:
Originally Posted by tripn4days View Post
Wow!

So after trying out my new scale and running some numbers, this plane of mine is going to have 5.23oz/sq ft of wingloading! Is there such thing as too little? The 1400kv hobbyking engine I bought is going to have ~12oz of thrust.

Soooooo what am I in for, exactly? That seems like a lot of power, yeah?

Is wingload calculated any differently for delta-wings? If not, seems like this puppy is gonna really scream at WOT, which I dont mind at all, considering how slow and docile she should be at low speeds and such light wingloading. I just wonder what kind of erratic behavior this thing's going to exhibit at the high end of the throttle?
The good thing is all that power is going to be controlled by the throttle . If you had full throttle ONLY --- it would be a handful !

Once properly set up ( CG , etc. ) , if you keep the control surface travel mild and use expo , it shouldn't be hard to handle . Like any plane , you'll probably get some torque roll with increased throttle .

Here is a case of possible TOO LITTLE wing loading , fast forward to 1:50 .

INDOOR FLYING / FAI F1D Aeromodelismo indoor F1D 室内飛行機 (6 min 58 sec)
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Old Feb 08, 2015, 05:51 PM
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Whoa.... Yeah, thats pretty light!
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