Ok i'm looking for Propellers Sizes. I have a 26 CC gas engine that i want to put a 3 bladed prop on. It currently has been running a 16X8 2 bladed prop. The recomended prop sizes for the engine are 16x8, 16x10, 18x6, 18x10.

But remember reading somewere in these Forums that when you switch to a 3 bladed prop the Diameter is smaller and pitch. Dont know if that is correct or Not . Suppose i wanted to go to a 4 bladed prop.

Is there a link to a forum and thread that has this information already?? That would be the easiest way i just cant find it. Or is there Someway to Gauge this??

I purchased a Master Airscrew 15x7 3-Blade G/F Nylon Propeller. to experiment with. and 2 normal props for the engine.

Master Airscrew 16x6 Maple Wood Scimitar Propeller

Master Airscrew 18x6 Classic G/F Nylon Propeller

Just in case the 3 balded doesnt work out. But would really like to learn more about how to guage propellers.
About all I know is the 15 is the diameter and the pitch 7 is suppose to be a measurment of the fluid dynamics.

7 inches for each complete 360 degree revolution. I picture it like this probably wrong but when the plane is flying it will move 7 inches foward for each Complete 360 degree revolution of the prop like a screw boring into a peice of wood with a certain pitch will bore into the wood so far for each 360 degree turn.

Well any help here would be Appriciated. A link to another Forum or your experiences with Sizing and gauging Propellers i know that there is alot more to it. ways to measure Thrust Ect.

I'm sure it can get quite in depth.

Thanks Link

Well after looking some i found this information.

For each increase of blade,,
decrease pitch or diameter to next lowest number available..

18X10 2blade =
18X8 3 blade =
18X6 4 blade

This is how i do it.I times the length x the pitch and come as close to the same numbers as possible,heres a couple examples.But the best way is to see how the plane behaves and acts in the air,nothing is better than that.I learned that here.
18x6=108
16x8=128
15x8=120
19x6=114
just an example.If ya want a better answer you did the best thing and ask.Then its just a waiting game for the answer.So if it was me id use a 15x8 3 blade.You picked a 15x7 so your very close or right on.You are right about the screw threads and movement.360 degrees at pitch of 7 equals 7 inch forward movement per 1 revolution of prop.

Thanks Buck for your answer that helps alot. I would have never thought of multiplying the 2 numbers i was looking for a 15X8 but tower didnt have that size and i got the closest i could to it. I looked on the internet through several different forums on this. and visited many links to differnt types of 3 bladed props that were 15X8 but there pretty pricey.

There is a zinger Site that has a 3 bladed wooden prop that size. But considering that i might damage the prop and i'm experimenting i didnt want to spend to much on the prop.

http://www.zingerpropeller.com/3_bladed_Propeller.htm

Appriciate the input[sm=thumbup.gif]

I have always liked Graupner props. They have a nice wide scale looking blade and just seem to be stump pullers. I have run 2 and 3 blade props on the same aircraft before and I always try and keep the pitch the same but lower the diameter by 1" when switching from 2 to 3 blade prop. Here is the web site for Graupner props:

http://www.hobby-lobby.com/grprop.htm

About Graupner Props. I just received 2 3 bladed Props one 12X8 for one of my smaller planes and a 15X8 for my bigger plane. Great looking props whith solid hubs unlike the MAS props which is a big plus.

But what i'm wondering about is the Important Notice i read on the box they Come in. Which i won't retype it all just the Part i'm very curious about and have never seen or heard of till now whitch states: (IN ORDER TO PRESERVE THE STRENGTH THE WATER CONTENTS MUST STAY TRAPPED IN THE MATERIAL)??For that reason they should be stored as cool and as moist as possable?? A lack of water content can be compensated eighter by putting propeller in boiling water for a short while or buy submerging it in water at ambient temperature for a couple of days??

First of all how Can you tell when it is lacking in water content and second it's Fiberglass which is reinforced Does it really need to have water content?. I just found this information intresting as i have never seen this with any other propeller. When i attempt to drill it will it squirt water out or have a seeping or sweating. lol

Sounds like the way we used to do it about a million years ago with nylon props.

Well, living in Louisiana we never have a shortage of humidity in the air. hahahaha. I don't know about your area. If you live in a desert area, I may be concerned. You maybe should contact Hobby Lobby to see what they recommend.