# RumbleBee-C Build

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#### Rktman

##### Eric
Gotta admit I was kind of intrigued with the idea of a BG that used a Vector Pod (angled up) to get the glider to boost straight, and I was looking for a larger, sturdy 18mm flier after building primarily 13mm models.

So I decided to give the RumbleBee-C a try, especially since it’s a 4X upscale of a proven 1969 1/2A design by Bob Singer called the BumbleBee.

Here’s the kit. I ordered the non-RC version, which would’ve included the electronics. It included the extra nose cone and body tube for the radio module, battery and servos along with a length of carbon tube linkage. I’m sure those parts will come in handy on down the road.

#### Rktman

##### Eric
First order of business is prepping the nose cone by cutting off the added shoulder length that included the loop for the shock cord and chute. The opening gets sealed by a 1/32” ply disc, which is liberally coated with epoxy to protect the NC. This isn’t just to keep things neat, it’s a necessity; the motor sits right up against the NC shoulder and that ejection charge can really do a number on unprotected plastic.

#### Rktman

##### Eric
Interestingly the motor pod gets fitted with an internal motor tube which is ejected with a streamer to lighten the model. It’s a neat system to bring the motor down safely while stripping off unneeded weight.

I elected not to use the included crepe streamer in favor of some plastic flagging tape with a length of mylar attached to wrap around and protect it.

#### Rktman

##### Eric
The pylon for the Vector Pod is lower at one end to angle the front of the engine pod “up” (it’s 7/8” high at the aft end and 1” at the forward end). I'll attach the engine pod later, as I find it easier to align the pylon perfectly straight horizontally and vertically on the fuselage when the motor tube isn't getting in the way.

Going old school with the flying surfaces with a hobby knife (the parts aren't laser cut; but I don't mind, I like the feeling of hand-crafting my builds. Up until lately, all my projects have been scratch-builds where I've had to trace templates onto balsa and hand slice out everything anyway, so no big deal).

One thing I noticed and really liked: the wings were marked off on 2 sheets of balsa that had already been preglued together, and it just so happened (or was done intentionally?) that the leading edge of each wing fell on the stronger C grain balsa sheet.

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#### Rktman

##### Eric
Once the wings were squared up and uniform with each other I sanded in the proper dihedral angle on each root edge. There's actually a better way to do this (more on that in a sec) but with kits you don't have a choice, the parts come precut. It's just that it’s less precise and takes a little longer in my opinion, but it's the standard practice and works well enough.

What I find is a better way (if I have a choice) is to cut both wings out as one piece on the same sheet of balsa, slice them part way through where they meet at the root edge, bevel the cut to the approximate angle with a folded piece of sandpaper or an emery board (adjusting as needed), then bending the wings up to the correct dihedral height and locking them in with thick CA and kicker. Makes for a stronger joint and takes all of 60 seconds vs maybe 10 minutes the other way. Just food for the thought and something helpful if you do—or decide to do—scratch built gliders. But I digress, so back to the build.

Bit of a side note: I coated the fuse with 2 layers of lacquer/dope. It might seem an excessive or unnecessary step but here in the hot humid south, I assure you it’s a necessity. Balsa tends to pretzel up when you have humidity in the high 90s, especially long thin pieces of balsa like fuselage sticks (although I’ve had even broad low-aspect wings like on this model become bowed or wavy if I don’t take steps to prevent it).

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#### Rktman

##### Eric
After rounding all the edges of my wings, stab and rudder and sanding all the balsa “fuzzies” off, I decided to dye my model rather than going the permanent marker route. I couldn't find a bright enough orange to use so ended up custom mixing more than one packet to get something closer to what I wanted.

It's plenty messy so I moved this part out to the garage and laid down lots of plastic and cardboard. If you decide to use this method to color your bird I'd suggest throw-away pans and gloves, and a metal laundry sink to dispose of the used dye. Never pour it down a porcelain sink or your toilet—it'll permanently stain them. I ended up digging a hole in the backyard to get rid of my used dye (it's biodegradable and you can't save and reuse the dye later anyway). Mine started forming weird lumps and chunks for some reason so all I could do was try to brush them off the balsa surfaces the best I could.

Wings came out pretty good, no warping. I had to flip them every 15 minutes or so to even out the drying though. Is that bright enough for you?

After 45 minutes in a hot garage everything was toasty dry and straight. And a nice eye-searing red-orange. Should make it plenty easy to see on the ground and in the air.

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#### Rktman

##### Eric
The wing joint came together nice and tight after presanding in the dihedral angle. The build itself is coming along much faster than expected, likely due to the fact that I've skipped quite a few steps that the RC version would have required and also that the instructions advised that no airfoiling is required. That alone would've set me back an hour or two to get just right. And I didn't tissue the flight surfaces like I generally do, which can be even more time consuming because you have to apply several coats of dope and wait for them to dry, then sand between each application etc. It's just nice to see something come together this quickly once in awhile.

Moving along, the stab gets added next to the fuselage bottom…

…followed by the wings, sanded flat on the joint bottom to more securely perch on the top of the fuselage boom. Now it's really beginning to look like a plane! I like the low aspect wings, they make the glider look really substantial. Actually it's quite a beefy, sturdy model with a completely different look and feel from the 13mm and A-B gliders I've previously built.

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#### Rktman

##### Eric
The angled pylon had to be notched slightly to clear the wings. This was the only hiccup so far in the build process, due to a 1/8” measuring difference in locating the wing LE. Once the pylon was on it was real easy to attach the motor pod and sight along the length of the fuse to align it perfectly. The slant of the pod is really visible here.

The final piece to complete the package is the rudder. Did my best to ensure that it went on perpendicular to the stab.

Some mylar to protect the wings from the exhaust and it's a wrap. Nice piece of eye candy if I do say so. Nice lines. In fact I just realized that if you flipped the design around it would make a real cool canard.

I had some time to do some trimming the other day and was surprised that all it took was a tiny pea-sized piece of clay on the aft end to get a pretty much textbook glide. I realize the RC version would’ve taken more tail-end ballast to get properly trimmed due to the electronics and battery up front, but the upside is that you'd never lose it, and with a C engine my guess is that you could get some pretty decent glide times. At any rate hopefully I'll get to maiden it in a week or so and let you know the results.

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#### XolveJohn

##### Well-Known Member
Nice thread! Just a couple points. If you wrap the streamer around the pod, it won't deploy. In the article I specify "fan folding" it back and forth, so it is collapsed in a Zig_zag fashion around the tube. A bit harder, but will always open that way. The CG was not that far off, because the RC pod is close to the proper CG. I never heard of dying balsa, new trick to me, cool. Bob Singer in the original BumbleBee article mentioned using magic marker. You have advanced the state of the art! Definitely do first flight with a B4-2. I would be scared to fly it free flight on the C6 unless had a mile square field and little wind. Good luck.

#### Crawf56

##### Pig Soooiiieee!!
TRF Supporter
Very good! I've never heard of dying a model.

#### Rktman

##### Eric
Nice thread! Just a couple points. If you wrap the streamer around the pod, it won't deploy. In the article I specify "fan folding" it back and forth, so it is collapsed in a Zig_zag fashion around the tube. A bit harder, but will always open that way. The CG was not that far off, because the RC pod is close to the proper CG. I never heard of dying balsa, new trick to me, cool. Bob Singer in the original BumbleBee article mentioned using magic marker. You have advanced the state of the art! Definitely do first flight with a B4-2. I would be scared to fly it free flight on the C6 unless had a mile square field and little wind. Good luck.
Thanks! I'll probably stick with the B motor since my flying fields aren't all that large. Also I'm not the spry young dude I once was and chasing it around in super humid 89 degree heat doesn't appeal to me much.

#### Rktman

##### Eric
Very good! I've never heard of dying a model.
I was pretty skeptical at first but this is my 3rd dyed glider with no warping problems. I still get nervous though so I make sure I flip everything every 15 minutes to even out the drying. So far so good.

#### XolveJohn

##### Well-Known Member
I have had problems with the 6" wide, 3/32" balsa warping in storage.
It seems to help to hold the stack together with a bunch of rubber bands. Probably change in humidity does it. I am worried that if you glue it after dying, the joint may not be as strong, not sure. CA does go in a ways.

#### WFWalby

##### Well-Known Member
TRF Supporter
Love the color. Did you weigh the dyed parts before and after to determine any weight gain?

#### terryg

##### Well-Known Member
Does the dye rub off onto your hands or is it fully bonded to the balsa?

#### Rktman

##### Eric
I have had problems with the 6" wide, 3/32" balsa warping in storage.
It seems to help to hold the stack together with a bunch of rubber bands. Probably change in humidity does it. I am worried that if you glue it after dying, the joint may not be as strong, not sure. CA does go in a ways.
The dye doesn't seem to affect CA, wood glue or epoxy adhering to the balsa at all that I can tell. My other 2 dyed gliders are doing fine and I've flown each 6 or 7 times already.

I keep my balsa sheets stacked on their sides in a long box with no problems. If I had the space I'd stack all the same width and thickness balsa together and flat. The air indoors is pretty dry because the summers here are so hot we have to use air conditioning, though I have received warped sheets through the USPS or FedEx because the boxes get exposed to humid outside air. I'm strongly considering only buying balsa online during winter.

#### Rktman

##### Eric
Love the color. Did you weigh the dyed parts before and after to determine any weight gain?
No, didn't think to do that but I'm sure the pigment doesn't add any more measurable weight than permanent markers. You get more even coverage than markers too.

#### Rktman

##### Eric
Does the dye rub off onto your hands or is it fully bonded to the balsa?
A little does still rub off after its dry, but no more than magic markers, and the color penetrates more deeply. After awhile it does stop rubbing off on your hands but I don't know if that's because if what's going to rub off already has or if time makes it "set" more permanently.

#### Rktman

##### Eric
Flight report

I think this is a case of a paradox wrapped in a dilemma; the glider did so well it ended in disaster.

This is all that's left after yesterday's maiden flight. The B4-2 boosted it straight and far higher than I expected and it transitioned into a fantastic glide with only a hint of occasional stall. It was great to see it hang up there doing a slow wide circle. Except the wind picked up and suddenly it wasn’t so great to see it getting farther and farther away and coming down far too slow while heading toward a long row of trees.

Long story short at 37 seconds into the flight it landed 45’ up in a tall pine almost 3 football fields away at the edge of the park. The wind picked up and I kept hoping the glider would break loose, but instead I watched an ugly scene as the branches chewed the glider to pieces. Wouldn’t have believed it if I hadn’t watched the carnage happen. The only thing that came down was the aft section and it landed in a patch of poison ivy. 2nd glider I’ve lost in a row at that park, so altogether not a really great day.

So—final assessment: great glider (non-RC version is what I built), and a quick and easy build well worth the investment in time. Fly it in a BIG field if you’re going to use a B or C engine and expect a long walk to retrieve it. I will definitely be rebuilding her and keeping the tail section to remind me to fly it only on low-wind or no-wind days in the biggest treeless area available.

#### Crawf56

##### Pig Soooiiieee!!
TRF Supporter
Rebuild and ever forward. Sounds like you need to use an A-size motor?

In the last century, I used to launch at a park that had a "tree free" area of about 100 yards X 100 yards. Launch angle, wind direction, and parachute/glider drift were the true challenges!

#### Rktman

##### Eric
Rebuild and ever forward. Sounds like you need to use an A-size motor?

In the last century, I used to launch at a park that had a "tree free" area of about 100 yards X 100 yards. Launch angle, wind direction, and parachute/glider drift were the true challenges!
A little voice kept telling me to use an A8-3 but did I listen? Of course not, I never listen to myself so now I gotta listen to that voice saying "told you so" over and over. Agreed, drift is always a challenge. Still surprises me how far a glider can get in only a few seconds.

#### Klatuso

##### Well-Known Member
TRF Supporter
Did you post the website where we might get this kit? Can't find it on a google search.

#### XolveJohn

##### Well-Known Member
Wow, good flight, too bad Murphies Law was in effect that day. Reminds me of an electric foamy plane flight I put into a tree at the model plane club field. Stuck pretty good. Guy brought out his potato cannon, uses hair spray for power, and a piezo trigger. It hit the plane.

Put a hole in the wing, still stuck. Tree won that day. Beware of them!

KLATUSO: I am out of the kits, but can get more together. Email me at
xolvejohn@gmail.com

Eric, probably better to use an A8 BOOSTER, instead of A8-3. Delay is too long.

#### Rktman

##### Eric
Wow, good flight, too bad Murphies Law was in effect that day. Reminds me of an electric foamy plane flight I put into a tree at the model plane club field. Stuck pretty good. Guy brought out his potato cannon, uses hair spray for power, and a piezo trigger. It hit the plane.

Put a hole in the wing, still stuck. Tree won that day. Beware of them!

KLATUSO: I am out of the kits, but can get more together. Email me at
xolvejohn@gmail.com

Eric, probably better to use an A8 BOOSTER, instead of A8-3. Delay is too long.

Will a booster motor still kick out the motor pod even if it doesn't have an ejection charge? If it does than it may alleviate a lot of my problems with ejection charge damage to engine pods on my RGs.

#### Rktman

##### Eric
Wow, good flight, too bad Murphies Law was in effect that day. Reminds me of an electric foamy plane flight I put into a tree at the model plane club field. Stuck pretty good. Guy brought out his potato cannon, uses hair spray for power, and a piezo trigger. It hit the plane.

Put a hole in the wing, still stuck. Tree won that day. Beware of them!

KLATUSO: I am out of the kits, but can get more together. Email me at
xolvejohn@gmail.com

Eric, probably better to use an A8 BOOSTER, instead of A8-3. Delay is too long.

BTW can you let me know when the RumbleBee-C kits are available?

Any suggestions on a flexible control box (transmitter?) that will work on both the RBC and eventually other models? (I'm as green as they get when it comes to RC but I'm a fast learner. Besides, I'm getting tired of losing my gliders).

#### XolveJohn

##### Well-Known Member
I used the Turnigy 5X radio in the RBC, it is mentioned in the instructions, but it would be good to read the article in Sport Rocketry, more complete. It is only $25. The tiny servo's from HK can be a bit of a challenge to use, have very fine wires. (DON'T HOT MELT THEM DOWN ON THE BOTTOM, CAN DESTROY, glue at edges). It is easier to use the BRICK from Spektrum, but$60 + xmtr. Does integrate the rcvr with 2 open frame servo's on one board, what most people use on ultra light models.
Then you can add elevator control that some people demand. I have little problem flying rudder only, but it is old school to folks these days.

A booster engine should kick out, I have heard of them used on other RG's. Do a ground test with a scrap tube to test if you want. Could always add a TINY amount of BP to the top of the engine, but I think there will be significant pressure when the propellant burns thru at the top. Gasses man, it's a blast!

#### Rktman

##### Eric
I used the Turnigy 5X radio in the RBC, it is mentioned in the instructions, but it would be good to read the article in Sport Rocketry, more complete. It is only $25. The tiny servo's from HK can be a bit of a challenge to use, have very fine wires. (DON'T HOT MELT THEM DOWN ON THE BOTTOM, CAN DESTROY, glue at edges). It is easier to use the BRICK from Spektrum, but$60 + xmtr. Does integrate the rcvr with 2 open frame servo's on one board, what most people use on ultra light models.
Then you can add elevator control that some people demand. I have little problem flying rudder only, but it is old school to folks these days.

A booster engine should kick out, I have heard of them used on other RG's. Do a ground test with a scrap tube to test if you want. Could always add a TINY amount of BP to the top of the engine, but I think there will be significant pressure when the propellant burns thru at the top. Gasses man, it's a blast!
Thanks for the info, will do some research on prices and sources and such. And since I still have the RBC motor pod I'll pick up some booster engines this weekend to try out.

#### Rktman

##### Eric

Been a while since I had a chance to do a replacement build but it was a quiet weekend so I jumped on it. Not sure when I’ll have another chance but at least it’s a start.

Broke a fuselage trimming another glider so I decided that enough is enough, so I’m going with a carbon fiber tube with the RumbleBee. Neither the balsa fuse nor the carbon tube even registers on the grams setting of my postage scale so I know I can go with at least a C motor without worrying about adding any more weight or affecting the CG point much, if at all.

Also decided that for now I’m limiting flights to A motors since my flying fields are not the largest and may move to a C if I get a chance to fly it at my other club’s more distant Bayboro venue near the coast. With over 3,800 acres of unobstructed recovery area my only concern would be losing sight of the glider, especially since there’s always at least a 5 – 10mph wind blowing.

#### XolveJohn

##### Well-Known Member
The booms used are basswood, not balsa. Note I have had reports that gluing to CF with either epoxy or normal CA tends to not be strong, fractures off easily. I do intend to use CF booms on my new design, but will either glass the parts on, or perhaps wrap the boom with thread and CA to provide an interface. Just a heads up. May want to glue a small trial piece of balsa to CF and test the strength of the joint.

There are special CA's for gluing to CF, but are not cheap.

A motor sounds small for the RBC, certainly use a booster motor.

#### Rktman

##### Eric
The booms used are basswood, not balsa. Note I have had reports that gluing to CF with either epoxy or normal CA tends to not be strong, fractures off easily. I do intend to use CF booms on my new design, but will either glass the parts on, or perhaps wrap the boom with thread and CA to provide an interface. Just a heads up. May want to glue a small trial piece of balsa to CF and test the strength of the joint.

There are special CA's for gluing to CF, but are not cheap.

A motor sounds small for the RBC, certainly use a booster motor.
Gorilla Glue Reinforced CA seems to work. Thanks for the warning, I'll keep an eye on the one other model that I used epoxy on.

I will probably airfoil the wings and stab this time to compensate for the A motor. The B engine I used last time took it up unnervingly high, much more so than I expected and I'm fairly sure it would've stayed aloft well over a minute since it had a pretty low sink rate. A 60 second flight would make me happy enough since longer duration ones seem to result in watching my gliders disappear forever into the distance. My club uses a larger field to launch in so that's where I'll maiden it. If the A doesn't quite do it at least I'll stand a chance of recovering it with a B.

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