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Old Sep 30, 2011, 06:53 AM
"The Judge"
sebbe's Avatar
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this guy with the 184mph funjet on youtube runs this:

Motor: ARC 3655-1.5
Battery: 6S1P
ESC: 100A
Prop: 7x9

@ 154Amps..

Going down one cell to 5s with the above setup, I would guess 120amps

The ARC 3655-1.5 motor is a 1850 kv motor, and the mega 40/2 is a 1595 kv.

so maybee the mega with the above setup would be 100 amps, it has lower kv..

So maybee maybee inhead calculations is right around 110-115 amps with that 7x13 propp and 5s and the mega motor..

just guessing...
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Old Sep 30, 2011, 07:44 AM
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For reference, the MEGA 16/40/1.5SE is a 1850kv motor....
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Old Sep 30, 2011, 02:33 PM
"The Judge"
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Yepp, I know, but that is to high kv... Im after 100 to 120 amps with 5s.. So I think the mega 40/2 will be fine..

what is SE ? I know C is combat = 5mm shaft.
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Old Sep 30, 2011, 02:56 PM
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X.5 winds can be terminated in two ways, R gives higher kv than S. (Gryphon: please take over from here...) The E option in a 16/xx/xx uses slightly longer rotor/magnets to lower the kv another 5% or so.
The X is a very low drag (as in efficient) model. For top speed in level flight, why have you got your mind set on 7inch props? I'm quite sure you'll find that the optimal diameter/pitch/rpm/watt will be with a smaller prop turning at higher rpm. My gut feeling leans towards a 6.5x6.5 pylon prop or maybe even smaller.
Just my 2C....
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Old Sep 30, 2011, 03:32 PM
"The Judge"
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well, it has been proven, 7" high pitch propps are the way to go, with this sized aircraft and aerodynamic, you will get the higher pitchspeed to do wunder. I think TheKid in the Escape thread did get very good results with a clipped 7x10 propp, and a few others..

You get higher pitchspeed with a 7x13 then you will ever with a 6x6 or 6.5x6.5 with the same amount of power in.. of corse you get higher thrust with a 6.5x6.5, but you dont need it. at least not with a plane this slick.

I dont have any "proof" yet, but I will get you some numbers later..

Spinning this 7x13 propp @ 20000rpm will get you same pitchspeed as a 6.5x6.5 @ 40000rpm, but the problem is to get that 6.5x6.5 propp to 40000rpm, you will need a LOT of power...

This is my ideas, I will try it, and report back later, Im not 100% sure the X plane is the best candidate, maybee this plane will be better? :

http://www.hjk-speedwings.de/epages/...oducts/PILF-X1

If I buy the PILF, it will sure be the test objekt, I think it a bit slicker then the X plane..
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Old Sep 30, 2011, 03:40 PM
"The Judge"
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ohh, thanks for the explanation on the windings, hehe, got a little carried away with my dreams...
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Old Sep 30, 2011, 03:41 PM
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Okay: thrust comes from diameter and pitch speed comes from prop pitch x rpm, right? The PILF you refer to is a F5D racer. You should rather compare the X-Plane to the T-1.
Please go ahead and prove me wrong, but I think you're comparing apples and bananas here.
(The T-1:
PILF - T1 Hotliner 27.06.2011.MTS (2 min 11 sec)
)
Btw: removed from their shop!!! It seemed sooooo promising!
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Old Sep 30, 2011, 03:53 PM
"The Judge"
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HJK-Speedwings Monster Testflug (2 min 54 sec)


this is a bigger model, running a 7x10 propp, with a slight slimmer model like the PILF I think the 7x13 propp with that extra pitchspeed will be perfect..

If you want a model to go 400km/h, it is almost impossible to get that speed straight and level with apc/graupner speed propps like 5x5, 6x6 or 6.5x6.5, these square propps need tons of power to reach 400km/h in pitchspeed, thats why you have to go up in diameter and much more in pitch.. Look at the guys in German speedcup, you dont see sqaure propps there..

I would love to get my hand on a 10x25 propp, this one would be insane with the motor and gearbox we have in our xplanes..

The fastest a sqaure propp (like above ) will go in a F5D or a Pylon is around 350km/h, over that you have to think the way I do now....

I am pretty sure I will reach higher speeds with my 7x13 propp then I would with a 6.5x6.5 propp ( given the same amount of power in)
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Old Sep 30, 2011, 03:59 PM
"The Judge"
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I wasnt sure the X plane would by the one for my project, I dont know how fast the Xplane is,,,, what I meant was, I am going to try reaching fast speeds up to 400km/h level flight with a plane that is fast AND a 7x13 propp..

If that fast plane will be the PILF or the Xplane, I dont know yet..
But that doesent matter, what matters is that I will prove that a 7x13 propp will get a "fast and slimm plane" faster then a square speedpropp with the same power in..

Maybee I am wrong ? we will see..
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Old Sep 30, 2011, 04:02 PM
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With a slimmer model you can exchange prop diameter for more pitch speed at the same level of watts and rpm... This is the point I'm trying to make!!
Our dilemma here: there aren't any over-cubic 6" props around....
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Old Sep 30, 2011, 04:10 PM
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Sebbe,

You think you will have enough pitch speed (400 KPH) let alone actual flight speed?

20,200 RPM is what I calculate you need for prop pitch speed to get to 400(you need even more for flight)...I doubt you can get that many RPM....I have not gone through the numbers.


Assume 70%-75% KV under HIGH load......Just rough numbers for you to play with.

I have to log off.

I still think you should find out which prop draws similar static numbers to your custom prop at around the 20,000 RPM range and then ask for some of the friends to do a test for you. That gets you a fair idea before motor purchase.
Can the guy who made the prop give you an equivalent prop "LOAD" recommendation?


p.s. Arctery did a good job of explaining C, E.


Gryphon
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Old Sep 30, 2011, 04:13 PM
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Quote:
Originally Posted by sebbe View Post
But that doesent matter, what matters is that I will prove that a 7x13 propp will get a "fast and slimm plane" faster then a square speedpropp with the same power in..

Maybee I am wrong ? we will see..
For this endeavor, I would choose an airframe with the capacity to run a larger motor, supersize ESC and the capacity to carry VERY LARGE LiPos. I don't think the German SpeedCup planes are built the way they are by accident...

The HJK Monster might be the one that's most obtainable to us non-Germans (or build a NinjaSpeed), but I would sure pay a huge stack of silver for a FluxKomPenSator, Chimera or the EisVogel
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Old Sep 30, 2011, 04:20 PM
"The Judge"
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Gryphon,,,You are right, I have to compare my propp (7x13), lets say with a 8x8, or a 9x7, and see wich one draws the same amount of power, then I can ask, BUT I think the numbers in flight would differ a lot with the 7x13 propp compared to "normal" propps..

Maybee same German speed guy can give me some numbers with this 7x13 propp, like watts and rpm in flight would be sweet

Gryphon, just do a calc with a 6x6 propp and see how many watts you need to get over 400km/h pitchspeed, this way I can compare with my 7x13 propp, when I have tested it..
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Old Sep 30, 2011, 04:27 PM
"The Judge"
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Quote:
Originally Posted by Arcteryxxx View Post
For this endeavor, I would choose an airframe with the capacity to run a larger motor, supersize ESC and the capacity to carry VERY LARGE LiPos. I don't think the German SpeedCup planes are built the way they are by accident...

The HJK Monster might be the one that's most obtainable to us non-Germans (or build a NinjaSpeed), but I would sure pay a huge stack of silver for a FluxKomPenSator, Chimera or the EisVogel
I know those planes are more suited for the job....

But I will see how fast I can get an airframe like the PILF or Xplane with a 7x13 propp, I know my limitation is 2-2.5kw with a 5s setup, but thats with the Mega 40/2, If I can find a motor that I can push to 3kw in short burstes like 5-7 seconds, then I think 400km/h is broken..

the problem is: 28mm inrunner and a kv value of 1700-1800 will not be easy to find that will take 150 amps with 5s lipo..

maybee I should go for a 36mm inrunner, I can cut the nose of the Xplane ..... hmmm..
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Old Sep 30, 2011, 04:37 PM
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The laws of physics will be your constraints anyhow, although even Einstein is challenged these days
Look for battery capacity, ESC and motor efficiency and decide on prop and the necessity of custom made components as you thoroughly document your findings along the way.
The Stryker speed record (Murdnunoc) at 204mph average was achieved by doing things scientifically.. You will never stumble upon a world record by accident. There are too many bright guys in this hobby to make that possible....
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