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??

[btomlinson]

Sounds like your CG was right on the ragged edge. The additional weight of the metal gear servo(s) was just enough to trigger the uncontrollable situation

[krayzc]

how did the plane fly inverted with those servo changes?

[RCFanatic12]

	Quote: Originally Posted by krayzc
	how did the plane fly inverted with those servo changes?

When I changed the aileron servos, it flew exactly the same as it did before. When I changed the elevator servos to the DS8411's (thinking that the DS821's weren't enough torque), inverted flight definitely wasn't as smooth as prior, but the plane was still controllable. The added tail weight of the 8411's must have offset the balance of the plane and finally caused it to bury itself in the ground in the tailspin. I did a quick finger balance check before takeoff and the plane balanced out pretty good, but I clearly needed to take the time to measure from the manufacturer's CG.

[plaster93]

Man how many times did it crash? or is this a double post? LOL

[luv2flyguy]

Dude you should never fly the plane without checking the CG first!! I'm not coming down on you but as a rule of thumb when you make changes as you did I would never fly any of my planes without checking the CG. Also I will never fly a newly assembled aircraft unless the CG is close to where it is called for, then you can make small changes to suit your flying style. Sounds as stated, that the CG was already on the ragged edge and the servo change was the straw that broke the camels back. Sorry to hear that you lost the plane, it really stinks no matter how it happens, hopefully the engine and electronics were ok, so you can use them in something else.

[zoomer260]

I had to add a half pound to the nose of a .90 size once !! I hate to imagine what would've happened if I hadn't balanced it. Still, with the added weight it was the fattest PIG !

[rede2fly]

personaly i dont think it was a cg thing. it would have been a handfull if it was that tail heavy. not just in a spin

[go29kev]

from some one who has had 2 of the h9 -260's the cg is very important. just a little one way or the other it will cause the plane to be unstable. the cg being off may not show up on normal flight and just seem to be a little out of trim but at slow speeds and in stall type flying like spins and stuff it shows up and causes a problem. on the extra just a little makes a big difference..
i always balance all my planes no matter if its new or one i have worked on. and to start with i find the middle of the cg range and set it up netural and then once the plane is flown and i feel there is no problems then i will adjust it and get it just right. IMO-going for the extream cg range on the first flight of any plane is iresponsible cause you never know. if something happens you wont know if it is a problem with the plane or a cg problem or something else. so being SAFE and taking a few extra mins to set a plane up right will save u time and $$$
i will try to post some pics in a few of how i done mine and it was dead on.

[go29kev]

the guy who tought me how to fly many years ago had the most simplest way to balance any plane to big to use a CG stand with and he used this methed on all of his planes. and that was to use the simple string methed. by placing the string in the center of the plane left to right and at the right cg location front to back u can get the all over balance including side-to-side and front-to-back all at once. i have used this methed on all my planes 90 sized and up. even on my 27% & 30% extras and also on my 1/3 scale f4u corsair. and all have test flew with very little trim changes. what a lot of people forget about is left and right balance is also important to a great flying plane.
i mark the cg on the correct points on the inside of the body and with a piece of alum. i make a bracket that has a eyelet in it, i mark the center of the piece of alum and the center of the body(side to side) and line the marks up keeping the eyelet centered on the cg mark and in the center of the plane. and useing a good qualty string i hang it from the work shop rafter keeping the table under the plane just as a safty measure. on the top end of the string i have a d-clip for easy hooking and unhooking. i have done this with planes weighing up to 25#'s (the heavest one i have so far is 25#'s)
here is some pics to try to help show ya how its done. and if you want to get it perfict then after you get it level left to right then you can sit the hatch on the plane just to the side of were it goes but in the correct position front to back so that you can get the effect of the hatch if any. but this is a very simple way to balance your planes that are to big or to heavy for the standard cg balancer and unlike them you can get the left to right at the same time. hope this helps you understand and you find it as simple and easy as i do.
you doint need all the complacted ways a simple string, ruler, and a few little pices of scrap and you can get the perfict balanced airplane and by taking a few mins (i can do it this way and be perfect in 10-15mins) you can only come out good.
this has worked for me and my dad and my granddad for the last 23 years so i beleave in it.

[rede2fly]

looks to be very interesting. i just might have to try it this way thanks for the tip and pics. when i stated i didnt think it was cg was because of all the former flights. it would have shown up before it did. i too had this plane.

[jack01]

I'm guessing CG too. Did the plane try to "hunt" in pitch, especially if you changed the throttle? Also, did it try to pitch up when you slowed down? If it did, it's definitely a CG thing.

It's speculation, since the plane was never found, but some believe this is what happened to Art Scholl during the filming of Top Gun. They believe the camera equipment made his Pitts (a very CG picky airplane), unrecoverable in the spin.

[66stang]

Even if it wasn't the cause, it's very risky to fly a plane of any size, let alone one as big as this with out checking the CG. You run the risk of not only losing an expensive plane, but also the risk of injury. There is just know excuse for not checking the CG and making sure it's correct. It's reckless and dangerous to do. Sorry for your loss, but please learn from it!

[8KCABrett]

Yep, CG is too critical a thing to not verify!

Also, for spin recovery, generally "in-spin" aileron will help to facilitate recovery, while out spin aileron will flatten the spin. So if spinning upright to the left, you would add left aileron, along with right rudder. Also, you need to do both of these things with the elevator still aft, and only push nose down elevator once you have the opposite rudder.

In R/C aircraft many pilots never really need to learn any recovery techniques since most will recover with neutral sticks right away. Full scale, and to varying degrees the larger scale models require positive recovery inputs, and in a particular order. . .especially when at aft CGs.

[RCFanatic12]

Just to clear this up, the plane was balanced after its original assembly. When I said wasn't "properly balanced", I meant that the plane was never balanced using a stand or other stable method to accurately gauge the plane's balance. It was simply balanced from the wing-tips using the finger-tip method and measuring from the manufacturer's CG. After I upgraded the wing servos and battery pack, I simply did a quick fingertip balance check at the field (not precisely measuring from recommended CG, though). I didn't feel the need to precisely balance because I didn't believe my upgrades were adding enough weight to make an impact, especially since I always felt the plane was a tad bit nose heavy.


go29kev - Wow, thanks for the tip and the pictures. I'm gonna have to try that method out on my airplanes. Sounds like it would be a very precise way to balance. Thanks man.