1QwkSport2.5r

This thread is intended for .20-.35 sized diesels which would likely be conversions since there aren't many purpose built diesels this size.


My smallest diesel (conversion) thus far. K&B .20 Sportster with Davis Diesel conversion head. I have a .28 Sportster that this head will fit as well. Haven't run it yet with the diesel head, but it's been run on glow fuel awhile. This .20 was not run much before I acquired it, but it was run hard (REAL hard) and seemingly put away with saltwater in it. I didn't have very high hopes that it would run all that well, but it actually runs nicely on glow. The piston and cylinder seal is quite nice despite being horribly abused previously. If I get some warm enough weather to run it this fall, I will. Otherwise it might have to wait until spring. It has a 9x6 prop on it now, with a likely target prop of 10x4-10x5 or maybe even a 10x6.

Some before pics (upon receiving and disassembling the .20) and with the engine cleaned up and diesel head fitted. She was awfully crusty when I got her..

Hobbsy

My Feedback: (102)

I have two Irvine 20 somethings, a .25 and older .20 black head with a Davis head. The .25 wears an AJ Coholic head. The .25 turns a Graupner 12x5 at 8,870.

1QwkSport2.5r

I don't know that I'd try a 12x5 on this .20 - the rod isn't as beefy in the .20 as it is in the .28, though it's been said a K&B 3.5cc conrod will fit the Sportster .20 and is much beefier. I'll see what happens. The small case Fox .40 supposedly won't handle diesel duty, but mine hasn't blown apart yet... Time will tell.

Those Irvines look nice, Dave. I picked up a Dykes ringed .25 sport for a friend of mine. I think I paid $20 for it from an estate.

Mr Cox

The Irvine .20 diesel are great, they are ABC engines while the glow version also came as a ringed one. The diesel engine has a much smaller carb than the glow version. So this is a good indicator of how any diesel conversion should be made I think. I.e. you need a good compression seal and a smaller carb for the lower revs.

There is also the PAW .19 RC engine which is still being made.

Below are a two pictures with the two Irvine engines, glow and diesel;

1QwkSport2.5r

I've been under the impression that the go-to metallurgy for diesels is iron/steel, but I can see ABC being a good metallurgy as well. I've heard some say that using an ABC engine for diesel use is a waste of the metallurgy, but on a sport engine, I don't see much difference. I'm not much a fan of ringed engines, especially for diesel use, but it certainly works. A couple of my bigger conversion engines are ringed while the rest are ABC or AAC.

Mr Cox

I don't think that there is any go-to metallurgy for diesels. It is more a historical reason that diesels where iron/steel constructions. It may not matter much so for sport applications, but the finest engines in my view are the ABC and AAC engines. You see this from Enya for instance, they started with iron/steel construction in their diesels then move to AAC and ABC constructions.

The Parra .15 engine is offered in all three versions, but I have not see any direct comparison numbers for them.

1QwkSport2.5r

I agree that ABC and AAC are the best with the latter probably the better of the two. I say this in general. In any engine whether it be glow, diesel, or otherwise, that proper sealing of the combustion chamber is paramount for best possible power production and the tapered bore engines are probably the king in this respect. Iron steel engines can't be overlooked either as they can have a superb piston/cylinder fit (from reputable manufacturers of course) as well with their main downside being that they have a heavier rotating assembly and slightly more friction since the whole piston is contact with the liner for the whole stroke of the engine and a tapered bore is only in close contact with the bore at the top of the stroke. Of course there is the oil film that prevents the piston from actually contacting the bore, but I don't think iron steel liners ever have much taper to them compared to an ABC/AAC engine.

aspeed

Iron/steel liners should have a taper just like an ABC or AAC, or ABN or whatever, if they are made right. A ringed motor, not. The old Cox stuff had a taper that was quite accurate, most of the reason they worked so well. For diesels, maybe the ABC might not be ideal when they get hot, as the liner will get looser, and the compression will get away. Steel, or AAC might be a better choice IMHO. I will admit my experience in diesels has not been good. I will try again soon after 40+ years. To keep on topic, I wonder how the car motors in the .21 sizes would hold up to the diesel stresses. There are some good choices like Picco and Novarossi. DD tried it with some success.

wnewbury

My PAW 19 diesel runs very well but the smell of the fuel thoroughly turns me off.

Mr Cox

The trick is to wipe everything down at the field and to leave the rags/paper towels there.
A small price to pay for a great day of flying.

1QwkSport2.5r

The conrods would be the questionable failure mode. DDD has a replacement conrod for the Traxxas 3.3 because the stock rod is somewhat weak. Airraptor says the Traxxas 2.5 makes a good airplane engine. That engine has a square bore/stroke ratio and is supposed to turn some respectable rpm with a prop. They're true ABC too.

I'm not so sure the taper lasts in an iron steel engine (if present to start with), but I don't have any bore gauges to check a liner to find out. Not saying it isn't true, I just haven't found any info that says they are supposed to be tapered?. I have checked some ringed engines for taper and some are indeed tapered. I have some STs that have a slight taper as does a ringed Fox liner. Not tapered as much as an ABC of course, but it's still there.

aspeed

The Cox .049s you could push the piston most of the way up the cylinder, and then there would be some resistance. After running for a while, the piston would go right up and through the top. It would then either be a little faster because of less friction, or it would not start. Some of the old Supertiger G .15s had very little taper, and we would lap out the bottom a bit. They ran a bit faster that way. It was a rush job at the factory I guess, not the way it should be. They were steel. It would be hard to measure, Likely just a couple tenthousandths ".

RichardGee

My Feedback: (156)

I have owned and run two dozen diesels in all sizes. Two of my best handling diesels were the Sharma .20 and PAW .35 TBR. Both were RC engines and would idle and throttle well. The Sharma was very crudely made, both inside and out, but started, ran, and throttled amazingly well. The PAW .35, while totally antiquated by today's model engine standards, was also an easy handling and well-behaved model RC diesel. It would idle forever and would in fact recover quite well from an extended idle.

aspeed

Funny how the crudest castings seem to run better than the nice shiny ones. Maybe the rough ports help, or the type of sand casting is more stable? I have noticed this as well.

1QwkSport2.5r

Its well noted that a rougher finish in the fuel flow path aids to fuel atomization, so I can see where a more crudely cast/machined surface will perform better than a finely polished piece. It's probably more important for a diesel to have those rougher surfaces (added turbulence) as the fuel doesn't atomize nearly as well as gasoline or glow fuel does since the only part of the fuel that evaporates is the ether.

earlwb

I have a PAW .19 diesel and a MVVS .25 diesel engine. The MVVS came that way from the factory too. MVVS made some diesel conversions for some of their engines. Where they had a glow and diesel head for them.

I also have a PAW .29 and a Aurora .35 PAW clone too. Plus some Drone .29's with one .29 converted for RC as well.

1QwkSport2.5r

How do those MVVS diesels run, Earl?

wnewbury

My 2 MVVS .15 diesels run strong. But I haven't tached them. They remind me of team race diesels, but I'm sure they're de-tuned. One has a throttle.

1QwkSport2.5r

I'll have to put an MVVS diesel on my wish list as well as an Enya diesel. The Enya SS15D looks like a nice engine.

earlwb

They run really strong. Being Schneurle ported with a large intake too. They do turn large propellers OK. But being more high performance they use more fuel though. So they aren't frugal on fuel consumption.

1QwkSport2.5r

I'd guess they're more of a higher revving diesel then - higher than the typical 10k?

I know some of the high performance diesels turn some crazy rpm, but I don't think they're RC.

Hobbsy

My Feedback: (102)

[TABLE]
[TR]
[TD]Prop.[/TD]
[TD="align: center"]Irvine 20
5mm carb[/TD]
[TD="align: center"]Irvine 20
6.5mm carb[/TD]
[TD="align: center"]MVVS 21
6.5mm carb[/TD]
[/TR]
[TR]
[TD]11x6[/TD]
[TD="align: center"]6300[/TD]
[TD="align: center"]6800[/TD]
[TD="align: center"]8000[/TD]
[/TR]
[TR]
[TD]10x6[/TD]
[TD="align: center"]7400[/TD]
[TD="align: center"]8400[/TD]
[TD="align: center"]9600[/TD]
[/TR]
[TR]
[TD]9x6[/TD]
[TD="align: center"]8000[/TD]
[TD="align: center"]11000[/TD]
[TD="align: center"]11500[/TD]
[/TR]
[TR]
[TD]8x6[/TD]
[TD="align: center"][/TD]
[TD="align: center"][/TD]
[TD="align: center"]13000[/TD]
[/TR]
[/TABLE]
These numbers are from an independent test on Mr. Davis' site.

Tim, are these numbers similar to yours for a .20 sized Diesel, Thanks, Dave

1QwkSport2.5r

Dave - I haven't run the Sportster .20 conversion yet. The weather around here was rubbish (rain and crazy wind) earlier this week and now we're in the low-mid 30s for temps.. I'll try running the .20 if the temps come up a little next week. I know my .20 turns an 8x6 at around 14k on 5/20 glow fuel but I'll likely not use that small of a prop on it using diesel fuel. I haven't tried any other props on it as it needed some break-in time last time I ran it. I'll post back when I run it and see what I get with it.

Hobbsy

My Feedback: (102)

Great, thanks, I may fire up the Irvine .20 today.

earlwb

Here are some pics of one of my old first model Drone .29's being test run. I made an adapter and put a Thundertiger .15 carb on it. The engine turns a 12x8 propeller at a little over 6100rpms. At idle the engine tends to cool off quite a bit and then it is sluggish getting back up to speed, at least until it heats up again. But then many RC diesel engines tend to have that problem. The Drone engines were long stroke engines with a really long stroke, so they tended to not turn high RPMs. But they could turn large props good though. The control line prop to use was a 11x10 or 11x12 prop as the higher pitch made up for the lower RPMs.