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Old Jun 10, 2012, 03:42 PM
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Thread: Grand Cruiser Crash: Need input on investigation

Back Ground: I really like this plane. My first one had many, many flights on it before it met its expiration date. I had sparred the main wing, installed flaps and was running a 4000 mah battery. Beautiful flyer. I pancaked her getting too cocky with some inverted flight going down wind at too low an altitude. I had to get another one. I built her even nicer than the first and had an RC lander C1 light system installed (it was not turned on during flight, fYI).

The Crash of my 2nd Grand Cruiser: This was her maiden flight and wind was 10-15mph, it might have been gusting to 17-20 mph. Its a little on the high side for wind but my confidence is high with this airplane because of my experience and familiarity with the airframe. It also happened to be on a funfly weekend for the local field, so lots of airplanes in attendance. Take off and rotation were buttery smooth. Easy flight to altitude an proceed into flying pattern around the field. Everything seems to be working great, as expected. I started my 3rd lap around the field as I was heading up wind, which seemed stiff and holding up the plane a little. I started a gradual left bank and the plane pulled into a hard bank as if I were yanking on the elevator. The plane made a hard left 360 degree turn . At this point I am fighting for control. For a second I seem to recover the plane out of the turn and then it begins to do the same thing and rolls back into the hard left bank. By the end of this full circle I have lost all my altitude cartwheeling the plane in to its end.

I am left confused. The plane was flying perfect.

Theories so Far: The wind was just gusting too hard and blew my plane right out of the sky. I have flown in stiff winds before but I can always bring her back. This bird went in after I lost complete control. This is why I think it was an electronics issue. Either a radio hit or a total loss of contact. I run a JR 9503 and receiver. Something to note was when I did a radio check post crash the rudder servo was locked over to the right and non responsive. I could hear it getting current but no motor or gear sounds. The rudder was in the opposite direction of my fatal last turns in the air. Not sure what to make of this. I wonder if the BEC over heated and I lost control. I am running two extra servos for the flaps but they were not deployed and the C1 lights were not on. I shouldn't get a hit on a 2.4 system but I've heard that it can happen and there were lots of other planes and radios on the field. The receiver and the antenna were buried a bit in the fuselage with the plethora of wires packed in there. I wonder if the receiver lost radio contact in the bundle but contact was lost at a location closer to me rather than farther away.

Anyway, at a loss. Bummed because it happened on the maiden and only after things seemed to be working great. Any input is appreciated.
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Old Jun 10, 2012, 03:52 PM
I fly 3-C Crash,Crunch,Crumble
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USA, NM, Clovis
Joined Feb 2010
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I generally lay out all components on the bench, and check them carefully for bad components, including connectors. If all is working well there, I proceed to do a range check. From there it is pure conjecture as to what happened. I lost a nitro powered pattern ship to a faulty switch on it's fourth flight once, and have never used a switch since. I only fly Electrics now, so the switch is not a problem. Good luck on your troubleshooting. Roy
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Old Jun 10, 2012, 06:21 PM
Shelter Kitty "Orange Death"
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United States, FL, Monroe
Joined Jan 2008
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Being a twin with 2 ESCs, was one of the BECs disabled?
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Old Jun 10, 2012, 07:00 PM
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No, both were connected. And I've heard that this is a problem. On my original Cruiser it was the same because that is the way it comes I believe. I had close to 50 flights on that one and its end came from pilot error. But that does add another theory.

Another thought I had was on the esc programming. I believe I had the voltage cutoff on high. Is that also a wrinkle?
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Old Jun 10, 2012, 08:41 PM
Shelter Kitty "Orange Death"
bartricky's Avatar
United States, FL, Monroe
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Quote:
Originally Posted by F1nut View Post
No, both were connected. And I've heard that this is a problem. On my original Cruiser it was the same because that is the way it comes I believe. I had close to 50 flights on that one and its end came from pilot error. But that does add another theory.

Another thought I had was on the esc programming. I believe I had the voltage cutoff on high. Is that also a wrinkle?
I will defer to someone who knows more about brushless twins.
I have a brushed twin so only one ESC.

But wondering if one BL ESC cut-off was set higher than the other might one motor quit earlier than the other?

My first thought was that one aileron servo came loose from it's mounting.
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Old Jun 10, 2012, 09:39 PM
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All servos and connections still functional save the previously mentioned rudder servo. It was in full right lock and non functioning. Not sure if that happened prior to crash or after.
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Old Jun 10, 2012, 10:06 PM
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This is the way the esc's were programmed:

Brake: Off
Battery Type: Li
Cut Off Type: Soft-Cut
Cut Off Voltage: High
Start Mode: Normal, as opposed to Soft, or Very Soft
Timing Mode: Middle, as opposed to Low or High
Governor Mode: Off
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Old Jun 10, 2012, 10:41 PM
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United States, TX, Fort Worth
Joined Jun 2000
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While conventional wisdom is that one should not run both BECs in a twin, I have gone along with using both BECs on 6 or 7 Rx-ready twin engine models as they are supplied. Some are two or three years old and none have ever had a single issue in hundreds of flights.

So, it is unlikely, IMO, that using both BECs is the cause.

One of my twins is a Dynam 310 (hate the name Grand Cruiser) and it has around 50 flights with no issues.....On both BECs.

No good theories come to mind on what actually caused you crash.....could be any number of things.
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Old Jun 10, 2012, 10:55 PM
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Any chance it was a simple stall/spin? Trying to do a good-looking, constant radius turn when it's windy can get your airspeed much lower than you think.
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Old Jun 10, 2012, 10:58 PM
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I can't rule out the possibility but I had so much airspeed after the first full turn I should have had some control over the wing. I had very little to no control for two full descent turns.
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Old Jun 10, 2012, 11:18 PM
To Slip is Divine
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Check all of your radio gear, did you find the letters: F U T A B A on any of them? If not, that may be your issue. (going back under my bridge now)
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Old Jun 11, 2012, 12:09 AM
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lol, fair enough.
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Old Jun 11, 2012, 01:52 AM
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Quote:
Originally Posted by tom1968 View Post
Any chance it was a simple stall/spin? Trying to do a good-looking, constant radius turn when it's windy can get your airspeed much lower than you think.
Happen a little to often to me. I think it looks like the wind, slowed the plane, and occurred the crash.
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Old Jun 11, 2012, 03:33 AM
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Letchworth, Great Britain (UK)
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Was your flight long enough that you would expect the battery to be running down? If both motors run off one battery, one lvc will invariably kick in before the other does (due to manufacturing/component tolerances) and, when that happens, the battery voltage will rise enough so that the other lvc is nowhere near its activation voltage. So, could assymetrical power have started the sequence of events?
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Old Jun 11, 2012, 03:21 PM
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So on the Dynam 310 should the voltage cutoff on the esc's be set to high or low?

Timing should be set to high for more power, no?
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