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Old Apr 08, 2012, 08:34 AM
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Hobby King SBach 1323mm 30e ARF Build

Soooo many SBach's out there right now, but couldn't find much about this one anywhere, and they don't include any instructions.

This is for the Hobby King SBach 1323mm 30e

Quick Reveiw: 4 stars out of 5. Mostly because they only include hardware for pull-pull rudder and it would have been VERY simple for them to include another control horn blank, push rod and have indicated better the spinner size needs. Also, the hardware was very cheap (mismatched in many cases and two of the blind nuts for the firewall were stripped/ruined) and the horizontal stab was covered in RED instead of the rest of the plane's "black" matra, plus lack of instructions. Also, the hardware for the wheel pants was...uh just inadequate, to say the least and one wheel pants was chipped. Other than that, the covering seems pretty good, and most of it looked pretty clean, and HK always packs these planes pretty well.

Specs for my build:
Hobby King 1323mm 30e Balsa ARF
Turnigy Plush 60A ESC
Turnigy SK3-4240 620kV motor (830W)
Nano-tech 4S 2650-3300mAh LIPO
Hitec HS-65HB Servos (4x) I just didn't trust the Corona 939MG's...too much noise/slop/jitter
Great Planes 2.5" Red Spinner
APC 14x8E (think 15" is too big) and I wouldn't mind trying a 14x10E for higher speed...
AUW is really close to 4.5lbs with 2650 mAh LIPO. w/o lipo, I'm right at 1720g.

I'll get some performance numbers up here once I complete the maiden.
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Old Apr 08, 2012, 08:36 AM
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I'll go back and annotate the photos.
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Old Apr 08, 2012, 08:46 AM
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Nice looking build

Have to say looking at some of the design aspects of the plane - these guys are getting the gist of design concepts and I have to admit within a year or under I can see these planes dominating the skies through performance alone - still a way to go...but each carnation looks better and better
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Old Apr 08, 2012, 09:16 AM
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Yeah, this is pretty good acro plane, I think, but it is no 3D-er (at least this version). Still needs better control surfaces, I think. But it will fly super slow and rolling harrier and loop and KE pretty well.
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Old Apr 08, 2012, 10:14 AM
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Some quick ecalc.ch numbers for that motor on 4S. The 14x10 is probably the best for maxing out the numbers from that motor if you have to stay below 15" prop. I only have a 14x7 and 13x8 for now...keep in mind ~2050g AUW with 2650mAh 4S Lipo. Will need about 2200g for 3300mAh.
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Old Apr 08, 2012, 11:02 AM
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I work thrust at 2:1 so everything is focused on finding a combo to fit that...based on what expected AUW would be...though you suspect that this won't be as easy to go all out 3d and perhaps would be better as a precision/some 3d capable where you could look for anything around 1.5 - 1.75 :1 thrust ratio -
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Old Apr 08, 2012, 03:30 PM
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I personally would glass that LG area = or add some CF in that area to beef it up...

Can't truly tell by the pics but looks suspect....but lets face it haven't seen any of the big Mfr's totally understand what forces are apparent in this area and how to remove the energy that causes LG ripouts/collapse
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Old Apr 08, 2012, 06:59 PM
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Heheheh. Glassing it doesn't help when the tail servo locks up and sends it into a death spiral. Sigh. Happy birthday.
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Old Apr 09, 2012, 12:29 AM
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Oh man! Crash and burn?

Hope not. That would totally suck. Great thread though. BTW, the Sullivan tail wheel is a MUCH better tail wheel system than 99% of most stock ones and can be added easily if you forget to put the stock one on. I do that a lot.
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Old Apr 09, 2012, 06:01 AM
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Yup. Haven't had one auger in like that for years. It flew nice before that, but it was really tail heavy on CoG. Rolled very nice, but had pretty nasty snap roll on high elevator pitch tendency. This needs way more weight up front, as I had 2650mAh bat as far forward as could go.

But something else happened when she crashed. Still not exactly sure, but it was spiraling in pretty hard. Might be I was just pulling too much elevator in panic, and it was snapping.

Tip stall is way worse than the sim on this bird, but it was pretty windy.

I really like the lines on this plane, and I think if I'd had a chance to get the CoG further forward, limit the throws more on the elevator and turned off the rudder to aileron mixing (which was backward due to servos being reversed), it would have been fine. Very nice straight lines inverted and upright at speed...
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Old Apr 09, 2012, 08:25 AM
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Notes from build: They glued one of the magnets in the canopy backward, so it was "pushing" instead of latching. Also, both the rear magnets pulled out of the hole, so only the front magnet was holding. You should be sure to carefully check these. I also messed up and didn't get the tail wheel assembly put in during the rudder CA attachement. Last, without any instructions, there was no CoG indication. I put a 10.6oz 2650mAh 4S in the battery tray as far forward as I could go (be sure to protect the lipo from the front firewall screws), and it was balancing about 4.5" back from LE. On a 13.2" wing root. Seemed too far back. That is about 1" behind the main spar, so I figured it was a bit tail heavy, but with plenty of power should be ok and not stall unrecoverably. It was VERY tail heavy, actually. I'm not sure how much the rudder servo mounted back there contributes, but it can't help, and likely you will need >3300mAh 4S or more to get it to balance well. I also don't particularly like the flex in the elevator with the small U-rod connector, but it wasn't too bad. Motor timing seems wrong, and will grind when going from a decreasing idle back to full throttle (or going full throttle from stopped).

Maiden: Taxied the plane around the long asphat drive way and culdesac at my home, and this plane looks phenomenal. Sleek long lines, turns well and runs nice. Maiden run up on grass was a bit draggy, but no tendency to flip up, and plenty of power. No real nasty veer left like the corsair or mustang. Nice straight run out, and a pretty steep climb (need to use less up elevator, unlike mustang to keep straight tail dragger track and just let it rotate up naturally, but oh well...was more worried about a nose over in the thick fresh spring clump grass). Rolls are EXTREMELY authoritative. Pretty. Lines are straight and just need a little right aileron and rudder trim. It was windy (15-25 MPH gusts), so hard to trim it consistently, but I have it close. Slow speed and about 5-7 MPH above stall, it really drops the tail, and then begins to die. CoG is way too far aft. Ok, but add some speed, and it is nice and straight. Inverted is good with the symetric wings. Tight loops have very severe snap roll tendency, so I probably have too much elevator throw...I can change that later. Rudder coupling to ailerons is set at 11% to do a flat slide turn with no banking (from my YAK 54 foamie). It is either reversed because servos are backwards from the Yak or way too much...either way, Knife Edges (plus the wind) aren't very good and roll out fast. Can't really try elevators to see how it balances in a stall drop because of the CoG, but snap rolls are very responsive (almost too fast). I figure top speed on this is around 60 mph with the 14x7, which is a little high, but maybe with the wind and on a full LIPO.

Then, tragedy. Either something snapped loose (the aileron was completely pulled from the CA hinges on the right side with no obvious damage or issue with the wing, which seems strange, post mortem) or I got blasted with interfereance. I'm not real sold on any of those explainations, and most likely (reviewing it in my mind over and over), I got into a high alpha dive/loop, and it kept snap rolling all the way into the ground. Pavement, to be exact. Straight in. I don't believe in coincidences much, and I've been trying to be honest with myself and figure out what happened. I fly a lot of foamie 3D, and really try to use a lot of elevator authority. It hurts me on my warplanes, because I always have to go back and limit the servo travel to avoid snap rolling in aggressive loops. In this case, I've been thinking about how CoG may affect you in a high alpha tight loop where the wing begins to stall out (this is what causes most snap rolls in tight elevator loops). If you have a very aft centered CoG, the tail will naturally want to swing down/out more...putting it into even MORE of a tight loop/angle of attack. Which with eventually just feed back on itself until it flips over (counter clockwise on these planes), which is exactly what it seems like I remember happening. And the more you yank and bank on the sticks, the worse the drag and more it wants to stall. So, I think I just learned a very valuable (expensive?) lesson. I've always tried to maximize the throws on my planes (and this one seemed not huge compared to my YAK foamie), but the surfaces are pretty big. I believe I simply had really bad CoG (was almost ready to land and try to address that...sigh, but two passes in high had made it slow and the tail to settle very badly, so I throttled up out of it and was playing a little more before trying a fairly fast speed landing to avoid stalling). Not fixing that sooner likely lead to my demise.
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Old Apr 09, 2012, 09:20 AM
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This thread seems extremely applicable. Pretty much supports what I was running through in my mind. In retrospect, I think (hard to remember everything that happened...need flight recorders...grin), but I *think* I even pulled off the throttle as it went into the spin/stall, as full power always seems to tighten these things into oblivion, and I'm almost certain I was probably trying to naturally correct for the roll with aileron...which is a bad no-no in spin/stall...but in this case, the reduced power probably aggrivated the control surface and wing stall and the rest is morbid history. I'm just shocked how much the aft CoG affected this model here. Granted, it was pretty severe (very nasty pigish wallowing and immediate nose up as I checked high altitude slow speed stall response)...oh well. Live and learn...I grow ever more wary of that effect, and have pushed aft CoG for hovers in my 3D planes, but they have insane wing loading and control surfaces. Always thought that aft CoG was dangerous, primarily only in planes with low thrust/weight ratios...in this case, I could easily pull out of a dropped tail stall with power...the ever tightening spin/spiral/snap hasn't slapped me in the head hard enough before, I suppose.
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Old Apr 09, 2012, 09:43 AM
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Ouch!!!

Post mortem is always difficult...unless something was obviously not right from start
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