VX270 Needle tuning through Flight performance questions

[eluminous]

Hi Al,

Five weeks ago you shipped me out a VX270 TT for my Whiplash which has had 10 litres of fuel through it and is starting to perform really, really well. I am very happy with it. The engine transitions well from idle to hover and then to IU 1,2 and 3 and runs smooth. The head speeds are set at 1750, 1850 and 1950 respectively.

When I unload the disc and/or pull the heli down from height with say 6-10 degrees of negative collective, the motor will pulse or surge and make a "Wah-Wah" type sound. I hear of this type of operation being mentioned a bit throughout the forums, but I am wondering if this is a case of the low needle being still a little "rich" in terms of tuning.

I am making the assumption that when the disc is unloaded the Governor is pulling throttle back onto the low needle. If the low is still a little rich, does it tend to create a situation where the engine is getting "spurts" of a too much fuel and creating the mentioned surges. Does this assumption sound right? I tried lowered the gain on the CGY 750's governor settings however this made no difference.

Head temps after a quick landing from "hard-ish" flying are around 70-80 Celsius (158-176F) taken on cylinder about 2-3 fins back from the top of head. Does this sound a little cold? If so, What is a good operating temp for this engine? Ambient temps are around 10-12 degrees Celsius.
My needle settings are a bit more rich from factory settings at (1 1/4 low, 1 3/8 high ). These are both 1/8th of a turn more than the stock manual settings for the 990 carb.

The plug looks quite good but like it's still on the slightly rich side. The ceramic firing end is a little grey with carbon rather than a golden colour, and the electrode is dark grey to almost greyish-black. I'm using a full synthetic mixed at 40:1.

As an aside: Congratulations on offering such a nicely modified engine available to the masses.

Cheers and thanks.

[Doug Darby]

Could you please post a picture of your plug.... Yes it sounds like it could be still a little rich but I am concerned by your use of the word "grey" to describe your plug color . Ususally when the plug turns from brown (light) to grey it's a sign of a lean condition.
As an aside, the Wah wah could also be a simple tail gain issue. I just read on another post that the same condition was resolved with a change in gyro gain.
I will try and post a pic of the plug color from one of my flights to day for you to compare to... A picture of your plug would be very helpful...

[Doug Darby]

From the MA Gas forum today..... "It would appear that my whole wah wah problem was nothing more then my gyro gain was way to low.*When I first set up the helicopter I was more worried about the engine tuning and and break in and did only the most basic gyro setup. It held the tail in flight and did not wage, so ok good to go for engine breakin.*As the wah wahs were there from day one, and as I leaned the engine they got better but did not go away I always thought the problem was engine tuning.*It should be noted that while the gyro gain was low it still held the tail fine and a couple other people that flew the helicopter did not notice it either.Using ATV's in the radio to set gyro gain I started out at +40, this weekend I have upped it to +65 and for the most part the wah wahs are now gone. I will up the gain some more till I start getting tail wags and back it off just a little.It sucks when it takes this long to find a basic problem."

These plug photos are pretty telling.... You can even see which side of the plug was towards the exhaust port as it is lighter in color than the intake side of the port.

[eluminous]

Thanks Doug,

I will post a pic of the plug tomorrow as it's dark now and won't represent the colours correctly if taken inside under incandescent/led light. I did try yesterday, but couldn't get a good macro shot.

Doug, the issue of the tail kicking by all accounts appears to be triggered from the engine tunings pulse/surge and/or the governor. These pulses directly move in relation to the engine note. If it was a tail gain issue, wouldn't the tail pulses more than likely happen irrespective to the engine surges and under varying flight conditions? Plus, when the engine is running up in IU 1,2 or 3, they disappear except under high speed descents when the disc is unloaded (back on the low needle). My gyro gain is running at close to 55% Futaba Gain and otherwise seems very solid and "very" responsive. However, I will up the gain tomorrow and try your suggestion. It can't hurt and just may be the ticket .

If I look at your plug I can see a heck of a lot of grey/light grey in it (along with some light-ish tan/brown). This "is" more the desired plug condition. What temp was your engine running at? When I looked at my plug I could definitely see more "dark" in it than yours and the grey I was referring to was of the "blacker" carbon type grey. Like it's still running a little cold. Plus the electrode on the end was darker than yours along with the flat spot/lip on the end of the plug thread. There is also still a little "wet" oil forming around the plug thread when I remove it. Not much, just a little. Do you get this?
Another point of difference might be worth noting: Don't you run your engine on a QD tuned pipe?

Anyway, today I leaned the low needle just a smidge (1/16) to test my theory, and the engine picked up a little more power under heavy cyclic/pitch loads. The "Wah Wah or ""Ding-a-Ding" engine pulses also slightly decreased (or became more subtle) when unloading the disc or doing fast descents. I then temperature tested using my same quick landing method from I.U. 3. The engine temp didn't seem to change much from two earlier flights and was still under 87 degrees taken close to the exhaust port directly on the head which was the hottest part (apart from the exhaust outlet part of the header which takes a direct hit from the exhaust gasses).

Doug/Flyers; could you please all chime in with your engine operating temps taken after some heavy flying. It would help me greatly to get a ball-park average. Or at least just allow me to draw a more broadly educated and informed assessment.

Thanks and Cheers for the collective input.
Steve

[Doug Darby]

Im running an RJX pipe on this motor at this time. The Low Speed needle does have a subtle effect on the full carb range like maybe 8-10 % through out the range so a change there may make the whole range a little leaner hence your imporvement.
As for Temps I have spent so much time measureing them in so many ways that I have all but given up on it and I just really solely on Plug color and performance. But when I was testing with a temp gun on the fins next to the pipe I was seeing 220 to 260 F on Hot Summer Days. When i switched to Cylinder Head temps I saw temps as high as 350+ under the spark plug. Others may chime in, but reading the plug, making small needle adjustments, and then watching and listening closely to the engine in heavy load maneuvers will always be the answer for me....
Let me know if I can help...

[eluminous]

Hey Doug. As you would be aware at this stage, I was getting to the point where it would have been worthwhile posting some pics of my plugs last couple of runs when I had the tail bevel gear incident.

However, It turned out that the engine was running too rich and needed to be leaned out quite a bit. They were actually open a bit more than the settings I posted at the start of this thread after rechecking.

The Whip will be back in the air soon for chapter 2

[Doug Darby]

Keep us posted..

[eluminous]

Will do...

[eluminous]

Hey Guys, here's an update.

Whip is back in the air and had another 5 litres of juice through it. Slowly leaning it out and is picking up more power every flight. I have got the new QD pipe sitting here waiting until I'm happy with the optimum tune on the muffler. I also popped a 17t pinion in and am much happier with how it revs and pulls through the harder moves. It does not bog at all on full 12.5 degree punchouts! Full pitch, tail first big power loops it drops rpm but holds it under torque quite well. I'm really happy with how it's working.

One thing to note is to take care installing the standard Zenoah clutch adapters. Mine had nearly .4mm runout on the two top clutch bolt seats when I measured it with a dial indicator. No matter where I rotated and positioned the adapter on the shaft, I could only get it down to 0.1 - 0.12mm. I ended up grinding down one seated area until it was within 0.01mm. Nice

Hope everyone is enjoying great flying days... I am now building Whip-Gas #2 (couldn't help myself).

Cheers