Wagabond with Bearhawk Upgrades

[Mattingly95969]

Has any one considered or built a Wagabond with Bearhawk upgrades? Bob Barrows improved his original design by changing to a different airfoil on the wing and giving the horizontal surfaces an airfoil shape. His changes made the stall even more docile and increased the top speed. The Bearhawk designs uses a metal coveted wing a single lift strut. That has to be more aerodynamic than two struts.

I’m not capable of doing the engineering to test these modifications on paper. Making changes can make the construction more time consuming. We have all heard about how changes can propagate themselves through a project.

Has any one been down this road? How much trouble did it cause?

[KWK]

The Wagabond plans have a wood framed wing. To get rid of the strut to the rear spar, you'd have to cover it in plywood or a wood lattice (such as is used in the Cygnet). You might need a few more ribs as well. Besides the aft strut, you'd also be rid of the diagonal bracing wires inside the wing. Using the metal wing parts from WagAero (which aren't a complete set) would have similar concerns. For this, you could select the aluminum sheet thickness by looking at airplanes of similar wing dimensions and speeds.

At these speeds, the airfoil profile is not a huge factor in drag. The USA-35-B has a lot of camber, but so does the 44xx used on some of the Bearhawks. A lot of camber basically builds some flap into the main airfoil, which the tailplane has to counteract in cruise. Switching to a less cambered airfoil would reduce the load on the tail and lower cruise drag some. Keeping the camber but making the tail airfoil more efficient would help a little. I see some of the Bearhawks used a Riblett airfoil which though it has a similar camber does have a lower pitching moment than the experimental NACA airfoils, which again unloads the tailplane.

I'll guess much of the improvement in drag reduction with the Bearhawk came from the relatively clean airfoil surface that flush riveted aluminum provides, along with getting rid of the aft struts. The LSA version does give good mph for the gph.

[Mattingly95969]

My thought was to use an entire Bearhawk wing structure, not just its airfoil on a Piper wing. The Bearhawk uses aluminum spars, ribs, and skin. This gives it the necessary rigidity to allow a single wing strut. The updated Bearhawk plans call for a Riblett airfoil, as well as other changes that lead to cleaner aerodynamics. It would be difficult to attribute how much any individual change contributed to the overall performance increases.

The reason for my original post was to hear from any builders who may be building a plane with such improvements, or seriously considered them.

KWK, your comments are valid. Thank you for your response. I think I was unclear with my question. It would be a “Fools Errand” to modify a Piper wing for the sole purpose of eliminating a lift strut. My thought is putting a wing on a Wagabond similar to the one used on the Bearhawk designs.

[KWK]

I see. I've had similar thoughts, such as putting the Cygnet wing on the Wagabond fuselage. I admire the light weight, low power design of the Cygnet but prefer doors on the sides per the Wagabond. I take it you're hoping for side-by-side seating with Bearhawk economy.

Structurally, you must move the fore and aft spar carry through tubes to match the spar spacing of the new wing. The forward wing strut becomes the only wing strut. You'll have to come up with new routing for the aileron cables.

Aerodynamically, you may have to adjust the incidence of both the main and tail wings. Here, Xfoil can be used to compare the lift versus angle of attack for the two airfoil profiles.

[KWK]

I’m not capable of doing the engineering to test these modifications on paper.

If you purchase and complete the Bearhawk wing, send me a note and I'll do the fuselage calculations for you. I might even get them right.

[mmoyle]

Is the wagabond fuselage the same as the Pacer/Tripacer? I have a set of QB Bearhawk wings and Pacer wings. Drawings for both. Your idea I think is doable. I don’t know what the difference is between the two wing mount arrangement without digging out the drawings. Wouldn’t be to difficult to add fir strips to create the NACA 009 airfoil on the horizontal stabilizer to improve stability and reduce drag. There are a couple issues or differences between the Pacer and Bearhawk….The Bearhawk flys nose down 2 degrees. The two Bearhawk I’ve flown in it doesn’t feel nose down compared to the sight view of my Pacer. The other is the Bearhawk engine thrust line is zero. The vertical stabilizer is off set 3/4” to one side to account for the torque of the engine. I suppose you could build an engine mount with the engine thrust angle 3 degrees to the right. Would fly faster with the flush rivet wings.. like comparing the Patrol to a Husky or cub with the same engine.. the patrol is faster.


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[Lee Finstad]

It sounds like what you’re describing is a Bearhawk Companion is it not?

[KWK]

It's not so large as the Companion, which is based on his 4 seater. Separately, he wrote to me he had made a Wagabond fuselage a while back.

[Mattingly95969]

I’m curious how the wing spare spacing of Bearhawks and Pipers compare. They might be the same. I realize there will be other modifications that will need to be made to mate the wings to the fuselage and make everything work correctly.

it is good to see some interest in this idea.

[mmoyle]

The centers on the wing spars are 31” for the Pacer/Tripacer. Bearhawk is 32”on center. And the rear spar wing mount is 1-1/2” lower than the front wing spar mount bracket, which is virtually the same as the Pacer. Moving that rear spar carry though tube aft 1” and changing out the rear door posts on either side isn’t that big of a deal. The Bearhawk lower strut mount is at a different angle and is located about 2” forward of the Pacer lower wing strut/s mount. Which isn’t an issue other than insuring when fabricating the upper wing strut fittings you align with the lower strut mount…might be a few degrees different. The difficulty will be making double damn sure the wings are perfectly aligned prior to drilling the wing spar mounts on the fuselage and the wing struts. There’s no room to fudge it…. Unless your doing what I am thinking about doing…modifying the Bearhawk wings to mount like a Cessna.



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