Stratus vibration at 1850rpm.

[Aviation addict]

Like on Chris' '1st Fight on new Stratus = Tail drift' posting, I too have tail drift on my Stratus.

I have the OS91SZ-H and the GY611 gyro.

As my canopy is away at paint, I've just been running the engine in gently and today was the first time I'd taken the headspeed above 1700. At 1500 and 1700rpm there was minimal vibration, just a little in the vertical stabiliser, but at 1850 rpm there was around a 3mm white froth on the fuel and the gyro drifted!

Any ideas what might be causing this vibration and upsetting the gyro?

I balanced the fan on a high point balancer then dialed it to 0.001" on the engine, plus I balanced the tail & hub, my blade tracking looks good and I think my 'paddles' are running true. I have RADIX main blades, and apart from weighing them individually as a basic check haven't balanced them as a pair or anything.My gap has settled at 0.029" by the way and seems to be constant at all points of the clutch/fan.

I take it that a well set-up Stratus (or any heli) should run with zero foaming in the tank at pretty much any speed.

Any ideas folks as to why my tank is foaming (a bit) at 1850rpm with a subtle vertical stabiliser vibration? I'd rather get rid of the vibration than ignore it and start adding thicker gyro foam to stop the drift.

[Zilly]

John,

I have spent months trying to get comfortable with the 611 on the Stratus and last week I finally chucked in the towl, I built a pair of Strati :wink: for a freind last week and installed CSM 720 Gyros in both, one was a conversion of his old YS powered Fury and one was a new kit with a new OS in it. Both of them flew straight off the deck with absolutely no drift at all, even though the OS was running really rich to the point of fourstroking it still sat rock solid in the hover.

So I bit the bullet and put my GY611 on eBay keeping the 9256 servo for the CSM, I installed it yesterday and ran the quick set up process and all I will say is WOW! Perfect stops in both directions, rock solid in the hover and I was able to do some great backwards loops with no drift on the tail like I was having on the 611.

I have a theory that the CSM720 mounting system which is excellent maybe partly responsible for the performance in the hover so maybe if you try using it with the 611 you may resolve the dirft issue however I would seriously recommend the 720 gyro over the 611 certainly for use in the Stratus

z

[Aviation addict]

Thanks Z. I have just gone and ordered 2 off the CSM0070 Anti Vibration systems (one for Raptor too).

Is foaming in the tank standard though for a Stratus at this headspeed? I think I may fit the Anti Vib system anyway, but would like to tackle the cause of the vibration if possible. Does vibration in the 'vertical stabilizer' and 'slight foaming in the tank' point at anything in-particular?

My 'Medium' is closed by the way and 'High' is at 1 1/2 right now - so not excessively rich or lean (I think).

[capebob]

There should be no tank foaming. I suspect that either your fan is not properly balanced or not installed with minimum rub-out. The very stiff carbon frames on the stratus transmit vibration which requires very careful dial-indicating when installing the fan.

Bob

[Aviation addict]

I did put the fan on a High Point balancer and drill it until it was random, then dial the fan onto the engine. The best I could do was 0.001" exactly. Is 0.001" too much? Should I get slight foaming with 0.001" in your experience?

If it's not likely to be the fan (with 0.001") then what other areas should I start looking at?

PS I did just notice that the two main rotor head blade bolts supplied with the kit from MA were different lengths. One was 2mm longer than the other. I made them both the same length last night but don't suppose this would account for the vibration - the bit that came off will have been a fraction of a gram.

[Alfred]

John
Something is out of wack.
Try re-aligning your engine, your fan might be balanced and have minimum runout but if the engine is just slightly offset, thne you will have a constant twisting motion between the Fan hub and clutchstack.
Try undoing all the bolts that hold the engine and use a Feeler gauge to insure an even gap all the way around the fan/clutchdriver. Then just carefully nip up a couple of bolts and check again..nip up the rest and check again..pull out one bolt at the time re-apply loctite and nip it up...until you have all of them done.
I am sure you know what you are doing, don't give up.
If I can get it working then it can't be too hard :wink:

My GY401 now locks solid in hover/backward flights and no change in vibration levels throughout the rpm changes.

[Zilly]

John,

You are still running in this engine, right? I would leave everything alone until you hve put at least four gallons through it and have leaned it out to its normal operating settings.

Until then you will be chasing ghosts.

z

[Alfred]

Ooops, I missed that.
If that engine is still running in don't bother, lots of parts are still getting to know each other

[Aviation addict]

Thanks guys. I'll check the engine alignment tonight anyway.

I've put 2 gallons through it so far so I guess its early days. Are the engine parts and gears likely to need more time to bed in then? I'm only human though, and so might have misaligned something somewhere along the line, although I was patient and took my time with the build...

My engine seems to be slid right back (aft) on the base plate mounting slots by the way to align nicely with the clutch assembly. Is this normal with the SZ?

[Zilly]

John, the one thing you could check now is that you are running the correct shims in the engine for your fuel, if you are running 30% I think its important with the SZ to run the no2 shim as well as the one that already in there.

z

[GM1]

Fuel foaming is a high speed vibration,usually directly related to the fan balance and alignment. To be honest, I've never had any success using a high point balancer to balance a fan, they just aren't sensitive enough. I use a Top Flite magnetic prop balancer with the collets turned backwards and a LOT of repetitions to get it right. Most of the MA aluminum fans are pretty close, requiring one or two small dimples on the top of the fan between the fins to balance, unless you install a GV-1 magnet then all bets are off and you do what you have to do to balance it. If the fan runout is not LESS THAN .001 inches, at 15000rpm, the vibration is significant and the fuel will foam and a 611 will many times drift. Eliminate the fuel foam and the gyro drfit goes away most times.
By the way, sometimes you can adjust the gyro drift on a vibrating model just by changing the rpm. I had one Fury that would drift left if the rpm was under 1500 and right if it was over 1500. AT exactly 1500, it was neutral. Weird!
Gordie

[Aviation addict]

Z - I'm using 20% Magnum with 0.016 of shims (2 thick ones) and a Viperhead.

Should I have a smooth running machine with exactly 0.001" or do I need to get it less than that?

If 0.001" should be ok, I'll look at the engine alignment next.

[Alfred]

If you have a look across the threats, it now becomes a normal occurence with:
Stratus + GY611 = gyro drift.
The MA metal fan is pretty spot on in balancing, it might be the tiniest off but is cetainly not the reason for high frequency vibrations and or fuel foaming.
I checked mine with the magnetic balancer and could read just the tiniest imbalance which I didn't bother to correct.
Having no higher vibrations then any of my other 4 helies and no gyro drift, plus seen multiple threats where others did have vibration problems even after extensive balancing the Fan to the highest degree seems to show this not to be the main issue.

As mentioned before in another threat, get a metric Dial indicator
0.001" = 0.0025mm
Using a metric Dial Indicator it's graduation is 0.001mm
Get it to or below 0.002mm measured on the inside hole of the fan seems to give the smoothest running.
Then insure your Fan/Clutch driver alignment i.e the gap has to be very close to spot on 360 degree around.
Real fuel foaming isn't just a new engine run-in problem, but a more serious issue.
On mine I could see the fuel slosh a bit forward and backwards while running in the engine and it was running very rich breaking from 4-2 stroking, but after just 3 tanks it was just about gone without a change of needle setting.
This is using a YS91 with Hatory 937

[Aviation addict]

Thanks Alfred.

Tonight I checked some basic things and did find that my flybar paddles were a fair few degrees away from being matched - alignment wise. I've therefore reset them. Could paddles running out of track with each other cause the tank to foam? I guess I'll find out at the field tomorrow (Wx permitting).

I also reset my clutch/fan alignment. If neither of the above has any affect I may have to re-dial the fan - but I'd rather exhaust all other possibilies first - as it's not one of my favourite jobs. We'll see what happens...

[Yellowjacket]

Shim the motor @ 20 k

Bill

[Aviation addict]

The results of my endeavors were, that getting my paddles in line definitely reduced my vertical stabilizer vibration down to nothing. Sadly the tank still foamed at bit at 1850rpm though.

I spent about 8 hours today, trying to shim the engine up, down, left and right (using bits of feeler gauge) to get all 360 degrees of the fan/clutch gap the same (then testing it) only to see more foaming.

At one point I loosened the clutch shaft bolts slightly and ran her on the the ground, shut down - then tightened in an X until tight. - That did seem to reduce the foaming at high speed. About 4 hours in I did get the vibration down to just a ripple at 1850, but managed to lose that setting unfortunately.

Interestingly my GY611 didn't drift the whole day so I must have reduced the vibration at bit by doing the paddles.

Right at the end of the day I did something rather stupid (but after 8 hours of messing I didn't care). I slackened off the 4 off engine base plate mounting bolts 1 turn and went through all my desired speed - 1500/1700/1850 but guess what ? No vibration. Not a thing. The fuel was like a lake on a calm day.
Elated - I tightened them back up slowly using the X pattern and you guessed it - she was foaming like a witch's cauldron again.

Has anyone ever tried making some 0.5mm (un-compressed) rubber shims in between the Main base plate and the Engine base plate in an attempt to (slightly) soft mount the engine? I'm getting desperate.

Reference my 0.016 viperhead shimming. I was told by one of the top US flyers in a PM that this would be fine with 20% Magnum in the SZ and that after running it in I could indeed reduce down from 0.016. Anyone got any comments on the shimming of the head - or the slightly soft mounting idea.

What a frustrating day!

PS: I tried going very rich - down to peak performance setting and this didn't make any difference whatsoever to the 'foaming' situation. I also checked that both plugs were working in the Viperhead. I think all of the above points at an 'Engine Alignment' issue rather than 'Fan balance' - yes / no ?

[Alfred]

I think all of the above points at an 'Engine Alignment' issue rather than 'Fan balance' - yes / no ?

Yes Yes Yes Yes

Re-check your fan alignment using the inside hole of the Fan.
MA's fan alignment technique as described in the manual spot on.
Double check that your Fan Hub to clutch-driver gap is between 020-030.
Check your Fan runout as shown in the picture below.
Just imagine that it shows the fan and not a clutch as this was taken when doing a Raptor 50.

[Zilly]

John, I have always had a little bit of foaming in the tank I think it may be due to the fuel magnet, If you have got rid of your gyro drift thats a pretty good sign that all is well, I would just get on with flying it.

You've got to bear in mind that you have a piston flying up and down at 15000 RPM bolted directly to a 1/4" piece of carbon fibre and you have a fuel tank mounted on a couple of bits of foam tape less than an inch away.

Your experiment with running the engine bolts loose is an interesting one as this illustrates my point, I am hoping that the new tank will have a better mounting system as I think the current one is not too good really.

z

[DavidH]

I have always had a little bit of foaming in the tank I think it may be due to the fuel magnet,

Have to change the subject and ask.

Can you explain how an OMI fuel magnet might cause foaming in the tank? It just like any other clunk.

David

[Zilly]

I know it sounds weird David but I can actually see the magnet as it moves around in the tank giving off white bubble either that or its my eyes playing up. Generally I notice it most when the tank is 3/4 full and you can see it in the cap of the Nalgene tank then if you tilt the Stratus sharply over to the left the magnet moves over into the middle of the tank where you dont see it as much.

Weird Huh!

z