Stratus vibration at 1850rpm.

[Zilly]

We have heatwave over here at the moment It got up to 38 degrees last week, I think we should have some fair weather for the 3DM however it could end up being hot and humid if its like it has been for the last few days.

z

[Aviation addict]

Guys,

I've still got a foaming tank at 1700 - 1900 rpm and a vibrating Vertical tail fin (with the engine fully tuned - 3/4 turn SZ on High needle). The vibration is pretty much always there - even at 1500rpm. It just intensifies with more headspeed.

Just out of interest I took the pre-assembled open tail gear box off and put it in my drill press and dialed it. The result surprised me some what - I found a 0.001" run out on the shaft. I realize that the bearings have a bit of movement in them - but when very gently turning the gears I had expected zero run-out. With the speeds the tail rotates at surely there must be zero. Has anyone come across this? Is it normal?

PS The 3D Masters was amazing,- the things those guys were doing.

[bkervaski]

I didn't read the entire thread but what solved this problem for me was to simply mount my 611 sensor under the battery tray. I haven't had any issues since. None.

[Aviation addict]

Thanks Bill. I'll consider relocating the Gyro sensor if I'm still getting drift once the heli is seen to be running smoothly at all headspeeds i.e. no foaming/high frequency tail vibration - but while I can clearly see vibration in the model I'll live with it and hope when the heli smooths out - the gyro behaves too.

Any comments anyone about the Tail Rotor output shaft 0.001" wobble?

I've written an e-mail to MA asking the same question, but would be keen to hear your comments.

[Aviation addict]

I'm so sick of my Stratus. It hasn't stopped foaming the tank since the day I completed building it.

This past week I've taken the engine out again and dialed the fan down to 1/2 a thou" and added another head shim to its now 0.02 but still she ripples the tank at 1500 and churns it at 1750 +.

I thought that the tail output shaft might have been slightly bent and so replaced it and have also fitted the new tank but while the Vertical tail fin looks good now, the tank is still on wash cycle.

In my desperate state I've tried every conceivable engine needle setting and have tried re-aligning the engine and (even) starter shaft hundreds of times with no success.

I wrote to MA and was told that a foaming tank points at an engine issue - but I swear my engine sounds good and that the fan is balanced and dialed to 0.0005".

The foaming really is significant (ie the fuel starts off Red but once in Idle up turns Pink with all the aeration-and strikes the top of the tank even when nearly empty) so is there anything else I could take a look at? Could 'main shaft alignment' for instance cause a foaming tank? What would the affect of a bent main shaft be too?

When in the air there does seem to be a kind of 'morse code' noise and the occasional twitch of the tail.

I feel as though I've been through all the obvious things - Blade balancing/Engine balancing - even Alignment. I'm now wondering about gear alignments, clearances and main shaft straightness and alignment. In short - Could you guys give me a list of anything and everything that could cause a fuel tank to foam vigerously please and I'll just have to go through the list....

I'm at my witts end here. I just can't imagine ever getting the machine to run smoothly. I'm definately beginning to wish I'd bought a different model!

I don't suppose they will be much help but I've attached some pics.

[Alfred]

I have a crack at it.
1st, it seems like a high quality build, looking at the pictures.
But, your Fan/clutchdriver gap appears to be too small from what the pictures show.
I run the YS91, so DaveH or others might want to comment on that.

Do you have one of these workbenches that you can take outside and tie the heli down too?
You will nee LARGE cable ties.
Remove the whole tail end so that just the mainframe is left including baldes etc.
Now run the heli up to hover speed slooowly..keep a good distance and run it up slowly.
Ensure that you have got plenty of weight on the bench..sandbags, cement bag etc.
Still foaming? It is the engine, I don't care how often you aligned the clutch.
This will eliminate or prove the whole tail drive/balance.

Is it just me or does it seem that the absolute majority of vibration/foaming involve the OS engines?

Have you double checked the gap between fan/clutch driver being equal all around?
You should use 2 Feeler gauges in between the fan/clutchdriver for alignement.
Leave all the bolts fairly loose that hold the engine to the frame. You should be able to easily wriggle the engine around.
Now find the Feeler gauge thickness that gives you drag when pushing it in the gap. Add the 2nd Feelergauge on the opposite site and now just slightly tighten one screw at a time..just touching...work your way around ..just a nip at a time.
Keep doing this until you have tighten them fully..It should take at least 5-6 times going around until they are really tight. This will prevent distortion and causing the engine being pulled one way or the other.
Now remove a screw at a time and apply Loctite tighten the sucker up.
Do the same with the rest.
Pull out the Feeler gauges once done and leave it to cure for at least a couple of hours.

Assuming that the removed tail assembly had no effect on reducing the vibrations and the above suggestions still have no effect, check the clutchstack bearings.

It's not the heli :wink: I am an accurate builder but no flying ace and mine is just fine.
But as I said before, the majority of vibe problems on Stratus seems to involve OS engines..coincidents?

[Aviation addict]

Thanks Alfred,

My clutch gap is 0.020 at present - so a little on the tight side. I'm going to reinsert the shims that I made to raise the A frames again and note the effect. The shims are 0.010 so we should have 0.030 after-wards.

I will not be able to try the 'taking the tail off' experiment for about 3 days due work commitments, but will give it a go. I'll be sure to tie her down tightly!

Have you had pretty severe foaming in the past just from (OS) Engine misalignment alone or too tight a clutch gap?

Thanks for the tips on getting the cap constant. I have been measuring all the way around but not doing it in a gradual way. Should have bought a YS.

[Zilly]

John,

Before you go strapping your heli to a bench, which I really would not recommend btw. You said your tail is twitchy and your engine is giving of a morse code sort of noise. I would say that the engine is running very rich so much so that is is almost fourstroking.

Your issues will defeintately be down to engine tuning and not the model.

Z

[Aviation addict]

Yes its a bizzare noise for a heli. Its not particularly noticable or loud but its there. As I say - 'morse code' seems the best way to describe it. It's totally random and out of sync with any of the rotating part frequencies. While doing its 'morse' bit it does seem to give a little twich for the gyro to sort out - while all the same time foaming the tank vigerously.

After dialling the fan to 0.0005" etc I was very supprised to see the massive amount of tank foaming I saw yesterday. It looked worse than before - when the fan was 0.001". I did have it doing quite a bit less foaming about 3 weeks ago, in fact I was happy to fly it a little back then as it was only foaming the surface at 1800rpm but I'm not going to fly it when the fuel turns turns from red to pink and looks like someone has got the tank in their hand and is shaking it for all they are worth even at 1700. The tank seems to ripple from run up through to 1500 where it turns to foaming then wash cycle at higher speeds.

I'm hopeful that increasing the gap will help matters and trying Alfred's alignment method. My engine is set at 1 full turn open on the High and the Middle closed - Idle about 1/8 turn leaner than default. Will try leaning it off a bit though and see if it improves matters.

[Zilly]

John, I tried to call you earlier to offer some assistance...

Firstly remove the head shim you have just added as this will probably be part of the cause. You mentioned that you had it better before you put the shim in. So step one take it out!!!

If you are running the middle valve closed I should imagine that won't be helping thigs much, why not set the needles to what the OS instructions recommend and take it from there, I imagine you have run a couple of gallons through it by now in which case it will be on its way to being run in.

Whenever I get problems that I can't trace down I always go back to the default settings and work my way forwards from there.

When you say in your last post that you had the set up working a lot better a couple of weeks back with only a little foaming then to be honest you had it about as good as it is going to get...... every Stratus that I have see fly has a certain amount of foaming due to where and how the fuel tank is mounted, I also find it gets worse as the sponge tape that supports the tank gets soaked in fuel and looses its softness.

I would look at what else you have changed since you had it in this state.

One thing I have learnt is not to change to many things at a time as you will chase your tail till you get fed up and take up flying kites instead. :wink:


z

[Aviation addict]

Z

Took the extra head shim out last night so am down to 0.16 again. Spent a little time carefully aligning the engine too as per Alfreds post. Reset the engine to default too. - but then started leaning her off again.

Flew her this morning before work and found that initially she was foaming at 1850. A friend then suggested wedging a piece of foam between the top of the new tank and the frame to see if the tank itself was moving or contributing to the problem. We wedged the foam in and the flew it. The news was very good over all, at 1850rpm with a full tank the surface was calm - at mid tank content it foamed a fair bit - then at low tank content the tank was calm. Overall I'm delighted.

I'm going to experiment with the bit of foam wedged between the tank and frame and see if its making any difference at all. I didn't have time to make a comparison. I was so happy to see the vigerous foaming had gone that I just flew her. The Stratus is a beautiful thing when working right! She does everything so much better then my Raptor 50 with amazing power!

Will come back with the results of the tank wedging experiment.

I'm prepared to accept the foaming for a couple of minutes around the mid tank content point given what I've been through - and what I understand is a kind of Stratus characteristic for most.

[Zilly]

John,

why not try removing another shim and see if it improves even more, you have a set up that you know works so you can always come back to this set up if you are not happy.

z

[Aviation addict]

Thanks Z.

Yes - when I can find the motivation I may try dropping from 0.016 to 0.012 and see what happens.