JACKKNIFE SWING-WING BUILD THREAD

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Rktman

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I’ve seen two or three videos on YouTube of the HDI2004 Swinger and the launches and glide recoveries looked really nice.
That's the frustrating part. I've talked to the guy (Rick Needham) that made those videos and compared notes, and I still can't figure out why his performs so great and mine doesn't. :questions:
 

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Here’s some cool information/reviews on some QCR stuff. I wonder if any of the plans are in there?
I think it's genius how they used square styrene tubing for a slide box. Strange how I can't find any from suppliers like Evergreen or Plastruct that can fit over a 1/8" spruce or carbon fiber fuselage anymore. That square tubing is a much better solution for a slide box than having to build one from thin ply.

Had to build my slide box for the glider below by gluing sections of ply and hard balsa together, and it was a PITA to get it to fit snugly but without binding.

Kepler slide wing-2.JPG

Kepler slide wing-1.JPG
 

Rktman

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Maybe ask the designer @Doug Holverson about it?
Tried that. He couldn't figure it out either. Like trying to unravel the mystery of the Bermuda Triangle. 😵

Fortunately someone gave me an original bagged Swinger kit, so I'm going to build that out and see how it performs. If it glides like it should, then maybe I can figure out what the difference is between the two. 🤞
 

TheAviator

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I think it's genius how they used square styrene tubing for a slide box. Strange how I can't find any from suppliers like Evergreen or Plastruct that can fit over a 1/8" spruce or carbon fiber fuselage anymore. That square tubing is a much better solution for a slide box than having to build one from thin ply.

Had to build my slide box for the glider below by gluing sections of ply and hard balsa together, and it was a PITA to get it to fit snugly but without binding.

View attachment 490680

View attachment 490681

This should do the trick for you. I've used it in the past for this purpose.
 

RocketScientistAustralia

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Ah the difference between engineering a solution and reverse engineering a solution. Chinese Stillsons wrenches come to mind. They look the same but don't work like the real ones.
1637350870681.png
These are real ones.. ...... Grab the blue one every time. Chinese copy below in red.
1637351247351.png
 
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TigerHawk

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square styrene tubing for a slide box. Strange how I can't find any from suppliers
Here’s some and looks like a decent price,
 

Rktman

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Here’s some and looks like a decent price,

This should do the trick for you. I've used it in the past for this purpose.
Thanks...took a closer look. Evergreen has a 3/16" OD diameter square tube with a 3.3mm ID that just might work. My carbon spars are 3.03mm, so 0.27mm play may be small enough to be workable. Going to order some before the Christmas rush gets any worse.
 

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Highly recommend it — Josh designs some good stuff. It's the only D glider I've built and flown...and it flies VERY well for such a large glider and being a canard design. It put in a 4 minute 9-second flight before I lost sight of it behind some low bushes. It was probably caught in a thermal for part of the flight, but it still surprised me. Luckily I was able to find it since it was launched in a farm field that had already been harvested.
 

TigerHawk

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Highly recommend it — Josh designs some good stuff. It's the only D glider I've built and flown...and it flies VERY well for such a large glider and being a canard design. It put in a 4 minute 9-second flight before I lost sight of it behind some low bushes. It was probably caught in a thermal for part of the flight, but it still surprised me. Luckily I was able to find it since it was launched in a farm field that had already been harvested.
Do you have a video of the launch and glide recovery? WOW, 4 minutes and 9-second flight, amazing!
 

RocketScientistAustralia

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Thanks...took a closer look. Evergreen has a 3/16" OD diameter square tube with a 3.3mm ID that just might work. My carbon spars are 3.03mm, so 0.27mm play may be small enough to be workable. Going to order some before the Christmas rush gets any worse.
3.3 ID will be clearance fit for 3.2(1/8") So 0.27 clear on your 3.03 tube might be loose. You'll probably want to order some thin strips as thin as you can get to shim it.
Your other option is to make a box section from 2 pieces of angle section. This would be exactly the size you need, but would introduce the weak point of a join. Lastly could you 3d print something better???
 
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Doug Holverson

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Tried that. He couldn't figure it out either. Like trying to unravel the mystery of the Bermuda Triangle. 😵

Fortunately someone gave me an original bagged Swinger kit, so I'm going to build that out and see how it performs. If it glides like it should, then maybe I can figure out what the difference is between the two. 🤞
I was thinking about this last night. I can only guess when it's hands off. My current guess is that the decalage is off. IIRC, it's 0.9° from the main wing.
 

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Do you have a video of the launch and glide recovery? WOW, 4 minutes and 9-second flight, amazing!
Wish I did. I've managed to get footage of rocket launches (especially the larger HPR ones) but gliders move too fast and are too small for me to track with my camera, unlike a slowly descending rocket on a 'chute or streamer.
 

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I’m beginning to think this project might be jinxed.
Took the glider out to retrim it and on the 6th toss or so, a wind gust caught it and sent it nose-diving into the ground — hard. Forward fuselage broke and the carbon fiber boom snapped off.

At this point I don’t know if I can salvage the most important parts again — the wing holder panels, hinges, and wings — since I already tore them off once and may have compromised their integrity. When I made repairs, I made sure the unit was cemented down real good, so it might not survive being removed a second time. Oh well, c’est la vie, I’ll just have to see how it goes.

I’ll probably have to rebuild everything from scratch, but on the bright side, at least I know where all the weak points are and will be redesigning things to make them less vulnerable. It’ll have to be in the ICU for a while. Despite the bad luck, this is a much better design than the very first one that I attempted as a BAR, so I’m not about to abandon the “quest”.

broken again.JPG

To be continued...
 

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Surgery went better than expected. I was able to remove the stab and rudder as one unit after repeatedly soaking the area where it was attached with CA debonder.

The wings and wing holder panels took a bit more coaxing — about an hour and a half of repeatedly soaking with debonder while trying to carefully pry it free without snapping or deforming it. In the end, sliding a single-edged razor blade slowly along the joint finally freed it.

I decided to finally ditch any balsa in the fuse and go entirely with a hollow carbon fiber rod. Virtually unbreakable, and it solves the problem of strategic weaknesses where balsa and carbon rod meet, as well as where the elastic is anchored in the forward end of the fuse. (That point is under a lot of stress from the pressure the stretched elastic exerts on it. It's one of the first areas to fail whenever it touches down nose-first).

rebuilt.JPG

In retrospect, I should have attached the wing plate/wings under the fuselage instead of on top. They would've been further away from the hot exhaust plume, and the angle of the elastic actuators would've been better (more directly in line with where they're anchored on the front of the fuselage). Something to keep in mind if I decide to do a version 3.

I was able to re-trim it without incident. I’ll admit it’s not the best long-distance flyer due to weight — it took 4.84 grams of tail weight to get a level glide — but at this point I’m just glad the prototype works. Guess I won’t have to worry about it getting away from me in the limited area I have to fly it.
 

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Surgery went better than expected. I was able to remove the stab and rudder as one unit after repeatedly soaking the area where it was attached with CA debonder.

The wings and wing holder panels took a bit more coaxing — about an hour and a half of repeatedly soaking with debonder while trying to carefully pry it free without snapping or deforming it. In the end, sliding a single-edged razor blade slowly along the joint finally freed it.

I decided to finally ditch any balsa in the fuse and go entirely with a hollow carbon fiber rod. Virtually unbreakable, and it solves the problem of strategic weaknesses where balsa and carbon rod meet, as well as where the elastic is anchored in the forward end of the fuse. (That point is under a lot of stress from the pressure the stretched elastic exerts on it. It's one of the first areas to fail whenever it touches down nose-first).

View attachment 491368

In retrospect, I should have attached the wing plate/wings under the fuselage instead of on top. They would've been further away from the hot exhaust plume, and the angle of the elastic actuators would've been better (more directly in line with where they're anchored on the front of the fuselage). Something to keep in mind if I decide to do a version 3.

I was able to re-trim it without incident. I’ll admit it’s not the best long-distance flyer due to weight — it took 4.84 grams of tail weight to get a level glide — but at this point I’m just glad the prototype works. Guess I won’t have to worry about it getting away from me in the limited area I have to fly it.
Could you move the whole tail forward or back incrementally until it balanced/ flew well? No extra weight.
 

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Could you move the whole tail forward or back incrementally until it balanced/ flew well? No extra weight.
Thanks, that's a really great idea, and definitely a tip I'll use with the next iteration. I usually build a mock up out of cardboard and other scraps just to confirm the CG location and flyability, something I can modify quickly and endlessly, so yours would be a terrific idea to use to finalize things. Kind of jumped the gun on this one though and went straight to building the prototype.
 

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Today was one of the few single-digit wind days at the park where I do my test launches, so I decided to give the glider another go. The results weren’t all that encouraging.

flight 2.JPG

First off, the wing plates got scorched once again; the pylon needs to be higher and/or the wings mounted below the fuselage for extra clearance.

Secondly, the launch wasn’t vertical. It did a wide 270° corkscrew and ended up taking a 45° angle of attack right before burnout. Haven’t figured out why it did that, everything is perfectly straight and aligned, unlike my first swing wing attempt as a BAR 6 years ago.
I guess it’s possible that it’s unstable (though the launch CG is quite a bit forward of the glide CG) or maybe due to rod whip.

Finally, the burn thread got tangled so the wings couldn’t deploy. Fortunately the glider did a flat, horizontal falling leaf kind of “recovery” and landed with no damage.

On the positive side, I confirmed that it can spit the motor on a streamer while still severing the burn thread successfully.

Well, this has been an interesting voyage of discovery. It may be a while before I attempt to build a version 3, but I'll know exactly what improvements and modifications to include.
 

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I had a thought about the possible cause for the erratic launch: there’s nothing keeping the folded-back wingtips from moving. Air rushing past during launch could cause them to flutter up and down relative to the fuselage and stab, and the change in angle would then play havoc with the glider’s upward trajectory. I need to devise a way to keep the wingtips locked down, but still be free to swing out when the burn thread is severed. At the moment I’m coming up empty. :dontknow:

wingtips.jpg

Additionally, a likely solution to the burn thread getting tangled is to shorten the small routing tube it passes through. That’s an easy fix that I’ve already taken care of (removed about 80% of its length).

IMG_7357-B.JPG


The glider probably has one more flight left in it before the exhaust damage gets fatal, so if these two problems are taken care of and things work as they should, I’ll be satisfied that I can move on to the next (improved) version 3.
 
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GuyNoir

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I think I have a possible clue for the erratic launch: there’s nothing keeping the folded back wingtips from moving. Air rushing past during launch causes them to move up and down (relative to the fuselage and stab) and the change in angle plays havoc with the glider’s upward trajectory. I need to devise a way to keep the wingtips locked down, but still be free to swing out when the burn thread is severed. At the moment I’m coming up empty. :dontknow:
Maybe a couple of small 1/32" dia. music wire fittings epoxied to the stab would hold those wings in place. If you locate them on the centerline of the stab, you wings can still pivot out at ejection. Just an idea for you.
 

Rktman

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Maybe a couple of small 1/32" dia. music wire fittings epoxied to the stab would hold those wings in place. If you locate them on the centerline of the stab, you wings can still pivot out at ejection. Just an idea for you.
+1
I like that there would be a negligible amount of air resistance/drag with those thin wires. 👍
 
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Rktman

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This should do the trick for you. I've used it in the past for this purpose.
Here’s some and looks like a decent price,
On a side note, the 3/16" square tubing from Evergreen arrived, and it's a perfect fit! The extra 0.27mm difference between the tube's I.D. and my carbon rod's O.D. provides just enough clearance to allow the styrene tube to slide easily without binding, and there's no looseness or wobble from the extra "air space". Just in case, I also bought some thin 0.133mm polystyrene sheet stock in the event it ever needs shimming due to heat expansion (the summers here can get notoriously hot).
Now I can clone the QCR Easy Slide i - IV series, as well as scratch build more 13mm and 18mm slide wings.
 
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