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Sep 16, 2020, 02:42 AM
looking up, down under
scruffy1's Avatar
Quote:
Originally Posted by slam555
no I only know this from what I did
just out of interest, do you use a wattsup meter or other to find how much power you are drawing, or do you just "wing it" (as it were) ?

not disputing your experience, just wondering on the details... my faith in science needs measurements to support a claim

the biggest asset of a bigger esc is likely heat dissipation, which would make it more reliable in delivering stated draw a poorly ventilated setting
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Sep 16, 2020, 02:36 PM
Registered User
I'm sorry to say I've just been wing'n it, I should get a watt meter, as I get deeper into the electrics, but as to say for right now I can calculate and figure the right motor and esc , and battery for my models
Sep 16, 2020, 04:22 PM
Registered User
Dickeroo's Avatar

Small KFm2 Drone on long and stable flight.


Just spotted this video of a small lightweight drone with a KFm2 airfoil flying out over a lake on a long ride. If you notice the young manís shirt, he has a silhouette on it of a KFm3 airfoil. The video is stable and steady with beautiful views of the surroundings.

Tiny Waypoint Drone! - 230g Autonomous Wing (15 min 31 sec)
Sep 16, 2020, 04:57 PM
Careful,.. confident,.. CRASH!
Dukejet's Avatar
Awesome!.. baby's face! Hahahah
Sep 19, 2020, 03:26 AM
flyin' fool
goldguy's Avatar
When you refer to power, exactly what do you mean?

A watt meter shows 'watts in' ........................ https://www.rcgroups.com/forums/show...6&postcount=28

It's the thrust that flies the model and how much power at the prop or 'watts out' can be measured. But, what we as modelers are interested in is not frying any of the components by installing the wrong prop, ESC or battery voltage. If your gaining more power by simply changing the ESC to a bigger one, then something else is not correct in your setup.
Last edited by goldguy; Sep 19, 2020 at 03:42 AM.
Sep 24, 2020, 09:01 AM
Jack
jackerbes's Avatar
Thread OP
Quote:
Originally Posted by goldguy
When you refer to power, exactly what do you mean?

A watt meter shows 'watts in' ........................ https://www.rcgroups.com/forums/show...6&postcount=28

It's the thrust that flies the model and how much power at the prop or 'watts out' can be measured. But, what we as modelers are interested in is not frying any of the components by installing the wrong prop, ESC or battery voltage. If your gaining more power by simply changing the ESC to a bigger one, then something else is not correct in your setup.
To me, if there is one thing that is a constant variable in a power system, it is the thrust a propeller produces at a given RPM and the power in Watts that is needed to get the prop to that RPM. If you go to place that has a lot of prop testing data like this one:

https://www.flybrushless.com/prop/search

And look at a given propeller you will see that as long as a motor has the size and Kv to attain a given RPM the input power will be very nearly the same with all motors. As an example I will choose a much used prop, the APC 10 x 4.7 Slow Fly prop (listed as the APC SF 10x4.7) and look at the 100 0r more different motors that prop was tested on you can see what I mean about the constant nature of the input power at a given RPM.

APC SF 10x4.7 test data - http://www.flybrushless.com/prop/view/39

Pick about the same RPM for any motor and you'll see the input power is about the same. At about 5000 RPM I see values of 58. 52. 63. and 60 for an average of 58.25 Watts. And look at the thrust produced at those same tests, it if very similar at about 430 grams or so.

And if I looked at the specs on the motors that produced those numbers you will see that their weights and Kv ratings vary considerably. But as long as they all have enough power producing capability to get the prop up to that same RPM, the plane would be flying exactly the same.

We have a reliable "rule of thumb" in the much used 3 Watts per gram of motor weight rule. That is a conservative value and considered to be the typical and safe input power (to the prop) you can expect from a typical quality brushless outrunner when it is running at partial throttle and drawing a safe and constant (no longer rising) number of Amps. It is normal that, at full throttle, the RPM increases, the current drawn increases, and the temperature in the windings increases. So if you want to fly at a constant full throttle setting you have to have a heavier motor so it can handle more Amps in the windings.

So choosing a motor has to start with your knowing about what prop you want to use and what the battery voltage will be and what it's practical to use RPM range is. As the battery voltage goes up the RPM will increase so the Kv rating should come down to keep it operating with a practical (for that prop) RPM range.

How much throttle you use as you fly is another consideration you have to take. If you are a full time full throttle flyer, you want a motor that is bigger. Big enough that you are only drawing 3 to 5 Watts per gram or so at that full throttle setting.

Jack
Sep 24, 2020, 04:00 PM
flyin' fool
goldguy's Avatar
I test a selection of props with my wattmeter and find the ones that keep everything in check. Then I go fly n' try them as some may give me a similar reading but don't perform the same.
Sep 29, 2020, 02:40 PM
scratchbuilder
Thomas B.'s Avatar

KFm2 with big flaperons


We are testing the KFM2 with wide flaperons ( around 30% of wing chord ) and simple slats. The results are very satisfying! The Buschtrottel style planes have great STol capabilities.
Wilga vs. Buschtrottel (4 min 0 sec)
Sep 30, 2020, 02:17 AM
Registered User
Thomas- excellent! Kanst du geben mehre Fotos und Beschreibung ueber diese Wilga?
Sep 30, 2020, 03:52 PM
Jack
jackerbes's Avatar
Thread OP
Kanst du geben mehre Fotos und Beschreibung ueber diese Wilga?

google translate...

Can you get more photos and descriptions about this Wilga?

Just curious, not criticising you...

Jack
Sep 30, 2020, 04:27 PM
Registered User
Sorry and thank you Jack for translation!
Sep 30, 2020, 06:46 PM
looking up, down under
scruffy1's Avatar
Quote:
Originally Posted by jackerbes
Kanst du geben mehre Fotos und Beschreibung ueber diese Wilga?

google translate...

Can you get more photos and descriptions about this Wilga?

Just curious, not criticising you...

Jack
it is (was) from hobbyking, n'est-ce pas ?

discontinued
Oct 01, 2020, 05:38 AM
Went to mow a meadow
frank48's Avatar
I found a video on youtube... Very nice!

PZL WIlga aus Depron (2 min 6 sec)
Oct 03, 2020, 09:32 PM
Slow Flight

Can a Kfm2 or KFm3 used in a Corsair?


i want to build a small Corsair and i want to kniw if a Kfm2 or kfm3 can be used.

i have not found foams plans yet but i am planning about 100 to 150 grams foam plane.


can anybody confirm this airfoil can be used?

thanks
Last edited by herreraa; Oct 03, 2020 at 09:33 PM. Reason: spelling
Oct 04, 2020, 02:46 AM
Reap the wild wind
headlessagain's Avatar
I built a small P-40 Warhawk a few years ago using a KFm wing (6mm and 3mm)
Have a look at this thread for possible plans that can be scaled up/down
https://www.rcgroups.com/forums/show...nd-more-Part-2
Warhawk P-40 RC Plane (2 min 25 sec)
Last edited by headlessagain; Oct 04, 2020 at 03:05 AM.


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