Mud Duck Aviation Forums

   Hello Greg, I was wondering how much down thrust is really needed?  I'm modifying the nose for a 'radial type' motor mount instead of the 'beam style'.  I'm biulding the MK II. I will be using a small gas engine.
   I'm making the nose cover (F-13) taller and it's going to be aircraft grade ply.  This is what I will bolt the engine to.( I've eliminated the area where the engine normally sits by moving the firewall (F-12) forward and 'combining' it with F-13)
  I've cut the forward fuse half's out (F-1), using the same angle that F-13 is normally at. I see that this is even more then the actual 'down' of the beam mount. So I'm going to take some of the 'down' out by cutting less of an angle....how much less ?  Will I need less down because of the weight of the engine?
   I've been following "leo's" on-going 'build and fly' on YOU TUBE.(see... puchmanlenny) He said he's not using any 'down', but he did mention that he's slightly nose heavy.
I'm ready to try ...."that looks about right method" and start cutting.....LOL. Any help/thoughts would be appriciated.

Hi David,

 The stock design has about 7 degrees of downthrust built into it.  The reason is to compensate for all the lift; more speed = more lift, and the downthrust is what helps fight it.  You may not need 7 degrees with that engine since you will be swinging a bigger prop, but I haven't performed this mod myself so I can't speak from experience exactly.  If Leo said he has no down thrust and reports that it flys great then I would start there.  you can always shim the engine if necessary.  I'm sorry I can't be more helpful, but I would use Leo's Duck as a reference.

Greg