Greetings Tony....

I am building a Zenith 801 with a 13b rotary.  While not a 701, many of the challenges I am solving will be the same you face, perhaps more so due to the smaller size of the 701.

I believe the maximum total FWF weight of the 701 is listed at 185 pounds, though 200 pounds is not an unheard of installation weight.  Going much above that gets you into increasing the span of the horizontal stabilzor and elevator to control the pitch at lower speeds.  Given that and the fact a stock bare block weight of a 2-rotor 13b comes in around 190 pounds I do not believe a 2-rotor 13b is a good option for the 701.

The next challenge is mounting I am not sure of Zenith's suggested thrust line for the 701, but the 801 is only 200mm from the top of the firewall.  Upright or plugs up, this is a pain when using a reduction drive inline with the shaft.

Thus, a single rotor most likely with end housings fabricated from something other than iron will solve your weight issues.  As to mounting, an offset reduction drive will solve this problem.  Counter this against the FWF ea-81 701's coming in around 200 pounds and mostly purchasable solutions, perhaps an ea-81 is a better option as of today.  Then again where's the fun in being like everyone else...

As a side note, what/who is the PFA?

Regards,

Scott

http://home.att.net/~the_stouts_zenith_801/

> I intend to build a Zenair CH801 (13B), at the moment it is not approved
> by the PFA, my second choice is a CH701. My dilemma is ; to match a rotary
> to 100hp efficiently would it be best to "make" a single rotor, run a 13B
> direct, de-rate a 13B/PSRU or use the Soob EA81 that I already have.
>
>