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Old Mar 05, 2007, 07:30 PM
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Stanwood WA
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Discussion Big prop or small prop.

Ok I have been toying back and forth with what is better for 3d flying.

Would you rather fly a prop at 12,000 rpms with a 14x8 prop or at 6,000 rpms with a 17X10 props??

My dilema is go with a 6s 1000 watts or 5s 1000 watts.

I have 5s batteries but can easily upgrade to 6s. However I think I want the bigger prop for 3d fun. 1000 watts on 5s is a bit higher amps but is also lighter in overall weight.

Please respond with your opinion and what you liked better.
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Old Mar 05, 2007, 07:43 PM
And You're Not
Timbuktu, Mali (Happy?)
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I don't know that the 14X8 is gonna turn twice the RPM as the 17X10 on the same watts.
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Old Mar 05, 2007, 08:36 PM
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for 3d it is always desirable to use large props, 2 main reasons :

a) A more powerfull gyroscopic efect makes high alpha (sub stall) flight easier because the hole plane acts more stable and predictable
b) The big disc of air makes your moving surfaces more effective at 3d

I think the difference is quite big
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Old Mar 05, 2007, 08:44 PM
zaksdad
USA, TX, DeSoto
Joined Apr 2006
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This is pretty much the same question I asked recently as far as the props are concerned, and what I wanted to know is which size range better take's advantage of an electric motors instant torque,sorry don't meen to hijack thread i just thank we're asking the same question.
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Old Mar 05, 2007, 08:51 PM
And You're Not
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Quote:
Originally Posted by Daniel Z
for 3d it is always desirable to use large props, 2 main reasons :

a) A more powerfull gyroscopic efect makes high alpha (sub stall) flight easier because the hole plane acts more stable and predictable
b) The big disc of air makes your moving surfaces more effective at 3d

I think the difference is quite big
I don't agree about the gyroscopic effect. If you want your plane to change attitudes very quickly, moving a huge prop disc is a hindrance.
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Old Mar 05, 2007, 08:52 PM
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Challenger 413's Avatar
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What plane is this going into?

Challenger413
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Old Mar 05, 2007, 09:12 PM
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jeffery, to achieve some extreme maneuvers is where the CG, control surfaces and angles acts primary, so the big prop helps you to do some 3d with presition, without unwanted behaves from the plane
As a fact, 40 old sized planes were flown at more speed on 10´props, today we use 13 and 14´for 3d planes (if we think about nitro), and 8´on pylon racers
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Old Mar 05, 2007, 09:23 PM
And You're Not
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Quote:
Originally Posted by Daniel Z
As a fact, 40 old sized planes were flown at more speed on 10´props, today we use 13 and 14´for 3d planes (if we think about nitro), and 8´on pylon racers
Right. So when you slap a 17" prop on a 40 sized plane the gyroscopic effect starts to make the plane harder to depart from it's heading into 3D. The control surfaces on most 40 sized planes aren't large enough to overcome the effect of the 17" prop, but can manage a 14" prop. What would you do, put a 20" prop on a 40 sized plane? It works against you.

And I will add that I have 40 sized electric 3D planes and have tried the larger and the smaller props.
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Old Mar 05, 2007, 09:32 PM
And You're Not
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Try Here

And Here
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Old Mar 05, 2007, 10:39 PM
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But what if we were talking about a 60 size plane, not a 40? A 14 inch prop isn't to small, and a 17 isn't to big for a 60 size 3D plane. So of the two, what would be best..

In my opinion, it's all comes down to your "style" of 3D. Jeffery, your explanations are correct that the 14" prop will let you change heading with less resistance, and strain on the airframe, but you might notice the loss of airflow over your control surfaces in hover and beyond stall situations. The 17" prop will help those situations. It will help a hover due to more gyroscopic effects as well as harrier and other high alpha flight, but it will slow down those "twitchy" fast transitions. It will hinder some of the other none twitchy stuff as well.

I had a Groove V2 (not really a 3D, but stay with me) that loved to do flat spins, knife edge spin, blenders and such, until I upped the motor to something with more power, and added 2 inches to the prop diameter... It lost that spin characteristic VERY fast. Yes, it now will harrier at a higher angle, and is rock solid while doing it, it's not a hovering plane, but with the 12 inch prop, it will easily stay in a hover, but for me.. that's not what the plane is about, needless to say, I'm in process of reverting to the smaller prop.

It all comes down to preference, If you like fast transitions, and like to use your space while flying, then a smaller prop is for you, if you just want to hang on the prop, and spend all your time in high alpha doing a few waterfalls and knife edges and harrier rolls, then take the larger prop, it will help to stabilize the plane.

When I first started reading up on foamies, everyone was flying 8 inch props on 30 inch planes (give or take) I always thought a larger prop would do better, until I tried it, took full throws to turn it, but it would "hang" with the best of them.

Disclaimer: I'm in no way saying that in a 60 size 3D ship with a 14 inch prop you will not be able to hover, or with a 17 inch prop, you wont be able to make the plane pop and snap, but the tendencies will change the way the bird "feels" with the different props.
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Old Mar 05, 2007, 11:06 PM
Paul Teesalu
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Small props for fast flying; large for slower *3D* type of flying.
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Old Mar 05, 2007, 11:25 PM
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Stanwood WA
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This is going on a Yak 52 from nitro planes. http://www.nitroplanes.com/yak523d5056n.html

I am more of a hover high alpha guy but like to do tumbles on occasions.

I have the 17X10 on there now and it spins up ot 6000 rpms now. I was told by a person with the same motor that it spins a 14X8 at 12000 (not confirmed but I have no reason not to believe them).
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Old Mar 06, 2007, 12:00 AM
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Jeffery, I have read your links, and I agree with you in not to use a 20`prop on a 40 size plane that would be overkill, but I just wanted to post a "rule of thumb" opinion not thinking about plane size

Anyway, the europeans love their diablotins (1500 wingspan) on 17 or 18`props, jason shulman has one also

Fishmasterdan, that plane is is not a super light wing loading plane so, whatever you do just keep it light, setups rocketing out of hover are heavy and are very difficult to control when 1 click can be too much or too little for controled 3d; just my opinion
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