pinnedup

I am having difficulties achieving and maintaining a tuned engine. I run a TT46 Pro in a World Models Sky Raider Mach II, using a McCoy MC-8 glow plug and Wildcat Premium fuel; 10% nitro and 16% oil. I have followed the guidance of the engine owners manual, that here on RC Universe and fellow flyers at the field. Using the fuel line pinch test and tach I have set the high idle needle valve at a point richer than the highest rpm, then adjusted the low speed idle to achieve smooth transition to full throttle. Initially I was having difficulties with is loading up on take off and made adjustments to the low speed needle valve, this continues to be a challenge. Now the engine looses power during mid flight with limited throttle response, in response to this I have richened the mixture but then have experience limited power and dead sticked due to an increased fuel consumption rate. On the ground the tune seems to be set correctly.

When the tune is good the plane is fast and does not hesitate, but I will get a pretty good tune but the next day, the engine tune requires tweaking. The tune requirements seem to change from day to day and as the engine heats up. The fuel supply line rests against the cylinder, possibly heating up the fuel, I have noted that the engine and fuel pressure line seam to get pretty hot. I have not noticed excessive bubbles in the fuel line; there is some insulation between the fuel tank and the fuselage. There is exhausted fuel on the plane's fusulage, the color of the exhuasted fuel is gray to black, I can also see fuel exhausted when running the plane on the ground, and at times a contrail in the air. Today when the plane lost power a mid flight there was not a visible contrial.

Any ideas what may cause this variation in engine tune?

AllTheGoodNamesAreTaken

My Feedback: (180)

You may have a fuel tank issue. Can you run a whole tank without any issues on the ground?

pinnedup

I have not run through a whole tank on the ground since prior to its maiden. I'll try it.

bkdavy

My Feedback: (1)

16% oil is to low for that engine in an airplane. either add some castor, or purchase Omega or Coolpower. You should have at least 18% oil, preferably 20% oil.

Remember to reset the high speed needle after EVERY low speed needle adjustment. As you lean out the low end, you're also leaning the high end. If you don't reset the high speed needle, you risk a high speed lean run.

Make your low speed needle adjustments in increments of 1/8 turn or less. Its very easy to miss the sweet spot if you're adjustements are to big.

Make sure you're needle valve isn't clogged. Take it out and disassemble it completely. Very small contaminants can have a very big affect.

Good luck.

broke_n_bummin

I would try an A5 short plug with the 10% nitro. Also, I've never been to Los Alamos, but I lived in Cloudcroft and had some of the same problems. When we moved to Eunice, the problems went away. I was told it was the constant barometric pressure change in the mountains (I was 12 and gullable). But later when I was at Ft. Carson in Colorado, I still had to retune the engine quite a bit, but mostly in the late spring and summer. Well, I'm back to being a flatlander again, and my engines pretty much stay tuned year round.

air-madness

Well, glow engine manuals tell the user to tune the high end first at WOT. When the high end is set the low can now be set since the proper flow of the needle has been acheived. I have never had to readjust the low needle when changing the high settings on a glow engine -- never. Now, a traditional two stroke you do. The low needle (not an air bleed type) really has no affect on the high needle period. The low needle only really affects in a range from idle to about quarter open on the carb barrel. There is actually a very informative (and full of debate) thread on RCU about this very topic. For example, I have an OS .10LA -- it has no low needle or air bleed needle, only the high. Not a single problem with it at idle or during transition. Actually, it is really a super bad engine (in a good way).

I would fire the engine up at half throttle, move the throttle to full and set the high needle. Once the needle is set to the proper richness move the throttle below half open and see how it is running. If it wants to sputter simply adjust the low needle until it doesn't (until it runs smooth at the throttle/idle level). Now, move the throttle to full quickly after it has ran a minute after you adjusted the low needle. Helpful hint: The transition from idle to full throttle should give no hesitation when done rapidly.

pinnedup

Thanks for the advice, based upon your responses and that of other club members the first change I will try is to increase the oil content in my fuel mixture by adding extra castor oil to bring the oil content up to 18%. I understand that in addition to lubrication, castor oil assists in remove heat from an engine. The life the extra lubrication would add to the engine would be a bonus and benefit to my other engines.

Thanks

da Rock

The black fuel residue shows either the engine is still breaking in or that you're running that engine too lean. Both situations require that you fly the engine a bit richer, no matter what.

First start of the day, start at three clicks over idle. Leave the engine alone once it starts until you hear it pick up a bit when it gets to operating temp. That'll take maybe 20 seconds. Take your time.

Every first start of the day, when the engine has done that 20seconds or so, move the throttle to full and turn your needle out until you can see and hear for sure that it's going rich. This is nothing but an insurance move. But do it. It insures the next step starts from "too rich". Now slowly lean the needle a click at a time. RPMs will come up and keep coming up until the engine sags. Immediately when you hear it start to drop off, give it 3 or 4 clicks rich. How many clicks rich exactly? Fly it and find out. And once you find out, every outing from then on, when you do this "first start of the day" ritual, you'll know.

I've been doing some prop tests the last week or so. I have a handheld "weather station". It has a density altitude readout. (Don't bother asking.) From one session to the next, I've seen the DA change over 2,000'. And the needle setting change on the test engine over 4 clicks. Is that normal. Nah, but not unusual. You need to do the "first start of the day" ritual EVERY time you go out.

da Rock

A gallon is 128 ounces. You'll need only 2.5 to 3 ounces to get 18%. But if I were you, I'd add enough to have 20%. Won't need over that nowadays, but 4% castor is enough for the insurance castor gives.

pinnedup

I added 5 ounces of Sig castor oil to a gallon of Wildcat Premium fuel (16% oil) to get a total oil content of 20% per da Rocks suggestion. I also looked at the Thunder Tiger owners manual, they also recommend 20% oil content in the fuel, sometimes it does help to read the directions. I have made no other adjustments at this time.
Finally got out and flew today, the engine required initial tuning but ran much better. The first flight was a little rich so I leaned it out some. Next flights went well, plenty of power and consistent through out the flights, it may be a little rich at low idle. The engine may still may require a little of fine tunning, I see how the next flying session starts out. It was a warm day in the mid 80s. The plane leaves a light contrail, there is quite a bit oil/fuel mixture on the fuselage but it is now pink not dark.
Thanks for the advice.