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Author Topic: Engine setting rich at take-off settles after wingover  (Read 3947 times)

Offline Dennis Toth

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Engine setting rich at take-off settles after wingover
« on: December 12, 2015, 02:45:25 PM »
Guys,
I have a general engine setting question. On several of my non-piped engines, open uniflow, full fuse, I find that I need to set a little richer at launch than what is needed for a steady 4-2-4. After launch it will hold the rich setting until the wingover then come up to a lean 4 cycle and perform the rest of the pattern very steady. It took a bit to work into the setting but once found is very repeatable. This would normally not be a problem but when the wind comes up it is not the most comfortable flying till it come in.

My question is has anyone experienced this and is there a tank layout, vent position or other (beside muffler pressure which I tried and the Fox 35 does not like) plumbing configuration that might allow launching closer to the flight setting?

Best,    DennisT
« Last Edit: December 16, 2015, 07:17:08 PM by Dennis Toth »
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Offline Tim Wescott

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Re: Engine setting rich at take-off settels after wingover
« Reply #1 on: December 12, 2015, 03:23:01 PM »
Could the vent tube be full from filling, and running out about the time you get to the wingover?

I've noticed that engines do seem to get "on the step" (or sometimes "omigod it's running awaaaaaaay"), but I don't know why.
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Offline Dennis Toth

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Re: Engine setting rich at take-off settels after wingover
« Reply #2 on: December 12, 2015, 03:39:30 PM »
Interesting point Tim. I thought this might be something to do with the tank pressure needing to stabilize. The full fill and vent line does happen with this ship. Might try a test of a partial fill and make sure the fill (uniflow) line is clear.

Best,    DennisT
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Offline Howard Rush

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Re: Engine setting rich at take-off settels after wingover
« Reply #3 on: December 12, 2015, 06:09:42 PM »
Quote from: Tim Wescott on December 12, 2015, 03:23:01 PM
Could the vent tube be full from filling, and running out about the time you get to the wingover?

I doubt it.  1/8"-OD tubing has an ID of about .1".  3" of that tubing has an internal volume of .012 fluid ounce.  If the engine burns an ounce of fuel a minute, the tube would empty in .72 second.
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Online Lauri Malila

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Re: Engine setting rich at take-off settels after wingover
« Reply #4 on: December 13, 2015, 01:42:54 AM »
Do you fill the tank completely full? If yes, try removing 5..10ml before start and see what happens. Vibration can do weird stuff for fuel head pressure if there is no air in tank as bumper. L
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John Leidle

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Re: Engine setting rich at take-off settels after wingover
« Reply #5 on: December 13, 2015, 02:41:10 AM »
  Dennis, I find that with the higher pitch props I have to set it rich on the ground & it unloads in the air.  After 2 laps.
                John
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Offline Dave_Trible

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Re: Engine setting rich at take-off settels after wingover
« Reply #6 on: December 13, 2015, 10:34:48 AM »
I would sure try pulling out a little fuel before takeoff to see what happens but my first thought is the engine isn't getting up to full temp and sealing well until it gets loaded in the wing over.  A more worn or loose fit engine might do this.  Try goosing it a little after you start it by momentarily covering the tank uniflow line or pinch  the fuel line to lean it some and warm it.  Maybe try another hotter glow plug or new/ different fuel. 

Dave
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Offline Brett Buck

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Re: Engine setting rich at take-off settels after wingover
« Reply #7 on: December 13, 2015, 10:43:05 AM »
Quote from: Dave_Trible on December 13, 2015, 10:34:48 AM
I would sure try pulling out a little fuel before takeoff to see what happens but my first thought is the engine isn't getting up to full temp and sealing well until it gets loaded in the wing over.  A more worn or loose fit engine might do this.  Try goosing it a little after you start it by momentarily covering the tank uniflow line or pinch  the fuel line to lean it some and warm it.  Maybe try another hotter glow plug or new/ different fuel. 

Dave

   My guess is that it is probably a temperature issue, but there may be some exhaust tuning effect going on.

      Brett
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Offline Phil Krankowski

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Re: Engine setting rich at take-off settels after wingover
« Reply #8 on: December 15, 2015, 02:25:03 PM »
Have you tried pointing the plane to the sky for a couple seconds before placing it for takeoff?

Cover each vent in turn for a second or so as well.

Phil
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Offline Dennis Toth

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Re: Engine setting rich at take-off settels after wingover
« Reply #9 on: December 15, 2015, 05:22:50 PM »
I normally point the nose up to clean up the run but it goes back (as it should) to the 4 cycle. I like the temperature idea, I might have to much oil that is cooling it down to much. I will try some straight Sig 5% that the LHS has in quart size. This is a Fox 35 and I may have added to much to get it to 28% along with some Aero One.

Best,    DennisT
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Offline Dennis Toth

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Re: Engine setting rich at take-off settles after wingover
« Reply #10 on: February 17, 2016, 06:31:56 PM »
We finally got some flying weather here in South FL and I made progress. I went back and searched the subject and found I was very close at one point but tried to pickup the speed by upping the pitch. I went to far which loaded the engine and caused the hard break. OK, first thing I lowered the oil to around 26% by blending in straight Sig 5% 50/50. This eliminated a quirk in the engine run where it would hit hard and you could feel it at the handle every now and then. Next, I again reread some of my old posts and I saw I only need to increase the pitch to 6.5" from 6". Last, I had about 15 extra laps at the end so I upped the nitro to 10%. This allowed keeping the rich launch setting and just a break at the tops and stayed consistent through all the maneuvers. Finally its were I wanted to be.

Best,   DennisT
« Last Edit: March 20, 2016, 06:36:43 PM by Dennis Toth »
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Offline Steve Helmick

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Re: Engine setting rich at take-off settles after wingover
« Reply #11 on: March 13, 2016, 02:13:51 PM »
While I haven't flown a Fox .35 stunt in years (and years), I've read that they don't like Uniflow very well. You could leave the cap off the overflow to see if that makes a difference.

I'm also a believer in getting the engine to full temp before setting the needle. I don't know if you can set a Fox .35 stunt with a tach (Dirty Dan said you can't, and I tend to believe him). But I would bet that you can use your tach to find out if it's fully warmed up. Might be you could use one of those keen little infrared guns, too. WAY too many times, I've been launching for somebody, and while they were walking out to the handle and getting the safety thong on, the engine leaned out. That's what happens when the temperature comes up. Lots of guys seemingly waste some time getting their pit box neat and moving it out of the way...they're really waiting for the engine to heat up before setting the NV.  y1 Steve
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Offline rustler

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Re: Engine setting rich at take-off settles after wingover
« Reply #12 on: March 14, 2016, 04:32:10 PM »
Round about 50+ years ago I had a profile model powered by a BB Amco 3.5cc diesel. It had to be set off very rich. Two loops and it would lean out to a good setting for the whole tank. If you didn't do the loops it would stay rich the whole tank. Never did figure out why. I still have the tank, maybe I should try to see if I can repeat the experience, but so much to do......etc.
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