Hello all,
I will start today building the GP ULTIMATE.
I need some help in choosing a motor because I am very confused with the engine choises of other builders.
Some are using .46 to .90 2 stroke. Others .65 to .91 4 stroke.
One thing is for sure. The plane will be a little bit heavy even without the engine.
I love 4 stroke engines but they are heavier and I am not sure if the are going to fit in the cowl.
As far as for 2 strokes I stopped using them for some years now but have no problem trying them again.
Suggestions are welcomed.
Besides that I need some info and maybe some pics on how to use dual ailerons.
Please help.
Thanos.

I am also about to start building this kit. I too like my 4strokes and have opted for an OS 70. Looking back at other posts on here, seems to be a popular choice...

Thanks skooby,
I am thinking of the OS 70 FL
it has the same power with OS 70 ULTIMATE and OS 70 SURPASS mkII ( I own them both ) BUT it costs less and its about
100 grams lighter.
Havent seen any revies yet for this engine.
Thanos.

I'd not heard of the OS 70 FL, sounds ideal... Good luck with your build!

i've had nothing but 2 strokes so far. I'm planning my first 4 stroke on my next project.
If you do decide to go with a 2 stroke, I highly recommend tower hobbies line. They are basically GMS engines, but with schnuerle porting. And of course a purple head.
High on horsies and light on the wallet. I've never had any problems with mine and they're easy to tune.
read this thread too on the tower .75

http://www.rcuniverse.com/forum/m_3457159/tm.htm


Just putting my two cents in

Just to correct one mistake.
os 70 ULTIMATE weight is 16.40 oz and os70 FL 16.50 oz.
os 70 ULTIMATE HP 1.2 and os 70 FL 1.1.
The only differense is the price about 100$ more for ULTIMATE.
My question is if the price difference worths it.
I am still thinking of it but have to decide soon.
Thanos.

The OS 70 Ultimate, and the OS 70 FL have not been receiving good feedback on the engine forum.
Search and you'll find info.

disclaimer: I have no first hand experience with either.

For a second I thought you might be serious. Thats a good one!LOL

I have no doubt that the O.S 70 is a great engine, but there is also the option of the Magnum 70 4 stroke which is basically an O.S copycat, and a heck of a lot cheaper. I have owned a few Magnum 4 strokes, and they are great engines. There is also the option of going with the Saito 72. I've never had a problem with any of my Saitos either. Come to think of it, I have never had much trouble with any of my 4 strokes. The worst engine I ever owned was a Tower Hobbies 2 stroke.

Regardless of brand, put a 70ish 4-stroke on that baby and you'll LOVE it!

Can't go wrong with OS 70 4st

I just finished one with a Saito 91.I am very impressed with the plane and engine combo.It flies very light.vertical is very good.I added a lot of lightening holes to the fuse and re-engineered the landing gear.It came out a hair over 6 pounds.With the Saito inverted it looks small in the cowl.

ckangaroo, you don't like tower hobbies engines? Or am I wrong? That's not cool to put that on here.
Hey if I'm wrong tell me why, I'm willing to learn anything. As far as I know they are GMS engines and I've have never had a problem with them.
I have a .46 that's on my su-31, a .46 on my gee bee dreamer and I had a .61 on my aero subaru. I love em

Thanks, for your help guys,
I will go for a saito 72 or os70 ultimate.
I think that the 91 will be a little heavy for that plane even if it has more power for unlimited vertical.
Has any one done the dual aileron modification ? Is it nessesary ? I would like to see some pics if possible.
How about installing rudder and elevator servos at the back of the fuse for better balancing ?

Thanks.
Will post some pics of building soon,

Thanos.

With an OS 70 and servos in the radio compartment, Mine balanced without adding weight

Thanos,
A Saito 91 is not too heavy.It weighs the same as a OS 70.With 1 servo in the tail, the battery was placed on the CG to balance it.
There is no need to go with dual aileron servos.One servo does just fine and saves weight

I just got done finishing up a GP Ultimate for a customer of mine and we put a YS 91 4 stroke on his Ultimate and it flys awesome. I also thought the CG might be a problem with the YS but this was not a problem as i thought it would be.

Does anyone know how big a prop or the ground clearance? You can use on this plane.

Thanks Tom

on the Ultimate I built with the YS we used a 14x8 with no issues. I also used 2.5" wheels

Warbirdairracer,
I am suprised you can fit a 14 inch prop with the stock landing gear.I had to change my landing gear for a taller one.
Here is a few pics of mine.

I would like to thank you all for your help.
Will attach pics of my project.
Thanos.

Thanos,
I would leave the OS70 ultimate well alone, I had one and it was ***** to put it politely. I am about ready to cover my GP ultimate and have a Saito 82a to go in it. I am currently using the Saito in my acro wot and I am well please with its performance.

Leigh.

Thanos,
I just finished building the lower wing and am now working on the fuse. I'm a little disappointed with the fuse. The plywood parts are not well laminated; some of them are separating. Also, I find the notches are not accurately located - I am having to modify the parts to make them fit. Have you noticed similar problems, or did I just get some bad parts? I had no problem with the lower wing or tail surfaces.

BTW, I'm putting a Saito 72 on mine.
Jon

I'm almost done with mine - that's an outstanding trimscheme BTW.

Using a Magnum .61 XLA-R for power - was an act of congress to make everything fit under the cowl, just to find that the Pitts muffler didn 't fit inside the cowl, requiring a nice big hole to be cut in the front mf my Stan's fibertech cowling I bought.

I said screw those ABS wheelpants, and bought a $12 pair of fiberglass pants for a U-Can-Do 46 and repainted them - if I had covered the plane in Red I wouldn't have even needed to repaint. $12 was well worth me not having to glue fill and sand the ABS pants.

I'd post a pic, but my webserver is down for repairs - maybe a little later on.

JPMacG,
The parts for the wing on mine fit real good and the fuse parts didn't fit so good.I don''t recall any ply parts delaminating.