will a 7" go further than a 4"

[lethal nacelle]

Hello there, since we have some 4" and 7" long range quads that can fly for half an hour, so I was wondering if there was a big difference in the range of both, in the sense of Wich could go the further away

[craggy bough]

7" is faster

So it will go further in the same amount of time

[lethal nacelle]

Ok

[nimble ginkgo]

yes

[grizzled night]

Yes and a 10 inch will go further than both, it's because smaller props have to spin faster therefore requiring higher kv motors which on the same voltage draw more amps, bigger props also don't need to spin as fast to generate the same thrust

[lethal nacelle]

"it's because smaller props have to spin faster therefore requiring higher kv motors which on the same voltage draw more amps" that is very much untrue, because smaller props require less torque than bigger props, so bigger props would consume more than smaller props because of the torque requierment, wich is why smaller quads use smaller batteries, the advantage of 7" is that even if it does draw more amps, it can hold more batteries than it draws amps from the battery if we used the battery size has the proportion (e.g you can use say a 2500mah battery on a 4" and it might draw 6A or a 5000mah battery on a 7" and it will consume 10A, it's not real numbers, but it works well enought) and my question wasn't about that, but more about what is the cruising speed of both if we want to fly both for the maximum range (e.g, the cruising speed on a flywoo explorer lr4 on a 3A/h 4s is about 30kmh to achieve the maximum theoratical flight time of around 35min, but I don't know what the cruising speed of a 7" is)

[grizzled night]

Cruising speed on a 7 inch should be about 65kmh, the 10 inch I'm building it will be about 95kmh and only draw 12-15 amps total

[lethal nacelle]

and how exactly did you determine it will only draw 12-15A ?

[grizzled night]

Motor charts and factoring in a 1.5x safety limit, also watching dvr of people with same setup and seeing what there amp draw is

[lethal nacelle]

you can add another 50% on top, motor charts are best case scenarios, and dvrs aren't always particularly reliable, especially if you want to do 95kmh cruising

[grizzled night]

Motor isn't gonna draw double what a chart says

[lethal nacelle]

if you base your amp draw on dvrs and motor charts, it might has well

everything depends on the prop and the load

[grizzled night]

Well I'm same prop same load, only thing different is altitude

[lethal nacelle]

well, at higher altitude, the air is thinner (the pression decreases by 2 when you double the height) so you will need to be higher in the throttle

[lethal nacelle]

and has you can see from this wonderful chart I just did (using the motor chart of a T-motor f2203.5 1500kv, an exceptionnally efficient motor) the throttle ramp really isn't linear, so if you increase the throttle by even a small percentage, it will have a massive impact on amp draw

[grizzled night]

Yah I see that on alot of 10 inch charts 80 to 90% doubles thrust lol. I'll be running a 75% throttle limit to protect my poor li-ion cells

[lethal nacelle]

and keep in mind, it's a really fricking efficient motor (a guy did a 6" quad that flies for 55min at 30kmh on 4s 5000mah using them, it's wild, and I really want to build it, but I don't have the budget rught now) and it's on a best case scenario, so it doesn't even include the motor heating up and loosing a crap ton of efficiency

[grizzled night]

Does he just use a throttle lock?

[lethal nacelle]

I don't believe so

[lethal nacelle]

here is the video https://www.youtube.com/watch?v=8HPyBR6HUCY

now that being said, he discharged his batteries to 2,0v

[grizzled night]

Oof

[lethal nacelle]

so the real life flight time might actually be like 45min

40-50min

but still

[grizzled night]

I plan to set my warning at 2.8v per cell

[lethal nacelle]

yeah, going under 2,5 is like going under 3,3 on a lipo

it's the no go zone

and 2.8 is the equivalent to 3.5 on a lipo

[lethal nacelle]

just to illustrate my earlier point, I collected the information of every 1300-1500kv 2806.5 motor my local fpv shop sold in an A/thrust level graph

[grizzled night]

Unfortunately don't read French so no clue what that says

[lethal nacelle]

nothing interesting, I didn't fill in anything else than the numbers, so what's interesting is the graph in itself (y axis is the amps, x axis is the throttle value