Merlin V12

[mu38&Bg#]

There is a formula to calculate propeller power. A google search for prop power calculator will turn up a few apps and calculations.

Thinking about the power the site quoted, 16HP isn't out of the question, but I expect much more than 800W from this engine, at least 8kW. What is the diameter of carb venturi?

Greg

 

[mayhugh1]

Greg,
Here is a link to a static thrust calculator that I used to sele t tbe prop for my 18 cylinder radial:

http://personal.osi.hu/fuzesisz/strc_eng/

Terry

 

[JRR]

There is a formula to calculate propeller power. A google search for prop power calculator will turn up a few apps and calculations.

Thinking about the power the site quoted, 16HP isn't out of the question, but I expect much more than 800W from this engine, at least 8kW. What is the diameter of carb venturi?

Greg

The Venturi diameter is .406".
John

 

[JRR]

There is a formula to calculate propeller power. A google search for prop power calculator will turn up a few apps and calculations.

Thinking about the power the site quoted, 16HP isn't out of the question, but I expect much more than 800W from this engine, at least 8kW. What is the diameter of carb venturi?

Greg

The Venturi diameter is .406".
John

 

[JRR]

There is a formula to calculate propeller power. A google search for prop power calculator will turn up a few apps and calculations.

Thinking about the power the site quoted, 16HP isn't out of the question, but I expect much more than 800W from this engine, at least 8kW. What is the diameter of carb venturi?

Greg

The Venturi diameter is .406"
John

 

[JRR]

There is a formula to calculate propeller power. A google search for prop power calculator will turn up a few apps and calculations.

Thinking about the power the site quoted, 16HP isn't out of the question, but I expect much more than 800W from this engine, at least 8kW. What is the diameter of carb venturi?

Greg

The Venturi diameter is.406"

 

[mayhugh1]

Greg,
Are you using a commercial carb? If so, what have you tried?
Terry

 

[mu38&Bg#]

The Venturi diameter is.406"

While that is at least half the required area to make full power it shouldn't be so restrictive as to limit power to what you're seeing. Of course, I haven't looked at this design closely and don't know what other factors may be limiting power output.

Greg

 

[JRR]

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

Terry
I removed the carby,witch was Jerry Howells 2 jet throttle from my 18 cyl and attached it to the inlet manifold and it ran.I then made an adaptor to fix it in correct place,but it didn't look correct.I wanted to use the castings (the one with the 2 vertical tubes) so I blocked up one and built the concept of Jerrys design in to it.If you like I could send a picture of the parts and what it looks like.
I expect there are many opportunities here to improve things but not being an expert in carburation I don't know what they are.
I would have though an idling prop would provide more air than a small fan, but that's just my opinion .In my case I think I should move the radiators to the front which will mean a lot work.
John

 

[mayhugh1]

John,
Yes, I would be interested in any pictures you could provide of your carburetor set-up.
Air flow through a radiator can be disappointing at times. If, in your photo, the black box at the rear of the engine is the radiator there may not be much air actually flowing through it. If you place your hand behind the radiator with the engine running, do you feel feel much hot air coming through it? I've seen lots of model multicylinder engines with the engine's fan blade behind a front mounted radiator, but without a shroud I'll bet most of the air is being pulled from behind the radiator rather than through it. Jerry Howell's V-4 was the best example I've seen of doing it the right way using a shroud. If you have a way of measuring the coolant temperature it would be interesting and easy to put one of those larger size computer fans right up against the radiator to see if you can measure a temperature drop in the coolant. In a radial, the engine heads are pretty efficient radiators, and prop is right up aginst them, and so that system works pretty well. In enclosed engines like the Merlin, we get little benefit from the prop wash.
By the way, it sounds like you've built several engines. I sure many of us would like to see more pictures of your work, if possible. - Terry

 

[mu38&Bg#]

John, it looks like this is your engine? http://www.homemodelenginemachinist.com/showpost.php?p=261990&postcount=7

If the radiator is at the back like that, a few small brushless fans would make a big improvement. They are available in a large range of sizes and flow ratings.

Greg

 

[JRR]

John,
Yes, I would be interested in any pictures you could provide of your carburetor set-up.
Air flow through a radiator can be disappointing at times. If, in your photo, the black box at the rear of the engine is the radiator there may not be much air actually flowing through it. If you place your hand behind the radiator with the engine running, do you feel feel much hot air coming through it? I've seen lots of model multicylinder engines with the engine's fan blade behind a front mounted radiator, but without a shroud I'll bet most of the air is being pulled from behind the radiator rather than through it. Jerry Howell's V-4 was the best example I've seen of doing it the right way using a shroud. If you have a way of measuring the coolant temperature it would be interesting and easy to put one of those larger size computer fans right up against the radiator to see if you can measure a temperature drop in the coolant. In a radial, the engine heads are pretty efficient radiators, and prop is right up aginst them, and so that system works pretty well. In enclosed engines like the Merlin, we get little benefit from the prop wash.
By the way, it sounds like you've built several engines. I sure many of us would like to see more pictures of your work, if possible. - Terry

Terry
I've taken on boarded all what you say, it all makes a lot of sense . I had though of making some changes to the position of the radiators so I think I will have to remove it from the "to hard basket " and change things around.
I would love show you some picture of my engines ( I wouldn't have done so unless you had asked) .As you will see I am able to do that but when it comes to download pictures you might have to wait awhile !
John

 

[JRR]

John, it looks like this is your engine? http://www.homemodelenginemachinist.com/showpost.php?p=261990&postcount=7

If the radiator is at the back like that, a few small brushless fans would make a big improvement. They are available in a large range of sizes and flow ratings.

Greg

Greg
Yes this my engine.It was posted by a friend of mine.I didn't know he had sent it until he introduced me to HMEM. I am very pleased he did.
John

 

[ZAPJACK]

Hi John,
i'm alsoo busy with the V12 Merlin.
But I don't see (or understand) witch the link between cranckshaft and supercharger gear.
LeZap

 

[mayhugh1]

Zapjack,
I'd love to follow your build if you're posting again.
Terry

 

[JRR]

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

Hi Terry
This was my solution to the carby on the Merlin and my alteration to the slip clutch.
I have put some pictures of my engines in photos.
John

 

[mayhugh1]

John,
Thanks for the photos. They should be very helpful when I get to that point.
I'm soon going to start on the cam, and so I'm beginning to plan for the valves and seats. The drawings show a 30 degree angle on the seat and a 45 degree angle on the valve. Did you seal your valves this way, and did you install separate seats or did you cut the seats directly in the head as the notes are encouraging?
Over time I've developed a techinque for making and sealing valves that has worked well for me, but I'm not going to be able to apply it to these castings. This extreme angle mis-match may work fine, but I have no experience with it nor have seen it used before. Since I'll only get one chance to get it right with these castings, I'd appreciate an opinion from someone who has already been successfully through it. - Terry

 

[JRR]

Terry,
I put the valve seat directly into the head and I think I used the 30/45 angles,it makes a lot of sense when you think about it because it will give a very narrow seat. I have made a tool using a round India stone dressed with an angle of 45 bonded to a length of .125 drill rod about 2 inches long with spigot to fit the valve guide ,used between finger and thumb to put on a very small seat ,works for me !
I will be very interested to hear how you go with the camshafts. I found this to be the hardest part and made a few before I got a pair ok
John

 

[gbritnell]

Terry,
I have never heard of anything like you have mentioned on cutting and matching valves and seats. The common practice is to cut the valve and seat at 45 degrees. In full sized practice there is what's known as a 3 angle valve job. That is where the seat is cut at 45degrees and the angle above is cut at 60 degrees and below the seat is cut at 30 degrees. With this method the seat width can be adjusted.
Naturally on small engines it would be really hard to do this but the method I have adopted over the years has worked quite well on my engines. The works whether you're machining into the head or machining valve seat inserts.
Make up a tool like I have attached. It is similar to full sized seat cutting where the cutter is aligned by the pilot. I make mine from drill rod and only use it by hand, no power. I lightly turn the tool until it knocks the corner off of the port. Once complete I lap lightly with some very fine grinding compound.
gbritnell

View attachment VALVE SEAT CUTTER INSTRUCTIONS.pdf

 

[petertha]

I've seen the 3-angle seat method referenced on Brian Perkins Hydra valve cages in Yahoo Groups R&R forum. Attached screen grab of Cad sketch (in Bristol Hydra folder, Files section). Possibly he describes this method somewhere in the posts, not sure though. Holy teeny-tiny angles.

https://groups.yahoo.com/neo/groups/R_and_R_engines/files/Bristol Hydra/