HobbyKing.com New Products Flash Sale
Reply
Thread Tools
Old Jun 19, 2011, 03:09 AM
hul
Registered User
hul's Avatar
Switzerland
Joined Mar 2003
2,115 Posts
Quote:
Originally Posted by yomgui View Post
Here’s some pictures of what I have for an APC 10x6E, it’s very close to the one quoted “P/D = 0.6” on your graph.
how close is this to Propcalc results? http://www.drivecalc.de/PropCalc/index.html

Hans
hul is offline Find More Posts by hul
Reply With Quote
Sign up now
to remove ads between posts
Old Jun 19, 2011, 10:46 AM
Registered User
yomgui's Avatar
France, RA, Cormaranche-en-Bugey
Joined Feb 2011
563 Posts
Hans,

It is also quite close when I compare my measurement of APC 8x4E to the Taipan 8x4 in Propcalc, the two props seem similar in shape (??).
Propcalc is calculating Ct, Cp and efficiency from the prop's shape and airfoil, with good results I think. Unfortunately, I don't have any prop to compare with it.

As Jack says, the problem is that using Ct and Cp is uneasy. And I'm sure that anybody can do very well without.

On the other hand it's possible to make an excel file that do the same thing as the many calcs available, but at different speeds...

Flybrushless.com gives a huge database from where it is possible to modelize numbers of motors in an easy way.
A "light" flight modele can be set (weight,wing area...)
Batteries can be easy to modelize too.

I think that with nothing else but being able to measure amps, volts and rpm, there can be a tool that can be very useful for someone looking for high performance in a particular domain:
-max efficiency in climb near stall speed,
-max flight time,
-max speed...

I've got a "small" worksheet that can do good job, but since there's some motors data from Doctor Kiwi at flybrushless i don't know if i can make it public.
yomgui is offline Find More Posts by yomgui
Reply With Quote
Old Jun 19, 2011, 10:49 AM
hul
Registered User
hul's Avatar
Switzerland
Joined Mar 2003
2,115 Posts
you can add props to Propcalc: edit -> propeller -> new

Hans
hul is offline Find More Posts by hul
Reply With Quote
Old Jun 19, 2011, 11:28 AM
Registered User
yomgui's Avatar
France, RA, Cormaranche-en-Bugey
Joined Feb 2011
563 Posts
That's true i should do that, it would give "theoretical" strength to my data.
I've got to look closer at this.

That's a little complicated because propcalc starts from airfoil to optain prop's coeffs, what i directly measure; and need to know the prop's shape which is uneasy.

Drivecalc don't use propcalc's data (does it?), that's "dommage"!
yomgui is offline Find More Posts by yomgui
Reply With Quote
Old Jul 02, 2011, 09:00 AM
Registered User
rgoble's Avatar
Dayton Montgomery, Ohio, United States
Joined Sep 2004
259 Posts
Quote:
Originally Posted by yomgui View Post
I've got a "small" worksheet that can do good job, but since there's some motors data from Doctor Kiwi at flybrushless i don't know if i can make it public.
Most of the test data on flybrushless is from Dr Kiwi. I don't mind if you include any of the data from the site but you might want to ask Dr Kiwi also. I haven't heard from him in a while but I doubt he would mind.

If you would like, and send me the excel file I may be able to work you test data into the site somehow, but I'm not sure of where it would go. It seems like it would be part of the props data, however since you are measuring amp draw that confuses the issue some since that would be dependent on the motor. Please let me know if that's something your are interested in.

In the mean time it looks like I have a lot of reading to do

Thanks,
Robert
rgoble is offline Find More Posts by rgoble
Reply With Quote
Old Jul 02, 2011, 01:01 PM
Dieselized User
gkamysz's Avatar
Chicagoland
Joined Feb 2000
7,403 Posts
Anyone read this?

http://www.ae.illinois.edu/m-selig/props/propDB.html

Greg
gkamysz is offline Find More Posts by gkamysz
Reply With Quote
Old Jul 02, 2011, 08:11 PM
Registered User
yomgui's Avatar
France, RA, Cormaranche-en-Bugey
Joined Feb 2011
563 Posts
I'll ask the good doctor when he'll be back!

I've made all this things with the wind tunnel because at first I was wishing to build an electric 1/12 scale Yak, just like a combat warbird, even if it's nearly unknown in france, so I had maybe wrong idea about it.

Anyway, I've tried to built a tool able to compare such things as max speed, flight time, max thrust at stall speed, and of course the efficiency of the prop...
it works quite well for my well known motors... might do the same with Dr.KIWI's motor data.


Greg, thank you very much, I love you!!!

This is exactely what I was looking for!

This is from the pdf on this page (John B. Brandt and Michael S. Selig):
"proper propeller selection for UAVs can have a dramatic effect on aircraft performance"

I had doubts about my airspeed recording accuracy, seems to be justify...
I can just compare, for the moment, the APC 9x4.5 thin elec figures.
The static tests from University of Illinois where runned at 4000 up to 6900rpm, i've made it at a bit more than 9150 rpm.
The pictures below show the comparaison between University of Illinois results and mine, poor man...
Static test looks OK but I'm making a little mistake on airspeed recording so that my advance ratio and my efficiency are a bit higher.
(I've bought an e-logger with pitot tube 2 days ago, so i shoud be able to compare speed at different position in the test room, waiting for it...)

Anyway, those kind of mistake will be a problem only the day we'll all know the airspeed of our aircraft and the exact real capacity of the batterie...

A tool using those kind of results should be better used in order to compare from a known setting to another.

Sorry I'm talking, talking, talking... and it's getting late...
yomgui is offline Find More Posts by yomgui
Reply With Quote
Old Jul 03, 2011, 09:39 AM
Registered User
yomgui's Avatar
France, RA, Cormaranche-en-Bugey
Joined Feb 2011
563 Posts
This morning I compared my results with those from Greg's link to the University of Illinois, for APC 9x4.5E at different rpm.

With a correction factor of 0.78 on airspeed (that's a lot!) what I obtained is shown on the three graphs below. The little red dots shows what I measured.

I don't doubt that the guys from UIUC did a very good job in estimating airflow speed. But in a way I found their results very pessimistic. My 78 cm wingspan Yak has a recorded top speed around 115 km/h, with 6x4 running at 19,000 rpm. With an efficiency so low as what I found with airspeed correction, this means the drag is very low, almost the same aerodynamic coeffs than the original Yak-3, I can't believe this...

The pitot tube should give answer about this...

guillaume

Thanks again Greg ! now I know I'm not totally fool!!!
yomgui is offline Find More Posts by yomgui
Reply With Quote
Old Jul 03, 2011, 04:16 PM
Registered User
Fourdan's Avatar
Antony (France)
Joined Sep 2003
3,016 Posts
Quote:
Originally Posted by yomgui View Post
This morning I compared my results with those from Greg's link to the University of Illinois, for APC 9x4.5E at different rpm.

With a correction factor of 0.78 on airspeed (that's a lot!) what I obtained is shown on the three graphs below. The little red dots shows what I measured.

I don't doubt that the guys from UIUC did a very good job in estimating airflow speed. But in a way I found their results very pessimistic. My 78 cm wingspan Yak has a recorded top speed around 115 km/h, with 6x4 running at 19,000 rpm. With an efficiency so low as what I found with airspeed correction, this means the drag is very low, almost the same aerodynamic coeffs than the original Yak-3, I can't believe this...

The pitot tube should give answer about this...

guillaume

Thanks again Greg ! now I know I'm not totally fool!!!
Bonjour Guillaume
Je suggere que tu mettes les unités sur l'axe couple
I suggest torque unity indication on vertical axis
Louis (92160 Antony France)
Fourdan is offline Find More Posts by Fourdan
Reply With Quote
Old Jul 03, 2011, 05:11 PM
Registered User
yomgui's Avatar
France, RA, Cormaranche-en-Bugey
Joined Feb 2011
563 Posts
Bonjour Louis!

Sur les graphes c'est le coeff de puissance pour P = Cp*rho*n^3*D^5, sans unité.

On the graphs it is power coeff Cp for P = Cp*rho*n^3*D^5, dimensionless.

Torque = P / omega

So APC 9x4.5E at 9100 rpm:
Cp = 0.04
rho = 1.225 at sea level (1.1 at home, 900 m high)
n = 9100 rpm / 60 = 152 rps
D = 9 inch * 0.0254 = 0.2286 m

P = 0.04*1.225*152^3*0.2286^5 = 107 Watts
omega = 9100 rpm * pi / 30 = 953 rad/s

Torque = 107/953 = 0.112 N.m
Thrust = Ct *rho*n^2*D^4 so if Ct = 0.11
Thrust = 8.5 N = 865 grams
More or less of course !

Guillaume
yomgui is offline Find More Posts by yomgui
Reply With Quote
Old Jul 03, 2011, 05:26 PM
Registered User
Fourdan's Avatar
Antony (France)
Joined Sep 2003
3,016 Posts
Bonsoir Guillaume
Tout est clair Ct & Cp
All is clear
Merci
Louis
Fourdan is offline Find More Posts by Fourdan
Reply With Quote
Old Jul 24, 2011, 05:33 PM
Registered User
yomgui's Avatar
France, RA, Cormaranche-en-Bugey
Joined Feb 2011
563 Posts
Quote:
Originally Posted by rgoble View Post
Most of the test data on flybrushless is from Dr Kiwi. I don't mind if you include any of the data from the site but you might want to ask Dr Kiwi also. I haven't heard from him in a while but I doubt he would mind.

If you would like, and send me the excel file I may be able to work you test data into the site somehow, but I'm not sure of where it would go. It seems like it would be part of the props data, however since you are measuring amp draw that confuses the issue some since that would be dependent on the motor. Please let me know if that's something your are interested in.

In the mean time it looks like I have a lot of reading to do

Thanks,
Robert
Sorry for answering so late!

I couldn't find an easy and simple way to present the props data, and it needs a study of wind correction and maybe better torque measurements.
Lot of things to do!
So i've just tried to translate my "little" excel sheet in approximative english

It's a bit complicated so i wrote something about it on a .doc file.

Everything can be download here:

http://g.rouby.free.fr/tetacalc/tetacalc.rar

It's really not perfect and easy to use, i'm afraind, but it might give an idea of what i'm looking for.

BTW, this is not really a "find my setup" software...

guillaume
yomgui is offline Find More Posts by yomgui
Reply With Quote
Old Jul 25, 2011, 05:20 PM
Registered User
Fourdan's Avatar
Antony (France)
Joined Sep 2003
3,016 Posts
Hi Guillaume

Rapid look on Tetacalc

Your "loose motor quality coef" (300 to 700) is not easy.
Suggestion
Better to speak "efficiency" or something like that :

bad motor 0.6
medium motor 0.7
quality motor 0.8
HQ motor 0.9

What is your ref N2826-1350 51g ?
Louis
Fourdan is offline Find More Posts by Fourdan
Reply With Quote
Old Jul 25, 2011, 07:18 PM
Registered User
yomgui's Avatar
France, RA, Cormaranche-en-Bugey
Joined Feb 2011
563 Posts
Hi Louis,

Thank you for looking at this!

Yes you're right, this coeff is not easy, i can't really explain it . !!!

It's just : (coeff / kv˛) / weight(kg)˛ = motor armature resistance Ri

A 80% efficiency motor should have the coeff around 300, 75% efficiency ---> 550/600.

Tetaclac is not really serious because it's just my tool, so it has some maybe "extravagant" things !

The N2826-1350 is an EMP motor, so equivalent Turnigy, 0.3 mm laminations.
the "calc" is a simple math model very similar to Drivecalc I think. The basic formulation is something like that:

rpm = kv * (U - ( Ri+a.rpm.I ) ) and Pout = ( rpm/kv ) * ( I - Io[rpm] )

The "dyno" one is another model, very accurate, where:

rpm = kv[I/U] * ( U-Ri.I-L[rpm] ) and Pout = ( I*rpm/kv ) - Po[rpm]

Well, it works well at home and seems to be accurate enough.

I don't know what are exactly the math behind the other calculators, so i made mine in order to be able to use props charts like that. I think it can be interesting to have real props performance data, even if wind tunnel data are just wind tunnel data. The calc is just a tool to read the data and compare props, any motor math model should be fine.

Anyway, i love the challenge !
yomgui is offline Find More Posts by yomgui
Reply With Quote
Reply


Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Mini-Review Turbo Ace 915 V2 9g Motor with Pictures, Video, Flight Tests, and Thrust Tests Tom Z Micro Helis 96 Aug 12, 2011 08:48 PM
Wind Tunnel Smoke zagisrule! Power Systems 22 Oct 19, 2008 01:54 PM
Question Wind Tunnel for kiteboarding tests? DougE Sailplane Talk 1 Jan 16, 2008 04:42 PM
Discussion Wind Tunnel Tests Aphorism's Dream Ornithopters 0 Apr 30, 2007 12:36 PM
sources of wind tunnel pics Tim Green Modeling Science 0 Feb 10, 2003 08:29 PM