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Old Feb 04, 2013, 02:37 PM
rip
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United States, FL, Niceville
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Quote:
Originally Posted by jaizon View Post
Are you going to use this plane for ALES? Just sport flying?
For the moment I am not going to participate on official ALES competitions. Only after I'm familiar with the technology I'll attempt to join that group of hard-core pilots.

We have unofficial sport competitions loosely based on ALES.

we can call them sport flying... but with a "serious" purpose.
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Old Feb 04, 2013, 02:39 PM
rip
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United States, FL, Niceville
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Quote:
Originally Posted by jackosmeister View Post
Its easy to solve now. But thats not the point

Teach a man to Fish


I big chunk of the equation comes down to budget as well, are you happy to use HK Gear, or do you want to use higher quality gear and get a lil more bang (or less weight etc)


Personally I didnt start flying toy planes to save money
Within reason I'm trying to use "good stuff". I use thunderpower batteries and scorpion motors and a Futaba radio... prob not top of the line... but is the level i want to stay... for the time being.

Once I'm satisfied with the Spirit ... I'll certainly try to get a more "competitive glider"...
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Old Feb 04, 2013, 02:55 PM
Crashing into the sky!
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Joined Aug 2007
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Nothing wrong with that gear.

I dont have a spirit (the plane at least) so am unsure what will fit, and what will balance.

But ill take a stab. Have a measure up (motor diameter in relation to where it wants to sit in the fuse to balance), and play with some lead before committing.

SII 3008-1090 scorpion
35A+ esc
3S 30C 1000+ (depending on balance and how much motor on time you want)
Aeronaut 11x6

~330W. Motors a smidge over loaded, but your flying it LMR anyway so itll be fine.
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Old Feb 04, 2013, 03:07 PM
rip
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United States, FL, Niceville
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Quote:
Originally Posted by jaizon View Post
I would give David a call at Esprit Model. (1) 321.729.4287
Thanks for the advice. David and I had a chat and I think I have a much clearer idea of what is going on now
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Old Feb 04, 2013, 03:09 PM
rip
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United States, FL, Niceville
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Quote:
Originally Posted by jackosmeister View Post
Nothing wrong with that gear.

I dont have a spirit (the plane at least) so am unsure what will fit, and what will balance.

SII 3008-1090 scorpion
35A+ esc
3S 30C 1000+ (depending on balance and how much motor on time you want)
Aeronaut 11x6
I am now leaning very heavily towards that same motor... Doing the numbers to "convince myself" ...

... Isn't this fun?
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Old Feb 04, 2013, 06:03 PM
rip
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Finally Deci
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Old Feb 04, 2013, 06:08 PM
rip
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United States, FL, Niceville
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Spirit Electric Conversion

Finally, parts ordered !

Motor: Scorpion SII 3008-1090
ESC: Scorpion 15V 35A
Batt: ThunderPower Pro Lite G6 TP2700 3S
Prop 1: Aeronaut FOLD 10 x 6
Prop 2: Aeronaut FOLD 11 x 7

Now to live with the decisions one makes
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Old Feb 04, 2013, 06:16 PM
rip
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United States, FL, Niceville
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Thank you all

I want to sincerely thanks to everybody who posted on this thread.

You all have been very helpful.

All oppinions matter and I benefited from your expertize even the dissagreements amongst posters.

Now on to build. I'll start another thread to document the building.

Thanks.
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Old Feb 08, 2013, 06:27 AM
rip
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Static Thrust vs pitch speed

Trying to understand the relationship. Can't look at one without looking at he other.

http://dc-rc.org/pdf/Model%20Propellers%20Article.pdf

I ordered two sets of props and may order more to do some testing.

Feels like a college course. LOL
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Old Feb 09, 2013, 06:41 AM
Grow old disgracefully!
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I am not sure if that is a statement or a question , but it is certainly an interesting subject.

If you think of the prop as an “air-screw” the pitch is the distance it would theoretically screw itself forward for one revolution.
But if the prop cannot move forward, the pitch becomes the cylinder of air “screwed” backwards by the prop in one revolution.
The volume of that cylinder of air represents the static thrust, so if the pitch is increased but rpm maintained the same a greater volume of air is moved and so the static thrust increases.
Pitch speed (pitch x rpm) multiplied by prop diameter should give the volume of air moved and so relate (loosely!) to static thrust.

That is a very simple concept, but unfortunately reality intrudes and it doesn’t work quite as simple as that. That is where the formulae in your linked document come in.
The prop is not 100% efficient and so the effective pitch is different to the geometric pitch.

If you think of the prop blades as a wing and the prop blades are at too great an angle of attack they become stalled like any wing, and the lift (thrust) reduces. This “wing” will also have its best lift/drag points = max prop efficiency.

Static thrust is only of interest at the point of launch when the model is not moving. Thrust drops off as the model accelerates, and the model stops accelerating when the thrust drops to a point where it equals the drag/weight of the model.

Such a simplified version is bound to stir up some arguments .

Dick
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Old Feb 09, 2013, 07:00 AM
rip
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Thank you. I am trying to simplify things myself. However subject is not easy to simplify.

I use a program called "scorpion calc" to try to find the best prop for a given motor.
I understand that I need to make sure the Amps, the Volts and the temperature stay within the motor limits. I got that.

The trick is to estimate which one is the best prop for my application. Model designers do not write down the size prop and the rpm the prop need to be turning. I depend on experience from other modelers or trying to follow a logic based on the engine recommended in the design,

To make matters worse the program suggests a "most efficient" prop. But efficiency is measured on the most watts out for a given watts in which results in a small prop with low pitch. Of course the setting will give the longer run times for a given battery but doesn't seem the proper prop for a model.
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Old Feb 09, 2013, 07:18 AM
Grow old disgracefully!
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Trouble is most performance calculators only work for static conditions, and your models is going to move. They also concentrate on motor efficiency, which usually boils down to the higher the rpm the more efficient the motor - but what you want a prop that is efficent at your flying speed.

None of the performance calculators can claim great accuracy, but I use MotoCalc and find it gives a good general indication of performance throughout the flight at varying speeds. Unfortunately it is not free, but it is good:-
http://motocalc.com/

Dick
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Old Feb 09, 2013, 09:07 AM
Grow old disgracefully!
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Just to amuse myself, I ran some figures through MotCalc for a similar motor and battery to yours with both the 10x6 and 11x7 props. The model is an all moulded 2m, but that won’t make much difference to these results.

The first 2 pictures show how thrust falls off from the static value (at launch) as the model speeds up, and how overall efficiency (including prop efficiency) rises.
The 11x7 (pic 2) has greater thrust and ultimately gives greater overall efficiency than the 10x6 (pic 1) provided you let he model fly faster.

The third pic shows how battery amps fall and motor efficiency rises as the model speeds up, which is why static performance is not the ultimate guide (this is with the 11x7).

Dick
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Old Feb 09, 2013, 02:02 PM
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My 2 cents.

With a normal sport glider, like a Spirit, the simplest way to think of it is to basically ignore pitch speed. It simply won't go fast enough for it to be much of a factor. Generally, one wants to use the biggest prop the motor can handle and weigh everything towards static thrust. My Specter 1800 will climb like a warmliner with a 10X6, will climb like a 3D ship with an 11X4, and actually suffers a bit with a 9.5X8 even though the level speed is a bit faster.

I also got two defective 11X6 props from HK. They both had bubbles in the plastic and would be unsafe at any speed so, if you are going to try HK props, make sure to read the reviews and make sure they aren't junk.

If you want to play with low pitched props; the folks at Air Craft World seem to have the best selection. You won't hurt anything trying higher pitches within the limits of your motor but I really think that 4"-6" pitch is best for most sport gliding.

Cheers!

http://www.aircraft-world.com/shopdi...=folding+props
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Old Feb 11, 2013, 04:54 PM
rip
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United States, FL, Niceville
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Quote:
Originally Posted by peterlngh View Post
With a normal sport glider, like a Spirit, the simplest way to think of it is to basically ignore pitch speed. It simply won't go fast enough for it to be much of a factor. Generally, one wants to use the biggest prop the motor can handle and weigh everything towards static thrust.
Well that DOES simplify picking the prop huh?
Pick the prop that gives the largest static trust for the given motor.
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