Hi all

I am looking to design and build a .60 sizedpattern plane. My first attempt had a couple of problems. The most significant was pitch up in knife edge. How can this be eliminated aerodynamically on my next design? What constitutes a 'perfect' elevator/rudder configuration?' Someone told me that the elevator must be moved down but I am skeptical of this as it is already below the line of the wing.

Also, what elevator moment to wingspan ratio is the 'golden rule' for a competitive pattern plane?
Lastly, is it possible to build a competitive .60 sized pattern plane fuselage out of foam/fibreglass composite?

When I say 'competitive' I am never going to win anything, I just don't want to be embarrased!!
Thanks
Gareth

there are hundreds and hundreds of threads about 60 size pattern plane in the classic patten forum. a lot of them are about fiberglass fuse planes.

A lot of planes have the opposite problem, i.e. they pitch "down" or to the belly.
One (amongst others) "fixes" for this is to lower the tailplane.

So in your case, you would actually want to RISE the tailplane, not lower it.

However, location of the CG is probably the most significant factor affecting knife edge pitching. Do you have a very forward CG?

Magne

Hi Gareth,

Search for 'rudder pitch coupling'
Here is an old thread of me:
http://www.rcuniverse.com/forum/m_15...tm.htm#1553776

The photo's got lost but it was a shoulderwing configuration with the stab placed low in the fuselage. It piched up strong. Placing the stab a bit above the wing position cured the problem.

To find the optimal position is a matter of trial and error. If you do not like to go that route have a look at the position of the elements in an existing design.

In shoulder wing configuration where the stab is well below the wing, it is probable that some of the wing's downwash is dumped onto the stab. This will tend to pitch the nose up.

In more conventional, lower wing configurations, I have a hard time believing that any wing downwash is being dumped onto a stab because the wing is below the stab (stab located above the wing in such config). In fact, in such conventional configs, you can move the stab an inch or more up and down and not affect pitch coupling in knife edge at all. Playing with wing incidence and stab incidence will affect pitch coupling considerably assuming the CG is fixed.

What I prefer is a CG at about 30% MAC and then trimming around that CG preference. Usually it means that the wing is at 1/3-2/3 degree positive, thrust is at 1/2-1 degree negative and stab is at zero. I try not to make the CG a trimming variable...I fix it and leave it alone. Some folks prefer a more forward CG and others a more aft CG. More forward CG, to a point, is probably OK, depending on how much back stick you like in inverted flight. Bryan Hebert preaches a CG at 25% MAC for example and it works great for Bryan and others that have tried it there.

More aft CG is more dangerous regarding unwanted pitch to belly on the typical 2x2 pattern planes of today. I wouldn't go beyond 33% MAC although the current crop of pattern planes can be flown with CGs as far back as 38-40% MAC.