Hey All

I am just about to start a SIG Four Star 120 building project. And have an engine question, I have looked at just about every thread as far as 4*120's go and cant quite find an opinion on my question. I am flying a trainer at the moment (SIG LT-40) and the 4* is my second plane. I am not too sure what engine to put in. I am leaning towards a Saito 120 but also concidering an OS FX 91. for simplicity's sake, I have no experience with 4 strokes. Because wher I live Johannesburg, South Africa we are about 5000 ft above sea level and my LHS said the FX91 will be underpowered and suggested an Irvine 150. Any comments?

Marcel

I don't think you will be happy with a 91FX, not enough power. Install the firewall 2 inches back and use a Zeonah 26. The engine is not that expensive, and you will have a easy starting engine that costs very little to fuel , and provides good power.

I built a 4*120 and originally intended to use a Ryobi 31cc engine. I moved the firewall back about 1.25". I changed my mind on the engine because I have to use the family van to transport the planes to the flying field and didn't want the smell of gas. I instead mounted a Super Tigre G 2300 and using a 16X7 APC prop and a Bisson Pitts muffler. I plugged one of the pipes and ran about a half gallon through it on the test stand. At this point I have about a dozen flights and it appears to be a good combination. Run the engine at mostly half throttle with plenty of power. I agree with Taildrager that the 91FX might not be big enough for the plane. I have no experience with the 91FX so it's just an educated guess on my part. Try a search on the 4*120 here at RCU and you should find some posts mentioning the engine also.





quote]ORIGINAL: Phuzzy

Hey All

I am just about to start a SIG Four Star 120 building project. And have an engine question, I have looked at just about every thread as far as 4*120's go and cant quite find an opinion on my question. I am flying a trainer at the moment (SIG LT-40) and the 4* is my second plane. I am not too sure what engine to put in. I am leaning towards a Saito 120 but also concidering an OS FX 91. for simplicity's sake, I have no experience with 4 strokes. Because wher I live Johannesburg, South Africa we are about 5000 ft above sea level and my LHS said the FX91 will be underpowered and suggested an Irvine 150. Any comments?

Marcel
[/quote]

Hello

I had a look at the Zenoah G26. Quite a nice engine, not to expencive either, although I have no experience with gas engines. It is quite heavy though? Ayyone have any experience with a G26 in a 4*120?

Marcel

There is a ton of information in the ‘Engine Conversions’ forum about modifications to the 4* 120 to accommodate a gas engine (firewall movement, servo placement, etc.).

Bill

I use a YS 120 4-stroke in mine, provides plenty of power, and it might be just the ticket for your altitude since it is "supercharged". The fuel flow on this pumped engine is never a problem, either.

Usually this plane builds tail heavy, so the added weight of a little gasser is no problem. The only dievation will be placing the firewall a bit back from the plans which is no big deal. My 4*120 came out at 12 lb with the RCS 140 that weighs a tad over 3 lb, and swinging a 16" prop is about as big as you can go without longer gear.

I had a fellow give me 1/2 a wing and a busted fuselage and I rebuilt it. First was taking of the covering that he applied with it seemed to be a thick paint of some sort and all the repairs from previous crashes. Made anew wing half fixed the fuse and installed a Super Tigre 2500 witha 7d carb. This thing recovered with monocoat is still really heavy and I really do not want to know how heavy. It flies reallygreat. t slow lands at a crawl and is a very responsive ship

I had a fellow give me 1/2 a wing and a busted fuselage and I rebuilt it. First was taking of the covering that he applied with it seemed to be a thick paint of some sort and all the repairs from previous crashes. Made anew wing half fixed the fuse and installed a Super Tigre 2500 with 7d carb. This thing recovered with monocoat is still really heavy and I really do not want to know how heavy. It flies really great. t slow lands at a crawl and is a very responsive ship

I think a new build that is light on the glue but reinforced on the fuse sides just aft of the trailing edge will fly perfect with a 2300 to a 3000 and people are giving them away as they had a bad carb. You van now buy a barrel made in china that will fix the carb and it is $15 do if you look on ebay a tigre can be had for as little as $50 and I have 8 of them all were smashed and bent cranks (easy fix) and not one cost me over $30 and I got one with a full C@H ignition conversion for $50 with the ignition and folks that is a cheap way to fly

You can convert a Ryobi 31cc weedwacker for about $50--$75.

Move the firewall back and slap it on there. Mount your elevator servos in the tail and maybe the rudder servo as well.

Beef up the LG mount.

Use a 10--12oz tank and fly it with the Ryboi for pennies compared to a glow engine.

I have a Thunder Tiger 1.20 pro two stroke on mine and love it. This is one of the best engines I have ever owned. Starts with a simple flip of the prop. Sometimes, I can just spin the spinner between my thumb and index finger and it'll start. It isn't too heavy and has plenty of power for this plane. It is also surprizingly easy on fuel. One of the best kept secrets of our hobby.

Andy

Have i well used os 120 fx 7 need the best starting settings for all three sooner is better

Thanks ahead Ken

Hey all

Thanks for all the input guys. Seems like there is quite a following to put gassers in a 4*120. I would love to experiment with a gasser but not to keen on doing any modifications to the plane. It is only my second RC plane that am building. I must say, this is a lovely kit to build, I am going slowly and steady and loving every minute of it. I will most definately buy a second one and hook it up to a G26.

But I have done some research and have come to the decision that it will either be a Saito 1.20/1.50 or a TT120 Pro.

Marcel

For what it is worth I intend to put two ST 90’s on mine as soon as I find a wing that is not broken.

Bill

You'd better reinforce the Landing Gear block or you'll find the plane scooting down the runway on it's belly with the landing gear bouncing along behind. Trust me, I know.

Here's how to do it:

There is a lite ply former right in front of the LG plate.
The belly sheeting on the bottom of the fuse---behind the LG p[late isn't as thick as the plate.

Build up the sheeting behind the LG plate with some lite-ply untill it's the same thickness as the LG plate. You should build up this sheeting for at least 1" behind the plate. 1.5" would be better.

Now cut and sand a balsa block about 3/4" wide and the full width of the fuse---in front of the lite-ply former thats in front of the LG plate. Glue it in place with some 5 minute epoxy.

At this point--you should have an even surface---the thickness of the LG plate. It should extend from in front of the former to beyond the LG plate about 1.5".

Now--CAP the whole thing with a piece of 1/4" hard play and glue it in with some 15 or 30 minute epoxy.

Now--run a few pieces of traingle stock along the fuse sides on top of that 1/4" plywood plate and glue them in with 30 minute epoxy.

You can use some kabob scewers---the kind like you'd use for grilling chunks of steak and peppers on the grill--to pin it in place. Kabob scewers are available at any grocery store. They are made from bamboo.

Drill a little hole through the sides of the fuse INTO that 1/4" plywood plate that you glued over the top of everything. Drill into the plate about 1/2" or maybe a bit more. The hole should be the right size so that the scewers fit snuggly. Not rediculously tight or loose. Just kinda snug.

Insert the kabob scewer through the sides of the fuse and into the plywood plate. Snap them off. Now drizzle a good amount of thin CA onto the scewer so that it works it's way all the way into the hole in the plywood plate.. It will soak up the CA like a dry sponge and get rock hard in a couple seconds.

Sand with some 60 or 80 grit and your done.

Trust me--you WANT to do this to the LG plate.

There is another weak area in the 4*120. It's right behind the wing saddle under the turtledeck and behind the cockpit.

Look at the lite ply in this area--behind the wing mounting block. Not much there. It will snap the fuse in 2 pieces on your first really hard landing. It always snaps right behind the cockpit.

You got a few options:

You can add some lite ply to the area, and glue it in with 15 minute opoxy. You'll have to come up with a way to make it strong--without adding a bunch of unneccessary wood and weight.

You can use some fiberglass and 30 minute epoxy. Spread the epoxy on the area in a thin layer and then add some 2oz or 4oz fiberglass cloth to the area. Apply more epoxy and spread it out as thin as you can get it. This will help a lot.

You can buy some carbon fiber tape and CA it onto the area.

You can add some simple balsa formers to the area.

What you want to accomplish is to SPREAD the LOAD on this area. It DOES take a large amount of stress on a hard landing--and there's not much wood or strength in this area. So figure out a way to strengthen it up and add more area for the load to disperce into the rest of the fuselage.

Good luck.

I am building a Sig four-star 120 and was concerned about using an OS FX .91 engine as it is at the bottom of the recommended engine range. I called Sig directly and they told me that an OS FX .91 would fly the plane just fine, as long as you are not planning on tearing up the sky. I have also built a Sig LT-25 and used the lowest recommended engine (an OS FP .25) and it flew just fine as well. Extra power is nice, but if it is the difference in flying what you have and putting out several bills to buy new, I'd say fly what you got.

I would say gas would be the way to go. If you find a good conversion engine, its cheaper than a new glow 2 stroke, and waaaaay cheaper to run. Even a good used gasser will keep cost down. Also, with a gasser, there is a pump built into the carb, so tank can be virtually anywhere in the plane, and cause of the better fuel economy, it can be a smaller tank too. As per tuning, there is probably someone in your club that can help. Its actually not that hard to tune them, just different. And once they are tuned, the settings stay put, unless a change is made in prop size or if the temps drop or raise considerably.
Either way you go, I hope you have fun.