[Norskie]

Experienced Flyers:
I'm flying a Carl Goldberg Ultimate ARF (60.5), which is spec'd for a 90-120 two stroke, but I'm currently running a 28CC gasser.
The instructions specify the CG as follows:

"Measure 2-3/8" [60mm] back from the LE of the lower
wing and make a mark. This will be where your model will
need to balance. The forward C.G. limit is 1-7/8" [48mm] from
Settings: the lower wing’s LE. The aft C.G. limit is 2-7/8" [73mm] from
the lower wing’s LE."

At 2-7/8" it flew nose heavy (I had to move the batteries forward and add nose wt to achieve this), so I've been slowly moving the CG back. Currently it is sitting 4" (1-1/8" more then the manual). I've tried contacting Great Planes, as they purchased Goldberg, about the accuracy of the instructions and they have been little help (simply replied it is correct ... and obviously it isn't).

I've been looking at the landing characteristics, with hot, fast landing as the nose heavy indicator. Given that I'm guessing at the CG, could some experienced pilots provide feedback on what other flight characteristics I should be looking for. I know it will become more twitchy as a move the CG towards the tail, but I'm hoping there are some other flight characteristics that indicate the relative CG location.

Thanks!

[Cougar429]

I maidened my friends 91 2-Stroke CG Ultimate Thursday evening and, compared to my Skybolt the only noticeable difference was the tendency to slow dramatically when turning at any bank angle over 45 degrees.

Mind you, one flight is limited and I kept the flight very tame to get it trimmed out and check control response. Anything over 1/2 throttle and the plane was a streak in the sky, which leads me to think vertical will be pretty exciting once we open the envelope. CG was set at the recommended location.

What's happening during your slow flight regime and have you tried it inverted? What elevator trim settings give you stable flight?

p.s. check out slow flight once at altitude. Landing is not the time to experiment as there is little time to correct or save the plane.

[Norskie]

Cougar429:
Inverted flight is fine and level. It rolls nicely into inverted with little need for down elevator.
At stable flight the elevator is trimmed to nearly parallel with the horizontal stabilizer.
It flies well and seems responsive, though not as responsive as my Somethin Extra.
Perhaps it is just the Ultimate biplane's landing characteristics, but it seems to have a lack of elevator authority on landing, and it is difficult to flare. It just wants to drop with very little glide (but maybe that is the way it is). In comparison, my 46 sized Phaeton II biplane floats nicely and has lots of elevator authority.

Thanks,

[Cougar429]

From what I can see the Phaeton has a semi-symetrical airfoil, compared to the fully-symetrical on the Ultimate. Slow flight would likely be less critical of AoA with the Phaeton.

Good luck. Any way we'll se some vids? We tried with the Ultimate, but it was getting late and lighting was not the best.

[bradleyban]

Norskie.....Where did you get your ultimate I'm looking for one of them something fierce and can't find one. I had connection with a guy on here for one but I didn't have the funds for it at the time. Now I can't get ahold of him and he hasn't logged on for over two weeks. I has a saito 180 just begging to go into an ultimate.

[Norskie]

Bradley:
The Goldberg Ultimate ARF 60.5" is no longer in production since Great Planes bought them. I picked mine up at Great Hobbies in the winter, while they were still available.
Some stock seems to be still around, though. Highflight RC just sold one for a steal of a deal, 2 weeks back ... some lucky flyer took it home for $190.
The Great Planes Ultimate is the same plane, just bigger and can be found in many places, though the saito 180 is on the lower end of the recommended engine size.

PS
I think have have solved the "CG" problem. I found a couple of websites that describe how to calculate the CG based upon the planes geometry.

[hellyeh]

One check i always do to determine the proper CG (good ballbark) is inverted flight . Just climb up to a comfortable altitude and roll the plane inverted . Be ready to correct with elevator , or ready to roll back upright and observe what it does when at neutral stick . If it loses altitude , it's nose heavy , if it gains altitude , it's tail heavy . (this is all assuming that your elevator is neutral with the horizontal stab during normal flight ) Adjust to your liking from there .

[bradleyban]

Thanks Norskie. Yeah that suck they are out of production thats why I'm having a hard time finding one. Dave patrick ultimate was the very same as the carl goldberg. The great planes ultimate is nice but like you said its a lot bigger and that mean more money and my 180 won't work so well with it. A friends of mine has one with a 220 in it and it won't do unlimited vertical. He's currently switching to a dle 55. should fix that....lol

[Norskie]

If you are looking for a 90 - 120 sized biplane, Seagull models have a Ultimate Bi-Plane 90 ARF. Great Hobbies carry it and more information can be found on Horizon Hobbies.