Hobbsy

My Feedback: (102)

Woops, double post.

Hobbsy

My Feedback: (102)

Mostly that hesitation during acceleration is caused by fuel pooling in the crankcase during slow idle, your suggestion of a higher idle during flight is a good one. Or side mounting the engine will eliminate it also, which is what I do almost exclusively. This K&B 1.00 is very clean running side mounted.

Jennifer Curtis

A diesel shouldn't have fuel pooling
at idle. They are so stingy they will
run on vapors at idle. (The low speed
needle if it has one is more a lower
midrange adjustment.)

Maybe the tank is mounted too high.

Jenny

Hobbsy

My Feedback: (102)

Since kerosene doesn't evaporate very well and our carbs are very poor at atomizing it, a rich mixture is required to get enough burnable fuel into the combustion chamber. Let one idle for about 3 or 4 minutes and then pull the back plate you'll see pooling. Plenty of it.

Jennifer Curtis

Maybe I'm missing this because all my
diesels are NOT conversions, and thus
have carbs designed for finer metering.

Jenny

Hobbsy

My Feedback: (102)

What you got, I like em all. Mine are Fox, Super Tigre, even a 4500, an LA .46 and .65 an Irvine .40, K&B 1.00, PAW .40 and a control line PAW .19 that Dr. Diesel is going to convert to RC and install a collector ring on it. All are conversions except the Irvine .40 and the PAW's. At one time I had a Fitzpatrick .61 Conversion with a head made by AJ Coholic. An engine ported for 17,000 rpm makes a great Diesel except it will not handle large props. It blows a lot of fuel out of the carb on large props.

1QwkSport2.5r

I've found my .40, .45, .50, and .51 conversions all consume a large amount of fuel. They all will drain a 2oz tank very quickly running flat out slightly rich and just tight of burping. Less than a few minutes for sure. I had to open the idle needle some - maybe 1/4-1/2 turn richer from its last setting on 5% glow fuel. Main needles are around 1 to 1-1/4 turns open which is pretty close to a peak setting on glow fuel. I may get better fuel mileage if I changed my mix a little bit. I'm currently using 31% ether, 20% castor oil, 2% Amsoil Cetane Boost, and 50% undyed home heating Kerosene. My fuel cans hold a little more than a quart so the extra few percent fit in the can fine. I suppose if I dropped the oil to 15% and added 5% more kerosene perhaps it'll burn a little less fuel?

1QwkSport2.5r

The tank is not too high. I'm using a 2oz Hayes tank 3" behind the engine and the CL of the tank is below the spraybar about 1/2-3/4". I've run some tests with muffler pressure and some without. The engines I'm using make more power and throttle/idle better using muffler pressure. They do however use more fuel than I expected them to. They will run the 2oz tank dry within a short 2-3 minute run flat out. They'll idle all day long on the 2oz tank though.

Hobbsy

My Feedback: (102)

Mr. Davis' recommendation in his Diesel 101 pamphlet is to run them right at the peak with a 50% greater load than the glow load, not any rich. There is plenty of oil and a cool engine compared to glow. Combustion is more complete at peak further increasing efficiency. I have run them that way since 1990 and they don't even show any wear. My Fox ABC .74 and my Webra .91 ABN are my most run and flown Diesel conversions. The Webra happily turns a 14x7 three blade at 9,000, it is drilled and tapped for a Fox .74 muffler.

1QwkSport2.5r

If I run it at peak needle and comp settings, the oil is really dark. Not black, but really dark brown. I read that the oil color from the exhaust should be roughly the color of maple syrup or a little lighter. Is this not true for conversion diesels?

Hobbsy

My Feedback: (102)

In my experience no two engines produce the same color exhaust oil, so I ignore it. This is about normal.

1QwkSport2.5r

The oil color I experience is significantly darker than that. About the color of root beer.

I know no two engines will show the same traits, but what I've experienced has been pretty consistent. The Foxes run a little lighter than the Tigres. I suppose it could be due to the Kerosene I'm using - it's sold undyed and without any additives for home heating purposes. Perhaps it's a dirty kerosene? I'm keeping my eyes open for a place that'll sell me some Jet A to try.

Hobbsy

My Feedback: (102)

One of these days maybe you could try some road Diesel at a local station. Just to see what happens.

1QwkSport2.5r

I had read some guys use #2 pump diesel too with better results than Kerosene but the diesel up here is mixed with 5-20% biodiesel. I don't know if that would be good or bad.

1QwkSport2.5r

I tried a couple more props today.
Italian SuperTigre G51, narrowed spraybar, stock silent muffler

13x4W APC - 10,300 peak, good idle and transition from 2,500rpm. 9.1lb thrust approx. On 5% glow fuel it turned 10,800rpm.
13x6 APC - 9,900rpm peak, same idle/transition. It would idle close to 2,000rpm but would stumble a little in the midrange. 8.23lb thrust approx.

gerryndennis

G'day Tim,

As soon as you idle your Diesel for any length of time the engine cools down and is therefore retarded. It won't come straight up to full power until it re-warms. I think I mentioned way back in the thread that throttling may be better on a richer tune (although power will be down a bit). A higher compression setting and rich idle will help by advancing the engine during throttle up but be careful not to go too far with the compression. All the things the others have said here.

A different fuel mix (more ether) might work better too?

I agree with you about the consumption. My OS 20 gets about 15 minutes out of a 2 oz tank at reasonably high power settings, but my 40 FSR seems use fuel at quite a rate. It's running at 13000 rpm on a 10X6 though, it might be better at lower rpm on a bigger prop. I haven't done enough running with it yet to form an opinion but I'll probably use an 8 or 10 oz tank when I get it in a model

Regarding exhaust colour, dark oil can indicate an over advanced situation, but as you say engines will vary a bit. So as long as you are sure you aren't over advanced dark oil on its own isn't something you need to worry about.

I got an 800 to 1000 rpm increase when I changed from hardware store kero to Jet A. I also get a lot cleaner running with zero carbon build up in the engine now. It might be interesting to try the pump Diesel or Jet fuel if you can get it. 20% biodiesel might make your exhaust smell like McDonalds.

You are on the right track measuring thrust I reckon, it's not just about rpm. While a larger prop might technically give a lower horsepower out put, it may well fly the plane better. The weight and design of the airframe makes a big difference to which prop works best on any given engine. At the moment a wide blade (Graupner) 10X5 is looking quite good on my 20 on a 60" vintage model but we will see.

Great to see your Diesel experiments continuing

Dave H

1QwkSport2.5r

Howdy Dave H.!

I'm not all that concerned about the exhaust oil color as much as the sound the engine makes while running. I set the compression advanced enough to run clean, but not sound rattly. I've tried running richer and more advanced compression, but when it goes back to WOT (or 80% in most cases), it still stumbles and burps a bit and most of the time doesn't recover and I have to increase compression a little bit which once it heats back up is over advanced and rattling a bit. The G51 I ran yesterday throttled much better in the midrange without the need to advance the compression (ignition) if I let it idle at 2,500rpm instead of say 2,000rpm.

I havent had time to really research finding cleaner kerosene/Jet A, but when I do I'll try it out and post about it here. As far as the biodiesel goes, I'm not sure where they get their base oil from to make the biodiesel - I'm also not so sure how much is really in the mix since the decals on the pump just say it contains between 5% and 20% biodiesel. I am curious as to the cleanliness of pump diesel versus kerosene - I've been told #2 pump diesel has more wax/paraffin in it and #1 diesel is very similar to kerosene. So I suspect the pump diesel may burn dirtier and possibly with less power. Only testing it out will confirm or deny my suspicions. Time will tell. I'm almost out of fuel and need to restock up on ether. I get about a half gallon from 2 JD ether cans which costs me about $12 to make. I'm happy it is fairly cheaper to mix my own versus buying premix.

Mr Cox

This has been discussed many times on this forum. I believe that the consensus was that the colour is an indication of the temperature and not the correctness in the settings themselves. So a small prop and high revs will give a dark exhaust even at ideal settings.

From my own experience I have maple syrup colour on large props and mild settings. Sometimes not using wide open throttle but only up to about 80% (or so) as the last part will give very little gain in rpm while the running and carb settings can change a lot. This is especially true for conversions I guess where the carb is designed for glow engine use and much larger revs.

On some diesel with a very crisp throttle response the mid range is set leaner than it would be on glow. While the carb may look like it only has a regular air-bleed on it, the midrange is also leaned out by having different bores above and below the carb barrel. This is used on the MVVS Junior (2cc) for instance.

So on your super-tiger engine you might want to play a little with the midrange setting, a wonderful feature they included there.

1QwkSport2.5r

I was thinking of adjusting the spraybar as its in the factory position now, but as long as I don't idle the engine super low, it does throttle okay. I'm still learning how to set the engines so with time and running the engines more, I'll get it nailed. I'll mess around with more props too as I get time.

1QwkSport2.5r

Tried bigger [fake] lumber today. Italian ST G51 and 14x6 APC. Same fuel I've been using. - 50% kerosene, 30% ether, 20% castor and a splash of Amsoil cetane booster.

7,680rpm peak and a crazy low rpm (with good recovery!!) idle down to 1,500rpm or less.
http://youtu.be/niOaaNYg2Jk

Hobbsy

My Feedback: (102)

Nice, I may be able to do that tomorrow with the new Bowman ring.

1QwkSport2.5r

Here's the weakling Fox .50 that I have turning (if I can ever get it to start) the same 14x6. There is something about this .50 that just makes it a piece of crap. I wish I had a means of making the Fox .50 head fit the .46; the .46 has a chance of turning better rpm.

http://youtu.be/0kg0IQfv3HE

Hobbsy

My Feedback: (102)

I believe that Mr. Davis would suggest richening the HS needle a little before any compression change, Then do the peaking with the needle.

1QwkSport2.5r

I already had the needle peaked before I took the last video. My Fox .50 does not like to restart warm without having to increase the compression a bunch to get it started if it isn't immediately restarted after shutting down. When I fired it up from cold, I did open the needle 5 clicks which started it fairly rich.

Hobbsy

My Feedback: (102)

The new .51 ring is here, well packaged as always.