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Engine basics => Engine set up tips => Topic started by: Randy Powell on May 30, 2007, 01:15:08 PM
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OK, I flew in a contest last weekend and had some problems with my second flight engine run. The plane is my 54oz, 620 square inch Slider. The engine is an OS40VF. .265 venturi, PA needlevalve. Fuel is Wildcat 10/22 half caster/half synthetic. Brand new gallon. The prop is a Bolly 11.3 x 4.5 depitched to 4.25. Pipe length is 18.5 inches on a Randy Smith "51" sized 3 chamber pipe. Ground rpm was 10,800
The first flight the run, from my neophyte perspective (I've only run this engine since late last fall) was near perfect. Nice and steady. The weather was in the mid-50s and overcast. Humidity was probably around 60% with probably an 8 mile an hour wind. I thought it was a bit fast at maybe 5.0 to 5.1 seconds a lap. But the engine ran near perfect, as I said.
The second flight, it had warmed up to about mid-60s and the humidity had dropped quite a lot. Just a little breeze . No change to the setup at all. Same ground rpm, but the fight was considerably faster. Maybe 4.9 second laps and it seemed I had lost that nice deceleration coming toward the ground.
So, here's the question. It was suggested to me that I should have either pulled the pipe out a 1/4 to 1/2 inch or reduced the needle setting to less rpm. Observers said that the engine was too leaned out. I haven't run this engine enough to tell by ear if it's too near the end of the power band. I know that you have to adjust the setup (pipe length, prop and such) depending on the conditions, but generally, as it gets warmer, do you have to either increase pipe length and/or reduce the rpm? Is there any sort of rule of thumb when it comes to changing setting for conditions with these engines? Would a bigger pipe, say a 60 sized pipe help (this was suggested by one expert flier I know).?
Thanks for any input. I'm just trying to learn this setup and engine.
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Hmmmmmmm......... thought the "other Randy" would have jumped in here by now! y1 We ran the VF 40 for quite a while but didn't experience that exact same problem.
I DID have a header leak at Flushing Meadows back in '97 and that gave me some problems similar to what you described. I learned right after that of the practice Paul W. was using. He made his gasket out of 5 min epoxy for the header to engine joint. Never had a leaky header again!
The beauty of the VF 40 was that once it was set up, you just flipped and flew.....
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Bill,
Hmmm... That's a good point. It didn't run away or anything. It just was a bit fast and probably flying .2 of a second faster laps. But it was steady. Could be a pin hole or a very slightly leaky header, I guess. I'll have to check that. For whatever reason, it didn't occur to me.
Thanks
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OK, I flew in a contest last weekend and had some problems with my second flight engine run. The plane is my 54oz, 620 square inch Slider. The engine is an OS40VF. .265 venturi, PA needlevalve. Fuel is Wildcat 10/22 half caster/half synthetic. Brand new gallon. The prop is a Bolly 11.3 x 4.5 depitched to 4.25. Pipe length is 18.5 inches on a Randy Smith "51" sized 3 chamber pipe. Ground rpm was 10,800
The first flight the run, from my neophyte perspective (I've only run this engine since late last fall) was near perfect. Nice and steady. The weather was in the mid-50s and overcast. Humidity was probably around 60% with probably an 8 mile an hour wind. I thought it was a bit fast at maybe 5.0 to 5.1 seconds a lap. But the engine ran near perfect, as I said.
The second flight, it had warmed up to about mid-60s and the humidity had dropped quite a lot. Just a little breeze . No change to the setup at all. Same ground rpm, but the fight was considerably faster. Maybe 4.9 second laps and it seemed I had lost that nice deceleration coming toward the ground.
So, here's the question. It was suggested to me that I should have either pulled the pipe out a 1/4 to 1/2 inch or reduced the needle setting to less rpm. Observers said that the engine was too leaned out. I haven't run this engine enough to tell by ear if it's too near the end of the power band. I know that you have to adjust the setup (pipe length, prop and such) depending on the conditions, but generally, as it gets warmer, do you have to either increase pipe length and/or reduce the rpm? Is there any sort of rule of thumb when it comes to changing setting for conditions with these engines? Would a bigger pipe, say a 60 sized pipe help (this was suggested by one expert flier I know).?
Thanks for any input. I'm just trying to learn this setup and engine.
HI Randy
I have been away and just returned home. On the engine run it sorta sounds like you may have just got a bad needle setting or had a little slug or something pass the spray bar. I would clean out the filter, spray bar, and re try the motor at the same settings. The VF runs just fine where you described running it at, And you should not need another pipe either unless something has happened to the one you have. The VF 40 will run well on the 40 or 51 pipe, the 60 pipe is Too big and you will loose the cycling and hold back in the wind with it, It would also make the venturie act like it was bigger than normal.
Question, are you running standard uniflow tank ? off or on pressure?
REgards
Randy
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Randy,
I checked for leaks. The system is tight.
The tank is standard uniflow without pressure. I imagine you're right and some crap got stuck in there. Launch RPM was 10,800, right where I'd been running it. I cleaned out the NVA and did get some crud, so I'm guessing that was it. Weirdly, I was using a CrapTrap filter and it appears clean. Hmmm...
Anyway, it seems fine now. I ran it in the yard and it was fine.
On a related note, I have a new favorite prop for it. It's an 11 x 4.2N Bolly. Checked the pitch and it's right on. Second is a cut down Gator prop. Basically like the Bolly but with somewhat wider tips.
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Other things to beware of:
Crap trap filters will leak air around the plastic/metal joint. I prefer all metal, screw together type filters...Many will say no. And many will wrap additional tubing around the filter. Why do you suppose? I prefer to avoid the problem to start with.
Also, You can get some real slow leakers around the header/tube and tube to pipe joints. I use two of those electric ties at each joint.
whatever...
W.
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On thing that I believe may have contributed is the 11% castor in the fuel.
Try cutting that back to about 5-7% and the total oil to 18-20% and I
think your problem would be solved. Castor's pretty good lube for our
engines, but can cause some gumminess in the fuel system also.
Jim Pollock H^^
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I've got two tye wraps at each joint. I'm pretty sure there are no leaks in the exhaust. Now I'm checking the NVA and fuel like. I did have one questionable fuel line connection and changed out the tubing. I've never had a problem with Crap Traps.
Let me be clear that that this was more a question of what to do with this specific engine as conditions change and a more general quesiton: as the weather gets colder (or hotter) do you generally go to a longer pipe? More or less pitch? Different plug? etc. The first run was great. But between the time of the first and second run, the weather cooled off considerably and the humidity picked up. The second run was set the same on the ground, but leaned out quite a bit in flight.
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Randy check out what PIG says about Pipe.
http://www.modelaircraft.org/mag/diva/index.html
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I've got two tye wraps at each joint. I'm pretty sure there are no leaks in the exhaust. Now I'm checking the NVA and fuel like. I did have one questionable fuel line connection and changed out the tubing. I've never had a problem with Crap Traps.
Let me be clear that that this was more a question of what to do with this specific engine as conditions change and a more general quesiton: as the weather gets colder (or hotter) do you generally go to a longer pipe? More or less pitch? Different plug? etc. The first run was great. But between the time of the first and second run, the weather cooled off considerably and the humidity picked up. The second run was set the same on the ground, but leaned out quite a bit in flight.
HI Randy
Typically most people never move the pipe in and out when the weather changes. Unless you are on the very edge of the envelope, it is broad enough to work in all condidtions. I never change my lenght thru out the year or when weather changes.
It really sounds like you just had a cooler air mass come in, bringing more oxygen to you motor and the mixture was just too lean. This will happen on any engine piped muffled , or open ex. You normally ALWAYs have to richen the needle when it is cooler and lean the needle when it is warmer.
My typical day will start off early in the morning with the needle having to be opened to about the 9:00 oclock position, as the heat of the day comes in going toward noon, I will have to slowly close it back toward the 10:00 or 11:00 oclock position, if it gets really how I may have to set the needle at 12:00 and if it cools off a good bit after 6:00 PM I am back turning the needle richer.
I think you will find this is not a problem any longer when you fly the setup again. Let us know
Regards
Randy
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Thanks, Randy. That's always been the case with the PA engines I've run, but I didn't know if there was something specific with the OSVF.
The thing has run like a clock previously, but then, the conditions have been more consistent.
Thanks for the information. Hopefully, I'll get to fly later in the week and we'll see. I've been pretty happy so far. I'd try the PA 40UL in the plane also, but it's built for the OS and the PA is just too light to balance. ;D
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Randy how do you mount your P/A Ultra so that the Vf can also be used? the P/A is smaller?
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Larry,
I use a, ah, unique sort of mounting system.
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Some folks emailed me to ask, wadda ya mean, unique?
edit
Uh, I haven't polished it yet so no cracks about the scratches. n1
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Randy,
OK, I got in 3 flights yesterday (in the wind and low clouds before the rain). It ran like a clock all three flights. So it appears to have been an aberration. By the way, I have a new favorite prop (at least for windy conditions). It's a Gator 3 blade with kinda wide tips. Worked quite well in the wind.
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Just a note here. So I increased the pipe length by a 1/4" inch in this plane and got a pretty decent run on the first flight at the last contest. Maybe a very small touch less power but very consistent run. On the second flight, I tried something that almost resulted in a bag of balsa. I tried setting the needle a just bit richer. About 10,600 versus the usual 10,800 or 11,000. I did this because I was expecting the wind to pick up some and I thought in my little noodle that a slightly richer run would be slow things down just a bit. Not a lot, but some. Bad decision. Instead, it went dead calm and the plane was practically falling out of the air. There is apparently a point at which the torque curve falls off rather suddenly. I suppose it shouldn't be a shock since the engine has a somewhat narrow power band to begin with. But the drop off in power was pretty abrupt and marked.
Sigh...
Live and learn. I'm slowly learning how to work this thing. Too many years with 4-2-4 runs I suppose. When it's on, it really on. When you miss it, it can become a very interesting flight.
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Hi Randy,
Good information has come out of this, for me anyway. On the screws that mount your engine blocks, do they go into tee nuts or what??
Thanks, Greg B
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Greg,
Sort of. I drill the 1/2" square mounts and insert a CF dowel. Keeps the crushing down to a minimum. Then I mark and drill through the dowel with a, what, #43 drill I think (for a 4-40 tap - I have a chart on the wall of the shop). Then I use furniture makers blind nuts. Pretty much like the DuBro jobs but out of actual steel and not the whatever pot metal that DuBro makes them out of. I clamp the aluminium block in place (with predrilled holes) and run a 4-40 tap through the blind nut, the CF and the aluminum block. Once that's all done, I use some 1/32" ply to make a retainer for the blind nuts so they can't back out.
Sort of labor intensive, but it works.
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Thanks Randy,
It looks good ! !