Engine Leaning Problem When Inverted. What Problem Beside Tank Height?

[Kafin Noe’man]

Hi all,

Question:
Beside the tank height problem, what could be the other reasons that cause the engine leaning when doing the inverted flight or outside/inverted maneuvers? And if it’s hard to equalize the lap time between the two, what’s the tolerance? 0.1 sec? 0.2 sec?


Best,
Kafin

[Chuck Matheny]

Hi all,

Question:
Beside the tank height problem, what could be the other reasons that cause the engine leaning when doing the inverted flight or outside/inverted maneuvers?


Best,
Kafin

Is this with an all metal "wedge style" tank and a side mounted engine...?
Are you using a muffler with a pressure line going back to the tank...?

Hold the model in your hands while it's running and keep your eyes on the fuel line while you "maneuver " the plane from right side up, to vertical and then to upside down.
see if you notice air bubbles in the fuel line when the plane is held inverted.
Could be a cracked fuel line that opens up when the plane is inverted..or a problem inside the fuel tank if you see air bubbles.

[Kafin Noe’man]

Is this with an all metal "wedge style" tank and a side mounted engine...?
Are you using a muffler with a pressure line going back to the tank...?

Hold the model in your hands while it's running and keep your eyes on the fuel line while you "maneuver " the plane from right side up, to vertical and then to upside down.
see if you notice air bubbles in the fuel line when the plane is held inverted.
Could be a cracked fuel line that opens up when the plane is inverted..or a problem inside the fuel tank if you see air bubbles.

The whole tank / engine system is a pump that runs most consistently when there are no pressure leaks

Hi Chuck,

Thank you for responding to my question.
The plane is a Built-Up Fuselage Vector 40. I use the all metal wedge style tank and a tongue muffler without any pressure line going back to the tank. It’s kinda hard to observe the fuel line with this setup, any tips on how to do it?

[Dan McEntee]

   Whether a profile model, or a full fuselage model, the position of the tank in relation to the engine can cause different runs from up right to inverted. If you can get a good, consistent run while flying up right, but when you fly inverted the engine changes, there is two way it can go First thing is to keep in mind that the engine will change and probably lean out just a bit when you pull the half loop to inverted. It may take a lap or so for the setting to show itself.  If you are flying consecutive laps and the engine leans out and runs faster, that means that your engine has to pull fuel up hill in that position, so when the model is sitting upright, you tank is too high. Lower it 1/8" and try another flight. If it is better but still a bit fast, lower it again but this time 1/16" and proceed from there.
   If when you half loop to go inverted, and the engine goes slower, gets more rich, you tank is too high when inverted and gravity is pulling fuel down hill into the engine. That translates into a position that is too low when sitting up right. Move t5he tank up 1/8" and test fly again and so on.
  On a a full fuselage airplane, and you need to lower the tank, but you are already against the engine bearing beams,  you must raise the engine by putting shims under the engine mounts. This doesn't happen very often, but is one reason why a lot of guys always put metal pads under their engine mounts right from the start, and then when installing the tank, put similar balsa shims under the tank. That will give you the agility to move the engine either way, up or down.
   This holds true with metal or plastic tanks. Plastic tanks are thicker that the standard metal tanks so when building you have to allow for that by making the area where you tank will sit a little lower by sawing the beams before building the engine crutch. It helps to make sure that you can move the tank up or down, and maybe even cock the pick up end of the tank outward when building the fuselage and making the tank area large enough to do all of this. The other solution is to learn to build custom tanks.
   Again, I want to point out that you need at least a lap sometimes for the engine to respond. From another thread where you have videos of yourself flying lazy eights, you may not be flying full successive laps inverted. But you still can listen to the engine run as you go through the eight, and see how it changes in each looping direction. If it is fine turning inside, but goes rich or slows down in the outside loop, you need to raise the tank in relation to the engine as it is sitting on it's wheels. if the engine speeds up in the outside loop, you need to shim the tank away from the mounts. Just make small changes with thin shims. Some guys use old playing cards for this, or metal shim stock because it won't get oil soaked. thin ply wood and balsa works also for temporary shims, and when you have it worked out, you can replace that with plastic or metal shims that will not get fuel soaked.
  Keep practicing!!
    Type at you later,
  Dan McEntee

[Chuck Matheny]

Hi Chuck,

Thank you for responding to my question.
The plane is a Built-Up Fuselage Vector 40. I use the all metal wedge style tank and a tongue muffler without any pressure line going back to the tank. It’s kinda hard to observe the fuel line with this setup, any tips on how to do it?

The silicone fuel line I use [usually either Dubro or Sullivan brand ]you can see fuel flowing through it.
If you have already experimented with various tank positions with no  results..then what I suggested is easy to try.
Is this a problem that just recently happened or is this the way your model has always behaved...?
An engine that is getting worn out..[or that has loose screws] will be more sensitive to tank position and will not allow a broad needle setting. same goes for an engine that has too big of a venturi..especially if it doesn't have a well pressurized fuel system.
So...people need to know if this problem of yours has just recently come up..or if this is a "set up problem" that has always been with this plane.
Dan's suggestion [to raise the engine] is a good one if you can't lower the tank any further than where you have it now.

[EricV]

You asked for things other than tank hight... so... Is this a new problem on an otherwise known good running setup? Has the idle also begun to get ratty? If so, when was the last time you changed the glow plug? I've had taters or weak plugs do this on inverted engines.

EricV

[Ken Culbertson]

Hi all,

Question:
Beside the tank height problem, what could be the other reasons that cause the engine leaning when doing the inverted flight or outside/inverted maneuvers?


Best,
Kafin

Plumbing.  If the pickup tube is not centered in the tank or the uniflow vent is in the wrong place you can get this. If the tank has vents that move in and out of the fuel the same can happen and having too long a feed tube might if the engine has a weak draw. Having said that it is still probably tank height.

Ken

I wrote this last night, so I missed the other posts all of which are spot on.  Is this a "New" tank or one you have used before?  I have had many a new tank come with the internal plumbing randomly placed.  Until going electric, I always took the back off of the tank and inspected it.  I have had some with the pickup tube only extending an inch into a 4oz tank!  Misplaced uniflow tubes are the most common but you are not using uniflow.  If the tank is good, then my next victim would be the venturi or fuel filter, OR as already mentioned, the glow plug.  Older motors have an issue with going rich once they have gone lean and, like stated below have a narrower needle valve range.  It would be natural for an engine to lean out going into inverted from a loop but it should go back to rich once level inverted.  Same in reverse.  It is telling you that it is still starved for fuel if it stays lean or you are running it on the lean side of it's power envelope.  If the engine just wants to run lean, and some do, go to a lower pitch prop and just let it.

Ken

[Dennis Toth]

What engine and plug are you using? What venturi size and needle valve unit? Who's tank and type are you using?

Sometimes when the plug is getting curded up it can cause weird thinks as it goes from upright to inverted. I would do to simple things: Change the plug to a new hot plug, change the fuel pickup tubing just to eliminate any issue with it.

Best,     DennisT

[Brett Buck]

Hi all,

Question:
Beside the tank height problem, what could be the other reasons that cause the engine leaning when doing the inverted flight or outside/inverted maneuvers? And if it’s hard to equalize the lap time between the two, what’s the tolerance? 0.1 sec? 0.2 sec?

     The engines themselves are not remotely symmetrical, so how the gas flows around inside it when it is running can be influenced by acceleration of maneuvering. So, unfortunately,  there are a myriad of possible issues. What engine, what prop, what tank, and how it is mounted? And while I hesitate to ask, is this engine modified, "blueprinted", or changed in any way from stock out the box from a manufacturer. 

     I note that with many modern engines (and some ancient ones), running it too slowly greatly exacerbates this tendency. Just about any modern engine on a stunt plane needs to have a 4" pitch prop, and the associated relatively high RPM. Or at least high by stunt standards - 11,000 - 12,000 in the air. That's because everything inside it is sized for running at high speeds, not chugging around at 8500 rpm like it was 1955 all over again.

      As far as tolerance goes, lap times are great, but get it right in the maneuvers, then see what lap time difference you have. If it is excessive, you will have to decide for yourself whether it is too far different. .1 or .2 seconds is not unreasonable depending on the level of the competition, assuming it ran OK in all other respects.

      Brett

[Steve Helmick]

If you can't adjust the tank height enough and you don't want to raise the engine, there IS a third alternative. Make yourself a custom tank with a non-symetrical cross section. It has been done for years and it works fine.

I got some disagreement with my post in your Lazy 8's thread, but adjusting tank height is a very good use for Lazy 8's. You can see and hear any rpm change quickly and easily. That said, I haven't done a Lazy 8 in decades, and I don't bother with checking lap times. It's either going fast enough to fly ok and give decent line tension, or it isn't. I do think you'll have to tighten up your Lazy 8's to make it easier to check for rpm changes by ear.

What is your line length? Do you use the same lines & handle for both airplanes? Getting neutral adjusted correctly and getting the correct line length is critical. It's HUGE to use dedicated lines/handle for each plane.   

You might find the Lazy 8 way of adjusting tank height more much more useful than a stopwatch. If the lap times are different upright/inverted by .2 seconds, but if there is no rpm change during a series of Lazy 8's, I'd go with the Lazy 8's.    Steve

[Chuck Matheny]

I think there is one thing that the Responders to this "Trouble Shooting Thread" can unanimously agree to.....WE DEMAND "FOLLOW UP" FROM THE OP once the problem is solved..... !!

I think the vast majority of my Combat Planes go rich on the outside manuevers...even when equipped with diaphram actuated  regulators this tendency is still there.

[Dan McEntee]

I think there is one thing that the Responders to this "Trouble Shooting Thread" can unanimously agree to.....WE DEMAND "FOLLOW UP" FROM THE OP once the problem is solved..... !!

I think the vast majority of my Combat Planes go rich on the outside manuevers...even when equipped with diaphram actuated  regulators this tendency is still there.

   He's on the other side of the globe, so there is a bit of a lag, or we are lagging behind him!
  Type at you later,
  Dan McEntee

[Chuck Matheny]

   He's on the other side of the globe, so there is a bit of a lag, or we are lagging behind him!
  Type at you later,
  Dan McEntee

That's what I figured....but over the years I've seen a lot of  advice  drift off into cyberspace unanswered.
On the bright side...millions of years from now...people living millions of light years from us will have all sorts of message traffic floating in about how to properly break in a Fox .35.

[Ken Culbertson]

 

....how to properly break in a Fox .35.

I thought they came from the factory broke 

[Kafin Noe’man]

Hi, thank you for all of your comments.

This post is actually started when I shared my Lazy 8 practice video with my Vector 40
and I was suggested that I should work with the tank height. I was told that the engine sounded leaning when performing the outside loop when in the lazy 8. Well, to be honest, I didn’t really aware of that when flying.

I didn’t feel much different in control when transitioning from the inside loop to the outside loop. Most probably it's because of my flying experience so I can't really tell the difference, yet.

But after reading your responses here, I think I'm gonna hold the decision to play with the tank height at the moment because:
1. From what I've read from various resources and comments, I need to settle into inverted flight for at least 5 level laps and time those compared to the upright. Dan also wrote "It may take a lap or so for the setting to show itself."  -- I’m still learning to be able to fly inverted more than 1 full lap, that's why there's no inverted flying on my video. I guess it's still hard to tell if the tank is in the wrong height or not since the only 'evidence' I have now is the lazy 8 video.

2. Dan wrote "But you still can listen to the engine run as you go through the eight, and see how it changes in each looping direction." What I hear is the engine leans out throughout the lazy 8, from the inside to outside loops, and back to the richer sound when back on level upright (I might be wrong though, I'm still not that good at judging how the engine sounds). -- I think this might be because of I'm still learning to fly inverted and feel less confident when upside down, so I'm turning tighter outside than inside. From what I've read, that will change the relative way the motor runs too because the load on it through the prop is higher when I turn tighter. 

3. And as Ken said, "It would be natural for an engine to lean out going into inverted from a loop but it should go back to rich once level inverted." -- I think if I only do the Lazy-8 which means I only go for an inside loop and then directly an outside loop, I wouldn't have the chance to hear if the engine go back to rich, would I?

4.

I note that with many modern engines (and some ancient ones), running it too slowly greatly exacerbates this tendency. Just about any modern engine on a stunt plane needs to have a 4" pitch prop, and the associated relatively high RPM. Or at least high by stunt standards - 11,000 - 12,000 in the air. That's because everything inside it is sized for running at high speeds, not chugging around at 8500 rpm like it was 1955 all over again.

I fly my Vector with ENYA 35XS, APC 10.5x4.5, 10,500-ish RPM, and 5.4 sec lap time. I might try to close the needle a bit by a click or two and see the difference.

In conclusion, rather than tinkering with the current tank setup, I think I would try to focus to fly the loops and Lazy-8 better first and do the inverted flights for more than 2 or 3 laps consecutively. I'll try to time the laps when I can do the inverted flights.

Does it sound a good plan?
Looking forward to hearing more from you guys!


Best,
Kafin

[Brett Buck]

4. I fly my Vector with ENYA 35XS, APC 10.5x4.5, 10,500-ish RPM, and 5.4 sec lap time. I might try to close the needle a bit by a click or two and see the difference.

In conclusion, rather than tinkering with the current tank setup, I think I would try to focus to fly the loops and Lazy-8 better first and do the inverted flights for more than 2 or 3 laps consecutively. I'll try to time the laps when I can do the inverted flights.

     The video was very helpful. I think it's probably OK right now for what you are doing.

    But, if you want to improve slightly, I would suggest a  tank shim, away from the motor mounts, lower in the fuselage by about 1/16". That's a pretty big shim, but, based on very painful experience from the early-mid 80s, this may not be easily fixable. It sounds to me like classic "schneurle effect" where, using inverted mount schneurle engines, we frequently got exactly this sort of response - going hard lean on outsides. For the most part, we never solved it for muffled engines, and even tuned pipe engines are prone to it, although you can mitigate it a bit with pipe tuning. It's this sort of thing that led to the explosion of the "engine rework" industry trying to solve it on a variety of late 70s schnuerle engines, particularly the OS 40FSR.

        The only thing I would suggest aside from the tank shim is to use a filter or some sort of diffuser, like a square of panty hose held over the venturi with a suitably-sized o-ring. This reduces the effects of the varying relative wind direction on the venturi.

     Brett

[kevin king]

I'm no expert but it looks like the inside loop is larger, and the outside loop is tighter, thus causing a leaner run.

[Steve Helmick]

"I think if I only do the Lazy-8 which means I only go for an inside loop and then directly an outside loop, I wouldn't have the chance to hear if the engine go back to rich, would I?"

My suggestion here is to do two or three consecutive Lazy 8's...unless there is zero wind...so that you can work on getting the loops equal size and closer together. IMO, this will give you a better chance to judge the engine rpm change and adjust the tank height.

I would also suggest trying to get the camera placed exactly upwind. And also, put a marker of some sort directly down wind from the camera, and have some sort of marker in circle center. Doing the Lazy 8's exactly downwind from the camera would reduce Dopler effect changing the engine sound on the video and give  better evidence of what the engine is doing, good or bad. Keep at it!  Steve

[Brett Buck]

"I think if I only do the Lazy-8 which means I only go for an inside loop and then directly an outside loop, I wouldn't have the chance to hear if the engine go back to rich, would I?"

My suggestion here is to do two or three consecutive Lazy 8's...unless there is zero wind...so that you can work on getting the loops equal size and closer together. IMO, this will give you a better chance to judge the engine rpm change and adjust the tank height.

I would also suggest trying to get the camera placed exactly upwind. And also, put a marker of some sort directly down wind from the camera, and have some sort of marker in circle center. Doing the Lazy 8's exactly downwind from the camera would reduce Dopler effect changing the engine sound on the video and give  better evidence of what the engine is doing, good or bad. Keep at it!  Steve

   It also reduces the parallax that is making the outside look a lot smaller. But it is clear from the character of the sound that it is going hard lean on outsides.

    Brett

[Lauri Malila]

..

[Howard Rush]

I've been wondering why Kafin is looking for a fix other than changing his tank height.  My first thought was that his tank is glued in.  My next hypothesis was that he, along with a number of advisory stunt fliers and along with fuel system engineers at a large commercial transport airplane maker, believes that the force on fuel in a fuel tank in flight is solely that from gravity.  Hence one cannot conclude anything about tank height from half an outside loop: one must time several laps inverted and several laps right-side-up. 

On the first flight of my first Impact, I thought I had a wing warp. Oddly, the remedy was to change the tank height.  I reckon Kafin would have fixed the problem with a trim tab. 

[Kafin Noe’man]

     The video was very helpful. I think it's probably OK right now for what you are doing.

    But, if you want to improve slightly, I would suggest a  tank shim, away from the motor mounts, lower in the fuselage by about 1/16". That's a pretty big shim, but, based on very painful experience from the early-mid 80s, this may not be easily fixable. It sounds to me like classic "schneurle effect" where, using inverted mount schneurle engines, we frequently got exactly this sort of response - going hard lean on outsides. For the most part, we never solved it for muffled engines, and even tuned pipe engines are prone to it, although you can mitigate it a bit with pipe tuning. It's this sort of thing that led to the explosion of the "engine rework" industry trying to solve it on a variety of late 70s schnuerle engines, particularly the OS 40FSR.

        The only thing I would suggest aside from the tank shim is to use a filter or some sort of diffuser, like a square of panty hose held over the venturi with a suitably-sized o-ring. This reduces the effects of the varying relative wind direction on the venturi.

     Brett

Thank you Brett, I will fly some more and see how it goes.

[Kafin Noe’man]

I'm no expert but it looks like the inside loop is larger, and the outside loop is tighter, thus causing a leaner run.

Hi Kevin, that could be one of the reasons. I need to fly some more so I can make more solid conclusion.

[Kafin Noe’man]

"I think if I only do the Lazy-8 which means I only go for an inside loop and then directly an outside loop, I wouldn't have the chance to hear if the engine go back to rich, would I?"

My suggestion here is to do two or three consecutive Lazy 8's...unless there is zero wind...so that you can work on getting the loops equal size and closer together. IMO, this will give you a better chance to judge the engine rpm change and adjust the tank height.

I would also suggest trying to get the camera placed exactly upwind. And also, put a marker of some sort directly down wind from the camera, and have some sort of marker in circle center. Doing the Lazy 8's exactly downwind from the camera would reduce Dopler effect changing the engine sound on the video and give  better evidence of what the engine is doing, good or bad. Keep at it!  Steve

   It also reduces the parallax that is making the outside look a lot smaller. But it is clear from the character of the sound that it is going hard lean on outsides.

    Brett

Will def. do this, Sir 

[Al Ferraro]

I would not change anything with your Vector till you improve your inverted flying to 4 laps to see if the engine settles back down. Right now you have a nice running engine to practice with. FYI my Vector ARF needed 1/8 pads under the engine as it ran to rich inverted, LA.46
Al

[Kafin Noe’man]

I've been wondering why Kafin is looking for a fix other than changing his tank height.  My first thought was that his tank is glued in.  My next hypothesis was that he, along with a number of advisory stunt fliers and along with fuel system engineers at a large commercial transport airplane maker, believes that the force on fuel in a fuel tank in flight is solely that from gravity.  Hence one cannot conclude anything about tank height from half an outside loop: one must time several laps inverted and several laps right-side-up. 

On the first flight of my first Impact, I thought I had a wing warp. Oddly, the remedy was to change the tank height.  I reckon Kafin would have fixed the problem with a trim tab.

Yes, you’re right Howard! One of the reasons is because the tank is already glued in.

If you know the back story, it took me almost 9 months to finaly get this Vector up in the air (at least) without much problem and pretty good engine run  . It feels like I wanna enjoy this time for a moment without having to do some repair that requires gluing. Hahaha

Meanwhile it’s very convenient to adjust the tank height with tank brackets on a profile fuselage, is there any similar system for the full fuselage?

[Ken Culbertson]

.... is there any similar system for the full fuselage?

Actually there is.  First you mount the engine higher than the mounts and you make a box behind the motor that lets you move the tank up or down at least 1/4".  Make shims to hold the tank in place and to adjust it up or down.  When I was using IC I used hard foam and old playing cards.  To move it up you take one card out of the top and put it in the bottom.   Just for future reference, never glue a tank in.

Ken
 

[Kafin Noe’man]

I would not change anything with your Vector till you improve your inverted flying to 4 laps to see if the engine settles back down. Right now you have a nice running engine to practice with. FYI my Vector ARF needed 1/8 pads under the engine as it ran to rich inverted, LA.46
Al

Thanks Al, this is probably what I’m gonna do in the meantine.
I need to fly more, so I can have more ‘solid evidence’ before deciding what to do next.

[Ken Culbertson]

Thanks Al, this is probably what I’m gonna do in the meantine.
I need to fly more, so I can have more ‘solid evidence’ before deciding what to do next.

It is not just evidence, it is building confidence and "muscle memory", a very over used term.  You don't know what that engine is going to do till you get it back to level flight and it unloads.  Going from rich in level flight to lean in a maneuver is natural, and until the advent of pipes, something we used to advantage.  Going lean and staying there or not going lean when it should is a problem.  I am not sure you have a problem yet and I will leave diagnosing it to those still in the IC game.

What you need to concentrate on now is mastering inverted flight.  One of the things I noticed in your video is that you are doing more of an "8" than a lazy eight.  This is not helping with learning inverted.  It should look more like a stretched-out infinity symbol.  Just *after* rounding the top of the maneuver, you stop turning and center the controls till you get to your level flight altitude then apply outside, counterclockwise, toward the wheels, anything but thinking "DOWN", control to loop back.  You need to do several at a time and stretch them out as much as possible.  The lazy 8 does not wrap your lines. I recommend just under 1/2 lap so that you get the feel for turning into the wind.  This may seem silly, but it is repetitive motion that builds muscle memory.  If you have to think about what control to give it, you are not there yet and if you need a lap or two to recover you are not there yet.  This is just like learning any sport, you are training your body to respond without thinking about it.  If you master this with something as simple as the lazy 8 you are going to spend far less time rebuilding as you get to the other maneuvers.

BTW,  yours level flight is about right for where you are in the learning curve.  To low and you will start thinking about the ground.  Ignore the ground, it has nothing to do with a properly flown pattern.  Too high and you will have trouble later judging 45 degrees.  You look to be flying level at about 8-10'.  I would stick with 8 and try to go back to that height whenever you are level or at the bottom of something.

Ken

Ken