Project Wraith

[Rktman]

Codename: Wraith, a clandestine black program stealth aircraft that utilizes an exotic propulsion system to enable it to transcend speeds in excess of Mach 5. Well, that’s the fictional background story behind this design idea anyway.

This build is a resurrected scratch design from years ago that I "temporarily" abandoned. It’s been languishing undeveloped for years (since mid-2018). Inspired by the B2 stealth bomber and the almost-mythical triangular SR-91 Aurora hypersonic aircraft, it originally took the form of a flying wing which I just couldn’t get to work. So I then tried a canard planform – another dead end. The prototype was made of cardboard, foam core board, and balsa but was admittedly too heavy to get out of its own way.


A BIT OF HISTORY

The idea originally took hold from this:



A napkin that somehow got folded into a delta shape vaguely reminiscent of the B2. The thought occurred that it’d make a really cool-looking glider. I think it would have if I could have gotten it to work. Try as I might I couldn't, so I went with Plan B.

Some inspired revising and sketching in Illustrator resulted in this:



A large D - G motor beast with wings made of three 1/8” x 3” x 36” balsa sheets glued together edge to edge to form the wings. Of course the prototypes (one full scale, the other with about an 11” wingspan) as already mentioned, also refused to work. So the project was shelved for the last 4+ years, until just recently when I stumbled across the dusty prototype remains in my closet.

Guess I just couldn’t scrap the idea and decided to give it one last try, impulsively pencil-sketching a revised design (below) that now incorporates a rear elevator flap. Guess I’m getting reckless in my senior years because this time I've decided to forego building a prototype to check feasibility. It either works or it doesn't so I'm going to go straight to a build despite being in uncharted territory. (To my knowledge I don't think there's ever been a free flight delta flying wing RG or BG design to use as a guide, at least not one without a prominent counterbalancing fuselage projecting from its forward end). Without it, I’m not absolutely sure that it’ll have a long enough moment arm to be stable. Guess we'll see.

Since my first foray into this planform didn't really fly (literally), fingers crossed I can get it to work this time.

 

[Rktman]

So far, here's where I'm at. My intent is a medium sized for-fun sport glider for small-field flying, so maximum duration flight times are not a concern. It’s currently designed with a bottom motor pod for two reasons: 1. The elastic that activates the rear flap would be exposed to the hot exhaust of the motor if the pod were on top, and could burn through. 2. It’s basically a flat-plate glider with no airfoil, and the topside will be occupied by a cockpit and maybe some air intakes, etc. It depends on the weight distribution requirements though. If more weight is needed up front, then the cockpit will be there if nothing else.

I want it to have that mysterious black Aurora triangle silhouette that witnesses have reported, but sporting that unique ziggurat wing trailing edge of the B2.




As a starting point for its CG, I used an online flying wing CG calculator. It pinned it 5.72” from the wing's leading edge. It’s just a rough estimate though, as the Wraith is not a flying wing per se, but a triangular delta flying surface. Further, it'll use an elevator flap to determine its glide angle and balance.




Edit: Per Frank's comment (post #4 below) using the winglib.com site's pure delta model instead of the site I used would put the CG closer to 5” from the glider wing’s forward apex.

Sheerly out of curiosity I had earlier folded several paper airplanes just to see where their CGs were located. Being roughly triangular, their CGs consistently fell 40% from the wing’s forward apex. It may be just coincidental that it's in the ballpark, but that would put this design’s CG somewhere between 5 ½” – 6” from the forward apex of its wings. I’m curious to see where it actually ends up – assuming it proves airworthy.

 

[Rktman]

“Measure twice, cut once”. The build.

Went old school -- printed out paper templates and began hand-cutting balsa. Although I originally was going with 1/16” C-grain to minimize weight, the thought of possible flexing, flutter, and failure under launch stress made me switch to 3/32”. That also gives me the option of going with a C motor.

 

[burkefj]

So far, here's where I'm at. My intent is a medium sized for-fun sport glider for small-field flying, so maximum duration flight times are not a concern. It’s currently designed with a bottom motor pod, since it’s basically a flat-plate glider with no airfoil, and the topside will be occupied by a cockpit and maybe some air intakes, etc. It depends on the weight distribution requirements though. If more weight is needed up front, then the cockpit will be there if nothing else.

I want it to have that mysterious black Aurora triangle silhouette that witnesses have reported, but sporting that unique ziggurat wing trailing edge of the B2.

View attachment 559488


As a starting point for its CG, I used an online flying wing CG calculator. It pinned it 5.72” from the wing's leading edge. It’s just a rough estimate though, as the Wraith is not a flying wing per se, but a triangular delta flying surface. Further, it'll use an elevator flap to determine its glide angle and balance.

View attachment 559489

You can use the wing calculator on delta wings just have the tip chord zero and set the CG % to where you want, Not sure why you are modeling with a swept wing, there is a model from winglib.com with your wing sweep and as a pure delta and at 20% MAC which gives about 45% of root chord or 20-25% of MAC. Note in winglib the span is for each panel so 7" in your case and the root would be 10.7 for your wing sweep.

 

[Rktman]

You can use the wing calculator on delta wings just have the tip chord zero and set the CG % to where you want, Not sure why you are modeling with a swept wing, there is a model from winglib.com with your wing sweep and as a pure delta and at 20% MAC which gives about 45% of root chord or 20-25% of MAC. Note in winglib the span is for each panel so 7" in your case and the root would be 10.7 for your wing sweep.

View attachment 559694

I used https://fwcg.3dzone.dk/ The Flying Wing CG Calculator site because I wasn't aware of winglib.com. Thanks for the new resource Frank!

 

[Rktman]

there is a model from winglib.com with your wing sweep and as a pure delta

View attachment 559694

Is the model you're referring to TL001?

 

[Rktman]

There aren’t many pieces to jigsaw together at this point, so things are progressing faster than my usual glacially-paced builds. Just need to even up some of the edges with sandpaper. The most time-consuming part is waiting for the glue to dry.




Fuselage shaped and waiting for the first layer of glue to dry (double glue joints are SOP).

 

[Rktman]

Fuselage stick attached and filleted.




Nose plate attached (pic is of the glider's bottom side). This is what the pylon hooks will grab onto.




Rudders (vertical stabs) cemented in place. The overhang will serve as a flap-stop.




Similarly, the elevator flap will bottom out against the rear of the fuselage to keep the flap at a neutral angle for launch.

 

[Rktman]

Moving along, I fabricated a small flap control horn from 1/32” ply. A Kevlar string will run from this to a point under the motor pylon, keeping the elevator flap pinned in place until the pop pod ejects, freeing the string. Well, that’s what I have in mind anyway. It should be a simple enough workable solution.






Elevator flap attached with Blenderm, and music wire elastic anchor installed.




Closeup of rudder trailing edge. The overhang angle allows the rear of the flap to rise 1/16” (6.5°). If it needs more angle during trimming, sanding with an emery board will make small adjustments possible.

 

[burkefj]

Is the model you're referring to TL001?

I just built a new wing on the site and put in your dimensions and sweep.

 

[Rktman]

Several quick tosses across the bedroom and it became obvious that it needs nose weight (not a surprise, as I was expecting it would require something like a thumb-sized slug of clay). Without it, it just flipped end over end like a falling leaf. Since it's going to take more than just a tiny bit, the cockpit will happen. No jet intakes or other greeblies though, they’ll weigh too much.

Had to slow down the build pace. To fabricate the cockpit I had to glue several pieces of ¼” balsa together and begin the slow process of carefully carving, shaving, and sanding it to an appropriate shape (or at least what I think is appropriate and convincing anyway). What I thought was hard balsa turned out to be quite soft and crumbly inside, so it's been slow going. I'm not complaining, it's actually kind of meditative, but at least Michelangelo had assistants to move things along. (No, I'm not comparing myself to Michelangelo…he'd probably do a better job than I'm doing…faster, and in marble no less).

Anyway, I want to sand and seal it reasonably smooth, then hollow out the underside to stash any additional weight that might be required.

ANYONE HAVE SUGGESTIONS ON HOW I CAN TEMPORARILY MAKE THE CANOPY DETACHABLE SO I CAN ADD/REMOVE WEIGHT? I’D WANT TO DO A COUPLE OF TRIMMING FLIGHTS BEFORE GLUING IT PERMANENTLY DOWN.

 

[waltr]

Anyway, I want to sand and seal it reasonably smooth, then hollow out the underside to stash any additional weight that might be required.

ANYONE HAVE SUGGESTIONS ON HOW I CAN TEMPORARILY MAKE THE CANOPY DETACHABLE SO I CAN ADD/REMOVE WEIGHT? I’D WANT TO DO A COUPLE OF TRIMMING FLIGHTS BEFORE GLUING IT PERMANENTLY DOWN.

A couple of straight pins?

 

[Rktman]

A couple of straight pins?

Great suggestion; simple and easy. I put in a pin fore and aft. That and a little masking tape should ensure it stays put during launch.

 

[BABAR]

A couple of straight pins?

Hair Pins have been something I have been playing with lately, the do a great job holding flat things together. Also potentially a way to add easily removable nose weight for practice flights.

 

[Hobie1dog]

nice Balsa work

 

[Rktman]

Hair Pins have been something I have been playing with lately, the do a great job holding flat things together. Also potentially a way to add easily removable nose weight for practice flights.

You mean those things that used to be called "bobby pins"? (I know, probably an archaic term. But then, so am I). Not applicable for the cockpit since it isn't flat, but it's a good idea I'll keep for when I'm doing glider trimming sessions.

 

[Rktman]

nice Balsa work

Thanks, appreciate that!

 

[Rktman]

Cockpit roughed out, with an initial coat of sanding sealer:




3 coats of sanding sealer later – decent enough, since it’s just for fun and not a scale model.




The hollowed-out interior:




I also gave the glider a nose job. The forward extension of the fuselage was intended as a spot to attach nose weight to, though I didn’t have a clear idea of how to do it in a “cosmetically pleasing” way. Because it was just functional, I didn’t care for the way it looked so I sliced it off – “blunted” it to give the glider a more pleasing profile.



Being the furthest point forward, it’s the most effective location to add nose weight, so I routed a hole into it and inserted half a lead split-shot fishing sinker into it and patched it over with CWF.

 

[Rktman]

I had second thoughts about using Kevlar string to lock down the rear flap, as it may not be tough enough to withstand the heat from the motor’s exhaust plume.

I substituted a thin length of music wire in its place, the way RC planes are set up. I used the motor pod’s pylon to lock it into place in a little groove in the fuselage.









Motor pod completed and waiting for the right temp/humidity conditions to paint.



Anxiously waiting for the right weather conditions to do a trimming session to see if the design flies or flops.



To be continued…

 

[Rktman]

Trimming session
Saturday, 2/4/23, 8:15am, 24°F, Wind: 5 – 7 mph

Very rewarding session despite the early morning and chilly temps. Elated my aerial experiment not only worked but displayed a pretty decent glide during its trimming session. Since the previous attempt at scratch-building a workable flying wing design failed, I really wasn't sure how well things would go this time.

I’m pretty stoked the glider operates the way I hoped, especially since I had to guesstimate the amount of nose weight required to make things work (it ended up being a bit short) so the hollow cockpit worked out great as a place to put the additional weight to get a decent glide path.

The estimated online CG location from Frank’s winglib.com site was 4.99” from the wing’s forward apex. After trimming, the CG is now centered at 5.875” (5 7/8”) from the glider’s forward wing apex, surprisingly not that far off (about 7/8”) considering the effect of the rear flap and the irregular wing trailing edge, which isn’t accounted for on the online calculator.




That’s the best of the video captures, as barely any grip space, an hour in 24°F weather and numb fingers made consistent tosses really difficult.

That aside, I’m happy with the project result: a pretty cool-looking, out of the ordinary sport glider that’s great for small-field flying.

 

[Rktman]

A few shots of the glider decked out in its minimal “stealth” livery.












And a fantasy concept rendering of the Wraith in flight:




I’m also considering building an 85% scale parasite version because: A) I’ve never fabricated a parasite glider before so it should be an interesting experience; B) No intricate flap hold-down mechanism or method is required. The glider’s cradle will function to restrain the flap in a neutral position; C) Flight prep will be much faster and simpler; D) I’ll be able to build the glider out of 1/16” balsa since there’s less stress on it during launch; E) I’m curious to see what the difference in flight time/performance will be. I’m considering doing a separate “spinoff” thread for the Mezzo Wraith.

The relative size difference doesn’t look like that much, but I’m expecting the weight difference to be.




Waiting for some cooperative weather to do a test flight and final trimming. In addition to the straight pins, I'll tape the cockpit down to make sure it stays put, just in case any weight adjustment is necessary. Hoping to capture some decent video footage, or at least some stills. Stay tuned.


…to be continued

 

[Cape Byron]

Looks great. Really nice work.

 

[Rktman]

Looks great. Really nice work.

Thanks, really appreciate that!

 

[burkefj]

Trimming session
Saturday, 2/4/23, 8:15am, 24°F, Wind: 5 – 7 mph

Very rewarding session despite the early morning and chilly temps. Elated my aerial experiment not only worked but displayed a pretty decent glide during its trimming session. Since the previous attempt at scratch-building a workable flying wing design failed, I really wasn't sure how well things would go this time.

I’m pretty stoked the glider operates the way I hoped, especially since I had to guesstimate the amount of nose weight required to make things work (it ended up being a bit short) so the hollow cockpit worked out great as a place to put the additional weight to get a decent glide path.

The estimated online CG location from Frank’s winglib.com site was 4.99” from the wing’s forward apex. After trimming, the CG is now centered at 5.875” (5 7/8”) from the glider’s forward wing apex, surprisingly not that far off (about 7/8”) considering the effect of the rear flap and the irregular wing trailing edge, which isn’t accounted for on the online calculator.




That’s the best of the video captures, as barely any grip space, an hour in 24°F weather and numb fingers made consistent tosses really difficult.

That aside, I’m happy with the project result: a pretty cool-looking, out of the ordinary sport glider that’s great for small-field flying.

Well, that and we chose and arbitrary 20% as your MAC number which yielded 4.99, so you are probably at a less conservative 25% or so now. Looks good, congrats.



"The estimated online CG location from Frank’s winglib.com site was 4.99” from the wing’s forward apex. After trimming, the CG is now centered at 5.875” (5 7/8”) from the glider’s forward wing apex, surprisingly not that far off (about 7/8”) considering the effect of the rear flap and the irregular wing trailing edge, which isn’t accounted for on the online calculator."

 

[shockie]

Great project! Idea: convert to a rear engine glider like the old Estes Sky dart with ejectable internal engine pod

 

[Rktman]

In the interest of full and transparent disclosure, I’ll have to say that the Wraith’s maiden flight was not what I was expecting or hoping for.

Had a chance to do a test flight this past Wednesday (2/22/23) and some tweaks may be necessary. In analyzing the video footage, the glider didn’t launch straight up, probably due to the 15 – 18mph wind. The motor pod pitched horizontal before releasing the glider upside down. The sudden activation of the elevator flap caused the glider to swoop up steeply and it appeared to recover right side up with another steep loop. At that point there wasn’t enough altitude for the glider to level out so it tried to core sample (thankfully no damage was sustained due to the wet sod).

If the double-digit winds were responsible, then flying it on calm low-wind days should ameliorate the problem. Angling the launch angle so that the glider is more on top of the pod would also help. (Due to the stiff winds, I had to face the back of the glider to the wind instead of downwind to keep it from being constantly blown off the pod hook).

If it still has that looping problem on a calm day, then going to a C6-3 might allow it enough altitude to level out. Another alternative would be to hang it on a larger rocket as a parasite glider. If none of the above works, I guess it’ll live life as a pretty HLG and shelf queen.

 

[burkefj]

Always test fly in calm winds....

 

[Rktman]

Always test fly in calm winds....

The day started out with single-digit winds and after a 2 hour 93 mile trip I couldn't bring myself to not fly. Guess I was pushing it. A larger glider put in a beautiful flight so I admittedly got carried away and put up the much smaller and lighter Wraith.

 

[Rktman]

Update:

Wraith flight 2
Got a chance to fly the Wraith on a relatively low-wind day, in this case 4 - 6 mph.

Launch rod was angled about 5° downwind since it tends to arc into any prevailing breeze. Sent it up on a B6-2 and it did much better than on its maiden flight several weeks ago. Pretty obvious the glider doesn't like double-digit wind conditions.

Although I hand-trimmed it for a nice shallow glide, it's pretty evident that it's still nose-heavy. I doubt the 2 straight pins and tape holding the cockpit down can account for much extra weight.

Proof that despite even the best hand-trimming session you can manage, only test flights will give you a true picture of how it'll behave once released at high speed and subject to any wind gusts.





Wraith flight 3

Wasn't sure I kept the glider in view of the camera so I did another flight, this time on a B4-2. Winds were starting to pick up by the time I got the glider prepped and on the pad (probably in the 7 - 10mph range). Unfortunately the wind direction changed suddenly (something not uncommon in the park I fly in) and a gust caught it just as it left the pad. It arced and didn't get as much altitude as the previous flight. It doesn't have enough mass to easily punch through breezes but I'm pretty happy and sure that I can get better performance by either removing some nose weight and/or adjusting the elevator for more upflap. I’m also considering doing a larger version (vs a smaller parasite downscale) to increase the wing area to get a more favorable wing-loading situation and flight duration.

One thing's certain: like its mythical namesake, it sure is a fast flier.

 

[Crawf56]

Well done you!