Original Bearhawk vs. B model question

[Greg L]

Here's a question I've been curious about for the builders/flyers of the original Bearhawk. Can you or have any of you made changes to an original Bearhawk to upgrade it to the "B" model. Principally, has anyone changed their wing from the original 4412 wing to the Riblett Airfoil wing? If so, does the wing location (Fore/Aft) on the fuselage change? Does the incidence angle change? Does the Horz. Stab. down force angle change as well? If anyone has changed wings, have you indeed noticed the different flight characteristics between the two wing/airfoil designs?

[jaredyates]

The only changed plane that I know of is 303ap, which was the prototype for the changes. I wasn't involved in the work but it sounded like a really big job. I have changed the incidence angle and found that to be quite doable.

[Battson]

The Bravo wings are a considerably different shape. Specifically, they are much deeper. The fuselage needs considerable modifications to allow the windows to open and wing roots to line up.

To do this properly means going back to bare steel and cutting / welding structural tubes in the fuselage, or welding in new cosmetic tubing - but that would be heavier... As Jared says, it's no mean feat.

Given the advantages of the Bravo wing are minor at best (not yet clearly defined would be more realistic), I doubt it's worth the trouble [at the time of writing].

Modifying the existing wings would be an easier path to the same outcomes.

[Sir Newton]

This is why I purchased a set of the older plans that have the A wing. There is a difference in the wing profile. & from a knuckle draggers perspective it is a minor change. I never looked at fuselage changes, I only compared draw# 4

[svyolo]

The is a couple of degree difference in horizontal stab incidence, which I don't think is hard to do. I believe the reduced downforce/drag is the one of the main reasons for a few extra knots. Changing wings would be an expensive (or lots of work if you scratch build) way to get a couple of knots.

[whee]

I’m going from memory and I’m sure I’ll be corrected if wrong:

Model B wings are 2” thinker in cord. That requires the door frame to be lowered 1” and the roof stringers to be raised 1”. You could bolt the wings on but you couldn’t open the door and the plane would look like a gull wing Stinson.

The reduction in the angle of incidence of the H-stab if from the change to a profiled h-stab vs the flat h-stab ground in the model B. The flat stab is set at -4deg while the profiled stab can be set to -3.

My BH has most of the updates except the wing. The B wing is a great wing but IMO there is no reason to change the wing unless you’ve got a wrecked airplane and need new wings. Even then I’m not sure it would be worth it.

[Sir Newton]

100% I would not change to the model B unless there was bent metal.

[nborer]

I'll pile on and say that there appear to be very little, and to channel Battson's post, "not yet clearly defined" or perhaps "not yet provably correct" performance enhancements demonstrated in going from the original wing to the Model B in terms of performance. Some good testimonials and points based on facts, but from a performance standpoint, I haven't been able to distill much of a difference from (my very limited!) analytical evaluation. I have a comparison of a 2D airfoil performance from my as-delivered airfoil in Drawing 4 (the 2D formblock profile) for my Model B vs. the NACA 4412 profile (very similar, as I understand, to the Model A - I have heard there are some minor differences between the as-drawn airfoil vs. the Abbott and von Doenhoff NACA 4412 profile). If you look at the drag polar (generated by computational evaluation tools, and "little v" validated) - the lift vs. drag coefficient (Cl vs. Cd - first plot) - you'll see that they are nearly identical, and if I put error bars on this, you'd call them analytically indistinguishable. However, this analysis does indicate that the 4412 is more aft-loaded, and has a higher inherent pitching moment, as seen in the moment coefficient vs. angle of attack plot (Cm vs alpha, second plot). So, that **may** effect tail incidence, though I can't say how much of the change in the Model B vs. Model A is due to a change in pitching moment of the airfoil vs. the profiled ribs. Based on the discussion above and others in this forum, it seems the profiled tail has a significant effect. I'll take experience over models!

The Model B design uses an airfoil that has a thickness-to-chord ratio of 13.5% (lots of side discussion on the "truth" of this number when looking at the provided airfoil drawing, but let's just go with it for now - it's somewhere between 13.5 and 13.8%), and a 4412 section is 12%, which I presume is very close to the Model A. On a 65-inch chord line, that'll translate to a difference of about 1 inch of spar depth (I don't know if the chord on the model A is also 65 inches; Whee notes above that the chord may differ by 2", but that won't be enough to make a big difference in the spar depth change, since 0.015 x 65 is pretty close to 0.015 x 63). Done right, that could save you some weight - thicker sections mean you may be able to design with smaller capstrips on your spars. There's probably also a small but measurable reduction in the shear flow through the skins that could allow you to go with thinner skins in certain sections due to the increased airfoil thickness, but that may be offset by the small increase in skin surface area and other factors, like minimum sheet metal gauge, damage tolerance, etc. I'm too lazy to do the math right now. I will say that I would be surprised in the weight difference in the spar caps alone would be enough to justify the switch.

I believe the Model B also has an extra foot of span... so that too could factor in to how the loads are transferred, the differences in performance, etc. The Model B also has slightly longer flaps, if I recall correctly, that go all the way to the wing root. Those will all have modest changes in everything from structure to stall speed, but in small enough increments that it would be difficult to quantify with certainty.

Bottom line... if someone gave me a Model A (or Model A kit), or I started building a model A before the B came out, then I'd build it and fly it and not look back. And then, I'd tinker, because tinkering is fun. I like the Model B wing; I think it's a smart design and I think, from a product line perspective, it does great things for multiple Bearhawk variants... but from an individual builder perspective, especially compared to an already solid performer in the Model A... meh.

If you want to re-wing for a love of tinkering, have at it and know it'll be a lot of work! But if you are chasing better performance... there are easier paths that likely yield better returns.

Happy tinkering!


model_B_vs_4412_polar_Re_3e6.pngmodel_B_vs_4412_Cm_Re_3e6.png

[Sir Newton]

You must be good at typing on a keyboard. I had to read this post twice :-)

[rodsmith]

I’m going from memory and I’m sure I’ll be corrected if wrong:

Model B wings are 2” thinker in cord. That requires the door frame to be lowered 1” and the roof stringers to be raised 1”. You could bolt the wings on but you couldn’t open the door and the plane would look like a gull wing Stinson.

The reduction in the angle of incidence of the H-stab if from the change to a profiled h-stab vs the flat h-stab ground in the model B. The flat stab is set at -4deg while the profiled stab can be set to -3.

My BH has most of the updates except the wing. The B wing is a great wing but IMO there is no reason to change the wing unless you’ve got a wrecked airplane and need new wings. Even then I’m not sure it would be worth it.

The B wing is 13.5% thick instead of the original 12% thick. With 66" chord that makes the B wing max thickness 8.91 thick vs the original 7.92. Agree that performance improvement wouldn't be worth the fuselage modification effort.

[Nev]

I'm wondering if it would be an idea to increase the amount of negative incidence on the horizontal stabilizer of my IO540 equipped Bearhawk with a view to giving better elevator control at slow speeds and forward CG.

At this stage I'm reasonably sure that most of the A models have a CG of 13 inches or more when loaded with just the pilot and minimal fuel. Whereas my B model in the same configuration would easily be at the forward limit of 10.5 inches. I've got no need to go near the aft limit so I plan to use a soft aft limit of 21 inches. However I do need to operate regularly on the forward limit. Even with two adults in the front and 3/4 fuel I would still be forward of 13 inches (without ballast at the cargo station).

Currently I'm getting quite used to the handling in this area, but I definitely think there's low hanging fruit there for a possible handling improvement.

Any thoughts appreciated.




One POB and minimum fuel:

CDEF367B-0D18-41DA-A1E8-4F4395BD4927.jpg

4 "fully grown" adults and full fuel. I don't plan to operate at this weight, just to illustrate the CG range on a B model with an IO540:

D6FC6923-3853-4F37-BDC5-0A4CEA7DFA5F.jpg

4 standard adults and 3/4 fuel, 65 pounds baggage:

6D644FFE-9618-4A35-ADF6-2EE0411F49DC.jpg

[Battson]

I would start with pilot technique, then move to gap seals, then VGs under the tail, and by then the problem will surely be solved.

[jaredyates]

Nev, here are the two steps that I used when making an incidence change:
1. Select a condition (a single total weight, a single CG position, and a single airspeed) that you want to optimize for, load to that condition and put yourself there.
2. While there, look back at the elevator counterbalance. If the elevator counterbalance is even with the leading edge of the horizontal stab, then no adjustment is necessary. If there is some elevator displacement, adjust a quarter inch and check again.
If you are flying at any condition other than the one that you selected to optimize for, you will have some elevator displacement and thus some extra drag.

[Sir Newton]

100% concur. When possible keep it simple & straight forward. I am adding fuel tanks so I can use fuel as ballast. I refuse to load something on board that is not useful to the overall mission. I will talk more about how the system will work & where the tanks are located when the design is completely flushed out. However ! The solution is going to BE simple, cost effective easy to understand & operator friendly & above all safe.

[Nev]

Thanks guys, exactly the advice I was looking for.