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

[mmcconville]

Had a chance to catch up on this thread and thought I'd put in a few thoughts here. This is a strange issue for sure. If I had a little clearer picture of what the model did it would help, "tailspin" is a layman term and doesent really explain what it did. I'm assuming it was a spin or a flat spin.

Here are a couple of thoughts. First, flying smooth is not in anyway an indication that the CG is correct. A more tailheavy airplane will require less elevator input to generate a given pitch result. An aft CG can feel smooth in some ways if the throw is reduced or if more expo is used. However it changes the stall charicteristic, pitch coupling, and general ease of flying it.
A few very easy and foolproof CG checks are this. First roll it inverted in level flight and let go. Does it fly level hands off, climb, or want to head to the ground and needs down elevator to fly level?
If the first or second are the case its way tailheavy.
Then pull to a 45 degree upline. do a 1/2 roll to inverted and let go.Does it now pitch toward the bottom, i.e climb (way tailheavy), continue up the 45 line with no elevator needed (tail heavy) or arch toward the ground needing some down elevator input to stay on the climbing inverted 45 line (CG is close to perfect.)

If the model is tailheavy, though it may fly around "smoothly", it is more sensative in pitch and is more difficult to fly consistently well. Only when the CG get so far aft that the static margin is near zero or worse does the model diverge meaning it becomes impossible to fly straight in pitch. If you pull up and let go it keeps climbing, if you push and let go it keeps diving. However, that is a GROSSly tailheavy situation, and a model can still be quite tailheavy but trim ok in pitch. Static margin is the distance between the CG and the center of lift of the wing. It has to be positive (CG in front of the CoL) unless you have a complex gyro/computer stabilization system between the stick and the elevator like the full scale F-16, but thats off topic.

As for checking CG on the bench, as long as the location stated in the manual is correct (it is on this model) , its irrelivant how you do it. Its a balance point and it doesnt move. Just choose the easiest method for checking it. Larger models are easier with two people, one at each tip. If the CG location is 4-1/2" back at the root rib, extend it to the tips, in a line perpendicular to the center line of the airplane. Easiest way to do that is mark it on the root rib of each panel, slide them onto the wing tube off of the fuse, and use a long piece of string. Stretch it wingtip to wingtip over the top of the marks on each root rib, and mark the point on each tip under the string.
The method someone showed to hang the model is also a great way to check, however be sure ALL of the parts are on the model. That pic looked like the canopy hatch was left off. Thats not good practice. The cockpit is behind the CG and since thats where most of the mass of the hatch is at, it will move the CG back when its put onto the model.

As for linkages, for sure Titanium Pro-Links are the best possible linkage. However the 4-40 rods than come with the 260 are more than adequate for a model that size. I used them on mine, with a DA-50 in the nose. I gurantee flex in the linkages isnt the cause of the problem.

As for popped glue joints causing some type of airframe twist, I'd bet a paycheck that isnt the case. To do what the model did, you'd have to pretty much fail most of the glue joints at the same time for the model to do that.

I believe its CG related, a set-up issue making the model hard to fly, or a radio issue (something uncommanded happened).

A few questions.

On elevator, aileron and rudder, how much throw (each direction) did you have on low and on high rate?
How much expo on each of these?
What rates were you on for each surface when this happened?

Hope this info helps some.

[go29kev]

	Quote: Originally Posted by mmcconville
	.......The method someone showed to hang the model is also a great way to check, however be sure ALL of the parts are on the model. That pic looked like the canopy hatch was left off. Thats not good practice. The cockpit is behind the CG and since thats where most of the mass of the hatch is at, it will move the CG back when its put onto the model. ...... As for popped glue joints causing some type of airframe twist, I'd bet a paycheck that isnt the case. To do what the model did, you'd have to pretty much fail most of the glue joints at the same time for the model to do that......... .

mmcconville- you are right the hatch will make a difference but in my post i beleave i said hatch off was ok for side to side but needed to have it for front to back. i left it off for the pic to show how i had it hanging. i do a ruff in cg check first to get it close then i set the hatch on the plane but to the side, but in the proper place front to back. I kinda just put it in place but to one side next to the string so its in the opeaning. that way its in the proper place front to back and the weight will be in the correct location. and then i do the final check for the front to back. but for the side to side i do leave it off because the hatch is centered on the body so leaving it off wont change the side to side blance.

and if the joints around the tail was giving the tail could have twisted. not saying it did just it could. on a plane like that any flex could cause a lot of funny things to happen and any one of them could cause a problem.

also something i found on both of mine was that the elevators are not truly solid with the way they mount. so they tend to flex and give. so to fix that i put a beed of silocon between them and the body and then put them on and it stoped the flexing. i know they are done that way to be removeable but its a pain to do that because of the linkages and i always just leave them on anyway so.
doint get me wrong i love the plane i just think h9 could have done a better job in the way its put together. i guess its just all the years of building my own planes i rather add a few oz of extra glue than lose a plane due to week glue joints. and with this plane a few extra oz of glue would not have hurt.

[RCFanatic12]

Mike, just wanted to say that I really appreciate your input on this topic. It's really hard for me to try and put into words exactly what happened in the air without a video to demonstrate. Once the plane was headed in a straight downline, I inputed minimal aileron to initiate a slow roll/tailspin. Without any other inputs on my part, the plane's tail began to violently whip around, the wings rocked from side to side, and the fuselage began to level out, as if I were trying to flat-spin (Note: all controls were deadsticked at this time).

Now with the knowledge that inverted fly is the correct way to judge CG, the plane always required very slight down elevator to keep it level while inverted, indicating that the plane was slightly nose-heavy, correct? I honestly can't remember its characteristics in a 45 degree upline. I had the privilege to let Chip Hyde put my Extra through its paces last summer, and he himself mentioned that it did fly a tad nose heavy, although he never mentioned any negative characteristics and it seemed to perform everything he threw at it with ease. I'll note that Chip completely changed my personal setup to meet his needs, including all exponential and throw rates.

But, Chip flew it before the airplane was converted to Spektrum, before the upgraded battery pack, and before the larger aileron servos were installed (the elevator servos were only upgraded the day of its final flight). Even after all these upgrades, I do not remember ever having to input up elevator (tailheavy) during inverted flight to keep it level. I know for a fact that I would remember such a characteristic since it would feel so awkward to perform.

One thing you have to understand is that I'm still a very inexperienced pilot compared to most on this forum and I've still got a lot to learn as far as understanding all of the actions and characteristics of a plane. What I feel is normal and predictable flight for my plane could be awkward and unstable to another simply because I haven't flown enough airplanes yet to have that kind of knowledge.

Based on what you said regarding balancing on the bench, it sounds like I did it right (measured from the root rib and extended it straight out parallel to the wing tips). I'm currently building another H9 Extra 260 and I think I might try the hanging method. With regard to linkages, I was just grasping at straws when I said they might be flexing. I might put Pro-Links on there just for kicks since they're so easy to make adjustments, but they don't make them long enough for the rudder on this plane.

Regarding control throws, I set it up with the manual as a reference, but I adjusted based on my preferences. My high rates were reduced slightly from what the manual recommended and my low rates were increased slightly (I thought I might not have enough throw for takeoff).

Elevator Low Rates - Up: 1" Down: 1 1/4" Expo: 15%
Elevator High Rates - Up: 3 1/4" Down: 3 1/4" Expo: 30%

Aileron Low Rates - Up: 1" Down: 1 1/4" Expo: 15%
Aileron High Rates - Up: 2 2/3" Down: 3" Expo: 25%

Rudder Low Rates - Right: 2" Left: 2" Expo: N/A
Rudder High Rates - Right 3 1/2" Left: 3 1/2" Expo: 25%

I always flew this plane on high rates. The last time I used low rates was on its maiden flight. Low rates were so unresponsive for my taste that I never even used them on takeoffs or landings.

Thanks for taking the time to respond and it really helps me out. Since I started flying last year, I'm learning new things each time I fire up my planes and I'm constantly learning on these forums from all the experienced guys. Thanks for the help.

[DKjens]

I'll just comment on your rates and your statement about always flying on high rates. Your elevator low rate is way high and with only 15% expo quite touchy. Your elevator high rate has to be way way touchy on only 30% expo. In a critical situation I can se you would be very likely to over control your elevator. On my 40% planes I probably have about the same movement on low rates (+1"/-1.25" at TE) which equates to much less in degrees than your, and with 40 - 50% expo, high rate (+/- 40-45degr) has 80% expo. Your other rates are not that critical. Also, I see more newbees than I care to remember smack their planes on landings due to landing on high rates. On high rate elevator you often forget to fly the plane, which is very important during landings, and I've seen over correct and/or panic and stall the plane several feet over the runway.
With the rates you list and the fact that you always fly on high rate with that little expo I suspect this accident is due to pilot error.

[brandonduley]

I've got a question. Why does the manual show a pull-pull rudder set-up for the Saito 220 but then shows the rudder servo mounted underneath the stabilizer for a DA-50?


They show it this way to help with balancing the airplane, you put the saito in your need your weight closer to the cg. put the da50 in your putting more weight up front, thus needing to put some weight in the tail of the plane to help balance the model, so you don't have to add weight to get it to balance properly

[RCFanatic12]

	Quote: Originally Posted by DKjens
	I'll just comment on your rates and your statement about always flying on high rates. Your elevator low rate is way high and with only 15% expo quite touchy. Your elevator high rate has to be way way touchy on only 30% expo. In a critical situation I can se you would be very likely to over control your elevator. On my 40% planes I probably have about the same movement on low rates (+1"/-1.25" at TE) which equates to much less in degrees than your, and with 40 - 50% expo, high rate (+/- 40-45degr) has 80% expo. Your other rates are not that critical. Also, I see more newbees than I care to remember smack their planes on landings due to landing on high rates. On high rate elevator you often forget to fly the plane, which is very important during landings, and I've seen over correct and/or panic and stall the plane several feet over the runway. With the rates you list and the fact that you always fly on high rate with that little expo I suspect this accident is due to pilot error.

When I first learned to fly, my instructor taught me with zero expo. None whatsoever. As a result, it taught me to be very respectful of the sticks and not to overcontrol in the neutral zone. My fingers don't jam the controls from side to side and I'm glad I was taught that way. That's why for my personal flying taste, I don't like the feeling of a bunch of expo because it makes me feel like I'm not in control of the plane and I just get sloppy with the sticks. That's simply how I like to fly, and I have yet to crash a plane out of stupidity or due to overcontrolling or stalling the plane.

In response to your comment about pilot error, did you read my descriptions of how the plane actually crashed? If I crashed the plane due to my own error or mistake, I never would've made this thread. With regard to newbies crashing on high rates while landing, I brought this plane in hundreds and hundreds of times on high rates with little expo and never once crashed or stalled the plane during a landing or touch & go, so I don't really see that as an issue. I apologize if this comes across as being rude or disrespectful; I don't mean it that way whatsoever.

[buttface]

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[dubd]

	Quote: Originally Posted by RCFanatic12
	When the plane was in a straight downline and I'd input slight aileron to initiate a tailspin, the plane would violently enter the spin and begin tossing the tail of the airplane around uncontrollably in a semi-circular motion and would eventually begin an awkward flat-spinning rotation. And before somebody else brings up another CG issue, the plane flew straight as an arrow in pitch and it flew smooth as can be during slow, stall speed flight; the tail never wanted to drop and the plane never required excessive elevator input to level it out. As far as the covering, I'd inspected the plane many times and I never noticed anything significant. One of the wing tips had some scarred up ultracote from a rough landing, but it wasn't like there was a bunch of loose covering hanging there.

How does inputting aileron initiate a tailspin? Wouldn't that initiate a downline aileron roll? You talk about the tail being tossed as if it was being moved independent of the airplane. Perhaps your hort or vertical stab broke in the air. Regarding the covering, it could come off in flight even if it looked okay on the ground. I've seen that happen before.

[RTK]

	Quote: Originally Posted by dubd
	How does inputing aileron initiate a tailspin? Wouldn't that initiate a downline aileron roll? You talk about the tail being tosses as if it was being moved independent of the airplane.

That is why I mentioned earlier that I think it has to do with some freak electronic problem when put into a down line. Something grounding or shorting out, causing this weird behavior. He mentioned it was repeatable and had done this many times. Nothing else makes sense either.

[flyin4fun]

almost sounds like your elevator halves were working opposite of one another like normal ailerons

[Black Bird]

Did you check out 13 year old Hugo huckin the hell out of his Extra 260. The more you defend your position, the more I beleive it was pilot error. 30% expo on high elevator, WoW. I also learned how to fly with zero exponential. I flew like crap. But that was me.

[Black Bird]

	Quote: Originally Posted by RCFanatic12
	Yes, my inexperience in the situation and my incorrect inputs eventually caused the model to crash, but that's not the point of my thread. What caused the plane to enter the maneuver in the first place??

	Quote: Originally Posted by RCFanatic12
	In response to your comment about pilot error, did you read my descriptions of how the plane actually crashed? If I crashed the plane due to my own error or mistake, I never would've made this thread.

We are trying to help. Please try to remain consistant with your posts. Inexperience, incorrect control inputs, and improper radio setup all point to pilot error. It is not a bad thing, you just need more practice and guidence. Have fun with your new Extra and PLEASE dial up that expo a little.

BB