Prop Size

[John PurdyParticipant @johnpurdy78347]

I’m in the process of making a Sparey 5cc diesel. In the original AeroModeller magazine article of May 1946 Sparey states he uses a 13″ dia. 6″ pitch prop but in Ron Chernick’s build notes on Model Engine News he says he uses a 16″ prop but doesn’t state the pitch. That’s quite a difference. What would/do other people use/think.

John

[DiogenesParticipant @diogenes]

Is it likely that Sparey was recommending the smaller for actually flying it, and Ron had fitted the larger one to ‘check’ his engine a bit for the purposes of running-in?

 

[bernard towersParticipant @bernardtowers37738]

I run mine on a 15 x 6 wood, it runs at just over 5000.

[KEITH BEAUMONTParticipant @keithbeaumont45476]

I  run mine usually with an 16×4 APC nylon and get 5000 RPM. Also Have a wood 14×6 that does not perform as well and sounds different to the 16″.

Keith

[John PurdyParticipant @johnpurdy78347]

Thanks for your replies. Sounds like a 15 or 16″ one with a 4 to 6 pitch is the way to go. Another question, did you have to open up the hole in the prop hub?  The plans show a 3/8″ dia. prop hub on the engine, but most of the props I’ve seen only have holes of 3/16 or 1/4″ dia. in the hub.

John

[KEITH BEAUMONTParticipant @keithbeaumont45476]

I did not follow that route and made a conventional spinner with the same thread as the propshaft. The propdriver face was plunge knurled. Drilling out the prop,with the re-balancing needed does not seem to add anything.

Keith.

[John PurdyParticipant @johnpurdy78347]

Keith

That sounds like maybe that is the way to go. Would mean a slight re-design of the front end of the crank so I guess it would be prudent to get the prop first to find the actual size of the hole in the hub (could always be bushed down if bigger I guess).

John

[KEITH BEAUMONTParticipant @keithbeaumont45476]

John,

I am pretty sure that I made the crankshaft with a 1/4″ BSF thread. I cannot check it at the moment as my garage/workshop door will not open.

Keith.

[KEITH BEAUMONTParticipant @keithbeaumont45476]

John,

Forget that. I am pretty sure it was 2 BA now I think back.

Keith

[bernard towersParticipant @bernardtowers37738]

Her indoors changed the locks Kieth?

[KEITH BEAUMONTParticipant @keithbeaumont45476]

Nothing so simple. It is a 15ft electric Roller Door. The break mechanism has sheared and it came crashing down just as I was about to go under it. It is 8 years old and H&s have changed the system since and I am told no spares are available, so I am in for a new ,expensive ,replacement,

Keith

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