HobbyKing.com New Products Flash Sale
Reply
Thread Tools
Old Jan 28, 2008, 12:06 PM
Sure it'll work
Flyextreme's Avatar
United States, CA, Torrance
Joined Nov 2005
4,279 Posts
Question
Thrust calculator (not much luck)

I've tried the various motor calculators with out much luck. All I want to know is....about how many ozs. of thrust I should exspect from...


Eflite Power 15
950 kv
3s 2200 25c
13 x 6.5 prop.
Align 35 A ESC

This seems to be just enough to power a 40 ozs 3D plane. What is the ideal thrust for that weight?...50 60 70 80 ozs.? I think more is better...but how much more?
Flyextreme is offline Find More Posts by Flyextreme
Reply With Quote
Sign up now
to remove ads between posts
Old Jan 28, 2008, 12:25 PM
Registered User
Dr Kiwi's Avatar
Chattanooga, Tennessee, United States
Joined May 2003
27,206 Posts
According to Motocalc you get plenty of thrust, but your 35A ESC will be toast, as will your motor (since it is rated at only 34A/42A burst).

Motor: E-flite Power 15; 950rpm/V; 2A no-load; 0.03 Ohms.
Battery: Thunder Power TP2100 (ProLite) (15C); 3 series x 2 parallel cells; 2100mAh @ 3.7V; 0.018 Ohms/cell.
Speed Control: Castle Creations Phoenix 45; 0.0026 Ohms; High rate.
Drive System: Direct; 13x6.5 (Pconst=1.69; Tconst=1) direct drive.
Airframe: Anything you want.
Motor Amps = 47.4
Motor Volts = 9.7
Input (W) = 459.4
Prop RPM = 6392
Thrust (oz) = 78.7
PSpd (mph) = 39.3
Dr Kiwi is offline Find More Posts by Dr Kiwi
Reply With Quote
Old Jan 28, 2008, 02:43 PM
Sure it'll work
Flyextreme's Avatar
United States, CA, Torrance
Joined Nov 2005
4,279 Posts
When I run this set-up static...I get about 37 amps peak...it just does't seem to have the ooompf!! I thought it would have.
Flyextreme is offline Find More Posts by Flyextreme
Last edited by Flyextreme; Jan 28, 2008 at 03:22 PM.
Reply With Quote
Old Jan 28, 2008, 02:44 PM
Sure it'll work
Flyextreme's Avatar
United States, CA, Torrance
Joined Nov 2005
4,279 Posts
When I run this set-up static...I get about 37 amps peak...it just does't seem to have the ooompf!! I thought it would have. 78.7 ozs of thrust is almost 2:1...I just don't see that.
Flyextreme is offline Find More Posts by Flyextreme
Reply With Quote
Old Jan 28, 2008, 03:06 PM
Registered User
Dr Kiwi's Avatar
Chattanooga, Tennessee, United States
Joined May 2003
27,206 Posts
What voltage is your pack maintaining at that 37A? If it is dropping toward 9v then you have 330W versus the predicted 460W - that might explain it?
Dr Kiwi is offline Find More Posts by Dr Kiwi
Reply With Quote
Old Jan 29, 2008, 02:58 PM
Sure it'll work
Flyextreme's Avatar
United States, CA, Torrance
Joined Nov 2005
4,279 Posts
Quote:
Originally Posted by Dr Kiwi
What voltage is your pack maintaining at that 37A? If it is dropping toward 9v then you have 330W versus the predicted 460W - that might explain it?

New,freshly charged...starting at 12.6 volts....25c 2200 it holds pretty steady at about 35 amps.I don't for sure about the volts holding. Maybe I should go back and run some further test. The Yak I have has a huge cowl opening ( a good 6" or so) with nothing to block the prop wash. Maybe that's sucking up some of my thrust. Since then... they have started including a cowl block. I'm going to make one or buy one and see if that helps....me thinks it will


Thanks again as always Doc, Bill
Flyextreme is offline Find More Posts by Flyextreme
Reply With Quote
Old Jan 29, 2008, 03:07 PM
We want... Information!
Bruce Abbott's Avatar
Hastings, New Zealand
Joined Jan 2001
5,193 Posts
Quote:
Originally Posted by Flyextreme
40 ozs 3D plane. What is the ideal thrust for that weight?...50 60 70 80 ozs.?
You want at least 1.5:1 thrust/weight, so 60oz minimum.

According to my calculations you should be getting about 60oz, but your ESC is overloaded (it should be rated for at least 40A, 50~60A would be safer).

Motor: E-Flite Power 15 (est); 950rpm/V; 2A no-load; 0.06 Ohms.
Battery: FlightPower 2500; 3 cells; 2500mAh @ 3.7V; 0.015 Ohms/cell.
Speed Control: Align 35A; 0.005 Ohms; High rate.
Drive System: APC 'E' 13x6.5 (ba); 13x6.5 (Pconst=1.17; Tconst=1) direct drive.
Airframe: Great Planes Sukhoi SU31; 555sq.in; 39.8oz; 10.3oz/sq.ft; Cd=0.042; Cl=0.1; Clopt=0.36; Clmax=0.89.
Stats: 138 W/lb in; 99 W/lb out; 18mph stall; 28mph opt @ 70% (25:25); 52mph level; 1641ft/min @ 42; -416ft/min @ -9.8.
Conditions: Sea Level, 101.3kPa, 20C

AirSpd (mph) = 0.0
Motor Amps = 36.9
Motor Volts = 9.25
Input (W) = 341.9
Loss (W) = 96.0
MGbOut (W) = 245.9
MotGb Ef(%) = 71.9
Prop RPM = 6684
Thrust (oz) = 60.6
PSpd (mph) = 41.1
Bruce Abbott is offline Find More Posts by Bruce Abbott
Reply With Quote
Old Jan 29, 2008, 07:29 PM
Registered User
Dr Kiwi's Avatar
Chattanooga, Tennessee, United States
Joined May 2003
27,206 Posts
I used a too high prop constant, so perhaps 38A or so is closer to the truth - though I'd be scared if my packs maintain such a low voltage.
Dr Kiwi is offline Find More Posts by Dr Kiwi
Reply With Quote
Old Jan 29, 2008, 11:02 PM
Sure it'll work
Flyextreme's Avatar
United States, CA, Torrance
Joined Nov 2005
4,279 Posts
Quote:
Originally Posted by Bruce Abbott
You want at least 1.5:1 thrust/weight, so 60oz minimum.

According to my calculations you should be getting about 60oz, but your ESC is overloaded (it should be rated for at least 40A, 50~60A would be safer).

Motor: E-Flite Power 15 (est); 950rpm/V; 2A no-load; 0.06 Ohms.
Battery: FlightPower 2500; 3 cells; 2500mAh @ 3.7V; 0.015 Ohms/cell.
Speed Control: Align 35A; 0.005 Ohms; High rate.
Drive System: APC 'E' 13x6.5 (ba); 13x6.5 (Pconst=1.17; Tconst=1) direct drive.
Airframe: Great Planes Sukhoi SU31; 555sq.in; 39.8oz; 10.3oz/sq.ft; Cd=0.042; Cl=0.1; Clopt=0.36; Clmax=0.89.
Stats: 138 W/lb in; 99 W/lb out; 18mph stall; 28mph opt @ 70% (25:25); 52mph level; 1641ft/min @ 42; -416ft/min @ -9.8.
Conditions: Sea Level, 101.3kPa, 20C

AirSpd (mph) = 0.0
Motor Amps = 36.9
Motor Volts = 9.25
Input (W) = 341.9
Loss (W) = 96.0
MGbOut (W) = 245.9
MotGb Ef(%) = 71.9
Prop RPM = 6684
Thrust (oz) = 60.6
PSpd (mph) = 41.1

Mam-O-man!!! that's a mouth-full...2:1 or 80 ozs thrust would be awsome. What about a 14 x 5 prop. I am going to run some more test. I have bigger ESCs. Do you think I can get close to 80 ozs. of thrust with the Eflite Power 15 with out going to a 4s pack and putting the motor too much at risk??? It does get a lot if airflow and would not be running at WOT much. Besides, I don't want to buy new lipos...and 4s gets pricey. And do you think a lot of that thrust would be getting absorbed into such a large cowl?

Thanks, Bill
Flyextreme is offline Find More Posts by Flyextreme
Reply With Quote
Old Jan 30, 2008, 03:09 AM
We want... Information!
Bruce Abbott's Avatar
Hastings, New Zealand
Joined Jan 2001
5,193 Posts
I don't think your cowl is blocking much. static thrust is produced mostly by the tips of the blades, and the inner 6" portion of a 13" prop is probably stalled.

You can try different props, just check the current draw to make sure you're not overloading the motor (keep it below 42A). You should also measure voltage and rpm to verify that the battery and motor are 'up to snuff'.
Bruce Abbott is offline Find More Posts by Bruce Abbott
Reply With Quote
Old Jan 30, 2008, 10:43 AM
Registered User
Dr Kiwi's Avatar
Chattanooga, Tennessee, United States
Joined May 2003
27,206 Posts
I may be a conservative old fool but I think that pushing the 42A burst rating is asking for trouble... I'd be inclined to stay closer to the 34A....if you need more, just get a bigger motor which can handle the power more easily.
Dr Kiwi is offline Find More Posts by Dr Kiwi
Reply With Quote
Old Jan 30, 2008, 12:30 PM
Sure it'll work
Flyextreme's Avatar
United States, CA, Torrance
Joined Nov 2005
4,279 Posts
I ran a few more test just to see what voltage was doing...I broke my 13 x 6.5 prop. so I used a 13 x 5....It peaked at 38 amps for a few seconds....kept it at WOT...and it seemed to go down to about 9.75 volts 32 amps untill the pack warmed-up a little....then went back up to 9.85 volts and stayed pretty steady there at 33 amps. 9.85-9.9 v.Of course I had less pitch. I do not have a tach...I wasn't thinking when I sold my nitro stuff and my tach went with it. I will find some time and do some more detailed testing.

Thanks guys for all of your input, Bill
Flyextreme is offline Find More Posts by Flyextreme
Reply With Quote
Old Jan 30, 2008, 02:14 PM
Registered User
Dr Kiwi's Avatar
Chattanooga, Tennessee, United States
Joined May 2003
27,206 Posts
That pack is not really doing well is it - I would have thought a 2200mAh, 25C pack (55A capable) should maintain more than 3.3v/cell at only 33A? At least it means that the motor won't exceed its limits.
Dr Kiwi is offline Find More Posts by Dr Kiwi
Reply With Quote
Old Feb 01, 2008, 02:17 AM
Sure it'll work
Flyextreme's Avatar
United States, CA, Torrance
Joined Nov 2005
4,279 Posts
Quote:
Originally Posted by Dr Kiwi
That pack is not really doing well is it - I would have thought a 2200mAh, 25C pack (55A capable) should maintain more than 3.3v/cell at only 33A? At least it means that the motor won't exceed its limits.
I could be off some. My tests were kinda "hap-hazzered" while I was bringing unused fully charged packs down for storage. Not controlled test at all. And no record....relying on my memory (bad idea). They had been setting for 2 or 3 days and the temp. has been in 40s...that might have some bearing on it...as they seemed to come up after they warmed up some. And of course I don't want to think that brand new batts. are not up to snuff..."Come Egore back to the laboratory".
Flyextreme is offline Find More Posts by Flyextreme
Last edited by Flyextreme; Feb 01, 2008 at 02:23 AM. Reason: add on
Reply With Quote
Old Feb 01, 2008, 10:25 AM
Registered User
Dr Kiwi's Avatar
Chattanooga, Tennessee, United States
Joined May 2003
27,206 Posts
A few cycles and a warm atmosphere should certainly make things better!
Dr Kiwi is offline Find More Posts by Dr Kiwi
Reply With Quote
Reply


Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Lift (thrust) Calculator HankF Electric Heli Talk 0 Aug 27, 2003 05:15 PM
Not to much left dirtdiver Aircraft - Electric - Airplanes (FS/W) 5 Apr 16, 2003 10:28 AM
Not much info on the Ripmax F-16 DownInFlames Parkflyers 0 Mar 17, 2003 04:41 PM
Zagi 480 SI Not Much Power Javawookie Foamies (Kits) 11 Apr 26, 2002 12:37 PM
EDF thrust calculator Doc Watson Electric Ducted Fan Jet Talk 8 Mar 07, 2002 10:43 AM