Filipvdm

This weekend I had my first dead stick landing.
I was flying inverted at low paste and the engine just stopped.
The engine is an ASP.46 and is installed upright. So far it never failed on me. I have been running it on the rich side (in my opinion).
But this time I decided to tune it more lean and it preformed a lot better. I had a few flights with this setting.

Is there a reason I should look out for why the engine stopped while inverted or was I just unlucky.

By the way, the landing was not that good. I lost the landing gear of my LA RACER and some minor structural damage.
There was quite a bit of wind and had to land downwind, there was no time to turn into the wind.
I thought I was going to make it but then I noticed some people in the path of landing and immediately brought the plane down way to hard.
I fact these people were far away and there was no need to rush the landing, but I guess I was too concentrated on the plane to have a good look where they were.

Filip

Insanemoondoggie

Check your fuel clunk in your tank . Sometimes the clunk well get stuck to the front of the tank . Especially , if you had a less than desirable landing or two.

Also , if you were running to lean , it could be your engine just quit at that point in time . Look at your exhaust residue , if it`s dark and has little sparklys in it, you were running lean.

To bad about your rough landing , but it is better to error on the safe side , when it comes to bystanders and rc airplanes. A little glue and you`ll be good to go again .

Nathan King

Aye yie yie! Little sparklies are NOT good. You have to run pretty darn lean to get that! [X(]

Missileman

Another possible cause is your clunk line inside your tank may be too long and got stuck in the back of the tank when you went inverted.
The clunk should be near, but not touching, the back of the tank.

Filipvdm

Thanks.
Checked the exhaust and it is clean, also checked the clunk and was ok to.
I really don't think the engine was running too lean. I would even think that running too rich could be a problem while flying inverted, while the engine could flood, or am I wrong.
It was the first time I flew so long inverted, I don't know, maybe it was just bad luck or dirt.
Anyway, when everything is fixed I will give it a good test inverted... while I am holding the plane

While checking the exhaust the gasket broke, I read somewhere that people install the exhaust without gasket. Is that a good idea?
They say the gasket only gives trouble, sucking in fals air. Seems a bit strange to me.

jetmech05

How new is your engine? I've had engines that just wouldn't run inverted until they had 10 flights or so on them

delman

On most planes the fuel tank center is a little below the carb, if you were running fairly rich with it inverted your tank would be higher than the carb - it could have flooded out. Just a possibility.

Missileman

For the Next inverted attempt you might want to fly a bit higher

Filipvdm

The engine is fairly new, lets say a bit more than a gallon.

My next attempt will be as high as I can hold it in my hand

alfredbmor

I definitively would check the center line of the tank against the center of the carb, if there is a difference bigger than 1/2" then your problem resides there.

JPMacG

My Feedback: (2)

Yes, check the height of the tank. Usually they are lower than they should be.... so when you go inverted the mixture becomes too rich. Try to get the tank located per the engine instructions by moving the tank or engine.

Filipvdm

Checked the hight of the tank, the center and the outlet of the tank is about one inch below the inlet of the carb. But I don't see much I can do abou it.

opjose

No.

This is a MISCONCEPTION.

The difference in height only affects fuel siphoning not actual engine operation or even inverted flight positions.

Remember that we would be unable to fly downlines, uplines, etc. if this were remotely true, let alone nose high tail draggers...


Missleman's suggestion is good ( as usual! ).

The clunk may be reaching the bottom of the tank rear, but when the plane goes inverted, the clunk may not be moving UP ( now down when inverted ) exposing it to air and causing bubbles in the line.

alfredbmor

Opjose, I am sorry for differing on your point of view, the most recently fact (That I own and have tested) that probes that a misaligned tank could cause a death stick is the Great Planes Venus 40. In the recommended set up by the manufacturer you have to bolt the engine up side down, causing a hard time to start the engine, once the engine is running and the tank is at its half of capacity, when you perform an inverted flight the engine will stop because of an over leaning condition. This problem is easily fixable by installing the engine at 90o. Then as a conclusion the position of the tank indeed affects the behavior of any engine. (Pumped engines excluded)

opjose

That you are having a problem when you invert the engine, points to a plumbing problem, not a "misaligned" tank or height issue.

Engine performance is NOT dependant upon orientation or the relationship to the tank ( unless you had the tank WAAAY back say 2ft in the fuse, etc. but at this point you have a bigger problem with flow "resistance" due to the fuel line length... the longer it is the more it resists fuel flow much like an electrical line ).

The only time it factors is with siphoning prior to startup.

This can lead to a flooding or hydro-lock condition if the user is not careful, when the tank is higher than the carb, or in the opposite case a lack of fuel to the carb when the tank is lower.

Once the engine is started, muffler pressure helps assure fuel flow to the carb under all attitudes.

What you've posted indicates a mistuned engine, plumbing problem or other internal carb problem.

Since you are seeing this with only 1/2 of a tank of fuel.... it is likely that your clunk is not traveling down to continue to be bathed in the fuel when the plane is inverted, causing the engine to lean out altogether.

On a properly plumbed system this should not happen.

That said, with 2/5 of a tank or less, even upright when you point the nose down by more than 20 degrees the clunk will become uncovered and your engine will cut out, but this is NOT related to the engine/plane being inverted or not, rather to the fact that the fuel flows forward while the clunk does not.... this WILL also happen in flight so you must be careful after you've run 1/2 out on your flights.

There is a video that illustrates this problem and kills the misconception that "fuel stays in the back" during flight.

BTW: I fly 85% of my 24+ engines inverted....

alfredbmor

Opjose:
No need to argue here. I have tested for several years this concept and have had some results, maybe your have just been lucky with your planes. As a kit builder and scratch builder I know how important is to mantain a level between the tank and carburetor to avoid the engine to run on richer or leaner conditions, or even cause an undesired death stick. I wish you can take a look at hundreds of threads regarding this issue. There is a big difference when the middle of a tank is positioned at 1/2" above the center of the carburetor than when it is 1/2" below the carburetor, I doubt that you can state that the tuning is still the same, do you?
Then is hard to affirm that when you invert the plane the missalignment of the tank is not an issue.
All opinions are well respect, and I know that there are many skilled contributors here at RCU, for some time now I have been reading many very accurate posts as well as others that are not that lucky.
In the case that I just described, there are a couple of threads where the people post that they are having death sticks or a hard time to tune the engine (Venus 40 threads), I remember some other ARFs, that had the same problem (One seagull warbird with australian markings) facts speak for their self.

Best regards Alfredo.

JPMacG

My Feedback: (2)

My personal experience is that even though the tank is pressurized by the muffler, fuel tank height, fuel tank size, and the amount of fuel in the tank all affect the mixture. I can hear my engines lean out as they burn through a tank. I can hold an airplane nose up and hear the mixture lean and nose down and hear it richen. I have a model with a particularly low tank that will not run inverted after being properly tuned upright. I also note that my 3D airplanes all are designed to have their fuel tanks close to the engine. So I too will respectfully disagree with opjose.

Rodney

I agree with Alfredbmor and JPMacG, tank position can be a big factor as proven by many years experience here. True, if using muffler pressure, it is somewhat less critical than with no pressure but still is effected. Unless you have a pumped line, distance between the tank and engine is also critical.

opjose

1/2" doesn't make any difference. Nor does it make any difference in my engine tuning. Nor have I been "lucky".

I've been persistent though in trying to eliminate problems that I erroneously thought at first were caused by tank/height differences... so I started testing...


Tank height difference only affect siphoning.

If you point your plane nose up ( as you should for tuning and testing ) your engine will lean out slightly.

Now remember that in this position the tank is at least 6" or more BELOW the carb even on a small plane, in addition with 1/2 tank of fuel or less the distance is even more. Try measuring the actual distance sometime.

As you move up in plane size the distance from the carb to fuel increases even more.


Any changes to engine performance when inverted reflect other problems.

If the behaviour of your plane changes when the engine is inverted or turned upright, ( other than siphoning ) you have a problem that needs fixing, least your engine cut out in flight when you do things such as point rolls, etc.

BTW: some engine manuals even go as far as to state the same thing... that inverted operation makes NO difference to engine performance.

For every thread here where someone maintains that tank/height difference effects engine performance/tuning, you'll also find some fairly experienced members ( Downunder where are you? Please chime in. ) that will tell you it's not the big factor being made out here.


Re: Rodney's comment.

Yes and no.

No in that distance itself makes no difference to the engine. It doesn't "know" how far away the tank is.

However much like an electrical wire, the longer the turbing, the more pressure required to obtain consistent fuel flow... so if the tank is far from the carb ( and we are not talking about minor tank height differences here ), you now have two adverse factors

1 - The restiction to flow imposed by the tubing length ( as proof try blowing through a piece of clean 4" tubing and another 12" in length... BIG difference ).

2 - The weight of the fuel in the line.


Re: JPMacG's comment.

Yes your engine leans out as the tank level drops, but this has almost nothing to do with the tank height difference.

It has more to do with the compressibility of the air (gas) in the tank.

As more air is introduced into the tank, the effect of tank pressurization decreases.

You can test this with a clean/new tank.

Fill it full of water, and blow into the vent tube. Note how lightly you have to blow to get fuel to flow out of the line that would normally go to the carb.

Now try the same thing with 1/3 of a tank.

Notice that you now have to introduce a much larger volume of air over time, and you must maintain a higher pressure level to obtain about the same flow rate.

The extra air acts as a "buffer" of sorts to the gas being introduced from the muffler.

Add to this the now much GREATER difference between the tank and the carb, ( not the 1/2"-1" tank height difference an inverted engine MAY introduce ) coupled with the weight of the fuel and you get your lean/rich effect.

One reason that Uniflow, three line plumbed systems work so well to offset this, is that fuel weight is removed from the system.

They eliminate the leaning/richening effect.


Both of the examples above can be empirically tested, I am not just relying on percieved "experience"...



Since your plane will not run inverted when it is "properly tuned" you have a problem that you may be overlooking...

e.g. a few engines use springs to "push" the throttle barrel up against the LS needle. as you flip the plane over this can change the tuning... or your lines are such that flow is not consistent when inverted, etc., etc.

You want to look into this, lest you experience deadsticks in flight.


BTW: My Funtana ( a 3D plane ) has it's fuel tank on the C.G. which is quite far from the engine itself.

alfredbmor

Filipvdm:
I believe that its here where your problem relies, try the following set up.

If for any reason you are unable to move the tank accordingly then consider turning your engine 90o, or so to reach a closer centerline position between Needle valve and center line of the tank.

Good luck.

opjose

While this difference will cause fuel to siphon back to the tank when the plane is sitting level on the ground, it will NOT affect engine performance in flight as suggested.... and if you don't believe this, go with a Uniflow setup to be doubly sure.

Of course you want to perform all engine tuning with only about 1/3 of a tank of fuel so you get your "worst case" taken care of.

You should also perform a nose up test with this amount of fuel, but not a nose down test, as the engine will shut off on you as the clunk becomes uncovered.

Rodney

There are at least two errors in opjose's comments. 1. the amount of air in the tank is inconsequential as it is the pressure, not volume that counts. You get the same amount of exhaust pressure whether the tank is full or empty and the flow rate is so small that volume falls out of the equation and 2. the flow friction due to the longer line difference between 1 inch and 12 is again inconsequential due to the very low flow rate-at most about 1 ounce per minute. If flow rate were high then this length would have some effect but not at these low flow rates, simple hydraulic equations verify these two comments.

opjose

1 - Sorta...

The higher volume of air takes longer to pressurize.... ( so yes it is the PRESSURE, but I stated it's the EFFECT of the pressure which changes... ) at low throttle the pressure from the muffler cannot offset the backpressure from the air in the tank as it empties, so the amount of air becomes a factor. Less air, less sustained backpressure.

You can observe this if you have a fuel bubble in the pressure line, as you back off from high throttle it will return to the muffler as the pressure drops. You get more movement back as the tank has less fuel in it.


2 - It is not inconsequential. At a lower flow rate the resistance is indeed less pronounced, but it is never-the-less there. Try it with the "blow" test to see, even at the flow rates we see at say 1/2 to WOT throttle there is enough resistence over a long length of cable to HELP lean out an engine. By the time you add up all of the tubing installed, most people may be surprised at how long the total length is.... couple this with fuel weight, etc. and you have your rich/lean condition causes.

alfredbmor

In any fluid, atmospheric pressure is a constant (All physics formulas).
When you attach a hose into a fluid recipient, and the other end of the hose to a lower place, the atmospheric pressure will make the fluid to run into the lower position.
In our engines this situation tends to flood our engines, and yes we have the chance to tune properly our engines to run but our needle valves will be set in a leaner position.
When we have the opposite situation, a tank in a lower position than the engines needle valve, then we have to tune our engines in the richer side because it will tend to go leaner to fast.
If we turn our engine and tank (as an inverted flight) the condition of our tuning will change (Dramatically or not depends of the engine, but indeed it changes). If we had it tuned for a leaner situation when the tank is inverted the atmospheric pressure will in turn tend to flood our engine and if we are flying at half throttle or less, our engine will just quit.

If opposite (Our carb. Is tuned for a richer situation) when the model plane is inverted, our engine will have a hard time to get the fuel into its carb. And most likely will absorb a lot of air and the engine will quit as well.

If there is not atmospheric pressure, then we are possibly talking about an uniflow tank (enclosed, fully pressurized tank) which is not this case and changes everything as well as pumped engines as it was mentioned earlier.

Many things change in our lives, maybe physics changed and I was not advert, if so please just ignore this post.

HighPlains

My Feedback: (1)

We live in many alternate universes. However in MY universe, the tank level makes a difference. 2 cycle model engines really operate best when the center of the tank is no more than 1/4 to 1/2 inch below the spraybar of the carb when on suction.