Battson wrote:

CamTom12 wrote:

That's all that's really needed. The vortex street is super draggy. Cutting down on that increases aero efficiency quite a bit.

The best visual I've ever seen is on wikipedia. Watch the two videos this link hits:

https://en.wikipedia.org/wiki/K%C3%A1rm ... g_problems

Does that flow pattern apply to a toroidal shape though? I thought that required a long cylindrical body?

As far as I know (not that far), the effect is mirrored on a toroidal when perpendicular to the relative wind. But with all the yawing that happens when I fly, who knows if there's a meaningful correlation.

It'd be neat to check, but I do know that many aircraft gain speed with wheel pants over naked wheels. So that tells me there's got to be something there.

There's definitely something there, virtually all fixed gear airplanes show some measurable gain in speed / reduction in drag with properly done wheel fairings.

Assuming that the drag becomes greater as you increase the size of the tire, the benefit of the wheel pant should more or less follow that same proportion. Again, IMHO, being able to reduce fuel consumption at the same cruise speed would turn into a big deal for a lot of operators.

Another thing to consider is the form factor (or fineness ratio, whatever) of the tire. The width of the tire (along the spanwise axis) as compared to the diameter (along the fore-aft or longitudinal axis). Aren't some bushwheels "fatter" proportionately than stock tires?

M6RV6 wrote:

Looks like a flat plate 1/2 way up the tire horizontally would work, also use it as a step??

I like the idea as it gives a second function to the structure. I am unsure if the orientation matters, due to the sort of rectangular form of the tire. Anyone have a guess?

If horizontal would work it would look somewhat like the gravel-guard like structure I have seen on larger bushplanes.

CamTom12 wrote:It'd be neat to check, but I do know that many aircraft gain speed with wheel pants over naked wheels. So that tells me there's got to be something there.

Yes naturally a toroid creates vastly more drag than a aerodynamically shaped surface.

I was thinking about the oscillating vortex shedding which occurs on a cylinder (like a stack) compared to just regular old turbulence (drag). I was wondering whether the flat plate fairing which someone suggested would actually help - because it seems like its targeting the oscillatory behaviour rather than the straight-up random turbulence.

I've been flying without wheel pants for about 9 months--old ones had cracked too much to repair, so new Stenes were ordered about 4 months ago, arrived quickly, and have yet to be installed by my IA. He did some fitting recently (everything it seems needs slight modifications to fit my airplane!), and I'm hoping to get them on soon.

For just local flights, I haven't noticed anything different--not enough variance on the AI to compare. But I have noticed on my longer cross country flights a slight reduction in speed, maybe a couple or three knots. In my draggy little airplane, that's not a huge issue. The big thing is that running through puddles or on a wet runway sure dirties up my airplane! So I'm looking forward to getting wheel pants back on, just to keep the airplane cleaner as much as anything.

Cary

Battson wrote:

CamTom12 wrote:It'd be neat to check, but I do know that many aircraft gain speed with wheel pants over naked wheels. So that tells me there's got to be something there.

Yes naturally a toroid creates vastly more drag than a aerodynamically shaped surface.

I was thinking about the oscillating vortex shedding which occurs on a cylinder (like a stack) compared to just regular old turbulence (drag). I was wondering whether the flat plate fairing which someone suggested would actually help - because it seems like its targeting the oscillatory behaviour rather than the straight-up random turbulence.

In fact, I can say for sure that a flat plate fairing does not help.

Thinking about it, one of the types of mud guards you see on aircraft are exactly that, a flat plate sticking our in a straight line behind the wheel, as pictured below. The orientation is correct too. BUT - those kind of mudguards are known for decreasing airspeed, not increasing it.

Battson wrote:In fact, I can say for sure that a flat plate fairing does not help.

Thinking about it, one of the types of mud guards you see on aircraft are exactly that, a flat plate sticking our in a straight line behind the wheel, as pictured below. The orientation is correct too. BUT - those kind of mudguards are known for decreasing airspeed, not increasing it.

Interesting! Yeah, I hadn't heard of they were known to decrease speed.

That and even if an oscillation were to happen, it would be limited to some pretty specific conditions I think.

So, back to the bushwheelpants idea, then

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glacier wrote: My 180 will do a reasonable cruise of 135-140 mph on 31's. "Reasonable" meaning not flat out, more like 13-ish gal per hour......

What's your pwer setting at that speed?
Mine does 135-140 with 850's at 21"/2300, burning about 11 gph.

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glacier wrote:3) I recently tried putting the hub caps back on to see if that would help the small amount of oscillation remaining with the 31's. It definitely did, eliminating it completely. And, while I am not 100% convinced yet, I may be cruising the same speed with lower power settings, or closer to 140 mph than 135 mph with the same power settings. I have not had enough really calm air over a few long cross countries to confirm this just yet.

What were symptoms of the oscillation? Visual? Feel? On my 56 182 I get a pretty healthy wobble in the instrument panel in cruise. The panel is mounted on rubber isolators. I just had the prop balanced to rule that out and started to think maybe the gear legs? Just got some hub caps from grove to try and curious to see if it helps and/or provides a couple mph

Hoeschen wrote:What were symptoms of the oscillation? Visual? Feel? On my 56 182 I get a pretty healthy wobble in the instrument panel in cruise. The panel is mounted on rubber isolators. I just had the prop balanced to rule that out and started to think maybe the gear legs? Just got some hub caps from grove to try and curious to see if it helps and/or provides a couple mph

When I look out the lower window at my tires, they are sometimes vibrating / oscillating (practically the same thing). Some times more than others. I assumed it's just because planes vibrate a lot, and they must have a normal mode or natural frequency close enough to the vibration pattern produced by the engine at cruise RPM. Depending on exactly where I set the RPM, the problem might be worse or better (I assume).

If it was driven by the airflow, kicking the plane well out of balance should stop the vibration instantly. It doesn't happen that way for me. But these are smaller Goodyear tires with a thicker, harder rubber. The same need not apply to 31 ABWs.

Battson wrote:When I look out the lower window at my tires, they are sometimes vibrating / oscillating (practically the same thing). Some times more than others. I assumed it's just because planes vibrate a lot, and they must have a normal mode or natural frequency close enough to the vibration pattern produced by the engine at cruise RPM. Depending on exactly where I set the RPM, the problem might be worse or better (I assume).

If it was driven by the airflow, kicking the plane well out of balance should stop the vibration instantly. It doesn't happen that way for me. But these are smaller Goodyear tires with a thicker, harder rubber. The same need not apply to 31 ABWs.

I've noticed the same on mine. I've thought it was the same as you do.

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glacier wrote:This has a period of about 2 seconds, a slow bobbing that can seen and felt. It is actually kind of annoying if the air is really calm; it won't set up if the air is not calm. It does go away if flown uncoordinated but then the speed goes down too.

I was just out and the air was very calm, so I was able to verify. 140-142 mph indicated (and GPS agrees), 23 squared, 13 gph. Density altitude right at zero.

Well, that seems to support the vortex street idea... Interesting.

The 850's on my old C150TD oscillated at cruise speed. Looking out the window, the mains just kinda wobbled left/right, coinciding with the flat plane of the leaf spring gear legs. No sign of that with 800's.