Catastrophic DFC Link Failure

[HFMan]

Had to happen sooner or later. Crashed my 700 DFC this weekend due to one DFC link breaking. The plastic ball link failed in a high speed, really large hurricane. The main rotor basically slowed to a complete stop in a matter of a couple seconds, and there was no hope of settling it down via Autorotation. Hard crash on skids & nose, and one battery caught fire but put itself out by the time we were able to make to to the crash site (took 5 minutes to get out there due to the very tall weeds).

Kontronik log shows that the KDE HD main gear stripped as the Kosmik tried to maintain RPM (which was impossible).

All electronics survived, both frames busted, one main blade fractured, struts broken, aluminum bottom plate & battery tray taco'd, both batteries lost, main gear stripped, canopy trashed- but head, boom and tail are fine. One of the pictures shows how hot the battery got, deposited aluminum from the bottom plate onto one of the struts. I'm really lucky this didn't totally flame out as we would have never gotten to it with the fire extinguisher in time.

Head Dampers are still as stiff as ever, so I don't think excessive flapping was the cause- it's just the crappy Align DFC design that is sure to fail at some point due to fatigue. She'll live to fly another day, but I'm gonna give some different head options a thought.

[charles.frank]

Uggg....I know of another pilot that had a dfc head failure on a g700 this past weekend. .I been looking at the kde sxts head and doing away with the dfc on my newely buily 700e dfc..I priced it all out. .with the sxts kit a new swash and the follwer arms is right about 200$..that's alot less than a catastrophic failure. .
Sorry for you loss. ..REBUILD AND FLY AGAIN!

Sent from my Goblin while pirouetting inverted.

[reALIGNed]

Well, if it is the plastic link that failed from fatigue, and you knew "it had to happen sooner or later", then blame yourself not the link. Every new season I replace all of my crucial wear and tear parts (plastic links too), preventative maintenance, to prevent this type of situation. Its like driving on bald tires........its going to happen sooner or later. Please don't start another DFC bashing post.

[Excalibur3]

Originally Posted by reALIGNed

Well, if it is the plastic link that failed from fatigue, and you knew "it had to happen sooner or later", then blame yourself not the link. Every new season I replace all of my crucial wear and tear parts (plastic links too), preventative maintenance, to prevent this type of situation. Its like driving on bald tires........its going to happen sooner or later. Please don't start another DFC bashing post.

+1 brother. I check my Heli every flight it won't run unmaintained for ever. All helis also need preventative maintenance and I love my DFC HV. Best Heli I've ever owned or flown.


TS3D#1
NanoCPX, TREX500DFC,
TREX700DFC HV, DX8

[HFMan]

Originally Posted by reALIGNed

Well, if it is the plastic link that failed from fatigue, and you knew "it had to happen sooner or later", then blame yourself not the link

These links (replaced during a maintenance inspection last month) have 30 flights. I maintain this heli meticulously and also love the way it flies. You've got some kind of gall jumping to faulty conclusions. This isn't bashing, it's fact and a bad design.

[HeliSmith]

Sad it had to be so much damage for a link failure.

[songer121]

i mean are you a 100% that it was the link that failed anyways?

there are so many things that could go wrong if everything is not in sync properly....

[reALIGNed]

Originally Posted by HFMan

These links (replaced during a maintenance inspection last month) have 30 flights. I maintain this heli meticulously and also love the way it flies. You've got some kind of gall jumping to faulty conclusions. This isn't bashing, it's fact and a bad design.

Upon admitting its a bad design, and knowing its flaws, then why fly it and push it into hard manouvers. And then when it fails (assuming it was a link) and crashes, and ends up costing all this money in repairs..........just doesn't make sense to me. I've heard it all before about the design flaw, (and I agree with the facts). But in the end result (your crash), I'm glad no one was hurt or killed.

[PetJumper]

Hi HF,

sorry fot the loss!

Are you sure, the linkage failed? I cannot really interpret your log file, but from looking at the main gear, this looks very much the same like a couple of KDE and Align mains I melted in my 800 last week - see picture. A motor spinning against a blocking main shaft will break out 5 to 10 teeth, and will not clear out the entire main gear as in your case.

Also, from your description it sounds like a main gear failure rather then a broken ball link. Such a ball link failure during a high speed hurricane would usually cause a boom strike instead of a slowing main rotor. The broken linkage could have been caused by ground impact.

My main gears melted during high-speed manouvers after about 5 minute in the air. Due to a worn-out motor bearing the Scorpion 5035 simply radiated way too much heat to the pinion. That motor is so powerful it doesn't really care if beariings are working properly - I guess the same holds for your KDE monster.

[Glenn Goodlett]

For what it's worth, I've had links to the pitch arms break and behave just how you have summarized and without a boom strike.

I also crashed this weekend with almost identical damage. Mine was a stripped/melted gear at the bottom of a loop.

[songer121]

man im sorry but you guys that are toasting these main gears "especially the black ones" are just doing something wrong it seems like.... ive done hundreds of flights and NEVER cooked a main gear black or white.

idk.....

[HFMan]

No doubt in my mind the DFC link breaking started the mess. You don't always get a boom strike- it depends on tightness of the blades, aerodynamics, and other factors. In this case, the blade pivoted along it's longitudinal axis (perhaps pivoted such that the pitch arm swung all the way over the top of the head and slammed into opposite pitch arm- there are marks on both arms suggesting they met with force) and was likely broadside to the wind, thus slowing down the rotor head very rapidly. The only other possible cause for sudden deceleration of the main rotor would be frozen main bearings or perhaps frozen OWB- all are still butter smooth. My notations in the Kosmik log pretty much back up the theory that the rotor slowed down rapidly, and the Kosmik was doing everything it could to bring the speed back up- but there was too much wind resistance. In 1.5 seconds the main gear stripped due to high amp pull (and it was at this point I knew I had nowhere near enough rotor speed to do anything). I tried to pull the helicopter upright, then hit TH and watched it drop straight down.

I have stripped a KDE gear on this same setup, not long ago- in a full throttle ascent into a loop. Patrick explained that with this power setup, the summer heat, the stainless steel Align pinions, the 200 amp Kosmik- you can strip gears. He indicated silicon grease on the main gear goes a long way towards reducing heat, which ultimately is what leads to gear failure. I only run 12.5 degrees collective, but that is still enough to pull a lot of amps. In this case, the gear stripping was likely inevitable- the only way to have prevented that would have been to react very quickly and engage throttle hold (in less than 1.5 seconds). Hard to do when the heli suddenly violently rolls one direction and you see the blades slowing almost instantaneously before your eyes.

[HFMan]

Originally Posted by Goodlett

I also crashed this weekend with almost identical damage. Mine was a stripped/melted gear at the bottom of a loop.

Goodlett, sorry about your crash. What motor/esc are you using in that setup? I know that when I stripped my first KDE HD gear, I actually was in the climbout when it stripped. I realized I still had enough friction to continue turning the head, so I limped back to home base with about 800 rpm. I first thought I would have to autorotate, but I was so far out in the field it would have been difficult to judge the flair due to the slightly hilly terrain. I was very fortunate that I had just enough friction to hobble it back.

[Glenn Goodlett]

I'm running the 800mx with the Edge 160. The motor has always come down blazing hot. This was the 6th flight on the KDE gear. Also I think the Align black gear takes the heat better than the KDE gear, but I acknowledge I may be wrong.

I hope to be flying again by this weekend if Aligntrexstore.com ships my order soon.

Edit- Just checked, my order has shipped. Also, it's hard to see from my photo but my gear is more melted than stripped. I'm going to try the KDE 700xf 495 motor just for kicks this time around.

[HFMan]

The 700XF-495 also gets hot, running at 5 degrees fixed timing via the Kosmik. I've measured temps as high as 175 degrees. I too am starting to question if the KDE gear is more temperature tolerant than the Align gear. It may be stronger, but I wonder if it breaks down faster due to heat. Hard to say- I've not flown the Align gear in the temperatures that the KDE has been exposed to.

[Glenn Goodlett]

I checked my 800mx temps as high as 185 F. I had hundreds of flights with the stock Align black gear, but after some maintenance I adjusted the gear mesh a little loose and continued to fly for many flights. The gear started to wear and exude lots of gear dust, so I decided to replace the gear. I had the KDE gear in hand so that is what I used. The mesh was perfect, but the gear lasted exactly six flights.

I think I will try the KDE motor and the Align gear this time around.

[xokia]

Sucks for the crash. Any chance we get get a picture of the link? I'd like to know what to look out for.

I had a trex 450 crash last weekend that one the aileron servo stopped working while doing tick toks. I ended up in a crazy spiral I couldnt realy control. It can be gut wrenching watching your heli head towards the ground knowing there is nothing you can do. The only positive is also knowing there was nothing you could do.

[ddj74]

Wondering if this is caused by motor being too hot and transferring the heat to pinion and over heating the gear making it soft.

[HFMan]

I think that's entirely possible. Patrick at KDE indicated that when align switched to stainless pinion gears, it was transferring more heat than previous gears.

[Spunjah413]

Originally Posted by ddj74

Wondering if this is caused by motor being too hot and transferring the heat to pinion and over heating the gear making it soft.

I was actually thinking that also right before I read your post. Surely something to investigate by the manufacturers.