2 hours flight time

[aerodolphin]

Hi, I'm designing an UAV for 8 or 9 Kg of weight, with 2 Kg of payload capacity.

I would like to know if it's possible to do it with an electric motor with Li-Po packs for a 2 hours mission?

There is some comercial UAV's like this that are electric and have a flight time of 2 hours. How this can be done?


Puma [5,9 Kg - 2 hours]
http://www.avinc.com/downloads/AV_PUMAAE_V10109.pdf

Skylark I [5,5 Kg - 2 hours]
http://www.elbitsystems.com/data/Skylark(1).pdf

Azimut 2 [6,5 Kg - 2 hours]
http://www.alcoretech.com/uavs/fiches/ALCORE_AZIMUT2001_A.pdf
600W reducted brushless
Ion Lithium or Ni-Mh

Biodrone [8,5 Kg - 2 hours]
http://www.alcoretech.com/uavs/fiches/ALCORE_BIODRONE_A.pdf
1200W reducted brushless
Cd-Ni or NiMh

What power system we should use for archive that?

Or it's better to consider a glow motor?

[vintage1]

Sure. Figure on around 15 watts per pound in economy cruise, and size the pack for that..

If you have 11kg AUW, that's 24 lb give or take..so you want 2x15x24 about 750 watt hours.

On a 20v 6s style pack, that's about a 37Ah pack. Probably 4 x 10Ah packs. Expensive..

The motor ain't bad tho - 1.5Kw is enough, and not that uncommon these days.

I've managed to easily get 45 minutes out of a very basic model. The key is to find the slowest speed capable of level flight, plus a little bit for safety, and stay with that, and prop for efficiency at that speed.

[Mark Wood]

UAV forum (http://www.rcgroups.com/uav-unmanned-aerial-vehicles-238/)

mw

[clolson]

For all these systems that publish 2 hour flight times ... I'd love to hear a few more details about the conditions. What flight speeds? What payload? Did they achieve this time with extra battery substituted in for payload?

We've achieved 1+ hour flights in our flying wing without working too hard at efficiency. That's at about 35-40 kts flight speed. If I bump the speeds up to 50-55 kts, the endurance drops to approximately a 1/2 hour. I ran the speed up to 65-70 kts and melted a speed controller. :-) In a full throttle dive our airframe topped out at 100+ and started looking pretty jet like on the low passes. I could slow down a bit more and stretch the battery even further that that one hour I achieved. I've got plenty of capacity for more battery so I could stretch things out even further. I don't expect that doubling battery will double the endurance though due to the extra weight.

There are many trade offs here and often these posted specs don't have as much meaning as they might first appear.

If I slow down to 25-30 kts air speed to get additional aloft time, how do I deal with a job that requires me to fly in 20-25 kts winds? I'm going to spend most of the flight inching upwind and not cover much ground.

So with useful payloads and at useful flight speeds, now how long can you fly?

Curt.

[Mick Molloy]

UAV forum (http://www.rcgroups.com/uav-unmanned-aerial-vehicles-238/)

mw

Mark did you move this over to UAV section?? not sure where from??

I think is might be more appropriate in the Aircraft - Electric - General section as it is not a specific UAV question more on motor power and duration, he might get more answers in that section than the UAV.

Cheers Mick

[spitfiremk9]

You are asking for the earth in my opinion, thats a lot of weight for electric power, certainly at the consumer end because don't forget, comercial systems are far more eficient than what you can buy down the hobby shop! 45 minutes flight is a pice of cake, where as an hour requires much more effort and if your going to chose to go with minimal power to weight ratio as has been suggested, getting airborne in anything other than zero windspeed is out! Like Curt said, in a 25knot wind your going to be watching your aircraft hovering above you for quite a long time. I use both electric and ic, with my most eficient electric I can achieve 2 hours+, but the airframe is ultra light and aerodynamic, has a massive wingspan and only has to carry 11oz payload. If you want "real world" duration then you have to use ic, now we are talking 6-7 hours on 1litre of petrol and remember, as your petrol is being consumed you are flying lighter, while your lipo's still weigh the same. One alternative, invent a system that allows in flight recharging!

[aerodolphin]

Yes. Thank you all the answers. I will go to the petrol engine. Will be better and with that I can archieve a long time flight with a good payload weight.

[smh20502]

What wing profile are you using? This will determine your flight time. The more efficient your wing the longer the flight time.

[smh20502]

Regarding wing profiles go to the below link to see a good selection. Check out the sailplane or flying wing designs. There is also the high lift foil shape also.

http://www.ae.uiuc.edu/m-selig/ads/coord_database.html#E

[cfe7]

Regarding wing profiles go to the below link to see a good selection. Check out the sailplane or flying wing designs. There is also the high lift foil shape also.

http://www.ae.uiuc.edu/m-selig/ads/coord_database.html#E


What kind of software do I need to read those DAT-files?

[smh20502]

you can open it with notepad but all you get are coordinates. The left column is the X axis the right column is the y axis. These files would probably be good for using in creating a template on some type of cad system. If you're creating by hand I'd say it'd be best to simply trace them from the .gif file.

look at the .gif file to see the shape

[ggtronic]

hello aerodolphin

i'm no UAV specialist, but i'v based all my work around the SKYLARK concept.
(i'v seen a complete video about it and its amazing ! )
The slim fuselage help to get more run time (better airflow), and the lower pod help
for stability (lower weight position at CG). I think that lower quality UAV hardware need more stable
plane to work with ?

vintage1 math really match my APfstick data here (http://ggtronic.dyndns.org/flight%20log.jpg),i need 40W to keep going foward, and little less with no attack angle block modification in windy condition.

Also, for safety concern within civil flight, i would not chose a direct foward
facing propeller concept .

watch my airflow test here (http://www.rcgroups.com/forums/showthread.php?t=944276)

The AZIMUT looks good too ?
I would not go with the PUMA :( ...

Power system : electric will get you more headach :p . harder to chose appropriate motor/propeller/battery ! In fact all the airplane concept need
to reach optimal performance because of electric limitation ! A regular yellow
gas CUB would do all this easy LOL, but i will never go back to gas plane
(personal tast) :D

[aerodolphin]

I'm thinking use the NACA4415 airfoil in a wing with a wingspan of about 2,5m and a cord of 0.3m.

"Also, for safety concern within civil flight, i would not chose a direct foward
facing propeller concept ." Yes, I will take that into account.