rmh

3.3 volts low voltage threshold is correct for most systems - inc Spektrum /JR DSM2/DSMX
The real problem with unknown crashes is typically -hate to say it again - the user not understanding how /why voltage depression takes place
2500 ma AA NIMH are probably, as a group , the worst batteries for rx packs - especially on 2.4 systems -- any brand

many of these batteries are 2C at very best and 1C in many cases
the old green 2700 ma Sanyos were simply disasters
if you must use NIMH, go to Cheap Batteries or NOBS Batteries and readup on different cell characteristics.

lopflyers

My Feedback: (12)

What? You crashed your 65 Vyper? I also suspect battery issues but am devastated about your loss. Please don't post pictures. I don't want to see them

turboromy

No, it is not 5.0v.
My meter has only 1 DC reading at 600V scale. So, it could be 5.1 or 5.9.
I got it only as a clamp meter to read amperage when I set up electric planes.
I am going to measure with a better tool and post it later on.

This 5.x v was before I recharge. I haven't yet measured after putting in that 35mah.
I doubt it would make much difference with 1.4% additional charge.

BTW, Vyper impacted left wing first almost at knife edge attitude and it really doesn't make sense both aileron servo gears are stripped, while it is still possible. It was the front area that took most of the impact. Touching down with left wing first and rotation around left wing tip maintaining that KE attitude explains almost no damage to wing structures.

Battery probably should have been replaced as a preventive measure, but I am leaning toward aileron flutter being the major factor at the moment.
I wish I had a chance to try other channels to tell if it was indeed a signal loss. I doubt anybody would have reacted differently though.

TheEdge

My Feedback: (788)

Had a similar case with a 2.1 Comp Arf Extra,
My Aileron servo's were not MG and although torque rating met the requirements of the specific surface/s, they gave out and I lost the plane.
I should add, that they went with a bang but what was heard very briefly prior to the bang was the flutter. Is there a chance that the aircraft was far enough away from you that you didn't hear the flutter and only heard the bang?

turboromy

I'm sorry for your loss. That CARF kits are something I really want to jump into.

Now, here's a biggest question.
How did you narrow culprit down to flutter instead of signal loss ?
Did you have enough time to try other channels while it is coming down ?
I didn't have that chance.
Even though I am leaning toward flutter but just can't yet assert it.

I thought flutter is only possible with loose connectors. One that happened on a buddy's aileron was due to the fact that aileron side servo horn was mounted over balsa area instead of a hard surface. Flutter was very visible, but still controllable and landed with no further damage.
Now I learned it is still possible on tight connectors, with plastic gears.

TheEdge

My Feedback: (788)

Flutter is caused by dyanmic instability, having good connections with no slop reduces the amount of vibration it experiences but undesrtand that he air rushing over the surface is a sustaining source of energy. The faster you go, the stronger the supply of energy.

jester_s1

RIght, good connections can reduce flutter, but they cannot prevent it. Mass balancing can prevent it, as can building the control surfaces with light weight.

los36

My Feedback: (1)

So, you charged your battery after the crash and it only accepted 35mAh? This was after 3 flights? You should discharge your battery and then fully charge it to check it's capacity. If it takes much less than its claimed capacity, it may indicate a failing battery pack.

turboromy

I ain't no expert in this area, but I'm quite sure it is not highest speed causes flutter, but it is certain range that gets in sync with structural natural frequency. I must have been flying in this range with 6s.

turboromy

I heard of giant flyers doing this.
Mass is added in forward portion of the aileron around hinge point so that it is naturally balanced with no servos connected.
Did I get this part right ?

If so, how do I mass balance aileron without forward portion ?
By forward portion, I mean those parts that go opposite direction of control surfaces, like (forward part of) upper part of large rudders.

If control surfaces are all backward of hinge point... is there a way to mass balance them ?

turboromy

Exactly....
I know I should have changed battery. Recycling (is this right term?) is something I haven't done for long time.
I did it with Nicd, decades ago when it wasn't easy to do. With all the nice electronics, I haven't done such with NiMH at all.
I'll check charged voltage first of all. I kinda suspect it may not even hit 6.0v since used state was below 6 for sure. 5.x it was...

All Day Dan

My Feedback: (5)

Turbo, it sounds more and more that you have a bad battery pack or now maybe a bad charger. If you are not cycling your batteries to determine their capacity, you have no idea whether they are good or bad. Keep in mind that all batteries are life limited. They will die eventually. Do you fly at Prado? I do The first thing I do when a guy goes in is ask him how old are his batteries. He usually does not know. That’s the first clue. If he does not know how old his battery is, he also does not know what the capacity is. I don’t even ask. Out comes the voltmeter and the mystery is solved. Dan.

fragile

The word crash is usually in the same sentence as Spektrum !

turboromy

I fly at Apollo. I have flown at Prado only a few times due to the distance. I am the asian guy with Alex. You probably know him better.
Geez... I forgot names of pilots there, but I remember Steve, Jarvis,... and the elevator guy whose name is on tip of my tongue.... I used dub him Robocop and he liked it.

I log almost all parts of my stuff including first flights as well as how many flights with "days in jail marks". This is a habit from my good old days of flying full scale.... long time ago, before Bush.

I totally am aware my battery may have not been up to the task. Still, I now strongly doubt that was the major problem.
I am pretty much convinced Futaba S9650 was not upto the task.
I wish there's way to tell how plastic material fails like they do on metal structures.

gsmarino2000

My Feedback: (2)

No, az, you are not the only one, drives me nuts. And about 99% of the time the Spektrum / JR comments are by people who don't have any real knowledge to back it up.

oil_can_harry

My Feedback: (2)

I fluttered my tango last year. Came in to steep with too much power. Heard a pop, then lost all control of the ailerons. The tango. Has large surface areas on the ailerons, rudder and stabilizer. The plane was going almost right over my head and I could see one servo rod hanging down. I managed to get the plane on the ground using the rudder and stabilizer. I actually stripped both servos and sheared one nylon clevis pin. The wrap around canopy was cracked, don't know how that happened. One of the threaded wood blocks for the wing screws was broke loose. There was a crack on the fuse behind the wing. The landing was a greased landing, but wasn't a hard landing. I was amazed at everything that was damaged over what I thought was a little flutter. I repaired everything and flew it more, but it never seemed to be the same. I lost it about 5 flights later and the motor died going fairly slow down wind and close to the ground. Tried to turn back in the wind and she stalled and went in. It wasn't torn up that bad, but it never flew great after I fluttered it so I junked it. You just don't realize when you flutter, what all it shifts and changes on the plane. Just my opinion. Everything was futaba.

turboromy

Thank for sharing your story. It is a very supporting phenomenon that supports my reasoning.
At first of this forum, I refused to believe flutter could do something onto the canopy.
I'll take your story as a living proof that flutter could damage beyond common sense can predict.

In case you didn't know, on electric planes, make sure you set up a kill switch. Not sure if this generally applied to different brand ESCs,
but at least on Castle, when the motor stops, recycling this kill switch revives the motor even though it would cause same problem again soon.
You should immediately land and resolve the issue, but this way it wouldn't crash at least.

lopflyers

My Feedback: (12)

I don't trust Nimh anymore, I changed all my receivers to LiFe.

blhollo2

My Feedback: (278)

we shall never know. But remember the good times you had with it and rebuild and make new memories! sorry for your loss, I hate when I lose a good plane.

TheEdge

My Feedback: (788)

Your statement is not correct, just because you have no knowledge or experience of these types of incidents doesn't mean that it is highly unlikely in fact, there were a great deal of these incidents occurring when ARF's began to really take off , I recall the Hanger 9 Cap and the Dave Patrick Extra were famous for flutter and stripping of both aileron servo's in and around the early years of 2000

rmh

The kits mentioned were not the best thought out setups------------

TheEdge

My Feedback: (788)

I enjoyed mine without issue.

turboromy

Here's some information that I did not include at the beginning thinking they were not important.
As I narrow the cause down to flutter, I guess I should get you guys more detail, and further ask your opinions.

Different views are very welcome of course.

Futaba 9650 were on each side of aileron and has plastic gear. This is a mini servo that are typically used on elevators in pair on full size patternship.
They were used on Vyper ailerons, 1 on each side. Most hardware was direct transfer from 3DHS osiris which had 9650 on ailerons.
3DHS recommends 9650 on Osiris aileron.
3DHS recommends standard size metal gear servos for Vyper. (this is the crashed model)

Crash was almost at knife-edge attitude with left wing low. Front area was heavily damaged including the motor mount.
Surprisingly wing structures were almost undamaged. In fact, a spectator suggested that I put right wing on site and sell it. (don't worry, I put all in a trash can)
My reasoning is left wing kind of softly impacted the ground or bush and caused a quick left yaw causing severe frontal impact.

Come to think of it, if plastic gears were damaged from crash itself, I can not imagine how wing structure themselves could have survived at almost re-salable condition.
Double aileron failure was initially scoffed at due to an extremely low possibility, but faster speed must have over stressed the gears for a while, and that final round out must have caused plastic gears fail from extreme stress. Again, as altitude was low and airplane was slowly rolling, I only had a chance to use aileron control.

Battery was old and tired (about 1 year, about 90 flights each 6 minutes avg), but doubt that was the contributing factor in this crash.

jester_s1

A year old battery with only about 100 cycles on it shouldn't be worn out. I agree with you; it probably wasn't a factor.

You asked about mass balancing control surfaces with no forward counterbalances. Yes, it can be done. One thing to do if you are building is to build them as light as possible and taper then back to the trailing edge. That moves the CG forward by itself. For large surfaces or on setups where that isn't possible, I've seen one poster on RCU who mounts a piece of threaded rod into the control surface with a small lead weight held forward of the hinge line. I haven't done it myself, but he says it works.

And you're right about the nature of flutter. It's not more speed= more flutter, but rather when the turbulence hitting the control surface reaches the resonant frequency of the surface. Moving the CG of the control surface forward raises that resonant frequency (much like shortening a pendulum) which makes it impossible for the plane to ever fly fast enough for the turbulence to reach it.

Uncas

My Feedback: (1)

My gut feeling after reading is that you suffered a mechanical failure, not a loss of signal.

I say this because the failure occured coincidently with a stressful pull out of vertical dive which somehow ripped the canopy off the plane and there was a loud bang. This is what you know with certainty.