PROP QUESTION PLEASE --three blades options
11-29-2014, 09:32 AM
#1
PROP QUESTION PLEASE --three blades options
A little help please , can someone explain the performance difference between a 17/10/3 blade and a 17/7/3 blade ?
I am not sure at the cost the three blade props I dont want to make a mistake
Thanks a ton !
I am not sure at the cost the three blade props I dont want to make a mistake
Thanks a ton !
11-29-2014, 09:55 AM
#2
Join Date: Dec 2007
Location: Davison, MI
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Hi LDM,
Try this Calc for your question. Input an known setup for your engine, note the HP needed and adjust the values to get the same horsepower needed on various props.
It's not perfect but will give you a good SWAG and can narrow the prop choices you need to buy for real world testing.
http://personal.osi.hu/fuzesisz/strc_eng/
Joe
Try this Calc for your question. Input an known setup for your engine, note the HP needed and adjust the values to get the same horsepower needed on various props.
It's not perfect but will give you a good SWAG and can narrow the prop choices you need to buy for real world testing.
http://personal.osi.hu/fuzesisz/strc_eng/
Joe
11-30-2014, 02:43 PM
#5
Who makes a 17-7 three blade? I have a couple of 17-8 Xoar three blade props. On a DLE 30 and RCGF 32. They work ok. Tried a 17-10 three blade on the DLE 30, slow acceleration and vertical greatly affected. Less pitch will give you more climb/lower speed power. More pitch more speed if you engine can turn it. Also more pitch will cause more engine heat and richer needle. I opted for less pitch and better power for take offs, go arounds and aerobatics. Here is the 17-8 Xoar on the 75" WS Macchi.
11-30-2014, 05:39 PM
#6
Hi Bean
Was useing a 17/10/3 from Bella and now going to try a 17/7/3 from Turnegy .
The 17/10/3 was used very successfully on the Eflight power 110 motor on 2 x4 cell packs .
The Bella props are thick but light , I dont know about the Turnegy props but giving them a try
Thanks Tail skid , its a 79" EPO P40 , My second one they fly great , I am looking for a more efficient prop--this is my first one below
http://youtu.be/6TqVe9sL1SA
Was useing a 17/10/3 from Bella and now going to try a 17/7/3 from Turnegy .
The 17/10/3 was used very successfully on the Eflight power 110 motor on 2 x4 cell packs .
The Bella props are thick but light , I dont know about the Turnegy props but giving them a try
Thanks Tail skid , its a 79" EPO P40 , My second one they fly great , I am looking for a more efficient prop--this is my first one below
http://youtu.be/6TqVe9sL1SA
Last edited by LDM; 11-30-2014 at 05:42 PM.
11-30-2014, 06:18 PM
#8
Join Date: Dec 2007
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Hi LDM,
When you input the air temp the air density is set by the calc automatically....
If you have some known RPM numbers for a given prop we can start there to get you some comparison numbers.
I'll take a wild guess so you can see the difference.... and say the 17x10x3 was turning 6000rpm (its a wild guess) than would give you a pitch speed of 56.8mph, static thrust of 11.96lbs and require 1.8hp.
The 17x7x3 would spin up to 6800rpm at the 1.8hp level..... this would give you a pitch speed of 45mph and 15.3lbs of static thrust.
I start with rpm numbers of a known set up, find the hp needed, and then input a new prop and adjust the rpm to match the known hp required. This will give you a good guide as to what to buy and test. As you can see by my example above you can easily get a prop that pulls hard but would be unflyable. In that example a 45mph pitch speed would be a real dog.
You can see what the change in pitch would do in the example above. But if you got real RPM numbers for a prop we can project much closer to your real set up. But as RBean said more pitch = more speed etc.
The trick is to get one good real world set of numbers then work from there.
Joe
When you input the air temp the air density is set by the calc automatically....
If you have some known RPM numbers for a given prop we can start there to get you some comparison numbers.
I'll take a wild guess so you can see the difference.... and say the 17x10x3 was turning 6000rpm (its a wild guess) than would give you a pitch speed of 56.8mph, static thrust of 11.96lbs and require 1.8hp.
The 17x7x3 would spin up to 6800rpm at the 1.8hp level..... this would give you a pitch speed of 45mph and 15.3lbs of static thrust.
I start with rpm numbers of a known set up, find the hp needed, and then input a new prop and adjust the rpm to match the known hp required. This will give you a good guide as to what to buy and test. As you can see by my example above you can easily get a prop that pulls hard but would be unflyable. In that example a 45mph pitch speed would be a real dog.
You can see what the change in pitch would do in the example above. But if you got real RPM numbers for a prop we can project much closer to your real set up. But as RBean said more pitch = more speed etc.
The trick is to get one good real world set of numbers then work from there.
Joe
Last edited by Joespeeder; 11-30-2014 at 06:20 PM.
