Problems test flying T-Rex 700

[Sesame]

Hi Guys

Yesterday was working with a mate of mine testing out his new 700 and we had a few problems. which culminated in the OS engine he's using failing internally. which bought the session to a premature halt.

The reason for the post is to ask a question re the head. while flying the 700 about very gently infact, he went up into a stall turn flicked the tail around as he bought it out the stall there was a massive blade noise. it sounded like the blade had stalled, the heli flipped out of control. I though when I saw it that one of the links had popped(or broken up to the blade holder. He was fast on the TH then he regained control and managed to float it down in an auto.

We checked it over thoughroughly and coule find NOTHING mechanically that would account for it, hes convinced it may be dampners that caused it, has anyone else had anything like this happen? the next couple of flights were uneventful, very gentle couple of easy stall turns and some soft circuits then of course then motor self destructed, even though rich reven though on little more than tickover, It just wasn't his day.

[SRH990]

I've got around 3 gallons through my 700 now and noticed that there seemed to be a bit of play in the dampers and I'd read a post or two about them wearing out quite quickly so I ordered a new set. They're now fitted and have the same small amount of play as the original set. I could add another spacer/shim to each side which would tighted it up a bit but to be honest it flys just fine for me as it is.

Sorry to hear about the engine failure, real bummer. What exactly failed?

[Sesame]

My mate sent me this picture this morning.

The cranks done in as is the liner, bit of a mess it looks like the lower collar on the bigend disintergrated, this was on I think either the 3rd or 4th tank, each one being run rich.

Its going back I believe for comments, so will keep you posted.

the one that concerns me is this head noise and losing control for a couple of seconds we didnt get to the bottom of it and why it happened

[robgt]

Wow, that con rod is totally fu... erm, broken!
Unreal.

Re: the noise out of the stall turn - the paddles are all done up tight aren't they?
No loose balls on mixer arms, and no loose mixer arms?

Cheers,
Rob

[Sesame]

Wow, that con rod is totally fu... erm, broken!
Unreal.

Re: the noise out of the stall turn - the paddles are all done up tight aren't they?
No loose balls on mixer arms, and no loose mixer arms?

Cheers,
Rob

Yup totally broken is the right term, I was flying it in gentle circuits at the time so I know it wasnt being stressed. It just went POP! and stopped. obviously.... I can say that the 700 Autos very nicely, loadsa time to land it LOL.


checked all the arms balllinks servo links etc. could find absolutely nothing, which would cause what happened. which is more worrying than when you do find a problem at least when you fly it you know youve repaired at least something

[SRH990]

I'd be interested to see what they have to say when the engine goes back, the piston shows no sign of the engine overheating and looks in perfect knick, backing up your comments about still running rich. As you say it looks like a total failure of the bigend, maybe this siezed?

Sorry I can't shed any more light on the head related issue, mine has been absolutely faultless, the only issue I've had has been the failure of a Carbsmart sensor within 3 flights and I can't blame Align for that!

[jamiem]

Ripmax will just give you 2 new engine. I had the exact same thing happen to a 50 hyper. I sent it back and 3 days later i had a brand new one with me, no letter or explanation for the failure though.

[BobJ]

Hi

I am not sure on the blade noise other than 90's do make more blade noise than smaller models but the big end is almost certainly too lean.
There is only one way a big end fails and that's the bronze bush picks up and siezes onto the crankpin, it then turns in the ali of the big end and the oilways are blocked, complete failure follows seconds later.
Obviously there could have been another reason for the bigend bush turning in the first place but it's very unlikely and impossible to check once the bigends blown.

As has been said Ripmax will most likely repair/replace the engine anyway.

Cheers
Bob J

[Sesame]

cheers Bob

I'm hoping for his sake that is what happens should know in the next day or two.

It wasn't just noise the whole thing went out of control for a second or two, as I said it was as if the blade holder link had come adrift and the blade completely stalled but it obviously wasn't. as it came back into control and landed safely.

its very strange, he was thinking along the lines of a problem with dampners but I cant see it causing that but hell change them anyway, which will mean stripping down part of the head and checking it anyway.

[SRH990]

Maybe it's worth checking the amount of collective and cyclic pitch at his current settings, it's certainly easy enough to stall the blades out with the travel available on a 700. Is travel excessive causing binding at the limits?

[andylinney]

Silly question - have the blades been properly balanced and checked - had a cheap set of Fibreglass blades that would do something very similar to what you were suggesting (one would osscilate and stall) at a certain headspeed - never tracked the problem down even checking all links and such like but once the engine has got sorted maybe try another set of proven blades to see if the problem can be recreated.

[robgt]

Was the receiver pack fully charged?
A low voltage receiver pack will do strange things to the servos when you load it up (pulling out of a stall turn could be enough...), making it look out of control.
If the receiver pack was low, but not empty, you would likely still have enough juice left to hit hold and auto down.

Just a thought?
Cheers,
Rob