Merlin V12

[JRR]

[ame]https://youtube.com/watch?v=_uyvY0tDU4M[/ame]

 

[Herbiev]

Nice build JRR. Where did you get the plans. How long did it take you to build it?

 

[JRR]

G'day Herbie
I bought all the castings and drawings from USA. I had it running 20 months later. Thanks for your nice comment.
I should have completed my address by adding Australia to it!
John

 

[mayhugh1]

JRR,
My hat is off to anyone who has finished one of these. Your twenty month build time is really impressive. Are you using a spark ignition or glow plug? Is your supercharger functional and building boost? - Terry

 

[JRR]

G' day Terry
I started building the oil pump first in March 2013 while waiting for the castings to arrive.It ran for the first time in November 2014. It is spark ignition and as for the supercharger it is turning at 30000 rpm but I cannot be sure if it is contributing any thing to the performance as I am not sure how to measure it, I suspect not much as it is too slow. I used the casting that was avaible for the crankshaft, that saved a bit of time.
I have to dismantle it soon to fix the water leaks from around the bottom of the sleeves and the last time I ran it , it passed a lot oil out from the exhaust pipes
I've had much enjoyment in that time but I am not expecting as much I this next phase!
John

 

[JRR]

Terry I will try to down load some pictures

 

[kvom]

Guess that's how it runs down under.

 

[mayhugh1]

JRR
Do you suspect the double o-ring seal design isn't adequate or do you recall any problems during fabrication? I'm concerned about all the coolant passages between the head and the cylinder block. Have you had leaks up there as well? Any tips or things you would have done differently if you were starting over? Thanks, - Terry

 

[mu38&Bg#]

.... as for the supercharger it is turning at 30000 rpm but I cannot be sure if it is contributing any thing to the performance as I am not sure how to measure it, I suspect not much as it is too slow.

What is the OD of the compressor wheel roughly?

Greg

 

[JRR]

Greg, the compressor wheel or impeller is 3" in diam.
John

 

[JRR]

JRR
Do you suspect the double o-ring seal design isn't adequate or do you recall any problems during fabrication? I'm concerned about all the coolant passages between the head and the cylinder block. Have you had leaks up there as well? Any tips or things you would have done differently if you were starting over? Thanks, - Terry
The answer to your first question is yes.If you check the drawing ( 2161a) you will see that the size of the o ring 028 is to big in in section so I used some made from 1 mm cord glued ends. I suspect that they have come apart
There appears to be no leaks from the heads.
I changed gear ratio on the prop drive from 48T/21T to 40T/ 29T as the prop revs was much to slow.
It's good to have someone to converse with on this project ,I suspect there are not many of us . John

 

[kvom]

Curious as to why prop speed matters on a model not mounted on an aircraft.

 

[mu38&Bg#]

Curious as to why prop speed matters on a model not mounted on an aircraft.

The slower the prop turns, the larger is has to be to absorb the power.

Greg

 

[mu38&Bg#]

A 76mm radial flow compressor spinning 30,000 RPM will develop very little pressure. Compressor maps of the KKK K27 76mm compressor suggest it has a pressure ratio of 1.1 at 30kRPM and it's surge limit is 0.02m^3/s. At 3600 RPM flow through the engine is <0.013m^3/s so the compressor is very near the surge line for sure. The compressor might make ~0.1bar (1.5psi) of pressure.

Greg

 

[rythmnbls]

A 76mm radial flow compressor spinning 30,000 RPM will develop very little pressure. Compressor maps of the KKK K27 76mm compressor suggest it has a pressure ratio of 1.1 at 30kRPM and it's surge limit is 0.02m^3/s. At 3600 RPM flow through the engine is <0.013m^3/s so the compressor is very near the surge line for sure. The compressor might make ~0.1bar (1.5psi) of pressure.

Yep, and while making about 1.1 bar of pressure it will absorb approximately 1-2 hp. Not good for overall efficiency.

Steve.

 

[JRR]

Curious as to why prop speed matters on a model not mounted on an aircraft.

To satisfy your curiousity I need air flow through the radiator. A 3 blade prop would be the way to go but I have no information as how to build one.
I made a copy of the one I made for my 18 cyl Hodgson which moves a lot of air at 3000 rpm. It's diameter and pitch is 32" x 16". With the original gearing this only give me 1315rpm @ 3000. With the 40T/ 29T teeth I can get 2175 rpm.
Can you advise me as to what would be a suitable diameter and pitch for a 2 blade prop if I reinstall the original gearing?
John.

 

[JRR]

A 76mm radial flow compressor spinning 30,000 RPM will develop very little pressure. Compressor maps of the KKK K27 76mm compressor suggest it has a pressure ratio of 1.1 at 30kRPM and it's surge limit is 0.02m^3/s. At 3600 RPM flow through the engine is <0.013m^3/s so the compressor is very near the surge line for sure. The compressor might make ~0.1bar (1.5psi) of pressure.

Greg

r
I never held out much hope that a supercharger would serve any use at this size, I think it's only there so we can say " yes it has a supercharger" but it was interesting to make.
John

 

[mu38&Bg#]

Are those RPM figures wide open throttle? With the 32x16 prop at 2175RPM that's only ~830W(1.1HP). The website was suggesting 16HP.

Greg

 

[mayhugh1]

JRR,
Could you please tell me what you used for a carburetor? If I hadn't just completed the prop gear over the weekend I might have changed my reduction ratio. Do you think the overheating problem would be solved by a small electric fan blowing air through a small radiator tucked away under the engine? That's what I've been planning for mine when I get to that point. I think I read that some of the planes that used this engine had to have an auxiliary radiator (no fan) under the plane to control engine temperature during long idling times on the runway. - Terry

 

[JRR]

Are those RPM figures wide open throttle? With the 32x16 prop at 2175RPM that's only ~830W(1.1HP). The website was suggesting 16HP.

Greg

Yes , Wide open . How do you arrive at that figure? I'm out of my depth when it comes to the mathamatical part of this hobby.
John