Payload as a % of AUW

[PeterLester]

In the case of fixed wing aircraft there will be some airflow towards the wing tips that results in wing tip vortices as shown here:
https://www.google.ca/search?q=vort...-sQTkp4A4&sqi=2&ved=0CEYQsAQ&biw=1920&bih=955

The same tends to have with propellers.... more so at slower speeds.
Therefore I suspect at certain speeds there will be a lot of prop noise.
And since noise like heat is a form of wasted lift energy, the flight times would be reduced slightly.
As far as prop wash affecting aerial videos..... likely not noticable.

Keep in mind that longer motor arms will almost always improve MR flight stability.

 

[atpfilms]

Interesting thread here and relevant to my topic...
My AUW currently with the gimbal and camera that I'm running is roughly 6200g.
2168g for frame and elec
2219 payload
1784 Batteries
I'm on a 6S hex w T-motor 3515-400KV running 14x4.8 CF props generating 780g each @ 50% thrust.
My flight times are sadly in the 6-7 min. range w 10800mah. I really want to improve that, so....
My plan was to switch to 16x5 Wooden props (or CF, haven't decided yet) and bump it up to 15000 or 20,000mah even. My issue is, I'm looking at an AUW of 7050g w 15000mah of battery or 7900g w 20,000mah of battery.
With those props, I'm looking at 1180g thrust per motor at 50% throttle. With 15000mah I'm at 1175 per motor. With 20,000mah I'm at 1316g per motor (only needing about 54% throttle to hit my 1316g per motor). Does anyone have any experience with a setup like this? I don't really see the downside to going with bigger props and a bit more weight, but I'd love to hear input. Also, input on CF vs. wooden props would be helpful. Has anyone tried Himodel wooden props? They're the right price for experimenting. Sorry if this is hijacking, but similar topic.

Well, I continue to see flight times that confound me based on my craft. This guy is claiming 12 min. with 8000-12000 mah, so even if we assume 12000, his AUW is 17+lbs, mine is 13.6lbs. Both running 6S. He's on Avroto 3515 - 400kv, I'm on T-motor 3515 - 400kv. He's using Maytech 45A w simon k, I'm using maytech 40A. Only real difference I see is he's running 15 x 5 CF props and I'm running 14 x 4.8. I highly doubt the slight difference in the props and ESC's make up for the 4lb weight difference. Anyway, its a nice looking machine he's got. What could account for the 5 minutes of difference in flight time?
http://www.rotordronemag.com/review-vulcan-900mm-skyhook-hexacopter/

 

[FerdinandK]

@atpfilms
Something (one ore more components) in your setup are not working as they should, or not matching. If you follow the 1/3rd rule (as you did) you should easily be able to crack the 20min (or more). You should check if motors and/or ESCs are getting hot, and definitely try different propellers. (Graupner 14x8, ...). If the data you provide is correct, you take 240Wh (22,2*10,8) with you, and the power to hover (when 6min) is around 2400W which is way to high for 6kg, these numbers would say, that you are flying at 2,5gr/W which is that bad, that it is impossible. At what voltage you stop flying? Are you sure, your batteries are still alive?

Here two similar machines of mine
24min flighttime with 2kg payload and 14" props:
https://vimeo.com/72753445
28min flighttime with 2kg payload and 18" props:
https://vimeo.com/68920363

Also 6S10800mAh is quite heavy, A 6S16000mAh GensAce has 1900gr. But no single point explains the 2,5gr/W (this number should be 10gr/W or at least 5gr/W), must be a combination, or some other severe error.

best regards
Ferdinand

 

[atpfilms]

@atpfilms
Something (one ore more components) in your setup are not working as they should, or not matching. If you follow the 1/3rd rule (as you did) you should easily be able to crack the 20min (or more). You should check if motors and/or ESCs are getting hot, and definitely try different propellers. (Graupner 14x8, ...). If the data you provide is correct, you take 240Wh (22,2*10,8) with you, and the power to hover (when 6min) is around 2400W which is way to high for 6kg, these numbers would say, that you are flying at 2,5gr/W which is that bad, that it is impossible. At what voltage you stop flying? Are you sure, your batteries are still alive?

Here two similar machines of mine
24min flighttime with 2kg payload and 14" props:
https://vimeo.com/72753445
28min flighttime with 2kg payload and 18" props:
https://vimeo.com/68920363

Also 6S10800mAh is quite heavy, A 6S16000mAh GensAce has 1900gr. But no single point explains the 2,5gr/W (this number should be 10gr/W or at least 5gr/W), must be a combination, or some other severe error.

best regards
Ferdinand

Thanks Ferdinand. Yes, the batteries are fine I think, but I just picked up a couple of 5000mah packs and I'll try those next time instead. I stop flying leaving the batteries at 3.9V/cell. I'll check everything over, try some different props and revisit.

 

[FerdinandK]

Ok, then it is clear, 3,9V a cell means battery almost full. You can fly under load until 3,5V on the safe side, if you are more progressive, know your machine and battery you can go down until 3,4V a cell.

best regards
Ferdinand

 

[atpfilms]

Ok, then it is clear, 3,9V a cell means battery almost full. You can fly under load until 3,5V on the safe side, if you are more progressive, know your machine and battery you can go down until 3,4V a cell.

best regards
Ferdinand

Great, thanks. I've heard different things regarding V/cell left in these lipo packs. I'll run them down to 3.5 and see what flight times I get. I'm guessing in the 10 min. range. Still might be able to improve upon that with different prop setup I'm guessing.