I just recently acquired a Bobcat 52 N.I.B. off the RCU classifieds. I'm planning on going with OS .75AX, 11 x 8P Graupner, retracts the whole 9 yards. i'm looking for some advice on engine location (forward/aft). I know that the farther forward the engine sits on the mount, the closer the propeller tips come to the wing trailing edge. Is there an optimum or minimum clearance I should maintain between the prop tips and the wing trailing edge? I could just mount the engine as far aft as possible but I know there is a CG issue to be addressed with larger engines on this airframe. This .75AX is pretty hefty (26 oz.). I want to leave enough clearance without having the engine unnecessarily too far to the rear. I've read through this entire thread twice and there is a wealth of knowledge and experience here that will enable me to be successful with this aircraft. I tried to get an idea by looking at all the photos in this thread but it is kind of hard to extrapolate a measurement from a picture. It will certainly eliminate what would normally be a lot of trial and error getting this aircraft set up correctly and flyable. Any input from any of you still following this thread will certainly be helpful and appreciated.
Since the engine is mounted backwards we'll talk about forward-backward relative to the whole plane.
As long as the prop clears the wing trailing edge by about 1/4" or more you should be fine. I would recommend 1/2" clearance just for safety purposes.
I find that with the 75 size engines, 1/2" forward or backward does NOT have a dramatic effect on the C.G.... and whatever there is can be fixed by moving the battery packs a bit.
I put my dual packs in the nose.
Remember that this plane will not fly like other prop planes you may own. Some points...
- It will seem to be "mushy" until it gets up to speed.
- If the wing incidence is not positive when the plane is sitting on the ground it will seem to stick to the ground until it has more than enough airspeed, then head straight up, loosing speed and control.
- Elevator "neutral" should exhibit a slight upward deflection.
- Slight aileron reflex helps your landings. Put this on a switch if you can and turn on the reflex when entering final. ( Practice high in the air IMMEDIATELY once the plane is trimmed... )
- Landings should occur slightly nose high, once the main gear touches down, try to keep the nose gear up to bleed off speed.
- You'll need lots of runway.