I have a few questions on the 120 size ultimate bi plane.

1: Where is the thrust line suppose to be? Where the two lines on the firewall intersect?
2: Where are the servo's for the elevator and rudder suppose to go? In the middle of the fuselage or under the elevator?

Thanks,

Dat

Line up the two lines on the firewall with the back of the engine.

e.g if you mount the engine inverted the horizontal line will correspond to the line on the engine or the line formed by the mounting tabs.

The vertical line will then align with the engine's tick marks and/or the engine mount's center marks.


If you mount the engine on it's side, it's just the opposite.

Re: Servos

Wherever you wish to place them.

I used seperate servos for my left and right elevators, mounted in the fuselage. The right servo for the left elevator, etc.

You could also use a pull pull rigging and also mount the rudder servo in the fuselage. That's what I did.

My balance was spot on with an O.S. 1.20 pumped.

With a heavier engine, move the servos to the tail to offset the heavier motor.

Thank you, that was very helpful.

I'm installing the fuel tank now, the manual is horrible for this. I can barely make out the picture and the text instruction is even worse. Can you tell me where you put your tank?

Yup the manual stinks.

I put the tank on the nose as the manual shows in the pictures.

I put foam around the tank and the wood formers where they would contact the tank.

I believe I built a small hard ply "tray" for the tank and used both foam and velcro to hold it in place. Usually I epoxy the tray in place, as this will add more airframe durability and strength.

I then put in a small cut to size sheet of ply, screwed in against one of the formers to hold the tank against slipping backward. e.g. it's up against the back of the tank, with a small piece of foam glued right on the wood. The foam butts up against the back of the tank.

I usually do this in place of any permanent epoxied wood restrainer as you NEED to periodically replace the tubing... ( it is a good idea to do this prior to each flying season ).

Wouldn't the CG change as fuel changes? I was thinking about putting it on the CG, how is your balance? Do you do 3D tricks like hovering? I know you have to be a little tail heavy to do those kind of tricks.

Yup it does change as you use up fuel, but that's normal and accepted.

Most Ultimates ( and for that matter most planes ) have the same setup.

Heck my Funtana 90 which hovers with ease, has the tank practically in the cowl!

The C.G. is calculated for a "worst case" ( empty tank ) situation.

By doing so there is no risk of configuring your plane in such a manner that it will be unflyable.

I've hovered mine at altitude, never close to the ground, and I really do not notice the c.g. variation.

That said with close to 1/2 an hour of flight time until the tank runs dry, I never run the tank down to more than 1/2 ( about 15+ minutes or so ) so that there is little risk of fuel starvation on downlines when the clunk gets uncovered.

( and YES the clunk gets uncovered constantly in downlines for those who doubt it, proven on film on other threads... )

My C.G. is about 1/2" further BACK than recommended... because of the weight of my smoke system and battery.

Thanks opjose, I will follow the recommended spot for the tank as well.