Can a fuel tank cause over compression????
05-30-2017 | 03:23 PM
#1
Can a fuel tank cause over compression????
Hi All:
When I got my MVVS D7 running as it should, things went to Hell in the air.
I adjusted the engine to what I though was a great setting and launched the plane. The thing ran like a sewing machine for I/2 tank and then became grosslyover compressed to a point where I decided to dump it to save the engine from potential damage. The second flight was the same story. The third time that I fired up the engine, I pointed the straight up while holding the plane. The engine went over compressed as it did in the air. I have no thoughts as to why this would happen!
The engine runs great on a test stand with almost no exhaust residue, very light yellow, and very little smoke.
The plane is a Tom Tom with built in tank, I will return to the test stand tomorrow to see how well the engine runs. If it runs well on the test stand, I will attach a profile tank on the outside of the fuselage to see if this makes a difference. I have seen this done before where the owner did not wish to dig the fuel tank out of the fuselage.
I pitted for my mate's Ollie .15 today and it ran very well. I also had great luck with my OS .40 with a Davis head.
I still think that I need a correct con rod with a bit of offset on the larger end.
Suggestions and/or comments?
Best wishes,
Franchi
When I got my MVVS D7 running as it should, things went to Hell in the air.
I adjusted the engine to what I though was a great setting and launched the plane. The thing ran like a sewing machine for I/2 tank and then became grosslyover compressed to a point where I decided to dump it to save the engine from potential damage. The second flight was the same story. The third time that I fired up the engine, I pointed the straight up while holding the plane. The engine went over compressed as it did in the air. I have no thoughts as to why this would happen!
The engine runs great on a test stand with almost no exhaust residue, very light yellow, and very little smoke.
The plane is a Tom Tom with built in tank, I will return to the test stand tomorrow to see how well the engine runs. If it runs well on the test stand, I will attach a profile tank on the outside of the fuselage to see if this makes a difference. I have seen this done before where the owner did not wish to dig the fuel tank out of the fuselage.
I pitted for my mate's Ollie .15 today and it ran very well. I also had great luck with my OS .40 with a Davis head.
I still think that I need a correct con rod with a bit of offset on the larger end.
Suggestions and/or comments?
Best wishes,
Franchi
05-30-2017 | 04:26 PM
#2
My Feedback: (66)
Hi All:
When I got my MVVS D7 running as it should, things went to Hell in the air.
I adjusted the engine to what I though was a great setting and launched the plane. The thing ran like a sewing machine for I/2 tank and then became grosslyover compressed to a point where I decided to dump it to save the engine from potential damage. The second flight was the same story. The third time that I fired up the engine, I pointed the straight up while holding the plane. The engine went over compressed as it did in the air. I have no thoughts as to why this would happen!
The engine runs great on a test stand with almost no exhaust residue, very light yellow, and very little smoke.
The plane is a Tom Tom with built in tank, I will return to the test stand tomorrow to see how well the engine runs. If it runs well on the test stand, I will attach a profile tank on the outside of the fuselage to see if this makes a difference. I have seen this done before where the owner did not wish to dig the fuel tank out of the fuselage.
I pitted for my mate's Ollie .15 today and it ran very well. I also had great luck with my OS .40 with a Davis head.
I still think that I need a correct con rod with a bit of offset on the larger end.
Suggestions and/or comments?
Best wishes,
Franchi
When I got my MVVS D7 running as it should, things went to Hell in the air.
I adjusted the engine to what I though was a great setting and launched the plane. The thing ran like a sewing machine for I/2 tank and then became grosslyover compressed to a point where I decided to dump it to save the engine from potential damage. The second flight was the same story. The third time that I fired up the engine, I pointed the straight up while holding the plane. The engine went over compressed as it did in the air. I have no thoughts as to why this would happen!
The engine runs great on a test stand with almost no exhaust residue, very light yellow, and very little smoke.
The plane is a Tom Tom with built in tank, I will return to the test stand tomorrow to see how well the engine runs. If it runs well on the test stand, I will attach a profile tank on the outside of the fuselage to see if this makes a difference. I have seen this done before where the owner did not wish to dig the fuel tank out of the fuselage.
I pitted for my mate's Ollie .15 today and it ran very well. I also had great luck with my OS .40 with a Davis head.
I still think that I need a correct con rod with a bit of offset on the larger end.
Suggestions and/or comments?
Best wishes,
Franchi
I run diesels frequently (all conversions with Davis heads) from OS 40FSR to Super Tigre 4500 and there's only one thing that I find to be a problem every so often: carbon deposit build up which increases compression and carbon build up under rings which make them stick. Properly addressed - the engines return to useful service every time.
05-31-2017 | 08:13 AM
#3
The amount of fuel, the engine temperature and the ideal compression settings are dependent on each other, there is nothing strange or wrong there. So, it sounds like the compression setting is too high to begin with, and when the engine heats up it becomes even higher, this makes the engine run warmer and so on. I believe that is referred to as a run-away situation.
So try to see how the engine reacts if you set it a little leaner, it should usually begin to missfire a little. If not, then you probably have the compression setting too high...
On the ground you can find the optimum (max power) setting by leaning the engine out, then increasing the compression setting to remove the misses, lean it out a little more and so on. At some point there is no gain any more, that would be the maximum power setting which you really shouldn't try to fly the engine at. You want to use a slightly lower compression setting from that position and a also slightly richer needle setting.
So try to see how the engine reacts if you set it a little leaner, it should usually begin to missfire a little. If not, then you probably have the compression setting too high...
On the ground you can find the optimum (max power) setting by leaning the engine out, then increasing the compression setting to remove the misses, lean it out a little more and so on. At some point there is no gain any more, that would be the maximum power setting which you really shouldn't try to fly the engine at. You want to use a slightly lower compression setting from that position and a also slightly richer needle setting.
05-31-2017 | 03:34 PM
#4
My Feedback: (1)
Frank is flying control line models so he needs to take off richer than radio model engines.
The fact that it took half a tank full of fuel in the air before it "went hard" suggests a tank or fuel feed problem to me. The symptoms suggest a partial fuel blockage causing the engine to go over lean. Could be some "grunge" in the tank. A flush with kero both ways may clear it. A fuel filter is often a good idea.
The fact that it took half a tank full of fuel in the air before it "went hard" suggests a tank or fuel feed problem to me. The symptoms suggest a partial fuel blockage causing the engine to go over lean. Could be some "grunge" in the tank. A flush with kero both ways may clear it. A fuel filter is often a good idea.
Last edited by qazimoto; 05-31-2017 at 03:39 PM.
05-31-2017 | 04:04 PM
#5
Hi Gazimoto:
I think that you are correct about the tank needing a good cleaning! After I was done "flying" the MVVS, I started it up and moved it through various flying attitudes. The engine did indeed become over compressed after running for awhile. That is why I asked the question. There is no room to install a filter so I may have to move the fuel line and filter outboard.
This gives me a bit of more latitude to solve this problem. Oh yes, the prop that I am using is a circa 1975 Taipan 8x6. It is a gray plastic and has always performed very well with the .15 Diesels. With the above combination, the Tom Tom is very fast!!!!
Be well my friend,
leomat
I think that you are correct about the tank needing a good cleaning! After I was done "flying" the MVVS, I started it up and moved it through various flying attitudes. The engine did indeed become over compressed after running for awhile. That is why I asked the question. There is no room to install a filter so I may have to move the fuel line and filter outboard.
This gives me a bit of more latitude to solve this problem. Oh yes, the prop that I am using is a circa 1975 Taipan 8x6. It is a gray plastic and has always performed very well with the .15 Diesels. With the above combination, the Tom Tom is very fast!!!!
Be well my friend,
leomat
06-01-2017 | 08:43 AM
#6
Hello Gazimoto:
I did flush the fuel tank with brake cleaner and found that it was indeed contaminated with what looked like particles of blue dope that I had painted the fuselage with when the plane was built. I will also sneak a small filter onto the line to prevent more paint from entering the engine.
I am also going to mount and level engine mounting pads on the engine mount. I think that the engine should be mounted in a stress free environment.
Cheers,
leomat
I did flush the fuel tank with brake cleaner and found that it was indeed contaminated with what looked like particles of blue dope that I had painted the fuselage with when the plane was built. I will also sneak a small filter onto the line to prevent more paint from entering the engine.
I am also going to mount and level engine mounting pads on the engine mount. I think that the engine should be mounted in a stress free environment.
Cheers,
leomat
