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Old Sep 05, 2011, 07:36 AM
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Delta or pod/boom - which is the best all-purpose FPV platform?

I was wondering what differences people have found in these two platforms? I know a lot of people are using zephyr or skywalker. I currently am using a WingDragon, but it seems to be getting too much drift and VTX interference due to its construction and size. Everytime you change a lipo or land rough the trim gets thrown out it takes half the next flight to get it safe. Also not self-correcting, so needs constant attention on the sticks. I'm new to RC and FPV, and would sacrifice aerobatics for stability. Are either of these former mentioned platforms better in this regard? Or another platform entirely?
Thanks
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Old Sep 05, 2011, 09:49 AM
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*best* depends on a ton of things you're trying to do. there is no "best".

popular are gliders hotliners pod & boom and delta wings. doesnt mean they're best.
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Old Sep 05, 2011, 12:41 PM
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I just started building a twin motor FPV plane after much deliberation over what configuration would be best.
The extra complexity of the two motors and ESCs is, in my opinion, more than offset by the ease of installing the motors and the better low speed handling (I expect!) due to having the propellers blowing over the wings.

Let's see how it works once its finished.
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Old Sep 05, 2011, 04:38 PM
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One thing to remember with twins - two props means more disc area (drag). Use smaller props and higher kV. Love my twin!
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Old Sep 05, 2011, 05:23 PM
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not sure how it works out with BLO's, but with gas and glow engines the added disk area gave you 15% more thrust vs a single engine of double the displacement.

that was the old rule of thumb anyway.
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Old Sep 06, 2011, 11:35 AM
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Anyone have experience with both platforms (or other) and can highlight the typical strengths/weaknesses of each?
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Old Sep 06, 2011, 11:46 AM
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It's kind of like comparing a sports car to a school bus. There is little comparison.

The Pod/Booms carry a lot of cargo and carry it well. They maneuver about as well as my living room couch.

The Deltas are faster and don't carry as much cargo. center of gravity is critical but they are quite nimble.

Twin motors split the difference. They're not quite as fast as a delta wing but can carry more cargo. They're fairly manueverable.

That said, my personal favorites are twin motors. I have a P-38 Lightning and a P-61 Black Widow that are excellent planes.

-Alex
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Old Sep 06, 2011, 11:55 AM
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Thanks IB. That answers my question exactly.
Side question: The #1 thing I like about my FireFly is that no matter how fast or orientation (even upsidedown), if I cut throtle and let go of the sticks, it will right itself, and go into a nice slow glide in wide circles. I often take it out of visual range, let go, and wait a couple of minutes for it to be in landing altitude.

If I could get a large AP platform to do that, I would be sold. Is it possible?

I've never had a delta wing, but like the idea as there are the Divinity and this as easy cheap scratchbuilds.
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Old Sep 06, 2011, 12:59 PM
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Check my blog for scratchbuilds. Just about everything I fly is a performance scratchbuild airplane. I have an AP platform I have yet to convert to FPV. It's a folding prop glider I built a few years ago. If you want, I can take a picture of it.

For aerial photography you will want to mount you AP camera under the wing. Put your video TX camera on a pan system such that throwing the langing gear switch pivots the video camera and lines the Video camera up with the still. This way you can focus on a good shot. Use the flap switch to take the photo.

Don't sweat over the prop in view. I actually really like having the prop out front. It makes it feel like you're inside the airplane. All that said, buy a Mountain models Magpie for FPV/AP.

-Alex
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Old Sep 06, 2011, 06:21 PM
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TheNiceGuy High wing, High lift, High dihedral / polyhedral give the qualities you want
A SIG Seniorita / Senior are the most successful "i have absolutely no help" R/C trainers and have been for decades because of what you describe wanting.

They are lightweight. (They weigh a full "class size" lighter than their size suggests)
They have an EXTREMELY high lift wing. If the speed increases, the plane WILL go increasingly vertical. If the plane points down, it'll naturally point itself up. (If you loop/roll one inverted at 300' and let go, it'll speed up & finish the loop HANDS OFF in 150' of altitude off speed increase alone)
Fairly extreme dihedral angle. If left in a bank, it will un-bank itself.
Extremely draggy airframe. They dont go anywhere in a hurry.


That's the style of construction you're looking for.





Deltas are a mixed bag with stability. Especially delta wings. High sweep angles work out to effectively give a few degrees of dihedral, but adding dihedral makes the wings fly increasingly worse. (Most GREAT flying high speed, aerobatic wings actually have anhedral to the wings to help negate the wing sweep!)
I've built a few kmf4 wings. Couple things going against them are getting all your equipment on the CG, kmf airfoils are REALLY DRAGGY & ineffecient (your flight times are GOING to go down vs "just having any random semi-sym airfoil". Even if it's "the outside of a shoe" random profile. Finally, they are NOT high-lift high-payload wings.
KMF4/Divinity's look the part like a Zypher at 30-40", but they typically fly less than a pound or two of weight. You'd REALLY want to scale one up. Probably 60-70".



i dont mind the props either, but I fly .2x-5x glow. one thing lots of electric guys don't know due to their prop/kv/v choices is even big props turn invisible to ccd's about 12-13,000rpm (about 2/3 throttle on what i fly). You fly at 15-17k they are completely invisible.
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Old Sep 07, 2011, 06:46 AM
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Here's teh FireFly I'm talking about:
FireFly with streamers (0 min 44 sec)

You can see teh basic design in the start of teh video. 4ply 5mm depron 24" ws with 1 10mm step on the bottom. Why does it self-correct so well? If I was to guess, I'd say it was teh delta wing shape, with battery weight front/under, and tail fin back/top - kind of opposing forces. Is this correct?
I'm very curious to try a wing for AP/AV/FPV if the frame can carry 1KG (all cargo, electronics, motor, etc), fly relatively slow and stable, and above all self-correct.
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Old Sep 07, 2011, 06:53 AM
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I think the self correction you're seeing is from the majority of mass being under the wing. This helps with righting itself in pitch, but would not help so much in roll. For self-righting in the roll axis, use dihedral.

To summarize what others have said: flying wings / deltas are maneuverable but somewhat unstable. Traditional designs (including pod and booms, twins) can be designed to be somewhat both maneuverable and stable. It is up to you as the designer to find the balance of maneuverability and stability that you're looking for.
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Old Sep 07, 2011, 07:12 AM
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deltas can have a HUGE amount of roll correction at speed with very little dihedral added. you can tell. some of them have horrible amounts coupling when trying to make their rolls axial.
what they lack is pitch correction. unlike other platforms, a flying wing (should) typically have zero trim change as speed changes. this is what makes other designs (virtually every real thermal glider, trainer and free flight designs) have lots of newbie safe factor. high lift wings that create more & more lift (vs stabilizer lift/aoa) as they go faster. causing pitch up. plane pitches up, slows down, lift decreases nose drops back.

you make these basic KF wings and they're straight, no dihedral & not very clean. you wind up with something that's not going to be as stable in roll as a built up delta/a hot wire with 2* tops of dihedral.

but if you like sport planes. go where you tell it planes. dihedral on delta wings is yuck. you want 1-2* of anhedral & they're amazing.



i know this sounds like harping on electrics (im not, its really more of a "if people knew half of what everyone else before them forgot we'd be better off!"), but i think some of it has to do with slow flight speeds electric wings have brought about too. a lot of the delta's now a days are nothing more than 30-50mph park flying cruisers. where you can get away with murder on things that don't fly all that well & people will say woooo that looks cool! where as 30-10 years ago flying wing deltas HAD to fly good. 'cause they were '100-150mph rockets with blur inducing roll rates. i mean 15 years ago you would have NEVER seen any kind of really popular delta plan with dihedral. they just fly bad. Now... People dont seem to know what anhedral is.
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Old Sep 07, 2011, 08:57 PM
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Quote:
Originally Posted by Toysrme View Post
...you make these basic KF wings and they're straight, no dihedral & not very clean...
I don't know if this was directed at me or not. If so, it's not well informed and not relevant to the thread. If not, it's still not relevant to the thread. Either way, lets see some pics (or plans) of your stable deltas!
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Old Sep 07, 2011, 09:41 PM
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directed at you? no. simply point out that almost all the KF wings out there are popular because of the ease of construction. laminate a couple sheets, or fold one over. they wind up straight wings.

deltas give a lot of effective dihedral, but more so as the speed raises. the flat striaght KF wings wont have as much self-righting in roll as an airfoiled, dihedral wing flying faster.
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