Jet Hanger Hobbies A-7 D/E ARF - Page 71 - RC Groups
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Feb 16, 2013, 03:41 PM
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I know! Thanks for your help..this my first scale EDF...I bought the e-turbax from Chris and it came with the esc HV160. I moved back to europe I didn't work on this project for nearly a year!
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Feb 16, 2013, 03:56 PM
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bri6672's Avatar
I see, we'll you can make it work its just going to take some strategizing.
Feb 17, 2013, 01:23 AM
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jefffassbinder's Avatar

Battery location

In front of the main gear your going to need to pull out the Drexel and take a good amount of material out. Don't use a bunch of Velcro. In fact when test fitting eliminate it. Later only a small piece will be needed.

When sliding you battery forward you can use the crease in the center of the ducting to rotate your pack in on at a time. Again no Velcro.

Your fan and ducting may be loose while you work on cg. Air valves for retracts and brake if used can be placed under fan and even aft of the bulkhead behind the fan system. As for esc placement there are many way in duct or mounted aft the motor in duct with just your power wire coming to battery.

Also if your using lower c batteries make sure you adjust current limiting and low voltage cut off or you will have your fan LVC on you. Lower c with smaller packs is dicey yes you can do it when you multiply c rating times capacity of your packs that are large because of a abundance of ions. But that work with larger wing areas. So.sometimes higher energy density can help you with lower capacity.

Get the cg on the lex or you'll not be happy. Keep weight to below 14lbs for a nice easy landing airplane.

Good luck.
Feb 17, 2013, 08:40 AM
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thanks a lot!
Feb 17, 2013, 09:43 AM
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bri6672's Avatar
Originally Posted by jefffassbinder

Also if your using lower c batteries make sure you adjust current limiting and low voltage cut off or you will have your fan LVC on you. Lower c with smaller packs is dicey yes you can do it when you multiply c rating times capacity of your packs that are large because of a abundance of ions.
There is nothing dicey about it, I don't care what the C rating is, as long as you have proper headroom.

To a test run on the ground ( full simulated flight ) as long as the minimum volts per cell is good and the packs are not getting to hot you are fine.

I had a 90mm F-18 a few years ago. It pulled right at 90 amps, I ran it on 20 c 7s 5000, those packs weighed the exact same as a 40c 6s 5000! That additional 20c of discharge weight as much as an entire 20c 5000 cell!

You have 20% headroom on discharge, you will be fine, but do a thorough bench flight and if the minimum voltage under load divided by the "10" cells is below 3.4 then you will need to lower your voltage cutoff like Jeff said.

Keep in mind as the packs age there ability to hold that current will go down and you will need to retire them when that happens.

It's a good idea to check that data every couple of months!!
Feb 17, 2013, 01:20 PM
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jefffassbinder's Avatar

C rating

Dicey is flying 20c 5000 with the stock setup not a 90mm here. Just remember at 3.75 minutes you need to be on the ground or the ground will reach up for you. I had three A7's so if had my share of experience. Don't get me wrong this is a great flying and looking airplane. Just need to be realistic with head room. A flight with 20c on a 1527 1.5 y is max 3.5 after that you controller with let you know. I've made it back on many missions on 20c but is far more fun to not have to worry about power. 12s for the above. The old 6000 mah falcons did well and are 25c. But 20c your asking for dicey at the 3 minute mark so be ready. The plane flys great with thrust. Without it not so much.
Feb 17, 2013, 02:04 PM
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bri6672's Avatar
Dude, amps are amps don't care if its a 120 not a 90... Your comments might be based on your experience but there are way to many other factors at play here.

Bottom line he already owns those packs! Bench test it on the ground, do a full simulated 3 min flight and check the data, If the cells are getting to low but are keeping capacity then you need a higher c, but the more weight you add the more power it will need to fly hence more mah etc. etc..

If your smart you set the timer for 2min and land, get down early but get a feel for the jet. Then slowly move the timer out, after checking avg volt per cell you get close to 3.7 then that's it, she won't fly longer than that with those packs.

With this jet the idea is to fly it as light as possible for the first few flights to get comfortable, even if that means short flights, then you can add heavier packs....
Feb 17, 2013, 05:23 PM
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jefffassbinder's Avatar

90MM, 100mm, 110mm, and 120mm

Fab, I've flown with all these fan sizes in this airframe. You have a limited amount of space for packs as you have learned. You can get up to 6600 on a 12s 2p situation but that is not ideal. 6000 mah is going to be the line and then weight no matter which size fan is going to have a cost. 90mm was the easiest to fly and land I can tell you but the fan needed to be at 75 % and above for much of the flight to stay on step. 120mm had great performance but lacked in time. 90mm-100mm can do 4-5 minutes depending on your conditions on 5000 packs. Notice I didn't mention C. The 110-120 size are best served with larger packs reason higher energy needed to feed the fan. The performance with 6000 packs at the 110 to 120 is really good. Great vertical and extended flight time.

I know you have 5000 packs and that fine for your initial flight checks but you're really are going to have to monitor at 20C. If your using a Eturbax on a 1527 1.5 y you can easily pull beyond 120amps. With larger packs at even 25c your going to be able to push more AMPS and also consume more AMPS. 5000 x 20c is = less than 120 amp so hence my comments. I just want you to have a good time flying. If you have another fan or motor combo then just read max amps from your controller. You have data log access? Then calculate. Bottom line anything in the 120 mm fan category is going to be pulling 105--120amp no problem.

So do the ground test as Bri6672 suggest.
Take a reading at full power for 1 minute
Then take a reading at half stick(please make sure to calibrate your throttle prior to doing this or you wont have a linear throttle response. It simple. Power on your radio and RX. Then with your throttle atv at 50% full throttle and idle positions. Now get a pack say a 5s or 6s pack put your throttle sick at 100% then connect the 5 or 6s pack to controller adjust your atv in the throttle channel move the number up slowly until you hear a beep. The WOT position is now calibrated now move your throttle stick to idle now move the idle position atv until you hear a double beep. Once this is done don't move the ATV numbers. Now your ready to test Full throttle, mid stick and 3 quarters stick.
First minute WOT
Then next minute go to say half throttle
Next minute let it ride at 75% stick with the above done.
Put your fan at idle with the fan just spinning to reduce the heat in the motor. Now disconnect your batteries and read the cell voltage.

If your below 3.6 V you know that you have only a few spare seconds to get to the runway.

Check your data log, it will tell you how many Mah you used during your testing. Make sure to choose this session which should be about 3 minutes run time.
And regardless of voltage how do your packs feel, are they warm say 100-120 F or are they something else cool and just like ambient or like hot dogs. If they are hot dogs at 3 minutes then your call on if you want to fly.

So data is great, but if the packs are saying this hill is to high to climb then you need to address your packs. Test and you decide. But 3 laps with this airplane happens fast and you will have that time to trim and get comfortable with large radius turns. Don't go sharp unless your on step hauling. This is why 3 laps and then set up for the landing on you initial test. Your the pilot, so it all your call but just sharing some of my flight experiences and means of finding out of packs capabilities.
Feb 17, 2013, 05:50 PM
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bri6672's Avatar
Jeff what do you mean when you say the packs are like hot dogs?
Feb 17, 2013, 06:17 PM
Mike Warren's Avatar
Originally Posted by bri6672
Jeff what do you mean when you say the packs are like hot dogs?
You "Ball Park Franks", they plump when you cook 'em
(Sorry, couldn't resist)
Feb 17, 2013, 06:19 PM
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bri6672's Avatar
Haha that's what I was thinking, plumping up
Feb 17, 2013, 06:26 PM
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bri6672's Avatar
The bottom line is the amps your pulling. If Jeff is right and you get 105-120 then you do need higher than 25c. If its the 93 you posted you should be fine just don't take the cells lower than 3.7 and use a clamp on meter because the castle data can be off by 10% or more.
Feb 17, 2013, 06:43 PM
"My grandma wants to fly jets"
heychas's Avatar
Wouldn't the math be as follows: 5000 mah battery at 25c = 5.0A x 25c (discharge rate) = 125A maximum load? Although this math works conceptually, I'm not sure it works in practice due to the lack of consistent manufacturer reports of discharge rates. I think the bench test might be the best way to go. By the way, in the old days there were only 20c-25c batteries and I believe many JHH A-7 were flown on those. And if you follow the current threads that try to track the real discharge rates often they don't get above 20 or 25 regardless what the claim on the label.
Feb 17, 2013, 06:45 PM
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bri6672's Avatar
Yep but you want about 20% headroom!
Feb 18, 2013, 03:07 AM
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thanks a lot for your help...stil undecided to buy new batteries or not...I will keep you updated!

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