RumbleBee-C Build

[XolveJohn]

Will look for that glue. With proper trimming, you should get way more than a minute with a B engine. Remember, you don't have the radio on it, so is lighter and has less drag. Just hope you don't catch a thermal.

 

[Maxout]

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.

Normal CA glue works just fine on pultruded CF. I use it all the time. The only time you see it popping loose is when it's used to reinforce a balsa tailboom. Even then, just check it regularly to make sure there aren't any loose spots. No big deal on a rocket, actually, but popped strands do change the trim on hand launched and catapult launched gliders just enough to hurt performance. If it's too big of an issue, a spiral wrap of kevlar tow secured with duco or ambroid is a lightweight option.

 

[Rktman]

Will look for that glue. With proper trimming, you should get way more than a minute with a B engine. Remember, you don't have the radio on it, so is lighter and has less drag. Just hope you don't catch a thermal.

3M EC2216 Scotch-Weld epoxy seems to be the best adhesive though expensive ($20 for 43ml from R.S. Hughes or $36.39 for 5.6oz from Amazon). It has high shear strength, remains flexible, & is used for commercial aircraft. Maybe overkill...so of course I'm going try it lol. I like to build for longevity– one reason that, try as I might not to get attached, it still upsets me to lose my gliders, especially great performers like the RBC.

 

[Rktman]

Normal CA glue works just fine on pultruded CF. I use it all the time. The only time you see it popping loose is when it's used to reinforce a balsa tailboom. Even then, just check it regularly to make sure there aren't any loose spots. No big deal on a rocket, actually, but popped strands do change the trim on hand launched and catapult launched gliders just enough to hurt performance. If it's too big of an issue, a spiral wrap of kevlar tow secured with duco or ambroid is a lightweight option.

Where do you source pultruded CF tubes and are they more expensive? Any downside to using square tubes, as I find them easier to mount flight surfaces on?

 

[Maxout]

Where do you source pultruded CF tubes and are they more expensive? Any downside to using square tubes, as I find them easier to mount flight surfaces on?

All of the tubes you're using are pultruded. It's a manufacturing method. They're the most affordable option because they're continuous cross section and hence can be mass produced. The other option are the various molded tubes, a process reserved for super light tubes and those of nonuniform cross section, such as tapered tailbooms. So a good quality 1/4" pultruded arrow shaft might be $5 (I've gotten as low as $2.50 for reasonable quality), whereas a tapered boom in that diameter range will start at $12 and go up from there (see goodwinds.com). This is one of the reason I have been very careful to only offer kits that work with pultruded carbon. The startup cost for anything molded is too high at this point (and I just spent $400 renewing my web hosting. ).

 

[XolveJohn]

You should try 1&1 hosting, only about $140 a year. And the simple editing program is so easy even I can run it, a computer klutz. Brought up in the DOS days, no wonder I hate the damn things. Now if you have a fancy shopping cart and stuff it may cost more, I just use paypal buttons.

A pal building RG's for the World Team is having the gluing problem.
I have not verified this problem, but will pass all these tips along to him.

It does seem like any glue does not penetrate into CF like it does in wood, but I see many people gluing to it, maybe he was using crummy glue, or too much accel, or something. Humidity or greasy fingers, who knows.

NEW THOUGHT. He is using really skinny RODS I think, only for mini-A motors. I bet deformation
or bending of the rod cracks the joint. If so, he should use a tube type rod. I sent him this thread ref. May get some feedback.

 

[Rktman]

You should try 1&1 hosting, only about $140 a year. And the simple editing program is so easy even I can run it, a computer klutz. Brought up in the DOS days, no wonder I hate the damn things. Now if you have a fancy shopping cart and stuff it may cost more, I just use paypal buttons.

A pal building RG's for the World Team is having the gluing problem.
I have not verified this problem, but will pass all these tips along to him.

It does seem like any glue does not penetrate into CF like it does in wood, but I see many people gluing to it, maybe he was using crummy glue, or too much accel, or something. Humidity or greasy fingers, who knows.

NEW THOUGHT. He is using really skinny RODS I think, only for mini-A motors. I bet deformation
or bending of the rod cracks the joint. If so, he should use a tube type rod. I sent him this thread ref. May get some feedback.

I've read that you also have to thoroughly clean carbon fiber rods of any oils, grease or manufacturing residue if you want a good adhesive bond. Alcohol seems to be a preferred cleaner for CF. I rough up the surface with sandpaper first to give it some "tooth" for the adhesive to grab onto (which by default removes any residues that may be on the rod).

 

[Rktman]

Roughing out the airfoil. Getting good practice with the feel and technique of the David Combi razor plane. Very happy with the tissue-thin curls I can shave off, though the left wing proved to be a little more stubborn. Guess it depends on the grain and hardness of the balsa since I had to adjust for a hair deeper cut to make any headway.

Now I know why I hated having to airfoil anything using only sandpaper; this cuts the time down by at least half. I’ll be using the sandpaper only to fine tune the curves. A good plane is such a worthwhile investment in terms of time saved. I’ll probably tissue the wings to add color and re-strengthen them after removing all that balsa.

 

[XolveJohn]

So you gave up on dying? Seemed cool, although messy and troublesome.

Yes, cleaning CF and sanding sounds good.

 

[Rktman]

So you gave up on dying? Seemed cool, although messy and troublesome.

Yes, cleaning CF and sanding sounds good.

I kinda had a hunch that getting a good airfoil might remove enough balsa that I might not be able to use a larger motor if I ever wanted to. Sure enough my airfoil turned out great but left the wings "floppy". The tissue won't really add any weight and the thinned out dope's weight penalty is negligible too but they really add a lot of strength. The color won't be as bright/deep but that's okay, I kinda like the look of wood under semitransparent color.

Re: the basswood fuselage boom, I should have known that's what it was. I usually recognize it by the tighter/finer grain, and remember wondering how a balsa boom of those dimensions could be so strong. That should've been the tip off but I guess I was more focused on getting it built and up in the air.

Kinda anxious to see how this version flies too, though this time I'll wait to maiden it at my club's much larger flying field instead of my usual thermal-laden park with its appetite for gliders.

 

[XolveJohn]

Yes, the 3/32 thick balsa could be a challenge to airfoil. HLG wings are normally 1/4", gives you more to work with. Here is a somewhat mind numbing ref on Ancient HLG Secrets:

https://www.modelresearchlabs.com/legacy.htm

The plane shaver is new to me, wish I knew about it long ago. Have worn out many a sanding block and paper. Today, foam cores are all the rage, with vacuum bagging and CF skin. Not good for small gliders, and tricky to master. I have done some foam cutting with hot wire, for electric planes. Rocketeers should experiment with foam wings, some manufacturers actually embed CF tubes in them when molding. And HLG, many lessons can be learned about construction and trimming. In the old days, hand launch gliders were used for BG by just adding a rocket pod.

A caution on the carbon booms, early RBG protos had problems with the 18mm engine ejections, were like a shot gun, and imparted enough force to the airframe to knock off the pod and sometimes the wing. Why I added 1/64" ply reinforce to the pylon. And the 1/4" hole in the pod to vent some gasses. It might be helpful to only use 1/2 the ejection charge, they really are too powerful. Mqke sure your joints are strong, perhaps reinforce with thin fiberglass.

 

[Rktman]

Yes, the 3/32 thick balsa could be a challenge to airfoil. HLG wings are normally 1/4", gives you more to work with. Here is a somewhat mind numbing ref on Ancient HLG Secrets:

https://www.modelresearchlabs.com/legacy.htm

The plane shaver is new to me, wish I knew about it long ago. Have worn out many a sanding block and paper. Today, foam cores are all the rage, with vacuum bagging and CF skin. Not good for small gliders, and tricky to master. I have done some foam cutting with hot wire, for electric planes. Rocketeers should experiment with foam wings, some manufacturers actually embed CF tubes in them when molding. And HLG, many lessons can be learned about construction and trimming. In the old days, hand launch gliders were used for BG by just adding a rocket pod.

A caution on the carbon booms, early RBG protos had problems with the 18mm engine ejections, were like a shot gun, and imparted enough force to the airframe to knock off the pod and sometimes the wing. Why I added 1/64" ply reinforce to the pylon. And the 1/4" hole in the pod to vent some gasses. It might be helpful to only use 1/2 the ejection charge, they really are too powerful. Mqke sure your joints are strong, perhaps reinforce with thin fiberglass.

1st flight will definitely be with an A booster motor. If I feel comfortable enough with the size of our field I'll try going with a half ejection charge on a B or C, thanks for the reminder.

Due to the lousy weather I haven't even had a chance to try out my Champ, but once I feel proficient enough I want to try some Dynasoar RC models. Vacuum bagging and skinning with CF is a bit too expensive, time consuming and messy to interest me since I'm not into competition flying. But who knows? Never imagined I'd someday get back into rocketry either.

 

[Rktman]

Finishing up the last of the tissuing. Just a coat of dope and the flying surfaces are done. Pretty happy that the color is real close to the dye job on the previous model.

 

[BABAR]

Eric

Nice build

I like the dye job, I am curious as to whether the soaked balsa grain swells up and when dries becomes a bit coarser (more coarse?). My first thought was you can’t sand it after you dye it, but maybe if dye penetrates deep enough, you can sand it smooth AFTER dying and still retain that bold even color. Obviously flew well. So point may be moot.

A zero delay engine will eject just fine. May be an interesting deployment, as without the delay the rocket will be at full velocity when engine kicks (as opposed to slowing a bit during delay from standard engine.). My guess is it will probably do a loop, should be cool.

 

[Rktman]

Eric

Nice build

I like the dye job, I am curious as to whether the soaked balsa grain swells up and when dries becomes a bit coarser (more coarse?). My first thought was you can’t sand it after you dye it, but maybe if dye penetrates deep enough, you can sand it smooth AFTER dying and still retain that bold even color. Obviously flew well. So point may be moot.

A zero delay engine will eject just fine. May be an interesting deployment, as without the delay the rocket will be at full velocity when engine kicks (as opposed to slowing a bit during delay from standard engine.). My guess is it will probably do a loop, should be cool.

It does seem to get slightly coarser, and I'm wondering if some 2000 grit sandpaper could be used to "polish" it smoother if one were competition flying and wanted every last bit of altitude? I just fly for sport so it doesn't really affect me. If I get lazy I'll use markers, but dying is the next step up in the looks dept (plus you can color everything at once), and while tissuing takes a bit more effort, it really makes for a nice finish and adds a ton of strength (in this case, required since I sanded away a good amount of balsa putting in a nice airfoil).

As XolveJohn suggested, I have the option of removing 50% of the ejection charge if I opt to go with a larger motor. It's going to be interesting to see what happens with a booster engine. I'd be way more concerned if the glider were a swing wing, slide wing, scissor-flop etc. since it would be hard on the glider to deploy wings at full speed.

 

[BABAR]

I would like to know if the dye goes deep enough that you can sand AFTER dying.

I have flown versions of astron falcon boost glider and the ejection charge has broken the spar. Never tried scraping out part of ejection charge. I'd be afraid I would mess it up.

When you tissue the balsa does it leave surface smooth or does it require finishing and sanding?

 

[Rktman]

I would like to know if the dye goes deep enough that you can sand AFTER dying.

I have flown versions of astron falcon boost glider and the ejection charge has broken the spar. Never tried scraping out part of ejection charge. I'd be afraid I would mess it up.

When you tissue the balsa does it leave surface smooth or does it require finishing and sanding?

Nope the dye doesn't penetrate deep enough to allow sanding the surface smoother without the lighter balsa color showing through.

I don't sand the final layer of dope (I use Minwax brushing lacquer—the odor is less suffocating) but use 400 grit on the initial layers to smooth it out and give it some "tooth" for the next coat. The final coat will be somewhat glossy but it won't be mirror smooth. It'll look slick, like balsa that's been surfaced with something. The only way to get balsa absolutely smooth is to use sanding sealer—lots of it—and that means weight. I like the look of the wood grain showing through though, especially if it's tinted by the color of the tissue.

 

[Rktman]

Just a quick update; it's taking awhile because I had to trash both wings and make new ones.
I underestimated just how much the humidity here can affect balsa. Was putting in the dihedral on the wings on the screened in porch out back and stepped away for just 15 minutes to vacuum up the balsa dust in the build room. When I came back the wings had turned into bright orange potato chips. The 87% humidity had apparently sneaked in through the unsealed wing roots and curled them badly...so badly that nothing I could do would permanently flatten them.

Lesson learned, listen to that little voice called common sense next time (my fault, got lazy and didn't bring them indoors like I knew I should've). Oh well, I'm getting real good practice airfoiling thin balsa and after this build I've got my tissuing method down to a real science—no more wrinkles and no more having to shrink it to fit, so some good came out of this re-do.

 

[XolveJohn]

You might want to put a dehumidifier in your build room!

I have lost some balsa from not storing right. Wrap the stack with rubber bands, seems to help. Trying to flatten warped wood by putting weights on does not seem to help. Also,use Sig lite-coat clear dope.

The HLG guys would yell at you for airfoiling such thin wood.
They use at least 1/4" thick. But that won't fly on an A motor.

 

[Rktman]

You might want to put a dehumidifier in your build room!

I have lost some balsa from not storing right. Wrap the stack with rubber bands, seems to help. Trying to flatten warped wood by putting weights on does not seem to help. Also,use Sig lite-coat clear dope.

The HLG guys would yell at you for airfoiling such thin wood.
They use at least 1/4" thick. But that won't fly on an A motor.

I only ran into the problem because silly me, I went outside where the humidity was ridiculously high. I don't really have any problems indoors because it gets so hot here we have to keep the house air-conditioned so the air is dry enough that I don't have storage problems.

I find it's hard to imagine that the original builder / designer of the Bumble Bee airfoiled 1/16" balsa. I'd think it'd make it too fragile for more than a flight or 2. The thinnest I've ever airfoiled was 3/32" on another scratch build, which was easier because it was a high aspect wing. Just curious to see what difference it makes on this build if any.

I'll probably go back to using a B motor with part of the ejection charge scrapped out. Any recommendations for what I can use for that that's non-metal?

 

[XolveJohn]

I have never had a problem using a 1/8" flat screwdriver. There is nothing to create sparks. Just dig in and dump it out, one half or a little more. The delay train top is hard and you can't hurt it.

The BumbleBee was only 1/2A engine, so 1/16" wood was fine.

 

[milehigh]

Very nice glider build.
Just make sure you do have that good sized field to launch with a B engine. Especially if there's any kind of thermal action going on. Back in the day many folks used to experience fly-aways with the original well-trimmed Bumblebees on mere 1/2A motors!

 

[Rktman]

Very nice glider build.
Just make sure you do have that good sized field to launch with a B engine. Especially if there's any kind of thermal action going on. Back in the day many folks used to experience fly-aways with the original well-trimmed Bumblebees on mere 1/2A motors!

Thanks! Weather permitting I'll be headed for a 3,800 acre farm field next weekend. Forecast is for 30mph gusts so I may even go with an A engine to keep it within sight. Will post results.

 

[Rktman]

I have never had a problem using a 1/8" flat screwdriver. There is nothing to create sparks. Just dig in and dump it out, one half or a little more. The delay train top is hard and you can't hurt it.

The BumbleBee was only 1/2A engine, so 1/16" wood was fine.

Just got through removing about half the ejection charge. Just as you said, very easily done, the delay charge is hard enough not to be affected by the scraping, I still have all my fingers and didn't burn down anything. Anxious to try out both the A8-0 and, winds permitting, the B with the half charge this weekend.

 

[Rktman]

The saga continues.
Got to maiden it this past Saturday. Let me mention from the start that airfoiling the wings in this situation is not a good idea (the instructions say “no airfoil is required” but I wanted to experiment with eking out even more duration time). I’ll admit it was probably a mistake. It was a spectacular fail—a loop and power prang into the corn stubble—that ended any hope of reflying it that day. Repairs shouldn’t take too long though (new set of wings, but this time without any airfoil).


The cause could also have been the small “Gurney Flap” I added to the tail to help pull the nose up without adding weight to the forward end.


Anyways, judging from the performance of the first model before it got trashed by a tree, I’m expecting a really great flight next month, weather permitting.

 

[Rktman]

Final Flight Report


Time to wrap up my little educational adventure into Gliders 201. Was able to put in a test flight
yesterday and it did not disappoint. Arrow-straight launch on a B4-2 followed by the quintessential
idealized transition into a slow circling glide. I was stoked at how well it was doing...at least until I
realized it was circling closer and closer to the edge of the park. Even though the wind was only at 5
mph it didn't look like it was about to come down anytime soon. It didn't. At a minute 5 I watched it sail
over the trees at the park's edge and start to come down over some buildings about a half mile away.

Not again! (Cue tamper tantrum). This was my 3rd build or rebuild. Ironically the glider is a little too
good. But that's not a bad thing, with some airfoiling and bare balsa it would make one heck of a competitive glider in the B motor class. I figure during Winter there's probably less thermal activity but my Rumble Bee was still airborn and 45' - 50' up when it passed over the trees and out of the park.

There's a happy ending to the story though. I drove over to where I thought it came down, a huge
compound for a commercial trucking outfit. Anyway long story short the guys in the main building really
went out of their way to help me search and even went up on the roof. I didn't have much hope but
that's where it was, on the roof 20 feet up.

So what did I learn? 1) Don't EVER put a lifting airfoil on the stab. Such a rookie mistake (and the real
reason it power looped). 2) Airfoiling the wings is okay if you want to eke out every fraction of a second for competition but isn't necessary for sport flying. 3) Removing a 3rd to a half of the ejection charge takes the violence out and really keeps the motor pod and/or fuselage from being damaged (thanks for the tip John). 4) This is a really successful low sink rate glider and I can now understand why it was designed as an RC glider: insurance that you'll get it back. 4) Don't go above a B motor unless it's the RC version. Even in a 308-acre park it's gotten away from me 100% of the time.

If you're looking for a great flier that's also a fast easy build, this one gets my 5 stars. I don't know if
John is still offering kits, but if not you can find the plans in the 2017 May/June issue of Sport
Rocketry.


Safely home with only a minor NC ding.

 

[XolveJohn]

Sweet looking bird! No, I don't have kits anymore, but some pieces parts are lurking around.
Was that a 5 minute flight, or 1 min, 5 seconds???

The wood is so thin that just rounding the edges is adequate, for a good airfoil you really need thicker wood, get out the razor plane, just not used on this design. Yes airfoiling the stab can create radical results, the boost trim of this model is delicate and sensitive. It took a few flights to refine the angle of the Vector Pod. The free flight version will boost the best. When you hang the radio pod on it, the flow disruption causes a slight "S" path, although still generally up! That is why I tried enclosing the radio in a box balsa fuselage, certainly helped but a lot more work, and the Vector angle changed, this is posted elsewhere.

You did not mention thermals, another great way to lose a bird. I would say wind is the biggest enemy, I watch the weather reports and jump on days that are less than 8 mph.

Remember that modifying engines in any way is not allowed at NAR launches, that trick being needed shows that many of the Estes engines EC's are sized for big rockets, and often are way too powerful for smaller tubes and volumes. On their composite motors there is a cap you can remove and just dump some out.

Good flying!

 

[Rktman]

Sweet looking bird! No, I don't have kits anymore, but some pieces parts are lurking around.
Was that a 5 minute flight, or 1 min, 5 seconds???

The wood is so thin that just rounding the edges is adequate, for a good airfoil you really need thicker wood, get out the razor plane, just not used on this design. Yes airfoiling the stab can create radical results, the boost trim of this model is delicate and sensitive. It took a few flights to refine the angle of the Vector Pod. The free flight version will boost the best. When you hang the radio pod on it, the flow disruption causes a slight "S" path, although still generally up! That is why I tried enclosing the radio in a box balsa fuselage, certainly helped but a lot more work, and the Vector angle changed, this is posted elsewhere.

You did not mention thermals, another great way to lose a bird. I would say wind is the biggest enemy, I watch the weather reports and jump on days that are less than 8 mph.

Remember that modifying engines in any way is not allowed at NAR launches, that trick being needed shows that many of the Estes engines EC's are sized for big rockets, and often are way too powerful for smaller tubes and volumes. On their composite motors there is a cap you can remove and just dump some out.

Good flying!

Thanks John, and that 1 min 5 sec flight was just when I stopped timing. It was up in the air at least another 30 seconds before I lost sight of it. It was on the cold side (44°F) so probably minimal thermal activity but I agree even a slight breeze (5mph in this case) negated the circling and carried it a crazy distance away. Thinking of trying an A8-0 to see if that'll get it up high enough. I'd be happy with a 30 sec flight if it meant getting it back safely.

I never do engine mods (this being one of the few exceptions) and though I'm strictly a sport flyer, who knows, maybe some day I'll enter an NAR competition so I appreciate you cluing me in on the safety rules. Out of the 15 or so gliders I've built and flown this one is sincerely a stellar performer. There are only 1 or 2 other kits that even come close.

 

[Crawf56]

Congrats on a good flight.

 

[Rktman]

Congrats on a good flight.

Thank you kind sir! The best part was getting it back.