Prop for a Weston Cougar on Jen .37

[arun 0]

"Nearly" finished my Weston Cougar. It has a Jen .37 up front and the recommended prop range for this is 8x6 - 11x4. Anyone care to suggest what a good size prop to start out with would be?

 

I've put a domed nut on in place of a spinner. Since the starter will make direct contact with the prop nut, is there anything I need to do to stop the starter just unscrewing the prop nut rather than cranking the engine?!

 

Cheers,

Arun

[Gerard 10]

Arun,

 

My Cougar has an Irvine 39 on board (lovely engine!) and it runs comfortably with an APC 11 x 4 prop. Both thrust and response are very good. Can usualy fly it around on about two thirds throttle with no problems.

 

You'll certainly enjoy flying the model.

[Nutz 0]

I use a Gruapner 10 x 5 on my OS32

[Jimbo 0]

is there anything I need to do to stop the starter just unscrewing the prop nut rather than cranking the engine?!

 

Yup, do it up sufficiently tight, or use your finger!

[Lofty 5]

is there anything I need to do to stop the starter just unscrewing the prop nut rather than cranking the engine?!

 

Yup, do it up sufficiently tight, or use your finger!

 

Use metal weld or stud lock..............maybe

 

 

P.s Or maybe better still! Weld the dame nut on

[CaptainBev 0]

Hi Arun,

 

If you can get the engine nut on as well as the dome nut that will probably be your best bet. You should be ok with that, otherwise something is wrong. You dont need to murder the nuts when doing them up as with some of the smaller engines you can pull the threads on the shaft and then you are really buggered. Dome nuts are always a bit wiggly to start with a starter, so once the engines run in a little it should start with a flick from a chicken stick or use the handle end of a rubber handled screwdriver about an inch in diameter. You can make your own from a bit of broom handle about 8" long and then wind electrical tape arond it to make a cushion about 3" down from the end.

 

Cheers.

[Bravedan 106]

Hi Arun, OK, so I'll add my 5p's worth and try to say why at the same time. Bottom Line first, I'd start with around 11x4, too, BTW.

 

You have an engine with a manufacturer's range of suggested props, so what affects the choice you make? Well, it's basically what you need the engine to do.

 

On a Fun Fly you are most of the time not going to need high flying speed, what you are going to need is fast response to throttle, a lot of instant airflow to use quickly over the surfaces to keep control when the plane is near or in the hover, so there is possibly little or no airflow from forward speed.

 

The larger the prop circle the more potential for windage over surfaces. The lower the pitch, the faster the engine can spin up and create it without overspeeding the plane or bogging down the revs by overloading the engine.

 

Generally speaking, the more forward movement speed you want, the more you reduce the prop diameter and therefore increase the pitch.

 

It's as much an art as a science and it's a good idea to have a range of props "in stock" to test for the best one for any application.

 

Indoors, where balancing is not quite so vital, I use hand clipped props to increase the options beyond the available commercial range to get the load/thrust balance "just" right.

 

Hope this helps...........

 

 

Dave

[hotrod 0]

Hi Arun

I go along with 11x4 that's what I used on my J'en37 but remember to use 5% nitro fuel,J'en's dont like anything higher.

Rod

[arun 0]

Thanks chaps, great advice all round Looking forward to getting it in the air - targeting next Sunday weather/family commitments allowing. Cheers.