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Author Topic: Difference in flight time from static to in-flight  (Read 743 times)

Offline Keith Renecle

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Difference in flight time from static to in-flight
« on: May 14, 2008, 11:29:32 PM »
Hi All,

I always read Will Moore's electric articles in Stunt News (thanks to Will for these fine articles), and have finally ventured into playing around with this technology. I found the article on using the Eagle Tree in-flight recorder particularly interesting, and I was wondering if the boffins out there have come up with a percentage to have an idea of the difference in current used when flying as opposed to running the motor statically. From the chart that Will posted, it seems somewhere around 60 to 70%. I have done plenty of bench testing, and my first model is almost ready to start flying, so this would help me. Thanks.

Regards,

Keith R
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Keith R

Offline Igor Burger

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Re: Difference in flight time from static to in-flight
« Reply #1 on: May 15, 2008, 12:12:44 AM »
Keith, it is variable also during the flight, I think my chards will show all:

http://www.olive.cz/pub/igor/1.jpg
http://www.olive.cz/pub/igor/2.jpg
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Offline Dean Pappas

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Re: Difference in flight time from static to in-flight
« Reply #2 on: May 15, 2008, 11:02:11 AM »
Yes Keith,
The in-flight average current is typically 3/4 of the static current. That is a good way of ballparking the prop diameter before the first flight. Figure thge pitch and RPM for the desired lap time and then adjust the diameter to get the current just under 10X the battery capacity in Amp-Hours. (or 10C) It'll drop to about 7-1/2C in-flight, and that will leave 1/4 of the battery capacity unused. That is good for LiPOs, and you can run an additional 10 or 15% for A123s.

I'd still fly a short (3 minute) flight to make sure that the full 6 minutes won't flatten the battery too far.

As Igor mentions, the in-flight current will vary almost 2:1 (peak to valley) for a good setup. I didn't look at his data-log curves but I am sure they show something similar.

Regards,
Dean Pappas
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Offline Dennis Toth

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Re: Difference in flight time from static to in-flight
« Reply #3 on: May 15, 2008, 11:52:29 AM »
Keith,

I was were you are a few months ago, I've flown both glow and diesel for over 45 yrs and like you think the no mess, strong constant power of ECL is the way to go. Finding information to get started took some time as there are endless combinations possible. So that said I will give you my take on getting set up.

Assuming that you are looking at the typical full stunter designed around a piped 40 or ST60 power level (basically something that would use around a 12x5 to 12x6, 2 blade prop, if you are going for a 70 size see post by Kim D). I start with a desired line length and lap time (for me 64ft at 5.0). From there you can get the target starting rpm for the prop selected (again for me 8800 rpm).

Then using Deans rule of setting the ESC in governor mode at 70% of the no load rpm i.e. Kv x V x 0.7 = target run rpm. You pick a battery size (10V, 14V, 18 V) and motor to fit the target formula (for me with the A123 10V battery the AXI 2820/8, other have used AXI 2826/10 with 14V lots of other motors will work). With this approach you will wind up with the in air amps around 70% of the static (mine are 51A static 36A in air).

You then set the capacity of the battery which for the most part is based on the flight time you want to fly, in my case 6 min (Flt time in mins X Air amps / (1-battery head room %) X 60 min/hr = Capcity in Amp hrs x 1000 = Cap in mah).

If you read through this board you will find that the most popular capacity is around 4000 mah for Lipo's, 4600 mah for A123. The difference is that the lipo's you need to leave about 30% head room extra capacity at the end of the flight, the A123 only need about 18% without reducing the pack life.

Other combinations are possible as the selection of motors/batteries/prop load are almost endless but I found that starting with the motor/battery brands mentioned on this board will get you in the air quickly and let you learn the basics. After that it all depends on how much money you want to spend to come up with your own package.

Best,           Dennis

Best,     Dennis
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Offline Keith Renecle

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Re: Difference in flight time from static to in-flight
« Reply #4 on: May 16, 2008, 11:50:58 PM »
Hi Guys,

Sorry about the late reply. My PC monitor stopped working. Thanks very much for all the info, and Igor thanks for the charts as well. I think that I will most likely get myself one of those Eagle Tree gadgets. I am looking forward to trying all of this out, and my model should be finished next week. If it works, I'll post some pics and info. Keep well and thanks again.

Keith R
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Keith R

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