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Cox Engine of The Month
Goldberg Li'l Jumpin Bean build thread (Finished!)
Page 2 of 3
Page 2 of 3 • 1, 2, 3
Re: Goldberg Li'l Jumpin Bean build thread (Finished!)
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
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
Ivanhoe- Diamond Member
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Re: Goldberg Li'l Jumpin Bean build thread (Finished!)
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
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Re: Goldberg Li'l Jumpin Bean build thread (Finished!)
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
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
Cribbs74- Moderator
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Re: Goldberg Li'l Jumpin Bean build thread (Finished!)
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.
Funny how pictures can throw that view.
PV Pilot- High Tech Balsa Basher
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Re: Goldberg Li'l Jumpin Bean build thread (Finished!)
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?
_________________
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...and never Ever think about how good you are at something...
while you're doing it!
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...and never Ever think about how good you are at something...
while you're doing it!
My Hot Rock & Blues Playlist
RknRusty- Rest In Peace
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Re: Goldberg Li'l Jumpin Bean build thread (Finished!)
PV Pilot wrote: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.
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Re: Goldberg Li'l Jumpin Bean build thread (Finished!)
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.
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.
Last edited by RknRusty on Wed Sep 12, 2012 11:06 am; edited 1 time in total
_________________
Don't Panic!
...and never Ever think about how good you are at something...
while you're doing it!
My Hot Rock & Blues Playlist
...and never Ever think about how good you are at something...
while you're doing it!
My Hot Rock & Blues Playlist
RknRusty- Rest In Peace
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Re: Goldberg Li'l Jumpin Bean build thread (Finished!)
RknRusty wrote: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
Cribbs74- Moderator
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Re: Goldberg Li'l Jumpin Bean build thread (Finished!)
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".)
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".)
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Re: Goldberg Li'l Jumpin Bean build thread (Finished!)
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
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
Cribbs74- Moderator
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Re: Goldberg Li'l Jumpin Bean build thread (Finished!)
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.cribbs74 wrote: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.
_________________
Don't Panic!
...and never Ever think about how good you are at something...
while you're doing it!
My Hot Rock & Blues Playlist
...and never Ever think about how good you are at something...
while you're doing it!
My Hot Rock & Blues Playlist
RknRusty- Rest In Peace
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Re: Goldberg Li'l Jumpin Bean build thread (Finished!)
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.
fit90- Diamond Member
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Re: Goldberg Li'l Jumpin Bean build thread (Finished!)
RknRusty wrote: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.
Re: Goldberg Li'l Jumpin Bean build thread (Finished!)
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.
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.
John Goddard- Diamond Member
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Re: Goldberg Li'l Jumpin Bean build thread (Finished!)
Isn't the Rubber Monkey the smaller cousin of the Wrench Ape?
fit90- Diamond Member
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Re: Goldberg Li'l Jumpin Bean build thread (Finished!)
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.
Cribbs74- Moderator
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Re: Goldberg Li'l Jumpin Bean build thread (Finished!)
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
Rolla
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Re: Goldberg Li'l Jumpin Bean build thread (Finished!)
Isn't the Rubber Monkey related to the Grease Monkey?
SuperDave- Rest In Peace
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Re: Goldberg Li'l Jumpin Bean build thread (Finished!)
SuperDave wrote:Isn't the Rubber Monkey related to the Grease Monkey?
Yeah, and the Elastic Ape is another relative
Ivanhoe- Diamond Member
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Re: Goldberg Li'l Jumpin Bean build thread (Finished!)
Then there's me.
The missing link
The missing link
John Goddard- Diamond Member
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Re: Goldberg Li'l Jumpin Bean build thread (Finished!)
JB:
There are lots of "missing links". They're called politians.
They feed on $$$$$$$$$$$$$$$.
There are lots of "missing links". They're called politians.
They feed on $$$$$$$$$$$$$$$.
Last edited by SuperDave on Thu Sep 13, 2012 9:39 am; edited 1 time in total
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Re: Goldberg Li'l Jumpin Bean build thread (Finished!)
John Goddard wrote: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.
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Re: Goldberg Li'l Jumpin Bean build thread (Finished!)
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
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
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re: noseheavy
Ron: did you ever figure out why the plane was nose heavy ? or was it less nose heavy when finished and covered ?happydad
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Re: Goldberg Li'l Jumpin Bean build thread (Finished!)
happydad wrote: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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