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AeroDagger Cranked Arrow Build

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Rktman

Eric
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The impetus for this self-designed scratch built glider project actually started on another thread here: https://bit.ly/32w0ftD where my goal was designing and building a traditional glider targeting minimum weight and maximum duration instead of my usual focus on strength and durability.

At the same time I also wanted to design a just-for-fun sport build with the same goals. So I'm doing both, and because I’ve always had a “thing” for designs like the Valkyrie XB-70, Concord, the Estes Raven BG, etc. I decided to go with a delta planform. There's just something cool about them.

Anyway, because deltas use vortex turbulence to produce lift, I decided on a *“cranked arrow” version to maximize lift. What that translated out to was adding strakes to the forward edge of the wings.

*https://bit.ly/3lyEqBs

My fictitious tongue-in-cheek face card above is my mind-sim of how it'll hopefully turn out. I always wanted to try a built-up wing so this is my chance to give it a shot while removing some weight at the same time.

I drew up my main wing layout below at the same time I was designing the glider on the other thread that's linked at the top.


Main Wing.jpg
 
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BABAR

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So the skeletal frame is covered with tissue? May need something a bit more flame retardant on the mid dorsal region for jet blast protection.

I am looking a a redesign of the CiCi. Looking for more roll stability. Would I be better off extending the delta or putting in some dihedral on the wings?
 

BABAR

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Would an elastic burn band work as a reliable attachment/release for the glider/pod link? Usually you can’t get an ejection charge to reliably do two things, but I think a slotted groove (same slot on both the outer pod pylons and the glider fuse) with the rubber band running across the lumen of the body tube just forward of the motor would definitely burn, would not significantly impede or vent the ejection gas. I’ll try to draw something up.
 

Rktman

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So the skeletal frame is covered with tissue? May need something a bit more flame retardant on the mid dorsal region for jet blast protection.

I am looking a redesign of the CiCi. Looking for more roll stability. Would I be better off extending the delta or putting in some dihedral on the wings?
Good idea. I've got some thin self-adhesive aluminum tape that's worked real well on my other gliders. It's a PITA to position dry, and using soapy water often leaves wrinkles that are hard or impossible to get out no matter how much I squeegee it. It won't look as good with the balsa skeleton obscured but I'd rather have that than a burned-through hole after its maiden flight. :eek:
 
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Rktman

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I am looking a a redesign of the CiCi. Looking for more roll stability. Would I be better off extending the delta or putting in some dihedral on the wings?
Dihedral would be the easiest and best solution IMO vs extending the main wing. Altering the size/shape of the main wing would affect the CG position.

Generally delta wings don't require dihedral (I don't recall the physics/aerodynamics of why) though the CiCi's wing isn't exactly a traditional delta shape (maybe a truncated delta?) but I find it fascinating that the glider obviously works without dihedral. Rob Edmonds was an engineer and he certainly knew what he was doing because it glides successfully.
 
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Rktman

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Would an elastic burn band work as a reliable attachment/release for the glider/pod link? Usually you can’t get an ejection charge to reliably do two things, but I think a slotted groove (same slot on both the outer pod pylons and the glider fuse) with the rubber band running across the lumen of the body tube just forward of the motor would definitely burn, would not significantly impede or vent the ejection gas. I’ll try to draw something up.
I was going with the Apogee Components universal pod hook but I'd be glad to see what you've got in mind (I'm a "show me" vs a "tell me" person...probably why asking for directions is hopeless unless I have a map that the person can point to lol).
 
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Rktman

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I put some scrap box balsa and cardboard to good use and made this prototype sometime in June in anticipation of this build. I originally was going to design this as a flying wing, but at the last moment I decided to change it to a canard…a bit harder but I like the profile better, and I’m more familiar with the peculiarities of canards, having built 12 to date, three of them self-designed scratch and 8 clones and 1 kit.

My little prototype glided surprisingly well despite being on the rather weighty side, so that was encouraging.

IMG_4528.JPG
 
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BABAR

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My little prototype glided surprisingly well despite being on the rather weighty side, so that was encouraging.
View attachment 438326
71BCF45D-077D-4592-A9CC-A5273A4D077B.jpeg

Not only do I like it but I may in some modification steal that from you. One of the issues with the CC and the CiCi2 gliders is these rudders that are put all the way at the far margins of the wings. I understand you can’t have one in the midline or it would get blasted by the jet blast but they certainly don’t have to be that far out. I can think of a way of doing this with a little bit of dihedral on the wings, putting two rotors on each but having them fit together in a more box like pattern which would be much more stable on boost. Thanks for the picture. You’ve inspired me today.
 

BABAR

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And I think you said that 3 degrees is the max incidence you recommend on a canard?
 

BABAR

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image.jpg


OK here’s the rubber band plan.

You have a hole in the pod tube just forward of the forward end of the motor. You put a half baffle plate just anterior to this to make sure that the course of the rubber band is directly anterior to the motor blast to make sure that it melts the rubber band. May need some JB Weld or something else on the baffle since it’s going to be close to the motor and may need some heat protection.

Before you start you feed the rubber band through the hole from the outside grab it with a crochet hook and pull it out the front and attach it to the hook on your nose cone. You can attach whatever else to the nosecone that you want including the shot cord or streamer .

The tension on the rubber band holds the glider in place in the slot on the pod. When the ejection charge fires the rubber band is instantly melted. Given it is stretched it will come out and release the glider.
image.jpg
 

Rktman

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And I think you said that 3 degrees is the max incidence you recommend on a canard?
My bad, I should have qualified that statement. I should've said 3° or so for gliders of this size in my experience. Bigger gliders may require more depending on weight and where the CG is located. My Ecee Thunder's max negative canard angle was 13.25°! (It had movable flaps that would lock at that angle during glide mode). George Gassaway's canard glider angle is 3.5°. I have a largish C powered canard that uses a 3.75° deflection. I'd start with 3° and tweak it if needed. I've started just tacking on the canard with my scratch-builts using shortened sewing pins so I can still change the angle as needed.
I believe your CiCi-2 canard's angle is negative 3°.
 
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BABAR

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Well, I need to post the CiCi2 flight, glider not recovered!
 

Rktman

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View attachment 438346

OK here’s the rubber band plan.

You have a hole in the pod tube just forward of the forward end of the motor. You put a half baffle plate just anterior to this to make sure that the course of the rubber band is directly anterior to the motor blast to make sure that it melts the rubber band. May need some JB Weld or something else on the baffle since it’s going to be close to the motor and may need some heat protection.

Before you start you feed the rubber band through the hole from the outside grab it with a crochet hook and pull it out the front and attach it to the hook on your nose cone. You can attach whatever else to the nosecone that you want including the shot cord or streamer .

The tension on the rubber band holds the glider in place in the slot on the pod. When the ejection charge fires the rubber band is instantly melted. Given it is stretched it will come out and release the glider.View attachment 438346
That looks like it has some fascinating potential, no offense but I'd rather stick to standard methods of pod attachment this go around rather than an experimental method.
 

BABAR

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That looks like it has some fascinating potential, no offense but I'd rather stick to standard methods of pod attachment this go around rather than an experimental method.
You are most kind.

Reminds me of med school Radiologist instructor.

He’d ask you a question.

If you gave a wrong answer, no matter how far off or stupid it was, he’d say,


“That’s a WONDERFUL answer to a DIFFERENT question!”

It’s been 35 years and I still remember that one,
 

Rktman

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Starting on the main wing framework. Borrowed the building board technique the free flight model plane guys use. Makes it real easy when assembled this way. Because I’m designing this to use 13mm motors in the 2.5 N-sec total impulse range I can’t afford to use soft, fragile contest balsa so I’m opting to use medium density to avoid shredding.

IMG_4523.JPG
 

BABAR

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Starting on the main wing framework. Borrowed the building board technique the free flight model plane guys use. Makes it real easy when assembled this way. Because I’m designing this to use 13mm motors in the 2.5 N-sec total impulse range I can’t afford to use soft, fragile contest balsa so I’m opting to use medium density to avoid shredding.

View attachment 438420
Okay, balsa quality neophyte here. (Sort of like the government, lots of experience without any real knowledge.)

I just go to hobby lobby for a 6x36” sheet at a time, or I order a 10 pack from Midwest. How do you know what “quality” or “grade” for any given sheet?
 

Rktman

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Okay, balsa quality neophyte here. (Sort of like the government, lots of experience without any real knowledge.)

I just go to hobby lobby for a 6x36” sheet at a time, or I order a 10 pack from Midwest. How do you know what “quality” or “grade” for any given sheet?
1605459146228.png


Balsa densities can be specified from suppliers like SIG or Specialized Balsa for a weighing/sorting fee.

This is Specialized Balsa's weight definitions for density. Weight definitions differ slightly among suppliers.
SOFT (aka "Contest balsa") = 6 to 9 lbs. per cu. ft.
MEDIUM = 9 to 12 lbs. per cu. ft.
HARD (fuselages, pylons, etc. where strength is important) = 12 to 16 lbs. per cu. ft.

Contest balsa is specialized and you'd only want to use it for competition gliders or where low weight is a necessity and strength isn't necessarily vital.
Medium grade balsa is good for general purpose use on glider flight surfaces and rocket fins.
Hard balsa is densest and heaviest and used where strength is paramount.

In all cases, C grain is the best and it's available in all 3 weight grades.
I used to visit A.C. Moore, which always had the best selection, and since I don't have a small portable scale I used to just look for C grain and heft likely looking pieces to compare weight and (surreptitiously) flex/bend the boards slightly to get a feel for stiffness/flexibility.
 
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Rktman

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Making some real progress. Just need to add the strakes and the framework is done.
It's times like this that make me glad I invested in a balsa a stripper. Such a simple tool, but when it comes to cutting consistent and repeatable widths of balsa, it makes life so much easier.

IMG_4551.JPG
 

Rktman

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Had a minor malfunction with my other build, but I’m back and got all the flight surfaces tissued on this project.
IMG_4629.JPG


Fuselage attached.
IMG_4637.JPG
 

Rktman

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Rudders installed.
IMG_4640.JPG


Canards attached, then tissued surfaces got coated with dope. The main wing required 4 coats of dope to stiffen and strengthen it. Of course that caused the tissue to wrinkle and pucker in some spots, but overall the wing surface is surprisingly rigid.
IMG_4651.JPG
 
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Rktman

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Was able to do a few initial trim tosses this morning before numb fingers and 28° weather forced me back inside.
Not unexpectedly, it’s nose-heavy since the main wing is pretty light in comparison. I had to add weight to the aft end to counterbalance the maybe too generous forward end thickness of the fuselage and the Apogee Components glider pod hook that at 1.2g, is a tad weighty for this glider.

Another thing I noticed is that it’s not tracking absolutely straight or consistently (it kind of "waggles") so I have a feeling I made the rudders too small to provide enough yaw control. My bad, I reduced their size from the version on the prototype, which didn’t have that problem. Hopefully I can remove the existing rudders without destroying the main wing that they’re glued to.

fuse front.JPG
 
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Rktman

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Got lucky, I was able to pry off the existing rudders without seriously damaging the wing. The Un-Cure debonder did a great job of softening the CA, I’m sure I would’ve had to scrap the wing without it.

IMG_5640.JPG


Here’s a comparison of the existing vs the new rudder size (outline), which matches what was on my prototype model.

rudder size comparison.JPG
 

Rktman

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Was able to do a longer trim session this morning. There’s a noticeable difference now that the new rudders are installed.

It still seemed a little nose heavy, and since I didn’t want to add any more weight to the rear end, I decided to add a flap to the trailing edge. Not bad, I was able to remove 0.65g of tail weight, and it only took a degree or less to get it to pull the nose up for a much improved glide. And reducing every bit of weight counts on a glider this size.

Final Ver1.JPG
 
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Rktman

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I’m not really liking having to add that flap on the aft end. It's been bothering me since it's more a band-aid fix rather than an optimized design.

So I decided to build a revised version #2, this time with a thinner forward end and a top-mounted fuselage that more closely duplicates my prototype. I was worried earlier that the front of the fuse needed to have more “meat” to avoid snapping, but since the canard actually fills the slot that’s cut into the fuse and serves to strengthen that area, I feel safe reducing the height and, subsequently, some of the weight.

And rather than adding more incidence to the canard (which could potentially create other problems during launch or flight) I’m going to airfoil it first to see whether it provides some more lift.
 

Ez2cDave

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Another thing I noticed is that it’s not tracking absolutely straight or consistently (it kind of "waggles") so I have a feeling I made the rudders too small to provide enough yaw control.
Eric,

It sounds like you are describing a "Dutch Roll" . . . Take a look at this short video . . . Is that the motion you are seeing ?

https://www.youtube.com/watch?v=Zmjam1evDD4

Dave F.
 

Ez2cDave

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Yup that looks like what I saw. Happily it doesn't do it anymore since I increased the size of the rudder to match what was on my prototype.
Good !

From what I have been reading, increasing Rudder Area is the solution for a Dutch Roll.

Dave F.
 
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