Last month I detailed my plans and preparation for an attempt at a 100km flight in a blog here.
Well yesterday the weather was ideal and my preparations (nearly) complete so I went for it and achieved a flight distance of 126km in a time of 2 hr 46 min 40 sec.
I can't attach my log file here because it's too big. It's 15MB and there's a 7MB limit. Any ideas how I can share it?
I exported the KMZ (2014-01-28%2006-32-40.tlog.kmz) to Google Earth and generated the following images showing the flight path, and the altitude/speed trace with some of the vital statistics.
[Click image to enlarge]
The airframe is a Bormatec Maja with 2.2m wingspan. It’s not the most aerodynamic airframe, but its advantage is its payload capacity which allowed me to carry 21600 mAh 6P4S Li Ion batteries with ease.
I stripped out absolutely everything I didn't need including the obvious things like FPV cables in the wings, and thanks to some advice on my previous blog I also removed a few things I wouldn't have thought of such as the RC receiver case and airspeed sensor.
The advice I had from other DIYDrones users was invaluable but the biggest factor in improving the performance was the testing I did. For each variable I wanted to examine I would fly multiple laps at different settings then analyse the log files to find the best performing setup. I give more details on that in the original blog.
For the actual record attempt there were a few things I’d never done before. One was flying without the airspeed sensor (I had flown with it switched off, but never with it physically removed) and the other was the 4 cell batteries. Probably both those things were the cause of the trouble I had getting the plane to fly at the 13m/s (47km/hr) I wanted. Initially it was much too fast. Over the period of a few laps I adjusted the cruise throttle percentage, the cruise speed and the min and max speeds to much lower than I really wanted which bought the speed down (and pitch up) to where I wanted it.
Key Stats
• Distance: 126km (according to Google Earth)
• Duration: 2hr 46min 40 sec
• Airframe: Bormatec Maja
• Wingspan: 2.2 m
• AUW: 3.25 kg
• Battery capacity: 21,600 mAh
• Average Speed: 45.6 km/hr
• Top speed: 68.3 km/hr
• Minimum speed 40.5 km/hr
• Duration: 2hr 46min 40 sec
• Barometer creep: -6m
Comments
Hi Elie
The battery is the NCR18650B. There are many vendors, I bought them from two different Ebay sellers because the first seller ran out. The link to the second seller is here. The discharge rating is 1C 2.9A which is low compared to LiPo's but in 6P it's plenty even for take off.
Actually I haven't calculated my current draw for the record flight. I didn't trust the current reading in the first few minutes so I tried re-calibrating the sensor during the flight. I didn't get it to a level I was happy with so I didn't trust it at all. I aborted the flight when the voltage was getting low (12.4V I think).
A 3s battery wouldn't have less weight, not for the same total energy. In other words if I dropped to 3S I'd need to add more P to get the same capacity. If I use the example of a 4S3P battery compared to a 3S4P battery, there are 12 cells in total. It doesn't matter how they are arranged, the weight, power and total energy is the same. At 4.2 volts and 1 amp per cell:
4S3P = 4 x 4.2 V x 3 x 1 A = 16.8 x 3 = 50.4 W
3S4P = 3 x 4.2 V x 4 x 1 A = 12.6 x 4 = 50.4 W
(I'm not really strong in this area, someone please correct me if I'm wrong)
HI Moglos,
It's a great work you did in the flight duration, can you please tell us what was the
1-The brand of the battery and its link. Also, what was the C of it.
2- And what was your constant amp draw at the cruise speed and what it is during take off?
3- If you have used a 3s battery, which has less weight, don't you think the flight duration would have been better. As no need for power torque in the cruise speed.
No they are not rechargeable.
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=301091233829...
That's not a rechargeable battery.
@ tommy: by my quick calculations that's about 1/2 the weight of the same capacity of Li Ion batteries. But they aren't rechargeable are they? I bet they're expensive (otherwise we would have heard of them as a consumer product).
Hi folks!
I have this battery at work. It's a proffesional battery from SAFT and each 3.6volt cell has 13000mah and only 100 grams!!
moglos, what was your average cruise current and voltage (not including launch and gliding to land)? I had read the Li-Ion batteries' voltage tends to sag more than Lipo. Perhaps with this much capacity, it's not so noticeable.
@Crashpilot: They flew in ~300m altitude.
@moglos: yes, they lost "some" planes, no option for us normal user ;-) ...
Yes I knew about it, that was incredible. I think they lost a few along the way didn't they. Wikipedia says that TAM5 that made it was the 25th air frame they made for the purpose.
@moglos: Thank you very much for your fast answer, after reading sebastians post it think your achievement is still very remarkable because you are using electric power system and off the shelf parts without a big oil company and a crowd of engineers supporting you (and a nice sattelite telemetry backlink...).
@Sabstian: Thank you very much for the link! That is beyond our hobby grasp until you round up a great deal of supporting money - but astonishing to see what was done in 2003 with a 2m X 2m plane - 38 hours flighttime..(and flightaltitude > 10K feet, I guess..)
Cheers Rob
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