News:



  • March 28, 2024, 09:05:57 AM

Login with username, password and session length

Author Topic: Cobra 3520/14 ideal propeller  (Read 1930 times)

Offline Guilherme Souza

  • Trade Count: (0)
  • Lieutenant
  • ***
  • Posts: 108
Cobra 3520/14 ideal propeller
« on: June 28, 2018, 01:39:06 PM »
Dear ALL

I use Cobra 3520/14 motor , Fiorotti Active  timer and Zippy compact 2700 5S 35 C .
My plane is Chupin and heavy plane 2050gr , 72 Oz

I m using a tri Blade propeller 12x5
But I'm using a Lot of battery. Almost 2000 mha per flight .

Which propeller do you think is better?

cobra 3520/14 like's high RPM or Low RPM ?

The only ( and last) choice os reduce the lines , to increase lap time and save battery. Today is 18,87 meters , 61,9 foot

Thank you

Guil


Enviado de meu Moto Z (2) usando o Tapatalk


Offline William DeMauro

  • 21 supporter
  • Trade Count: (0)
  • Captain
  • *
  • Posts: 796
Re: Cobra 3520/14 ideal propeller
« Reply #1 on: June 28, 2018, 02:57:45 PM »
What you probably need is more battery. I’m running a similar setup on a 6s battery and using 1950 out of a 2800 thunderpower on about 65’ of lines at around 65-66 oz
AMA 98010

Offline Tim Wescott

  • 2016 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 12804
Re: Cobra 3520/14 ideal propeller
« Reply #2 on: June 28, 2018, 03:04:51 PM »
Rule of thumb is 0.7 W-h/oz (watt-hour per ounce) for a 6-minute flight, with a steady-speed timer.  I can't answer to the Fioretti timer, but the Igor timer uses more than a steady-speed setup.  That rule of thumb predicts 51W-h.  You're using 41W-h.  So you're already running much lower than expected.

Run more battery.
AMA 64232

The problem with electric is that once you get the smoke generator and sound system installed, the plane is too heavy.

Offline Guilherme Souza

  • Trade Count: (0)
  • Lieutenant
  • ***
  • Posts: 108
Re: Cobra 3520/14 ideal propeller
« Reply #3 on: June 28, 2018, 03:19:07 PM »
Rule of thumb is 0.7 W-h/oz (watt-hour per ounce) for a 6-minute flight, with a steady-speed timer.  I can't answer to the Fioretti timer, but the Igor timer uses more than a steady-speed setup.  That rule of thumb predicts 51W-h.  You're using 41W-h.  So you're already running much lower than expected.

Run more battery.
Hi Tim

When do you say run more battery what It means?
Do I need to change to a bigger battery?
The problem is that I cant change the battery .
I need to change the propeller ir the lines

Thank you

Enviado de meu Moto Z (2) usando o Tapatalk


Offline Joseph Daly

  • 2016 supporter
  • Trade Count: (0)
  • Commander
  • *
  • Posts: 253
Re: Cobra 3520/14 ideal propeller
« Reply #4 on: June 28, 2018, 04:13:22 PM »
What prop are you running?

Offline Guilherme Souza

  • Trade Count: (0)
  • Lieutenant
  • ***
  • Posts: 108
Re: Cobra 3520/14 ideal propeller
« Reply #5 on: June 28, 2018, 04:15:39 PM »
What prop are you running?
Hello Joseph

I m using 12x5 tri Blade Igor style carbon prop.

Thank you


Enviado de meu Moto Z (2) usando o Tapatalk


Offline Joseph Daly

  • 2016 supporter
  • Trade Count: (0)
  • Commander
  • *
  • Posts: 253
Re: Cobra 3520/14 ideal propeller
« Reply #6 on: June 28, 2018, 04:27:29 PM »
Which Igor 12x5? He has 2. If your running the 12x5uct prop, go to the 12x5n prop. It will use less battery. Believe or not you can even get away with running his 11x5 prop. Which will you less battery also.
Hope this helps

Offline Guilherme Souza

  • Trade Count: (0)
  • Lieutenant
  • ***
  • Posts: 108
Re: Cobra 3520/14 ideal propeller
« Reply #7 on: June 28, 2018, 04:48:39 PM »
Which Igor 12x5? He has 2. If your running the 12x5uct prop, go to the 12x5n prop. It will use less battery. Believe or not you can even get away with running his 11x5 prop. Which will you less battery also.
Hope this helps
Joseph

I'm not using original Igor prop .

My plane is very heavy and my battery is chinese .
I dont know If Cobra motor Works better with high RPM or Low .
I Will try 13,5x 5.5 wood prop tomorow.
Thank you


Enviado de meu Moto Z (2) usando o Tapatalk


Offline Joseph Daly

  • 2016 supporter
  • Trade Count: (0)
  • Commander
  • *
  • Posts: 253
Re: Cobra 3520/14 ideal propeller
« Reply #8 on: June 28, 2018, 06:16:51 PM »
If you go to 2 bladed prop, you should use less battery. For the weight and size of plane a 5s 2800 are on the smaller size.

Offline jose modesto

  • 22 supporter
  • Trade Count: (0)
  • Captain
  • *
  • Posts: 842
Re: Cobra 3520/14 ideal propeller
« Reply #9 on: June 29, 2018, 05:31:19 AM »
Following Joe’s recommendation, try the yatzenco 13.4 x6.3 two blade wood prop
They are light and low low pitch.
 You can reduce your RPM to the mid 7,000

I used the prop listed with same weight model with the TP 5s 2800
My model is 71 oz 880 si thick airfoil
Jose modesto

Offline Vitalis Pilkionis

  • Trade Count: (0)
  • Commander
  • ****
  • Posts: 145
Re: Cobra 3520/14 ideal propeller
« Reply #10 on: June 29, 2018, 06:53:05 AM »
If you don't use Igor's 12x5N 3B prop, which weights 18 grams and therefore provides with extremely low forces of gyroscopic precession, then you don't have to bother about 5" pitched props either, because the motor you use most likely has self oscillated vibrations at other rpm range than axi 2826. I have noticed myself that higher pitched props provides me with much better mah economy.
2 bladed props certainly should increase mah economy even further, but that may shorten electric motor bearings life.
I also think that 2000 mah consumption for a complete stunt flight is perfectly fine, unless you made a mistake. In my opinion a 5S battery with 2700 mah is a bit too small in capacity for 2kg ship, I'd recommend to go for 3000mah or try 6S.

Vitalis

Offline Guilherme Souza

  • Trade Count: (0)
  • Lieutenant
  • ***
  • Posts: 108
Re: Cobra 3520/14 ideal propeller
« Reply #11 on: June 29, 2018, 07:10:40 AM »
If you don't use Igor's 12x5N 3B prop, which weights 18 grams and therefore provides with extremely low forces of gyroscopic precession, then you don't have to bother about 5" pitched props either, because the motor you use most likely has self oscillated vibrations at other rpm range than axi 2826. I have noticed myself that higher pitched props provides me with much better mah economy.
2 bladed props certainly should increase mah economy even further, but that may shorten electric motor bearings life.
I also think that 2000 mah consumption for a complete stunt flight is perfectly fine, unless you made a mistake. In my opinion a 5S battery with 2700 mah is a bit too small in capacity for 2kg ship, I'd recommend to go for 3000mah or try 6S.

Vitalis
Thank you Vitalis

Unfortunally here in Brazil is Very difficult to find batterys
Thunder Power is almost Impossible here for us each one is 120 US dollars with ALL taxes.
Somepeople travel and bring this batterys to fly or to sell but it is very expensive.
I'm doing I 6S 2700 with my old batterys, I really want to try .

I Will do some test with 2 Blade props and hight pith ( I have 14x6 , 13x6 and 13,5x5.9)

But I have more one problem with 2 Blade props the plane increase speed in the Pattern .

I Will do the tests and show the resulta

Thank you
Guil

Enviado de meu Moto Z (2) usando o Tapatalk


Offline Guilherme Souza

  • Trade Count: (0)
  • Lieutenant
  • ***
  • Posts: 108
Re: Cobra 3520/14 ideal propeller
« Reply #12 on: June 29, 2018, 08:25:37 AM »
You could always build a smaller lighter plane.
Yes you até right , but is not possible now.
My buildind skills are not só good.
I Will buy a composite plane soon .

Thank you



Enviado de meu Moto Z (2) usando o Tapatalk


Offline Guilherme Souza

  • Trade Count: (0)
  • Lieutenant
  • ***
  • Posts: 108
Re: Cobra 3520/14 ideal propeller
« Reply #13 on: July 01, 2018, 03:47:48 PM »
Dear All

Thank you for ideas
Today I did a lot of flights trying different props
The first I used was a 13.4x5.9 wood prop , very good one flight of t2 minutes and OK
I change the battery and did a full pattern flight , very good and  in the cellmeter showing 18 %
I try 13x6 carbon and wonderfull , In the second flight I change some parameters in JetBox to make the plane get slower when nose down
It worked very well
and in the end of flight in cell meter 22 % of battery
I charge this same battery to check again and in the charger show 1600 mha , this is very good because with tri blade prop I used 1950 mha
Now I'm satisfied with the results .
I know that a 3 blade prop is better , but to save my battery's I will use 2 blade prop .

Thank you for all help

Guil

Offline Fred Underwood

  • Trade Count: (0)
  • Captain
  • *****
  • Posts: 807
Re: Cobra 3520/14 ideal propeller
« Reply #14 on: July 01, 2018, 04:20:50 PM »
Some of the cell meters lose accuracy especially in the % function. 

% remaining isn't a very firm value to begin with.  From my reading, the % remaining is related to the cell voltage and calculated off of an algorithm or known curve.  There are more than one set of values/curves and they don't always agree. 

A friend with low % remaining (18-19%) said that his replacement mah was about 1650.  That doesn't make sense.  Even my well used Zippy batteries have 2500 mah.  If I use 1650 mah by replacement, I should have about 33% remaining.  Interesting that when I put the pack on my Powerlab 6 after a flight, he had about 33% remaining, and his meter said 18%.  Of course either my charger and/or his meter could be wrong, but the % remaining or % used should agree with what is in a full pack meaning a % of 2500 - 2800 mah depending on the age and use of the pack.  Try a friends meter, or depend on mah refilled/estimated full pack mah for the actual % used.

For reference, I will have about 20% remaining at 3.75V at the end of a flight with several minutes rest, and that % is falling fast below that voltage.

Hope that makes sense and helps.
Fred
352575


Advertise Here
Tags:
 


Advertise Here