Model Boat Mayhem

Technical, Techniques, Hints, and Tips => Other Technical Questions... => Topic started by: kiwimodeller on May 09, 2010, 10:53:39 AM

Title: Reversable prop question
Post by: kiwimodeller on May 09, 2010, 10:53:39 AM
Greetings all, I have a reversable prop and am having trouble deciding which is the forward direction. The blades are roughly "D" shaped. When going forward should the straight edge or the curved edge of the blade be leading? Thanks, Ian.
Title: Re: Reversable prop question
Post by: Big Ada on May 09, 2010, 11:18:57 AM
Can you post a photo of it?.

Len.
Title: Re: Reversable prop question
Post by: Circlip on May 09, 2010, 11:58:10 AM
Should be curved edge trailing. :-))

  Regards  Ian.
Title: Re: Reversable prop question
Post by: John W E on May 10, 2010, 08:56:03 PM
hi there Ian

If you look at a standard brass prop - you will find that the leading edge is the curved edge and the straight edge is the trailing edge.  At least on Raboesch props - this is the case. (This is on their 'Class A' style props).

So, taking that the prop will spend most of its life rotating in a forward direction. I would take it that the variable pitch prop would be the same as the Raboesch props - as the curved edge is the leading edge.

Have a look on the world-wide-web at the modern-day variable pitch props, you will see that the blades are 'swept back' with a curved leading edge.

aye
john e
bluebird
Title: Re: Reversable prop question
Post by: Circlip on May 11, 2010, 06:22:32 AM
Stands to reason that there would be a difference between aero and hydro dynamics Kiwi, supose it depends whether the engine is in front of or behind the prop. On an airscrew, the preggy bit is at the back, so yes , nearest the engine.

  The three designs for VP's that I have, by messrs Starnes, Turner and Stuart show the designers have hedged their bets by making the blades with equal curvature on front and back.

  So with regards to my answer, I bow to others experience.

  Regards Ian.