airfoil shaped ribs and gap seals on the BH

[Mark Goldberg]

Today, I had the opportunity to talk with a Bearhawk owner who first flew his plane with everything like mine - original. Then he added the wood strips just on his hor stabs after tearing some fabric on a fence. Then he added some gap seals between his hor stabs and the elevators. The gap seal comes in three ft sections from Spruce and is what Pat Fagan used. The difference here is that these things were done one by one and not all at the same time resulting in good info on each change.

The airfoil shaped ribs did add control authority and added stability. But this pilot felt like the gap seals actually gave more additional control authority than the airfoil shaped ribs.He said the airfoil shaped ribs did 30% and the gap seals did 70%. I was surprised with this but Bob Barrows wasn't. Bob said the gap on his BH design is wider than the Patrol & LSA. He wasn't surprised of what this pilot was reporting. Bob thinks both the airfoil shaped ribs and gap seals are something worth doing. Just thought I would pass this along to you guys building. I might have to put those gap seals on myself. Mark

[bestbearhawk1231]

Mark, are there patterns available for the airfoil shaped ribs?

[Mark Goldberg]

Not really. We make some wood strips that our existing customers glue to their flat ribs on the hor stabs and vert stab. They are $250 a set. That is the best I can offer now. Mark

[Battson]

Here's the ribs installed.


At low speeds more authority would be good, but at cruise I find the elevator is sensitive. Mark, did the person you're talking with mention whether the added control was most noticeable during the cruise, slow flight, or across all regimes?

[Mark Goldberg]

He didn't say specifically. Mostly though he talked about the ability to arrest the descent in a steep approach to small, short strips. Mark

[JCD23]

Why are there nut plates in these Horizontal Stabilizer airfoil ribs?

[Battson]

Because we wanted a way to attach the stabiliser root fairing securely.

[Helidesigner]

Interesting. Thanks for the information. I expect gap seals to be more effective too. Maules and other tube spar horizontal tail planes use seals with good improvements. I plan on sealing mine after I get some hours on it. Mark

[max_burke]

Probably a dumb question but would the airfoil shaped Patrol horizontal stabilizer work on the 4-place Bearhawk?

[marcusofcotton]

Probably a dumb question but would the airfoil shaped Patrol horizontal stabilizer work on the 4-place Bearhawk?

The concept works and Avipro has wood strips they sell to attach to the T25 strips to do the same, good reports. I understand the Patrol stab itself is entirely different as to the idea of taking a Patrol stab and mounting it on a 4 place.

Mark J

[Papa Foxtrot]

It seems like it would be fairly simple to accomplish if you're plans-building. The formula for both the LSA and Patrol is the same. If the stab rib is X in length, then then max thickness is .09X at .3X. Then use the bottom of the airfoil template as the "french curve" to draw the airfoil.

[Zzz]

If I wanted to fab the ribs myself, is there any documentation on the profile? Papa Foxtrot, you mentioned using the bottom of the airfoil template. Is that formula method something from the Patrol plans? Is the profile the same top and bottom?

[alaskabearhawk]

Pat Fagan got a copy of the Patrol plans for the airfoil shape and scaled them for the 4 place. The airfoil is symmetrical, I copied his templates. Bob said any symmetrical airfoil with the widest point at 30% of the chord would work. After doing a bit of research, I found out that all 4-series NACA airfoils are at their widest at 30% and the NACA series from 0006 to 0012 have been used for exactly that…the horizontal stab on many designs. I eyeballed a plot of the NACA 0006, 0009, 0010 and 0012 airfoils against the small, grainy pictures of the Patrol ribs on the parts section of the Bearhawk Store site. Out of all those, the 0006 looked the closest.

Remember, the vertical stab can also take an airfoil shape. Just an FYI for those that are doing a profiled vertical stabilizer. I spoke with Bob about some questions I had reference the profiled ribs I’m making for the vertical stab and we got talking about the alignment. Bob told me the best would be to align the top of the stab with the fuselage centerline and the bottom gets the 3/4in offset. I had aligned the front spar with the tail post, but now I see it will probably have a tiny bit of left offset at the top when viewed from the front. I’m assuming this will help compensate for the increased lift generated by the profiled tail. He said if I just aligned it with the tail post I would have to hold a bit of left rudder in flight or adjust the trim tab (if installed).

https://www.youtube.com/watch?v=rUyTOwfnQiI