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Old Oct 07, 2006, 05:06 PM
Purples a fruit
punkrockd's Avatar
United States, CA, Walnut Creek
Joined Aug 2006
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how do i find cg on a delta

hi, i'm trying my hands on a delta home made plane.

its measurements are 25 1/4 from le to te wing is 23in span basically a triangle, but off each end of the te i measured 4 1/4 inchs upward toward the le and cut the wing tips straight and square because i want to install 2 vert fins (like a zagi), basically like a long triangle with the te corners knocked off. i plan on using a small outrunner like a bp21 mounted as a pusher in the plane with the cut out for the mount and prop.
i'm just wanting some advice as to figure out the cg. is it the same as a conventional plane.

thank you
this is my first delta/wing homebuild
dario
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Old Oct 07, 2006, 06:00 PM
Sussex, UK
RobinBennett's Avatar
Crawley, West Sussex, UK
Joined Jun 2004
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It's often about half way between the nose and the tail.

The technical method is here:
http://www.airfieldmodels.com/inform...amic_chord.htm
Once you've found the MAC, the CG should be about 15% of the way back, as for a flying wing, except deltas aren't quite as critcal as a flying wing.

It sounds like you're building something similar to a superfly, so you could have a look at the plans at www.superflyrc.com and scale their CG position to fit your plane
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Old Oct 07, 2006, 06:06 PM
Purples a fruit
punkrockd's Avatar
United States, CA, Walnut Creek
Joined Aug 2006
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thank you robin, yes it looks alot like the superfly. just bigger. and flat. its just 6mil depron, and i might sheet with 3 mill and form an airfoil, i dunno kinda just winging it

but thank you for helping me out

this is good fun
dario
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Old Oct 08, 2006, 02:39 PM
Registered User
USA, CA, Dublin
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um so when you're trying to find the mac, do you include the elevons or not?
thanks
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Old Oct 08, 2006, 03:14 PM
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Florida
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Yes, the elevons are included. Always include the control surfaces on any flying surface (wing, stabilizer, etc.).
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Old Oct 08, 2006, 05:23 PM
Purples a fruit
punkrockd's Avatar
United States, CA, Walnut Creek
Joined Aug 2006
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thanks again robin,
i flew it today and it flew great. i'm still messing with the cg a bit and the reflex. with the 2408-21 with an apc 7x4 running on a tp 1320 3c the plane had unlimited vertical and controls are very good. i could float it around with just very little throttle, and at full throttle it is quite fast. it definatly is alot more fun then my stryker. the power to weight is as good as my profile 3d plane, if not better. i'm definatly building more of these at diffrent scales.

good ole' fun
thanks
dario
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Old Oct 08, 2006, 07:29 PM
Purples a fruit
punkrockd's Avatar
United States, CA, Walnut Creek
Joined Aug 2006
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well i stuffed it. it rolls so fast that i over corrected and up wasnt up. darted in the ground, its fixable just ruined my battery. too bad. loved the tp 3c 1320. it just slightly was crunched. very small and minor bat damage, i've seen some bad ones.

any of you guys ever run a pack after sustaining minor damage?

d
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Old Oct 09, 2006, 03:03 PM
Sussex, UK
RobinBennett's Avatar
Crawley, West Sussex, UK
Joined Jun 2004
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It's not recommended but lots of people have tried it.

You could try running it with the plane on the ground and the battery not strapped into the plane. Then charge it somewhere extra safe from now on, because every time you use or charge it there's an (extra) risk of it igniting.

Could have put more padding infront of the battery? I've crashed my superflea loads of times without that much damage.
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Old Oct 09, 2006, 04:33 PM
Purples a fruit
punkrockd's Avatar
United States, CA, Walnut Creek
Joined Aug 2006
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yeah i should have done that. next plane will be diffrent. i charged the battery and it smelled similar to rubbing alcohol so i discharged it and stabbed it in water. tomarrow i'll throw it away. i'm new to lipo batts, and i'd rather buy a new one then risk loosing my apartment or an inflight melt down.

thanks for the help robin, i'll post again when i get some more depron and get the build on.

thank you
dario
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Old Oct 09, 2006, 05:52 PM
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Joined May 2006
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I've ruined a TP 1320 3s on a wing before. I knew it was bad because the pack was physically punctured and I smelled that sweet smell. When that hapens, its over--although if the damage is isolated to only one cell you can remove that one and downgrade to a lower cell count. One way to test for micro-punctures is to let the battery sit in a closed container for a period of time, such as an hour or overnight, and sniff the air to see if you smell the sweet smell.

If it's not punctured, why the heck not keep using it, assuming you have a safe place to charge and store it (i.e. fireplace). I've seen some people, although mostly newbies, using batteries like the TP2100 3s deformed almost to the point of looking like silver sweet potatoes, yet still function.

It would probably help to charge it on a balancer frequently, if not every time (ideal), in case one of the cells has an effectively lower capacity due to the crash.
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Old Oct 10, 2006, 05:32 AM
My plans are in my blog
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Kotzebue, Alaska
Joined May 2006
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I do believe li-polys have a tiny vent built in (read this somewhere). My packs from Batteries America are fine, and do have that sweet smell all the time (container is a large ceramic jar, sealed with a gasket).
BTW I was inspired by this thread yesterday to draw up plans simular to the SuperFly planes, and intend to have a try at it. The ZagNutz we built recently are interesting flyers. we're still beginners to flying wings, though.
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Old Oct 10, 2006, 03:45 PM
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Joined May 2006
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Interesting. I was under the impression all cells were vacuum-sealed, although I’ve heard people report the sweet smell coming from packs stored in containers. My suggestion should probably be corrected—perhaps the sweet smell is not a sign that the packs are dead, but not smelling the smell would at least let you know they’re not punctured.
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Old Oct 10, 2006, 05:42 PM
Purples a fruit
punkrockd's Avatar
United States, CA, Walnut Creek
Joined Aug 2006
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alright!! hey rusty, if you can post your progress. the plane i built was really fun. faster then a stock stryker b.

but it rolls super fast. so i would set the ailerons real low or lots of expo.

mine was just a flat piece of 6mil depron.


very fun
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Old Oct 11, 2006, 04:54 AM
My plans are in my blog
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Kotzebue, Alaska
Joined May 2006
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Punkrockd... my supply of foam sheet material (BP Hobbies 'C' Foam) hasn't come in yet (the other items did arrive, so any day now I think). I had a question concerning the tail arrangment, and posted a new thread, but no responces yet. My question concerns the tails on the SuperFly planes, being near the middle area, vs. on the tips, and using the ZagNutz directions where a flat wing system needs tails on the tips. My intentions are to create folded airfoils with flat bottoms (easier for this beginner to do). I assume the SuperFly planes have the proper "molded-in" tip reflex, or whatever its called, which eliminates the death spirl. Putting tails on the tips helps in this regard. Not sure if tails on the top, near the middle, would serve the same purpose on flat bottom wings though...
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Old Oct 11, 2006, 08:27 AM
Purples a fruit
punkrockd's Avatar
United States, CA, Walnut Creek
Joined Aug 2006
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that is outta my league. on my delta i had very little reflex with elevons and i guess i'd have to try diffrent arangments with the vert stabs.

i live in sacramento, i've looked every where for bluecor and the other stuff like it.

i'll end up ordering some of the really thin epp and end up doing the same.

d
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