Page 25 - Volume 15 Number 6

Topping Governor was not being reset enough to prevent the propeller speed from indeed reaching the primary governor’s maximum RPM setting ... 1,900 in the case of the F90-1. Thus, we experienced the phenomenon discussed above: The unstable jump from a negative to a positive blade angle as the primary governor reacted to the momentary overspeed situation by releasing oil from the prop back into the engine. The springs and counterweights sent the blade angle to a higher value. But remember, starting from a negative angle, this action causes less, not more, resistance to rotation! The governor cannot work properly until the blade angle jumps forward through flat pitch and finds itself with a positive, not negative, value.
As stated above, I am lucky that both sides were mis- rigged the same. Otherwise, I am sure I would have left the runway.
It is my belief that the primary reason for having the Fuel Topping Governor is the necessary protection that it stands by to provide whenever Maximum Reverse is selected. We could probably fly thousands and thousands of King Air hours without an FTG and never notice the difference ... if the rigging is halfway correct. However, it is surely comforting to know that we have our little FTG friend standing by to save us from harm in Max Reverse if we and/or the mechanic did not do our jobs
correctly. That the FTG can provide one more overspeed protection device in normal operation? I personally think that’s just where we “store” it until we select Maximum Reverse the next time!
As you have perhaps been taught, something that prevents blade angle from being able to change will render both the primary and overspeed propeller governors inoperative since they both accomplish their jobs by varying blade angle. Yes, that’s true. That is where the FTG would be helpful in flight. But you know what? In my 49 years being around King Airs I have yet to hear of that “unable to change blade angle” scenario ever happening. Comforting, eh? KA
King Air expert Tom Clements has been flying and instructing in King Airs for over 46 years and is the author of “The King Air Book” and “The King Air Book II.” He is a Gold Seal CFI and has over 23,000 total hours with more than 15,000 in King Airs. For information on ordering his books, contact Tom direct at twcaz@msn.com. Tom is actively mentoring the instructors at King Air Academy in Phoenix.
If you have a question you’d like Tom to answer, please send it to Editor Kim Blonigen at editor@blonigen.net.
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KING AIR MAGAZINE • 23