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Understanding numbers - weight - power 😭

shadeyB

Well-known member
#1
hi pilots
The weather is due to be good tomorrow and in my mind the time has come to maiden my F-16 😊
I can build, paint, fly, crash ,repair & repeat and that’s pretty much what I have been doing for the past 7 years. All builds have been from guess work and previous lanes - flight experience and trial and error ....... yes crashes also and lots of them lol

i have never really understood the numbers for watts amps mah , I have watched numerous videos but no one really explains it how I want to hear it lol
moving forward I intend to bench test stuff (after I make a rig up) this should help me understand stuff more. I learn by trying - hands on & not classroom style.

Here it is........ I ran a watt meter test on my Covid Viper and it spat numbers out at me with abbreviations I don’t know 🤔
can you help and advise on best performance from the numbers before I chuck her up in the air
Other than the motor in her I do have another EDF lying in the hangar but no idea what Kv both are 😊

Jet weighs 814g , 70mm 12 blade fan

static test with turnigy watt power meter

3s / 2200mAh / 45c / weight 205g - total weight 1019g
11.23Vm
.128Ah
28.79Ap
328.2Wp
1.4Wh

4s / 2200mAh / 45c / weight 272g - total weight 1086g
15.4Vm
.071Ah
48.23Ap
747.5Wp
1.1Wh

4s / 3000mAh / 40-50c / 317g total weight 1131g
15.4Vm
.118Ah
48.58Ap
757.8Wp
1.8Wh

What I think I know with abbreviations / Vm = Volts / Ap =Amp draw from ESC / assuming Wp=power
the rest is guessing
I should have did thrust/weight test ?

sorry for long winded post pilots but I need to understand these numbers moving forward
help with the above would be greatly appreciated and how I could change things to improve performance and flight time 👍
 

Merv

Well-known member
#2
My guess is:
Vm = voltage mean
Ah = amp hours
Ap = amps peak
Wh = watt hours
Wp = watt peak

watts = amps x volts, so using your numbers, my guess, you had a peak voltage of 15.59 (757.8Wp / 48.58Ap = 15.59)

If you want the plane to go fast use the 4S batteries, the 2200 4S may be slightly better. The thrust to weight ratio would be helpful.
 
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Merv

Well-known member
#3
Here are some guidelines that may help. It’s the total flying weight of the plane that you need, including motor and battery.

• 50 to 70 watts per pound is the minimum level of power, good for park flyers and lightly loaded slow flyers.
•70 to 90 watts per pound is perfect for trainers and slow-flying aircraft.
•90 to 110 watts per pound is good for fast-flying scale models and some sport aerobatic aircraft.
•110 to 130 watts per pound is what you want for advanced aerobatics and high-speed aircraft.
•130 to 150 watts per pound is needed for lightly loaded 3D models and ducted fans.
•150 to 210+ watts per pound gives unlimited performance for any 3D model.
 

shadeyB

Well-known member
#4
My guess is:
Vm = voltage mean
Ah = amp hours
Ap = amps peak
Wh = watt hours
Wp = watt peak

watts = amps x volts, so using your numbers, my guess, you had a peak voltage of 15.59 (757.8Wp / 48.58Ap = 15.59)

If you want the plane to go fast use the 2200 4S battery. The thrust to weight ratio would be helpful.
Thanks Merv 👍 no idea how to get thrust to weight ratio 😊🧐
I did put it on a set of scales / nose 1st, zeroed the current jet weight then hit the power 😍 that was fun lol with my wife screaming (**** are you doing in the kitchen with that ?) lol
weight on scales totalled at 1138g
does that help

total jet weight with battery 2.4lb
 

shadeyB

Well-known member
#6
You are going to have a fast plane on 4S, about 300 watts per pound. Well above the 150 w/p in the guidelines.
WOOHOOO
THANKS Merv 👍
how do I get more thrust from this 🤪 it’s a 80amp ESC and by the looks of the draw I’m maxing out at 58.
the original had 5 blade however I assumed replacing with a 12 blade which is what’s in it now would improve performance?
im guessing the edf that’s in it is around 2200 Kv ? I had it in my viggen long time ago
if I replaced the unit with 3000Kv what would the effects be , I’m guessing more RPM = more thrust ? which I turn would incur more amp draw and more battery drain ?

thanks again
 

Sero

Well-known member
#7
My guess is:
Vm = voltage mean
Ah = amp hours
Ap = amps peak
Wh = watt hours
Wp = watt peak

watts = amps x volts, so using your numbers, my guess, you had a peak voltage of 15.59 (757.8Wp / 48.58Ap = 15.59)

If you want the plane to go fast use the 4S batteries, the 2200 4S may be slightly better. The thrust to weight ratio would be helpful.
I think Vm is minimum voltage, thats what my watt meter displays.

Thanks Merv 👍 no idea how to get thrust to weight ratio 😊🧐
I did put it on a set of scales / nose 1st, zeroed the current jet weight then hit the power 😍 that was fun lol with my wife screaming (**** are you doing in the kitchen with that ?) lol
weight on scales totalled at 1138g
does that help

total jet weight with battery 2.4lb
1138 grams is 2.5 lbs so your a bit over 1:1 power to weight ratio. I'm assuming you are doing all your tests with a fully charged battery, so as it depletes the power will go down.
 

Merv

Well-known member
#10
I’m guessing more RPM = more thrust ? which I turn would incur more amp draw and more battery drain ?
Yes & Yes
Just take care not to overload the motor. It always a good idea to leave a bit of head room. Don’t run things to the absolute limits.
 

shadeyB

Well-known member
#11
Yes & Yes
Just take care not to overload the motor. It always a good idea to leave a bit of head room. Don’t run things to the absolute limits.
Yeah I understand 👍🏻 That’s my point of trying to understand the numbers lol
Just trying to get a good performance, speed included but optimum operating values and flight times

I read it as 2.4lbs with battery and 1138grams of thrust, which is 2.5 lbs.
2.4lbs is all up weight
When on the scales and zeroed out , hit the power and reading is 2.5 lb

So where does the 700x Wp reading come into the equation?
 

Sero

Well-known member
#12
So where does the 700x Wp reading come into the equation?
Watts is a how much power the motor uses (amps x Volts + watts). It won't determine thrust because all power systems don't have equal efficiency but is useful as a guideline when matching motors/props to planes.
 

shadeyB

Well-known member
#13
Watts is a how much power the motor uses (amps x Volts + watts). It won't determine thrust because all power systems don't have equal efficiency but is useful as a guideline when matching motors/props to planes.
Thanks 😊 going to start to play about with set ups and understand better
1:1 power to weight ratio you mentioned
I’m assuming that’s enough for an EDF?
 

Sero

Well-known member
#14
4s / 2200mAh / 45c / weight 272g - total weight 1086g
15.4Vm
.071Ah
48.23Ap
747.5Wp
1.1Wh
15.4 volts x 48.23 amps =739 watts.

Your voltage would have been a bit higher when the power meter calculated the peak watts, a bit of voltage sag. Are you doing your tests with a fully charged battery?
 

Sero

Well-known member
#15
Thanks 😊 going to start to play about with set ups and understand better
1:1 power to weight ratio you mentioned
I’m assuming that’s enough for an EDF?
I'm not experienced enough with EDF's but I suspect you will be fine. EDF's generally don't do well at low speed/power settings but are good once you gain speed. With a 1:1 ratio the plane should get going easily from a standstill.
 

Merv

Well-known member
#16
I agree with @Sero, you will have plenty of power.
There is another relationship to understand. It takes the same amount of power (watts) to move a lot of air slowly or a small amount of air fast. On a test stand a larger diameter shallow pitch prop will always produce more thrust than a smaller diameter high pitch prop or EDF. BUT At airspeed, the higher exit velocity EFD will have a higher top speed. Think of a transmission, a low gear has lots of pull & low speed VS a higher gear, less pull at the start but higher top speed.
 
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shadeyB

Well-known member
#17
15.4 volts x 48.23 amps =739 watts.

Your voltage would have been a bit higher when the power meter calculated the peak watts, a bit of voltage sag. Are you doing your tests with a fully charged battery?
well yes at 98 %
no wheels as yet lol I just chuck it 😂👍

I agree with @Sero, you will have plenty of power.
There is another relationship to understand. It takes the same amount of power (watts) to move a lot of air slowly or a small amount of air fast. On a test stand a larger diameter shallow pitch prop will always produce more thrust than a smaller diameter high pitch prop or EDF. BUT At airspeed, the higher exit velocity EFD will have a higher top speed. Think of a transmission, a low gear has lots of pull & low speed VS a higher gear, less pull at the start but higher top speed.
in the words of Yoda
much to learn you have
I understand the pitch of a prop n thrust but EDF is a different world to me
 

Merv

Well-known member
#18
well yes at 98 %
no wheels as yet lol I just chuck it 😂👍



in the words of Yoda
much to learn you have
I understand the pitch of a prop n thrust but EDF is a different world to me
An EDF is going to act similar to a small diameter high pitch prop. In that it will move a small volume (diameter) of air very fast.
 

shadeyB

Well-known member
#19
An EDF is going to act similar to a small diameter high pitch prop. In that it will move a small volume (diameter) of air very fast.
Took her out to the filed today
and she flies good , decent speed too
there seems to be lag both sides of the throttle ? I have calibrated the ESC however nothing happens on stick till 1/8th position then she starts up 😍
not the easiest plane to chuck yourself while on the sticks lol
again at top end of throttle position you get nothing/no difference the last 1/4 of the throttle ?
I know EDF‘s are clear;y different to props but with prop I get full range from throttle ? Do I need new ESC ? She is a pretty 6 years old
 

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Merv

Well-known member
#20
I have calibrated the ESC however nothing happens on stick till 1/8th position then she starts up ..... at top end of throttle position you get nothing/no difference the last 1/4 of the throttle ?
Thats not right, I would calibrate the ESC again. If is still the same, it may be time for a new ESC.

EDFs do have a bit slower reaction to throttle input than a prop.