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Engine basics => Engine set up tips => Topic started by: Larry Wong on March 28, 2007, 01:03:37 PM
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Question I'm making a tank for my P/A 40 and notice that the needle valve is almost 3/4" of the beam were the other engines all have 1/2" of the beam ( O S 40 & 46 V F ) the pick up frome tank should be about the same hight as the needle valve. has any one have this problem? The P/A 40 is the older type not ultra lite. were should the tank hight be? HB~> HB~> HB~>
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Question I'm making a tank for my P/A 40 and notice that the needle valve is almost 3/4" of the beam were the other engines all have 1/2" of the beam ( O S 40 & 46 V F ) the pick up frome tank should be about the same hight as the needle valve. has any one have this problem? The P/A 40 is the older type not ultra lite. were should the tank hight be? HB~> HB~> HB~>
HI larry
This has never been a problem either on ST 40 46 60s or PAs or other motors that are not exact 1\2 inch.
It normally run with a 1 inch tank, either on the beams or just off shimmed 1\16 inch...just like a OS 40 would.
The measure point is not where the needle is but where the fuel comes out into the venturie, which is below the needle in the PA 40.
If your using motor pads on top of the wood mounts you will have to add the same distance to the tank to start off with
and as with ALL motors , the location of the fuel pickup line and the uniflow line inside the back of the tank, will affect tank location.
Regards
Randy
Randy
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I hope this isn't a thread hijack, but since Larry and I fly together I know he won't mind.
I can appreciate the sensitivity of an engine to tank height with a METAL tank having fixed-location metal tubes for pickup and uniflow. But how about plastic CLUNK tanks, where the clunk starts out well below tank or NVA centerline while on the ground and then moves around in maneuvers? Does the same basic "get the tank centered on the NVA or slightly above" rule still apply? Larry and I were having a hard time getting my Vector 40 (Magnum 36 new style, .250 delrin venturi, ST NVA, 4oz rectangular clunk plumbed for kinda-uniflow, 11x5 Zinger) to run consistently a few days ago. Big surge in rpm at launch followed by unpredictable run in the air, plus used up all 4oz in 4 mins flat. What is the accumulated wisdom on clunk tank positioning?
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I hope this isn't a thread hijack, but since Larry and I fly together I know he won't mind.
I can appreciate the sensitivity of an engine to tank height with a METAL tank having fixed-location metal tubes for pickup and uniflow. But how about plastic CLUNK tanks, where the clunk starts out well below tank or NVA centerline while on the ground and then moves around in maneuvers? Does the same basic "get the tank centered on the NVA or slightly above" rule still apply? Larry and I were having a hard time getting my Vector 40 (Magnum 36 new style, .250 delrin venturi, ST NVA, 4oz rectangular clunk plumbed for kinda-uniflow, 11x5 Zinger) to run consistently a few days ago. Big surge in rpm at launch followed by unpredictable run in the air, plus used up all 4oz in 4 mins flat. What is the accumulated wisdom on clunk tank positioning?
Hi Mike
The plastic clunk tanks work on the average position of the pickup and uniflow line, However in practical applications you really need to run it and see if the motor slows or speeds up during inverted-rightside up flight. You can also tach the motor on the ground level inverted and flip it over to see how much RPM difference there is.
This will help get you close.
Now about your plastic tank...sounds like you have a lot more trouble going on than just the height.
as cheap as they are to make, I would recommend trying another one. If it works better you can try to duplicate that on the first tank.
If you have more questions please tell me more about what the tank is doing, I don't know what "kinda uniflow is"
The surge could be the tank is too far away from the motor, or the pickup tubing is too long and is against the back of the tank until the centrifugal force slings it to the outer side.....
Regards
Randy
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Randy,
I fly with these guys also, and would like to add that Mike's Magnum has been exceptionally hard to start from the beginning. Could this indicate tighter than average machining tolerances? What do you consider a reasonable bench run break-in time for the Magnum?
Thanks,
Kim Mortimore
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Randy,
I fly with these guys also, and would like to add that Mike's Magnum has been exceptionally hard to start from the beginning. Could this indicate tighter than average machining tolerances? What do you consider a reasonable bench run break-in time for the Magnum?
Thanks,
Kim Mortimore
Hi Kim
I have never seen a Magnum 36 that was too tight, but normally after a few runs you should be able to fly teh motor. It sounds like with the extremely bad fuel milage he may have something else wrong, leak in the back plate pin hole in the case...etc. Impossible to tell without looking at it
Randy
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Hi Randy:
A quick run down to the garage reveals the front of the tank is 4.5" behind the NVA, and (more relevant I would think) the end of the clunk line is 8" behind the NVA. I think this may well be the answer to the "surge on takeoff" (sometimes even followed by engine stopping)...I had not taken into account the length of the feed line. I have room to move the tank at least 1.5" closer to engine.
The engine is on 1/16th shims, needed to get the thrust line to line up with the cowl opening, but the tank is on the bearers, i.e. 1/16 above the NVA centerline when model is upright. Probably should get it even as a starting point.
Plumbing is: Feed line brass tube at 9:00 position (seen from front of model) with slight angle inside tank to point the flex tube at rear outside corner of tank. Clunk moves freely from top to bottom of rear outside corner. Copper ram air tube on outside of nose, connected with fuel tubing to vent line of tank at 4:00 position. Vent line inside tank is solid brass, curved to about 3/4 of the way to the outside rear corner (thus "kinda uniflow"). Overflow line from top of tank out opening in bottom of cowl. Tried running with overflow plugged (which I would expect to work best) and open (which did work best).
Perhaps should re-do the vent/uniflow line to tie it to the clunk so they move together, a setup that works great on the round 6oz clunker feeding the ST51 in my Score (with overflow blocked during flight).
I will try to post a photo.
OK, now this definitely IS a hijack. Sorry, Larry.
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Here's the plumbing on that Magnum.
Engine has two hours of bench time at 6 min runs, lots of thermal cycles. Kim must have been so engrossed with his cool All Australian on Sunday that he missed seeing that the Magnum starts easily by hand now, just a few flips. I was careful to tighten all the backplate and head screws before Sunday's flight tests. One thing to do is chage to different fuel line to eliminate the possibility of a pinhole somewhere. Actually I had a few decent flights, just not predictable enough for comfort in the pattern.
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My flying buddy was having some issues with his motor run, using a clunk tank, and what he did was rotate the "lid" of the tank (with the feed and vent pipes), effectively moving the pivot point of the clunk.
Worked a treat on his model
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Surging at take off acceleration coupled with high fuel consumption is indicative of poor fuel draw. That is also reinforced by the statement that it worked better with the overflow vent open (not uniflow) as uniflow does require a little more draw than open vent as there is slightly less pressure inside the tank on uniflow than on open vent types. I would suspect, like Randy indicated, a case pressure leak of some type OR the venturi being too large. As venturi opening size goes up fuel consumption does also and fuel draw goes down. The 0.250 with a ST NVA should not be too large, so I would recheck the actual diamater at the point where the needle body passes through the venturi and also closely check for air leaks at that area. (venturi to case leaks and needle body to venturi leaks.
Another thing--- how much oil content is in the fuel? Too much oil leads to poor draw and the needle has to be opened WAY up to get enough volitiles to give power. Try someone elses fuel that is running good on their engines. Also pressure check the tank and plumbing for leakage carefully-- Trying another tank is a simple test as indicated above.
Let us know what you find.
Bigiron
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Here's the plumbing on that Magnum.
Engine has two hours of bench time at 6 min runs, lots of thermal cycles. Kim must have been so engrossed with his cool All Australian on Sunday that he missed seeing that the Magnum starts easily by hand now, just a few flips. I was careful to tighten all the backplate and head screws before Sunday's flight tests. One thing to do is chage to different fuel line to eliminate the possibility of a pinhole somewhere. Actually I had a few decent flights, just not predictable enough for comfort in the pattern.
HI Mike
Looking at the pictures the tank i s really far away from the motor, you will do better and have better draw moving the tank forward....try the things suggested here and let us know how it is working
Regards
Randy
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Thanks everybody (and especially Larry, whose thread I swiped):
One thing not mentioned yet is using muffler pressure. Anything wrong with this concept on this engine? My LA series OS engines all love muffler pressure, 25, 40 and 46.
I will move the tank forward and check all the things suggested. Will not have a chance to test fly till Saturday (that darn "work" thing) and will report back.
As for tank height (which started this thread) the NVA is 9/16 off the bearers and the feed line (at the centerline of the 1.5" thick tank) is 12/16 off the bearers, i.e. 3/16 LOWER than the NVA when model is upright, the opposite of what I understand the conventional wisdom to be. I think I will leave tank height as is and try some of the other suggestions. One change at a time is a good rule.
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When I use clunk tanks, I often set them up with a center vent. Goes in and is angled to the inside, center of the tank. You can adjust what is nominally tank height by changing the height of the vent. Just move the vent up and down in the tank and it will act like you moved the tank. Can't remember where I leaned that trick. Could have been Brett or someone. But whatever, it works.
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Hi Randy:
Can you clarify what you mean by "inside center of the tank?" We are talking about the tube to either the ram air inlet or the muffler pressure line, right? And inside the tank the brass tube is bent to end where, at least for starters?
I have a Sullivan rectangular 4oz angle-plug tank (plug fits into angled facet on tank front at about 45 degrees rather than all-forward as with tank in photos) that I will also try. The angle feature allows it to be moved much closer to the engine without tying the fuel lines in knots.
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Sorry it wasn't clear. What would be considered a "uniflow" vent (in other words, not the pick up and not the overflow), on a tank with the exit out the front and not a slant tank (though that doesn't really matter except for the explanation), the vent enters the tank and is bent at a 45 degree angle (or thereabouts) to the inboard side of the tank. This usually puts it outside the fuel in the tank once the plane is airborne. Or soon after anyway. The tube terminates about half way between the front and the back of the tank and in initial adjustment is about the height, measured from the motor mounts, as the needle valve of the engine. It can be twisted up or down to raise or lower the relative height of the termination of the tube relative to the motor mounts. This acts just like raising and lowering the tank with a hard tank.
What can I say? It works. I'm Brett or someone could post the reasons based on fluid dynamics, but like a lot of things, I don't have the math.
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Thanks Randy. I will set up the tank as described and try it Sunday. Will let you all know what comes of it. I have moved the tank about 2" closer to the engine too, to shorten the distance the engine has to pull the fuel. Should (I hope) end the surge on takeoff.
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Sucess! Set up the in-tank brass tubes per Randy P's suggestion and got a good steady run. Launched at 10900 with a 11-4 Zinger Pro, 5.2 sec laps, consistent upright and inverted. Moved the tank 1.5" closer to engine, no more surge and flameout on takeoff. Also am getting 5.5 minutes on 4 oz, enough to do the full pattern without sweating the clover. I think the Magnum wants a little more prop, will try 11-4.5 Thunder Tiger next.
Another thing I learned is, Never post on a control line forum that your engine "starts easily by hand." Today it would start easily for everyone EXCEPT me, to the great amusement of the hecklers in the gallery. My moto mojo was not working for me today, no doubt due to my hubris in making such a portentious claim.
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Mike,
Glad it's working for you.