RC India

I am a little confused about the 2 special offers. They are centred around the 2812 and 2822 motors. If I am to use these on a depron aircraft which will be under 250 grams (inclusive of Rx, Servos, Motor and prop but excluding battery), which combination should I go in for?

Also, doesn't the 9X6 prop provide for higher speeds as compared to the 7X4?

Pl advise.

Regards,

VC

I am taking this query as a 'Teaser' from VC as I am sure he would already know what I am sharing with you.

CF 2822 - 1200Kv, max 150W
CF 2812 - 1600Kv , max 135W

Though the Kv are not significantly different, both of these motors are apt for 3D/Trainer Gliders and Sports/ moderately slower Jets (@2200kv more apt for Jet) receptively with different Lipos Cell counts. This may not be a thumb rule, as people have always successfully experimented diverse Kv for different planes types.

1. The over all pitch speed depends on i)The actual pitch of the prop ii) the sustainable Kv of the motor for prescribed Max prop dia  iii)Type/planform of the prop like Slow flyer/ Sports (DD/RD).  The Sustainability of the Kv comes in the picture because if you increase the dia of the prop beyond the capability of the motor, the motor would eat too much amp (danger!!) and the achieved Kv would reduce. Compare this to your domestic electricity (esp in small towns) as you put more load (switch on Geyser/Ac), the voltage drops.

2. The diameter of the Prop determines how big Plane (WS/weight) you can use on. There are some implications of the Wing Span on the biggest Prop Dia that can be used, due to torque effect generated.


9x6 has a 6" pitch and 7x4 has a 4" pitch. So 7x4 is more apt for higher Kv motor applications like sports/jet, keeping the Dia not in consideration as that is mostly governed by the 'AMP' capability (and this Wattage) of the actual motor in question.

Say you need X Oz of thrust. To achieve that, your power system must displace Y volume of Air at STP.  So a 9x6 prop may  rotate slowly and achieve that, but your 7x4 has to spin at much faster Kv (thus actual pitch speed and fater moving plane) to displace same amount to air volume, and produce thrust due Newton's 3rd law of motion.

I have given a link for the CF 2822 static test result in RCDhamaka's original post . Below is for CF 2812. Please follow these as reference and before you put it on the plane, do your own static test as well on the actual motor sample you get.

http://www.headsuprc.com/servlet/the-1529/EMAX-CF2812-Outrunner-Brushless/Detail
 
Notwithstanding the Kv difference, the 2822 has better scores over its cousin 2812.

PS: Both these beauties are little overkill for a 250g AUW foamy. Consider 20-25g C10/C20 motors instead.

"Both these beauties are little overkill for a 250g AUW foamy."

In that case, what AUW would be a good match for the 2822 combo?

Thanks for all the info.

Regards,

VC

Both the motors can pull a model in the range 400-660+ grams. I am putting the 2822 in a 450g AUW 34" WS 3DBatix Extra 330.

Hello sir,,,,,,,,,,sneha here,,,,,I agree with you..........Thanks lot......

wow and it took 8 months for you to agree... kiddin :)

This weekend I used CF 2812 - 1600 with a 8x4 prop, Was able to fly cessna (510g). Was a bit under powered I think as I used almost 3/4th of throttle always. The motor/Esc was not even warm, but the spec says it gives more than 700gm thrust with 8x4 prop, but I couldnt feel that. (May be because of the wide nose I have for Cessna, vikas might have seen that  :giggle:)

Wide is an understatement :D Too bad we couldn see it fly. :(

sneha i can't understand that you live in Delhi or UP?

city:delhi
state:uttar pradesh

??? ??? ???
 :giggle: :giggle: :giggle: :giggle: ;D ;D

:) Send me sms on weekends if there are plans to fly, I read the posts after returning from flying.

Hello sir,,,,,sneha here,,,,,I lived in Delhi but belong from UP,,,,,,,Now, I edit my profile may in future there is no problem ,,,,,,,,,,,Thanks for suggest me.........

I am sorry to say Sneha but are you really interested in RC or just looking for free hits to the links in your signature., Anwar please take care of it.

Took care of that ;)  Good bye Sneha !

Eagle eyed vikas. :) Good one.