DP Ulty
 

My DP Ulty is powered with a YS FZ140 and flies great. I do notice, however, that the second half of the axial roll (from inverted to upright) is faster than the first half (upright to inverted). Much like an airplane with dihedral. Since the DP Ulty obviously doesn't have any dihedral I don't have a clue why it's doing this.

Anyone have any ideas?:eek:

RE: DP Ulty
 

Before blaming the plane, would suggest looking at the roll first.

Any roll takes a short amount of time to initiate, and if same controls are held in place, should speed up slightly, wind conditions ect not being a factor. So what you are saying sounds reasonable.

Secondly, when trying to do a roll with precision, it is different. If you are adding elevator at appropriate spots for a linear roll, it is very very common for people to add more aileron with the stick as the roll progresses. This is responsible for changing the roll rate.

Just some thoughts that may be occurring. With the plane on the ground and everything on, try doing a roll in your mind and see if the ailerons are affected when you bump the up and down elevator. Work towards moving the sticks without affecting the other surface. Add ail and see if the elevator moves and vica versa, move the elevators and see if the ail move also.

Ed

RE: DP Ulty
 

In many full scale biplanes and models as well. the center of mass is slightly below the actual rolling axis in straight and level flight. When you roll from upright level flight to inverted, you are "lifting" the center of mass "up" and around the outside of the roll. As soon as you depart level inverted flight, as the center of mass departs top dead center, it acts like a pendulum seeking the lowest point and therefore gives a kinetic "boost" to the rate of roll. In a full scale airplane this would manifest itself as lighter stick pressure for a given roll rate (initially). For us holding a transmitter, it could mean less stick displacement for a given roll rate. Hope this didn't sound like total BS but if I took you for a ride in a Stearman or Great Lakes Bipe you would see what I mean.

BOB

RE: DP Ulty
 

Thanks for the replies.
As to my flying initiating the differential roll rate, that's certainly a possibility and my be that I'm not used to flying a bipe. However, I don't see this with the other pattern and IMAC type (mono) planes I'm flying.

The center of gravity issue also has merit. I've got a fairly large battery pack in the Ulty because of the number of servos. It's situated low in the fuse and may be initiating the pendulum effect.

Nothing is ever easy!

RE: DP Ulty
 

The ultimates require a bit of aileron differential to straighten out the rolls (i.e. the ailerons need to go a little more up than down.) Without it, they do a slight barrell roll, which is most noticeable when rolling on vertical up-lines.
If you use rudder in your rolls, the second half of the roll will slow as you are using rudder opposite the direction of your aileron input. The top wing gives the same effect as having dihedral, so this gives the rudder power in the roll axis. This is fixed by programing rudder to aileron mixing. You'll mix it so that when you add rudder, the ailerons automatically counter with roll opposite the direction of the rudder input. You know it's right when your knife edges don't try to roll out on you. The rudder to aileron mix will reduce the coupling effect and help to even out your roll speed problem.
Biplanes take a lot of time to set-up for acro, but are well worth it. Once you have the mixing nailed, the planes are awesome.

RE: DP Ulty
 

i hope to have this ultimate up in a few weeks.....