I believe there is a Bergey Dealer that's a member of this forum. However, Let me put in what I remember when we were Bergey and Whirlwind, and Wincharger Dealers-Installers.
First, as I THINK, I remember, Bergeys have an offset bend at the end of the Tail FIN. VACUUM pulls the tail around, from the wind getting stronger and rushing past the blades. A well tuned machine, will not pass any large amount of wind through the blades. It gets thrown off to the sides and around the machine. I have climbed up and BY HAND, steered machines out of the wind. You can effectively light a cigarette with a match, behind a spinning blade. Been there-done that. This is NOT BS. It was on other brand machines, including my own 4KW with 15½' Blade span. Cable down to the ground to manually furl the machine, jammed up on the side of the pulley it went through. I tried to copy Jacobs machines, as much as possible.
Bergey also did NOT furl all the way to roughly 90°. It hit the stops at around 75°. The degree of rise of the tail, is not as exaggerated as much as the design here. That way, it furls a bit easier, but, also maintains nearly full output, without burning stators and exploding blades and such. I'm also thinking, the tail vane JUST sticks out from the diameter of the blades, and, is quite small compared to what you guys build.
We sold them in the late 70's-early 80's so, they MIGHT be built out of the USA for all I know, now. Haven't had contact with my x-partner for several years.
We had our tower specs modified by Mike, owner of Bergey, so we could install their NEW 10KW machines on our towers. They were even going to put them as an option for them to sell to Dealers-Customers. My partner went out to Oklahoma City and visited the factory.
The Motored yaw system, I would not use. We sold a Whirlwind 4KW, down in Paris, Arkansas, and had to take it down and have it factory rebuilt. It had a 4 blade metal fan that gear drove the yaw gear. It was activated by the wind and when I S L O W L Y crawled up the tower (100'), The machine was hanging by 1 bent bolt. Anyway, I found a piece of debris that was stuck in between the fiberglass housing and the shaft that went from the fan, down into the housing. The fan would not turn, so, the machine ran away, totally shattered the 1 piece 16' blade, and about shook the machine off the tower. IF y'all try a yaw system, and it fails, yer screwed, WORSE than what y'all have now. TRUST ME ON THIS.
We put a 24V Wincharger on a 100' tower, up on the high bluff, above Greers Ferry Lake, in Arkansas. Had to crawl up that one, with 1 guy wire broken and the blade in a jillion pieces, and THAT generator was held by a BROKEN piece of bolt. Talk about scary climbing. Managed to get it tied off to the tower, and then, lowered to the ground. Winchargers have a dual "SHOE" brake, like car drum brakes. Faster speed, more pressure applied. THIS ONE, burned through the shows, and the machine ran away.
I could tell y'all a bunch of stories. This IS all from experience.