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General Topics => RC General Topics => Topic started by: roby on December 13, 2013, 08:53:56 AM



Title: prop selection...what is _x_..can we determine it manually?
Post by: roby on December 13, 2013, 08:53:56 AM
also please suggest me a substitute of these props at rcbazaar, 9x10.. i couldn't find 1
and can any prop work well (of nearbout same sizes)


Title: Re: prop selection...what is _x_..can we determine it manually?
Post by: maahinberi on December 13, 2013, 09:51:56 AM
What is the wingspan and weight of your plane? Also, what motor are you using?
P.S.
The first number in the prop is the diameter of the prop.
The second number is the pitch.(Both in inches)

The diameter is self explanatory.
The pitch is the number of inches the prop will move forward for one full rotation of the prop.

The pitch does not affect static thrust too much but comes into play when the plane is moving. Generally, the more the pitch, the faster your plane will go.

You can use the following to calculate how a particular size prop will behave:
http://www.ecalc.ch/motorcalc.htm

10 seems too high a pitch. Ideally, any 9inch (diameter) prop should work but it depends on the weight of your model and the motor that you have


Title: Re: prop selection...what is _x_..can we determine it manually?
Post by: K K Iyer on December 13, 2013, 11:37:29 AM
@roby
In almost all cases the pitch for general purpose models will be 50-75% of the diameter (except speed models). Eg, 9x5, 9x6, 8x4, 8x6.
Suppose your motor is able to turn a 6 inch pitch prop at 6000 rpm.
This is 100 revs per sec. So a 6 inch pitch prop will move forward 50 ft/sec.
This about 55 kmph or 35 mph.
(We are ignoring slip and unloading for the moment)
However the model can reach this speed only if the motor has enough POWER to produce the required THRUST.
Power depends on your motor's rated max wattage. A thumb rule for this is 50 watts per pound of model weight (or 110 watts per kg) for a trainer.
Thrust depends on prop dia. Starting point is 1.5 times the pitch. Thumb rule is 3 to 5 gms per watt.
Thumb rule for required thrust is minimum 1/3rd of model weight for level flight.
Suppose your model weighs 500 gms.
It will need about 250 gms thrust for safe climb.
This will need 50 to 60 watts depending on prop efficiency (ie, ability to convert power into thrust)

If you are a beginner, you will probably not have a wattmeter, tachometer, electronic weighing scale, different props to try, or a means of measuring thrust.

A simpler option is to look at the specs of models (similar to yours) on the site of Hobbyking, RcBazaar etc. Use a similar setup of battery, Esc, motor and prop.

Best option for initial success is to go flying with others in Delhi, and then get a beginners ARF trainer model.
Best of luck.



Title: Re: prop selection...what is _x_..can we determine it manually?
Post by: roby on December 13, 2013, 11:49:09 AM
my wingspan is 1 meter and motor specifications: emax 2822, 11.1v, ideal with propellor 9"-10"
esc 20amp
so what do u suggest?

thank you maahinberi and kk sir :)


Title: Re:
Post by: maahinberi on December 13, 2013, 11:50:18 AM
Roby, I believe your plane is a scratch build, am I right? People would be able to help you out better if you post th specifications of your plane (weight, wingspan, pictures), ESC, battery and motor


Title: Re: prop selection...what is _x_..can we determine it manually?
Post by: roby on December 13, 2013, 11:56:06 AM
you are right...and here are some pics and specifications of my plane


Title: Re: prop selection...what is _x_..can we determine it manually?
Post by: prateek13 on December 13, 2013, 12:07:45 PM
Hope this helps you :
http://www.youtube.com/watch?v=dPOG8PM6nMM


Title: Re: prop selection...what is _x_..can we determine it manually?
Post by: K K Iyer on December 13, 2013, 12:26:11 PM
Not getting any picture in reply no. 5 & 6.
Upload successful?


Title: Re: prop selection...what is _x_..can we determine it manually?
Post by: prateek13 on December 13, 2013, 01:30:15 PM
My video can be seen
Reply #5- no media


Title: Re: prop selection...what is _x_..can we determine it manually?
Post by: roby on December 13, 2013, 01:44:09 PM
http://youtu.be/JES8ePi39TE

these are pics..i was not able to upload pics ...they were more than 200kb... so i combined pics and uploaded them in youtube.. please check them and suggest changes if necessary.


Title: Re: prop selection...what is _x_..can we determine it manually?
Post by: maahinberi on December 13, 2013, 01:51:12 PM
Can you give the size and kv rating of the motor, as well as the current rating on the esc and the battery that you are using. Again, wingspan and weight of the plane(including all electronics) would be helpful


Title: Re: prop selection...what is _x_..can we determine it manually?
Post by: utkarshg13 on December 13, 2013, 02:36:44 PM
You could go for following props with that plane. i had flew with almost every prop of similar size with that plane.
http://www.rcdhamaka.com/index.php?main_page=product_info&cPath=3_48_80&products_id=754
or check these websites. I hope you will find what you need on these:
www.rc4all.co.in, edallhobby, rcelectro, rcbharat


Title: Re: prop selection...what is _x_..can we determine it manually?
Post by: roby on December 13, 2013, 04:04:10 PM
cf2822 11.1v  kv rating and max current is not given


Title: Re: prop selection...what is _x_..can we determine it manually?
Post by: utkarshg13 on December 13, 2013, 04:14:41 PM
The motor given is EMAX CF2822 1200KV. Another link for your propeller demand is:
http://www.rcelectro.com/rc-products/Propellers


Title: Re: prop selection...what is _x_..can we determine it manually?
Post by: utkarshg13 on December 13, 2013, 04:15:11 PM
you live in delhi?


Title: Re: prop selection...what is _x_..can we determine it manually?
Post by: utkarshg13 on December 13, 2013, 04:17:34 PM
The recommended prop size for this motor is 9"X6". Max. current rating is 40A.  So, any prop which is somewhat close to this could be used.


Title: Re: prop selection...what is _x_..can we determine it manually?
Post by: roby on December 13, 2013, 04:47:40 PM
yes , i study there utkarsh... but right now i'm at my hometown...winter brakes :D


Title: Re: prop selection...what is _x_..can we determine it manually?
Post by: utkarshg13 on December 13, 2013, 04:56:47 PM
ooohh. Actually i needed a propeller balancer and a helping hand tool. someone told me it is available in delhi for low price.... damn expensive on Hobbyking..


Title: Re: prop selection...what is _x_..can we determine it manually?
Post by: roby on December 13, 2013, 05:18:36 PM
its nt true... a 4 channel radio wud cost sum 20,000 bucks,, rc things are damn expensive here.. i order them from rcbazaar


Title: Re: prop selection...what is _x_..can we determine it manually?
Post by: K K Iyer on December 13, 2013, 05:41:09 PM
@roby
40 amps?
Seriously doubt it. At 11v it means 440w, or over 1/2 hp.
It will burn if loaded so high.
The Esc will also burn, as yours is probably rated for 20 amps.
Different sources quote different specs for this motor.
I think it will only take 10-12 amps.
With 3s lipo, i suggest 8x4 prop.
With 2s try 9x5 or 9x6.
Don't use a 10x4.7 or higher with 3s.

Tell us where you are, or locate flyers near you by searching on this forum.
STRONGLY RECOMMEND showing your model to an experienced modeller.
There are potential problems waiting to catch you unawares (Eg, lack of dihedral, control horns located far from (instead of close to) hinge lines, bulky structure on top of fuselage (what is it, a cabin?), whether CG position is correct or not etc)

The above is intended to give your model every chance to survive its test flight, and not to discourage you.
Don't rush it, take your time.
Best of luck.


Title: Re: prop selection...what is _x_..can we determine it manually?
Post by: roby on December 13, 2013, 06:54:32 PM
this was what i was thinking @kk sir.
it is 20 amps and the last flight was smooth enough..
But its not safe to use this configuration again right?


Title: Re: prop selection...what is _x_..can we determine it manually?
Post by: K K Iyer on December 13, 2013, 07:29:31 PM
@roby
So you flew it? Congrats!
Hope you took a video.
What prop did you use finally? And 2s or 3s lipo?
If the Esc and/or motor hot, reduce the prop size/pitch.


Title: Re: prop selection...what is _x_..can we determine it manually?
Post by: roby on December 13, 2013, 07:52:59 PM
got the exact specifications:
motor:
weight: 39g
KV rating:1600 rpm/V
Maximum thrust:500gms


Title: Re: prop selection...what is _x_..can we determine it manually?
Post by: roby on December 13, 2013, 07:54:06 PM
esc:
Weight-21g
Constant current-20 A


Title: Re: prop selection...what is _x_..can we determine it manually?
Post by: roby on December 13, 2013, 07:56:35 PM
servo:
Torque1.2kg/cm@4.8v, 1.4kg/cm@ 6V
Weight- 10g
Speed- 0.10/60deg @4.8v, 0.09/60deg @ 6v
Voltage- 4.8v-6v


Title: Re: prop selection...what is _x_..can we determine it manually?
Post by: roby on December 13, 2013, 08:00:13 PM
and the battery is the only section in which i did not follow my theoretical notes

required battery
3 cell Lipo battery
11.1v
max capacity- 1300-2000 mah
weight-120g

but i used 1250mah...slightly lower than required..
hope this will work fine in future


Title: Re: prop selection...what is _x_..can we determine it manually?
Post by: roby on December 13, 2013, 08:03:02 PM
please read all my five posts of my configuration and suggest any changes if necessery.
your ideas will be greatly appreciated.


Title: Re: prop selection...what is _x_..can we determine it manually?
Post by: K K Iyer on December 13, 2013, 08:43:04 PM
@roby
You did not say what prop you used.
See this. From emaxmodel.com
http://www.emaxmodel.com/pic/201101/28164550.jpg

A few suggestions from an old timer, if you don't mind:
- Avoid sms language (it is against forum rules)
- try to give all info in one post, not piecemeal. Don't expect your readers to hunt up and down.


Title: Re: prop selection...what is _x_..can we determine it manually?
Post by: roby on December 13, 2013, 10:30:09 PM
thanks for your advice sir, i'll keep that in mind. I'm a beginner and learning from you all :)
the propellor is 9" or 10" theoretically...the thing is i don't know how to measure it


Title: Re: prop selection...what is _x_..can we determine it manually?
Post by: K K Iyer on December 13, 2013, 10:42:41 PM
Just measure from tip to tip (dia)
Look closely at the hub and on the front of the blade near the hub. Usually something will be printed/embossed there. Like 9060, 1047 etc.