franchi

HI All:

After getting what I perceive as the ideal comp and fuel adjustments on the ground, the engine goes over compressed after about one lap. I can not get a compression setting that is low enough to take off without this happening. I am thinking that I do not have enough ether in my fuel to keep the engine cool enough to prevent overheating and over compression.

Perhaps a leaking back plate?

Any suggestions?

Tia,

Fanchi

Mr Cox

Sounds more like a tank position problem, you could try putting it further out?

greggles47

Franchi,

I suspect the tank is mounted too far inboard and the engine is richening up in flight. Too much fuel = increased compression.

Otherwise how much ignition improver are you using?

franchi

Hi Guys:

WOW too rich! I never thought of that before! The tank is a nice wedge uniflow that has worked well with other engines.

I ain't very smart but I am sure that the engine is too lean as it is very hot when it lands! I do not think that an engine that is too rich and overcompressed would get hot while running. Again what do I know about running Diesel engines? I will switch tanks to determine if indeed it is a tank problem.

This engine is mounted on a full size Flite Streak. The engine has been chromed and fitted by Bob Oge so it should be correct!

I am using 1.5% Amsoil DII.

Any more thoughts about this problem!

Stay well my friends,

Franchi

Mr Cox

That fact that it runs hot just shows that it is not "happy", I think. It is not necessarily any evidence of a too lean setting...

The compression ratio and fuel ratio are linked inversely, i.e. a leaner setting needs a higher compression setting and vice versa. So if the engine runs richer in the air it will then show signs of overcompression as well. You can try to mimic this on the ground, if you want to. Tune the engine as usual and then richen the needle and see what happens...

If the engine would lean out during flight it would start to miss instead.

franchi

Hello Mr. Cox:

Yes, it goes lean, over compressed in the air and misfires no matter how rich and undercompressed when I launch it .I have changed tanks and nva to no avail.

Any more suggestions?

Stay well,

Franchi

Mr Cox

I don't know how it can go lean, overcompressed, and missfire all at the same time, something doesn't add up...

It could well go lean and missfire, but it cannot go overcompressed at the same time. To correct for that then move the tank inwards, and try again.
It could also be due to the engine getting unloaded in the air, this effect is largest for low pitch props so then try a higher pitch prop and see if that changes anything.

What engine and prop size are you currently using?

steve111

Franchi, if you really want to see a diesel run hot, going overcompressed is the way to do it. A lean setting will run a bit hotter than normal, but ultimately the misfire will cause it to be self-limiting, so a lean diesel won't get as stinking hot as a lean glow.

As Mr Cox says, having it misfiring and overcompressed at the same time doesn't make a lot of sense. I've seen plenty of misfiring diesels and quite a few overcompressed ones, but never the two things together. I also don't think I've ever seen a misfiring diesel get really hot.

qazimoto

My Feedback: (1)

Franchi, you say that you're using 1.5% DII. How much Ether and Oil are you using and what's the engine. Iron/Steel engines like lots of Castor.


Bob Orge certainly is a competent engine man.

Is the piston tight in the chromed bore?

Has the p/l combination been run in on the bench?

We've become used to taking engines out of the box ready for use.

However some piston materials do tighten up in the early stages of running in.

The crutial question is does the same engine heat up under load during a decent run on the ground?

franchi

Hi All:

I just came in from running my ETA Mach II engine and the smell of the fuel brought back memories!

I think that the engine was going over compressed and sagging rather than what I described as misfiring. I just needed a hit of Diesel fuel to bring on an accurate flashback! Lol

The engine is a ST G/20 .15D an the prop is a Cox 8x4 gray plastic.

As Mr. Cox suggested, I am going to move the tank outboard about .125" and see what happens. If this does not work, I will try .250" and then ????

Thanks very much for all of the help!

Stay well my friends,

Franchi

franchi

Hello Gaz et.al.:

Perhaps this engine just needs more time on the bench. I will call Bob about this question.

Yes, there is a great p&c fit It is an iron and steel p&c set up.

Thanks for the replies..

Stay well my friends,

Franchi

My fuel consists of 25% castor oil

35% ether

1.5% Amsoil DII

The remainder is kero

steve111

In answer to your initial question, then, I don't think there's any way you've got too little ether.

Have you tried it with a bigger prop, something like an 8x6 or 9x4? It won't need as much compression, and won't be revving as hard - might just make a difference.

franchi

Hello All:

When I asked about too little ether in my fuel I was concerned about the possible loss of ether due to "old" fuel. A friend who has used Diesels all of his life suggested that this may be the problem. Since the ETA engines started quickly and ran well, I doubt that the ether content is low.

Thanks for all of the suggestions

Franchi

Mr Cox

An 8x4 is a fairly low load, and with the low pitch it will also unload a lot in the air.
I suggest trying with an 8x6, or even 9x6 instead and see if that changes anything

Jennifer Curtis

My PAW .15 does something like yours if there isn't
enough ether. Basically it runs hotter with less ether.
It also takes more compression with less ether, both
because it is harder to ignite with less ether, and the
needle is set "leaner" due to less fuel to air ratio
with higher kerosene percentage.

So the engine starts off ok, but due to running hotter
and with higher compression, the heat builds up and
the engine begins to labor (running over compressed)
Mine is an RC so I can lower the throttle and the engine
will cool down a bit and run better till I land and re-adjust.
(I notice that the engine is really hot.)

In a case like this, I lower the compression a bit, till
it begins to miss consistently, then run at full throttle
until it heats up again and smooths out a little and
has enough power to take off. As it continues to
heat up, the compression rises and the plane flies ok.

When I'm done for the day, I go home and mix up
some new fuel, and the problem goes away.

I had this problem more when I used Snap starter
fluid for ether. When I found out it has less actual
ether in it than John Deere starting fluid, I switched
and the problem stopped happening so much.

By the way, I use an APC 9x5 propeller. I'm not
sure, but I think it is turning about 11,000 rpm.
It used to turn about 14,000 but its old and worn. (which
is why I need to wait for it to build up flying power).


Jenny

DaveyMo

Ladies and Gents:

The perpetual "noob" in me strikes again. In the discussion above, I'm confused about the effects of moving a tank. Raising and lowering it, I can understand. However Franchi refers to inboard and outboard tank movements in what seem to me increments too small to effect centrifugal force and fuel draw. I must be missing something here! Can anyone help straighten out my gray matter? Thanks!

Davey Mo

Jennifer Curtis

drawing fuel inwards against centrifugal force is
similar to drawing it upwards against gravity.

Jenny

DaveyMo

Jenny:

At first I scratched my head regarding your explanation, then the light bulb finally came on. I realized that when Greggles and Franchi discuss inboard and outboard tank mounting adjustments, they refer to just one end of the tank (i.e., the fuel pick-up end). Is this correct?

Thanks for your enlightenment!

Davey Mo...

Mr Cox

The engine is in an control line, CL, plane. There the centripetal forces dominate over gravity, and moving the tank outboard will have a similar effect as to moving it downwards on an RC plane.

qazimoto

My Feedback: (1)

Yes it is correct!

For a side mounted C/L engine we're talking about the relative positions of the tank fuel pickup and the centre line of the NVA hole in the venturi in the Horizontal plane . I'll try to post some explanatory pics later today.

steve111

I'm always pretty happy to see around 12000 on a 9x4 with any sport .15 diesel. 11000 with a 9x5 would be in the same ballpark. If you've got a PAW .15 that used to do 14000 on a 9x5, you need to do whatever you can to get it back that way, because that's just spectacular. In fact, it's over .6 bhp.

qazimoto

My Feedback: (1)

It seems to me that a Cox 8x4 prop would be ideal for an Super Tigre G20/15D in a control Line model. It was a high performance engine in it's day and designed to rev-up. Mine love APC 7x6" props.

An 8x6 or 9x 4 or 9x5 is just too much load for it.

On the other hand an APC 8x5 on my Oliver mk3 pulls along very nicely in a c/l Peacemaker. I changed it to an APC 9x4 and it was still too fast. It could probably turn even more diameter.

Horses (or props) for courses... .

Jennifer Curtis

No that is NOT correct.

In an RC plane it is not the position of the fuel pickup,
it is the level of the fuel in the tank. This is why we notice
the engine running lean near the end of a flight.


On a control line plane, the fuel sloshes to the side of the
tank the same as water in a bucket when you swing it around.
(try the bucket thing if you haven't) Centrifugal force is pulling
the fuel horizontally just like gravity pulls it down.

Moving the tank outwards, away from the center of the flight
circle, makes the engine have to suck harder to pull the fuel
against the centrifugal force into the carburetor.

You could have a very large tank, mounted even with the
engine, but with the pickup very far on the other side.
The engine would only have to suck the fuel "up" a short
distance, even though it would go through a long tube
to get there.

If you can't picture this, think of a watering can. The spout
goes to the bottom of the can, but when the can is full,
you only have to tip it a little to get it to pour.

Jenny


from the en

qazimoto

My Feedback: (1)

Jenny,

I'm not disagreeing with you. What you say is correct (of course) but I need to elaberate with some pictures.that explain what I mean. Right now I'm busy watching Eurovision. I'll do it in the morning.

Jennifer Curtis

You had me questioning myself. There is no way that
engine was producing 0.6 HP It may have made 0.4 HP
because I remember it being comparable to my OS 26 surpass
(on 5% nitro). I went and checked my logbook, and there it was:
23 years ago, apc 9x5 at 14,000 rpm on standard equal parts fuel.
I could have written it wrong (an 8x5 prop would give about 0.4 hp)
but I'm sure it wasn't a 4" pitch. I remember it was too slow at 4".

My log also showed that the con rod wore out very quickly at
only 49 flights. After fixing it I could only get around 12,000 rpm.
Flights were not as "bright" bit still fun, and fuel consumption
got really low.

I tached the engine yesterday, at 10,500 rpm with the same
apc 9x5 prop. That is a pretty dramatic drop, but the plane
still flies, and is still great fun. I doubt parts are still available,
so I probably won't fix it when it is all used up. I'm pretty
happy with over 23 years of regular flying on one engine.

Jenny