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Author Topic: picking the right propeller  (Read 5609 times)
Yaroslav Melnikov
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« on: May 09, 2012, 05:41:13 PM »

in this topic please share your ideas about your experience of choosing a right prop for your F2D motor.
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Yaroslav Melnikov
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« Reply #1 on: May 09, 2012, 06:27:22 PM »

Before my notes - a bit of simple theory.

There are several technical terms to define the propeller's characteristics such as: diameter, pitch, disc area relation, hub, bore, blades shape and sizing etc. All these characteristics are calculated to design the optimal propeller accordingly to motor specs and the flight parameters you expect to get.

Besides all the terms there are two main ones you need to operate with: Pitch and Diameter


Pitch: Is the displacement a propeller makes in a complete spin of 360° degrees. This means that if we have a propeller of 5” pitch it will advance 5 inches for every complete spin as long as this is made in a solid surface; in a gas environment (air), the propeller will obviously slide with less displacement, but at least you have an idea.

The more the pitch is - the faster a model flies as the prop with higher pitch grabs through more air. But there is the back side of it - the more the pitch is the more power the engine needs to turn the prop that's why in aviation the props with relatively high pitch are called "heavy props". While the flight the upcoming air helps to rotate the propeller and the higher the speed is the more air helps to rotate the prop. That's why the props with high pitch are better at the high speeds and worse at low speeds since it's harder for the engine to turn that prop. So the perfect propeller must very the pitch, setting it to low number at low speed and high number while the speed increases.
  
However, for our combat planes we use only a fixed pitch propellers and as every fixed-pitch propeller it must be a compromise, because it can be efficient at only a given combination of airspeed and r.p.m.

Diameter: It's simple - the larger the diameter, the more air the prop is able to grab through. But again, the larger the diameter - the more power the engine needs to rotate the prop. And also there is a small trick here - the larger the prop - the more it causes air drag.

here are good sources:
http://www.allstar.fiu.edu/aero/flight63.htm
http://www.rc-airplane-world.com/propeller-size.html
« Last Edit: May 09, 2012, 06:39:08 PM by Yaroslav Melnikov » Logged
Yaroslav Melnikov
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« Reply #2 on: May 09, 2012, 07:15:48 PM »

And here is the most interesting part starts - choosing the propeller that fits your needs.

So our dilemma is as follows - the model must be fast flying level (at a maximum speed) and has a fast speed in turns.
Why is it the dilemma?? Because the speed in turn drops by a third at least and normally it's just a half of the maximum model's speed!
So it's obvious the prop efficient in flying level and fast won't be efficient flying in turns and very wise balance should be maintained here as we need both high level speed (easier to chase and get you opponent's model) and high turn speed (ability to out-turn you opponent's model in continuous sharp turns).

Here are the tips to pick the right prop:
1) the larger diameter prop gives a lot of thrust at low and near zero speeds, so if your priority - to obtain a high speed in turns - that would be your choice. Also combat models at the aerodynamic point of view are called super-efficiency-controlled as the static thrust/mass ratio is about 6:1 (!) the more that ratio is the sharper turn a model able to perform without loosing its speed to a critical (stall).

2) the smaller prop diameter - the higher speed the model performs, as the prop actually causes an air drag.


All the theory written above is nothing without a practical backup, so to understand it better, I would suggest you to do the following:
- Pick ANY F2D propeller you like with relatively large diameter (Seryogin, AKM Sabre, etc)
- Trim the prop down with every mm cut-off: 163mm, 162mm, 161mm, 160mm, 159mm, 158mm, 157mm

I guarantee, how much you are going to be surprised with the model's behavior in the air and the level speed!!!

So what at the end you should do - pick a few props (the same maker!) that work better to your opinion and just fine tune your engines before every contest with those props.

Turn your props knowledge against your opponents and increase your chances to with the combat!
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Yaroslav Melnikov
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« Reply #3 on: May 09, 2012, 07:20:18 PM »

Having all these said, to me all the new props purchasing is getting to a competition between my ideal (trimmed to my needs) prop and the new prop. As it's always great just to buy, plug and play without all this BS with prop's trimming  Grin

« Last Edit: May 10, 2012, 02:56:35 PM by Yaroslav Melnikov » Logged
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« Reply #4 on: June 01, 2012, 08:49:51 PM »

My thought is pick the prop your motor likes. Got 5 2010 foras 2 like ak prop(power motors) 2 like nn prop and 1 that likes A  prop. All are very good motors, but each is a bit better with prop that it likes. Not every motor seems to like same prop, test them and see. Got a few new props to test AKM sabre and TS M this weekend. I expect TS M to be good in turns and low flight, well see on sabre
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« Reply #5 on: June 03, 2012, 01:06:30 AM »

Tested akm sabre and TS m today. As expected TS m was good in turns seemed to have very precise control through and out of turns. As for sabre... I think I'm in love with it! Very good!!! Tested both 6mm and 8mm mufflers with sabre 
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Yaroslav Melnikov
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« Reply #6 on: June 04, 2012, 02:49:39 AM »

I think AKM props (Sabre, DSD and others) performance is better due to the special Russian resin ED-20 is used in aviation industry. It's quite temperature resistant (keeps properties at relatively high temp.), so at high RPM it might vibrate less the the other props made of German resin "Larit"
As per the maker the props are made of that resin show quite stable result both cold and hot weather.
To me TS-M seems to be superior at about 22C and down. Try to fly TS-M when it cools down in Arizona a bit. I'm telling you man - you'll be surprised  Wink
What diameter you flew AKM prop though?
« Last Edit: July 27, 2012, 02:14:59 PM by Yaroslav Melnikov » Logged
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« Reply #7 on: June 04, 2012, 09:17:31 PM »

I trimmed down to same length as TS m or nn prop for 6 mm, for 8 mm a bit bigger but still cut down a bit. I will measure soon!  As for resin...hmm interesting. In the heat here smaller props seem to just spin not make much power. I've tested rpm with tach and found weird results. Would think higher rpm would be better flyn airplane... Not in my case.  Ak prop turned 28200 nn prop 28800 a prop 29200 all with same motor. My motor liked ak and nn way better than a prop which had highest rpm.. Weird huh.  Now here is kicker flyn partner tached super prop on his motor at 26800 and it was very very good. Not sure what to think!
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Yaroslav Melnikov
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« Reply #8 on: June 05, 2012, 05:43:13 PM »

...In the heat here smaller props seem to just spin not make much power. I've tested rpm with tach and found weird results. Would think higher rpm would be better flyn airplane... Not in my case.  Ak prop turned 28200 nn prop 28800 a prop 29200 all with same motor. My motor liked ak and nn way better than a prop which had highest rpm.. Weird huh.  Now here is kicker flyn partner tached super prop on his motor at 26800 and it was very very good. Not sure what to think!
it depends, just go through a bit of the theory I posted up here - if a prop is heavy loaded by pitch >> less RPM on the ground >> higher level speed.
and it's obvious if the motor shows high RPM with the prop of the same diameter - it means the pitch is relativity small and you'll never see high level speed in there, but might be very good in sharp turns as due to ability to keep high rpm

But still... Regardless the prop size and showing low RPM on the ground, the motor can be really fast in the air. I had a motor resulting 22.65 sec/10 laps with 6mm muffler showing only 26,500 RPM on the ground, and that was with 0.45mm head clearance!  Shocked  And the most interesting part - that motor was very quiet  Cool
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