Folks,

I have admired the looks and size of the Great Planes ultimate bipe kit for sometime now and have just received it as a gift. I have done extensive research here at RCU and most agree that in it's stock form the kit builds on the heavy side. I have several options open to me as far as how I want to power this particular bird, and am looking for some real life recommendations from the collective, So here it goes. I have available for use both an Irvine .53 2 stroke and a OS 61 fx 2 stroke. I have read where some consider a .46 to be marginal on this bird. I realize that that the Irvine is a stouter engine than most .46's out there and is probably more in line (power wise) as say an OS .50. Secondly, I have read that the OS .61 may require some heavy modifications to the cowl, which is really no big deal, but I would question as to whether or not anyone has mounted the .61 inverted for a better fit under the cowl? The third alternative I am considering is electric power. Can the airframe be lightened enought o make this a viable good performing aternative? If i did decide to go electric I would have to buy most of the components while I have the engines on hand. any real life experiences or suggestions would be greatly appreciated.


Thanks, Skunk39

I don't know about the electrics, but I don't think the .53 would have any problems pulling the plane around, especially with a bit of lightening here and there. I built mine years ago as a younger lad who didn't think much about lightening the airframe while building, and my Webra .50 pulls it almost out of sight vertically straight off the runway. It won't pull out of a hover, but it'll hold one pretty well. If that Irvine has similar power I would think it'd be a good match for the plane, again especially if you lighten it during the build.

No hands on experience yet as I still have the kit in a box.
My research pointed me towards a .70 fourstroke engine and that's what I intend to use once it's built.

I think that OS61fx will be perfect power and you should use it.


/Edit/ Cobra99, that's a looker! Great covering, do you have any tip for building the GP U40?

I agree. At first glance it looks just like the Carl Goldberg Ultimate ARF, then click the small pic to open the larger version and then it's obvious it's not the CG version

I don't know where you read that a 46 was underpowered for this plane. Thsi plane was designed for a .40-.46 2 stroke, so the 46 is on the upper end of recommended engin sizes. I have an OS 46 AX engine on mine and I think it's a great combo. IMHO a 60 is going to way too much for it. Not considering the added weight, you also need to think about how much you're going to need to beef up the airframe for that much of a motor. I know that in this day and age everybody thinks that they need to shove the biggest motor they can find on a plane, but that's not always needed. I think that this plane flies great with the 46 AX on it, almost like it was made for that engine. It does everything I want it to do with no problems

That's just my 2 cents worth

Ken

If you can build light then try a light build but this is a good quality plane. If you need to buy an engine then try a fourstroke. Combined with it's looks the sound is superior with the four stroke. It doesn't require speed but torque helped by a fourstroke will make it fly a lot more smoothly.

I agre 100% with RCKen, as I fly my GP ultimate with a TT pro 46. It is plenty of power for this plane, balance well with no added weight.

From soneone who has flown the GP Ultimate for three years now and loves it...... use the OS 70 (what I use) or the Saito 82..... personally, I am an OS flyer but you won't go wrong with either.... I would not go as far as the OS61FX due to the weight and size..... don't over power this plane without building in some strength. This is a fantastic flyer when built stock; the OS 70 moves it around very nicely.....

Build straight and enjoy.

Thanks! I just wish I could get that metallic Monokote to stop wrinkling. [:@]

As for building tips, just build light. I didn't, and it still flies great, but I know it could be better. I think some of the lightening holes in the fuse could be enlarged, along with creating some on the top of the fuse just forward of the canopy. Also, if you can make room for it, a pull-pull rudder system wouldn't be a bad idea. I don't fly this plane at full throttle anyway, but even in a low power dive I get a hint of flutter out of the rudder from time to time. It's just a huge surface and there's not much else that can be done I'm afraid.

Other than that, just build how you normally would, and enjoy!

navy18, I was just wondering if you had any problems getting the os70 to fit inside your cowl and if you used the stock muffler or not? I am currently building one of these planes and am leaning toward the os70 but have not ruled out an evolution 46 (which I have on the shelf collecting dust.)


Just wondering.

navy18, I was just wondering if you had any problems getting the os70 to fit inside your cowl and if you used the stock muffler or not? I am currently building one of these planes and am leaning toward the os70 but have not ruled out an evolution 46 (which I have on the shelf collecting dust.)


Just wondering.

Logan,

The 70 is the engine for this kit.... if you have a 46, I would consider it but would start saving for a 70..... the cowling does not fit inside cleanly; I made a headcut for the top and then used the standard muffler from the OS70. I will take a pic if I go flying tomorrow and post it. You will really like this plane... flies great but do not, I say again, do not go higher than suggested on the elevator travel.... I did and almost lost it on the first flight... I had my hands more than full. After I got her down, I put it back where it belonged and the rest is history.

Enjoy.....

Navy18,
I built the horizontal stab and one elevator tonight. I have a little 4 year old boy who is right there helping me. He solo flew his airplane just before he turned 4.(I built him a fanfold banshee and put a small electric motor with 7 degree throws and he puts it around the sky very well.)
I think you are right on motor choice. My wife told me to go ahead and get the motor so, as soon as I can get to the hobbie store, that is what i am going to get. Besides, you just can't beat the torque and sound of a 4.
I have another ? for you. Did you build this plane stock or did you incorporate any mods? I like to toss my planes around and I am considering counter balancing the rudder. I am also considering putting servos in each side of the wing. If you just used one servo, how does the one servo perform and did you use a high torque or digital servo?
Sorry for all of the questions, I just want this plane to be right, and the experiences from other modelers is information well taken!

Thanks for the help.

I would consider a Saito 91.It is a lot lighter than a 60 2 stroke.
You can pull out of a hover.The airframe can be lightened a lot.It is way overbuilt in the fuse.
I used 1 high torque servo for all the ailerons and it is extremely sensitive on 3d rates and no sign of flutter flying around full throttle.
Here is a pic of mine.It is a very well behaved plane at all speeds.

Logan,

Although I have seen modifications on the larger Ultimates, I have not seen a need for them on this plane. The rudder is already much lasrger than it actually needs to be; if you like the look, I see no problem with counterbalancing.... I have seen no reason to think she needs it. I also thought about the 2 servo question (in the wings) until I flew a friends; once again, it is a weight addition without a true need. With all four ailerons connected, 1 Hitec HB475 servo as indicated on the plans has worked well. The beauty of this plane is partly due to its size and wing.... it is a great flyer if built stock and nicely powered. The only problem I see with the 70 is not ulimited vertical; but I flip this think around so much, I usually don't fly straight up very long.... a friend suggested the Saioto82 for that but I don't think it would enhance the fun I have with it now. Take care when you fit the upper wing; if you get it right the first time, it is a great way to setup a bipe... I use locknuts that I replace every other month to hold it down nice and tight.

No problem with the questions, that what is great about RCU.

I'm about to start building my Ultimate soon. I was going to modify the build using two servos in the wing, however, I will use two Futaba S-301s. That gives me a direct slop free linkage (I don't really like the torque rod setup from past experience), reduced weight compared to 1 standard servo, more torque per aileron and faster response. The only downside is buying two slightly more expensive servoes and the added modification to the wing.

-tychoc

Spicoli,
Very nice looking bipe. I have a saito 91 in my hog bipe, but I hate to take it out of the thing, I just love the hog too much. What engine do you have in your plane? I've pretty much ruled out a 2 stroke. I have a lot of planes with 2 strokes, and only my hog has a 4. Its time for another one I think. Going to the hobbie store tomorrow to purchase an OS70. I really don't care if it will pull out of a hover or not. I have other planes that I can do that with. I just want a bipe that is a little more (or a lot more) acrobatic than my hog.

Navy18,
I built the rest of the tail feathers tonight and after getting a good look at the rudder I decided to leave it stock. You're right, it is plenty big enough. I also decided to go with the single servo setup. I have a few high torque, high speed servos I bought for my raptor helicopter, so I think I will rob one of those for this project.
Also for you and anyone else, this is my first kit build of this magnatude, so any advise or tips or problems you guys found out building this kit would be greatly appreciated.

thanks. Tim

Loganjoel,
I have a Saito 91 in mine
I had to change the landing gear to get more height for the prop.
I would consider setting up the wings and tail with a incidence meter

Navy18,
I was just wondering if you could post picts of your engine set-up and how you ran your stock muffler. I have an os70 and the way it is looking, I will have to make a head cut out but the muffler wants to go out of the side of the cowl instead of on the bottom. I really don't want to cut another hole in te side of the cowl.

If you could post some picts, that would be great.
Thanks, Tim

Logan,
I turned the muffler just abit to get it heading down; I will post a pic or two after Church when I can get one downloaded.... I don't remember having too much trouble with the setup.