I just started flying my escapade inverted. It has an OS FS 52 Surpass. From the beginning i have been flying the escapade with this engine setup on the rich side. engine smokes good in the air. good power. climbs nicely. Couple weeks ago I started doing more inverted flights. I noticed when I flip the plane over I see more exhaust smoke. the engine sounds richer - much richer. I feel the loss of power. I figure becuase the engine is now inverted that the glow plug is getting cooler with more fuel. Am I correct? does that mean I can lean it out some more or should I just leave the carb setting as it is?

The tank location is suspect. Most likely it sets too low in the fuselage, and when you go inverted it becomes too high.

HighPlains has a good theory. Also, there is no need to run your engine rich. That won't do as much damage as running it lean will, but there's no reason not to run it to it's fullest potential.

I run my .52 2 clicks rich. Set needle at max and back out 2 clicks.

Works fine for me.

Tom

Depending on engine size, prop size/weight, weather and geographic details, and the brand of engine, how far rich of peak you should set your high speed needle can vary significantly.

I was trying to tune a Magnum XLS .46A last spring for some club racing, and I had dialed it in like my Enya, Super Tigre, and Thunder Tiger 2-strokes. It would run really strong initially and then sag and bog down after a few minutes of flying. I discovered that I had to richen the high speed needle almost a full half turn rich of peak. The Magnum unloaded more in the air than my other two-strokes, and what sounded like a great tune on the ground ended up too lean while flying full throttle up in the air.

There is no such thing as a "factory" or "recommended" needle setting. Glow engines have a wide range of carburetor adjustment specifically because there are so many variables; altitude, humidity, temperature, prop size, prop weight, prop load, prop balance, spinner weight, spinner balance, glow plug heat, glow plug length, fuel quality, fuel lubrication content percentage, fuel lubrication content type, fuel nitromethane percentage, fuel tank placement, fuel tank distance from carburetor, quality of o-rings, quality of gaskets, and presence/condition/quality of on-board fuel filters all affect engine tuning.

If backing out 2 clicks is working for you, that's great. When it turns out to not be great anymore, however, don't be afraid to take the time to experiment a little bit and see how the engine responds to minor adjustments. "Rich enough" when it's 65F degrees and 50% humidity usually isn't "rich enough" when it's 93F degrees and 85% humidity.

So if I'm inverted there shouldn't be engine performance differance?

The fuel tank should be level with your carb.

No big difference.

If your carb is adjusted properly and the fuel plumbing is non-restricting, you'll have no problems.

The fuel tank height issue is a bit of a myth that is often propegated here.

Turning the plane over will offset the tank height by all of .5 to 1"... not enough to even register for most planes.

Remember that if such a different was that important to our planes, we would never be able to perform uplines or downlines.

That said, proper tuning does involve adjusting the plane with the nose up and down, to verify that the engine will run correctly at all attitudes.

It is normal to see SOME change when the plane goes nose up or down, but you are also moving the fuel tank a good 4-8 inches or MORE up or down when you do that...

This is MUCH more of a difference than the plane experiences when inverted.

You don't tune an engine for smoke, you tune an engine correctly, a few hundred rpm under it's max you re getting with the prop being used. If you want to see more smoke then add some more oil to your fuel. Fuels that have no Castor smoke very little. Fuel tank set up can effect an engine when the plane is inverted. The engine doesn't know it is mounted upside down but you set up has to be correct.

What Gray Beard said and here's some literature from Saito's website.



Upright, Inverted, or Side Mount ?? Any engine orientation is OK. A frequent question is can I run the engine inverted ? A scale or pattern type model looks better with the engine inverted. Inverted engines run fine but can be a real inconvenience when starting. Attaching a glow-plug ingniter, and keeping it on, can be a real pain. Also fuel may accumulate inside the piston when inverted, causing hard starting, or possibly engine damage when forced over with an electric starter. This latter problem with inverted engines is minimized if you turn the engine over by hand 5 or 6 rotations before attaching the glow plug battery; any excess fuel inside the piston will run out the exhaust (if the exhaust points downward). If you are new to 4-stroke engines it is preferable to mount the engine vertical or sideways. It is important to note that the centerline of the fuel tank should be level with the carb or a little lower; if you invert the engine the tank may be a long way above the carb and you may have fuel running down into the carb making it difficult to get the fuel mixtures correct. Therefore, before deciding on an engine mounting orientation remember to consider the tank location. If the idle mixture is set correctly there should normally be no need for an on board glow system.
The dreaded <u>&ldquo;hydro-locking&rdquo;</u>. Often mention is the term &ldquo;hydro-locking&rdquo; with inverted engines. It is easy with an inverted engine to get the piston full of fuel and it will be difficult (or maybe impossible) to turn over the engine by hand and application of a strong electric starter may damage the engine. The instructions with engines purchased from the Horizon Hobbies (distributor in North America) suggest that in such a situation you should remove the glow-plug and drain the excess fuel. While this will work, I suggest that procedure is inconvenient, unnecessary, and undesirable. It does nothing except wear out the glow-plug thread, maybe strip the thread in moments of frustration, and certainly waste a lot of time. There is a simple fix; (with glow-plug igniter removed) just pick up the model and tilt it sideways so that the exhaust port points down, turn over the prop by hand and you will see the excess fuel that was in the cylinder run out the exhaust.
For an inverted engine you should first make sure you can easily turn over the engine by hand before applying an electric starter.</p>

Big Ed covered most of the variables, trying to make the point that every setup has different sensitivities. What you didn't cover is changes in the fuel head under a "g" load. I've had some high performance planes that an 1/8" change in the tank height made the difference between leaning out in turns and killing the plug, to going from lean to rich. Other mild sport aircraft much less so, but when I configure a plane, I expect the engine to run the same regardless of orientation. Properly setting up the fuel tank position relative to the carburetor is part of this process.

Right, that's where tank height differential comes into play...

Having too much offset will lead to siphoning, but that is a completely different problem.

All too often improper plumbing setups will flood the engine during fueling, and novices will blame the tank height.

I have a couple of planes with inverted engines, that I must clamp or close the fuel line while fueling to prevent hydro-lock upon trying to start the engine.

Not as much as you may believe.

Hold the nose of your plane up while tuning and you are adjusting the carb for flow when the tank height is a good 8+ inches BELOW the engine.

The plane leans a bit, but it's not all that dramatic once the engine is properly adjusted.

The relatively LOW amount of difference when mounting an engine inverted hardly affects an engine at all.

If it did we could not fly uplines.

If the offset was 12+ inches then there MAY be issues with the weight of the fuel in the lines, etc...

However the often touted "tank height" difference affecting engine performance is largely a myth.... much like the "fuel stays in the back of the tank" myth on downlines... often repeated by even VERY experienced people who never bothered to empirically test this... I can't believe Clarence Lee said that in his articles... ugh.

The collected experience of 60 years worth of C/L stunt fliers says otherwise, as does my own personal experience where as little as 1/8" is very noticeable in flight with some engines.

Of course muffler pressure can mask the problem somewhat. Ditch the muffler pressure for Uniflow plumbing and it will become readily apparent.

Largely? Well we are making some progress. Your example of just holding the engine up or down might have validity if the airplane worked in a 1 g environment. Just about any sport model can pull 10 g in a loop. Start doing horizontal eights and you want the engine to maintain the same power capability in both positive and negative portions of the maneuver. If operating a suction style carburetor equipped engine, tank position will get you there.

Hi!
It's not a myth! Tell any pylon racer(or any one that has been around this hobby for more than 20 years) and he will laught at you!!!

The tank must always be mounted so that the center of the tank is inline with center of the carb (or more precisely the carb intake orifice) when the airplane sits horizontal. This is something all experienced fliers know!

The reason for this is the fuel pressue alters with hight! Simple as that ,and all our engines react on altering fuel pressures,some more some less.

Yes it is a myth and it is also VERY easy to prove as such.

Mount any engine in a test stand with a considerable length of tubing.

Just make sure that the tubing is unobstructed during testing and does not get compressed or pinched.
Also make sure you have your pressure line(s) set up correctly.

Get it running, and then move the tank 1-2 inches above the carb centerline.

You'll see absolutely no difference.

Now drop it by the same... again no difference.

This is far more of a differential than you would ever see in mounting an engine inverted or permitted by moving a fuel tank up or down in a typical fuselage.



Now ( assuming you've put in a good bit of tubing ) drop or raise the tank a good 12+ inches.

Almost no change if any.


Have some more tubing available?

With the engine running, swing the tank around to subject it to multiple "G"'s of force....

Again little to no difference.


Give it a shot, it's an easy test to do.... something I've -actually- done.


Highplanes:

In a 10G environment the tank differential again doesn't mean anything. Been there, tried that, noted the results.

You are looking at a tiny fraction of an ounce difference in the fuel lines because of this offset.

The kicker is that under the conditions you say, e.g. pulling a 10g loop, the tank is WAAAAAY below or above the plane anyway...

e.g. in an up line the tank can be a good 10+ inches below the carb as it pulls that 10g loop.... and yet your engine still runs.

The inverted differential or the offset afforded by moving a tank up and down in a fuselage is no more different in this case than moving the tank back or forward by .5".

You should take a look at the videos of the fuel tank and fuel levels in the "fuel stays in the back of the tank" myth thread...

If the pilot believes a typical .5 - 1" centerline offset is affecting their loops, they really need to look elsewhere for the cause of their problems.




The mantra around here for engine problems unfortunately from the "more experienced" set is all to quickly said to be a tank height difference.

If the user is experiencing hydro lock... then may be something to suggest...

However newbie's are often told... "if you mount the engine inverted, you'll have to move the tank down to get the engine to operate properly" when that is completely UNTRUE and an often repeated fallacy.

Jaka,

At the Winterfest race, Dub Jett was telling people that had high wing quickies (which was all of them), that if the airplanes nose didn't droop 1/4 from the centerline sideview, that they needed to run an oval tank to move the fuel higher in the fuselage. Those that had the droop ran fine with the regular round tanks.

That Dub Jett guy? He don't know nothing

Highplanes and Jaka:

I offer further empirical proof....

-

Take any profile plane with a side mount tank.

I used my OMP Edge 540 for this test... it has a perfect setup to adjust the tank.

Fly the tank and note it's characteristics... particularly in high "G turns and waterfalls, etc.

Remove the tank and mount it to a ply plate that has holes for the tank wire ties.

Use the plate to raise or lower the tank a good 2", by affixing the plate to the existing wire tie holes.

Fly the plane again WITHOUT touching the needles, put it through the same routines.

You'll note ABSOLUTELY NO DIFFERENCE IN PERFORMANCE.

Throw whatever you want at the plane... the engine will not care about the tank height.

I had a lot of problems flying an ASP 120 size 4 stroke inverted. The best I could do was to get the fuel tank (centre-line) about 3 inches above the carby. The engine had hard starting because of fuel locking and wouldn't run anymore than a few minutes (it would slowly load up with fuel and finally quit in a haze of smoke). Leaning did not make much of a difference.

I didn't want to go to the expense of a fuel pump or regulator and initially tried an extra length of narrower guage fuel line looped over the top of the fuselage with an inline filter. This worked in that it gave me a reliable running. The engine still tends to load up if idled more than a minute or two, but clears (relatively) quickly and runs clean WOT.

My theory is that the extra length of fuel tube, narrower guage and inline filter added enough resistance to slow the fuel flow so the engine could handle it. I still get fuel lock/hard starting on the occasions I don't get the engine running on the first few turns, but I can live with this.

Now thats interesting HP and no doubt that is with his round bubbless tanks as opposed to the rectangular Tetra's. Oh man in this heated debate Cutaway is gonna kill me if I admit I only use my leftover tetras stash in my Ukies anymore

Anyway Just wanted to ring in here say I do feel the tank/Spraybar height relationship is an important consideration That should always be taken into consideration.

MercerAUST any conventional Muffler/suction fuel system with a three inch discrepancy i.e. the tank center three inchs above the spraybar is going to be endemic and prone to hydrolock as well as flooding.

John

Hmm got an early morning gotta go Clear some of the fella's engines, its inevitable

John,

I've known and discussed model engines with 4 engine designers over the past 25 years. All were involved with high performance engines though two were also designers of sport engines. One trait that all have or had was an extreme attention to detail, and considerable experimentation with all aspects of building and operating model engines. You can learn a lot when people with that kind of experience share their thoughts with you.

Indeed and that is why I so enjoyed my sojourns to the Winterfest so much when I was still able. The saturday late night pit sessions were magical and what you could learn as the music of the full scale dragsters right behind the airplane pits roared off into the night.

What a place and what a time.

John

The bottom line is that your issue was NOT with the fuel tank height, but rather with flow of fuel prior to start...

You effectively leaned out the low end by installing the more restrictive tubing, something that could have been done by adjusting the LS needle instead.

I'll bet if you apply your solution and move the tank up or down more, you'll get exactly the same performance either way.

BTW: I find the ASP needles to be extremely touchy... just like their Magnum brethern.



So newbies are best advised to worry about TUNING issues and forgo the "fuel tank height is causing performance problems" nonsense.

Hydo-lock is a completely different story however and if this is an issue there are many ways to deal with it.