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Saturday, November 19, 2011

P-38 Counter-Rotation Mod

The Hobby King P-38 did very well in my recent review - but that's even more reason to upgrade the airplane.
The MAS 9x7x3-blade pusher and puller props run about 
$11 each.  The pusher should be installed on the #2 engine
(pilot's right) to minimize P-factor when single engine.
 I've added two upgrades: one big; one small:
  1. Counter-rotating motors and props
  2. Improved nose gear servo
The HK P-38 ships with custom propellers that work well and look great.  Each blade has to be inserted and screwed into the two piece hub.  How hard would it have been to provide three clockwise rotation blades?  Obviously too hard, cause they didn't.

The great news is how easy the Master Airscrew 9x7x3-blade pusher/puller series props fall right into this airplane, while still using the great looking stock spinners.  The only modification required is to slice about 1/8" off the plastic spinner sleeve that slides over the motor shaft.  Once the inner shaft is shortened, the thinner prop depth of the MAS 3-blade installs exactly the same way as the original.

After installing the pusher prop on the pilot's right side motor (engine #2), all that is left to do is switch any two of the three electric motor ESC leads on that side to reverse the motor's spin direction:
Since the original props were 9.5" in diameter, this new MAS config should yield a higher top speed, assuming similar pitch.  Drag from the rudder offset is also gone.

Maybe I'll dip the tips in yellow?

My second upgrade was to swap the cheap nose gear retraction servo to a Hitec Carbonite Micro Feather at a cost of about $15.  My hope is that the longer throw and greater torque will help keep the NG from collapsing when rolling over uneven surfaces.

Total cost to upgrade the P-38: about $37, bringing the TCO to about $175.  This plane flies so well, it remains a bargain.

No more torque and P-Factor!

In the Air:

I thought the P-38 was already a joy - but this mod takes it up another notch.

The plane has a lot of power on 4S.  The MAS 9x7x3 combo increases the top speed, but at the expense of static thrust (which is plentiful).  The plane effectively has unlimited vertical, but it does slow down some on the way to becoming a dot. The crown jewel is arrow-straight tracking at all airspeeds and throttle settings.

This plane has strong aerobatic prowess for a warbird, and the counter rotation makes it even better.  Knife edge flight can be held indefinitely on either edge with some coupling to iron out.  Spins are tight but controllable, upright or inverted, either direction.  Bat turns are impressive.  Loop and roll aerobatics remain symmetrical seven ways to Sunday.

Beautifully behaved; straight as an arrow; airspeed agnostic.  The 38 is a much more cooperative aerobat than it should be.  This counter-rotating twin boom design is on to something special.
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