Boll Aero 18

[cobra428]

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

 

[seagar]

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.

 

[radfordc]

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

 

[radfordc]

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

 

[radfordc]

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

 

[omidn]

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

 

[radfordc]

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

 

[Drei]

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

 

[radfordc]

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

 

[tomol409]

Has anyone yet got a Bollaero to start and run?

 

[samuel10]

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.

 

[zimma]

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

Video

(I hope that link works)

 

[zimma]

hi do you need a glow plug for this engine.

Samuel.

No it is a compression ignition "diesel" engine.

 

[Maxine]

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

Video

(I hope that link works)

Nice job!

Maxi

 

[samuel10]

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

 

[samuel10]

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 .

 

[zimma]

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.

 

[zimma]

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.

 

[samuel10]

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?.

 

[zimma]

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.