Three to Two blade prop?

[SIMON CRAGG]

I would like to change the three bladed prop (13x7x3) on my Dynam 109 for a two bladed prop. Can anybody advise as to what size / make / type would be a direct replacement? Many thx.

[Keith Berriman]

Simon when two blade prop people go to three blade we are advised to reduce by one inch so maybe you increase by one inch ?

[Denis Watkins]

Yes lads, 1", and the 2 blade always feels better in the air

[Bob Cotsford]

You can apply the same rule to the pitch, ie try 14*7, if you don't have ground clearance for a 14" prop then a 13*8 should work. The standard seems to be APC-E props for electric. Ideally though, check the current with a wattmeter to reduce the risk of frying anything!

ps - there is rarely a 'direct replacement' in the model world, just thr preferred alternative. 

And there are lot's of preferences out there, everyone has their own. 

 

Edited By Bob Cotsford on 27/06/2018 11:26:09

[SIMON CRAGG]

I asked the same question to Motion RC and they came up with a 15x6, which is similar to the 13x8 and 14x7 as all = 21" one way or the other. Looks like ground clearance is the next hurdle. I have to make an admission here...........I have watt meter but have no idea how to use it, could one of you "experts" explain in idiot-proof language please?. Many thx for you help so far.

[Bob Cotsford]

Just plug the meter in between the battery and the ESC. Both of mine then display the current, voltage and power being used. At this point it helps to know the current rating of your motor and ESC! As you slowly open the throttle you will see the current increasing, don't let it exceed the ratings of your setup or the magic smoke will escape. It helps to have a selection of props on hand to try.

[SIMON CRAGG]

Posted by Bob Cotsford on 27/06/2018 16:04:14:

Just plug the meter in between the battery and the ESC. Both of mine then display the current, voltage and power being used. At this point it helps to know the current rating of your motor and ESC! As you slowly open the throttle you will see the current increasing, don't let it exceed the ratings of your setup or the magic smoke will escape. It helps to have a selection of props on hand to try.

Sounds straightforward enough. I know the ESC is 40amp, but how do I tell what the motor is rated at? Its a BH3720A-KV500 shich means nothing to me!. Do I just make sure I do not exceed the 40amps, or do I have to worry about amps and volts etc? Many thanks for your help so far!

[Dave Hopkin]

Posted by SIMON CRAGG on 27/06/2018 17:45:54:

Its a BH3720A-KV500 shich means nothing to me!. Do I just make sure I do not exceed the 40amps, or do I have to worry about amps and volts etc? Many thanks for your help so far!

If this is the correct motor (its BM not BH) **LINK**

Then its rated for 3 to 4 Cell Lipos

With a max current of 35a continious 49a burst

[SIMON CRAGG]

Yes, thats the one, but 500kv not 650. So as long as I do not go over 35 amps when I am trying different props (and checking the Watts to which develops the most power), I am good to go?.

[Simon Chaddock]

Simon

Just one last observation. The best static (measured) power you achieve does not necessarily transfer to the best flight performance.

Yes if you keep below the manufacturer'd specification limits for the various components (assuming they are actually correct!) you should avoid "frying" anything but the overall "best flight performance" equation is quite complex and includes how you like the plane to fly so it might need a bit of experimentation to determine what works best for you.