Modifing a CG Shoestring. Should I?

I am going to be be cloning a CG Shoestring (42" ws) and will be most likely putting an FP 35 on it. Is there any benefit to lengthing the fuse, beefing up the tail moments, or any other mods that might have been tried and found to be beneficial to using a more "modern" powerplant? I am not sure the actual weights involved from the kit plans that show a Fox without a muffler to adding an OS fp 35 with a muffler, but I am sure that I will end up nose heavy. Am I right about this? Am I on the right track? Any help would be appreciated

Thank you!

LAST EDITED ON Dec-20-03 AT 06:49 PM (CST)
 
I built a kit version last summer and powered it with an OS .25FP. More than enough power. It is on loan now and flys fine as built. They are a pain to put together as designed and I hear Brodaks is coming out with it and has had it modified for easier assy.
I have built four over the years and every one of them tends to come out slightly nose heavy, which in this case is good. Great trainers for basic stunt and just fun flying. Not as sensitive or fast as a Flite Streak. The rubber band method of securing the wheels seems like a good idea, except when the bands break during a rough landing, they always snap back into the wing covering, making for a lot of bottom patches. Just make the gear permanent. Do not use the plywood control horn. That has to be a sick joke. It will work, but not for long.

I fliy mine with a 25LA and it's perfect. Mine is stock with the exception of some lighter wood used in a few areas.

The plane flies great and is fun!

Only problem I've heard already on the Brodak Shoestring is that it won't be legal for Foxberg racing around here, same as their Buster, Dangit. But should be a good build and easy enough, meanwhile I'll build a couple for racing and see how light the Brodak kit builds too.

Mine has an MVVS .15 diesel for power.
Chris Brainard

Why is this? Externally they are the same. Goldberg control line series is now a part of Brodaks, so it should be legal for Foxberg.

I just got out my copy of the rules for Foxberg as it is flown in the Topeka and Wichita areas. The rules originate sometime in the 1980's and they were last modified around October 1997.

Remember, this event actively seeks to hold technological advances at bay in favor of participation. Since a bunch of folks participate, I can't really say they are wrong.

The part of the rules that would seem to cause a problem are quoted here:

From paragraph 2:

"
a - The plane must be a Carl Goldberg profile stunter, or a direct copy thereof. (Kit wood substitution is permitted) See note #2.

b - The engine mpounts and plywood doublers may be lengthened rearward for strength, but they cannot be thickened or thinned.

c - The plywood doubler on the elevators may be enlarged, and placed on both the upper and lower surfaces for strength. The wood elevator horn may be replaced with a metal or nylon one.

d - All remaining items must be per the kit, including rudder offset (3/8") and line sweep. Engine offset may be remover or increased.

e - No additional wing sheeting will be permitted, nor will any wing thinning or fuselage reduction be allowed.

f - Landing gear must be of the two wheel type with a minimum of 5 inches between the wheels. Either wire or sheet metal type shown on the plans is permitted. "

For the purposes of this discussion, that basically hits the important parts of the rules.

What you may not know is the event originally only allowed the Goldberg Shoestring. The other Goldberg kits in the series were not part of the event. The "Note #2" in subparagraph a reads as follows:

"Note #2 - The Carl Goldberg profile stunter kits now permitted are Shoestring, Cosmic Wind and Buster."

So they have expanded the designs permitted before.

No use building a "questionable" model and forcing the CD to rule on the spot. That doesn't make anyone happy. At this point, the simple thing would be to ask BigIron to talk to the folks in his club and see if they would add the Brodak kits to Note #2.

Dave Rolley

LAST EDITED ON Dec-25-03 AT 11:35 AM (CDT)
 
Dave, I would LOVE for the Brodak and RSM kits to be included. I have proposed it to the club several times and been overridden EVERY time. The original intent was to get an event that the majority of sport modelers could compete with and have a reasonable chance of placing or even winning, thus showing them the fun of head to head competition. The requirement of stock engine and stock kit (or direct copt thereof) would eliminate the alibi of argument of "speed secrets" allow expreienced fliers to win. This worked VERY WELL for many years, but then Dallas and some other areas started allowing changes such as taking the offset out if the rudder, racing wheels, shifting the leadouts forward, and a host of other "minor changes". That has led to a great reduction of participation in that eveny in this area.

I still fly my STOCK PLANE AND ENGINE. I do think that the fuel tank type and size rule needs to be changed to allow any tank and just go with say four stops, or only a given size (capacity) tank, say 1,25 oz, or perhaps a combination of both say 1.25 oz tank AND a minimum of four pit stops.

I will try once more this Feb to get the other planes in the rules.

Bigiron

Leave it to the "experts" to take a perfectly good popular event and just DESTROY it by making "improvements"

My opinion. Bigiron13

I hope you are successful with the rules change to allow the Brodak models. Of all the changes I've heard for the event, this one makes the most sense.

For those of you that might be interested, BigIron can pit a hot Fox 35 like noone else. I pitted for him once. Flogged that engine until I couldn't lift my arm. He hits it twice and it runs.

I think Mr. Holliday is thinking fairly much along the same lines. He wants us to run a monthly Foxberg event here in KC allowing not only the Shoe and Buster kits, but the Superfly, Skyray etc. 2 oz tnak or whatever but more importantly, required pits.

He also wants shutoffs for safety.

Fp will be more than plenty of power. I wouldn't modify it much if any. Add three inches in the middle of the wing and an inch on the nose and two on the aft of the fuse if anything.

I got an old Fox stunt 35 on mine and it chugs around fairly well.

Bigiron

The neatest mod I've found for the airplane was something Bart Klapinski suggested for a Ringmaster. It is easier to do than to describe.

Where the leading edges join, there is a plywood joiner. Cut a new plywood joiner that has a 1/2" wide tongue sticking forward of the leading edge by about 1". Slot the fuselage to accept this tongue and install the plywood fuselage doublers after mating the wing to the fuselage. This traps the plywood tongue between the doublers and prevents the cracking at the wing/fuselage joint that plagues the profiles. I know the Shoestring has the cheek cowl on the inboard side that helps this problem, but this mod significantly improves the joint.

Rather than change moments, I would cut new horizontal tail parts from 3/16 sheet instead of the kit 1/8 th sheet and increast the span by 2". Aluminum sheet landing gear instead of the wire also helps, but is not necessary.
Steve

. . .could score a 500-point pattern with a full-size Cessna Skymaster on baling wire! That's not a fair comparison. LOL

An OS FP 35 is way too much mill for this plane. Agree that an OS 25, or Fox 29/35 Stunt is a better choice. For that matter, an OS 20 FP would work fine. Or any old baffle 29/35. I have had Johnson Ss on them. Redheads are good.

I've had three Ss, two are still flying. I would beef up the TE wing butt joint, same as with a Ringmaster.

I broke a fuse in half just aft of the TE once. Use your favorite method of strengthening the fuse, like running 1/32 ply on both sides, from front to rear, or whatever. Don't use contest balsa for the fuse if you are going to construct it as in the kit, with one slab of balsa. The doublers are pretty good as is (they go to the high point of the wing), but don't use lite ply, unless you are really anal about weight, and then only on the IB side.

Can't remember how far the motor mounts go back, but run them to the wing. You can drill out the unseen part for lightness.

Always use the cheek cowl. Put a nice paint job on it, and rub it out for looks.

S's have a light feel to them. I prefer the authoritative feedback of a Flight Streak.

After reading the previous comments, agree that the short fuse couplings could be lengthened for improved, smoother flying. But it really is not necessary. Currell

All right! Thanks guys... Once again information shared here is greatly appreciated!

It just so happens that I have a like new FP .25 and I think that will be the best change from what I first described. I was planning on making the LG permanent, and the tail parts with 3/16. The wing is already built, having been recycled from a previous plane, but is still straight and only missing the tip on one side.

I am left with one question... Why not use light ply for doublers? I try to keep the weight as low as possible without going crazy about it. I am just getting ready to do the final assembly on a scratch built Ringmaster and used the light ply, but I installed aluminum pads to mount the engine to something solid.

Gents

I believe that the Brodak version of the Goldberg original should meet everyone's requirements. The outlines are true to the original but the leading edge has been changed to a piece of 3/16 square with 1" wide sheet to replace the 1" solid and the tip pieces were designed to connect with lap joints whereas the tip pieces in the two kits that I have only fit where they touch and that's not very often.

We did, however, take the liberty to increase the thickness of the tail feathers to 3/16. As the parts are going to be laser-cut, tracing the outlines onto 1/8 sheet is no big ask

The first example built to the new drawing was completed in August and weighed 26oz ready to fly. It completed the full F2B pattern on its maiden flight. I suspect, however, that the pattern was not necessarily of 500 point quality. None-the-less the model was built and flown by the current Australian Vintage Stunt National Champ.

For interest, it was powered by an OS Max 25 with a Zinger 9 x 5 prop.

I have acquired said example and plan to fly it with an OS 20 FP-S.

It was the internal, "Wing" modifications that I was told made it illegal. I was also told the Buster wasn't legal either.

Hey combine that with the tank you have to get from somebody who has them, cuzz they aren't available anymore with airplane kits you need to scratch build or hopefully score off ebay and you have an event that your lucky is so popular, cuzz otherwise it'd die.

However, if you want a good looking, fun flying airplane, the String and the Buster probably are just about it. Not as fidgity in the air as the Streak. Real solid balloon busters.

Phil, you have seen mine on my bench and you know that I got a OS 35 FP lurking on the bench for it as well. Go ahead and put one of yours on it so you can keep up with me!!!! LOL

Bill

>S's have a light feel to them. I prefer the authoritative
>feedback of a Flight Streak.

Currel;

Amazing difference in perspective. My experience with the Streaks I built was that they were always light on feedback when being flown at the same speed as the Goldberg 'String. Considering the and the lighter weight, longer tail moment and small control surfaces of the Streak, this made sense. The usually heavier weight of the 'String combined with the larger control surfaces and normal nose heavy (as built) always made it feel much heavier on the lines than a 'Streak.

Granted - if you put a 36X or ST 35 on the Streak and cranked up the lap speed, you got more feedback.

Both were/are fun designs. Thanks to John Brodak, another generation of flyers has the chance to enjoy both of these classics in kit form.

Phil: Lite ply is undesirable as an outboard doubler, because it crushes too easily. When you tighten your engine down, it will take a set, without a whole lot of pressure. Also, it is not the best material to serve as a platform for a .29 or .35, especially a vibrating older engine, like a Fox. You may be able to use it on the inboard side, though. My (theoretically) super lite Ringmaster has this.

Bkruger: All of my Streaks somehow communicated more confidence at the handle. Maybe it was simply more pull, or something more subtle, related to aerodynamics and response. I have flown 4 Streaks and 3 Shoestrings (and 2 Busters) as a data base. But maybe it is just me.

It would be a shame if the Brodak Bergs aren't Foxberg Legal. Because: these new models will be easily available, whereas original Carl Goldberg kits are getting increasing harder to find, although it hasn't reached crisis proportions, yet. And not everyone wants to scratch build.

Why would internal wing mods be a (Foxberg) show stopper?

Just lookin at it, I don't know why it wouldn't be legal, though I worry about pitting a built up leading edge instead of the solid baseball bat.

What's going to have to happen is someone, possibly myself, will have to build one and take it to the contest and see what they say.

I PUT AN OLD OS 20 IN MINE AND ADDED 1 INCH ALL AROUND ON THE 3/16 INCH TAIL SURFACE .ITS REALLY FAST WITH THE OS 20 , BUT MINE IS VERY LIGHT.( MONEYCOTE) I THINK THE SHOESTRING FLIES GREAT AND THE EXTRA TAIL SURFACE IN MY OPINION MAKES IT FLY BETTER. IF I WAS BUYING A NEW MOTOR I WOULD GO WITH THE LA 25.

Neal

>Just lookin at it, I don't know why it wouldn't be legal,
>though I worry about pitting a built up leading edge instead
>of the solid baseball bat.
>
>What's going to have to happen is someone, possibly myself,
>will have to build one and take it to the contest and see
>what they say.
>
>From somewhere near Parkville, Mo.
>William Crane
>AMA 6733

It should be no problem. Construction changes are allowed so long as the exterior remains the same. If it is built up construction, then the same cut out areas need to be there. The Stuka Stunter, for instance, used sheeted flaps with cut out lightening holes. You can make these of solid wood if you wish, so long as you insert the cut out lightening holes. If the leading edge was a solid block on the original design (as in the Shoestring) and you make it built up, it should not make any difference. If the original had a carved and hollowed block for the turtle deck and you mold it, that should not make any difference. These changes are legal.

LAST EDITED ON Dec-21-03 AT 07:10 PM (CST)
 
has this.
>
>Bkruger: All of my Streaks somehow communicated more
>confidence at the handle. Maybe it was simply more pull, or
>something more subtle, related to aerodynamics and response.
>I have flown 4 Streaks and 3 Shoestrings (and 2 Busters) as
>a data base. But maybe it is just me.

Currell;

There are a lot of things that play a factor here. CG, tip weight, and leadout position all come to mind. My Streaks have always been so light on feedback as set up stock that I never recommended them or used them for beginning flyers. Just too "twitchy" for a novice. Great, however, for sport slow combat years ago. Great now for sport flying.

The difference is most likely how you set your ships up versus how I set my ships up.

I will bet that if I change any of the parameters listed above, I would see and feel a considerable delta in control response. Another thing that I have done with the Streak is just increase the size of the stab and elevator. Keep a 60-40 ratio between the stab/elevator - the stock stab is 30 sqi, stock elevator about 20 sqi. Increase total area to about 60 or 65 sqi. You might have to shorten the tail by about 1/4" to avoid nose weight. Huge difference in the feedback.

Interestingly, from what I heard, GMA first started with a nose 1/2" to 1" longer than what the 'Streak ended up with, but shortened it to deal with a harmonics problem. With our lower vibe engines today, that IS interesting. Let's see - lengthen the motor mounts to the wing cutout add about 1/2" to the nose, and ...

Bob

3/32" plywood doublers that are 4-ply or 5-ply work very nicely. Strong and not heavy. Don't go for the cheaper, cruddy 3-ply stuff.

I never did care for the Streak CG right on the spar. Too itchy twitchy for me.