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

[Ivanhoe]

I'd not try to do anything about the CG position until you have it fully covered and complete. Trying the balance when it is uncompleted could be very misleading.

The original kit plan shows the CG as about 1" back from the L/E, I have (scratch)built two models from this plan, and the CG came out in the right place, as built, on both. I can't for the life of me see how it could come out really nose heavy, TAIL heavy I could understand with any kit, but with such a short nose it's very odd.

Wilf

[Ken Cook]

Hi Ron, glad to see it coming together. In regards to tip weight. Back in the day, Ambroid and Testor's used to come in lead tubes. After the tube was used up, it became the tip weight after it was rolled flat. This isn't the case with 1/2A's as you don't require that much. A 1/4 oz. piece of lead weighs approx 7 grams. You shouldn't require the full 1/4 oz. I file or use side cutters to cut a piece leaving about 5/8 of it's original size. I use 5 grams and I use a small scale to weigh it. In the event that your wingtip braces are in the way, you just need to drill through them. Trying to maintain your leadout wires straight and no rubbing on any members is also important. The last thing you need is a control wire to jam up. This is really essential at the termination at the bellcrank where the crush sleeve can snag the rib. I use heat shrink tubing in that area bringing the tubing to the middle of the next rib bay to avoid problems like that. The Goldberg bean flew remarkably well for an older design. The one I fly was built in 64 and is still going strong today. Mine is twitchy and it's more than likely to be a result of the small Perfect bellcrank. The nylon Sig is more suitable for 1/2A and more than likely is what your model was provided with. Seeing that you replicated the original nose design, I would certainly think the plane wouldn't be nose heavy either. I've mentioned this before, when in doubt of the CG I use the 1/3rd rule. Balancing the wing approx 1/3 of the distance generally provides you with a flyable starting point. Many times this can be where the front leadout guide is located on the print. This doesn't always work but most of the time is satisfactory. It usually leaves the plane in a nose heavy condition if anything and rarely tail heavy. Using the miniature control horns in my opinion is more critical to shortening a plane's life more than anything else. Dubro makes a good 1/2 A horn approx 3/4 in height with plenty of adj. I also found a product that golfers use which is a fine lead tape ribbon used on clubs. It comes in thin strips and wraps cleanly and out of sight so to speak. This product can be used during trimming wrapping a tail wheel wire etc. Ken

[Cribbs74]

Ken,

It appears that the leadout guides are cocked in the picture, but they are actually in line with what is on the plans. Mine did come with the Sig Bellcrank so we shall see if it's twitchy. As to the tip weight it is not lead and is actually a steel block so it would be hard to trim down. I will probably buy some lead or just use some pennies. I will keep an eye out for the lead tape.

Wilf,

These plans I am using are just a photocopy of the originals so I am not sure why there is no CG mark on them.

Ron

[PV Pilot]

I was thinking the leadout tubes were crooked also and there would be sever rib rubbing right there. As far as the plans were concerned in that area, I swayed away from the plans to make sure there were straight pulls on those leads to the bellcrank with equal distance between rib cutouts for the travel of the bellcrank and swing of the leads. Found out the hard way years ago to make sure the crimps and tag ends of the leads were covered with shrink tube or cut back so they would not snag.

Funny how pictures can throw that view.

[RknRusty]

My Bean came with 14g of wingtip weight. I e-mailed Brodak and they told me to cut it in half. I did and 7g works right. The primer, paint and shrink covering will change the balance a good bit. I tend to lay it on thick, primer, paint and clear gloss Lustrekote. That alone will probably swing the balance to the rear. I'll look at my plans this afternoon and find the recommended CG for you. Have you put your metal tail skid on yet?

[Cribbs74]

I was thinking the leadout tubes were crooked also and there would be sever rib rubbing right there. As far as the plans were concerned in that area, I swayed away from the plans to make sure there were straight pulls on those leads to the bellcrank with equal distance between rib cutouts for the travel of the bellcrank and swing of the leads. Found out the hard way years ago to make sure the crimps and tag ends of the leads were covered with shrink tube or cut back so they would not snag.

Funny how pictures can throw that view.

I am going to sink those into the tip LE tonight I think. I will verify they are straight before I glue down. Right now I am not snagging on anything and each leadout has a nice smooth pull.

[RknRusty]

My leadouts


RE: my previous post about balance. I used 1-1/4" lightweight foam tires. That helps reduce weight in front of the CG. And they roll on grass better.

[Cribbs74]

My Bean came with 14g of wingtip weight. I e-mailed Brodak and they told me to cut it in half. I did and 7g works right. The primer, paint and shrink covering will change the balance a good bit. I tend to lay it on thick, primer, paint and clear gloss Lustrekote. That alone will probably swing the balance to the rear. I'll look at my plans this afternoon and find the recommended CG for you. Have you put your metal tail skid on yet?

Ok I will attempt to cut it in half then. No, I have not put the skid on yet. I did lay it on the tail and it still wanted to flip itself upside down. I will check CG when I am done covering and painting

[SuperDave]

Ron:

Just as a side-note, I found the wing ribs on the Brodak BR rather flimsy so I reinforced mine with 1/16" square basswood (from my Spit project). The Brodak BR is intended to be built on a Brodak wing jig ergo the excessive wing rib holes. (Curious that the Brodak wing rib jig is not available and I believe that is just another example of Brodak being "proprietorial".)

[Cribbs74]

I finished covering and painting the Bean tonight. It came out OK couple little wrinkles, but overall OK. However, guess what? This blithering idiot forgot to add tip weight!

This is third model in a row I've done that. So....... The top covering is coming off tomorrow. Anyway color scheme is cream and sky blue.





https://i.imgur.com/1O4sk.jpg

[RknRusty]

I finished covering and painting the Bean tonight. It came out OK couple little wrinkles, but overall OK. However, guess what? This blithering idiot forgot to add tip weight!

This is third model in a row I've done that. So....... The top covering is coming off tomorrow. Anyway color scheme is cream and sky blue.

Looks nice. No need to remove any covering. Just make a surgical slit to open a flap of covering on the underside of the wingtip and put some 5 minute epoxy on the weight and drop it in place. On the bottom so it's not as visible and the epoxy will never let go. Cover it with a round-edged patch. If you've never patched Ultracote before, you'll be amazed at how invisible it is. I have patches on some wings that I have a hard time finding. You really can't see it.

[fit90]

Rusty has a great point-round the edges for iron on covering patches. If you leave the corners square they can begin to peel up easier and are easier so see.

[andrew]

Just make a surgical slit to open a flap of covering on the underside of the wingtip and put some 5 minute epoxy on the weight and drop it in place. On the bottom so it's not as visible and the epoxy will never let go.

Rusty's procedure will work just fine.

Before you add a permanent weight, why don't you tape a coin to the wingtip first. You can then adjust the weight to your satisfaction before epoxying it in.

[John Goddard]

Johnnies tip time

Next time you're getting a new tyre fitted or even just your old ones balanced
ask the Rubber Monkey if you can have a handful or wheelweights which are
self adhesive these days and v handy for our purposes.

[fit90]

Isn't the Rubber Monkey the smaller cousin of the Wrench Ape?

[Cribbs74]

I'll give it a shot. If it doesn't work well the covering will come off. Like I said it has a couple wrinkles on the LE that I am not happy about.

[Godsey3.0]

When I covered my Skyray I ended up with a ton of wrinkles on the Leading Edge as well. It was an earlier attempt at covering though. I have considered tearing off the covering but it flies nice so I will leave it. Save my spare covering for when I have to recover it.

Rolla

[SuperDave]

Isn't the Rubber Monkey related to the Grease Monkey?

[Ivanhoe]

Isn't the Rubber Monkey related to the Grease Monkey?

Yeah, and the Elastic Ape is another relative

[John Goddard]

Then there's me.

The missing link

[SuperDave]

JB:

There are lots of "missing links". They're called politians.

They feed on $$$$$$$$$$$$$$$.

[PV Pilot]

Johnnies tip time

Next time you're getting a new tyre fitted or even just your old ones balanced
ask the Rubber Monkey if you can have a handful or wheelweights which are
self adhesive these days and v handy for our purposes.

Johnny's tip-o-the day is a good one, and one I use also. I don't use the tape on the stick on weight for self adhesion. A blob of epoxy on the untaped side to be assured it doesn't come off.

Looking good Ron.

Don't get to crazy now, it will fly with a few wrinkles on the leading edge. You start stripping the covering off and it can weaken glue joints and pull balsa wood. Proceed carefully if you do that.

[Cribbs74]

Ok, Finished, I am happy with this one. I see where I could have done better, but the reality is I will turn it into kindling anyway........

So, I still need to fuel proof it as I always use Testors paint as I can brush it on. No spray painting in the Embassy Suites!

I usually shoot a coat of Clear Monokote over these things when done. It works well. I love how the Bean looks, real sleek, I hope it flies as good!

Click on the links if you can't see the pics.





https://i.imgur.com/2caU0.jpg



https://i.imgur.com/Mb03d.jpg



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



https://i.imgur.com/3rych.jpg

[happydad]

Ron: did you ever figure out why the plane was nose heavy ? or was it less nose heavy when finished and covered ?happydad

[Cribbs74]

Ron: did you ever figure out why the plane was nose heavy ? or was it less nose heavy when finished and covered ?happydad

Less nose heavy, but still nose heavy.......... As much as I don't want to add weight I am going to have to if I want this thing to stunt well.

Ron

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