# Flywheel design/ proper weight and diameter



## johnlaudano (Jul 28, 2012)

I'm working on a home built V-twin with an 83cc displacement. It's my own design loosly based on J. Howell's "Bill". 
It has a 1.43 bore and a 1.56 stroke. I'd like it to run at between 500 and 1000 rpm.
I need advice on how to determine the proper size flywheel. 
Thanks.


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## kuhncw (Jul 28, 2012)

Sorry I don't have a theroetical method to give you for calculating flywheel size.  I'd put as much flywheel on the engine as possible that still looks reasonably in scale with your engine.  Perhaps others will have a better answer for you.

Regards,

Chuck


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## Jasonb (Jul 29, 2012)

I can't help with a formula either but get as much weight in as possible.

If you are making it similar to "Bill" then that will limit your dia but if you add a sub-base then you could run bigger. My thoughts would be something in the region of 5-6" dia and 1.5" thick for a solid iron flywheel.

The other option is add a second flywheel to the other end of the crankshaft, I've done a vertical IHC that had twin flywheels and a good size takeoff pully.

J


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## Maryak (Jul 29, 2012)

Hi,

This is my way and so far it's worked OK. Anyway I hope it helps get you started.

Flywheel Size Calculation 
 


 
 
 
 

A model   steam engine of 1" bore and 1.5" stroke 
supplied   with steam at 50 psi running at 500 rpm 
Allowable   speed variation 2% 
 

Flywheel   diameter 6" 
 
 


 
 
 
 

1.   Calculate the energy per revolution generated by this engine 
 
 
 
 

E = 2PLA 
 
 
 

Where 
 
 
 

P =   pressure in psi 
 
 

L = Length   of stroke in ft 
 

A = Area of   piston in ins2 
 


 
 
 
 

E= 50 x 0.25 x PI x 0.52 
 

E= 9.817 ft lb 
 


 
 
 
 

2.   Calculate the energy given up when the speed slows by 2% E1 = 0.196 ft lb 
 


 
 
 
 

3.   Calculate the Angular velocity at 500 rpm 
&#937;= 52.360 rads/sec 
 


 
 
 
 

4.   Calculate the velocity and its' variation due to speed change V= &#937; x r 
 
 

V1 = 13.090 ft/sec 
 

V2 = 12.828 ft/sec 
 


 
 
 
 

5.   Calculate the weight of the flywheel to overcome the above E1 = W(V12 - V22)/2g 
 

W= 1.861 lb 
 


 
 
 
 

6. 1 ins3 of steel weighs 0.28   lbs calculate the size of the rim  Steel   Required 6.647 ins3 

Flywheel   circ= 18.850 ins 

X Section = 0.353 ins2 

5/8" X   Section = 0.391 ins2 


Best Regards
Bob


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## Jasonb (Jul 29, 2012)

Bob, its an IC engine so may need a few adjustments, also a marine type vertical so solid disc flywheel.

J


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## Maryak (Jul 29, 2012)

Thanks Jason,

I guess the main thing is to calculate the energy deficiency to be overcome I imagine for an IC engine this would relate to cylinder BMEP or horsepower which can be converted to ft lbs or even dare I say NM's 

Best Regards
Bob


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## Maryak (Jul 30, 2012)

I did a bit of research into solid disk flywheels for IC engines and attached is a PDF which may help.

Best Regards
Bob 

View attachment IC Flywheel.pdf


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## Rustkolector (Jul 30, 2012)

I have a Bill engine and it won't run much below 1000 RPM. The flywheel, as designed, just can't get it over compression. I believe the compression ratio is 5:1. A two cylinder wouldn't be as susceptible low speed compression stall, but will be affected at some point. My suggestion for multi cylinder engine operation at this low speed range is to keep the compression at 4:1, and make the flywheel as large as reasonably possible. And, whatever the flywheel size chosen, put as much mass at the rim of the flywheel as possible.

Jeff


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## Maryak (Jul 31, 2012)

Jeff,

I have been messing about with this flywheel thing for a couple of days now and I think I am finally somewhere about the mark for a solid disk IC engine flywheel.

Attached is a spreadsheet with "Bill's" parameters plugged in as near as I can guess (BMEP).

I hope it helps and I would be happy to be told I'm wrong, because I'm married and it's not unusual for this to happen.

Best Regards
Bob 

View attachment IC Flywheel.xls


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## johnlaudano (Jul 31, 2012)

Thank you everyone. Looks like I've got a bit of work to do.


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## johnlaudano (Jul 31, 2012)

This is my engine as completed. It won't run as completed due to the flywheel size and perhaps too much compression. I plan to use all your input to make it work.
John


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## jason-b (Jul 31, 2012)

Are you using separate air and gas feeds to the inlet valve? I would have thought there is a risk of it sucking from the gas only when the carb is closed and then when the carb is open there is less vacuum to open the gas regulator so it just sucks in air.

J


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## kuhncw (Jul 31, 2012)

That is a nice looking engine and the flywheel looks nicely in proportion to the rest of it.  

Please tell us more about what you mean by "it won't run".  Does this mean it runs, but not at the low rpm?  What is you calculated compression ratio?  Jeff mentioned targeting 4 or 5 to 1.  The suggestion of a second flywheel is also good.

Please post some more photos showing the engine from other views.  I like the look.

Good luck.

Chuck


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## Rustkolector (Jul 31, 2012)

John, 
Nice looking engine. We all would like to see more views of it. 

I see you are using a propane fuel system and my guess it that the fuel system is your primary "running" issue. Using an RC type carb with propane is tricky and not always successful unless you can tune it to the engine. With an RC carb and propane, the carb throat is usually too large and the throttle has to be closed significantly to get enough restriction to pull the needed negative pressure on the demand regulator. Once the engine is running and the throttle position is changed, the fuel/air ratio then immediately changes and the engine usually quits, or runs poorly. If you don't have a venturi matched to your engine (which is unlikely) you have to duplicate one to get throttle response and RPM range. 

For propane use, the ideal venturi can be duplicated by installing a properly sized orfice bushing at the air inlet to the carb. Start small (~.100" dia.) and work up in size until you get the throttle response and RPM range you want. Open up your spark gap as far as possible on propane. 

Another item to consider later. Jerry did not use the throttle to vary the speed of the Bill engine. Propane was his backup fuel when no liquid fuels worked well in the Bill engine. He stayed with the gasoline carb, and used ignition timing to vary the speed. The Bill engine speed range can be varied over 1000 RPM by changing only the spark setting. 

Like Chuck said, a better discription of your "won't run" experiences so far might help. You are at the fun part now, so keep at it. You'll get it running.

Jeff


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## johnlaudano (Aug 1, 2012)

Your thoughts about the R/C carb are correct. I did replace the carb with a simple venturi tube and needle valve; I got it to run on one cylinder afterwards. (an ignition problem has stalled progress until next week). In order to make it run I had to add a makeshift flywheel (an old lathe chuck). It was certainly too heavy but bolstered my confidence when it ran. Now I'm searching for stock to make a proper flywheel. More photos below.
Also, am I responding in the proper manner? Is"quick reply" the proper place to continue the thread or is "post reply" the proper method"?


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## Rustkolector (Aug 1, 2012)

John,
Neat engine indeed! I can certainly see the Bill engine lineage. 

What is your design compresssion ratio?

Sounds like you have the fixes pretty much figured out. Keep us posted.

Jeff


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## kuhncw (Aug 1, 2012)

Hello John,

Thanks for posting the additional photos.  Nice job on the engine.  

Would you mind posting dimensions for your current flywheel, such as diameter, rim width, rim thickness, and hub diameter?  I am curious and cannot quite judge the size from the photos.

It sounds like you have a new flywheel planned.  I don't know if the dimensions would work out for you, but sometimes it works to buy a short piece of very thick wall steel tubing and bore the tube Id to fit your existing flywheel diameter.  I did this on a small hit and miss engine, a Little Brother,  to add flywheel inertia.

Please keep us posted.

Regards,

Chuck


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## johnlaudano (Aug 1, 2012)

The flywheel is 3 1/4 diameter 1 1/2 wide with a 1/4" undercut. I plan to go as big as 4" but that is starting to become problematic for the boat this would power. (my own design inspired by an Aquariva)
The compression ratio is nearly 10:1. I'm guessing everyone will see this as a problem.
The ignition is via TIM-6 electronics and a Howell-supplied coil.


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## johnlaudano (Aug 4, 2012)

Success of sorts today; It runs. Does anyone know how I can upload a .MOV file?


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## rhitee93 (Aug 4, 2012)

johnlaudano said:


> Success of sorts today; It runs. Does anyone know how I can upload a .MOV file?



I link them here from Youtube.  You can set them as private in Youtube so that only people with the link can see them.


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## kuhncw (Aug 4, 2012)

Hi John,

I'm glad to hear you've got the engine running and will soon have some video up.  What are the changes yoiu made to get it running?

Regards,

Chuck


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## johnlaudano (Aug 5, 2012)

Good idea. have a look. [ame="http://youtu.be/KFRBsLZa5sE"]http://youtu.be/KFRBsLZa5sE[/ame]

100%

100%


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## johnlaudano (Aug 5, 2012)

Chuck,
The temporary flywheel and a second coil did the trick. Now I need to make a proper flywheel and get slightly heavier intake valve springs.


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## kuhncw (Aug 5, 2012)

John, congratulations on getting the V Twin to run and thanks for the video.  That is quite a flywheel setup you have.  How does the second coil fit into the system?  Are you running two coils or did you replace the original?

You mentioned earlier that you plan to use the engine in a boat and were concerned about flywheel size.  Do you plan to experiment with lower compression ratio, which should let you use a smaller flywheel?

Regards,

Chuck


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## johnlaudano (Aug 5, 2012)

Chuck,
As the engine dosent have a distributor and the TIM-6 wouldn't reliably fire two plugs simultaneously, I used two TIM-6's and two coils and two hall sensors. It'somewhat redundant and expensive but it works.
I am thinking about lower compression.


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## johnlaudano (Feb 16, 2014)

Bob, thanks again for providing me the Excell spreadsheet for calculating flywheel sizes. i've used it twice and the wheels came out exactly right. The link below takes you to a video of my two cylinder propane-fired engine. It's 50cc and has a 360 degree crank. its going into a 61" mohogany boat.
John
Middletown CT

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


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## johnlaudano (Feb 16, 2014)

See more here.
John

http://www.homemodelenginemachinist.com/f31/twin-mahogany-boat-21924/


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