Winglets 4 place model b

[planecrazy]

Has anyone experimented with winglets on the model b. I like the look and have heard great things concerning performance?

[fairchild]

Do those go good with hot sauce ? :-)

[Bdflies]

Breaded or naked?

[planecrazy]

I like them both ways!

[PaulSA]

Seriously..........

Winglets are really for swept wing aircraft where you get a spanwise flow and therefore larger vortices at the tips. Sure, you get a bit of spillage around the tips on a straight wing but I doubt the weight and complexity of winglets are worth the effort.

[nborer]

In general, winglets can be beneficial if your wing is highly loaded in cruise. The low wing loading of the Bearhawk means that you're cruising well beyond the most efficient point, where lift-induced and parasitic drag are equal. Airliners, which benefit from winglets, tend to cruise at higher altitudes where the lift coefficient of the wing ends up being much higher, and therefore lift-induced drag is a greater part of the total drag. You can get the induced drag benefit from winglets or span extensions, and most airliners are span-limited for a variety of reasons (fitting into parking spots, highly tapered wingtips, etc.). We don't have these "problems" on the Bearhawk.

Net/net, unless you plan to do lots of flying at very slow airspeeds, your winglets will just take away from your useful load and add parasite drag to the cruise portion of the flight. There are probably a couple of tip treatments that could be helpful... say, a Hoerner tip...

[zkelley2]

In general, winglets can be beneficial if your wing is highly loaded in cruise. The low wing loading of the Bearhawk means that you're cruising well beyond the most efficient point, where lift-induced and parasitic drag are equal. Airliners, which benefit from winglets, tend to cruise at higher altitudes where the lift coefficient of the wing ends up being much higher, and therefore lift-induced drag is a greater part of the total drag. You can get the induced drag benefit from winglets or span extensions, and most airliners are span-limited for a variety of reasons (fitting into parking spots, highly tapered wingtips, etc.). We don't have these "problems" on the Bearhawk.

Net/net, unless you plan to do lots of flying at very slow airspeeds, your winglets will just take away from your useful load and add parasite drag to the cruise portion of the flight. There are probably a couple of tip treatments that could be helpful... say, a Hoerner tip...

That all said, you should see an improvement in climb performance when you're slow and your induced drag is the vast majority of drag and parasitic is low.

But then again, has anyone done tuft testing on a bearhawk?

[PaulSA]

The reason induced drag is high on swept wing aircraft is because of spanwise flow. The sweep means that to calculate the lift, you have to resolve the airflow into that perpendicular to the chord and spanwise. So you get a double whammy. Firstly, effective CL is lower than an equivalent size straight wing so you need a higher AoA to achieve the same lift. Secondly, the spanwise flow is all "wasted" and causes large vortices (and therefore drag) at the tips. Which is why you often see fences and winglets on swept wing aircraft.

So why sweep the wings? Well, at high altitude and mach, straight wing aircraft run into issues with shock waves forming, especially on the top surface where the air is accelerated. By sweeping the wing, you effectively slow the air perpendicular to the chord and delay shock waves. The extra drag discussed above is more than compensated for by the reduction in drag due to shock waves.

[svyolo]

I think on a Hershey Bar of a wing keeping the high and low pressure airflow separated is about the best you can do. Tip plates or Hoerner tips. The Hoerner tips look cooler. I might do them eventually but just want to get airborne first. I will start with the stock CF tips I bought from Bob.

I also like the idea of a "fence" to separate the airflow between the flap and ailerons.

[nborer]

This is about as simple as wings get (by design) - no sweep, no twist, little dihedral, incompressible flow, with a mid-aspect ratio wing. As PaulSA mentioned, there is little spanwise flow, so the lift distribution isn't "pushed' towards that outboard portion of the wings - a good thing, as this helps to reduce induced drag and reduce the tendency to have wingtip stalls. I ran a quick analysis at the climb condition, and these (admittedly simple) tools confirm that the only real challenge are some very moderate tip losses. I used simple round tips in my geometry; we'd probably get a little help with the Hoerner tips (though I don't know that I'd trust VSPAero to pick up that nuance with either of their solvers). This was for the Model B wing with the Riblett airfoil.

As for fences... those are generally for high angle-of-attack operations... it's not clear yet that there is a problem with spillage at the flap/aileron or other junctions in slow flight. That would require some pretty hefty CFD solvers, wind tunnel tests, or in-flight tests with a camera on some tufts during slow flight and stall. Has anyone noticed any issues that they can trace to these junctions?