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Old Jun 27, 2012, 02:12 AM
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Maple Valley, WA
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Thanks Sully for that amazing lesson. I am in awe by those of you with that kind of knowledge. I guess my brain was never wired for left-brained, technical thinking. (I'm highly right-brained dominate, all the tests I've taken through the years proves it). I admit much of that still goes right over my head but I am beginning to make sense of the overall idea. Thank you so much for taking the time to help clarify something that has always been a big mystery. I have cut and pasted that all into a word doc so I can go back to it down the road, which I most certainly will.

So it seems I'm left with weight versus performance. If I choose a 4S, 4000 40+C battery, it will be able to handle the amp load but not without pushing her into the "Morbidly Obese" category which causes such a problem with hand tossing. I can go 3S, 4000 40+C battery, shave off some ounces but lose out on that extra wattage, which to my understanding is unused horsepower.

One of my fans is cracked, assuming from the impact. I'm also concerned about that electrical smell and smoke. Can LVC cause that and if so, does that mean the internal guts are now compromised? This is why I think I would still like Don to take a look. I need to make sure I can continue to use this setup, get a replacement fan unit and make sure I'm using the RIGHT BATTERY!! (face palm).
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Old Jun 27, 2012, 10:15 AM
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Aros,
4s is better then 3s but this requires using correct Kv motors. You are trying to power the plane with almost double the watts as most people. This is fine but it comes at a cost in battery weight. You did not say if you had thrust tubes installed? Lack of thrust tubes could cost you 25% of your thrust which wasts the whole high power package. I would always choose 4s, but with your power system 3s and thrust tubes would have been a much lighter option. On a plane with that much power it is really important to do static tests to see if problems crop up. Twins are always a pain and if you loose a motor on this one on take off it's curtains.

Take care -- Stacker
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Old Jun 27, 2012, 11:38 AM
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I understand. No I did not install thrust tubes. I tried making some but they kept splitting on me when I tried installing. #9 should be the best setup yet. Now that I am beginning to understand the relationship of the proper battery in relation to my high-watt setup, who knows? Maybe #9 might actually make it to a hole whopping 10 flights.
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Old Jun 27, 2012, 01:56 PM
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United States, WA, Ravensdale
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Quote:
Originally Posted by Aros View Post
Thanks Sully for that amazing lesson. I am in awe by those of you with that kind of knowledge. I guess my brain was never wired for left-brained, technical thinking. (I'm highly right-brained dominate, all the tests I've taken through the years proves it). I admit much of that still goes right over my head but I am beginning to make sense of the overall idea. Thank you so much for taking the time to help clarify something that has always been a big mystery. I have cut and pasted that all into a word doc so I can go back to it down the road, which I most certainly will.

So it seems I'm left with weight versus performance. If I choose a 4S, 4000 40+C battery, it will be able to handle the amp load but not without pushing her into the "Morbidly Obese" category which causes such a problem with hand tossing. I can go 3S, 4000 40+C battery, shave off some ounces but lose out on that extra wattage, which to my understanding is unused horsepower.

One of my fans is cracked, assuming from the impact. I'm also concerned about that electrical smell and smoke. Can LVC cause that and if so, does that mean the internal guts are now compromised? This is why I think I would still like Don to take a look. I need to make sure I can continue to use this setup, get a replacement fan unit and make sure I'm using the RIGHT BATTERY!! (face palm).
No worries... glad to help when I can. Going to a 3S setup will cut down on the weight, but will also reduce the fan RPM -- so you'll be pushing less air out the tail (lower efflux). Somewhere in there, there's a trade-off between having that extra thrust with the 4S and the added weight of the 4S battery.

I've only crashed 2x SR-71's so far... but I can tell you that my 4S setup crashed going a lot faster than my 3S setup! My vote would be to keep the 4S setup... personally, I think the extra weight (and slightly higher wing loading) is compensated for by the extra thrust. Those hand launches are going to become a problem again if you drop back down to a 3S setup -- you need the punch of the 4S to get this mysterious lady going! Then you also have to consider that you may have to add weight to balance the plane on a 3S setup... now you're right back to the same wing loading that you would have had on the 4S, without the extra thrust to push it along.

To help grip the plane for hand launching, you may want to consider just cutting out a small piece of 1/8" plywood (maybe an inch wide by 2 inches long) and mounting it vertically underneath the fuselage -- just cut a thin slit in the belly, somewhere near the CG and epoxy it in. It will give you something solid to hold on to, and will even add a bit of directional stability when it's in flight. It's not going to give you the "scale" look... but for me, I'd much rather have a non-scale plane that flies than a scale one that has an overwhelming tendency to crash.

As for that burning electrical smell... I'd definitely check out the ESC's. I've never seen a motor smoke, but I have damaged an ESC in one of my helicopters, and it started smoking right away. If you haven't already gutted #8, you may want to cut the belly open so you can see the ESC's... then power it up and see if one of them is getting really hot or smoking. That power surging that you had also leads me to think it might be ESC related... but I don't think that hitting LVC would directly cause it (the burning smell, that is). My guess is that one of your ESC's got damaged in the final flight of Lucky #7. It could have very well been LVC that caused the motor to quit on #7... and the resulting crash may have damaged the ESC itself.

Looks like I may be moving back up to the Seattle area next spring/summer to work on the new Air Force Tanker Flight Test Program at Boeing Field. I haven't decided where to live yet, but maybe we can get together with a pair of flying Habu's one day!

-Sully
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Old Jun 27, 2012, 04:15 PM
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Maple Valley, WA
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Very good comments again Sully...I think you are right. Ultimately - especially with this power setup I've invested in - it makes sense to stay with the 4S setup even with a higher wing load for the reasons you mentioned. Your plywood grip is a good idea. I actually think I found a good setup with those "bowling ball holes" I cut out. I was surprised how much better and more confident the hand toss was with the three hole configuration. If only I could have saved her a few moments later.

I've got all the pieces taken apart. I was going to ship them to Don for him to have a look if he would be so kind. Hopefully everything is still okay.

You let me know when you're back up to my neck of the woods and we most certainly will have to get a couple Habu's in the air!
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Old Jun 27, 2012, 10:49 PM
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When I look to size a lipo I look at the amp draw first. In your case it is 120 amps. I then size for 30C which will be 120/30= 4 A/hr = 4000 mah then I buy a 40C version of the lipo to be safe. That would be the minimum lipo size I would use. On some of my other power systems around 600 watts which is like 40 amps, I run 4S 2200 lipos. So 40 amps/2.2 = 18.18C discharge rate so a 20C will work but if I buy a 30C or 40C then it will hold voltage better and not stress out the lipo so much.
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Old Jun 27, 2012, 11:07 PM
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If I had your smarts Don #8 would still be sitting in my garage ready for her next sortie. Hell, maybe even #1 would be.
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Old Jun 27, 2012, 11:17 PM
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Believe me I have had my share of mishaps, that is how I got some of those "smarts"
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Old Jun 28, 2012, 05:15 PM
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It occured to me that it would be wise to put a couple ferrite chokes on the esc signal leads. With this kind of current, it would not surprise me if there was interferance generated. The ferite chokes should help eliminate any cross talk.
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Old Jun 28, 2012, 06:14 PM
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ferrite chokes?
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Old Jun 28, 2012, 08:24 PM
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Here's a pic from Don's website. In this case, the ring is installed on the UBEC.



the ferrite ring is used to dampen rf noise. I would use one one each signal harness of the ESCs. RF harmonics could have caused the issues that you experienced.
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Old Jun 28, 2012, 09:10 PM
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The 60 amp ESCs he has already have those on them. All the Hobbywing ESCs with switching BECs have ferrite rings installed on the servo lead.

Don
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Old Jun 29, 2012, 09:12 AM
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Well.... that's good, scratch that theory.
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Old Jun 29, 2012, 03:53 PM
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The good old days...

I stumbled across this picture... thought it might be interesting for those other Habu followers out there...

-Sully
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Old Jun 29, 2012, 05:40 PM
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Nice! Looks like the M-21s!
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