engine tuning problems and more
 

hi to you all, i finally finished my first spad plane ,put the engine in and started tuning,and there started the problems: at first i had bubbles in the fuel line ,after asking some people i found out that the vibration caused them so i've put some foam between the fuselage and the tank and they stopped! so today i started tuning the engine .as i was playing with the rpm i decided to test the up and down of the plane. with full throttle i've pointed the plane down and then up slowly and it stopped! any ideas?my engine is a os 40 .thanks

RE: engine tuning problems and more
 

You are set too lean. You don't adjust for max rpm, you want to be on the rich side. Go to full throttle and pinch the fuel line just before it gets to the carbeurator. You should hear it rev up some before it lets off. If not adjust richer on the HSN. Then you can try to point the nose up at full throttle and it should stay at same rpm.

RE: engine tuning problems and more
 

Use the pinch test.

At full throttle:
Briefly pinch the carb supply line close to the carb. If the engine
1. Dies immediately - it's too lean
2. Runs for a while, does not pick up speed, then dies - it's too rich
3. Picks up speed briefly then starts to die - it's right

Dr.1

RE: engine tuning problems and more
 

Hi!
The pinch test isn't accurate enough! I know of no racers that uses that metod to set their engines.
The most common way of setting an engine is by era! That simple! Have an experienced flier show you how this is done.

RE: engine tuning problems and more
 

so its a problem of how rich or lean the engine runs! if i run it rich will this problem stop?if not what should i look next?i know from my trucks that if in idle i pinch the line and it revs up a bit and then stop its ok .but at their engines we have a high speed and a low speed to adjust ,at planes ?
as for a experienced flier at these places its so hard to find one, we even have shops (where we buy fuel)that they don't know even what glow plug to use!
they only flier i trust is about 165 km away.

RE: engine tuning problems and more
 

The pinch test is a very good measure of how the plane will fly for the "non-racing" crowd.

You need to couple this with nose up and nose down tests at high, middle and low throttle.

Basically adjust the high end needle until the engine runs at full throttle w/o cutting out while level on the ground with some smoke coming out of the muffler.

PINCH the fuel line and release.

If the engine speeds up immediately, lean it out a bit and try again.

Do this until the engine no longer speeds up when you pinch it, at full throttle, then back off about 3-4 clicks, making it a bit richer.

Now take the trottle down to idle.

Let the engine sit for 3 minutes.

During this time the RPM's should remain steady.

If the engine starts out fast, but slows down over time, it is too rich on the low end.

If the engine dies when you throttle down, it is too lean.

If it remains somewhat constant in speed, then pinch the tube going to the carb, and see how it reacts.

This time keep it pinched until the engine shuts off, but note how the engine reacts.

If it, sped up GREATLY then died after a few or many seconds, it is too rich.

If it sped up a little then died, it is probably OK.

If it slowed down almost immediately then died it is too lean.

Adjust the low end needle until the engine will maintain constant RPM's at idle.


Once you have this set, run the engine back up to full throttle and point the nose up about 45 degrees and hold it.

The engine should speed up somewhat but not die. Hold this for 30 seconds.

Then bring the nose 45 degrees down and hold for 30 seconds. The engine SHOULD slow down, but it should not die out.

If it dies nose up, it is too lean on the high end.

If it dies nose down, it is too rich on the high end.

Adjust until neither position results in the engine dying out.

Now take it back down to HIGH idle or about 20-25% throttle and do the same test.

As before if it dies nose up, it is too lean on the low end ( low speed needle ).

If it dies nose down, it is too rich on the low end ( low speed needle ).

Rinse, lather and repeat.

You are best off doing the tuning and nose up tests with about 1/2 to 1/3 of a tank of fuel.

You should have a bit more fuel in the tank for the nose down tests however.

RE: engine tuning problems and more
 

If it's an LA engine, close the airbleed screw about 1/8 of a turn and try it again.

RE: engine tuning problems and more
 

As for setting the RPM (if your using a tachometer).

Put it at full throttle
get it to it's max rpm, lean or richen whichever makes the rpm's go up
then when you have reached max rpm richen it about 200-400 rpm's

Obviously this is just a starting point, you still need to do all the tests to make sure it's running properly.

Good luck
Austin

RE: engine tuning problems and more
 

Yeah, and on some LA's it's almost impossible to lean them out too much...

I've had to enlarge the bleed opening to make the engine leaner.

RE: engine tuning problems and more
 

G'day Mate,
Easy to fix, DON"T point it down, all that does is expose the clunk to air, that air goes to the carby, engine stops, only point it up, & if the engine picks up some revs, it is OK, if it stops quickly it is too lean.
I know what you are thinking, this guy doesn't know what he is talking about, what happens when it's in a dive, well, this is what happens, the fuel stays at the back of the tank, & the clunk stays in the fuel, engine keeps running.
The only way that the fuel can go to the front of the tank in a dive, is if the fuel is moving faster than the plane, & of course that can only happen if the plane suddenly STOPS, then the fuel will move forward. The tank, fuel, plane & everything attached to it are all moving at the same speed, so nothing can move around inside the plane, it obvious, if you think about it.

RE: engine tuning problems and more
 

I agree with "don't point it down", however, just wanted to set the record straight.

When the plane is in a dive, the fuel may or may not be at the back of the tank. A plane in a dive will probably hit its terminal velocity fairly quickly, which will cause the fuel to fall to the front of the tank. There was a video posted in one of the forums a few months back that showed this phenomenon very clearly. Go [link=http://richter-lackierung.de/aktualisierung_2006/5MBVersionflycamefuntana.wmv]here[/link] to see the demonstration video,

What keeps your engine from dying during a dive is the residual fuel in the line. When the clunk is exposed during the dive, there will be a small bubble formed in the line, which will quickly pass through the needle valve. Most dives don't last more than a few seconds, and the airplane has plenty of time to recover.

I had one plane that had a very short feed line. In a dive, the engine would die every time. I added a couple inches to the feed line, and the problem went away.

When tuning the low end, remember to make small adjustment. 1/8 turn or less, and ALWAYS reset the high speed needle after EVERY low speed needle adjustment. This is crucial to ensuring you have the proper settings. The high speed needle setting affects both high and low end.

Brad
(edited to add video link)

RE: engine tuning problems and more
 

G'day Brad,
If the plane reaches terminal velocity, so does the fuel in the tank, so it stays where it is, for the fuel to move forward, it must be moving faster than the plane, how can it be moving faster? Gravity can't do it, because the plane & everything in it, is moving faster than terminal velocity.
The only way that any of this can happen, is if the plane is slowed down, by possibly a large prop, acting as a break, but that is unlikely, as most pilots don't throttle back enough to cause this slow down effect, they do full power dives, usually the plane pays the price, by snapping the wings, when it is pulled out of the dive.

RE: engine tuning problems and more
 

You are making a conceptual error related to "terminal velocity". Terminal velocity is that point at which the gravitational acceleration is exactly countered by the drag of air (essentially friction) on the air frame. Since the fuel in the tank is not experiencing the air flowing against it, it continues to experience the gravitational acceleration. It will "feel" 1 G downward force.

Watch the video, and you'll see it in action. Terminal velocity is not free fall. Your assumption that the fuel would not move is correct for free fall in a vacuum, where the object would continue to accelerate, and would not reach a terminal velocity. (for you purists, I know we're not talking about relativistic speeds. Newton is a close approximation for what we're dealing with).

Brad

RE: engine tuning problems and more
 

thank you all for helping me out,you are great! many thanks to opiose! you are a tuning master!i'll make copy's of your post and share it with fellow beginners ! you are all great!!!
i'm also very happy cause my question opened a subject thats really helpful for all beginners trying to understand and to learn more!
heres a new question : i've noticed that when i close the air with my finger so that fuel will come from the tank to the engine,after some seconds it goes back slowly .is this normal or do i have more problems ? when the engine is working its all fine.

RE: engine tuning problems and more
 

yeah its a os 40 la

RE: engine tuning problems and more
 

Then obviously you have never raced in the US. The pinch test is a superior method for new flyers to learn and is far more accurate than other commonly proposed subjective methods.

And yes tuning to a pinch is very common here in pylon.

John

RE: engine tuning problems and more
 

well i'm back home now and the results are:up at full throttle full tank it started ok ,took up rpm at about 10-15 of 30 sec stayed there,then down started ok until sec 3 lost rpm burped then died .i turned the screw with the spring clockwise (i hope i'm doing it ok) all over again up ok ,down burped at about sec 10.now it does not start and fuel goes back quicker .ideas?

RE: engine tuning problems and more
 

With an LA engine turning the low speed screw CLOCKWISE, will make the mixture RICHER.

The reverse is true of the high speed needle.

That the fuel siphons back into the fuel tank indicates that the high speed mixture is too rich as well.

In effect you've OPENED the mixture screw to the point that the fuel flows ( back ) far too freely.

When correctly set it should flow back slowly.

RE: engine tuning problems and more
 

As bkdavy says, this is a quite common misconception in the RC world.

Terminal velocity is NOT the speed of free fall in a vacuum.

In effect the fuel in the tank is not being subjected to the air resisting the plane's motion... and free fall is FASTER than terminal velocity speed, so the fuel falls forward.

This can and will lead to deadsticks on prolonged downline manouvers especially once the tank falls below 70-60% fuel remaining.

What keeps the engine running is the remaining fuel in the lines coupled with a lower throttle.

A full speed dive ( which still may be slower than 1G acceleration downward ) can quickly deplete the remaining fuel leading to a deadstick.

Manouvers such as blenders permit a plane to "fall" nose down for quite a long time... something that got me into this discussion, as my Funtana had a pronounced tendancy to deadstick at the bottom of a long blender...

The video shows all of this quite well and helps dispell the "fuel remains at the back" myth.

RE: engine tuning problems and more
 

Well that is why you must tune the engine with more fuel in the tank when you perform the nose down tests.

The idea is to keep the clunk in the fuel.

Do this on a tank that is less than almost full and you may indeed expose it, leading to poor results and/or tuning.

The problem with this, is that it is effectively a "best case" test for a nose down state.

In lieu of the presence of a header tank, it's better than nothing though.

What offsets the above is that the engine will run a bit leaner in flight anyway, so this test is safe.


However the nose up test can be made with far less fuel in the tank, so you can tune the engine for it's worst case condition...

e.g. nose up, running leaner as the tank empties.