TWIN BOOM GLIDER CONCEPT

[Rktman]

A bit of background

Originally inspired by the Lockheed P-38 Lightning, this twin boom glider design has actually been a back-burner project for the past 6 years, and over that time it’s gone through quite a few iterations (eight in total), only some of which are shown above. (An early prototype of the current version can be seen in the lower right corner).

The original versions were all slide pod systems, but I could never get the burn string to reliably release. It would always jam in the hole through which it was threaded. It didn’t matter what the material was either: cotton thread, thin elastic, dental floss – the result was always the same. Enlarging the burn thread hole, changing its shape, or moving its location didn’t make a difference.

I even considered that the internal motor pod could’ve been twisting and trapping the burn thread in place, so I used a wire and aluminum tube setup to prevent it. (Once in launch position, the wire would thread into the tube, preventing any twisting of the internal motor pod).




It finally worked in a ground test and the maiden flight of my last slide pod version, but by then I’d lost any confidence I had about the reliability of using a burn string. Another thought (inspired by the Apogee Rockets Texas Twister) was to use an internal slide pod system.




However, after mulling it over for a few weeks, I thought about the added weight of using this method and how I’d have to add more wing area to compensate, and decided to go with something far simpler: a BG that ejects the motor on a streamer to shift its CG. I’ve since decided to use unswept wings with a straight taper, making it easier to attach the twin boom at the wing’s dihedral break.

I also decided to revise the stab and rudder configuration. I just felt too uncomfortable about having the stab so close to the path of the ejecting motor and hot exhaust plume, so I lowered it. It now spans the dual fuselage rods for better clearance and adds more support to the aft end of the rods. The rudders were also relocated to the stab ends

Sketch of the final design:




Final cardboard and balsa prototype.

 

[Rktman]

This should be a relatively fast build; there’s not much to assemble. I was going to use bamboo skewers for the fuselage booms because surprisingly, they’re a tiny bit lighter than carbon rods. I decided in favor of strength after considering the possible flexing, flutter and failure of bamboo under boost.

For lack of a better name, I was using “Gemini” but thought it was too obscure, so for convenience’s sake I’m just calling this experimental glider TB-8 (Twin Boom glider, version 8). If anyone has some more imaginative, appropriate, or overall cooler name suggestion they’d like to propose, I’d be glad to consider it.

Started on the wings by marking the airfoil sections.

 

[BABAR]

I think I have your name problem solved.

call it the Boom Boom Glider

Or Chicka Boom Boom

 

[Rktman]

I think I have your name problem solved.

call it the Boom Boom Glider

Or Chicka Boom Boom

Gotta love it!

 

[Charles_McG]

I've long been a fan of the Centuri Hummingbird. I hope to upscale it someday.

 

[Rktman]

Wings are airfoiled and the dihedral angle was put in.
Central fuselage and 2mm carbon rods attached.

 

[James Duffy]

Here's an unreleased Estes twin-boom concept from the late '60s/early '70s era. The photo came from a stash of Estes photos that Jonathan Dunbar purchased some years ago. You can clearly see some sort of string actuator to enable a change from boost to glide mode in the first photo.



The model still exists at the Estes HQ. Bill Stine pointed out that it even sneaked into a recent catalog in a photo of classic, scale, and prototype models.

James

 

[Rktman]

Here's an unreleased Estes twin-boom concept from the late '60s/early '70s era. The photo came from a stash of Estes photos that Jonathan Dunbar purchased some years ago. You can clearly see some sort of string actuator to enable a change from boost to glide mode in the first photo.

View attachment 543392 View attachment 543393

The model still exists at the Estes HQ. Bill Stine pointed out that it even sneaked into a recent catalog in a photo of classic, scale, and prototype models.

James

Early free-flight precursor to the RC-only Estes Centurian and Strato Blaster? I admire the old-school solutions before RC became a "thing". It looks like that string controls an auto-elevator setup.

 

[Rktman]

Tail and rudders attached. (Wood skewer is just a temporarily tacked-on alignment guide).

 

[Rktman]

Added color with sharpies. Balsa surfaces received two coats of dope (clear lacquer) to strengthen things and keep the heavy humidity from warping flight surfaces.

The cutout section on the top rear of the motor pod is to accommodate a 1” x 15” streamer.




Comparison of the updated version above (29.2g including nose weight) vs the original version below (41.5g). Original booms were made of basswood.




Waiting for an opportunity to do some hand-trimming and then a low-wind day to maiden this.

...to be continued

 

[Doug Holverson]

There was also the barely remembered Centuri Hummingbird that had twin booms. But it was made out of cardboard, had small wings, and had too little CG shift at ejection.

 

[Rktman]

There was also the barely remembered Centuri Hummingbird that had twin booms. But it was made out of cardboard, had small wings, and had too little CG shift at ejection.

I downloaded the templates a long time ago just for kicks, and often wondered whether a paper airplane made out of stiff cardboard would fly as well or better when attached to a booster pod. Something to try if I ever have an idle moment...

 

[Charles_McG]

I owned an original, and cloned it at original scale, BT50 and BT60.

The original was pre-BAR, so long lost to history. The Clone flew off i to the sunset (literally) in one of those rare flights where it glides like a performance glider - into a soybean field 500’ away.

 

[Doug Holverson]

I'm dusting off 18 year old CAD files with the working names of Kitty or Gammie (which is like a Zoomie, but bigger, slower, and less aggressively vicious) which was a reworked Hummingird. It's balsa, has bigger wings, and a bigger CG shift. Stay tuned....

 

[Crawf56]

A long time ago in a galaxy far, far away.......

Estes T25 Centurian (without canopy). Always liked the twin boom designs.

 

[Rktman]

Got a chance to maiden the TB-8. Not bad quasi-successful first outing on an A8-3, so I’m relatively happy. It’s a huge improvement over the previous 5 versions and 9 problem-plagued flights.

The ejection charge kicked it pretty hard and it did a 360° before settling into a glide. Obviously needs more reworking and trimming, as it doesn’t have sufficient roll stability (I’ll increase the dihedral by either slicing open the existing dihedral line and increasing the angle, or adding another dihedral panel. The tips should’ve been raised 13/16” instead of 3/4”, so I’m about 1/16” off. Under the circumstances I might add slightly more than that).

Conjecture/hypothesis: part of the lack of complete roll stability might have to do with the fact that it has, in essence, two fuselage booms. With only a single fuselage boom, its roll center would’ve been along only that axis. With two, it might be trying to stabilize its roll corrections around both at the same time, causing the glider to rock and seesaw around the combined axis of both.

Comment: Now I know why other commercial kits like Estes’ Centurion and Strato Blaster had swept wings: built-in roll stability without having to angle the wingtips up for dihedral, which makes attaching the twin fuselage boom problematic. It’s also clear why every dual boom glider I’ve ever seen, whether a kit or scratch-built, is always an RC model. With control surfaces, you can literally make anything glide (I’ve seen unlikely shapes like Halloween witches, superhero figures, even a flat plank).

Anyway, back to other planned adjustments I’m considering. I noticed it also began to stall toward the end — easily fixed by adding some more nose weight. I may also add more wingspan to my next version; an additional 2” wouldn’t hurt.

 

[waltr]

Wow, the ejection really kicked it. It looked like it may have done a few loops.
Not bad for first flight of a new design.

 

[mh9162013]

Holy ejection charge, Gliderman!

Great work!

 

[shockie]

Early free-flight precursor to the RC-only Estes Centurian and Strato Blaster? I admire the old-school solutions before RC became a "thing". It looks like that string controls an auto-elevator setup.

Does the motor eject...? with a streamer? Back then you could just eject the motor without a recovery system.

Somebody ought to use some photogrammetry to determine it's dimensions.

I wonder if Larry Renger is the glider designer?
He had used an auto-elevator or pop-elevator on his original Sky Slash.

 

[BABAR]

Back then you could just eject the motor without a recovery system.
.

depending on field rules you still can. I do it routinely.

 

[Rktman]

Wow, the ejection really kicked it. It looked like it may have done a few loops.
Not bad for first flight of a new design.

Holy ejection charge, Gliderman!

Great work!

Thanks guys, appreciate it. Need to do a little bit of tinkering to fine tune it, then do a follow-up flight. Stay tuned.

 

[flyingeagle]

I have several boost rocket gliders but not sure how to get color on them without effecting the glider performance. I recently purchased the Estes Super Orbital Transport and I would like the glider to match the booster rocket. I have seen videos on you tube on the Semroc Orbital Transport with matching glider in white with several successful flights. Some guys are saying, leave the glider in a raw state for a best glide performance. You can’t put water slide decals on raw balsa wood. I thought about markers but I had never seen those in white. To get a straight line with markers the balsa would wick the ink into the wood and spread. What do you guys do to paint them and get a good glide out of them? Do I seal them or just give them a paint mist or both? I don’t care for the raw look. It looks like an unfinished kit. I’m not flying them in competition but would like to get them to look as good as the package art. The gliders I see here look good but how do they perform in flight?

 

[waltr]

If performance is not an issue then Aerogloss sanding sealer and dope does well. Do a very light (thinned) coat with the sealer, lightly sand then thin coat of dope for color.

My booster gliders are raw balsa with a stripe or two with markers. Yes, the edges are a little fuzzy from bleed. But they fly very well.

Eric,
Your question about flat center and dihedral tips:
When I flew RC gliders a beginners kit had this plan form. It was completely stable with hands off the controls.
I think your twin boom needs to tip sections raised, more dihedral to provide the roll stability.

How much incidence do you have from wing to stab?
This is a critical settings for good recovery from boost and stable pitch.

 

[Rktman]

I increased the dihedral on the carboard/balsa prototype quite a bit to see if it decreased the tendency to rock, and it definitely increased the roll stability. I dialed in quite a bit more than necessary just to see the results. Glide during trimming tosses shows no evidence of the former seesaw rocking.




I went even more extreme when I cranked up the dihedral on my glider. It’ll definitely decrease time aloft, but this is more an experimental, small-field, for-fun project that I’m not anxious to lose to an unexpected thermal.



...to be continued.

 

[Rktman]

If performance is not an issue then Aerogloss sanding sealer and dope does well. Do a very light (thinned) coat with the sealer, lightly sand then thin coat of dope for color.

My booster gliders are raw balsa with a stripe or two with markers. Yes, the edges are a little fuzzy from bleed. But they fly very well.

Eric,
Your question about flat center and dihedral tips:
When I flew RC gliders a beginners kit had this plan form. It was completely stable with hands off the controls.
I think your twin boom needs to tip sections raised, more dihedral to provide the roll stability.

How much incidence do you have from wing to stab?
This is a critical settings for good recovery from boost and stable pitch.

I tried to limit the stab incidence to 1°, but I may have accidentally gone maybe a half degree or so over, judging by the nose weight I had to add. Fortunately the amount of incidence isn't enough to cause a loop on launch, and it does transition to glide really quickly. First time I've had a glider do such a wild loop at ejection.

I have several boost rocket gliders but not sure how to get color on them without effecting the glider performance. I recently purchased the Estes Super Orbital Transport and I would like the glider to match the booster rocket. I have seen videos on you tube on the Semroc Orbital Transport with matching glider in white with several successful flights. Some guys are saying, leave the glider in a raw state for a best glide performance. You can’t put water slide decals on raw balsa wood. I thought about markers but I had never seen those in white. To get a straight line with markers the balsa would wick the ink into the wood and spread. What do you guys do to paint them and get a good glide out of them? Do I seal them or just give them a paint mist or both? I don’t care for the raw look. It looks like an unfinished kit. I’m not flying them in competition but would like to get them to look as good as the package art. The gliders I see here look good but how do they perform in flight?

I finish my gliders the same as @waltr using 2 thinned coats of dope/lacquer and sanding between each coat. Protects the balsa from humidity and wet grass/ground. Also strengthens the balsa. I use color markers over the doped surface, so the markers don't wick and spread like it would with raw balsa (takes a while to dry and become "permanent" though). Straight lines aren't a problem. I just use a fine point marker, especially when I want to get a clean straight line along the edge of a colored area.

 

[Rktman]

Got a chance to do another test flight today, the only perfect single-digit wind, 61° F morning in weeks.
Results were much improved. No visible side-to-side rocking with the increased dihedral angle. My hypothesis about multiple fuselages may hold some water after all. It may require more than the usual amount of dihedral angle to compensate, perhaps double (but not to the degree that I used in this experiment.

Looking at the previous video, I think I probably inadvertently put in a little too much decalage in the stab too. I’ll have to be more cognizant of avoiding that, both to avoid looping on launch and having to offset it with superfluous nose weight.

Overall, I’m still happy at the results and what I learned, and I can finally wrap up this long-running side project concept glider. I’ll do a TB-8.2 version with a slightly longer wingspan and a few other tweaks as a between-builds project, so will update this thread sometime in the future when that happens.

BTW: finally decided on a name: Occam’s Razor. Look up the principle and you’ll realize why.

 

[BABAR]

I need to check this forum section more often. Nice work!

 

[Hobie1dog]

thanks for the video good job.