franchi

Hi All:

I read a page concerning adjusting a Diesel engine. It was very different than what I have been using formany years. I may have been doing it all "wrong" for many years.

The new information stated that one should:

Allow the engine to gain operating temperature. Perhaps a minute of running.

Back off the compression until the engine begins to miss from being under compressed.

Lean the NV until the miss dissapears.

Reduce the compression until the engin begins to miss due to being under compressed.

Repeat these steps until the engine is running at its peak.

Does less fuel mean less compression?

For a flying setting, should one adjust the engine to be a bit rich and increase the compression to adjust for unloading in the air? Does increassing the compression compensate to advamce the timing of the engine to compensate for the increase of rpm due to unloading in the air? I did this and the engine was very over compressed while in the air!

Still learning,

Franchi

Lou Crane

Franchi,

Sounds reasonable, given that the initial minute warm-up included backing off compression to missing, then bringing it back up just enough to smooth the run.


Fine-dialing the settings should work better once engine temperature is stabilized.

The general idea is that the prop unloads as the plane reaches flying speed, allowing greater RPM, so comp and needle should match the in-air RPM. Yes, a bit higher comp and a bit richer needle. Adjust from there depending on how the engine responds in flight.

Jim Thomerson

I've flown various diesels in Old Time Stunt control line airplanes. Start the diesel, let it warm up, check the color and amount of oil in the exhaust. Fly the airplane. If the engines loads in maneuvers, it is over compressed. If it misses in maneuvers, it is too lean. Once you get a satisfactory flight, be very reluctant to change settings.

gcb

Franchi,

Are you sure you read that correctly? After the engine has reached operating temperature I usually back off a little on compression to make sure it is not over-compressed. After that I usually increase compression and tweak the needle for max until I get to the flat spot where increasing compression does not increase RPM. This yields a starting point where, as Jim says, you need to fly the plane so the engine will unload and you can make final adjustments.

Of course there is seldom just one way of doing things.

George

steve111

I'm with Jim, in being reluctant to change a good setting. Most of my diesels can be persuaded to start on the last good compression setting without too much trouble. Generally I'll open the needle 1/2 to 1 turn. The engine will usually be misfiring due to not having enough heat in it, but as you lean it out and it warms up, the misfire clears, and away you go. All that presumes you have a good setting to start with - if not, George's advice is good.

gerryndennis

Hi Franchi,

Someone has got it a bit backwards. If you back off the compression until it misses then lean the needle it will miss even more! You will never get to the peak this way, the engine will simply stop due to being under compressed and over lean.

It's all about advancing and retarding the ignition point, a retarded diesel will miss, while an overly advanced one will go hard, slow down, sound metallic, overheat etc. Leaning, reducing compression, and cooling will retard the ignition; richening, increasing compression, and heat will advance it. The correct setting is a balance of mixture and compression plus the effect of the temperature, hence the requirement to allow the engine to warm up before finalising settings. ( There are other factors such as prop load, fuel mix etc but assuming these aren't changed...)

The normal way to do it is to lean until it misses, then increase compression to smooth it out then lean some more, rinse and repeat. Minimum fuel and maximum compression as my diesel instructor used to say (by which he meant minimum compression for the needle setting but because the needle was leaned the compression was also higher than before)

There is a compression setting to match each needle setting so you don't have to go fully lean for flying unless you want maximum power/endurance. Same for compression, you can run quite under compressed for a lower power setting. This is what used to happen in 'the day' to set up free flight models. You would start your trimming flights rich and under compressed, sometimes with the propellor on backwards so that you would avoid crashing due to too much power.

Yes you will probably need to increase the compression slightly above that required to just stop the missing to allow for the prop unloading in flight, but don't go too far. The best way to damage a diesel is to over compress it.

Diesels seem to throttle better if set a bit on the rich side, either on the top end or at idle.

You can often start on the flying compression setting but you will probably have to richen the mixture until it warms up (as per Steve111). This seems to be the way many people go with modern engines converted to diesel ie richen a bit, hit with your electric starter and lean to max having never touched the compression.

Vintage diesels may require the compression adjusted before starting depending on the prop load. A big (high load) prop requires low compression to run therefore may require an increase of compression to start, while a small load prop may require a reduction in compression to start. The same applies to modern engines.

Dont be afraid to adjust both compression and mixture each time you start if that is what is required.

Dave H

Also still learning

gerryndennis

BTW Steve111, I just received that ED Racer that you were looking at with Dave Owen the other day. It ended up with a conical piston and is running great.

Dave H

Mr Cox

Where did you get the instructions from? It doesn't sounds right to me at all...

A leaner setting requires higher compression ratio, while a richer setting will allow for a lower compression ratio setting.

Once up to temperature I would lean the mixture until it misses and then increase the compression ratio until the missing stops. If the revs now are higher than before, then you are going in the right direction. If there is no gain in rpm with the new setting then use the lower compression setting to reduce the load on the engine.

When the engine unloads in the air, it needs more fuel not higher compression ratio (in general), so set the engine richer on the ground with the same compression ratio. On RC engines there will always be some misses at reduced throttle settings, don't raise the compression too much much to remove this, it will just lead to an overcompressed setting at the high end.

franchi

Hi All:

Thanks for all of th replies.

I will try to get out today to fly a Diesel to see wha the results are with the G20/.15D powered Flite Streak.

I have been tuning my Diesel engines as described above for many years and never had a problem. However the last time that I flew, the engine kept going lean and overcompressed once in the air. Today, I will be more observant!

I really enjoy the Diesel "difference" as I find them to be quite a bit fun!

At the present timem I have the folowing planes frady to fly:

MVVS .15D7 in a Tom Tom

Fox .15 Davis Head In a home built stunter

O.S. FP .40 with Davis Head in a scratch built Zero Stunter

G20/.15 in a Flite Streak

When the last gallon of Diesel fuel is gone I will stop flying Diesels. I can not get much enjoyment from flying Desels when fuel is $70.00 per gallon!

How much are you chaps paying for Diesel fuel around the world? Can you purchase ether?


Stay wll my friends,

Franchi

greggles47

Franchi,

Ether is available via a couple of team race experts, who buy in bulk to supply those who need it.

Yes diesel fuel is expensive, but if you stop to count the cost of things you enjoy, you'll find a way of stopping just about everything.

steve111

My fuel costs me about $17 a litre. About as much as it costs to drive my car 130 km, or for a couple of decent hamburgers, or for about a third of a carton of beer. Guess what gives the most enjoyment (no disrespect to a decent beer).

qazimoto

My Feedback: (1)

I guess that mine would be under $20 a Litre as well.

It's struck me as deeply ironic that individuals in the US can legally buy enough automatic firearms to equip the Army of a small third world country, yet can't buy Ether because it's a dangerous material.

:-)

ffkiwi

I've been mixing my own for decades-at current NZ prices for the constituents a typical diesel mix-25% oil, 33% ether, 40% kero and 2% DII would cost me ~NZ$20.66 or US $17.56 a litre. 64.5% of the fuel cost is in the ether.The figures from the Aussie forum members are comparable taking the exchange rate into account. Currently ether is more than twice as expensive as nitromethane! [the example above is based on the current retail prices for oil and nitro on popular outlets such as TradeMe (www.trademe.co.nz)-but my actual costs are lower because I have decent stocks of the components obtained some time ago. Depending on your source-it should be quite feasible to produce diesel fuel for ca US $18/A$19/NZ $20 per litre. Your choice of oil will impact on the cost-the example above was based on Klotz Benol, Klotz Supertechniplate would increase the cost by about $1 per litre

By the way-at $70 per US gallon-your diesel works out at US $18.40 per litre-or NZ $21.50 a litre-I don't think you have any reason to gripe-you're paying pretty much the same as anyone else in real dollar terms-and most of us are mixing our own, so can't benefit from bulk component sourcing like a commercial fuel supplier.

ChrisM
'ffkiwi'

franchi

Hi All:

Thanks for all of the replies.

NO, iidividuals CAN not purchase automatic firearms in the U.S legally except with a Class 3 firearms license. The last time that I checked the class 3 license was $250.00 but to transfer the weapon was $2500.00. This fee had to be paid each time that the weapon was sold to another holder of a class 3 lincense holder. Of course one is investigated and approved by the BTAF before he is issued a class 3 license. I think that this law went into effect in 1936.

We can not purchase ether because we may use it to manufacture drugs. I remember being a child and purchasing 3 oz. of ether to run my model Diesel engine. I was about 9 years old and it cost me 15 cents per oz. form the local drug store, No questions were asked! A friend of mine who spent his career as a chemist, spent a great deal of time attempting to find a source of ether. No luck.

I do not think that I was complaining about the high cost of Diese fuel but perhaps stating the difference in cost between Diesel and glow fuel. Let's see: $15.00 for glow fuel vs. $70.00 for Diesel. Easy choice for me. Lol

Stay well,

Franchi

ffkiwi

I've never understood the utter misconception prevalent among some newer (particularly in the US) diesel users that diesels are somehow ''much cheaper to operate"-that hasn't been the case in real money terms since the 1950s as far as relative fuel costs are concerned. The lower specific fuel consumption pales into insignificance once the cost of fuel is factored in. There are multiple reasons for taking up diesels-but cheaper running costs doesn't enter in to it....
As a junior I did much the same as you did-bought ether from the local chemist-but that was in the late 60s and early 70s...although back in my junior days I didn't even need to go to that extent-the club mixed its own diesel and glow fuel which it sold to members pretty much at cost. For a modest additional charge the local chemist would crush a couple of capsules of amyl nitrate into the diesel mix he'd made up for you. But the club diesel mix was 33:33:33 and the glow was 75:25-if you wanted any other mix you had to source it yourself-either from the local model shop or the local chemist.....

ChrisM
'ffkiwi'

Recycled Flyer

I seem to recall 'reviews' between high nitro glow fuels and model diesel fuel on a famous website that claimed it was about equal in price, and yet the diesel had less fuel consumption.

Perhaps the memory has been milked?

qazimoto

My Feedback: (1)

I've never worked it out before but 10% Nitro content glow fuel cost me just under $AUD7 a Litre, and 25% just over $AUD10 a Litre. You'd have to amortize the cost of a glow plug and the starting battery or device as well I suppose. Even so diesel fuel is more expensive by volume than glow by a factor of 200 to 300%. To get the volume cost in US Gallons you have to multiply by about 3.8, and adjust for the exchange rate difference.

But the cost of diesel isn't really an issue for me either. I spent almost $10 on lunch at work today, and bought coffee for a colleague and myself late this afternoon for about $8, and the bottle of white wine I took home to have with my wife with dinner was another $10. Life's expensive!