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

[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.

[RCFanatic12]

	Quote: Originally Posted by 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.

	Quote: Originally Posted by jack01
	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.

Not 100% sure what you mean by 'hunt', but I'm guessing you're referring to the plane not wanting to fly in a straight line in pitch and the tail/nose wanting to wander/move around from side to side?? If that's the case, then the answer is no. During vertical uplines and straight downlines, the plane flew as straight as an arrow; it was when I inputed aileron during downlines to enter a tailspin that the plane went out of control. During uplines, the plane responded perfectly to aileron input.

As far as the plane wanting to pitch up or down during slow flight, the answer is definitely not. I made numerous low speed touch and go passes and the plane flew perfectly smooth and my landings were as stable as they’ve ever been. If this was truly a CG issue, wouldn't the plane pitch up or down during slow, stall speed flight??? This is what I’m failing to understand about this entire crash.

[jack01]

	Quote: Originally Posted by RCFanatic12
	[font=Tahoma][color=black]Not 100% sure what you mean by 'hunt', but I'm guessing you're referring to the plane not wanting to fly in a straight line in pitch and the tail/nose wanting to wander/move around from side to side?? If that's the case, then the answer is no. During vertical uplines and straight downlines, the plane flew as straight as an arrow; it was when I inputed aileron during downlines to enter a tailspin that the plane went out of control. During uplines, the plane responded perfectly to aileron input. As far as the plane wanting to pitch up or down during slow flight, the answer is definitely not. I made numerous low speed touch and go passes and the plane flew perfectly smooth and my landings were as stable as they’ve ever been. If this was truly a CG issue, wouldn't the plane pitch up or down during slow, stall speed flight??? This is what I’m failing to understand about this entire crash.

Based on what you said, it wasn't a CG issue. If the CG was too far aft, it probably would have either climbed inverted, climbed when the speed slowed down, constantly required elevator input to keep it level, or possibly all three.

So the plane did upline rolls perfectly, but it went into the spin on a downline roll without any rudder or elevator input?

Here's another question, did you have a PCM reciever? If so, what is your failsafe set to?

[RCFanatic12]

	Quote: Originally Posted by jack01
	Based on what you said, it wasn't a CG issue. If the CG was too far aft, it probably would have either climbed inverted, climbed when the speed slowed down, constantly required elevator input to keep it level, or possibly all three. So the plane did upline rolls perfectly, but it went into the spin on a downline roll without any rudder or elevator input? Here's another question, did you have a PCM reciever? If so, what is your failsafe set to?

And just to confirm all three that you just mentioned, the plane never climbed while inverted, never tried to climb at slow speeds, and it never required constant, unnecessary elevator input to maintain pitch.

Yes, after I performed a hammerhead and the plane was headed downline, the slightest aileron input without any elevator or rudder input would throw the airplane into that deadly spin. If I kept all controls deadsticked after the hammerhead, the plane would track downline straight as an arrow.

I used a JR PCM receiver until Nov. 2007, which was when I upgraded to the new JR X9303 DSM2 2.4Ghz & R921 receiver. My failsafe's were set at neutral on all surfaces and was set to idle on the throttle servo.

[66stang]

I've had a couple of plane I built that later had adendums that changed the CG to another location. Check with Horizon and see if a change in the manual could be the problem. If the CG is different than was in your manual. Also could you of had a binding problem with a servo?

[RCFanatic12]

There's only one addendum listed on Horizon's website and it's only related to an error in engine size recommendations. I'll call them in the morning to see if there's been a change that may not be on their website. Also, how exactly would I know if I had been having a binding problem. All of my servos seem to have been working just fine over the past few months and they all function properly after my range checks.

[66stang]

Is it possable that the battery became loose. Rolling around the airframe changing the cg in flight?

[66stang]

I've got it. A stripped rudder servo arm. Try holding the servo arm and move the servo under power.

[RCFanatic12]

	Quote: Originally Posted by 66stang
	Is it possable that the battery became loose. Rolling around the airframe changing the cg in flight?

Since these crazy tailspins began a month ago, I've landed the plane safely many times and everything was always securely in place. The battery pack was placed on an elevated platform in the fuselage, wrapped in foam and triple wrap-tied around the platform and the plugs had electrical tape around the fittings so nothing wiggled loose. It was pretty secure and I probably would've noticed if something was wrong.

	Quote: Originally Posted by 66stang
	I've got it. A stripped rudder servo arm. Try holding the servo arm and move the servo under power.

I just went out and checked and put it under power (luckily all my electronics survived). It's working just fine and has plenty of strength when I hold the servo arm; I have aluminum servo arms on all my servos and since it was an 8611A, that makes it a metal on metal connection, which would take a lot to strip it. The servo itself is pretty old and isn't quite as crisp as my new 8611A's, but it held the airplane solid as a rock in a knife-edge.

The only factor that I'm thinking could've caused an issue are my linkages. They're pretty strong 4-40 steel linkages, but they can still definitely flex a lot under stress. I wish I could've done titanium pro-links, but they only make them up to 5" (needed 5-1/2" for my elevators). The rudder linkage is only about

Thanks for helping me out.

[go29kev]

[quote=RCFanatic12;420451]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. quote=]

the wing tip is not the place to do it, this is copyed from the manual.

1-Measure back 5" from the leading edge at the root rib
and mark the location with a felt-tipped pen on the
bottom of the wing. This is the recommended center
of gravity (CG). The CG range for your Extra 260 is
between 4 3/4 and 5 1/4".
2-Fully assemble the model. With the airplane upright,
lift the airplane with your index fingers to find the
balance point. The balance point (CG) should be
at the mark made at the root rib. If not, add the
necessary weight to the nose or tail to obtain the
correct balance.
(updated wording for #1)-

Balancing the Model
Step 1 on page 40 of the manual
The first sentence should read "On both sides of the fuselage, measure back 5" from the leading edge at the fuselage and mark both places with a felt-tipped pen."

if you did it at the tips then it will most likely be off because the extra wing is tapered from root to tip in both thickness and from front to back.
that is another reason i use the string deal because its dead center of the front-back and side to side. but i know everybody has their own ways of doing it this is just the easyist way i have found to do it.