Webra 145 R and AAR
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All this discussion was originally from the discussion group
on the NSRCA web site
The Problem:
My setup is as follows: Webra 145 red head, greve pipe at 31.5", os typeF plug, cool power 15%, APC 17*12, 10lb. 2oz. Prophecy. Current settings on engine are 1 turn on high speed needle, 1 1/16 on low speed needle. I am guessing low 8k for top end rpm on the ground slightly rich {have not tached the 17*12 but I was getting high 8600 or so with 17*10. Engine starts good and idles reliably but transition is not very linerier. In flight it sounds good with straight and level flight at a little less than half throttle, when pulling to a 45 up line it sags momentarily but recovers, on tall verticals or loops it will sag toward the top and loose roughly 1\2 of it's rpm and that is with me adding throttle through the maneuver, engine with not regain good power unless you go to at least 3\4 or better with throttle. I get no smoke trail out of engine until full throttle and oil out of the pipe is pretty dark but not black, top third of piston and ring is black like cyl. temps have been high. Condition is better with low speed needle set richer but it's easy to flood on start ups and is hard to keep running when cold {must keep a very fast Idle speed until your in the air}. I have found trash in the pump and pump screws came loose twice, last week I pulled pump apart again and no trash was found but screws where loose, I cleaned all parts in warm water and dish soap, removed tank and cleaned, ran large fuel tubing from clunk to carb. All fuel is filtered from the jug and I have a filter between tank and pump. That is about all I can think of, any suggestions would be greatly appreciated.
Brian Billings
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The 31.5" pipe length you quote, what is that from? In other words
what is the distance from the plug to the first baffle in the pipe?
Jerry (Try sticking a length of dowel into the pipe to find the first
baffle).
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That is from the center of the glow plug to the end of the large portion of the pipe, does not include the stinger. Not sure where the first baffle is located.
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According to the Piedmont website the baffle is 4" ahead of the aft end of the pipe so that puts you at ~27.5" from plug to baffle. When I tried the Greve pipe that Piedmont sells, I found that to be too long (way down in power compared to my ES pipe at ~24" plug to baffle).
Lee, Jim W., Matt - Are these needle settings close? I haven't run the ProMixII carb in a while.
It sounds to me like the pipe may need to be shortened some, and the low end richened up a bit. You also probably got the motor a bit hot when the pump got FOD'd and that's why the internals are a bit dark.
Jerry
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If you're having problems in the mid-range lengthen the pipe. Currently, I'm running mine at 28 1/2" plug to baffle. If there's still a stumbling point in the mid-range throttle the engine up to the point where it is stumbling right before it clears out with any additional throttle. Lean the high speed needle until the engine runs clean. Go to full throttle and tweak the high speed needle as required. If the engine hesitates in flight when throttling up from idle, richen the low speed needle. The high and low speed needles are not fully independant. If you richen one you might need to lean the other.
The Webras will not tolerate lean runs. If the engine has a weak point it's the con rod bushing at the wrist pin. A few flights of lean run, and it's shot (look for marks where play in the bushing/wrist pin allows the piston skirt to touch the inside of the backplate) which will cause a difficult needle setting. The other side of the coin is that with a good setup and use of after run oil the Webra will just keep on going. The one I'm using now is my primary engine for the last 12 months (flew it at the Nats last year) with no maintenance and the orginal factory rear bearing.
Lee Davis - Piedmont Models
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Brian, have you experimented with increasing the pump pressure? Maybe the upline mid-range is starving due to not having enough fuel but WOT creates enough extra suction to pull the fuel through.
If you haven't already tried this why don't you increase the pump pressure by 1/4 turn at a time and see if it helps.
BTW, you're correct that the throttle is very non-linear. Once my carb is about half open the engine is much closer to full throttle than mid throttle. I added a mix to my radio to introduce an expo behavior with the throttle and this tremendously improved how linear the throttle response is on my throttle stick. This made the plane much easier to fly.
Good luck, Keith Black
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Jerry I think you are
correct. The low end and particularly middle, sound like they are lean. Brian
was going to get his pump re-adjusted for a little more output, but I haven't
spoken to him lately and I don't know if that helped or not.
As far as needle settings, I still run the older carb and Im not sure about the
newer one. Be that as it may, the settings are very close to what I use on my
older set-up; however, the needles are different so that is just coincidence
maybe.
matt
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Just an update on my webra- Focus. I replaced the piston, ring and rod, I installed the cline system with a regular backplate with pressure tap. The tank pressure runs 7.5 to 8.0 PSI. I now have 1.5 gals fuel through the engine with 10 flights today. I set it up for 8000 and 2000 rpm's. The engine now runs flawless. There are no stumbles in midrange, no hesitations on advancing throttle and best of all, no sags on long up lines. On the 3 point up top hat, I set the throttle at 3/4 to start up and it's still at 3/4 pulling across on the top. Now maybe I can get down to business.
Jim Ivey
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Bob, I was very careful running this motor in, ran several tanks through engine before flying and monitored the cylinder head temp the whole time. Motor ran great the first weekend out with the plane but the next weekend motor was having trouble from the first start of the day and I was unable to fly due to troubles, sagging mainly. I sent motor to piedmont for check out and they said it ran fine and had no problems. I can hold engine against compression with no leak down felt but the discoloration of the ring and top of piston does add credence to your theory, plus it does seem like there is less compression once engine has been ran to operating temperature. I would put a piston, ring and liner in it if I new my problems would go away but I am afraid that it is not the root of my problem but a outcome of the sagging in flight.
Hi
I'm sticking my nose in here, but I've been running the Greve (Piedmont) set up for some time now and at their setting it WORKS, very well. I agree with Jerry, by the way, the numbers are wrong, based on my theory, but it works so I have not messed with it. Reading your symptoms, I suspect you have a bad ring, allowing blow by into the crank case, which changes with temp, which changes the crank case pressure, which changes the "pump performance", which changes the temp, which changes........ I have found that long before the ring is worn enough to cause loss of compression/power it will upset the pump/regulator (speaking of the OS here) because of combustion blow by into the crankcase. Not enough leakage to effect peak performance, but with crankcase pressure at 8-12 lbs (I think those are the numbers) and combustion pressure at probably thousands of lbs a little leakage could double the case pressure and screw things up. I have found replacing the ring sometimes ring and cylinder to solve this, anyway, the theory as to way is just that, theory/speculation.
Hope this helps
Bob