Consider having the body tube end just after the synchro box and before the mixer box.

This will-

This tube will be approximately 52" long.

This end, complete with ring could also support a brace to the back supports.

The backboard has a slope of 12.175 degrees.

The Seat back has a slope of 15 degrees in the center. This is less if the butt "pocket" is included.

Re: Pilots of different weights: Normally the heavier pilots will be taller. Consider having an adjustable seat instead of the pedals. This will allow the balance arm length to increase as the balance weight decreases. The seat should move down slightly as it moves ahead (in-line with the tail tube?) so that the shorter person’s ankle has the same angle with the pedals as the tall person.

A problem with this is that the seat may no longer be a part of the structure.

Extend seat so that shorter person, on cushion, still has plenty of seat under him.

The seat belt could/should attach to/near the bolts for attaching the rear supports, which are located in the lower back corners of the seat. Consider attaching the seat belt harness to the lower vibration mount bolt.

The shoulder harness must attach to a structurally sound member and the tension on the rearward straps should be as close to horizontal as possible. Consider two 1/8" diameter wire cables going from the two top back corners of the seat to the tailboom attachment flange. Consider attaching the 2 sholder harness to the vibration mount bolts.

As an alternative to the 1/8" dia. Wire consider small diameter carbon tubing; which will give strength in compression as well as tension.

This will also give some additional bracing to seat back.

The seat back should be approximately 6" higher so as to accept the "Y" shoulder harness.

The width wise tube, at the front of the seat is used to brace the backboard and also as a tie-down.

Bracing must be located below seat. Consider using netting in this area also since it will provide a storage pocket and also the netting will not give as much resistance to airflow. Make sure that it would not interfere with cyclic stick.

Seriously consider locating the power train controls, and possibly gauges also, here. See document A038.doc.

The width on the back face must be wide enough for 2-1/4" dia. gauges.

Should it also match the width of the tube at this point?

The lower backboard is subjected to large downward loads, caused by the downward prying on the tube by the two rear legs on landing.

Consider using seat from Aircraft Spruce for Male mold, if it is wide enough,