Author Topic: Runs Lean (Read 3272 times)

EddyR · « **on:** September 09, 2012, 02:28:31 PM »

I know you have heard it before.Dirt in the needle valve and he doesn't know enough to clean it out. Nope ,that is not the problem. Plane is my Bearcat with DS.61 light. Strong low RPM motor that runs in strong four cycle most of the flight. Here is how it started and it does it the same each flight. Start out strong four cycle and just a touch of two cycle at the top off the wingover. Two inside loops and inverted flight then partway through the outside loops it goes lean. It is so lean that it fades as more loops are tried. Never will come bask to a four cycle even at the end of the run.It goes lean at the same place in the flight each time. Tank is modified or kit uniflow the same as many before it. Uniflow stops part way back on outside wall. First I cleaned the needle valve,same problem. I changed all tubing,SP. Changed needle valve assembly,SP. Tested the Tank under pressure and changed the filter,SP. Yesterday I built a new tank and took the old one apart and took all the tubing out to check it. When I had the back off I found the pick up tube loose at the back but it may have come loose when I used the touch on it to loosed the back. I put the tank back together and I found a new problem. A leak along the seam there the tank sides come together and it is right next to the uniflow tube spot where it is attached on the inside. Several years ago I has leaks in this spot on Brodak tanks. This tank may have been a Brodak kit. It took a lot of pressure for the tank to leak under water. I checked the motor for leaks right at the beginning of the problem. Very simple set up and easy to see. There is no muffler pressure the uniflow is open to the air. I will fly it Tuesday and find out if the problem has gone away. Any one had this same problem where it goes lean at the same spot every time???

Alan Buck · « **Reply #1 on:** September 09, 2012, 05:38:42 PM »

Hi, Ed try a PA spray bar needle valve. some of DS needle valves may leak when they get hot

EddyR · « **Reply #2 on:** September 09, 2012, 06:02:51 PM »

Alen I started with a PA and went to a ST and back to the PA.

Chris Wilson · « **Reply #3 on:** September 09, 2012, 08:11:08 PM »

Perhaps that rear muffler is heating the fuel tank as the run progresses, changing the viscosity of the fuel with it and thus giving a lean run towards the end.

Insulate the tank and try again.

EddyR · « **Reply #4 on:** September 09, 2012, 09:03:08 PM »

Quote from: Chris Wilson on September 09, 2012, 08:11:08 PM

Perhaps that rear muffler is heating the fuel tank as the run progresses, changing the viscosity of the fuel with it and thus giving a lean run towards the end.

Insulate the tank and try again.

It runs OK on the ground and it ran Ok before this started. I flew it with out the cowl and it ran lean. Muffler runs cool on this motor. I did do that when it was first flown and it was not needed. It ran OK on 100 degree days. My Rustler .40 burns balsa but never effected the run. I think it has something to do with the tank???

Ed

Chris Wilson · « **Reply #5 on:** September 09, 2012, 09:18:49 PM »

Quote from: Ed Ruane on September 09, 2012, 09:03:08 PM

My Rustler .40 burns balsa but never effected the run........

I have a Rustler 51 waiting for a model and wonder if the same care is needed for it too(?)

RandySmith · « **Reply #6 on:** September 09, 2012, 10:22:27 PM »

Quote from: Chris Wilson on September 09, 2012, 08:11:08 PM

Perhaps that rear muffler is heating the fuel tank as the run progresses, changing the viscosity of the fuel with it and thus giving a lean run towards the end.

Insulate the tank and try again.

HI
It would go rich if that were happening, so Ed needs to look at other items.
Is the engine fully broken in?

Randy

Steve Helmick · « **Reply #7 on:** September 09, 2012, 10:23:56 PM »

Quote from: Ed Ruane on September 09, 2012, 09:03:08 PM

It runs OK on the ground and it ran Ok before this started. I flew it with out the cowl and it ran lean. Muffler runs cool on this motor. I did do that when it was first flown and it was not needed. It ran OK on 100 degree days. My Rustler .40 burns balsa but never effected the run. I think it has something to do with the tank???
Ed

Sounds like a perforated uniflow tube...tho possibly too much prop load or not enough oil. The 12-5 APC runs well on the DS .61 SE Lite, but dunno about your RE version, which I think may be AAC instead of ringed?

Steve

Chris Wilson · « **Reply #8 on:** September 09, 2012, 10:59:13 PM »

Quote from: RandySmith on September 09, 2012, 10:22:27 PM

HI
It would go rich if that were happening, so Ed needs to look at other items.
Is the engine fully broken in?

Randy

Oops, of course Randy - egg on face!

John Leidle · « **Reply #9 on:** September 10, 2012, 05:36:52 AM »

I'd try a wire tie on the fuel line where it goes onto the NVA and every place where the fuel tubing goes over a metal tube of any kind.
John

EddyR · « **Reply #10 on:** September 10, 2012, 06:13:15 AM »

I have tried all of the above fixes. The motor is not new but has strong compression and starts with one flip. 13-5 very thin prop. Tom recommended a 13-5. It now has a new custom tank in it. Maybe the tank seam leak or the loose pick up vent was the problem but that seems a stretch. The lean run timing is so predictable it seems like a tank issue?

?
I have fixed this problem many times over the years but this time I am missing the fix. Many years ago I had this happen on my Cobra and it was a bug in the uniflow tube where it entered the body.New rotors and breaks on the Mustang today so I will fly it tomorrow.
Ed

Lauri Malila · « **Reply #11 on:** September 10, 2012, 02:21:53 PM »

Hi.

I've had similar issues with our engine (MB), especially when I tried to use it at rich setting, 4-stroking all the time.
My problems were caused by the engine running too cold. When engine is far out from thermal balance, it will heat up during the first maneuvres. Heating causes better burning which causes higher RPM.
This happens to me usually in the morning when temperature and relative humidity is low but there is still water mist in the air. Our engine is very sensitive to that, mainly because of integrated AAC construction & piston scavenging, which makes it propably the coolest engine on planet. But combined with ultra light weight, it's not an easy combination.
Anyway, my solution for the leaning-out problem was to increase compression. Also, as I have lots of power to waste, I also build up the stability by choking the exhaust end.
I have fixed quite a few Discovery Retro engines for people suffering from same kind of problems. The most common repair is to set back the factory settings (venturi, compression) and to remind of how important it is to use correct type of fuel. For example, several synthetic oils don't work with DR at all, causing erratic running. Then people think that the engine can be tamed down by adding some shims. That messes up the thermal balance and lowers power. The next natural step is that they drill the venturi bigger which messes up the harmony even more.
So, providing that your fuel system is OK, I recommend to increase compression step-by-step, and perhaps to try with all-castor fuel.

Lauri

EddyR · « **Reply #12 on:** September 11, 2012, 04:18:10 PM »

TANK

The replacement tank made the problem go away. I can now set it and it stays steady at that setting for the complete flight.
I want to thank everyone for the help. This has been a tough one to solve. I have seen tanks leaking bad and the motor ran well for most of the flight. I would have changed the tank sooner but it required a special built tank to fit the plane. I still do not understand what was happening.
Ed

Steve Helmick · « **Reply #13 on:** September 11, 2012, 08:55:30 PM »

So, that's a ST head on your DS .60?

Steve

Steve Fitton · « **Reply #14 on:** September 11, 2012, 09:05:46 PM »

Quote from: Steve Helmick on September 11, 2012, 08:55:30 PM

So, that's a ST head on your DS .60? Steve

Its a super-sekrit modification done by an engine guy down in Florida. Turns the lowly DS-61 into a powerhouse rivaling a ROJett 76.

EddyR · « **Reply #15 on:** October 29, 2012, 06:25:55 AM »

The replacement tank did not solve the problem. Motor still would go lean in the triangles and stayed lean.
BUT I DID FIX IT. I stopped using the uniflow and used original venting out the bottom of the tank. The only line open is the overflow. Now for the first time the motor stays at the RPM set at the beginning of the flight. It also is using more fuel but the motor is running much slower. The uniflow may not have been the problem it may have been the method of getting the air into the uniflow vent.It is a long trip for the air on this wide body to get from the pickup tube on the outside of the body to the tank.

. I found this answer to the motor run the day before the Hunterville contest but the morning of the contest the motor would not start

I had forgotten to connect the tank line to the needle valve

Later that day it ran fine.

Ed

Pat Johnston · « **Reply #16 on:** November 02, 2012, 12:52:06 PM »

Ed,
I had almost exactly the same problem with my DS 60 Lite on my first Bearcat. Similar to yours. It turns out that it was an easy cure by adding oil to the fuel. Some engines just like a bit more oil. Mine did. I add 8 ounces of Castor to 5% Powermaster. That settles it down nicely. I have one OS 35FP which will tell me if I don't have enough oil, the very same way.
BTW, is that my Bearcat design you are flying?
Pat Johnston
Skunk Works

EddyR · « **Reply #17 on:** November 02, 2012, 05:24:12 PM »

Pat
The Bearcat is the 1968 Rabe Bearcat. The wing is very thin. I don't have a lot of full patterns on it with all the motor run problems I had. I am sure your version would be a big improvement. I would build another if you have one with about 650 sq" and a better airfoil. I built this one to fly classic but it came out much to heavy to be a good flyer. It is fun to fly and everone likes to see it fly.

Ed

Pat Johnston · « **Reply #18 on:** November 03, 2012, 09:18:05 AM »

Ed,
I just designed one at 617 squares for electric. I have to admit that a 650 incher would be great for a DS60RE like you have. Could be good for serious electric setups for the larger planes. On a personal level, at 140 pounds, I can't handle a large plane in the wind with enough grace to do a decent flight. Trying to stay around 600 inches to keep the weight and pull down.
Let us know how adding oil to your fuel works. A tank or two will tell you if tht is a problem right a way.
Pat Johnston
Oil Division
Skunk Works

EddyR · « **Reply #19 on:** November 03, 2012, 01:33:24 PM »

Pat I sent you a email.

Ed

Author Topic: Runs Lean (Read 3272 times)

John Leidle