H9 Extra 260 crashed after violent, uncontrollable tailspin.....

[RCFanatic12]

My 27% H9 Extra 260 had well over 100 great flights on it up until yesterday when I buried it into the ground after going into a deadly, uncontrollable tailspin. It always flew like a champ and never put me into any unpredictable or uncontrollable situations and was always a smooth flying aircraft. That is what makes this crash so puzzling and I'm dying to understand what caused this to happen. Here's all the details, and I know it may get long (I'll try to keep it short), but please read because I'm going crazy trying to figure this out.

Bought the plane in Mar. 2007 and flew amazing for almost an entire year. My setup was an Evolution 45GX2, JR PCM10X radio, two JR DS8411's in the ailerons, one JR8611A on the rudder, and two JR DS821's on the elevators. In Nov. 2007, I converted the plane to Spektrum and the plane continued to fly exactly the same, no flight characteristics changed. Also note, the airplane had never been properly balanced since its assembly, but it flew so smoothly through all types of maneuvers (including tailspins & blenders) that it couldn't of been an issue. In the beginning of February 2008, I upgraded the battery pack from a 6V 1400mah NiMH to a 6V 2300 mah NiMH and I upgraded the wing servos from the existing JR DS8411's to two JR 8611A's. Once again, I never properly balanced the airplane after the upgrades.

This was when my problems began. During normal flight and standard maneuvers, the plane flew exactly the same as it always had, except for tailspins. My first flight since the upgrades, I did a hammerhead and went into a slow tailspin with minimal aileron input (zero elevator input) as I have countless times before, but this time, I lost complete control of the plane and it entered a violent tailspin, throwing the tail around and it began to enter a flat-spin. I instantly throttled up and inputed opposite aileron and rudder and the airplane pulled itself out of the nasty maneuver. After I calmed myself down, I tried the same tailspin again with the same crazy results.

This had been going on for the past month, and I flew the plane for the first time in a while this weekend. I risked the maneuver again after ten minutes of smooth flying to see if it was still doing the same thing, and of course it did. I landed the plane and upgraded the elevator servos to DS8411's, thinking that my DS821's weren't providing enough torque. I took off again, flew around for five minutes and risked the maneuver again and it still did the same thing. A few flights later, I tried the maneuver one final time, but this time was the last. The plane violently entered the uncontrollable maneuver and began violently flat-spinning, except this time my increased throttle/opposite aileron & rudder input weren't enough to save it and it buried itself in the ground.

I’m puzzled by this crash…. Any ideas of what could cause such an accident??

[FlyguyXII]

Sorry to hear about the 260 going in. Most likely cg due to heavier battery possible causes improper inputs to exit the spin. Opposite rudder and down elevator standard exiting inputs.

[adrian]

we always called it the death spiral - many issues the cause - mostly pilot error trying to hard to do to many things and not letting the plane sorta fly out of the problem - this all causes wing stalls and other things and you the pilot trying to catch it in panic and actually causing even more problems - sorry bud!!!

[rcflyguy]

where were the batteries in the fuse?

[superdh]

your "departure" (thats what some full size pilots call spins) sounds like it was exagerated by an aft c.g. that was at a critical point

if its possible, relocate all the parts temporarily and check the c.g. now to see if thats where the problem really lies

adding power and opposite aileron may have forced the plane out of its spin in the past but that is not the correct technique for stopping spins, applying opposite aileron stalls the already stalled wing even more and usually deepens the spin(except maybe as you found it can force the aircraft to stop)

correct spin recovery technique does vary with airframes but most models only require you to neutralise everthying and cut the power, most models will recover faster if you cut the power, nuetralize the ailerons and apply opposite rudder just like i learned to do in fullsize...cessna 152's spin great

[mmcconville]

Sounds like the model was quite tail heavy. I'd say the new larger battery was probably located behind the CG right? So it shifted the CG even further back.
Always a good idea to check the Cg and start at the recomended location.

[DKnippen]

Sorry to here this. But seeing that you've had many flights with no issues I would next look at the rudder servo. Sounds like it or something was locking up.?

[RCFanatic12]

Thanks for all the replies. I'll try and respond to most of them.

	Quote: Originally Posted by FlyguyXII
	Sorry to hear about the 260 going in. Most likely cg due to heavier battery possible causes improper inputs to exit the spin. Opposite rudder and down elevator standard exiting inputs.

Although I haven't accurately weighed them, my 6V 2300mah weighs roughly the same as my 6V 1400 pack, which was why I never saw the need to re-balance, although the crash proves it was just enough to offset my balance. As far as my inputs, thanks for teaching me proper technique for in the future. I've only been flying for a little over 1 year so I've still got a lot to learn.

	Quote: Originally Posted by adrian
	we always called it the death spiral - many issues the cause - mostly pilot error trying to hard to do to many things and not letting the plane sorta fly out of the problem - this all causes wing stalls and other things and you the pilot trying to catch it in panic and actually causing even more problems - sorry bud!!!

I panicked; the plane was tailspinning so erratically that I felt like I had to do something to try and save it. What you said makes perfect sense, though.

	Quote: Originally Posted by rcflyguy
	where were the batteries in the fuse?

Yep, they were in the fuse behind the CG. Once again, both batteries weighed roughly the same and I never thought I'd need to accurately rebalance the entire plane.

	Quote: Originally Posted by superdh
	your "departure" (thats what some full size pilots call spins) sounds like it was exagerated by an aft c.g. that was at a critical point if its possible, relocate all the parts temporarily and check the c.g. now to see if thats where the problem really lies adding power and opposite aileron may have forced the plane out of its spin in the past but that is not the correct technique for stopping spins, applying opposite aileron stalls the already stalled wing even more and usually deepens the spin(except maybe as you found it can force the aircraft to stop) correct spin recovery technique does vary with airframes but most models only require you to neutralise everthying and cut the power, most models will recover faster if you cut the power, nuetralize the ailerons and apply opposite rudder just like i learned to do in fullsize...cessna 152's spin great

I wish I could relocate the parts, but the crash completely shattered the center of the fuselage, ripped the gear off, and tore the firewall off (the engine was completely in tact and still securely bolted to the firewall, lol). I wish I had taken pictures; it was pretty destructive.

As far as my technique, I learn something new everyday. Now you say that neutralizing everything, applying opposite rudder, and cutting power will recover the plane; in such an erratic tailspin, I felt the need to input opposite aileron to slow the spin, opposite rudder to stop the flat-spin, and increase throttle to straighten out the tail and pull out of it, and in the past it had always worked. Whenever I'd try neutralizing controls and pulling back the throttle, it would simply continue the tailspin without sign of slowing down.

	Quote: Originally Posted by mmcconville
	Sounds like the model was quite tail heavy. I'd say the new larger battery was probably located behind the CG right? So it shifted the CG even further back. Always a good idea to check the Cg and start at the recomended location.

If you're the same Mike that designed this airplane, there's no better input than from the man who built it. Yes, the battery pack was behind the CG and was clearly enough weight to offset the balance. I quickly finger balanced the plane from the wing-tips before take-off, but I obviously need to take the time and measure from the manufacturer's CG. Anyways, I'd like to compliment you on your design. This was a fantastic airplane and I'll be buying another to replace it. Chip Hyde flew my Extra last summer and it handled everything he could throw at it (at the time, he mentioned it was a tad nose heavy).

	Quote: Originally Posted by DKnippen
	Sorry to here this. But seeing that you've had many flights with no issues I would next look at the rudder servo. Sounds like it or something was locking up.?

The rudder servo itself seems to be fully functional; the only factor is that maybe my linkages were flexing under the stress??? I might upgrade to titanium pro-links on my next one.


My Conclusion: Judging by everything you guys have told me, installing the heavier metal geared servos on the wings and mounting the larger battery pack offset the balance just enough to cause these eratic tailspins. Installing the heavier DS8411's on the elevators simply made the plane so tail-heavy that it finally buried itself. This has taught me that balance is the absolute most critical factor with these planes and from now on, if I make even the slightest change to my airplanes, it will be properly balanced again using manufacturer's recommended CG before take-off. Thanks for all your help.

[ibange]

Remember also that not only did you affect your balance with those heavier components, but also your all up weight. A heavier wing loading will work with the balance to make the plane even more susceptible to spins.