Prop size

I am presently working my way through a Humbug 1.5 glow motor but have not found any reference to prop size, anyone got any ideas or is there a table available for this sort of thing. Where are you Tug?

Prop size and pitch will be determined by the speed and power of the engine.

A low speed engine of the same power, will run a coarser pitch prop of the same diameter, than a high speed motor.

I wouldn't think the precise size is hugely critical, but ISTR from my aero-modelling days that a 1.5cc engine would take a prop of 7" to 8" dia and around 5" pitch. The larger diameter might give better starting dur to flywheel effect and also keep the revs down on a new engine. I don't think that you'll do any harm at around those sizes.

When I built my Boll 1.8 ci, I used a (-actually, I'll have to check - oops), I think it would be a fairly 'safe' place to start for initial set-up with the Humbug - but happily defer to those with greater experience, I'm a rank beginner.

I think at least it would give you a sense of 'what it wants'

Edit - just seen Clive's post - better advice, maybe..

Edited By DiogenesII on 22/07/2023 13:10:38

Edited By DiogenesII on 22/07/2023 13:16:51

Hi Bernard - still here in Beccles

Clive's advice is sound - early runs on say a 8 x 4 and a 7 x 4 for general running will be fine. Keeping the pitch at 4" or below allows the engine to rev without being loaded. You could use a 6" pitch on bench running but that would usually be much better suited to flying situations. I very rarely (bench) run my engines on 6" pitch props for that reason

I have a FROG Talisman control liner with a Frog 150 in it. So nippy it's getting difficult to handle these days so it flies on a 7 x 4 prop to slow it down a bit

Getting small props may prove difficult - so much these days are aimed at electric motors but Leeds Model Shop might be a good start.

Just to get you in the mood here's a new model - it's an enlarged 30" span KK Ranger with an OS 20FP glo motor converted to diesel.

See you at Lowmex?

Best - Tug

these questions take me back a few years i had a mills 1.3 engine but could not start it as i had a small 6 inch

nylon prop on the mills i was advised it was too small and not heavy enough and was given an 8 inch wooden prop

and it started and ran straight away.

Yes I’ll be there Tug. And thanks everyone for the input, I will look into getting a couple.

Edited By bernard towers on 22/07/2023 13:57:32

Here you go Bernard - these Graupner props from Leeds Model shop will be ideal and reasonably priced too.

**LINK**   The 7 and 8" dia are on the second page

LMS are very efficient on dispatch so can recommend them

Edited By Ramon Wilson on 22/07/2023 18:17:32