Goldberg Li'l Jumpin Bean build thread (Finished!)

[Cribbs74]

Ahhh back in the hotel. Build time!

This go around is a Goldberg Jumpin Bean. This is the re-kitted Brodak version.

I love the laser cutting. That's about it though. The plans are designed for someone who has experience building like most Goldberg plans are. I think the biggest problem with the kit is the hardware. Once again I am faced with the cheap plastic wheels and the kit does not have the firewall and nacelle pieces the the originall kit has. What it does provide is a plastic engine mount which is functional, but unsightly in my opinion.

Luckily the kit supplies some wing bracing shenanigans for building the wing that will function as nacelles. I will attempt to re-create the look of the original Bean that in my opinion was a great looking Goldberg model.

Not many pieces in this kit and I have knocked out most of the wing this evening. I should have it finished within the week. Oh! Forgot to mention the most important part. The powerplant will be the first Cox engine I ever purchased the venerable Black Widow!



https://i.imgur.com/j7TGo.jpg

[Ivanhoe]

I think those plastic engine mounts are cheap and nasty, and I'm really not sure how strong they are either. Here's my 'Bean, scratchbuilt from the original CG plan



I would really advise you to add some strengthening to the fuselage behind the wing, the 'Bean is VERY weak at this point, mine has a couple of bamboo skewers superglued along each side after a previous version snapped here every time it was landed "heavily"
(i.e crashed!)

Wilf

[PV Pilot]

Here are some pics Ron of the LJB wing bracing I mentioned in the saturday control line blues video thread.


The 1/16" strip of craft plywood where the trailing edges meet. that whole area got a wrap of epoxy coated fiberglass tape once it was ready.


A lengthwise pic of the rib and wingtip bracing. I also sheeted top and bottom of the wingtips with 1/16" ply just because that soft basla tip seemed very,,soft. Did I need to do all of the rib bracing??,,probably not, but I was waiting for parts and supplies to show up so I had some time to kill. One thing is for sure, absolutely no wing warp when I put on the Ultracoat iron on covering.

[lousyflyer]

Be sure to remove the charred brown wood at the glue joints. Charcoal doesn't bond well to anything.

[RknRusty]

As fragile as it looks, the Bean's wing is nearly indestructible. I've broken the rear fuse in so many places I can't count them. Done CA field repairs and kept flying.

The nose is the next weak point with that stupid plastic mount. After mine snapped completely off, I made a new nose piece and re-installed the plastic mount with doublers to brace it. I had to make shims to take up the gaps beneath it, but once it was all epoxied together it was tough as nails. Believe me, I tested it repeatedly. When I took it out to test fly, that's when my Cox handle broke in two and she did a full power vertical dive into the sidewalk. No damage at all. I was furious, it took me a week of nights to remake the nose before that flight but it held.


After this mod, the nose never broke again. Not because I didn't try.

Crash after crash and the wing never took any damage. The only time it got hurt was when the poorly field-repaired nose broke loose in flight, the engine rocked over and chopped the outboard lead edge in half. Kind of funny at the time. You can see that repair in the first picture too.

[Cribbs74]

That's funny!

It was your's and Wilfs' Bean's that inspired me to build one of my own. Both your suggestions dually noted!

I have epoxied the mount and the homemade nacelles in place tonight. The wing does look flimsy on mine Rusty, I have snapped the tips off twice just trying to line things. Which leads leads me to this rant......

The kit has poorly cut patterns as nothing is aligning properly! The leading edge tapers from left to right so where it meets in the middle is not the same thickness plus, when cut to the plans the mount for the bellcrank was way too large. Little things about the fit of the pieces are just slightly off. I am not totally impressed to be honest. I hope my Brodak clown is better.

Here is a picture of tonight's progress.



https://i.imgur.com/E70xf.jpg



https://i.imgur.com/Mrld5.jpg

[RknRusty]

It looks good despite the kit problems. I don't recall any of that kind of trouble. Your joints look nice, the fiberglass is a good idea. I don't see all of those blocks you braced the ribs with in your earlier post, did you remove them?

Your nacelles should help a lot. I would pack the gap between the front of the nacelle and the motor mount with epoxy and sawdust. I also recommend a 1/8" or 3/16" balsa brace between W2 and W1 where the crank mount is. Just to distribute some of the stress on W1. W1 is a double thick rib if I remember correctly, but mine broke. Probably from pulling it out of the stooge.

[PV Pilot]

Yep. A bit of massaging balsa before glueing anything is needed. Test fit, and test fit again,,,,and again

Those were my blocks and braceing pics Rusty.

[Cribbs74]

Yep. A bit of massaging balsa before glueing anything is needed. Test fit, and test fit again,,,,and again

Those were my blocks and braceing pics Rusty.

I like your bracing on the wingtips Keith. I am thinking they are not up to the task as kitted. How much of a pain were those to cut out?

Ron

[Cribbs74]

It looks good despite the kit problems. I don't recall any of that kind of trouble. Your joints look nice, the fiberglass is a good idea. I don't see all of those blocks you braced the ribs with in your earlier post, did you remove them?

Your nacelles should help a lot. I would pack the gap between the front of the nacelle and the motor mount with epoxy and sawdust. I also recommend a 1/8" or 3/16" balsa brace between W2 and W1 where the crank mount is. Just to distribute some of the stress on W1. W1 is a double thick rib if I remember correctly, but mine broke. Probably from pulling it out of the stooge.

Yeah that was PV's mod. Great minds must think alike as that was my plan. I was going to epoxy the gap and use the remainder of the nylon tape to wrap the nose.

[RknRusty]

Yep. A bit of massaging balsa before glueing anything is needed. Test fit, and test fit again,,,,and again

Those were my blocks and braceing pics Rusty.

I like your bracing on the wingtips Keith. I am thinking they are not up to the task as kitted. How much of a pain were those to cut out?

Ron

Oh shoot, I thought that was your picture, Ron. That's why I asked if you had removed the blocks, and was going on about the wing being stronger than it looked. DUH!

[PV Pilot]

Not to bad, just trace and cut, epoxy and clamp. Then a bit of profile sanding for the tips. Looks like yours are glued up already. I dont remember if those wing tips snapped out of a full sheet,,but if they did, you can trace a pattern and glue them in place if you desire .( if you still have that pattern/sheet).

[Ivanhoe]

"I have snapped the tips off twice just trying to line things"

As far as I can see in your photos, the wingtips seem to be a single piece of 1/8" in this kit, in the original CG kit they were two layers of 1/16" with the grain at differing angles, FAR stronger. I have never managed to break the wing yet, and the fuselage (with it's strengthening) has also stood up well to multiple abuse, but of course one big advantage of scratchbuilding is the ability to select the wood you use, with a kit you are stuck with what they give you!

Wilf

[Cribbs74]

Yeah I am going to have to do something to strengthen them.

Ron

[andrew]

Yeah I am going to have to do something to strengthen them.

Ron --

Laminating tips from 1/16" stock with the grain at 90 degrees is likely the best method, but since you've already got them in place, there are a couple of options available.

One would be to laminate 3x5 card stock, brown wrapping paper or typing paper to the top and bottom of the tips. Paint with slightly thinned white glue, add paper and clamp using wax paper as a release agent. They will have to be clamped flat to keep them from warping while drying.

A second method, and probably easier, is to add a gusset. The tip rib has a solid vertical piece that can be used for the base of the gusset. Cut the gusset, test fit, and glue in. You can always sand a slight bow into the top and bottom if you don't want the covering to touch. I've attached a poorly drawn picture of what it might look like. Grain on the gusset should run horizontally.

andrew

[Cribbs74]

Yeah I am going to have to do something to strengthen them.

Ron --

Laminating tips from 1/16" stock with the grain at 90 degrees is likely the best method, but since you've already got them in place, there are a couple of options available.

One would be to laminate 3x5 card stock, brown wrapping paper or typing paper to the top and bottom of the tips. Paint with slightly thinned white glue, add paper and clamp using wax paper as a release agent. They will have to be clamped flat to keep them from warping while drying.

A second method, and probably easier, is to add a gusset. The tip rib has a solid vertical piece that can be used for the base of the gusset. Cut the gusset, test fit, and glue in. You can always sand a slight bow into the top and bottom if you don't want the covering to touch. I've attached a poorly drawn picture of what it might look like. Grain on the gusset should run horizontally.

andrew

Good idea Andrew, I like the gusset option. I may just go that route with some ply.

[PV Pilot]

Like Wilf posted, the original CG kit wingtips were jigsaw puzzle pieces, that reversed the grain as you assembled, which made them considerably stronger. The new kits as you all know are just a lazer cut, which is a quicker manufacturer, but you sacrifice strength in my view.

If you go the gusset route, make sure to sand the above wing covering points off of the gussets, or it will "tent" the covering and you will have little dimples in the covering that are out of profile from the way it should look. Even with my little balsa block and wedge braces, I had to remove those points because I could see that they would poke that covering up in places. Just sight down the wing from all angles and view it as already having covering on it,, any point you see above that covering profile, needs to be knocked down.

I Rit dyed the nylon engine mount to a dark black color to match my scheme I had in mind. Before the boiling and dyeing process, the mount was a scary stiff mold of nylon. After quite a few dippings in the hot dye it softened it considerably, made it a bit more plyable. Just some food for thought.

[Cribbs74]

Like Wilf posted, the original CG kit wingtips were jigsaw puzzle pieces, that reversed the grain as you assembled, which made them considerably stronger. The new kits as you all know are just a lazer cut, which is a quicker manufacturer, but you sacrifice strength in my view.

If you go the gusset route, make sure to sand the above wing covering points off of the gussets, or it will "tent" the covering and you will have little dimples in the covering that are out of profile from the way it should look. Even with my little balsa block and wedge braces, I had to remove those points because I could see that they would poke that covering up in places. Just sight down the wing from all angles and view it as already having covering on it,, any point you see above that covering profile, needs to be knocked down.

I Rit dyed the nylon engine mount to a dark black color to match my scheme I had in mind. Before the boiling and dyeing process, the mount was a scary stiff mold of nylon. After quite a few dippings in the hot dye it softened it considerably, made it a bit more plyable. Just some food for thought.

That's a lot to chew on Keith. Between all the suggestions I should be able to come up with something.

Luckily I am choosing a blue and cream color scheme so the plastic should blend in. Good idea on the Rit dye though.

[RknRusty]

Speaking of poor cuts of parts, the rudder for my Brodak Streak had the grain running parallel to the fuse, which I think is completely wrong. I cut a new one with vertical grain from thicker wood and sanded an airfoil shape on the inboard side, because I used no offset. I don't know if that thin foil is effective at turning the tail in, but it looks cool.
Though I haven't snapped one, the Bean's tips really are flimsy. Mine curved a little downward when I shrink-wrapped them.

[PV Pilot]

lol, Not a big meal Ron, just a nibble. I get kinda "breathy" when I explain that stuff just so it is understandable with a better description. No worries with all the suggestions, you'll get it. The good thing is that it is all right here on CEF if you need to take a break and check those tips and suggestions.

Good call on the rudder Rusty. Just a little bit of rethinking can save many headaches down the road. In a pinch for those around with less money, you can coat that thin grain sheet with a thin layer of epoxy on both sides.

One of the reasons I sheeted the tips and added bracing, because I knew how much Ultracoat or most iron-on's like to pull hard when it final shrinks. It's is just a simple glue joint attaching that tip to the wing and that didn't look good to me. It doesn't seem to matter where you start when you iron-on on a light structure or what technique you use, it will pull it this way or that and try to warp. A bit of braceing and luck and I got a nice flay wing with no warp afterwards. The newer Ultralite Ultracoat has less shrinkage pull and is much easier to work with, plus it is lighter weight per square foot.

[RknRusty]

One of the reasons I sheeted the tips and added bracing, because I knew how much Ultracoat or most iron-on's like to pull hard when it final shrinks. It's is just a simple glue joint attaching that tip to the wing and that didn't look good to me. It doesn't seem to matter where you start when you iron-on on a light structure or what technique you use, it will pull it this way or that and try to warp. A bit of braceing and luck and I got a nice flay wing with no warp afterwards. The newer Ultralite Ultracoat has less shrinkage pull and is much easier to work with, plus it is lighter weight per square foot.

I haven't used Ultralite yet, but I do like Ultracote. It has a wide difference in heat between glue activation and shrinking temps. And it will shrink tightly with the iron. Monokote, on the other hand, has a higher glue activation temperature and is only a fine line hotter before it starts to shrink. And it takes more heat than the iron has to get the final stretch, meaning I have to put the heat gun on it(maybe I was just impatient).

I can do it all with the iron with Ultracote with much more control of the temp that glues it, and the speed it shrinks. It makes wingtips and curves much much easier. I avoid the gun whenever possible. Unfortunately I now have 3 rolls of Monokote. Another thing about Ultracote is you can stick it to sheeting at a heat low enough that it doesn't bubble as much as Mono. I chased bubbles all over the sheeting on the Streak.

[Cribbs74]

Tonights progress,

Mounted the bellcrank and installed the leadouts. Also installed the control rod and the center sheeting.

I made some braces for the wing tips which was a bit tricky as I couldn't run it down the center due to the leadout location. I epoxied some cloth over the gap in the nose. It would have been nice to have been able to ply the tips except I only have access to so much here in the hotel. Tomorrow will be sanding, painting and covering.

I have about 12hrs into it so far. This thing is turning out very nose heavy. Anyone else experience this? Also need to add the tip weight. Hopefully I remember before I cover this time. The weight supplied in the kit is a massive chunk of steel. I think it's too much.



https://i.imgur.com/ihXKm.jpg



https://i.imgur.com/4I058.jpg

[happydad]

[quote="cribbs74"]Tonights progress,

Mounted the bellcrank and installed the leadouts. Also installed the control rod and the center sheeting.

I made some braces for the wing tips which was a bit tricky as I couldn't run it down the center due to the leadout location. I epoxied some cloth over the gap in the nose. It would have been nice to have been able to ply the tips except I only have access to so much here in the hotel. Tomorrow will be sanding, painting and covering.

I have about 12hrs into it so far. This thing is turning out very nose heavy. Anyone else experience this? Also need to add the tip weight. Hopefully I remember before I cover this time. The weight supplied in the kit is a massive chunk of steel. I think it's too much.




Ron: try placing temporary weights on the elevator, or pennies, to counter balance the nose heaviness. just to see how nose heavy the beast is?? is this a thing with your planes? my sterling BRM was pretty close to CG with a black widow, the same engine you used. of course i am not complete yet. i lost 1/2 of the engine mount again. "something happens when you get old, but i can't remember what it is" anon. happydad

[Cribbs74]

[quote="happydad"]

Tonights progress,

Mounted the bellcrank and installed the leadouts. Also installed the control rod and the center sheeting.

I made some braces for the wing tips which was a bit tricky as I couldn't run it down the center due to the leadout location. I epoxied some cloth over the gap in the nose. It would have been nice to have been able to ply the tips except I only have access to so much here in the hotel. Tomorrow will be sanding, painting and covering.

I have about 12hrs into it so far. This thing is turning out very nose heavy. Anyone else experience this? Also need to add the tip weight. Hopefully I remember before I cover this time. The weight supplied in the kit is a massive chunk of steel. I think it's too much.





Ron: try placing temporary weights on the elevator, or pennies, to counter balance the nose heaviness. just to see how nose heavy the beast is?? is this a thing with your planes? my sterling BRM was pretty close to CG with a black widow, the same engine you used. of course i am not complete yet. i lost 1/2 of the engine mount again. "something happens when you get old, but i can't remember what it is" anon. happydad

I am beginning to wonder...... With the BRM it was a tad undersized so it may have accounted for the nose heaviness. However, this is a kit build so by rights it should be somewhat balanced from the get go without adding weight. I did add the nacelles and the epoxy, but it shouldn't have made it that nose heavy. I'll add weight if needed. Another thing I noticed is no CG anywhere on the plans.

Ron

[happydad]

[quote="cribbs74"]

Tonights progress,

Mounted the bellcrank and installed the leadouts. Also installed the control rod and the center sheeting.

I made some braces for the wing tips which was a bit tricky as I couldn't run it down the center due to the leadout location. I epoxied some cloth over the gap in the nose. It would have been nice to have been able to ply the tips except I only have access to so much here in the hotel. Tomorrow will be sanding, painting and covering.

I have about 12hrs into it so far. This thing is turning out very nose heavy. Anyone else experience this? Also need to add the tip weight. Hopefully I remember before I cover this time. The weight supplied in the kit is a massive chunk of steel. I think it's too much.





Ron: try placing temporary weights on the elevator, or pennies, to counter balance the nose heaviness. just to see how nose heavy the beast is?? is this a thing with your planes? my sterling BRM was pretty close to CG with a black widow, the same engine you used. of course i am not complete yet. i lost 1/2 of the engine mount again. "something happens when you get old, but i can't remember what it is" anon. happydad

I am beginning to wonder...... With the BRM it was a tad undersized so it may have accounted for the nose heaviness. However, this is a kit build so by rights it should be somewhat balanced from the get go without adding weight. I did add the nacelles and the epoxy, but it shouldn't have made it that nose heavy. I'll add weight if needed. Another thing I noticed is no CG anywhere on the plans.

Ron

no CG shown. doesn't that mean it will fly the matter where the actual CG is? LOL.

the reason i suggested adding small weights or pennies to the elevator is to give US an idea how much nose heavy the plane is. if it's a little nose heavy you could 1 or 2 things, but if it is very nose heavy something else is wrong. enter rusty.
happydad

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