""Help"" no pulling power on take-offs,,,
10-12-2004, 12:34 AM
#1
""Help"" no pulling power on take-offs,,,
I get 7500 RPM with a Zinger 20-8 "pro" on my MVVS 35cc (Red Head gasser),,, I may be able to lean it a bit more, but it only has 2 gallons run threw it and I lean it a little at a time,,,
the problem,,,
I can give full throttle on my take-offs yet I have NO pulling power at all !!, I have no real power at all until I get in the air and do a circuit, after that first circuit the power comes on and it pulls fine, it will then pull straight up for 200 300 feet, and top speed seems good,,, after that first circuit and the power has comes on, I can fly very very slow for a couple circuits then give full throttle and the power comes on as it should,,,
I know it sounds as if it's getting hot before the take-off,,, but I don't think it is,,, because, while checking the RPM I can run it at full throttle on the ground for 1/2 a minute or longer and the motor does NOT act as if its getting hot (I can run it up and down the RPM band for a full tank while checking the RPM and it never acts as if it's getting to hot), plus once it stalled as I was taxiing so it cooled down before I could start it again, then I started it a took off real quick and it acted as it always does,,,
another thing,,,
my carb is linear to my throttle stick, the carb is 1/2 open at mid stick,,, but,,, once it's up in the air and the power is good, it has the same top speed at 1/2 throttle as it does at full throttle, what's with that ?,,,
any help will be greatly be appreciated !! !!
Jim
the problem,,,
I can give full throttle on my take-offs yet I have NO pulling power at all !!, I have no real power at all until I get in the air and do a circuit, after that first circuit the power comes on and it pulls fine, it will then pull straight up for 200 300 feet, and top speed seems good,,, after that first circuit and the power has comes on, I can fly very very slow for a couple circuits then give full throttle and the power comes on as it should,,,
I know it sounds as if it's getting hot before the take-off,,, but I don't think it is,,, because, while checking the RPM I can run it at full throttle on the ground for 1/2 a minute or longer and the motor does NOT act as if its getting hot (I can run it up and down the RPM band for a full tank while checking the RPM and it never acts as if it's getting to hot), plus once it stalled as I was taxiing so it cooled down before I could start it again, then I started it a took off real quick and it acted as it always does,,,
another thing,,,
my carb is linear to my throttle stick, the carb is 1/2 open at mid stick,,, but,,, once it's up in the air and the power is good, it has the same top speed at 1/2 throttle as it does at full throttle, what's with that ?,,,
any help will be greatly be appreciated !! !!
Jim
10-12-2004, 01:08 AM
#2
Senior Member
RE: ""Help"" no pulling power on take-offs,,,
Jim,
About what you describe on take off, the only thing I could think of is the engine leaning out by a certain degree, as a result of the forward acceleration, during the T/O run.
Try checking the mixture in nose-up attitude. Richen it a little anyway and check if this behavior goes away.
The RPM you are getting seems to be good. Do you hear the engine 'unload'; getting to higher RPM, as it is flying at speed? What kind of silencer are you using? I cannot tell from your description, about the carburettor's behavior, except for extensive unloading at part throttle, with no more to go as you wall it in flight.
After 2 gallons through the engine, it should be ready to set the mixture at its final setting; no need to run it overly rich.
About what you describe on take off, the only thing I could think of is the engine leaning out by a certain degree, as a result of the forward acceleration, during the T/O run.
Try checking the mixture in nose-up attitude. Richen it a little anyway and check if this behavior goes away.
The RPM you are getting seems to be good. Do you hear the engine 'unload'; getting to higher RPM, as it is flying at speed? What kind of silencer are you using? I cannot tell from your description, about the carburettor's behavior, except for extensive unloading at part throttle, with no more to go as you wall it in flight.
After 2 gallons through the engine, it should be ready to set the mixture at its final setting; no need to run it overly rich.
10-12-2004, 01:46 AM
#3
RE: ""Help"" no pulling power on take-offs,,,
""the only thing I could think of is the engine leaning out by a certain degree, as a result of the forward acceleration, during the T/O run"",,, yes, now that I think of it it did seem that the more I leaned the motor the less power I had on my take-offs,,, but why does it stop acting like this after that first circuit when the speed has come up ?,,,
""Richen it a little anyway and check if this behavior goes away"",,, yes, it did it at lower RPMs, it did it when the motor was only revving at 6300 and 6600 on the ground,,,
"""Do you hear the engine 'unload'; getting to higher RPM""',,,yes, I can hear the motor does unload, but only after that first circuit !!
""What kind of silencer are you using?"" the inveted muffler , the same one in the photo in the link, I cut about 1/4 inch off the stingers,,,
http://www.rcuniverse.com/forum/ZDZ_...2241869/tm.htm
Jim
""Richen it a little anyway and check if this behavior goes away"",,, yes, it did it at lower RPMs, it did it when the motor was only revving at 6300 and 6600 on the ground,,,
"""Do you hear the engine 'unload'; getting to higher RPM""',,,yes, I can hear the motor does unload, but only after that first circuit !!
""What kind of silencer are you using?"" the inveted muffler , the same one in the photo in the link, I cut about 1/4 inch off the stingers,,,
http://www.rcuniverse.com/forum/ZDZ_...2241869/tm.htm
Jim
10-12-2004, 02:01 AM
#4
RE: ""Help"" no pulling power on take-offs,,,
I must add,,,
the cowl on my plane has a short lip that forces air in the direction of the carb's throat, now I am thinking that on the takeoffs when the speed is slower the air goes in the carb and leans it, then once in the air the air is pushed by the carb so the motor runs fine,,, see my plane in the link,,,
http://www.rcuniverse.com/magazine/a...article_id=132
thanks for you help and quick reply !!
PS, I have been around all kinds of motors in my life time, and I can say this MVVS is one nice motor,,,, thanks again !!
Jim
the cowl on my plane has a short lip that forces air in the direction of the carb's throat, now I am thinking that on the takeoffs when the speed is slower the air goes in the carb and leans it, then once in the air the air is pushed by the carb so the motor runs fine,,, see my plane in the link,,,
http://www.rcuniverse.com/magazine/a...article_id=132
thanks for you help and quick reply !!
PS, I have been around all kinds of motors in my life time, and I can say this MVVS is one nice motor,,,, thanks again !!
Jim
10-12-2004, 03:28 AM
#5
Senior Member
RE: ""Help"" no pulling power on take-offs,,,
You're welcome, Jim.
So you are getting more RPM from this 35 cc engine, that the ZDZ 40 cc engine.
That is nice!
I believe the problem you are encountering is related to engine and tank installation, more than it relates to the engine itself.
If you have a spare Walbro carburettor, on another engine, it may be good practice to try if this MVVS behaves the same with it.
Keep me posted.
So you are getting more RPM from this 35 cc engine, that the ZDZ 40 cc engine.
That is nice!
I believe the problem you are encountering is related to engine and tank installation, more than it relates to the engine itself.
If you have a spare Walbro carburettor, on another engine, it may be good practice to try if this MVVS behaves the same with it.
Keep me posted.
10-12-2004, 01:01 PM
#6
RE: ""Help"" no pulling power on take-offs,,,
on the first couple flights I had a larger fuel line on it, it did the same thing on the take-offs with the larger fuel line,,, so I changed it to the smaller fuel line, with the smaller fuel line the top RPM increased about 300 RPM, but the take-offs remained the same,,,
it seems to me that it uses a lot of fuel, I have a 20oz tank in it, and it uses the whole tank for a normal flight !!
Jim
it seems to me that it uses a lot of fuel, I have a 20oz tank in it, and it uses the whole tank for a normal flight !!
Jim
10-13-2004, 04:09 AM
#7
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RE: ""Help"" no pulling power on take-offs,,,
Jim
I have a 1.60 "Red Head" petrol (Gas) engine which happily swings an 18x8 Bambula. My 13.8 pound CMP 72" Su-31 is flown with authority, although being overweight vertical is limited. The cowl on this ship is definitely a little large (and round) hence the need for the big fan. I had a ProZinger 18x8 wood on it at first. Worked well, but the bambula gives a little more thrust I find. I tached it on this prop at 6,700 rpm steady at WOT on the ground warm pre-flight. Engine is inverted, w/ Bisson Inverted Pitts Muffler, unmodified.
I tried it with a (standard) wood Zinger 20x6 i had on hand. Very poor performance from this prop.
Maybe try a Menz S or Bambula prop?
To me, it sounds like your low end "L" needle may be a little rich, and after the plane "clears" the fuel the mix leans in flight as the motor unloads it picks up?
They are my thoughts. My little 1.60 has about 20 flights on it now, uses a Bisson inverted Pitts muffler, and gets better and better, feeding on 32:1 95 RON unleaded / Mobil Racing 2T synth oil mix. The 2.15 sounds the same, only bigger!
I fly the Sukhoi at near full power for 10~12 minutes, and get through 1/3rd of a Sullivan 16 Oz tank! Great economy. You are using far too much fuel, for sure! Mine did that for the first 5 or so flights while I had the "L" needle very rich, due to the motor being very tight when new.
Thinking .....
A small twin using either the 1.60 or 2.15 jugs would be great ...
fiery
I have a 1.60 "Red Head" petrol (Gas) engine which happily swings an 18x8 Bambula. My 13.8 pound CMP 72" Su-31 is flown with authority, although being overweight vertical is limited. The cowl on this ship is definitely a little large (and round) hence the need for the big fan. I had a ProZinger 18x8 wood on it at first. Worked well, but the bambula gives a little more thrust I find. I tached it on this prop at 6,700 rpm steady at WOT on the ground warm pre-flight. Engine is inverted, w/ Bisson Inverted Pitts Muffler, unmodified.
I tried it with a (standard) wood Zinger 20x6 i had on hand. Very poor performance from this prop.
Maybe try a Menz S or Bambula prop?
To me, it sounds like your low end "L" needle may be a little rich, and after the plane "clears" the fuel the mix leans in flight as the motor unloads it picks up?
They are my thoughts. My little 1.60 has about 20 flights on it now, uses a Bisson inverted Pitts muffler, and gets better and better, feeding on 32:1 95 RON unleaded / Mobil Racing 2T synth oil mix. The 2.15 sounds the same, only bigger!
I fly the Sukhoi at near full power for 10~12 minutes, and get through 1/3rd of a Sullivan 16 Oz tank! Great economy. You are using far too much fuel, for sure! Mine did that for the first 5 or so flights while I had the "L" needle very rich, due to the motor being very tight when new.
Thinking .....
A small twin using either the 1.60 or 2.15 jugs would be great ...
fiery
10-13-2004, 05:57 AM
#8
Senior Member
RE: ""Help"" no pulling power on take-offs,,,
ORIGINAL: fiery
To me, it sounds like your low end "L" needle may be a little rich, and after the plane "clears" the fuel the mix leans in flight as the motor unloads it picks up?
................
Thinking .....
A small twin using either the 1.60 or 2.15 jugs would be great ...
fiery
To me, it sounds like your low end "L" needle may be a little rich, and after the plane "clears" the fuel the mix leans in flight as the motor unloads it picks up?
................
Thinking .....
A small twin using either the 1.60 or 2.15 jugs would be great ...
fiery
How about taking two 58 cc jugs and putting them together, to make a twin?
MVVS has already done that in the 7.2cid 112 cc twin...
You could be right about the problem Jim is seeing, being an adjustment problem, but because he is not seeing an overheating problem, in extended full throttle runs and the RPM he is getting is great, it looks to me more like a tank and installation related issue.
