Check This Out - Serious Mid Air Damage

[JohnJ]

Take a look at the attached pictures, it shows a well used Trex 450 that the owner has been using for more than a year and although it's suffered a few prangs it flies perfectly well most of the time.

However the pilot has just started testing the heli in Idle Up before attempting the same with his 500 and on both occasions this has happened!

The heli flew OK in normal mode but within thirty seconds of flicking I.U. in a hover about ten feet high the heli disintegrated when the main shaft bent to the angle as seen in the photos.

The head was spinning perfectly well before it stopped instantly causing the tail to shear at the base, the only damage on impact was to the Flybar, even the blades are unscathed!

The blades & SWASH assembly dident rotate even once after the incident as there is no damage to the Anti Rotation Bkt.

The two shafts were from two different sources so not a dodgy batch, personally I've never seen this before and wondered if anyone has any ideas?

Must have taken some extreme force to cause this

John

[machasm]

Soft main shaft.
Out of balance head/blades.
Slight bend in main shaft.

[xygax]

Broke.!

[tiddler]

A main bearing locking up maybe?

Or.......... there was a temporary warp field that formed around the tip of one blade causing it to briefly travel at the speed of light and therefore creating a massive imbalance to the weight of that blade culminating in the resulting bend in the main shaft and the unavoidable consequences. i.e. The loss of uniform lift............ Maybe

[davew]

Are they those cheap fibreglass blades from China?

Is it possible he has a soft throttle curve in normal mode but maybe 100% flat in IU ? If so badly out of balance blades coupled with a high Kv motor and maybe large pinion could all be too much for it.

[JohnJ]

Graham - You win the most plausible explanation that sounds like a real possibility

It's really bizarre as the main cog is still intact with no teeth missing and it was flying perfectly well in normal mode!

The blades are cheapo type but he assured me they were balanced before use.

He flies a 500 pretty well so it really is a mystery and I did suggest he just lays the 450 to rest and accept it's jinxed

[glen_j]

i've seen this with the softer mainshafts on the beam e4 and dragonus 450 helis with a very high headspeed. what motor and pinion does he have? were the mainshafts genuine align shafts?

[JohnJ]

i've seen this with the softer mainshafts on the beam e4 and dragonus 450 helis with a very high headspeed. what motor and pinion does he have? were the mainshafts genuine align shafts?

The first one was an Align job but this one was made by ANother brand and he said it bent more than the first one.

He has now bought some superior stainless steel shafts rather than the cheapo's so we shall see what happens next time.

Not sure of pinion but yes maybe it needs a Tacho measurement to make sure he's in the right ball park area for his headspeed!

[chugga-bug]

My Beam did this. Freaked the life out of me! Lol
That was down to the original mainshafts being made from cheese straws!

[Biggles]

Broke.!

The professional term is F.U.C.T.

Failed Under Constant Testing!!!!!!!!!!!!!!!!!!!

[Kwickkwack]

Had a similar thing happen to me with a Mini Titan
had a flight with it, changed the pack was about 10 seconds into a hover then bang, bent shaft and beleive or not it fell out of the sky
All repaired now

[Mart61]

That's bizarre John. I reckon it's gonna be one of those situations that science is at a loss to explain.

[Farmer Giles]

did he flick to IU in flight ?

if there was a big step from normal to IU in his throttle curves then the extra torque and higher headspeed could have accounted for it.. maybe twisted the main shaft and then it gave way a few seconds later..

I'd have thought the main gear would have stripped first though...

2p

[scallybert]

The heli flew OK in normal mode but within thirty seconds of flicking I.U. in a hover about ten feet high the heli disintegrated when the main shaft bent to the angle as seen in the photos.

I hate it when the terms 'normal mode' & 'idle up' are used as if they have a specific meaning.

Perhaps that's the problem...

[JohnJ]

I hate it when the terms 'normal mode' & 'idle up' are used as if they have a specific meaning.

Perhaps that's the problem...

Nope don't see the your issue here

Not as if we are talking to people that don't know what we are referring to!