Prop size help
 

Hi guys,
I have a Seagull Space Walker 2 with an OS 46AX. The OS manual suggests "sport" 10.5x6, 11x6-8 and 12x6-7. What do you guys recommend? I'm not looking for top speed but more of an easy sport flyer.

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RE: Prop size help
 

A 10 X 7 or 11 X 6 will work just great. Good Luck, Dave

RE: Prop size help
 

Don't trust the manual. I have an Evolution 46 and was very successfully recomended to use a 10 by 6 by a very experienced rc pilot. My manual called for an 11 by 6 and my engine barely ran at all.  Different planes want different proppellers but I would start with 10 by 6.</p>

RE: Prop size help
 

drube,

You might want to check out this web site. Some good info here: [link]http://www.rd-rc.org/[/link]

If it does not bring up the prop size chart; look at the bottom and look for "prop selection guide".

RE: Prop size help
 

10x6-8
11x5-6
12x4
12.25x3.75
those are your props that you can use (not including speed props)

the 10x6 is not enough prop for then engine, that isnt a bad thing (pick the prop you like) but you wont get as much power as you could

i would use a 11x5 for sports flying.

RE: Prop size help
 

Drube,

Here is a good reference article:

http://findarticles.com/p/articles/m...g=content;col1

RE: Prop size help
 

Thanks Dave, I was going to pick something in the middle but figured I better ask you guysfirst since Iknow nothing about props. lol n
Thanks for the links guysthere'stons of info to take in.
Ok, now I was thinking of going with a wood prop or should I choose something else.
I'm sure this topic has beencoveredmany times before here so sorry in advance.

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RE: Prop size help
 

After you are flying a bit and can tell if the airplane flies worse or better, go buy an bunch of props of differen sizes and brands. You will find that props make a considerable difference in how the engine runs and how the airplane flies. Keep the props that are not the best because they may well be the best on the next airplane/engine combination.

RE: Prop size help
 

save this for a reference, I got it here a long time ago. Its kinda handy.:)

RE: Prop size help
 

Thanks Jim, that makes sense.
I do have 1 more question though.
When speaking of "thrust" would that be the same as torque on a V8, more pull? The bigger the prop more thrust, smaller prop more top end?

RE: Prop size help
 

Thanks!
Much easier to understand what's going on when you see it on a chart.

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RE: Prop size help
 

A simplified explanation to your questions (not considering actual energy losses, efficiency, etc.):

The thrust or pulling force of any propeller comes:

1) From the area of the rotating disk times the differential pressure of that stream of air before and after the prop.

2) Or from what is the same: the mass of air moved by the disk times the differential velocity of that stream of air before and after the prop.

The power that the propeller receives from the engine is rpm times torque (twisting force at the shaft), and that is constant for each throttle position.

Max torque occurs at rpm lower than max rpm.
Max power occurs at rpm higher than the rpm’s of max torque.

An engine should be loaded with a propeller able to move as much air as it is possible to be moved for that max torque or max power.
That is achieved by balancing the jigsaw formed by the area of the rotating disk (which is proportional to the square of the diameter of the propeller) versus differential pressure (which is proportional to the rpm’s and to the angle of the blade (pitch of the propeller)).

Big diameter propellers of low pitch: Better efficiency, more “air grab” at low forward speed of the model, higher breaking effect during landing, better engine idle, good for 3-D and high drag models (it is like the first gear of a car’s transmission).

Smaller diameter propellers of high pitch: Lower efficiency, less “air grab” at low forward speed of the model, lower breaking effect during landing, poor engine idle, good racers and low drag models (it is like the highest gear of a car’s transmission).

That is the reason for which the engine manufacturer gives us a range of propellers that will perform good.
For diameters above that range, the rpm’s will drop below the max torque.
For diameters below that range, the rpm’s will go too high above the max power, with possible damage of the moving parts.

RE: Prop size help
 

RE: Prop size help
 

Never rely soley on prop charts or other's advice when it comes to props. It only costs $1.83 to try a new size.
.45s were put on this earth as a replacement for what used to be the standard sport engine, the .40.
Sport .40s did most of their best work with 10x4, 10x5 and 10x6 props...11x4 props and up usually gave diminishing returns when comparing vertical pull. Along came the .45s and their ability to turn 11 inch props as well as a .40 could turn 10 inch props gave the average sport flyer a new combo that could put some marginally heavy planes "over the top" as far as vertical performance and brute force aerobatics are concerned.

RE: Prop size help
 

Prop size depends greatly on which plane the engine it's mounted to. I wouldn't use the same prop from a pattern style plane to a Space Walker, yet you could use the same engine on both planes. Lower pitch would be your choice.
Try 11X5 or 11X6. I think jumping to a 12X4 is too extreme, more a 3D prop for a 3D plane.

Wood, is $3.39.

http://www3.towerhobbies.com/cgi-bin...?&I=LXLG02&P=7



I fly a variety of sport planes, and like vertical performance, going up high sometimes. Some planes have pretty wide wingspans and larger control surfaces, so a higher pitch prop in both of those instances is a mistake. You can't get vertical performance with a 7 pitch prop and top speed with a 7 pitch may cause the sport plane to flutter or fatigue.
I change to a 6 pitch, then 5 pitch, if I need to to get the vertical heights I want and slow landing speeds. For every pitch you go down, effectively you can increase 1" of the prop diameter. So the load is similar from a 10X6 to a 11X5, and 12X4.

RE: Prop size help
 

Actually an 11x6 APC is a better match for that engine than a 10x6.

RE: Prop size help
 

Thanks guys! That's a lot of info to digest..lol I'm going to start with a 11x6, I can't wait to get her broke in and in the air. I'm headed to the local field to talk to an instructer tomorrow to get the ball rolling. I fly my G4.5 for hours nightly and pick the brains of the LHS guys..lol

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