Building a Sig Four Star 120

[Gerald]

I've got the wing and tail surfaces ready for covering. Starting on the fuselage now. Have any of you overpowered one of these? I'm planning on using a MVVS 160 gasser.

I've made a few improvements to the standard build. Used Robart hinge points pin hinges instead of the CA easy hinges. Also tapered the control surfaces instead of leaving them as fat 3/8" thick slabs. The rudder area has been increased by adding the top portion of the vertical stab to it, making it an aerodynamicly balanced unit like in the Extras, etc.

I plan to glass the fuselage and tail surfaces and the wing will get covered in Sig Koverall and doped.

Share your Four Star 120 experiences here. :cool:

[Gerald]

Why was my post moved here from the Giant scale area? This plane is IMAA legal.

[Mike Smart]

Sorry Gerald,

Here in the UK, Giant Scale refers to large scale models. As this wasn't a scale model, I moved the thread.

Mike

[Gerald]

Mike, it seems that here "giant scale" can mean "giant size". For example, an IMAA legal model need not be a scale model of a real aircraft. I have heard of this kind of differing interpretation before though when the subject giant scale is discussed.

It may make sense to divide the categories at some point into giant scale-models, and giant-scale models ;).
But the forum here on RCgroups seems so little used that maybe it is reasonable to combine the two subjects right now. There are many issues in common to both that set them apart from smaller models. For example the power systems are usually quite different often being gasoline powered. The issues with airframe strength, hardware fittings, heavy duty covering materials, powerful servos, etc are of concern to giant models in general.

There already exists a scale forum in this same section. Wouldn't scale detail issues be the same regardless of the size of the plane? Maybe the scale forum is a better place to discuss those topics. Would a post get moved from the scale forum to here if the wingspan exceeded 81"?

I don't really have strong feelings about where this post goes but I just thought this forum needed a little boost and the Four Star 120 is my only model of that size at present. :cool:

[Mike Smart]

Hi Gerald,

We'll assume your interpretation is correct until someone complains:D
Personally speaking, to me a scale model is a scale model, whether it be a parkflyer or a 1/3 scale Hurricane. Back in the electric scale modelling forum, I believe we miss quite a few nice scale models because people post them in Parkflyers. Fortunately a few, like Dreamer, post in both and we get to see some of the little gems.

Mike

[Adam Neat]

Hi Guys; Mike according to the IMAA they have several definitions for a "Giant" model. 80" span or larger for a monoplane. 60" span or larger for a biplane. Or 1/4 scale or larger.
So there are some overlapping qualifications there but for a "sport" type plane they just need to be big

Gerald here is a link to a guys web page that has been using a 31cc Ryobi conversion in a 4 star 120. I was planning on doing a conversion on a Ryobi and came across it.
http://www.geocities.com/CapeCanaveral/Hangar/1071/4star.htm


Adam

[Gerald]

Hey Adam, that's quite a coincidence because I just found that web page you linked to today and had looked at it before seeing your post.

I've got the engine mounted now and I don't think I'll have any balancing issues with this one. It's quite a bit lighter and mounts like a glow engine. But it's still 26cc and rated at 3.8HP. That's an 18x8 prop that will be used.

[Adam Neat]

Nice Gerald!! That engine has the battery powered ignition right?
Not having a flywheel saves lots of weight. I believe I see you are using some type of rubber mount for vibration. :cool: Ive also noticed that guys running the larger engines are using some type of tail bracing, and thats probably not a bad idea. I dont know if the original plane had them or not.
I was considering a 4 star 120 myself, we will say what happens for Xmas. ;)

Let us know how it turns out/flies.
Adam

[Gerald]

The ignition is a microprocessor controlled solid-state unit. It has electronic spark advance curve programmed. The weight of the ignition unit as shown is about 5.5oz.

[Gerald]

I'm using a Du-bro #688 motor mount. It has urethane vibration isolators where it bolts to the firewall. I was able to leave the firewall in the stock location but I did beef it up by laminating an aditional third layer of 1/8" birch plywood, so it's nearly 1/2" thick. It should run smooth with the electronic ignition but this is added insurance. I want a heavy-duty motor mount for the huge thrust it will have. I'll be running a tuned pipe on it which should push it over 4HP.

[Gerald]

The kit has provisions for optional tail bracing wires and I intend to use them. I had to move the location of the hard-points where it mounts to the fin slightly because of how I modified the rudder.

The rudder area has been increased by about 30% by converting the upper portion of the fin into an aerodynamicly balanced rudder extension. This keeps the looks the same, doesn't add drag, and takes a lot of load off of the rudder servo. I suspect it should also reduce the risk of flutter.

I used Robart hinge points instead of the CA 'easy-hinges' that came with the kit. This is much stronger and allows a full 45deg rudder deflection without stiffness or excessive gap.

[Gerald]

I finally got the big Four-Star finished and in the air. Here's a couple pictures.

[Gerald]

In the air>

[Goekeli]

Gerald,
How about a flight report? How much fuel is through the engine now and how many flights? What is your AUW? I'm getting really close to building one.

Joe !~)