Why do foamies Deltas are so poorly efficient? - Page 3 - RC Groups
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Apr 18, 2018, 09:23 PM
flyin' fool
goldguy's Avatar
FACT .................I must be from another planet, because I've built true delta designs for indoor that had 'walk beside' speed and I've got a screwed up knee.

FACT ............... Even built a cardboard delta sloper that flew at zero ground speed.
https://www.rcgroups.com/forums/show...light=Warp%209

THEORY ....... I know what I'm doing??????
Last edited by goldguy; Apr 19, 2018 at 02:01 PM.
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Apr 18, 2018, 09:40 PM
Registered User
Quote:
Originally Posted by goldguy
I learned the theory, and the facts, as I progressed through the hobby over the decades (), mostly to correct my mistakes. That way I got in lots of flying, not much reading and was able to see it in action. All we had was model magazines published once a month and most of us were all on the same learning curve. Today, you guys are way to spoiled.

I usually recommend a proven simple conventional design to start with. If it's built as designed, then the student can spend more time learning the skills of flying, rather than fiddling and fussing to even get it flying in the first place.

Generally ..................... flying wings, deltas, swept swings and planks require a bit of patience to fine tune and can be frustrating to get it right.

I've watched lots of people teach themselves to fly with many different designs with little input from others. So, it also depends on the individuals too. I have FB that have been in the hobby as long or longer than me and still haven't mastered the skills.
One thing I noticed is new people are afraid to mess with things. I've always messed with my planes and my guitars, whatever I own to make it my own and learn how it works....hack away. And the second thing is knowing what affects what, which is doing the reading and doing the hacking....

Therefore wings are really easy for me. I use an online CG calculator measuring things accurately, and I set static margin at 12%. I put it there by moving things around and I leave it there. It may not be perfect, probably a bit nose heavy but that's OK. I learned what "reflex" is. I start with a few mm reflex almost always less than what people advertise. I maiden. I fine tune the reflex.... done.

So wings have been very easy and good to me....baseball been belly belly good....
Apr 19, 2018, 02:23 AM
flyin' fool
goldguy's Avatar
Same here. I'm an avid sloper and combat is our favorite activity. We fly mostly wings sporting the PW51 airfoil, which requires very little, if any, reflex.

For power fun I still favor a flattie tractor delta or a modified delta over a tapered/plank wing design. They are rock steady fliers, great in the wind and can fly more extreme aerobatics. Even with just elevens they excel at 3D. Quiet too, and yes, can fly slow too.
Last edited by goldguy; Apr 19, 2018 at 04:00 AM.
Apr 19, 2018, 04:51 AM
Registered User
being efficient and getting long flight times are sort of 2 different things although being efficient helps get more flight times.

Your flight time are going to be effected by how much power you are drawing. The ez flyer is a relaxed slow flying plane that is quite happy just cruising along at slow speeds. Compared to a delta design that is a bit more fun you might find yourself giving more throttle alot more often. servos are working harder etc

it might even be that the same power setup for the ez flier is just not suited to the delta and is actualy costing you flight time.

idk just a though i dont know much about aerodynamics, fluid dynamics and all the very complicated science that is behind flight so probably wrong
Apr 19, 2018, 05:52 AM
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Extreme Sports's Avatar
Quote:
Originally Posted by goldguy
We fly mostly wings sporting the PW51 airfoil, which requires very little, if any, reflex.
That's the way it should be - it was designed for planks and has the necessary reflex built in. . Some interesting info on it from the originator: http://www.rcsoaring.com/rcsd/RCSD-2006-06.pdf - see p28.

I'm also a big fan of wings, but with correx airfoils, one usually takes what one gets. There are some techniques to shape the airfoil so I might give one of these plank foils a try sometime....

All my wings are correx, of course. Here are two examples. The little flame decorated one has been clocked at over 100mph, which is way too fast for my flying site. The larger orange one (1.2m span, ~700g AUW) is getting around 0.8Wh/km, which is already pretty efficient for any plane of that size, let alone a correx SPAD that comes apart to fit in a grocery shopping bag. I've just rewound its motor and am getting 10% less current for the same thrust. I recon a double pack of 18650's and some more streamlining might just get me over the 100km distance target!

Did I mention I'm a big fan of wings
Apr 19, 2018, 10:19 AM
Registered User
That flamed one might be perfect for my next plane... looking to do something fast, but stable. Maybe a delta is what I'm looking for instead?, but I think having some actual "wings" will help in roll stability.

Only thing I would change is get those verticals further back, they look darn close to the CG so they're probably not doing much.

My first attempt at a fast plane was more similar to your first one in shape, I think part of the problem is the motor but it is very "bursty" in speed and when I try to do a loop, I do a corkscrew instead...dumb thumbs? I added expo but didn't change a thing, so frustrating I want to retire that thing... and since I gave it a heavy fast motor and heavy battery, hand tossing is insane....sorry I'm getting way off-topic.
Apr 19, 2018, 11:45 AM
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Extreme Sports's Avatar
Quote:
Originally Posted by rotagen
... looking to do something fast, but stable. Maybe a delta is what I'm looking for instead?, but I think having some actual "wings" will help in roll stability.
You can't go wrong with a Mugi, and I see you've already posted in the thread GG started. It was one of the planes that got me flying again after ~25 years out of the hobby. You can power it to be super fast or reasonably slow. Very stable if built true. Could be built from FFF or similar if 2mm correx is not available, but obviously won't be as tough. But hard to find a simpler design that is not a flat plate or kfm airfoil. The Mugi guys were promising to bring out an easier to fly version, but Morgan got involved in real life and the plane never surfaced. So I started a series of gradual changes that resulted in the planes pictured above. All plans are in this thread: https://www.rcgroups.com/forums/show...tor-WITH-PLANS. All are pretty well behaved and could be built from foam. Obviously the later ones are improvements on the first designs

Quote:
Originally Posted by rotagen
Only thing I would change is get those verticals further back, they look darn close to the CG so they're probably not doing much.
Might want to re-calibrate your gut feel . This one tracks on rails. It is unbelievably stable. It's basically a HK radjet planform with a few modifications - larger strake, Mugi style verticals and different wing-tips. And, of course, my signature indestructible pool noodle fuselage. But it can be tough to get it launched, and unless you've flown around 80mph, I don't recommend it....it is very small and very fast...you have to stay ahead of it. A Mugi is probably a better intro to fast planes.

Gil, I hope you don't mind these slightly OT discussions on your thread. I included the link as foam plus a pool noodle could be an option for you given your concern of possibly injuring others at your flying area. I might have linked this thread in one of your other posts, if so, my apologies.
Apr 19, 2018, 12:24 PM
Registered User
ES thanks for the input I can tell u know what you're talking about.

That flame one has to be more stable in roll direction than a delta, but that's just my bias. I bet if you took those verticals off it would have zero effect if you kept the same CG.

I do indeed have some 2mm coro but I wish I didn't buy light blue... hmm I should paint it for visibility.

It's between the mugi and a slight forward-swept pusher of my own design, (opposites?) I find the kungfu to be super stable and graceful but for some reason I want a pusher... I'm shooting for about 60mph, fast enough for me.

As an aside, I also tried the baby shark as a fast plane but I screwed something up in my build and it never flew right, these guys had vids of it flying crazy fast on a little blue wonder type thing at 3000kv and 3S... burnout danger?, I have some similar motors, I think I had the wrong idea putting a real heavy motor/battery in my first attempt at a fast plane. For some reason I think the shark would be more stable than a delta but I have no true delta experience....perhaps mugi it is.

http://www.nanoplanes.net/bshark.html
Last edited by rotagen; Apr 19, 2018 at 12:32 PM.
Apr 19, 2018, 01:26 PM
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Extreme Sports's Avatar
Quote:
Originally Posted by rotagen
I bet if you took those verticals off it would have zero effect if you kept the same CG.[/url]
I hope your addiction for scratch building never extends to gambling....you gonna lose a LOT of money .

Due to the enlarged strakes, the CG is much further forward than you'd guess (almost at the intersection of the wing and strakes) - so there is a substantial moment arm for the verticals to provide yaw stabilization

I wish we got coloured correx locally. We've probably got the cheapest, most readily available 2mm correx in the world, but it is only white, and, if you are very lucky, sometimes black.
Apr 19, 2018, 01:43 PM
Registered User
OK I zoomed in, you might have at most 2 inches between the center of those verticals and CG, but it might be enough to move a mosquito fart. Only way to tell if it's doing anything is to do my suggested experiment...I guarantee you'd be surprised, there are quite a few wings without verticals so the point is moot, go to nurflugel forum, frankly who cares.

Care for a game of poker? and not some cheesy holdem? Hehe. Never lost a big money game in my life, oh college those were the days.

ebay is your friend, got it there cheap but you gotta keep an eye out, orange would have been better but coro sucks anyways, light is might. I should sell you mine.
Apr 19, 2018, 02:24 PM
Registered User
Extreme Sports's Avatar
Definitely stay out of casinos....just measured and it is almost 6 inches!. The orientation of the photo probably distorts.

But back to topic: I'm not 100% sure of this, but this thread has had me thinking about why a glider like configuration is more efficient than a pure wing for maximum duration flying. Here is my logic:
  • Max duration will be achieved at that speed close to that where drag is minimised (for non-gliders, the optimal efficiency of the propulsion system is also a factor and this might push the optimal speed slightly away from the lowest total drag speed...this is why in real planes the speed for max endurance is usually not the same as the speed for max distance).
  • Form/parasitic drag increases by the square of speed, so you want the plane to have a fairly low speed for minimum drag. But at low speeds, induced drag dominates, so maximising flight duration is primarily about minimizing induced drag. The way to do this is by increasing the aspect ratio. Some full size sailplanes have aspect ratios above 40:1. RC gliders seem to range from ~7:1 to as much as 20:1 (there are issues with minimum chord sizes that apparently limit the chord).
  • My guess is that at these high aspect ratios, a flying wing simply won't have the necessary yaw stability to be flyable, even with all the twist and duckeron tricks....hence the need for a conventional fuselage and tailplane. This is the bit I'm not 100% certain about - there have been a few massive, high aspect ratio flying wings, but they look to be well beyond the scope of us hobbyists - see the pictures below.
  • Probably then, for given aspect ratio, it would be true that a well designed flying wing would be more efficient than a conventional layout. The catch is simply that, within the realm of us hobbyists, a flying wing can't achieve the high aspect ratios that a normal glider layout can, and so, overall, a high aspect ratio glider style plane will give the longer flight endurance.

As I said, I'm not 100% sure of this, but I did build a fairly high aspect ratio wing (~8:1), but quickly added a tail after getting into an unrecoverable spin on the first set of flights. It flew OK (apart from the spin), but I'm pretty sure it would have become yaw unstable if I'd pushed the aspect ratio much higher.

Gil, here is some more reading for you on drag and aerodynamics: https://www.faa.gov/regulations_poli...a/gfh_ch03.pdf
Apr 19, 2018, 02:38 PM
Registered User
OK I stand corrected that must be a big wing.... but back to gambling...... you keep advertising but where is the location and is there beer and music? Just kidding around.

Yes I think it boils down to tailed planes are much better at keeping the wings level, and you can have a tiny thin fuselage and small tail surfaces way back there to lessen drag. But they're just not much fun those gliders with thin long wings, however... you can drink a beer while flying and possibly play a little texas foldem... but then so could a chimp....wombats however are very poor poker players...and

As the ezflyer thread concentrates on UFOs, we need to start focusing on gambling. Don't mind me.

One thing I read and I found to be sorta true, a fatter wing (bigger chord/wingspan) I forgot how aspect ratio puts the fraction...duh.... has more lift at slower speeds, but perhaps the drag is a drag for the sailplane geeks....who know very little of odds,bluffing, etc and tend to raise on an inside straight...don't u let that deal go down.
Apr 19, 2018, 02:58 PM
An itch?. Scratch build.
eflightray's Avatar
batata003 has decided to ask in the Modelling Science forum.


.
Apr 19, 2018, 07:27 PM
flyin' fool
goldguy's Avatar
Some of you guys are overthinking this hobby.

I was chucking around model gliders successfully seventy years ago when I was just five years old. I just followed the instructions that came on the package.

The rules haven't changed since.
Apr 19, 2018, 07:37 PM
Kimbers Keeper.
BHOFM's Avatar
Quote:
Originally Posted by goldguy
Some of you guys are overthinking this hobby.

I was chucking around model gliders successfully seventy years ago when I was just five years old. I just followed the instructions that came on the package.

The rules haven't changed since.
I have been trying to tell people here that for years!

Until some one comes up with a better flux capacitor the
rules won't change!


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