Can someone clearly describe how to set the cg on this plane. Top wing, or bottom, and how far back, near the edges of fuse or out at the wing tips. Also what engine is recommended, the manual suggests a 52 four strike. The english is so bad. I was considering an OS 72 FS. Is this engine going to be too big or too heavy for this plane. My plan was to assemble the plane then use weights to figure out how much weight is needed to balance it, then use a bigger heavier engine, if necessary, rather than adding weight to the nose, as I've heard of so many other bipes needing to balance. I've been flying several years now, but I have never assembled a bipe other than a GWS Tigermoth.

I'm guessing that you have the 40 sized bipe. If so, the manual from a World Models Bipe can be used for cg, the planes are the same size and might actually be a clone if you bought the right one. Anyway, here is the link.

http://www.theworldmodels.com/para/i.../pdf/A009S.pdf

I had an Ultimate from nitro last year, just to give a heads up, if you hear any flutter throttle back and land immediately and land. I had one of the tabs that hold the outer struts to the wing come loose. It stripped the servos and the plane was destroyed. Anyway, now I have a new bipe of the same size and installed a 52 fs which should power it just fine (I haven't taken it out yet though).

I hope that helped... take care
Jerry

You want to set the C.G. to OCCUR at 100mm from the front of the leading edge of the TOP wing, when the plane is balanced upright at this point.

I fly the Ultimate 40S with a Tower Hobbies .46 ( a real stump puller ) which is more powerful than the OS .72 four stroker.

I've seen others fly the plane with everything from a GMS .32 2 stroke ( there is a review here on this at RCU ) up through an OS AX .55 2 stroke.

The .72 will fit, but it is about the largest four stroker you can get on the plane, not because of weight, but rather due to the cowling.



As far as the strut tabs go.

Just build your plane carefully.

The strut tabs are fairly strong, and if the strut comes loose, this is more of a builder's problem.

I've cartwheeled this plane nose-wingtip-tail-wingtip-nose-etc. accross an airfield with no visible damage.

I flew the plane immediately afterwards and for two weeks after that before I noticed that I had cracked one of the strut supports.

In spite of that I flew and landed the plane w/o incident. That is how durable the "box" shape of the wings are!

It is ONE TOUGH PLANE!

I epoxied a bit of triangle stock against the repaired tab, and painted this white.


After close to 300 flights I was waiting for this plane to crash so I could replace it with one of the two "backup" Ultimates I had purchased from NitroPlanes. ( I liked the plane THAT much! )

I finally cracked it up several weeks ago. While easily repairable, I decided it was time to "redo".

I believe I have the .40 sized model, however the manual above is not for the same plane as mine. The model I have is set up for 2 aileron servos.

Aside from the servos and wing struts the planes are almost identical. The wingspan, length, wing placement, weight, CG and recommended throws are the same (or very very close). My old one, like the one you have, balanced fine with a SuperTigre 45, and that’s a heavy setup. You asked for a CG… I would put it at 81mm (3.2 in) from the LE of the top wing in the center as p11 of that manual. The control throws shown on the same page should be fine for a first flight also. There were a lot of people using this manual the past year or so to set the CG for this bird.

I also don't believe my plane to be a World Models plane as there are'nt any World Models markings anywhere on the instructions.

Your plane isn't a world models ultimate... The two are very similar in size. That being said, the placement of the CGs should be very similar. So, if the World Models ultimate has a cg of 3.2" from the leading edge of the top wing (in the center of the wing), it stands to reason the the CG of your biplane would be in a close spot. Or you can set your CG out to 100mm from the LE of the top wing as opjose stated his was at.

The plane will tolerate the C.G. being set as far back as 120mm.

100mm is best for the Nitroplanes Ultimate. There are other threads here on this being the ideal spot to start out with.

I also have the WM plane which IS slightly different in construction.

It's C.G. needs to be further forward, hence the descreptancies.

That's what I was thinking. There were likely some differences between the two. I didn't want to start too far back, but didn't want to be nose heavy either Since my plan is to buy an engine whose weight will balance the plane. As we all know, A nose heavy plane flies terrible, a tail heavy plane flies once.