Martin Baker MB 5

[Chris Freeman 3]

On Saturday we took delivery of the counter rotating unit that was the reason for the build of this airframe. The unit looks great and now needs to be tested so it has been mounted in the old faithful Stick! We need to use larger wheels to get some more prop clearance.

[Roy Thompson]

Look Forward to seeing your contra in action.

[Peter Jenkins]

Whilst I applaud the design and build of your contra unit, there are commercially available contras that use 3 blade props - check out this link if you are interested.  They turn 22 in to 20 in props and the revs are about 4,000 flat out.  Since these are designed for aerobatics and push out over 3,000 watts you might want to reduce the throttle movement to a lower figure to give a more scale like power output. The sound off the props is amazing.  Not cheap though!

[Chris Freeman 3]

Still not flown the unit yet, hope to get it done this weekend if things go according to plan which they seldom do.

 

The commercial units are nice but as you say very expensive especially when staying in Africa. The big problem that you have with the commercial units are the size of the spinners, the scale projects all have massive spinners. I am also not sure what a nose over will do to the unit. 

[Peter Jenkins]

Nose overs are usually expensive!  I fly F3A aerobatics and the aircraft tend not to nose over but with 55 mm diameter wheels they can be tripped up by rough lsnding zones - of course pilot error landing in strong and gusting winds, a prerequisite for most competition days(!),  also takes its toll.   The props are all carbon fibre as they need to be stiff to avoid flexing and, worst case touching, as they pass each other.  That means expdnsive!  My experirnce has been that either one or both props need replacing should you get a nose over.  The prop shafts are concentric and while they might tolerate a gentle nose over the inner shaft is likely to suffer a minor bend that means a replacement.

 

You can 3D print appropriate size spinners if you have the skills and equipment to do that.  The usual range of spinners is between 80 and 82 mm for the rear one.

 

Contras are fragile in that respect as I'm sure you will find if your MB5 tips over.  Hope it doesn't happen very often and preferrably never.

[Bruce Collinson]

With my standard of landings, I’d be tempted to rig a nose skid until ground handling qualities are determined, then remove it.

B