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RETjet Nutball-ish Slender Delta(great plane, beta stages!)

Vimana89

Well-known member
#1
Overview
Here's my latest(and first truly successful) attempt at a basic, single pusher prop, 3CH slender delta type plane. This is also my first truly successful scratch built plane of my own design! Unlike previous(and potentially future) designs which employed elevons or a tail plane for AET, this slender delta plane is set up for RET. I did a little research, and found that other hobbyists have successfully built and flown RET deltas, some of which were a bit on the lower aspect side. Early on in my building career, I envisioned a few models that were sort of a delta/teardrop/almond shape with a round back. Some were wider, others more slender. I sort of shelved the idea for a while. I also had some pretty sketchy experiences with the Nutball, which to me is a cool concept, but I was never able to control it well. I also always found it too pitchy and the wind resistance is just non existent. I decided to "risk it for the biscuit", and combine my slender delta idea with the rear end of a Nutball, and got the lean teardrop shape I had envisioned early on, figuring that perhaps it would yield a plane somewhat similar in handling to a Nutball, but without the pitchiness and with much more wind resistance, but with a bit more sensitive roll axis and more delta-like handling, even as a RET configuration. The dihedrals came out long and wide without sacrificing much of the plane's aspect ratio, due to the rounded back. The fuselage is the basic high-mounted pusher nose nacelle I've been using lately, based off the Kolibri Flyer and it's straight slender delta prototype (thanks to @Dr. Looping Looie for all the help and inspiration!)
 

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Vimana89

Well-known member
#2
Status Updates

Prototype Maiden Report and Handling Assessment: Flew on maiden launch, but the duration was brief due to inexperience and crash. Two more short launches and flights with crashes due to handling and inexperience, with the nose getting progressively more battered. After the third launch and crash, I rip part of the front fuselage paneling off because its hanging and creating drag, leaving a skeletal and partially open nose, but everything inside still ticking. Without much confidence, I launch again, but this time I anticipate the handling, and the nose damage doesn't seem to affect the plane too much, because it gets into the air once again, displaying pretty much the same handling characteristics as the first launch. This is where the magic happens! Launch four leads into an awesome flight, with steep climbs, clean banking, sharp turns, and when I got daring, tight, clean loops! I expected a long, graceful loop that ran wide, but this, by some strange physics, was closer to a backflip, but clean and tight. I busted off three of them, and did a low swoop and rapid pull up, and at the end of the flight, I decided to see how slow I could go on the landing approach and it turned out pretty good.

As far as handling, the pitch was smooth and perfect. The most so out of any RC plane I have flown, including RTF retail planes and kit builds(although I admit my experience is limited). I wasn't jerky, but it wasn't sluggish, and the plane could climb fully vertical. One of my main difficulties with the Nutball had actually become one of this plane's best features. The roll/bank was crisp and clean, but overly touchy. Slender delta wing planes have a touchy roll axis to begin with, but so does the Nutball, from my experience, so that feature stayed consistent between all three planes(the Nutball, a basic slender delta, and the RETjet). I flew this plane at about 75% throttle max. I really didn't go any higher, and not sure if it would have had any negative effect due to imperfect thrust angle or anything, I just wasn't confident to fly this plane at high speeds.

This, I believe however, was greatly exaggerated by one or two design imperfections; the main one being, after learning from experience what over-discharging was and why my two 650 3s batteries were not charging anymore...I only had 850s laying around, so that's what I used for my latest couple designs, including this one. Slender wing planes with their high wing loading don't really seem to like heavier batteries, which is probably why @Dr. Looping Looie uses a 600 on the Kolibri Flyer. I have ordered a couple of cheap 550's and will use one for my next build. That was almost certainly a factor. The second is a possibility that maybe my dihedrals were a little too drastic. I don't even have the angle measurement, I just sort of went by gut feeling/eye and cut out a quick gauge so both sides would be even, which has since been discarded. If anyone has a recommendation on what type of angle would work best for dihedrals given my wing shape, give me a heads up! As far as I know, more drastic dihedral gives more auto-leveling, but makes the roll a bit more sensitive as well? Inquiring minds want to know.:unsure:

The last handling quality, which is also a bit of an imperfection, was a nose-down tendency. I'm not sure this is inherent to the design,I know the Funjet on Multiflight has a bit of nose-down tendency. I believe the culprit is an imperfect thrust angle, because for a high mounted pusher forward of the CG, there's no exact formula that I know of for thrust angle. I gave it some downward thrust to blow down on the back end and counteract the lever effect that pushes the nose down, but it seemed not to have eliminated the issue. I tried to trim in a bit of up elevator, but for some reason the elevator servo(was using FT 5g servos on this build) was unresponsive to trim. Maybe the servo is getting old, maybe there was slop or tension in the push rod. The plane was still quite flyable, it just needed to be given some bit of up elevator of varying degrees at all times.

Overall, the plane displayed great potential and was a lot of fun. I have footage from flights three and four(the good one), displaying the plane's tight loops and turns and some of its steep climbing ability. I'm in the process of converting them and getting them properly uploaded to my new, empty Youtube channel. This design has some fun and distinctive handling qualities and aerobatic abilities, and it has a unique, exotic, Sci-Fi-esque look in its profile and the way it maneuvers.
 
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#7
Awesome!
That wing shape looks pretty cool! I cant wait to see some footage!
Is it the same fuselage as my one? If you want, you can use my plans and just change the wing. Also, do you want to try canards on this one?
 

Vimana89

Well-known member
#8
It is based on your fuselage by eye but slight differences in shape and construction. I may start using your tile plans for the fuselage and just change the wing shape when I experiment, or just use the exact same thrust angle on my fuselage. Canards sound like a good idea. I would probably have been experimenting with them here or there sooner, but I'm not sure about angle and placement to get the best effect. My next build of this one could possibly feature canards, they would have a unique look on this particular plane for sure, and any increase in stability is extremely welcome.I'd be willing to give it a shot, but the main things for sure it will have are a lighter battery and slightly less dihedral.
 

Vimana89

Well-known member
#9
I'll take a close look at how the canards are set up on the Kolibri. should they be straight or have some sort of pitch? Also, another thing I've heard about that I might try on some sort of future build are called strakes, which are basically just super low-profile canards, more like little turbulence generators really, the concord has these on the nose on close inspection. Any experience with these?
 

Vimana89

Well-known member
#13
I'll also probably make my canards not much different from yours or exact, the low profile and curved shape on the Kolibri canards go perfect with the shape of this plane rather than the bigger more angled/pointy ones on some other planes.
 
#14
@Vimana89 Canards usually increase pitch stability because they are designed to stall before the main wing, which makes the aircraft put its nose down and get more speed. To increase this effect, they are angled upwards and much smaller than the main wing, so that they reach a critical angle of attack earlyer. But high sweep deltas are pretty unstallable, here they have a positive effect by moving the CG forward and replacing the elevator trim needed on tailless aircraft. But you want them to be right If you also want good performance in high speed flight, because they make the nose pitch up.
Go ahead and test it out!
 

Vimana89

Well-known member
#15
I will add canards to the next version of the RETjet and see how it handles with the 550 MAH battery. I finished the tailed AET that I was working on concurrently. It looks nice and is trimmed in with a bit of up elevator to counter the slight nose down tendency of my fuselage thrust angle.
 

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Vimana89

Well-known member
#16
As far as footage, all the free services I used want me to pay because my vid is too big. I guess I'll just have to subscribe or get a temporary pass
 

Vimana89

Well-known member
#18
So I flew the AET and just when everything was going great, I got the nastiest unrecoverable tip stall and smashed my plane. I'm going to try repairing, and adding larger winglets.
 

Vimana89

Well-known member
#19
Nose is cobbled back together on the AET, cut down the extreme VS a bit and added bigger winglets. I'll see what happens, not too salty if I crash again because then I can just focus on the RETjet.
 

Vimana89

Well-known member
#20
I'm going to need to change the thread name to include the AET version, because with proper size winglets It's pretty good. Finally on one of these slender deltas does the roll axis feel good and locked in. I rolled this plane intentionally and successfully. It climbs nice. Only problem it still has is sometimes when maneuvering more aggressively it drops altitude a lot, and it feels like it's still wing loading from the 850. My last fligh was awesome, but it dropped too low at one point and I had this scrapey touch and go crash trying to pull up. I think when my lighter batteries come in, both of my designs will handle much better.