Need long flight times

[iseeit]

I currently own a very nice SkyJib 8 HL but can only get about a 9 true minutes of flight time, with a 8,000mAh and a GH3 payload.

I’m now looking to build a new machine that will give me longer flying times for my doing infrared (my main business) scans of solar farms. I was thinking smaller/lighter as in a hex, to help extend the times but while speaking to sales person for about 45 minutes I was told the following:

Stay with an Octo and get about 1200mm boom width together with HL U5 motors and bigger props (16x5). The motors will not have to turn as much, due to the bigger props, therefore you save power, therefore longer flight times.
I'm looking to get at least 15-20 minutes per autonomous flight.

Is bigger better?

 

[kloner]

we manufacture an arm kit that converts dji 450, 550 and TBS discos to 900mm,,,, your able to swing up to 15" props. Trappy has engineered a motor/prop/esc/battery combo that can get over an hour and travel upwards of 30 kilometers.... if something like that interests you inquire with team-blacksheep.com or watch the aerialmob arm thread at fpvlab.com..... it is in the TBS forum there.

 

[iseeit]

Do you agree with this theory of bigger frame, bigger props gets longer flight times?

 

[Scott Drysdale]

Absolutely true....... its a laws of physics issue..... slower props produce less drag and enable more airtime if all the other factors are adjusted to accommodate this. Ecalc for Multirotors will tell you the same thing to some extent..... Also to turn larger diameter props, the motors need to have more torque relative to speed/rpm....... that means the KV rating of the motors is much less, whereas motor size and weight must increase to allow for more torque.... and that means more $$$.

I currently own a very nice SkyJib 8 HL but can only get about a 9 true minutes of flight time, with a 8,000mAh and a GH3 payload.

I’m now looking to build a new machine that will give me longer flying times for my doing infrared (my main business) scans of solar farms. I was thinking smaller/lighter as in a hex, to help extend the times but while speaking to sales person for about 45 minutes I was told the following:

Stay with an Octo and get about 1200mm boom width together with HL U5 motors and bigger props (16x5). The motors will not have to turn as much, due to the bigger props, therefore you save power, therefore longer flight times.
I'm looking to get at least 15-20 minutes per autonomous flight.

Is bigger better?

 

[iseeit]

One shop suggested:
Tiger U5 (400kv), Tiger 16x5 props + 10,000mAh?

If bigger is better then how about:
Tiger U7 (420kv), Tiger 17x5 props + 16,000mAh?

 

[Scott Drysdale]

That sounds about right to me...... And obviously, the bigger MR airframes allow for bigger prop diameters. The rapid price increase is a direct reflection of the law of gravity which is not quite exponential but close enough...... 32ft/sec/sec or 9.81 m/sec/sec....

One shop suggested:
Tiger U5 (400kv), Tiger 16x5 props + 10,000mAh?

If bigger is better then how about:
Tiger U7 (420kv), Tiger 17x5 props + 16,000mAh?

 

[kloner]

the u7 are awesome but i'd highly recomend going with there pro esc's with them,,, lots of commutation problems are going on. i have a 3520 octo and a u7 hex, the hex has twice the flight times of the octo with the same weights.... and 20 amp hour is a good target for a heavy lifter with these sizes,,,,

 

[iseeit]

How about this then: 8 Tiger U7 490kv, 8 Tiger Pro 70A ESC, 4 pair of Tiger 18" props.

 

[gadgetware]

the u7 are awesome but i'd highly recomend going with there pro esc's with them,,, lots of commutation problems are going on. i have a 3520 octo and a u7 hex, the hex has twice the flight times of the octo with the same weights.... and 20 amp hour is a good target for a heavy lifter with these sizes,,,,

Would you mind sharing the general specs for your hex setup (frame, size, loads)? And what kind of times are you getting?

 

[R_Lefebvre]

Absolutely true....... its a laws of physics issue..... slower props produce less drag and enable more airtime if all the other factors are adjusted to accommodate this. Ecalc for Multirotors will tell you the same thing to some extent..... Also to turn larger diameter props, the motors need to have more torque relative to speed/rpm....... that means the KV rating of the motors is much less, whereas motor size and weight must increase to allow for more torque.... and that means more $$$.

This is sort of true, in a round-about way.

What you guys really need to be talking about is disk loading. It's all about disk loading. The lower the disk loading, which is rotor disk area divided by weight, then the more efficient the machine will be. This is what leads to the idea everybody has of larger, slower turning propellers. The problem is hexacopters and octocopters are not efficient layouts to use large propellers on a reasonable sized frame. If you look at the way they lay out, you'll see that quadcopters are much easier to achieve higher disk area in a small frame size. But with a quad, you have no redundancy, reduced stability, and of course, not as "sexy" as an octocopter.

iseeit, what exactly is your mission profile? Do you need to fly a GH3 for 20 minutes? That will be quite a feat. I've not seen something like that done. I'm sure it is possible, but would take quite a machine.

I currently have a 500 size helicopter that has proven to fly for 20 minutes, at up to 100 km/h, while carrying an SX260 camera for mapping missions. Runs on just 4S 10,000mAH, fits in the back seat of a compact car easily. You could get 4 of them in the trunk of a compact car.

And a 700 size heli would lift your GH3 for 20 minutes. I've flown it for 24 minutes with a 2 lb ballast, and that's not yet a full battery load.

This type of work is much easier, and cheaper to do with a helicopter.

 

[kloner]

my hex is an 1100mm hexacrafter, flys a gh3-4 18 minutes on 20 amp hours of packs drawing 52 amps continuos and that's with 40-50% leftover just in case. for whatever reason accidents always happen towards the end of the packs so to prevent, we make sure to land with fuel.... it's also an faa rule for full size so were

single rotor helis are not the safest close range aerial machines but i know several using them,,,, that's a different forum

 

[R_Lefebvre]

Is that 6S? Which motors and props? I've never seen machine specs for something with that performance, so I'd like to see how it's done. I'm just curious about how big and heavy a multirotor with those specs is.

Understood about your concern with SRH. I design them with the concept of "industrial" applications, not typical commercial shoots. Plus, a 500 size, really isn't that big or dangerous.

 

[R_Lefebvre]

Playing around with eCalc... Assuming frame weight of 1500g, 1000g of camera and gimbal payload, 4S20,000 batteries, U7-420 motors with 19" props, it shows 57A draw in a hover, pretty close to what you're saying. It's showing 18 minutes. So it looks like I got the specs roughly figured out. But that's 18 minutes total with no reserve. The statement about 40-50% reserve though, that would suggest it would fly for 30-35 minutes which is impossible. Even by your own numbers: 20Ah of battery at 52A will only last 23 minutes if you drain them 100%, just basic math.

AUW of 6.8kg or 15 lbs.

But which props are you using? I assumed 19" but now I see that they only recommend up to an 18". That drops the flight time to 17 minutes.

So that's a 4S setup. I'm guessing you're running them on 6S 20,000. So try those numbers:

18" props, 8200g AUW, 54A hover, 18.7 minutes flight. But motors risk overheating.

17" props, 57A hover, 17.8minutes flight. All the numbers look good. But no 40-50% reserve after 18 minutes.

 

[kloner]

you can almost throw a 500 down if it was coming at ya,,,, 450 would be better

6s on u7 with 60 amp esc and 16" prop

this current sensor is on one of the battery leads, other is straight to the pcb.... so it's half the data.... double amp draw and mah for the right numbers.... 20 amp hours, gh3 3 axis gimbal, etc.... super nice in that aspect till the crappy esc's got me and ate this thing.... some commutation problems from an incompatible simonK firmware that maytec put on these and sold.... ridiculous, but it's almost rebuilt

 

[Scott Drysdale]

Thanks R_Lefebvre.... That rings very true as does the concept of wing loading on fixed wing aircraft. I also recall that heavier wing loading enables the fixed wing to flt more stable in wind much better so there are always trade-offs......
But at what point does one consider disc loading too low such that MR oscillation in a light breezed cannot be resolved by Basic and Attitude tuning?

This is sort of true, in a round-about way.

What you guys really need to be talking about is disk loading. It's all about disk loading. The lower the disk loading, which is rotor disk area divided by weight, then the more efficient the machine will be. This is what leads to the idea everybody has of larger, slower turning propellers. The problem is hexacopters and octocopters are not efficient layouts to use large propellers on a reasonable sized frame. If you look at the way they lay out, you'll see that quadcopters are much easier to achieve higher disk area in a small frame size. But with a quad, you have no redundancy, reduced stability, and of course, not as "sexy" as an octocopter.

iseeit, what exactly is your mission profile? Do you need to fly a GH3 for 20 minutes? That will be quite a feat. I've not seen something like that done. I'm sure it is possible, but would take quite a machine.

I currently have a 500 size helicopter that has proven to fly for 20 minutes, at up to 100 km/h, while carrying an SX260 camera for mapping missions. Runs on just 4S 10,000mAH, fits in the back seat of a compact car easily. You could get 4 of them in the trunk of a compact car.

And a 700 size heli would lift your GH3 for 20 minutes. I've flown it for 24 minutes with a 2 lb ballast, and that's not yet a full battery load.

This type of work is much easier, and cheaper to do with a helicopter.

 

[gadgetware]

6s on u7 with 60 amp esc and 16" prop

this current sensor is on one of the battery leads, other is straight to the pcb.... so it's half the data.... double amp draw and mah for the right numbers.... 20 amp hours, gh3 3 axis gimbal, etc.... super nice in that aspect till the crappy esc's got me and ate this thing.... some commutation problems from an incompatible simonK firmware that maytec put on these and sold.... ridiculous, but it's almost rebuilt

Thanks for the info. I'm interested in your setup as I'm trying to come up with a good config to carry a GH3 + gimbal.

I'm curious what Gimbal are you using? Also what's your AUW including the batts?

I'm trying to figure out the values on your video. Are you sure the mAh and current values should be doubled, or accurate? If so that means your mAh consumed on the 9-minute flight is 10,334 mAh (5167x2) which is over 50% of your total mAh available with 20aH of batts. At 80% batt use that means that the max flight time would be about 14 minutes. (9/(10334/16000)). When I do the calcs with double the displayed current numbers (about 70 amps) I get the same estimated flight time. Since you're getting at least 18 minutes then something doesn't seem right. If those numbers aren't doubled, then that's more in line with your measurements of 18 minutes with juice left over on the packs.

It's late so I'll apologize in advance if I've messed up the calcs!

 

[kloner]

that is that gimbal. this was a forward flight in alot of wind, usually the amp draws are around 50-55 hovering in no wind. it flies what it flies, with my jib and the same gimbal/packs i land within 7 minutes, with this thing i'm dying by 10-15 minuts to land cause i feel like i've flown too long, even after 60 flights....

heres some footage from the rig... done one man, my guys hate the desert

however, the hex and a red make some serious amp draws, up over 130.... so theres a line where it's efficient to where it's just doing it's thing like other combos. it is in transition to changing over to all kde gear, hoping for more efficiency and performance....

 

[R_Lefebvre]

Thanks R_Lefebvre.... That rings very true as does the concept of wing loading on fixed wing aircraft. I also recall that heavier wing loading enables the fixed wing to flt more stable in wind much better so there are always trade-offs......
But at what point does one consider disc loading too low such that MR oscillation in a light breezed cannot be resolved by Basic and Attitude tuning?

That's a good question, I don't know the answer. I've seen a 35 minute quad fly quite well in a reasonable wind. I was really surprised.

But you'll notice that the 1+ hour quads, you'll never see them fly unless it's dead calm. Well, part of the reason is because the structure is so light weight, they'd simply break-up in-air.

So somewhere between here and there... That's why I'm working on helis. The difference between a 1 hour heli and a 160 km/h machine is just a turn of a knob for more head speed.

 

[kloner]

below 35-40% throttle is where the loading is too low to respond to,,, like 32% hover and your likely a toilet bowl

 

[R_Lefebvre]

Hover throttle does not tell you what the disk loading is. Hover throttle tells you if your motors are too powerful. I have a quad that hovers at 30%, and it definitely does not toiletbowl. It's a heavy F450, with 10" props. Nothing unusual about that. But it has monster motors on it capable of over 100 km/h straight-line speeds. I've even flown it with 12" props (yes, really an F450 with 12" props) and it was still fine, no toilet bowl, but now it hovered at 25% throttle.

For example, you can take *any* multirotor, with any fixed disk loading. Change the motors to ones from the exact same family with just a higher KV, and the hover throttle will go down, but your disk loading didn't change.