Propellers

[jander14indoor]

Since we have a dedicated board for WS now, I thought it might help to organize by kicking off topics around the typical WS questions. Content of string to be driven by subject line (I hope).

[gyourkoshaven]

Do propellors have to be tilted upwards for the plane to get lift?

[andrewwski]

No! I wouldn't tilt the prop upward - to me that seems like it's going to give you a lot harder time making the plane stable.

You want the prop to be perpendicular to the motor stick. The lift comes from the wings.

You may, however, aim the prop a tad to the left, as that assists in turning.

[gyourkoshaven]

I thought you were supposed to do that to the tail stabilizer.

[smartkid222]

there are many ways to create a turn. tilting the fin-horizontal stabilizer-rudder, is one. aiming the prop to left is another. Making the left side of the wing longer than the other also has something to do with turns- (creates more lift on the left side to copensate for the smaller flight path diamter).

[carneyf1d]

Making one side of the wing longer takes the torque caused by the prop and produces a small amount of lift on one side to level the plane. With big wright stuff planes that are 7 grams, have big wings and fairly small props its not a big issue. But getting back to the main concern of prop angle. A lot of people have the prop with 0 degrees of up and down angle(directly perpendicular to the motor stick) and around 2-3 degrees of left thrust (assuming you're plane is turning left). Others even create a small downthrust on the propeller by angling it 2 degrees or so downward. Be careful not to angle it too far.

[blue cobra]

How good is the assembly that comes with the Ikara props? Is a Harlan thrust bearing worth the $2.25? How is it attached to the fuselage- with music wire? How many would I really need? Should I get teflon washers?

[andrewwski]

Depending on the Ikaras you get it may or may not come with an assembly. The ones I got with an assembly one year are pretty bad. They only have a thin piece of plastic to attach them with - there's no good way to attach them to a reasonably sized motor stick.

Yes, the Harlan thrust bearing is much better. I always attached it in the method he recommended - wrap with thread and then coat with glue.

And most people seem to recommend the pennyplane bearings over the S.O. ones.

[jander14indoor]

The advantage of the penny plane bearings is you can remove the prop and prop wire without cutting.

You'll need some sort of thrust bearing, the teflon washers work well.

You can also attach by wrapping tightly with a couple of layers of balsa cement soaked tissue instead of thread. No wire needed.

Jeff Anderson
Livonia, MI

[Cyrus_D]

Can anyone link me or reference me on how moving the tail hook closer or farther from the prop will increase/decrease its speed?

[jander14indoor]

Probably not because it has little effect on prop speed. That is driven more by aircraft drag, prop pitch and diameter, and torque (which is driven by winds and rubber width, NOT hook length).

Hook distance has a little more effect on energy stored and returned, but not large until you get to silly extremes.

Note, many students seem impressed by the slow turning props on well tuned planes and ask how its done. Actually you don't directly control prop speed, its a by-product. As you make your plane more efficient by losing weight and minimizing drag, it takes less power to pull the plane through the air, you can use thinner rubber with less torque, and the speed naturally drops.

You can also slow a prop on a given setup by increasing the prop pitch, but then you have to increase torque (increase rubber width so less turns possible) to fly it and the net trade off for flight time is a wash.

Concentrate on light weight, efficient trim and matching prop and rubber to the plane. Slow prop speed naturally falls out of that.

Jeff Anderson
Livonia, MI

[Cyrus_D]

Thanks Jander, I will really take note into that.

[smartkid222]

I belive someone last year on the thread reccomended the Harlan penny plane thrust bearing over the SO one? is there a reason for this?

[jander14indoor]

In the past, Harlan's Penny Plane prop hanger had the split rear allowing you to remove the prop and wire from the plane to change props easily.

The SO prop hanger did not. Just a hole in front and one in back. Had to cut the prop axle to remove and change props, and a new wire required for the new prop.

I assume its still the same, but I don't know as I make my own prop hangers.

Jeff Anderson
Livonia, MI

[blue cobra]

What's the best shape to cut the propeller into?