I modified the Blue Angel model in the Ikarus Aerofly simulator by introducing anhedral to the tailplane a la Curare, to see what it would do.

The effects were most noticeable in knife edge flight.

There were two effects:

- The anhedral reduced the tendency to pitch towards the belly in knife edge.
- The anhedral reduced the tendency to roll out of knife edge.

To get both effects to "zero" it was necessary to also increase wing dihedral. That is, when enough anhedral was introduced to remove the tendency to pitch towards the belly, the anhedral caused the aircraft to roll _into_ knife edge. To remove that tendency, it was necessary to increase wing dihedral.

This agrees with the Curare design, which does use a bit more wing dihedral than most other pattern designs that don't use any tailplane anhedral.

Now the pitching effect in knife edge is caused by the change in how the downwash from the wing hits the tailplane in knife edge vis a vis straight and level flight.

This shouldn't really be affected by the presence or not of a pipe under the wing centre section. So the amount of anhedral needed to remove the tendency to pitch towards the belly in knife edge should not change whether a pipe is hung under the fuselage or not. This agrees with Prettner's Magic design which used as much tailplane anhedral as the Curare, with the pipe hidden in the upper fuselage rather than hung below the wing centre section.

What probably will change to a greater or lesser degree, with hanging the pipe under the wing or not, is the value of wing dihedral required to cancel any rolling tendency in knife edge, given a value of tailplane anhedral already chosen to cancel the pitching tendency.

So omitting the pipe, I think you should be looking at changing wing dihedral, not tailplane anhedral.

But by how much?

For my simulator tests, I use my Multiplex transmitter and have all the mixers and so on set up as I would for a real pattern model.

I found that by using the mixers it is possible to trim the plane to stay true in knife edge in both pitch and roll, with or without tailplane anhedral, for a range of reasonable values of wing dihedral.

So with a modern transmitter you will be able to "zero" the model in for true knife edge flight, whether you use a pipe or not, and whether you stay with Prettner's recommended anhedral or not - or even without anhedral (Curare modified back to Super Sicroly... Super Curaricroly? Super Sicrolare? ).

My recommendation therefore would be to keep Prettner's suggested tailplane anhedral and wing dihedral, use your mixers to zero in the model, and look for evidence requiring a change in wing dihedral (wings rocking at low speeds, aircraft rolling into or out of turns etc) when flying the model.

My guess is you won't find much reason to change wing dihedral, and in the end building a Curare as per Prettner's plans will do you nicely, pipe hung under the fuselage or not.

With best regards,

George