Unexplainable Crash... Help!

[qcman]

Hi guys I was flying my SR at the park tonight & all was going well. Was doing a pass across in front of me horizontally (nothing too hard at all) in IU mode & the heli just went straight down as hard as can be into the dirt. It appeared as if it went full negative as I believe it hit skids first.I don't think I did anything as the pilot to cause this one... all the others in the past yup that was me...

I couldn't even hit TH it was so abrupt. My initial reaction was maybe something let go perhaps a link or something or swash separation.. Swash is okay it appears. Of course lots of broken stuff, frame boom etc & the usual suspects. Some links were off but with the impact being so hard I expect some would be. Shaft collar is still in place too as I thought maybe it had slipped.

Is it possible it lost signal or something interfered with it to cause this? I am using it with the DX6i. Would a popped linkage do that? I expect it would make it roll or something if it was a ball link or one of those type of things. I didn't really check to see if it was still bound but I did hit TH after impact & everything stopped. I was just standing there dazed with that WTF look on my face...

Anyways would appreciate some help figuring out the cause of this one as I'm a little concerned it could happen again.


Thx,

Cam

[Bladecpnitro]

Usually 1 blade link off will make it climb out of sight in idle up but will come down after switching back to normal mode, although very unstable and wobbling. 2 blade links off result in an uncontrollable Sr all the way to the crash site. I've never seen one just spike the ground hard like that unless you were already having problems with it spiking up and down due to the center hub and rotor head sticking. Silicone spray works good on those plastic against plastic parts.

[qcman]

Thx for the reply. I'm using a Micro Heli metal Center hub actually not the plastic one.It has been bashed a few times though has been working well of late as I had not crashed in a very long time & had dozens of flights with it. I haven't noticed any binding as in strange pitch changes up or down. Oh well I'll get her rebuilt & carefully make sure things are working okay.

This is a very strange accident for me though & it is a little nerve rattling to think I really don't know what happened. At least when I screw up it is no fault of the bird...

Cam

[Velislide]

A little bit of wind will cause the SR to lose altitude extremely fast, just dart straight down.

[DKS_ONE]

Mmmmm, depends on the attitude of the heli, if pitched forward a bit, then ya, it'll do that. Given he was flying forward we can assume that, but it would have to have been a fairly stiff wind and I'm sure pilot would have noticed that. And the link theory doesn't hold up that well either, I had the elevator link pop off the swash in flight one time, hairy experience. It made it lift and drop pretty aggressively depending on which side of the disc the wind hit. I got it down in one piece, popped link on and flew again. For it to drop all three links would have to have come off at the same time. Highly improbable!! Truth is, there's not a lot that can explain this one, you checked the usual suspects, swash and main shaft collar. Those were the only two mechanical things that came to mind for me. The only other thing I can think of is like you mentioned, some kind of interference or an electronics failure. Problem with that is they can crap out in so many ways and not even show it. The only real likely culprits are Tx and Rx because other electronics would likely cause additional issues. I suppose it could be the BEC in the esc, if it jammed out the servos might go bananas... Have you powered any of the components up to see how they function since the crash? It's possible the fault is still there and you may be able to see the evidence if not the faulty part

[Bladecpnitro]

I have flown close to a car that wind was blowing over and catch a hard down draft that would nearly put the Heli in the dirt if I weren't ready for it. Sounds like yours went in way harder than that though.

[qcman]

Originally Posted by Bladecpnitro

I have flown close to a car that wind was blowing over and catch a hard down draft that would nearly put the Heli in the dirt if I weren't ready for it. Sounds like yours went in way harder than that though.

Oh yeah this was like a downward pitch pump.......

[qcman]

Originally Posted by DKS_ONE

Mmmmm, depends on the attitude of the heli, if pitched forward a bit, then ya, it'll do that. Given he was flying forward we can assume that, but it would have to have been a fairly stiff wind and I'm sure pilot would have noticed that. And the link theory doesn't hold up that well either, I had the elevator link pop off the swash in flight one time, hairy experience. It made it lift and drop pretty aggressively depending on which side of the disc the wind hit. I got it down in one piece, popped link on and flew again. For it to drop all three links would have to have come off at the same time. Highly improbable!! Truth is, there's not a lot that can explain this one, you checked the usual suspects, swash and main shaft collar. Those were the only two mechanical things that came to mind for me. The only other thing I can think of is like you mentioned, some kind of interference or an electronics failure. Problem with that is they can crap out in so many ways and not even show it. The only real likely culprits are Tx and Rx because other electronics would likely cause additional issues. I suppose it could be the BEC in the esc, if it jammed out the servos might go bananas... Have you powered any of the components up to see how they function since the crash? It's possible the fault is still there and you may be able to see the evidence if not the faulty part

Thx for the insight DKS yeah I did power it back up after & the electronics seem to be working okay but I haven't given it a real good look or taken the broken stuff off as I was too pi$$ed off to do it last night right after it happened. I was about 12-15' off the ground & was flying almost perfectly flat as I was moving forward very slowly. It pretty much hit flat on the skids.

I'm leaning to a Rx or Tx issue too at this point. You could tell it was flying nice & then was "lost" in a split second but was like a full negative pitch was applied the way it dropped.

I won't get a chance to dismantle it right away but will later this week & will look at the parts more carefully. So far it's right up there with the Caramilk secret....

Cam

[qcman]

Originally Posted by Velislide

A little bit of wind will cause the SR to lose altitude extremely fast, just dart straight down.

Thx no I'm sure it wasn't that as this was at full speed vertically....

[DKS_ONE]

Originally Posted by qcman

Thx for the insight DKS yeah I did power it back up after & the electronics seem to be working okay but I haven't given it a real good look or taken the broken stuff off as I was too pi$$ed off to do it last night right after it happened. I was about 12-15' off the ground & was flying almost perfectly flat as I was moving forward very slowly. It pretty much hit flat on the skids.

Dude, I've been there... good idea to put it down for a day or two, maybe even a week and then come back to it. Don't feel quite so angry then... lol!

Originally Posted by qcman

I'm leaning to a Rx or Tx issue too at this point. You could tell it was flying nice & then was "lost" in a split second but was like a full negative pitch was applied the way it dropped.

It may be difficult to recall, but did you hear the motor overspeed? May not have been high enough drop to have it build up but if it went negative would likely hear the motor ramp up quite a bit. Might be worth going over the menus in your Tx to see if there's anything that looks out of place, especially something that might change with flight mode switch. Just throwing things out there.

Originally Posted by qcman

I won't get a chance to dismantle it right away but will later this week & will look at the parts more carefully. So far it's right up there with the Caramilk secret....

Cam

[chippy54]

I had a problem similar to this when hovering my Sr in the back yard but it went the opposite direction. It shot up and to the left and smashed into the house wall before i had time to react with throttle hold. The problem was in the tx. The throttle pot had failed and gone full speed without input. Checking the monitor shows the throttle stuck at full no matter what position the stick is in so i think this dx6i will have to go in for repair. I am rather glad it wasn't my 450 3d i was flying at the time. I was a bit lucky as a friend of mine had just got a dx8 and he sold me his dx6i for a bargain price so i can send my old one off for repair and still be flying. So it might be a good idea to check your tx.

[Jumna]

QC, something exactly like that happened to me a while back, and it an instantaneous downward slam! Even made a similar post title: https://www.helifreak.com/showthread.php?t=226599 It was swash separation for me.

Chippy, last year I had to send in my Dx6i for repair for a throtle pot problem. HH was good about it and it was a warranty repair.

[John Shipley]

I have had the same problem happen 3 different ways. 1. I was doing a high speed pass, gave it a little down to pick up speed, was doing great, went to give it a little up, gave it down instead and ....splat 2. Was doing the same as above, but had been flying a lot of planes that day, was going a little fast on the pass and gave it a little less throttle (negitive pitch on a heli) and ....splat. 3 Was making yet another high speed pass, when suddenly the heli dives into the ground.....I had done nothing this time. What had happened, was I popped an upper link off. What this does is makes the blade that has no link, have no pitch and now you are trying to keep the heli up with only one blade......and splat.
If everything on your heli turns out to be OK, then you probably had a pilot error. I would check the elv. servo to make sure it does not have a broken gear. I saw a 500 go in the same way as you describe and when I told him to check the upper links, his eyes lit up and he said...."you know the uper link was off when I picked the heli up".....problem solved........If you are using the MH swash, it can drive the head parts further than the stock swash. On a stock swash, because it is plastic, the outer arms will flex as you reach the end of travel. On a MH swash, you can overdive the limits and it will pop the links. So in your set up, be sure to set you limits just a tad before they bottom out........J

[qcman]

Jumna thx I wil recheck the swash for possible separation. I'm only using my original stock one that is almost a year old now.

John it of course could be pilot error though I just had a sense for a split second that something failed. Diagnosing links etc. is hard as the flybar cage on the top has a ball broken off one side & other stuff was popped off as well. I broke a blade in half the other Xtreme one is fine.

The frame is busted in 2 places so that needs replacing. My B400 land gear is toast too. I may have to try a B450 set as I don't know if I can still get the B400 skids at my LHS. I'll get it torn down maybe tomorrow night & see if I can find something. The servos seemed to all move okay on a quick test after the crash but I will inspect them closer as well.

Thx again to everyone!!


Cam

[qcman]

A bit of an update I think it was caused by worn head parts. Since I rebuilt it has been popping stuff steady & tonight a paddle control frame popped off in flight (no crash thankfully) but it broke the anti-rotation collar off.

So I am going to replace the head parts & go from there. But I think this was the likely cause of the nasty crash so a word to the wise check your head parts...

Cam

[DKS_ONE]

Originally Posted by qcman

A bit of an update I think it was caused by worn head parts. Since I rebuilt it has been popping stuff steady & tonight a paddle control frame popped off in flight (no crash thankfully) but it broke the anti-rotation collar off.

So I am going to replace the head parts & go from there. But I think this was the likely cause of the nasty crash so a word to the wise check your head parts...

Cam

I've had links pop off in flight, not fun.

[nbells]

Thinking back ...... I had a few crashes last year where I was about 12 - 15' off the deck and for no apparent reason the heli would just plunge to the deck .... it was like someone shot the thing outta the sky.

On inspection, I could not find anything wrong or missing. It was so annoying. perfect days, very little wind, sun shining etc etc so why did it just fall out of the sky ? ..... Rather than dwell on it, I decided to fix it up as best as I could.

It used to do my head in, never being able to find a reason and I was beginning to doubt my flying skill ..... well, what skill I have !

Then one day speaking to an Old heli hand ..... he said, its a bad servo.

Cut a long story short ... I got a servo checker... one that does all 3 servos at once and put them through the continious test procedure .... and after about 5-10 mins, one servo would just take a jump and start to "jitter" ... then it would come ok again.

Never had a problem after that ... now I always check my servos after every crash. I hook them up and run them for 10 mins. no need to dismantle them, just leave them on the heli and watch the swash go crazy for 10 mins.

I change ALL head components after a crash and loctite the usual bits. I also run with the MH swash.

Oh .... I now run with DS76 digital servos, the same as used on the Blade 450, never had another falling out of the sky event again !

nbells

[qcman]

Thx Nbells,

Yeah I wondered about servos too I did check them after the crash & they seem to be working okay. I looked at them as best I could under a magnifying glass & I can't see any stripped gears. God knows they should be for what I have done to them in the last year. I am going to replace all of the head parts before any lift off as they are clearly worn. I can pop stuff off with minimal effort. Not to mention it has ejected a couple of parts in my most recent flight.

Is this the cause of this it is hard to say? Mine didn't look like it was shot out of the sky but rather like the Almighty punched it with his fist into the ground. Do you think I should be replacing my servos too for good measure? I can get some online for a reasonable price I think.I don't think they are bad though....

The other thing was the heli had been flying great for at least a few months over the winter indoors with no crashes so it was running the best it ever had ironically. And then kaboom!!

Imagine a crash that I might not have been the cause of... hard to imagine



Cam

[nbells]

Cam

Its cheaper to get a servo tester .. do as I did .. then run them for 10 mins ...

Who knows ... maybe .. maybe not ..... but just thought I would mention the servos.

Best of luck and let us know what you find .... if anything

Nigel