I just got my Saito 120S for this airplane. I'm having second thoughts due to its great weight and size. It appears that I will have to move the fire wall back 1/2 inch and may have to add up to 2 oz tail weight with the servos and battery in the far back of the radio compartment.

Should I exchange the engine for the 100. This will require no fire wall modification and may be up to 14oz lighter after balance consideration. I'm not sure if I need the extra power either, as I don't fly 3D. I do need adequate power for IMAC basic though.

Wing loading w/100~19oz/sf, weight ~8lb
Wing loading w/120~21oz/sf, weight ~9lb

Did I get the wrong engine?

Did you not know about these changes before you ordered your 1.20? IMO stay with the 1.20 and have the extra power on reserve. I would think that with this motor, weight would not be an issue. My 2 cents.

I had this kit with an OS 1.20FS and I would say this is minimum for even basic flying.I don't think the 100 would be enough.Maybe consider a 1.08 or 1.20 2 stroke.I have a friend who has one with an OS 1.08 and it has way more power than my 1.20 did.I think a 1.20 2 stroke would be awesome,I like the way the four strokes sound on an Ultimate,but for your situation,the 2 stroke may be the way to go.
Mike

If anything, trade up to a Saito 150 and discover an awesome aerobipe!

I had this plane and powered it with a YS120FZ. The plane was a monster with that engine. I had modified the plane such that I used two elevator servos and mounted them in the tail where the elevator pushrods were supposed to exit so I didn;t have a CG issue. I've flown the plane with a YS91AC. It still had unlimited very with the YS91, but I personally prefered the YS120 setup, but the plane was a bit heavier with the 120. My guess is the Saito 120 has power somewhere between the YS91 and YS120.

You pointed out the exact same thing I had to think about. Is the extra power worth the wing loading. I can tell you that my YS91 setup gave me a much more nimble plane because of the lower wing loading. I decided to use the YS120 and sacrifice some agility for raw power.

I guess I thought the balance issue could be resolved with proper placement of components. I now realize that may be wishful thinking. The engine length issue is something different. The Saito 120 is 138 (5.44 in) mm long. I looked at the plans again, and realize I will have to move the fire wall 3/4 to 1 inch aft. This wall also impact other nose area structure including the sides, bottom, and other formers. The Saito 100 is 115 mm long and will fit in perfectly.

The thing is, everyone I've ever talked to says a 120 4C is perfect for this airplane.

AAARRRRG!

At the moment I have an OS120SP powering the Ultimate. It is 166 mm long with the special OS mount. The only option was to put the battery as far as possible back. The first engine + mount were only 115 mm long.
The engine power is not so important, as long as it stays running. I have seen some death sticks (I experienced only one) and one thing is for sure, the Ultimate is not a very good glider.

Bye,
Vincent

I flew an OS 108 powered CG Ultimate for several years. It would easily do knife edge loops and had plenty of power BUT, and a big But, it was heavy and when you cut the power it came down like an elevator. It was not easy to land because of the high sink rate caused by the extra weight and high drag natural with biplanes. I think it would have been much more enjoyable to fly with a bit less power and weight. Just my opinion.

I flew an OS 108 powered CG Ultimate for several years. It would easily do knife edge loops and had plenty of power BUT, and a big But, it was heavy and when you cut the power it came down like an elevator. It was not easy to land because of the high sink rate caused by the extra weight and high drag natural with biplanes. I think it would have been much more enjoyable to fly with a bit less power and weight. Just my opinion.

What would you recommend for an engine for this plane? I am thinking a 4 stroke but could be convinced a .91 to 1.08 2 stroke might be ok. Your comments aare appreciated.
Jeff

I would use a YS91FZ

ive flown 2 ultimates for almost the past 10 years.

powered both with supertigre .90 with a jtec side muffler. wieght is 8.5lbs. i can take off, then pull vertical right after and go maybe 300ft up (give or take..) and hang on prop until i over control it. still naturally nose heavy, just havent gotten around to putting wieght in back... too much fun!

for a plane in its category, the ultimate is a very good dead stick. not a trainer by no means, but not a brick either. depends on the wieght/wing loading naturally.

i ve even flown a 60in convert witha gas engine. it was nose heavy at the time, but not too bad..

guess im just used to my 'baby' flight characteristics...

as for the original question, use the 120, should be fine. not like a YS, but im sure it will do everything u want it to do.

I'm mostly hearing "go for the 1.20". Are you guys just a bunch of power nuts, or what?

BTW, Horizon says the 120S is 820g (29 oz) but the pamphlet that all Saito engines come with says 900g (32 oz). Which is right?

I guess the big question now is if I go with the 120, will my low speed performance be completely ruined, or barely noticeable. I can handle the structural mods.

Heck, I'm not even sure if my LHS will let me exchange it considering it was special ordered.

Still confused :disappoin

I had an ultimate when they first came out.. had a SuperTigre 90 in the nose, and it'd go vertical out of site with an APC prop. Mine never had any bad habits, it was actually my best flyer until the battery decided to short itself in the air. It had a pretty slow landing speed as well. It would knife edge loop well too. I actually found a kit recently, and was thinking about the 120 OS since I have it laying around not doing anything, but my OS 91fx may fit the bill even nicer since it's lighter.

just my own 2 cents.. well maybe it was 3, but who's counting
deck

I don't understand why you think the firewall needs moving back. AFAIK, the Saito 120 isn't any bigger (or heavier) than an OS 120 Surpass. The only deviation from the plans/instructions I did on mine was to use two aileron servos instead of one with the torque rods. And my notes on the model don't say anything about balancing issues. I keep rather detailed notes on all my models, so if it had been felony nose heavy, I would have written it down.

Engine, fuselage servos, tank, etc., were all mounted normally. I did replace that egg-shell cowl with a nice glass one, but I undersatand such is included in the kit now.

I have seen one of these fly with an OS 91 Surpass; but "marginal" would be a good word to describe it. I agree with the others, the 120 four-banger is nowhere near being "too much engine".

Steve

I have an ASP 1.08 turning an APC 15x8 around 8500. Model weighs 9lb. The 1,08 is light and provides vertical performance, and also, slow vertical acceleration.... when it runs properly!

The 1,08 is in a .60 size crankcase, and mostly fits in the cowl except for the cyclinder head.

No lead necessary.

Go with the YS91FZ it has more power than the 120 you have now. It is probably lighter too.

You shouldnt have to move the firewall any. The planee is designed for a 120. I have seen quite a few of these with 120 saitos and YS 120 without moving the firewall.

Good luck with your choice and enjoy the plane. It is a real good flyer!!!!!!!

I'm planning on a YS91 for mine (if I ever get around to finishing it). A few years ago a friend was flying his with an OS120FS and the engine quit. I couldn't believe how fast the the thing dropped. He was kinda high when he realized it quit but never made it back to the field and landed on a fence. This was about 7-8 years ago so today's 120's might be lighter.

From other posts, I've read where the YS91 will give unlimited verticle but maybe not enough for a strong pull out of a hover but I don't intend to use this plane for 3D type maneuvers......but then ya never know.

Best of luck...........Mark

The distance on the plans between the firewall and the prop washer is exactly 5-1/8 inches. The length of the Saito 120S + engine mount is 6 inches. Either I move the firewall or the front of the cowling. Last time I checked, a 6 inch engine will not fit under a 5 inch hood. I would much rather move the firewall than change the basic propeller position.

It doesn't sound like anyone is recommending the 100. I guess I'll stick with the 120.

I fly the arf with a Saito 150...no complaints here

Well, I'm definitely keeping the 120 now. My LHS wouldn't exchange it because it was a special order. He's a very small operator an I'm glad he can stay in business. It's probably a good engine choice anyway.

I looked at the plans for a third time, and if I use separate left and right beam mounts, I can put the carb right next to the firewall with a very small clearance gap. With this set-up, the prop washer is only about 1/4 inch forward of plan. That's probably not enough to worry about.

Next question is, if I have to, how do I mount my battery pack in the tail. Do I make a sort of battery pack mount/hatch cover and screw it to the aft fuse structure? Suggestions here are welcome.

BTW, I do anticipate balance problems primarily because I like to fly with the C.G. at the aft most position. I find this to result in the most honest flying airplane for aerobatics.

Thanks for the support.

ilikeplanes :

I had the exact setup years back . The Saito 120 was a great combo! I would suggest that you at least make 2 cutouts in the aft fuselage and mount 2 elevator servos . That will help with the balance . This was my alltime favorite plane and will have to build it again now that is back. Also strengthen the ply ribs that you mount the interplane struts on . They will break after a while of use.

Dude; just move the cowl forward a bit.

Lots of us have used 120 four strokes without moving the firewall, putting the battery in the tail, etc. This is a pretty straight-forwrd kit to build, as are most CG products.

You are over-complicating a relatively easy-to-build model.

I understand and applaud your desire to get everything just so, but I also think you are causing yourself a lot of unnecessary angst here. Unless there are issues with your particular kit, or you aren't telling us something, if you just build the thing per the instructions, with perhaps a simple mod or two such as separate aileron servos, you will end up with a great model.

Steve

I have two CG Ultimates. One with a OS 120 Four Stroke, and one with a Webra 120 two stroke and cline fuel regulator on it. I have not flown the one with the Webra, since it is not quite finished yet. The one with the OS has been flown many times and it performs all basic aerobatics very well. However it is not full 3D capable due to it's lack of power. If I would use another four stroke, I definitely go with a YS 140 L or Saito 180 and two stroke well as you can see I used the Webra ! If you are not intending to do any 3D flying with it, then I guess your Saito 120 will fly it around OK.
Why don't you consider putting the servos in the tail instead of adding any lead ?
Be also sure to beef up the wing. I sheeted mine because I like to throw it around in the air.
This must be the most easiest and fun bipe out there. You will have a blast.
Just my $0.02

Rodger on the ply rib mod. It's already done. 1/32 birch ply doubler both sides of tab area. Dual aileron servos too. Not quite sure about the dual elevator servo. Seems excessive for those little elevator surfaces.

unnecessary angst? I thrive on angst (my sick personality)
Anyway, moving the cowling forward doesn't appeal to me aesthetically. It would cause me too much angst.

I thought about the Webra. I have one in a Sukhoi and it's a great motor. It's a big lump with the Bisom muff though.

Later