prop selection...what is _x_..can we determine it manually?

Started by roby, December 13, 2013, 08:53:56 AM

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roby

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)

maahinberi

#1
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
Maahin Beri - Introduction and Hangar
Seagull Arising Star, Seagull Low Wing 40, AviSport (SPAD), Phoenix Scanner, VortexRC Speedster, Martian 220 Racing Quadcopter.

K K Iyer

@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.


roby

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 :)

maahinberi

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
Maahin Beri - Introduction and Hangar
Seagull Arising Star, Seagull Low Wing 40, AviSport (SPAD), Phoenix Scanner, VortexRC Speedster, Martian 220 Racing Quadcopter.

roby

you are right...and here are some pics and specifications of my plane

prateek13

Award | OFNA Nexx8 | Art-Tech Edge 540T | Glidiator V2 | Hawker Tempest | Cessna Citation Jet
Turnigy 9X
FPV Platforms : CF Tricopter| HK EPP FPV | Bixler 1 | Bixler 2 | DJI Phantom 2 +H3 3D

K K Iyer

Not getting any picture in reply no. 5 & 6.
Upload successful?

prateek13

Award | OFNA Nexx8 | Art-Tech Edge 540T | Glidiator V2 | Hawker Tempest | Cessna Citation Jet
Turnigy 9X
FPV Platforms : CF Tricopter| HK EPP FPV | Bixler 1 | Bixler 2 | DJI Phantom 2 +H3 3D

roby



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.

maahinberi

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
Maahin Beri - Introduction and Hangar
Seagull Arising Star, Seagull Low Wing 40, AviSport (SPAD), Phoenix Scanner, VortexRC Speedster, Martian 220 Racing Quadcopter.

utkarshg13

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
"If you were born with wings, do every thing you could, for flying."

roby


utkarshg13

"If you were born with wings, do every thing you could, for flying."

utkarshg13

"If you were born with wings, do every thing you could, for flying."

utkarshg13

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.
"If you were born with wings, do every thing you could, for flying."

roby

yes , i study there utkarsh... but right now i'm at my hometown...winter brakes :D

utkarshg13

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..
"If you were born with wings, do every thing you could, for flying."

roby

its nt true... a 4 channel radio wud cost sum 20,000 bucks,, rc things are damn expensive here.. i order them from rcbazaar

K K Iyer

@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.

roby

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?

K K Iyer

@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.

roby

got the exact specifications:
motor:
weight: 39g
KV rating:1600 rpm/V
Maximum thrust:500gms

roby


roby

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