just flyin

hey everybody im new here at rcu but ive been flying for about 2 years.i have wanted to build kit
for a long time and i just got started yesterday. its a goldberg anniversery cub and i plan on building
the full wing version and powering it with an o.s. .91 fs.
anyway i have a question for all the pros here. is it common to have to modify or sand laser cut kit pieces?
some of the laser cut parts in my kit are just a little to long, are these parts defective or should i just
cut sand and fit them to match the plan?

also any advise tips or tricks for the rest of the build would be very helpful.


thanx
greg

summerwind

which parts?

keep in mind that the plans are paper and paper expands and contracts with humidity.

with that said, the parts usually are right, but trimming won't hurt to work with your plan sheet as it is. check the fuse and wingspan specs against the plans and see what that is.

first thing to cover though is which parts and where they go.

just flyin

im refering the two laser cut pieces for the trailing edge of the elevator halfs.
i took your advice and measured the plan for fuse length and wing span
and both were spot on.


thanx

summerwind

you will also want to check various other parts to the plans.
need to verify that it's just these 2 parts that are off.
if the other parts of the kit are off, then your plan has expanded or contracted from it's original size.


my current build is an older Great Planes kit. i have 3 of these kits. one plan is right on, while the one i used from the older kit makes one think the parts are oversized...they are not.

my Dad built the kit you are building and he told me that everything was plug and play.
i never built mine though.

Dr1Driver

Your paper plans will shrink and expand with changes in the humidity. Check your pieces by stated dimensions, if the plans show them. If not, simply build the plane as the parts fit. For example, build the wing length to the shortest of the L.E., T.E., and spars. Simply sand or cut off the excess of the other pieces. Same thing for the fuselage. Square the longerons with the firewall and build from there. Place the bulkheads where the longerons will curve smoothly. To further complicate things - to save money, some manufacturers will give you some "overage". If a wing spar is supposed to be a finished 47", they may provide a "stock" length of 48" to keep from cutting it to length.

This isn't rocket science. If you build your plane square and straight and square, it will fly well.

TFF

Sometimes parts just dont fit like legos and they have to be made to. The newer the kit design the better the fit, but in any building situation it is about problem solving to get the finished product. Make them work; if you got new ones they are going to have the same error.

qldviking

I have found it curious how many say that plans shrink and expand with humidity. I live on the tropical coast with a huge variation in humidity, and when I 1st read about this issue I got curious, so I cut a piece of stainless sheet to fit a side doubler on the plans of a 108" cub and over the last yr been watching it closely. While there has been a little variation, its been minimal, only a fraction of a mm. In That time our humidity has varied from hi 90's to as low as 10% relative. What I did find that varied a lot was the ply and even more so the balsa pices I had for test pieces, with a notched stainless template to suit, and they varied in all dimensions over the months.

As for the parts of a kit all fitting, I have yet to build a kit where I didnt need to tweak the odd piece here and there, but thats building anyway. I just double check and check again before trimming.

summerwind

and of course we haven't said it yet, but "welcome to kit building"

seriously though, you checked the plan to spec dimensions and these are right, so just trim away.
you picked i nice kit to build, and it's a Cub, it'll fly fine.

AH1G

Interesting question...
I'm building an old GP Skybolt and the plans have either shrunk over the years or they were never correct. The fuselage plans were short and while building the wings, if I lined up the first wing rib was according to the plans, the second out 1/32" off, the second 1/16" etc. and it followed throughout the wing construction. The tips were 3/8" long. The LE and TE matched (all8 pcs.) so I built it according to the pre- notched LE and TE. May be the the LE and TE balsa was notched incorrectly? I don't think so...

summerwind

that's what i'm talking about.
i have 3 Patriot kits, 2 from the early 90's when they were made.........the 3rd is from when they reproduced them. all 3 kits have identical size parts. only one set of plans matches up though.
paper does shrink and expand.

even Formica laminate top builders know how laminate which is made from paper expands and contracts.........that's why you see seams opening up in countertops.

twn

Lay out the plans and make it fit right.... My Goldberg Ultimate plans were messed up. One side of the wing was printed longer than the other side LMAO. I just build it to be identical in size and layout to the other side. Plans aren't usually perfect but if you precheck before u construct you can catch most of it.

A lot of the laser cut stuff in my ultimate kit didn't fit completely right either. sand little bits until it fits...

Insanemoondoggie

I just put the finishing touches on my CG Cub last nite. This is my second CG Cub . The tail feathers don't match the plan and you have to fit and sand to make them work. Also , if this is a reissued kit from GreatPlanes, make sure to check your wood. The turtle deck stringers were 2 inches short and all the straight stock was unusable . I ended up stripping and recovering the tail feathers and wing off my old Cub and putting them on the new one. If this is the way the new Goldberg kits are going to come from GreatPlanes this well be my last Goldberg kit. You would be ahead to scratch build ,than to spend the time to straighten this kit out. .
Make sure you check all your wood out in the kit , most of it in mine was used to start my wood stove. Because of all the kit issues , it took me a very long time to finish, as I had to hand cut alot of the parts.. The reissued kit is no where near the quality of the old GB kits. Hopefully , this kit was just a fluke and they have dealt with the problems.
Goood luck and take your time .

just flyin

thank everyone for all the great insight . i am really looking forward to flying thing .
i just finished fitting up the stabilizer and elevator halves ,so far with some sanding its comming together nicley
ill get some pics ASAP.

thanx again

Insanemoondoggie

, I just reread my post and I didn't mean to come across so negative. Sorry about that. The kit I built had a lot of issues, which is not the norm for Great Planes and they did offer to replace the kit . Their customer service has been great.
The die cut parts do take some shaping , my stab came out a 1/4 inch shorter than the plans , by the time I had them shaped , but with a little tweaking they will come out nicely.
I clipped the wing and installed dual aileron servos and a Saito .72 . Was going to go with an after market landing gear , but ended up using the kit ones, but modded them for extra strength . I would recommend using 30 min epoxy for your fuse doublers as the area where the wing mount bolts attach , is a weak spot. Touch a wing tip and it well bust the cabin up. I also went with Sulivan push rods and push rod exitguides and had to glass around the wood dowel that holds the stabs together , to make the elevator half's more rigid.
I have had 4 Cubs, 1 with the full wing and 3 with the clipped wing. I prefer the clipped wing, and with a .91 fs. I think you would enjoy it more . There is a noticeable difference between the 2. Take your time and you'll have a very nice flying Cub .
Oh and welcome to the kit forum.

just flyin

insanemoondoggie, i didnt think that your post was negative just truthful.

also could u tell me more about how you glassed the dowel that joins the elevators?

thanks again

Insanemoondoggie

Where the dowel attaches to the elevator halfs . I epoxied the dowelto the halfsthen wrapped the joint witha small piecefiberglass , both sides . The elevator control horn set on it, I'll get some pics ,if that well help. But I'm headed out to maiden the Cub here in in few mins and well have to do it this evening.
With a Saito .72 , servos mounted on the CG and a 2700 m. 6 volt battey pack shoved all the way in the nose , it balancedout perfect . I also installed tail wires on it and a sullivain tailwheel , so it may be a tad heavier in the tail than stock . With a TT.91 ,you may want to look ahead as to where you well need to mount your battery and your servos as you proceed with the build.
When you build the fuse , you'll notice there is not fuel tank floor, they use foam and set the tank on top the battery . I did this on my first one , it worked , but was hard to keep every thing in place. After I beefed up the landing gear area, where the landing gear wires go thru the the fuse , I installed a tank floor and allowed a 1/2 inch for foam, for it to set on. Worked out slick and still had room to rap my battery in foam and mount it under the tank floor. Just food for thought.

DaveB

just flyin,

Why so much power?

My Goldberg Cub flew very nicely with a .40 2 stroke and/or a .52 4 stroke. My advice: back off on the power, unless you plan to clip the wings. Even at that, I believe you are over powering the Cub with a .91.

DaveB

just flyin

i know .91 fs is overkill but i got it super cheap. a guy that i fly with needed some cash so he sold me a complete harier 3d airplane with engine,radio,reciever and 6 servos for $125. he told me that it had a .70 4 stroke and when i disasembled it i found that it was an os .91 fs.
do you think that is gonna be problem?

ronwc

My Feedback: (404)

I built a flown a lot of J-3's, and the Goldberg is a great one. Build it as instructions say, don't worry about parts being slightly off, just trim if needed. An OS 91 is way overkill, but will work if that's what you have - most have flown have used 40 to 70 size engines - the main one I fly now has an old 46. Below is a J-3 kit I modified into a twin with two St 40's, would have flown with two 25's -

just flyin

insanemoondoggie,

on the fin and rudder do you have to make the piece that goes through the stabilizer and into fuse?


thanx

MinnFlyer

My Feedback: (4)

If that's the only engine you have, you can use it, but it is a LOT of power for that plane. I would prop it with as low a pitch you can get and be prepared to fly at half throttle.

That said... If it's not too late, seriously consider the clipped-wing version. It will still be a gentle floater, but it won't have so much wing holding it back.

The original Cub was designed with a wing that was too big to compensate for the tiny engine they put in it - you sure don't have THAT problem!

The clipped wing flies MUCH better as it generates so much less adverse yaw.

Insanemoondoggie

Yes , you cut it out of the 1/4 x 3/4inch stock.
An other issue , you may run into , is running out of cowl room. I set my engine back as far as it would go and still have room for the throttle lever to open and close, and the .72 just fits . Fiberglass Specialties make an extended cowl for 4 strokes , if you run into problems.

OLDFLYER2

My Feedback: (5)

I 'M USING A SAITO 62 IN MY CLIPWING AND IT JUST BARLY FITS . BUT IT SHOULD BE MORE THAN ENOUGH FOR THIS PUPPY. I MUST SAY TIS IS A VERY STOUT KIT. SHOULD STAND UP TO A LOT OF MY DUMB MISTAKES.

OLDFLYER2

My Feedback: (5)

MY CLIPWING

Daddyo57

My Feedback: (15)

I just finished a Goldberg Cub that was the laser Cut Kit, it wasnt too bad and the Elevator wasnt exactly like the plans but that isnt a problem. The only things I didnt like was the Fuselage cuts were round where they needed to be square, a fair amount of time with a file squared it all up. also on the laser cut wing ribs the supplied spar material was a bit bigger than the cutouts for them, again with sanding and filing. Like Insane suggested, get the Fiberglass Specialties cowl and it will last forever. One option you might consider, when I built my first GB Cub, I didnt care for the single aileron servo so I used the servo on the hatch method and went with dual servos, worked great. I prefer the older style kit by far to the new laser cut kit personally but it is till a great kit if you done mind sanding and filing. If money isnt too much of an issue you should consider using the Fabric iron on covering and painting it, it isnt that much heavier and with that .91 it wont matter I built my first one and used an OS .61 4 stroke fabric covered and painted and it flew sweet!!!! the last one I just finished had a Saito 80 Twin and was covered in L-4 military colors using the Monokote Olive Drab, looked good but it is a pain to use. the GB Cub is a very good flier and is also very tough if you have a less than perfect take-off or landing. I went crazy on the one I just completed and built a set of articulating landing gear for it for looks and function. BTW, there were standard J-3 Cubs used in the the military so it is still scale to not have the greenhouse windows if you want. I just found an old style Goldberg Cub kit in my attic that I dint know I had!! funny... guess I have some trading stock. Keep us up to date on the build! Couple pics of mine. One other thing, Goldberg says to take the struts off to fly, if you beef them up and maybe even make some supports that go from the middle of the strut to the wing, you can fly with them on no problem and it looks more scale.