Fun, Learning, Friendship and Mutual Respect START  HERE


Unregistered
Go Back   HeliFreak > R/C Batteries and Charging Support > LiIon, LiPo, NiCd & NiMh General


LiIon, LiPo, NiCd & NiMh General General Battery Support


Reply
 
LinkBack Thread Tools Display Modes
Old 03-29-2007, 08:23 AM   #1 (permalink)
Registered Users
 
Posts: 771
 

Join Date: May 2006
Default Electric: power+rpms=flight time (How long can I fly?)

Something to think about regarding the power put into a machine at the rpms some of you guys use. To increase rpms the input power increases exponentially, not linearly. For instance,.. say I fly at 2000 rpms and you fly at 2200 rpms. Many will think that's only a 10% increase, so it should take 10% more power. Many of us know this to not be true, but I've never known the "real relationship". A very smart friend of mine who is an engineering type, explained the power relationships and it's rather eye-opening. To make the above change actually requires 33% more power (1.33 times the original input power). The formula works like this,... you divide the new rpm by the old rpm, CUBE the difference, and multiply times the input power. I threw together a little spreadsheet to demonstrate, using my logo 10 setup (the one that will fly old/smooth style 3D for 9+ minutes but not the radical stuff you guys do these days). At 2000 rpms, I average 525 watts, or 28 amps on a 5S 4500 pack. The spreadsheet shows that going up to 2100 would mean 1.16 times the current input power ((2100/2000,.. which is 1.05) to the third power), which is 1.16. Going to 2200 takes 1.33 times the input, etc, etc. Flight times go down relative to current, so going from 2000 to 2100 takes me down from 9.5 to 8.2 minutes. Going to the "normal" (at least these days) 2500 rpms, would roughly half my flight time to 4.9 minutes. It can be said that the increased revs will require less pitch, which is true, but load difference from the tiny pitch change is minuscule compared to the load increase of rpms so it's virtually irrelevant.


current watts, rpm, new rpm, multiplier, new watts, cells (*3.7), capacity(mah), current, new current, flight time, new flight time

525 2000 2100 1.16 608 5 4500 28 33 9.5 8.2
525 2000 2200 1.33 699 5 4500 28 38 9.5 7.1
525 2000 2300 1.52 798 5 4500 28 43 9.5 6.3
525 2000 2400 1.73 907 5 4500 28 49 9.5 5.5
525 2000 2500 1.95 1025 5 4500 28 55 9.5 4.9
525 2000 2600 2.20 1153 5 4500 28 62 9.5 4.3
525 2000 2700 2.46 1292 5 4500 28 70 9.5 3.9
525 2000 2800 2.74 1441 5 4500 28 78 9.5 3.5
525 2000 2900 3.05 1601 5 4500 28 87 9.5 3.1
525 2000 3000 3.38 1772 5 4500 28 96 9.5 2.8

Here are the important fields, a little more readable

rpm, new, multiplier, flight time, new flight time

2000 2100 1.16 9.5 8.2
2000 2200 1.33 9.5 7.1
2000 2300 1.52 9.5 6.3
2000 2400 1.73 9.5 5.5
2000 2500 1.95 9.5 4.9
2000 2600 2.20 9.5 4.3
2000 2700 2.46 9.5 3.9
2000 2800 2.74 9.5 3.5
2000 2900 3.05 9.5 3.1
2000 3000 3.38 9.5 2.8
gwright is offline        Reply With Quote Quick reply to this message
Sponsored Links
Advertisement
 
Old 03-29-2007, 08:50 AM   #2 (permalink)
Registered Users
 
Posts: 10,980
 
My HF Map location
Join Date: Mar 2005
Default

Thanks Gary!
__________________
Dan Da Dawg - JR X9303
Hexa F550 on 3S + 6S TREX 500 + 6S TREX 600 + Blade mSR + Blade mCPx2 Brushless + 12S Rave FBL ENV
DebianDog is offline        Reply With Quote Quick reply to this message
Old 03-29-2007, 04:17 PM   #3 (permalink)
Registered Users
 

Join Date: Oct 2005
Default

Knew it wasnt linear but to see the actual figures is great, good work!
__________________
800 XXtreme, 700 Xxtreme, pimped to the max
2 x Logo 600 V-Bar, Pyro, Jive HV 90, 9451's, 9256
480 Xxtreme, Pimped, HVBK Serves, Best 500 out there!
Just gotta love that smell of electric flight :!: Align - NEVER
Klinger is offline        Reply With Quote Quick reply to this message
Old 03-30-2007, 02:09 AM   #4 (permalink)
Registered Users
 
Posts: 13,576
 

Join Date: Apr 2005
Default

NICE!!!

And this is why you want VStabi/CSM/Flybarless.. you can lower headspeed and keep cyclic rate You gain alot.
__________________
Gone fishing.. or hunting or something..
http://heli.dacsa.net
MrMel is offline        Reply With Quote Quick reply to this message
Old 03-30-2007, 02:40 AM   #5 (permalink)
Registered Users
 

Join Date: Jun 2006
Default

Great info - never thought about that.

Do you know if putting on longer blades also have the same non-linear effect on power?
__________________
Best regards
Lorents

1 x Mikado Logo 14
2 x Mikado Logo 10
Lorents is offline        Reply With Quote Quick reply to this message
Old 03-30-2007, 07:04 AM   #6 (permalink)
Registered Users
 
Posts: 771
Thread Starter Thread Starter
 

Join Date: May 2006
Default

I don't know. Longer is definately more efficient, as I've seen many times with planes (larger, slower turning props with the same input power are more efficent), but I don't know how you'd calculate any delta. Of course if you just bolt on longer blades and try to spin them the same rpms, you're just wasting a lot more power than you need to.

Hey,.. maybe we can strap 5 foot blades on a logo 10 and hover it at 10 watts per pound!! <G>
__________________
Gary Wright

Champaign Il
Helifreak user # 7001
gwright is offline        Reply With Quote Quick reply to this message
Old 03-30-2007, 09:35 PM   #7 (permalink)
BobbySmith
 

Default

Hey yea really good stuff Gary!
  Reply With Quote Quick reply to this message
Old 03-30-2007, 11:10 PM   #8 (permalink)
Registered Users
 

Join Date: May 2005
Default

> And this is why you want VStabi/CSM/Flybarless.. you can lower headspeed and
> keep cyclic rate You gain alot.

Bingo.

> Do you know if putting on longer blades also have the same non-linear effect on
> power?

I have visions in my head of a test rig for collecting data to answer these questions. The required test rig is actually rather simple. All you have to be able to measure is the torque required to spin a given set of blades at a given RPM. If you know the torque and RPM, you know the power!

The torque measurement would be independent of the drive system used so one doesn't have to worry at all about its overall efficiency. I would like to collect data for producing various amounts of lift at various headspeeds.

Now, if I could just turn those visions into action and real hardware... I'm slowly collecting blades to do the tests with (currently have Mikado wood 500, Mikado fiberglass 500, Mikado CF 500, TT CF 550, Radix 600, SAB 690 and SAB 710) and have the power system to spin any of those to sufficient headspeeds.

- John
JKos is offline        Reply With Quote Quick reply to this message
Old 03-30-2007, 11:27 PM   #9 (permalink)
Registered Users
 
Posts: 13,576
 

Join Date: Apr 2005
Default

I think its just to turn to E-airplane guys, they know this probably.
Since its exactly their way, running a prop at a certain pitch, then changing prop-size to bigger/smaller etc.
__________________
Gone fishing.. or hunting or something..
http://heli.dacsa.net
MrMel is offline        Reply With Quote Quick reply to this message
Old 03-31-2007, 09:17 AM   #10 (permalink)
Registered Users
 

Join Date: May 2005
Default

MrMel,
Yeah, we should be able to gleam some info from them. But I want to get real data for our blades. I would love to test a bunch of different blades and build graphs of the results for comparison purposes. It would apply equally to electric or nitro.

- John
JKos is offline        Reply With Quote Quick reply to this message
Old 03-31-2007, 09:20 AM   #11 (permalink)
Registered Users
 
Posts: 13,576
 

Join Date: Apr 2005
Default

Yeah it would be nice, I switched from 690 to 710 on my E-Raptor the other day, total flight-time stayed about the same, but peak watts went though the roof.


Edit: with through the roof I mean 95amps/4000 watts from my A123 batts (42C), and they still going strong.
__________________
Gone fishing.. or hunting or something..
http://heli.dacsa.net
MrMel is offline        Reply With Quote Quick reply to this message
Old 04-27-2007, 06:29 PM   #12 (permalink)
Registered Users
 
Posts: 1,371
 
My HF Map location
Join Date: Apr 2004
Default

hey , yeh! I do agree with this, great work Gary , I bet I know who your smart good friend is , Starys with a C, YEH!
__________________
Team Minicopter , and USA X-era distributor
misskimo is offline        Reply With Quote Quick reply to this message
Old 05-24-2007, 01:53 PM   #13 (permalink)
Registered Users
 
Posts: 362
 
My HF Map location
Join Date: Apr 2007
Default

Quote:
It can be said that the increased revs will require less pitch, which is true, but load difference from the tiny pitch change is minuscule compared to the load increase of rpms so it's virtually irrelevant.
Interesting and accurate numbers in theory, but I do not completely agree with the statement above. I believe the difference in pitch resulting from say a change from 3000 to 2000 rpm affects the torque, and thus power/current requirements enough to affect the numbers measurably. After all, the same amount of lift has to be generated to keep the helicopter in the air.
n808 is offline        Reply With Quote Quick reply to this message
Old 10-05-2007, 11:35 AM   #14 (permalink)
Registered Users
 

Join Date: Mar 2007
Default

I've checked my FDR stats for Trex 450 and 600. The resulting formula more looks like this:

(High rpm / Low rpm )^2 = High Amp / Low Amp

So it's a SQUARE not a CUBE relations.

Examples:

Trex 600 hovers:
at 1850 rpm with 24A
at 2000 rpm with 28A

(2000/1850)^2 = 28 / 24

Trex 450:
2950 rpm - 16A
2650 rpm - 13A

(2950/2650)^2 = 16 / 13
0636 is offline        Reply With Quote Quick reply to this message
Old 09-21-2008, 08:03 PM   #15 (permalink)
 

Join Date: Jan 2008
Default

an eagle tree logger will verify this, very interesing as losses due to ineffeciency are always there.
greg006 is offline        Reply With Quote Quick reply to this message
Old 09-21-2008, 08:05 PM   #16 (permalink)
 

Join Date: Jan 2008
Smile

forgot to mention, the new downloaded magazine from readyheli has a dyno type of set up using an eagle tree logger, this gives amazing insight of a helis performance under load
greg006 is offline        Reply With Quote Quick reply to this message
Old 11-22-2008, 06:31 AM   #17 (permalink)
Registered Users
 
Posts: 50
 

Join Date: Nov 2008
Default

great info gary
i'm trying to put it to good use so i dont mess any more lipo's up,
becomming realy good at it..
just a question to anyone realy.
how do you know / measure,, how many rpm's you are doing ???
lets say in a 6foot hover
artfulldodger is offline        Reply With Quote Quick reply to this message
Old 11-29-2008, 07:21 AM   #18 (permalink)
Registered Users
 
My HF Map location
Join Date: Apr 2004
Default

tachometer. Be sure to have a friend do it for you unless you get one of those boom mounted tachs.
conrod is offline        Reply With Quote Quick reply to this message
Old 11-30-2008, 06:39 PM   #19 (permalink)
Registered Users
 
Posts: 64
 

Join Date: Oct 2007
Default

Hello guys,

I think put on the Trex 500 esp neu 1907H/1.5Y motor + cc45HV esc and 8S lipo.

How much need capacity on the lipo and how much I`m get min per one flight?


Thanks for answer.

Evaldas

Last edited by epkencijus; 12-03-2008 at 04:39 AM..
epkencijus is offline        Reply With Quote Quick reply to this message
Old 01-16-2009, 09:15 PM   #20 (permalink)
Registered Users
 

Join Date: Jan 2009
Default

Hi Everyone,

This is my inaugural post on Helifreak, so apologies for any perceived lack of forum etiquette.

I currently have a 3 cell lipo (1000mAh weighing 88g) where one cell is puffing up after flight. Looking to replace it with a 1500mAh weighing 124g, or an 1800 weighing 145g. I understand the additional mass will add more load and therefore draw more current, but would the additional capacity account for this and the overall flight time increase?

Just trying to establish whether its worth paying the addition $ for a higher capacity LiPo when the net effect on flight time is negligable.

Any thoughts replys would be greatly appreciated.

Cheers.

HBK2, Esky3900kV, Stock everything else.
doolz is offline        Reply With Quote Quick reply to this message
Reply




Quick Reply
Message:
Options

Register Now

In order to be able to post messages on the HeliFreak forums, you must first register.
Please enter your desired user name, your REAL and WORKING email address and other required details in the form below.
User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.
Password:
Confirm Password:
Email Address
Please enter a valid email address for yourself. Use a real email address or you will not be granted access to the site. Thank you.
Email Address:
Location
Where do you live? ie: Country, State, City or General Geographic Location please.
Name and Lastname
Enter name and last name here. (This information is not shown to the general public. Optional)
Helicopter #1
Enter Helicopter #1 type and equipment.
Helicopter #2
Enter Helicopter #2 type and equipment.
Helicopter #3
Enter Helicopter #3 type and equipment.
Helicopter #4
Enter Helicopter #4 type and equipment.

Log-in


Thread Tools
Display Modes

Posting Rules
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On




Copyright © Website Acquisitions Inc. All rights reserved.
vBulletin Security provided by vBSecurity v2.2.2 (Pro) - vBulletin Mods & Addons Copyright © 2020 DragonByte Technologies Ltd.

SEO by vBSEO 3.6.1