View Full Version : Sceadu Binding in the Head
I was inspecting my Sceadu this evening, and found that the ball links which connect to the washout arms opposite the Y links were nearly worn through, adn close to failing.
The interferance happens at full collective, and large cyclic inputs.
I noticed the blade grips have 2 holes for the ball to mount, and I would like to know what kind of effects on cyclic it would have to move them to the inner holes. This would increace the pitch range to the head, and not necessitate the swash moving as high to get full pitch, thereby lessening the binding. I just don't want a heli that takes 25 secinds to complete a roll.
Any ideas?
Ivan
rob_jones
01-17-2006, 10:50 AM
How much cyclic pitch are you using? Both of my Sceadus have 7 degrees and roll quite snappily.
If you use the inner blade grip holes, you run an increased risk of blade flutter. I'm not saying it will happen, but the likelihood is increased. Especially if you use blades with a rearward CG.
By cyclic pitch you mean the amount of deflection the blades get when the flybar is locked and the cyclic is moved? I will have to check that.
I am using the TT600's on the sceadu, and I haven't had a hint of flutter so far. I am not sure how well the chordwise CG is on them though.
rob_jones
01-17-2006, 11:25 AM
Yes. To check the cyclic pitch range:
Set the collective to 0 degrees.
Make sure the flybar is parallel to the centerline of the copter.
Put a pitch guage on one blade and move the ELEVATOR to full deflection and measure the pitch. Then move to the opposite deflection and measure again.
Rotate the head exactly 90 degrees (while still at 0 collective), and now move the AILERON to full deflection each way.
Typically, 6-7 degrees is plenty. Too little and the cyclic response will be slow. Too much and you'll bog it down in hard flying, cause linkage binding, and run the risk of a boom strike.
It is at about 6.5º cyclic deflection. I reckon it ought to do well then. I was able to move the linkages to ajust the position of the swash at full collective, to help minimise the binding. I will test fly after I get done charging the batteries and see how it does.
rob_jones
01-27-2006, 10:14 AM
Okay, let us know how it does!
It is doing ok. I had tried some longer offset balls on the bell links for the swash, to try and get a bit more cyclic authority, but it was too much, the cyclic rate was not improved much, and the blades would growl and the headspeed would go way down.
I switched form the KSJ paddles back to the sceadu paddles, and that seemed to help more with the cyclic rate. They are kind of easy around neutral cyclic, but have more bite at full travel than the KSJs. Someday, when I get some $$ I will get V paddles and make it really lively.
After a few more flights, I have found that I can bend the flybar in flight, so I think a stiffer flybar is in order, maybe one from a venture or raptor. The one that is in there now seems that it hasn't been heat treated at all, and is very soft. Might be a project for my Intro to machining class to make one.
Anyway, the saga continues.