Chris Walby Posted September 22, 2017 Share Posted September 22, 2017 I am having some fun with a 38” electric twin I am about to build and while selecting a suitable prop for the motors I already have may have a potential problem or perhaps not! It is a warbird, but only stand away scale and really more practice balsa bashing for me. So how close can/should I run a prop to the fuselage as upping the diameter yields suitable gains in thrust (well within the motor/esc ratings) that I am looking for? Is 8mm (5/16) a bit close on a 8 inch prop? I could just make the wings slightly longer or move the nacelles out a bit… but how far? No clue about prop tip vortex and its interaction, but I assume it won’t end with a prize! Quote Link to comment Share on other sites More sharing options...
Nigel R Posted September 22, 2017 Share Posted September 22, 2017 Time for a 3 blade? Quote Link to comment Share on other sites More sharing options...
Denis Watkins Posted September 22, 2017 Share Posted September 22, 2017 Go with your plan Chris, a miss is a miss. As long as the prop is free to rotate. Ground clearance of course, is another matter, and related to bumpy ground, and hard or soft undercarriage. A 1 inch ground clearance can work, but is easily adjusted at the building stage. Quote Link to comment Share on other sites More sharing options...
Chris Walby Posted September 22, 2017 Author Share Posted September 22, 2017 Thanks guys, Nigel good idea but not much choice in 3 blades as tractor & pusher to get what I want out of the motors. Dennis as its hand launch/belly landing ground clearance only becomes an issue on the low fast pass! I'll report back on the 8mm clearance once built & flown! Quote Link to comment Share on other sites More sharing options...
Chris Walby Posted September 24, 2017 Author Share Posted September 24, 2017 Final bump in case anyone else has any helpful advice, then I'll get on with the build, cheers Quote Link to comment Share on other sites More sharing options...
McG 6969 Posted September 24, 2017 Share Posted September 24, 2017 Hi Chris, Except if you're planning to build a Cessna Skymaster, I don't see the need for a genuine 'pusher' prop. I suppose you simply want the tractor propellers to contra-rotate, so why not using CW and CCW props from any suitable size (from multirotors)? As you're using 8", plenty of choices for 7"-3 bladed screws, giving you an additional 1/2" clearance to your fuselage. Cheers Chris Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted September 24, 2017 Share Posted September 24, 2017 Chris Compared to all the other losses the prop and its wash suffer a bit of fuselage interaction will not be noticeable and the benefits of using the biggest possible diameter are very real. I doubt a smaller 3 blade will ever match the performance of a bigger 2 blade even taking into account any fuselage interaction About the only thing you may notice from a close running prop is an increase in noise as the prop tip vortex hits the fuselage but even so it will be nothing like the racket you get from a pusher running close to the wing trailing edge! . Quote Link to comment Share on other sites More sharing options...
Martin Harris - Moderator Posted September 24, 2017 Share Posted September 24, 2017 Take a look at a full size DC3 - clearance isn't exactly massive (ISTR mention of the propeller tips being a foot from the pilot's heads) and various full size references quote a minimum distance from a prop tip to airframe as 1 inch radially and a foot longitudinally so interaction shouldn't be a major consideration. Ducted fans certainly manage with minimal clearances! Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.