# Boll Aero 18



## radfordc (Jan 14, 2010)

The Model Engine News website provided free plans to the Boll Aero 18 diesel engine.
http://www.modelenginenews.org/plans/BollAero18.pdf

I started this project last week and have the case and cylinder parts done so far.

Charlie


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## radfordc (Jan 14, 2010)

Here is what has been done so far. 

View attachment IMG_0256[1]


View attachment IMG_0256[1]_thumb


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## Deferr (Jan 14, 2010)

I am anxious to see the process for this build. Very neat design. Can't Wait!


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## Metal Butcher (Jan 14, 2010)

Hi Charlie, and welcome back!

Its been a while since I saw you post a build, which was the John Deere.

I hope everything is O.K.

-MB


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## Maryak (Jan 15, 2010)

Metal Butcher  said:
			
		

> Hi Charlie, and welcome back!
> 
> Its been a while since I saw you post a build, which was the John Deere.
> 
> ...



Me too.

Best Regards
Bob


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## GailInNM (Jan 15, 2010)

Coming along nicely Charlie.
The Boll is a nice size and should be a good runner.
Gail in NM


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## radfordc (Jan 15, 2010)

Thanks. I still lurk here everyday to see what others are doing. I just haven't been in my shop for a long while.

Charlie


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## radfordc (Jan 17, 2010)

Today's work was finishing the machining on the cylinder and making the piston, rod and contra-piston.  

View attachment IMG_0258[1]


View attachment IMG_0258[1]_thumb


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## radfordc (Jan 28, 2010)

Two steps forward and three steps back. I had to make a new piston and contra-piston since the first ones had zero compression. Much better now. All that's left is to finish the carb.

Charlie


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## slick95 (Jan 28, 2010)

Dig that engine Charlie,

You going to mount it on a plane and fly it? Nice build 

Jeff


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## radfordc (Jan 28, 2010)

I don't think it will ever fly. I'll be happy if it ever starts!

Charlie


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## Metal Butcher (Jan 28, 2010)

radfordc  said:
			
		

> I don't think it will ever fly. I'll be happy if it ever starts!
> 
> Charlie



Nice airplane engine Charlie. I am confident that you'll get it to start.

Remember the lyrics to that old song, "Don't worry, Be happy".

-MB


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## omidn (Feb 3, 2010)

hi dear:
i want to build a bollaero engine,but i have some problems,if u can help me i will be graetefull.i have the plan and i see your post in the forum and photo of your work.these are my question about the plan:

1-i don't know what is the contra-piston and where be should it placed?
2- what is the fuel of bollaero18?
3-i can't understand about fuel sytem in plan?why the exhust hole and fuel injection hole are in the same level?how does fuel system work and how does is spray fuel to cylinder?
4- can u send how do parts(piston,contra-piston,...)place in the plan?(their sequences)
5-what is "mill transfer pessage"?
i apologize if i write many questions or my english grammer is not good.
i am waiting for your reponse.

plz send e-mail: [email protected]     :bow:


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## radfordc (Feb 3, 2010)

I can't really provide all the info you want, but I can recommend a site that does have it. http://modelenginenews.org/ This site covers many of the technical items you're confused about.

Charlie


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## omidn (Feb 3, 2010)

thanks dear,i read that site but i can't find may answers in that,can u help me?what is the fuel of the"bollaero18"? :bow:


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## John Rudd (Feb 3, 2010)

omidn  said:
			
		

> thanks dear,i read that site but i can't find may answers in that,can u help me?what is the fuel of the"bollaero18"? :bow:



The fuel is 'special' diesel fuel

Its a mixture of kerosene/ether/castor oil and IPN......

Castor Oil 20 - 25% 
Ether 30% 
Paraffin (Kerosene) 45 - 50% 
Iso-propylnitrate 2 - 2.5%


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## LADmachining (Feb 3, 2010)

Hi Omidn,

The fuel for the engine is the same as for most other small diesels - a typical mix is equal parts of ether, kerosene and castor oil. The engine will run on varying mixtures of these three ingredients. 

Most of the questions you have asked are on the Modelenginenews.org site - the fuel question is answered in the FAQ (use the navigation menu on the left of the screen).

The plan would be much easier for a beginner to understand if there was a cut-away drawing of the engine.

The inlet and exhaust port holes in the liner are at different levels - this is what sets the timing. The position of the holes in the crankcase do not make any difference to the engine timing.

The fuel from the tank connects to the bottom of the spray bar (part 8-3). The fuel is drawn out of the spray bar by the air passing through the venturi into the engine. The amount of fuel delivered is varied by the needle (8-4), and the amount by which is obscures the spray bar jet hole (#61).

The contra-piston fits into the top of the cylinder, the flat face of the contra-piston facing the main piston.


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## Bill Mc (Feb 4, 2010)

Hi Charlie - I can see where the Boll-Areo 18 will become a great beginners (newby) project. The materials are not hard to obtain and the plans are explicit in detail. Probably the beginners will ask for more rudimentary things like photos of actual machining operations and how to set them up. We must strive to assist these fellows as much as we can. This is one of the main reasons for this wonderful site of ours. The only critical item is to ensure that tolerances are met. They MUST be very accurate to ensure adequate compression as this is a diesel engine. This engine could easily be modified to support a glow plug to lessen the constraints placed upon it. - Billmc


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## omidn (Feb 5, 2010)

hi dears LADmachining and John Rudd:


i am very grateful from your attention to my question.i am a beginner in model engine.can i have your e-mail address to ask some question if it is possible?

thank u very much. :-*

i have one question,what is the "mill transfer passage" in the plan?


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## Paulsv (Feb 5, 2010)

Hi guys! I am a relative newbie, both here on the site and to model engineering. I am interested in the BollAero as a possible first project. I am also looking at the MLA-17 (http://www.statecollegecentral.com/metallathe/MLA-17.html), another compression ignition (diesel) engine. Its plans come with a 30 page booklet that gives a lot of explanation, which I as a newbie find helpful.. The MLA-17 does not have a contra piston, which seems simpler, but on the other hand it has a threaded backplate, which I am a little afraid of.

It's not real clear from the plans, but as I understand it, the contra piston is a press fit in the top of the cylinder, so that it will stay in place, but still be able to be moved by the compression screw, in order to adjust the size of the compression chamber. Is that correct? It seems that the fit of the contra-piston in the cylinder would therefore have to be very precise, and presumably would have to be lapped to a precise fit. Do I have the concept correct?

Charlie, I hope I am not hijacking your thread by posting this question here. Your pictures and description are great. You make it look easy, and that gives me some encouragement, so I appreciate it.

Also, for Omidn, you should check out this site: http://www.modelenginenews.org/  If you click on "Resources" in the left column, and look at the "FAQ" and "How To" sections, there is a lot of helpful information, including information on the fuel and how to obtain it.


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## cobra428 (Feb 5, 2010)

omidn,
Look at this site. It has a number of engine types and how they work.Should answer a lot of your questions

http://www.animatedengines.com/

Tony


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## seagar (Feb 5, 2010)

I have been using deisel engines engines in model aero aircraft and boats for more years than I wish to remember and I totally agree with John Rudds fuel mixture.The addition of the nitrate smoothes out thr running of the engine and you will get far better performance .Equal parts of ingrediants will run the engine,but it will be harder to start and will run harsh and rough in comparison.

Ian (seagar)
Coffs Harbour 
Australia.


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## radfordc (Feb 5, 2010)

Getting the proper fit of the contra-piston is a trick. It has to fit tight in order to maintain compression. The modelenginenews website shows a method for making them that makes things much easier. You basically turn the contra-piston with thin, tapered sides that can compress just enough so the piston can be installed. As described, the contra-piston should go into the top of the cylinder with about 4 pounds of force and should be pushed out of the cylinder by the force of compression. Mine is probably a little too tight now but its really easy to get it too loose.

Charlie


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## radfordc (Feb 5, 2010)

The only source of diesel fuel I could find on-line was Tower Hobbies and only in 1 gallon cans! That's a bit more than I need to test my engine.

I've read about making diesel fuel using the auto parts "starter fluid" spray cans and decanting the ether out of them. Who has done this?

Charlie


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## radfordc (Feb 5, 2010)

omidn  said:
			
		

> i have one question,what is the "mill transfer passage" in the plan?



Look at the picture of the cylinder in reply #7. The two slots on the side of the cylinder are the transfer passages. You make them with a 3/16" end mill by cutting (milling) the cylinder.

Charlie


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## omidn (Feb 7, 2010)

thank Charlie,but what are"mill transfer peesage used"for? :bow:


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## radfordc (Feb 7, 2010)

Transfer passages allow fuel/air mixture to "transfer" from the crankcase to the cylinder. The the fuel is sucked into the crankcase below the piston; the piston descends and compresses the mixture and then when the piston uncovers the transfer ports the fuel mixture flows up the passages into the cylinder.

Charlie


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## Drei (Feb 20, 2010)

Hi Omidm,

I have read youre questions about the Boll Aero 18.. I m am going to attempt the engin too but I have almost the same questions as yours but latley I ve done some reserch, with positive results 
I found an 'answer' about the fuel used..You can read more from this link which I have found very informative  http://www.modelenginenews.org/sugden/sugden_build.html. 
There are many good questions with very informative answers..

Goodluck
Andrei


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## radfordc (Feb 20, 2010)

If you intend to run your engine be sure to make the crankshaft using either the spline or collect to secure the prop driver. I used the "original" method and can't keep the prop from spinning off when trying to get enough compression to start the engine.

Charlie


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## tomol409 (Apr 6, 2012)

Has anyone yet got a Bollaero to start and run?


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## samuel10 (Nov 11, 2012)

radfordc said:


> Two steps forward and three steps back. I had to make a new piston and contra-piston since the first ones had zero compression. Much better now. All that's left is to finish the carb.
> 
> Charlie[/
> hi do you need a glow plug for this engine.


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## zimma (Nov 11, 2012)

If anyone is interested, here was my BollAero18 on first run.

Video

(I hope that link works)


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## zimma (Nov 11, 2012)

samuel10 said:


> hi do you need a glow plug for this engine.


 
Samuel. 

No it is a compression ignition "diesel" engine.


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## Maxine (Nov 11, 2012)

zimma said:


> If anyone is interested, here was my BollAero18 on first run.
> 
> Video
> 
> (I hope that link works)



Nice job!

Maxi


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## samuel10 (Nov 12, 2012)

what fires the engine if there is no glow plug?
great little engine like to know how it works .
thankyou.


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## samuel10 (Nov 12, 2012)

Thank you for the video what tolerance did you use on the piston and cylinder? the drawing just gives you a std size to work off .


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## zimma (Nov 12, 2012)

samuel10 said:


> what fires the engine if there is no glow plug?
> great little engine like to know how it works .
> thankyou.


 
Hi, Might be worth checking out Wikipedia and google for how compression ignition and diesel engines work. Basically when the piston compresses the mixture, it reaches enough pressure/temperature that it self ignites.


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## zimma (Nov 12, 2012)

samuel10 said:


> Thank you for the video what tolerance did you use on the piston and cylinder? the drawing just gives you a std size to work off .


 
Samuel.

I machined the inner bore of the cylinder liner down to just short of 0.5" with a boring bar. I passed a 0.5" reamer through the hole to give me a better finish than my boring bar could give me. 

I then chucked up a 0.5" Acrolap Barrel Lap in the chuck and hand lapped in the liner with progressively finer pastes. I was able to add a little taper to the bore to give me the required pinch at the top of the stroke.

Once machined I made a piston and contra piston to just over size so it wouldn't fit into the bore. Maybe 3-4 thou oversized. I made an aluminium outside split lap and lapped down the outside of the piston and contra piston to give it the required fit. I kept lapping the contra piston until it was a tight fit in the bore at the top, taking quite a bit of effort to push it in. I did the same with the piston so it was tight at the top of the bore, but moved reasonably freely at the bottom of the bore (thanks to the slight taper)

I didn't take any measurements of the final sizes or taper. I guess the taper would be in the region of 1 to 2 thou over 1 inch.

What I found as equally important as the fit of the cylinder in the bore, was the fit of the liner in the crankcase. My first attempt had a sweet piston/liner fit, but I got bubbles coming up from the bottom of the crankcase up past the liner and bubbling out of the exhaust port.

First run, the propeller was quite tight. I ran it over a bit by hand and it loosened up a little. Once the mixture was in and there was a bit of oil on the piston, I got a great seal with superb compression.

Hope all this helps get yours running.


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## samuel10 (Nov 14, 2012)

hi zimma me again does there have to be a taper or can it be .01mm clearence which is close to .0005"thou. will it still run?.


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## zimma (Nov 14, 2012)

samuel10 said:


> hi zimma me again does there have to be a taper or can it be .01mm clearence which is close to .0005"thou. will it still run?.



Hiya, the idea of the taper is so that when the piston is rising and the compression is getting bigger, the fit gets tighter and supports more compression., and as the piston lowers, the fit gets looser and the friction is reduced. I guess if your fit is good enough to give excellent compression without being too tight then a taper is not required.

I have no idea if 0.01mm is enough, as i just machined the liner to approx size with good finish, and then just lapped the cylinder to fit. I did no measurements on these bits other than the starting dimension of the liner bore which was 0'500(ish)" prior to lapping due to the reamer i used.

Hope this helps.


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## lensman57 (Nov 14, 2012)

samuel10 said:


> what fires the engine if there is no glow plug?
> great little engine like to know how it works .
> thankyou.


 
Hi,

As explained by the other gentleman, the ignition is achieved by compression, once a gas is compressed the temp goes up untill it reahces a critical point where combustion takes place,  but this is not all, for this class of compression engines the fuel required has to have an accelerator ( oxygenator) added to it to aid the ignition. In the old times that accelerator was either Ether or some other derivative of it such Amyl ether, these days because of security reasons such fuels are difficult to mix at home and have to be bought over the counter.  
For your information there is another type of compression ignition engine called Glow Plug, these have a special plug or more accurately, a heater element that aids the start up using a current from a small battery and once the engine starts the current is disconnected, the fuel for this type of engine is generally called Glow plug fuel and is more easily available.

Regards,

A.G


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## zimma (Nov 15, 2012)

lensman57 said:


> For your information there is another type of compression ignition engine called Glow Plug, these have a special plug or more accurately, a heater element that aids the start up using a current from a small battery and once the engine starts the current is disconnected, the fuel for this type of engine is generally called Glow plug fuel and is more easily available.


 
Ahhh, that explains a few things for me too  I had incorrectly assumed that a glow plug engine was just a spark engine, but using a different type of plug.  I should really know these things, as my current engine build is a glow..... That's another fundamental build mistake avoided


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## lensman57 (Nov 16, 2012)

Hi Zimma,

Just to add to my previuos post, the glow plug does not cease functioning after the ignition starts, depending on the design, the miniature filament would still assist ignition , hence glow plug. This is apparently mostly achieved by a ctalytic process between the plug and the fuel and heat.
I have also been told that a glow plug engine is slightly more forgiving in manufacturing tolerances than a full compression ignition engine. Getting a Boll Aero to start is a difficult task itself, getting it to run is on another level, therfore congratulations to gentleman with the build log.

Regards,

A.G


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## samuel10 (Nov 17, 2012)

Hi is it hard to modify this engine to take a glow plug if so what would be the changes.
I am looking at machining. a simple engine i have built a small steam/air engine that worked great just looking to take this hobby further. any similar simple glow drawing would be great.


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## samuel10 (Dec 4, 2012)

On th fuel side of things how do you cut the.40mm which is .016 thou slot .
and has anyone gogt a better drawing of the fuel system .


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