da 70 thread
- Thread starter orthobird
- Start date
so i got my 70 back from DA several weeks back. i was practicing for an IMAC event and just last weekend, i installed the motor. i flew her yesterday 3 times and today 2 times. yesterday, the 1st flight, wow, it was soooo sooooo rich. after the flight, i leaned the HSN and LSN by 1/16th. 2nd flight yesterday, still very very rich. i did HSN lean by 1/16th, and 3rd flight, still very very rich. i am using a flacon 24 x 10 CF prop. so today, before 1st flight, i leaned it again, and the flight was better than friday. then i landed her and leaned her again. however, both flights today, i noticed that after 6 or so minutes of flying, which all i did was fly a very high oval pattern, since i was scared she could deadstick, on each flight today, it sounded like she was going to turn off on me, did it twice each flight, and maybe 20 seconds apart.
let us look at telemetry parameters
#1 rpm max= 7620 T max = 346, 247
#2 rpm max = 7620 T max = 341, 259
#3 rpm max = 7620 t max = 342, 281
#4 rpm max = 7800 t max = 356, 307
#5 rpm max = 7710, T max = 351, 318
between flight 3 and 4, i had done ground running to tune it, instead of flying it, then landing and tuning. so those number reflect more improved tuning.
unusual how after increased tuning, (leaning), the RPM max went down some .
one cylinder stayed same temp, but the other one became progressively hotter as i leaned it out.
the 5th flight, it sounded the best in the air.
on the ground, each time, sounded good, but once she was up in the air, and not under load, then the engine sounded like it was 4 stroking or mis-firing. if i did an up-line, this would become less.
anyone have any ideas?
today, i will remove the fuel tank and re do all the plumbing again. i am wondering if it is a problem with fuel flow.
let us look at telemetry parameters
#1 rpm max= 7620 T max = 346, 247
#2 rpm max = 7620 T max = 341, 259
#3 rpm max = 7620 t max = 342, 281
#4 rpm max = 7800 t max = 356, 307
#5 rpm max = 7710, T max = 351, 318
between flight 3 and 4, i had done ground running to tune it, instead of flying it, then landing and tuning. so those number reflect more improved tuning.
unusual how after increased tuning, (leaning), the RPM max went down some .
one cylinder stayed same temp, but the other one became progressively hotter as i leaned it out.
the 5th flight, it sounded the best in the air.
on the ground, each time, sounded good, but once she was up in the air, and not under load, then the engine sounded like it was 4 stroking or mis-firing. if i did an up-line, this would become less.
anyone have any ideas?
today, i will remove the fuel tank and re do all the plumbing again. i am wondering if it is a problem with fuel flow.
Bdegan
50cc
Ortho,
Those are large temperature variances. Also very high temps.
And the fact that the engine ran very rich.
Makes it sound like there is an air flow issue. Sounds like air is packing into the cowl but not exiting or flowing through.
What plane ? Can you post some pictures of your set up ?
Those are large temperature variances. Also very high temps.
And the fact that the engine ran very rich.
Makes it sound like there is an air flow issue. Sounds like air is packing into the cowl but not exiting or flowing through.
What plane ? Can you post some pictures of your set up ?
yes sir. sure can. i have gone thru this before, but i will be more than glad to go over it again. this is an Extreme Flight Yak 91".
the bottom of the cowl is open, and so is the bottom of the fuselage, along the pipe tunnel. there are two area open here.
regarding the temps, i will post and quote what i have mentioned before. please chime in and tell me if you have any experience with my explanation, or if you believe my theory or postulate is wrong. i will tell you this, before this engine went back to DA, its temps were even higher, and during flight, i would notice temps into 400's/ once temps got into 450 F range, then the engine would fade, i would back off the throttle, and temp would go down, and then it would keep on running. what happened, the reed valves got chewed and spit out the cylinder, causing damage to one cylinder, so i returned it.
when i was experiencing these high temps, this is what promoted me to redo the baffles and the air exit area. when the temps were 400 or so, the bottom of the pipe tunnel was not open.
to me, it seems temps are way better, and consider, you are in toronto, and i am in shreveport, LA. today the ambient temp was 98 Degrees F or so. (HOT!!!)
10235=3695-IMG_5491.jpg
the bottom of the cowl is open, and so is the bottom of the fuselage, along the pipe tunnel. there are two area open here.
regarding the temps, i will post and quote what i have mentioned before. please chime in and tell me if you have any experience with my explanation, or if you believe my theory or postulate is wrong. i will tell you this, before this engine went back to DA, its temps were even higher, and during flight, i would notice temps into 400's/ once temps got into 450 F range, then the engine would fade, i would back off the throttle, and temp would go down, and then it would keep on running. what happened, the reed valves got chewed and spit out the cylinder, causing damage to one cylinder, so i returned it.
when i was experiencing these high temps, this is what promoted me to redo the baffles and the air exit area. when the temps were 400 or so, the bottom of the pipe tunnel was not open.
to me, it seems temps are way better, and consider, you are in toronto, and i am in shreveport, LA. today the ambient temp was 98 Degrees F or so. (HOT!!!)
10235=3695-IMG_5491.jpg
and i quote myself:
For the temperature, this gets even more complicated and interesting. for years, people measure their engine temps by using a infra-red thermometer of sorts. or at least, this is how i assume people make these measurements. they have then reported these temps, and after some while, people get an idea of what "normal" range should be.
when using the infrared thermometer guns, you must keep in mind that if you point it to the front of the engine, while the propeller is spinning, the temperature that is read is of the surface of the front of the motor. be it the cylinder or the crankcase or whatever you point it at. this type of info, lets say, you get the temp of the engine soon after cranking it on, or, you check it upon landing, or if you run it on the ground, and check the temp there, whatever, you first will need to appreciate the cooling of the engine and how the engine dissipates heat.
i told you this would get complicated. After having had performed many experiments, i have concluded that the temperature in the front of the engine, when the engine is running, and there is a propeller connected forcing air onto the engine, the cylinder temperature in the front of the cylinder is way cooler than the temperature in the back of the cylinder (sometimes difference is greater than 100 degrees F). the temperature in the top of the cylinder (closest to spark plug) gets hotter than the temperature of the cylinder closer to the crankcase. the crankcase temperature is way lower than the cylinder temps (can be over 100 degrees cooler). the hottest area on the engine is the area directly behind the cylinder and the highest area (fins) area as well. if you put a sensor at this spot, you will get the "hottest temp". interesting, if you have a muffler in this location that is very close to the back and top of the cylinder, this can alter the reading due to making it a false reading. that is, the heat of the muffler may be adding to the actual temp of the cylinder. this seems to not be a problem on twin cylinder engines, due to the mufflers or headers usually pointing down.
More interesting observations: the temperature peaks during flight occur during up-lines, knife edge flight, hovering and flat spins, etc.. really make it hotter!!!! usually temperatures are not sustained, but peaks due to whatever flight maneuver you are doing that increases the load on the engine. Also interesting is that cooler days can lower the temperature down significantly more than the actual ambient temperature compared to another day. for instance, i was flying in 95 degrees temp, and the engines peaks temps were in 320's, then another day, temps were in 85 and high engine temps did not get over 280, all other variables were unchanged (altitude, prop diameter/pitch, needle settings, gas oil mixture, gasoline octane rating).
i will attach a diagram depicting the position of the temp sensor.
10237=3696-sensor position for da 70.jpg
For the temperature, this gets even more complicated and interesting. for years, people measure their engine temps by using a infra-red thermometer of sorts. or at least, this is how i assume people make these measurements. they have then reported these temps, and after some while, people get an idea of what "normal" range should be.
when using the infrared thermometer guns, you must keep in mind that if you point it to the front of the engine, while the propeller is spinning, the temperature that is read is of the surface of the front of the motor. be it the cylinder or the crankcase or whatever you point it at. this type of info, lets say, you get the temp of the engine soon after cranking it on, or, you check it upon landing, or if you run it on the ground, and check the temp there, whatever, you first will need to appreciate the cooling of the engine and how the engine dissipates heat.
i told you this would get complicated. After having had performed many experiments, i have concluded that the temperature in the front of the engine, when the engine is running, and there is a propeller connected forcing air onto the engine, the cylinder temperature in the front of the cylinder is way cooler than the temperature in the back of the cylinder (sometimes difference is greater than 100 degrees F). the temperature in the top of the cylinder (closest to spark plug) gets hotter than the temperature of the cylinder closer to the crankcase. the crankcase temperature is way lower than the cylinder temps (can be over 100 degrees cooler). the hottest area on the engine is the area directly behind the cylinder and the highest area (fins) area as well. if you put a sensor at this spot, you will get the "hottest temp". interesting, if you have a muffler in this location that is very close to the back and top of the cylinder, this can alter the reading due to making it a false reading. that is, the heat of the muffler may be adding to the actual temp of the cylinder. this seems to not be a problem on twin cylinder engines, due to the mufflers or headers usually pointing down.
More interesting observations: the temperature peaks during flight occur during up-lines, knife edge flight, hovering and flat spins, etc.. really make it hotter!!!! usually temperatures are not sustained, but peaks due to whatever flight maneuver you are doing that increases the load on the engine. Also interesting is that cooler days can lower the temperature down significantly more than the actual ambient temperature compared to another day. for instance, i was flying in 95 degrees temp, and the engines peaks temps were in 320's, then another day, temps were in 85 and high engine temps did not get over 280, all other variables were unchanged (altitude, prop diameter/pitch, needle settings, gas oil mixture, gasoline octane rating).
i will attach a diagram depicting the position of the temp sensor.
10237=3696-sensor position for da 70.jpg
well, i just got back from working on the YAK in the shop. i have removed all the lines from tank inside and out all the way to the carb "nipple"...
did not see anything wrong really. well, maybe....
the inside: this is original VITON tubing from mcmaster Carr. there was a taildragger RC felt clunk. outside: tygon line from PSP cap to the carb nipple. nothing in between. there is a filter on fuel line into tank (3 line tank system). there is also a liter on vent side. (i guess this could be clogged, i better look at that).
the tygon line from the PSP cap to the carb appeared stiff and old (although i installed it last october).
and, it appears the line may have "contracted" and where it went from the canopy area into bottom of motor box, looks like it may have been under a pinch. Maybe??!!
ok
i replaced the felt clunk with a PSP clunk, i used a brand new VITON tube to the PSP cap from the clunk. then, i obtained a new TYgon line, longer than the one i removed by 1.5", then i reattached everything. ( i better look at the air vent filter, i would just be amazed if this is clogged!!!)
did not see anything wrong really. well, maybe....
the inside: this is original VITON tubing from mcmaster Carr. there was a taildragger RC felt clunk. outside: tygon line from PSP cap to the carb nipple. nothing in between. there is a filter on fuel line into tank (3 line tank system). there is also a liter on vent side. (i guess this could be clogged, i better look at that).
the tygon line from the PSP cap to the carb appeared stiff and old (although i installed it last october).
and, it appears the line may have "contracted" and where it went from the canopy area into bottom of motor box, looks like it may have been under a pinch. Maybe??!!
ok
i replaced the felt clunk with a PSP clunk, i used a brand new VITON tube to the PSP cap from the clunk. then, i obtained a new TYgon line, longer than the one i removed by 1.5", then i reattached everything. ( i better look at the air vent filter, i would just be amazed if this is clogged!!!)
Bdegan
50cc
Ok. You have definitely done your homework.
Everything you have said is what a few of us have found. We are using Jeti radios and temp sensors mounted to the back of the cylinder heads.
Now I haven't put any telemetry on my 70 yet as it's not in a plane.
We have also seen temps run much higher than what a lot of folks quote as normal or safe.
Your plane looks like it has plenty of air exit. The temp variance between cylinders is the most puzzling though.
This is not meant as a brand war or one is better than the other. But we all know another brand that had issues with fuel delivery in their twin. The two cylinders were not getting even fuel distribution. A redesign of the reed block and position change was required to fix it.
Now, DA has been doing engines for years and know their stuff. But could it be in the realm of possibility that this particular engine is having uneven fuel delivery between the cylinders ?
I guess we wouldn't know if there are temp variances with other 70's unless others are checking or running telemetry on their engines.
If i get my 70 into an airframe. I can set up the temp sensors and see if I am getting a similar variance. But it may be a while.
Sorry I don't have an answer. Just raise more questions.
Everything you have said is what a few of us have found. We are using Jeti radios and temp sensors mounted to the back of the cylinder heads.
Now I haven't put any telemetry on my 70 yet as it's not in a plane.
We have also seen temps run much higher than what a lot of folks quote as normal or safe.
Your plane looks like it has plenty of air exit. The temp variance between cylinders is the most puzzling though.
This is not meant as a brand war or one is better than the other. But we all know another brand that had issues with fuel delivery in their twin. The two cylinders were not getting even fuel distribution. A redesign of the reed block and position change was required to fix it.
Now, DA has been doing engines for years and know their stuff. But could it be in the realm of possibility that this particular engine is having uneven fuel delivery between the cylinders ?
I guess we wouldn't know if there are temp variances with other 70's unless others are checking or running telemetry on their engines.
If i get my 70 into an airframe. I can set up the temp sensors and see if I am getting a similar variance. But it may be a while.
Sorry I don't have an answer. Just raise more questions.