Bristol prop

[Chris Beer]

ok call me thick , but my bristol m1 has a 6" domed spinner. that means alot of prop will be covered, with an 80fs i was thinking about  a 13x6 zinner but only 7" of prop will hit air. should i go big on pitch to compensate or as big on every thing or not worry.

theres not alot written about this model ,which is good as i wont be tripping over loads at flight line but a bugger when you need advice.

thank you.

[Simon Chaddock]

Hi

Early rotory engines were relatively large in diameter so quite a bit of the prop was always blanketed, but as these engine rotated relatively slowly for their power they turned a huge diameter prop. In any case as about 90% of the thrust comes from the outer third of the blade the loss of thrust is not great, however the bluff shape of the engine does add considerable airframe drag so top speed was limited. On the Bristol they hoped the big spinner would improve things abit.

The best answer to the issue of a scale spinner is of course - use a scale diam prop! Remember that if you have the engine torque to turn it, apply the power gently at slow air speed. True scale tends to have scale flying characterisitics!

Simon 

[Bob Imp]

I was worried when I first built one of these!  Mine flew fine with just a couple of inches of prop. out beyond the spinner.   Lovely looking aircraft on the ground as well as in the air. Wonder they`re not seen more often but I suppose the complicated build puts people off.   Pity!

[Ernie]

Hi Chris,

If you are interested in filling up that open cockpit, this might be of interest...I've got  lots more, also some pix of the pudding basin spinner somewhere in the big joke thats called a filing system, If you need them

ernie

[Chris Beer]

thankyou ernie, any and all help greatfully recieved.

[Ernie]

Hi Chris, This is the best that I have of the spinner, sorry it's a bit soft

ernie

[Ernie]

Hi Chris, I've just found another

ernie

[Chris Beer]

thankyou ernie. that prop looks huge, i might try a 14 or 15" prop. a good view of downward viewing holes

[Evan Pimm]

You will ned to use the normal prop that the engine uses, anything much bigger will not fly the model as the engine's power output is very much RPM dependant. As for the size of the spinner and what's left of the prop sticking out, well to be honest it doesn't seem to make a lot of of difference to the thrust available. As this is a slow model you can get away with the old 'more diameter, less pitch' thing, but keep the engine in the rev range where it will deliver the power needed.

Evan. 

[Simon Chaddock]

Yes you must keep the engine in its rev range so that limits what you can do with the prop.  You can go slightly bigger with a finer pitch but too fine and the thrust will fall off badly in flight.  The answer of course to a scale diameter prop and pitch is to gear the motor down - just like all the big piston engines did. It needs a bit of good engineering to do well but it looks fantastic.