earlwb

Here is my example made circa 1947. .29 cubic inch displacement. When I first got it, I was bummed out some as it didn't have any compression. But when I disassembled it, I discovered it had 1 and 1/2 head gaskets on it. yes that is one complete gasket and 1/2 of the second gasket. After reassembling it and oiling it, it now has pretty good compression. But I am not sure that fiber gasket will hold or not. I plan on making some thin aluminum head gasket/shims up later. I think I'll replace the head screws and cylinder base screws as they seem to be a little bit too short for the engine.I don't know if the original screws were that short to start with, but the boles are more deep so it is easy to use some slightly longer screws.
So does anyone know if the engines used fiber head gaskets or soft metal head gaskets?

Oh yeah here is a pretty good history and story line about the Drone engines. http://modelenginenews.org/ad/drone.html

The engines were arguably the first production model diesel engines made in the USA. They were notable in that they were a fixed compression design and did not have a variable compression head on them. The original fuel was 75% ether and 25% oil at the time. the engines weren't designed to rev up high, like the old gasoline spark ignition engines, they turned modest RPMs, but they turned larger props or props with high pitch angles on them. For control line the standard prop was a 11x10 size wood prop.

When they frst came out they were very popular. They had a lot of power and could fly control line planes without overheating like some of the model gasoline engines were prone to do. Plus they weighed a lot less and did not need to carry along a heavy battery or ignition coil and spark plug for the engine inside the plane. The engines and the pilots who used them actually won many contests and competitions ot the time too.










The connecting rod sort of looks like it was hand filed to shape. The piston gudgeon pin still has the small copper or brass end caps on it to protect the cylinder from the gudgeon pin.




I plan on scratch builiding my own ball bearing Drone engine from a set of castings I got fromDavis Diesel Development a while back.

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I have four of the second ball bearing versions of the Drone diesel. All four had fiber head gaskets. All four blew after a couple runs the best lasting 18 runs. Of course these engines were over 55 years of age when I ran them. I had some soft alumunium hwad shims made up with various thickness. My notes indicate .020 .030 and .039" shims. Maybe others and extra of each size. With larger props 13/7 or 14/6 two of the .020 shims worked well with modern model diesel fuel. Jack

gmedson

Hi Earl - Those are beautiful castings from DDD, aren't they?

I have a variable compression head on my plain-bearing Drone. Has socket-head screw for compression adjuster, bearing against a contrapiston in the head.

According to a note in Tim Dannels' AMEE, Leon Schulman said that variable-compression heads were offered as accessories but not as original equipment.

Regards. -Gary

earlwb

Thanks for the information Jack. Yeah I had my doubts about the old fiber gasket, it looked like after 64 years it might have decomposed or something. it looks more like a thin layer of asphault like stuff now. I'll make up some new thin metal shims or gaskets before I try running it.


Gary, yeah I thinkDDD did a nice job on the mold for these castings. I did happen across a couple of bronze bushings and a couple of nice ball bearings to use with the engine castings. So one of these days I'll get started on it. I think the thing about machining the castings and making the parts is all of the special fixtures and tools you need to custom make to do the machining. You can spend all day making a fixture just to machine something for a minute or less.
it would be nice to run across one of those variable compression heads one of these days, that I can get. I might try to make one myself too.

ddd

All engines in the USA at the time used fiber rather then metal head gaskets. It saved many a Drone by blowing. Thanks for showing our Drone castings which are listed Ebay for those that need to repair or build a Drone.

gmedson

Earl - Diesel heads are not difficult to make. I model mine on Davis heads, using a Helicoil for the compression adjuster with a very long set screw or socket-head screw at a right angle, bearing against the Helicoil. This squeezes the coil and provides interference with the adjuster so it holds its setting. Neat arrangement!

I have tried both iron and aluminum contrapistons in the head bore and have not found significant difference. Although I want to believe that iron should be better because it should hold heat better at low rpm and idle. I use Viton o-rings and have found that one is enough. I really do think that using an o-ring seal is good for maintaining combustion temp at low throttle and idle because the ring insulates the contrapiston so it does not cool off so fast...

O-ring makes it super easy to get a good fit with enough friction so that engine does not drop its contrapiston while running. Although this should not happen if there is a vent hole between top of contrapiston pocket and the atmosphere so that pressure is always lower than beneath the contrapiston...

Probably fussiest thing is to get the fins to come out even, using the slitting saw.

Good luck with your Earl/Drone!

Regards. -Gary

earlwb

Thanks for the info Dave. I'll try some fiber gaskets before I try some metal ones.

Yeah, I have been meaning to make a diesel head or two myself. Thanks for the info Gary.

You know, I forgot to mention it. But when you look at the pic of the disassembled engine above. You'll see where the factory made the intake port cutout notch for the cylinder on both sides. So one could flip the piston over and reverse the cylinder top and thus you could have the exhaust going either left or right.There is a notch on the piston corresponding to the intake port in the cylinder. It is probably mentioned in the old instructions sheets that came with the engines when new. But I don't have the instruction sheet.

If anyone has an interest here is a good article on running a fixed compression ignition engine like the Drone:
http://modelenginenews.org/faq/fc_diesel_ops.html

Jim Thomerson

The 1947 Drone I have was second-hand and had no head gasket. I ran it on Eric Clutton fuel and thought it a hair overcompressed. I got a 1948 Drone off eBay, also no gasket, and had to replace the front gasket. I was going to cut some metal gaskets as mentioned above but chickened out and bought an Aerodyne adjustable head. I have not run it yet.

earlwb

Thanks for the information Jim.

I got crazy and decided to try my old 1947 vintage Drone engine out on the test stand. It took a lot of flipping before I figured out that the needle valve unit is messed up. With the needle screwed all the way in, it would start, but run too rich, But not wanting to quit, I ran a few of small tanks of fuel through it using a pair of needle nose pliers to squeeze the fuel line to lean it out more. It actually worked. Anyway i got around 6,100 rpms out of it using a Master Airscrew 12x8 Scimitar series prop.

I got the idea from when I was a kid and I had broken off the needle valve in a rich running position, but it wasn't turning or moving. So I rigged up a simple metal pinch clamp with a screw and wing nut and spring. i could adjust the richness of the fuel like that. it was crude but it worked until I could get a new needle valve. Anyway in hind sight, I could have been the first using a remote needle valve adjustment at the time.

I thought I would use my can of Davis Diesel fuel with some extra castor oil added to it, instead of mixing up a batch of ether and oil only fuel and see if it would run or not. Anyway, once I figured out the needle valve wasn't letting the engine lean out, and it would just barely get lean enough to start, I was in business then. I had made up a quart of it and had it in a old pre-mix quart gasoline can. I till have some left after running all of these engines I have been playing around with for the last few months.

After I fix the needle valve maybe I'll try some different mixes of fuel. But as long as I could hold the needle nose pliers with just the right pinch, the engine ran quite well. Plus I could hand flip start it after only letting it cool off to a little hotter than warm. So I think it will work out OK.
One interesting thought is one could sorta get a two speed throttle effect with it if they used two needle valves, rich and leaned out just about right.

When I studied the needle valve unit. I suspect someone tried to use the wrong needle valve for the spray bar. The needle needs to be longer. The needle may even need to be a little larger in diameter. So I could go with a remote needle valve and leave it as is, or make a new longer needle valve, or replace the entire unit. I have a few control line needle valve spray bar assemblies, so I'll need to look and see which ones fit the best. I'll also look at what the thread size is for the needle valve, if I have a tap for it, I could make a new one and machine up longer needle for it. So I could save the old spray bar and still use it too.

I took these pics of it running real slow before I started pinching the fuel line to lean it out more. It actually ran pretty slow, sort of a not bad idle speed. Albeit it was running rough though.

Jim Thomerson

Looks like one of the old Austin-Craft NVA's. I have those on both my Drones.

earlwb

Yeah it is hard to say but it is likely the Austin-Craft NVA unit. So yours might have the same problem if you run the engines. But since it almost reaches in to the needle seat, maybe if I carefully file or cut it down a little so it can go in about 1/16" or 1/8 of a inch deeper it might work then. But it doesn't look like the OEM needle that came on the engines originally.

earlwb

I got lucky and acquired a second Drone .29 Diesel engine. This one is a earlier model with the rear fuel tank mounted on it. The earliest models had a Gitz cap installed on them for refueling the engine. They quit putting it on in the later models. Later near the end of the 1947 model production run, they left the rear fuel tank off entirely.

This engine didn't have a needle inside the holder, so I'll need to fabricate one up. But in looking at the spray bar, it was drilled all the way through straight without a seat for the needle to run up against. So I assume that the needle fits closely inside the hole and you close off the hole in the spray bar to lean or richen up the air fuel mixture. Anyway, it is something I had forgotten about. I think the old Fox .35 Stunt engines with the flat tip needle do the same thing too. except they have a tapered flat tip like a screwdriver tip on the needle end.

I was surprised to find that this particular engine was never used or run. In looking at the mounting tabs and the crankcase, there are no marking or wear spots at all on it. The piston and cylinder also look very pristine and clean too. The main reason I think for why it was not run was that the needle in the needle valve is missing. The needle valve assembly looks like it is the type they put on the Drone engines at the factory though.







Now when I studied the needle valve assembly so I could determine what I could use to make a needle for it. I found that the inside hole was drilled all the way through straight. There is no seat inside for the needle.  So I looked at my other engine and sure enough it was drilled through straight as well without a seat inside. But it isn;t quite straight all the way through though, the fuel inlet side appears to be slightly smaller for the inner hole, but that may have been a machining step causing it to appear to be tapered slightly.




So as I understand it, the needle is a more or less snug or close fit inside the tube and the idea is to block off the spray bar hole in the tube with the needle. So it doesn't really need a long sharp pointy taper to the needle itself. You just need it long enough to block off the hole in the spray bar.



In this case on my first engine I think I only need to cut off about 1/8 of a inch from the needle valve holder so that the needle valve can screw in a little farther to block off the spray bar hole in the tube.

SGC

Earl, going by the serial No's your later aquisition would be a later production model.?

earlwb

It sure looks that way. The first engine is 9811 versus the current acquisition of 9901. So someone must have lost the fuel tank on the first one then. The serial numbers are close enough together that the two engines could be from the same production run.
Thanks for noticing.

earlwb

I ran across a link to a PDF with an Autobiography for Leon Shulman, the guy who designed and manufactured the Drone engines.
<cite>https://www.modelaircraft.org/files/ShulmanLeon.pdf

</cite>

earlwb

I took the liberty to fabricate a replacement needle for the one Drone engine I got. It didn't turn out too bad at all. I left it a little long in case I need to move the needle in or out a little to get it to work at its best. I used a short length of .062 inch piano wire for the needle. I simply chucked it up in my micro drill press and used a Dremel tool with a grinding stone tip to grind the taper in the needle.

I was entertaining the thought of machining up a adapter with a carburetor to replace the screw on intake venturi stack. But much to my surprise the threads are a rare 5/16 x 32 size and thread. So I had to special order the tap and die from the UK. So it'll be a while before I can try a carb out on the engine. I think one of the .15 air bleed carbs that I have ought to work out perfect for it.

I also took a closer look at my first engine that I had bench run last week, and found that the spray bar was offset too far to the left, causing the little hole in the spray bar to be offset to the left, right on the inner edge. So that meant that the needle could not be screwed in all the way. So I readjusted it to center the hole better. I also went ahead and cut off about 1/8 of a inch from the needle holder so that there is less of a chance of it bottoming out again. In screwing it in or out, it is working much better now.

My new DIY needle inserted and soldered in place on the needle holder.


The needle valve assembly reinstalled back on the engine.

earlwb

I had forgotten about it, but I found a copy of a article about making a variable compression head for a Drone Diesel. The drawing info is readable but the article is a little hard to read. I would give credit for who posted it first, but I forget who did it. Thanks anyway for making it available as I repost it here too.

earlwb

I test ran the Drone engine again after correcting the needle valve assembly. It is running better now. But it acts like the prop is a little too small as its fixed compression ratio with the fuel I am using leaves it struggling to keep up with the prop. Sort of like a retarded ignition timing. I didn't have a 13x6 prop that I hadn't reamed out already. So later I'll try it with a 13x6 prop and see if that loads it down just right or not. I am running Davis Diesel Development fuel, the ABC blend, with some little extra castor oil in it. As the engine warms up good, it starts running better, but doesn't quite make it to that perfect sweet spot.

I got to thinking that also the 1 quart fuel container is down to a little less than 1/4 full now. So the fuel might be getting a little stale as the ether evaporates everytime I open the container to draw some fuel out to run a diesel engine with it. It might do better with fresh fuel.






Here is a video I made of it. I was curious as to how loud the engine was without a muffler. So I measured its noise with a DB meter and I was measuring between 85 to 90 DB at about ten feet from the engine. As the engine warmed up good, it just about came out running OK with the 12x8 Master Airscrew Scimitar series prop on it.

http://www.youtube.com/watch?v=nTbJcE61aLU

[youtube]http://www.youtube.com/watch?v=nTbJcE61aLU[/youtube]


Now just in case the club requires a muffler for it. I found that a Fox .15 Schnuerle engine muffler almost fits OK. I took about 2 thousandths of a inch off one of the inner lips of the muffler's flange and the muffler slips right on there just right now. A couple of screws for a muffler clamp and its ready to go. Maybe I ought to paint it black with some BBQ grill paint.

KeroPower

The video reminds me of the time (times) I have tried running a glow engine on diesel fuel and full throttle. It ran, but the compression wan't quite high enough. Made those missing sounds.

Sounds like the Drone only needs a tad more compression (or more ether) for a nice smooth run.

But then again does it really neeed to be perfect to fly? Just put it on a light high wing floater and let it rip.

Running under-compressed can't hurt it. [8D]

The Drone sure follows the KISS principle.

earlwb

Yeah I can agree undercompressed is much safer than being overcompressed. It does just about make it to optimum speed as the engine heats up good. Way back when these were popular for a couple of years, the lean runs as the control line plane's fuel tank ran empty would setoff detonation and less oil lubrication effects causing the rear part of the crankshaft bushing to wear out faster.
I want to try a 13x6 prop on it and see if that adapts it better for running on my fuel.A 13x7 prop might be even better still.
The trick is that no one has any videos of a Drone engine running way back in 1947-1948 so we can guage how ours are running today. That slight miss on the engine may be perfectly normal.

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Photos of one of my BB Drones with muffler and motor mount. Jack

earlwb

Nice Drone engines there Jack.
Do you know what fuel you used, and the prop size that you ran on the engine(s)?

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earlwb, I have used Red Max, Olde English Mix, Aerodyne and Davis fuel. Best RPM with Aerodyne followed by Davis. My best BB Drone turns an APC 13/7 Sport prop at 6,900 to 7,000 RPM on Aerodyne fuel. The more I run them the better they get. Buiding a Lanzo Airborn 810 sq. in. for SAM LER event for a BB Drone with the APC 13/7 prop. Jack

earlwb

Thanks for the information.
yeah i think I need to run a larger prop now for sure.

earlwb

I had finally gotten lucky and as able to acquire a Drone .29 BB model compression ignition (diesel) engine to study, et cetera. These appeared in 1948 and replaced the earlier bushed crankshaft version. It appears to have never been run or used at all, as the cylinder and piston appear to be unused nor are the screw holes in the mounting tabs scarred either. The serial number stanped on the engine's mounting lug is 11522.