There are two separate issues - at least. A dipole antenna is simply a 1/2
wave antenna fed in the middle, so that a 1/2 wave is on each side. In
effect, each half element reacts with the other half. A 1/4 wave ground
plane simply replaces one of the elements with a plane perpendicular to the
other.

The second issue is polarity. It just happens that many dipoles happen to
be mounted horizontally, while verticals are mounted vertically. A dipole
can also be mounted vertically. Polarity should be the same or there will
likely be a severe signal decrease between stations. By convention,
aircraft vhf communications is vertically polarized.

It is difficult to analyze your problem with the sketchy information given,
but basically an antenna is an antenna. If your 1/4 ground plane does not
work at all, a dipole will not work, either. Replace of one with another
will simply postpone finding the real problem.

The most likely problem is the antenna connectors. Unless they are
assembled correctly, the entire system will fail.

Even though the location of your antenna may not be the best, it should be
adequate for what you want. Your champ is a fabric airplane, so you will
need a "ground plane for the 1/4 wave vertical. This can be as simple as a
24" wire attached to the base and extending out. In fact, that will turn it
into a dipole. But even that will not cure a bad connection. It is also
possible the radio has a problem, but I would not expect that.

Find someone who can assist you to check things out. It is very difficult
to diagnose the real problem without being there.

Colin N12HS