Redcatcher

My Feedback: (6)

I have 2 choices for my Goldberg Ultimate ARF; OS 1.08 or OS .91 4-stroke. The debate is power vs weight . I have read the threads that have previously discussed the issue, but want to get your experienced opinions again. Would the plane fly well with the 4-stroke .91? Isn't the OS1.08 with muffler getting to heavy for the plane?

I am especially interested in the opinion of flyer who have owned and or flown this biplane with various engine combinations. Thanks for your help.

Redcatcher.

SearchMan

Redcatcher,
I am in the final stages of completing my CG Ultimate (basically need to balance and set up the throws and have some nice weather). My Ultimate has a Saito 100 four stroke in it and that was per Goldberg Models tech support recommendation - they said to keep it light.

I have read threads on this site and others who fly this plane with four strokes up to a Saito 180! One of my flying buddies has an OS 91 FX two stroke in his and it flies great. I haven't put mine on the scale yet, but it feels really light - I'll let you know what it weighs after I put it on the scale.

SearchMan

mancha

OS 91FX will allow your ultimate top performance, keep it light so you can enjoy it!!

helicool

My Feedback: (6)

Ive got one with Saito 150 in it. Takes off in 10-15 feet and will go vertical just about as long as you can see it.

noahb

My Feedback: (67)

Go with the OS 108. They run very sweet. I has a GBM Ultimate with this setup. It ran great, had unlimited vert. I would not pay too much attention about the weight issue. I know have one with a Saito 180 and I would not trade anything for it. As far as weight, well they may come in a little faster, but nothing that an avg. pilot would even care about. The os 108 has lots more power then the 91 and even though it may weigh more, you can plan ahead with servo placement and negate most if not all of any lead placement. My Ultimate has the Saito 180 and the bal. is just fine. When I ran mine with the os 108, I ran a 15x8 apc and it flew great, would climb unlimited and landed very good. These planes have lots of wing area and drag, it's nice to have a little more power. Either engine would fly this bad boy, but I really think you would enjoy the 108. Let me know if you need any more info. BTW, these are great airplanes.
Larry

Jim Schwagle

My Feedback: (1)

Stick with the 91.

caf2461

My Feedback: (6)

My CG Ultimate arf flys very well with an OS 91 surpass and a 14 x6 prop. It will do all pattern stunts and hang on the prop in a hover. It will not climb out of a hover. With enough entry speed it will climb out of site. I built it light with standard servos. Do I need more power- no. Do I want more power - of course, but I do not want the weight and only for 3d stuff. You will have a fast and nice flying sport bipe with your 91 fs that is as capable as the full size ultimate.

I will leave mine alone until I can free up my Webra speed 1.20 from my CG extra (wicked combo) or I just get bored (not there yet). If I install it I will need stronger servos, beef up the firewall and increase the diam of the aileron connecting rods. My only fear is it will be a different plane then. It is nice to fly something that can be graceful and scale like without making the knees wobble. This is the only one I have not overpowered!

BTW- balance will be right on the money per plans with the 91. If you go with a heavier motor the battery can be move to a shelf built behind the pilot canopy.

Redcatcher

My Feedback: (6)

Thanks to you all who have responded! Your comments ARE helpful . I probably can't loose since both engines will power the plane fine. At this point I am leaning toward the OS .91 4-stroke because I think "Light is Right."

Next question? I have seen the engine mounted upright, inverted, and side mounted. Comments on the pros and cons on which way to mount the engine . Which works best AND preserved the beautiful looks of the Ultimate? Thanks for your input.

Redcatcher

Jim Schwagle

My Feedback: (1)

I would mount sideways. Fits fine and you don't run into the problems running inverted involves. Just make sure you have adequate cooling. Remember, exit area should be at least 3 times entry area. Also, with the shape of the cowling I don't think upright or inverted will look very good. If you want, you can get a slightly deeper cowl from Stans Fibertech that will allow the mounting of a Pitts style muffler.

GalenB

My Feedback: (18)

Recatcher,

I have a Saito .91 with a Slimeline pitts muffler with the 70 degree pipes an Ultimate turning a 15X6 ot 14X8 APC prop for in my CGB Ultimate. It flies extremely well and I often receive comments about how nice and scale it flies. The .91 FS will not hover it or give you unlimited vertical, but it is more than enough power to fly it well. In fact, I have been thinking about putting a YS .63 in mine since that engine will turn a 13X6 APC at 11,000 RPM and is lighter than the Saito with the Slimline muffler.

SearchMan

GalenB
How much does your Ultimate weigh with the Saito 91? I have a Saito 100 on mine with a stock Saito muffler. I won't be flying mine for another month or so depending on the weather - it's cold here in Northern Illinois!

Jim

RLDIII

My Feedback: (1)

It depends on your power expectations. As I see it, For a .91 four stroke to give really good performance, you will either need to have an EXCEPTIONAL .91 four stroke, or a VERY light CG Ultimate, or both. The problem I see is that given the marginal quality of the wood in the CG kit, it is HARD to build one really light. I have flown one with a YS 1.20 and also a friends with a 1.08 stroke (ASP not O.S.) and they BOTH were unlimited. However, the 1.20 four strokes gave more low end "grunt" (instant response) while the 1.08 had just a little lag while the RPM's came up. The 1.08 probably had the edge on maximum straight-line speed though.

Have fun,

Lee

GalenB

My Feedback: (18)

My Ultimate weighs in at 9.5 lbs dry. It flies very well on my Saito .91, but it flew great on the Saito at 8.5 lbs. That was before the cowl and pitts muffler were added... It didn't look as nice, but it flew great. Your 1.00 will fly it very well. What prop are you using?

Scott H.

My Feedback: (1)

Redcatcher,

My vote from experience on this plane is the O.S. 1.08, 15x8 APC, 15% CoolPower. Keep it at 10lbs or less. You are really gonna dig it!

The 91FS just doesn't have the stones to make this plane really fun. And that is what the Ultimate is all about...Having big fun!

I had a CGB Ultimate, the kit version. Flew well at 10 lbs with the ASP 1.08, but didn't have the omph to really rock.

When I sold it to a friend, I made him the deal, that if he would get an OS 1.08 for it, I'd give him $100.00 back for the ASP.

He finally did, man what a rocket! Multiple snaps on the vertical up. The 1.08 is superior in quality to the 2 stroke 91FX. It will outlast it by a long shot. Hand flips easily, no messing with the needles, and is very smooth. Runs great on 10-15% Coolpower. Doesn't have overheating problems.

I'm building another Ultimate (different kit), and I'm not selling this one! What an awesome flying plane. Every stable should have one.

I've got a Y.S. 120SF for the new girl. They sound so sweet on just a straight pipe w/3 blade prop. I'm expecting about the same performance (slightly bigger kit).

The ASP is going on my US60. It should move that plane right along.

Best of luck. Happy flying!

Scott H.

Redcatcher

My Feedback: (6)

Scott H.

This forum is awesome. Everyones input is appreciated. I have never run my OS .91 4-stroke so I don't know what to expect power wise. I gather from your post the .91 isn't as strong as I thought. Anyway for a near 9 pound airplane to have good performance a STRONG .90 would be the minimum.

I guess I will have to get a Pitts muffler for the OS 1.08. Will a Pitts muffler fit fully inside the cowl?

Thanks again to everyone for the comments. And a big thanks to RC Universe.

Redcatcher

Jim Schwagle

My Feedback: (1)

No. Much of it will hang out. You can purchase a deeper cowl from Stans Fibertech made for the CG Ultimate that will better enclose the pitts. Watch the weight. The kit should come in around 8.5 pounds. Lighter is always better, when properly built.

Scott H.

My Feedback: (1)

On all three accounts. Lighter is better, everything sticks out of an ultimate cowl, and Stan's does make a nicer one that is a little bigger.

The head will stick out the side of the cowl as well. Make sure you've got some room around the engine and muffler for vibration and air flow.

You know, that 91FS will do really well on a 60 size aerobat!

If I can find the pictures of my old Ultimate I'll post them. I think there is a shot that shows how the engine fits in the cowl.

Happy building,

Scott H.

SearchMan

GalenB,

Thanks for weighing your Ultimate - I just threw mine on the scale (digital grocery scale) and my dry weight is 8Lbs 2.9oz. I'm hoping that will allow some pretty good vertical with this bird. This Ultimate looks awesome and I can't wait to get it in the air!

Jim

djlyon

I flew mine with an ASP 108 (kinda like a OS108), Pitts muffler and 15/8 prop. Great combination. I wouldn't go with less power.

flytheedge

My Feedback: (84)

I'm setting mine up with a Magnum 120 4-Stroke and Byron 15& Nitro fuel. Should fly it awesome. The biplane is a 60 size biplane.
Clint

Ralpher

My Feedback: (58)

Here's my Ulty with YS91 inverted. Uses remote glow igniter (glow driver not needed), remote fueler and the YS straight header with silicone extension. Runs strong, silky smooth idle and does everything in the book. Power-O-plenty!

Flies great, keeps up with other club members GB Ultys with OS 1.20's, but sounds better (IMHO)