Trim Tabs

[BTAZ]

Finished welding the elevators but looking for input on whether to have one or two elevator trim tabs(I put them in both but haven't cut the trailing edge tube yet). At the Antique Fly in at Casa Grande, AZ last week saw a four place BH where one trim tab appeared to be disabled/patched over. Most other airplanes(and my flying Christavia) only have one.

Is the second one necessary?

[John Massaro]

Hi Brad,
Saw your Cristavia at CGZ last Saturday, but couldn't find you around. Yeah, I was wondering about the 4 place BH as well.

[marcusofcotton]

Finished welding the elevators but looking for input on whether to have one or two elevator trim tabs(I put them in both but haven't cut the trailing edge tube yet). At the Antique Fly in at Casa Grande, AZ last week saw a four place BH where one trim tab appeared to be disabled/patched over. Most other airplanes(and my flying Christavia) only have one.

Is the second one necessary?

Hope not. With my light prop/engine combo, that is one area I'm looking to save aft weight. Maule uses only the left side, as others as you pointed out. Many have commented on sensitive trim, though servo action is probably the bigger culprit there.

Mark J

[alaskabearhawk]

The original BH design had tabs on both elevators, spanning two bays on each side. At some people's request Bob redesigned it to span only one bay each. Technically it functions as a servo tab that is adjustable. Did the BH in question have the larger (original) tab? Those elevators are pretty large and my concern would be the differential torque induced by only having one elevator half being driven by the tab on one side. Maule has a tab only on one side, but it's a trim tab, not a servo tab...big difference.

Here is what I posted on the “unofficial” BH group a few years back:

"I’m learning a lot about trim tabs lately. I found out that a servo action trim tab is a Flettner-Ruder or Klappe, invented by Anton Flettner and patented in 1918:

http://en.wikipedia.org/wiki/Anton_Flettner

http://de.wikipedia.org/wiki/Flettner-Ruder

Servo tabs are used in quite a number of aircraft. Stephens Akro and Laser 260 being a couple of experimental types that have the Flettner tab, along with the BH.

This link has an interesting discussion of trim tabs from an engineer's perspective:

http://www.airmech.co.uk/forums/show....php/3662-TABS

Learning...always learning. Neat stuff."

FWIW, I'm leaving mine as designed.

[alaskabearhawk]

Sorry. I didn't realize I was posting in the LSA section. My bad...

[marcusofcotton]

My mistake first leading you astray, sorry...

Excellent post on the trim vs servo, yes plenty of neat stuff!

[kestrel]

I have disabled one tab on my 4 place and it was a very good upgrade. However, mine has the older large tabs, I'd question the value of making the same change to the new smaller tabs.


--
Bearhawk

[JakeP]

My first post here! I also was at the Casa Grande fly-in on Saturday. We somehow missed seeing a Bearhawk tied down but saw one take off in the afternoon as we were walking out to the dirt parking lot.

Anyway, we are building LSA 41. As we read the plans, it seemed logical that there were two trim tabs, and it does't obviously appear that it would be a problem, other than a minor weight addition. It looks from the videos that I've seen that the prototype has only one, but Mark's has two. I also seem to recall reading an article that Barrows mentioned something about the trim being a bit weak. We haven't found anything conclusive about this, but we're not particularly worried about it either way at this point. Curious, but not worried