Maintainer - Bill Wallace, wewallace@watcgl.uwaterloo.ca
This is release 0.4 of this faq.
Some of the information here was taken from a pamphlet written by Dave Larkin. He sends a much more descriptive faq to people interested in ordering, and he has one of the most comprehensive lines of diesel engines at very competitive prices.
Other information has been taken from Eric Clutton's (small) pamphlet, as well as articles people have posted to the net, and comments that people have sent in via email.
Diesels are relatively quiet, fuel efficient, don't require a starter, glow plug battery, run cool (very good for in a cowl), are not sensitive to muffler back pressure (or rather are mildly sensitive) and have a very large flat section on the torque curve (roughly the same torque from about 4000 rpm to 10000 rpm, peaking at around 10000.) Since diesel is less corrosive than glow fuel, diesel engines generally die by trying to be flown underground rather than by wearing out (though they can wear out, I had a McCoy 0.049 that was fairly worn out, but considering the age ...)
A PAW 0.049 diesel runs $43 Canadian, so they are quite comperable to glow engines in that size. They are good engines for powered gliders for someone's first plane because of the noise and because a minimal amount of starting equipment is required (no glow battery, no starter (although they are hard to start the first few times)).
There are high performance diesels that don't follow the maxims above. They aren't very quiet, run very hot, and run around 12-16 krpm. I personally don't have experience with these, and so can't comment on them. They do get the good fuel economy though, and my understanding is that they aren't all that sensitive to muffler pressure, meaning that tuned pipes won't help.
Irvine diesels are reasonably high performance, and run very differently from the PAW diesels. I can't comment more since I haven't run any. Maybe someone could comment.
You can often get a few diesels from your local hobby store. They should be able to get MVVS diesels (very nice) and Irvine (very nice again). They also might be able to get the nice webra diesels. If you need to order one, here are some possibilities:
Both MVVS and Irvine engines should be available from your local hobby store or from Tower Hobbies. Webra diesels can probably be special ordered.
MVVS makes some very nice diesels quite reasonably priced. They include both a glow head and a diesel head. I haven't run any, but have examined them and found them to be quite nice.
Irvine also makes some nice schnuerle diesels. They currently make a 20,40 and 0.049 (replica). The are designing a 60 sized diesel that should be suitable for pattern type planes (if someone tries it, tell me and I will add that info to this list.)
Davis Diesel Developments makes diesel conversions for regular glow engines. I ran an 0.049 with a DDD head. It ran well, though it was VERY hard to start the first time, until I figured things out. There is a spring in the diesel head that keeps the compression screw from unscrewing. The spring had gotten wedged underneath the screw and kept me from compressing sufficiently to start the diesel. I can now hand start it, especially when it is hot. I have sold this since, becuase the crankshaft broke. This has been noted as a problem with the reed valve engines.
Other people have said that the DDD conversions are fine for ball bearing engines, but shouldn't be used for plain bearing engines since the crankcase tends to become oval around the crankshaft. Even BB engines sometimes give out. Diesel engines designed from scratch last longer and perform a bit better.
There are four types of fuel tubing that are fine for diesels. The black tubing is fairly flexible and can be taken on/off connections without heat. Unfortunately, you can't see through it. Tygon tubing is transparent, but is very stiff. I haven't used either gradsol or neoprene. I recommend using black tubing inside fuel tanks (for the flexibility), and tygon from the tank to the engine, with a short section of black tubing attached just before the engine to allow easy connections.
Hayes tanks are fine for diesel the way they come, but I haven't found any other fuel tanks that have bungs to be appropriate. Note that metal fuel tanks are fine. Note that the stoppers sold for gas are not appropriate for diesel fuel. They do last better than the regular white ones, but eventually the decompose (and make the engine very hard to run.)
Do NOT run a line to the muffler since water will then accumulate in the fuel tank. Water is not soluble in diesel and thus doesn't get flushed out of the tank very well.
All brands of plastic and fabric covering that I have tried are fine with diesel. Also, epoxy, dope, polyester resin are fine. I don't know about CA, or carpenters glue (I don't usually let those be exposed, you shouldn't either.) You can't use oil based paints, and I suspect latex paints might be a problem as well.
You can buy fuel ready made or mix your own. The ingredients are: oil (should be castor), ether (to help ignition), kerosene (the main power ingredient) and a cetane booster (to help running at high RPM's.)
If you want to mix your own fuel, here are some formulas:
33% castor, 33% kerosene, 33% ether, 1% Cetane booster - the standard fuel for breaking which has been used for many years. Quite a number of people have written me and told me that this has too much oil in it for running generally. This is the fuel I started on.
22% castor, 41% kerosene, 35% ether -what most people have recommended to me as a general running fuel in modern diesels (although PAW recommends more oil, several people have said they run better on less oil, take you choice.) This is my current mixture, although I haven't run enough yet to decide how I like it.
16% castor, 50% kerosene, 35% ether -what some people are recommending for modern ball-bearing engines.
7% castor, 2% cetane boost, remainder kerosene, perhaps with some amount of ether. The modern running fuel for racing diesels. Note that this is VERY hard on an engine. The needle valve must be set just right as well as the compression screw. A very small turn wrong in either will cook an engine on this mixture. To these formulas add the remaining 2-4% cetane boost. Cetane boosts are: Amyl Nitrate, Amyl Nitrite, or Iso Propyl Nitrate These are necessary to smooth ignition above 10000 rpm. Eric Clutton says that "Octane 104 Plus" also works, but I would seriouly question that as it octane and cetane are opposite measurements of the same type of thing (ie high cetane means low octane & vice-versa).
To get the ether, you can order it from Red Max (say Eric Clutton sent you) if you have a US address. Otherwise, buy "Auto Starting Fluid", freeze it for an hour, turn it upside down and spray out all the propellent. Use a can opener to open it and pour out the ether. You will need to use a bit more of this since it contains oils as well as ether.
Red Max will mix up fuel to your specs, given that your order is at least 4 gallons I believe (I haven't done this, so I don't actually know how many gallons).
The initial starts can be a pain. Try not connecting the fuel line, but priming it. Turn it over two turns upright, then two on each side. Keep a GOOD hold on the prop when you turn it since it can fire. Start with low compression and slowly increase until it fires. If it doesn't fire you might need a starter the first time. Be VERY careful since hydraulic lock is very easy to get with a diesel.
After this, set the needle valve out 2-3 turns, connect the fuel line and draw fuel through it. Start flipping again. When it starts, adjust the compression till it just misfires occasionally. Run it about 2 minutes, and then kill it. Then, run half a tank through, then two more tanks being careful not to let the engine overheat (do this by running at low compression, rather than at a speed you could fly at.) At that point, you should be able to start getting enough power out to fly, though if is still overheating, be careful. To tune it, start leaning it out. When it starts misfiring, add compression. At some point, adding compression won't help much. Richen it 1/2 turn, and decompress the engine till it misfires occasionally. Then compress just till it smooths out and picks up speed. If it doesn't pick up, then it is a little lean still. Do it again, until it picks up speed after compressing. Don't compress past this point, since the engine can be destroyed by that (just like running a lean glow engine.) You can run 1/4 turn rich the first hour or so to ensure that it doesn't overheat in the air. Diesels do NOT have enough power to fly until broken in a bit. They WILL overheat if you don't break them in, and are cantankerous during this period. However, this results in longer life. ABC diesels don't need as much break in, but still need more than a glow engine. Plain bearing diesels require LOTS of break in but give you lots of power when they are broken in.
After this, starts should be fairly easy. Just prime the engine, and flip it a few times. I usually start on my second or third flip. The first start of the day will probably require a bit of extra compression, say 1/2 turn or so, and maybe a couple of extra flips.
These are prop ranges for the PAW series of diesels. Other similar diesels will run similar props, but racing diesels need much smaller props as they turn them much faster.
0.1cc 0.006ci 3x1.5 or 4.5x2 cut down to 4"
0.2cc 0.012ci 4.5x2, 5x2, 4x3
0.5cc 0.03 ci 6x3 to 7x3
0.8cc 0.05 ci 5.7x3 to 7x4
1 cc 0.06 ci 7x4
1.5cc 0.09 ci 7x6 to 8x4
2.0cc 0.12 ci 8x4 to 9x5, or 10x4
2.5cc 0.15 ci 8x4 to 10x4
3.0cc 0.20 ci 9x6 to 11x6
3.5cc 0.28 ci 10x6 to 12x6
6.0cc 0.40 ci 10x8 to 14x6
.49 ci 11x7 to 14x6
.60 ci 12x7 to 18x6
Diesels don't run cool until after break in. During break in, they can get quite hot, just as hot as a glow engine. They also burn lots of fuel during break in. Do try to keep them cool, and shut them off if they get too hot during break in.
Choose a diesel the same size for a fast plane, or one size smaller for a slower plane. A diesel generally gives about the same power, or a bit less than an equivalent 2 cycle glow engine (equivalent in terms of ABC, schnuerle, ball bearings.) However, it turns a bigger prop, and thus is more efficient. That is, the output power to waste power is larger than for an equivalent glow. I haven't run any diesel larger than a 28 sized, and would appreciate comments on 40's and 60's, especially the MVVS 60.