aiax_00

Hi ,
This Saturday I was at the field to fly my new U CAN Do 3D .50 airplane from Greate Planes. Because it was the first flight I fly with small speed, always the throttle was below 50%. For two or three times the elevator goes to flutter.
I am very confused because the speed was very low, engine running at 25% throttle in that moment.

I will give you some specs about the plane.
It is the U Can Do 3D from Greate Planes (1480 wing span) with an OS .50 Sx ringed engine. The prop is Master Airscrew 11x5 G/F Nylon Propeller.
The elevator is drived by 2 Futaba 9001 coreless servos, one for each half of the elevator. I used the original push-rods from the kit (they are 180mm long and 2mm in diameter). I will try to attach a picture.

Doug D.

Couple of suggestions. Seal the hinge line on the elavator with some clear packing tape. And replace the push rods if you feel they are to weak.
Try a higher torgue servo if you can get one. Yours looks like a standard one that comes with the radio.
Also go with a 12x4 or 13x4 prop. The 11x5 can still generate to much speed even at lower throttle settings.

Good luck and have fun !!!

WCB

In the picture it looks like your clevis is attached to the last hole on the elevator control horn. Try using a longer servo arm (to achieve more throw) and attach the clevis to the first hole in the control horn (to reduce flutter). This is what I use on mine and I have never experienced flutter. As you already know this plane does not like high speed so throttle management is essential.
WCB

Rodney

Most times flutter is because of to much slop in the control system, could be hinges, to large a hole in the control horns or servo arms, push rods that flex etc.

jlkonn

My Feedback: (1)

I would agree with WCB.
I am just now getting back into the hobby after a 20 years abscence and I am assembling a UCD 60 so I have "kept my ear to the ground" regarding flutter.
You want to give the mechanical advantage to the servo and not the control surfact.
Like WCB suggests use the outermost hole in the elevator control horn and then use the servo arm length to gain additional surface throw if needed. Also make sure you have no play in the elevator or servo holes where the pushrod connects.
Hope this helps!
JLK

GarySS

My Feedback: (13)

I've just got done flying my UCD.46 for the first time. Before flying I changed my control hardware to 4-40 size all around. Sullivan wire horns, 4-40 clevises and push rods, larger control arms for my Futaba 9202, 9201 servos, sealed hinge lines with monokote strips (a pain with all of those color changes). Lastly I made sure that I had a 4-40 nut on each pushrod end that had a threaded clevis. I noticed when checking everything over that one aileron flexed more than the other. It was because I hadn't tightened one of those nuts down enough. Made a difference.

No flutter for the first couple of flights using an OS.91 with a 15x4W prop. I made sure I was not high on the throttle in anything but UP.

Tall Paul

The pushrod is too close to the surface.
Move it out to the last hole on the horn.
When you want more surface deflection, make the control arm on the servo longer.
You should be using the longest arm that comes with the servo anyway.

aiax_00

Many thanks for your answers,

First of all I have to say that I change the push rods. Now they are 3mm in diameter and I use steel clevis for them.

What I have to say is that at the original push rods from the kit I am sure there is no play in the elevator or servo holes where the push rod connects. I use very precise drills to eliminate such thing.

Regarding the connection of the push rod to the surface...they recommend 57mm of surface travel in one way and 57mm in the other. So the only way to achieve this was to use the hole which is close to the elevator and the one which is fare at the servo arm.

Like I say I change the push rods now, I put steel clevis with some small rubber pieces on the clevis and I will change the coupling hole on the elevator like you said.


I will come with news after the next flight


PS:
Regarding the prop...I used 11x5 recommended by Towerhobbies but in the engine manual OS recommend props in the range 11x6...10 or 12x6 for SPORT and in the range 12x7...9 for AEROBATIC.

delman

I would suggest using an apc 12x4 or 13x4 but not the wide blade - more thrust and less speed even at higher throttle after removing the sloppiness in the linkages as suggested above.

delman

My linkage is set up like Tall Paul using Dubro large servo arms and the furthest out hole on the control surface horn. Hopefully you have a radio with exponential or dual rates or both - then you set your low rate for normal flying and high rate for 3d with max throw using exponential for less sensitvity near center stick travel on elev, ail, and rudder. I find my high rates touchy but my son flies the 46 u-can-do only on high rates.

jlkonn

My Feedback: (1)

Do you think that you can use the standard control horns and drill them out to accept the Dubro 4-40 ball links and still leave enough mat'l?
Thanks!
JLK

zx32tt

My Feedback: (9)

you might be able to use a large Futaba "wheel" and drill it to accepe the ball link. Otherwise, get some Hvy Duty Dubro horns for your servo's. They will give the the proper mechanical advantage, (to the servo) that you need.
Z

aiax_00

Hi,

I want to tell you that I solve the problem. How? Very simple. I change the pushrods with other ones 3mm in diameter. I change the connection of pushrod to the surface from the outermost hole in the control horn to the one closer to the surface, the next one. Now the total travel of the surface is 45mm instead of the 57mm recommended by Greate Planes for 3D. And Finlay I used steel clevis of course.

Ed_Moorman

My Feedback: (1)

With just about all 3D planes in this size, you need to stay with a 4" pitch prop or less. And every time you descend, throttle to idle.

One of the guys at my field lost the stab on his UCD 46. I recommend you run Kevlar or weed eater (string trimmer) line around the stab tips, fin tip and fuselage bottom. It adds nothing in weight and stiffens up the whole assembly.

Flypaper 2

Another thing is to put weights on the forward end of the balance tab. Unhook the pushrod and balance till the surface will almost go to the level position.