fallingleaf

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Hi All. I think my previous post was deleted Grrr. Essentially I am transitioning from an UltraSport 60 with an os61fx (my seccond glow plane after a basic trainer) to a more snappy aerobatic plane. I love bipes so am thinking of building an Ultimate biplane (Goldberg kit). I love fourstorkes and the scale sound they have but alas, I live in New Zealand and by the time I factor in shipping this won't be a cheap build. So I am looking at two strokes for the plane and am thinking of the os120ax. I fly traditional aerobatics but 3d does interest me, although I am not building this kit of that purpose.

So what do people out there, (from your experience with the plane) think about this engine/plane match? Will the 120ax be too much power or should I be looking at a lesser two stroke? I don't want to rip the wings off or anything! Or alternatively is there anyone would knows of a comparable fourstroke that will give me good performance and a price similar to the 120ax ($249US)?

Thanks for the help! I would like to do a build thread once I get it too!

daveopam

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If you have the 1.20 it will be good but a little overpowered. A .90 size two stroke is perfect for sport flying. The plane your talking about will fly fine even on the heavy side.

David

alfredbmor

I have built the same bipe and use a Magnum 4 stroke 120 size and I feel that it does not have the punch I am looking for, the engine is taching a little higher than 9000 rpm with a 15 x 6 wood prop. (15% nitro fuel). I understand that the OS 120 AX can handle bigger props using the same amount of nitro and I am planning to aquire it this month at Tower, This month is on the best 100 deals and I can use the three months payment convenience.

fallingleaf

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Thanks for that alfred, that the sort of advice I am looking for. I considered that 120 fourstroke magnum as a possibility given its good pricepoint, but that feedback about its performance relative to the Ultimate really helps! I am sure with the 120ax I will have power a plenty to spare, but I always figure its better to have more power than no enough. Least it will swing a bigger prop which will appear more scale, and I can always dull down the pitch a little so the plane doesn't end up on mars. I was thinking a Zinger 15x6-10 initially then see what happens.

Does anyone know if the stock 120ax muffler with the 90degree adapter will fit inside the ultimate cowling? Or is is necessary for a hug cut-out to make it fit? Cheers!

eurof2

I thought mine was going to be overpowered with a ST 90, but a 1.20!!! That thing should take off vertical!!! Should be fun though as long as the balance is kept correct.

fallingleaf

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Choice! Well I bit the bullet and just ordered the shipment of goodies off tower including the 120ax. i am hoping the 'powerbox' muffler will fit in the cowel with minimal trimming and I hear it is slightly tuned to the engine which is a good thing in my book. Prefer not to mess around with a pitts muffler if I don't have to despite the added looks advantage ofthe pitts! 16oz tank with fuel filler valve and initally a 15x10 prop as reccomended in the 120ax manual.

Will be going with dual elevator servos (dependant on balacing) either at the rear or at the stock location, pull-pull rudder and two aileron servos. I may custom build my landing gear out of some durallium I have lying around (approx 3mm thick...nice and strong + LIGHT)....just for those who are interested. Thanks to those who chimmed in on this thread!

alfredbmor

I installed a 16 oz tank on mine, it also has a smoke pump installed in the CG. My Engine is around 32 oz I believe that the OS 120 is almost the same weight. I did the dual elevator option and instll them at the rear of the fuse, here is a link to my build.
http://www.rcuniverse.com/forum/m_49...ltimate/tm.htm
I hope it can be helpful.

mmattockx

I built the Ultimate a lot of years ago and used a ST90 on it. It was somewhat porky at around 8.5lbs and the 90 flew it fine for sport flying and IMAC style aerobatics. It did not have unlimited vertical like everybody wants now, but it would pull straight up for a solid 350-400ft. I think the 120 would be a great match (it does have a throttle, after all) and the plane will not be grossly overpowered with it. The weight is no issue, the model has near 1000sqin of wing and a bit of extra weight will not be noticeable. It also makes a great candidate for a small gas engine for this reason.

A couple of things to know with the 120 up front:

1) Do not use the single aileron servo, it will not be strong enough. Use a servo in each wing panel for a much stiffer arrangement. You can flutter the ailerons with a lot of power and the standard single servo set up.

2) A dual elevator servo set up would be a good idea as well, considering the extra power and engine weight to offset.

3) You may have prop clearance issues with a 15" prop. I ran a 13x8 and had no problems but I never tried bigger so I never worried about it.

Hope it turns out good for you,
Mark

alfredbmor

Mark, you are right about dual aileron set up, when I built mine many other builders had it done the same way, I just followed the right way.
As for fluttering I used clear monokote at the upper side of the hinge lines to reduce the risk, I am still aware of it everytime I fly it.
About the prop clearances do not worry about that I have tried the 16 x 6 and clearance is ok but it is to much for my engine to load fine so I am flying with a 15 x 6 by now, that is the reason why I wanted to change for an OS 120 AX. (I am using the stock wire landing gear)

fallingleaf

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Cheers guys, that's great feed back. I am sure ow that I made a good choice in that engine...its all shipping now so the fingers are twidling for a good winter build! I am currently building a Greg Chapman 'Omega' sailplane off some plans at the moment so once that is done I am sure I will have the building skills back up to scratch...a little rusty!

Most of my build methodology and choices for the ultimate have actullay been inspired bt your build thread Alfred and also Truwood's (which sadly met its demise on the maiden flight). I will definately be using dual aileron servos and twin elevator ones too. Whether in the centre or rear of the fuse will be determined on balancing. Im not really a fan of having the servos so exposed at the rear so may mount them internally similar to the ailerons. Having siad that, such an option could be complicated to install so may just stick them in like everyone else has. I wil also be sealing all control surfaces in the same method Alfred has, but on both sides.

I don't know too much about props but from consensus the 15x10 seems to be the best suited to the Ultimate and the 120ax, and clearance appears to be good from some pictures I have seen. Anyone have expierience with what prop would go good? 16x8 seemed a little big for me and I want to keep te rev's up to maintain fuel draw (not using a pump) but not at the expense of over-reving the engine!.

I am also thinking of simply getting some aluminium landing gear rather than that stock wire...looks a little thin! Any opinions on the quality of the ABS cowling? Obviously ibreglass would be better but If I can live with the stock ABS I will (I don't have a bottomless wallet!).

alfredbmor

My ABS cowling is still there (With some cracks and patches), fair enough but lighter than the fiberglass and that is why I keep it.
I will be ordering the engine by the end of this month so I can't feed you back with prop options by now.

fallingleaf

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Thanks for that, great to get feed back from friendly fellow modlers! I will see what the cowling is like when I see it in the flesh and then make a call...I can always order the fiberglass one at a later stage. I may actually reinforce the ABS one with a little fiberglass around the seams and any cutouts for good measure if I go that way.

Chuckar

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I have a YS 120 in mine it has more than enough power I am using the ABS cowl no big problems yet I think the O.S. 120 would be great I have TNT gear 3/16 thick the engine is swinging a APC 16-7 love this plane.

2slow2matter

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I too had the ultimate from goldberg, but I had the ARF. I put a magnum 120 up front and it was a dog. that engine stinks. i have other magnums (mostly 91 FS) and I love them. I wouldn't recommend the 120 if it were free.
However, I'm now flying the seagull models bipe that is essentially the same airplane with a saito 125 up front, and it has power to spare. The OS 120 AX will be awesome with it. I've seen it flown with a YS 140, so overpowering it isn't a problem. And prop clearance? I'm swinging a 16 inch prop on mine (and a 15 inch with the old magnum 120) and had lots of clearance to spare, so don't worry about that!
Have fun.

fallingleaf

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Choice, more positive ffed back its great! I am still curious if this 'powerbox' muffler with the 120ax will fit in the cowling, or if I will have to make a substantial cut out and have it bulging out underneath the nose [&o] If the latter I would prefer the pitts then, but I have heard of people having problem when they fitted the pitts muffler to the ax [:-] choices choices!

flygilmore

I, too, have the ARF version of this plane and haven't decided on what motor to get-unfortunately, funds are kind of short now so I may look for something used but in good shape. I would love the 1.20 AX too, but wonder what I would put it on in the future. How would a .91FX do for spirited performance?? I don't want to hover this plane-I have many others for that!!

alfredbmor

I will tell you what I have seen. This particular bip seems to be adequate for a good number of engines and displacements, I know that it flies well with a Super Tigre 90 but wont do knife edge loops, but it does almopst all aerobatics fine with limited vertical. I have seen it with a YS 120 and the performance is awesome (unlimited vertical) but it is on the heavy side and if the engine stops at midair it will be the end of the plane, so I think that the best is to keep it light with a powerful light engine, then it is going to be fun.

deckerv

My Feedback: (21)

I had one years back with a tired old SuperTigre 90 and loved it! DO put dual servos for ailerons though. I had the single servo setup and it did flutter after a little while. Went to two servos in the bottom wing and no problems since then. It finally met it's demise with a battery going bad on me in flight though .

fallingleaf

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I am just waiting for all my stuff to arrive from Tower. I just pranged my Ultra Sport 60 into a tree the other day (depth perception got the better of me on final approach), so lost about 2/5 of the left wing Bugger. So will focus on fixing that up prior to starting the ultimate methinks. Will proable post any build comments and questions on the epic thread below.

http://www.rcuniverse.com/forum/m_38...24/key_/tm.htm

NM2K

My Feedback: (14)

Sorry to hear about your US 60. I crashed my wife's brand new Falcon 56 with brand new radio (Blue Max 6-channel) and a brand new OS.35S R/C into the tops of leafless (winter) trees back in 1972. You should have heard the sound of cold Monokote (Super Monokote back then) as it hit the tree. Thankfully, one of the club president's sons climbed the tree and recovered everything. It was flying again in a month. Only time I've ever done that. I was demo flying for an out of state friend with a bad case of the flu. That'll learn me to fly when sick.

I've seen the kit built Ultimate Bipes (Goldberg) fly with a four-stroke .91 and 1.20 four-strokes. To me, the 1.20 four-stroke was perfect for my style of flying (pattern-like), although the four-stroke .91 flew it well enough for the average sport flyer. A two-stroke 1.20 might be interesting too. I have one of the new Ultimate Biplane ARFs and a well broken-in Thunder Tiger 1.20 Pro two-stroke. I'm tempted...<G>

I have always wanted to see the Ultimate Biplane kit be powered by the K&B .65 that was shown on my original kit's plans. I'll bet it would have flown similarly to the one I saw that was powered by an OS .91 four-stroke. Which wasn't bad and was probably very scale-like.


Ed Cregger

fallingleaf

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Cheers Ed. Yeah, it wasn't the most pleasant sound when it hit the tree I tell ya! The re-build is already underway though. I have stripped all the monokote off and dovetailed in new spars with super strength araldite epoxy. Manage to plot replacement ribs off the salvaged ones and now it requires ALOT of sanding to get the leading edge to match the otherside as I use some hard grained balsa for added strength. Weight will be the same as before.

Sorry to hear about that crash back in 72'...I certainly will be giving any tree whatsoever a VERY wide berth in the future thats for sure!

carlosponti

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know a guy who used to have one with a saito 180 in it. definitely had a lot of power.

alfredbmor

I have just ordered an OS 1.20 AX engine for my Ultimate, hopefuly it will be here on friday.
I also ordered a 16 x 8 APC prop that will be the entry level prop for my application, I have read that this engine can swing a 17 x 6 prop after one or two gallons.
Either way the 16 x 8 will be enough for my Ultimate.

fallingleaf

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Yeah I got the 15x10 wooden zinger prop for mine but will most likely up it to a 16x8. It will look more scale-like and probably provide better performance. See how it goes after afew flights and runs....when it gets here and I build it that is! Fingers crissed customs don't ping me for the engine [>:]

fallingleaf

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Choice...all my stuff just arrived. Nice kit, 120ax looks beautiful! I can answer my own question now and that is that the 120 ax 'power box' muffler DOES NOT fit inside the stock sized ultimate biplane cowling. Using the 90 degree adapter it projects out the bottom of the cowl half its diameter which is approximately 2cm. So i can imagine that it would look a little bulbus hanging out down there!
This leaves me with either getting a pitts muffler or just rolling with it as is! Haven't made my mind up yet but I would be interested to hear if there is anyone out there with a 120ax/pitts combo and how it performs fuel pressure wise and noise/power wise?
I deally I would like to get the fiberglass version of the stock cowl. You can get ones with the bottom extended but IMHO these look abit weird and spoil the lines of the plane.