Prop size vs engine size
01-04-2003, 06:26 PM
#1
Prop size vs engine size
I may have posted this else where but not sure. 
I have an OS 40 and 2 46-L engines.
Rather then go with higher nitro fuel would a bigger prop give me a bit more speed?
Also how can you tell when you go to big on the prop?
Say i'm usinfga 10X 4 and want to go with a 10X8 or an 11X6.
I need this info bad.All suggestions very much appreciated
I have an OS 40 and 2 46-L engines.
Rather then go with higher nitro fuel would a bigger prop give me a bit more speed?
Also how can you tell when you go to big on the prop?
Say i'm usinfga 10X 4 and want to go with a 10X8 or an 11X6.
I need this info bad.All suggestions very much appreciated
01-04-2003, 06:36 PM
#2
Engine/prop thrust
Hi Gang,
I recal reading a post not long ago but never got to give my input.
Some one wanted info on testing and measuring the thrust of the engine.
Heres how I did it and this came from a Bell Helicopter engineer.
Plece the craft on level wood platform.
Try to get the best scale you can.
(Avoid fishing scales)
.Use a thin non stretchable cord.
Run the engine up.
Also make sure there is nothing at the rear for the prop blast to blow against.
Tie the craft in an open area.
Run up full throttle and then slide back down slow.
Go back slow and slide down fast.
Repeat these steps several times and your readings at full bore should always come out the same
I recal reading a post not long ago but never got to give my input.
Some one wanted info on testing and measuring the thrust of the engine.
Heres how I did it and this came from a Bell Helicopter engineer.
Plece the craft on level wood platform.
Try to get the best scale you can.
(Avoid fishing scales)
.Use a thin non stretchable cord.
Run the engine up.
Also make sure there is nothing at the rear for the prop blast to blow against.
Tie the craft in an open area.
Run up full throttle and then slide back down slow.
Go back slow and slide down fast.
Repeat these steps several times and your readings at full bore should always come out the same
01-05-2003, 07:53 PM
#6
Prop size vs engine size
One way to select prop size:
1. Choose pitch
high pitch = high level flight speed
low pitch = good climb rate and acceleration
2. Choose diameter
large diameter = low rpms
small diameter = high rpms
This is the way I do it. Type of airplane and flying style decides pitch. Then I choose a diameter that puts a suitable load on the engine with the pitch I chose.
If you are using a 10x4 and want more speed, you must increase pitch. If you increase pitch to 8, you will have to decrease diameter to 9 or even 8 to allow the engine to rev up to "where it belongs" (typically 12-14k for a 40LA...?)
The 10x4 is a prop that gives you good climb rate, but it is not the best for speed. So I think, as Geistware and MikeL suggested, that a 9x7 or 8x8 is what you are looking for. But theory is theory, and the best way to find out is to try a few different types and see what you like best.
Hope this helps!
Tore S.
1. Choose pitch
high pitch = high level flight speed
low pitch = good climb rate and acceleration
2. Choose diameter
large diameter = low rpms
small diameter = high rpms
This is the way I do it. Type of airplane and flying style decides pitch. Then I choose a diameter that puts a suitable load on the engine with the pitch I chose.
If you are using a 10x4 and want more speed, you must increase pitch. If you increase pitch to 8, you will have to decrease diameter to 9 or even 8 to allow the engine to rev up to "where it belongs" (typically 12-14k for a 40LA...?)
The 10x4 is a prop that gives you good climb rate, but it is not the best for speed. So I think, as Geistware and MikeL suggested, that a 9x7 or 8x8 is what you are looking for. But theory is theory, and the best way to find out is to try a few different types and see what you like best.
Hope this helps!
Tore S.
01-05-2003, 08:47 PM
#7
Prop size vs engine size
Originally posted by sandal
One way to select prop size:
1. Choose pitch
high pitch = high level flight speed
low pitch = good climb rate and acceleration
2. Choose diameter
large diameter = low rpms
small diameter = high rpms
This is the way I do it. Type of airplane and flying style decides pitch. Then I choose a diameter that puts a suitable load on the engine with the pitch I chose.
If you are using a 10x4 and want more speed, you must increase pitch. If you increase pitch to 8, you will have to decrease diameter to 9 or even 8 to allow the engine to rev up to "where it belongs" (typically 12-14k for a 40LA...?)
The 10x4 is a prop that gives you good climb rate, but it is not the best for speed. So I think, as Geistware and MikeL suggested, that a 9x7 or 8x8 is what you are looking for. But theory is theory, and the best way to find out is to try a few different types and see what you like best.
Hope this helps!
Tore S.
One way to select prop size:
1. Choose pitch
high pitch = high level flight speed
low pitch = good climb rate and acceleration
2. Choose diameter
large diameter = low rpms
small diameter = high rpms
This is the way I do it. Type of airplane and flying style decides pitch. Then I choose a diameter that puts a suitable load on the engine with the pitch I chose.
If you are using a 10x4 and want more speed, you must increase pitch. If you increase pitch to 8, you will have to decrease diameter to 9 or even 8 to allow the engine to rev up to "where it belongs" (typically 12-14k for a 40LA...?)
The 10x4 is a prop that gives you good climb rate, but it is not the best for speed. So I think, as Geistware and MikeL suggested, that a 9x7 or 8x8 is what you are looking for. But theory is theory, and the best way to find out is to try a few different types and see what you like best.
Hope this helps!
Tore S.
Thanks sandal and the rest who responded.
Learn something new everyday.
Small prop for more speed.
I see where the rest also suggested a smaler prop.
Well I have an order here for TH so I may as well pick up a dozen props of different sizes.
Many thankd Guys
01-05-2003, 08:53 PM
#8
Prop size vs engine size
Originally posted by MikeL
The 9x7 should give you more speed than the 10x4.
The 9x7 should give you more speed than the 10x4.
I just measured the prop and it sure is a 10 inch.
Sure looks small but I guess thats what they wanted for a trainer.
I reduced the dihedral from 2 inches to only a half inch so with a smaller prop I should be able to zip around a bit faster.
Thanks for the post
01-06-2003, 08:20 PM
#9
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Prop size vs engine size
I reduced the dihedral from 2 inches to only a half inch so with a smaller prop I should be able to zip around a bit faster.
You can get aerobatic trainers that are the next step from a trainer that are designed to teach you the basics yet still provide manageable landing characteristics.
01-06-2003, 10:10 PM
#10
Prop size vs engine size
Originally posted by Crashem
If the plane has too much dihedral for your liking maybe you should look at a shoulder or low wing sport planes. Trainers be defination are designed for stability. If you modifiy the specs too much you may end up creating a unmanageable plane.
You can get aerobatic trainers that are the next step from a trainer that are designed to teach you the basics yet still provide manageable landing characteristics.
If the plane has too much dihedral for your liking maybe you should look at a shoulder or low wing sport planes. Trainers be defination are designed for stability. If you modifiy the specs too much you may end up creating a unmanageable plane.
You can get aerobatic trainers that are the next step from a trainer that are designed to teach you the basics yet still provide manageable landing characteristics.
I did reduce it and balance the thing.
This weekend if the weather is OK i'll see how it does.
I have a Avistar on the way here and I understand it's good step up from the Super Select-40 trainer and even better with an OS 46-L engine on it.
I'm looking for something with a bit more zip until I get my pitts built up.
Thanks for the post and GL Flying
