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From: Budd Davisson
Subject: fixed trim tab versus servoed trim tab
BH'ers, I just came back from flying Pat Fagan's rehabilitated Smokey Bearhawk and I just want all of you to know that his modification to the trim tab system has made what was a good airplane into one that is as nearly perfect as an airplane ever gets.
It's never been a secret that even though I've always thought the Bearhawk to be the most practical, best performing four-place homebuilt ever designed, I was never crazy about the fact that the trim tab was servoed. To clarify for any who may not recognize the term, a servo tab differs from a straight trim tab in that, when adjusted, it is not fixed in position in relation to the elevator: the trailing edge of the tab moves in relation to the elevator, when the elevator moves. The direction it moves determines whether it is "helping" the elevator, thereby making felt pressures lighter (like power steering), or "slowing" the elevator and making it feel heavier. In the case of the BH, it is making the elevator lighter. Bob will tell you that he didn't design it to servo, that's just the way the geometry of the linkage turned out. The amount of servo action is slight and something anyone can get used to quickly. However, I thought it detracted from the airplane's overall handling and gave it a vaguely "abnormal" feeling.
As designed, when in level flight and the elevator is pressured one way or the other, the trim tab servo action multiplies the effect of that pressure giving more elevator action than is expected. The result is a "pitchy" feel to the airplane. So, in cross country you're better off not touching anything or you'll slightly upset the stability. This isn't a huge deal, but in turbulence it can keep you busy. And it's not in keeping with the strong stability of the airplane on the other axis.
Pat's system uses a push/pull shielded cable to move the trim tab via the trim wheel and it stays stationary in relation to the elevator. So, right at neutral, when you move the elevator, you aren't getting the "power assist" from the servo tab. Where a BH usually feels unusually light in pitch, when compared to Cessna/Piper/Beech products, Smokey now feels just like any of the aforementioned Spam cans: it is now very normal in pitch.
I flew the airplane at the same time that long time BH pilots Kevin Deuscher (spelling?) and Scott Williamson did and we were all wildly enthusiastic about the improved handling.
On downwind coming back in to land, I said to Pat, "I now don't see why anyone would even consider building a four-place other than a Bearhawk."
I'm certain that given the reaction of three BH pilots known to him, Bob B will come out with a similar fix soon. He has already done the preliminary engineering for it so it should be a fairly easy project for him.
Anyway, just thought ya'll would like to know. Smokey is alive and very, very well!
Budd Davisson
PS Pat's airplane is so smooth and slick handling, it's hard to describe. He has about 700 hours on it and is approaching 50 since the rebuild.
Subject: fixed trim tab versus servoed trim tab
BH'ers, I just came back from flying Pat Fagan's rehabilitated Smokey Bearhawk and I just want all of you to know that his modification to the trim tab system has made what was a good airplane into one that is as nearly perfect as an airplane ever gets.
It's never been a secret that even though I've always thought the Bearhawk to be the most practical, best performing four-place homebuilt ever designed, I was never crazy about the fact that the trim tab was servoed. To clarify for any who may not recognize the term, a servo tab differs from a straight trim tab in that, when adjusted, it is not fixed in position in relation to the elevator: the trailing edge of the tab moves in relation to the elevator, when the elevator moves. The direction it moves determines whether it is "helping" the elevator, thereby making felt pressures lighter (like power steering), or "slowing" the elevator and making it feel heavier. In the case of the BH, it is making the elevator lighter. Bob will tell you that he didn't design it to servo, that's just the way the geometry of the linkage turned out. The amount of servo action is slight and something anyone can get used to quickly. However, I thought it detracted from the airplane's overall handling and gave it a vaguely "abnormal" feeling.
As designed, when in level flight and the elevator is pressured one way or the other, the trim tab servo action multiplies the effect of that pressure giving more elevator action than is expected. The result is a "pitchy" feel to the airplane. So, in cross country you're better off not touching anything or you'll slightly upset the stability. This isn't a huge deal, but in turbulence it can keep you busy. And it's not in keeping with the strong stability of the airplane on the other axis.
Pat's system uses a push/pull shielded cable to move the trim tab via the trim wheel and it stays stationary in relation to the elevator. So, right at neutral, when you move the elevator, you aren't getting the "power assist" from the servo tab. Where a BH usually feels unusually light in pitch, when compared to Cessna/Piper/Beech products, Smokey now feels just like any of the aforementioned Spam cans: it is now very normal in pitch.
I flew the airplane at the same time that long time BH pilots Kevin Deuscher (spelling?) and Scott Williamson did and we were all wildly enthusiastic about the improved handling.
On downwind coming back in to land, I said to Pat, "I now don't see why anyone would even consider building a four-place other than a Bearhawk."
I'm certain that given the reaction of three BH pilots known to him, Bob B will come out with a similar fix soon. He has already done the preliminary engineering for it so it should be a fairly easy project for him.
Anyway, just thought ya'll would like to know. Smokey is alive and very, very well!
Budd Davisson
PS Pat's airplane is so smooth and slick handling, it's hard to describe. He has about 700 hours on it and is approaching 50 since the rebuild.
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