Rc-Warehouse-USA

My Feedback: (28)

Generally will a smaller ballanced prop produce a smoother idle compared to running a larger balanced prop?
KA

the-plumber

Think about flywheel effect . . .

Rc-Warehouse-USA

My Feedback: (28)

I am confused?

CptCliffhanger

My Feedback: (6)

larger prop smoother!! Mor dampning, and weight to carry you through compression.

Rc-Warehouse-USA

My Feedback: (28)

Does a spinner help to smooth out viration?

BobH

My Feedback: (2)

The only thing that helps smooth out vibration is by perfectly weighting all the moving masses. This includes the spinner, backplate, and prop. Plus the engine itself produces more or less vibration depending on its materials and design. Some engines vibrate more than others. Gas engines vibrate more than glow engines, for the most part. The twins run a little smoother because their pistons typically counter ballance each other to smooth things out. Hopes this helps.

the-plumber

To some extent.

In power trains where a flywheel is used, a heavy flywheel will dampen vibrations more than a light flywheel. A large prop and spinner contain more mass than a small prop and no spinner, so the large prop/spinner setup has more inertia and thereby is more resistive to vibration; the combination of large prop and spinner makes for a heavier flywheel.

Because of the higher inertia in a heavy flywheel compared to a light flywheel, the engine cannot accelerate the heavy flywheel as quickly and "throttle response" suffers.

If maximum throttle response is the objective, use a small prop and no spinner. If smooth operation is the objective, use a large prop and a spinner.

An inherently unbalanced engine can be smoothed to a great extent by a large flywheel - and single cylinder engines are by definition unbalanced when running : there is no way to offset the change in acceleration of the reciprocating parts during the compression and power strokes. In a 2-stroke engine those two events happen every rotation; the piston/crankshaft speeds up under power and slows down during compression. Four stroke engines have the two events half often as in a 2-stroke, and are perceived as being "smoother".

Absent a flywheel, acceleration-induced engine vibration is transmitted to the engine mount.

Welcome to the wonderful world of model airplane engines and the damage they do just by running.

BobH

My Feedback: (2)

Flywheels are used for energy storage. That may or may not translate to a change in vibration. I would think that that would depend on the ballance of the fly wheel. But using the optimum engine/ prop spinner combintaion will help with your engine's transitions from lo to hi and back as well as the idle. For more information about flywheels try this link.
http://www.upei.ca/~physics/p261/pro.../flywheel1.htm

ml3456

Also, without cutting the prop in half or using some extremely complicated weighting, each blade of a prop could have a different center of gravity that can cause vibration. Look at how the heli guys balance their blades to reduce vibration.

Mark

rmh

Uh-four strokes are smoother?
how?
the four stroke SINGLE or boxer twin, fires every other revolution.
So the prop has one more revolution to slowdown (no perpetual motion here).
The largest four stroke singles - the "performance YS engines" will shake the balls off a pool table -simply from the high power pulse - then the air load slows the prop - - etc..
Smooth is best from an engine with most power impulses per revolution -all things being equal.
I have run ignition singles that are incredibly smooth - They use a tailored spark curve which damps the power around 3000 rpm - and at very low idle .
adding flyweight does help any engine - for making things smooth - but it does soak up some energy to do it. (no perpetual motion.)
I once designed a mout setup which aligned the engine along the crank axis -then had an adjustable snubber to soften the power pulse.
The purpose of it ---was to tune the harmonics of the model to cancel the torsional inputs from the engine -and it did work - we called it the Rotormount.
Harmonics are crazy things -sometime a minute change will completely stop them

ryans1000

I have a new .40 hangar 9 twist with a lot of vibration. I have a question about the engine mount.

From the factory, the engine mount fingers leave about 1mm of space between themselves and each side of the engine compartment on my Twist. However, I have an oversized engine in the twist (mvvs .77 2 stroke) and the engine is a bit big for the mount and is pushing/stretching the mount fingers against the wooden sides of the engine compartment. Does this cause excesssive vibration because i'm getting a lot of vibration. My engine is used but its the first time i've ran it so i'm not sure if something is wrong with the engine or if its the way its mounted.

Ryan

the-plumber

IC engines have two events wherein the rotating mass undergoes acceleration : compression and power; those events cause the vibration emanating from the engine itself.

The event rate for 4 strokes is half that of 2 strokes.

rmh

correct - half as many but the time period doubles per rpm comparison - the decay in prop speed betwen power strokes is therefor greater.
- for same prop load at an given rpm - two stroke vs four stroke - each four cycle power stroke must be stronger to equal the two stroke which accelerates the prop at twice the frequency.
OR the rpm drops-------
The prop is a heavy load but a poor flywheel.
The primary "vibration" is simply the amplitude of each reaction to prop acceleration..
FWIW- a friend did the tests on a accelerometer at NASA with a printout - It was almost exactly as we predicted.
Make sense?