Vibrations, vibrations and vibrations ....

rsv1cox wrote:Mauricio "Sully” Sullenberger......Miracle on the Soybeans.  

Way to be a pilot Mauricio landing undamaged with no elevator control.  And a great fix on that servo too.

Bob

Ken Cook wrote:            I have found many times that the hole is not square to the faces of the prop. I have the luxury of placing them on a lathe and truing up both faces. So no matter how much one balances a prop, it's not going to compensate for that problem. In addition, many times one blade is slightly longer than the other. One could want to go crazy trying to figure out all of this. Put another prop on it and try it again.

pkrankow wrote:Those flexible props are very hard to balance, if they can even be balanced.  If you are past the always crashing stage with your flying then switch to a more rigid prop such as Master Airscrew glass filled props.  Any quality brand of prop, glass reinforced or wood, will also preform well.

Sometimes a prop will perform smoother if you rotate the installation half a turn.  If the out of balance is the same as the engine is out of balance the vibration will be very bad, while if the prop is out of balance opposite tge engine the vibration will suddenly be minimal.  This just takes loosening the prop and advancing to the next blade and retightening.  

It is best to have everything properly balanced, but the engine is never in balance since it is a 1 cylinder.  Having the propmbalanced minimises vibration more reliably than an off balance prop will.

Phil

1/2A Nut wrote:The MA 5.5x4.5 has made this one fast are you ok with the speed? Perhaps it is time to make a plane built for
speeeeeeeeeeeeeeeeeeeed hehehe. That prop cut down to a 4.75x4.5 will make the plane go basaltic. I see it
took off from the ground with ease that is a plus. "Mauricio The Speed Flyer"

Some data for you my friend:



Uploaded by:
AmpAbuser AKA 1/2A Nut AKA Brad
Uploaded on Apr 2, 2018

Best peak: 20,187 rpm
19,784 rpm at 1:59 minutes into the vid Prop speed 84 mph
Estimate 74 mph flying speed during that pass
Static peak: 15,584 rpm / 10oz thrust / 66 mph pitch speed / 84w
Best idle 8,702 rpm

balogh wrote:Yes Mauricio I must admit I also often saw servos killed by vibration. When it hits mid-air the first thing I try is throttle down or stop the engine. I have always managed to land without major damage so far. Especially in my larger planes  the long elevator and rudder pushrods tend to vibrate and this constant load damages the plastic gears sooner or later. I often pull the 2 rods slightly together with rubber bands to prevent vibration.

Electrical or cable soldering failures as results of vibration are less frequent  in my experience. I always balance my props but large balsa planes are like drums that induce the formation of fuselage and pushhod vibration. I am just trying to mitigate it in my Sig Wonder that I built a few months ago and took out flying yesterday.